The recent bloom of nanomaterials has kindled a strong demand for new cell inactivation technology that can replace the conventional cell inactivation process with high throughput, free chemicals usage and outstanding efficacy to all pathogens to overcome the critically global issue, i.e. microbial infection. Herein, we construct a macroscopic carbon nanotube (CNT) sponge using a simple self-assembly method. Based on the technology of 1D nanostructure assisted electroporation, an electroporation disinfection cell (EDC) equipped with CNT sponge achieved superior cell inactivation performance (<0.00001% microbe survival rate) within a contact time of 5 s at an extremely low applied voltage (2 V), trace energy consumption (20 J L−1) and outstanding durability (>60 min). The CNT sponge EDC can be easily powered by batteries or solar cells and shows the best energy consumption performance among all the cell inactivation technologies. Cell inactivation using the CNT sponge EDC has significant potential for practical applications.

•UVC irradiation could degrade BIT efficiently.•Both direct photodegradation and indirect photodegradation via OH contributed to BIT degradation.•The photodegradation of BIT was a pH-depended process.•The photodegradation pathway of BIT was proposed.Benzisothiazolinone (BIT) is a kind of non-oxidizing biocide widely used in reverse osmosis process for wastewater reclamation. Most BIT would reside in the RO (reverse osmosis) concentrates and show adverse effects on aquatic life when it is discharged into surface water. This study analyzed the photodegradation of BIT under UVC (254 nm) irradiation and found that UVC irradiation was as an efficient way to degrade BIT, of which the process could be well described by pseudo first order kinetics. As the results of BIT self-sensitization and light shield, the BIT photodegradation constant increased from 0.19 to 0.23 min−1 with increasing BIT concentration from 3 to 40 μM, and then followed by a decrease of the constant with further increasing BIT concentration. Radical species quenching experiments indicated that the photodegradation of BIT could be attributed to both direct and indirect photodegradation. Studies of the effects of pH suggested that non-charged state BIT (BIT0) in neutral and basic solution was much more photodegradable than protonated state BIT (BIT-H+) in acidic solution. The solution anion of HCO3− showed a slight promotion on BIT photodegradation. With the help of quadrupole time-of-flight mass spectrometry (QTOF-MS), the main intermediates of BIT photodegradation were identified. By employing the anion chromatography and HPLC tandem with triple quadrupole MS, the intermediates were quantified and the degradation pathway was proposed. This study could offer valuable suggestions for the efficient degradation of BIT and other similar emerging pollutants in wastewater reclamation and contribute to reclaimed water safety and sustainability.

•An S-shape relationship between TOD and inactivation was purposed for reclaimed water ozonation.•A practical model (L-I model) is developed and verified to simulate reclaimed water disinfection performance.•The effects of water quality and microbial resistance on inactivation are quantified by L-I model.Ozonation is broadly used as a disinfection technique for inactivation of pathogens in drinking water or reclaimed water. The conventional Chick-Watson model (C-W model) considering ozone exposure is sub-optimal in predicting the inactivation performance by ozonation in reclaimed water. In this study, the Escherichia coli (E. coli) and the Bacillus subtilis (B. subtilis) spore were used as test microorganisms and ozonation experiments were carried out upon different systems. The relationship between experimental inactivation and TOD was found to follow an S-shape curve. A novel and practical empirical model (L-I model) was set up to simulate the inactivation performance in reclaimed waters, regarding the transferred ozone dose (TOD), the instantaneous ozone demand (IOD) and the microbial resistance to ozone as the main parameters. According to the data fitting results, the parameters for E. coli and B. subtilis spores were determined. With TOD in 0–20 mg L−1 and IOD in 2–5 mg L−1, the calculated inactivation rates of the two test microorganisms could successfully match the experimental data derived from the batch ozonation test and the semi-continuous ozonation test for reclaimed water disinfection. The squared correlation coefficients (R2) for different tests range from 0.86 to 0.96 and the average relative errors (δ) are 0.08–0.59. This result verified that the L-I model is a practical way to simulate performances of ozonation systems for reclaimed water disinfection. Based on the model, the effects of water quality (IOD) and microbial resistance on disinfection performance were also analyzed.Download high-res image (106KB)Download full-size image

Chlorination is essential to the safety of reclaimed water; however, this process leads to concern regarding the formation of disinfection byproducts (DBPs) and toxicity. This study reviewed the formation and control strategies for DBPs and toxicity in reclaimed water during chlorination. Both regulated and emerging DBPs have been frequently detected in reclaimed water during chlorination at a higher level than those in drinking water, indicating they pose a greater risk to humans. Luminescent bacteria and Daphnia magna acute toxicity, anti-estrogenic activity and cytotoxicity generally increased after chlorination because of the formation of DBPs. Genotoxicity by umu-test and estrogenic activity were decreased after chlorination because of destruction of toxic chemicals. During chlorination, water quality significantly impacted changes in toxicity. Ammonium tended to attenuate toxicity changes by reacting with chlorine to form chloramine, while bromide tended to aggravate toxicity changes by forming hypobromous acid. During pretreatment by ozonation and coagulation, disinfection byproduct formation potential (DBPFP) and toxicity formation potential (TFP) occasionally increase, which is accompanied by DOC removal; thus, the decrease of DOC was limited to indicate the decrease of DBPFP and TFP. It is more important to eliminate the key fraction of precursors such as hydrophobic acid and hydrophilic neutrals. During chlorination, toxicities can increase with the increasing chlorine dose and contact time. To control the excessive toxicity formation, a relatively low chlorine dose and short contact time were required. Quenching chlorine residual with reductive reagents also effectively abated the formation of toxic compounds.Download high-res image (147KB)Download full-size image

•LED UV/chlorine oxidation can significantly degrade Carbamazepine (CBZ).•LED UV/chlorine is much more efficient than LED UV/H2O2 for CBZ degradation.•OH and Cl are two dominant radical species for CBZ degradation by LED UV/chlorine.•LED UV/chlorine is most efficient at pH 8.5 because OCl− is the main active species.•Oxidation byproducts exhibit acute toxicity and cytotoxicity.Carbamazepine (CBZ) is a ubiquitous micropollutant in wastewater and reclaimed water. In this study, we evaluated CBZ degradation by light-emitting diode (LED)-driven UV/chlorine oxidation. Under LED irradiation of 280 nm (LED280) and 310 nm (LED310), UV/chlorine could efficiently degrade CBZ. Compared with LED UV/H2O2 treatment, LED UV/chlorine oxidation achieved a CBZ degradation rate that was one order of magnitude higher. The CBZ degradation followed pseudo-first-order kinetics, and the rate constants (kobs,CBZ) for LED280 UV/chlorine and LED310 UV/chlorine increased from 0.072 to 0.91 min−1 and 0.044 to 0.65 min−1, respectively, when chlorine dosage increased from 0.07 to 0.14 mM. Under neutral conditions, the generated OH and Cl accounted for over 80% of the CBZ degraded by LED UV/chlorine. The maximum kobs,CBZ for LED UV/chlorine was observed at pH 8.5; kobs,CBZ decreased when solution pH increased to 9.5 or decreased to 5.5. This is because the main UV-absorbing chlorine species in the LED280 and LED310 systems is OCl−, which is different from those in low-pressure mercury lamp/chlorine systems. The acute toxicity for CBZ solution treated by LED UV/chlorine increased at lower fluence (<752 mJ/cm2) and decreased at higher fluence (>1233 mJ/cm2). However, the cytotoxicity to Chinese hamster ovary cells and adsorbable organic halide content of CBZ solution both increased after chlorination and LED UV/chlorine. The lowest electrical cost for the degradation of CBZ by LED UV/chlorine occurred under neutral conditions with a chlorine dosage of 0.4–0.7 mM (28.4–49.7 mg/L).Download full-size image

