Sludge Disposal Research Articles

Performance assessment and economic aspects for water reclamation from UASB reactor effluent: Influence of coagulant type and membrane pore size

ABSTRACT This paper investigates the influence of coagulant type in coagulation, flocculation and sedimentation processes and membrane pore size on the performance and economic aspects of water reclamation from UASB reactor effluent. The methodology involved laboratory-scale experiments using two different coagulant types (a modified tannin coagulant, TANm, and a polyaluminum chloride, PACl) and membrane filtration tests with microfiltration (MF) and ultrafiltration (UF). Compared to PACl, TANm had a smaller effect on the pH, consumed less alkalinity, and generated less sludge. However, PACl was more efficient in removing turbidity (89–97%), organic matter (70–72%), and phosphorus within the dosage range of 25 to 100 mg.L−1. Both membranes achieved high removal rates for turbidity and organic matter. Despite the higher flux decay, the MF system could have higher operating flux and lower fouling resistance. The operating costs were higher for the C/F systems, which was attributed to the cost of coagulants and sludge disposal. The system with MF membranes had a lower total cost, and the estimated payback period for the investment was between 0.73 to 0.24 years, based on the values charged for reuse water. This information can be used to optimize the design and operation of UASB-based water reclamation systems.

Synergistic treatment of sewage sludge and food waste digestate residues for efficient energy recovery and biochar preparation by hydrothermal pretreatment, anaerobic digestion, and pyrolysis

The safe disposal of sewage sludge (SS) and food waste digestate residues (DR) is a tough issue considering the difficulty of dewatering and the environmental risks from heavy metals and pathogens. This study combined hydrothermal pretreatment (HP), anaerobic digestion (AD), and pyrolysis to synergistically dispose of SS and DR to enhance dewaterability, recover energy, and prepare biochar with heavy metal immobilization. The results showed that the solid contents of centrifuged cakes increased after HP at 180 °C of SS with the addition of 25% and 50% mass fractions of DR. The centrate from co-HP had a high chemical oxygen demand (COD) and was further treated by AD at 37 °C, producing 193.75 and 210.39 mL/g CODinput (25 °C and 1 atm) of cumulative CH4 under the addition of 50% and 75% mass fractions of DR, respectively. The methanogenic types in AD converted from hydrogen utilization to acetic acid utilization with increasing DR ratio. Zn, Cu, Ni, and Pb were primarily left in the biochar after 50% mass fraction of DR was mixed in the HP combined with pyrolysis at 700 °C; the chemical fractionation of Zn, Cu, Cr, and Pb in the biochar increased to over 85% of the residual fractions, resulting in the lowest potential ecological risk index (15.22, low risk). The CH4 produced from the AD of the co-HP centrate (50: 50, w/w) can supply heat for the HP process, reducing the energy input by 89%. This co-disposal strategy can effectively recover carbon resources from solid wastes to reduce carbon emissions.

Energy and exergy analyses, and elemental distribution of microwave-assisted auger pyrolysis of textile dyeing sludge and furfural residue

Microwave-assisted pyrolysis has emerged as a promising treatment method for textile dyeing sludge (DS) and furfural residue (FR), demonstrating the potential to address environmental issues and harness their energy. In this study, microwave-assisted auger pyrolysis of DS and FR was conducted, and the mass balance, elements distribution, energy, exergy and sustainability analysis were investigated. The results indicated that the distribution ratios of carbon (46.14–76.29%), hydrogen (15.04–47.96%), and oxygen (3.62–36.55%) in chars decreased with increasing temperature. As the pyrolysis temperature increased during FR pyrolysis, there was a higher thermal energy loss and a decrease in energy efficiency, energy yield, and exergy efficiency. The pyrolysis temperature and the type of solid wastes are key factors in determining both energy efficiency and exergy efficiency. The energy/exergy utilization efficiencies for FR pyrolysis (57.03–82.24%/55.90–81.82%) surpassed those for DS pyrolysis (26.46–38.93%/23.35–36.65%). The highest energy and exergy efficiencies for DS (i.e. 38.93% and 36.65%) and FR (i.e. 82.24% and 81.82%) were achieved at 450 °C. FR pyrolysis had a lower environmental impact than DS pyrolysis. This study aimed to provide insights into the treatment and disposal of sludge and FR through microwave pyrolysis, considering both energy and exergy aspects.

