A mixed culture, prepared by acclimatising Chlorella vulgaris (C. vulgaris) to municipal wastewater (MWW), was used in two reactors: one was inoculated with activated sludge (AS), and the other was not (NAS). Under 12:12h light: dark, mixing, and a hydraulic retention time of 1.17 d, both systems removed ∼92% of 270mg-COD/L, 57% of 70mg-N/L, and 27% of PO43--P, while achieving a sludge volume index of 42mL/g. C. vulgaris disappeared and was replaced by other algae, including cyanobacteria, indicating that inoculation is not necessary. Higher dissolved oxygen production, IC uptake, and nitrification occurred in the NAS reactor than in the AS reactor, supported by a higher abundance of the autotrophic/aerobic community in the NAS reactor. Genomic data revealed latent mechanisms (denitrification, N-fixation, nitrate/nitrite reduction, multiple phosphorus pathways) than mass balance. Pure algae seeding is not essential, but activated sludge seeding could affect performance.

Electrically enhanced microalgae-bacteria systems for wastewater treatment under low-temperature conditions.

Scale-up and performance evaluation of an electrodialysis process in a municipal wastewater treatment plant

A-OHO biological process for municipal wastewater treatment based on carbon-nitrogen element regulation: Total nitrogen removal, low-energy pathway, and microbial mechanism

Wastewater treatment plants are widely recognized as hotspots for antibiotic resistance. Although activated sludge processes are not designed to lower the abundance of pathogens or antibiotic resistance genes (ARGs), their effects on the pathobiome and antibiotic resistome require in-depth investigation. To this end, we collected wastewater samples before and after activated sludge process from five municipal wastewater treatment plants, each characterized by different inlet composition and treatment capacity. We extracted both intracellular and extracellular DNA and performed shotgun sequencing to characterize the bacterial community, pathobiome, and antibiotic resistome. Our aim was to assess the effects of activated sludge processes on bacterial community composition, the abundance of potentially pathogenic bacteria and high-risk ARGs, and the potential horizontal mobility of detected ARGs. Our results showed that activated sludge processes significantly reduced the abundance of potentially pathogenic bacteria and several high-risk ARGs. Notably, while the prevalence of plasmid-associated ARGs decreased following treatment, ARG-carrying contigs assigned to bacteriophages increased, particularly in extracellular DNA samples. Overall, activated sludge processes demonstrated a beneficial microbiological effect by lowering potentially pathogenic bacteria. However, the enrichment of viral particles carrying ARGs highlights a potential risk for ARG spreading during the following processes. These findings underscore the importance of analyzing both intracellular and extracellular DNA to fully understand the role of activated sludge in mitigating antibiotic resistance and pathogens in wastewater.

The Baltic Sea remains one of the most contaminated marine seas globally, receiving diverse pollutant inputs from land-based and maritime sources. This study quantifies the concentrations and loads of microplastic (MP) in ship-generated greywater (GW) and evaluates their potential contribution to Baltic marine MP pollution. Eight GW streams from five vessels were sampled, and fifteen MP polymer types were identified and characterized. MP concentrations ranged from ≈38,000MP/m3 in mixed accommodation-laundry-galley (ALG) stream to≈602,000MP/m3 in laundry GW. Polyethylene terephthalate (PET) was the dominant polymer (58%), detected in all GW samples, while polypropylene (PP, 16%) appeared in only three streams from two vessels. Estimated annual MP loads from the studied Roll on - Roll off - Passenger (RoPax) vessels ranged between≈1.24 and 7.59 billion particles, which are typically delivered to municipal wastewater treatment plants (MWTPs) via Port Reception Facilities (PRFs). Considering the total Baltic fleet's greywater discharge of ≈5.4 million m3/yr in 2022, up to 1.1 trillion MP/yr could have been released directly to the sea, with ≈93% originating from passenger ships. If this volume generated in 2022 were instead delivered to PRFs and treated at MWTPs, ≈6 million - 651 billion MP/yr could still enter the Baltic environment, depending on the treatment efficiencies and technology configurations employed at the MWTPs. These results demonstrate that ship-generated GW is a significant yet understudied source of microplastic (MP) to the Baltic Sea. Moreover, while advanced systems with tertiary treatment technologies on board and ashore can remove ≈95 - 99.9% of MP, residual emissions remain substantial given the large wastewater volumes generated. Effective mitigation strategies should therefore focus on source identification and prevention within shipboard systems, particularly in laundry, galley and accommodation operations, to minimize MP inputs into GW streams and, ultimately, the marine environment.

Enhanced denitrification performance of constructed wetlands for wastewater treatment plant effluent using zero-valent iron-based mixing solid carbon sources.

