Effects of salinity and betaine addition on anaerobic granular sludge properties and microbial community succession patterns in organic saline wastewater.

In this study, the effects of different salinity gradients and addition of compatible solutes on anaerobic treated effluent water qualities, sludge characteristics and microbial communities were investigated. The increase in salinity resulted in a decrease in particle size of the granular sludge, which was concentrated in the range of 0.5-1.0 mm. The content of EPS (extracellular polymeric substances) in the granular sludge gradually increased with increasing salinity and the addition of betaine (a typical compatible solute). Meanwhile, the microbial community structure was significantly affected by salinity, with high salinity reducing the diversity of bacteria. At higher salinity, Patescibacteria and Proteobacteria gradually became the dominant phylum, with relative abundance increasing to 13.53% and 12.16% at 20 g/L salinity. Desulfobacterota and its subordinate Desulfovibrio, which secrete EPS in large quantities, dominated significantly after betaine addition.Their relative abundance reached 13.65% and 7.86% at phylum level and genus level. The effect of these changes on the treated effluent was shown as the average chemical oxygen demand (COD) removal rate decreased from 82.10% to 79.71%, 78.01%, 68.51% and 64.55% when the salinity gradually increased from 2 g/L to 6, 10, 16 and 20 g/L. At the salinity of 20 g/L, average COD removal increased to 71.65% by the addition of 2 mmol/L betaine. The gradient elevated salinity and the exogenous addition of betaine played an important role in achieving stability of the anaerobic system in a highly saline environment, which provided a feasible strategy for anaerobic treatment of organic saline wastewater.

Effect of gradual increase of salt on performance and microbial community during granulation process.

Salinity was considered to have effects on the characteristics, performance microbial communities of aerobic granular sludge. This study investigated granulation process with gradual increase of salt under different gradients. Two identical sequencing batch reactors were operated, while the influent of Ra and Rb was subjected to stepwise increments of NaCl concentrations (0-4 g/L and 0-10 g/L). The presence of filamentous bacteria may contribute to granules formed under lower salinity conditions, potentially leading to granules fragmentation. Excellent removal efficiency achieved in both reactors although there was a small accumulation of nitrite in Rb at later stages. The removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in Ra were 95.31%, 93.70% and 88.66%, while the corresponding removal efficiencies in Rb were 94.19%, 89.79% and 80.74%. Salinity stimulated extracellular polymeric substances (EPS) secretion and enriched EPS producing bacteria to help maintain the integrity and stability of the aerobic granules. Heterotrophic nitrifying bacteria were responsible for NH4+-N and NO2--N oxidation of salinity systems and large number of denitrifying bacteria were detected, which ensure the high removal efficiency of TN in the systems.

The effect of fine grits and fine debris concentrations on the MLVSS/MLSS ratio of an activated sludge system.

This study embarks on an explorative investigation into the effects of typical concentrations and varying particle sizes of fine grits (FG, the involatile portion of suspended solids) and fine debris (FD, the volatile yet unbiodegradable fraction of suspended solids) within the influent on the mixed liquor volatile suspended solids (MLVSS)/mixed liquor suspended solids (MLSS) ratio of an activated sludge system. Through meticulous experimentation, it was discerned that the addition of FG or FD, the particle size of FG, and the concentration of FD bore no substantial impact on the pollutant removal efficiency (denoted by the removal rate of COD and ammonia nitrogen) under constant operational conditions. However, a notable decrease in the MLVSS/MLSS ratio was observed with a typical FG concentration of 20 mg/L, with smaller FG particle sizes exacerbating this reduction. Additionally, variations in FD concentrations influenced both MLSS and MLVSS/MLSS ratios; a higher FD concentration led to an increased MLSS and a reduced MLVSS/MLSS ratio, indicating FD accumulation in the system. A predictive model for MLVSS/MLSS was constructed based on quality balance calculations, offering a tool for foreseeing the MLVSS/MLSS ratio under stable long-term influent conditions of FG and FD. This model, validated using data from the BXH wastewater treatment plant (WWTP), showcased remarkable accuracy.

