Sewage Sludge Research Articles

Sludge reduction, nitrous oxide emissions, and phosphorus removal by oxic-settling-anaerobic (OSA) process: the effect of hydraulic retention time

This paper presents a study on reducing sewage sludge by an oxic-settling-anaerobic (OSA) pilot plant compared to the conventional activated sludge (CAS) process in view of resource recovery and moving towards plant carbon neutrality. The OSA plant was supplied with real wastewater and the anaerobic reactor was operated under two hydraulic retention times (HRT) (4 and 6 h). Greenhouse gas (GHG) emissions were monitored for the first time to determine the OSA process’s production mechanism. The results highlighted that under the lowest HRT (4 h), the removal efficiencies of COD and PO4−P, increased from 75 to 89% and from 39 to 50% for CAS and OSA configurations, respectively. The observed yield coefficient was reduced from 0.58 gTSS gCOD−1 (CAS period) to 0.31 gTSS gCOD−1 (OSA period). A remarkable deterioration of nitrification efficiency under OSA configuration was obtained from 79% (CAS) to 27% (OSA with HRT of 6 h). The huge deterioration of nitrification significantly affected the GHG emissions, with the N2O-N fraction increasing from 1% (CAS) to 1.55% (OSA 4 h HRT) and 3.54% (OSA 6 h HRT) of the overall effluent nitrogen, thus suggesting a relevant environmental implication due to the high global warming potential (GWP) of N2O.Graphical abstract

In Situ Treatment of Domestic Food Waste and Bioflocculated Sewage Sludge in Decentralized Wastewater Treatment Plant

In Situ Treatment of Domestic Food Waste and Bioflocculated Sewage Sludge in Decentralized Wastewater Treatment Plant

Composted Sewage Sludge as Soil Amendment in Colombia: Challenges and Opportunities to Scale Up

Composted Sewage Sludge as Soil Amendment in Colombia: Challenges and Opportunities to Scale Up

Investigation of PAH content and hazard assessment in sewage sludge in Gwangju

Investigation of PAH content and hazard assessment in sewage sludge in Gwangju

The fate of Volatile Fatty Acids (VFAs) during the thermodynamic transition from hydrothermal carbonization to hydrothermal liquefaction: HtC-to-HtL

The valorization of biomass via hydrothermal treatment, a green and reliable thermochemical process, produces high-value chemicals. This study focuses on the transformation of Volatile Fatty Acids (VFAs) during the transition from Hydrothermal Carbonization (HTC) to Hydrothermal Liquefaction (HTL) and their impact on product quality. Conducted with anaerobically digested sewage sludge, the hydrothermal treatment varied temperatures from 280 °C to 340 °C. The primary objective was to investigate VFA concentrations and their link to hydrochar yield and gaseous by-product composition. A high-performance Parr 4577A hydrothermal reactor facilitated these experiments. For VFA assessment, a Shimadzu Nexis 2030 plasma GC-BID with an HP-FFAP column was utilized for the first time. The study revealed a U-shaped COD concentration curve (peaking at 10,510 mg/l at 340 °C) and an S-shaped Total Phenols profile (highest at 1314 mg/l at 325 °C). Notably, VFA concentrations dipped significantly at 295 °C and 325 °C but were higher at other temperatures, suggesting a complex underlying mechanism. This variability is partially attributed to the reduction in hydrochar mass yield with increasing temperature (46% at 280 °C to 31% at 340 °C) and a surprising spike in CO2 concentration (90% at 310 °C). These findings emphasize the critical role of carboxylation reactions in the HTC-to-HTL transition, enhancing the quality of liquid hydrothermal products.

