The simulation of nutrient fluxes in wastewater treatment plants with EBPR

The introduction of enhanced biological phosphorus removal (EBPR) for wastewater treatment not only affects the activated sludge plant itself, but also the connected process units, particularly those involved in sludge treatment. The consequences hereof are still little known, although problems may appear if phosphorus from digester supernatant is recycled to the activated sludge plant. This study illuminates the influence of EBPR on the plant performance by combining models for individual process units in simulation scenarios for the whole plant. The mathematical models are based on information from literature and previous experimental studies. The results contribute to the assessment of the overall environmental impact of wastewater treatment and support the evaluation of process alternatives. Four scenarios are presented by quantifying steady state nutrient fluxes within the plant flowscheme and to the environment: (I) the operation with separate thickening of excess sludge, (II) the operation with combined thickening of primary and excess sludge via primary clarification, (III) the influence of primary sludge fermentation in order to produce volatile fatty acids and (IV) the plant performance at increased phosphorus level in the influent. Moreover, the findings indicate that at the current Swiss wastewater composition EBPR seems to be feasible, favorably supported by primary sludge fermentation. However, substantially increasing phosphorus concentrations in the influent would exceed the capacity of the process and make an EBPR plant questionable.