Millions of tons of waste activated sludge (WAS) produced from biological wastewater treatment processes cause severe adverse environmental consequences. A better understanding of WAS composition is thus very critical for sustainable sludge management. In this work, the occurrence and distribution of several fundamental sludge constituents were explored in WAS samples from nine full-scale wastewater treatment plants (WWTPs) of Beijing, China. Among all the components investigated, active heterotrophic biomass was dominant in the samples (up to 9478 mg/L), followed by endogenous residues (6736 mg/L), extracellular polymeric substances (2088 mg/L), and intracellular storage products (464 mg/L) among others. Moreover, significant differences (p < 0.05) were observed in composition profiles of sludge samples among the studied WWTPs. To identify the potential parameters affecting the variable fractions of sludge components, wastewater source as well as design and operational parameters of WWTPs were studied using statistical methods. The findings indicated that the component fraction of sewage sludge depends more on wastewater treatment alternatives than on wastewater characteristics among other parameters. A principal component analysis was conducted, which further indicated that there was a greater proportion of residual inert biomass in the sludge produced by the combined system of the conventional anaerobic/anoxic/oxic process and a membrane bioreactor. Additionally, a much longer solids retention time was also found to influence the sludge composition and induce an increase in both endogenous inert residues and extracellular polymeric substances in the sludge. 相似文献
• ZnO-NP disrupted metabolic/catabolic balance of bacteria by affecting DHA activity.• ZnO-NPs toxicity was related to Zn2+ ion, interaction with cell and ROS generation.• Exposure to ZnO-NPs resulted in changed bacterial community structure at sludge.• The change in the EPS content was observed during exposure to ZnO-NPs. The unique properties and growing usage of zinc oxide nanoparticles increase their release in municipal wastewater treatment plants. Therefore, these nanoparticles, by interacting with microorganisms, can fail the suitable functioning of biological systems in treatment plants. For this reason, research into the toxicity of ZnO is urgent. In the present study, the toxicity mechanism of ZnO-NPs towards microbial communities central to granular activated sludge (GAS) performance was assessed over 120-day exposure. The results demonstrate that the biotoxicity of ZnO-NPs is dependent upon its dosage, exposure time, and the extent of reactive oxygen species (ROS) production. Furthermore, GAS performance and the extracellular polymeric substances (EPS) content were significantly reduced at 50 mg/L ZnO-NPs. This exposure led to decreases in the activity of ammonia monooxygenase (25.2%) and nitrate reductase (11.9%) activity. The Field emission scanning electron microscopy images confirmed that ZnO-NPs were able to disrupt the cell membrane integrity and lead to cell/bacterial death via intracellular ROS generation which was confirmed by the Confocal Laser Scanning Microscopy analysis. After exposure to the NPs, the bacterial community composition shifted to one dominated by Gram-positive bacteria. The results of this study could help to develop environmental standards and regulations for NPs applications and emissions. 相似文献
• The NPs aggregation in the electrolyte solution is consistent with the DLVO theory.• In NaNO3 and low Ca(NO3)2, EPS alleviates the NPs aggregation by steric repulsion.• In high Ca(NO3)2, EPS accelerates the NPs aggregation by exopolysaccharide bridging.• Ag2S NPs have stronger stability compared with Cit-Ag NPs in aqueous systems. Extracellular polymeric substances (EPS) in activated sludge from wastewater treatment plants (WWTPs) could affect interactions between nanoparticles and alter their migration behavior. The influence mechanisms of silver nanoparticles (Ag NPs) and silver sulfide nanoparticles (Ag2S NPs) aggregated by active EPS sludge were studied in monovalent or divalent cation solutions. The aggregation behaviors of the NPs without EPS followed the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The counterions aggravated the aggregation of both NPs, and the divalent cation had a strong neutralizing effect due to the decrease in electrostatic repulsive force. Through extended DLVO (EDLVO) model analysis, in NaNO3 and low-concentration Ca(NO3)2 (<10 mmol/L) solutions, EPS could alleviate the aggregation behaviors of Cit-Ag NPs and Ag2S NPs due to the enhancement of steric repulsive forces. At high concentrations of Ca(NO3)2 (10‒100 mmol/L), exopolysaccharide macromolecules could promote the aggregation of Cit-Ag NPs and Ag2S NPs by interparticle bridging. As the final transformation form of Ag NPs in water environments, Ag2S NPs had better stability, possibly due to their small van der Waals forces and their strong steric repulsive forces. It is essential to elucidate the surface mechanisms between EPS and NPs to understand the different fates of metal-based and metal-sulfide NPs in WWTP systems. 相似文献
• Energy is needed to accelerate the biological wastewater treatment.• Electrical energy input in traditional technology is indirect and inefficient.• Direct injection of electricity can be a game changer to maximize energy efficiency.• Microbial electrochemical unit for decentralized wastewater treatment is proposed. It has been more than one century since the activated sludge process was invented. Despite its proven stability and reliability, the energy (especially the electrical energy) use in wastewater treatment should evolve to meet the increasingly urgent demand of energy efficiency. This paper discusses how the energy utilized in conventional biological wastewater treatment can be altered by switching the indirect energy input to a direct electricity injection, which is achieved by the electrode integration providing extra thermodynamic driving force to biodegradation. By using electrodes instead of oxygen as terminal electron acceptors, the electrical energy can be utilized more efficiently, and the key of direct use of electrical energy in biodegradation is the development of highly active electroactive biofilm and the increase of electron transfer between microbes and the electrode. Furthermore, the synergy of different microbial electrochemical units has additional benefit in energy and resource recovery, making wastewater treatment more sustainable. 相似文献
