Increase In Methane Yield Research Articles

Symbiotic Bacteroides and Clostridium-rich methanogenic consortium enhanced biogas production of high-solid anaerobic digestion systems

The high-solid anaerobic digestion (AD) for anaerobic co-digestion of palm oil mill effluent (POME) and oil palm empty fruit bunches (EFB) has low degradation efficiency. The enhancement of biogas production and EFB degradation efficiency by Bacteroides and Clostridium-rich methanogenic consortium was investigated. A Bacteroides and Clostridium-rich methanogenic consortium have xylanase, FPase, endo-glucanase, and exo-glucanase activity of 9.2, 1.3, 2.1, and 1.5 IU·mL−1, respectively with EFB degradation efficiency of 57.5%. Methane production (79 m3-CH4·tonne−1-EFB) by Bacteroides and Clostridium-rich methanogenic consortium augmentation was increased by 67.2%. The real application of bioaugmentation in the feedstock mixing tank before a feed to the AD reactor significantly increased methane yield (376.7 mL-CH4·g-1-VS−) by 85.5%. Bioaugmentation of Bacteroides and Clostridium-rich methanogenic consortium increased the number of hydrolytic bacteria and strengthened symbiotic relationships with indigenous microorganisms resulting in high biogas production, accelerated hydrolysis, and reduced solids accumulation of the high-solid AD process.

Assessment of electrooxidation as pre- and post-treatments for improving anaerobic digestion and stabilisation of waste activated sludge

This study evaluates the effects of electro-oxidation as a means for enhancing sludge stabilisation. Boron-doped diamond electrodes were used to treat waste activated sludge and digestate under different operating parameters (current density, conductivity, pH, and time). Electro-oxidation runs affected the solubilisation of organic matter, which seemed to improve anaerobic digestion and dewaterability characteristics.Among the tested parameters, pre-treating sludge via electro-oxidation under alkaline conditions (Treatment T5) resulted in the highest increase in soluble organic material compared to that in the control, with total organic carbon (TOC) and soluble chemical oxygen demand (COD) values of 2753 and 7819 mg L−1, respectively (control TOC and COD values were 385 and 1073 mg L−1). This pretreatment also achieved a high hydrolysis rate (higher concentration in volatile fatty acids) with a concomitant increase in methane yield (approximately 18%). On the other hand, the application of electro-oxidation as a post-treatment for improving digestate dewaterability resulted in noticeable changes in the release of water during drying due to protein and aliphatic matrix modification of the sample.

Co-digestion of sewage sludge and fat, oil, and grease with BioAmp pretreatment under mesophilic conditions

This study investigated the potential benefit of co-digesting sewage sludge (SS) and settled/mixed fat, oil, and grease (FOG) with BioAmp pretreatment, a bio-additive product, for a utility. BioAmp was found to increase the soluble chemical oxygen demand (SCOD)/COD ratio of FOG (from 4.19 to 4.49), consequently enhancing volatile solid (VS) reduction (from 75.9 to 84.8%). The ratio of SS and FOG for co-digestion was based on their actual daily production volume, resulting in FOG content ranging between 15 and 20% VS for co-digestion assays. Co-digestion of SS and mixed FOG waste after BioAmp pretreatment produced the highest cumulative methane yield (CMY) of 400 mL/g VSadded, which is 98% higher than that of mono-digestion of SS (202 mL/g VSadded). Kinetic analysis demonstrated a synergistic effect in co-digestion of FOG and SS with both increased CMY and degradation rate constant. For the utility, co-digestion can increase methane yield by 141%; however, 7.77% more biosolids are produced and 6% more total nitrogen will return to mainstream, a potential burden to nutrient management. Overall, the results of batch test demonstrated the benefits of co-digestion of SS and FOG with BioAmp pretreatment in terms of increased CMY, degradation rate constant, and VS reduction. The analysis of the utility showed that co-digestion can produce more biogas but also increase more biosolids and total nitrogen return.

