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Lipid-rich wastewater from the local dairy industry (cheese whey) in the Galilee, Israel was hydrolyzed by using two different sources of lipase as hydrolytic enzymes: fungal ( Candida rogusa lipase-AY ) and animal porcine pancreatic lipase(PPL). Pretreatment efficiency was verified by comparative biodegradability tests of raw and treated wastewater samples. Simultaneous hydrolysis and anaerobic digestion in the same reactors were also tested. Enzymatic pretreatment of these samples at a concentration of 0.05 w v -1 showed organic matter removal of 90% and methane formation increases of 140% for the fungal source enzyme (i.e., AY), while for the animal source enzyme (i.e., PPL) was 86 and 130%, respectively. Enzymatic pretreatment led to significant methane formation which was obtained only for moderate substrate concentration (initial chemical oxygen demand of 15 gL -1 ); While in high concentrated lipid-rich wastewater led to methane yield inhibition. The main finding was that the combination of AY enzyme with Candida rugosa fungus (i.e., enzyme mixture) led to a high efficiency in methane production (+152%) and organic materials removal (more than 90%). In summary, the use of fungal hydrolytic lipase mixed with Candida rugosa fungus is a promising method for enhancing methane production during the biodegradation of fat and grease-rich wastewaters.

The population growth is causing an increase in the generation of effluents (mainly organic fraction of municipal solid waste (OFMSW) and agro-industrial waste), which is an old problem in agro-industrial countries such as Brazil. Contrastingly, it is possible to add value to these residual biomasses (residues) through the application of new technologies for the production of bioenergy. Anaerobic digestion (AD) of sewage sludge is being applied in many effluent treatment plants for the sustainable and economically viable production of biogas. However, the biogas produced from AD (sludge) or co-digestion (sludge with other residues) presents a concentration of methane between 60 and 70% on average, which is relatively low. This review is aimed at analyzing studies involving (i) production of lipases by solid-state fermentation (SSF) by different microorganisms for the application in enzymatic pretreatments prior to the anaerobic treatment of effluents; (ii) pretreatment followed by AD of various residues, with an emphasis on OFMSW and sewage sludge; and (iii) more recent studies on anaerobic co-digestion (AcoD) and hybrid technologies (pretreatment + AD or AcoD). There are many studies in the literature that demonstrate the enzymatic pretreatment or AcoD applied to the optimization of methane production. Nevertheless, few studies report the combination of these two technologies, which can improve the process and reduce or eliminate the costs of biogas purification, which are major challenges for the viability of this route of bioenergy production. KEY POINTS: • Municipal and agro-industrial wastes have potential as medium for lipase production. • Enzymatic pretreatment and anaerobic co-digestion are low cost for high-methane production. Graphical abstract Interactions among various factors optimization methane production from enzymatic pretreatment and AcoD.

In order to improve the methane yield, the alkaline and biological pretreatments on anaerobic digestion (AD) were investigated. Three treatments were tested: NaOH, biological (enzyme and fungi), and combined NaOH with biological. The maximum reducing sugar concentrations were obtained using Enzyme T (2.20 mg/mL) on the 6th day. The methane yield of NaOH + Enzyme A was 300.85 mL/g TS, 20.24% higher than the control. Methane yield obtained from Enzyme (T + A) and Enzyme T pretreatments were 277.03 and 273.75 mL/g TS, respectively, which were as effective as 1% NaOH (276.16 mL/g TS) in boosting methane production, and are environmentally friendly and inexpensive biological substitutes. Fungal pretreatment inhibited methane fermentation of maize straw, 15.68% was reduced by T + A compared with the control. The simultaneous reduction of DM, cellulose and hemicellulose achieved high methane yields. This study provides important guidance for the application of enzymes to AD from lignocellulosic agricultural waste., (Copyright © 2017. Published by Elsevier Ltd.)

Pretreatment of lignocellulosic biomass is necessary to enhance the hydrolysis, which is the rate-limiting step in biogas production. Laccase and versatile peroxidase are enzymes known to degrade lignin. Therefore, the impact of enzymatic pretreatment was studied on a variety of biomass. A significant higher release in total phenolic compounds (TPC) was observed, never reaching the inhibiting values for anaerobic digestion. The initial concentration of TPC was higher in the substrates containing more lignin, miscanthus and willow. The anaerobic digestion of these two substrates resulted in a significant lower biomethane production (68.8-141.7 Nl/kg VS). Other substrates, corn stover, flax, wheat straw and hemp reached higher biomethane potential values (BMP), between 241 and 288 Nl/kg VS. Ensilaged maize reached 449 Nl/kg VS, due to the ensilation process, which can be seen as a biological and acid pretreatment. A significant relation (R(2) = 0.89) was found between lignin content and BMP., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

