ZnO nanoparticles (NPs) have been detected in various wastewater treatment plants. It is widely assumed that size has a crucial effect on the NPs toxicity. Concerns have been raised over probable size-dependent toxicity of ZnO NPs to activated sludge, which could eventually affect the treatment efficiencies of wastewater treatment facilities. The size-dependent influences of ZnO NPs on performance, microbial activities, and extracellular polymeric substances (EPS) from activated sludge were examined in sequencing batch reactor (SBR) in present study. Three different sizes (15, 50, and 90 nm) and five concentrations (2, 5, 10, 30, and 60 mg L⁻¹) were trialled. The inhibitions on COD and nitrogen removal were determined by the particle size, and smaller ZnO NPs (15 nm) showed higher inhibition effect than those of 50 and 90 nm, whereas the ZnO NPs with size of 50 nm showed maximum inhibition effect on phosphorus removal among three sizes of ZnO NPs. After exposure to different sized ZnO NPs, microbial enzymatic activities and removal rates of activated sludge represented the same trend, consistent with the nitrogen and phosphorus removal efficiency. In addition, apparent size- and concentration-dependent effects on EPS contents and components were also observed. Compared with the absence of ZnO NPs, 60 mg L⁻¹ ZnO NPs with sizes of 15, 50, and 90 nm increased the EPS contents from 92.5, 92.4, and 92.0 mg g⁻¹ VSS to 277.5, 196.8, and 178.2 mg g⁻¹ VSS (p < 0.05), respectively. The protein and polysaccharide contents increased with the decreasing particle sizes and increasing ZnO NPs concentrations, and the content of protein was always higher than that of polysaccharide.

To simultaneously achieve biological denitrification and bio-energy recovery from sludge, the effects of nitrite on the two-phase anaerobic digestion (AD) of waste activated sludge were explored. Herein, effects of nitrite on the acidogenic phase are optimized, and the corresponding influence mechanisms are investigated. The experimental results show that the optimal nitrite treatment conditions for improving the acidogenic phase are an initial pH of 8.0, a nitrite addition concentration of 500 mg NO₂⁻-N·L⁻¹, and a fermentation time of six days. By comparing the effects of nitrite and nitrate on the acidogenic phase, it was found that it was the nitrite, not the nitrate, that significantly enhanced the sludge organic solubilization, hydrolysis, and acidification, which are primarily attributed to the redox property of nitrite. Based on an analysis of different forms of soluble nitrogen concentrations, there was no obvious accumulation of nitrite or nitrate during the acidogenic phase. An analysis of the methane production and the volatile solid (VS) degradation during the two-phase AD revealed that the nitrite improved the methane production from the methanogenic phase and enhanced the VS degradation of sludge during the entire two-phase AD process. These findings could provide references for simultaneously treating nitrite-rich wastewater and improving anaerobic sludge digestion via two-phase system.

This study aimed to evaluate the impacts of morphological-controlled ZnO nanoarchitectures on aerobic microbial communities during real wastewater treatment in an aerobic-photocatalytic system. Results showed that the antibacterial properties of ZnO nanoarchitectures were significantly more overwhelming than their photocatalytic properties. The inhibition of microbial activities in activated sludge by ZnO nanoarchitectures entailed an adverse effect on wastewater treatment efficiency. Subsequently, the 16S sequencing analysis were conducted to examine the impacts of ZnO nanoarchitectures on aerobic microbial communities, and found the significantly lower microbial diversity and species richness in activated sludge treated with 1D-ZnO nanorods as compared to other ZnO nanoarchitectures. Additionally, 1D-ZnO nanorods reduced the highest proportion of Proteobacteria phylum in activated sludge due to its higher proportion of active polar surfaces that facilitates Zn²⁺ ions dissolution. Pearson correlation coefficients showed that the experimental data obtained from COD removal efficiency and bacterial log reduction were statistically significant (p-value < 0.05), and presented a positive correlation with the concentration of Zn²⁺ ions. Finally, a non-parametric analysis of Friedman test and post-hoc analysis confirmed that the concentration of Zn²⁺ ions being released from ZnO nanoarchitectures is the main contributing factor for both the reduction in COD removal efficiency and bacterial log reduction.

