No abstract

A cross-flow ultrafiltration (UF) membrane separation was applied to anaerobic process for treatment of a wastewater containing high proportion of particulate COD. A synthetic wastewater with the total strength of 5000 mg COD·1−1 consisting of soluble and particulate COD (cellulose) in the ratio of 1:1 was fed to the reactor. The reactor was operated for 190 days at two loading rates, i.e. 1.5 and 2.5 kg COD·m−3·d−1. More than 98% of COD removal was consistently achieved throughout the duration, and the system was furthermore likely to accommodate much higher loading. Although the permeate COD was always kept at less than 80 mg COD·1−1, soluble COD of reactor broth accumulated up to 1200 mg COD·1−1. The biomass concentration saturated around 15 000 mg ML VSS·1−1. There was no tendency for cellulose to accumulate in the reactor over the whole period, which constituted only 1-2% of the total solids retained in the reactor. The methanogenic activity of the sludge increased 3.4 times for H2/CO2 and 10 times for acetate after 40 days operation. Afterwards, however, a further cultivation caused declines to 50% of the respective peak values for both substrates, because of a low sludge loading. The methanogenic activity using cellulose as a test substrate also exhibited a similar tendency. The membrane permeate flux deteriorated significantly with the cultivation time, owing to the change in rheological properties of the reactor mixed liquor that had been caused not only by increment of MLSS but also by accumulation of soluble high molecular organics.

A mathematical model is proposed herein to describe the dynamic behavior of the denitrification process in a fluidized bed biofilm reactor. The model basically consists of the following four submodels: bioparticles fluidization, bulk liquid flow pattern, substrate conversion within biofilm and biofilm thickness development. As for intrinsic denitrification reaction, a consecutive two-step reaction kinetics with nitrite as an intermediate product is adopted. All parameters needed for simulation were experimentally determined. Verification of the model was obtained in a dynamic state using a laboratory-scale fluidized bed denitrification reactor under well defined conditions.

cis-1,2-Dichloroethylene (cis-DCE) is frequently found at significant concentrations in groundwater which is contaminated with tetrachloroethylene or trichloroethylene. Under anaerobic conditions, cis-DCE can be biotransformed via reductive dechlorination to ethylene. Several factors affecting this transformation were investigated using anaerobic sewage sludge as an inoculum. The reductive dechlorination of cis-DCE was observed at 25°C and 15°C but not at 35°C. Supplying a suitable electron donor (organic substrate or hydrogen) was necessary to sustain reductive dechlorination. Glucose, yeast extract, propionate, and hydrogen stimulated dechlorination, while methanol and acetate did not. Anaerobic enrichment cultures capable of dechlorinating cis-DCE to ethylene were developed from the sludge. In the presence of either glucose, yeast extract or propionate (100 mgCOD/l), 0.46 mg/l of cis-DCE was almost completely dechlorinated to ethylene within 4 days by the cultures at 25°C. Transformation rate was somewhat lower in the culture fed with hydrogen. Dechlorinating ability was sustained even in the cultures fed with low concentrations (10 mgCOD/l) of glucose or hydrogen, although the transformation was sometimes insufficient. These results suggest that anaerobic bioremediation processes can be used for removal of chlorinated ethylenes from contaminated groundwater.

Tetrachloroethylene (PCE) is one of the most common groundwater contaminants in Japan. PCE can be completely dechlorinated to ethylene (ETY) and ethane (ETA) by anaerobic microorganisms in the presence of a suitable electron donor. This study was conducted to examine the feasibility of using an anaerobic filter for the degradation of PCE in a bioremediation process. Laboratory-scale anaerobic filters were operated at 25°C using ethanol as the electron donor. Rapid start-up of the reactors was achieved by using anaerobic completely PCE-dechlorinating enrichment cultures as the inoculum. During the continuous operating periods, low concentrations (2.8 mg/L) of PCE were almost completely dechlorinated to ETY and ETA at hydraulic retention times of 49-15 hours with 100 mgCOD/L of ethanol. PCE concentrations as high as 80 mg/L was dechlorinated to ETY with a relatively low supply (200 mgCOD/L) of ethanol. Results of this study suggest that the anaerobic filter system is a feasible bioremediation process for the cleanup of groundwater which is contaminated by chlorinated ethylenes.