혐기성 미생물 Lactobacillus acidophilus를 이용한 역삼투막 생물반응기에서

유기성분의 제거효과에 관한 연구

강익중

경원대학교 화학공학과

A Study on the Removal Effects of Organic Components in the Ultrafiltration Bioreactor Using Anaerobic Lactobacillus acidophilus

I. J. Kang

Department of Chemical Engineering, Kyungwon University, Songnam, 461-701, Korea.

INTRODUCTION

Recently the treatment of organic components as well as metal ions in the drinking water has attracted attention because of their effects of human body1). Benzene, toluene, phenol, dye stuffs and surfactants are in the drinking water, and these are toxic and have low oxidation rate by an aerobic microorganisms2∼3). In the biological treatment temperature and pH have influence on microorganisms. Activated sludge method by an aerobic microorganism is useful to a great deal of wastewater treatment, but it raise the difficuties of inability of removal of organic component, occurence of large amount of sludge and maintenance4∼7). We judged ultrafiltration using anaerobic microorganism was favorable method for the drinking water treatment8∼11). Gram positival anerobic bacteria Lactobacillus acidophilus is able to remove organic components in the anaerobic state and has advantage of low cost because of simple cell culture medium. From the our basic experiment it was clear that Lactobacillus acidophilus was able to decompose organic components in the drinking water and make clean water by consuming organics as a substrate in hungry state.

Above the filtered cell mass a coarse filter paper was placed to provide the cell extra room for growth and eliminate the partial closing of pores of the ultrafiltration membrane which is in contact with the cells. In order to minimize the back diffusion of organic components from the cell layer to the feed solution, two layer of polysulfone ultrafiltration membrane were used. For the sake of an offer of appropriate space to cell growth and the minimalization of permeation rate decrease by cell contamination, we proposed the bioseparation reactor system of ultrafiltration membrane / cell / filter paper / ultrafiltration membrane by inserting filter paper into an interval between membrane and the cell layer. We have a plan practically to use the data of the removal effects of organic components according to the temperature and pH in the bioreactor.  Ultrafiltration membrane was made of polysulfone. We got the purification ability out of the bioreactor by using Methyl Red, Methylene Blue, Methyl Orange, Thymol Blue and SDS(Sodium dodecyl benzene sulfonate) as a basic organic material.

EXPERIMENTAL

Cell Culture and Medium

Lactobacillus acidophilus, commercially available cell, provided by Hanmi pharm. co was grown on the milk as a medium. The seed was prepared by putting the pure cell into culture medium and homogenated. The cell was inoculated to MRS agar medium12), stored at a constant temperature 4℃ and used as occasion demands. Shaking culture was conducted in 250ml Erlenmeyer flask with rotary shaker at 40℃ and shaking speed 250rpm. Fresh cell weight(FCW) and dry cell weight(DCW) were checked in order to identify cell growth. The culture solution was filtered by whatman No.1 paper, washed with the equivalent volume of deionized water and the FCW was measured by chemical balance on a measuring dish after the water was removed by vaccum pump. And then the DCW of the cell of constant weight from dry oven at 60℃ was determined. The cell was grown in the culture medium and an appropriate cell number 1.0×109 was maintained.

Preparation of Ultrafiltration Membrane

Polysulfone(Aldrich) 20gr, used as a ultrafiltration membrane material, was added into NMP(N-methyl-2-pyrrolidon) 80g, dissolved by shaking 24hours at 40℃ and the solution was stored at 4℃. The solution was spreaded thinly, leaved alone for 60 second and the solvent NMP was dried. The membrane produced was gellated in 20% sulfuric acid-distilled water solution for 10 minutes.

Membrane Characterization

The PWP(Pure Water Permeability) of the ultrafiltration membrane was measured for the pure water and organic components at the fermentation pressure of 5∼20 kgf/cm2. The peculiar character of ultrafiltration membrane was analized by measurring the quantity of water permeated per each hour. The PR(Permeation Rate) of the membrane was also measured at the pressure 5∼20 kgf/cm2. In order to obtain the value of separation factor(f) the relative concentration of organic components before and after permeation was measured.

Bioreactor

The Bioreactor was composed of four parts as shown in Fig.1. The organic component of the proper concentration was flowed from reservoir into membrane bioreactor by pressure apparatus. The organic component was removed and separated in the membrane reactor by the anaerobic Lactobacillus acidophilus added.

Analysis of Organic Components

The concentration of Methyl Red, Methylene Blue, Methyl Orange and Thymol Blue was determined by measuring absorbance of the UV-Visible spectropho-

tometer(Perkin-Elmer 202). The maximum absorption wave lengths were 430nm, 664nm, 466nm and 597nm respectively. The concentration of SDS was checked by ethyl violet(MW:492.1) coloration method13) at 611nm of the UV-Visible spectrophotometer.

RESULTS AND DISCUSSION

The results from this experiment were as follows. Fig.2 shows permeate flux variation with pressure difference at feed temperature 25℃. Fig. 3 and Fig.4 show color removed effects(%) in the variation to temperature and pH respectively. The color removal effects of Methyl Red was the highest value of 95%. The values of Methyl Orange, Methylene Blue, Thymol Blue and SDS were 92%, 82%, 63% and 53% respectively as shown in Fig.5. From the results of the experiment, it was found out that the highly concentrated organic components can be removed with high removal effects and it is possible to remove the small amount of organic components in drinking water by the small amount of Lactobacillus acidophilus. The experiment for the perfect removal of small amount of metal ions and organic components will be continued.

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