Organic Sludge Research Articles

Extraction and analysis of microplastics in wastewater sludges of a multi-product pulp and paper mill

Pulp and paper wastewater sludges are waste streams produced in major quantities across the world. The recycling of these organic sludges, for example to soil amendments, is desired in the circular economy but carries the risk of potential pollutants to be also introduced into the environment. Pulp and paper wastewater sludges have been scarcely studied matrices in the microplastic research due to their complex composition. In this study, we optimized an extraction process for microplastics from pulp and paper wastewater sludges, and quantified and characterized microplastics down to 20 μm in primary sludge and biosludge generated at the wastewater treatment plant of a multi-product pulp and paper mill in Finland. The occurrence of microplastics was high in primary sludge, 900–1600 microplastics g-1 dry weight, while the maximum number of detected microplastics in biosludge samples remained at 210 g-1 dry weight. Biosludge samples suffered from larger amounts of remaining solids after the extraction process, thus compromising the detection of smaller microplastics (<100 μm) and increasing the uncertainty related to the interpretation of the results. The most prevalent microplastic shape in all samples was fragment, and the most recurring polymer types were polyethylene and polypropylene, while a polystyrene-based copolymer represented approximately 10% of identified microplastics in primary sludge. The present study advances the development of microplastic analysis of the challenging pulp and paper wastewater sludges and brings novel information to the progressing discussion of their circulation potential.

Practical implications of adding powdered activated carbon in advanced wastewater treatment for process and plant design

ABSTRACT The addition of powdered activated carbon (PAC) in advanced wastewater treatment is increasingly recognized for its effectiveness in removing micropollutants from secondary effluents. This study investigates the implications of PAC dosing on treatment performance, particularly in terms of natural and effluent organic matter (OM) removal, turbidity reduction, and sludge characteristics. Results indicate that while PAC incorporation significantly enhances the adsorption of OM, it necessitates higher coagulant dosages to achieve comparable or improved turbidity levels. The study also reveals that lower pH levels facilitate the removal of OM, thereby increasing the availability of adsorption sites on PAC for micropollutants. Moreover, PAC addition results in the formation of larger, denser flocs that settle faster, leading to a reduction in sludge volume by approximately 20%. However, the increased coagulant demand and the subsequent rise in sludge volume highlight the need for the optimized process design to balance treatment efficiency with operational costs. This research provides valuable insights for the design and operation of wastewater treatment plants, emphasizing the importance of tailored coagulant dosing and process adjustments when integrating PAC into existing treatment frameworks.

Sea cucumber, Neostichopus grammatus, density and tank cleaning frequency affect abalone, Haliotis midae, growth in integrated multitrophic aquaculture

AbstractThe integrated multitrophic aquaculture (IMTA) of sea cucumber and abalone has been proposed as a potential bioremediation tool that stimulates increased abalone growth. This study assessed the role of sea cucumber stocking density and frequency of tank cleaning in IMTA on growth, water, and sludge bioremediation. The study was conducted for 16 weeks and was made of four treatments and four replicates; abalone cocultured with sea cucumber (low density—27: 1 g [abalone (ab): sea cucumber (sc)]) with tanks cleaned once a week (L1); abalone cocultured with sea cucumber (low density) with tanks cleaned twice a week (L2); abalone cocultured with sea cucumber (high density—15:1 g [ab:sc]) with tanks cleaned once a week (H1) and abalone cocultured with sea cucumber (high density) with tanks cleaned twice a week (H2). Rearing water nitrite was significantly lower (p = 0.001) at high stocking density of sea cucumbers, but sludge was unaffected. Tanks cleaned once weekly had higher sludge organic matter (p = 0.015) and sludge sulfur content (p = 0.020) and lower sludge carbon (p = 0.003) and nitrogen content (p = 0.049). At the end of the experiment, the stocking density of sea cucumber and frequency of tank cleaning affected abalone mean weight [p = 0.047; p = 0.011, respectively] without a significant interaction (p = 0.517). Abalone in H1 had a higher mean weight and shell length than abalone in L2 and H2 but was similar to those in L1. The stocking density and frequency of cleaning used in this study had no effect on the growth of sea cucumbers [p = 0.150; p = 0.470, respectively]. This study has shown that in an abalone–sea cucumber IMTA system, the stocking density of sea cucumber and the frequency at which tanks are cleaned influence abalone growth and bioremediation of the rearing water. Our result suggests H1 as the best density (ab:sc) and cleaning frequency. The tank cleaning frequency alone affects the tank sludge quality; tanks need not be washed too frequently as, in addition to causing animal stress, cleaning markedly increased carbon and nitrogen level of tank sludge. Both these effects are likely to negatively impact abalone growth.

