•pH affected performances of anaerobic fermentation of spent mushroom compost (SMC).•The maximum volatile fatty acid (VFA) concentration was 3479.59 mg/L at pH 10.0•Acetate was the dominant kind of VFAs with a range of 53–71% for all conditions.•NH4+-N was released in range of 19.56–27.12 mg/g VS.•PO43−-P was released in range of 3.47–15.76 mg/g VS.To enhance volatile fatty acid (VFA) production from spent mushroom compost (SMC), the effect of pH from 4.0 to 12.0 was investigated in this study. The results indicated that higher VFA concentration was achieved under alkaline condition compared to acid condition and control. The maximal VFA concentration was 3479.59 mg/L at a pH of 10.0, which was 50.63% higher than the control without pH control. Acetate accounted for more than 50% of total VFAs in all pH values. The NH4+-N and PO43−-P release was in range of 19.56–27.12 mg/g VS and 3.47–15.76 mg/g VS, respectively. Furthermore, the Logistic-based model could well explained the VFA production in this study. Therefore, alkaline fermentation can be considered a promising technology for VFA production from SMC and the optimal pH should be selected as 10.0.

•Two-stage A/O-MBR showed a pretty performance for landfill leachate treatment.•Microbial community structure was successfully studied via high-through sequencing.•Relationships between primary microbes and environment was analyzed with PCoA.In this study, a laboratory-scale two-stage anoxic/oxic (A/O) combined membrane bioreactor (MBR) was operated for 113 d for the treatment of landfill leachate. The average removal of chemical oxygen demand (COD), ammonia (NH4+-N) and total nitrogen (TN) achieved 80.60%, 99.04% and 74.87%, respectively. A mass balance evaluation suggested that the removal of COD, NH4+-N and TN occurred mainly in the second A/O process, and the total removal capacity of COD, NH4+-N and TN were 125.60 g/d, 24.35 g/d and 22.40 g/d, respectively. High-throughput sequencing analysis indicated that the Proteobacteria (44.57–50.36%), Bacteroidetes (22.09–27.25%), Planctomycetes (6.94–8.47%), Firmicutes (3.31–4.53%) and Chloroflexi (3.13–4.80%) were the dominated phyla in the bacterial community during the operation period. At the genus level, Nitrosomonas, Nitrobacter, Planctomyces, Saprospiraceae and Pseudomonas showed relatively high abundance, which played an important role in the removal of pollutants.

Biochar produced from sludge cake conditioned with rice husk flour and FeCl3 (biochar-conditioned) was used to enhance sewage sludge dewaterability. The pyrolysis temperature and dosage of biochar-conditioned were optimized, and the effect of biochar produced from raw sludge cake (biochar-raw) and biochar-conditioned on the sewage sludge dewaterability was compared. Moreover, the mechanisms of biochar-conditioned improving sludge dewaterability as a skeleton builder were analyzed. The optimal pyrolysis temperature of biochar-conditioned was 400 °C. The biochar-conditioned contained the sludge-based biochar with a high content of iron and rice husk-based biochar. Compared with biochar-raw, biochar-conditioned prepared at 400 °C was more effective at enhancing the sludge dewaterability, and the optimal biochar-conditioned dosage was 70% dry sludge (DS). Compared with adding FeCl3 alone, the sludge specific resistance to filtration decreased by 63.9%, the net sludge solids yield increased by 39.2%, and the net percentage sludge water removal increased to 98.36%. Large cracks made the sludge cakes permeable, so that more sludge moisture was filtered from the sludge cake. In addition, adding biochar-conditioned reduced the turbidity and SCOD of sludge filtrate and adjusted the sludge pH to neutral. Using biochar-conditioned to condition the sewage sludge as a skeleton builder is promising.Keywords: Permeability; Sludge biochar; Sludge conditioning; Sludge dewaterability; Sludge filtrate

A new granular acid-activated neutralized red mud (AaN-RM) was successfully prepared with powdered AaN-RM, powdered straw, and hydroxypropyl methylcellulose (HPMC) for effective phosphate adsorption. The maximum phosphate adsorption capacity of granular AaN-RM reached 86.69 mg/g, which was much higher than that previously reported. Its excellent phosphate adsorption capacity was mainly attributed to high specific surface area caused by complex mineralogy of iron and aluminum and addition of powdered straw. The mass ratio of different ingredients, sintering temperature, and time affected the characteristics of granular AaN-RM greatly. When the mass ratio of powdered straw increased from zero to 33%, the total pore volume of granular AaN-RM increased from 0.0056 to 0.0375 cm3/g; however, the effective chemical compositions reduced when the addition of powdered straw was too high. With increasing the sintering temperature and time, the polymerizability of granular AaN-RM was significantly improved, but a too high sintering temperature and too long sintering time resulted in the conversion of part FeCl3·2H2O to FeOCl and FeCl2 and part Al(OH)3 to Al2O3, leading to a weaker attraction for phosphate. The optimal mass ratio of powdered AaN-RM, powdered straw, and HPMC was 71:22:7; the sintering temperature and time were 225 °C and 30 min, respectively.Keywords: Granule adsorbent; Mass ratio; Red mud; Sintering temperature; Sintering time