Effect of lysozyme combined with hydrothermal pretreatment on excess sludge and anaerobic digestion.

Anaerobic digestion (AD) is widely employed for sludge stabilization and waste reduction. However, the slow hydrolysis process hinders methane production and leads to prolonged sludge issues. In this study, an efficient and eco-friendly lysozyme pre-treatment method was utilized to address these challenges. By optimizing lysozyme dosage, hydrolysis and cell lysis were maximized. Furthermore, lysozyme combined with hydrothermal pretreatment enhanced overall efficiency. Results indicate that: (1) When lysozyme dosage reached 90 mg/g TS after 240 min of pretreatment, SCOD, soluble polysaccharides, and protein content reached their maxima at 855.00, 44.09, and 204.86 mg/L, respectively. This represented an increase of 85.87%, 365.58%, and 259.21% compared to the untreated sludge. Three-dimensional fluorescence spectroscopy revealed the highest fluorescence intensity in the IV region (soluble microbial product), promoting microbial metabolic activity. (2) Lysozyme combined with hydrothermal pretreatment significantly increased SCOD, soluble proteins, and polysaccharide release from sludge, reducing SCOD release time. Orthogonal experiments identified Group 3 as the most effective for SCOD and soluble polysaccharide release, while Group 9 released the most soluble proteins. The significance order of factors influencing SCOD, soluble proteins, and polysaccharide release is hydrothermal temperature > hydrothermal time > enzymatic digestion time.(3) The lysozyme-assisted hydrothermal pretreatment group exhibited the fastest release and the highest SCOD concentration of 8,135.00 mg/L during anaerobic digestion. Maximum SCOD consumption and cumulative gas production increased by 95.89% and 130.58%, respectively, compared to the control group, allowing gas production to conclude 3 days earlier.

Bioenergy recovery and carbon emissions benefits of short-term bio-thermophilic pretreatment on low organic sewage sludge anaerobic digestion: A pilot-scale study.

Sewage sludge in cities of Yangzi River Belt, China, generally exhibits a lower organic content and higher silt contentdue to leakage of drainage system, which caused low bioenergy recovery and carbon emission benefits in conventional anaerobic digestion (CAD). Therefore, this paper is on a pilot scale, a bio-thermophilic pretreatment anaerobic digestion (BTPAD) for low organic sludge (volatile solids (VS) of 4%) was operated with a long-term continuous flow of 200 days. The VS degradation rate and CH4 yield of BTPAD increased by 19.93% and 53.33%, respectively, compared to those of CAD. The analysis of organic compositions in sludge revealed that BTPAD mainly improved the hydrolysis of proteins in sludge. Further analysis of microbial community proportions by high-throughput sequencing revealed that the short-term bio-thermophilic pretreatment was enriched in Clostridiales, Coprothermobacter and Gelria, was capable of hydrolyzing acidified proteins, and provided more volatile fatty acid (VFA) for the subsequent reaction. Biome combined with fluorescence quantitative polymerase chain reaction (PCR) analysis showed that the number of bacteria with high methanogenic capacity in BTPAD was much higher than that in CAD during the medium temperature digestion stage, indicating that short-term bio-thermophilic pretreatment could provide better methanogenic conditions for BTPAD. Furthermore, the greenhouse gas emission footprint analysis showed that short-term bio-thermophilic pretreatment could reduce the carbon emission of sludge anaerobic digestion system by 19.18%.

Removal of particulate matter and dissolved organic matter from sedimentation sludge water during pre-sedimentation process: Performances and mechanisms.

