EFFECT OF ORGANIC LOAD ON BIOGAS PRODUCTION RATES OF ANAEROBIC PROCESSING OF SEWAGE SLUDGE AND FOOD WASTE MIXTURE

Abstract

The objective of this study is to examine the influence of organic loading on biogas yield and biogas composition in a laboratory reactor for the anaerobic processing of a mixture of food waste and urban sewage sludge. The study applied organic loads from 0.5 g/l*d to 3.5 g/l*d, which were achieved by increasing the amount of food waste in the feedstock mix. The study was conducted in a 15-liter laboratory reactor, which was loaded daily with a mixture of 357 g of city sewage sludge and 0.72, 144, and 216 g of food waste. The temperature of 37±0.5 ºC was maintained in the laboratory bioreactor. During the study, it was found that by increasing the load of the bioreactor in the range of 0.5-3.5 g/l*d, the average biogas yield increased from 15.38 l from one kg of raw materials (only sewage sludge was used for the study) to 73.0 l/kg, when a mixture of sewage sludge and food waste was used and an organic loading of the bioreactor of 3.5 g/l*d was achieved. Methane concentration in biogas decreased from 64.8% (at 0.5 g/l*d organic loading) to 58.7 % (using 3.5 g/l*d organic loading). The calorific value of biogas decreased from 22.9 MJ/m³ to 21.0 MJ/m³ when the organic load of the bioreactor changed from 0.5 g/l*d to 3.5 g/l*d, and the energy value of the processed raw material increased from 0.370 MJ/kg to 1.53 MJ/kg.