Sludge Wastewater Treatment Plant Research Articles

Catalysing water treatments: A Comprehensive Examination of sludge, its treatment and Energy Valorisation Solutions

The escalating production of sewage sludge in WasteWater Treatment Plant (WWTP) due to urban population growth and its management poses a substantial risk to the energetic and environmental efficiency of WWTP. This paper aims to explore the potential for sludge as a renewable energy source to reduce reliance on traditional energy through a systematic literature review of peer-reviewed articles and case studies. This overview demonstrated that various treatment methods such as anaerobic digestion, incineration, gasification, and pyrolysis are the most used and the most promising in terms of their energy outputs and effectiveness. The paper discussed the complexity of sludge composition, its financial burden on WWTP, and the crucial role in the success of these systems. Moreover, a comparative analysis of the different valorisation techniques was conducted that highlighted the energy production potential existing within each method and its underlying constraints while emphasising on the proper sludge management for overall efficiency. Finally, this paper recommended the need for sustainable, cost-effective approaches, considering legal standards for efficient WWTP.

Goat manure formula in sludge cake wastewater treatment plant as organic fertilizer

The use of activated sludge in wastewater treatment plants (WWTP) in industry gives a by- product in the form of sludge cake. Sludge cake presents a new problem for the environment because its accumulation causes the land to become unproductive, disrupts aesthetics, increases microbial activity, and pollutes water and soil, which can be harmful to humans and the environment. PT X is one of the industries that produces 80 kg/day of sludge cake. Based on laboratory results, X WWTP sludge cake has the potential to be used as an organic fertilizer. However, the use of sludge cake as organic fertilizer does not meet fertilizer quality standards and does not provide optimal results for plants. Goat manure is known to increase the organic fertilizer content of sludge cake in accordance with fertilizer quality standards. This research aims to find the best formula for adding goat manure to WWTP sludge cake which is carried out using four treatments, namely sludge cake without treatment, and the addition of goat manure 1.4 kg, 2.1 kg, and 2.8 kg. The stages of the research include the preparation of raw materials, the manufacture of organic fertilizers, and testing the content of organic fertilizers. The results showed that there was an increase in physical and chemical parameters on organic fertilizers, namely pH (6.6), C (22.14%), N (3.55%), P (4.65%), K (0.45%), Ca (0.52%), and Mg (0.26)), as well as a decrease in water content (15.40%) at the end of composting. The addition of goat manure with a combination of other additives to X TWP sludge cake can meet organic fertilizer quality standards. The addition of 2.1 kg of goat manure is the best formula to increase organic fertilizer.

Study of biooil production from sewage sludge of a municipal wastewater treatment plant by using hydrothermal liquefaction

To overcome the problem of rapid depletion of natural energy reserves and consequent pollution caused by them, this work explored the possibility of utilizing sewage sludge biomass to produce biooil using hydrothermal liquefaction pathway. In this study, effect of different reaction parameters such as reaction temperature, residence time, and sludge-to-water ratio on solid biomass conversion and bioyield and its higher heating value were investigated. Although maximum conversion of (99.7%) and highest biooil yield (22.01 wt.%) was achieved at 330?C, however optimum temperature was chosen as 300?C which produced conversion efficiency and yield of biooil very close (98.07% and 21.5 wt.%, respectively) to what was obtained at 330?C as lower temperature is beneficial for overall economy of the process. Similarly, a residence time of 60 minutes and sludge-to-water ratio of 1:6 was screened to be producing optimized yield of biooil. The higher heating valu of different fractions biooil was much improved (30.18 MJ/kg of acetone phase and 38.04 MJ/kg of dichloromethane phase) as compared to that of raw feedstock (12.74 MJ/kg). Carbon balance performed on the products indicated that maximum amount of carbon went to biooil phase (53.4 wt.%). However, a significant portion of carbon was lost (33.9 wt.%) due to the limitation of experiments at lab scale which involves evaporation and drying to reach final products. The Fourier transform infrared spectroscopy spectral analysis of different biooil phases showed that it was mainly made up of alcohols, alkane, ketones, aldehydes and carboxylic acids.

