Fraction Of Sludge Research Articles

Insights into thermal hydrolyzed sludge liquor - Identification of plant-growth-promoting compounds

This study proposes a new path to utilize thermal hydrolyzed sludge (TH sludge) as fertilizer given high value chemical compounds that can promote plant growth were identified in the liquid fraction of TH sludge (TH liquor). Together with micro- and macro-nutrients released/synthesized during thermal hydrolysis, the feasibility of using TH liquor as organic fertilizer was evaluated. Besides high contents of N, P and K, total free amino acids (FAAs) and plant-growth-promoting FAAs (including glutamic acid, leucine and cystine) also presented in high concentration (4.98–6.48 and 1.12–2.73 g/100 g) in the TH liquor. For the first time, phytohormone compound, indole-3-acetic acid, was observed and the content was the highest in TH liquor with 165 °C treatment (165 °C TH liquor). Meantime, 165 °C TH liquor did not have negative impact on the growth of soil microbes, and this product, instead, demonstrated stimulating effect on the plant growth. These results suggest that 165 °C TH liquor has a great potential to be an organic fertilizer. The remaining solids of TH sludge could be converted to valuable biochar. The holistic approach of using TH liquor as organic fertilizer and producing biochar could realize nearly zero-waste discharge in sludge management.

Optimization of process parameters for enhanced biogas yield from anaerobic co-digestion of OFMSW and bio-solids

The effects of mesophilic anaerobic co-digestion (AcoD) of organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) on enhancement of biogas production were investigated under different types of sludge combinations (primary sludge PS, waste-activated sludge WAS and mixed sludge MS), varying mixing ratios of OFMSW and MS (50:50, 70:30, 80:20, 90:10, v/v) and varying total solid TS concentrations (6, 9, 12, 15%). The co-digestion of OFMSW with MS resulted in the biogas yield of 138 mL/gVS over mono-digestion of OFMSW (39 mL/gVS). Co-digestion of OFMSW + PS and OFMSW + WAS yielded biogas of 107 and 129 mL/gVS, respectively, which is less than that of OFMSW + MS (138 mL/gVS), respectively. The co-digestion of OFMSW with MS showed a 2.5 times increase in biogas yield over OFMSW digestion alone and 23% and 7% higher biogas yield than OFMSW + PS and OFMSW + WAS, respectively. The highest biogas yield of 967 mL/g VS was observed at TS concentration of 9% and OFMSW to the MS mixing ratio of 80:20, respectively. The biogas yields at different TS percentages were modelled using Gompertz and Logistic models and fitted well.

Comparative study of Fenton, Fe2+/NaOCl and Fe2+/(NH4)2S2O8 on tannery sludge dewaterability, degradability of organics and leachability of chromium

In this work, a comparative analysis of Fenton, Fe2+/NaOCl and Fe2+/(NH4)2S2O8 assisted advanced oxidation processes was carried out to study its efficacy in enhancing tannery chemical sludge dewaterability. Experimental results showed that, after conditioning of sludge at optimum pH, oxidant and catalyst dosage, capillary suction time (CST) was decreased by 75 ± 5 % and moisture content of sludge cake (M.Ccake) was reduced to 74 ± 2 % for all processes at 10 min reaction time. Among the three processes, Fe2+/(NH4)2S2O8 process was noted to have larger impact on the breakdown of sludge cells, which is reflected in terms of its highest amount of total organic carbon, protein and total dissolved solids present in the separated sludge fractions. In addition, Fe2+/(NH4)2S2O8 process was also observed to leach out largest fraction say 73.3 % of chromium present in the raw sludge into the treated sludge filtrate. The investigation carried out through zeta potential and scanning electron microscopy reveals the role of a two-step mechanism, namely oxidation followed by coagulation in enhancing the sludge dewaterability. Further studies on the possibility of utilizing dried treated sludge as biomass fuel could be carried out.

Iron recovery from the coarse fraction of basic oxygen furnace sludge. Part I: optimization of acid leaching conditions.

