Enhanced Biomethane Production Research Articles

Enhanced biomethane production from Scenedesmus sp. using polymer harvesting and expired COVID-19 disinfectant for pretreatment

This study evaluates the repurposing of expired isopropanol (IPA) COVID-19 disinfectant (64% w/w) to pretreat algal biomass for enhancing methane (CH4) yield. The impact of harvesting methods (centrifugation and polymer flocculation) and microwave pretreatment on CH4 production from Scenedesmus sp. microalgal biomass were also investigated. Results show minimal impact of harvesting methods on the CH4 yield, with wet centrifuged and polymer-harvested biomass exhibiting comparable and low CH4 production at 66 and 74 L/kgvolatile solid, respectively. However, microalgae drying significantly increased CH4 yield compared to wet biomass, attributed to cell shrinkage and enhanced digestibility. Consequently, microwave and IPA pretreatment significantly enhanced CH4 production when applied to dried microalgae, yielding a 135% and 212% increase, respectively, compared to non-pretreated wet biomass. These findings underscore the advantage of using dried Scenedesmus sp. over wet biomass and highlight the synergistic effect of combining oven drying with IPA treatment to boost CH4 production whilst reducing COVID-19 waste.

Microbial community dynamics and functional potentials in the conversion of oil palm wastes into biomethane.

Oil palm processing generates substantial waste materials rich in organic content, posing various environmental challenges. Anaerobic digestion (AD), particularly for palm oil mill effluent (POME), offers a sustainable solution, by converting waste into valuable biomethane for thermal energy or electricity generation. The synergistic activities of the AD microbiota directly affect the biomethane production, and the microbial community involved in biomethane production in POME anaerobic digestion has been reported. The composition of bacterial and archaeal communities varies under different substrate and physicochemical conditions. This review discusses the characteristics of POME, explores the microbial members engaged in each stage of AD, and elucidates the impacts of substrate and physicochemical conditions on the microbial community dynamics, with a specific focus on POME. Finally, the review outlines current research needs and provides future perspectives on optimizing the microbial communities for enhanced biomethane production from oil palm wastes.

Bioelectrochemically enhanced biomethane production from low-rank coal using multiple microbial strains

Although microbial in-situ gasification of coal has been established to be an environmentally friendly and sustainable mining method, the low efficiency of methane production via coal micro-gasification limits the commercial applicability of this technology. In this regard, the application of electric fields can contribute to enhancing the efficiency of anaerobic microbial coal degradation. In this study, to investigate the effects of low-intensity electric fields on coal degradation by different exogenous microbial species, we conducted laboratory-scale batch anaerobic fermentation experiments at 0.9, 1.5, and 2.2 V using a micro-gas measuring device to quantify biogas production. The results revealed that application of a low-intensity electric field can promote the production of methane by different microbes, with the highest gas production (7.92 mL/g) obtained at 1.5 V, representing an increase of 131.58 % compared with fermentation conducted in the absence of an applied electric field. The electrodes facilitated the microbial utilization or dissolution of organic matter on the coal surface, leading to a reduction in surface functional groups, with the fermentation medium mainly comprising aromatic hydrocarbons. The coal particles at the anode appeared rough. Collectively, our findings in this study revealed that the application of electric fields contributed to a modification of microbial metabolism and promoted an enhancement of methane production. We believe these findings have important implications for enhancing the microbial production of biomethane from coal.

Anaerobic Treatment of Food Waste with Biogas Recirculation under Psychrophilic Temperature