Cow manure stabilizes anaerobic digestion of cocoa waste

Anaerobic digestion of a mono-feedstock often causes low methane yields and process instability. An effective strategy to overcome these barriers is co-digestion with animal manure. The obtained process improvement is often attributed to buffer capacity, nutrients, vitamins and trace metals, and microorganisms present in manure, but it remains unknown which factor plays the key role in digester performance. Here, we investigated anaerobic digestion of cocoa waste in four different treatments: mono-digestion, addition of synthetic nutrients, co-digestion with sterile cow manure, and co-digestion with raw cow manure. Co-digestion with raw manure resulted in the highest methane yield of 181 ± 39 L kg−1 VS (volatile solids), similar to the co-digestion with sterile manure, i.e., 162 ± 52 L kg−1 VS. The supplementation of synthetic nutrients to the anaerobic digestion of cocoa waste only temporarily increased methane yield, indicating that this will tackle a lack of nutrients in the short term, but has a limited long-term contribution to the stabilization of the process. Hence, because of the inability of synthetic nutrients to stabilize the digestion process and the similarity between the digesters fed sterile and raw manure, both at the physico-chemical and microbial level, the key contribution of manure co-digestion with cocoa seems to be the provision of buffering capacity.

Anaerobic co-digestion of fruit and vegetable waste: Synergy and process stability analysis

ABSTRACT Anaerobic mono- and co-digestion of fruits and vegetable waste (FVW), slaughterhouse waste (SHW), and cattle manure (CM) under mesophilic conditions (35°C) were conducted through biochemical methane potential tests to investigate how the FVW in a co-substrate formulation improves the methane yield, the degradative synergy between substrates, and especially the stability of the process. The co-digestion of FVW:SHW and FVW:CM were evaluated with volatile solids (VS) ratios of 1:2, 1:1, and 2:1. The results indicated that the highest synergistic effect was found in the co-digestion FVW:CM at 1:1 VS ratio. However, the co-digestion FWV:SHW at 1:2 VS ratio increased the methane yield by 74.2% compared to the mono-digestion of FVW (776.3 mL CH4 g VSadded −1). As a critical condition in these processes, the stability was evaluated using the early warning indicator VFA/TA (volatile fatty acids/total alkalinity). The co-substrate SHW promotes greater stability in methane production as the soluble carbohydrate content in FVW increases. It was proposed that the high protein (49.04 ± 0.96% VS) and ammonia content (693 ± 3 mg L−1) of SHW leads to the formation of a dampening system known as a carbonate-acetic buffer. It was concluded that balanced distribution between carbohydrates, proteins, and lipids is crucial to increase methane yields, and the low methane productions were associated with low N-NH4 + concentrations (FVW:CM co-digestions). The results obtained in this study can serve as a basis to design full-scale digesters under similar operating conditions and with the same substrate:co-substrate relationships. Implications: The production of methane from the anaerobic digestion process of food, and lose waste presents a viable alternative of valorization and could help to mitigate environmental impacts. However, anaerobic digestion from these substrates carries high instabilities and low methane yields. The need to increase these yields and contribute to process stability must be considered in the selection of a co-substrate. In this context, this work aims to evaluate the best fruits and vegetable waste: co-substrateformulation, that promotes higher methane yield, a synergy between substrates, and to improve the AD process stability in the presence of perturbations in the substrate composition. We believe that our results could be helpful for the design processes for methane production from fruit and vegetable waste, to contribute to competitiveness with conventional energies and promote the sustainability of these processes.

An integrated strategy to enhance performance of anaerobic digestion of waste activated sludge

Anaerobic digestion (AD) is an essential process in wastewater treatment plants as it can reduce the amount of waste activated sludge (WAS) for disposal, and also enables the recovery of bioenergy (i.e. methane). Here, a new pretreatment method to enhance anaerobic digestion was achieved by treating thickened WAS (TWAS) with ferric (as FeCl3) and nitrite simultaneously for 24-hour at room temperature. Biochemical methane potential tests showed markedly improved degradability in the pretreated TWAS, with a relative increase in hydrolysis rate by 30%. A comparative experiment with the operation of two continuous-flow anaerobic digesters further demonstrated the improvement in biogas quantity and quality, digestate disposal, and phosphorus recovery in the experimental digester. The dosed FeCl3 (i.e. ~6 mM) decreased the pH of TWAS to ~5, which led to the formation of free nitrous acid (FNA, HNO2) at parts per million levels (i.e. ~6 mg N/L), after dosing nitrite at 250 mg NO2−–N/L. This FNA treatment caused a 26% increase in methane yield and volatile solids destruction, 55% reduction in the viscosity of sludge in digester, and 24% less polymer required in further digestate dewatering. In addition, the dosed Fe(III) was reduced to Fe(II) which precipitated sulfide and phosphorus, leading to decreased hydrogen sulfide concentration in biogas, and increased percentage of vivianite in the total crystalline iron species in digested sludge. Our study experimentally demonstrated that combined dosing of FeCl3 and nitrite is a useful pretreatment strategy for improving anaerobic digestion of WAS.