Sedimentation sludge water (SSW), a prominent constituent of wastewater from drinking water treatment plants, has received limited attention in terms of its treatment and utilization likely due to the perceived difficulties associated with managing SSW sludge. This study comprehensively evaluated the water quality of SSW by comparing it to a well-documented wastewater (filter backwash water (FBW)). Furthermore, it investigated the pollutant variations in the SSW during pre-sedimentation process, probed the underlying reaction mechanism, and explored the feasibility of employing a pilot-scale coagulation-sedimentation process for SSW treatment. The levels of most water quality parameters were generally comparable between SSW and FBW. During the pre-sedimentation of SSW, significant removal of turbidity, bacterial counts, and dissolved organic matter (DOM) was observed. The characterization of DOM components, molecular weight distributions, and optical properties revealed that the macromolecular proteinaceous biopolymers and humic acids were preferentially removed. The characterization of particulates indicated that high surface energy, zeta potential, and bridging/adsorption/sedimentation/coagulation capacities in aluminum residuals of SSW, underscoring its potential as a coagulant and promoting the generation and sedimentation of inorganic-organic complexes. The coagulation-sedimentation process could effectively remove pollutants from low-turbidity SSW ([turbidity]0 < 15 NTU). These findings provide valuable insights into the water quality dynamics of SSW during the pre-sedimentation process, facilitating the development of SSW quality management and enhancing its reuse rate.

Evaluation of the shear stability of aerobic granular sludge from a pilot-scale membrane bioreactor: Establishment of a quantitative method.

This work established a quantitative method to access the shear stability of aerobic granular sludge (AGS) and validated its feasibility by using the mature AGS from a pilot-scale (50 tons/day) membrane bioreactor (MBR) for treating real municipal wastewater. The results showed that the changing rate (ΔS) of the peak area (S) of granule size distribution (GSD) exhibited an exponential relationship (R2≥0.76) with the shear time (y=a-b·cx), which was a suitable indicative index to reflect the shear stability of different AGS samples. The limiting granule size (LGS) was defined and proposed to characterize the equilibrium size for AGS after being sheared for a period of time, whose value in terms of Dv50 showed high correlation (R2=0.92) with the parameter a. The free Ca2+ (28.44-34.21 mg/L) in the influent specifically interacted with polysaccharides (PS) in the granule's extracellular polymeric substance (EPS) as a nucleation site, thereby inducing the formation of Ca precipitation to enhance its Young's modulus, while Ca2+ primarily interacted with PS in soluble metabolic product (SMP) during the initial granulation process. Furthermore, the Young's modulus significantly affected the parameter a related to shear stability (R2=0.99). Since the parameter a was more closely related (R2=1.00) to ΔS than that of the parameter b or c, the excellent correlation (R2=0.99) between the parameter a and the wet density further verified the feasibility of this method.

Temperature-dependent microbial mechanism and accumulation of volatile fatty acids in primary sludge pretreated with peroxymonosulfate.

For revealing the influence of temperature on volatile fatty acids (VFAs) generation from primary sludge (PS) during the anaerobic fermentation process facilitated by peroxymonosulfate (PMS), five fermentation groups (15, 25, 35, 45, and 55 °C) were designed. The results indicated that the production of VFAs (5148 mg COD/L) and acetic acid (2019 mg COD/L) reached their peaks at 45 °C. High-throughput sequencing technology disclosed that Firmicutes, Proteobacteria, and Actinobacteria was the dominant phyla, carbohydrate metabolism and membrane transport were the most vigorous at 45 °C. Additionally, higher temperature and PMS exhibit synergistic effects in promoting VFAs accumulation. This study unveiled the mechanism of the effect of the pretreatment of PS with PMS on the VFAs production, which established a theoretical foundation for the production of VFAs.

The adaptive regulation mechanism of Anammox granule sludge under calcium ions stress: Defense modes transformation.

Anammox granular sludge (AnGS) has received considerable attention due to its low carbon footprint (less aeration energy and carbon source consumption) and high biomass density, but growth rate and stability are still the bottlenecks of AnGS process. Calcium ion (Ca2+) is essential for the growth of anaerobic ammonium oxidation bacteria (AnAOB) and plays an important role in the formation and stability of AnGS. Response of AnGS to Ca2+ under different concentrations was comprehensively investigated by multi-spectral and metagenomics analysis in four aspects: nitrogen removal performance, surface morphology, extracellular polymeric substance (EPS) composition and characterization, and microbial community. The nitrogen removal efficiency was significantly enhanced at appropriate Ca2+ concentration (2 mmol/L), owning to the more favorable morphology and functional microbial composition of AnGS. However, the nitrogen removal performance of AnGS declined with the Ca2+concentration increased from 2 to 8 mmol/L, due to the negative effects of excess Ca2+on EPS, mass transfer efficiency, and functional microorganisms. Meanwhile, an unexpected slight "rebound" of nitrogen removal efficiency was observed at Ca2+ = 6 mmol/L and attributed to the defense mode transformation of AnGS (from "ion stabilization" to "precipitate shield" modes) against excess Ca2+ stress. Based on the findings, the response mechanism of AnGS to Ca2+ with different concentrations was established. Our results enhanced the understanding of the interaction between AnGS and Ca2+, which may be valuable for filling the theoretical gap in enhancing the granulation and stability of AnGS and providing a reference for the practical operation of the AnGS process.

