This review presents the state-of-the-art sludge reduction technologies applied in both wastewater and sludge treatment lines. They include chemical, mechanical, thermal, electrical treatment, ...addition of chemical un-coupler, and predation of protozoa/metazoa in wastewater treatment line, and physical, chemical and biological pretreatment in sludge treatment line. Emphasis was put on their effect on sludge reduction performance, with 10% sludge reduction to zero sludge production in wastewater treatment line and enhanced TS (total solids) or volatile solids removal of 5–40% in sludge treatment line. Free nitrous acid (FNA) technology seems good in wastewater treatment line but it is only under the lab-scale trial. In sludge treatment line, thermal, ultrasonic (<4400kJ/kg TS), FNA pretreatment and temperature-phased anaerobic digestion (TPAD) are promising if pathogen inactivation is not a concern. However, thermal pretreatment and TPAD are superior to other pretreatment technologies when pathogen inactivation is required. The new wastewater treatment processes including SANI®, high-rate activated sludge coupled autotrophic nitrogen removal and anaerobic membrane bioreactor coupled autotrophic nitrogen removal also have a great potential to reduce sludge production. In the future, an effort should be put on the effect of sludge reduction technologies on the removal of organic micropollutants and heavy metals.
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•State-of-the-art sludge reduction technologies were reviewed.•Advantages and disadvantages of sludge reduction technologies were discussed.•Free nitrous acid technology seems good in wastewater treatment line.•Thermal pretreatment and TPAD are superior in sludge treatment line.•Future perspectives of sludge reduction technologies were elucidated.
Antibiotics, the most frequently prescribed drugs of modern medicine, are extensively used for both human and veterinary applications. Antibiotics from different wastewater sources (e.g., municipal, ...hospitals, animal production, and pharmaceutical industries) ultimately are discharged into wastewater treatment plants. Sorption and biodegradation are the two major removal pathways of antibiotics during biological wastewater treatment processes. This review provides the fundamental insights into sorption mechanisms and biodegradation pathways of different classes of antibiotics with diverse physical–chemical attributes. Important factors affecting sorption and biodegradation behavior of antibiotics are also highlighted. Furthermore, this review also sheds light on the critical role of extracellular polymeric substances on antibiotics adsorption and their removal in engineered biological wastewater treatment systems. Despite major advancements, engineered biological wastewater treatment systems are only moderately effective (48–77%) in the removal of antibiotics. In this review, we systematically summarize the behavior and removal of different antibiotics in various biological treatment systems with discussion on their removal efficiency, removal mechanisms, critical bioreactor operating conditions affecting antibiotics removal, and recent innovative advancements. Besides, relevant background information including antibiotics classification, physical–chemical properties, and their occurrence in the environment from different sources is also briefly covered. This review aims to advance our understanding of the fate of various classes of antibiotics in engineered biological wastewater treatment systems and outlines future research directions.
•Various influencing factors of energy use in WWTPs are characterized.•Benchmark energy consumption in WWTPs in different countries are highlighted.•Energy recovery or saving technologies in WWTPs ...are summarized.•Recent advances in optimization of energy recovery technologies are highlighted.•Feasibility and challenges of energy self-sufficient WWTPs are explored.
Energy efficiency optimization is crucial for wastewater treatment plants (WWTPs) because of increasing energy costs and concerns about global climate change. Energy efficiency optimization can be achieved through a combination of energy recovery from the wastewater treatment process and energy saving-related technologies. Through these two approaches energy self-sufficiency of WWTPs is achievable, and research is underway to reduce operation costs and energy consumption and to achieve carbon neutrality. In this paper, we analyze energy consumption and recovery in WWTPs and characterize the factors that influence energy use in WWTPs, including treatment techniques, treatment capacities, and regional differences. Recent advances in the optimization of energy recovery technologies and theoretical analysis models for the analysis of different technological solutions are presented. Despite some challenges in implementation, such as technological barriers and high investment costs, particularly in developing countries, this paper highlights the potential for more energy self-sufficient WWTPs to be established in the future.
The distribution of 14 ARGs, intI1, and 16S rDNA were analysed in 4 wastewater treatment plants (WWTPs), 2 effluent receiving areas (ERAs), and Hangzhou Bay (HZB). The results showed that each ...integrated WWTP (IWWTP) received higher abundance of ARGs than pharmaceutical WWTPs (PWWTPs), and IWWTPs removed ARGs more efficiently than PWWTPs. The WWTP effluents greatly contributed to the ARGs pollution in the water environments of the ERAs and HZB, and the total abundance of the ARGs displayed a distance decay pattern. In coastal sediments, more ARGs were accumulated in remote sites. The correlation analysis showed that the occurrence of ARGs was more related to 16S rDNA and intI1 in the WWTPs. Three macrolides resistance genes (ermB, mphA, and vatB) had strong correlations with 16S rDNA and intI1 in all the sample groups. Our study clearly reveals the link between land WWTPs discharge and emerging pollution of ARGs in coastal environments.