In this study, a fungal mash rich in hydrolytic enzymes was produced by solid state fermentation (SSF) of waste cake in a simple and efficient manner and was further applied for high-efficiency hydrolysis of mixed food wastes (FW). The enzymatic pretreatment of FW with this fungal mash resulted in 89.1 g/L glucose, 2.4 g/L free amino nitrogen, 165 g/L soluble chemical oxygen demand (SCOD) and 64% reduction in volatile solids within 24h. The biomethane yield and production rate from FW pretreated with the fungal mash were found to be respectively about 2.3 and 3.5-times higher than without pretreatment. After anaerobic digestion of pretreated FW, a volatile solids removal of 80.4±3.5% was achieved. The pretreatment of mixed FW with the fungal mash produced in this study is a promising option for enhancing anaerobic digestion of FW in terms of energy recovery and volume reduction., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

AbstractThis study explores a novel enzymatic pretreatment approach in anaerobic reactors for dairy wastewater, using lipase AY Amano to enhance methane production and modify microbial and archaeal community composition. Batch and semi-batch reactors with a total volume of 2000 mL were used to treat dairy wastewater with initial COD of 2000 and 15,000 mg L−1, respectively. In a new novel approach, the semi-batch reactors underwent a three-phase operation: 30 days of acclimation, 30 days of rest, and 30 days of active operation. Adding lipase (0.05% wv−1) as a pretreatment significantly increased methane yield over the 90 days by 135–138% compared with the control (without enzyme addition). The organic loading rate reached 0.22 g COD day−1 L−1. Furthermore, 30 days after the end of the semi-batch reactor approach (120 days from the start), reusing sludge in batch reactors increased methane yield by 114–122% compared to the control. This increase was linked to the emergence and shift of new methanogenic communities within the sludge. Integrating hydrolytic enzymes into the anaerobic treatment enhances performance and sustainability by fostering methanogen-enriched microbial communities. This is crucial for maximizing methane production but may increase costs, requiring further economic feasibility research. [ABSTRACT FROM AUTHOR]

Crude hydrolytic extracellular enzymes (CHEEs) generated by a mixed culture of microorganisms during fermentation have a high potential as economically feasible biocatalysts for the hydrolysis of complex organic wastes. This study investigates the feasibility of CHEEs as substitutes for commercial enzymes based on a series of anaerobic batch tests for CH4 production fed by pretreated waste activated sludge (WAS). The results showed that cellulase presented the highest CH4 yield of 99.1 mL·CH4/g·COD of WAS among the samples pretreated with single commercial enzymes, with a yield 34% higher than that of the control sample. A higher diversity of commercial enzymes used in the pretreatment led to higher CH4 production from WAS. The sample pretreated with a mixture of four commercial enzymes (amylase + protease + cellulase + lipase, APCL) presented a CH4 yield of 216.0 mL·CH4/g·COD of WAS. The WAS prepared with CHEEs resulted in a CH4 yield of 211.9 mL·CH4/g·COD of WAS, which is comparable to the performance of the sample pretreated with APCL. The results of the batch tests using pretreated WAS for different APCL concentrations showed that the CH4 yield of WAS pretreated with CHEEs was comparable to the CH4 yield of 0.34 g·APCL/g·COD of WAS. [ABSTRACT FROM AUTHOR]

Abstract The rapid depletion of natural resources and the environmental concerns associated with the use of fossil fuels as the main source of global energy is leading to an increased interest in alternative and renewable energy sources. Particular interest has been given to the lignocellulosic biomass as the most abundant source of organic matter with a potential of being utilized for energy recovery. Different approaches have been applied to convert the lignocellulosic biomass to energy products including anaerobic digestion (AD), fermentation, combustion, pyrolysis, and gasification. The AD process has been proven as an effective technology for converting organic material into energy in the form of methane-rich biogas. However, the complex structure of the lignocellulosic biomass comprised of cellulose, hemicelluloses, and lignin hinders the ability of microorganisms in an AD process to degrade and convert these compounds to biogas. Therefore, a pretreatment step is essential to improve the degradability of the lignocellulosic biomass to achieve higher biogas rate and yield. A system that uses pretreatment and AD is known as advanced AD. Several pretreatment methods have been studied over the past few years including physical, thermal, chemical and biological pretreatment. This paper reviews the enzymatic pretreatment as one of the biological pretreatment methods which has received less attention in the literature than the other pretreatment methods. This paper includes a review of lignocellulosic biomass composition, AD process, challenges in degrading lignocellulosic materials, the current status of research to improve the biogas rate and yield from the AD of lignocellulosic biomass via enzymatic pretreatment, and the future trend in research for the reduction of enzymatic pretreatment cost. Graphical abstract Image Highlights • Most research applied enzymatic pretreatment prior to mesophilic batch AD process. • large variations in methane improvement were observed among different studies. • 15–35% more methane recovery can be most likely achieved via enzymatic pretreatment. • Cellulose, β-glucosidase, and xylanase were primarily used in the literature. • The economic feasibility of enzymatic pretreatment should be further investigated. [ABSTRACT FROM AUTHOR]