Environmental impact of sewage sludge co-digestion with food waste and fat-oil-grease: Integrating plant-wide modeling with life cycle assessment approach

Anaerobic co-digestion of fat-oil-grease (FOG) and food waste (FW) with sewage sludge (SS) in wastewater treatment plants is a method used to increase biogas production. In this study, digestion scenarios were compared using plant-wide modeling and life cycle assessment: Scenario-0 (mono-digestion of waste-activated sludge (WAS)), Scenario-1 (co-digestion of WAS with FOG), and Scenario-2 (co-digestion of WAS with FW). Scenario-0, with the highest energy use and landfilling of FOG/FW, has the worst environmental impact. Scenario-1 and Scenario-2 minimize the environmental load by energy recovery and avoiding landfilling of organic waste. Scenario-wise, the change in greenhouse gas (GHG) emissions from treatment was negligible. However, due to the impact of landfilling, GHG emissions in Scenario-0 were 21% and 30% higher than in Scenario-1 and 2, respectively. The environmental benefit of anaerobic co-digestion of FOG/FW with SS is not only in the contribution to energy production but also in the recycling of organic waste.

Use of the nitrogen/ oxygen isotope fractionation technique for tracing nitrogen removal from activated sludge in municipal wastewater treatment plants

The dual isotope fractionation technique of nitrogen and oxygen has been successfully applied to analyze microbially-driven nitrogen transformations and partitioning in aquatic ecosystems, but not in municipal water treatment facilities. Nitrogen removal efficiency in wastewater treatment plants using activated sludge is critical and difficult to monitor. Here, we tested the nitrogen and oxygen isotope fractionation technique for capacity to trace nitrogen removal from municipal wastewater. Long-term monitoring of Anaerobic/anoxic/aerobic (A2/O) process municipal wastewater treatment plants revealed that nitrogen removal performance gradually improved with increasing seasonal temperatures. The δ15N value of activated sludge increased from 5.18‰ (January) to 6.37‰ (June). An increase in temperature promoted the increase in NO3--N from 1.23 mg/L (January) to 6.06–7.02 mg/L (June to August) in the aerobic reaction. The δ15NNO3 decreased from 17.82‰ to 37.37‰ to 4.09–17.68‰, and variability in utilization of light and heavy isotopes gradually decreased. The slope of the ratio δ15NNO3:δ18ONO3 gradually decreased from 21.58 ± 12.15 (January) to 0.57 ± 0.51 (August). The dynamic response of δ15N values in sludge and isotopes in water revealed the migration transformation of nitrogen and realized the differential analysis to denitrification performance with seasonality. It also provided a technical basis for long-term stable nitrogen removal system.

The occurrence of heavy metals and antimicrobials in sewage sludge and their predicted risk to soil — Is there anything to fear?

The study assessed the occurrence of legally-monitored heavy metals and unmonitored antimicrobials in sludge from small, medium, large and very large municipal wastewater treatment plants (WWTPs), and the predicted environmental risk and risk of resistance selection associated with sludge administration to soil. The temporal variations of the studied compounds in sludge and associated risks to soil were determined by sampling over a year.Although the highest concentrations of heavy metals were noted in sludge from the largest WWTP, i.e. from 1.50 mg/kg (mean 1.61 mg/kg) for Cd to 2188 mg/kg (mean 1332 mg/kg) for Zn, the obtained values only reached a few percent of the legal limits. The same WWTP also demonstrated lower concentrations of antimicrobials compared to the smaller ones. The highest concentrations of antimicrobials, ranging from 24.04 μg/kg for trimethoprim to 900.24 μg/kg for tetracycline, were found in the small and medium WWTPs. However, due to lack of regulations at the national and EU levels, the results cannot be compared with legal limits. Principal Component Analysis (PCA), cluster and heatmap analysis separated samples according to WWTP size. Small WWTP demonstrated correlation with antimicrobials (tetracycline, trimethoprim, clindamycin, ciprofloxacin and ofloxacin), while the large and very large WWTP revealed correlations with heavy metals (Cu and Cr).The obtained environmental risk quotients confirmed that the heavy metals did not present a threat, measured either as individual risk quotients (RQenv), cumulative risk (RQcumulative) or risk of mixture of heavy metals (RQmix-metals). In the case of antimicrobials, only tetracycline demonstrated moderate RQenv, RQcumulative and RQmix-antimicrobials in the small WWTP sludge, with values of 0.1 to 1. Our findings highlight the importance of monitoring sewage sludge before soil application, especially from small WWTPs, to reduce the potential environmental impact of antimicrobials. They also confirm our previous data regarding the environmental risk associated with various toxic compounds, including emerging contaminants, in the sludge from small WWTPs.