Analysis of environmental impact reduction effect of applying high-speed flash mixer in sewage sludge dewatering process

Analysis of environmental impact reduction effect of applying high-speed flash mixer in sewage sludge dewatering process

Comparative analysis of hydrogen-rich syngas production from various feedstocks using bubbling fluidized bed

Any carbon-based materials, including any trash that contains carbon, may be converted into sustainable energy through the thermochemical process known as gasification. The bubbling fluidized bed (BFB) is used for sewage sludge (SS), plastic waste (PW), and refuse-derived fuel (RDF) gasification. The sensitivity analysis of gasification processes is examined. The maximum H2 selectivity in RDF gasification is 70 %, followed by SS (65 %) and PW (62 %) at S/B=2. PW gasification, although producing more H2, generates more CO and CO2 than RDF and SS because to its high carbon content. At 700°C–800°C, three feedstocks have good H2 selectivity. RDF gasification has the best selectivity of all component products over the temperature range. The H2/CO molar ratio range (1–2) for chemical synthesis suggests steam to biomass (S/B) values of 1.2–2.6 for RDF and SS. As S/B value increases, CO/CO2 molar ratio increases, which compresses CO2 for CO production, improving syngas quality, notably for power generation. In PW gasification, the H2/CO ratio (≤2) is expected at >750°C. Pressure only effects H2/CO and CO/CO2, in PW gasification. The evaluation of lower heating value (LHV) and cold gas efficiency (CGE) involves exploring a range of selected parameters. Elevated reaction temperatures positively influence both LHV and CGE; however, this is not the case for S/B ratio and reaction pressure. Among the gasification processes, PW gasification exhibits the highest LHV, while SS gasification demonstrates the highest CGE. Besides, the gasification efficiency (ƞG) is found about 35–41 % at the S/B=2, which is lower than the efficiency in terms of CGE (57.6 %) due to the energy consumption increase as the temperature increased. O2/S increases negatively affect product composition but allow parameter indicator value adjustment to parameter indicator of the desired syngas product quality.

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.

A comprehensive comparison between two strategies to produce polyhydroxyalkanoates from domestic sewage sludge

Biopolimer materials, such as polyhydroxyalkanoates (PHA), are essential to restrain the use of petroleum-based plastic material fostered by European Union regulation. Despite the recent development regarding the production of PHA, the scale-up of sewage sludge-based technology is still in its infancy since the literature lacks studies on the environmental impact of the process. This work aims to stand as a pioneer study reporting the direct greenhouse gas (GHG) emissions and carbon footprint (CF) of two sewage sludge-based PHA production strategies. The two strategies, aerobic dynamic feeding (ADF) and aerobic/anoxic enrichment (AE/AN), were monitored and compared based on the system's efficiency in removing carbon and nutrients, PHA's production and productivity, nitrous oxide direct emissions and the CF. The produced PHA accounted for 38.21 g PHA g−1 volatile suspended solids (VSS) % and 14.54 g PHA g−1 VSS %, for ADF and AE/AN, respectively. The N2O emissions were lower for ADF than the AE/AN enrichment, 0.39 N2O–N L−1 and 0.98 N2O–N L−1, respectively, as was the CF, which accounted for 3.56 kg CO2 day−1 and 6.91 kg CO2 day−1 for ADF and AE/AN respectively. This innovative study provides valuable insights into comparing the two above-mentioned strategies and a pilot for structuring and designing future studies comprehensively considering the environmental consequences of the process in future life cycle assessments.

Biochar Application Improved Sludge-Amended Landscape Soil Fertility Index but with No Added Benefit in Plant Growth

Co-application of sewage sludge (SS) with biochar in landscape/forestry soil is a common strategy for enhancing soil fertility and reducing the bioavailability of potential toxic elements (PTEs) derived from SS, such as Cd, Pb, Cu, Zn, and Ni. However, due to variability of biochar quality and uncertainties in responses of different plant species, whether the co-application benefits the landscape/forestry plant system remains elusive. Here, we tested the effectiveness of three types of biochar (SS-derived biochar (SB), rice straw-derived biochar (RB), and litter-derived biochar (LB)), which were added to soil amended with SS at 50% (w/w) at rates of 1.5%, 3%, and 4.5% as growth media for the landscape plant Aglaonema modestum (A. modestum). We analyzed the substrate’s physicochemical properties and assessed the alleviation of phytotoxicity by biochar application. A significant increase in the fertility index of substrate was observed in all the treatments with biochar addition. The addition of biochar reduced the potential mobility of PTEs while increasing their residual fraction in media. Nonetheless, it has been found that the addition of biochar has ineffective or even negative effects on A. modestum growth (height, biomass, root length) and nutrient absorption. Importantly, the reduction in root biomass and the increased activity of root antioxidant enzymes (SOD, POD, CAT, and MDA) indicate contamination stress of biochar on the roots of A. modestum. Toxic elements of concern—namely Cu, Cd, and Pb—were not significantly higher in tissues of A. modestum saplings planted in biochar-SS-amended soil. However, elevated levels of other elements that may pose toxicity concerns, such as Ni and Zn, increased in tissues at high biochar dosages. Based on the Entropy–Weight TOPSIS method, it was further confirmed that compared to the treatment without biochar, all treatments except for 3.0% LB application resulted in poorer A. modestum comprehensive growth. Our results emphasize the need for detailed research on the response of specific plants to biochar in specific environments, including plant adaptability and the unexplored toxicity of biochar, to understand the large variations and mechanisms behind these ineffective or negative effects before the large-scale co-utilization of SS and biochar in landscape/forestry soils.

