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The complex structure and biochemical composition of the cell wall of microalgae impede their anaerobic digestion. To enhance the microalgae anaerobic biodegradability, various pretreatment approaches have been utilized. In this study, the enzyme and hydrothermal pretreatment methods were evaluated for microalgal biomass pretreatment and biogas yield. The optical and scanning electron microscopy along with Fourier transform infrared spectroscopy analysis confirmed the efficient action of both the pretreatment methods. The hydrothermal pretreatment resulted in more structural changes, though the increase in enzymatic concentration was also found to have a pronounced effect on both structural and chemical changes. The FTIR spectra determined that mostly the protein and carbohydrate structures of the microalgal cells were affected. Further upon quantitative analysis, it was observed that 10% dose (w/w) for 24 h of exposure time released significantly more soluble chemical oxygen demand compared to others. The multi-enzyme 10% dose for 24 h resulted in significantly higher biogas production potential (P) of 768.92 mL g−1 VS at a maximum biogas production rate (Rm) of 32.16 mL g−1 d−1 with a very short lag phase (λ) of 0.09 days at the end of 30 days, in comparison to untreated and other pretretment conditions in this study. Both the pretreatment approaches in the present study enhanced the microalgal biomass disintegration, digestibility and biogas production. However, more research is required to optimize the process parameters of these pretreatment approaches to make them more reasonable and applicable.

Spirulina subsalsa (MF191711) isolated from the waterlogged area of Punjab, India, was identified by 16S rRNA sequence analysis. The Placket- Burman design and central composite design (CCD) were used to screen and optimize the significant cultural factors. The most desirable results correspond to the optimal conditions: 11.5 pH, 20 °C temperature, 81 μmolm−2 s−1 light intensity, 25 days growth period, 15 mM CaCl2, NaNO3 5 mM and 2 mM K2HPO4, which were very proximate to the CCD predicted optimal values. These optimal conditions resulted in 1.60-fold higher biomass compared to basal conditions (0.987gL−1). Further, co-digestion of 70% paddy straw with 30% microalgal biomass resulted in the highest ultimate biogas yield (P:260.03 mLg−1VS) with reduced lag phase (λ:3.84 d) and increased rate of biogas production (Rm:8.16 mLg−1d −1), compared to paddy straw and microalgal biomass individually. Thus, it can be concluded that co-digestion of Spirulina subsalsa with paddy straw results in enhanced biogas production.

The microalga was isolated from Muktsar, the southwestern zone of Indian Punjab and identified as Asterarcys quadricellulare BGLR5 (MF661929) by 18S rRNA sequence analysis. The optimization of various cultural factors by the Plackett–Burman and central composite (CCD) designs helped in discerning the significant cultural factors for the increased production of biomass and other functional components (chlorophyll, carbohydrate, lipid and protein). The optimal cultural conditions as per the model were pH 9.9, 81 μmol m−2 s−1 light intensity, 22 °C temperature, growth period of 25 days, NaNO3 12 mM, 15 mM NH4Cl, and 7 mM K2HPO4. In comparison to the basal condition biomass (0.886 g L−1), a 0.42-fold increase in biomass yield was attained. Further, the highest yield of biogas (P: 361.81 mL g−1 VS) with enhanced biogas production rate (Rm: 8.19 mL g−1 day−1) was achieved in co-digesting paddy straw with Asterarcys quadricellulare biomass in 1:1 ratio compared to their digestion individually. Further, the co-digestion resulted in the positive synergistic effect which increased the observed biogas yield compared to the estimated yield by 11–58% depending upon the amount of algal biomass and paddy straw used. Hence, the present study signifies that the biomass of Asterarcys quadricellulare BGLR5 can be utilized as a co-substrate with paddy straw to enhance the biogas yield.

