Anaerobic treatment of industrial biodiesel wastewater by an ASBR for methane production.

ABSTRACT

A mechanically stirred anaerobic sequencing batch reactor (5 L, 30 °C) containing granular biomass was used to treat the effluent of an industrial biodiesel production process with the purpose to produce methane. Process stability and efficiency were analyzed as a function of applied volumetric organic load (AVOL of 1,000 to 3,000 mgCOD/L), reactor feed time, and cycle length (8-h cycles with 10-min or 4-h feeding and 4-h cycles with 10-min or 2-h feeding). Batch operations (B) with 1,000 to 3,000 mgCOD/L involved 10-min feeding/discharge (1) 1.0-L influent with 4-h cycle and (2) 2.0-L influent with 8-h cycle. Fed-batch operations (FB) with 1,000 to 3,000 mgCOD/L involved 10-min discharge and the following feeding (1) 1.0-L influent in 2 h with 4-h cycle and (2) 2.0-L influent in 4 h with 8-h cycle. At 1,000 mgCOD/L (AVOL of 18 to 1.29 gCOD/Lday), kinetic parameter values were 1.03 and 0.92 h(-1) at conditions B-1000-4 h and FB-1000-8/4 h, respectively. At both conditions, removal efficiency was 88 %, and cycle length could be reduced to 3 h (B-1000-4 h) and 5 h (FB-1000-8/4 h). At 2,000 mgCOD/L (AVOL of 2.38 to 2.52 gCOD/Lday), kinetic parameter values were 1.08 and 0.99 h(-1) at conditions B-2000-4/2 h and FB-2000-8/4 h, respectively, and removal efficiencies were 83 and 81 %. Cycle length could be reduced to 3 h (B-2000-4/2 h) and 6 h (FB-2000-8/4 h). At 3,000 mgCOD/L (AVOL of 3.71 to 3.89 gCOD/Lday), conditions allowing stable operation were B-3000-4 h, FB-3000-8/4 h, and FB-3000-4/2 h. Stability could not be obtained at condition B-3000-8 h, and the best results were obtained at condition FB-3000-8/4 h. Specific methane production ranged from 41.1 to 93.7 NmLCH(4)/gCOD, demonstrating reactor application potential and operation flexibility.