Utilization and treatment of tuna condensate by photosynthetic bacteria

Factors affecting the growth of Rhodocyclus gelatinosus R7 and the reduction of organic matter (represented as COD) was further investigated in the diluted tuna condensate (COD=20,000 mgl(-1)) incubated under anaerobic-light (3000 Lux) condition. Supplementation of yeast extract in the medium significantly increased the biomass and the pigment content of R. gelatinosus and its optimum concentration was 3.0 gl(-1). The highest biomass was 6.24 gl(-1) with COD removal of 38%. Without yeast extract, the corresponding values were 3.96 gl(-1) and 24%, respectively. The optimum concentration of MgCl2 for cell growth was found to be 10 mM but the pigment content decreased significantly as the concentrations of MgCl2 higher than 5 mM. Addition of cobalt chloride (1-160 mu M) and ferrous sulphate (10-120 mu M) gave results with no significant difference from the control. Controlling the pH at 7.0 during the cultivation in a 21 fermenter exhibited higher values of biomass and COD reduction than without pH control. With the added yeast extract (3 gl(-1)) and MgCl2 (5 mM) as well as controlling the pH at 7.0, the highest biomass obtained was 8.14 gl(-1) with the COD removal of 59%. Four folds increase of biomass (to 12.27 gl(-1) compared to 3.96 gl) was achieved by repeated addition of the fresh tuna condensate (COD=60,000 mgl(-1)) every 40 h. The cell contained 56% protein, 2.21 mg carotenoid and 22.52 mg bacteriochlorophyll/g dry cell weight. The COD removals were 66% and 46% after 5 and 7 days cultivation, respectively.