Sludge Wastewater Treatment Plant Research Articles

Effect of humic substances on the anaerobic digestion of secondary sludge in wastewater treatment plants: a review

Effect of humic substances on the anaerobic digestion of secondary sludge in wastewater treatment plants: a review

Polyhydroxyalkanoates production by an advanced food-on-demand strategy: The effect of operational conditions

Despite the increasing number of studies related to the polyhydroxyalkanoate (PHA) production from sewage sludge of wastewater treatment plants, there is still a gap in the correlation between the operational conditions, such as the organic loading rate (OLR), and the intracellular polyhydroxyalkanoate (PHA) content, productivity and final recovery of the polymer. Therefore, this work aims to provide experimental data on PHA productivity and purity in view of scaling up the process to an industrial level taking into account process parameters. In view of that, three OLR were applied during the selection of PHA-accumulating bacteria in sewage sludge. Then, the biomass was harvested and subjected to batch accumulation experiments at two organic loads per dosage by employing a tailor-made software to adopt an automated feed-on-demand strategy, which allowed for 30–56 h of accumulation tests in stand-alone mode. Finally, an improved protocol for PHA extraction has been applied. Experimental results show that the maximum PHA content (60% w/w) was achieved using the highest organic load per dosage during the accumulation test with the biomass selected at the highest OLR (1.8 g COD L−1 d−1). Also, the extraction protocol efficiency was proven with four samples with different PHA content, achieving recovery yield as high as 78 ± 3 % with a purity of 89 ± 2 %, thus demonstrating that the adopted strategy might be beneficial for industrial use.

Derivation of Optimal Operation Factors of Anaerobic Digesters through Artificial Neural Network Technology

The anaerobic digestion of sewage sludge in South Korean wastewater treatment plants is affected by seasonal factors and other influences, resulting in lower digestion efficiency and gas production, which cannot reach optimal yields. The aim of this study was to improve the digestion efficiency and gas production of sludge anaerobic digestion in a wastewater treatment plant (WWTP) by using data mining techniques to adjust operational parameters. Through experimental data obtained from the WWTP in Daegu City, South Korea, an artificial neural network (ANN) technology was used to adjust the range of the organic loading rate (OLR) and hydraulic retention rate (HRT) to improve the efficiency and methane gas production from anaerobic sludge digestion. Data sources were normalized, and data analysis including Pearson correlation analysis, multiple regression analysis and an artificial neural network for optimal results. The results of the study showed a predicted 0.5% increase in digestion efficiency and a 1.3% increase in gas production at organic loads of 1.26–1.46 kg/m3 day and an HRT of 26–30 days. This shows that the ANN model that we established is feasible and can be used to improve the efficiency and gas production of sludge anaerobic digestion.

Concentration of the main persistent organic pollutants in sewage sludge in relation to wastewater treatment plant parameters and sludge stabilisation

Concentration of 16 polycyclic aromatic hydrocarbons (PAHs), 7 polychlorinated biphenyls (PCBs), and 11 organochlorine pesticides (OCPs) in sewage sludge from 40 wastewater treatment plants (WWTPs) was investigated. Relationship between pollutant sludge contents, main WWTP parameters and type of sludge stabilisation was carefully evaluated. Average load of PAHs, PCBs, and OCPs in different sludges from Czech Republic was 3096, 95.7 and 76.1 μg/kg dry weight, respectively. There were moderate/strong correlations among the individual tested pollutants in sludge (r = 0.40–0.76). Relationship between total pollutant contents in sludge, common WWTP parameters and sludge stabilisation was not evident. Only individual pollutants such anthracene and PCB 52 correlated significantly (P < 0.05) with biochemical oxygen demand (r = −0.35) and chemical oxygen demand removal efficiencies (r = −0.35), suggesting recalcitrance to degradation during wastewater treatment. When sorted according to the design capacity, a linear correlation between WWTP size and pollutant contents in sludge was evident with growing WWTP capacity. Our study indicated that WWTPs with anaerobic digestion are prone to accumulate a statistically higher content of PAHs and PCBs (P < 0.05) in digested sludges compared to aerobically digested ones. The influence of anaerobic digestion temperature of treated sludge on tested pollutants was not evident.

