Sludge Wastewater Treatment Plant Research Articles

Combustion reactivity of sewage sludge hydrochar derived from hydrothermal carbonization via thermogravimetric analysis

Wastewater treatment plant sludge contains a high concentration of organic compounds that can be used to produce fuel viahydrothermal carbonization (HTC). This study investigated the combustion reactivity and kinetic parameters of hydrochars produced to understand the combustion behavior of the solid fuel derived from HTC. The hydrochar was produced at various temperatures ranging from 150 to 300 °C, reaction times ranging from 30 to 150 min, and solid loadings ranging from 10% to 30%. The combustion behavior of sewage sludge (SS) and hydrochar was evaluated using thermogravimetric analysis with a constant air flow rate (100 mL/min) and heating rate (10 °C/min) from ambient temperature to 900 °C. It was observed that the HTC temperature, reaction time, and solid loading influenced the combustion characteristics and kinetics of the hydrochar. Additionally, the hydrochar exhibited higher ignition and burnout temperatures and a lower peak temperature than SS, indicating superior performance and reactivity in combustion. The combustion kinetic analysis also revealed that the hydrochar had a range of lower activation energy (29.12–41.60 kJ/mol) than SS (52.95 kJ/mol). Therefore, hydrochar derived from SS has the potential to be used as a substrate for solid fuel production for future renewable energy sources.

Seasonal variation of antibiotic resistance genes in activated sludge of a full-scale municipal wastewater treatment plant: Contribution of activated sludge functional taxa and clinically relevant taxa

It has been demonstrated that antibiotic resistance genes (ARGs) exhibit seasonal variations in municipal wastewater treatment plants (MWTPs), but their relationship to bacterial phylogeny structure remains unclear. Using advanced metagenomic techniques and machine learning approach, the current study conducted a year-long investigation to explore the relationship between ARGs and the bacterial community of activated sludge in a full-scale MWTP in Beijing, where seasonal dynamics are remarkable. High abundance of ARGs, notably the clinically relevant high-risk ARGs, was observed in winter and spring, the cold season in Beijing. Seasonal patterns were also observed in the diversity of ARGs and the overall bacterial community. Machine learning-based random forest classification models were utilized to identify biomarkers for ARGs and bacterial genera as indicators of seasonal differences. Subsequent analysis of the relationship between ARGs and bacterial biomarkers was examined using random forest regression models. Results showed that the enrichment of potential pathogens such as Mycobacterium, Clostridium and Pseudomonas was high in winter and spring, strongly contributing to the abundance of high-risk ARGs (ermB, aac(6′)-I, tetM, blaTEM, and mefA) during cold season. Conversely, functional taxa associated with activated sludge, such as Thauera, displayed seasonal fluctuations and a preference for ARGs with minor clinical implications. Metagenomic binning further illustrated the contribution of Mycobacterium to ARG enrichment in cold season. Our findings highlight the collective impact of human-derived clinically relevant taxa and functional bacterial taxa in activated sludge on the seasonal dynamics of ARGs in MWTPs. Additionally, this study offers valuable insights into the safe disposal of the excess sludge from MWTPs.

Method evaluation for viruses in activated sludge: Concentration, sequencing, and identification

Activated sludge (AS) in wastewater treatment plants is one of the largest artificial microbial ecosystems on earth and it makes enormous contributions to human societies. Viruses are an important component in AS with a high abundance. However, their communities and functionalities have not been as widely explored as those of other microorganisms, such as bacteria. This gap is mainly due to technical challenges in effective viral concentration, extraction, and sequencing. In this study, we compared four kinds of concentration methods, two sequencing approaches, and four identification bioinformatic tools to evaluate the whole analysis workflow for viruses in AS. Results showed flocculation, filtration, and resuspension (FFR) could get the longest DNA lengths and ultracentrifugation obtained the highest DNA yields for viruses in AS. Based on the results of present study, FFR and tangential flow filtration with the membrane pore size of 100 kDa were most recommended to concentrate viruses in AS samples with huge volumes. Besides, different concentration methods could get different viral catalogs and thus multiple methods should be combined to get the whole picture of viruses in the system. In addition, geNomad was the most recommended identification tool for viruses in the present study and the long-read sequencing could improve the assembly statistics of viruses when compared with the short-read sequencing. For the 8192 viral operational taxonomic units in this study, 95.1 % of them were phages and belonged to the same lineage at the order level of Caudovirales. Virulent phages dominated the AS system and Pseudomonadota were the main host. Taken together, this study provides new insights into methods selection for virus research of AS.

