RESPONSE OF MIXED CULTURES OF CHLORELLA-VULGARIS AND HETEROTROPHIC BACTERIA TO VARIATION OF PH

The effects of hydrogen ion concentration on the growth of heterotroph ic bacteria and alga Chlorella vulgaris, one of the dominant species i n waste stabilization ponds were investigated in fed batch cultures. G lucose used as a source of organic carbon was fed daily in granular fo rm and pH was controlled between 3.0 and 11.5 by addition of either HC l or NaOH. Heterotrophic bacterial densities were highest between pH 4 .0 and 5.5, but the growth rate of Chlorella vulgaris was optimum at p H 4.5-8.0. Clorella vulgaris was sensitive to alkaline pH values, with maximum growth rates, mu(max) of 2.03, 1.12 and 0.75 d(-1) at pH 7.0, 9.0 and 10.0, respectively. The saturation constants, K-s, for the sa me pH values were 181, 157 and 52 mg/l, respectively. The optimum tota l biomass yield was 0.381 mg POC/mg glucose and was observed at pH 5.5 similar to 8.0, but the magnitude was strongly influenced by the pre- culture pH conditions. Glucose metabolism was significantly affected a t alkaline conditions than at acidic conditions. These results also su ggest that in a mixed culture with bacteria, algae are largely respons ible for glucose metabolism, with apparent saturation constants at pH 7.0 of 27 mg/l and 181 mg/l for bacteria and Chlorella vulgaris, respe ctively.