Enhancing synergistic partial nitrification-anammox coupling via step feed and granular sludge technology for optimized nitrogen removal in municipal wastewater treatment.

Developed by Marais and Rabinowitz, the A2/O process is a pivotal biotechnology for biological nitrogen and phosphorus removal, developed by optimizing the five-stage Phoredox protocol. Renowned for its efficient configuration and straightforward operation, it has been extensively adopted in municipal and industrial wastewater treatment projects globally, including numerous facilities in China. However, the conventional A2/O process faces inherent operational challenges: the conflicting SRT requirements between autotrophic nitrifying bacteria (needing long SRT for stable nitrification) and PAOs, intense competition for carbon sources among PAOs and denitrifying bacteria, and the inhibitory effects of residual nitrate and DO on phosphorus release and denitrification. To address these issues, a range of optimization strategies has been developed, including SRT adjustment, carbon source distribution optimization, the integration of biofilm carriers, the addition of external carbon sources, and innovative modified configurations such as the Reversed A2/O, JHB, UCT, and MUCT. These approaches synergistically mitigate nitrate interference and enhance nutrient removal efficiency by decoupling microbial SRT demands, supplementing readily biodegradable carbon sources, and optimizing hydraulic flow paths. Future research should focus on deepening the understanding of the metabolic mechanisms underlying nitrogen and phosphorus removal, developing sustainable and efficient external carbon source systems, refining multi-mode reactor design for engineering scalability, optimizing combined processes for ultra-low C/N ratio wastewater treatment, and advancing low-temperature adaptation technologies. These efforts aim to further improve the process’s efficacy, stability, and sustainability, enabling it to meet increasingly stringent environmental discharge standards.

Wastewater treatment plants increasingly rely on anaerobic digestion and biogas utilization to reduce operational costs, enhance energy self-sufficiency, and support circular-economy objectives. This study provides a comprehensive, year-round assessment of sludge production, sludge characteristics relevant to digestion, biogas generation, and energy performance at a municipal wastewater treatment plant. The plant generated on average 68.0 m3/d of thickened primary sludge and 24.0 m3/d of excessive sludge (total 92 m3/d), with low daily variability throughout the year. Biogas production remained highly stable, with an annual average of approximately 1300 m3/d and limited daily variation. Although monthly averages ranged from 1004 to 1728 m3/d, within-month variability was low to moderate, indicating that digestion processes responded consistently to changes in sludge quantity and composition. The weak correlation between sludge volume and biogas output (r = 0.29) showed that, besides sludge quantity, factors such as organic content and digester operating conditions also influence biogas yield. Energy performance indicators demonstrated strong self-sufficiency potential: the facility produced 1,095,047 kWh of electricity, covering 56.72% of its annual demand. The high coefficient of determination for self-sufficiency (R2 = 0.871) confirmed a strong linear relationship between biogas-derived energy production and reduced grid dependence. Operational correlations further highlighted system coherence, with cogenerator and boiler usage strongly inversely related (r = −0.85) and biogas production positively associated with heat output (r = 0.66). Overall, the results demonstrate a stable and efficient sludge-to-energy system and provide a detailed dataset supporting future optimization of anaerobic digestion processes.