Evolution of chlorinated paraffin and olefin fingerprints in sewage sludge from 1993 to 2020 of a Swiss municipal wastewater treatment plant

Exposure of humans to chlorinated paraffins (CPs) and chlorinated olefins (COs) can occur via contact with CP-containing plastic materials. Such plastic materials can contain short-chain CPs (SCCPs), which are regulated as persistent organic pollutants (POPs) under the Stockholm Convention since 2017. Municipal wastewater treatment plants (WWTP) collect effluents of thousands of households and their sludge is a marker for CP exposure. We investigated digested sewage sludge collected in the years 1993, 2002, 2007, 2012, and 2020 from a Swiss WWTP serving between 20000 and 23000 inhabitants. A liquid chromatography mass spectrometry (R > 100000) method, in combination with an atmospheric pressure chemical ionization source (LC-APCI-MS), was used to detect mass spectra of CPs and olefinic side products. A R-based automated spectra evaluation routine (RASER) was applied to search for ∼23000 ions whereof ∼6000 ions could be assigned to CPs, chlorinated mono- (COs), di- (CdiOs) and tri-olefins (CtriOs). Up to 230 CP-, 120 CO-, 50 CdiO- and 20 CtriO-homologues could be identified in sludge. Characteristic fingerprints were deduced describing C- and Cl-homologue distributions, chlorine- (nCl) and carbon- (nC) numbers of CPs and COs. In addition, proportions of saturated and unsaturated material were determined together with proportions of different chain length classes including short- (SC), medium- (MC), long- (LC) and very long-chain (vLC) material. A substantial reduction of SCCPs of 84% was observed from 1993 to 2020. Respective levels of MCCPs, LCCPs and vLCCPs decreased by 61, 69 and 58%. These trends confirm that banned SCCPs and non-regulated CPs are present in WWTP sludge and higher-chlorinated SCCPs were replaced by lower chlorinated MCCPs. Combining high-resolution mass spectrometry with a selective and fast data evaluation method can produce characteristic fingerprints of sewage sludge describing the long-term trends in a WWTP catchment area.

Chemically activated hydrochars as catalysts for the treatment of HTC liquor by catalytic wet air oxidation

Hydrothermal carbonization (HTC) is a highly efficient and valuable technology for treating wet solid wastes and producing solid carbon-based materials named hydrochar. In this work, a hydrochar coming from the HTC of an anaerobic digestion sludge of wastewater treatment plant was used to assess the influence of several activation agents, a base (KOH) and different chloride salts (FeCl3, ZnCl2, and CuCl2) with the exact molar quantities, to develop materials with enhanced surface area and potential inclusion of metal active species for application in wet air oxidation processes. The KOH as an activating agent increased the surface area of hydrochar up to ca. 1000 m2/g of BET surface area. The employment of CuCl2 and FeCl3 as activating agents allows Cu- and Fe-rich doped materials of remarkable surface areas with 49.1 and 42.5 wt% of each metal, respectively. Likewise, the catalytic behavior of the different synthesized carbon-based materials as metal-free and metal-doped catalysts was evaluated for the Catalytic Wet Air Oxidation (CWAO) of a HTC aqueous liquor from a HTC process of animal manure to produce a valuable stream of higher biochemical methane potential in anaerobic digestion. CWAO effluents increased the proportion of carboxylic acids as final by-products due to the oxidation of more complex organic compounds of the initial effluent (ketones, phenols, aromatics and olefins). The CWAO treatments improve the anaerobic digestion rate in biochemical methane potential tests, although the methane production was limited by the lower TOC concentration of the treated streams after CWAO. This research contributes to developing sustainable and efficient strategies for the HTC-liquor treatment, using its solid hydrochar as catalysts, closing the loop of a Circular Economy.