Characterizing the Organohalogen Iceberg: Extractable, Multihalogen Mass Balance Determination in Municipal Wastewater Treatment Plant Sludge.

The large number and diversity of organohalogen compounds (OHCs) occurring in the environment poses a grand challenge to analytical chemists. Since no single targeted method can identify and quantify all OHCs, the size of the OHC "iceberg" may be underestimated. We sought to address this problem in municipal wastewater treatment plant (WWTP) sludge by quantifying the unidentified fraction of the OHC iceberg using targeted analyses of major OHCs together with measurements of total and extractable (organo)halogen (TX and EOX, respectively; where X = F, Cl, or Br). In addition to extensive method validation via spike/recovery and combustion efficiency experiments, TX and/or EOX were determined in reference materials (BCR-461 and NIST SRMs 2585 and 2781) for the first time. Application of the method to WWTP sludge revealed that chlorinated paraffins (CPs) accounted for most (∼92%) of the EOCl, while brominated flame retardants and per- and polyfluoroalkyl substances (PFAS) accounted for only 54% of the EOBr and 2% of the EOF, respectively. Moreover, unidentified EOF in nonpolar CP extracts points to the existence of organofluorine(s) with physical-chemical properties unlike those of target PFAS. This study represents the first multihalogen mass balance in WWTP sludge and offers a novel approach to prioritization of sample extracts for follow-up investigation.

Syntrophic Growth of Biomaibacter acetigenes Strain SP2 on Lactate and Glycerol

A moderately thermophilic Gram-positive chemo-organotrophic bacterium, strain SP2, was isolated by serial dilutions with crotonate and yeast extract as substrates from a butyrate-degrading methanogenic enrichment obtained from thermophilically digested sludge of the Kuryanoskaya wastewater treatment plant (Moscow, Russia). Cells of strain SP2 are spore-forming rods, sometimes occurring in short chains. The bacterium is an obligate anaerobe that grows at temperatures from 20 to 70 °C (55–60 °C optimum) within a pH range of 3.5–8 (7.5 optimum) and with NaCl concentrations of up to 2.5%. The strain utilized yeast extract and simple sugars as carbon and energy sources. Thiosulfate was used as an electron acceptor when grown on sucrose, resulting in the formation of hydrogen sulfide and the accumulation of elemental sulfur globules inside the cells. Strain SP2 is phylogenetically related to Biomaibacter acetigenes strain SK-G1T as revealed by comparison with the 16S rRNA gene (99.9% identity) and genome (ANI 99%, dDDH 90%) of both strains. It is interesting that strain SP2 was capable of syntrophic conversion of glycerol and lactate when co-cultivated with hydrogenotrophic methanogen, which was not previously shown for the SK-G1T type of strain. The isolation and in-depth study of new facultatively syntrophic microorganisms is important for wastewater treatment ecotechnologies due to their ability to switch to an alternative source of carbon and energy and therefore greater resistance to changing environmental conditions in bioreactors.

Contemporary Drift in Emerging Micro(nano)plastics Removal and Upcycling Technologies from MunicipalWastewater Sludge: Strategic Innovations and Prospects.

Annually, huge amounts of microplastics (MPs) are added to farmlands through sewage sludge (SS)/biosolid applications as a fertilizer. Most research emphasizes the enormity of the problem and demonstrates the fate, impacts, and toxicity of MPs during SS treatment processes and land applications. None has addressed the management strategies. To address the gaps, the current review evaluates the performance analysis of conventional and advanced sludge treatment methods in eliminating MPs from sludge. The review uncovers that the occurrence and characteristics of MPs in SS are highly governed by factors such as population density, speed and level of urbanization, citizens' daily habits, and treatment units in wastewater treatment plants (WWTPs). Furthermore, conventional sludge treatment processes are ineffective in eliminating MPs from SS and are accountable for the increased small-sized MPs or micro(nano)plastics (MNPs) along with altered surface morphology facilitating more co-contaminant adsorption. Simultaneously, MPs can influence the operation of these treatment processes depending on their size, type, shape, and concentration. The review reveals that research to develop advanced technology to remove MPs efficiently from SS is still at a nascent stage. This review provides a comprehensive analysis of MPs in the SS, by corroborating state-of-the-knowledge, on different aspects, including the global occurrence of MPs in WWTP sludge, impacts of different conventional sludge treatment processes on MPs and vice versa, and efficiency of advanced sludge treatment and upcycling technologies to eliminate MPs, which will facilitate the development of mitigation measures from the systematic and holistic level.