•265 nm LEDs was more effective for E. coli disinfection.•No synergic effect for disinfection from the combination of 265 and 280 nm LEDs.•280 nm LEDs significantly reduced the reactivation processes.•Protein-damaging may be one reason that inhibited the reactivation.•New reactivation rate constant with clear physical meaning was introduced.Studies on ultraviolet light-emitting diode (UV-LED) water disinfection have shown advantages, such as safety, flexible design, and lower starting voltages. However, information about reactivation after UV-LED disinfection is limited, which is an important issue of UV light-based technology. In this study, the photoreactivation and dark repair of Escherichia coli after UV-LEDs and low pressure (LP) UV disinfection were compared. Four UV-LED units, 265 nm, 280 nm, the combination of 265 + 280 (50%), and 265 + 280 (75%) were tested. 265 nm LEDs was more effective than 280 nm LEDs and LP UV lamps for E. coli inactivation. No synergic effect for disinfection was observed from the combination of 265 and 280 nm LEDs. 265 nm LEDs had no different reactivation performances with that of LP UV, while 280 nm LEDs could significantly repress photoreactivation and dark repair at a low irradiation intensity of 6.9 mJ/cm2. Furthermore, the UV-induced damage of 280 nm LEDs was less repaired which was determined by endonuclease sensitive site (ESS) assay. The impaired protein activities by 280 nm LEDs might be one of the reasons that inhibited reactivation. A new reactivation rate constant, Kmax, was introduced into the logistic model to simulate the reactivation data, which showed positive relationship with the maximum survival ratio and was more reasonable to interpret the results of photoreactivation and dark repair. This study revealed the distinct roles of different UV lights in disinfection and reactivation, which is helpful for the future design of UV-LED equipment.Download high-res image (168KB)Download full-size image

•The degradation kinetics of NOM by UV/chlorine was studied.••OH and •Cl contributed for NOM oxidation by UV/chlorine•HPSEC-DOC results revealed the higher reaction rate for high MW than medium MW.•UV/chlorine showed potential risk with forming DPBs and cytotoxicity.The degradation of natural organic matters (NOMs) by the combination of UV and chlorine (UV/chlorine) was investigated in this study. UV/chlorine oxidation can effectively degrade NOMs, with the degradation of chromophores (∼80%) and fluorophores (76.4–80.8%) being more efficient than that of DOC (15.1–18.6%). This effect was attributed to the chromophores and fluorophores (double bonds, aromatic groups and phenolic groups) being preferentially degraded by UV/chlorine oxidation, particularly reactive groups with high electron donating capacity. Radical species •OH and •Cl were generated during UV/chlorine oxidation, with the contribution of •OH 1.4 times as high as that of •Cl. The degradation kinetics of different molecular weight (MW) fractions suggests that UV/chlorine oxidation degrades high MW fractions into low MW fractions, with the degradation rates of high MW fractions (>3000 Da) 4.5 times of those of medium MW fractions (1000–3000 Da). In comparison with chlorination alone, UV/chlorine oxidation did not increase the formation (30 min) and formation potential (24 h) of trihalomethanes, but instead promoted the formation and formation potential of haloacetic acids and chloral hydrate. Adsorbable organic halogen (AOX) formed from UV/chlorine oxidation of NOM were 0.8 times higher than those formed from chlorination. Cytotoxicity studies indicated that the cytotoxicity of NOM increased after both chlorination and UV/chlorine oxidation, which may be due to the formation of AOX.

•UV irradiation showed synergistic efficiency with chlorine for PVA degradation.•OH and Cl radicals play important roles in the oxidation process of PVA.•Acidic media are more efficient than basic and neutral media for PVA degradation.•A possible degradation pathway via alcohol to carbonyl was proposed.Polyvinyl alcohol (PVA) is widely used in industry but is difficult to degrade. In this study, the synergistic effect of UV irradiation and chlorination on degradation of PVA was investigated. UV irradiation or chlorination alone did not degrade PVA. By contrast, UV/chlorine oxidation showed good efficiency for PVA degradation via generation of active free radicals, such as OH and Cl. The relative importance of these two free radicals in the oxidation process was evaluated, and it was shown that OH contributed more to PVA degradation than Cl did. The degradation of PVA followed pseudo first order kinetics. The rate constant k increased linearly from 0 min−1 to 0.3 min−1 with increasing chlorine dosage in range of 0 mg/L to 20 mg/L. However, when the chlorine dosage was increased above 20 mg/L, scavenging effect of free radicals occurred, and the degradation efficiency of PVA did not increase much more. Acidic media increased the degradation efficiency of PVA by UV/chlorine oxidation more than basic or neutral media because of the higher ratio of [HOCl]/[OCl−], higher free radical quantum yields, and the lower free radical quenching effect under acidic conditions. Results of Fourier Transform Infrared Spectroscopy showed that carbonyl groups in degradation products were formed during UV/chlorine oxidation, and a possible degradation pathway via alcohol to carbonyl was proposed.Download high-res image (111KB)Download full-size image

•Correlations of water reuse to local water resource and GDP levels were analysed.•Centralized water reuse framework and utilization patterns were identified.•Characteristics and applications of centralized water reuse systems were discussed.•A case study on the multiple-application water reuse model is conducted.•The importance of water reuse for urban sustainable management was highlighted.In the context of rapid urbanization and water shortage, many cities of the world, especially megacities in rapidly developing zones, have urgent needs in improving their sustainable water management without compromising the local socioeconomic development. Water reuse has been increasingly recognized as a sustainable water management strategy. The results of this paper have shown that the development of water reuse in China is found to have positive correlations to local water resource availability and GDP levels, and the water reuse rate in some megacities has already reached 35–60%. Centralized water reuse systems have widely gained favor. Thus, a centralized water reuse framework with three utilization patterns is proposed. Particularly, a multiple-utilization model that applies a hierarchical use structure is found to be viable for meeting multiple water quality requirements. Other patterns address environmental and cascading ways in maximizing the value of reclaimed water use. A case study in a Chinese megacity, Tianjin, is demonstrated where a large-scale centralized water reuse project with a multiple barrier treatment approach and a hierarchical distribution and use structure has contributed to water reuse development in a safe, reliable and economical manner. This paper can be beneficial to water authorities and practitioners for long-term urban water management in other rapidly developing cities and regions that have encountered similar water-related problems.Download high-res image (143KB)Download full-size image

•Mixed cultivation enhanced significantly microalgal biomass production.•Microalgal TAG production was improved significantly by mixed cultivation.•Mechanism of enhancing biomass production by mixed cultivation was revealed.•H. pluvialis could grow heterotrophically with SAPs released by S. LX1.•SAPs released by H. pluvialis improved the photosynthetic activity of S. LX1.Compared with monoculture, the mixed culture of certain microalgal strains showed important advantages, including higher biomass production, better resistance against sudden disruptions, and so on. In this study, the growth and lipid accumulation properties of Scenedesmus sp. LX1 (S. LX1) and Haematococcus pluvialis (H. pluvialis) were investigated in mixed culture using domestic secondary effluent as medium. In the mixed culture with initial biomass ratio of 4:1, 1:1 and 1:10 (S. LX1:H. pluvialis, w:w, dry weight), the total biomass production and triacylglycerol (TAG) production were enhanced significantly compared with the monocultures, and reached 0.51–0.54 g·L−1 and 6.9–9.3 mg·L−1 after 13-day cultivation, respectively. Further analysis revealed that interspecific nutrient competition between S. LX1 and H. pluvialis caused lower total nitrogen (TN) concentration in the medium of mixed culture, serving as an environmental stress to enhance the TAG accumulation. Furthermore, the soluble algal products (SAPs) released by H. pluvialis could improve the photosynthetic activity of S. LX1; while the SAPs released by S. LX1 could be assimilated by H. pluvialis for heterotrophic growth. The mutually beneficial relationship based on the effects of SAPs was the main mechanism of enhancing the total biomass produciton in the mixed culture.Mixed cultivation enhanced microalgal growth, nutrient removal and TAG production.Download high-res image (149KB)Download full-size image

