Biodegradation of Organic Wastes Containing Surfactants in a ...

APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Sept. 1996, p. 3292–3297 0099-2240/96/$04.0010 Copyright q 1996, American Society for Microbiology

Vol. 62, No. 9

Biodegradation of Organic Wastes Containing Surfactants in a Biomass Recycle Reactor A. KONOPKA,1* T. ZAKHAROVA,1† L. OLIVER,2 D. CAMP,1 1

AND

R. F. TURCO2

2

Department of Biological Sciences and Department of Agronomy, Purdue University, West Lafayette, Indiana 47907 Received 25 March 1996/Accepted 21 June 1996

The microbial biodegradation of simulated graywater, containing 21.5 mg of linear alkylbenzene sulfonate liter21, was investigated with a continuous-flow bioreactor with 100% biomass recycle. Low concentrations of organic matter in the ultrafiltration eluate were achieved at hydraulic residence times as short as 1.6 h and for periods of up to 74 days at a hydraulic residence time of 6 h. Upon a shift from the chemostat to the biomass recycle mode, the increase in biomass with time approximated a linear rather than an exponential function. Biomass densities as high as 6.8 g of cell protein liter21 were reached; this was 50-fold higher than the steady-state biomass level in chemostats fed the same medium. We assessed physiological changes in the microbial community after a switch from the chemostat to the biomass recycle mode. Over 150 h, there was a two- to fourfold decrease in the respiratory potential of the microbes. After this decrease, respiratory potentials were relatively constant up to 74 days of operation. A decline in reactivity was also indicated by increasing lag periods before growth in response to organic nutrient inputs and by a decrease in the proportion of cells able to reduce tetrazolium dye. However, the bioreactor system was still capable of rapidly metabolizing inputs of organic matter, because of the very high biomass concentrations. It appears that