In this study, the distribution profiles, emission characteristics, and health risks associated with 43 volatile and semi-volatile organic compounds, including 15 phenols, 18 polycyclic aromatic hydrocarbons (PAHs), 6 BTEX, and 4 other compounds, were determined in the wastewater treatment plant (WWTP) of a coking factory (plant C) and the succeeding final WWTP (central WWTP). Total phenols with a concentration of 361,000 μg L⁻¹ were the predominant compounds in the influent wastewater of plant C, whereas PAHs were the major compounds in the final effluents of both coking WWTPs (84.4 μg L⁻¹ and 30.7 μg L⁻¹, respectively). The biological treatment process in plant C removed the majority of volatile organic pollutants (94.1%–99.9%). A mass balance analysis for plant C showed that biodegradation was the main removal pathway for all the target compounds (56.6%–99.9%) except BTEX, chlorinated phenols, and high molecular weight (MW) PAHs. Chlorinated phenols and high MW PAHs were mainly removed via sorption to activated sludge (51.8%–73.2% and 60.2%–75.9%, respectively). Air stripping and volatilization were the dominant mechanisms for removing the BTEX compounds (59.8%–73.8%). The total emission rates of the detected volatile pollutants from plant C and the central WWTP were 1,640 g d⁻¹ and 784 g d⁻¹, respectively. Benzene from the equalization basins of plant C and the central WWTP corresponded to the highest inhalation carcinogenic risks (1.4 × 10⁻³ and 3.2 × 10⁻⁴, respectively), which exceeded the acceptable level for human health (1 × 10⁻⁶) recommended by the United States Environmental Protection Agency. The results showed that BaP exhibited the highest inhalation non-cancer risk, with a hazard index ratio of 70 and 30 for plant C and the central WWTP, respectively. Moreover, the excess sludge generated during wastewater treatment should also be carefully handled because it adsorbed abundant PAHs and chlorinated phenols at coking plant C (58,000 μg g⁻¹ and 3,500 μg g⁻¹) and the central WWTP (622 μg g⁻¹ and 54 μg g⁻¹).

In the present work, acute impact of heavy metals on activated sludge was investigated, specifically the release of biopolymers and nitrogenous soluble microbiological products (N-SMP) that significantly impact tertiary effluent quality. Based on the previously reported studies, Hg²⁺ and Ag⁺ were selected as representative “non-essential” heavy metals, while Cu²⁺ was selected as the “essential” heavy metal. Stress tests show that under the present experimental conditions, adding a higher concentration of heavy metals to the activated sludge increases the concentration of biopolymers and SMP in the supernatant; N-SMP increased more significantly than carbonaceous products, implying a greater risk of formation of toxic nitrogenous disinfection by-products or membrane fouling in relevant tertiary treatment processes. The severity of the release of SMP into the supernatant depended on the heavy metal, with an order of Hg²⁺ > Ag⁺ > Cu²⁺ (“non-essential” > “essential”) under identical molar concentrations. The mass balance of typical organics (e.g., biopolymers) in SMP and extracellular polymeric substances (EPS) in activated sludge was analyzed, and a negative correlation between the organics in the SMP and tightly bound EPS was observed, implying that a significant fraction of the SMP could be quickly released from the tightly bound EPS under heavy metal shock conditions and could be related to cell response or damage.

Carbamazepine (CBZ), a widely detected pharmaceutical in wastewaters, cannot currently be treated by conventional activated sludge technologies, as it is highly resistant to biodegradation. In this study, the degradation kinetics and reaction mechanisms of CBZ by hydroxyl radical (OH) and sulfate radical (▪)–based advanced oxidation processes (AOPs) were investigated with a combined experimental/theoretical approach. We first measured the UV absorption spectrum of CBZ and compared it to the theoretical spectrum. The agreement of two spectra reveals an extended π–conjugation system on CBZ molecular structure. The second–order rate constants of OH and ▪ with CBZ, measured by competition kinetics method, were (4.63 ± 0.01) × 10⁹ M⁻¹ s⁻¹ and (8.27 ± 0.01) × 10⁸ M⁻¹ s⁻¹, respectively at pH 3. The energetics of the initial steps of CBZ reaction with OH and ▪ were also calculated by density functional theory (DFT) at SMD/M05–2X/6–311++G**//M05–2X/6–31 + G**level. Our results reveal that radical addition is the dominant pathway for both OH and ▪. Further, compared to the positive ΔGR0 value for the single electron transfer (SET) reaction pathway between CBZ and OH, the ΔGR0 value for SET reaction between CBZ and ▪ is negative, showing that this reaction route is thermodynamically favorable. Our results demonstrated the remarkable advantages of AOPs for the removal of refractory organic contaminants during wastewater treatment processes. The elucidation of the pathways for the reaction of OH and ▪ with CBZ are beneficial to predict byproducts formation and assess associated ecotoxicity, providing an evaluation mean for the feasibility of AOPs application.

