ASSESSMENT OF ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL FOR DAIRY MANURE TREATMENT

Abstract

The goal of this research was to evaluate the potential for enhanced biological phosphorus removal (EBPR) as a nutrient removal technique for dairy manure. A critical factor in EBPR is the availability of carbon (C) from volatile fatty acids (VFAs), particularly acetic and propionic acids. Volatile fatty acids are the preferred energy source for phosphorus accumulating organisms (PAOs), the organism responsible for EBPR. The specific objectives of this research were to determine the VFA production, or fermentation, potential of dairy manure and to identify critical growth parameters needed to model EBPR. Volatile fatty acid production was determined using laboratory-scale reactors and gas chromatography. Acetic, propionic, and butyric acids accounted for 57, 23, and 20% of the total VFA measured, respectively, while valeric acid concentrations were below the detection level of the gas chromatograph. Fifteen percent of the readily biodegradable COD was converted to VFA-COD. The wastewater treatment design software, BioWin, was used to identify the most critical growth parameters in modeling EBPR. The effluent phosphate (PO4) concentration was sensitive only to PAO growth parameters, suggesting that wellestablished populations of other heterotrophs would not interfere with EBPR, provided that environmental conditions favorable to growth of sufficient PAOs are maintained, and the sludge retention time is short enough to prevent growth of nitrifiers. The most critical microbial growth parameters in BioWin with respect to PO4 concentration included one kinetic growth parameter, PAO maximum specific growth rate, and five stoichiometric parameters for PAOs: growth yield, aerobic PO4 uptake rate per unit Poly-3-hydroxy-butyrate (PHB) utilized for growth, PHB yield per unit VFA uptake, PO4 release per unit VFA uptake, and fraction of PO4 taken up that can be released. These results suggest that sufficient VFA can be created by fermenting dairy waste, and improved EBPR design for treatment of dairy waste can be achieved by quantifying the six critical parameters.