| The ultimate disposal of biosolids has been, and continues to be, one of most expensive problems faced by wastewater utilities in the United States. Typically, excess solids processing and disposal costs can account for 20 to 50 percent of the total operation and maintenance costs of a municipal wastewater treatment facility (EPA, 1979; WERF, 1998). The solids disposal problem is expected to grow with increasing sewered populations and with more stringent regulatory requirements for the treatment of municipal wastewaters.; The objective of this research was to develop a process for reducing the mass of waste biosolids generated in an activated sludge treatment plant by promoting biomass growth on intracellular products released by ozonation. For this purpose, excess biosolids from laboratory-scale activated sludge reactors were exposed to ozone as a cell-lysing agent to partially solubilize intracellular material. The lysed biosolids was then returned to the aeration tank to be used as a growth media. The results indicated that the proposed process can reduce the mass of waste biosolids production from an activated sludge plant by 30 to 60 percent, depending on the ozonation rate and period employed.; Ozonation of biosolids samples from laboratory reactors and from the Las Cruces Wastewater Treatment Plant at similar ozone loading rates indicated a greater decrease in the mass of biosolids from the laboratory than in the samples from the Las Cruces Wastewater Treatment Plant. This finding indicates that if ozonation of biosolids is practiced at field-scale activated sludge wastewater treatment plants, longer ozonation periods, higher ozonation rates, and/or treatment of larger volumes of waste biosolids may be required to obtain mass reductions similar to those obtained with laboratory biosolids in this study.; The application of the ozonation process was further studied using a compute simulation model. A number of different scenarios were evaluated to determine the possibility of zero biosolids wastage from an activated sludge plant. The model results indicated that it may be possible to run a field-scale wastewater treatment plant without producing any waste biosolids, using appropriate ozonation rates and adjusting the volume of biosolids to be processed through the ozonation. |