Environmental risks and agronomic benefits of industrial sewage sludge-derived biochar

The main objective of the present work was to assess the ecotoxicological safety of the use of thermochemically treated sewage sludge from the wastewater treatment plant (WWTP) of a distillery plant as a soil additive in agricultural soils based on its physicochemical characteristics and the bioaccumulation of selected elements in the plant tissues of maize (Zea mays). We have carried out physicochemical characterization (pH, EC, Corg, Cinorg, CEC, N, H, ash content, PAHs) of sewage sludge feedstock (SS) and sludge-derived biochar (BC) produced by slow pyrolysis at a temperature of 400 °C. The effect of 1% (w/w) amendment of SS and BC on soil physicochemical properties (pH, EC, Cinorg), germination of ryegrass, soil rhizobacteria and microorganisms, as well as on the accumulation and translocation of selected elements in maize (Zea mays) was studied. The results show that pyrolysis treatment of distillery WWTP sludge at 400 °C increases pH (from 7.3 to 7.7), Corg(from 28.86% to 36.83%), N (from 6.19% to 7.53%), ash content (from 23.59% to 50.99%) and decreases EC (from 2.35 mS/cm to 1.06 mS/cm), CEC (from 118.66 cmol/kg to 55.66 cmol/kg), H (from 6.76% to 1.98%) and Σ18 PAHs content (from 4.03 mg/kg to 3.38 mg/kg). RFA analysis of SS and BC showed that pyrolysis treatment multiplies chromium (Cr) (2.2 times), nickel (Ni) (2.96 times), lead (Pb) (2.13 times), zinc (Zn) (2.79 times), iron (Fe) (1.26 times) in the obtained BC, but based on an ecotoxicological test with earthworms Eisenia fetida, we conclude that pyrolysis treatment reduced the amount of available forms of heavy metals in BC compared to SS. We demonstrated by a pot experiment with a maize that a 1% addition of BC increased soil pH, decreased EC and Cinorg and had no significant effect on heavy metal accumulation in plant tissues. According to the results of the three-level germination test, it also does not affect the germination of cress seeds (Lepidium sativum). There was a significant effect of 1% BC addition on soil microbial community, and we observed a decrease in total microbial biomass and an increase in fungal species variability in the soil. Based on these results, we conclude that BC represents a promising material that can serve as a soil additive and source of nutritionally important elements after optimization of the pyrolysis process.

Understanding machine learning predictions of wastewater treatment plant sludge with explainable artificial intelligence.

This study investigates the use of machine learning (ML) models for wastewater treatment plant (WWTP) sludge predictions and explainable artificial intelligence (XAI) techniques for understanding the impact of variables behind the prediction. Three ML models, random forest (RF), gradient boosting machine (GBM), and gradient boosting tree (GBT), were evaluated for their performance using statistical indicators. Input variable combinations were selected through different feature selection (FS) methods. XAI techniques were employed to enhance the interpretability and transparency of ML models. The results suggest that prediction accuracy depends on the choice of model and the number of variables. XAI techniques were found to be effective in interpreting the decisions made by each ML model. This study provides an example of using ML models in sludge production prediction and interpreting models applying XAI to understand the factors influencing it. Understandable interpretation of ML model prediction can facilitate targeted interventions for process optimization and improve the efficiency and sustainability of wastewater treatment processes. PRACTITIONER POINTS: Explainable artificial intelligence can play a crucial role in promoting trust between machine learning models and their real-world applications. Widely practiced machine learning models were used to predict sludge production of a United States wastewater treatment plant. Feature selection methods can reduce the required number of input variables without compromising model accuracy. Explainable artificial intelligence techniques can explain driving variables behind machine learning prediction.