Estimating national sludge generation and disposal from US drinking water and wastewater treatment plants

In the United States (U.S.), the management of sludges generated from drinking water and wastewater treatment are overseen by the state agencies and much of that information, especially quantities incinerated or landfilled, are not communicated to the U.S. Environmental Protection Agency (U.S. EPA). Instead, estimates of beneficial use or disposal of sludges have been periodically quantified through time- and resource-intensive surveys of facility operators. Simple methods to estimate annual sludge generation and disposal, informed by publicly available state-level data, were developed. The generation of drinking water treatment plant (DWTP) sludge was estimated using water supply data and a sludge generation factor (SGF) based on existing literature. A process-averaged SGF, 1.3% as wet-weight per gallons treated, resulted in 35–40 mmt dw sludge/year from 2000 to 2015, yielding 150 kg DWTP sludge dw/person-year. Based on publicly available data from 15 states, WWTP sludge was approximately 1–2% of landfilled waste composition. State-level data regarding the (1) generation or (2) disposal of municipal wastewater treatment plant (WWTP) sludges were used to extrapolate national estimates. From 2010 to 2020, the US generated (1) 7.5-6.8 or (2) 7.9–7.1 mmt dw WWTP sludge/year. National figures for WWTP sludge incineration could not be estimated based on limited data. The development of transparent and simple estimation methods that utilize publicly-available data will help improve generation, disposal, and recycling estimates at the national level.

Hybrid conditioning of ionic liquid coupling with H2SO4 to improve the dewatering performance of municipal sludge.

Municipal sludge generated from wastewater treatment plants can cause a serious environmental and economic burden. A novel hybrid conditioning strategy was developed to enhance the dewatering performance of sludge, employing 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C4mim][CF3SO3]) treatment combined with H2SO4 acidification. Following conditioning, the capillary suction time ( ), the specific resistance of filtration (SRF), and moisture content of the treated sludge were decreased to 1.99 ± 0.24 (s·L/g TSS), 1.33 ± 0.05 (1012m/kg), and 72.01 ± 0.94%, respectively. The results were superior to those achieved with sludge treated solely by H2SO4 acidification or [C4mim][CF3SO3] alone. The biomacromolecules within the sludge flocs were dissolved by [C4mim][CF3SO3], while simultaneously, the microorganisms were inactivated. Consequently, the colloidal-like structures of the sludge flocs were destroyed. Additionally, the ionizable functional groups of the biomacromolecules were instantly protonated by the introduced H+ ions, and their negative charges were neutralized during the H2SO4 acidification process. The presence of H+ ions promoted the weakening of electrostatic repulsion between the sludge flocs. As a result, an enhancement of sludge dewaterability was obtained after treatment with [C4mim][CF3SO3] and H2SO4 acidification. The finding of the intensification mechanism of sludge dewaterability brought by hybrid treatment of acidification and [C4mim][CF3SO3] provides novel insights into the field of sludge disposal.

Structural Analysis of Heat-Calcined Modified Sewage Sludge From WWTP in Gas Complex For Environmental Risk Assessment

Thermal processing of sewage sludge (SS) wastewater treatment plant WWTP has received increasing attention in recent years. Heat calcination valorise the carbon rich organic fraction of SS, while effectively reducing SS volume. The refractory metals (thermally stable, i.e. Zn, Cu and Cr) are less volatile at different temperatures at 200 and 400 °C of thermal processes and they are enriched in the residues. To gain insights into mineralogical analysis, physicochemical, microstructure properties and heavy metals ( HMs ) were characterized by proximate, ultimate field emission x-ray fluorescence ( XRF ), scanning electron microscopy ( SEM ), attenuated total reflectance-Fourier transform infrared ( ATR-FTIR ) spectroscopy, x-ray diffraction ( XRD ) and UV-vis spectrophotometer. Such analysis plays a crucial role in the effective management of WWTPs and in evaluating the environmental risks associated with the disposal of wastewater sludge’s. It aids in assessing the potential value of these sludge’s as fertilizer, considering factors such as the presence of potash and iron, for agricultural purposes, or as building materials, considering the presence of silica and calcium oxide. The assessment is carried out utilizing X-ray fluorescence (XRF) technology. Furthermore, a case study is included to illustrate typical situations in a WWTP, emphasizing the main challenges and limitations linked with ships, as well as wastewater management and disposal. Additionally, the specific scenario of gas complex GP1/Z is scrutinized to suggest a wastewater treatment solution, which involves evaluating potential locations for the treatment plant and determining the appropriate treatment methods to be implemented.