Alternative sources of energy are the demand of the modern world. For generating different alternate fuels, utilization of lignocellulolytic biomass is on top of the priority list, for which cellulase enzymes are required specifically. In this context, the aim of the presented paper was the partial purification and characterization of cellulolytic enzymes from Trichoderma reesei inoculated digested biogas slurry. The enzyme was produced at previously standardized conditions (Incubation period: 15 day, Spore concentration: 108 spores/ml, Slurry concentration: 25%). The cellulolytic enzymes viz. CMCase, Cellobiase and FilterPaperase produced were then partially purified by ammonium sulphate precipitation (0-30 and 30-80%) and dialysis followed by ion exchange chromatography using DEAE-cellulose column. Twelve fold purification was achieved for cellobiase. Specific activity of 20.18 U/mg was measured. Two isoforms of Cellobaise (C-I and C-II) were found with 21 and 32 fold purification, respectively. Upon characterization, the optimal pH and optimal temperature values for cellobiase came out to be 7.5 and 55°C for C-I and 25°C for C-II. Carboxymethyl cellulase was partially purified up to 10.4 fold with specific activity of 1.87 U/mg of protein and Fpase was purified to 11.3 fold with 1.47 U/mg of protein specific activity. Partially purified enzyme activities were compared with that of commercial enzymes. This is a novel work where cellulases were extracted and partially purified from digested slurry from biogas plant, which is very significant with reference to not only disposal of digested biogas slurry but also its value addition for industrial applications.

The present investigation reports the optimization of process parameters for biogas production from water hyacinth (Eichhornia crassipes). The different parameters like particle size, inoculum concentration, incubation temperature, metal ions and pH were optimized for biogas production. Maximum biogas was observed with water hyacinth of 1cm size, 40 % inoculum concentration. The temperature of 45°C along with neutral pH i.e. 7 was found to be most suitable for biogas production in the presence of manganese chloride (0.2 mM). Under optimized conditions, 44.9 l biogas/kg water hyacinth, 360.09 l/kg total solids and 397.95 l biogas/kg volatile solids were produced in a period of 40 days. The water hyacinth has proven to be a good source of biogas production and thus can be utilized as a potential feedstock for the biogas production.

Growing environmental concerns and increasing demands from end-use sectors have increased the glob-al market for microbial products. Optimizations of production parameters hold great importance for the industry. The present study was aimed at optimization of submerged state fermentation conditions for production of lignocelluloly-tic enzymes from digested biogas slurry by Phanaerochaete chrysosporium MTCC 787. Enzyme activities for differ-ent enzymes i.e. endoglucanase, exoglucanase, β-glucosidase; xylanase and mannanase; laccase, lignin peroxidase and manganese peroxidise, using P. chrysosporium MTCC 787 were maximum at 50% concentration of digested slur-ry and showed maximum value of xylanase i.e. 187.41U/ml. Effect of temperature (25°C, 30°C and 35°C) on lignocellu-losic bioconversion showed that at 30°C, maximum value of manganese peroxidise (167.5 U/ml) was obtained. High-est enzyme activites were obtained at selected inoculum size i.e. 10⁷spores/ml, e.g. 85.29 U/ml xylanase was ob-tained. Incubation period of 8 days and pH of 7.0 came out to be best conditions for P. chrysosporium MTCC787 to produce maximum enzyme activity e.g. xylanase 95.47U/ml at pH 7.0 and xylanase 144.96U/ml at 8 day incu-bation.This work presents a novel concept in optimization of fermentation process to produce lignocellulolytic en-zymes as this work is focussed on utilization of digested biogas slurry as a substrate for enzyme production and enhancement of the production with microbial source, which is environment friendly.

Reasonable creation of renewable energy is being fervently debated. The biofuels, produced from food crops are restricted in their capacity to accomplish biofuel generation targets, mitigation of climate change and socio-economic development. These issues have exaggerated the curiosity in flourishing biofuels generated from non-food feedstocks like agricultural wastes, forest wastes, municipal wastes, and microalgae, which substantially offer golden opportunities in the longer run. The anaerobic digestion (AD) of agricultural residues is the potential alternate of energy production (357.85 bcm biomethane) and has the capability of reducing greenhouse gas emissions (GHG) (979 Mt CO2 eq. per year). This makes it a potential contributor to attain climate neutrality by 2050. However, the various physical, structural and compositional factors impeding the hydrolysis of agricultural residues in AD are to be eliminated. Conjoint application of biological pretreatment with other pretreatment approaches has proven to be more efficacious than applying individually. Furthermore, the well-planned policies are vital in making the AD technology adoption viable and successful. The policies regarding bioenergy production must make sure to supply food and feed items sustainably by the agricultural sector. This paper reviews the utilization of lignocellulosic agricultural wastes for biogas production, various aspects of biomethanation process like inhibitions and possible solutions for their alleviation, enhancement of biogas production, its environmental and techno-economic and policy aspects. Value addition of biodigested slurry by the production of industrial enzymes, vermicompost, fertilizer and mushroom cultivation, are also included in the paper.