Thermal Inertia Performance via TRNSYS Software of Recycled Wastewater Treatment Plant Sludge as a Construction Material Additive to Ecological Lightweight Earth Bricks

This research investigates the thermal performance of earth bricks made with different percentages of wastewater sludge additive (0%, 1%, 3%, 7%, 15%, 20%) in terms of cooling and heating loads, time lag and decrement factor. The simulation of a reference house (2.5m,10m,6m) using TRNSYS software allows for the evaluation of these parameters, external wall thicknesses, bulk density, thermal conductivity, and specific heat capacity are employed as inputs in dynamic thermal inertia model. The results showed that the use of bricks with higher sludge additive percentages resulted in a drop in cooling and heating loads, the lowest cooling and heating loads of 1720 KWH and 1534 KWH respectively were recorded with the highest percentage of wastewater sludge additive of 20% and the biggest wall thickness of 30cm, it was also noted that the use of higher wastewater sludge additive percentages and bigger wall thicknesses led to higher time lags and lower decrement factor, the highest time lag of 15 hours and the lowest decrement factor of 0.019 were as well recorded with the highest wastewater sludge additive of 20%, and the biggest wall thickness of 30cm. These results were attributed to the higher specific heat capacity, and lower thermal conductivity of the bricks with higher wastewater sludge additive percentages.

Occurrence and risk assessment of p-phenylenediamines and their quinones in aquatic environment: From city wastewater to deep sea

p-Phenylenediamines (PPDs) and PPD-derived quinones (PPD-Qs) have been considered emerging pollutants recently. Their available data on sediment and sewage sludge are limited, especially the ecological risks. Here, typical PPDs and PPD-Qs were measured in the sludge of wastewater treatment plants and surface sediment of a developed river basin (including reservoirs, estuaries, and rivers) and deep-sea troughs. The total concentrations of PPDs (∑PPD) were highest in sludge (range: 9.06–248 ng g−1), followed by surface sediment of the Dongjiang River basin, China (3.33–85.3 ng g−1), and lowest in sediment of the Okinawa Trough (0.01–7.46 ng g−1). The median value of ∑PPD in surface sediment of rivers (9.54 ng g−1) was higher than those in reservoirs (4.28 ng g−1) and estuaries (5.26 ng g−1). N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) was the major congener in all samples, accounting for over 60 % of ∑PPD. For quinones, 6PPD-Q and IPPD-Q were frequently detected in sludge, only trace 6PPD-Q was detected in the sediment of estuaries (nd-0.62 ng g−1) and rivers (nd-5.24 ng g−1), and both of them were absent from the sediment of the Okinawa Trough. The occurrence of PPDs in the trough may be the in-situ release of microplastics, and due to the low-light and weak alkaline conditions of deep-sea water, quinones may hardly photodegrade from PPDs. The PPD concentrations in sludge were positively correlated with local GDP, and the annual PPD emission from sludge will exceed 1370 kg in China. The results of ecological risk assessments indicated low risks for PPDs in sludge-amended soil, median risks for several PPDs in river sediment, but median to high risks for 6PPD-Q contamination sludge-amended soil. For the first time, we explored the potential environmental risk of PPDs and related quinones in sludge used as a soil conditioner.

