抄録
Wastewater treatment plant of our laboratories consists of a neutralization tank and a plain sedimentation tank. Active growth of algae, especially a few species of Euglena and Chlorella, was observed in the sedimentation tank in spite of average detention time of 20 hrs. Freshly deposited sediments which mainly consists of algae were estimated to be 5-10g/m2 day. Chlorella sp. isolated from the sedimentation tank grew in a glycine and a glucose medium and specific growth rates (μ) of 3.35 and 2.70 day-1 were obtaind.
Although only a little growth was observed in a pepton medium, the isolate could grow pormptly in the medium under the co-existence of some bacteria isolated from the tank. This result indicates that symbiotical growth of algae and bacteria may take place in the actual sedimentation tank.
Algal growth in the tank favoured the reduction of BOD and trace amounts of metal ions in wastewater. Freshly deposited sediments contained considerable amounts of metals (e.g. Hg++30-100 mg /kg, Cu++ 2400-2700 mg/kg, Pb++2500-10700 mg/kg), whereas wastewater contained 0.1-8.0μg/1, 0.02-0.35 mg/l, and 0.01-3.6 mg/l, respectively. Heavy metals in the sediments were stable under anaerobic condition and no release of metal ion to the aqueous phase was observed for 7 months period. No release nor volatilization of mercury from the sediments was also obsered under anaerobic and aerobic conditions.
