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IMPROVED P REMOVAL OF COD-LIMITED, SEPTIC, WASTEWATER VIA PREFERMENTATION

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Enhanced Biological Phosphorus Removal (EBPR) requires the presence of volatile fatty acids (VFAs) in the anaerobic zone of any biological nutrient removal (BNR) wastewater treatment system. Unless the sewage is strong and septic (i.e. the influent already has a high VFA concentration) VFAs must be produced. This VFA production is accomplished either within the anaerobic zone of the BNR system or it is done prior to the BNR system in a separate anaerobic process called prefermentation in which hydrolysis and acidogenic fermentation takes place, producing VFAs in a separate step. Prefermenters as a separate unit process were developed by Dr. James Barnard in South Africa along with researchers at the University of Cape Town in the mid 1970s when BNR systems were first developed at full scale. In the United States, however, prefermenters have until recently rarely been considered even when they might arguably have been advantageous. Because of the very few quantitative comparisons of identical systems with and without prefermenters, design engineers often disagree on the necessity of a prefermenter and make decisions based on their prior experience.

The objective of this research was to provide a controlled comparison of identical continuous flow BNR processes both with and without prefermentation in order to provide a stronger, more quantitative, technical basis for design engineers to evaluate the potential benefits of prefermentation to EBPR in treating domestic wastewater. In addition, the even less understood effect of prefermentation on denitrification kinetics and anoxic phosphorus (P) uptake was studied and quantified. Other aspects of BNR performance, which might change due to use of prefermentation, will also be addressed, including anaerobic stabilization.

The following bulleted list summarizes important findings to date developed during the course of this research:



The effect of prefermentation upon P removal depends upon the COD: TP ratio found within the influent wastewater. Specifically, for septic wastewaters containing a low COD: TP ratio (i.e. COD-limited), prefermentation enhances EBPR.


Increased anaerobic P release, aerobic P uptakes, and greater specific denitrification rates observed due to prefermentation correlated with greater PHA formation and glycogen consumption during anaerobiosis.


Prefermentation increased RBCOD, SBCOD, and VFA content of septic domestic wastewater. Most of the data remains to be analyzed however so the significance of the increases have not yet been assessed.


Prefermentation increased specific anoxic denitrification rates found in the anoxic zones of the activated sludge system.


COD mass balances on the activated sludge systems suggests that anaerobic stabilization (e.g. direct fermentation of COD to gaseous end products in the anaerobic zone, possibly via glycogen) is potentially significant for warm, septic influent wastewater but this is still being evaluated using both pilot and full scale data.


A full evaluation of the data will be presented in the poster in October.
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Document Type: Research Article

Publication date: 2003-01-01

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