Biochemical methane potential,biodegradability,alkali treatment and influence of chemical composition on methane yield of yard wastes

Abstract

In this study, the biochemical CH₄ potential, rate, biodegradability, NaOH treatment and the influence of chemical composition on CH₄ yield of yard wastes generated from seven trees were examined. All the plant parts were sampled for their chemical composition and subjected to the biochemical CH₄ potential assay. The component parts exhibited significant variation in biochemical CH₄ potential, which was reflected in their ultimate CH₄ yields that ranged from 109 to 382 ml g^-1 volatile solids added and their rate constants that ranged from 0.042 to 0.173 d^-1. The biodegradability of the yard wastes ranged from 0.26 to 0.86. Variation in the biochemical CH₄ potential of the yard wastes could be attributed to variation in the chemical composition of the different fractions. In the Thespesia yellow withered leaf, Tamarindus fruit pericarp and Albizia pod husk, NaOH treatment enhanced the ultimate CH₄ yields by 17%, 77% and 63%, respectively, and biodegradability by 15%, 77% and 61%, respectively, compared with the untreated samples. The effectiveness of NaOH treatment varied for different yard wastes, depending on the amounts of acid detergent fibre content. Gliricidia petals, Prosopis leaf, inflorescence and immature pod, Tamarindus seeds, Albizia seeds, Cassia seeds and Delonix seeds exhibited CH₄ yields higher than 300 ml g^-1 volatile solids added. Multiple linear regression models for predicting the ultimate CH₄ yield and biodegradability of yard wastes were designed from the results of this work.