Food waste has emerged as a pressing concern, and thus advanced techniques to valorize food waste into nutrition rich materials as well as renewable energy are highly important. The exceptional biodegradability of food waste renders it a highly suitable substrate for anaerobic treatment. This leads to energy production and a reduction in the carbon footprint. Nevertheless, in frigid territories like Canada, the conventional mesophilic anaerobic digestion at 30–40 °C can require substantial amounts of energy. Consequently, this study introduces a new approach to treat food waste at psychrophilic temperatures (1–20 °C). Lower temperatures can negatively impact cellular processes during anaerobic treatment, rendering substrates less accessible to microscopic organisms. To address this challenge associated with lower temperatures, the study introduces an innovative biogas recirculation strategy. The primary objectives of this study are to assess the viability of anaerobic treatment for food waste at psychrophilic temperatures and to investigate the effectiveness of reintroduction of the produced biogas to the anaerobic system in enhancing biomethane generation and stability of the system. Batch experiments were conducted on food waste in various assessments, both with and without biogas recirculation. The outcomes revealed a methane concentration ranging from 68% to 93% when biogas recirculation was employed, whereas without this technique, methane concentration varied between 10% and 45%. Moreover, with biogas recirculation, the reduction in volatile solids reached a maximum of 92%, and there was an 82% decrease in chemical oxygen demand. In conclusion, the utilization of the recirculation of biogas at the psychrophilic temperature range enhanced biomethane production and reduction of volatile solids and chemical oxygen demand. This study underscores the potential of employing anaerobic treatment with reintroduction of produced biogas into the system in cold regions as an economically viable and sustainable choice for treating food waste with nominal energy consumption.

Experimental analysis on the effects of trace metals as micronutrients in enhancing biomethane production

Anaerobic digestion (AD) of microbial biomass has proven to be a significant breakthrough technique in producing biogas rich in methane. The quantity of biogas obtained by anaerobic digestion processes varies significantly based on the nature and characteristics of the substrates used. This research work focuses on the use of trace metals such as Fe, Cu, Zn, Mn, Mg, Ni in proper proportions to enhance the microbial consortium thus aiding in the production of biogas of desired quality. The substrate used for this study is Food Waste and Cow dung. Food waste from the college canteen was used as the substrate and cow dung was used as an inoculum for providing a catalytic effect in the anaerobic reactor. Food waste and cow dung in the ratio 75:25 was fed into the anaerobic digesters with varying concentrations of micronutrients supplemented to the reactors operating at a pH range maintained between 6.8 and 7.2 under room temperatures (22–27 ºC). The effect of these micronutrients on the anaerobic digestion process was observed by analysing the biogas yield, pH, alkalinity, total solids, and volatile solids of the samples. Sulphates of Fe, Cu, Mn, Ni and Chlorides of Zn and Mg was used in this study. Fe, Cu, Zn, Mn, Mg, Ni were fed to the anaerobic reactor at varying concentrations to arrive at the optimum dosage for the chosen substrates. The optimum dosage for the chosen substrate concentration was taken as that concentration which yielded maximum biogas yield with less retention time. Fe at concentrations varying from 1 mg/l–5 mg/l was fed to the anaerobic reactor and the optimum dosage for the chosen substrate concentration was noted at 1 mg/l. The reactor with an Fe concentration of 1 mg/l showed an increase in biogas production rate of about 68% compared to the sample without Fe supplementation as well as the ones with other dosages greater than 1 mg/l and less than 1 mg/l of Fe dosage. Each nutrient is subjected to an individual dosage analysis before arriving at the optimum dosage and then a mixture of the arrived optimum dosages will be analysed for further study. The process set-up will be conducted for a minimum retention period of 20 days and terminated when the results show a deep fall in the biogas production for consecutive days. Biogas produced for the nutrient supplementation of 1 mg/l of Fe, 0.5 mg/l of Cu, 1 mg/l of Zn, 0.5 mg/l of Mn, 1 mg/l of Mg and 0.5 mg/l of Ni yielded a biogas of 850 ml/g VS in 10 day retention time. Triplicate samples study were conducted and biogas yield measured daily to arrive at concordant results. The results showed an increase in the biomethane yields of the substrate by about 60% compared to the reactors which had no micronutrient supplementations. Furthermore, the study summarized that not all micronutrients are essential for a successful microbial metabolism to take place in an anaerobic digester as the micronutrient Manganese at varying dosages of 0.5 mg/l, 1 mg/l and 1.5 mg/l showed an antagonistic effect on the microbial activity in the reactor. The results obtained from this study showed a significant improvement in the quantity of biogas produced from the substrates supplemented with micronutrients at optimum dosages thus arriving at an efficient and effective method for treating waste in a sustainable way.