Microalgae biomethanization is driven by anaerobic sludge associated microorganisms and is generally limited by the incomplete hydrolysis of the microalgae cell wall, which results in a low availability of microalgal biomass for the methanogenic community. The application of enzymatic pretreatments, e.g., with hydrolytic enzymes, is among the strategies used to work around the incomplete hydrolysis of the microalgae cell wall. Despite the proven efficacy of these pretreatments in increasing biomethanization, the changes that a given pretreatment may cause to the anaerobic sludge associated microorganisms during biomethanization are still unknown. This study evaluated the changes in the expression of the metatranscriptome of anaerobic sludge associated microorganisms during Chlorella sorokiniana biomethanization without pretreatment (WP) (control) and pretreated with commercial cellulase in order to increase the solubilization of the microalgal organic matter. Pretreated microalgal biomass experienced significant increases in biogas the production. The metatranscriptomic analysis of control samples showed functionally active microalgae cells, a bacterial community dominated by γ- and δ-proteobacteria, and a methanogenic community dominated by Methanospirillum hungatei. In contrast, pretreated samples were characterized by the absence of active microalgae cells and a bacteria population dominated by species of the Clostridia class. These differences are also related to the differential activation of metabolic pathways e.g., those associated with the degradation of organic matter during its biomethanization.

Abstract Microalgae have been considered as one of the most promising biomass resources for the generation of biodiesel, whereas algal residues (AR) after lipid extraction need to be utilized to enhance its economy and sustainability. This study proposed an integrated biochemical method for microalgae Chlorella sp. processing to achieve a high energy yield (12.33 KJ g−1VS). The microalgae were first pretreated with mixed enzymes for lipid extraction. After that, the AR obtained from the lipid extraction of microalgae was co-digested with energy grass (GR) Pennisetum hybrid for methane production. Results indicated that the lipid yield from microalgae was enhanced by 54.45% with mixed enzymes pretreatment of cellulase, xynalase and pectinase compared to that without enzymatic pretreatment. The maximal methane yield (207.35 ± 15.66 mLCH 4 g−1VS) of AR and GR co-digestion was obtained with the AR and GR VS ratio at 1:3. Energy yields evaluation based on the biodiesel and methane yields indicated that the energy yield for this two-step combined method was 169% higher than that for biodiesel alone. Thus, the proposed integrated approach was verified to be applicable for microalgae processing for energy production. Graphical abstract Image 1 Highlights • Chlorella sp. was a promising feedstock for biodiesel and methane production. • Enzymatic pretreatment effectively improved the lipid yield of microalgae. • The highest methane yield was obtained in the co-digestion of AR:GR = 1:3. • Coupled biodiesel and methane produced 169% more energy than biodiesel alone. [ABSTRACT FROM AUTHOR]

Microalgae biomethanization is driven by anaerobic sludge associated microorganisms and is generally limited by the incomplete hydrolysis of the microalgae cell wall, which results in a low availability of microalgal biomass for the methanogenic community. The application of enzymatic pretreatments, e.g., with hydrolytic enzymes, is among the strategies used to work around the incomplete hydrolysis of the microalgae cell wall. Despite the proven efficacy of these pretreatments in increasing biomethanization, the changes that a given pretreatment may cause to the anaerobic sludge associated microorganisms during biomethanization are still unknown. This study evaluated the changes in the expression of the metatranscriptome of anaerobic sludge associated microorganisms during Chlorella sorokiniana biomethanization without pretreatment (WP) (control) and pretreated with commercial cellulase in order to increase the solubilization of the microalgal organic matter. Pretreated microalgal biomass experienced significant increases in biogas the production. The metatranscriptomic analysis of control samples showed functionally active microalgae cells, a bacterial community dominated by γ- and δ-proteobacteria, and a methanogenic community dominated by Methanospirillum hungatei. In contrast, pretreated samples were characterized by the absence of active microalgae cells and a bacteria population dominated by species of the Clostridia class. These differences are also related to the differential activation of metabolic pathways e.g., those associated with the degradation of organic matter during its biomethanization. [ABSTRACT FROM AUTHOR]

Abstract: This study aimed at evaluating the effect of increasing organic loading rates and of enzyme pretreatment on the stability and efficiency of a hybrid upflow anaerobic sludge blanket reactor (UASBh) treating dairy effluent. The UASBh was submitted to the following average organic loading rates (OLR) 0.98Kg.m−3.d−1, 4.58Kg.m−3.d−1, 8.89Kg.m−3.d−1 and 15.73Kg.m−3.d−1, and with the higher value, the reactor was fed with effluent with and without an enzymatic pretreatment to hydrolyze fats. The hydraulic detention time was 24h, and the temperature was 30±2°C. The reactor was equipped with a superior foam bed and showed good efficiency and stability until an OLR of 8.89Kg.m−3.d−1. The foam bed was efficient for solid retention and residual volatile acid concentration consumption. The enzymatic pretreatment did not contribute to the process stability, propitiating loss in both biomass and system efficiency. Specific methanogenic activity tests indicated the presence of inhibition after the sludge had been submitted to the pretreated effluent. It was concluded that continuous exposure to the hydrolysis products or to the enzyme caused a dramatic drop in the efficiency and stability of the process, and the single exposure of the biomass to this condition did not inhibit methane formation. [Copyright &y& Elsevier]