Performance and microbial community analysis of a full-scale hybrid anaerobic-aerobic membrane system for treating molasses-based bioethanol wastewater

We evaluated the efficacy of a full-scale combined biophysicochemical system for treating molasses-based bioethanol wastewater in terms of organic substances, nutrient, and dark brown color removal. The main organic removal unit, i.e., the upflow anaerobic sludge blanket [UASB] reactor, achieved 80.7% removal and 4.3 Nm3 methane production per cubic meter of wastewater with a hydraulic retention time of 16.7 h. Downflow hanging sponge [DHS] reactors were important in reducing the biochemical oxygen demand [BOD], and the lowest possible organic waste intake prevented excessive biomass formation. The BOD removal efficiency was 71.2-97.9%. The denitrification upflow anaerobic fixed bed [UFB] reactor achieved 99.2% total nitrogen removal. Post-physicochemical membrane treatment reduced the total phosphate, color, and remaining organic matter by 90.4%, 99.1%, and 99.8%, respectively. We analyzed the microbial diversity of the sludge from the UASB reactors. Methanosaeta was the dominant archaeal genus in the system, followed by Methanolinea, Methanomicrospillum, Caldiserica, Bacteroidetes, and Deltaproteobacteria

Evaluation of treatment characteristics and sludge properties in a UASB, reactor treating municipal sewage at ambient temperature

The evaluation of treatment characteristics and sludge properties of an upflow anaerobic sludge blanket [UASB] process was investigated using a pilot-scale 1.15 m[3]reactor. The UASB, inoculated with digester sludge, was operated at a hydraulic retention time of 8 h at sewage temperatures ranging from 10.6 to 27.7 °C for more than 1100 days. The stable removal efficiencies for total COD[Cr] and SS were 63 +/- 13% and 66 +/- 20%, respectively. The average concentration of the retained sludge increased to more than 24.5 gSS/L of the column volume after two years of operation. In summer, the water temperature increased above 20 °C, and biodegradation of solid organic matter was enhanced. The solid retention time was evaluated to be as long as 293 +/- 114 days; this is sufficient for mineralisation of solid organic matter, as indicted by a low sludge conversion of 0.029 gVSS/gCOD[removed] and a growth yield of 0.132 gVSS/gCOD, determined by seasonal sludge profiling. The bacterial communities, based on bacterial 16S rRNA genes in the retained sludge, were significantly diverse. Bacteroidetes and Firmicutes were the dominant phyla of the decomposers of solid organic matter in the library. A Ruminocoecus-related clone detected in the Firmicutes phylum acted as a cellulose decomposer

Intermittent effluent recirculation for the efficient treatment of low strength wastewater by an EGSB reactor

In order to establish the appropriate methane fermentation technology for low strength wastewater, a 2.0 L EGSB reactor was operated at 20°C with 0.3 - 0.4 g COD/L of sucrose-based synthetic wastewater for 500 days. At the start up period, the reactor was operated in EGSB mode with a 5 m/h up flow velocity by continuous effluent recirculation. However, the EGSB reactor exhibited insufficient COD removal [50-60%] at COD loading of 7.2 - 9.6 kg COD/m3.day due to the low COD concentration in the sludge bed. Therefore, we proposed the new operation mode by switching to UASB mode [without recirculation, 0.7 m/h up flow velocity] for 30 minutes and EGSB mode for 10 minutes in 40 minutes cycle. Moreover we added sodium sulfide to make the low ORP condition. In this operation, COD removal increased dramatically, from 65% to 91%. Additionally, physical properties of the retained sludge were well maintained in this operation mode. Furthermore, the retained sludge possessed appropriate levels of methanogenic activity [0.2-0.4 g COD/g VSS/day] at 20°C