Effect of inoculum to substrate ratio on the performance of modified anaerobic inclining-baffled reactor treating recycled paper mill effluent

Abstract

Three start-up techniques were investigated to evaluate the suitability of the bench-scale modified anaerobic inclining-baffled reactor (MAI-BR) for the treatment of recycled paper mill effluent (RPME) and to achieve an improved understanding of the inoculum to substrate ratio (ISR). The ISR ratios used were 3.53, 1.17, and 10.63 g volatile suspended solids (VSS)/g chemical oxygen demand (COD) for the first, second, and third start-ups, respectively. On a 30-d duration, the first start-up succeeded in removing 72% of the COD with an effluent pH of 6.2 and a methane production of 0.076 L/d. The second start-up was considered unfavorable after 16 d because of low methane production and effluent pH level. The third start-up with a 21-d duration was the best because of its 87% COD removal, 6.82 effluent pH, and 0.164 L/d methane production. The effluent volatile fatty acid (VFA)/alkalinity ratios were concurrently varied as 0.56, 0.45, and 0.034 for the first, second, and third start-ups, respectively. Subsequently, the VSS/TSS ratio of 0.78–0.86 formed in the reactor was sufficient to control biomass washout. The third start-up demonstrated that an ISR of more than 10 g VSS/g COD is an important factor that leads to a successful and efficient start-up operation. The batch feeding rate must be as low as 0.1 g COD/L d. Furthermore, the VFA/alkalinity ratio of the third start-up was excellent. The bench-scale unique design of the MAI-BR showed good performance in the RPME treatment within a period of less than one month.