Dual role of grass clippings as buffering agent and biomass during anaerobic co-digestion with food waste

Abstract

There is a dire need to replace the chemical buffers that regulate the redox environment in single-stage anaerobic digestion (AD) of food waste (FW).Hence, the applicability of grass clippings (GC) as an eco-friendly buffering agent and biomass during the anaerobic co-digestion of FW was explored. A focus was primarily given on the effects of GC on the redox environment and acidogenesis. Concomitantly the production of volatile fatty acids, hydrogen and methane in mesophilic conditions was monitored. Organic load and substrate to inoculum ratio were kept constant in all the experiments, and no chemical buffer was used. The results revealed that GC regulated the redox environment by inhibiting rapid pH drop in the digester with 10 % GC. The addition of 2, 4, and 6 % GC promoted acidogenesis with increased production of acetic and butyric acids; whereas, 8 and 10 % GC promoted solventogenesis with ethyl alcohol production. Hydrogen generation from the experiments with GC was in the range of 27-30 % of the total biogas, which was marginally higher than from the control (25 %). Methane concentration was negligible in the biogas generated from all experiments. The acidi cation rate, VFA production/consumption rate, speci c hydrogen yield, hydrogen conversion e ciency, and volatile solid removal were maximum and minimum in the reactors with 6 and 10 % GC, respectively. From the above results, it can be concluded that the addition of GC to FW would regulate the sudden pH changes and enhance the production of value-added biochemicals, to make the process cost-effective.

Impacts of Anaerobic Co-Digestion on Different Influencing Parameters: A Critical Review

“…Defa ted spent coffee grounds (DSCG); macroalgae, MC (Cladophora sp); glycerin (G); spent coffe grounds (SCG); spent tea waste (STG); chicken manure (CM); cotton gin trash (CG); goat manur (GM); corn stover; and Sophora flavescens residues (SFR). In the classical anaerobic system, chemical buffering methods using chemicals suc as sodium bicarbonate, calcium oxide [68], HCl, and NaOH, were reported as able t maintain the ideal pH setting [43,69]. Nevertheless, these agents are said to have a cos and may unfavorably hinder bioacid-and methane-forming microbes [68].…”

“…In the classical anaerobic system, chemical buffering methods using chemicals such as sodium bicarbonate, calcium oxide [68], HCl, and NaOH, were reported as able to maintain the ideal pH setting [43,69]. Nevertheless, these agents are said to have a cost and may unfavorably hinder bioacid-and methane-forming microbes [68]. As a result, an organic co-substrate that primarily operates as a stabilizing agent to maintain pH during single-stage AD of FW is urgently needed.…”

“…In light of this, the mesophilic anaerobic codigestion of FW and grass clippings (GC) feedstock was examined as an environmentally beneficial neutralizing agent. The results showed that using GC to prevent pH decline in the biodigester helped to alleviate the redox environment and increase the chosen bioproducts, making the process more economical [68]. The acetic-acid-rich food waste assisted the derivation of lignin and depolymerization of cardboard without the help of the pretreatment step.…”