A life cycle-based comparison study of sludge recycling technology incorporating subjective and objective evaluations

Inadequate land capacity and low sludge recycling rates have become a major global environmental challenge. Low organic sludge content and inadequate waste management policy mean that there is an urgent need to improve sludge solutions in China, which has the world's largest WWT capacity. Decision-makers face difficulties in selecting sustainable sludge-to-resource technologies given the existence of multiple social, environmental and economic objectives, and also in optimizing the allocation of sludge between different available technologies. In this paper we used a combined analytic hierarchic process (AHP) and entropy weight (EW) method to evaluate four recycling technologies: aerobic composting (AC), dry-incineration (DI), hydrothermal carbonization (HTC) and pyrolysis (PY), in terms of five economic, environmental and land resource indicators. The results showed that human toxicity was viewed as the most important indicator, while economic value of sludge product was the least important. HTC had the best overall performance of the evaluated technologies while PY was the least attractive. However, all four sludge recycling technologies showed greater potential for reducing carbon emissions and human toxicity than landfilling when sludge dewatering was included. Sensitivity analysis showed that adjustments to AHP weights only had a limited impact on the technical ranking. Finally, the result was further verified by a particle swarm optimization algorithm. Considering capacity constraints, the optimal proportion of the four technologies was found to be 44.9%, 42.7%, 0 and 12.4% for HTC, DI, PY and AC respectively. The paper demonstrates the effectiveness of combining subjective and objective methods to evaluate multiple indicators, providing decision-makers with a practical analysis framework for waste technology selection.

High Aluminum content in the aquifer of Camaçari industrial pole, state of Bahia, Brazil: Correlation with natural and anthropogenic environmental factors using multivariable analysis

&lt;p class="MsoNormal"&gt;This work used multivariable analysis to correlate groundwater high aluminum content in the area of the Liquid Effluent Treatment Center—CETREL of the Camaçari Industrial Pole, with natural environmental factors: geology, hydrogeology, precipitation, soil and vegetation; and anthropic: equipments of treatment and disposal of industrial waste from CETREL. This company made available data from 99 monitoring wells, period 2006–2016, with aluminum content above (0.2mg/L) the limit established by the Ministry of Health Ordinance Nº 888, 5 April 2021. Previous studies have indicated that there is no correlation of aluminum in groundwater of the Camaçari Industrial Pole with other metallic contaminants; also, that aluminum in the studied region is disseminated in the geological matrix, clayey soils, and poor and leached Cerrado soils. The Kruskal-Wallis test indicated significant correlation of high aluminum content with the treatment/disposal areas, geology, soil and vegetation; and no correlation with precipitation and hydrogeology. The four environmental factors indicating the highest average aluminum content (±C&lt;sub&gt;95%&lt;/sub&gt;), in descending order, are: Clayey Soils, Organic Sludge Farm I, Marizal Formation, and Herbaceous-Subshrub Vegetation. The multivariable analysis indicated that, the most influential factors on the high aluminum content in groundwater of the CETREL region, are all ultimately associated with the leaching of aluminum present in the solid matrix. As CETREL processes are not correlated with aluminum residues, the results were an important information for the company environmental managers.&lt;/p&gt;

High Aluminum content in the aquifer of Camaçari industrial pole, state of Bahia, Brazil: Correlation with natural and anthropogenic environmental factors using multivariable analysis