Enhancing biomethane production from citrus waste: An integrated approach of hydrothermal carbonization and anaerobic digestion for sustainable waste management

This study investigates the energy recovery potential of bio-oil derived from hydrothermal carbonization (HTC) of citrus waste through anaerobic digestion (AD). The bio-oil, a complex mixture containing 30-50% of the original carbon from biomass, serves as a valuable substrate for AD. Leveraging the HTC pretreatment, the hydrolysis step in AD becomes more efficient, facilitating faster degradation rates. Anaerobic digestion of the bio-oil was conducted in a high-loading hybrid anaerobic reactor. The reactor underwent stabilization using tomato liquid fraction, followed by bio-oil feeding with an applied volumetric loading of 5 g COD/L-d under mesophilic conditions. Remarkably, COD removals exceeded 90% when utilizing the tomato fraction and surpassed 80% in the bio-oil feed. Additionally, methane yield approached theoretical levels, highlighting the effectiveness of combining HTC and AD technologies. The study demonstrates that the integration of HTC and AD offers a promising alternative for the sustainable utilization of citrus industry wastes, showcasing high removal efficiencies and methane production. This approach aligns with circular economy principles, providing a pathway for efficient waste valorization and renewable energy generation.

Enhanced biomethane production from waste activated sludge anaerobic digestion by ceramsite and amended Fe2O3 ceramsite

Wastes recycling and reutilization technique could simultaneously fulfill waste control and energy recovery sustainably, which has attracted increasing attention. This work proposed a novel waste reuse technology utilizing ceramsite and amended Fe2O3-ceramsite made from waste activated sludge (WAS) as additives to promote the yield of methane from WAS anaerobic digestion (AD). Experimental results demonstrated that compared to the control (85.05 ± 0.2 mL CH4/g-VS), the cumulative methane yield was effectively enhanced by 14% and 40% when ceramsite and Fe2O3-ceramsite were added. Further investigation revealed that ceramsite, especially the Fe2O3-ceramsite, enriched the populations of key anaerobes involved in hydrolysis, acidification, and methanogenesis. Meanwhile, potential syntrophic metabolisms between syntrophic bacteria and methanogens were confirmed in the Fe2O3-ceramsite AD system. Mechanisms studies exhibited that ceramsite and Fe2O3-ceramsite reinforced intermediate processes for methane production. The favorable pore structure, enhanced Fe (III) reduction capacity and conductivity also contributed a lot to the AD process.

Unlocking the power of synergy: Cosubstrate and coculture fermentation for enhanced biomethane production

The energy crisis, shortage of conventional fuels, and increasing pollution have directed the research toward renewable energy. Methane is one such form of energy that can be used as fuel directly or for electricity generation. It is one of the conventional fuels produced as biogas in triable and rural areas from organic waste using household biogas digesters. However, adapting such technology at commercial and global scales needs to withstand many challenges like purity and quality of methane, yield, cost of production, and efficient utilization of biomass residues. Generally, organic residues from industries and agricultural fields have higher applicability due to availability in abundance but their complex nature slower down the degradation process. In addition, some of the residues are rich in carbon while some are rich in nitrogen which might affect the product yield hence coculture and codigestion are effective approaches to valorize the waste. Coculture provides the possibility to exploit multiple pathways to degrade polymer compounds along with transformation into methane while codigestion might balance the availability of nutrients. The approach has proved promising but commercial exploitation needs further exploration for the compatibility and stability of coculture.