Influence of the azo-dye amaranth on the trophic structure of activated sludge in a model experiment.

The textile industry generates significant amounts of wastewater containing high concentrations of azo dyes. An important point in the process of purification of azo dyes is their influence on the activated sludge (AS) in wastewater treatment plants. Azo dyes, such as amaranth, play the role of xenobiotics. This article seeks to answer the question of how organisms manage to respond to xenobiotics remains very important and open, i.e., how they will react to toxic conditions. The aim of this research was to study how these changes are expressed in terms of the different trophic levels of AS. In our experiment, it was found that the dominant trophic units are significantly changed due to the xenobiotic entering the system. The data reveal the significant development of the bacterial segment (genusPseudomonasand azo-degrading bacteria) at times of large amaranth removal. In the most active phase of amaranth biodetoxification (48h), the culturable bacteria of the genus Pseudomonas change by about 40%, while the azo-degrading bacteria change by about 2%. Fauna organisms have a sharp change in the dominant groups-from attached and crawling ciliates and testate amoebas to the mass development of small and large flagellates. This is of great importance because micro- and metafauna play an important role in the detoxification process by ingesting some of the xenobiotics. This role is expressed in the fact that after dying, macro-organisms release this xenobiotic in small portions so that it can then be effectively degraded by adapting to the amaranth biodegradation bacteria. In this study, it is clear that all these events lead to a decline in the quality of AS. But on the other hand, these allow AS to survive as a microbial community, and the fauna segment does not disappear completely.

Estimation of the consumption level of four drugs in Beijing using wastewater-based epidemiology

Objective: To estimate the consumption level of four drugs in Beijing using wastewater-based epidemiology (WBE). Methods: The primary sludge from one large wastewater treatment plants (WWTPs) was collected in Beijing from July 2020 to February 2021. The concentrations of codeine, methadone, ketamine and morphine in the sludge were detected through solid-phase extraction-liquid chromatography-tandem mass spectrometry. The consumption, prevalence and number of users of four drugs were estimated by using the WBE approach. Results: Among 416 sludge samples, codeine had the highest detection rate (82.93%, n=345) with a concentration [M (Q1, Q3)] of 0.40 (0.22-0.8) ng·g-1, and morphine had the lowest detection rate (28.37%,n=118) with a concentration [M (Q1, Q3)] of 0.13 (0.09, 0.17) ng·g-1. There was no significant difference in the consumption of the four drugs on working days and weekends (all P values>0.05). Drug consumption was significantly higher in winter than that in summer and autumn (all P values <0.05). The consumption [M (Q1, Q3)] of codeine, methadone, ketamine and morphine in winter was 24.9 (15.58, 38.6), 9.39 (4.57, 26.72), 9.84 (5.18, 19.45) and 5.67 (3.57, 13.77) μg·inhabitant-1·day-1, respectively. For these drugs, there was an upward trend in the average drug consumption during summer, autumn and winter (the Z values of the trend test were 3.23, 3.16, 2.19, and 3.32, respectively and all P values<0.05). The prevalence [M (Q1, Q3)] of codeine, methadone, ketamine and morphine were 0.0056% (0.003 4%, 0.009 2%), 0.0148% (0.009 6%, 0.026 7%),0.0333% (0.0210%, 0.0710%) and 0.0072% (0.003 8%, 0.011 7%), respectively. The estimated number of drug users [M (Q1, Q3)] was 918 (549, 1 511), 2 429 (1 578, 4 383), 5 451 (3 444, 11 642) and 1 173 (626, 1 925),respectively. Conclusion: Codeine, methadone, ketamine and morphine have been detected in the sludge of WWTPs in Beijing, and the consumption level of these drugs varies in different seasons.