Filamentous bacteria-induced sludge bulking can alter antibiotic resistance gene profiles and increase potential risks in wastewater treatment systems.

Sludge bulking caused by filamentous bacteria is a prevalent issue in wastewater treatment systems. While previous studies have primarily concentrated on controlling sludge bulking, the biological risks associated with it have been overlooked. This study demonstrates that excessive growth of filamentous bacteria during sludge bulking can significantly increase the abundance of antibiotic resistance genes (ARGs) in activated sludge. Through metagenomic analysis, we identified specific ARGs carried by filamentous bacteria, such as Sphaerotilus and Thiothrix, which are responsible for bulking. Additionally, by examining over 1,000 filamentous bacterial genomes, we discovered a diverse array of ARGs across different filamentous bacteria derived from wastewater treatment systems. Our findings indicate that 74.84% of the filamentous bacteria harbor at least one ARG, with the occurrence frequency of ARGs in these bacteria being approximately 1.5 times higher than that in the overall bacterial population in activated sludge. Furthermore, genomic and metagenomic analyses have shown that the ARGs in filamentous bacteria are closely linked to mobile genetic elements and are frequently found in potentially pathogenic bacteria, highlighting potential risks posed by these filamentous bacteria. These insights enhance our understanding of ARGs in activated sludge and underscore the importance of risk management in wastewater treatment systems.

Assessment and optimization of wastewater treatment plant in terms of effluent quality, energy footprint, and greenhouse gas emissions: An integrated modeling approach.

Wastewater treatment plants (WWTPs) can benefit from utilizing digital technologies to reduce greenhouse gas (GHG) emissions and to comply with effluent quality standards. In this study, the GHG emissions and electricity consumption of a WWTP were evaluated via computer simulation by varying the dissolved oxygen (DO), mixed liquor recirculation (MLR), and return activated sludge (RAS) parameters. Three different measures, namely, effluent water quality, GHG emissions, and energy consumption, were combined as water-energy-carbon coupling index (WECCI) to compare the effects of the parameters on WWTPs, and the optimal operating condition was determined. The initial conditions of the A2O process were set to 4.0 mg/L of DO, 100 % MLR, and 90.7 % RAS. Eighty scenarios with various DO, MLR, and RAS were simulated under steady-state condition to optimize the biological treatment process. The optimal operating conditions were found to be 1.5 mg/L of DO, 190 % MLR, and 90.9 % RAS, which had the highest WECCI of 2.40 when compared to the WECCI of the initial condition (1.07). This optimal condition simultaneously reduced GHG emissions by 1348 kg CO2-eq/d and energy consumption by 11.64 MWh/d. This implies that controlling DO, MLR, and RAS through sensors, valves, and pumps offers a promising approach to operating WWTPs with reduced electricity consumption and GHG emissions while attaining effluent quality standards. Additionally, the nitrous oxide stripping rate exhibited linear relationships with the effluent total ammonia and nitrite concentrations in the aerobic reactor, suggesting that monitoring dissolved nitrogen compounds in the effluent and reactor could be a viable strategy to control MLR and DO in the biological reactor. The digital-based assessment and optimization tools developed in this study are expected to hold promise for application in broader environmental management efforts.

Co-regulating the pore structure and surface chemistry of sludge-based biochar for high-performance deodorization of gaseous dimethyl disulfide.

