In this study, the effects of different ratios of glucose to acetate on enhanced biological phosphorus removal (EBPR) were investigated with regard to the changes of intercellular polyhydroxyalkanoates (PHAs) and glycogen, as well as microbial community. The experiments were carried out in five sequencing batch reactors (SBRs) fed with glucose and/or acetate as carbon sources at the ratios of 0:100 %, 25:75 %, 50:50 %, 75:25 %, and 100:0 %. The experimental results showed that a highest phosphorus removal efficiency of 96.3 % was obtained with a mixture of glucose and acetate at the ratio of 50:50 %, which should be attributed to more glycogen and polyhydroxyvalerate (PHV) transformation in this reactor during the anaerobic condition. PCR-denaturing gradient gel electrophoresis (DGGE) analysis of sludge samples taken from different anaerobic/aerobic (A/O) SBRs revealed that microbial community structures were distinctively different with a low similarity between each other.

Solidification is a very effective way to alleviate heavy metal impacts to the environment. In this paper, an improved method was adopted herein for the solidification/stabilization (S/S) of sediments with cement-based additives and low content of cement in S/S materials. Sediments in Xiangjiang River, containing high concentrations of Cu, Cd, and Pb, were solidified/stabilized by binders of cement, fly ash, and bentonite. Admixtures such as sodium lignosulfonate, sodium lauryl sulfate, and triethanolamine were used to improve the bonding properties of S/S, which had never been investigated before. Results demonstrated that the addition of concrete admixtures had significant effects on the S/S of sediments. Sequential extraction method indicates that the concentrations of heavy metals changed significantly after solidification and were more stable over time, with the exception of Pb. In addition, SEM images indicated that the main hydrated product was ettringite. Large quantities of calcium silicate hydrates (CSH) formed and filled the solidified sediment in 60 days. The results provide further insights into the transformation of heavy metals during S/S.

In this study, Fe(II)-loaded granular activated carbon (GAC) was used as a heterogeneous persulfate catalyst for the pretreatment of mature landfill leachate. The effects of Fe2+ dosage, persulfate concentration and initial pH on the degradation of the organic pollutants in the landfill leachate were investigated. In single factor experiments, the maximum Chemical Oxygen Demand (COD) removal rate reached 66.8, 66.2 and 76.3% at an Fe2+ dosage of 127 mg L−1 (Fe2+/S2O82− = 254 mg mol−1), a persulfate concentration of 0.5 mol L−1 (i.e. S2O82−:12COD0 = 1.08) and an initial pH of 3, respectively. Obviously, pH played a more important role in the persulfate oxidation treatment than the other two factors. The synthetic experimental results showed that the COD removal rate exceeded 87.8% when the reaction conditions had a controlled Fe2+ dosage of 127 mg L−1, persulfate concentration of 0.5 mol L−1 and initial pH of 3.0, simultaneously. The recycle experiments displayed that the catalytic ability of reused Fe(II)-GAC declined considerably and the COD removal rate dropped by approximately half after reusing three times. But the catalytic ability of the catalyst used could be well recovered after regeneration at 550 °C in a N2 atmosphere. Finally, fluorescence excitation–emission matrix (EEM) spectroscopy preliminarily explained the degradation mechanism of the landfill leachate.

Nanoscale zerovalent iron (nZVI) was reported as an effective material for the removal of bromate. However, its reactivity may be weakened due to its aggregation. In this study, nZVI was dispersed onto modified activated carbon (pretreated by nitric acid or/and ammonia) by impregnating carbon in ferrous sulfate with NaBH4 as reducing agent. The nZVI supported on modified activated carbon (nZVI/MAC) was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). Good distribution of nZVI particles (about 50 nm) on the MAC was observed. The removal efficiencies of bromate by AC, nZVI, and nZVI/MAC were respectively evaluated. Experimental results indicated that nZVI/MAC showed the highest removal efficiency to bromate. In addition, the effects of initial bromate concentration (0.78–3.91 μmol/L) and pH (2.0–10.0) were investigated by batch experiments. Kinetic studies showed that the simultaneous adsorption and reduction of bromate by nZVI/MAC followed pseudo-first-order kinetics. Finally, bromine mass balance demonstrated that bromide was the only product for bromate reduction by nZVI/MAC, suggesting that bromate in aqueous solution was first adsorbed onto nZVI/MAC and subsequently reduced to innocuous bromide by nZVI.

