Land application of organic manure, crop residue, and biosolid, an important means for the disposal and recycling of wastes, has been shown to significantly increase the amount of dissolved organic matter (DOM) in soil. However, limited information is available on the dynamics of DOM, the concentration is usually expressed by dissolved organic carbon (DOC), and its influence on Cd behaviors in paddy soil amended with and without organic materials during rice (kinmaze) growing season. In this study, in situ field experiments were conducted to investigate the dynamics of DOC in paddy soil amended with green manure (GM), pig manure (PM), and chemical fertilizer (F) and its effect on Cd mobility and bioavailability. The results showed that DOC concentrations in soil solutions extracted from different depths were higher in GM and PM plots than those in F plot, and DOC concentrations all declined with time and rice growth. DOC concentrations in the root zone soil for all treatments were higher than those in the non-root zone due to root exudation and the higher pH value. The temporal dynamics of DOC in the root zone were found to be correlated to rice growth stage, as DOC concentrations decreased in the initial stage (week 1 to 6) of rice seedling and then gradually increased and reached the highest levels with 30.42 mg DOC L−1 for GM, 28.88 mg DOC L−1 for PM, and 19.19 mg DOC L−1 for F at rice heading and flowering stage (week 10), hereafter decreased again until when the rice was harvested. However, soil DOC in the non-root zone exhibited a continuous decrease trend and remained at a relatively low level after week 10 with 15.36 mg DOC L−1 for GM, 15.31 mg DOC L−1 for PM, and 8.43 mg DOC L−1 for F. The dynamics of water soluble Cd displayed statistically significant positive relationship with DOC (r0.01 = 0.765, n = 9) regardless of soil depth and root presence/absence, suggesting that DOC enhanced the mobility and transport of through the formation of Cd-DOC complexes. As a result, DOC could increase the potential uptake of Cd by rice as well as the downward Cd migration to deeper soil. In these experiments, the uptake of Cd by rice grown in the GM and PM plots reached 5.55 and 3.71 mg plot−1, respectively, which were much higher than that in the F plot with 1.88 mg plot−1. The amounts of Cd downward migration were 17.0 mg plot−1 for GM plot, 14.74 mg plot−1 for PM plot, and 4.13 mg plot−1 for F plot, respectively. It could be concluded that the application of green manure and pig manure to Cd-contaminated paddy soil will increase the risk of Cd uptake by rice and Cd downward migration into groundwater. For this reason, care should be taken when organic manures was applied to contaminated soil to remediate or alleviate soil pollution and maintain soil fertility as well as provide nutrients for plant growth.

•Flower-like CuO microstructure was prepared by MW-US assisted method.•The prepared CuO can catalyze the reduction Cr(VI) by tartaric acid under simulated solarlight.•The formation of ≡Cu(II)-tartaric acid complex play a key role in the reduction of Cr(VI).•The catalyst can operate effectively at a relatively wide range of pH.In this study, flower-like CuO was successfully synthesized by a microwave–ultrasound assisted method and well characterized by X-ray diffractions, Fourier transform infrared spectrum, scanning electron microscopy, transmission electron microscopy, specific surface area, UV–vis diffused reflection spectra, X-ray photoelectron spectroscopy and point of zero charge. The photocatalytic performance of the as-prepared CuO was examined on the Cr(VI) reduction in the presence of tartaric acid under simulated solarlight irradiation. The results show that the developed CuO catalyst exhibited good photocatalytic activity with 100% reduction of Cr(VI) after irradiation of 30 min under the test condition of c(Cr(VI)) = 100 μM, catalyst loading = 400 mg/L, c(tartaric acid) = 4 mM and initial pH = 3. The reaction mechanism was proposed. The effects of test parameters, such as catalyst loading, tartaric acid concentration and initial pH, on Cr(VI) reduction efficiency were also investigated. It is worth mentioning that the developed catalyst can work at a relatively wide range of pH with quite high catalytic performance.