Predicting microbial community compositions in wastewater treatment plants using artificial neural networks

BackgroundActivated sludge (AS) of wastewater treatment plants (WWTPs) is one of the world’s largest artificial microbial ecosystems and the microbial community of the AS system is closely related to WWTPs' performance. However, how to predict its community structure is still unclear.ResultsHere, we used artificial neural networks (ANN) to predict the microbial compositions of AS systems collected from WWTPs located worldwide. The predictive accuracy R21:1 of the Shannon–Wiener index reached 60.42%, and the average R21:1 of amplicon sequence variants (ASVs) appearing in at least 10% of samples and core taxa were 35.09% and 42.99%, respectively. We also found that the predictability of ASVs was significantly positively correlated with their relative abundance and occurrence frequency, but significantly negatively correlated with potential migration rate. The typical functional groups such as nitrifiers, denitrifiers, polyphosphate-accumulating organisms (PAOs), glycogen-accumulating organisms (GAOs), and filamentous organisms in AS systems could also be well recovered using ANN models, with R21:1 ranging from 32.62% to 56.81%. Furthermore, we found that whether industry wastewater source contained in inflow (IndConInf) had good predictive abilities, although its correlation with ASVs in the Mantel test analysis was weak, which suggested important factors that cannot be identified using traditional methods may be highlighted by the ANN model.ConclusionsWe demonstrated that the microbial compositions and major functional groups of AS systems are predictable using our approach, and IndConInf has a significant impact on the prediction. Our results provide a better understanding of the factors affecting AS communities through the prediction of the microbial community of AS systems, which could lead to insights for improved operating parameters and control of community structure.2jzZ-nU4sRefzvXQz6KqH6Video

Construction of a Novel Sampler for Advanced Collection of Sludge and Sediments in Wastewater Treatment Plants

Construction of a Novel Sampler for Advanced Collection of Sludge and Sediments in Wastewater Treatment Plants

Promoting vivianite recovery: Crucial role of tightly-bound extracellular polymeric substances

Vivianite is an important bio-induced product of dissimilated iron reduction (DIR), which exists widely in activated sludge and digested sludge of wastewater treatment plants (WWTPs). Extracellular polymeric substances (EPS) surrounding dissimilatory iron-reducing bacteria (DIRB) were reported to be transient media for microbial extracellular electron transfer (EET) and DIR. However, what happens when a layer of EPS envelops microbial cells during vivianite recovery? This study tried to assess the relationship between iron reduction and electron transfer by stripping EPS layer-by-layer, then clarified the delamination of different EPS layers on the performance of vivianite recovery. After stripping total EPS (PC-EPS batches) of DIRB, the Fe (III) reduction efficiencies (RFe), Fe (III) reduction rate (VFe), and vivianite formation efficiency (RV) decreased by 33%, 37%, and 30%, respectively. Tightly bound-EPS (TB-EPS) was confirmed to play a crucial role in vivianite formation, which contributed 28–51% to vivianite recovery and 34–55% to iron reduction. Electronic shuttle substances were contained in TB-EPS, which enhanced the EET rate and efficiency between cells and Fe (III). The polysaccharide content of TB-EPS was positively related to adhesiveness between cells and mineral, as well as the iron reduction efficiency. Furthermore, redox proteins (PpcA, OmcB) were embedded in EPS, which shortened the distance of electron hopping to across the EPS layer and further accelerated vivianite recovery from wastewater. Long-term operation of anaerobic reactors confirmed that TB-EPS played critical roles in bio-induced vivianite formation.

