BACTERIAL INOCULUM DENSITY AND PROBABILITY OF PARA-NITROPHENOL BIODEGRADABILITY TEST RESPONSE

This study has been carried out to establish a model linking probabili ty of positive response in para-nitrophenol biodegradability test to c ontrolled variables of the test (suspended solids, SS; total bacteria, AODC; cultivable bacteria, CFU; specific biodegraders, MPN). Series o f dilution of 11 raw inocula (6 activated sludges, 5 river waters) wer e tested. They reveal very dispersed values of biomass measured as SS, AODC, and CFU and quite comparable values of specific biodegraders fo r each category of inoculum (river or sludge). The proposed model fits well the empirical distribution of the experimental frequency of posi tive results versus inoculum density for each controlled variable. The constants k of the model, representing the fraction of biodegraders f or each inoculum, were tested by the likelihood ratio test and were pr oven to be different from one another according to the biomass descrip tor and the origin of the inoculum. The probabilistic model, in the ca se of para-nitrophenol biodegradation, indicates that standardized off icial tests (closed bottle, AFNOR, Sturm, and MITI I) are seldom optim al under those conditions. It allows the determination of which inocul um concentration can lead to a high probability (e.g., 99.9%) of obser ving para-nitrophenol biodegradation by raw inocula. (C) 1995 Academic Press, Inc.