Identification of potential waste seeds of wildly growing tree species for the production of biogas.

Abstract

In this experimental study, seeds of wild tree species namely Acacia nilotica, Prosopis juliflora, Albizia lebbeck, and Leucaena leucocephala were explored as potential feedstocks for anaerobic digestion and compared with cattle manure which is a commonly used feedstock. These seeds occur abundantly as waste biomass in tropical and subtropical parts of Asia, Africa, and the USA. An experimental investigation was carried out in large 300-L anaerobic digesters under semi-continuous feed mode for 90days. The average specific methane production yield observed was 0.208Nm3/kg volatile solids (VS) for A. nilotica, 0.227Nm3/kg VS for P. juliflora, 0.219Nm3/kg VS for A. lebbeck and 0.210Nm3/kg VS for L. leucocephala which was found to be higher than cattle manure's yield of 0.146Nm3/kg VS. Experimental analysis revealed an average methane content of more than 52% for all the seeds and a total volatile solid mass removal efficiency of 41.60% for A. nilotica, 44.19% for P. juliflora, 43.76% for A. lebbeck, and 41.41% for L. leucocephala which was higher than 29.7% for cattle manure. The experimental investigations showed that they have a higher biogas production potential than cattle manure indicating their huge scope and suitability as alternative feedstocks, and their use can also mitigate the ecological risk seeds pose by growing into invasive trees.