Enhancement of hydrolysis efficiency and biogas production by treatment of secondary sludge with bacteriophage lysozymes

Abstract

Anaerobic digestion of secondary sludge from wastewater treatment plants can degrade sludge while producing methane that can be burned as bioenergy. Hydrolysis of secondary sludge is the first step in anaerobic digestion, but is the rate-limiting step. In this study, to speed hydrolysis of secondary sludge, lysozymes from bacteriophage species T4, T7 and λ were applied to batch tests. The volatile suspended solids were removed by lysozymes at efficiencies of 23.6–50.1 %. Use of the lysozymes increased the reaction coefficient of biogasification of volatile suspended solids by 0.4–1.0 d−1, regardless of the origin of sludge, or sources of lysozyme. The removal efficiency of volatile suspended solids and methane yield had significantly positive correlation (p < 0.001). Relative abundances of genera Simplicispira (10.3 → 5.2 %), Dokdonella (4.9 → 3.9 %), and Thermomonas (2.7 → 1.2 %) were high in original secondary sludge, and maintained relative abundance over other genera even after lysozyme treatment. To increase the ratio of microbes to organics, sludge samples from various sources were aerated and cultivated with 40 g/L glucose. In experiments on this cultivated sludge, Klebsiella (3.7 → 23.0 %) Kosakonia (1.8 → 19.0 %) and Dysgonomonas (0.0 → 15.3 %) sharply increased after lysozyme treatment, due to their fast growth. Treatment with bacteriophage lysozymes can significantly increase sludge reduction.