Di-(2-ethylhexyl) phthalate (DEHP) has been classified as a priority pollutant which increased the healthy risk to human and animals dramatically. Hence, a novel biochemical system combined by DEHP-resistant bacterial flora (B) and a green oxidant of persulfate (PS) activated by Nano-Fe₃O₄ was applied to degrade DEHP in contaminated soil. In this study, the resistant bacterial flora was screened from activated sludge and immobilized by sodium alginate (SAB). Nano-Fe₃O₄ was coated on biochar (BC@Fe₃O₄) to prevent agglomerating in soil. X-ray diffraction (XRD) and scanning electron microscope (SEM) were utilized to characterize BC@Fe₃O₄. Results demonstrated that the treatment of biochemical system (SAB + BC@Fe₃O₄ + PS) presented the maximum degradation rate about 92.56% within 24 days of incubation and improved soil microecology. The 16S rDNA sequences analysis of soil microorganisms showed a significantly different abundance and a similar diversity among different treatments. Kyoto Encyclopedia of Genes and Genomes (KEGG) functional genes difference analysis showed that some metabolic pathways, such as metabolism of cofactors and vitamins, energy metabolism, cell growth and death, replication and repair, were associated with the biodegradation of DEHP. Besides, DEHP was converted to MEHP and PA by biodegradation, while DEHP was converted to DBP and PA by persulfate and BC@Fe₃O₄, and then ultimately degraded to CO₂ and H₂O.

Present study aims to examine the efficiency of co-vermicomposting amended with activated sludge and E. fetida earthworm for bioremediation of diesel and gasoline from contaminated soil. The diesel and gasoline removal efficiency and degradation rates coefficients were estimated with gas chromatography (GC) analysis and first-order kinetics. The removal of gasoline and diesel in different co-vermicomposting processes with and without E. fetida ranged between 65-100% and 24.94–63.93%, respectively within 90- day experiment. Removal of gasoline and diesel increased in soil with addition of earthworm (E. fetida); higher degradation rate coefficients (k) were observed for co-vermicomposting with earthworm compared with co-vermicomposting processes. The highest k (0.014) for diesel degradation was estimated for microcosm reactor 4 (R4), where high numbers of E. fetida accelerate the less biodegradable organic contaminant from the soil matrices. The reasonable survival rates of earthworms in exposure to high concentration of petroleum-derivatives contaminated soils indicated increased activity of ligninolytic diesel–degrading earthworms and microorganisms. Therefore, co-vermicomposting amended with activated sludge is suggested as feasible and promising technologies for bioremediation of high content of organic contaminants from the soil matrices.

In this study, a multidisciplinary approach investigated the enzymatic degradation of micropollutants in real, not modified, municipal wastewaters of a plant located in Italy. Stir Bar Sorptive Extraction combined to Gas Chromatography-Mass Spectrometric detection (SBSE-GC-MS) was applied to profile targeted pollutants in wastewaters collected after the primary sedimentation (W1) and the final effluent (W2). Fifteen compounds were detected at ng/L - μg/L, including pesticides, personal care products (PCPs) and drugs. The most abundant micropollutants were bis(2-ethylhexyl) phthalate, diethyl phthalate and ketoprofen. Laccases of Trametes pubescens MUT 2400 were very active against all the target micropollutants: except few cases, their concentration was reduced more than 60%. Chemical analysis and environmental risk do not always come together. To verify whether the treated wastewaters can represent a stressor for the aquatic ecosystem, toxicity was also evaluated. Raphidocelis subcapitata and Lepidium sativum tests showed a clear ecotoxicity reduction, even though they did not evenly respond. Two in vitro tests (E-screen test and MELN assay) were used to evaluate the estrogenic activity. Treatments already operating in the plant (e.g. activated sludge) partially reduced the estradiol equivalent concentration, and it was almost negligible after the laccases treatment. The results of this study suggest that laccases of T. pubescens are promising biocatalysts for the micropollutants transformation in wastewaters and surface waters.

This study developed a process of genetically engineered bacteria Rhodococcus erythropolis expressing Nirs and AMO combined with membrane bioreactor (MBR), nanofiltration (NF) and reverse osmosis (RO) membrane (pRho-NA-MNR) for advanced treatment of landfill leachate. Results demonstrated that pRho-NA-MNR presented higher removal rate of chemical oxygen demand (COD), biological oxygen demand (BOD), ammonia nitrogen (N–NH₄), total nitrogen (TN) and total organic carbon (TOC) than activated sludge (AS-MNR) system. Administration of pRho-NA increased nitrification by converting N–NH₄ to nitrite (N–NO₂) and Nitrate (N–NO₃), and promoting denitrification by converting N–NO₂ to nitrogen (N₂) in the landfill leachate treatment, promoted the pH control, increased sludge activity and effluent yield, shortened phase length adaptation under alternating aerobic-anoxic conditions. pRho-NA increased the nitration and denitrifying rate in the aerobic and anaerobic stage in the system by increasing Cyt cd1 and Cyt c expression in the activated sludge. Nitrogen removal by nitrification and denitrification was positively correlated to the concentration of Nirs and AMO expression. Treatment with pRho-NA promoted pollutant removal efficiency of membrane bioreactor, nanofiltration and reverse osmosis membrane processes in landfill leachate. In conclusion, data suggest that pRho-NA-MNR facilitates the formation of granular sludge and enhances comparable removal of nitrogen and organic compounds, indicating the practice of this process should be considered in landfill leachate treatment system.