Effect of varying organic loading on the production of biogas from pretreated wheat straw in batch reactor

Abstract

Pakistan is a developing country and is experiencing a shortage of energy due to its rapidly growing population. Therefore, there is a need to explore the untapped energy potential of lignocellulosic biomass. But its complex structure is the main hurdle to biodegradation. Pretreatment helps in breaking this recalcitrant structure which improves degradability. Digestion parameters are important factors for smooth anerobic digestion. Optimum organic loading is vital to reduce or avoid acid accumulation, improve reactor stability, and increase biogas yield. This study, therefore, carried out to assess the impact of varying organic loading (OL) on production of biogas from pretreated wheat straw in batch reactor. Wheat straw (WS) was used as substrate and subjected to sodium hydroxide (NaOH), titanium dioxide (TiO2) and combined pretreatment. Pretreated WS was fed to reactors based on volatile solids at four different loadings of 10, 20 30 and 40 gVS/L. The results revealed that 10 gVS/L has the maximum biogas production in all the three pretreatments. The NaOH pretreated wheat straw at 10 gVS/L has produced 56%, 146% and 172% more biogas compared to OL 20, 30 and 40 gVS/L respectively. Similarly, TiO2 pretreated wheat straw had high biogas yield at organic loading of 10 gVS/L, which was 74%, 214% and 292% more than the higher organic loadings respectively. Combined pretreatment had maximum biogas yield than NaOH and TiO2 individually. Maximum total solids (TS) and volatile solids (VS) removal was also observed in case of combined pretreatment of WS at OL of 10 gVS/L. Biogas production, VS removal and stability of the reactor declined with an increase in OL from 10 gVS/L to 40 gVS/L, which can be attributed to increase in VFAs production in the higher organic loading.