•β-FeOOH was prepared by a microwave–ultrasound assisted method.•The synthesis parameters were optimized by response surface methodology.•The interaction between microwave and ultrasound had a influence on the catalytic properties of the prepared β-FeOOH.•The β-FeOOH sample exhibited considerable catalytic activity in weak alkaline solution and under visible light irradiation.In this study, nanoparticles of single-phase akaganeite (β-FeOOH) were synthesized by an ultrasound–microwave assisted method. The synthesis parameters were optimized by means of response surface methodology. X-ray diffractions (XRD), Fourier transform infrared spectrum (FTIR), UV–vis diffused reflection spectra (UV–vis DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and specific surface area were used to characterize the as-prepared samples. The catalytic activity of the prepared β-FeOOH was evaluated in a heterogeneous photo-Fenton-like process using methyl orange as target pollutant. It is found that the reaction temperature and interaction between microwave and ultrasound have a significant influence on the catalytic properties of the prepared β-FeOOH samples. The β-FeOOH prepared at microwave power of 400 W, ultrasound power of 200 W, reaction temperature of 70 °C and reaction time of 3 h, exhibited considerable catalytic activity in weak alkaline solution and under visible light irradiation, which would be of great promise for the industrial application of this catalyst to oxidize organic pollutants for wastewater treatment.

Ammonium and hydronium jarosite were prepared by hydrothermal method with urea as the homogeneous precipitant. X-ray diffraction, field-emission scanning electron microscope, X-ray photoelectron spectrum, UV–vis spectra and fourier transform infrared spectrum were used to characterize the resulting products. The photodegradation efficiency of the prepared ammonium and hydronium jarosite was studied in a photo-Fenton-like process using methyl orange (MO) as target pollutant. The photocatalytic degradation of MO over synthetic ammonium and hydronium jarosite under various conditions, such as catalysts loading, H2O2 concentration and initial pH, has been investigated. Results show that ammonium and hydronium jarosite have satisfactory photocatalysis effect in degradation of MO azo dye, and that the reactivity of hydronium jarosite toward the mineralization of MO was higher than that of ammonium jarosite. The novel ammonium and hydronium jarosite catalysts would be important for industrial applications due to their high photoactivity, little iron leaching and low cost.Highlights► Hydronium and ammonium jarosite could catalyze the oxidation of methyl orange in photo-Fenton-like process. ► The oxidation process is essentially heterogeneous, not homogeneous. ► Hydronium jarosite has stronger reactivity than ammonium jarosite.

In this study, a series of bath experiments were carried out to investigate the photoreduction of Cr(VI) by small molecular weight organic acids (SOAs) over jarosite, a mineral found in acid mine drainage (AMD). The results demonstrated that jarosite or SOAs alone was unable to effectively transform Cr(VI) to Cr(III) even if exposed to an illumination of mimic solar light. However, an addition of jarosite significantly enhanced the reduction of Cr(VI) by SOAs under the same condition. The photocatalytic reduction of Cr(VI) was strongly influenced by pH, the initial concentrations and the structures of SOAs. Of the tested two SOAs, the reaction rates of photocatalytic reduction of Cr(VI) were in the order of oxalic acid > citric acid. The reaction obeyed to zero-order kinetics with respect to Cr(VI) with excess SOAs. A possible mechanism for photoreduction of Cr(VI) by SOAs over jarosite was proposed.Highlights► Jarosite was obtained through oxidation of FeSO4 by A. ferrooxidans. ► Jarosite was an efficient photocatalyst for Cr(VI) reduction by organic acids. ► Jarosite photoreduction of Cr(VI) depended on the structures of organic acids.

