Recovery of Reducing Sugar from Food Waste: Optimization of Pretreatment Parameters Using Response Surface Methodology

Abstract

Renewable energy sources, environmental pollution and climate change have been the main focus of research nowadays. Increase in energy demand and pollution and consequent depletion of fossil fuel reserve have forced scientists to look for alternative source of energy. Bioethanol is the most promising replacement fuel for petrol. The advantage of bioethanol is low Green House Gas (GHG) emission and high octane number. Traditionally, bioethanol is generated from sugar-rich crops like corn, sugarcane, beetroot etc., which are considered as first-generation sources. The second-generation sources of bioethanol constitute agricultural residues, municipal and industrial wastes, energy deficit crops etc. This study focuses on bioethanol synthesis from food waste, one of the major constituents of Municipal Solid Waste (MSW). As per estimations, more than 55 million tons of municipal solid waste is generated in India per year; the yearly rise is assessed to be about 5%. About 50% of the MSW is due to organic waste. Carbohydrates, proteins and starch are the main constituents of food waste. Reducing sugars are the building unit of carbohydrates and starch in food. The main objective of this study is to increase the recovery of reducing sugar from food waste using different pretreatment methods and simultaneously optimizing the conditions using Response Surface Methodology (RSM), a statistical tool. Characteristics of food waste such as pH, total solids, volatile solids, total organic carbon, total inorganic carbon, and total sugar were determined using standard procedures. Dilute sulphuric acid (0.5–2.5% v/v), sodium hydroxide (1–3.5% w/v), and hydrogen peroxide (0.5–3.5% v/v) were used as pre-treatment reagents. Strength of the reagents and time of autoclaving (0–60 min) were varied. Temperature and pressure of 121 °C and 1 bar, respectively, were kept constant during the pretreatment. Central Composite Design (CCD) was used to obtain optimum conditions for recovery of reducing sugar from food waste. Reducing sugar concentration in the hydrolysate after each experimental run was determined using 3, 5 Dinitrosalicylic acid method. The highest yield of reducing sugar—0.67 g/g of food waste was observed using 1.5% (v/v) dilute sulphuric acid as pre-treatment reagent and 30 min of autoclaving. Sodium hydroxide yielded a maximum reducing sugar of 0.129 g/g of food waste and Hydrogen peroxide produced a maximum yield of 0.37 g/g of food waste.