Sludge Treatment Research Articles

Effect of Combined Application of Treated Sewage Sludge and Inorganic Fertilizers on Yield and Yield Attributes of Maize Crop (Zea mays L.)

Effect of Combined Application of Treated Sewage Sludge and Inorganic Fertilizers on Yield and Yield Attributes of Maize Crop (Zea mays L.)

Soil application of activated hydrochar derived from sewage sludge enhances plant growth and reduces nitrogen loss

Sewage sludge treatment and disposal is a considerable environmental and economic burden, and is considered a major global challenge. Here, sewage sludge treatment and disposal were studied with a focus on hydrothermal carbonization and the use of hydrochar (HC) as a soil amendment after Fenton-reaction activation. The underlying hypothesis was that enhanced adsorption of nutrients (e.g., ammonium) by activated HC (AHC) increases their availability, thus enhancing plant growth and reducing environmental impacts such as greenhouse gas emission and N leaching relative to conventional soil-amendment techniques.The impact of AHC on lettuce plant growth, N leaching, ammonia volatilization, soil trace-gas emissions, and respiration was studied in a net-house planting experiment. Four treatments were tested in quadruplicate using sandy loam soil with addition of either AHC, urea fertilizer, or AHC plus urea, and a control with no amendment.Activation-induced changes in AHC surface properties (indicated by SEM and XPS analyses) resulted in an NH4+ adsorption capacity 60 % higher than that of untreated HC. The AHC + urea soil treatment yielded the most enhanced plant growth, followed by urea and AHC treatments with comparable growth rates. Least growth occurred in the control with no amendment. Nitrogen loss through gas emissions, per kg of lettuce, was lowest with AHC + urea treatment, although its mean N emission as nitrous oxide (N2O) was notably higher at 2.3 mg N2O-N kg−1 than for other treatments (∼0.4 mg N2O-N kg−1). Dissolved-N leaching was reduced by up to four times with AHC treatment due to its higher NH4+ adsorption capacity, indicating reduced environmental impact of the AHC amendment.AHC application is therefore considered a sustainable soil amendment, enhancing plant growth and reducing N loss and sewage environmental impact.

Reviewing Improved Anaerobic Digestion by Combined Pre-Treatment of Waste-Activated Sludge (WAS)

The anaerobic digestion of wastewater treatment sludge (WAS) produces a “green” biogas while reducing the amount of residual sludge. To increase the yield of biogas, several individual or combined pre-treatment methods of WAS can be used. These pre-treatment methods substantially reduce the amount of volatile suspended solids (VSSs) and their associated total chemical oxygen demand (TCOD). Pre-treating the sludge will increase the methane yield by 15 to 30%. Although the individual methods have been dealt with in research and large-scale operations, the combined (hybrid) methods have not previously been reviewed. Here, different hybrid treatment methods are reviewed, including (1) thermochemical hydrolysis pre-treatment, using an alkaline or acid addition to enhance solubilization of the sludge cells and increase biogas production; (2) alkaline and high-pressure homogenizer pre-treatment, combining a chemical and mechanical treatment; (3) alkaline and ultrasound pre-treatment, capable of solubilizing organic sludge compounds by different mechanisms, such as the fast and effective ultrasound disruption of cells and the increasing effect of the alkaline (NaOH) treatment; (4) combined alkaline and microwave pre-treatment, which enhances sludge solubilization by at least 20% in comparison with the performance of each separate process; (5) microwave (MW) and peroxidation pre-treatment of WAS suspended solids (SSs), which are quickly (<5 min) disintegrated by MW irradiation at 80 °C; (6) ultrasound and peroxidation pre-treatment, with ozone and peroxides as powerful oxidizing agents; and (7) pulsed electric field (PEF) pretreatment. All literature findings are assessed, discussing relevant operation conditions and the results achieved.

