EFFECT OF TWO CHEMICAL PRETREATMENTS IN THE ANAEROBIC HYDROLYSIS OF THE RICE STRAW / EFECTO DE DOS PRETRATAMIENTOS ALCALINOS EN LA HIDROLISIS ANAEROBIA DE LA PAJA DE ARROZ

Resumen

Rice (Oryza sativa) is an important staple food for approximately half of the world population. In addition to the grains, also the straw can be used if not needed as organic fertilizer for the fields. Although rice straw has potential to be used for anaerobic digestion (AD) to produce biogas, its large-scale application is still limited. The utilization of rice straw for AD must particularly be developed regarding the pretreatment of the lignin biomass for the hydrolysis process and the biogas yield and quality. Among the pretreatment methods, the alkalization method was found to be effective. In the present research the effects of rice straw pretreatment were analyzed following a multifactorial approach. For this purpose, calcium hydroxide (Ca(OH)₂) and potassium hydroxide (KOH) were applied at different concentrations. Furthermore, the reaction time and inoculum-to-substrate ratio were included as part of the study. The highest hydrolysis yield was observed at a reaction time of 4 h, with an alkali concentration of 10 g per g rice dry matter, and an inoculum-to-substrate ratio of 50%. Here also the maximum concentration of volatile fatty acids was observed with 187±30 mg L^-1. The results showed that the additional effort of a pretreatment of rice straw can be worthwhile to improve the AD and to increase the biogas yield.