A straightforward and eco-friendly preparation method for porous sludge biochar (SBA-3) was developed to deodorize gaseous dimethyl disulfide (DMDS) using ion exchange to adjust micropore structures coupled with carboxyl functionalization. Compared with the unmodified sludge biochar SBA-1 and SBA-2 treated with ion exchange, the pore size of SBA-3 decreased accompanied with increasing specific surface area and micropore volume. The Brunauer-Emmett-Teller (BET) specific surface area and micropore volume were 176.35 and 0.0314 cm³ g-1, which were 2.02 and 1.71-fold larger than those of SBA-2, as well as 20.60 and 78.5-fold larger than those of SBA-1, respectively. Meanwhile, the amount of -COOH on the surface of SBA-3 increased from 0.425 to 1.123 mmol g-1, which was 2.64-fold larger than that of SBA-1. The adsorption behavior between DMDS and SBA-3 could be well described by the quasi-second-order kinetic model and Langmuir isotherm model. The maximum monolayer adsorption capacity was 35.12 mg g-1 at 303 K. Thermodynamic and DFT calculations indicated that the adsorption of DMDS on SBA-3 was exothermic with the deodorization mechanisms involving pore filling and chemisorption.

Fecal Sludge Management and Sanitation Safety: An Assessment in Addis Ababa, Ethiopia.

Background: Sanitation safety practices and risks associated with fecal sludge management are crucial for public health and the environment. This study assessed sanitation safety practices and risks in Addis Ababa, Ethiopia, at different stages of fecal sludge management. The research aimed to understand the current state of sanitation facilities, practices, and associated risks and identify areas for improvement. Materials and Methods: A mixed methods/approach was employed, utilizing household surveys, risk assessments, and sanitary inspections. A total of 384 study subjects were interviewed using face-to-face interviews and observations. Results: The findings revealed that the majority of households (97.7%) had consistent access to toilets, with flush/pour flush toilets being the most common type (47.4%). Factors such as odors in toilets or septic tanks, open defecation by children, and the use of untreated wastewater for food production were significantly associated with sociodemographic factors. Risk assessments indicated that 67% of households fell into the low-risk category, while 33% were classified as intermediate risk. The study identified non-compliance issues during sanitary inspections at transfer stations (45%), a wastewater treatment and disposal facility (61.5%), and in the management of wastewater and sludge in the sewer line (64%). These findings call for urgent actions to address improper feces disposal, inadequate maintenance of sanitation facilities, and unsafe practices in fecal sludge management. Conclusion: This study identified concerning issues in fecal sludge management, including improper feces disposal, inadequate facility maintenance, and non-compliance with safety standards during emptying, transport, treatment, and disposal. Urgent action is needed to address these risks. Promoting proper disposal techniques, improving facility maintenance, education programs, strengthening regulations, providing training and protective equipment, and investing in enhanced sanitation facilities and wastewater treatment methods are essential for improving sanitation safety practices.

Multiple drivers and mechanisms of solid-water interfacial interactions in sludge dewatering: Roles of polarity and molecular structure of extracellular polymeric substances.

Water occurrence states in sewage sludge, influenced by sludge physicochemical properties, are crucial for sludge dewaterability and have recently been regarded as a research hotspot. Here, the multifold characteristics of sludge flocs during hydrothermal treatment, including rheological properties, solid-water interfacial interactions, and the polarity distribution and molecular structure of extracellular polymeric substances (EPS), were systematically investigated, and the impact of these characteristics on sludge dewaterability was explored in depth. Hydrothermal treatment at 80 °C and 100 °C induced the conversion of free water into bound water, while an increase in temperature to 180 °C resulted in a significant decrease in bound water content, approximately 4-fold lower than at 100 °C. In addition to the conventional view of decreased sludge surface hydrophilicity at high temperatures, the decline in bound water was associated with the reduction in sludge apparent viscosity. XAD resin fractionation identified the hydrophobic/hydrophilic EPS (HPO-/HPI) ratio as an important factor determining water occurrence states. Especially, hydrolysis of HPI-related hydrophilic proteins and subsequent increase in HPO-related tryptophan-like substances played a dominant role in reducing sludge viscosity and facilitating the release of bound water. Protein conformational analysis revealed that the disruption of α-helix structures and disulfide bonds significantly reduced EPS water-holding capacity, providing strong evidence for the potential of targeting these dense structure units to enhance sludge dewaterability. These findings provide a holistic understanding of multidimensional drivers of water occurrence states in sludge, and guide directions for optimizing sludge treatment efficiency through EPS modification.