Lessons learned from a one-year study of Legionella spp. cultivation from activated sludge samples

Risk assessment and management of Legionella spp. contamination in activated sludge in wastewater treatment plants is carried out using the culture method. Underestimation of Legionella spp. is frequently reported in the literature, but a comprehensive long-term study of the performance of the method under comparable conditions is still lacking. The aim of this study is to evaluate the recovery rate and limit of detection of the culture method for Legionella spp. from activated sludge samples collected during the different seasons of the year. Activated sludge samples spiked with Legionella pneumophila subsp. pneumophila strain Philadelphia-1 (mean concentration 5.2 ± 0.35 logCFU/mL) were analysed monthly for one year using the culture method. Three different sample pre-treatments were compared, namely filtration, acid treatment and thermal treatment, and the recovery rate and limit of detection were assessed for each. The recovery rate of the culture method for Legionella spp. depended on the type of sample pre-treatment and the season of activated sludge sampling, while the limit of detection depended only on the sample pre-treatment. The best performance of the culture method, defined as the combination of the highest recovery rate and lowest limit of detection, was obtained for the filtered acid pre-treated samples (recovery rate: 89 ± 4 %; limit of detection: 1.3 logCFU/mL in 83 % of the samples). The lowest limit of detection was observed for the filtered thermally pre-treated samples (1.0 logCFU/mL in 93 % of the samples). Simultaneously, both thermally pre-treated samples showed up to a third lower recovery rates than the other pre-treatments in winter, while untreated and acid pre-treated samples showed consistently high recovery rates (>80%, logCFU/mL). The recovery rates of the unfiltered and filtered thermally pre-treated samples showed significant weak to strong positive correlations with the organic and phosphorus load in the influent as well as with the water and atmospheric temperatures, indicating that the recovery rate depends on the seasonal variation of the wastewater composition. This study presents new insights into the detection and quantification of Legionella spp. in activated sludge samples and considers seasonal dependencies in analytical results.

Occurrence, distribution, and fate evaluation of endocrine disrupting compounds in three wastewater treatment plants with different treatment technologies in Türkiye

Nowadays, two of the endocrine disrupting compounds (EDCs) in the group of alkylphenols (APs), nonylphenol (4-NP) and octylphenol (4-t-OP), have attracted great scientific and regulatory attention mainly due to concerns about their aquatic toxicity and endocrine disrupting activity. This paper investigated the occurrence, distribution behavior, fate, and removal of 4-NP and 4-t-OP in liquid and solid phases of three full-scale wastewater treatment plants (WWTPs) with different treatment technologies comparatively. In this context, (i) advanced biological WWTP, (ii) wastewater stabilization pond (WSP), and (iii) constructed wetland (CW) were utilized. In all three investigated WWTPs, the concentrations of 4-NP (219.9–19,354.4 ng/L) in raw wastewater were higher than those of 4-t-OP (13.9–2822.4 ng/L). Within the scope of annual average removal efficiencies, 4-NP was treated highly in advanced biological WWTP (93.5 %), while it was almost not treated in WSP (3.1 %) and treated with negative removal (<0 %) in CW. While 4-t-OP was treated at a similar removal rate (93.5 %) to 4-NP in advanced biological WWTP, it was treated moderately in WSP (52.5 %) and very poorly in CW (12.4 %). It has been determined that the most important removal mechanism of both 4-NP and 4-t-OP in WWTPs is biodegradation, followed by sorption onto sewage sludge. According to the mass balance performed in advanced biological WWTP, the biodegradation rates for 4-NP and 4-t-OP were found to be 70.4 % and 86.6 %, respectively, while the sorption onto sewage sludge were determined to be 23.3 % and 6.8 %. One of the critical findings obtained within the scope of the study is that while the concentrations of both metabolites, especially 4-NP, in wastewater and sewage sludge, decreased considerably under aerobic conditions, on the contrary, their concentrations increased significantly under anaerobic conditions. Both compounds were detected at higher concentrations in primary sludge compared to secondary sludge in advanced biological WWTP, while in WSP, they were determined at higher concentrations in anaerobic stabilization pond sludge compared to facultative stabilization pond sludge. Besides, it was also determined that the sorption behavior of these alkylphenols is much more dominant than desorption.

