Abstract
Photographic processing wastewater bears high level of COD which is partially biodegradable. The process comprising three steps has been proposed. The wastewater is treated biologically in the first step, and the remaining nondegradable components are converted into biodegradable compounds by ozone in the second step and are treated again biologically in the final step. In this study, the activated sludge process combined with membrane separation has been applied to this first biological step and its effluent was ozonated.
MLSS was about 10, 000mg/l for 5 days of the hydraulic retention time (RT) for the wastewater from color developing process, and the overload, RT less than 5 days, caused great depression of sludge activity. MLSS was about 60, 000mg/l for one day of RT for the mixture of wastewater from various photographic processes. Five or more days of RT was necessary to obtain 90% or more COD removal for the wastewater from color developing process, and 10 or more days of RT was for the mixture. BOO of effluent from the first biological step increased in the beginning of ozonation and reached a maximum level, and then decreased gradually. Results of liquid chromatography and UV spectrophotometry suggested that ozone broke down the benzene ring of nondegradable aromatic compounds and converted them into biodegradable compounds. On-off control of ultra-filtration membrane unit was successful in long-term stable operation without cleaning because the clogging was prevented by waterhammer and bachwashing when the circulation pump was switched on and off.
