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Anaerobic co-digestion is a realistic approach to concurrently manage agriculture residue and harness renewable energy. To achieve the anaerobic degradation requirements and to recompense the nitrogen deficiency of rice straw, it should be digested with another nitrogen-rich co-substrate to advance its characteristics. This study exhibits the necessity of co-digestion to improve physicochemical and biochemical progression compared to mono-digestion. The individual effect of carbon/nitrogen (C/N) ratio, food/microorganisms (F/M) ratio and pH, in addition to their interaction effects on methane yield (mL CH4/g-VSadded) were explored in this study. A central composite design – response surface methodology was used for defining the experimental design for anaerobic co-digestion of rice straw and hydrilla verticillata. Results of this study showed significant interaction of C/N ratio and F/M ratio, and individual response parameters on methane yields. The optimum condition for anaerobic co-digestion (C/N ratio 29.7, F/M ratio 2.15 and pH 7.34) showed methane yield of 287.6 mL CH4/g-VSadded, 1.84 fold (156.32 mL CH4/g-VSadded) higher than mono-digestion (control). Model validation proved the high adequacy of the model and methane yield is good output response variable for co-digestion study and it is necessary to optimize the transient variation in C/N ratio, F/M ratio and pH.

One of the primary concerns in the use of biodiesel is its susceptibility towards radical-mediated oxidative reactions. The presence of unsaturated methyl esters renders biodiesel vulnerable to oxidation. It necessitates strategic interventions, which among a few others, includes the use of antioxidant additives. Natural antioxidants have multiple significant advantages over their synthetic counterparts. In the present study, the activity of methanolic passion fruit seed (PFS) extract as an antioxidant additive for waste cooking oil (soybean) biodiesel has been evaluated. The PFS extract contained a high proportion of phenolic compounds and exhibited excellent antiradical activity against model radical DPPH, which encouraged us to explore the case of unstable biodiesel further. At a concentration of 200 ppm, the PFS extract augmented the fuel's resistance towards oxidation to levels where it could comply with European and the Indian specifications for blend-stock biodiesel. The performance of PFS extract was comparable to that of synthetic antioxidants, including butylated hydroxyanisole and butylated hydroxytoluene. The present study substantiates the utility of plant extracts rich in phenolics as an antioxidant additive for biodiesel.

Owing to fossil fuel depletion, the conversion of lignocellulosic biomass into bioethanol has gained momentum in the field of transportation sector. In the present study, liquefaction of sorghum stalks has been performed for the production of fermentable sugars and their subsequent conversion into bioethanol. Pretreatment, delignification, enzymatic hydrolysis are three sequential steps involved in the liquefaction process. About 82% of hemicellulose hydrolysis was attained by the pretreatment of sorghum stalks at 121 °C with 0.2 M sulfuric acid for 120 min. Further, the pretreated residue was de-lignified with 1–5% (w/v) sodium hydroxide which resulted in 85–98.7% removal of lignin. Subsequently, around 65–99.6% of cellulose hydrolysis was attained at an optimum enzyme loading of 30 mg protein/g of glucan. The optimum liquefaction condition of sorghum stalks was achieved by performing the pretreatment process at 121 °C with 0.2 M sulfuric acid for 120 min, delignification at 121 °C with 2% NaOH for 20 min and enzymatic hydrolysis at 50 °C with 30 mg protein/g of glucan for 72 h. Furthermore, 18.4 g/L and 74.7 g/L xylulosic and cellulosic ethanol was produced from pretreatment and enzymatic hydrolysis derived hydrolysates, respectively. Finally, 97.7% of sorghum stalks liquefaction was achieved, in which 84% of holocellulose (cellulose and hemicellulose) converted into 494 g of fermentable sugars which is further converted into 225 g or 285 mL ethanol per kg of sorghum stalks (equivalent to 285 L ethanol per ton of biomass).

Rubber seed comprises of 40–48% shell and 52–60% kernel by weight of seed was subjected for oil extraction study. The effects of process parameters such as extraction time (3–12 h), kernel size range (0.5–3 mm), ratio of kernel to solvent (0.03–0.09 g/ml), and variety of solvents (polar and non-polar) on Soxhlet extraction process were studied. Design of experiment (DOE) schemes was considered to prepare an experimental matrix using central composite design (CCD) approach. Response surface methodology (RSM) was applied to optimize the process parameters to achieve maximum oil yield. The maximum oil recovery, 49.36 wt% was obtained during the experiment conducted with hexane as solvent, 0.08 g/ml solute to solvent ratio, average kernel size of 1 mm and 8 h extraction time. Physico-chemical properties of oil obtained from the rubber seed were estimated to measure its suitability for biodiesel production. Proton nuclear magnetic resonance ( 1 H NMR) spectra of the obtained rubber seed oil (RSO) revealed 13.17% linolenic, 39.86% linoleic, 27.06% oleic and 19.91% saturated fatty acid in its composition. These compositional data were qualitatively confirmed with Fourier transform infrared (FT-IR), thermal gravimetric (TG) and differential scanning calorimeter (DSC) analyses of extracted oil samples.