The simulation of nutrient fluxes in wastewater treatment plants with EBPR

The introduction of enhanced biological phosphorus removal (EBPR) for waste water treatment not only affects the activated sludge plant itself, but als o the connected process units, particularly those involved in sludge treatm ent. 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 pe rformance by combining models for individual process units in simulation sc enarios for the whole plant. The mathematical models are based on informati on from literature and previous experimental studies. The results contribut e to the assessment of the overall environmental impact of wastewater treat ment and support the evaluation of process alternatives. Four scenarios are presented by quantifying steady state nutrient fluxes within the plant flo wscheme and to the environment: (I) the operation with separate thickening of excess sludge, (II) the operation with combined thickening of primary an d excess sludge via primary clarification, (III) the influence of primary s ludge fermentation in order to produce volatile fatty acids and (IV) the pl ant performance at increased phosphorus level in the influent. Moreover, th e findings indicate that at the current Swiss wastewater composition EBPR s eems to be feasible, favorably supported by primary sludge fermentation. Ho wever, substantially increasing phosphorus concentrations in the influent w ould exceed the capacity of the process and make an EBPR plant questionable . (C) 1999 Elsevier Science Ltd. All rights reserved.