Removal of sediment mud of lake and sea bottom and bioconversion to the biodegradable plastic using self-flocculated photosynthetic bacteria

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Focusing on the purification of sediment mud and bioconversion of mud to biodegradable plastic, firstly, chemical analyses of sediment mud were carried out. Sediment mud was consisted of 5% organic matters and 95% of sea sund and contained large amount of phosphorous compounds, After anaerobic digestion of mud suspension (200 g/l artificial sea wate) at 30 C for 7 days, ca. 2 g/l of acetic acid and Ca. 20 mg/l of phosphate ion was released into the broth. Using this anaerobic digestion liquor, a photosynthetic bacterial cultivation was carried out under anaerobic light condition (10 klux illumination) at 30 C.After 3 days culture, ca. 3 g/l of biomass was produced and almost phosphate was removed. Biomass produced contained 62% (dry basis) of polyhydroxybutyrate (PHB). Thus, the possibility of simultaneous purification of sediment mud and production of PHB was observed.Furthermore, high cell density culture of a newly isolated photosynthetic bacteria, Rhodovulum sp. which had the sel-flocculating ability was carried out using a new single tower bioreactor system to purify the anaerobic digestion liquor under aerobicculture condition eliminating light illumination. By this culture system, maximum biomass concentration attained 42.5 g/l after 750 hour culture with artifitial digestion liquor (acetic acid was a carbon source) and PHB content was ca. 30% even under aerobiccondition. In addition, a computer simulation was carried out using several biochemical engineering constants such as growth yield and some specific consumption rates. As the results, the estimations were in good agreement with the data obtained by experiments.Thus, a new bioreactor system become possible to develop by these investigations using this self-immobilizing photosynthetic bacteria. This indicates the possibility of the purification of sediment mud and simultaneous production of biodegradable plastic from sediment mud.