In order to analyze the characteristics of fossil source CO2 emissions in the AAO process of municipal wastewater treatment, in-situ monitoring in a typical AAO process of a municipal wastewater treatment plant in North China was conducted in this work. The CO2 emission flux of each main process unit (selection tank, anaerobic tank, anoxic tank, aerobic tank, sludge return gallery, and secondary sedimentation tank) from September 2023 to August 2024 was obtained, and the 24 h day and night continuous change pattern and the emission contribution of fossil source CO2 was analyzed. Through 12 months of continuous monitoring, the direct CO2 emission fluxes of major process units such as selection tank, anaerobic tank, anoxic tank, aerobic tank, sludge return gallery, and secondary sedimentation tank were (30.20±2.85), (43.50±5.81), (44.41±4.69), (2 736.82±213.26), (82.68±7.21), and (11.59±1.15) g·(m2·d)-1, respectively. In summer, the AAO process showed "double peaks" of direct CO2 emission flux in 24 h, with peak periods at 06:00-09:00 [average 12 443.14 μg·(m2·s)-1] and 21:00-24:00 [average 12 395.38 μg·(m2·s)-1], both of which were 20% higher than the average value of direct CO2 emission flux in summer for 24 h. In winter, the AAO process showed a "single peak" of direct CO2 emission flux in 24 h, with peak periods at 09:00-12:00 [average 16 705.90 μg·(m2·s)-1], which was 21% higher than the average value of direct CO2 emission flux in winter for 24 h. The direct CO2 emission flux in winter [24 h average 13 811.81 μg·(m2·s)-1, CV=9.0%] was higher than that in summer [24 h average 10 388.41 μg·(m2·s)-1, CV=14.4%] but with smaller fluctuations. The monthly direct CO2 emission monitoring results showed that the average direct CO2 emission flux of the AAO process for 12 months was (1 094.86±80.97) g·(m2·d)-1 with large-size monthly fluctuations (CV=35.6%); the peak occurred in March 2024 [1 737.74 g·(m2·d)-1], which was 59% higher than the average value of 12 months. The direct CO2 emission intensity of the AAO process varied significantly with the seasons. The average direct CO2 emission intensities in spring, winter, summer, and autumn were (3 546.76±616.24), (3 089.66±363.98), (2 738.55±120.38), and (2 267.45±229.33) kg·d-1, respectively. The direct CO2 emissions of different process units were obviously different, and the aerobic tank was the main source of CO2 emissions in the AAO process, with an average annual emission flux, average annual daily emission intensity, and average annual emission factor (measured in CO2/COD) of (2 736.82±213.26) g·(m2·d)-1, (2 859.14±214.32) kg·d-1, and (3.83±0.75) kg·kg-1, respectively, which were significantly (P < 0.001) higher than those of other treatment units. The direct CO2 emission flux was significantly positively correlated with oxidation-reduction potential (ORP; P < 0.000 1), DO (P < 0.05), NO3--N (P < 0.05), and NO2--N (P < 0.05) and was significantly negatively correlated with TP (P < 0.01), NH4+-N (P < 0.01), and pH (P < 0.05). The direct CO2 emissions from fossil sources in the municipal wastewater treatment process were estimated based on the measured values of direct CO2 emissions, and the overall fossil source direct CO2 emission range of the AAO process was (38.05±5.31)-(148.41±20.72) g·m-3 (converted into fossil source CO2 emissions per m3 of wastewater treated). Direct CO2 emissions from fossil sources accounted for approximately 28.7%-67.1% of the greenhouse gas emissions of the whole plant calculated by the Intergovernmental Panel on Climate Change (IPCC) method. The direct CO2 emissions from fossil sources in municipal wastewater treatment plants are underestimated by the IPCC carbon emission accounting system, and it is recommended to include direct CO2 emissions from fossil sources in the carbon emission accounting system of wastewater treatment plants.

The dilution factor (DF) quantifies the extent to which wastewater is diluted after being discharged into a receiving water body. It serves as a critical indicator for establishing effluent discharge standards and assessing aquatic ecological risks. Although extensive research has been conducted on river DF, limited attention has been paid to the rationality of DF calculation methods. Typically, the accumulated wastewater volume (AWV) within a catchment-rather than the wastewater volume in the nearby receiving river-is commonly used for DF calculation. During this process, the delineation of the sub-catchment plays a critical role in determining AWV. However, the impact of sub-catchment delineation on DF calculation remains unclear. This study utilizes a comprehensive dataset comprising streamflow records from 235 hydrological stations, effluent discharge data from 544 municipal wastewater treatment plants (WWTPs), and sub-catchment information within the Yellow River Basin to examine the influence of sub-catchment delineation on DF. The results revealed that when the sub-catchment area was less than 3 000 m2, there was no significant correlation between DF and streamflow. However, this correlation became pronounced when the sub-catchment area ranged between 3 000 and 5 000 m2. This trend may have primarily resulted from the higher spatial heterogeneity in the distribution of WWTP within smaller sub-catchments compared to that within larger ones. Such heterogeneity led to greater variability in AWV and consequently in the DF. As the sub-catchment area increased, the spatial geographic elements such as number of WWTPs became more spatially homogenized, and the spatial distribution of geographic elements such as WWTPs became more homogeneous, resulting in more stable AWV estimates. This spatial averaging effect highlights the correlation between DF and streamflow in larger sub-catchments. When sub-catchment boundaries were not defined, and wastewater discharge was assumed to flow throughout the entire river network in the Yellow River Basin, the resulting DF was significantly underestimated. Using such underestimated DF values as basis for regulatory decision-making may lead to overly stringent effluent discharge standards that do not reflect actual environmental capacity. Therefore, accurate delineation of sub-catchment boundaries is essential. It is recommended that pollutant transport models be used in combination with observed pollutant concentration data in the river to determine an appropriate sub-catchment boundary. Based on DF results that incorporated sub-catchment boundaries, the median DF values were 6 358.8 for the main stream and 28.5, 21.5, and 5.1 for third-, fourth-, and fifth-order tributaries, respectively. Additionally, the median DF values for rivers in the upper, middle, and lower reaches of catchment were 1 346.5, 9.3, and 48, respectively. Notably, temporal variation in DF was much smaller than spatial variation. These findings provide valuable insights for applying DF at the regional scale and for developing region-specific effluent discharge standards.

