Nylon fibers as supporting media in anaerobic hybrid reactors: its effects on systems performance and microbial distribution

The performances of three anaerobic hybrid reactors with various nylon fiber densities per packed bed volume (33, 22, and 11 kg/m^3 in R1, R2, and R3, respectively) as supporting media were evaluated through their ability to remove organic compounds in cassava starch wastewater. In addition, the distributions of non-methanogenic and methanogenic population in the reactors were investigated. During a 6-month operation, the organic loading rate was increased in stepwise from 0.5 to 4.0 kg COD/m3/day and the hydraulic retention time (HRT) shortened to 5.4 days. The COD removal efficiency was more favorable in R1 (87%) and R2 (84%) than in R3 (70%). The total biomass in the reactors with greater nylon fiber densities was also higher and increased from 20.4 to 67.3 g VSS and to 57.5 g VSS in R1 and R2, respectively. When the HRT was further shortened to 3 days, however, the efficiency of both reactors demonstrated a declining trend and reached 74% in R1 and 61% in R2. The distribution of microbial populations involved in the reactors was determined using the Most Probable Number technique. The result showed the lowest number of methanogens in R3 which correlated well to its relatively low efficiency. The number of non-methanogens in all reactors was, nonetheless, comparable. By shortening the HRT to 3 days, the methanogenic population in R2 diminished in both attached and suspended biomass whereas a slight reduction was detected only in the attached biomass of R1.