Carbon footprint analysis of wastewater treatment processes coupled with sludge in situ reduction

The goal of this study was to assess the impacts or benefits of sludge in situ reduction (SIR) within wastewater treatment processes with relation to global warming potential in wastewater treatment plants, with a comprehensive consideration of wastewater and sludge treatment. The anaerobic side-stream reactor (ASSR) and the sludge process reduction activated sludge (SPRAS), two typical SIR technologies, were used to compare the carbon footprint analysis results with the conventional anaerobic - anoxic - oxic (AAO) process. Compared to the AAO, the ASSR with a typical sludge reduction efficiency (SRE) of 30 % increased greenhouse gas (GHG) emissions by 1.1 - 1.7 %, while the SPRAS with a SRE of 74 % reduced GHG emissions by 12.3 - 17.6 %. Electricity consumption (0.025 - 0.027 kg CO2-eq/m3), CO2 emissions (0.016 - 0.059 kg CO2-eq/m3), and N2O emissions (0.009 - 0.023 kg CO2-eq/m3) for the removal of secondary substrates released from sludge decay in the SIR processes were the major contributor to the increased GHG emissions from the wastewater treatment system. By lowering sludge production and the organic matter content in the sludge, the SIR processes significantly decreased the carbon footprints associated with sludge treatment and disposal. The threshold SREs of the ASSR for GHG reduction were 27.7 % and 34.6 % for the advanced dewatering - sanitary landfill and conventional dewatering - drying-incinerating routes, respectively. Overall, the SPRAS process could be considered as a cost-effective and sustainable low-carbon SIR technology for wastewater treatment.

Preparation and environmental impact assessment of NI-N modified sludge activated carbon electrode materials

With the activated sludge in urban sewage treatment as the precursor material, the carbon material is prepared by high temperature carbonization, and then the nickel-nitrogen modified activated carbon material is prepared by potassium hydroxide activation, urea and nickel doping. Electrochemical experiments with activated carbon materials show that it has a good specific capacitance of 345.9 F/g at 1 A/g current density. After 2 000 cycles at a current density of 10 A/g, it still maintains 84.53% capacitance, shows found that the main source of influence is the power consumption in the process of sludge carbonization.

The impact of struvite presence on the thermal decomposition of sewage sludge, including formation of NOx emissions

Monoincineration of sewage sludge (SS) is becoming a prevailing type of SS treatment due to its contamination and the ability to achieve enriched concentration of valuable inorganics in the end ash. In order to improve the recovery potential, particularly of inorganic, phosphorous (P) bearing species, thermal transformations of organic as well as inorganic SS compounds have to be considered. While important gains in predictive capability have already been made through extensive description of organic part decomposition, P is mostly present in the inorganic part of SS, together with notable amount of nitrogen (N). Current models consider these species in a simplified manner, making the ability to predict P and N fate during thermal treatment limited. The present work focuses on development and implementation of a one step reaction kinetics mechanism for struvite, a common P and N bearing compound in SS, which also presents an important route for P and N recovery. The new mechanism is implemented into an existing SS organic fraction decomposition mechanism and validated using 0D multiphase reactor simulations in Chemkin software. Results reveal up to 10 s faster temperature increase and decomposition of SS with the presence of struvite due to emission of NH3 and H2O occurring already from 350 °C onwards. The NH3 emissions are especially important as they lead to higher NOx formation. The work presents large potential for improving thermal decomposition prediction as well as emission mitigation strategies if struvite is included in the thermal decomposition models of SS. The developed methodology allows efficient implementation of also other P and N bearing species in the inorganic part of kinetic mechanism.

Enrichment of nutrients from anaerobically digested centrate minimizing microplastics content using a combination of membrane processes

Centrifuge effluent, or centrate, is a liquid stream generated in the sludge line of wastewater treatment plants in the sludge dewatering process. Nutrients are solubilized in the anaerobic digestion of the sludge, mainly in the form of ammonium-nitrogen and phosphates. Thus, when the dewatering of the digested sludge is performed (usually by centrifugation), a sludge liquor stream enriched in nutrients is generated. However, it also contains microparticles, including microplastics, since most of the microparticles from the wastewater are transferred to the sludge treatment line in wastewater treatment plants. In this work, microplastics in centrate have been analyzed (counted and identified), and membrane technologies (ultrafiltration and forward osmosis) have been applied to concentrate nutrients and to obtain a microplastic-free stream for further nutrient recovery. Two alternative configurations have been compared, changing the application order of these processes. The results showed that obtaining a stream with a concentration higher than 6000 mg/L of ammonium has been possible by using ammonium sulfate (150 g/L) as a draw solution in the forward osmosis process. On the other hand, as a consequence of the ultrafiltration application, microparticles were concentrated in the reject stream up to 800 microparticles/L. At the same time, the permeate presents a lower concentration of microplastics without reducing the concentration of the nutrients. In this way, this pioneering study enables the production of a nutrient-enriched stream with reduced microplastic concentrations, that could be applied to the agricultural soil as biofertilizer.