Biogas has become a promising energy substitute to fossil fuels. Lignocellulosics, being cheap and renewable resource, could be very well used as a feedstock for biogas generation. Paddy straw is an abundant lignocellulose which is rich in organic matter like cellulose, hemi-cellulose and lignin. It is generally disposed off by burning causing environmental pollution whilst it can be used for biofuel generation. The digestibility of paddy straw is low due to high lignin and silica content. The present study was carried out to enhance paddy straw digestibility and biogas production through sodium hydroxide (NaOH) pretreatment. The paddy straw was pretreated with NaOH by soaking (24 h) in different concentrations of NaOH (2, 4, 6, 8 and 10%) and supplementing with microwave irradiations (30 min, 720 W, 180 °C). 4% NaOH-30 min microwave was found to be the best pretreatment which resulted in 65.0% decrease in lignin content and 88.7% reduction in silica content. This increased digestibility due to reduced lignin and silica content resulted in 54.7% increase in biogas production. Scanning Electron Microscopy of pretreated paddy straw revealed breakdown of lignocellulose structure resulted from the tearing of different layers of cell wall of paddy straw.

Paddy straw was pretreated with Thermoascus aurantiacus MTCC 375, a ligno-cellulolytic thermophilic fungus, to enhance its biodegradability. The potential of microbial pretreatment under aerobic condition on paddy straw digestibility was investigated at regular intervals of 1, 2, 3, 4 and 5 days by determining the change in proximate (total solids (%) and volatile solids (%)) and chemical composition (cellulose, hemicellulose, lignin and silica content). The pretreatment of 5 days significantly (P ≤ 0.05) reduced the concentrations of cellulose, hemicelluloses, lignin and silica content in the paddy straw by 34.25, 39.19, 34.12 and 10.59%, respectively. A maximum of 30% increase in biogas production was observed from one day pretreated paddy straw as compared to untreated paddy straw. However, biogas production from paddy straw supplemented with enzyme containing digested biogas slurry without giving aerobic treatment was found to be more than the samples given aerobic treatment. In both cases, biogas production was greater than the control by 63.2 and 30.7%, respectively. Key words: Paddy straw, pretreatment, lignin, Thermoascus aurantiacus, biodegradability, enzyme containing digested biogas slurry, biogas production

Paddy straw pretreated with Coriolus versicolor MTCC 138, is a ligno-cellulolytic fungus,used to enhance its biodegradability. The potential of microbial pretreatment on paddy straw digestibility was investigated at regular intervals of 5, 10, 15, 20 and 25 days by determining the change in proximate (TS% & VS%) chemical composition (cellulose, hemicellulose, lignin and silica content). Results suggest that, 5 days of pretreatment was appropriate. The pretreatment significantly (P ≤ 0.05) reduced the concentrations of cellulose, lignin and silica in the paddy straw by 19.3, 19.1 and 32.5%, respectively. Thepresent data showed that C. versicolor is capable of producing high quantity of ligno-cellulolytic enzymes for the reduction of lignocellulose biomass in less incubation time. However, biogas production was found to increase by 26.2% in 5 days pretreated sample. Key words: Paddy straw, pretreatment, silica, Coriolus versicolor, biogas production.

Objectives: The objective of the present study was to analyse the efficiency of fodder beet and napier grass as a substrate for biogas production. Methods/Analysis: Proximate (total solids, volatile solids, ash, total organic carbon) and chemical (cellulose, hemicellulose, lignin and silica) analysis of fodder beet and napier grass PBN233 (fresh and digested form) was done to analyse the composition of substrate which affects biogas production. Biogas production studies were conducted following single phase digestion in 2 liter capacity biogas digesters. Percent nitrogen was also estimated in fodder beet and napier grass. Findings: Digested form of fodder beet and napier grass, which is generally wasted, was found to produce 102.9 litre biogas/kg volatile solids and 92.4 litre biogas/kg volatile solids, respectively. Novelty/Improvement: The present study has explored the comparative potential of fodder beet and napier grass PBN233 as a substrate for biogas production.