Tessaracoccus caeni sp. nov., a novel member of Propionibacteriaceae isolated from activated sludge in Hefei, PR China.

A floc-forming bacterial strain, designated HF-7T, was isolated from the activated sludge of an industrial wastewater treatment plant in Hefei, PR China. Cells of this strain were Gram-stain-positive, catalase- and oxidase-negative, facultatively anaerobic, and rod-shaped. Growth occurred at 20-42 °C (optimum, 28 °C), at pH 5.5-10.5 (optimum, pH 7.5) and with 0-8.0 % (w/v) NaCl (optimum, 1 %). The major fatty acid was anteiso-C15 : 0. The polar lipid profile contained phosphatidylglycerol, diphosphatidylglycerol and phosphatidylinositol. The DNA G+C content was 67 mol% from whole genomic sequence analysis. Based on the results of 16S rRNA gene sequence analysis, this strain should be assigned to the genus Tessaracoccus and is closely related to Tessaracoccus arenae CAU 1319T (95.87 % similarity), Tessaracoccus lapidicaptus IPBSL-7T (95.19 %) and Tessaracoccus bendigoensis Ben 106T (94.63 %) but separated from them by large distances in different phylogenetic trees. Based on whole genome analysis, the orthologous average nucleotide identity and in silico DNA-DNA hybridization values against two of the closest relatives were 75.21-76.50 % and 14.2-24.4 %, respectively. The phylogenetic, genotypic, phenotypic and chemotaxonomic data demonstrated that strain HF-7T could be distinguished from its phylogenetically related species and represents a novel species within the genus Tessaracoccus, for which the name Tessaracoccus caeni sp. nov. is proposed. The type strain is HF-7T (=KCTC 49959T=CCTCC AB 2023019T).

Utilization of Sludge from the Communal Wastewater Treatment Plant (WWTP) in the Asrama Dinas Lingkungan Hidup (DLH) Jagakarsa of South Jakarta City as Basic Material for Organic Fertilizer

Asrama DLH Jagakarsa has a communal wastewater treatment plant (WWTP) that produces sludge that has not been treated. Asrama DLH residents directly apply the sludge from the communal WWTP as fertilizer for plants. Fecal sludge contains organic substances that provide nutrients to plants. However, there is a possibility that it still contains pathogenic bacteria and metals that can be harmful to plants. This research aims to utilize the fecal sludge from Asrama DLH Jagakarsa WWTP as organic fertilizer with additional ingredients in the form of humic acid. During fertilizer manufacturing, the bacteria and metals are removed. The analysis used includes the composting process conditions analysis, characteristics tests to determine the content of feces and fertilizers, and analysis of the application to plants. Analysis of the conditions in the composting process is the analysis of the pH value of organic fertilizers. Characteristic tests include soil variation (V1), WWTP sludge (V2), and organic fertilizer (V3). Analysis of the application of plant growth was carried out by testing the variation of soil 100% (P1), soil 80% + 20% fecal sludge (P2), and soil 80% + 20% organic fertilizer (P3). The laboratory analysis includes the analysis of nitrogen, phosphorus, potassium (NPP), and water content which will be compared with the quality standard of the Decree of the Minister of Agriculture Number 261 of 2019. The plant that is used as an indicator of the success of organic fertilizer in plant growth is the kale plant. The best value was obtained in the variation of organic fertilizer (V3), namely the NPP content and water content, respectively, which were 4.52%, 2.57%, 0.05%, and 19.84%. This shows that organic fertilizer increases NPP elements and plant growth.