Sludge-derived biochar improves sludge electro-dewatering performance: Conductivity analysis

The application of Coupled Electro-dewatering (EDW) with Carbon Materials has demonstrated significant potential in the efficient deep dewatering and solid-liquid separation of activated sludge. In this study, Fe-loaded sludge-based biochar (SBB) was synthesized via FeCl3 impregnation, and the physicochemical properties of SBB were comprehensively characterized using XRD, Raman spectroscopy, BET analysis, FTIR, and XPS. The results demonstrated that the elevation of pyrolysis temperature facilitated the formation of graphitic carbon and graphitic nitrogen structures within the SBB, thereby augmenting current transport in the solid phase of the sludge. Meanwhile, the Fe material present on the surface of SBB undergoes dissolution in the sludge supernatant, thereby releasing Fe ions into the liquid phase and augmenting the conductivity of the liquid system. After the addition of SBB, the sludge showed an increase in Zeta potential and conductivity, along with a pH shift towards acidity, thus improving the conditions for EDW processes. The results obtained from the EDW analysis demonstrated that the application of SBB@800 significantly contributed to the enhancement of both initial current and dewatering limit, leading to a notable reduction in sludge water content from 57.2 % to 40.7 %. This study emphasizes the influence of temperature on physicochemical properties of SBB and its role in EDW, proposing an environmentally friendly approach for advanced sludge treatment using carbon materials and EDW synergy while providing insights for designing carbon materials to enhance EDW performance.

Optimization of Microbial Fuel Cell Operational Parameters for the Treatment of Brewery Sludge

AbstractThis study investigates the potential of a salt bridge‐mediated microbial fuel cell (MFC) for power generation and wastewater sludge treatment in breweries. Unlike traditional “one‐parameter‐at‐a‐time” methodologies, this study uses a three‐variable Box–Behnken design response surface methodology to optimize critical MFC operational parameters. The effects of parameters such as solution pH, salt bridge molarity, and temperature were studied in the range of 4 to 10, 1 to 5 M, and 20 to 45 g L−1. The optimum operating parameters were found to be solution pH of 5.853, salt bridge molarity of 3.343 M, and temperature of 32.5 °C for chemical oxygen demand and biological oxygen demand removal efficiencies of 92.485 % and 88.51 %, respectively. Temperature was found to be the most significant factor affecting the reactor's performance.

Investigating the Potential of Water Treatment Sludge for Improvement of the Geotechnical Properties of Gypseous Soil

Investigating the Potential of Water Treatment Sludge for Improvement of the Geotechnical Properties of Gypseous Soil

Sustainable Sludge Management in China: Quantifying GHG Emissions and Exploring Its Reduction Strategies