Quantification of linear alkylbenzene sulphonates in complex sludge samples: Influence of matrix effects in calibration methods

Linear Alkylbenzene Sulfonates (LAS) are among the priority organic pollutants in sludge owing to their high concentrations, due to its use as a major cleaning agent (surfactant) in laundry detergents and household cleaning products, and to the concentration limits of 2,600 mg/kg outlined in the EU directive draft for land application of sludge. In this work, a method has been optimized and validated for the accurate quantification of LAS homologues C10-C13 in different types of samples in the sludge treatment and disposal process including primary, secondary, and digested sludge, compost, and soil. The type of matrix had a significant impact on the method’s validation process, resulting in the need of the use of distinct dilution factors for each matrix. Overall, the procedure propose involves a cost-effective and user-friendly technique that combines both extraction and clean-up in a single step (ultrasound-assisted extraction and dispersive solid phase extraction). Analytical determination is conducted using liquid chromatography-tandem mass spectrometry. The method demonstrated excellent accuracy (relative recoveries exceeding 84.5 % across all types of sludge samples) and the limit of quantification enables the measurement of LAS concentrations up to 1000 times lower than the concentration limits stipulated in the EU directive draft. For an accurate quantification, three calibration approaches were tested (external calibration, standard addition, and matrix-matched calibration). Standard addition was the preferred method for quantitative analysis. It helps mitigate matrix effects that could otherwise distort the accuracy of analyte measurements, making it crucial for quality control, especially in monitoring applications where matrix effects may introduce bias into concentration calculations.

Effective sludge management: Reuse of biowaste and sewer sediments for fired bricks

ABSTRACT This study partially replaced the clay with sewer sludge (SS) and rice husk (RH-SS) to make fired bricks. The brick samples were examed in terms of shrinkage, water absorption, and compressive strength. Besides, they were analyzed via XRD and metal extraction to determine the heavy metal residuals in the products. The results showed that it was possible to fabricate fired bricks using sewer sludge or rice husk-blended sludge with up to 30% by weight. These brick samples complied with the technical standard for clay brick production, in which the compressive strength was more than 7.5 MPa, water absorption was from 11–16%, and the linear shrinkage was all less than 5%. The rice husk addition helped mitigate the heavy metal residuals in the bricks and leaching liquid, in which all the values were lower than the US-EPA maximum concentration of contaminants for toxicity characteristics. Implications: Previous studies have proved the possibility of mixing sewage sludge from different origins (sewage sludge, river sediment, canal sediment, sewer sediment, etc.) with clay and some wastes to make bricks. In which, mostof the studies used sewage sludge from wastewater treatment plants, very fewdealt with lake/river or sewer sediment. This study shall be the first to study the possibility of employing sewer sediments with the addition of rice husk powder to achieve two targets, including (1) the reuse of biowaste and sludge for brick fabrication and (2) the reduction of heavy metals in final calcined bricks. Different ratios of the rice-husk blended sewer sludge (RH-SS) – clay mixture shall be tested to find the optimized compositions. The results showed that it was possible to fabricate fired bricks using sewer sludge or rice husk-blended sludge with up to 30% by weight, which meant reduce 30% of clay in the brick production. The final products were proved to meet the quality standard in terms of compressive strength (more than 10 MPa), water absorption(from 11–16%), and the linear shrinkage (less than 5%). Larger scale of this study can be an evident to recommend for policy change in the waste reuse in construction field.