•C. pyrenoidosa well adapted to the straw hydrolysate medium and grew fast.•Protein content in biomass increased with more amount of nitrogen in medium.•Biomass composition widely varied with the nitrogen concentration in medium.•Biomass rich in valuable protein and fatty acids was obtained in medium.Heterotrophic cultivation of Chlorella pyrenoidosa based on straw substrate was proposed as a promising approach in this research. The straw pre-treated by ammonium sulfite method was enzymatically hydrolyzed for medium preparation. The highest intrinsic growth rate of C. pyrenoidosa reached to 0.097 h−1 in hydrolysate medium, which was quicker than that in glucose medium. Rising nitrogen concentration could significantly increase protein content and decrease lipid content in biomass, meanwhile fatty acids composition kept stable. The highest protein and lipid content in microalgal biomass reached to 62% and 32% under nitrogen excessive and deficient conditions, respectively. Over 40% of amino acids and fatty acids in biomass belonged to essential amino acids (EAA) and essential fatty acids (EFA), which were qualified for high-value uses. This research revealed the rapid biomass accumulation property of C. pyrenoidosa in straw hydrolysate medium and the effectiveness of nitrogen regulation to biomass composition at heterotrophic condition.

•A capillary-driven photobioreactor (CPBR) was proposed for microalgae cultivation.•The CPBR was competitive in attached microalgal biomass production.•Nutrients were transported via capillary action and rapidly utilized by microalgae.•Cellular composition of attached microalgae was mainly lipid and carbohydrates.•Light utilization efficiency of CPBR can be 10 times higher than suspended systems.Microalgae cultivation is a promising candidate for autotrophic sequestrating CO2 transformation into renewable bio-products. However, potential of microalgae has not been fully explored due to the bottlenecks of biomass harvesting during large-scale microalgae cultivation. A novel capillary-driven photobioreactor (CPBR) is proposed in this study for attached microalgae cultivation obtaining high biomass productivity and overcoming the biomass harvesting limitation in traditional suspended cultures. Performances on microalgal growth, cellular composition, nutrients uptake from water, and corresponding light utilization efficiencies were investigated and emphasized. During 12 days of system operation, attached microalgal biomass on the carriers were in the range of 83.6 g/m2-footprint area of 121.5 g/m2-footprint area, corresponding to light utilization efficiency of 3.3% to 4.8%. With proper carriers packing density of 16% to 32%, obtained biomass productivities of CPBR were approximately 10 g/m2/d (footprint area). Biomass composition analysis revealed that lipid and carbohydrates contents in attached microalgal biomass were higher than in suspended microalgal biomass with same cultivating conditions, proving the potential of microalgae cultivated in CPBR as feedstock of biofuels.

•Non-oxidizing biocides control RO membrane biofouling, inorganic/organic foulings.•Burkholderiales ruled mature biofilm and was sensitive to non-oxidizing biocides.•Pseudoxanthomonas ruled primary biofilm and was resistant to non-oxidizing biocides.•More organic and inorganic foulings occurred on the inlet part of RO membranes.•Fouling profiles of RO membranes differed from those in RO influent.Fouling of reverse osmosis (RO) membranes is a severe problem for desalination of dyeing wastewater with high chemical oxygen demand (COD). In this paper, fouled RO membranes in a pilot-scale desalination system of biologically treated dyeing wastewater containing high COD (143–228 mg/L) with or without injection of non-oxidizing biocides were analyzed. The two non-oxidizing biocides used are K5030 (a kind of isothiazoline biocide) and FR110 (an inorganic base type of combined chlorine agent), respectively. For the RO membrane from the system without non-oxidizing biocide injection to the influent, a typical biofilm occurred on the RO membrane in a short operation time of 19 days. The injection of non-oxidizing biocides caused a decline of nearly 99.0% in active biomass on the RO membrane. Burkholderiales ruled mature biofilm on the RO membrane without injection of non-oxidizing biocide. Pseudoxanthomonas exhibited a certain resistance to non-oxidizing biocides and ruled the bacterial community on the RO membrane with injection of non-oxidizing biocides. Fe, P and Al were major inorganic elements on RO membranes, decreasing with injection of non-oxidizing biocides. Hydrophobic neutral (HON) fraction was the most major organic component of dissolved organic matter (DOM) on RO membranes, decreasing notably with injection of non-oxidizing biocides.Download high-res image (161KB)Download full-size image

Reuse of secondary municipal effluent from wastewater treatment plants in water bodies could effectively alleviate freshwater resource shortage. However, excessive nutrients must be efficiently removed to prevent eutrophication. Compared with other means of advanced wastewater treatment, microalgae-based processes display overwhelming advantages including efficient and simultaneous N and P removal, no requirement of additional chemicals, O2 generation, CO2 mitigation, and potential value-added products from harvested biomass. One particular challenge of microalgae-based advanced municipal wastewater treatment compared to treatment of other types of wastewater is that concentrations of nutrients and N:P ratios in secondary municipal effluent are much lower and imbalanced. Therefore, there should be comprehensive considerations on nutrient removal from this specific type of effluent. Removal of nutrients and organic substances, and other environmental benefits of microalgae-based advanced municipal wastewater treatment systems were summarized. Among the existing studies on microalgal advanced nutrient removal, much information on major parameters is absent, rendering performances between studies not really comparable. Mechanisms of microalgae-based nitrogen and phosphorus removal were respectively analyzed to better understand advanced nutrient removal from municipal secondary effluent. Factors influencing microalgae-based nutrient removal were divided into intrinsic, environmental, and operational categories; several factors were identified in each category, and their influences on microalgal nutrient removal were discussed. A multiplicative kinetic model was integrated to estimate microalgal growth-related nutrient removal based majorly on environmental and intrinsic factors. Limitations and prospects of future full-scale microalgae-based advanced municipal wastewater treatment were also suggested. The manuscript could offer much valuable information for future studies on microalgae-based advanced wastewater treatment and water reuse.

•Shortened AOC testing time to 3 days.•Improved AOC test accuracy by indigenous microbial culture in reclaimed water.•Verified consistency of the yield coefficients of indigenous microbial cultures.•Confirmed the stable AOC results of various indigenous microbial cultures.Assimilable organic carbon (AOC) is an important indicator of the biological stability of reclaimed water. In this study, a new rapid and more stable method for AOC measurement in reclaimed water was proposed. Indigenous microbial culture from secondary effluent was used as the inoculum, and bacterial growth was determined by the quantity of adenosine triphosphate (ATP) in the form of luminescence instead of plate count. ATP luminescence had a high correlation with biogrowth both in pure acetate solutions and reclaimed waters. ATP luminescence analysis could be determined in 5 min. Three days of 10000 cells/mL inoculum incubated at 25 °C were enough for the bacteria to reach the stationary phase. The good correlations between ATP luminescence and the added acetate-C concentration illustrated the applicability of monitoring AOC level by luminescence method. And in reclaimed water samples, indigenous microbial culture produces the highest AOC results compared with the pure strains. This indicated that the integrity of indigenous microbial culture ensured the full utilization of matrix carbons, which demonstrated the advantage of indigenous microbial culture compared with the selected pure bacteria in the traditional AOC test. The average ATP content per cell of 3.95 × 10−10 nmol/cell was derived, and this value was stable in both the acetate solutions and reclaimed waters. Furthermore, the average yield coefficient of 1.5 × 105 RLU/μg acetate-C (4.1 × 10−3 nmol ATP/μg acetate-C) was obtained from different indigenous cultures. Additionally, the indigenous microbial cultures from different secondary effluents would produce the similar AOC results for the same water sample, indicating the consistency of this assay. The ATP luminescence-AOC assay provides a faster, more stable and accurate approach for monitoring the biological stability of reclaimed waters.Download high-res image (208KB)Download full-size image

More than 10% of the people in the world still suffer from inadequate access to clean water. Traditional water disinfection methods (e.g., chlorination and ultraviolet radiation) include concerns about the formation of carcinogenic disinfection byproducts (DBPs), pathogen reactivation, and/or excessive energy consumption. Recently, a nanowire-assisted electroporation–disinfection method was introduced as an alternative. Here, we develop a new copper oxide nanowire (CuONW)-modified three-dimensional copper foam electrode using a facile thermal oxidation approach. An electroporation–disinfection cell (EDC) equipped with two such electrodes has achieved superior disinfection performance (>7 log removal and no detectable bacteria in the effluent). The disinfection mechanism of electroporation guarantees an exceedingly low operation voltage (1 V) and level of energy consumption (25 J L–1) with a short contact time (7 s). The low operation voltage avoids chlorine generation and thus reduces the potential of DBP formation. Because of irreversible electroporation damage on cell membranes, no regrowth and/or reactivation of bacteria occurs during storage after EDC treatment. Water disinfection using EDCs has great potential for practical applications.

