Evaluation of Methanogenic Potential and Parameter Analysis of Solid Waste Biomass.

Abstract

Anaerobic digestion is a process of conversion of organic biomass into bio-methane and bio-hydrogen. Bioenergy has enough potential to compete with other sources of energy. Plenty of produced agricultural waste in Pakistan is enough to compensate energy thirst of the country and have potential to replace costly fossil fuels. This study aims to examine the physico-chemical properties of lignocellulosic and organic solid wastes as well as bio-methane/bio hydrogen potential. The lignocellulosic biomasses such as wheat bran, cotton waste, barley straw, lentil straw, rice bran, peanut peel straw, wheat straw, almond shell, bagasse, corn straw, corn cob, newspaper waste, para grass, kallar grass, rice straw and some other organic solid wastes were subjected to bio-methane potential assays by developed inoculum. The chemical compositions of biomasses such as neutral detergent fibre, acid detergent fibre, acid detergent lignin, cellulose, hemicellulose, carbohydrates, proteins and ultimate analyses were determined. The results of analyses has shown that no pretreatment was required to adjust physical characteristics. The proximate, ultimate and chemical composition analyses were used to predict the theoretical bio-methane potentials in silico. Experimental bio-methane potential of lignocellulosic biomasses were 267.7 (wheat straw), 255.3 (almond shell), 222.2 (corn cob), 247.6 (sugar cane bagasse), 293.2 (maize straw), 292.2 (wheat bran), 317.6 (cotton waste), 216.9 (barley straw), 279.1 (lentil straw), 269.6 (rice bran), 255.7 (peanut peel straw), 187.4 (newspaper waste), 281.5 (para grass), 289.9 (kallar grass) and 302.4 (rice straw) ml/g VS (volatile solid). These experimental bio-methane potential of lignocellulosic biomasses were much less than predicted bio-methane potentials. Prediction of bio-methane potentials was not as fit accurately as being assessed for methane potential of biomasses. It merely provided the extent of biodegradability. The biodegradability and methane potential were inversely related to the lignin content of lignocellulosic biomasses. Both biodegradability and bio-methane potentials of solid organic wastes i.e. 426.8 (kitchen waste), 461.9 (fruit wastes) and 444.4 (vegetable wastes) ml/g VS (volatile solid) were higher as compared to xvii lignocellulosic biomasses due to absence of lignin component. The developed inoculum reduced digestion time of organic solid wastes as compared to lignocellulosic biomasses. During anaerobic digestion of lignocellulosic and organic wastes, the volatile fatty acids were produced varied from 53-58% acetic acid, 30-35% butyric acids and 6-13% propionic acid. The relative percentage of volatile fatty acids indicated that similar type of metabolic pathways were involved in digestion process. The nitrogen-rich chicken manure and carbon-rich rotten potatoes were co-digested by the bio-methane potential assay. Co-digestion of chicken manure and rotten potatoes has yielded significantly higher bio-methane potential i.e. 304.5 (mixture of equal percentage), 341.2 ml/g VS (volatile solid) (mixture of one-third chicken manure) as compared to mono-digestion of chicken manure and rotten potatoes 226.1 and 291.1 ml/g VS (volatile solid), respectively. It is because of balanced carbon to nitrogen ratio in co-digestion of mixtures. The energy content on a dry basis and methane potential has been assessed to find economic feasibility of biomass and higher potential in methane as compared to dry mass of biomasses. Hence, bioenergy production from biomass is economically favorable. The bio-hydrogen in addition to bio-methane is another gaseous fuel. The bio-hydrogen produced from a different type of food waste by pure and mixed cultures. These food wastes yielded high hydrogen potential on pure cultures digestion as compared to mixed culture. The order of hydrogen potential was Bacillus sp. 2.8> Bacillus sp. 2.5> mixed cultures. Bio-methane and hydrogen are economically feasible, high energy fuel and have potential to replace fossil fuel. The process can be optimized to generate maximum bioenergy from the lignocellulosic and organic solid waste biomasses.