Exploiting the Thermotolerance of Clostridium Strain M1NH for Efficient Caproic Acid Fermentation from Ethanol and Acetic Acid.

A novel thermotolerant caproic acid-producing bacterial strain, Clostridium M1NH, was successfully isolated from sewage sludge. Ethanol and acetic acid at a molar ratio of 4:1 proved to be the optimal substrates, yielding a maximum caproic acid production of 3.5g/L. Clostridium M1NH exhibited remarkable tolerance to high concentrations of ethanol (up to 5% v/v), acetic acid (up to 5% w/v), and caproic acid (up to 2% w/v). The strain also demonstrated a wide pH tolerance range (pH 5.5-7.5) and an elevated temperature optimum between 35 and 40°C. Phylogenetic analysis based on 16S rRNA gene sequences revealed that Clostridium M1NH shares a 98% similarity with Clostridium luticellarii DSM 29923T. The robustness of strain M1NH and its efficient caproic acid production from low-cost substrates highlight its potential for sustainable bio-based chemical production. The maximum caproic acid yield achieved by Clostridium M1NH was 1.6-fold higher than that reported for C. kluyveri under similar fermentation conditions. This study opens new avenues for valorizing waste streams and advancing a circular economy model in the chemical industry.

Effect of low-temperature thermal-alkali pre-treatment on waste activated sludge solubilisation

The study was aimed to examine the effects of alkaline and thermal-alkaline pre-treatment on sewage sludge solubilisation with different alkali and its doses ranging from 40 mg alkali/g TS to 120 mg alkali/g TS. Initially, the effect of alkali pre-treatment was monitored with four alkali at room temperature, to further enhance soluble chemical oxygen demand (sCOD) and reduce treatment time, thermal-alkaline pre-treatment was performed with varying temperature from 40 to 70 °C. To explore and optimise the effects of temperature, alkali, and alkali doses on COD solubilisation, response surface methodology was employed. Statistical analysis of the variance was conducted to identify the relationship between experimental data and the proposed model. The thermal-alkaline process was optimised for maximum COD solubilisation with optimal conditions achieved at 65.61 °C of 66.57 mg alkali /g TS for NaOH and 27 °C of 20 mg/g TS for KOH. The maximum COD solubilisation achieved at these optimised conditions for NaOH and KOH was 21.28 % and 16.13 %, respectively. The results demonstrated a significant improvement in protein and carbohydrate concentration and a 16–20 % reduction in sludge solid content after thermal-alkali pre-treatment.

Removal of Cefuroxime from Soils Amended with Pine Bark, Mussel Shell and Oak Ash

The global increase in antibiotics consumption has caused hazardous concentrations of these antimicrobials to be present in soils, mainly due to the spreading of sewage sludge (or manure or slurry) and wastewater, and they could enter the food chain, posing serious risks to the environment and human health. One of these substances of concern is cefuroxime (CFX). To face antibiotics-related environmental pollution, adsorption is one of the most widely used techniques, with cost-effective and environmentally friendly byproducts being of clear interest to retain pollutants and increase the adsorption capacity of soils. In light of this, in this work, three low-cost bioadsorbents (pine bark, oak ash, and mussel shell) were added to different soil samples (at doses of 12 and 48 t/ha) to study their effects on the adsorption of CFX. Specifically, batch experiments were carried out for mixtures of soils and bioadsorbents, adding a range of different antibiotic concentrations at a fixed ionic strength. The results showed that the addition of pine bark (with pH = 3.99) increased the adsorption to 100% in most cases, while oak ash (pH = 11.31) and mussel shell (pH = 9.39) caused a clearly lower increase in adsorption (which, in some cases, even decreased). The Freundlich and linear models showed rather good adjustment to the experimental data when the bioadsorbents were added at both doses, while the Langmuir model showed error values which were too high in many cases. Regarding desorption, it was lower than 6% for the soils without bioadsorbents, and there was no desorption when the soils received bioadsorbent amendments. These results show that the addition of appropriate low-cost bioadsorbents to soils can be effective for adsorbing CFX, helping in the prevention of environmental pollution due to this emerging contaminant, which is a result of clear relevance to environmental and human health.