Wastewater reclamation and reuse is a promising way to relieve water scarcity by substituting for natural water consumption by industrial cooling. However, health concerns regarding cooling water originating from reclaimed water are increasing because an abundance of antibiotic-resistant bacteria (ARB) has been detected in reclaimed water. To assess the potential increase of ARB risks in reclaimed water after reuse for industrial cooling, the prevalence of six types of ARB was investigated in water and sediment samples from Lake Gaobeidian, which serves as an artificial circular storage reservoir for reclaimed water for cooling reuse. The effect of treated wastewater and cooling water drainage on the ARB distribution in water and sediment samples was also studied. The results showed that the concentration levels of six types of ARB in lake water samples were as high as those in treated wastewater. The annual median concentrations of total heterotrophic bacteria (HPC) and ARB in discharged cooling water after usage were 0.6-log and 0.4-log higher than those in treated wastewater and the cooling water intake site, respectively, indicating that the process of cooling water usage enhanced the proliferation of HPC and consequently increased the concentrations of ARB. Furthermore, the percentages of penicillin-, ampicillin-, and cephalothin-resistant bacteria in water were 30–57%, 36–48%, and 23–40% higher than those in sediment, respectively. However, the proportions of chloramphenicol-resistant bacteria in water were 35–85% lower than those in sediment. Quantitative evaluation of antibiotic resistance showed that HPC in water had a significant tolerance to penicillin and chloramphenicol, with 50% inhibitory concentrations reaching 22.90 mg L−1 and 29.11 mg L−1, respectively.

The purpose of this study was to give a worldwide overview of the concentrations of typical estrogenic endocrine disrupting chemicals (EDCs) in the effluent of sewage plants and then compare the concentration distribution of the estrogenic EDCs in ten countries based on the survey data of the estrogenic EDCs research. The concentrations of three main categories (totally eight kinds) of estrogenic EDCs including steroidal estrogens (estrone (E1), estradiol (E2), estriol (E3) and 17α-ethynylestradiol (EE2)), phenolic compounds (nonylphenol (NP) and bisphenol A (BPA)) and phthalate esters (dibutyl phthalate (DBP) and dibutyl phthalate (2-ethylhexyl) phthalate (DEHP)) in the effluents of sewage plants reported in major international journals over the past decade were collected. The statistics showed that the concentration distributions of eight kinds of EDCs were in the range of ng·L−1 to μg·L−1. The concentrations of steroidal estrogens mainly ranged within 50.00 ng·L−1, and the median concentrations of E1, E2, E3 and EE2 were 11.00, 3.68, 4.90 and 1.00 ng·L−1, respectively. Phenolic compounds and phthalate esters were found at μg·L−1 level (some individual values were at the high level of 40.00 μg·L−1). The median concentrations of BPA, NP, DBP and DEHP were 0.06, 0.55, 0.07 and 0.88 μg·L−1, respectively. The concentrations of phenolic compounds and phthalate esters in the effluents were higher than that of steroids estrogens. The analysis of the concentration in various ten countries showed that steroids estrogens, phenolic compounds and phthalate esters in sewage plant effluents were detected with high concentration in Canada, Spain and China, respectively.

Phosphorus has been considered as one of the most important limiting resources of large-scale production of microalgal biofuel. The approaches to increase biomass yield per phosphorus, along with the lipid accumulation properties of Scenedesmus sp. LX1, were investigated in this study. It was found that practical biomass yield per phosphorous was reduced with the increase of initial phosphorus (P) concentration, but increased with light intensity. The highest biomass yield per P of 4,500 kg-biomass/kg-P was achieved at initial phosphorus concentration of 0.05 mg · L−1 under the light intensity of 320 μmol photon · m−2 · s−1. Furthermore, the lipid content per biomass and triacylglycerols (TAGs) content per lipid were found to be positively correlated to biomass yield per P. With the biomass yield increased from 2,800 kg-biomass/kg-P to 4,500 kg-biomass/kg-P, the lipid content per microalgal biomass and TAG content per lipid increased from 18.7 % to 35.0 % and from 69.5 % to 83.0 %. These results suggested a possible approach to achieve high biomass production and high lipid content simultaneously.

A novel ozonation system based on micro-bubble technique was applied as a disinfection process in this study. The effect of inlet ozone concentration on the disinfection performance was comprehensively investigated. Bacillus subtilis spore was used as a model microorganism to evaluate the disinfection performance. In the micro-bubble ozonation system is operated at the same ozone dosage, the log reduction under high inlet ozone concentration was extremely higher than that under low inlet ozone concentration within 3 min of contact time. When the contact time was 3 min, the log reduction at the inlet ozone concentration of 140 mg/L was 5.2, which was nearly ten times of that at the inlet ozone concentration of 40 mg/L (0.5-log reduction). In addition, the ozone utilization efficiency was also enhanced by increasing the inlet ozone concentration. A decrease in bubble diameter was found under higher inlet ozone concentration and the interfacial area per unit volume of the micro-bubble was significantly higher due to the reduction in bubble diameters. This observation can well explain the increase in mass-transfer coefficient (KLa) and the enhancement in the ozone utilization efficiency. The result of this study showed that raising inlet ozone concentration is a promising method which could enhance the disinfection performance in a micro-bubble ozonation system.

Microbial growth is an issue of concern that may cause hygienic and aesthetic problems during the transportation and usage of reclaimed water. Assimilable organic carbon (AOC) is an important parameter which determines the heterotrophic bacterial growth potential of water. Pseudomonas fluorescens P17 and Spirillum sp. NOX are widely used to measure AOC in drinking water. The AOC values of various reclaimed water samples determined by P17 and NOX were compared with those determined by the new strains isolated from reclaimed water in this study. It showed that the conventional test strains were not suitable for AOC measurement of reclaimed water in certain cases. In addition to P17 and NOX, Stenotrophomonas sp. ZJ2, Pseudomonas saponiphila G3 and Enterobacter sp. G6, were selected as test strains for AOC measurement of reclaimed water. Key aspects of the bioassay including inoculum cell density, incubation temperature, incubation time and the pH of samples were evaluated for the newly selected test strains. Higher inoculum density (104 CFU·mL−1) and higher incubation temperature (25°C) could reduce the time required for the tests. The AOC results of various collected samples showed the advantages of the method proposed based on those five strains in evaluating the biologic stability of reclaimed water.