This study aims to evaluate the emissions of greenhouse gases (GHGs) stemming from the sludge treatment sector in China and to investigate the feasibility of novel technologies in curtailing these emissions, with the aim of fostering sustainable sludge management methodologies. Employing a life-cycle assessment (LCA) methodology, the research computed the comprehensive GHG emissions resulting from sludge treatment, taking into consideration diverse elements such as treatment techniques (e.g., landfills, incineration, and land application) and the geographical variations among China’s 660 municipalities. Findings indicate that the total amount of GHG emissions from sludge treatment amounted to 18.54 Mt CO2-eq in 2017, with incineration registering the highest emissions (10,011.53 kg CO2-eq/t dry sludge (DS)), followed by landfills (717.51 kg CO2-eq/t DS) and land application (276.41 kg CO2-eq/t DS). The geographical dispersion of emissions characteristics reveal notable regional disparities, with the top 1% of cities responsible for 34.2% of the overall emissions. The concentration of emissions in the top 1 percent of cities underscores the necessity for tailored mitigation measures that consider localized sustainable development challenges. Principal component analysis (PCA) demonstrates that economic determinants and treatment scales exert substantial influence on emissions, underscoring the imperative of aligning Sustainable Development Goals (SDGs) with economic advancement. To curtail the carbon footprint associated with sludge treatment and enhance sustainability, the study evaluated the emission mitigation potential and expenses of diverse technologies, encompassing thermal conversion, anaerobic digestion, hydrothermal treatment, and wet oxidation. These technologies have the capacity to slash GHG emissions by 0.09–0.46 t CO2-eq/t DS in comparison to traditional approaches, while concurrently advancing resource recuperation and principles of circular economy. For instance, gasification could diminish GHG emissions by 0.33–0.46 t CO2-eq/t DS, whereas anaerobic digestion could yield reductions of 0.09–0.30 t CO2-eq/t DS. The implementation of these innovative technologies across 660 Chinese municipalities could potentially curtail total GHG emissions from sludge treatment by 15–40%. Nevertheless, further enhancements are imperative to refine their environmental and economic efficiency and guarantee enduring sustainability. By deploying these technologies and embracing optimization tactics, China’s sludge treatment sector can make a substantial contribution towards attaining national carbon neutrality objectives and advancing sustainable development.

Aerobic Granular Sludge Treatment of Piggery Wastewater: Solution to the Problem of Non-Filamentous Bulking and Analysis of Microbial Community Structure in Practical Application

Aerobic Granular Sludge Treatment of Piggery Wastewater: Solution to the Problem of Non-Filamentous Bulking and Analysis of Microbial Community Structure in Practical Application

Separation and recovery of elements from drainage water arising in soilless tomato cultivation − Application of electrocoagulation

Soilless tomato cultivation requires significant water and nutrient inputs, resulting in the generation of drainage water (DW) with varying macro- and micronutrient compositions. This poses challenges for effective nutrient’s reuse due to technological and economic constraints. This study investigates the feasibility of using electrocoagulation, employing aluminum electrodes, to treat DW. The experiment involved three different current densities (2 A/m2, 4 A/m2, and 8 A/m2) and a 24-hour hydraulic retention time (comprising 4 h of electrocoagulation followed by 20 h of stirring). Treatment performance, kinetics, sludge characteristics, and energy consumption were evaluated. The elemental composition of the electrocoagulation-treated DW, including P, N, S, Cl, Ca, Mg, K, Na, Mo, Mn, Fe, Zn, Cu, B, organic compounds, and Al, was analyzed. The results showed that higher current densities resulted in increased pollutant removal rates and efficiencies. Importantly, the electrocoagulation process facilitated phosphorus recovery at pH < 7.0, ranging from 95.3 ± 0.6 % (at 2 A/m2) to 99.9 ± 0.1 % (at 8 A/m2), with corresponding energy consumption between 6.03 kWh/kgP and 29.98 kWh/kgP. Electrocoagulation as a drainage water treatment not only offers phosphorus recovery, but can also recovery B, and – to a certain extent – S, Mg, K, Mn, Zn and Cu. Other elements, such as Na and Cl, remained at stable levels. This allows for the separation of valuable elements (P) from those that interfere with cultivation (Na, Cl). This research could contribute to the development of a precise treatment process to address nutrient and pollutant management challenges in agricultural wastewater.

From sewage sludge and lignocellulose to hydrochar by co-hydrothermal carbonization: Mechanism and combustion characteristics

This investigation focuses on fabrication of hydrothermal carbon (HTC) using the co-hydrothermal carbonization (Co-HTC) method from the raw materials of sewage sludge (SS) and lignocellulose. The as-prepared hydrochar (HC) was characterized and analyzed by using ultimate analysis, proximate analysis, scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, and Fourier transform infrared spectroscopy (FTIR) to investigate its fuel properties, surface morphology, and molecular structure. Particularly, the HC obtained from the Co-HTC process with pine sawdust as raw material exhibited several advantages in terms of carbon content (40.40 %), fixed carbon (FC) content (41.82 %), and high heating value (HHV, 14.87 MJ/kg). Synergistic effects were achieved from the components in the Co-HTC system, leading to increased carbon content, retention of organics, energy yield, HHV, and HC yield. Notably, the Co-HTC treatment of pine sawdust and SS demonstrated the most notable synergistic effect. Thermogravimetric analysis and combustion characteristic index (CCI) values showed that softwood lignin, represented by pine sawdust, exhibited better performance during combustion, with a CCI value of 21.78 (10−7 min−2 °C−3). In short, Co-HTC of hydrochar from lignocellulose and SS can represent a promising approach to resource utilization for obtaining solid fuel.