The integration of omics and cultivation-dependent methods could effectively determine the biological risks associated with the utilization of soil conditioners in agriculture

In the circular economy, reusing agricultural residues, treated biowaste, and sewage sludges—commonly referred to as soil conditioners—in agriculture is essential for converting waste into valuable resources. However, these materials can also contribute to the spread of antimicrobial-resistant pathogens in treated soils. In this study, we analyzed different soil conditioners categorized into five groups: compost from source-separated biowaste and green waste, agro-industrial digestate, digestate from anaerobic digestion of source-separated biowaste, compost from biowaste digestate, and sludges from wastewater treatment plants. Under Italian law, only the first two categories are approved for agricultural use, despite Regulation 1009/2019/EU allowing the use of digestate from anaerobic digestion of source-separated biowaste in CE-marked fertilizers. We examined the bacterial community and associated resistome of each sample using metagenomic approaches. Additionally, we detected and isolated various pathogens to provide a comprehensive understanding of the potential risks associated with sludge application in agriculture. The compost samples exhibited higher bacterial diversity and a greater abundance of potentially pathogenic bacteria compared to other samples, except for wastewater treatment plant sludges, which had the highest frequency of Salmonella isolation and resistome diversity. Our findings suggest integrating omics and cultivation-dependent methods to accurately assess the biological risks of using sludge in agriculture.

Hybrid solar drying of sludge from kraft pulp mills

Abstract Sludge generated from kraft pulp mill wastewater treatment plants (WWTPs) is typically non-inert solid waste and is commonly disposed of in landfills. In this study, a novel approach for repurposing WWTP sludge from a kraft pulp mill in Brazil for energy generation was assessed. With the global cellulose market projected to reach $ 61 billion by 2033, there is a growing need for sustainable energy solutions and disposal of associated industrial byproducts. This study investigated the performance of a hybrid active solar dryer for reducing the moisture content of sludge to enhance the feasibility of sludge burning in a biomass boiler. Through rigorous experimentation and design of experiments (DOE) planning, optimal parameters for the hybrid dryer were determined, specifically, a volumetric airflow rate of 1.1 m/s and an entrance temperature of approximately 51 °C. This innovative approach not only addresses the environmental concerns associated with sludge disposal, but also contributes to the broader goal of advancing sustainable technologies in the midst of global energy challenges.

Long term study on the fate and environmental risks of favipiravir in wastewater treatment plants and comparison with COVID-19 cases

In recent years especially during COVID-19, the increased usage of antiviral drugs has led to increased interest in monitoring their presence in wastewater worldwide. In this study, it was examined the occurrence, fate and environmental risks of favipiravir which is used for COVID-19 treatment in two wastewater treatment plants (WWTPs) with different treatment processes in Istanbul, Turkey. Favipiravir was measured in WWTPs influent samples, effluent samples and sludge samples with maximum concentrations of 97 μg/L, 64.11 μg/L and 182.47 μg/g, respectively. Favipiravir had removal efficiency below 55 % for both WWTPs. Mass balance analysis showed that favipiravir removal in WWTPs mainly attributed to biodegradation/biotransformation. Statistical analysis revealed a significant correlation between favipiravir concentration and COVID-19 incidence in Istanbul. The microbial distribution analysis indicated that comparison of collected COVID-19 pandemic sludge and post-pandemic period sludge samples, a noteworthy reduction in the Chloroflexi and Actinobacteriota phyla at the phylum level was observed. Environmental risk assessment using risk quotients ranged from 168 to 704, indicating that the presence of this antiviral drug posed significant ecological risks to aquatic organisms. The study concluded that WWTPs were releasing antiviral drugs into the environment, thereby posing risks to both the aquatic ecosystem and public health. The results of this study demonstrate the persistence of favipiravir in WWTPs and offer crucial supporting data for further research into the advancement of wastewater treatment technology. Also, this study shows wastewater based monitoring is supplementary and early warning system for determining the occurrence of antiviral drugs.