Enhancing Biomethane Production from OFMSW: The Role of Moderate Temperature Thermal Pretreatment in Anaerobic Digestion

Enhancing Biomethane Production from OFMSW: The Role of Moderate Temperature Thermal Pretreatment in Anaerobic Digestion

The Implementation of Waste Biomass Substrates as Feedstock for The Production of Bio-Electricity Through Microbial Fuel Cells (MFCS): A Short Review

Lignocellulosic biomass plays a pivotal role in sustainable energy production, with a focus on indirect biomass fuel cells (IDBFC) and direct biomass fuel cells (DBFC). IDBFCs require the initial conversion of biomass into simpler forms like sugars, biogas, syngas, or biocharfor subsequent electricity generation. In contrast, DBFCs offer a more direct approach, generating electricity from biomass without intermediate steps. Lignocellulosic biomass, composed of cellulose, lignin, and hemicellulose, has diverse applications, from bioethanolto direct electricity generation. However, the complex composition of lignocellulosic compounds, including carbon, hydrogen, oxygen, phosphorus, nitrogen, and sulfur, poses challenges for efficient enzymatic hydrolysis, a crucial factor in achieving high power density inMicrobial Fuel Cells (MFCs). MFCs use microorganisms to convert substrates into electricity, influenced by factors like substrate degradation rate, circuit resistance, electron transfer rates, proton mass transfer, electrode materials, and operational conditions. The selection of proper electrode materials is vital for optimising MFC performance. At the heart of MFC performance are electricigens, microorganisms facilitating electron transfer from biomass to the anode through direct or indirect mechanisms. Direct electron transfer (DET), relying on physical contact between microorganism membranes and the anode, is preferred for its efficiency and eco-friendliness. The paper also explores the importance of nutrient supplements (macro and micro) in enhancing bio-methane production and process stability in agro-industrial biogas mono-digestion plants. Nutrient balance significantly affects microbial generation time, degradation rates, and gas production in anaerobic digestion processes. In conclusion, understanding the intricate interplay between lignocellulosic biomass energy fuel cells, electricigens, and their performance factors is crucial for advancing sustainable energy production. MFCs show promise in utilising sludge and various waste biomasses, positioning them as practical, reliable, and versatile power sources in the evolving landscape of renewable energy technologies.
 Keywords: Lignocellulosic waste, bioenergy, microbial fuel cells (MFCs), electricigens

Harnessing Digestate Potential: Impact of Biochar and Reagent Addition on Biomethane Production in Anaerobic Digestion Systems

This article reports on an experiment that aimed to investigate the effects of digestate and cosubstrate input with varying biochar concentrations on methane production in anaerobic digestion processes. The findings revealed distinct trends in methane production among the substrates. Further investigations were conducted to evaluate the effects of different types of biochars on biomethane production from raw cattle manure digestate. Four conditions were tested: one raw digestate condition and three digestate conditions containing 1% of a different biochar type to one another. BC1 (PEFC-certified spruce BC) and BC2 (oak wood BC) showed promising results in enhancing biomethane production. About 884.23 NmL of methane was produced, with a yield and productivity of 22.80 NmL.g−1 and 1.62 NmL.g−1.day−1 with BC1. However, BC3 (cow and chicken manure digestate BC) demonstrated lower biomethane production compared to raw digestate. Additionally, the study explored the effects of adding reagents to digestate. Hematite and iron chloride salt did not show any positive effects on biomethane production when biochar was introduced, while activated carbon powder significantly improved biomethane production rates by approximately 11.18%.

Cost-effective bio-methanation via oxalic acid coupled sonication pretreatment of Gracilaria salicornia

Gracilaria salicornia (macroalgae) can be used for the production of biofuels such as biomethane. Because of the complex cell wall structure in macroalgae, disintegration is crucial for anaerobic fermentation. The main goal of this study is to implement the combination of oxalic acid and ultrasonic pretreatment (SP) techniques over macroalgae Gracilaria salicornia in order to generate energy-efficient biomethane. A combination of ultrasonic pretreatment and oxalic acid (OSP) improves macromolecule availability in anaerobic fermentation, leading to enhanced biomethane production. Ultrasonic pretreatment was initially performed at 20–180 W for 5–60 min. A maximum solubilization of 9.19% was obtained, with a SCOD of 496 mg/L, at optimal conditions (140 W intensity, 30 min). Oxalic acid was added in various dosages from 0.01 to 0.1 N to optimize OSP conditions, enhance disintegration efficiency, and maximize biomethane production. With a SCOD of 914 mg/L and 16.93% SCOD solubilization, the best result was observed with 0.06 N oxalic acid dosage. A maximum biomethane production was achieved in the OSP sample (0.252 L/g COD) compared with the control (0.22 L/g COD) and SD (0.139 L/g COD) samples. As compared to SP, OSP was proved to be more energy-efficient. It was concluded that OSP was an efficient energy source for field applications. Combined OSP was a successful strategy for the production of energy-efficient biomethane.

