Multiple evaluations of use of digested slurry from methane fermentation of household food waste in vegetable growing in Ho Chi Minh City, Vietnam

Abstract

With the ultimate aim of constructing a recycling loop in Ho Chi Minh City (HCMC) by introducing the source-segregation of household food waste, applying methane fermentation technology to treat it, using the biogas generated as energy and the resulting digested slurry for agriculture, multiple evaluations were made of the use of digested slurry as follows: 1) a physiochemical analysis of the digested slurry obtained by methane fermentation of household food waste in HCMC; 2) a crop growth experiment using the slurry on green mustard; and 3) a simulation of transporting the digested slurry and applying it in agriculture. The digested slurry had a lower ammonia nitrogen content and a smaller ratio of ammonia to total nitrogen than those in previous studies of digested slurries from food waste in other countries. It also had a low harmful contaminant content. The crop growth experiment using the slurry clarified the positive effects of digested slurry on green mustard: plant yield and height, and the width of the biggest leaf produced per seedling, were significantly greater than when no nitrogen was applied. Yield was highly correlated with the ammonia nitrogen application rate, and almost the same fertilization effects as those with chemical fertilizer are expected to be obtained if fertilization design were based on the ammonia nitrogen levels in the digested slurry. No definitive effects of the digested slurry on soil were found. The simulation revealed that the transport and application of digested slurry in the suburbs of HCMC would likely be more efficient than in Japan due to the longer period for application and smaller required storage capacity of digested slurry throughout the year in a climate warmer than that in Japan.