Role of waste-based geopolymer spheres addition for pH control and efficiency enhancement of anaerobic digestion process.

In anaerobic digestion processes, pH has a vital role due to the direct impacts on the microbial community. An eco-friendly approach has been applied to control pH in anaerobic bioreactors, using waste-containing fly ash geopolymer spheres (GS) instead of powdered chemical compounds, to promote continuous alkalis leaching. The influence of GS porosity and concentration on the behavior of anaerobic sequential batch reactor treating cheese whey was evaluated. Results showed that the use of GS with the highest concentration and porosity promoted an increase in methane yield up to 30%, compared to the assay with powdered chemical compounds addition. In addition, GS boosted butyric acid production to the detriment of propionic acid, which favored methane production by a factor up to 1.2. This innovative approach indicates that GS addition can regulate pH in anaerobic digesters treating challenging wastewaters and, simultaneously, improve not only its efficiency but also the sustainability of the entire process.

Enhancement of methane yield from cotton stalks by mechanical pre-treatment

Cotton stalks (CS) are lignocellulosic agricultural by-products, a potential source for biogas production, but pretreatment must be considered since hydrolysis is the rate-limiting stage for lignocellulosic biomass substrates. This study investigates the feasibility of mechanical pretreatment of CS to enhance methane production. Batch anaerobic digestion of CS samples with particle sizes ranging from 0.5 to 65 mm was carried out in 1 L eudiometer batch digesters for 48 days at 37°C. Results showed that methane yield was inversely proportional to particle size, and the quality of biogas was good (54.0–55.2% CH4). Significant increases in methane yield were observed with 20.3% and 26% for samples with a particle size of 3 mm and 0.5 mm, respectively, compared to untreated CS. The coefficient of anaerobic energy turnover was relatively low (20.2–25.5%). Reduction of the CS particle size to 3 mm or less is recommended to achieve effective methane conversion and decrease the retention time in an anaerobic digester from 31 to about 25 days. However, to offset the high energy demand required for grinding, further research should be conducted in combining size reduction with chemical and physicochemical pretreatment.

Hydrothermal pretreatment of sewage sludge enhanced the anaerobic degradation of cationic polyacrylamide (cPAM)

Cationic polyacrylamide (cPAM) is a widely used flocculant to dewater sewage sludge (SS) for high-solids anaerobic digestion (AD), and its degradation is crucial since it would release toxic acrylamide (AM) once entering environment. Hydrothermal treatment (HTT) is an efficient method to enhance the AD efficiency of SS. However, the effects of cPAM on AD of SS and the degradation of cPAM during HTT-AD process have not be studied. The study showed cPAM at 20 mg/g TS increased methane yield of SS from 127.0 to 138.9 ml CH4/g TS in HTT-AD process, and the biodegradability of cPAM was 76.3%, which was much higher than that (7.4%) without HTT. In HTT-AD process, the enrichment of certain microbes (e.g. Gelria sp.) was observed, which might be related with cPAM degradation. HTT decreased the molecular weight (MW) of cPAM, and resulted in the production of 2-hydroxy-ethyl-trimethylammonium, ammonia, trimethylamine, and ethanol. Methane potential tests of the main HTT products also showed they were easily to be degraded. Overall, HTT-AD integrated process was an efficient method to reduce environmental risk of cPAM as well as increase energy output (biogas), and the study also provided insights into the degradation mechanism of cPAM during HTT.

