High conversion of wastewater into biomass of photosynthetic bacteria was investigated. This biomass is possibly utilized as feed for fish or extraction source of PHA (polyhydroxyalkanoate). As a fundamental investigation, batch experiments were carried out using purple nonsulfur bacteria Rhodobacter sphaeroides to determine the growth rate and yield and to quantify CO2 release/uptake during substrate assimilation. The substrates used for this study were five kinds of VFA namely, acetate, propionate, n-butyrate, n-valeric acid and n-caproate. Growth rates for n-valeric acid and n-cvaproate were lower than those for other VFAs. Yields, defined as carbon in bacteria divided by removed organic carbon, for n-butyrate, n-valeric acid and n-caproate exceeded 1 due to simultaneous CO2 uptake and no net greenhouse gas emission. Maximum CO2 uptake was 17% of removed DOC (dissolved total organic carbon) in the case of n-valeric acid supplemented with 2.00 g/l of NaHCO3.