Photoreactivation is considered to be one of the principal disadvantages of the application of ultraviolet disinfection, but knowledge about the photoreactivation potential is limited since few studies to model photoreactivation have been carried out. In order to develop a model for the prediction of the photoreactivation potential, the photoreactivation of Escherichia coli, fecal coliforms, and total coliforms in the tertiary effluent of a wastewater treatment plant was investigated using traditional plate count methods in this study. The tested bacteria were exposed to various UV doses (5–80 mJ/cm2) with a low-pressure UV-collimated beam apparatus and then put under sunlight lamp to experience photoreactivation for up to 72 h. All tested bacteria underwent photoreactivation with a similar trend. When the UV dose increased from 5 to 20 mJ/cm2, the maximum reactivation value of E. coli decreased from 105 to 10 CFU/mL over 8 h, and the reactivation rate decreased from 3.6 to 3.0 × 10−4/h. Based on the photoreactivation results, an exponential model was developed to predict the possible maximum photoreactivation level (Nm = αD− βN0). This simple photoreactivation potential prediction model contains only two variables (UV dose and initial bacterial count), with two constants related to the microorganism species. This model can be easily generalized and is helpful for the optimum design of UV disinfection systems.

The increasing usage of organic nitrogen-rich wastewater- or algal-impacted waters, and chloramines for secondary disinfection, raises concerns regarding the formation of haloacetonitriles, haloacetamides and other nitrogenous disinfection byproducts (N-DBPs). Previous research obtained contradictory results regarding the relative importance of chlorination or chloramination for promoting these byproducts, but applied chlorine and chloramines at different doses and exposure periods. Additionally, mechanistic work, mostly using model precursors, suggested that haloacetonitrile and haloacetamide formation should be correlated because hydrolysis of haloacetonitriles forms haloacetamides. In this work, the formation of dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm) were compared across a range of chlorine and chloramine exposures for drinking waters, wastewater effluents, algal extracellular polymeric substances (EPS), NOM isolates and model precursors. While chlorination favored formation of DCAN over DCAcAm, chloramination nearly always formed more DCAcAm than DCAN, suggesting the existence of haloacetamide formation pathways that are independent of the hydrolysis of haloacetonitriles. Experiments with asparagine as a model precursor also suggested DCAcAm formation without a DCAN intermediate. Application of 15N-labeled monochloramine indicated initial rapid formation of both DCAN and DCAcAm by pathways where the nitrogen originated from organic nitrogen precursors. However, slower formation occurred by pathways involving chloramine incorporation into organic precursors. While wastewater effluents and algal EPS tended to be more potent precursors for DCAN during chlorination, humic materials were more potent precursors for DCAcAm during chlorination and for both DCAN and DCAcAm during chloramination. These results suggest that, rather than considering haloacetamides as haloacetonitrile hydrolysis products, they should be treated as a separate N-DBP class associated with chloramination. While use of impaired waters may promote DCAN formation during chlorination, use of chloramines may promote haloacetamide formation for a wider array of waters.

Dechlorination with tetravalent sulfur is widely used in wastewater treatment processes after chlorination. Dechlorination can remove certain genotoxic disinfection by-products (DBPs). However, the reactions occurring during dechlorination of chlorinated secondary effluent and their genotoxic chemicals are still very complex, and the related genotoxicity changes remain unknown. Therefore, the effects of dechlorination on genotoxicity in secondary effluent and its fractions and typical genotoxic chemical after chlorination were evaluated.The dissolved organic matter in the secondary effluent sample was separated into four fractions with XAD-8 resin. Genotoxicity of secondary effluent and its fractions was evaluated by SOS/umu test, an ISO standard method. The concentration of typical genotoxic chemical named ofloxacin was determined by liquid chromatography with a mass spectrometer and a fluorescence detector.Dechlorination with the addition of Na2SO3 notably decreased the genotoxicity in the chlorinated secondary effluent, especially in the presence of high ammonia nitrogen concentration in the sample before chlorination. The Na2SO3 addition significantly decreased the genotoxicity of the secondary effluent and its genotoxic ofloxacin prior to chlorination. The genotoxicity in the fractions containing hydrophobic acids (HOA) increased after chlorination, while addition of Na2SO3 decreased the genotoxicity induced by chlorination. Tryptophan found in HOA exhibited genotoxicity after chlorination, while dechlorination decreased the genotoxicity in chlorinated tryptophan induced by DBPs.Dechlorination was found to decrease the genotoxicity of chlorinated secondary effluent. The decrease was associated with the reduction of genotoxicity in genotoxic chemicals in secondary effluent prior to chlorination and DBPs.

The actual harmful effects of industrial wastewater can not be reflected by the conventional water quality index. Therefore, the change in dissolved organic matter and the genetic toxicity of petrochemical wastewater were observed in the current study by examining the wastewater treatment plant of a large petrochemical enterprise in Northwest China. Using XAD-8, MSC, and DA-7 resins, the wastewater was separated into six fractions, namely, hydrophobic acid (HOA), hydrophobic neutral (HOB), hydrophobic alkaline, hydrophilic acid, hydrophilic alkaline, and hydrophilic neutral. Umu-test was used to detect the genetic toxicity of the wastewater samples, and fluorescence spectra were also obtained to examine genetic toxic substances. The results show that wastewater treatment facilities can effectively reduce the concentration of organic matter in petrochemical wastewater (p<0.05). However, the mixing of aniline wastewater can increase the amount of organic carbon (p<0.05) and can overload facilities. This finding shows that the mixed collection and joint treatment of different types of petrochemical wastewater can affect the water quality of the effluent. Particularly, hydrophobic substances can be difficult to remove and account for a relatively large proportion of the effluent. The mixture of aniline wastewater can increase the genetic toxicity of the effluent (p<0.05), and biologic treatment can not effectively decrease the toxicity. Most of the genetic toxicology may exist in the HOA and HOB fractions. Fluorescence spectroscopy also confirms this result, and tryptophan-like substances may play an important role in genetic toxicity.

Chlorination of wastewater can form genotoxic, mutagenic, and/or carcinogenic disinfection byproduct (DBPs). In this study, the effect of bromide on genotoxicity in secondary effluent of a municipal wastewater treatment plant during chlorination was evaluated by the SOS/umu test. The presence of bromide notably decreased the genotoxicity in secondary effluent during chlorination, especially under conditions of high ammonia concentration. Bromide significantly decreased the concentration of ofloxacin, a genotoxic chemical in secondary effluent, during chlorination with high concentration of ammonia, while genotoxic DBPs formation of humic acid and aromatic amino acids associated with bromide limitedly contributed to the changes of genotoxicity in secondary effluent under the conditions of this study. By fractionating dissolved organic matter (DOM) in the secondary effluent into different fractions, the fractions containing hydrophilic substances (HIS) and hydrophobic acids (HOA) contributed to the decrease in genotoxicity induced by bromide. Chlorination of HOA without bromide increased genotoxicity, while the addition of bromide decreased genotoxicity.

Due to its capability for producing various microcystins, Microcystis aeruginosa is recognized as one of the most toxic, bloom-forming cyanobacteria. In this study, the fates of intra- and extracellular microcystin-LR (MC-LR) were investigated when the mixotrophic golden alga Poterioochromonas sp. (ZX1) was grazing on M. aeruginosa cells. In the control groups, the total MC-LR concentration increased with the growth of M. aeruginosa with an MC-LR content per cell of 0.5–1.5 × 10−8 μg cell−1. In the treatment with ZX1, the total MC-LR decreased linearly throughout the incubation period. In particular, intracellular MC-LR disappeared with a loss of M. aeruginosa cells in the first few days. Part of the intracellular MC-LR was released to the medium under the grazing stress, resulting in an increase of extracellular MC-LR. The degradation rate of MC-LR was positively related to the initial abundance of ZX1 and negatively related to that of M. aeruginosa. The inhibition ratio of MC-LR production dropped sharply from 98 to 67% when the initial abundance of M. aeruginosa increased from 106 to 107 cells ml−1. However, it increased from 84 to 99% when the initial ZX1 abundance increased from 104 to 105 cells ml−1. The effective removal of both M. aeruginosa cells and MC-LR was observed under lower M. aeruginosa abundance (<106 cells ml−1) and higher ZX1 abundance (>1% of M. aeruginosa abundance). Light had little impact on MC-LR degradation, but MC-LR degradation decreased due to the loss of ZX1 after 10 days of darkness. This study showed that the interactions between M. aeruginosa and ZX1 were strongly influenced by their initial abundances.

