Potential energy from residual biomass of rice straw and sewage sludge in Egypt

Sewage sludge and rice straw residues are produced with high amounts in Egypt. The possibility of using these residues as a renewable energy for heat and power generation replacing fossil fuels and solving disposal problems. Theoretical energy potential from rice straw and sewage sludge were calculated in this study via different processes. Anaerobic digestion, as a natural and eco-friendly source of renewable energy, was chosen as a case study and applied for sludge and mixture of sludge and rice straw with mixing ratios (2 and 4%, rice straw to sludge based on weight). The digestion process was performed using batch reactors under anaerobic conditions and mesophilic temperature at (35 +/- 1 degrees C). The results of energy calculation showed that the direct combustion represents the highest technique for recovering energy from rice straw. On the other hand, the anaerobic digestion of sludge with rice straw improved carbon to nitrogen ratio. Consequently, an increase in biogas yield for 4% mixture reached six times compared to solo sludge. Furthermore, a significant decrease in pathogens and organic contents of the digested sludge and mixture was observed which provide the possibility of using the effluent of the digester in the agriculture and land application. Moreover, the biogas analysis showed that methane was the highest component (60-63%) followed by carbon dioxide which means that the biogas produced from digestion of sludge and rice straw is attractive source of renewable energy. (C) 2018 The Authors. Published by Elsevier B.V.