&lt;p class="MsoNormal"&gt;This work used multivariable analysis to correlate groundwater high aluminum content in the area of the Liquid Effluent Treatment Center—CETREL of the Camaçari Industrial Pole, with natural environmental factors: geology, hydrogeology, precipitation, soil and vegetation; and anthropic: equipments of treatment and disposal of industrial waste from CETREL. This company made available data from 99 monitoring wells, period 2006–2016, with aluminum content above (0.2mg/L) the limit established by the Ministry of Health Ordinance Nº 888, 5 April 2021. Previous studies have indicated that there is no correlation of aluminum in groundwater of the Camaçari Industrial Pole with other metallic contaminants; also, that aluminum in the studied region is disseminated in the geological matrix, clayey soils, and poor and leached Cerrado soils. The Kruskal-Wallis test indicated significant correlation of high aluminum content with the treatment/disposal areas, geology, soil and vegetation; and no correlation with precipitation and hydrogeology. The four environmental factors indicating the highest average aluminum content (±C&lt;sub&gt;95%&lt;/sub&gt;), in descending order, are: Clayey Soils, Organic Sludge Farm I, Marizal Formation, and Herbaceous-Subshrub Vegetation. The multivariable analysis indicated that, the most influential factors on the high aluminum content in groundwater of the CETREL region, are all ultimately associated with the leaching of aluminum present in the solid matrix. As CETREL processes are not correlated with aluminum residues, the results were an important information for the company environmental managers.&lt;/p&gt;

Electrochemically assisted remediation of a highly chlorinated organic polluted sludge: A full-scale case study

Electrochemical technology has emerged as an effective method to remediate soils in a laboratory environment. However, its practical application is often challenging due to the complexity of adopting small-scale parameters and identifying all the potential problems during the operation of electrokinetic plants. Here, a prototype demonstration in a space environment (Technology Readiness Level 7) is reported to remediate a 5 × 5 m2 plot of a leachate pond from a landfill containing dense sludge contaminated with chlorinated organic compounds. Bench-scale tests (50 kg per mock-up) were initially carried out to evaluate the effects of the key parameters (electric field, surfactants, and electrode materials) and demonstrated the feasibility of reducing contaminant concentrations in the sludge through dehalogenation and volatilisation. The average electro-osmotic flux was 0.23 cm day−1, comparable to that reported for silty soils. Iron electrodes enhanced electrokinetic water transport and reduced acidification, while glassy carbon electrodes increased water volatilisation, acidity near the anode, and dehalogenation of chlorinated hydrocarbons. Based on these findings, the full-scale design and operating conditions were selected. After 590 h of operation, the total pollutant concentration was reduced by 34 %, mainly due to volatilisation, using a sequence of six iron-electrode arrays at 1 V cm−1, which increased the sludge temperature over 60 °C. An evaporation rate of 0.021 cm d−1 and an electro-osmotic flux of 0.62 cm d−1 were achieved, consistent with the bench tests. These findings demonstrate the potential of electrokinetic plants for the remediation of sludges and provide expertise applicable to future remediation at other contaminated sites.

Resource Utilization of Residual Organic Sludge Generated from Bioenergy Facilities Using Hermetia illucens Larvae.

Residual organic sludge generated from bioenergy facilities (BF-rOS) is often disposed instead of recycled, thus contributing to further environmental pollution. This study explored the resource utilization of BF-rOS using Hermetia illucens larvae (BSFL). When BF-rOS was fed to BSFL for two weeks, the dry weight per individual BSFL was approximately 15% of that of BSFL that were fed food waste (FW). However, the dry weight increased by approximately two-fold in BSFL that were fed effective microorganism (EM)-supplemented BF-rOS containing 60% moisture. However, under both conditions, the BSFL did not mature into pupae. In contrast, the highest dry weight per BSFL was observed with the BF-rOS/FW (50%:50%) mixture, regardless of EM supplementation. Furthermore, the highest bioconversion rate was observed when the BSFL were fed the BF-rOS/FW (50%:50%) mixture, and the frass produced by the BSFL contained fertilizer-appropriate components. In addition, the nutritional components of the BSFL exhibited a nutrient profile suitable for animal feed, except for those fed BF-rOS only. In conclusion, this investigation demonstrates that BF-rOS should be recycled for fertilizer production by mixing it with FW as a BSFL feed, which generates the valuable insect biomass as potential nutrition for animal feeding.