Current status of biomethane production using aqueous liquid from pyrolysis and hydrothermal liquefaction of sewage sludge and similar biomass

Pyrolysis and hydrothermal liquefaction (HTL) are potential technologies for renewable energy production and waste valorization using municipal wastewater sewage sludge and other lignocellulosic biomass. However, the organic-rich aqueous pyrolysis liquid (APL) and HTL aqueous phase (HTL-AP) produced currently have no apparent use and are challenging to manage. Furthermore, the toxic organic compounds in them can be harmful to the environment. Anaerobic digestion (AD) may be a viable method to manage the liquids and recover energy in APL and HTL-AP in form of methane-rich biogas. Integrating thermochemical processes with AD could promote a circular economy by recovering resources and reducing environmental pollution. The challenge, however, is the presence of toxic compounds recalcitrant to anaerobic biodegradation such as phenols and nitrogen-containing organics that can inhibit methane-producing microbes. This review presents information on APL and HTL-AP characterization and biodegradability. Feedstock composition and process operational parameters are major factors affecting APL and HTL-AP composition, subsequent toxicity, and degradability. Feedstocks with high nitrogen content as well as increased thermochemical processing temperature and retention time result in a more toxic aqueous liquid and lower methane yield. Dilution and low AD organic loading are required to produce methane. More comprehensive APL and HTL-AP chemical characterization is needed to adopt suitable treatment strategies. Pretreatments such as overliming, air stripping, partial chemical oxidation, adsorption, and solvent extraction of toxic constituents as well as co-digestion and microbial acclimatization successfully reduce toxicity and increase methane yield.

Does lipid stress affect performance, fate of antibiotic resistance genes and microbial dynamics during anaerobic digestion of food waste?

The dissemination of antibiotic resistance genes (ARGs) in food waste (FW) disposal can pose severe threats to public health. Lipid is a primary composition in FW, while whether lipid stress can affect ARGs dynamics during anaerobic digestion (AD) process of FW is uncertain. This study focused on the impacts of lipid stress on methane production, fate of ARGs and its microbial mechanisms during AD of FW. Results showed that high lipid content increased methane yield but prolonged hydrolysis and lag time of methane production compared to AD of FW without oil. Moreover, variations of ARGs were more susceptible to lipid stress. Lipid stress could facilitate the reduction of total ARGs abundances compared to the group without oil, particularly restraining the proliferation of sul1, aadA1 and mefA in AD systems (P < 0.05). Mantel test suggested that integrons (intl1 and intl2) were significantly correlated with all detected ARGs (r: 0.33, P < 0.05), indicating that horizontal gene transfer mediated by integrons could be the driving force on ARGs dissemination. Network analysis suggested that Firmicutes, Bacteroidetes, Synergistetes and Proteobacteria were the main potential hosts of ARGs. In addition, under the lipid stress, the reduction of host bacteria was responsible for the elimination of several specific ARGs, thereby affecting ARGs profiles. These findings firstly deciphered ARGs dynamics and their driving factors responding to lipid stress during anaerobic biological treatment of FW.

Assessing the use of crude glycerol from biodiesel production as an alternative to boost methane generation by anaerobic co-digestion of sewage sludge

In this work, the effect of the addition of crude glycerol (GL) (1 and 3% (v v−1)) from biodiesel production on anaerobic digestion of sewage primary sludge (PS), was evaluated through biochemical methane potential tests. Parameters such as pH, volatile acid/alkalinity ratio, chemical oxygen demand, volatile solids (VS) and carbon/nitrogen (C/N) ratio were monitored to assess process stability and performance. The methane yield from the co-digestion experiments of the binary mixture comprising PS and GL corresponded 223.8 mL CH4 g−1 VS and 368.8 mL CH4 g−1 VS for the tests supplemented with 1 and 3% GL, respectively, which represent an increase in methane yield of 61% and 167% compared to the control test conducted only with PS (138.2 mL CH4 g−1 VS). For each percentage increase in the applied VS load, the percentage increase in methane yield was found to be 4.7% and 5.7% for the tests with 1% and 3% glycerol, respectively. At the highest GL content, the maximum daily biogas generation rate was reached (i.e., 56.8 mL g−1 VS d−1). However, for this particular condition, an initial instability period with methanogenesis inhibition of 5.8 days was noticed, likely related to the accumulation of intermediate volatile acids. Overall, the results suggest that the use of crude glycerol as a co-substrate for the digestion of sewage sludge is interesting alternative to maximize the generation of biogas and methane, although its quantity should be controlled to avoid overload conditions which may compromise the stability of the system.