Removal of artificial sweeteners in wastewater treatment plants and their degradation during sewage sludge composting with micro- and nano-sized kaolin

This study surveyed the fates of artificial sweeteners in influent, effluent, and sewage sludge (SS) in wastewater treatment plant, and investigated the effects of Micro-Kaolin (Micro-KL) and Nano-Kaolin (Nano-KL) on nitrogen transformation and sucralose (SUC) and acesulfame (ACE) degradation during SS composting. Results showed the cumulative rate of ACE and SUC in SS was ∼76 %. During SS composting, kaolin reduced NH3 emissions by 30.2–45.38 %, and N2O emissions by 38.4–38.9 %, while the Micro-KL and Nano-KL reduced nitrogen losses by 14.8 % and 12.5 %, respectively. Meanwhile, Micro-KL and Nano-KL increased ACE degradation by 76.8 % and 84.2 %, and SUC degradation by 75.3 % and 77.7 %, and significantly shifted microbial community structure. Furthermore, kaolin caused a positive association between Actinobacteria and sweetener degradation. Taken together, kaolin effectively inhibited nitrogen loss and promoted the degradation of ACE and SUC during the SS composting, which is of great significance for the removal of emerging organic pollutants in SS.

Management of industrial wine residues: physicochemical, bacterial and fungal dynamics during composting processes

To foster a circular bioeconomy throughout the management of industrial solid wine residues in the wine industry, this work presents the physicochemical and microbiological dynamics of the composting process with white grape pomace, stalks and wastewater treatment plant sludge from the same winery. Three composting windrows of 41 m3 were constructed with 0, 10 and 20% sludge addition. Physicochemical parameters were assessed following the Test Method for the Examination of Composting and Compost (TMECC), and the diversity and dynamics of the bacterial and fungal communities involved in the composting process were assessed via a high-throughput sequencing metabarcoding approach. The addition of sludge increased the moisture content, bulk density, and pH after six months of turned windrow composting. No effect of sludge addition on the macronutrient composition of the compost was observed. The Shannon‒Wiener index differed among stages and treatments. Bacterial diversity increased over time, while the fungal community appeared to be highly affected by the thermophilic stage, which led to a reduction in diversity that slightly recovered by the end of the process. Furthermore, the sludge exhibited high bacterial diversity but very low fungal diversity. Consequently, the design of on-site biologically based strategies to better manage wine residues can produce soil amendments, improve fertilization, reclaim damaged soils, and ultimately reduce management costs, making composting an economically attractive and sustainable alternative for waste management in the wine industry.Graphical

Treatment of sewage sludge with γ‐ray irradiation for volatile fatty acids and lipid production

AbstractThe production of value‐added products from sewage sludge is considered to be one of the solutions for the sustainable management of sludge in wastewater treatment plants (WWTPs). The presence of carbon, nitrogen, and phosphorus sources has made the sewage sludge of WWTPs a valuable and low‐cost substrate for the production of fermentative products. In the current study, a process was developed for microbial lipid production from two types of sewage sludge from a WWTP in northern Isfahan: anaerobic digester inlet sludge (DIS) and anaerobic digester outlet sludge (DOS). This process was based on the release of volatile fatty acids (VFAs) from the sludge by combinations of γ‐ray irradiation, anaerobic digestion, and acidogenic fermentation followed by utilization of VFAs in a microbial process by the oleaginous yeast Cryptococcus aureus UIMC65. After γ‐ray irradiation, the acidogenic fermentation of the treated sludge released 72% of the organic matter content of the sludge with acidification efficiency of 12% leading to 0.516 g L−1 VFAs. The oleaginous fermentation of the released VFAs for 7 days was accompanied by production of 1.58 g L−1 dry cell biomass with 40% lipid content. The results of this study indicate that the sewage sludge from urban WWTP has the potential to be used for the production of microbial lipids.

