2-STAGE METHANOTROPHIC BIOREACTOR FOR THE TREATMENT OF CHLORINATED ORGANIC WASTE-WATER

A two-stage continuous methanotrophic bioreactor was developed for the treatment of wastewater contaminated by chlorinated organic solvents, The chosen design eliminated the problem of competitive inhibition du ring cometabolic biodegradations by separating the consumption of grow th substrate (methane) and the degradation of chlorinated organics int o two stages. In the first stage, a mixed methanotrophic culture was g rown in a dispersed-growth continuous how stirred tank reactor (CFSTR) . In the second stage, trichloroethylene (TCE) and/or cis-1,2-dichloro ethylene (cDCE) contaminated wastewater was mixed with the suspended c ells from the growth reactor and fed into a plug-how reactor (PFRI) wh ere the cometabolic degradation occurred. The mixed methanotrophic cul ture in the CFSTR was grown in a copper-free, iron-enriched nitrate mi neral salts medium to induce methanotrophic cells to produce soluble m ethane monooxygenase enzymes which are highly active in cometabolic de gradations. Formate and oxygen were added prior to the PFR to enhance the chlorinated organic degradation rates and capacities, A kinetic mo del that incorporates chlorinated organic transformation capacity and competitive inhibition was used to develop the reactor design and to p redict treatment performance for TCE and/or cDCE. Model predictions we re verified by comparisons with experimental data. A bench-scale two-s tage reactor (with a 4-h wastewater retention time) was demonstrated t o be capable of treating wastewater mixtures containing TCE (4.7 mg/l) and cDCE (4.8 mg/l) to below the maximum contaminant levels (MCLs. 5 mu g/l each) continuously for at least 31 d. The optimal overall mater ial cost of methanotrophic cell growth, formate amendment, and oxygen amendment for the treatment of TCE and cDCE wastewater (5 mg/l each) t o the MCLs was estimated to be $0.17 per 1000 liters of wastewater. (C ) 1997 Elsevier Science Ltd.