Modification of the coffee industry sludge-based adsorbent using acid treatment for the removal of tartrazine dye from aqueous solution

The massive amount of industrial sludge produced annually poses an environmental concern, and improper sludge disposal may harm the environment. To address this issue, sludge has been converted into a cost-effective adsorbent for treating wastewater containing dyes. This study aims to modify the coffee sludge-based adsorbent using various treatment methods for tartrazine dye removal. The raw sludge was modified through physical treatment (PT) via oven drying and calcination, chemical treatment (CT) using phosphoric acid and nitric acid, and physicochemical treatment (PCT) method. The modified sludge adsorbents were characterised using Micromeritics ASAP 2020 for nitrogen adsorption analysis. Subsequent batch adsorption experiments were performed using the best-modified adsorbent of PCTS-HNO3 prepared by physicochemical treatment method with nitric acid to assess the effect of various factors, including initial pH (3-11), adsorbent dosage (0.05-0.25 g/L), and initial concentration of tartrazine dye (25-100 mg/L), with a contact time of 2 hours. The best process conditions were achieved at 0.15 g/L of adsorbent dosage, initial pH of 3 and initial concentration of 50 mg/L with almost 100% dye removal. The characterization results revealed that the BET surface area of the modified adsorbent was significantly increased from 363.32 m2/g of RS to 599.64 m2/g for PCTS-HNO3 adsorbent. The Langmuir isotherm model provided an excellent fit to the adsorption isotherm data, with correlation coefficients R2 ≥ 0.99 and a maximum adsorption capacity (qmax) of 99.01 mg/g. The kinetic study observed that the adsorption process adheres remarkably well to the pseudo-second-order kinetic model, signifying chemisorption adsorption. The results of this study indicate that the modified coffee sludge-based adsorbent proves to be a viable and cost-efficient solution for eliminating tartrazine dye from aqueous solutions.

A Landlord/lady Perspective on Emptying and Transportation of Faecal Sludge in informal settlements of Eldoret town, Uasin Gishu County, Kenya

Emptying, transportation and disposal of faecal sludge in informal settlements of Eldoret Kenya is still a big challenge. This study aimed to identifying actors and factors determining emptying costs and constraints limiting improvement in service provision with the use of a questionnaire and a review of secondary data. A total of 35 respondents were issued questionnaires. The data showed that most of the households were using septic tanks as the preferred method of Onsite Sanitation Systems (OSS). The study also noted that there were no price regulations for faecal sludge emptying services. Through the study, it was found that the private exhausters were charging the customers exorbitantly and there was a need to create a regulatory framework to manage the costs. It was also found that due to the high-water table within the environs of Eldoret and Uasin Gishu County at large, there was a risk of groundwater contamination, especially for the neighbors who solely depended on water from their wells for their daily household use. It was established that the emptying charges were directly proportional to the capacity of the exhauster and the haulage distance to the wastewater treatment plant. In summary, the paper recommends adequate allocation of funds, the involvement of all key stakeholders, the creation of awareness and education in the FSM and the creation of a legal framework or policy governing the management and disposal of FS as we move towards the realization of SGD 6.

Degradation of tetracycline based on activated persulfate by microbial-induced calcium carbonate precipitation as templates modified sludge biochar

The template method is capable of enhancing the catalytic sites by controlling the size and properties of the material. However, the integration of the template and biological methods requires further development. In this study, an environmentally friendly modified sludge biochar (TBC) was successfully synthesized by modifying sludge with biosynthetic calcium precipitation as a template. TBC effectively activated peroxydisulfate (PDS), achieving a tetracycline (TC) removal efficiency of 95.07 %. Active species identification and electrochemical analyses confirmed that the main mechanism for TBC to activate PDS in degrading TC involved the non − radical pathway, including singlet oxygen (1O2) production and direct electron transfer. The CO functional group was the main active group to produce 1O2. Additionally, the adsorption of TBC also played a role in TC removal. Experimental results indicated that TBC exhibits significant stability and reusability. This study offers novel insights into utilizing the template method for PDS activation to degrade TC and presents a viable approach for the rational disposal of sludge.

