Improving the biodegradability of grain distillery wastewater for use as UASB substrate by combinations of ozonation/enzymatic pre-treatments

The effect of ozonation and enzyme combination pre-treatments on the composition of grain distillery wastewater (GDWW) was investigated. Exposure of UASB granules to these pre-treated GDWW was evaluated by determining the effect on granule activity, visual appearance and lipid content of the granules. Pre-treatments involving a pre-ozonation step were found to be more effective in reducing the lipid and COD content of GDWW. The higher the lipid and COD reduction achieved by the pre-treatments the higher the granule activity after 24 d exposure, the lower the lipid content in the granule and the less severe the formation of an encapsulating layer.

Removal of 3-chlorobenzoate using an upflow anaerobic sludge blanket reactor under light conditions

The possibility of 3-chlorobenzoate removal from water using an upflow anaerobic sludge blanket (UASB) reactor without the addition of any extra dechlorinating culture under light conditions has been studied on a laboratory scale. Benzoate removal was observed in the first three months of operation under light conditions, but the 3-chlorobenzoate removal was not observed. After three months of operation under light conditions, the 3-chlorobenzoate concentration in the UASB reactor effluent gradually decreased to less than 1 mg·L−1. The 3-chlorobenzoate concentration in the effluent did not increase under dark conditions. The DOC concentration in the effluent decreased according to the removal of the 3-chlorobenzoate by the UASB granules. These results indicated that granules in the UASB reactor provided the 3-chlorobenzoate removability after 80–100 d of adaptation to the 3-chlorobenzoate, and that the UASB reactor is useful for 3-chlorobenzoate removal.

Microbial distribution in UASB granules and its resulting effects

Microscopic (SEM and TEM) examinations of biogranules sampled from various UASB (Upflow Anaerobic Sludge Blanket) reactors indicated that microbes are densely packed. The microbial distribution is strongly dependent upon the degradation thermodynamics and kinetics of individual substrates. Biogranules degrading carbohydrates exhibited typically a layered distribution with a surface layer populated with hydrolytic/fermentative acidogens, a mid-layer comprising syntrophic colonies and an interior comprising acetotrophic methanogens. On the other hand, those substrates having a rate-limiting hydrolytic/fermentative step did not exhibit any layered pattern; instead, bacteria were interwined and distributed evenly. These observations have two implications. Biogranules are developed through evolution instead of random aggregation of suspended microbes. Furthermore, biogranules should be less vulnerable to the changes of mixed liquor condition, because the large majority of microbes inside the biogranules are shielded from the hostile mixed liquor environment. The latter is supported by experimental evidence that biogranules are more resistant than suspended sludge to the toxicity of hydrogen sulfide, heavy metals and aromatic pollutants in wastewater.

Startup of thermophilic (55°C) UASB reactors using different mesophilic seed sludges

Performances during startup of three 2.8-litre UASB (upflow anaerobic sludge blanket) reactors operated under thermophilic condition were investigated. All reactors were seeded with mesophilic sludges: one with flocculent digester sludge (Reactor-F), another with UASB granules (Reactor-G), and the third with disintegrated granules (Reactor-D). The reactors were operated in parallel at 55°C and 24 hours of retention time, using sucrose and milk as substrate at COD (chemical oxygen demand) loadings up to 10 g-COD/l·day. Immediately after temperature was step-increased from 37°C to 55°C, all reactors encountered sludge washout and deterioration of COD removal efficiency; however, the impact of temperature increase was more severe on Reactor-F. Sludge granulation took place in all reactors; first granules became noticeable after 45 days in Reactor-D, and after 90 days in Reactor-F. Reactor-G and Reactor-D were capable of removing 95% of soluble COD after 75 days, while Reactor-F after 110 days. Throughout this study, there was little difference in performance between Reactors G and D. The thermophilic granule were estimated to have a yield of 0.099 g-VSS/g-COD, and a methanogenic activity of 0.71-1.55 g-methane-COD/g-VSS·day, comparable to that of mesophilic granules.