Dampak Pupuk Organik Cair dan Kompos IPAL Karet Terhadap Pertumbuhan Bibit Kelapa Sawit (Elaeis Guineensis Jacq) di Main Nursery

Oil palm plants (Elaeis guineensis Jacq) are one of the important commodities in the plantation crop industry, capable of providing economic value as a source of foreign exchange income for the country. The increase in oil palm area is also accompanied by an increase in damaged plants (TR/TTM). So it is necessary to rejuvenate the plants to get quality seeds. The aim of this research was to determine the effect and best dose of Eco Farming liquid organic fertilizer treatment with rubber wastewater treatment plant sludge compost on the growth of oil palm (Elaeis guineensis Jacq.) seedlings in the main nursery. This research was carried out at the Teaching and Research Farm, Faculty of Agriculture, Jambi University and lasted for 3 months, starting in September-November 2022. This research used a Completely Randomized Design (CRD) with 5 treatments, namely: k0 = 40 mL.L-1 Eco fertilizer water Farming, k1 = 30 mL.L-1 Eco Farming fertilizer water + 100 g compost from waste sludge from WWTP, k2 = 20 mL.L-1 water from Eco Farming fertilizer + 200 g compost from waste sludge from WWTP, k3 = 10 mL.L-1 Eco Farming fertilizer water + 300 g of WWTP sludge waste compost, k4 = 400 g of WWTP sludge waste compost. The variables observed included seed height (cm), increase in tuber diameter (mm), increase in number of leaves (strands), shoot dry weight (g), root dry weight (g), ratio of root shoot and root volume (ml). The results of the research showed that the application of Eco Farming liquid organic fertilizer and waste compost from rubber wastewater treatment plant sludge was able to increase growth in the variables of seed height, root dry weight and root volume. However, it has not been able to increase the increase in tuber diameter, increase in number of leaves, shoot dry weight and root shoot ratio. Treatment of 10 mL.L-1 of Eco Farming fertilizer water + 300 g of IPAL waste sludge compost gave the best average growth of 6 month old oil palm seedlings in the main nursery.

Optimal deployment of thermal hydrolysis and anaerobic digestion to maximize net energy output based on sewage sludge characteristics

Thermal hydrolysis (TH) is widely employed in combination with anaerobic digestion (AD) to efficiently treat primary sludge and waste-activated sludge in municipal wastewater treatment plants. In this study, four different scenarios—conventional AD (S1), TH–AD (S2), AD–TH–AD (S3), and characteristics-based AD–TH–AD (S4, primary AD only for primary sludge)—were evaluated to determine the optimal deployment of TH and AD for treating primary sludge and waste-activated sludge to maximize net energy output. The maximum net energy output of 4899 MJ/t-TSfed (per ton total solids of sludge fed) was achieved in S4 when assuming the recovered heat was only used for AD heating and surplus heat was wasted, and the net energy output of S4 was 70.8 % higher than that of S1 and 48.6 % higher than that of S2. This remarkable improvement was attributed to a reduction of > 15.2 % in refractory compounds, resulting in a 17 % increase in methane yield. Importantly, this study provides the first comparison of refractory compounds between inter-thermal hydrolysis (inter-TH) and pre-thermal hydrolysis (pre-TH) using a simulated A2O process. Overall, this study provides innovative insights and strategies for enhancing the TH and AD process performance based on the specific characteristics of sewage sludge derived from wastewater treatment plants.