Fate and removal of pesticides in solid and liquid phases of metropolitan, urban and rural-scale wastewater treatment plants

In this study, the change of occurrence, distribution, seasonal variation and removal of pesticides, atrazine (ATZ), chlorpyriphos (CPR) and chlorfenvinphos (CFV), were investigated both in liquid and solid phases of three different types of wastewater treatment plants (WWTPs). Treatment configurations of the studied WWTPs consist of a metropolitan advanced biological treatment system (4-stage Bardenpho), urban-scale waste stabilization pond (WSP) and rural-scale horizontal subsurface flow constructed wetland (HSSCW).ATZ removal efficiencies (59.8 %–92.4 %) were higher than CPR and CFV removal efficiencies at all WWTPs. CPR and CFV are removed at 78.5 % and 53.1 % efficiency, respectively, from the influent of advanced biological treatment system. CPR and CFV removals were 21.6 and 22.7 % at WSP, respectively.One of the important findings is that ATZ and CFV were removed at higher percentages in primary treatment than in biological treatment in advanced biological WWTP. Sorption onto sludge has been evaluated as an effective removal mechanism for pesticide elimination, at least as much as biodegradation/biotransformation. All investigated pesticides were detected in higher concentrations in primary sludge (168.8–399.5 μg/kg) compared to secondary sludge (21.9–146.3 μg/kg) in advanced biological WWTP and in facultative sludge (447.8–1044.7 μg/kg) compared to anaerobic sludge (250.0–613.0 μg/kg) in WSP. It was determined that ATZ was the most treated compound in the liquid phase under anaerobic conditions among the studied pesticides. In line with these results, approximately 45 % removal efficiency was determined for CPR and CFV in the anaerobic digestion process present in advanced biological WWTP.

Anaerobic sludge digestion elevates dissemination risks of bacterial antibiotic resistance in effluent supernatant

Anaerobic digestion following a variety of pretreatments is a promising technique for the reduction of excess sludge in municipal wastewater treatment plants (MWWTPs), and eliminations of possible pathogens, viruses, protozoa, and other disease-causing organisms. Notwithstanding a rapidly increasing health concern of antibiotic resistant bacteria (ARB) in MWWTPs, dissemination risks of ARB in anaerobic digestion processes are still poorly understood, especially in the digested supernatant. Taking the representative ARB with respect to the common tetracycline-, sulfamethoxazole-, clindamycin- and ciprofloxacin resistance, we investigated the compositions of ARB in the sludge and supernatant, and quantified their variations along the entire anaerobic sludge digestion process following ultrasonication-, alkali-hydrolysis- and alkali-ultrasonication pretreatments, respectively. Results showed that the abundance of ARB was diminished by up to 90% from the sludge along anaerobic digestion coupling with the pretreatments. Surprisingly, pretreatments clearly boosted the abundance of specific ARB (e.g., 2.3 × 102 CFU/mL of tetracycline-resistant bacteria) in the supernatant that otherwise remained relatively low value of 0.6 × 102 CFU/mL from the direct digestion. Measurements of the soluble-, loosely-bound- and tightly-bound extracellular polymeric substances components revealed a gradually intensified destruction of the sludge aggregates along the entire anaerobic digestion processes, which could be likely responsible to the increase of the ARB abundance in the supernatant. Furthermore, analysis of the bacterial community components showed that the ARB populations were strongly correlated with the occurrence of Bacteroidetes, Patescibacteria, and Tenericutes. Interestingly, intensified conjugal transfer (0.015) of antibiotic resistance genes (ARGs) was observed upon returning of the digested supernatant to the biological treatment system. It implies the likelihood of ARGs spreading and subsequent ecological risks upon anaerobic digestion towards reducing excess sludge, and therefore requires further attentions for the excess sludge treatments especially of supernatant.

Distribution and ecological risk of polycyclic aromatic hydrocarbons in wastewater treatment plant sludge and sewer sediment from cities in Middle and Lower Yangtze River