Chlorination is widely used in wastewater reclamation, however harmful disinfection byproducts (DBPs) may be formed during disinfection. These DBPs are considered as a potential and important source of endocrine-disruption. In this study, the effects of chlorination on estrogenic and antiestrogenic activities in biologically treated wastewater were evaluated by yeast two-hybrid assay. For the first time, chlorination was found to increase the antiestrogenic activity of wastewater notably and decrease the estrogenic activity. By fractionating dissolved organic matter (DOM) in wastewater into different fractions, it was found that the polar compounds (PC) fraction of DOM was the key fraction involved in increasing antiestrogenic activity during chlorination of wastewater. Furthermore, fluorescence spectroscopy analysis on different fractions of soluble organic compounds in wastewater suggested that the PC fraction contained most of the aromatic amino acids and humic/fulvic acid, which were then demonstrated as the precursors of antiestrogenic DBPs through chlorination experiments of tryptophan, humic acid, and tannic acid.

Recalcitrant volatile organic compounds with low biodegradabilities pose challenges for biofiltration technologies. In this study, the effects and mechanism of adding ozone on the performance of a biofilter were investigated. A biofilter treating chlorobenzene was set up and operated continuously for 265 days under different inlet ozone concentrations. Results showed that ozone below 120 mg m−3 could notably enhance the biofilter performance. The average chlorobenzene removal efficiency increased from 40 to 70% and then to 90% while the inlet ozone concentration rose from 0 to 40 mg m−3 and 120 mg m−3. Reducing ozone concentration resulted in a decrease in removal efficiency from 90 to 40%. Further analysis indicated that the thickness and extra-cellular polymer substance content of the biofilm were remarkably reduced while inlet ozone concentration was gradually increased. Meanwhile, the specific surface areas of the filter bed were found to increase from 784 to 820 and 880 m2 m−3. A respiratory quinone profile showed that the dominant quinone shifted from ubiquinone-8 to menaquinone-9(H2) after ozone was added. This indicated that some Gram-positive bacteria with thick cell wall became the dominant species under ozone compression.

Allelochemical ethyl 2-methyl acetoacetate (EMA) can significantly inhibit the growth of bloom-forming Microcystis aeruginosa. In order to assess the implication of the damage of EMA on the algal photosynthetic apparatus, the effects of EMA on the algal ultrastructure and pigment composition were investigated. At initial exposure time to EMA (0–40 h), algal allophycocyanin, phycoerythrin and carotenoid degraded firstly; chlorophyll a increased, especially by 47% in the algae exposed to 2 mg L−1 of EMA; phycocyanin was not significantly affected; lipid bodies increased remarkably. After 40 h of EMA exposure, chlorophyll a decreased gradually, especially by 45% in the algae exposed to 4 mg L−1 of EMA; lipid bodies greatly reduced but cyanophycin granules accumulated; thylakoid structures were dissolved or disappeared with the presence of numerous vacuoles. These results showed that all ophycocyanin, phycoerythrin and carotenoid were more sensitive to EMA than other pigments, the cells of M. aeruginosa was stressed by EMA with the occurrence of cyanophycin granules and the photosynthesis pigments and ultrastructure of M. aeruginosa were quickly destroyed by EMA with exposure time increasing.

Cryptosporidium and Giardia are two typical species of pathogenic protozoans that seriously endanger water quality. Previous works indicated that detection of Cryptosporidium and Giardia with modified United States Environmental Protection Agency (USEPA) method-1623 using a membrane filtration-elution for sample concentration attained better recovery and lower cost compared to the USEPA method-1623. Several improvements of membrane filtration-elution step as well as immunomagnetic separation (IMS) steps were investigated and an optimized method for detection of Cryptosporidium and Giardia in wastewater reclamation system was recommended in this paper. The experimental results show that an overnight soak of the membrane after scraping and vortex agitation before elution could enhance and stabilize the recovery. Increasing turbidity to 4 NTU by adding kaolin clay before filtration could effectively improve the recovery of low-turbidity water. Washing the concentrate after centrifugation and twice acid dissociation both reduced the impact of water quality to protozoan recovery. Protozoans in different water samples were determined by this optimized method, and the recovery of Cryptosporidium and Giardia were above 70% and 80% respectively, much higher than the acceptance of method-1623.

Algal-bloom control is an important issue for water environment protection as it induces several negative impacts on the lives of aquatic organisms, aquaculture, landscaping, and human health. The development of an environment-friendly, cost-effective, and convenient alternative for controlling algal bloom has gained much concern. Using the allelopathy of aquatic macrophytes as a novel and safe method for algal-bloom control is a promising alternative. This paper reviews the development and potential application about allelopathy of aquatic plants on algae, including the allelopathic research history, the potential research problems, the research methodology, and the reported aquatic macrophytes and their inhibitory allelochemicals. Potential modes of inhibition action of allelochemicals on algae, possible ways for application, and future development directions of research on algal-bloom control by aquatic macrophytes were also presented.

The effects of chlorine dioxide and chlorine disinfections on the genotoxicity of different biologically treated sewage wastewater samples were studied by umu-test. The experiment results showed that when chlorine dioxide dosage was increased from 0 to 30 mg/L, the genotoxicity of wastewater first decreased rapidly and then tended to be stable, while when the chlorine dosage was increased from 0 to 30 mg/L, the genotoxicity of wastewater changed diversely for different samples. It was then found that ammonia nitrogen did not affect the change of genotoxicity during chlorine dioxide disinfection of wastewater, while it greatly affected the change of genotoxicity during chlorine disinfection of wastewater. When the concentration of ammonia nitrogen was low (< 10–20 mg/L), the genotoxicity of wastewater decreased after chlorine disinfection, and when the concentration of ammonia nitrogen was high (> 10–20 mg/L), the genotoxicity of wastewater increased after chlorine disinfection.

Bioassays were performed to investigate the effects of the novel allelochemical, ethyl 2-methylacetoacetate (EMA), isolated from the reed (Phragmitis australis) on the growth of three common species of algae; Scenedesmus obliquus, Selenastrum capricornutum and Chlamydomonas reinhardtii. The results demonstrated that EMA has three quite different types of effect on these three species of algae. The growth of S. capricornutum was significantly inhibited by EMA during the whole cultivation period. The EC50 values of EMA on S. capricornutum was 0.6 mg L−1(7 days). However, the inhibitory effect of EMA on S. obliquus was apparent during the first 4 days of batch cultivation and then the inhibitory effect disappeared, and a stimulating effect was observed instead. The EC50 value of EMA on S. obliquus was 0.43 mg L−1(4 days). In addition, following the addition of EMA, the cells of S. obliquus and S. capricornutum became significantly larger than the normal untreated one and the algal cells changed morphologically. The microstructure of the algal cells was disrupted by the addition of EMA. There was no significant inhibition of the growth of C. reinhardtii by EMA, but cell motility was affected.