Reduction of sewage sludge and N2O emissions by an Oxic Settling Anaerobic (OSA) process: The case study of Corleone (Italy) wastewater treatment plant

Biosolid management is becoming one of the most crucial issues for wastewater treatment plant (WWTP) operators. The application of the Oxic Settling Anaerobic (OSA) process allows the minimisation of excess sludge production. This study compares conventional activated sludge (CAS) and OSA layouts in a full-scale WWTP (namely, Corleone - Italy). Extensive monitoring campaigns were conducted to assess treatment performances regarding carbon and nutrient removal, greenhouse gas (GHG) emissions, excess sludge production, and biomass activity (by means of respirometric analysis). Results showed that the effluent quality consistently met the Italian discharge limits. However, with the implementation of the OSA process, there was a decrease in ammonium removal efficiency, which could be attributed to reduced nitrifier activity related to reduced biomass production and extended anaerobic conditions affecting the nitrification process. On the other hand, the OSA configuration significantly increased phosphorus removal, indicating a high phosphorus content in the resulting waste sludge. A worsening of the sludge settling properties was observed with the OSA configuration likely due to decreased EPS concentrations. The sludge production in the OSA configuration decreased by 17.3 % compared to CAS. Nitrous-oxide measurements did not show a variation between CAS and OSA configurations, confirming that the OSA process can be a suitable solution for reducing WWTP's carbon footprint.

Conversion of recycled sludge waste into high value-added ceramics as engineering construction materials: Fabrication, characterization and performance evaluation

Sludge from municipal wastewater treatment plants usually exhibits extremely homologous traits with clay in both mineralogical component and chemical composition, and accordingly it can be utilized as an alternative feedstock for clay to fabricate engineering construction materials and advance sludge valorization. In this work, different proportions of wastewater treatment plant sludge (WTPS) were incorporated into kaolin to develop value-added construction ceramic materials. The thermal behavior, crystalline composition, physicochemical performance, microscopic characteristics and sintering mechanism of value-added ceramics were investigated. The results showed that WTPS not only contained a large amount of inorganic components such as SiO2, Al2O3 and Fe2O3, but also rich organic compounds, which contributed to the formation of pore structure inside the ceramics during sintering. Different WTPS addition did not affect the types of crystalline components in sintered ceramics, but markedly impacted the sintering behavior. Only when the WTPS dosage reached 40 wt%, the original mixtures would be fully sintered into construction ceramics with the apparent porosity of 11.30 %, thermal conductivity of 0.50 W/(m·K), bulk density of 2.22 g/cm3, linear shrinkage and volume shrinkage of 14.95 % and 38.86 % respectively, as well as vastly low water absorption (0.58 %) and excellent flexural strength (84 MPa). However, with the WTPS content up to 50 wt%, the flexural strength of sintered ceramics was reduced to 50 MPa, despite the elevated sintering degree, which was related to the high formation of liquid phase and the violent expansion of several closed pores. Therefore, converting WTPS into high value-added construction ceramic products is an operable and beneficial way to achieve sludge waste recycling, reduction and stability.

Analysis of Machine Learning Models for Wastewater Treatment Plant Sludge Output Prediction

With China’s significant investment in wastewater treatment plants, urban sewage is effectively collected and treated, resulting in a substantial byproduct—sludge. As of 2021, a total of 2827 wastewater treatment plants have been constructed across 31 provinces, municipalities, and autonomous regions in China, with a processing capacity of 60.16 billion cubic meters. The production of dry sludge amounts to 14.229 million tons. The treatment and utilization of sludge pose significant challenges. The scientific calculation of sludge production is the basis for the reduction at the source and the design of sludge treatment and energy utilization. It is directly related to the construction scale, structure size, and equipment selection of the sludge treatment and utilization system and affects the operation and environmental management of the sludge treatment system. The wastewater treatment process using microbial metabolism is influenced by various known and unknown parameters, exhibiting highly nonlinear characteristics. These complex characteristics require the use of mathematical modeling for simulations and control. In this study, nine types of machine learning algorithms were used to establish sludge production prediction models. The extreme gradient boosting tree (XGBoost) and random forest models had the best prediction accuracies, with the former having RMSE, MAE, MAPE, and R2 values of 4.4815, 2.1169, 1.7032, 0.0415, and 0.8218, respectively. These results suggested a superiority of ensemble learning models in fitting highly nonlinear data. In addition, the contribution and influence of various input features affecting sludge output were also studied for the XGBoost model, and the daily wastewater inflow volume and surrounding temperature features had the greatest impact on sludge production. The innovation of this study lies in the application of machine learning algorithms to achieve the prediction of sludge production in wastewater treatment plants.