Practical strategies of phosphorus reclamation from sewage sludge after different thermal processing: Insights into phosphorus transformation

In the context of circular economy and global shortage of phosphorus (P) fertilizer production, it is crucial to effectively recover P during the treatment and disposal of sewage sludge (SS). Although thermal treatment of SS has been widely applied, a targeted P reclamation route is not yet well established. This study has comprehensively investigated and compared the physicochemical properties of SS and solid residues (hydrochar (HC), biochar (BC), sewage sludge ash (SSA), hydrochar ash (HCA), and biochar ash (BCA)) after application of three typical thermal treatment techniques (i.e., hydrothermal carbonization (180‒240 °C), pyrolysis (400‒600 °C) and combustion (850 ℃). P speciation and transformation during thermal processes were extensively explored followed by a rational proposal of effective P reclamation routes. Specifically, thermal processing decomposed organic P and converted non-apatite P to apatite P. Orthophosphate-P was found to be the main species in all samples. Physicochemical properties of the resulting thermal-derived products were significantly affected by the thermal techniques applied, thereby determining their feasibility for different P reclamation purposes. In particular, ash is not recommended for agricultural use due to higher harmful metals content, while acid leaching can be an alternative solution to synthesize non-Fe-containing P products because of the lower co-dissolved Fe content in the leachate. HC and BC offer the option for synthesis of Fe containing products. Eventually, HC and BC demonstrate great potential for agriculture application, however, a comprehensive risk assessment should be conducted before their real-world applications.

Human and ecotoxicological risk assessment of heavy metals in polymer post treatment sludge from Barekese Drinking Water Treatment Plant, Kumasi

The disposal of polymer post-treatment sludge (PTS) from Barekese Water Treatment Plants (WTPs) as organic fertilizer and aquatic feed is a common practice in Ghana, necessitating a thorough evaluation of its ecological and human health risks. This study aims to assess the suitability of PTS samples for soil amendment and fish feed, scrutinizing potential hazards to consumer health and soil. PTS samples were collected from five distinct lateral sections of three clariflocculator tanks. Potentially toxic metals such as Cd, Zn, Pb, Cu, Ni, and Cr were determined using a flame atomic absorption spectrophotometer. The mean concentration of 7.82 ± 2.43, 0.31 ± 0.021, and 0.78 ± 0.042 mg/kg for Mn, Zn, and Pb respectively. The concentrations of Ni, Cr, and Cd were below their detection limits (BDL) in all PTS samples. Upon detailed exposure assessment, ingestion emerged as the primary exposure route for both adults and children, with non-cancer risks (NCR) determined to be below 1 for both age groups. Additionally, an exploration of potential cancer risks (CR) associated with heavy metal exposure in the PTS samples revealed values below the tolerable intake levels ranging from 10−4 to 10−6 for both adults and children (10−8 and 10−9, respectively). This study also employs various ecological indices, such as Nemerow's synthetic pollution index (PN), single factor pollution index (PI), geo-accumulation index (Igeo), contamination factor (CF), potential ecological risk index (PERI), pollution load index (PLI), polymetallic contaminant index (IPD), and ecological risk index (ERI). These indices consistently highlight a low contamination status and ecological sensitivity. Consequently, the study indicates that the presence of metals in the PTS samples does not pose a significant threat to the surrounding environment and human health. Furthermore, this research underscores the inadequacy of relying solely on regulatory limit values in assessing the health risks of waste materials. Such comprehensive assessments are crucial for safeguarding aquatic and human populations.

High-Temperature Ash Melting and Fluidity Behavior upon the Cocombustion of Sewage Sludge and Coal.