Enhanced biomethane production with a low carbon footprint via anaerobic co-digestion of swine wastewater with rice husk

An electricity-assisted anaerobic co-digestion (EAAD) process was developed and compared with conventional anaerobic co-digestion (AD) using piggery wastewater and rice husk as feedstocks. Various methodologies, including kinetic models, microbial community analyses, life-cycle carbon footprints, and preliminary economic analysis, were integrated to comprehensively evaluate the performance of the two processes. The results demonstrated that EAAD exhibited a positive improvement of 2.6 % to 14.5 % in biogas production compared to AD. The suitable wastewater-to-husk ratio for EAAD was found to be 3:1, which corresponded to a carbon-to‑nitrogen ratio of approximately 14. This ratio demonstrated positive co-digestion effects and electrical enhancements in the process. According to the modified Gompertz kinetics, the biogas production rate in EAAD ranged from 1.87 to 5.23 mL/g-VS/d, significantly higher than the range of 1.19 to 3.74 mL/g-VS/d observed in AD. The study also investigated the contributions of acetoclastic and hydrogenotrophic methanogens to biomethane formation, revealing that acetoclastic methanogens accounted for 56.6 % ± 0.6 % of the methane production, while hydrogenotrophic methanogens contributed to 43.4 % ± 0.6 %. No significant difference in the methanogenic reaction pathways was observed between AD and EAAD, indicating that the introduction of an external electric field did not alter the predominant pathways (p > 0.05, two-sample t-test). Furthermore, retrofitting existing AD plants with EAAD units can reduce the carbon intensity of piggery wastewater treatment by 17.6 % to 21.7 %. The preliminary economic analysis indicated a benefit-cost ratio of 1.33 for EAAD, confirming the feasibility of implementing EAAD for wastewater treatment while simultaneously producing bioenergy. Overall, this study provides valuable insights into upgrading the performance of existing AD plants by introducing an external electric field. It demonstrates that EAAD can achieve higher and cost-effective biogas production with a lower life-cycle carbon footprint, thus enhancing the sustainability and efficiency of the biogas production process.

Twin-Screw Extrusion Mechanical Pretreatment for Enhancing Biomethane Production from Agro-Industrial, Agricultural and Catch Crop Biomasses

This study aimed to evaluate the effects of mechanical treatment through twin-screw extrusion for the enhancement of biomethane production. Four lignocellulosic biomasses (i.e., sweetcorn by-products, whole triticale, corn stover and wheat straw) were evaluated, and two different shear stress screw profiles were tested. Chemical composition, particle size reduction, tapped density and cellulose crystallinity were assessed to show the effect of extrusion pretreatment on substrate physico-chemical properties and their biochemical methane production (BMP) capacities. Both mechanical pretreatments allowed an increase in the proportion of particles with a diameter size less than 1 mm (from 3.7% to 72.7%). The most restrictive profile also allowed a significant solubilization of water soluble coumpounds, from 5.5% to 13%. This high-shear extrusion also revealed a reduction in cellulose crystallinity for corn stover (i.e., 8.6% reduction). Sweetcorn by-products revealed the highest BMP values (338–345 NmL/gVS), followed by corn stover (264–286 NmL/gVS), wheat straw (247–270 NmL/gVS) and whole triticale (233–247 NmL/gVS). However, no statistical improvement in maximal BMP production was provided by twin-screw extrusion. Nevertheless, BMP kinetic analysis proved that both extrusion pretreatments were able to increase the specific rate constant (from 13% to 56% for soft extrusion and from 66% to 107% for the high-shear one).