Hydrothermal liquefaction potential of wastewater treatment sludges: Effect of wastewater treatment plant and sludge nature on products distribution

The rapid growth of urban populations necessitates the development of more efficient and environmentally sustainable methods for waste treatment and resource recovery. Hydrothermal liquefaction (HTL) has emerged as a promising technology for converting organic waste into bio-crude oil. In this study, the HTL products of various waste fractions (Fat, oil, and grease (FOG), food waste, primary and secondary sludge, and digestate) produced or handled by four wastewater treatment plants in Denmark were analysed. Additionally, the effect of mixing the produced waste was investigated. The HTL experiments were conducted at temperatures 300, 325, and 350 °C, with a residence time of 20 min and dry matter content of 16.7%. The highest HTL bio-crude yields were obtained at a temperature of 325 °C for all feedstocks except FOG (300 °C). The mixing of wastes resulted in a positive synergistic effect, presenting an energy recovery between 62 and 76% and bio-crude yields higher than expected due to interactions between the feedstock's biochemical composition. Based on the biochemical composition and on the feedstocks fraction, two models are proposed for the prediction of bio-crude yields, with an error between 4 and 5% in absolute terms. In addition, important process water parameters, as well as the nutrient recovery and heavy metal load of the solid residues are analysed and discussed, giving a comprehensive overview of the potential of different wastewater treatment plant sludges.

Primary settling changes the microbial community of influent wastewater to wastewater treatment plants

The continuous immigration of bacteria in influent wastewater strongly impacts the microbial community of activated sludge (AS) in wastewater treatment plants (WWTP), both in terms of species composition and their abundance. Therefore, it is of interest to elucidate the route of immigrating bacteria into the biological tanks, including the effect of primary settlers. These are commonly used pretreatment units that can possibly selectively increase or reduce the relative abundance of certain bacteria. Species-level identification of the microbial composition of influent wastewater before and after primary settling was carried out in four full-scale municipal WWTPs biweekly over one year by 16S rRNA gene amplicon sequencing. Overall, 37–49% of incoming COD was removed in the primary settlers. Most genera and species were present in the wastewater to all four plants and the trend of these were investigated across the primary settlers. Approximately 50% of the genera had the same trend across at least three WWTPs. Few genera significantly increased in relative read abundance (3.7%) after settling, while 22.3% showed a significant reduction in relative abundance. We investigated process-critical species in AS, such as known nitrifiers, polyphosphate-accumulating organisms, and filamentous bacteria. Most taxa were affected similarly in all WWTPs including multiple genera involved in bulking in AS. However, some genera, e.g., important polyphosphate-accumulating bacteria, had inconsistent trends across WWTPs, suggesting that the characteristics of the wastewater are important for the trend of some bacteria through primary settling. In all cases, primary settling changed the microbial community of the influent wastewater, posing an obvious candidate for upstream control to optimize the assembly of the microbial communities in activated sludge.

Occurrences of typical PPCPs during wastewater treatment and the composting of sewage sludge with micron-sized and nano-sized Fe3O4