The effect of biosurfactant rhamnolipid (RL) on hydrolysis and acidification of waste activated sludge (WAS) was investigated. The results indicated that RL could greatly reduce the surface tension of sludge, resulting in stimulating the hydrolysis rate of WAS and enhancing the production of short-chain fatty acids (SCFAs). With the increase of RL dosage from 0.2 to 0.5 g/g DS, the maximum soluble chemical oxygen demand (SCOD), protein and carbohydrate concentration increased correspondingly. After 6 h of hydrolysis, SCOD, protein and carbohydrate concentration increased from 371.9, 93.3 and 9.0 mg/l to 3,994.5, 800.0 and 401.4 mg/l at RL 0.3 g/g DS, respectively. Furthermore, the release of NH4+-N, PO43−-P and the accumulation of SCFAs also improved in the presence of RL. The maximum SCFAs was 1,829.9 mg COD/l at RL 0.3 g/g DS, while it was only 377.7 mg COD/l for the blank test. The propionic acid and acetic acid were the mainly SCFAs produced, accounting for 50–60% of total SCFAs.

•Mature landfill leachate was effectively pretreated by ultrasonic activated persulfate oxidation.•Integrated Taguchi and RSM method well optimized the operating variables.•The TOC removal efficiency was 77.32% at optimal conditions.•The process exhibits the synergistic effect of sono-catalysis and persulfate oxidation.A novel advanced oxidation process (AOP) using ultrasonic activated persulfate oxidation was used to pretreat mature landfill leachate. The effects of different operating variables (e.g., the initial S2O82− concentration, pH, temperature, ultrasonic power and reaction time) on the oxidation performance were investigated regarding the total organic carbon (TOC) removal efficiency, and the variables were optimized using the integrated Taguchi method and response surface methodology (RSM). Based on the Taguchi method under L16 (45) arrays and a grey relational analysis, the most significant variables included the initial S2O82− concentration, temperature and reaction time. The concentrations of these variables were further optimized using RSM. Using the integrated optimization method, the optimal conditions included an initial S2O82− concentration of 8.5 mM, a reaction temperature of 70 °C and a reaction time of 2.46 h, which resulted in a TOC removal efficiency of 77.32%. The experimental results showed that the enhanced TOC removal from mature landfill leachate by sono-activated persulfate oxidation could be attributed to the combined effects of ultrasonic catalysis and sulfate radical-AOP. Overall, ultrasonic activated persulfate oxidation is a promising method for the pretreatment of landfill leachate.

The individual alkaline or microwave pretreatment has been proved to be effective in disintegration and acidification of waste activated sludge (WAS). In this study, the effects of combined alkaline and microwave pretreatment at different pH and specific energy input (Es) on WAS disintegration were investigated using response surface methodology (RSM). Combined pretreatment achieved disintegration degree (DD) of 65.87% at Es of 38,400 kJ/kg TS and pH 11.0. The ANOVA further demonstrated that pH showed more significant effect on DD than Es. Anaerobic batch experiment results showed that combined pretreatment not only significantly improved volatile fatty acids (VFAs) accumulation but also shortened the time for the highest VFAs accumulation. The maximal VFAs accumulation (1500 mg COD/L) obtained at Es of 28,800 kJ/kg TS and fermentation time of 72 h, which was about two times that of the treatment without microwave (850 mg COD/L) at 96 h. The analysis of VFAs composition showed that the VFAs mainly consisted of acetic and iso-valeric acids, accounting for 57.3–70.1% of total VFAs.