Effect of separation pretreatment on environmental and economic performance of sludge resource utilization

As a new technology for accurate utilization of sludge resources, sludge inorganic–organic matter separation (IOMS) has attracted wide attention. This study examined the impact of this pretreatment on environmental and economic performance of sludge composting and incineration using life cycle assessment (LCA) and whole life costing (WLC). LCA results indicated that IOMS pretreatment reduced the energy conservation and emission reduction (ECER) values of composting and incineration by 56 % and 76 %, respectively. Meanwhile, WLC exhibited that IOMS pretreatment could cut the break-even year of incineration from 11 years to 4 years. The combination of organic sludge incineration/composting with inorganic sludge sintering ceramsite reveals excellent environmental and economic performance. The application optimization hypothesis analysis of these two routes in various provinces of China indicates that Jiangsu has the greatest development potential and should become a major promotion region.

Prognostic Modelling of Biomethane Production from Waste: Application of Extreme Gradient Boosting

The escalating fossil fuel prices and greenhouse gases need urgent attention for a sustainable solution. The present study explores as modern machine learning approaches can be employed to prognosticate the complex biomethane generation process from organic wastes, like biowaste or food waste. The research investigates the use of organic sludges and how intelligent approaches can be employed to comprehend the complex nonlinear processes involved in biomethane production. Linear regression and Extreme gradient boosting (XGBoost) based prediction-models were developed and assessed employing a diverse set of statistical parameters, including R, R2, Mean Squared Error (MSE), Mean Absolute Error (MAE), and Kling-Gupta Efficiency (KGE). The results show that the XGBoost model beat the classical Linear Regression (LR) model in both the training and testing phases. During training, the XGBoost had an impressive R2 value of 0.99994, indicating a perfect fit to the data. In contrast, LR achieved an R2 value of 0.65464. Similarly, during the test period, XGBoost outperformed LR with R2 values ​​of 0.9553 to 0.9902. Furthermore, XGBoost reduced prediction errors, with significantly lower MSE and MAE values ​​than LR. Taylor’s graph better illustrates the excellent performance of the XGBoost over LR in both training and testing. These data demonstrate the ability of XGBoost to predict biomethane production, as well as its ability to improve the biomethane production process.

Phosphorus recovery coupling with one-stage partial nitritation/anammox process for the treatment of high-nutrient permeate from anaerobic membrane bioreactor treating concentrated organic sludge

High-solid anaerobic membrane bioreactors (AnMBRs) are widely applied in solid waste treatment; however, the nutrient removal of the permeate, which possesses high mineral content, nitrogen, and COD concentration, is challenging. In this study, a hydroxyapatite-based one-stage partial nitritation/anammox (HAP-PNA) process was combined with an AnMBR treating concentrated organic sludge for permeate polishing, focusing on the enhancement of phosphorus recovery by influent Ca/P ratio optimization, alkalinity control and the effect of HAP formation on nitrogen removal. The total nitrogen and phosphorus concentrations of high-solid AnMBR permeate were 737 ± 5 mg/L and 90.9 ± 1.9 mg/L, respectively. The reactor operated at the nitrogen loading rate of 0.73 kg-N/m3/d and realized 81.6% nitrogen removal efficiency (NRE) and 0.6 kg-N/m3/d nitrogen removal rate. Denitrification reduced the nitrate produced during the anammox reaction, promoting a 25.7% COD removal and improving the NRE. The phosphorus removal efficiency (PRE) and sludge settleability were significantly enhanced by the addition of calcium, and a maximum PRE of 73.2% was achieved when the influent Ca/P ratio was 2.7. The reactor showed high stability and nitrogen removal performance, even when the phosphorus removal rate/nitrogen removal rate ratio was as high as 0.12. This study demonstrates the excellent capability of the one-stage HAP-PNA process for permeate treatment with high phosphorus content.

Impact of low and high temperatures on aerobic granular sludge treatment of industrial wastewater.

