STUDIES ON BIO-DEGRADABLE PLASTIC FROM ACTIVATED SLUDGE

EXPERIMENTS OF PHB PRODUCTION UNDER NITROGEN LIMITED CONDITION

Abstract

We studied on the optimum condition for micro-organism to produce biodegradable plastic (PHB) in activated sludge. The first experiment was made to confirm the production of PHB under nitrogen limited condition. Carbon content of dried activated sludge had risen rapidly after nitrogen in medium was completely consumed, white precipitate was extracted from dried activated sludge with hot chloroform and n-hexane after another 48 hours. We identified it was PHB by use of X-ray diffraction, DTA and CHNS-elemental analyzer. The second experiment was made to investigate the effect of carbon sources and cultivation period on PHB content under nitrogen limited condition. Consequently, CH₃COONa was better than glucose as carbon source for production of PHB. Content of PHB was stabilized to its maximum stage around 250 hours by continuous process and it was achieved to 12% of dried sludge weight basis. The third experiment was performed to grasp the difference of production rate of PHB and carbohydrate. PHB was slowly accumulated than carbohydrate. Consumption of PHB, observed with decrease of TOC in medium was also slow.