In this study, a new reuse process of the coarse fraction of basic oxygen furnace (BOF) sludge based on iron recovery by the ferrous sulfate production was proposed. This study was based on three main steps: (i) characterization of the steel waste, (ii) evaluation and optimization of the recycling process, and (iii) characterization of ferrous sulfate produced. Acid leaching was used to solubilize the iron for obtaining ferrous sulfate heptahydrate. The ferrous sulfate crystallization was performed by adding anhydrous ethanol (EtOH). A multivariate optimization for iron leaching and ferrous sulfate precipitation in the same solution was employed. This optimization consisted of screening steps using a full factorial design followed by optimization. The coarse fraction of BOF sludge was predominantly composed of iron in metallic form (82.5%, dry weight). The sulfuric acid concentration and leaching time had significant effects on Fe(II) solubilization. The desirability function predicted the following optimized conditions: 20% (v/v) sulfuric acid solution, 200min of leaching time, 7.00g of waste, and 110mL of anhydrous EtOH, producing 19.60g of ferrous sulfate heptahydrate (yield of 70.8%). The characterization of ferrous sulfate was performed by X-ray diffraction, scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The characterization of the ferrous sulfate produced evidenced the effectiveness of the optimized process condition. Graphical abstract.

Elemental concentration and migratability in bioplastics derived from organic waste

In line with the Circular Economy approach, the production of polyhydroxyalkanoate (PHA) with organic waste as the feedstock may a biotechnological application to reduce waste and recover high-value materials. The potential contaminants that could transfer from bio-waste to a PHA include inorganic elements, such as heavy metals. Hence, the total content and migratability of certain elements were evaluated in several PHA samples produced from different origins and following different methods. The total content of certain elements in PHA ranged between 0.0001 (Be) and 49,500 mg kg−1 (Na). The concentrations of some alkaline (Na and K) and alkaline earth (Ca and Mg) metals were highest, which are of little environmental concern. The feedstock type and PHA stabilisation and extraction procedures affected the element contents. Several sets of experiments were conducted to evaluate the migration of elements from the PHA samples under different storage times, temperatures, and pH levels. The total contents of some heavy metals (As, Cd, Fe, Hg, Ni, Pb, and Zn) in PHA produced from fruit waste or crops (commercial PHA) were lower than those in the PHA samples produced from the mixture of the organic fraction of municipal waste and sludge from wastewater treatment. Both the PHA obtained by extraction from wet biomass (acid storage) with aqueous phase extraction reagents and commercial PHA were below the migration limits stipulated by the current Toy Safety Directive and by Commission Regulation (EU) October 2011 on plastic materials and articles intended to come into contact with food under frozen and refrigerated conditions.

Optimizing anaerobic digestion of organic fraction of municipal solid waste (OFMSW) by using biomass ashes as additives

The purpose of this study is to test alternative additives for trace element (TE) supplementation and process stabilization during anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) and sewage sludge. Process instabilities due to acidification are a typical problem in waste fermentation. Provision with minerals and TE is crucial for microorganisms in AD to work effectively, allowing higher organic loading rates within the digester without risking acid accumulation. In batch-fermentation tests, different mixture configurations of OFMSW, digested sewage sludge and biomass ashes were evaluated. Based on an extensive characterization of the TE contained in wood ashes, suitable combinations of digested sewage sludge and OFMSW as a baseline substrate together with ash additives were derived. While high dosages of ash reduced biogas production, 1:1 mix of ash and OFMSW facilitated higher CH4 yields (6%). The supplementation of ashes increased the pH-value within AD and CO2 precipitation through metal oxides in situ elevated the CH4 concentration in biogas up to 98%. Therefore, ashes may increase the efficiency of AD and serve as a basis for a new gas purification method, minimizing technical effort. Additional investigations are needed to examine long-term effects as well as financial and legal aspects such as possible ways of digestate usage. As a further area of research, the transferability of batch-test results into practical applications is identified.

Anaerobic hybrid membrane bioreactor for treatment of synthetic leachate: Impact of organic loading rate and sludge fractions on membrane fouling

In the present study, the treatment of synthetic landfill leachate was carried out using a lab-scale anaerobic hybrid membrane bioreactor (An-HMBR). The reactor was operated for 250 days at two days of hydraulic retention time (HRT). Average chemical oxygen demand (COD) removal efficiency was ≥ 88% at steady-state conditions at 100% raw leachate. As organic loading rate (OLR) increased from 1.6 to 13.9 Kg COD m−3 d−1, flux gradually declined from 70 to 52 L/m2 h (LMH) within 250 days. Chemical membrane cleaning enhanced the flux up to 75% of the initial flux at the final stage of the reactor. Reversible fouling (>90%) dominated over irreversible fouling (<8%). Membrane fouling was mainly caused by extracellular polymeric substances (EPS) fraction, which resulted in cake layer formation on the ceramic membrane used in the An-HMBR system. Membrane resistance increased with variables in the following order OLR > MLSS (mixed liquor suspended solids) > EPS > SMP (soluble microbial products). A nonlinear regression model developed for prediction of membrane resistance at different OLR can predict with an error of ±7%.