Wastewater treatment produces a large amount of sludge, where the minimizing of the disposed sludge is essential for environmental protection. The co-combustion of sludge with coal is a preferable method for sewage sludge disposal from the economic and environmental perspective. The co-combustion of sludge has been widely used in the industry with the advantages of large processing capacity. The melting characteristics of ash are an important criterion for the selection of the co-combustion methods and furnace types. In this study, two types of sludge and four types of coal with different ash melting points were selected, where the ash melting behavior upon co-combustion is investigated by experimental and thermodynamical approaches. Especially, the slag fluidity upon co-combustion is explored via a modified inclined plane method. It has been found that the presence of SiO2 and CaO in sludge substantially enhances its fusion temperature owing to the high content of CaO, while SiO2 acts as a solvent, facilitating the co-melting of other oxides and raising the sludge fusion temperature. Fe2O3 exhibits a specific mass fraction within the range of 10-20%. Furthermore, the presence of CaO and SiO2 prohibits the flow ability of the slag at high temperatures, and Fe2O3 promotes the flow ability for sludge at high temperatures. With increasing base/acid ratio, the sludge flow velocity increases remarkably and peaks at 1.6. The interaction between Fe-Ca and Si-AI significantly affects the fluidity significantly. The findings are expected to optimize the condition of co-combustion and desirable furnace design for the incineration of sludge.

Global prevalence of organohalide-respiring bacteria dechlorinating polychlorinated biphenyls in sewage sludge

BackgroundMassive amounts of sewage sludge are generated during biological sewage treatment and are commonly subjected to anaerobic digestion, land application, and landfill disposal. Concurrently, persistent organic pollutants (POPs) are frequently found in sludge treatment and disposal systems, posing significant risks to both human health and wildlife. Metabolically versatile microorganisms originating from sewage sludge are inevitably introduced to sludge treatment and disposal systems, potentially affecting the fate of POPs. However, there is currently a dearth of comprehensive assessments regarding the capability of sewage sludge microbiota from geographically disparate regions to attenuate POPs and the underpinning microbiomes.ResultsHere we report the global prevalence of organohalide-respiring bacteria (OHRB) known for their capacity to attenuate POPs in sewage sludge, with an occurrence frequency of ~50% in the investigated samples (605 of 1186). Subsequent laboratory tests revealed microbial reductive dechlorination of polychlorinated biphenyls (PCBs), one of the most notorious categories of POPs, in 80 out of 84 sludge microcosms via various pathways. Most chlorines were removed from the para- and meta-positions of PCBs; nevertheless, ortho-dechlorination of PCBs also occurred widely, although to lower extents. Abundances of several well-characterized OHRB genera (Dehalococcoides, Dehalogenimonas, and Dehalobacter) and uncultivated Dehalococcoidia lineages increased during incubation and were positively correlated with PCB dechlorination, suggesting their involvement in dechlorinating PCBs. The previously identified PCB reductive dehalogenase (RDase) genes pcbA4 and pcbA5 tended to coexist in most sludge microcosms, but the low ratios of these RDase genes to OHRB abundance also indicated the existence of currently undescribed RDases in sewage sludge. Microbial community analyses revealed a positive correlation between biodiversity and PCB dechlorination activity although there was an apparent threshold of community co-occurrence network complexity beyond which dechlorination activity decreased.ConclusionsOur findings that sludge microbiota exhibited nearly ubiquitous dechlorination of PCBs indicate widespread and nonnegligible impacts of sludge microbiota on the fate of POPs in sludge treatment and disposal systems. The existence of diverse OHRB also suggests sewage sludge as an alternative source to obtain POP-attenuating consortia and calls for further exploration of OHRB populations in sewage sludge.7vWBgxzBnCPA6QWxMbshMgVideo

Synchronous in-situ sludge reduction and enhanced denitrification through improving electron transfer during endogenous metabolisms with Fe(Ⅱ) addition

