Primary municipal wastewater effluents have a high potential for reuse in agriculture as a fertilizer or irrigation water, and as a source of nutrients for the cultivation of certain microorganisms, yielding high-value chemicals as metabolic end-products, due to their high organic content. Another future possibility is using wastewater treatment facilities for oil production, in addition to treating water to conform to Environmental Protection Agency (EPA) standards. This could be accomplished by treating the wastewater with oleaginous microorganisms, which can convert part of the biochemical oxygen demand of the wastewater into oils and store between 20% and 60% of their mass as oil. To achieve these goals, elimination of indigenous microorganisms present in the wastewater effluent from the primary clarifier while improving the biodegradability of the wastewater is necessary.

The paper will describe the use of ozone to disinfect and improve the biodegradability of primary-treated municipal wastewater. Ozone was considered for this purpose due to its high disinfection efficiency involving a wide range of microorganisms and its ability to improve the physicochemical quality of various types of wastewater. Using compressed air as feed gas with a flow rate of 2 SCFH (standard cubic feet per hour), batch samples of primary effluent were treated with five different applied ozone doses (0.5, 1.5, 3.0, 4.5, and 5.5 %w/w). The effectiveness of ozone disinfection was measured by performing microbial colony counts (in CFU/mL) on the wastewater before and at various treatment times during ozonation. Effects on biodegradability were evaluated using the BOD/COD ratio while changes in the nutrient content of the primary effluents were determined by measuring nitrite, nitrate, and phosphate concentrations.