During the processes of secondary iron hydroxysulfate mineral formation, Fe2+ ion was oxidized by the following three methods: (1) biooxidation treatment by Acidithiobacillus ferrooxidans (A. ferrooxidans); (2) rapid abiotic oxidation of Fe2+ with H2O2 (rapid oxidation treatment); (3) slow abiotic oxidation of Fe2+ with H2O2 (slow oxidation treatment). X-ray diffraction (XRD) patterns, element composition, precipitate weight and total Fe removal efficiency were analyzed. The XRD patterns and element composition of precipitates synthesized through the biooxidation and the slow oxidation treatments well coincide with those of potassium jarosite, while precipitates formed at the initial stage of incubation in the rapid oxidation treatment showed a similar XRD pattern to schwertmannite. With the ongoing incubation, XRD patterns and element composition of the precipitates that occurred in the rapid oxidation treatment were gradually close to those in the biooxidation and the slow oxidation treatments. Due to the inhibition of A. ferrooxidans itself and its extracellular polymeric substances (EPS) in aggregation of precipitates, the amount of precipitates and soluble Fe removal efficiency were lower in the biooxidation treatment than in the slow oxidation treatment. Therefore, it is concluded that Fe2+ oxidation rate can greatly affect the mineral phase of precipitates, and slow oxidation of Fe2+ is helpful in improving jarosite formation.Highlights► Slow oxidation of Fe2+ is helpful in jarosite formation. ► The already-formed schwertmannite can be gradually transformed to jarosite. ► Precipitates formation can be inhibited probably by EPS from A. ferrooxidans.

In order to accurately predict the types of biogenic iron hydroxysulfate precipitates in acidic, sulfate-rich environments facilitated by Acidithiobacillus ferrooxidans, different initial concentrations of Fe2 +, K+, Na+, and NH4+ are selected and tested in batch experiments for the formation of the precipitates. The critical equations of jarosite formation in FeSO4–K2SO4–H2O system or FeSO4–(NH4)2SO4–H2O system could be described as Y = − 22120.8077 − 0.04257x + 0.006170x2 (R2 = 0.9979) or Y = 0.03540 − 0.002950x + 7.407E − 5x2 (R2 = 0.9934), respectively, where Y is the threshold or critical values of the molar ratio of Fe/K or Fe/NH4 for jarosite formation, and x (mmol/L) is the initial concentration of Fe(II). Schwertmannite is the sole biogenic secondary ferric mineral when molar ratio of Fe/K or Fe/NH4 is higher than Y in the system with a given initial Fe(II) concentration. The precipitates are an admixture of schwertmannite and jarosite, or pure jarosite when the Fe/M molar ratio is lower than Y. The crystallinity of the secondary ferric minerals increased with the increase of initial Fe(II) concentration in the medium with a fixed K+ concentration. It is observed that the capacity of monovalent cation in promoting jarosite formation is K+ > NH4+ > Na+, as exhibiting that the capacity of K+ in this process is about 75 and 200 times greater than NH4+ and Na+, respectively. Obviously, both the initial concentration of Fe(II) and molar ratio of Fe to monovalent cation determine the types of biogenic iron hydroxysulfate precipitates.Highlights► Study on the formation of precipitates in acidic, sulfate-rich environments. ► Relationships between mineralogy and initial Fe(II) conc. and Fe/K molar ratios. ► Both the initial Fe(II) and K+ determine the type of iron precipitates.

The bioleaching technique with Acidithiobacillus species has been shown to be an efficient and cost-effective means in removing heavy metals from tannery sludge. However, tannery sludge dissolved organic matter (DOM) is toxic to Acidithiobacillus species and results in decreasing the efficiency of Cr removal from sludge. Here we report the role of an acid-tolerant DOM-degrading heterotrophic microorganism P. spartinae D13 successfully isolated from local tannery sludge in improving activities of A. ferrooxidans LX5 and A. thiooxidans TS6. In tannery sludge DOM-rich liquid culture medium coinoculated with P. spartinae D13 and Acidithiobacillus species, the activities of A. ferrooxidans LX5 and A. thiooxidans TS6 are increased by 33- and 12-fold, respectively. In four successive batches of tannery sludge bioleaching trials by circulating 10% of acidified bioleached sludge, the addition of Pichia spartinae D13 could shorten bioleaching time by 3 days in the first batch and obtained more than 90% of Cr removal efficiency within 6 days. However, the effectiveness of P. spartinae D13 in improving bioleaching maintain only four successive recycle or batches until P. spartinae D13 inoculum is replenished in the fifth batches. Therefore, for enhancing the activity of Acidithiobacillus species in bioleaching system, P. spartinae D13 should be added periodically at a given batch interval.