The creation of large amounts of excess sludge and residual nitrogen are critical issues in wastewater biotreatment. This study introduced Fe(II) into an oligotrophic anaerobic reactor (OARFe) that was implemented to modify an anoxic-oxic process to motivate in-situ sludge reduction and enhance denitrification under an effective electron shuttle among organic matter, nitrogen, and Fe. The addition of 15 mg L−1 Fe(II) resulted in a sludge reduction efficiency reached 32.0% with a decreased effluent nitrate concentration of 33.3%. This was mostly attributed to the electron transfer from Fe(II) to organic matters and nitrogen species in OARFe. The participation of Fe(II) led to the upregulation of Geothrix and Terrimonas, which caused active organic matter hydrolysis and cell lysis to stimulate the release of extracellular polymeric substances (EPS) and substance transfer between each layer of EPS. The higher utilization of released bioavailable dissolved organic matter improved endogenous denitrification, which can be combined with iron autotrophic denitrification to realize multiple electron donor-based nitrogen removal pathways, resulting in an increased nitrate removal rate of 58.2% in the absence of external carbon sources. These functional bacteria associated with the transformation of nitrogen and carbon and cycling between ferrous and ferric ions were enriched in OARFe, which contributed to efficient electron transport occurred both inside and outside the cell and increased 2,3,5-triphenyltetrazolium chloride electronic transport system activity by 46.9%. This contributed to the potential operational costs of chemical addition and sludge disposal of Fe-AO being 1.9 times lower than those of conventional A2O processes. These results imply that the addition of ferrous ions to an oligotrophic anaerobic zone for wastewater treatment has the potential for low-cost pollution control.

Preparation of high-strength ceramsite from coal gangue and printing and dyeing sludge: Design strategy and modelling mechanism

Disposal and harmless utilization of coal-based solid waste, industrial sludge, and other bulk industrial solid waste is a sustainable and economical approach. In this study, coal gangue and printing and dyeing sludge were recycled to reconstruct high-strength ceramsite using a simple and scalable method. The high silica and alumina contents in coal gangue provided a foundation for ceramsite preparation, and the iron oxide in the printing and dyeing sludge could reduce the sintering temperature. The optimal synthesis conditions were as follows: Coal gangue: printing and dyeing sludge = 40:60; sawdust content of 9mass%; sintering temperature of 1175 °C for 15 min; and preheating temperature of 400 °C for 10 min. The designed ceramsite exhibited high compressive strength of 27.26 MPa, low 1-h water absorption of 1.26%, and bulk and apparent densities of 998 and 1597 kg/m3, respectively; thus, it was categorized as high-strength ceramsite. In determining the modelling mechanism during the sintering process, the silicon and aluminum distributions on the ceramsite surface obtained under the optimal preparation conditions was highly consistent, forming a silicoaluminate that supported the ceramsite strength. Sawdust addition increased the pore structure of the ceramsite. The heavy metals contained in the raw materials were well-immobilized in the ceramsite, indicating that the prepared ceramsites were free from secondary contaminants. Use of bulk solid waste to prepare high-strength ceramsites is a feasible resourceful and harmless utilization method, which is of great significance for bulk solid waste disposal and reuse.

Is Africa Ready to Use Phycoremediation to Treat Domestic Wastewater as an Alternative Natural Base Solution? A Case Study

This review outlines the potential of phycoremediation as a natural, cost-effective solution for domestic wastewater treatment in Africa, particularly focusing on its application in less densely populated and rural areas. The urgency of improving sanitation access, a key objective in both the Millennium Development Goals (2000–2015) and the Sustainable Development Goals (2015–2030), is underscored by the fact that half of Africa’s population suffers from diseases linked to inadequate water and sanitation facilities. South Africa, a focal point of this study, faces significant challenges in wastewater management. These include the limited capacity of wastewater treatment plants to handle the burgeoning wastewater volumes due to population growth, unregulated discharges causing fluctuating pollution levels, and high operational costs leading to improper sludge disposal and odor issues. Compounding these problems are frequent power outages, financial constraints impacting wastewater treatment plant operations and maintenance across Africa, and a lack of skilled personnel to manage these facilities.

Proposal of an Encapsulation-led Disposal Method for Tannery Sludge – A Circularity Approach

In the context of achieving sustainable development goals, continuously pushing possible extended research and attempting to implement the respective outcomes in expanding a circular economy for a broad range of products are high priorities. In this paper, we considered disposable tannery sludge as a matter of concern and proposed an innovative framework for placing tannery sludge in the economic value chain via an encapsulation technique-based construction product development. We used polypropylene plastic and a cement-water matrix as encapsulation materials, and the encapsulated tannery sludge bodies were tested for their drop strength, water absorbing behaviour, ability to leach chromium and tendency to lose weight upon ignition. Value of water absorption for the prepared double layered encapsulated tannery sludge bodies was 1.332%, the drop strength performance index arrived was 90% and 0.0001 µg/g of Chromium leaching was found in Toxicity Characteristic Leaching Procedure (TCLP) and shown 67% weight loss in thermogravimetric (TGA) analysis. The results confirmed the possibility of ecocompatible disposal and recirculation of tannery sludge for the sustainable production of building blocks in the form of encapsulated bodies. The outcomes of our work add upon a new perspective to the existing literature regarding the environmentally positive utilization of tannery sludge in the production of building blocks.