•SCFAs production from food waste was greatly enhanced by the APG addition into anaerobic fermentation system.•0.2 g/g TS was the optimal APG dosage for SCFAs production.•APG favored solubilization, hydrolysis and acidification but inhibited methanogenesis.•The activities of key enzymes related with SCFAs production were improved by APG.Short-chain fatty acids (SCFAs) are the valuable products derived from the anaerobic fermentation of organic solid waste. However, SCFAs yield was limited by the worse solubilization and hydrolysis of particulate organic matter, and rapid consumption of organic acid by methanogens. In this study, an efficient and green strategy, i.e. adding biosurfactant alkyl polyglycosides (APG) into anaerobic fermentation system, was applied to enhance SCFAs production from food waste. Experimental results showed that APG not only greatly improved SCFAs production but also shortened the fermentation time for the maximum SCFAs accumulation. The SCFAs yield at optimal APG dosage 0.2 g/g TS (total solid) reached 37.2 g/L, which was 3.1-fold of that in blank. Meanwhile, the time to accumulate the maximum SCFAs in the presence of APG was shortened from day 14 to day 6. The activities of key enzymes such as hydrolytic and acid-forming enzymes were greatly promoted due to the presence of APG. These results demonstrated that the enhanced mechanism of SCFAs production should be attributed to the acceleration of solubilization and hydrolysis, enhancement of acidification and inhibition of methanogenesis by APG.

•The removed of melamine (MA) was mainly performed by activated sludge adsorption instead of biodegradation.•High concentration of MA could not easily removal and had adverse impacts on biological wastewater treatment.•MA inhibited the enzyme activities of NOR, NR, NIR and PPX, which were closely relevant to nitrogen and phosphorus removal.•High MA concentrations promoted the metabolism of glycogen, thereby providing the advantage for the growth of GAOs.Melamine (MA) is a significant raw material for industry and home furnishing, and an intermediate for pharmacy. However it is also a hazardous material when being added to food as a protein substitute due to the high nitrogen content. In this study, the behavior of MA in activated sludge was investigated. Experiments showed that MA was removed during biological wastewater treatment process, and the removal was mainly achieved by activated sludge adsorption instead of biodegradation. Low levels of MA (0.001–0.10 mg/L) in wastewater had negligible influence on the performance of activated sludge, but high levels of MA deteriorated biological nitrogen and phosphorus removal. The presence of MA (1.00 and 5.00 mg/L) decreased total nitrogen removal efficiency from 94.15% to 79.47% and 68.04%, respectively. The corresponding concentration of effluent phosphorus increased from 0.11 to 1.45 and 2.06 mg/L, respectively. It was also observed that MA inhibited the enzyme activities of nitrite oxidoreductase, nitrate reductase, nitrite reductase and exopolyphosphatase, which were closely relevant to nitrogen and phosphorus removal. Further investigation showed that the presence of high MA concentrations promoted the consumption and synthesis of glycogen, thereby providing the advantage for the growth of glycogen accumulating organisms.

•D201-Cl resin exhibited greater bromate adsorption capacity.•The adsorption kinetics agreed with the pseudo-first-order model.•The equilibrium data can be well described by Freundlich and Redlich–Peterson model.•The resin showed excellent regeneration performance and reusability.Bromate, a cancerigenic disinfection by-product (DBP), has been increasingly concerned in recent years. In this study, macroporous Cl-type strong base anion exchange resin (D201-Cl) was used to remove trace levels of bromate from aqueous solution. Batch sorption experiments were performed to evaluate the influence of various factors such as initial bromate concentration, contact time, solution initial pH and temperature on the uptake of bromate. D201-Cl resin exhibited higher bromate removal efficiency (residual concentration of bromate was under the maximum contaminant level (MCL) of 10 μg·L− 1 at all conditions investigated) and broader pH scope of application (4.50–9.92). The maximum sorption capacity reached to 105.5 mg·g− 1 at 298 K. The kinetics data were well described by pseudo-first-order kinetic model, and Freundlich isotherm model and Redlich–Peterson isotherm model fitted the sorption isotherms (R2 > 0.99). Thermodynamic analysis showed that the sorption process was spontaneous and endothermic. In addition, D201-Cl resin still maintained high bromate removal efficiency after regenerated by 0.1 M NaCl solution for five cycles. The results indicate that D201-Cl resin is a low-cost and efficient sorbent for bromate removal from drinking water, especially for trace levels of bromate.