The goal of this study was to unravel the impact of high and low temperatures (T) on glycogen-accumulating microorganisms (GAOs) which were stimulated in an aerobic granular sludge plant fed with industrial wastewater, which is derived from the cleaning of trucks transporting chocolate and beer. Among GAOs, Candidatus Competibacter (Ca. Competibacter) was the most abundant. The long-term impact on (1) anaerobic dissolved organic carbon (DOC) uptake, (2) sludge morphology, and (3) microbial community composition was investigated. In addition, the short-term impact of T changes on the anaerobic uptake rate was evaluated. High T (above 38 °C) and low T (below 11 °C) had a negative impact on the relative read abundance of Ca. Competibacter and the anaerobic DOC uptake. Nevertheless, the carbon removal efficiency and the settleability of the biomass were not affected. Denitrifiers such as Thauera and Zoogloea were promoted over Ca. Competibacter under high T and low T, respectively, indicating their positive contribution to granulation maintenance.

Strength characteristic and micro-mechanism of organic dredged sludge solidified by cement incorporating sodium persulfate

Cement-based solidification is a widely used sustainable technology for transforming waste dredged sludge (DS) into backfill materials. This study developed a novel solidification/oxidization synergistic (SOS) method, using Portland cement as a binder and sodium persulfate (SP) as an oxidant, for treating the organic DS with different fulvic acid (FA) content. The results demonstrated that adding SP could significantly improve the UCS of the cement-solidified DS doped with FA. When the FA content was 4%, the 28-day UCS of the sample with 25% cement content was only 160.5 kPa. The addition of 6% SP increased the UCS to 2225.5 kPa, which was 15.1 times that of the sample without SP. However, excessive SP hydrolyzed to produce a large amount of sulfuric acid, leading to a low pH value of the pore solution. This in turn hindered further persulfate activation and cement hydration, which was detrimental to the strength of cement-solidified DS.

Enhanced methanogenic degradation and membrane fouling associated with protein-EPS by extending sludge retention time in a high-solid anaerobic membrane bioreactor treating concentrated organic sludge

The improvement of organic sludge destruction efficiency and methanogenic performance is a key concern during anaerobic digestion toward maximum energy recovery. In this study, a high-solid anaerobic membrane bioreactor (AnMBR) was operated continuously for the treatment of organic sludge from Japanese small-scale collective wastewater treatment facility (Johkasou), and digestion efficiency was enhanced by the optimizing solid retention time (SRT). Degradation efficiency of the substrate improved from 36 % to 52 % and the biogas yield was enhanced from 0.37 to 0.51 L/g-VSfed when the SRT was extended from 30 to 60 d. The net energy yield of AnMBR at SRT 60 days was 9.83 kJ/g-VSfed, and the corresponding energy sufficiency ratio was 181 %, indicating that SRT extension could enhance substrate destruction with significant energy recovery potential. However, a long SRT is characterized by high mixed liquor total solids (MLTS), small particle size, high extracellular polymeric substances content, and poor filterability, which exert detrimental effects on membrane operation. Membrane fouling was effectively controlled by regulating the flux at a sustainable rate. The low fouling region and transition region of operating flux were determined as 0.21–4.6 L/m2/h (LMH) and 1.5–5.7 LMH, respectively, when MLTS was 25–50 g/L, and the main contributors to membrane fouling were high protein fractions and small sludge flocs. The current study proposes a promising method to promote digestion efficiency and provided adequate guidance for membrane operation at super-high MLTS by presenting practical engineering applications of AnMBRs in solid waste treatment.