The objective of this study was to conduct a comparative study of the distribution and ecological risk of polycyclic aromatic hydrocarbons (PAHs) in the sewage collection and treatment system of four cities located in the middle and lower reaches of the Yangtze River. The results revealed that the mean concentration of 16 ΣPAHs was higher in the sewer sediments (1489.45 ng·g−1) than in the sewage sludge (781.78 ng·g−1). PAH monomers were detected in all cases, with higher mean Pyr, Chr, BbF and BaP concentrations. PAHs with 4–6 rings were dominant in both sewage sludge and sewer sediment monomer PAHs. With the isomer ratio method and positive definite matrix factor (PMF) method, the results showed that the major sources of PAHs in sewage sludge were petroleum sources, coal tar, and coking activities, whereas PAHs in sewer sediments were primarily from wood combustion, automobile emissions, and diesel engine emissions. Of all the PAH monomers, BaP and DahA had the highest toxic equivalents, although their levels were not the highest. Based on the assessment of ΣPAHs, it was concluded that both sewage sludge and sewer sediments had medium ecological risk. The results of this study provide reference information for the control of PAHs in the wastewater collection and treatment system of the middle and lower reaches of the Yangtze River.

Pharmaceuticals Account for a Significant Proportion of the Extractable Organic Fluorine in Municipal Wastewater Treatment Plant Sludge

Fluorine mass balance studies have shown that monomeric per- and polyfluoroalkyl substances (PFAS) with perfluoroalkyl chain lengths of ∼5–14 carbon atoms (i.e., “conventional” PFAS) account for a fraction (∼2%) of the extractable organic fluorine (EOF) in municipal wastewater treatment plant (WWTP) sludge. The identity of the remaining EOF has thus far been unclear but may be partly attributable to fluorine-containing pharmaceuticals and pesticides used throughout society. To test this hypothesis, we applied high resolution mass spectrometry-based suspect screening to samples of municipal WWTP sludge which had been previously subjected to a fluorine mass balance. Sixteen pharmaceutical substances (including transformation products [TPs]), one pesticide, and thirteen conventional PFAS were confirmed at confidence levels 1–4 and (semi)quantified, revealing concentrations ranging from 0.07 to 155 ng/g dw. Notably, eight pharmaceutical substances did not meet the OECD definition of PFAS. When converted to fluorine equivalents, the newly detected organofluorine substances increased the percentage of known EOF from ∼2% to ∼27%, of which ∼22% was attributed to pharmaceutical and pesticide substances, with the greatest contributions from ticagrelor TP (4.0%), ezetimibe (3.9%), and bicalutamide (3.5%). These data highlight the importance of considering both unconventional and non-PFAS organofluorine substances in addition to conventional PFAS when closing the organofluorine mass balance in WWTP sludge.

Optimizing Utilization of Hazardous Waste and Biomass as Solid Fuel for Co-Firing

Continuously high use of fossil fuels may lead scarcity of these energy sources in the future. Therefore, it is necessary to develop renewable energy to ensure its availability. One of the efforts in the development of renewable energy and the aims of this study is to examine the utilization Fly Ash (FA), Bottom Ash (BA) combined biomass sludge of Wastewater Treatment Plant (WWTP) and municipal solid waste) materials as an alternative energy source (briquette raw materials) for co-firing in textile industry boilers. Briquettes were made with a composition of 60% FABA and 40% biomass which were then varied in composition. The parameters measured were proximate, calorific value, and shatter index. The feasibility test of briquettes was carried out using a Tanner diagram, where all briquettes made can be burned as fuel. Optimum briquettes quality was measured based on the criteria according to the Minister of Environment and Forestry Regulation No. 06/2021. The results showed that the composition of three briquettes that had optimum quality and met the criteria were briquettes with composition 10%FA:50%BA:40%Biomass (variation of WWTP sludge and biomass) with a calorific value and sulfur content of 3,578 Kcal/kg and 0,70%; 3,890 Kcal/kg and 0,82%; and 3,864 Kcal/kg and 0,96%.

Is the petrochemical industry an overlooked critical source of environmental microplastics?

