Factors Affecting the Quality of the Plant Influent and Its Suitability for Prefermentation and the Biological Nutrient Removal Process

To understand wastewater quality transformations in the sewer system, a full-scale study focused on the characteristics of the influent wastewater in a middle-sized wastewater-treatment plant receiving only municipal sewage. The objective was to identify conditions in which prefermentation prior to the biological nutrient removal (BNR) process would be useful. Prefermentation aims at increasing the fraction of readily biodegradable organic matter in the wastewater. A correlation between weather conditions and the presence of readily biodegradable organic matter in the feed wastewater was found, but contrary to the expectations, wet weather periods deteriorated the quality of the feed water more than the cold period. Moreover, influent load showed seasonal variation which changes in discharged wastewater could not explain. During the warm water period, significant biological oxidation and nitrogen removal took place in the sewer system, but the plant influent water contained readily biodegradable organic matter and potential for its formation during the warmest period. It was concluded that prefermentation would be mostly needed during the wet weather period. In addition, the study offered valuable information about the seasonal behavior of the sewer network.