Abstract The valorization of agricultural waste into functional materials offers a sustainable route for developing advanced water treatment technologies. In this study, microalgae biomass was converted into biochar and subsequently functionalized with amine groups via a one-step mussel-inspired polymerization and Schiff-base addition reaction. The resulting novel amine-functionalized biochar (AFBC) was incorporated into cellulose acetate (CA) membranes using the nonsolvent-induced phase separation (NIPS) method to fabricate hybrid ultrafiltration membranes. Comprehensive structural and physicochemical analyses confirmed the successful functionalization of the biochar and its uniform distribution within the CA matrix. AFBC incorporation significantly enhanced the membrane's hydrophilicity, porosity, and surface charge, leading to improved rejection of natural organic matter (NOM). The membrane containing 4 wt.% AFBC achieved a flux of 169.1 LMH and 64.1% NOM removal efficacy during municipal wastewater filtration, outperforming the pristine CA membrane (81.8 LMH, 31.1% removal). Moreover, the modified membrane demonstrated complete bacterial removal, partial elimination of other contaminants, and a high flux recovery ratio (82.7%), indicating excellent antifouling properties. These findings establish AFBC as a promising sustainable filler for the development of high-performance hybrid membranes for eco-friendly municipal wastewater treatment. Graphical Abstract

This study evaluated the performance of a pilot unit for the combined removal of microplastics and total suspended solids at the municipal wastewater treatment plant of Mykonos, Greece. The pilot unit was installed downstream of the two-stage conventional activated sludge line and operated in semi-continuous mode to demonstrate its function under real effluent conditions. Across five experimental loops, influent microplastics concentrations ranged from 633 to 5843 microplastics/L, while effluent values were reduced to 96–263 microplastics/L, corresponding to an average removal efficiency of 86 ± 8%. In parallel, total suspended solids decreased by 95 ± 3%, turbidity by 93 ± 7%, and chemical oxygen demand by 70 ± 20%, while pH and conductivity remained stable. Influent water showed pronounced variability in chemical oxygen demand, total suspended solids, and turbidity due to irregular wastewater deliveries, yet the pilot consistently stabilized the effluent quality. A correlation analysis revealed strong associations between turbidity, total suspended solids, and chemical oxygen demand in the influent, while effluent data indicated close links between microplastics removal and particulate reduction. These findings confirm the robustness of the organosilane-based agglomeration process and highlight its potential as an advanced treatment stage to reduce MP emissions, improve effluent stability, and mitigate environmental risks in receiving environments such as the Mediterranean Sea.

Conventional wastewater treatment in industrialized countries effectively removes readily degradable organic matter and nutrients but often fails to sufficiently reduce micropollutants. To overcome this gap and assess the resulting benefits in effluent quality and downstream conditions, advanced processes such as ozonation and powdered activated carbon dosing followed by cloth filtration can be implemented to enhance micropollutant elimination and reduce biological effects in treated effluents. In this case study, a municipal wastewater treatment plant was evaluated following the implementation of a two-step advanced treatment system during summer and fall 2023. To assess changes in effluent quality, effect-based methods were combined with targeted chemical measurements of indicator substances. To investigate potential ecological responses downstream, the benthic invertebrate community in the receiving river was analyzed additionally as an ecologically relevant endpoint shortly after the upgrade. Following implementation, advanced treatment substantially reduced both toxic effects and concentrations of the indicator substances compared with conventional treatment. Nevertheless, residual adverse effects were still observed in the receiving water, as indicated by active biomonitoring with gammarids and gastropods and by patterns in the benthic invertebrate community. In addition, the techniques applied in this study showed that there will be room for further optimization in the upgraded WWTP.

Sustainable nutrient removal without chemical addition: Pilot-scale performance of a biochar-enhanced hybrid biofilm system in municipal wastewater treatment.

A droplet-based electricity generators (DEGs) system for harvesting secondary effluent energy.

Meso- and microplastics accumulate and transfer hazardous contaminants from wastewater treatment plants to the environment.

Unsupervised and supervised machine-learning modeling of the operational parameters enriching the anammox microbiome in a full-scale municipal wastewater treatment plant

Do households or hospitals have a larger contribution to carbapenemase-producing Enterobacteriaceae in municipal wastewater?