Akaganéite (β-FeOOH) is a major iron oxyhydroxide component in some soils, marine concretions, and acid mine drainage environments. Recently, synthetic β-FeOOH has been found to be a promising absorbent in the treatment of metal-contaminated water. It has been recognized in previous study that akaganéite could be formed via FeCl2 chemical oxidation under specific conditions. Here we report a novel and simple method for akaganéite bioformation from FeCl2 solution oxidized by Acidithiobacillus ferrooxidans LX5 cells at 28 °C. After acclimation in modified 9K medium containing 0.2 M chloride, Acidithiobacillus ferrooxidans cells had great potential for oxidization of Fe2+ as FeCl2 solution, and then resulted in the formation of precipitates. The resulting precipitates were identified by powder X-ray diffraction and transmission FT−IR analyses to be akaganéite. Scanning electron microscopy images showed the akaganéite was spindle-shaped, approximately 200 nm long with an axial ratio of about 5, and the spindles had a rough surface. X-ray energy-dispersive spectral analyses indicated the chemical formula of the crystalloid akaganéite could be expressed as Fe8O8(OH)7.1(Cl)0.9 with Fe/Cl molar ratio of 8.93. The biogenetic akaganéite had a specific surface area of about 100 m2 g−1 determined by BET method.

Iron (oxyhydr)oxides play important roles in the fixation of toxic elements and also in the distribution of nutrients for plants in soils. Aakaganéite and schwertmannite, as the iron oxyhydroxides having an analogous tunnel structure, have been widely recognized in Fe-rich environments. The objective of this study was to examine the formation of akaganéite/schwertmannite via biooxidation of 0.1 M of ferrous solution containing only Cl−, SO42− or both the anions with a Cl−/SO42− mole ratio of 1, 3, 6, and 10 by chloride-acclimated Acidithiobacillus ferrooxidans cells. Results showed that ferrous iron in chloride/sulfate-containing solutions could be easily biooxidized to ferric iron, and subsequent Fe(III)-hydrolysis/precipitation could result in the formation of large quantity of akaganéite/schwertmannite precipitates. The resulting precipitates were identified to be the pure akaganéite (Fe8O8(OH)7.1(Cl)0.9, the pure schwertmannite (Fe8O8(OH)4.42(SO4)1.79, and the main schwertmannite phase (Fe8O8(OH)8−2x(SO4)x, with 1.09≤ × ≤1.73), respectively, under different Cl−/SO42− mole ratio conditions. Obviously, sulfate inhibited drastically the bioformation of akaganéite but facilitated schwertmannite phase occurrence in the ferrous solution containing both sulfate and chloride. However, the presence of chloride ion in initial ferrous solution containing sulfate and Acidithiobacillus ferrooxidans cells would affect the morphology and other characteristics of schwertmannite generated.

Secondary minerals such as Fe(OH)3 and jarosite are often hypothesized to be formed in sludge during bioleaching processes involving Acidithiobacillus ferrooxidans and be responsible for the lower solubilization efficiencies of sludge-borne metals. Schwertmannite is a ubiquitous mineral formed in acid mine drainage (AMD) impacted environments. However, the authors report for the first time the occurrence of schwertmannite as the sole secondary Fe mineral in a dissolved organic matter (DOM)-rich tannery sludge bioleaching system and its scavenging effect on soluble metals in bioleached sludge. The tannery sludge bioleach solution with pH ∼3 was mainly rich in Fe, Cr(III), SO42- and Acidithiobacillus ferrooxidans, but also contained high concentrations of DOM (300–400 mg C L−1). The ocherous precipitate that formed rapidly within 40 h in the sludge bioleach solution during incubation was identified to be pure schwertmannite by XRD and FTIR. Results of SEM coupled with EDS analyses showed that the schwertmannite was present as spherical particles with a diameter of about 1 μm and its chemical formula could be expressed as Fe8O8(OH)4.6(SO4)1.7. Newly formed schwertmannite contained about 2.43% Cr(III) derived from already solubilized sludge-borne Cr(III) by bioleaching, suggesting a strong adverse influence of schwertmannite formation on solubilization efficiency of metals from sludge. Biogenic Fe mineral synthesis experiments varying the concentrations of DOM and metals indicated that the occurrence of schwertmannite as a monominerallic phase in the sludge bioleaching environment was predominantly attributed to the presence of insufficient concentrations of monovalent cations and the high content of DOM. Moreover, the short reaction time, high SO42- concentration and low pH value in this system also facilitated the existence of monominerallic schwertmannite.