Tetracycline-resistant bacteria (TRB) are of concern as emerging microbial contaminants in reclaimed water. To understand the effects of UV disinfection on TRB, both inactivation and reactivation profiles of TRB, as well as 16 tetracycline-resistant isolates from secondary effluent, were characterized in this study. The inactivation ratio of TRB was significantly lower (3.0-log) than that of heterotrophic bacteria (> 4.0-log) in the secondary effluent. Additionally, the proportion of TRB significantly increased from 1.65% to 15.51% under 20 mJ/cm2 ultraviolet (UV) exposure. The inactivation rates of tetracycline-resistant isolates ranged from 0.57/s to 1.04/s, of which tetracycline-resistant Enterobacter-1 was the most tolerant to UV light. The reactivation of TRB, tetracycline-resistant isolated strains, as well as heterotrophic bacteria commonly occurred in the secondary effluent even after 20 mJ/cm2 UV exposure. The colony forming ability of TRB and heterotrophic bacteria reached 3.2-log and 3.0-log under 20 mJ/cm2 UV exposure after 22 hr incubation. The final inactivation ratio of tetracycline-resistant Enterobacter-1 was 1.18-log under 20 mJ/cm2 UV exposure after 22 hr incubation, which is similar to those of TRB (1.18-log) and heterotrophic bacteria (1.19-log). The increased proportion of TRB and the reactivation of tetracycline-resistant enterobacteria in reclaimed water could induce a microbial health risk during wastewater reuse.Download full-size image

Most natural algicides including macrophytic allelochemicals are known to selectively inhibit algal growth. The investigations on the modes of action about the species-specific algicides are little. In this study, the effects of allelochemical ethyl 2-methyl acetoacetate (EMA) identified from reed (Phragmites communis) on the growth, physiological, and biochemical processes of green alga Selenastrum capricornutum were investigated. The results showed that EMA had multiple effects on the growth of S. capricornutum under different initial algal densities (IADs). The algal growth was inhibited by EMA at low IADs, but stimulated at high IADs. Further, the potential modes of action of EMA on S. capricornutum were explored from ultrastructure, metabolic activity, reactive oxygen species level, and lipid peroxidation to trace the microenvironment changes in the algal cells. Damage in cell structure occurred at low IAD, but cells were well developed with increased metabolic activity at high IAD. The reactive oxygen species (ROS) levels were increased under both conditions. The increase of ROS level was acute at low IAD but slow at high IAD. EMA caused significant lipid peroxidation, i.e. oxidative damage on membrane lipids at low IAD but not at high IAD. Based on these results, the initial algal density is considered an important factor to influence algal growth and physiological and biochemical responses to EMA, the effects of EMA on S. capricornutum may be “hormesis-like”, and different ROS increase ratio may be directly related with different responses of S. capricornutum to EMA.

The prevalence of antibiotic-resistant bacteria in municipal wastewater treatment plants (WWTPs) is becoming a concern of public health. In order to acquire information on the emission of antibiotic-resistant bacteria from WWTP effluents into natural waters, both average antibiotic tolerance and concentrations of antibiotic-resistant bacteria in the effluent of a WWTP in Beijing, China were investigated. A new index of IC50/MIC ratio (the antibiotic concentration required to inhibit 50% of total heterotrophic bacteria compared to the highest minimum inhibitory concentration value of a group of pathogens according to a specific antibiotic, as defined by CLSI) was used to reflect the average antibiotic tolerance of total heterotrophic bacteria in the secondary effluent. The results showed that the IC50/MIC ratios of heterotrophic bacteria in the secondary effluent to penicillin, ampicillin, cephalothin, chloramphenicol and rifampicin were > 2, > 1, > 1, and 1.08, respectively, which reflected a significantly high general level of heterotrophic bacteria found in the secondary effluent resistant to these five antibiotics. The concentrations of penicillin-, ampicillin-, cephalothin-, and chloramphenicol-resistant bacteria were as high as 1.5 × 104–1.9 × 105, 1.2 × 104–1.5 × 105, 8.9 × 103–1.9 × 105 and 2.6 × 104–2.0 × 105 CFU/mL, and the average percentages in relation to total heterotrophic bacteria were 63%, 47%, 55%, and 69%, respectively. The concentrations of tetracycline- and rifampicin-resistant bacteria were 840–6.1 × 103 and 310–6.1 × 104 CFU/mL with average percentages of 2.6% and 11%, respectively. Furthermore, our study found that five- and six-antibiotic-resistant bacteria were widely distributed in four types of enterobacteria from the secondary effluent. The presence of multiple-antibiotic-resistant bacteria from effluents of WWTPs into natural waters could pose a serious problem as a secondary pollutant of drinking water.Research Highlights► A new index of IC50/MIC ratio (the antibiotic concentration required to inhibit 50% of total heterotrophic bacteria compared to the highest minimum inhibitory concentration value of a group of pathogens according to a specific antibiotic, as defined by CLSI) was developed to reflect the average antibiotic tolerance of total heterotrophic bacteria in the secondary effluent. ► Both average antibiotic tolerance and concentrations of bacteria resistant to six antibiotics were evaluated in the effluents of the municipal wastewater treatment plant. ► Five- and six-antibiotic-resistant bacteria were widely distributed in four types of enterobacteria from the secondary effluent.

•We investigate fate of TCs, TRB and eight TRGs in modified AAO process.•TRB and THB, tetM and tetO, tetE and tetX showed significant correlation.•Relationship between RPP genes, EM genes and TCs were examined for the first time.•TRGs can only be partly removed by ozonation.The fate of trace tetracycline, tetracycline resistant bacteria (TRB) and tetracycline resistant genes (TRGs) in an improved anaerobic-anoxic-oxic (AAO) wastewater treatment plant (WWTP) was investigated in this study. Quantitative real-time polymerase chain reaction (qPCR) and conventional heterotrophic plate count method were used to measure eight tet genes (tetA, tetB, tetC, tetE, tetM, tetO, tetS and tetX) and TRB, respectively. The TRB percent of total heterotrophic bacteria (THB) is about 1.31–24.1% in WWTP influent. Tet gene abundance in the WWTP varied greatly among the gene types. The concentrations of TRGs in effluent samples ranged from 7.11 × 10−9 to 1.53 × 10−4 copies/copy 16S rRNA gene. TRB and THB, tetM and tetO, tetE and tetX, but not the others, showed a significant correlation with each other (p < 0.01). The relationships between ribosomal protection protein genes, enzymatic modification gene and corresponding concentrations of antibiotics were found to be considerably significant (R2 = 0.898, p < 0.01 for ribosomal protection protein genes and R2 = 0.872, p < 0.05 for enzymatic modification gene).

Coupling of biodiesel production and wastewater treatment based on microalgae is a promising approach for handling the energy crisis of declining fossil fuel reserves. A freshwater microalga, Scenedesmus sp. LX1, isolated in a previous study, was tested for its ability to remove nutrients and accumulate lipid while growing in secondary effluent. Compared with 11 other species of high-lipid content microalgae obtained from the algae bank, Scenedesmus sp. LX1 adapted better to secondary effluent and achieved the highest biomass (0.11 g L−1, dry weight) and lipid content (31–33%, dry weight). In secondary effluent, the specific growth rate (r) and maximum population growth rate (Rmax) of Scenedesmus sp. LX1 was 0.2 day−1 and 0.23 × 106 cells (mL day)−1, respectively, and inorganic nutrients could be efficiently removed by over 98% in 10 days. Upon a trigger of nitrogen deficiency on day 10, lipid content increased from 14% to 31%, and the highest lipid accumulation rate during cultivation was 0.008 g (L day)−1.

Macrophytic allelochemicals are considered an environment-friendly and promising alternative to control algal bloom. However, studies examining the potential mechanisms of inhibitory allelochemicals on algae are few. The allelochemical ethyl 2-methyl acetoacetate (EMA), isolated from reed (Phragmites communis), was a strong allelopathic inhibitor on the growth of Microcystis aeruginosa. EMA-induced antioxidant responses were investigated in the cyanobacterium M. aeruginosa to understand the mechanism of EMA inhibition on algal growth. The activities of enzymatic antioxidants superoxide dismutase (SOD) and catalase (CAT), and the contents of non-enzymatic antioxidants reduced glutathione (GSH) and ascorbic acid (AsA) of M. aeruginosa cells were analyzed after treatments with different concentrations of EMA. Exposure of M. aeruginosa to EMA caused changes in enzyme activities and contents of non-enzymatic antioxidants in different manners. The decrease in SOD activity occurred first after 4 h of EMA exposure, and more markedly after 40 h. CAT activity did not change after 4 h of EMA exposure, but increased obviously after 40 h. The contents of AsA and GSH were increased greatly by EMA after 4 h. After 60 h, low EMA concentrations still increased the CAT activity and the contents of AsA and GSH, but high EMA concentrations started to impose a marked suppression on them. EMA increased dehydroascorbate (DHAsA) and oxidized glutathione (GSSG) contents during all exposure times. After 60 h, the regeneration rates of AsA and GSH (represented by the AsA/DHAsA ratio and GSH/GSSG ratio, respectively) were reduced by high EMA concentrations. These results suggest that the activation of CAT and the availability of AsA and GSH at early exposure are important to counteract the oxidative stress induced by EMA, and the inactivation of SOD may be crucial to the growth inhibition of M. aeruginosa by EMA.