Revealing the functional potential of microbial community of activated sludge for treating tuna processing wastewater through metagenomic analysis.

Reports regarding the composition and functions of microorganisms in activated sludge from wastewater treatment plants for treating tuna processing wastewater remains scarce, with prevailing studies focusing on municipal and industrial wastewater. This study delves into the efficiency and biological dynamics of activated sludge from tuna processing wastewater, particularly under conditions of high lipid content, for pollutant removal. Through metagenomic analysis, we dissected the structure of microbial community, and its relevant biological functions as well as pathways of nitrogen and lipid metabolism in activated sludge. The findings revealed the presence of 19 phyla, 1,880 genera, and 7,974 species, with Proteobacteria emerging as the predominant phylum. The study assessed the relative abundance of the core microorganisms involved in nitrogen removal, including Thauera sp. MZ1T and Alicycliphilus denitrificans K601, among others. Moreover, the results also suggested that a diverse array of fatty acid-degrading microbes, such as Thauera aminoaromatica and Cupriavidus necator H16, could thrive under lipid-rich conditions. This research can provide some referable information for insights into optimizing the operations of wastewater treatment and identify some potential microbial agents for nitrogen and fatty acid degradation.

Acute inhibitory effects of tire wear particles on the removal of biological phosphorus：The critical role of aging in improving environmentally persistent free radicals.

A comparative study explored how photoaging, ozonation aging, and Fenton aging affect tire wear particles (TWPs) and their phosphorus (P) removal in activated sludge. Aging altered TWPs' properties, increasing surface roughness, porosity, and generating more small particles, especially environmental persistent free radicals (EPFRs) in ozonation and Fenton aging. Post-aging TWPs (50 mg/L) inhibited sludge P removal significantly (p < 0.05), with rates of 44.3% and 59.6% for ozonation and Fenton aging, respectively. In addition, the metabolites involved in P cycling (poly-ß-hydroxyalkanoates: PHA and glycogen) and essential enzymes (Exopolyphosphatase: PPX and Polyphosphate kinase: PPK) were significantly inhibited (p < 0.05). Moreover, TWPs led to a decrease in microbial cells within the sludge and altered the community structure, a situation exacerbated by the aging of TWPs. P-removing bacteria decreased (e.g., Burkholderia, Candidatus), while extracellular polymeric substance-secreting bacteria increased (e.g., Pseudomonas, Novosphingobium). Pearson correlation analysis highlighted EPFRs' role in TWPs' acute toxicity to microbial cells, yet, emphasizing particle size's impact on the sludge system's purification and community structure.

Fenton-conditioning of landfill leachate biological sludge enables biochar for efficient Cr(â ¥)removal: Occurrence of oxygen-centered free radicals.

Fenton-conditioning is commonly used to improve dewatering ability for municipal biological sludge, however, its application in industries is scarce. In this study, biochar (FT-BC) was successfully synthesized from a Fenton-conditioned landfill leachate biological sludge under oxygen-limited. As compared to the corresponding blank and poly ferric-pretreated biochars (BC and PF-BC), moderate Fenton conditioning of the sludge could enable good removal performance for Cr (Ⅵ) by FT-BC. It was found that the oxygen central free radicals (OCFRs) on the biochar surface was intensively promoted due to Fenton electrophilic addition of ·OH onto the oxygen-containing functional groups in biomass. The amounts of OCFRs correlated positively well with the removal efficiency, indicating these persistent free radicals (PFRs)would mainly responsible for the reductive immobilization of Cr(VI)on the FT-BC surface. This study is expected to provide a new method for reclamation of industrial biological sludges with poor agglomeration by introducing simple Fenton pre-conditioning.

Utilization of industrial wastes in non-sintered bricks: microstructure and environmental impacts.