Polyhydroxyalkanoates (PHAs) Production: A Feasible Economic Option for the Treatment of Sewage Sludge in Municipal Wastewater Treatment Plants?

Sludge is a by-product of municipal wastewater treatment plants (WWTPs) and its management contributes significantly to the operating costs. Large WWTPs usually have anaerobic sludge digesters to valorize sludge as methane and to reduce its mass. However, the low methane market price opens the possibility for generating other high value-added products from the organic matter in sludge, such as polyhydroxyalkanoates (PHAs). In this work, the economic feasibility of retrofitting two types of WWTPs to convert them into biofactories of crude PHAs was studied. Two cases were analyzed: (a) a large WWTP with anaerobic sludge digestion; and (b) a small WWTP where sludge is only dewatered. In a two-stage PHA-production system (biomass enrichment plus PHAs accumulation), the minimum PHAs cost would be 1.26 and 2.26 US$/kg PHA-crude for the large and small WWTPs, respectively. In a single-stage process, where a fraction of the secondary sludge (25%) is directly used to accumulate PHAs, the production costs would decrease by around 15.9% (small WWTPs) and 19.0% (large WWTPs), since capital costs associated with bioreactors decrease. Sensitivity analysis showed that the PHA/COD (Chemical Oxygen Demand) yield is the most crucial parameter affecting the production costs. The energy, methane, and sludge management prices also have an essential effect on the production costs, and their effect depends on the WWTP’s size.

Feasibility and potential of separate anaerobic digestion of municipal sewage sludge fractions

Feasibility of the separate anaerobic stabilization of primary (PS) and secondary (SS) sludge fractions produced in municipal wastewater treatment plants (WWTP) was studied at volatile loading rates (VLR) of 0.57–2.05 and 0.27–0.57 kg VS/(m3∙d) for PS and SS, respectively, corresponding to 16–30 and 14–28 d of hydraulic retention time (HRT). Laboratory-scale semi-continuous anaerobic reactors were operated at 35°C. The operational performance and quality of the final stabilized sludge were monitored. PS and SS showed opposite thickening abilities exhibiting a need for direct feeding of PS to the digesters. Biodegradability was obtained as 52(±1) and 40(±5)% volatile solid (VS) removal for PS and SS, respectively. Optimum VLR was determined according to the highest methane yield (specific methane production), VS reduction and dewaterability of the stabilised sludge. An inhibitory effect was observed at higher VLRs in PS digestion inducing a gradual reduction in the methane yield and daily production. High oil and grease content was subject to a substantial reduction in PS digestion showing a dependency on HRT. Conversely, a considerable degree of augmentation took place in the stabilised SS with no correlation to HRT at values lower than 30 d. Efficient reduction in the oil and grease content improved dewaterability in stabilised PS whereas high oil and grease content prevented an improvement for stabilised SS. Major benefits were obtained as lower HRT and high stability with higher methane production and fertilizing (N and P content) characteristics for digestion performance and stabilized SS, whereas direct feeding and higher HRT for PS digestion were determined as beneficial.&#x0D;

Feasibility and potential of separate anaerobic digestion of municipal sewage sludge fractions

Feasibility of the separate anaerobic stabilization of primary (PS) and secondary (SS) sludge fractions produced in municipal wastewater treatment plants (WWTP) was studied at volatile loading rates (VLR) of 0.57–2.05 and 0.27–0.57 kg VS/(m3∙d) for PS and SS, respectively, corresponding to 16–30 and 14–28 d of hydraulic retention time (HRT). Laboratory-scale semi-continuous anaerobic reactors were operated at 35°C. The operational performance and quality of the final stabilized sludge were monitored. PS and SS showed opposite thickening abilities exhibiting a need for direct feeding of PS to the digesters. Biodegradability was obtained as 52(±1) and 40(±5)% volatile solid (VS) removal for PS and SS, respectively. Optimum VLR was determined according to the highest methane yield (specific methane production), VS reduction and dewaterability of the stabilised sludge. An inhibitory effect was observed at higher VLRs in PS digestion inducing a gradual reduction in the methane yield and daily production. High oil and grease content was subject to a substantial reduction in PS digestion showing a dependency on HRT. Conversely, a considerable degree of augmentation took place in the stabilised SS with no correlation to HRT at values lower than 30 d. Efficient reduction in the oil and grease content improved dewaterability in stabilised PS whereas high oil and grease content prevented an improvement for stabilised SS. Major benefits were obtained as lower HRT and high stability with higher methane production and fertilizing (N and P content) characteristics for digestion performance and stabilized SS, whereas direct feeding and higher HRT for PS digestion were determined as beneficial.&#x0D;

