Kinetic model of biogas production from co-digestion of Thai rice noodle wastewater with rice husk and different type of manure with ash supplement

Abstract

In recent decades up to now, researches on alternative energies have been intensified particularly those on biomethane and biohydrogen from agriculture wastes and municipal wastes. The objective of this research was to study the biogas production from anaerobic co-digestion of Thai rice noodle wastewater with rice husk and different types of animal manure (chicken manure, cow manure, and quail manure), with and without ash supplement. There were 27 experiments conducted in batch digesters at room temperature (28-30 °C) and each experiment was triplicated. Each digester contained 10 g of animal manure, 10 g of rice husk, and 200 ml total working volumes of Thai rice noodle wastewater. Five different amounts of ashes (0, 2, 4, 6, 8 and 10 g) were supplemented. The results showed that the co-digestion of Thai rice noodle wastewater with chicken manure, rice husk, and 6 g of ash supplement gave the highest methane percentage, cumulative methane production and bio-methane potential (BMP): average value of 71.5%, 1,846 mL and 311.2 mLCH4/gVSremoved respectively. This co-digestion gave the initial pH of 7.0 and it was sustained in an optimal range (pH 6.8-7.5) until the digestion stopped (45 days). Slow release of nutrients from slowly digestible substrates helped to balance the digestion steps, sustaining pH to around 7. In contrary, other sub-optimal ratios produced the final pH was lower than its initial pH, and the AD process could fail or produced less methane. In the kinetic study, it was also found that traditional Gompertz and Monod-type models for single substrate digestion could not describe the biogas evolution curve satisfactory. Two-substrate models were used instead and able to describe the experimental data very well.