Methanotrophic bacteria for nutrient removal from wastewater: attached film system

It was hypothesized that nutrient removal from waste­ water could be achieved by using methane oxidizing bacteria (melhan­ otrophs). Because methane is inexpensive. it can be used as an energy source to encourage bacterial growth to assimilate nitrogen and phos­ phorus and other trace elements. This initial feasibility study used syn­ thetic nutrient mixtures and secondary sewage effluent as feed to a lab­ oratory-scale methanotrophic attached-film expanded bed (MAFEB) reactor operated at 35"C and 20"C. The MAFEB system operated successfully at low nutrient concentrations under a variety of nutrient­ limited conditions. Using a synthetic nutrient mixtufe with a nitro· gen:phosphorus feed ratio (w / w) of 9: I, phosphate concentrations were reduced from 1.3 mg PI L to below 0.1 mg PI L, and ammonia was reduced from 12 mg N/L to approximately I mg NIL on a continuous flow basis, with a bed hydraulic retention time of4.8 hours. The average nutrient uptake rates from synthetic nutrient mixtures were 100 mg nitrogen and 10 mg phosphorus/L of expanded bed/d. Nutrient assim· ilation rates increased with increasing growth rate and with increasing temperature. Nitrogen/phosphorus uptake ratios varied from 8 to 13, and the observed yield varied from 0.11 to 0.16 g volatile solids (VS)I g chemical oxygen demand (COD). Nutrient removal from secondary sewage effluent was successfully demonstrated using sewage effluent from two local treatment plants. Nutrient concentrations of 10-15 mg NIL and 1.0-1.8 mg P/L were reduced consistently below I mg NIL and 0.1 mg P/L. No supplemental nutrients were added to the sewage to attain these removal efficiencies since the nutrient mass ratios were similar to that required by the methanotrophs. Removal rates were lower at 20 D C than at 35 D C, but high removal efficiencies were maintained at both temperatures. Effluent suspended solids concentrations ranged from 8 to 30 mg volatile suspended solids (VSS)/L, and the effluent soluble COD concentration averaged 30 mg/L. Water Em'iron. Re...... 64, 756 (1992).