Microplastics (MPs) are ubiquitous in the environment and have been verified to be harmful to organisms. The petrochemical industry is a possible contributor, for it is the primary plastic producer but is not focused on. In this background, MPs in the influent, effluent, activated sludge, and expatriate sludge of a typical petrochemical wastewater treatment plant (PWWTP) were identified by the laser infrared imaging spectrometer (LDIR). It revealed that the abundances of MPs in the influent and effluent were as high as 10310 and 1280 items/L with a removal efficiency of 87.6%. The removed MPs accumulated in the sludge, and the MP abundances in activated and expatriate sludge reached 4328 and 10767 items/g, respectively. It is estimated that 1440,000 billion MPs might be released into the environment by the petrochemical industry in 2021 globally. For the specific PWWTP, 25 types of MPs were identified, among which Polypropylene (PP), Polyethylene (PE), and Silicone resin were dominant. All of the detected MPs were smaller than 350 µm, and those smaller than 100 µm prevailed. As for the shape, the fragment was dominant. The study confirmed the critical status of the petrochemical industry in releasing MPs for the first time.

Microplastics profile in sludge from a university wastewater treatment plant and the influence of chemical digestions on Nile red stained microplastics

Many of the microplastics (MPs) entering wastewater treatment plants (WWTPs) become entrained in the waste sludge. Here, we assessed the effects of five common digestion methods on the degradation and fluorescence intensity of Nile-red stained MPs. Crumb rubber (CR), cellulose acetate (CA) and polyamide (PA) dissolved in an acid-based digestion; Polyethylene terephthalate (PET), polylactic acid (PLA) and CA degraded in alkali solutions; and CR was destroyed by 30 % H2O2. Fenton’s reagent resulted in little to no damage to the polymers and removed > 95 % of the organic matter, making it the best choice for MP analyses. We then applied Fenton’s reagent to extract MPs in the primary sludge and dewatered sludge from a modern WWTP at the University of Mississippi. There is limited research on MPs in university WWTPs, where the wastewater inflows and composition vary greatly depending on activities and populations on campus. Abundances of putative MPs ranged from 13.2 ± 3.8–380.0 ± 46.4 particles/g (dry weight), with higher levels in the primary sludge and dewatered sludge with students on campus. The majority of MPs were fibers < 500 µm. Over 20 polymers were identified by using µ-FTIR, with polyester (26.4 %), nylon (14.9 %), and polyethylene (12.2 %) most abundant. There was little change in the composition of polymers in the sludge over time. Overall, we found that Fenton’s reagent coupled with µ-FTIR is an effective approach to characterize MPs in WWTP sludge, and that sludge could serve as a source of MPs to the environment depending on its disposal.

A Scoping Review of Options for Increasing Biogas Production from Sewage Sludge: Challenges and Opportunities for Enhancing Energy Self-Sufficiency in Wastewater Treatment Plants

Treating municipal wastewater is a complex and costly process. With rising energy costs and sustainability targets, wastewater treatment plants (WWTPs) are looking for alternatives to reduce operating costs and carbon dependence. Anaerobic digestion is the most common and established technology used in WWTPs to treat sludge since it can potentially improve energy recovery and reduce sewage treatment costs, mainly due to the generation of biogas. Biogas is a renewable energy resource and can be used in several applications, including heating and producing electricity. By exploring the biogas potential, WWTPs can reduce their operating costs and energy demands. The objective of this paper is to conduct a scoping literature review in order to provide the key concepts underpinning alternatives to improve biogas production and utilisation in WWTPs. In addition, this study aims to provide an overview of the current state-of-the-art that may serve as a quick reference for the research community, WWTP operators, and engineers, including definitions and a general overview of the current state of biogas technologies around the world. Methods to increase biogas production, including co-digestion, pre-treatment, and biological hydrogen methanation, are reviewed, and the alternatives to using biogas are also summarised. This review has identified that co-digestion was the most efficient technique to improve biogas production and methane yield, while pre-treatment of sludge improved sludge biodegradability and reduced sludge treatment costs but also enhanced biogas production. Although many studies have explored different methods to improve biogas production in WWTPs, there is still a need for further investigation, especially regarding the techno-economic feasibility of these methods in full-scale facilities. The current challenges are mainly related to the need for extra investment and increased operating costs to integrate the new techniques into the current system. There is a great interest in alternatives to improve energy efficiency and self-sufficiency in WWTPs. This work provides an important review of the increasing number of recently published research papers that focus on improving biogas generation from sewage sludge in WWTPs.