New pollutants, pharmaceuticals and personal care products (PPCPs), accumulate in sewage sludge (SS) in wastewater treatment plants (WWTPs), posing risks to the environment and to human health. In the present study, the fates of typical PPCPs, carbamazepine (CBZ), triclosan (TCS), ibuprofen (IBU) and galaxolide (HHCB), were examined during WW treatment. Additionally, SS collected from a WWTP was used for aerobic composting to investigate the influences of micron-sized Fe3O4 (M-Fe) and nano-sized Fe3O4 (N–Fe) on the degradation of these PPCPs and the succession of microbial communities during the composting process. The results showed that the mean concentrations of CBZ, TCS, IBU and HHCB in the influent of the WWTP were 926.5, 174.4, 8869, and 967.3 ng/g, respectively, and in the effluent were 107.6, 47.0, 283.4, and 88.4 ng/g, respectively. The removal rate averaged ∼80%, while the enrichment rates of the PPCPs in SS ranged from 37.2% to 60.5%. M-Fe and N–Fe reduced NH3 emissions by 32.9% and 54.1% and N2O emissions by 26.2% and 50.8%, respectively. Moreover, the addition of M-Fe and N–Fe effectively increased PPCP degradation rates 1.12–1.66-fold. During the whole process, the additions of M-Fe and N–Fe significantly shifted microbial community structure, and the abundances of Proteobacteria, Chloroflexi, and Actinobacteria were increased during the thermophilic stage, marking them as key PPCP-degrading phyla. Taken together, our results indicated that the addition of M-Fe and N–Fe is an effective method for improving the quality of end compost and accelerating the degradation of PPCPs.

Sludge drying and dewatering processes influence the abundance and characteristics of microplastics in wastewater treatment plants

Wastewater treatment plants (WWTPs) have been identified as high-load receptors of microplastics (MPs) from different sources. However, the influence of specific treatment stanges requires further research. The main objective of this research was to evaluate the abundance and chemical characteristics of MPs in the sludge of two major wastewater treatment plants in the Agadir metropolis (Central Atlantic of Morocco). The Aourir plant receives urban influents and the inputs of the M'zar facility were urban and industrial. Samples were collected from the sludge matrices after primary settling, clarifying, dewatering, and drying systems. In addition, the effect of seasonality on MP load was assessed. The results showed that a higher abundance was noticed in raw sludge than in dewatered one in Aourir WWTP, while in M'zar WWTP, a very low decrease is noticed in dried sludge compared to raw sludge. The concentration of MPs in the summer season was significantly higher compared to other seasons for Aourir WWTP, while the winter season was higher for M'zar WWTP. Moreover, the most abundant shapes were fibers and the fraction 100–500 μm was the most preponderant. Eleven polymers were identified by ATR-FTIR, being polyester, polyethylene, polypropylene, and polystyrene the most abundant ones. Scanning Electron Microscopy coupled with Energy Dispersive X-ray revealed the visible degradation and fragmentation of MPs from sewage sludge and their ability to adsorb inorganic elements. It was estimated that between 2.2 × 107 and 7.4 × 108 MPs were evacuated with the sludge per day. The obtained findings confirmed that WWTP sludge acts as a vector of MPs with a high level of hazard to various matrices, such as landfills, agricultural soils, and groundwater. Overall, consideration must be given to the regulatory system managing the fate of sewage sludge to mitigate the collateral effects and provide solutions.

Eco-Friendly Cement Mortar with Wastewater Treatment Plant Sludge Upcycling

This study aimed to investigate the technical feasibility of replacing cement in mortar production with sludge generated in wastewater treatment plants (WWTPs), prepared using different treatments. The sludge used in the experiments was processed using four different methods to investigate the effect of processing on the mechanical strength of the specimens. The sludge was then mixed with mortar in different proportions, and samples were produced for flexural and compressive strength tests. The results showed that specimens with 7% sludge from the burned treatment exhibited the highest resistance, surpassing the standard. Specimens with sludge from the drying treatments showed similar results. This study found that using sludge in mortar production could lead to energy savings compared to traditional cement production methods. Moreover, the incorporation of sludge resulted in mortars that met the specifications of the EN 998-1:2018 standard, thereby indicating their technical feasibility. Therefore, this study demonstrated the potential of using sludge from WWTPs as a substitute for cement in mortar production, which could contribute to the reduction in the environmental impacts caused by civil construction and the development of sustainable alternatives for the disposal of sludge generated in WWTPs.