Comprehensive carbon footprint analysis of wastewater treatment: A case study of modified cyclic activated sludge technology for low carbon source urban wastewater treatment

To reduce pollution and carbon emissions, a quantitative evaluation of the carbon footprint of the wastewater treatment processes is crucial. However, micro carbon element flow analysis is rarely focused considering treatment efficiency of different technology. In this research, a comprehensive carbon footprint analysis is established under the micro carbon element flow analysis and macro carbon footprint analysis based on life cycle assessment (LCA). Three wastewater treatment processes (i.e., anaerobic anoxic oxic, A2O; cyclic activated sludge technology, CAST; modified cyclic activated sludge technology, M-CAST) for low carbon source urban wastewater are selected. The micro key element flow analysis illustrated that carbon source mainly flows to the assimilation function to promote microorganism growth. The carbon footprint analysis illustrated that M-CAST as the optimal wastewater treatment process had the lowest global warming potential (GWP). The key to reduce carbon emissions is to limit electricity consumption in wastewater treatment processes. Under the comprehensive carbon footprint analysis, M-CAST has the lowest environmental impact with low carbon emissions. The sensitivity analysis results revealed that biotreatment section variables considerably reduced the environmental impact on the LCA and the GWP, followed by the sludge disposal section. With this research, the optimization scheme can guide wastewater treatment plants to optimize relevant treatment sections and reduce pollution and carbon emissions.

Influence of adding strategy of biochar on medium-chain fatty acids production from sewage sludge

Production of medium-chain fatty acids (MCFAs) from sewage sludge has dual effects on valuable sludge disposal and renewable energy generation, while low efficiency limits its application. Biochar addition is considered an effective method to improve MCFAs production. In this study, the influence of biochar adding strategies (i.e., adding biochar in acidification or chain elongation (CE) processes) on MCFAs production was explored. Results showed that by adding biochar in the acidification process, MCFAs accumulation increased by over 114%, accompanied by the highest carbon conversion efficiency (134.66%) and electron transfer efficiency of MCFAs (94.22%) by the terminal CE. Adding biochar before the acidification process better enriched CE bacteria (e.g., Paraclostridium) and strengthened the dominant metabolic pathway. In contrast, the biochar added before the CE process priorly enriched the bacteria capable of degrading organics, like unclassified_f__Dysgonomonadaceae, norank_f__norank_o__OPB41, and Acetobacterium. The differences in excessive ethanol oxidation and short-chain fatty acids accumulation induced by varied adding strategies might be responsible for this.

Sludge‐based geopolymer materials: A review

AbstractSludge refers to the solid waste produced after sewage treatment. Unreasonable disposal of sludge can cause environmental pollution. Nonetheless, the sludge contains large amounts of silica‐aluminate, which has pozzolanic activity by treatment, and the sludge can be used as a sustainable building material. The previous studies have recommended that it is reasonable to produce geopolymers, that is, a green low‐carbon cementitious material with excellent mechanical and durability properties, from sludge. This article provides an overview of recent advancements in the study of sludge‐based geopolymer. It delves into the mechanisms behind alkali‐activated geopolymer, examines the feasibility of preparing geopolymer from sludge, and discusses various preparation methods. Additionally, it elaborates on the impact of incorporating different auxiliary materials on sludge‐based geopolymer. The comprehensive performance of sludge‐based geopolymer, encompassing mechanical properties, durability, and setting time, is thoroughly summarized. An environmental assessment is conducted, evaluating heavy metal leaching and the lifecycle of sludge‐based geopolymer. Finally, we briefly discuss some problems in the current research and development trends in the future on sludge‐based geopolymer. The aim of this article is to provide comprehensive support and guidance for both the research and practical engineering applications of sludge‐based geopolymer.