Powdered-acid-activated-neutralized red mud (Aan-RM), the chemico-physically modified product of red mud, was for the first time employed with hydroxypropyl methylcellulose and powdered straw as the main ingredients for granular Aan-RM production for phosphate removal. In order to better understand the phosphate adsorption characteristics of granular Aan-RM, the influence of operational parameters on the performance of granular Aan-RM and the possible adsorption mechanisms involved were investigated. The results demonstrated that the adsorbent dosage, adsorption temperature, and initial solution pH influenced the adsorption performance of granular Aan-RM significantly. The maximum phosphate adsorption capacity of granular Aan-RM reached 153.227 mg/g with the granular Aan-RM dosage of 3.0 g/L, adsorption temperature of 40 °C, and initial solution pH of 6.0. The whole adsorption process was well described by nth-order kinetic model and Langmuir–Freundlich isotherm. Meanwhile, X-ray photoelectron spectroscopy (XPS) analysis of P 2p peak on granular Aan-RM after phosphate adsorption demonstrated that 79.01 % of the phosphate was adsorbed through precipitation and ion exchange mechanisms with strong chemical bonds, and 20.99 % of the phosphate was adsorbed through surface deposition mechanism with weak chemical bonds.

Bauxsol is a chemico-physically modified product of red mud and is a promising material for the removal and recovery of phosphorus from wastewater. In this study, response surface methodology (RSM) and artificial neural network (ANN) were employed to develop prediction models and also to investigate the interactions of independent experimental factors for phosphorus adsorption onto acid-activated Bauxsol. The experimental results indicated that HCl activation was effective to improve the adsorption capacity of Bauxsol. The maximum adsorption capacity of acid-activated Bauxsol was 55.72 mg/g (as P) with HCl concentration of 10.20 mol/L, temperature of 41.00 °C, and time of 5.60 h, which increased by 10.53 and 6.62 times compared with the raw red mud and Bauxsol before acid activation, respectively. The relative importance of HCl concentration in RSM and ANN models was 51.78 and 54.25 %, respectively, which illustrated that HCl concentration played the predominant role on improving the adsorption capacity of Bauxsol. The predictive capability of RSM and ANN models was compared, and the results showed that both models provided excellent predictions with R2 > 0.93. However, the ANN model showed the superiority over RSM for estimation capability.

Humic acid-coated Fe3O4 (HA-Fe3O4) nanoparticles as magnetic adsorbents were prepared with co-precipitation of humic acids and Fe3O4 nanoparticles. TEM analysis indicated that the average diameter of the spherical HA-Fe3O4 core was about 15 nm. TGA characterization showed that the HA-Fe3O4 nanoparticles contained about 50% (w/w) HA. The characteristic absorption of HA at 1604/cm and 1701/cm was observed in the FIRT spectra of HA-Fe3O4 nanoparticles. The HA-Fe3O4 nanoparticles exhibited a typical superparamagnetic characteristic with a saturation magnetization of 77 emu/g, which resulted in an easy solid–liquid separation with an external magnet. The HA-Fe3O4 nanoparticles were applied for methylene blue (MB) adsorption and results showed that the HA-Fe3O4 nanoparticles possessed much higher adsorbed amount of MB than the bare Fe3O4 nanoparticles and HA powders. The HA-Fe3O4 nanoparticles remained stable in a broad pH range of 3–11. The adsorption kinetics can be described by a pseudo-second-order equation, and the time when 50% of the MB was adsorbed (t1/2) was 7 min. The adsorption isotherm of the HA-Fe3O4 nanoparticles agreed well with Langmuir adsorption equation, and the maximum adsorbed amount of MB was 0.291 mmol/g. Desorption of the saturated HA-Fe3O4 nanoparticles was easily carried out with a mixture of methanol and acetic acid with a volume ratio of 9:1.Highlights► HA-Fe3O4 nanoparticles showed a high saturation magnetization of 77 emu/g. ► HA-Fe3O4 nanoparticles had a high capacity for methylene blue adsorption. ► Sorption kinetics could be described by a pseudo-second-order equation. ► Sorption isotherm agreed well with Langmuir equation. ► Desorption of HA-Fe3O4 was conducted with a mixture of methanol and acetic acid.