This study investigated the distribution of ARGs from WWTPs to natural bay, and explored the effects of wastewater discharge to the spread of ARGs in coastal environment. Display omitted
•The abundances of 14 ARGs from WWTPs to natural bay were investigated.•WWTP effluents contributed to the ARGs pollution in the coastal environment.•The intI1 and 16S rDNA might have different impact on the detected ARGs.•Heavy metals and nutrients had strong positive correlations with the distribution of ARGs.
The production of biochar from sewage sludge pyrolysis is a promising approach to transform the waste resultant from wastewater treatment plants (WWTPs) to a potential adsorbent. The current review ...provides an up-to-date review regarding important aspects of sewage sludge pyrolysis, highlighting the process that results major solid fraction (biochar), as high-value product. Further, the physio-chemical characteristics of sewage-sludge derived biochar such as the elemental composition, specific surface area, pore size and volume, the functional groups, surface morphology and heavy metal content are discussed. Recent progress on adsorption of metals, emerging pollutants, dyes, nutrients and oil are discussed and the results are examined. The sewage sludge-derived biochar is a promising material that can make significant contributions on pollutants removal from water by adsorption and additional benefit of the management of huge volume of sewage. Considering all these aspects, this field of research still needs more attention from the researchers in the direction of the technological features and sustainability aspects.
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•Sewage sludge utilized as potential precursor for biochar production.•Pyrolysis approach and process conditions for biochar production.•Characterization aspects of sewage-sludge derived biochar.•Mechanisms associated with the adsorptive removal of water pollutants.
Microbial communities are responsible for biological wastewater treatment, but our knowledge of their diversity and function is still poor. Here, we sequence more than 5 million high-quality, ...full-length 16S rRNA gene sequences from 740 wastewater treatment plants (WWTPs) across the world and use the sequences to construct the 'MiDAS 4' database. MiDAS 4 is an amplicon sequence variant resolved, full-length 16S rRNA gene reference database with a comprehensive taxonomy from domain to species level for all sequences. We use an independent dataset (269 WWTPs) to show that MiDAS 4, compared to commonly used universal reference databases, provides a better coverage for WWTP bacteria and an improved rate of genus and species level classification. Taking advantage of MiDAS 4, we carry out an amplicon-based, global-scale microbial community profiling of activated sludge plants using two common sets of primers targeting regions of the 16S rRNA gene, revealing how environmental conditions and biogeography shape the activated sludge microbiota. We also identify core and conditionally rare or abundant taxa, encompassing 966 genera and 1530 species that represent approximately 80% and 50% of the accumulated read abundance, respectively. Finally, we show that for well-studied functional guilds, such as nitrifiers or polyphosphate-accumulating organisms, the same genera are prevalent worldwide, with only a few abundant species in each genus.
A total of 17 groups of wastewaters from the chemical industrial parks and matched receiving river waters were collected in the east of China. The measured total concentrations of 21 analyzed PFAS ...analogues (∑21PFAS) in the influents and effluents of the wastewater treatment plants (WWTPs) were in the range of 0.172–20.6 μg/L (mean: 18.2 μg/L, median: 3.9 μg/L) and 0.167–93.6 μg/L (mean: 10.8 μg/L, median: 1.12 μg/L), respectively, which were significantly higher than those observed in the upstream (range: 0.0158–7.05 μg/L, mean: 1.09 μg/L, median: 0.482 μg/L) and downstream (range: 0.0237–1.82 μg/L, mean: 0.697 μg/L, median: 0.774 μg/L) receiving waters. Despite the concentrations and composition profiles of PFAS varied in the water samples from different sampling sites, PFOA was generally the major PFAS analogue in the research areas, mainly due to the history of PFOA production and usage as well as the specific exemptions. The calculated concentration ratios of the short-chain PFCAs and PFSAs to their respective predecessors (PFOA and PFOS) in most of the samples far exceeded 1, indicating a shift from legacy PFOA and PFOS to short-chain PFAS in the research areas. Correlation network analysis and the calculated concentration ratios of PFAS in the effluents versus influents indicated transformation may have occurred during the water treatment processes and PFAS could not be efficiently removed in the WWTPs. Wastewater discharge of chemical industrial parks is a vital source of PFAS dispersed into the aquatic environment.
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•PFAS in the matched wastewaters and receiving waters were studied.•The total PFAS levels were incredibly high in some sites.•PFOA predominated the PFAS profiles in the wastewaters and receiving waters.•Wastewater treatment plants are relatively ineffective in removing PFAS.•Wastewater discharge impacts the PFAS in the surrounding aquatic environments.
