Mineral washing from rice straw to improve its combustion properties

Indonesia has abundant potential for rice straw which can be developed as an alternative fuel. However, rice straw has an ash content with a high mineral content which can cause problems in applications involving high temperatures. This study aims to determine the effect of washing rice straw on the fuel quality improvement of rice straw. Sun-dry rice straw that has been cut into 1-2 cm was soaked in tofu industrial wastewater at a ratio of 0.5 kg in 10 L. Sampling for the measurement of ash and mineral content was carried out at 0 (without treatment), 3.75, 7.5, 15, 30, 60, 120, and 720 min. Ashing was carried out using a furnace at a temperature of 550 °C for 2 h. The ash was then analysed using XRF Spectrometry to determine its mineral content. Measurement of the caloric value of rice straw was carried out using a bomb calorimeter. Results showed that soaking straw in tofu wastewater decreased the ash content from 16.0 to 13.67 (% DS) and increased the calorific value from 13.60 MJ/kg (without soaking) to 15.77 MJ/kg (soaking by 720 min.). Soaking was also able to reduce important minerals such as K (17.94% to 9.69%), S (3.40 to 2.06%), Cl (0.91% to 0.3%).