Pre-coating of stainless-steel mesh support material with wastewater treatment plant sludges in a dynamic membrane filtration process

This study focuses on wastewater treatment plant sludges to be deposited on large aperture meshes. In a column reactor that is filled with treatment plant sludges, a series of batch experiments were performed with varying sizes of stainless-steel mesh modules (75 to 300 μm) as a support media to form a dynamic membrane. Primary, secondary, and polyelectrolyte-added sludges were used both individually and in combination to investigate the performance (filterability, permeate quality, and dynamic layer formation ability) of the varying pore-size meshes at high fluxes. The results were superior when primary and secondary sludges were combined in the creation of a dynamic cake layer, as opposed to individual sludge usage. Mesh sizes were shown to have no effect on performance, providing turbidity of <10 NTU for a short duration (10 min) of filtration. Cake formation rates were calculated as 23.0 NTU/min, 19.48 NTU/min, 7.62 NTU/min, and 6.94 NTU /min for 100, 150, 200, and 300 μm support meshes, respectively. For the first time in literature, effluent water turbidity decreases to <5 NTU for 300 μm support mesh at high fluxes. Scanning electron microscope images showed that fibers that may originate from the primary sludge could enhance the formation of stable cake layer. This study is important for creating high-performing dynamic membrane filtration on large aperture meshes, which can be used as a cost-effective and reliable filter for wastewater treatment.

Multimedia distribution and release characteristics of emerging PFAS in wastewater treatment plants in Tianjin, China

Legacy and emerging PFAS in the air, wastewater, and sludge from two wastewater treatment plants (WWTPs) in Tianjin were investigated in this study. The semi-quantified nontarget PFAS accounted for up to 99 % of ƩPFAS in the gas phase, and aqueous film-forming foam (AFFF)-related PFAS were predominant in wastewater (up to 2250 ng/L, 79 % of ƩPFAS) and sludge (up to 4690 ng/g, 95 % of ƩPFAS). Furthermore, field-derived air particle-gas, air-wastewater, and wastewater particle-wastewater distribution coefficients of emerging PFAS are characterized, which have rarely been reported. The emerging substitute p-perfluorous nonenoxybenzenesulfonate (OBS) and AFFF-related cationic and zwitterionic PFAS show a stronger tendency to partition into particle phase in air and wastewater than perfluorooctane sulfonic acid (PFOS). The estimated total PFAS emissions from the effluent and sludge of WWTP A were 202 kg/y and 351 kg/y, respectively. While the target PFAS only accounted for 20–33 % of the total emissions, suggesting a significant underestimation of environmental releases of the nontarget PFAS and unknown perfluoroalkyl acid precursors through the wastewater and sludge disposal. Overall, this study highlights the importance of comprehensive monitoring and understanding the behavior of legacy and emerging PFAS in wastewater systems, and fills a critical gap in our understanding of PFAS exposure.

Research Progress on Pollution Characteristics, Degradation, and Transformation of Typical PPCPs in the Process of Wastewater Treatment

Pharmaceuticals and personal care products (PPCPs) have received extensive attention as a new type of pollutant inin the 21st century, and the ecological and health risks caused by PPCPs have gradually been recognized by government regulatory agencies. Daily use of PPCPs has led to their frequent detection and high concentrations in the influent, effluent, and sludge of wastewater treatment plants, but traditional wastewater treatment processes can't remove them effectively. Most research about enhancing the removal of PPCPs through microbial degradation, photodegradation, and ozonation is still in the laboratory research stage, and the removal effects are not satisfactory when applied to actual sewage treatment. Therefore, the effective removal of PPCPs from domestic wastewater is a critical technical problem that urgently needs to be studied and solved in the coming years. At present, many scholars do not have a comprehensive understanding about the degradation and transformation behaviors of microbes, ultraviolet, and ozone for typical PPCPs in the wastewater treatment process, so it is necessary to conduct a systematic analysis and discussion. In this study, 16 typical PPCPs frequently detected in sewage treatment plants were selected as research objects through a literature review. The occurrence, removal characteristics, and sludge adsorption properties of typical PPCPs in wastewater treatment plants were analyzed and summarized. The degradation and transformation behavior of typical PPCPs under microbial, ultraviolet, and ozone treatments in the wastewater treatment process were also discussed. Finally, based on current research gaps, some research directions for the removal and transformation of PPCPs in wastewater were proposed:① investigation into the removal characteristics of PPCPs by actual biochemical treatment; ② study on the mechanism of microbial degradation and transformation of typical PPCPs during biochemical treatment; ③ study on the degradation and transformation mechanism of typical PPCPs by UV/ozone in an actual sewage system; and ④ research on the application technology of removing PPCPs from sewage via microbial degradation, photodegradation, ozone oxidation, etc. The relevant results of this study can provide a reference for the pollution control of typical PPCPs in the sewage treatment process.

