The potential use of anoxygenic phototrophic bacteria for treating latex rubber sheet wastewater

Abstract

A total of 92 isolates of the purple non sulphur photosynthetic bacteria (PNSB) were isolated from 23 samples of wastewater obtained from rubber sheet manufacturing processes from various places of southern, Thailand. The isolate DK6 had the best potential for use in wastewater treatment as it can out-compete indigenous strains of PNSB when grown with them under conditions of microaerobic-light conditions. The isolate DK6 was identified as being most closely allied to Rhodopseudomonas blastica. The optimal pH and temperature for cell growth were between 6.5-7.5 and 30ºC, respectively. Optimum growth of DK6 was obtained after supplementing the wastewater from a latex rubber sheet processing plant with 0.50% (NH₄)₂SO₄ and 1 mg/L nicotinic acid under conditions of microaerobic-light (3000 lux). Using these optimum conditions for growth, indigenous microorganisms reduced the initial chemical oxygen demand (COD) of the wastewater from 7,328 to 3371 mg/L a reduction of 54% and the biochemical oxygen demand (BOD) (initial BOD 4967 mg/L) by 70%. Using the same conditions and either a pure culture of DK6 or a mixed culture (DK6 plus indigenous microorganisms) a reduction of 90% of both COD and BOD was achieved. Chemical analysis of the cultures after treatment of the enriched wastewater shows that the protein content of the pure DK6 was 65.2% of the dry weight,  and in mixed culture the protein content was 66.7%. Hence, single cell protein (SCP) may be a possible bi- product of the treatment process.