Biogas production from paddy straw offers a great potential as an alternative to fossilfuels. But, lignin and silica adversely affect the efficient utilization of paddy straw. Henceforth, the potential of biological pretreatment of paddy straw by a lignocellulolytic fungus, Pleurotus florida was investigated whereby the straw was inoculated with different spore concentrations of Pleurotus florida for different durations. Biodegradability of paddy straw was determined at different incubation periods and the selected pretreatment was further used for biogas production studies. An incubation period of 30 days was found to be the optimum pretreatment period in enhancing paddy straw digestibility with 19.3% increase in cellulose and 55.1% decrease in lignin. The biologically degraded paddy straw resulted in 15.4% increase in biogas production than that of the untreated paddy straw. DOI: http://dx.doi.org/10.3126/ijls.v6i1.5550

Optimisation of laccase production by Thermoascus aurantiacus microbial type culture collection (MTCC) 375 using paddy straw as substrate and digested biogas slurry as medium was carried out. Laccase production by a thermophilic mould, Thermoascus aurantiacus MTCC 375, was optimised in solid state fermentation (SSF) by a conventional ‘one variable at a time approach ‘andfurther by response surface methodology. Enzyme activity was strongly affected by three independent variables namely incubation temperature, incubation period and inoculum level. The optimised conditions for maximum laccase (715.0 Ug−1 of paddy straw) production were 45°C temperature, 107 spores ml−1 and 4 days incubation period. The enzyme titre (715.0 Ug−1 of paddy straw) attained in the validation experiment of this study is higher than those reported in the literature. An overall (2.65 fold) increase in laccase production was achieved in SSF due to statistical optimisation compared to that of a conventional ‘one variable at a time approach ’. All these cultural conditions were found to have statistically significant (P < 0.05) effect on enzyme production.

Biofuel and Bioenergy generation from paddy straw offers a great potential as an alternative to fossil-fuels. Association of holocellulose with the protective structures such as lignin and silica adversely affects the conversion of paddy straw into the desired product. In this context, paddy straw was pretreated with different concentrations (0-10%) of various chemicals viz. NH 3 , Na 2 SO 3 , Na 2 CO 3 and NaOH by soaking for 48h and by irradiating with microwave (720W, 180 o C) for 60 min. Chemicalmicrowave pretreatment was found to be better than the chemical-alone pretreatment. Amongst the various chemical pretreatments, 4% Na 2 CO 3 -microwave and 4% NaOH-microwave was found to greatly enhance the paddy straw digestibility and biogas production where 44.3% and 65.6% increase in cellulose, 15.0% and 68.3% decrease in lignin, and 84.5% and 92.5% decrease in silica was observed resulting in 54.4% and 60.9% increase in biogas production, respectively.

The present paper reports biogas production from biologically pretreated paddy straw in a solid state digester made of HDPE plastic (124 litre capacity). The trial was conducted with a mixture of 10 kg pretreated paddy straw, 20 kg cattle dung slurry, 20 kg cattle dung and 20 litre water. The chemical and proximate analysis of the feed was done and biogas production profile was studied over a period of one month. Parallel trial was also conducted with untreated paddy straw. The result indicated that 253.89 litre biogas/kg pretreated paddy straw was produced, which is 39.3% higher than the untreated paddy straw.

Lignocellulosic biomass is a useful but an inconvenient form of energy, and paddy straw (PS) is one of the most abundant lignocellulosic wastes on the earth. Lignocellulosics generally have a high content of cellulose having combustion energy of 15 kJ/g which, when converted to methane, have a combustible energy of 50 kJ/g. But lignin and silica are the main deterrents for the microbial action on the cellulose/hemi-cellulose component of PS. In order to break the protective shield made by lignin and silica and to enhance the PS digestibility, the PS was pretreated with different concentrations (2, 4, 6, 8 and 10 %) of sodium carbonate by soaking the PS in sodium carbonate solution for the periods of 24 and 48 h and simultaneously irradiating the other set with microwaves (power 720 W, temperature 180 °C) for 30 and 60 min. The change in chemical composition of PS was the factor determining the enhancement in PS digestibility. Sodium carbonate (4 %) + microwave (60 min) pretreatment was found to be the best amongst the other pretreatments with 84.9 % desilication of PS and 44.3 and 54.4 % increase in cellulose and biogas production, respectively.