Liquid and solids separation for target resource recovery from thermal hydrolyzed sludge

This study proposed an integrated process for biogas generation and biochar production from thermal hydrolysis pretreated sludge (THP sludge). In this study, the liquid and solids fractions of THP sludge were separately processed for the first time. The liquid fraction of THP sludge (THP-L) reached the biodegradability (262.6 ± 5.1 mL CH4/g tCODfeed) on the 15th day during anaerobic treatment, while the solids fraction of THP sludge (THP-S) only contributed 31.0% to the total methane production and required more than 30 days digestion time. We investigated the feasibility to convert THP-S into biochar to realize the higher value of the solids fraction. The results prove the produced biochar can be used as slow-release fertilizer. Preliminary energy analysis was performed to evaluate the energy efficiency of the integrated approach, namely, methane generation from THP-L coupled with biochar production from THP-S. The process realized energy surplus of 0.81 MWh/tonne dry sludge. In addition, THP-L digested sludge showed better dewaterability, lower yield stress and reduced viscosity during digestion. The proposed new sludge treatment process therefore has lower operating cost and higher value returns.

Density-Based Separation of Microbial Functional Groups in Activated Sludge.

Mechanistic understanding of how activated sludge (AS) solids density influences wastewater treatment processing is limited. Because microbial groups often generate and store intracellular inclusions during certain metabolic processes, it is hypothesized that some microorganisms, like polyphosphate-accumulating organisms (PAOs), would have higher biomass densities. The present study developed a density-based separation approach and applied it to suspended growth AS in two full-scale domestic water resource recovery facilities (WRRFs). Incorporating quantitative real-time PCR (qPCR) and fluorescence in situ hybridization (FISH) analyses, the research demonstrated the effectiveness of density-based separation in enriching key microbial functional groups, including ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB) and PAOs, by up to 90-fold in target biomass fractions. It was observed that WRRF process functionalities have significant influence on density-based enrichment, such that maximum enrichments were achieved in the sludge fraction denser than 1.036 g/cm3 for the enhanced biological phosphorus removal (EBPR) facility and in the sludge fraction lighter than 1.030 g/cm3 for the non-EBPR facility. Our results provide important information on the relationship between biomass density and enrichment of microbial functional groups in AS, contributing to future designs of enhanced biological treatment processes for improved AS settleability and performance.

Effect of addition of coal sludge to polymeric material on thermal effects in analysis by TG/DTG/DSC methods

The paper presents the application of thermal analysis methods in the study of various materials: coal sludge, polymeric material and composites of a polymer with coal sludge (fraction of coal sludge in composites: 1%, 3% and 5%). TG/DTG/DSC curves obtained during measurements in air atmosphere were analyzed. Polymers are used in many industries, that is why their thermal characteristics are so important. On the other hand, the mining industry, forced to supply power plants better quality fuel, must perform more thorough coal cleaning. This results in a continuous increase in waste in the form of coal sludge. The best method of disposing of these wastes is thermal utilisation (combustion and co-combustion), as well as use in composites with other materials. The aim of the study was to demonstrate the effect of the addition of coal sludge to the polymer on the energetic effect and the rate of mass change of the material sample during the thermal process by TG/DTG/DSC methods.

Changes in lead and chromium contents in sewage sludge evaluated using both single extractants and sequential method

ABSTRACT The aim of this study was to evaluate changes in lead and chromium amounts in sequentially separated fractions and available forms of four sewage sludge (SS). Lead and chromium sequential extraction in SS was performed using BCR method. Single extractants were used to assay available and bioavailable forms of metals. It was found that Pb and Cr were detected in the largest amounts in organic forms, while the lowest levels were recorded for exchangeable ones. Sewage sludges from the small installations contained significantly lower amounts of metals (both available, bioavailable and sequentially separated fractions of sewage sludge) in comparison with those originating from the large treatment installations. Generally amounts of metals detected in sewage sludge were small in the years of this study, which should be considered a positive trend. Additionally, the bioavailability index (φ) and risk assessment code (RAC) indicated no negative impact of metals contained in the analysed SS on the soil environment.

