Thermal Pretreatment for Improvement of Biogas Production and Salinity Reduction by Zeolite

Abstract

The anaerobic digestion of organic waste for biogas production can be affected by some variables such as temperature; concentration of the biogas feed solution, bacteria populations, and pressure. This study investigated the effects of thermal pretreatment at 50, 75, and 100 ºC on the biogas produced by simultaneous anaerobic digestion of cow manure, mushroom waste, and wheat straw at thermophilic temperature. Moreover, the effects of a zeolite on reducing the salinity of the wastewater were evaluated. Cow manure, mushroom waste, and wheat straw were mixed to yield a mixture with an optimum carbon to nitrogen ratio of 20-30 and TS of 25-35%. Each thermal pretreatment was prepared in four replicates and placed in a steam bath with a temperature of 55 ºC. The amount of gas produced by each thermal pretreatment was measured every day for 15 days. On day 15, the electrical conductivity of the produced wastewater was measured and the wastewater was exposed to a modified zeolite. The results showed that the greatest level of biogas was produced by thermal pretreatment at 75 ºC, which gave the biogas yield of 0.197 L/gVS after 15 days observation while, the other thermal pretreatments at 50, and 100 ºC gave the biogas yield 0.147, and 0.169 L/gVS, respectively. The highest amount of biogas was achieved on the third day for every three thermal pretreatments. Moreover, the modified zeolite reduced the wastewater salinity by 25%. These results confirmed that thermal pretreatment at 75 ºC is an effective pretreatment for biogas production improvement from the mixture of cow manure, mushroom waste, and wheat straw, and the modified zeolite could be used for salinity reduction of wastewater discharged from the process.