Sludge degradation, nutrient removal and reduction of greenhouse gas emission by a Chironomus-Azolla wastewater treatment cascade.

Wastewater treatment plants (WWTPs) are a point source of nutrients, emit greenhouse gases (GHGs), and produce large volumes of excess sludge. The use of aquatic organisms may be an alternative to the technical post-treatment of WWTP effluent, as they play an important role in nutrient dynamics and carbon balance in natural ecosystems. The aim of this study was therefore to assess the performance of an experimental wastewater-treatment cascade of bioturbating macroinvertebrates and floating plants in terms of sludge degradation, nutrient removal and lowering GHG emission. To this end, a full-factorial experiment was designed, using a recirculating cascade with a WWTP sludge compartment with or without bioturbating Chironomus riparius larvae, and an effluent container with or without the floating plant Azolla filiculoides, resulting in four treatments. To calculate the nitrogen (N), phosphorus (P) and carbon (C) mass balance of this system, the N, P and C concentrations in the effluent, biomass production, and sludge degradation, as well as the N, P and C content of all compartments in the cascade were measured during the 26-day experiment. The presence of Chironomus led to an increased sludge degradation of 44% compared to 25% in the control, a 1.4 times decreased transport of P from the sludge and a 2.4 times increased transport of N out of the sludge, either into Chironomus biomass or into the water column. Furthermore, Chironomus activity decreased methane emissions by 92%. The presence of Azolla resulted in a 15% lower P concentration in the effluent than in the control treatment, and a CO2 uptake of 1.13 kg ha-1 day-1. These additive effects of Chironomus and Azolla resulted in an almost two times higher sludge degradation, and an almost two times lower P concentration in the effluent. This is the first study that shows that a bio-based cascade can strongly reduce GHG and P emissions simultaneously during the combined polishing of wastewater sludge and effluent, benefitting from the additive effects of the presence of both macrophytes and invertebrates. In addition to the microbial based treatment steps already employed on WWTPs, the integration of higher organisms in the treatment process expands the WWTP based ecosystem and allows for the inclusion of macroinvertebrate and macrophyte mediated processes. Applying macroinvertebrate-plant cascades may therefore be a promising tool to tackle the present and future challenges of WWTPs.

Concentration properties of biopolymers via dead-end forward osmosis

Extracellular polymeric substances (EPSs) in excess sludge of wastewater treatment plants are valuable biopolymers that can act as recovery materials. However, effectively concentrating EPSs consumes a significant amount of energy. This study employed novel energy-saving pressure-free dead-end forward osmosis (DEFO) technology to concentrate various biopolymers, including EPSs and model biopolymers [sodium alginate (SA), bovine serum albumin (BSA), and a mixture of both (denoted as BSA-SA)]. The feasibility of the DEFO technology was proven and the largest concentration ratios for these biopolymers were 94.8 % for EPSs, 97.1 % for SA, 97.8 % for BSA, and 98.4 % for BSA-SA solutions. An evaluation model was proposed, incorporating the FO membrane's water permeability coefficient and the concentrated substances' osmotic resistance, to describe biopolymers' concentration properties. Irrespective of biopolymer type, the water permeability coefficient decreased with increasing osmotic pressure, remained constant with increasing feed solution (FS) concentration, increased with increasing crossing velocity in the draw side, and showed little dependence on draw salt type. In the EPS DEFO concentration process, osmotic resistance was minimally impacted by osmotic pressure, FS concentration, and crossing velocity, and monovalent metal salts were proposed as draw solutes. The interaction between reverse diffusion metal cations and EPSs affected the structure of the concentrated substances on the FO membrane, thus changing the osmotic resistance in the DEFO process. These findings offer insights into the efficient concentration of biopolymers using DEFO.