Modeling and optimization of biomethane production from solid-state anaerobic co-digestion of organic fraction municipal solid waste and other co-substrates

ABSTRACT One of the simplest methods for increasing productivity in biogas production is co-digestion. Co-digestion leads to more biogas yield as well as more nutrient bioavailability. This study reports the modeling and optimization of biomethane potential tests from different combinations of organic fraction of municipal solid wastes (OFMSW), cow manure (CM), and municipal sewage sludge (MSS) in solid-state. The simplex-centroid mixture design (SCMD) and artificial neural network (ANN) models were validated with a high correlation to the real data (R2 = 0.99). Experimental results indicated that the maximum amount of CH4 production of 436 mL CH4/g VS occurs at the identical weight percent of the three substances (33.33%). The maximum methane yield was found to be 445.9 mL CH4/g VS as obtained by the genetic algorithm (GA) optimization process, while 448.5 mL CH4/g VS (448.5 ± 3.05) of methane was produced experimentally. Therefore, integration of the SCMD and ANN model with the GA optimization is useful in the prediction of biomethane production. This research is the first in providing the best combination of co-treating and co-utilizing OFMSW with CM and MSS in the solid-state for biowaste management.

ИССЛЕДОВАНИЕ СОСТАВОВ ТЯЖЕЛЫХ МЕТАЛЛОВ И ФОСФАТОВ В ПОЛИМЕРНЫХ ВЕЩЕСТВАХ БИОМАССЫ АКТИВНЫХ ИЛОВ

Introduction. Heavy metals discharged with wastewater can lead to a toxic effect on the microbiocenosis of activated sludge and significantly decrease the degree of wastewater treatment, which dictates the need for a more detailed study and search for ways to detoxify activated sludge at the recycling stage and, at the same time, solve the problems of the neutralization of sewage sludge for safe soil disposal. To ensure the adequacy of the approach to the choice of the methodology for the neutralization of sludge, including sewage sludge, it is necessary to perform compositional analysis of their organic fractions and heavy metal compositions. Methods. To determine the quantitative content of organic components in activated sludge, a sample of sludge was dried to an air-dry state and then subjected to separation into fractions using a method based on the different solubility of compounds with the use of different solvents. Then, extractants were added step by step to the weighted samples of sewage sludge weighing about 2 g each (in a volume 20 times greater than the weight of the weighted sample (40 ml)). Results. The results of the study show that polysaccharides are the dominant form of the organic fraction (polymers) in sewage sludge. Most heavy metals were identified in acidic polysaccharides, humic-like acids and lipids. Significant concentrations of phosphates were observed for the same components of polymer substances in the biomass of activated sludges. Conclusion. The products of extraction of polymer substances of the activated sludge biomass and the content of heavy metals in them may indicate the biosorption of heavy metals by zoogleal accumulations (having a polysaccharide structure) of activated sludges in aeration tanks during biological treatment. Therefore, extracellular biopolymers can be a “target” in the development of targeted technologies for the neutralization of activated sludges.

An urban biorefinery for food waste and biological sludge conversion into polyhydroxyalkanoates and biogas

This study focuses on the application of the concept of circular economy, with the creation of added-value marketable products and energy from organic waste while minimizing environmental impacts. Within this purpose, an urban biorefinery technology chain has been developed at pilot scale in the territorial context of the Treviso municipality (northeast Italy) for the production of biopolymers (polyhydroxyalkanoates, PHAs) and biogas from waste of urban origin. The piloting system (100–380 L) comprised the following units: a) acidogenic fermentation of the organic fraction of municipal solid waste (OFMSW) and biological sludge; b) two solid/liquid separation steps consisting of a coaxial centrifuge and a tubular membrane (0.2 μm porosity); c) a Sequencing Batch Reactor (SBR) for aerobic PHA-storing biomass production; d) aerobic fed-batch PHA accumulation reactor and e) Anaerobic co-digestion (ACoD). The thermal pre-treatment (72 °C, 48 h) of the feedstock enhanced the solubilization of the organic matter, which was converted into volatile fatty acids (VFAs) in batch mode under mesophilic fermentation conditions (37 °C). The VFA content increased up to 30 ± 3 g COD/L (overall yield 0.65 ± 0.04 g CODVFA/g VS(0)), with high CODVFA/CODSOL (0.86 ± 0.05). The high CODVFA/CODSOL ratio enhanced the PHA-storing biomass selection in the SBR by limiting the growth of the non-storing microbial population. Under fully aerobic feast-famine regime, the selection reactor was continuously operated for 6 months at an average organic loading rate (OLR) of 4.4 ± 0.6 g COD/L d and hydraulic retention time (HRT) of 1 day (equal to SRT). The ACoD process (HRT 15 days, OLR 3.0–3.5 kg VS/m3 d) allowed to recover the residual solid-rich overflows generated by the two solid/liquid separation units with the production of biogas (SGP 0.44–0.51 m3/kg VS) and digestate. An overall yield of 7.6% wt PHA/VS(0) has been estimated from the mass balance. In addition, a preliminary insight into potential social acceptance and barriers regarding organic waste-derived products was obtained.