Influence of fibrous material on the composting, with the inclusion of different biocatalysts

The manuscript demonstrate which percentage indexes of fibrous and organic material are necessary in composting windrows, the replacement of the biocatalyst (feces) by organic sludge, with the purpose of forming an alternative quality fertilizer. Individual windrows were designed with different compositions based on 10 calculations of different proportions. The three different materials used in the composting process for each treatment (T1, T2, T3, T4 and T5 with animal feces as biocatalyst, and T6, T7, T8, T9 and T10, with sludge as biocatalyst). Each treatment consisted of 1kg of material with the following proportions: T1 - 70% of fibrous material and 30% of organic material; T2 - 50% fibrous material and 50% organic material; T3 - 30% fibrous material and 70% organic material; T4 - 10% fibrous material and 90% organic material; T5 - 0% of fibrous material and 100% of organic material, where the following parameters of the organic fertilizers generated were analyzed: physical - granulometry; density and porosity, chemical – Organic Matter; pH; P; K; Ca; Mg; At; SB; Al; H and CTC. All treatments are within the classification range of soil with weak acidity, since the pH and OM content were between 7.01 and 10.8% respectively. Thus, even with the variation of the organic biocatalysts used, the indices and required levels of the physicochemical parameters analyzed, of all treatments, regardless of the fiber content, were above the references expressed in the literature, demonstrating a high quality in the fertilizers produced.

Kinetics and isotherms of adsorption of arsenic (III) in aqueous solution using activated carbon with nanoporous structure obtained from organic sewage sludge

El objetivo de la investigación fue estudiar el proceso de adsorción de iones de As (III) con carbón activado de estructura nanoporosa obtenido de lodos orgánicos de aguas residuales. La obtención del carbón activado se realizó mediante una activación química usando ZnCl2 y una activación térmica a 650 °C. Los ensayos de adsorción se realizaron colocando en contacto 16 g/l de carbón activado con soluciones de 0.247, 0.406, 0.564, 0.683 y 0.801 mg/l de As (III) en vasos precipitados de 1 l a un tiempo de 24 horas. Todos los ensayos fueron sometidos a una velocidad de agitación de 720 RPM, a temperatura de 28 °C ± 0.5 y al pH natural de las muestras en laboratorio, el cual fue 3. Los resultados de la caracterización de carbón indicaron que este adsorbente presentó una estructura nanoporosa con presencia de grupos funcionales (hidroxilo y carboxilo). En cuanto a los ensayos de adsorción de As (III), se determinó que el carbón activado logró reducir la concentración del metal hasta 0.004 mg/l, valor que está por debajo de los establecidos por la Organización Mundial de la Salud (OMS) para el consumo de agua. Finalmente se concluye que el carbón activado presentó una eficiencia de 98.4 % de adsorción de iones de As (III) y los datos experimentales mostraron un mayor ajuste al modelo de pseudo-segundo orden y a la isoterma de Freundlich, lo cual indica que el proceso de adsorción de As (III) se realiza en centros enérgicamente heterogéneos mediante una interacción físico-química entre el metal y el adsorbente.

Unveiling the origin, fate, and remedial approaches for surfactants in sewage-fed foaming urban (Bellandur) Lake

Foam formation in surface water bodies has become a global phenomenon, but the solutions to this crisis are often insufficient. Foam formation in water bodies is attributed to surfactants and requires a comprehensive assessment of various sources of surfactants to evolve mitigation strategies. The study is focused on thoroughly analyzing surfactants in the water and foam fractions of a large waterbody in Bangalore (India) spanning around 1000 acres (400 ha), which has been foaming for two decades. Results revealed that the key surfactants originate predominantly from anthropogenic sources with a small component emerging from naturogenic sources. Anthropogenic surfactants were found to be predominant (96.5%), with linear alkylbenzene sulphonates (LAS) of various C-chain lengths 12–20 being the most prevalent. Naturogenic surfactants derived from bacterial genera Pseudomonas exhibited significant microbial diversity, accounting for over 19% of total bacterial population in both the water and organic sediments of the lake. Modelling studies and field validation efforts were carried out to understand the fate of LAS in the foaming lake. The results indicated that these surfactants donot degrade under the prevailing conditions and timeframe as wastewater traverses through the lake, and their presence was also observed in the organic sludge sediment. Modeling the underlying processes revealed that a minimum dissolved oxygen (DO) concentration of 3.5 mg/l enables the degradation of over 90% of surfactants within the residence time of 8–10 days in Lake. Additionally, the process of desludging could contribute to an additional increase to the overall efficiency of surfactant removal, simultaneously removing legacy sorbed surfactants to sediments.