Recycling industrial solid wastes as building materials in the construction field exhibits great environmental benefits. This study designed an eco-friendly non-sintered brick by combining multiple industrial solid wastes, including sewage sludge, fly ash, and phosphorus gypsum. The mechanical properties, microstructure, and environmental impacts of waste-based non-sintered bricks (WNBs) were investigated comprehensively. The results revealed that WNB exhibited excellent mechanical properties. In addition, steam curing could further promote the strength development of WNB. The compressive strength of WNB with 10 wt% of sewage sludge reached 13.5 MPa. Phase assemblage results indicated that the incorporation of sewage sludge promoted the generation of ettringite. Mercury intrusion porosimetry results demonstrated that the pore structure of WNB varies with the dosage of sewage sludge. Life-cycle assessment results revealed that the energy consumption and CO2 emission of WNB were 45% and 17% lower than those of traditional clay bricks. Overall, the development of WNB in this study provided insights into the co-disposal of industrial solid wastes.

Ecotoxicological assessment, in freshwater environment, of wastewater sludge coupled and uncoupled with micro-polyvinyl chloride on algae and water fleas.

In the frame of bioeconomy and circular economy, wastewater sludge (WS) could be a good candidate for its use in agriculture as fertilizer, due to its high content of organic matter, N and P, but on the other hand, it is full of toxicants such as heavy metal, microplastics, detergent, antibiotics, and so on that can reach groundwater and water bodies in leachate form. In this study, we have investigated different sludge concentrations in the eluate form, combined and not with PVC on two different freshwater organisms Selenastrum capricornutum and Daphnia magna, using ecotoxicity tests. At the endpoint, we have evaluated inhibition growth rate, oxidative stress, and pigments production for S. capricornutum, while in case of D. magna, we have assessed organism immobilization and development. From our results, it emerged that at the higher WS concentration, there was not inhibition growth rate, while at oxidative stress, it was higher in algae treated with WS and PVC. Higher Chl-a production was shown for algae treated with 0.3 g/L of sludge coupled with PVC, where higher phaeopigments production were recorded for algae treated with 0.3 g/L of WS. D. magna has shown an opposite trend when compared with algae, where at the highest WS concentrations supplied was corresponding to an increased mortality explaned as the highest immobility percentage. PRACTITIONER POINTS: Wastewater sludge is used in agriculture as fertilizer. PVC microplastic presence and associate ecotoxicity was tested. PVC presence increased oxidative stress in S. capricornutum. D. magna was significantly affected by sludge concentrations supplied.

Impact of polystyrene nanoplastics on primary sludge fermentation under acidic and alkaline conditions: Significance of antibiotic resistance genes.

As a part of industrial or commercial discharge, the influx of nanoplastics (NPs) to the wastewater treatment plants is inevitable. Consequently, it has become a must to understand the effects of these NPs on different unit processes. This study aimed to investigate the impact of three different concentrations of polystyrene nano plastics (PsNPs) on the fermentation of primary sludge (PrS), implemented in batch anaerobic bioreactors, at pH 5 and 10, considering the pH-dependent nature of the fermentation process. The results showed that PsNPs stimulated hydrogen gas production at a lower dose (50 µg/L), while a significant gas suppression was denoted at higher concentrations (150 µg/L, 250 µg/L). In both acidic and alkaline conditions, propionic and acetic acid predominated, respectively, followed by n-butyric acid. Under both acidic and alkaline conditions, exposure to PsNPs boosted the propagation of various antibiotic resistance genes (ARGs), including tetracycline, macrolide, ß-lactam and sulfonamide resistance genes, and integrons. Notably, under alkaline condition, the abundance of sul2 gene in the 250 µg PsNPs/L batch exhibited a 2.4-fold decrease compared to the control batch. The response of the microbial community to PsNPs exposure exhibited variations at different pH values. Bacteroidetes prevailed at both pH conditions, with their relative abundance increasing after PsNPs exposure, indicating a positive impact of PsNPs on PrS solubilization. Adverse impacts, however, were detected in Firmicutes, Chloroflexi and Actinobacteria. The observed variations in the survival rates of various microbes stipulate that they do not have the same tolerance levels under different pH conditions.