A Comparison of the Carbon Footprints of Different Digested Sludge Post-Treatment Routes: A Case Study in China

As the “carbon peaking and carbon neutrality” strategy advances, carbon emissions have gradually become a significant indicator in selecting and evaluating sewage and sludge treatment solutions. This study compared the carbon footprints of different digested sludge post-treatment routes, taking the Lu’an project in China as an example. Considering anaerobic digestion and digested sludge post-treatment options, the carbon footprints are as follows: 347.7 kg CO2 (land application) &lt; 459.7 kg CO2 (composting-involved land application) &lt; 858.4 kg CO2 (brickmaking). In general, land application was superior to brickmaking from the perspective of carbon footprints. The power consumption incurred by aerating and turning and the direct N2O and CH4 emissions during composting increase the composting-involved land application carbon footprint. However, digested sludge that is not subject to high-temperature sterilization and compost is phytotoxic and can be fetid, which is a limitation of its applicability. And the composted sludge has a lower N ratio and water content, so the same N input means more sludge usage, which is conducive to solving the disposal problem of large amounts of sludge. Thus, if possible, composting-involved land application should be a preference, and improvements to the technique are required to minimize energy consumption and direct N2O and CH4 emissions.

Enhanced methane production from waste activated sludge by potassium ferrate combined with thermal hydrolysis pretreatment.

Anaerobic digestion of waste activated sludge (WAS) was one of the directions of sludge treatment, but how to effectively improve the production of methane as a resource product of anaerobic digestion of sludge still needs further research. The study examined how the combination of potassium ferrate (PF) and thermal hydrolysis (TH) pretreatment affected methane production from sludge. The results demonstrated a positive synergistic effect on methane production with PF-TH pretreatment. Specifically, by employing a 0.05 g/g TSS (total suspended solids) PF in conjunction with TH at 80 °C for 30 min, the methane yield increased from 170.66 ± 0.92 to 232.73 ± 2.21 mL/g VSS (volatile suspended solids). The co-pretreatment of PF and TH has been substantiated by mechanism studies to effectively enhance the disintegration and biodegradability of sludge. Additionally, the variation of microbial community revealed an enrichment of active microorganisms associated with anaerobic digestion after treated with PF + TH, resulting in a total abundance increase from 11.87 to 20.45% in the PF + TH group.

Insight into the effect of CaO2 addition on the prevalence and removal of antibiotic resistance genes during anaerobic sludge fermentation under ambient conditions

This study investigated the effect of CaO2 and its related hydrolysis products on the prevalence and removal of antibiotic resistance genes (ARGs) during anaerobic fermentation of waste activated sludge (WAS) under ambient conditions. Comprehensive analyses were conducted to elucidate the mechanisms underlying the effects of CaO2 addition, focusing on the microbial community structure, host bacteria, cell membrane permeability and the interaction between ARGs and environmental factors. Results showed the alkalinity, oxidation and calcium of CaO2 synergistically contributed to the elimination of ARGs. The top ARGs, such as sulI, sulII, tetC, tetX and ereA, were effectively reduced by 43.9–84.9 % with CaO2 addition during the ambient anaerobic fermentation. Ca(OH)2 treatment also shows good effectiveness in removing typical ARGs, followed by H2O2 treatment, while NaOH treatment increases ARGs abundance and raise the risk of their transmission. Among the influencing factors, the abundance and diversity of microbial community, organic matters, calcium and pH were the primary factors for ARGs migration. The effective reduction of Proteobacteria was an important reason for the removal of typical ARGs, particularly sulfonamide resistance genes. CaO2 also downregulated the relative abundance of autoinducer and functional genes related to outer membrane proteins (OMPs) and ARGs dissemination, thereby inhibiting ARGs transmission. This work provides a deep insight into the advantage of CaO2 in reducing ARGs, thus expanding its potential application in sludge treatment and ARGs elimination.

