DOI: 10.14457/tu.the.2017.345
title: Technical feasibility of anaerobic digestion for utilizing municipal solid waste from Talaad Thai market, Thailand

description: Agriculture is the most important sector in the economy of Thailand. The data reported by Food and Agriculture Organization (FAO) states that Thailand produces over 10 million tonnes of fruit and vegetables annually. As a result, large amounts of fruit and vegetable waste rich in biodegradable organics are generated. Anaerobic digestion (AD) is a potential technology from an environmental point of view and also beneficial to society as it provides a clean fuel and fertilizer.In this study, the mixed wastes from the vegetable market in Talaad Thai was used as the feedstock. The granular sludge from up-flow sludge blanket reactor, Pathum Thani Brewery Co., Ltd., Thailand, was used as the inoculum. To determine the influence of feedstock to inoculum ratio (F/I) and temperature on methane generation, biochemical methane potential (BMP) experiments were conducted at different F/I ratios at 37 degree Celsius and ambient temperature (30±4 degree Celsius). The effects of external alkalinity were also studied by adding NaHCO3 concentrations ranging from 0 to 1200 mg/g VSadded. To confirm again the optimum temperature, BMP assays were conducted at optimum NaHCO3 concentration and two temperature conditions of 37 and 50 degree Celsius. The reuse of digestate from anaerobic digesters as sources of alkalinity and inoculum was also investigated in the study. The optimum conditions found out in the BMP tests were applied for the lab-scale BIOCEL reactor.Results and findings obtained in this study are summarized as follows:- After 53 days of experiment time, without adding NaHCO3, the optimum conditions of F/I ratio and temperature were at 0.5 and 37 degree Celsius, respectively. The results depicted that the higher the F/I ratio, the lower biogas and methane yield. The F/I of 0.5 at the temperature of 37 degree Celsius gave the highest biogas and methane yield at 851 mL/g VS and 306 mL/g VS, respectively. - At the F/I  ratios of 2.0, 3.0, 4.0, and 5.0 g VS/g VS, higher hydrogen production was observed for both temperature conditions. - The results also showed that adding buffer improved the biogas production and methane contents at F/I of 1.0 and 2.0, significantly.  - When the optimum condition of NaHCO3 was operated at temperature of 37 and 50 degree Celsius, the achieved results depict a better performance at reactors of 37 degree Celsius. The thermophilic reactors shorten the digestion time compared to the mesophilic reactors. However, the final biogas and methane yields at thermophilic reactors were lower than that of mesophilic reactors.- The study found an economic option to reduce bicarbonate adding into AD reactors by recycling digestate as an inoculum source for new processes. When the digestate is recycled, the sodium bicarbonate can be reduced at the concentration of 150 mg per gram VS added.- At the optimum conditions obtained from BMP test, AD performance of the lab-scale reactors was higher than that of BMP reactors. When using UASB sludge as inoculum, the methane yield was 404 and 756 mL/g VS in BMP and lab-scale reactor, respectively. When using digestate as inoculum, the methane yield was 395 and 672 mL/g VS in BMP and lab-scale reactor, respectively. In conclusion, this study successfully demonstrated the potential of utilizing the mixed vegetable waste from Talaad Thai market as a renewable energy source through anaerobic digestion.