•Composting of bioleached dewatered sludge (BS) in a commercial scale was studied.•BS composting drastically reduces ammonia emission and improves compost quality.•Factors inhibiting ammonia volatilization in BS composting were evaluated.Sludge bioleaching technology with Acidithiobacillus species has been commercially adopted for improving advanced dewatering of sludge in China since 2010. However, up to now, little information on bioleached dewatered sludge (BS) composting is available. Here, we report the changes of physicochemical and biological properties in BS composting and evaluate compost product quality compared to conventional dewatered sludge (CS) composting in an engineering scale composting facility. The results showed that the amount of bulking agents required in BS composting was only about 10% of CS composting to obtain optimum moisture content, reducing about 700 kg bulking agents per ton fresh sludge. pH of BS composting mixture was slightly lower consistently by about 0.2–0.3 pH units than that in CS mixture in the first 30 days. Organic matter biodegradation in BS system mainly occurred in the first 9 days of composting. In spite of higher content of NH4+-N was found in BS mixture in related to CS mixture; unexpectedly the cumulative ammonia volatilization in the former was only 51% of the latter, indicating that BS composting drastically reduced nitrogen loss. Compared to CS composting system, the relative lower pH, the higher intensity of microbial assimilation, and the presence of water soluble Fe in BS system might jointly reduce ammonia volatilization. Consequently, BS compost product exhibited higher fertilizer values (N + P2O5 + K2O = 8.38%) as well as lower heavy metal levels due to the solubilization of sludge-borne heavy metals during bioleaching process. Therefore, composting of BS possesses more advantages over the CS composting process.

To assess the feasibility of biogenic schwertmannite to act as a sorbent for removing arsenite from groundwater, a series of biogenic schwertmannite-packed column adsorption experiments were conducted on simulated As(III)-containing groundwater. Empty bed contact time (EBCT), As(III) concentration in effluent, and the removal efficiency of As(III) through the column were investigated at pH 8.0 and temperature 25 ± 0.5 °C. The results showed that the breakthrough curves were mainly dependent on EBCT values when the influent As(III) concentration was 500 μg L−1 and the optimum EBCT was 4.0 min. When the effluent As(III) concentration reached 10 and 50 μg L−1, the breakthrough volumes for the schwertmannite adsorption column were 4 200 and 5 600 bed volume (BV), with As(III) adsorption capacity of 2.1 and 2.8 mg g−1, respectively. Biogenic schwertmannite could be regenerated by 1.0 mol L−1 NaOH solution, and more than 80% of As(III) adsorbed on the surface of schwertmannite could be released after 3 successive regenerations. The breakthrough volume for the regenerated schwertmannite-packed column still maintained 4 000–4 200 BV when the As(III) concentration in effluent was below 10 μg L−1. Compared with other sorbents for As(III) removal, the biogenic schwertmannite-packed column had a higher breakthrough volume and a much higher adsorption capacity, implying that biogenic schwertmannite was a highly efficient and potential sorbent to purify As(III)-contaminated groundwater.

A novel phenanthrene (PHE)-degrading strain named as Sphingomonas sp. GF2B was isolated and identified from a farmland soil. Effects of a synthetic surfactant (Tween-80) and a rhamnolipid biosurfactant on PHE degradation by Sphin-gomonas sp. GF2B were investigated at different concentrations of the surfactants. The results showed that Sphingomonas sp. GF2B was able to mineralize up to 83.6% of PHE within 10 days without addition of surfactants. The addition of Tween-80 to the reaction medium inhibited greatly PHE biodegradation, with only 33.5% of PHE degraded. However, the biosurfactant facilitated PHE biodegradation, with up to 99.5% of PHE degraded. The preferential utilization of PHE as a carbon source and the enhanced solubility of PHE by the biosurfactant were likely responsible for the higher biodegradation efficiency of PHE in the presence of the biosurfactant. Therefore, it could be concluded that the application of the biosurfactant to PHE-contaminated soils was perhaps a feasible way to facilitate the PHE biodegradation.