The distribution of metallic elements in a submerged membrane bioreactor(MBR) was revealed at different temperatures using inductively coupled plasma-optical emission spectrometry(ICP-OES), and the role of extracellular polymeric substances(EPS) was probed by integrating scanning electron microscopy(SEM) with confocal laser scanning microscopy(CLSM) over long-term operation. More metallic elements in the influent were captured by suspended sludge and built up in the fouling layer at lower temperature. The concentration of metallic elements in the effluent was 5.60 mg/L at 10°C operational temperature, far lower than that in the influent(51.35 mg/L). The total contents of metallic elements in suspended sludge and the membrane fouling layer increased to 40.20 and 52.19 mg/g at 10°C compared to 35.14 and 32.45 mg/g at 30°C, and were dominated by the organically bound fraction. The EPS contents in suspended sludge and membrane fouling layer sharply increased to 37.88 and 101.51 mg/g at 10°C, compared to 16.87 and 30.03 mg/g at 30°C. The increase in EPS content at lower temperature was responsible for the deposition of more metallic ions. The strong bridging between EPS and metallic elements at lower temperature enhanced the compactness of the fouling layer and further decreased membrane flux. This was helpful for understanding the mechanism of membrane fouling at different operational temperatures and the role of EPS, and also of significance for the design of cleaning strategies for fouled membranes after long-term operation. 相似文献
The highest removal efficiencies of COD and TN were achieved under 10 mg/L of Al3+.The highest TP removal efficiency occurred under 30 mg/L of Al3+.EPS, PS and PN concentrations increased with the addition of Al3+.Sludge properties significantly changed with the addition of Al3+. Aluminum ions produced by aluminum mining, electrolytic industry and aluminum-based coagulants can enter wastewater treatment plants and interact with activated sludge. They can subsequently contribute to the removal of suspended solids and affect activated sludge flocculation, as well as nitrogen and phosphorus removal. In this study, the effects of Al3+ on pollutant removal, sludge flocculation and the composition and structure of extracellular polymeric substances (EPS) were investigated under anaerobic, anoxic and oxic conditions. Results demonstrated that the highest chemical oxygen demand (COD) and total nitrogen (TN) removal efficiencies were detected for an Al3+ concentration of 10 mg/L. In addition, the maximal dehydrogenase activity and sludge flocculation were also observed at this level of Al3+. The highest removal efficiency of total phosphorus (TP) was achieved at an Al3+ concentration of 30 mg/L. The flocculability of sludge in the anoxic zone was consistently higher than that in the anaerobic and oxic zones. The addition of Al3+ promoted the secretion of EPS. Tryptophan-like fluorescence peaks were detected in each EPS layer in the absence of Al3+. At the Al3+ concentration of 10 mg/L, fulvic acid and tryptophan fluorescence peaks began to appear, while the majority of protein species and the highest microbial activity were also detected. Low Al3+ concentrations (<10 mg/L) could promote the removal efficiencies of COD and TN, yet excessive Al3+ levels (>10 mg/L) weakened microbial activity. Higher Al3+ concentrations (>30 mg/L) also inhibited the release of phosphorus in the anaerobic zone by reacting with PO43-. 相似文献
● N2H4 addition enhanced and recovered anammox performance under Cr(VI) stress. ● N2H4 accelerated electron transfer of Cr(VI) reduction for detoxification. ● N2H4 enhanced anammox metabolism for activity recovery from Cr(VI) inhibition. ● Extracellular Cr(VI) reduction to less toxic Cr(III) was the dominant mechanism. The hexavalent chromium (Cr(VI)) would frequently impose inhibition to anaerobic ammonium oxidation (anammox) process, hindering the efficiency of nitrogen removal in wastewater treatment. Hydrazine (N2H4), which is an intermediate product of anammox, participates in intracellular metabolism and extracellular Cr(VI) reduction. However, the roles of N2H4-induced intracellular metabolism and extracellular reduction in nitrogen removal under Cr(VI) stress remain unclear. The addition of 3.67 mg/L of N2H4 increased the anammox activity by 17%. As an intermediate, N2H4 enhanced anammox metabolism by increasing the heme c content and electron transfer system activity. As a reductant, N2H4 accelerated the reduction of c-Cyts-mediated extracellular Cr(VI) to the less toxic Cr(III). Extracellular Cr(III) accounts for 74% of the total Cr in a Cr(VI)-stressed anammox consortia. These findings highlight that N2H4-induced extracellular Cr(VI) reduction is the dominant mechanism for the survival of anammox consortia. We also found that N2H4 increased the production of extracellular polymeric substances to sequester excessive Cr(VI) and produced Cr(III). Taken together, the study findings suggest a potential strategy for enhancing nitrogen removal from ammonium-rich wastewater contaminated with Cr(VI). 相似文献
Aerobic granules which form through a cell-to-cell self-immobilization process have been intensively studied and developed for wastewater biotreatment. However, the microbiological origin of this phenomenon is still largely unknown. This study investigated the possible role of metabolic energy in the development of aerobic granules. Results showed that aerobic granulation was positively related to ATP-dependent N-acylhomoserine lactones (AHLs) and extracellular polymeric substances (EPSs) production. Inhibited ATP synthesis by a chemical uncoupler, 3,3′,4′,5-tetrachlorosalicylanilide, led to significant reduction of AHLs and EPSs production, which in turn prevented aerobic granulation. This study for the first time demonstrated the involvement of ATP-dependent AHLs in aerobic granulation. 相似文献