The effect of mineral additives on the process of chlorine bonding during combustion and co-combustion of Solid Recovered Fuels

The use of solid recovered fuels (SRF) is often associated with an increased risk of chloride corrosion because these fuels can be high in chlorine and alkali. One way to reduce the risk of chloride corrosion is the co-combustion of fuel mixtures in the presence of a mineral additive containing chemical compounds that bind the emitted chlorides. This paper concerns the influence of mineral additives – constituting waste material, on the process of the binding of emitted chlorides. One of these waste materials could be a halloysite, not yet used in power industry. The research has shown its high chloride binding effectiveness, comparable to that of kaolin (known in literature as a mineral additive effectively binding chloride). Moreover, the studies have shown that SRF combustion in the presence of stabilized, dried and granulated sewage sludge, with a 25% mass fraction of sewage sludge, allows reducing chloride emissions. Studies are based on tests in a calorimetric bomb.

Direct Lewis-Brønsted acid ethanolysis of sewage sludge for production of liquid fuels

Ethanolysis carried out under Lewis-Brønsted acid catalysis was investigated as a possible process to valorize the organic fraction of urban sewage sludge, with the aim of selectively obtaining liquid biofuels. In a single reactive step, the conversion of lipids into fatty acid ethyl esters, of carbohydrates into ethyl levulinate, furanic compounds and ethyl glycosides and of proteins into ethyl ester of amino acids was achieved. The optimization of reactive conditions was conducted using pure chemicals as model compounds. The effect of the co-presence of water was also considered. Then, real samples of sewage sludge (as dried and wet centrifuged samples) were reacted in ethanol in the presence of the appropriate combination of homogeneous Lewis-Brønsted acid catalysts, namely 1 %wt aluminium chloride hexahydrate and sulfuric acid respect to ethanol. After 6 h at 453 K, 99% of lipids and almost 60% of initial complex sugars were effectively converted into the abovementioned target products. Conversions and yields were quite similar to those obtained by reacting pure compounds singularly, confirming the robustness of the process and its applicability to differently composed sludge. At the end of the reaction, products were easily recovered and purified from the alcoholic phase, whereas only a very limited amount of solids remain as inert materials. Final refined biofuels have high calorific values (37 and 40 MJ kg−1) and actually represent the 68.5 and 59.2% of the initial energy content of starting sludge, respectively. This strategy combines valorization of the starting organic fraction of sewage sludge and a considerable reduction of final solid waste (in a stabilised form) to be disposed of. Finally, through a preliminary feasibility study, this acid ethanolysis resulted in a competitive alternative to the anaerobic digestion of mixed sewage sludge to obtain biofuels.

Enhanced biogas production from municipal solid waste via co-digestion with sewage sludge and metabolic pathway analysis

The present study intends to evaluate the potential of co-digestion for utilizing Organic fraction of Municipal Solid Waste (OFMSW) and sewage sludge (SS) for enhanced biogas production. Metagenomic analysis was performed to identify the dominant bacteria, archaea and fungi, changes in their communities with time and their functional roles during the course of anaerobic digestion (AD). The cumulative biogas yield of 586.2 mL biogas/gVS with the highest methane concentration of 69.5% was observed under an optimum ratio of OFMSW:SS (40:60 w/w). Bacteria and fungi were found to be majorly involved in hydrolysis and initial stages of AD. Probably, the most common archaea Methanosarsina sp. primarily followed the acetoclastic pathway. The hydrogenotrophic pathway was less followed as indicated by the reduction in abundance of syntrophic acetate oxidizers. An adequate understanding of microbial communities is important to manipulate and inoculate the specific microbial consortia to maximize CH4 production through AD.