Infectious Diseases, Livestock, and Climate: A Vicious Cycle?

Ruminant livestock are a significant contributor to global methane emissions. Infectious diseases have the potential to exacerbate these contributions by elevating methane outputs associated with animal production. With the increasing spread of many infectious diseases, the emergence of a vicious climate–livestock–disease cycle is a looming threat.

Bio-methane production from tomato pomace: preliminary evaluation of process intensification through ultrasound pre-treatment

The effect of ultrasound pre-treatment (for 5, 15, and 30 min) on tomato pomace methane yield was evaluated. With respect to the control (238.0 m3CH4/tVS), no improvement was recorded for the substrates pre-treated at 80 µm (0.6 W/mL). 18.9% and 5% higher methane yields were, instead, recorded from the substrate pre-treated for 15 min with an ultrasound wave’s amplitude of 152 µm (0.9 W/mL) after 4 and 22 days of AD, respectively. However, the main achievement arising from the ultrasound application at 152 µm amplitude was the degradation kinetics speed up (89.7% faster maximum methane production rate after 15 min US). Nonetheless, the methane yield increase was not high enough as to compensate the electricity requirement of ultrasonication (between 3.3 and 19.5 MJ/kgVS) as verified through the energy assessment. The dataset that has been presented and discussed lead to preliminary considerations that may be useful in view of a possible scale-up of the process. When equipoising higher quantities of treated biomass and recovered methane, the process might turn economically convenient; however a new energy feasibility assessment and capex–opex evaluation would be required.

Increasing the Methane Potential of Oat Husks Using a Novel Extrusion Pre-Treatment Technology Prior to Anaerobic Digestion

Oat husks are produced during the milling process of oats. Oat husks are a lignocellulosic material that have the potential for valorization thereby improving the circular economy of agricultural by-products. However, due to the high lignocellulosic content, there are limited valorization pathways for oat husks. To improve the anaerobic digestibility of oat husks, pre-treatment was investigated as a method to aid valorization. A novel extrusion process was used in an attempt to fragment the lignocellulosic structure of oat husks prior to anaerobic digestion. The extrusion pre-treatment was investigated to determine the effect it may have on altering the methane yield and digestibility of oat husks. Biochemical methane potential assays were undertaken using oat husks with no pre-treatment and extruded oat husks. These assays demonstrated that extruded oat husks produced a significantly higher methane yield of 264 ml/gVS fed, which was 27% greater than the methane yield produced from the untreated oat husks. Similarly, the total solids degradation was also significantly higher for extruded oat husks treatment compared to the untreated oat husks. Overall, the extrusion process demonstrated an increased methane yield for oat husks compared to previously published data. The biomethane potential tests suggest that extruded oat husks would be a feedstock suitable for anaerobic digestion.

Development of a continuous‐flow anaerobic co‐digestion process of olive mill wastewater and municipal sewage sludge

AbstractBACKGROUNDOlive mill wastewater (OMW) represents an environmental problem due to its high organic load and relevant concentration of phenolic compounds (PCs). OMW treatment and disposal represents a relevant challenge and cost for olive mills and multi‐utilities in charge of waste management in Mediterranean countries. The goal of this study was to develop an anaerobic co‐digestion (co‐AD) process of OMW and sewage sludge (SwS) from municipal wastewater treatment.RESULTSDifferent volumetric OMW:SwS ratios up to 100% OMW were fed in continuous 1.7‐L bioreactors. The reactors fed with raw OMW (rOMW) performed better than those fed with OMW dephenolized by adsorption (dOMW). At a 23‐day hydraulic retention time, the best performances were obtained in the reactor fed with 25% rOMW, with a 105% increase in methane yield in comparison to the 100% SwS test. At a 40‐day hydraulic retention time, the reactor fed with 40% rOMW attained a 268 NLCH4/kgvolatile solids methane yield. The conversion of phenolic compoundsreached 70% when the hydraulic retention time was increased from 23 to 40 days. A cost–benefit analysis indicated that both rOMW co‐AD in existing digesters and phenolic compounds recovery from OMW followed by co‐AD of dOMW can lead to relevant additional revenues for the multi‐utilities in charge of wastewater management.CONCLUSIONThis work proves that, using the existing network of SwS anaerobic digesters, it is feasible to co‐digest the entire OMW production in regions characterized by intense olive oil production, thus attaining a relevant increase in methane production yield (a 144% increase in comparison to 100% SwS). © 2020 Society of Chemical Industry (SCI)

