고농도질소를 함유한 중금속폐수의 생물학적처리

Abstract

Heavy metal pollution problems have became one of the most important environmental issues in Korea. This is because the metal contaminants can cause serious toxic effects in biota in aquatic and soil environments. Metal plating wastewater has been usually treated by the physico-chemical methods such as chemical precipitation, reverse osmosis and evaporation. Characteristics of the wastewater, however, became increasingly complicated as the industry developed and combined treatment of the wastewater for the small scale factories became more common. Treatment of metal plating wastewater requires more effective technologie in terms of performance and economics that would be applied to the small scale metal industries

The long term goal of this study was to develop a metal plating wastewater treatment system that can be practically employed for the small scale metal industries. The specific aims of this study were : 1) to find and optimize the growth conditions of sulfate reducing bacterial consortia for an efficient removal, 2) to develop an anaerobic process packed with a floating granular media, 3) to develop a simultaneous removal process of heavy metals and nitrogen utilizing sulfate reducing bacteria(SRB), sulfur denitrification bacteria(SDNB), and heterotrophic denitrification bacteria(DNB).

To find effective treatment conditions for the electroplating wastewater treatment by SRB, the bacteria activity, removal capacity of heavy metals, and possibility of nitrogen removal were investigated with respect to a wide range of COD/sulfate ratios in an anaerobic continuous reactor. During the start-up period when COD/sulfate ratios were gradually increased from 1.53 with the fixed COD concentration of 500 mg/L as glucose, successful sulfate reduction rate(above 95%) was achieved. Furthermore, in order to determine the activities of SRB at varying COD/sulfate ratios, influent COD concentrations were controlled to maintain COD/sulfate ratios at 0.18, 0.33, 0.5, 0.82, 1.2 after fixation of sulfate concentration of 2000 mg/L in the feed electroplating wastewater. At the relatively low values(0.18, 0.33) deficiency of organics in the feed affected the activity of SRB. Sulfate reduction efficiency was 61% and 59%, at the COD/sulfate ratio of 0.82 and 1.2, respectively. The further increase of the ratio did not appear to increase the reduction efficiency. Indicating sulfide inhibited the SRB's activity at the high COD/sulfate ratios. From the results, economic COD/sulfate ratio was determined to be 0.33 to reduce sulfate 2000 mg/L.

The amount of external carbon source supplied could be determined on the basis of heavy metal concentration in the wastewaters since sulfate reduction rate can be controlled by the external carbon. Heavy metals were effectively removed by SRB at above pH 6.4 regardless of metal species, but removal efficiency decreased dramatically at pH 5.4 to decrease of SRB activity caused by unfavorable pH condition. Consequently, at least, pH 5.4 or higher was necessary for the neutralization of electroplating wastewaters to maintain the stable activity of SRB.

In case of the heavy metal inhibition test in a nitrification reactor, the results of Phase 1 showed about 20% inhibition, and maximum inhibition up to 75% was observed at the later phase experiments. The removal possibility of ammonium nitrogen(400mg/L) in electroplating wastewaters was tested by utilizing a putative symbiotic relationship of three different microorganisms. Nitrates of high concentration effectively removed in a single anaerobic reactor containing alkalinity of 3000mg/L(as CaCO3) and COD of 1000 (mg/L) by the putative symbiotic relationship of SRB, SDNB, and DNB.

The results from this study will contribute to an understanding of biological removal mechanism of heavy metals and nitrogen in the electroplating wastewater and to development of this treatment technologies in the future.