Comparative study of Fe0-H2O2, Fe0-PMS and Fe0-PDS systems for the removal of refractory organics from bio-treated landfill leachate

Aiming at the excellent performance of advanced oxidation technology (AOP) in removing organic matter, the efficiency and mechanism of Fe0 activated H2O2, PMS and PDS in the removal of refractory organic matter in bio-treated landfill leachate (BTL) were systematically compared. The results showed that the removal effect of the three systems on organic matter was affected by the dosage of oxidant, the dosage of zero-valent iron, the initial pH value and the reaction time. After treatment with the three systems, the content of humic substances and aromatic organics in MBR effluent and the degree of molecular polymerization could be effectively reduced. Due to different ROS dominance in the three systems, there were differences in the efficacy of organic matter removal. The activation mechanism of Fe0 included homogeneous activation of Fe2+ and heterogeneous activation of in situ formation of iron oxides. Finally, considering various factors, such as the organic removal effect, oxidant toxicity, sludge yield, economy and potential impact of byproducts, the Fe0-H2O2 system was superior to the other systems in the selection of treating refractory organics in landfill leachate MBR effluent.

Bioenergy recovery and carbon emissions benefits of short-term bio-thermophilic pretreatment on low organic sewage sludge anaerobic digestion: A pilot-scale study

Sewage sludge in cities of Yangzi River Belt, China, generally exhibits a lower organic content and higher silt contentdue to leakage of drainage system, which caused low bioenergy recovery and carbon emission benefits in conventional anaerobic digestion (CAD). Therefore, this paper is on a pilot scale, a bio-thermophilic pretreatment anaerobic digestion (BTPAD) for low organic sludge (volatile solids (VS) of 4%) was operated with a long-term continuous flow of 200 days. The VS degradation rate and CH4 yield of BTPAD increased by 19.93% and 53.33%, respectively, compared to those of CAD. The analysis of organic compositions in sludge revealed that BTPAD mainly improved the hydrolysis of proteins in sludge. Further analysis of microbial community proportions by high-throughput sequencing revealed that the short-term bio-thermophilic pretreatment was enriched in Clostridiales, Coprothermobacter and Gelria, was capable of hydrolyzing acidified proteins, and provided more volatile fatty acid (VFA) for the subsequent reaction. Biome combined with fluorescence quantitative polymerase chain reaction (PCR) analysis showed that the number of bacteria with high methanogenic capacity in BTPAD was much higher than that in CAD during the medium temperature digestion stage, indicating that short-term bio-thermophilic pretreatment could provide better methanogenic conditions for BTPAD. Furthermore, the greenhouse gas emission footprint analysis showed that short-term bio-thermophilic pretreatment could reduce the carbon emission of sludge anaerobic digestion system by 19.18%.

Comprehensive competitiveness assessment of four typical municipal sludge treatment routes in China based on environmental and techno-economic analysis

To find a sustainable and effective municipal sludge treatment route requires a systematic assessment of the comprehensive competitiveness of diverse sludge treatment routes. Four typical treatment routes in China including co-incineration in coal power plants (CIN), mono-incineration (IN), anaerobic digestion (AD) and pyrolysis (PY) were selected in this study. A novel assessment model integrating life cycle assessment (LCA), techno-economic analysis (TEA) with analytic hierarchy process (AHP)-Entropy method was established, and comprehensive competitiveness indicated by comprehensive index (CI) of the four routes was deeply evaluated. Results displayed CIN route (CI = 0.758) showed the best comprehensive performance for its best environmental and economic performance. This was followed by PY route (CI = 0.691) and AD route (CI = 0.570), indicating the enormous potential of sludge PY technology. IN route showed the worst comprehensive performance (CI = 0.186) owing to its high environmental impact and lowest economic benefit. It was noted that greenhouse gas emissions and severe toxic potential were the main environmental challenges faced by sludge treatment. Besides, result of sensitivity analysis revealed that the comprehensive competitiveness of diverse sludge treatment routes was improved with the increase of sludge organic content and sludge reception fee.