Packed-Entrapped-Mixed Microbial Cells for Small Wastewater Treatment

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Abstract
The primary goal of the research is to develop and evaluate a biological treatment system in which mixed microbial populations are physically immobilized by entrapment. The immobilized system was evaluated initially for its ability to remove simple benzene-based compounds from a synthetic wastewater as a model for treating pesticide-containing waters. Cellulose triacetate was used as the preparation of monocarrier and combined cellulose triacetate and calcium alginate were used for the preparation of bi-carrier. Phenol was used as substrate to test the entrapped mixed microbial cell process. Process performance including steady state, shock load and comparison of entrapped microbial cell process with and without entrapped microbial cell was investigated. It was concluded that the critical loading rate for phenol synthetic wastewater appeared to be 9 g COD/L/day. The COD removal efficiency could be maintained higher than 90%. Because of the low effluent suspended solid concentration, conventional-secondary-settling tanks could be eliminated. Also, the process could take both concentration and hydraulic shock loads of phenol synthetic wastewater successfully without the need of external sludge recycling. The equalization and external sludge recycling facilities equipped in the conventional wastewater treatment plant could be eliminated. When the process is operated only at low COD loading rate (less than 1.3 g/L/day), entrapped cells might not be required. However, when operated at higher loading rate, combined adsorbed and entrapped cells appeared to remove phenol more efficiently. For the application, mono-carrier (cellulose triacetate) is preferable to bi-carrier (cellulose triacetate and calcium alginate), since it is easier to prepare and the operational performance is better. Therefore, the application of packed-entrapped mixed microbial cell process for treatment of small-toxic-organic wastewater holds great potential.

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