EXPERIMENTAL STUDY ON A SOLAR-HEATED BIOGAS DIGESTER USING SHALLOW SOLAR POND IN COLD CLIMATE

Abstract

In northern Egypt, the ambient temperature almost below 20°C during winter months, which is insufficient for the anaerobic digestion (AD) and affecting negatively the biogas yield, especially for the floating dome digester(Indian model) due to the heat losses through the gas holder. Since the slurry temperature is a crucial factor for the AD rate, this investigation aims to heat a concrete pre-constructed floating dome biogas digester (Family-scale digester) during winter season for enhancing the fermentation rate by utilizing the extracted heat of integrated shallow solar pond (SSP) using dairy cattle dung comparing to a previous work of un-heated digester. The solar-heated digester was evaluated under the same operating conditions of the un-heated digester except the slurry temperature and similar values of both the solar radiation intensity and ambient temperature during 30 days without feeding as a digestion time taking into consideration the slurry temperature, pH, daily, cumulative (m3/month) and specific (m3/kg VS) biogas yield as well as the total net gained energy. The obtained results revealed that, the average slurry temperature of the solar-heated biogas digester system increased by 12.3°C which led to increase the average daily, cumulative and specific biogas yield by about 129 % higher than the un-heated digester with average methane content of 70% and total net gained energy of 553.1 MJ/month.