Low-temperature torrefaction assisted with solid-state KOH/urea pretreatment for accelerated methane production in wheat straw anaerobic digestion

Low-temperature torrefaction assisted with solid-state KOH/urea applied onto wheat straw was proposed to break down the lignocellulosic material to enhance biomethane production in anaerobic digestion (AD). The optimization of key parameters applying the Box-Behnken design and response surface methodology showed that an addition of 0.1 g/gstraw KOH/urea at 180 °C while torrefying for 30 min was the optimal condition for producing biomethane. Results indicate that co-applying KOH and urea in torrefaction synergistically enhanced the biodegradability of straw by effectively removing lignin and largely retaining cellulose, giving rise to a 41 % increase in the cumulative methane production compared to untreated straw (213 mL/g-volatile solids (VSraw)) from batch AD. Additionally, the nitrogen- and potassium-rich digestates helped to improve soil fertility, thus achieving a zero-waste discharge. This study demonstrated the feasibility of using solid-state KOH/urea assisted low-temperature torrefaction as an effective pretreatment method to promote methane production during AD.

Taxonomic and enzymatic basis of the cellulolytic microbial consortium KKU-MC1 and its application in enhancing biomethane production

Lignocellulosic biomass is a promising substrate for biogas production. However, its recalcitrant structure limits conversion efficiency. This study aims to design a microbial consortium (MC) capable of producing the cellulolytic enzyme and exploring the taxonomic and genetic aspects of lignocellulose degradation. A diverse range of lignocellulolytic bacteria and degrading enzymes from various habitats were enriched for a known KKU-MC1. The KKU-MC1 was found to be abundant in Bacteroidetes (51%), Proteobacteria (29%), Firmicutes (10%), and other phyla (8% unknown, 0.4% unclassified, 0.6% archaea, and the remaining 1% other bacteria with low predominance). Carbohydrate-active enzyme (CAZyme) annotation revealed that the genera Bacteroides,Ruminiclostridium,Enterococcus, and Parabacteroides encoded a diverse set of cellulose and hemicellulose degradation enzymes. Furthermore, the gene families associated with lignin deconstruction were more abundant in the Pseudomonas genera. Subsequently, the effects of MC on methane production from various biomasses were studied in two ways: bioaugmentation and pre-hydrolysis. Methane yield (MY) of pre-hydrolysis cassava bagasse (CB), Napier grass (NG), and sugarcane bagasse (SB) with KKU-MC1 for 5 days improved by 38–56% compared to non-prehydrolysis substrates, while MY of prehydrolysed filter cake (FC) for 15 days improved by 56% compared to raw FC. The MY of CB, NG, and SB (at 4% initial volatile solid concentration (IVC)) with KKU-MC1 augmentation improved by 29–42% compared to the non-augmentation treatment. FC (1% IVC) had 17% higher MY than the non-augmentation treatment. These findings demonstrated that KKU-MC1 released the cellulolytic enzyme capable of decomposing various lignocellulosic biomasses, resulting in increased biogas production.

Techno-economic assessment of enhanced Biogas&Power-to-SNG processes with high-temperature electrolysis integration

Biogenic energy sources are essential elements of the decarbonization pathways, but are strongly constrained by the limited availability. In this context, Biogas&Power-to-X technologies are strongly supported as a promising solution to foster renewable power generation and drive sector coupling opportunities. This work investigates enhanced Synthetic Natural Gas (SNG) production processes for the repurposing of biogas plants. As an alternative to combined heat and power applications via internal combustion engines, the Italian legislation is supporting biogas-to-biomethane upgrading, focusing on the transport market. The proposed integrated plant scheme is a flexible solution based on Power-to-Hydrogen and methanation, able to exploit both electric and gas grid connections, enhancing biomethane production. Advanced process schemes are studied combining solid oxide electrolysers that exploit the methanation waste heat as input thermal energy and flexible PEM electrolysers that improve the part-load operation. The calculated efficiency at max load is about 55% for the Power-to-Methane block and nearly 75% for the overall integrated plant. Results show limited sensitivity of efficiency to input power variations, making the system suitable for the recovery of surplus renewable power generation.

