Testing the biodegradability of wastewater treatment plant outfalls: role of bacterial inocula

A simple procedure of batch experiments is described allowing the determination of the Biodegradable Dissolved Organic Carbon (BDOC) content of different effluent outfalls from wastewater treatment plants. The bioassay is based on the DOC reduction of treated wastewater samples inoculated with natural consortia of bacteria taken from river sediments or aquarium filters. This test allows routine determination of BDOC within a short period of time (less than 8 days). BDOC represents a still significant proportion of the treated effluent DOC: from 50% to about 70%, depending on the effluent. The origin of bacterial inocula have no influence on these proportions, but are the main parameter for the rate of biodegradation. Testing the biodegradability at 10°C and 20°C appears to be significant as it influences biodegradation processes and must be done for a complete ecological evaluation of the biodegradability of wastewater treatment plant effluents.