Advancements in machine learning modelling for energy and emissions optimization in wastewater treatment plants: A systematic review

AbstractWastewater treatment plants (WWTPs) are high‐energy consumers and major Greenhouse Gas (GHG) emitters. This review offers a comprehensive global overview of the current utilization of machine learning (ML) to optimize energy usage and reduce emissions in WWTPs. It compiles and analyses findings from over a hundred studies primarily conducted within the last decade. These studies are organized into five primary areas: energy consumption (EC), aeration energy (AE), pumping energy (PE), sludge treatment energy (STE) and greenhouse gas (GHG). Additionally, they are further categorized based on learning type, the scale of application, geographic location, year, performance metrics, software, etc. ANNs emerged as the most prevalent, closely trailed by FL and RF. While GA and PSO are the predominant metaheuristic approaches. Despite increasing complexity, researchers are inclined towards employing hybrid models to enhance performance. Reported reductions in energy consumption or GHG emissions spanned various ranges, falling within the 0–10%, 10–20% and &gt;20% brackets.

Characteristics and aging of microplastics in waste activated sludge under persulfate and hydrothermal co-treatment: Impact of solid content and temperature

Activated persulfate and hydrothermal treatment (HTT) are often employed to treat waste activated sludge, which can improve the efficiency of subsequent sludge treatment and change the distribution of pollutants in the sludge. However, the impact of sludge solid content and temperature on the occurrence and aging of microplastics (MPs) during HTT remains poorly understood. This study investigated the effects of persulfate-HTT (SPS-HTT) co-treatment on the migration, occurrence, and aging of MPs in sludge with different solid contents (2% and 5% solid content). The results indicated that SPS-HTT co-treatment triggers both the disruption of sludge flocs and the melting deformation of MPs at high temperatures, leading to variations in the increasing trend of MP concentration in the solid-liquid phase at different solid contents. 5% solid content sludge showed a weak release of MPs from the solid phase. The proportion of fiber MPs first increased and then decreased with increasing temperature, while no significant changes were observed in the color and type of MPs. Higher temperature and solid content induced the melting deformation of MPs, exacerbated the aging of polypropylene MPs, and resulted in rough surfaces, higher carbonyl index, and variations in crystallinity. Moreover, the correlation between the carbonyl index and aging indicators increased with increasing solid content. The MP-derived dissolved organic matter under HTT primarily comprised soluble microbial by-products and humic acid-like substances. These findings underscore the significance of sludge solid content in affecting the migration and aging of MPs during HTT, and offer novel insights into the application of HTT to MP management in sludge treatment.

Efficient removal of toxic organics and reduction of Cr(VI) to Cr(III) from tannery sludge: A comparative study of microwave pyrolysis and conventional pyrolysis

The efficient and safe treatment of tannery sludge (TS) are causing significant concern. Pyrolysis stands as a pivotal technology in the realm of sludge treatment, offering the benefits of degrading organic matters within TS while simultaneously transforming the sludge into energy and other valuable substances. In order to develop an effective pyrolysis method with good resource recovery performance, this study employs microwave pyrolysis (MP) and conventional pyrolysis (CP) at temperatures ranging from 300 to 900 °C to investigate the transformation of chromium morphology. The results indicate that TS experienced a weight loss of 43 % during the pyrolysis process, with a combined average activation energy measured at 169.58 kJ/mol. MP, due to its more uniform and efficient heating, resulted in pronounced solid degradation, leading to increased pyrolysis gases. This enhanced the removal of organics at lower temperatures and contributed to the ring opening of aromatic hydrocarbons in the high-temperature segment. MP effectively reduced Cr(VI) to Cr(III) in TS, whereas CP showed relatively ineffective reduction of Cr(VI). Furthermore, metal compounds in TS treated by both MP and CP predominantly existed in the residue as FeCr2O4 and Cr2O3 at high temperatures. This suggests that more Cr(III) was immobilized in the pyrolysis residue. This study revalues the significance of MP as a promising treatment for TS, holding the potential for resource utilization.