The widespread application of sewage sludge produced from wastewater treatment plants for agricultural use has been regarded as a primary source of microplastics (MPs) into soils. However, little is ...known regarding MPs in sludge-based fertilizers and their relevant fate in soils as being applied in agriculture. We comprehensively investigated the abundance, polymer size, type, and morphology of MPs in dewatered sludge, sewage sludge composts, sludge-based fertilizer-amended soils, and earthworms by stereoscopy and micro Fourier transform infrared (μ-FTIR) spectrometry methods. The results clearly showed that the quantity of MPs in soils exhibited a close correlation with the application rate of sludge-based fertilizers. The total abundances of MPs were 545.9 and 87.6 items/kg in soils after annual amendment with 30 (field A) and 15 t/ha (field B) of sludge composts, which is significantly higher than that without compost application (field C, 5.0 items/kg). Correspondingly, MPs were found in earthworms with low quantities of 1.8 and 0.4 items/individual in fields A and B, respectively, while no MP was detected in field C. We speculate that sludge composts may act as a vehicle of MPs into soils and then enter soil biota and in turn influence the spread of MPs in the environment.
Aquatic environments are identified as an ideal setting for acquisition and dissemination of antibiotic resistance, and human exposure to antibiotic resistant bacteria (ARB) and antibiotic resistance ...genes (ARGs) in aquatic environments may pose an additional health risk. Quantitative microbial risk assessment (QMRA) has been suggested as a suitable method to evaluate and quantify this health risk. However, information about the exposure to ARB and ARGs in aquatic environments is lacking for many scenarios and dose-response models regarding the ARB infections are not developed yet. This review summarizes the current knowledge regarding the ARB and ARGs in aquatic environments and highlights the challenging questions remaining to be answered to better forecast the health risks caused by ARB and ARGs in water environments. The questions include what are the missing information needed to quantify the human health risks caused by exposing to ARB and ARGs in aquatic environments? what are the suitable markers to evaluate the ARB/ARGs contamination in aquatic environments? how frequently do the ARG selection and propagation occur in aquatic environments? and are there any unknown hot spots? Studies on the above topics will contribute to better management of antibiotic resistance dissemination in water environments and its risks on human health.
Abbreviations
3GC
3
rd
generation cephalosporins
ARB
Antibiotic resistant bacteria
ARG
Antibiotic resistance gene
CFU
Colony forming unit
DBP
Disinfection by-products
eDNA
Extracellular DNA
EPS
Extracellular polymeric substances
HGT
Horizontal gene transfer
ISCR
Insertion sequence common region
MAR
Multiple antibiotic resistant
MIC
Minimum inhibitory concentration
MGE
Mobile genetic elements
MSW
Municipal solid waste
QMRA
Quantitative microbial risk assessment
VBNC
Viable but non-culturable
WWTP
Wastewater treatment plant
•The culturable bioaerosol concentrations of global WWTPs are 102–105 CFU/m3.•WWTPs have unique core pathogenic communities and distinct continental divergence.•Sources and environmental factors ...affect the distribution of airborne pathogens.•Potential health risks are associated with the core determined airborne pathogens.
Wastewater treatment plants (WWTPs) have been recognized as one of the major potential sources of the spread of airborne pathogenic microorganisms under the global pandemic of COVID-19. The differences in research regions, wastewater treatment processes, environmental conditions, and other aspects in the existing case studies have caused some confusion in the understanding of bioaerosol pollution characteristics. In this study, we integrated and analyzed data from field sampling and performed a systematic literature search to determine the abundance of airborne microorganisms in 13 countries and 37 cities across four continents (Asia, Europe, North America, and Africa). We analyzed the concentrations of bioaerosols, the core composition, global diversity, determinants, and potential risks of airborne pathogen communities in WWTPs. Our findings showed that the culturable bioaerosol concentrations of global WWTPs are 102–105 CFU/m3. Three core bacterial pathogens, namely Bacillus, Acinetobacter, and Pseudomonas, as well as two core fungal pathogens, Cladosporium and Aspergillus, were identified in the air across global WWTPs. WWTPs have unique core pathogenic communities and distinct continental divergence. The sources of airborne microorganisms (wastewater) and environmental variables (relative humidity and air contaminants) have impacts on the distribution of airborne pathogens. Potential health risks are associated with the core airborne pathogens in WWTPs. Our study showed the specificity, multifactorial influences, and potential pathogenicity of airborne pathogenic communities in WWTPs. Our findings can improve the understanding of the global diversity and biogeography of airborne pathogens in WWTPs, guiding risk assessment and control strategies for such pathogens. Furthermore, they provide a theoretical basis for safeguarding the health of WWTP workers and ensuring regional ecological security.
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