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.

Co-digestion’s perpective on biogas production from sewage sludge and food waste: a systematic review

Co-digestion’s perpective on biogas production from sewage sludge and food waste: a systematic review

Effects of Pyrolysis Temperature on Biochar Physicochemical and Microbial Properties for H2S Removal from Biogas

Sludge is produced in sewage treatment plants and is still a problematic waste type after anaerobic digestion. A sustainable sludge management strategy would be to pyrolyze it and obtain biochar suitable for use in biofilters. This article examines the physical and chemical properties of biochar obtained by pyrolyzing sewage sludge at a temperature of 300–600 °C. The pyrolyzed sludge was used in the biofilter as a filler. The results demonstrated biochar packing materials after pyrolysis at 300 °C, 400 °C, 500 °C, and 600 °C, which exhibited porosities of 35%, 42%, 67%, and 75%, respectively. During the research study, it was established that the biofilter showed excellent efficiency (between 55 and 99 percent) when using carbon pyrolyzed at temperatures of 500 °C and 600 °C. In this study, the average growth rates of the number of sulfur-oxidizing microorganisms were 1.55 × 104 CFU/g at the first stage of the biofilter, 2.63 × 104 CFU/g at the second stage, 3.65 × 104 CFU/g at the third stage, 5.73 × 104 CFU/g at the fourth stage, and 2.62 × 104 CFU/g at the fifth stage. The number of sulfur-oxidizing microorganisms in the packing bed of biofilters during the 60-day period of the experiment constantly increased. The experimental results of H2S purification in biogas were compared with mathematical modeling results. These comparative results revealed a consistent trend: the model-estimated filter efficiency also reached 70–90 percent after 60 days of investigation.

Binary solid wastes derived clinker: Raw feed system design validation and thermodynamic simulation investigation

Solid waste derived clinker design methodology was established based on thermodynamic simulation and experiment validation via the recycling of incinerated sewage sludge ash (ISSA) and recycled concrete fine (RCF). Compared with 1000 °C and 1100 °C, 1200 °C was the optimum temperature for C2S-rich clinker synthesis due to the highest simulated belite content after sintering. A utilization rate of 95 % was achieved, accomplishing the maximization of solid waste recycling. Due to the CaCO3 phase formation by the reaction of high-content belite (46.8 %) with CO2, carbonated 1200ARS eco-cement showed higher compressive strength than OPC and other eco-cements. The lowest porosity (18.1 %) with dense microstructure was also obtained by carbonated 1200ARS. Benefiting from the high CO2 reactivity of belite, 1200ARS displayed the optimum CO2 sequestration capacity with a higher carbonation degree (30.1 %) than other batches, providing a promising direction for future development of the low-carbon cement industry to achieve environmental sustainability.

Study on the overall performance of e-waste dismantling industry polluted cultivated land utilization from a holistic view

The utilization of heavy metal-organic polluted cultivated land caused by the e-waste dismantling industry was affected by multi-dimensional factors. Thus a comprehensive evaluation of these multi-dimensional impacts was necessary for the technical selection and solution of cultivated land utilization. This study attempted to conduct a total benefit simulation analysis on the redevelopment of polluted cultivated land, which was of great significance to decision-making. With a systematic framework designed including the casual relations between components, a system dynamics model was constructed to simulate the technological, economic, and ecological benefits of different polluted cultivated land-used modes, along with which a questionnaire was designed to investigate and analyze the associated social effects. Based on these, the total benefits of the land-use mode were evaluated and optimized within the framework of the “technological-economic-ecological-social” evaluation system. This study included microscale, mesoscale, and macroscale, with multi-dimensional and complex influencing factors, and had advanced research value. The results of the system dynamics model simulation showed that remediation plants played a decisive role in pollutants removal. The flower industry had the highest net present value, but its ecological performance was poor. The overall analysis showed that the scenario of utilization after remediation had the highest performance score, which was attributed to high pollutant removal, low cost, and high carbon sink. This study was meaningful for providing research ideas of comprehensive benefits of polluted cultivated land utilization and also helpful for decision-making. This paper also provided research ideas for other industries such as contaminated site remediation and sewage sludge treatment.