Evaluating the influence of calcined eggshells and ultrasonication in the Co-digestion of avoidable and unavoidable Food Waste and OLS regression analysis of the reactor system

Abstract

The technological advancements in the bio-conversion of food waste (FW) into biogas signify substantial advancements in the field of waste management. However, persistent operational challenges like rapid acidification and difficulties in maintaining the C/N ratio in mono-digestion remain, despite extensive research efforts. The present study aims to evaluate the reactor performance in co-digestion, specifically using a 1:1 ratio of unavoidable food waste (UAFW) and avoidable food waste (AFW), with the addition of calcined eggshells as an additive. Further, the study employs Ordinary Least Square (OLS) regression modeling to predict the biogas production from the co-digestion process. The experimental process involves ultrasonication pretreatment, focusing on calcined eggshells for their ability to preserve carbohydrates via Ca(OH)2, an alkaline material. The semi-continuous operation of the reactor spanned for 120 days and was divided into three phases with varying Organic Loading Rates (OLR) from 0.6 to 2.2 gVS/l/d. Characterization studies such as SEM, FTIR and TGA-DTA were performed to validate the pretreatment method and addition of egg-shells. Results indicated increased OLR led to higher Volatile Solids (VS) reduction. This was attributed to the calcined eggshells' role in adsorbing NH4+ and NO3− ions while maintaining pH levels, resulting in significantly higher biogas production. The multiple regression models used in the study yielded promising results, surpassing simple linear regression, with an adjusted R-squared value > 0.9 and p-value <0.05. The model effectively anticipated the specific methane yield, demonstrating the capability to improve energy production by co-digesting AFW and UAFW. The study presents an opportunity to divert organic waste from landfills, reduce greenhouse gas emissions, and promote sustainable waste management by using bio-waste additives, reducing reliance upon synthetic chemicals.