•A fouled RO membrane in a full-scale plant for wastewater reclamation was autopsied.•Organic matter (occupied 75% of the deposit) was the major problem for RO membrane.•Hydrophobic acids and hydrophilic neutrals were the largest fractions in deposit.•Hydrophilic neutrals on RO membrane were produced by microbes instead of depositing.•Inorganic scaling of the RO membrane was mainly caused by element Fe, Ca and Si.A fouled RO membrane from a full-scale municipal wastewater reclamation plant was autopsied to elucidate fouling characteristics and behavior associated with feed water quality. Organic pollution (occupied 75% of the deposit) was the major problem for the RO membrane. The deposit dissolved in NaOH solution was 2.37 g-DOC/m2 and largely comprised of microbial-derived organic matter (OM) and humic-like OM. Hydrophobic acids (HOA) and hydrophilic neutrals (HIN) were the two largest fractions in the deposit among the six fractions of HOA, hydrophobic bases (HOB), hydrophobic neutrals (HON), hydrophilic acids (HIA), hydrophilic bases (HIB) and HIN. HOA fraction could deposit on the membrane easily and should be monitored as key fractions to predict the organic fouling of RO membrane. HIN fraction occupied 34.2% of the total DOC in the deposit, but it was suggested that HIN fraction in the deposit was produced by the microorganisms on the membrane instead of depositing. The inorganic scaling of the RO membrane was mainly caused by element Fe, Ca and Si. The content of Fe was the highest (349.18 mg/m2), since Fe deposited on the RO membrane much more easily than other elements. Ca presented the lowest deposition ratio (0.0017%) due to the effective function of the antiscalant.

•Factors affecting cytotoxicity formation were investigated.•A method for evaluating cytotoxicity formation potential was developed.•AOX formation could serve as a surrogate for cytotoxicity formation.•UV254 could serve as a surrogate for cytotoxicity formation potential.Toxic and harmful disinfection byproducts (DBPs) were formed during wastewater chlorination. It was recently suggested that cytotoxicity to mammalian cells reflects risks posed by chlorinated wastewater. Here, ATP assays were performed to evaluate the cytotoxicity to mammalian cells. Chlorination significantly increased cytotoxicity of treated wastewater. Factors affecting cytotoxicity formation during wastewater chlorination were investigated. Quenching with sodium thiosulfate and ascorbic acid decreased the formed cytotoxicity, while ammonium kept the cytotoxicity stable. The chlorine dose required for the maximum cytotoxicity increase was dramatically affected by DOC and ammonia concentrations. The maximum cytotoxicity increase, defined as the cytotoxicity formation potential (CtFP), occurred when wastewater was treated for 48 h with a chlorine dose of 2·DOC + 11·NH3N + 10 (mg-Cl2/L). During chlorination, the amounts of AOX formation was found to be significantly correlated with cytotoxicity formation when no DBPs were destroyed. AOX formation could be used as a surrogate to estimate cytotoxicity increase during wastewater chlorination. Besides, the CtFP of 14 treated wastewater samples was assessed ranged from 5.4–20.4 mg-phenol/L. The CtFP could be estimated from UV254 of treated wastewater because CtFP and UV254 were strongly correlated.Download full-size image

•UV/chlorine showed synergistic degradation of DDBAC than UV and chlorination.•DDBAC degraded through both UV photolysis and radicals oxidation during UV/chlorine.•Degradation pathway of DDBAC during UV/chlorine oxidation was proposed.•Formation of chlorinated products decreased with extended UV/chlorine oxidation.•UV/chlorine oxidation was efficient at DDBAC detoxification.Benzalkonium chlorides (BACs), as typical cationic surfactants and biocides widely applied in household and industrial products, have been frequently detected as micropollutants in many aquatic environments. In this study, the combination of UV irradiation and chlorine (UV/chlorine), a newly interested advanced oxidation process, was used to degrade dodecylbenzyldimethylammonium chloride (DDBAC). UV/chlorine showed synergistic effects on DDBAC degradation comparing to UV irradiation or chlorination alone. Radical quenching experiments indicated that degradation of DDBAC by UV/chlorine involved both UV photolysis and radical species oxidation, which accounted for 48.4% and 51.6%, respectively. Chlorine dosage and pH are essential parameters affecting the treatment efficiency of UV/chlorine. The pseudo first order rate constant (kobs, DDBAC) increased from 0.046 min−1 to 0.123 min−1 in response to chlorine dosage at 0–150 mg/L, and the degradation percentage of DDBAC within 12 min decreased from 81.4% to 56.6% at pH 3.6–9.5. Five main intermediates were identified and semi-quantified using HPLC-MS/MS and a possible degradation pathway was proposed. The degradation mechanisms of DDBAC by UV/chlorine included cleavage of the benzyl-nitrogen bond and hydrogen abstraction of the alkyl chain. Trichloromethane (TCM), chloral hydrate (CH), trichloropropanone (TCP), dichloropropanone (DCP) and dichloroacetonitrile (DCAN) were detected using GC-ECD. The formation of chlorinated products increased rapidly initially, then decreased (TCM, TCP, DCP and DCAN) or remained stable (CH) with extended treatment. The actual formation of TCM peaked at 30 min (50.3 μg/L), while other chlorinated products did not exceed 10 μg/L throughout the process. Based on the luminescent bacterial assay, DDBAC solution underwent almost complete detoxification subjected to UV/chlorine treatment for 120 min, which is more effective than UV irradiation or chlorination alone.

•Ozone removed methylisothiazolone (MIT) and its toxicity to Daphnia magna Straus.•MIT ozonation rate constant and activation energy were determined.•Change of pH from 3 to 9 had limited impact on MIT ozonation rate.•MIT ozonation pathway had been proposed using time-of-flight mass spectrometry.•Relationship between ozone consumption and MIT reduction were tested for application.Methylisothiazolone (MIT) is a common biocide that is widely used in water-desalination reverse-osmosis processes. The transformation of MIT during water treatment processes is poorly understood. The kinetics and mechanisms involved in the degradation of MIT during ozonation were investigated in this study. Ozonation was found to be a useful way of degrading MIT in water, and the degradation rate constant was 0.11 (±0.1) × 103 L/(mol·s). The degradation rate constant did not change when the pH was increased from 3 to 9. The pre-exponential factor A and the activation energy Ea for the ozonation process were 7.564 × 1013 L/(mol·s) and 66.74 kJ/mol, respectively. The decrease in the MIT concentration and the amount of ozone consumed were measured, and the stoichiometric factor α for the ozone consumption to MIT removal ratio was found to be 1.8. Several ozonation products were detected using time-of-flight mass spectrometry. Almost 32% of the organic sulfur in the MIT was oxidized to release sulfate ions, which caused a decrease in pH. Sulfur atoms were oxidized to sulfone species and then hydrolyzed to give sulfate during ozonation. Addition reactions involving carbon–carbon double bonds and the oxidation of α-carbon atoms also occurred. MIT was found to be lethal to Daphnia magna Straus (D. magna) with a median lethal concentration of 18.2 μmol/L. Even though the primary ozonation products of MIT still showed some toxicity to D. magna, ozone could minimize the toxic effect after a long reaction time.