Ensiling water hyacinth for enhanced biomethane production: effect of co‐ensiling with maize straw and eggshell powder as additive

AbstractBACKGROUNDThe invasion of water hyacinth (WH) on water bodies comes with adverse consequences for humans and the environment. Using WH as a substrate for affordable and clean energy production is one way of controlling the invasiveness of the aquatic plant. In this study, ensiling was carried out with and without the addition of maize straw (MS) and eggshell powder (ES) to determine the effect of higher total solids (TS) and butyric acid contents on the biomethane potential (BMP) of WH. The silages were stored at ambient temperature for 210 days. The kinetics of biomethane production was determined using three different kinetic models.RESULTSEnsiled WH without MS and ES had a reduced BMP after 210 days. However, a combination of higher TS (40%) and butyric acid contents, resulting from the addition of MS and ES, significantly increased the BMP of WH by 64% after 210 days of ensiling. The kinetic study showed that the dual‐pool kinetic model described the BMP of ensiled and co‐ensiled WH better than the first‐order and modified Gompertz models.CONCLUSIONSIncreasing TS and butyric acid contents by co‐ensiling with MS and ES is a low‐cost and sustainable method of enhancing biomethane production from WH. In this way, the invasive nature of WH can be effectively controlled (since a large quantity can be harvested and stored) and circular economy can be enhanced through the effective utilization of waste. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Multi-functional of TiO2@Ag core–shell nanostructure to prevent hydrogen sulfide formation during anaerobic digestion of sewage sludge with boosting of bio-CH4 production

Herein, we report a novel supplement called TiO2@Ag core–shell nanostructure that revealed a high removal of hydrogen sulfide gas with boosting the bio-methane production from the anaerobic digestion process of sewage sludge. TiO2@Ag core–shell nanostructure was synthesized by the deposition of Ag shell NPs on TiO2 core NPs using a reduction method. The prepared samples of the core–shell and its components were characterized using different techniques such as XRD, SEM, TEM and AFM. A concentration of TiO2@Ag core–shell NS (50 mg/L) was supplemented with anaerobic bioreactors to study their effect on the removal of hydrogen sulfide from the anaerobic digestion of sewage sludge compared to silver and titanium dioxide nanoparticles alone. The results showed a 3-fold increase in the produced bio-methane upon the use of TiO2@Ag core–shell NS with a high removal of hydrogen sulfide (91.9 %) compared to using only silver nanoparticles or titanium dioxide nanoparticles. Concisely, the prepared TiO2@Ag core–shell NS was multifunctional and more active than its components in removing hydrogen sulfide, enhancing bio-methane production, and detoxifying hazardous materials from sewage sludge.

Depolymerization of corn stover by urea-hydrothermal pretreatment for efficient biomethane production and microbial community analysis of anaerobic digestion

The present study investigated the depolymerization products, biomethane production, and microbial community of corn stover (CS) depolymerized with urea using a hydrothermal approach. For the combined depolymerization, urea concentrations of 0%–4%, hydrothermal temperatures of 150 °C, and retention times of 10–50 min were utilized. Hydrothermal depolymerization predominantly converted the solid phase of CS to total volatile fatty acids and oligomers, whereas the addition of urea facilitated the breakage of the ester bonds in the lignocellulose structure, making more components accessible. Additionally, the level of total volatile fatty acid and total phenol increased up to 552.0% and 1559.5% more than the control, which was correlated to the depolymerization of solid components in CS. The urea and hydrothermal parameters had apparent effects on the compositions of the hydrolysate. Accordingly, the depolymerization with 2% urea and 10 min of hydrothermal time produced 22.3% more cumulative biomethane yield with 7 days less T80 (the time required to produce 80% of the total potential biomethane). The microbial community analysis revealed that the combined depolymerization could facilitate the acetate–methane pathway by fostering the growth of Proteiniphilum, DMER64, Sedimentibacter, and Methanosarcina, thereby enhancing biomethane production. These findings demonstrated that the combination of urea and hydrothermal depolymerization could improve the anaerobic conversion efficiency of CS to biomethane.