Improving methane yield of oil palm empty fruit bunches by wet oxidation pretreatment: Mesophilic and thermophilic anaerobic digestion conditions and the associated global warming potential effects

Palm oil production is a significant agricultural industry in the South East Asia region and the empty fruit bunch by-product OPEFB is a lignocellulosic biomass left after palm oil recovery, which has shown to be recalcitrant to bioconversion. Pretreatment experiments were carried out in this study to mitigate the recalcitrance of this material using oxygen assisted hydrothermal pretreatment (with 3–9% oxygen loading in the form of H2O2) followed by batch anaerobic digestion at both mesophilic and thermophilic conditions. The optimal pretreatment for OPEFB was found to be with 6% oxygen at mesophilic condition resulting in 43% increase in methane yield over the control while at thermophilic conditions, the ultimate methane yield was ultimately lower, but received within a shorter time period. The gate-to-gate process was analyzed for global warming potential impacts and it was concluded that for the production of methane at the optimal condition resulted in the lowest greenhouse gas emissions (30% less than the control).

Synergistic Co-Digestion of Microalgae and Primary Sludge to Enhance Methane Yield from Temperature-Phased Anaerobic Digestion

A two-stage temperature-phased mesophilic anaerobic digestion assay was carried out to study the interaction between various biological pretreatment conditions and the possible synergistic co-digestion of microalgae and primary sludge. The study of growth kinetics of the biochemical methane potential test revealed that a maximum of 36% increase in methane yield was observed from co-digestion of a substrate pretreated by thermophilic aerobic conditions (55 °C and HRT = 2 days) and an 8.3% increase was obtained from the anaerobic pretreated substrate (55 °C and HRT = 3 days). Moreover, no synergistic effects on methane yields were observed in co-digesting the substrate pretreated with high temperature (85 °C). The study also identified specific conditions in which interaction between biological pretreatment and co-digestion might substantially reduce methane yield. Careful optimization of operating conditions, both aerobic and anaerobic pretreatment at moderate thermophilic conditions, can be used as a biological pretreatment to enhance methane yield from the co-digestion of microalgae and primary sludge.

Pretreatment of Animal Manure Biomass to Improve Biogas Production: A Review

The objective of this research is to present a review of the current technologies and pretreatments used in the fermentation of cow, pig and poultry manure. Pretreatment techniques were classified into physical, chemical, physicochemical, and biological groups. Various aspects of these different pretreatment approaches are discussed in this review. The advantages and disadvantages of its applicability are highlighted since the effects of pretreatments are complex and generally depend on the characteristics of the animal manure and the operational parameters. Biological pretreatments were shown to improve methane production from animal manure by 74%, chemical pretreatments by 45%, heat pretreatments by 41% and physical pretreatments by 30%. In general, pretreatments improve anaerobic digestion of the lignocellulosic content of animal manure and, therefore, increase methane yield.

Impacts of Cellulase and Amylase on Enzymatic Hydrolysis and Methane Production in the Anaerobic Digestion of Corn Straw

The impacts of enzyme pre-treatments on anaerobic digestion of lignocellulosic biomass were explored by using corn straw as a substrate for enzyme pre-treatment and anaerobic digestion and by utilizing starch and microcrystalline cellulose as substrates for comparative analysis. The cellulase pre-treatment effectively improved the enzymatic hydrolysis of cellulose, decreased the crystallinity, and consequently showed 33.2% increase in methane yield. The methane yield of starch increased by 16.0% through amylase pre-treatment. However, when the substrate was corn straw, both the efficiencies of enzymes and methane production were markedly reduced by the lignocellulosic structure. The corn straw’s methane yields were 277.6 and 242.4 mL·CH4/g·VS with cellulase and amylase pre-treatment, respectively, which was 11.7% and 27.9% higher than that of the untreated corn straw. It may imply that the lignocellulose should be broken up firstly, enzyme pre-treatments could have great potentials when combined with other methods.