Problematik vid höga flöden - Gästrike Vatten AB

ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL AND PRIMARY SLUDGE
HYDROLYSIS DURING HIGH-FLOW CONDITIONS: THE RESULT OF THREE YEARS
FULL-SCALE EXPERIENCES AT DUVBACKEN WASTE WATER TREATMENT PLANT
J. Örnmark
Master Thesis in Engineering Chemistry, Umeå University, Sweden
Gästrike Vatten AB, Box 954, SE-801 33 Gävle, Sweden
ABSTRACT
Enhanced biological phosphorus removal (EBPR) is a well-established technology for the
treatment of municipal wastewater without the use of chemical precipitation. The method is
being applied at Duvbacken wastewater treatment plant since 2004, where it gives an
approximate 95 % reduction of the affluent phosphorus during normal operating conditions.
However, after long periods with high water flows and low organic loadings, the process has
been known to deteriorate leading to increased effluent phosphorus concentrations and a need
for chemical precipitation.
This report is the result of three years full-scale operation and optimization experiences with
EBPR at the Duvbacken wastewater treatment plant. The result includes an identification of
critical parameters responsible for the process failure during high-flow and low organic
loading conditions. Full-scale measures were conducted including an operating strategy for
the process during, and after, high-flow conditions. The results were found to be successful
leading to a more stable process, less effluent peaks, minimal usage of precipitation chemicals
and a lower energy consumption.
Keywords: Enhanced biological phosphorus removal (EBPR), volatile fatty acids (VFA),
primary sludge hydrolysis, phosphate-accumulating organisms (PAO), excessive aeration,
aeration control, low loading, high-flow conditions, phosphate uptake, phosphate release
INTRODUCTION
Enhanced biological phosphorus removal (EBPR) is a well-established technology for the
treatment of municipal wastewater without the use of chemical precipitation. This is achieved
by specific types of bacteria; phosphorus accumulating organisms (PAO). These naturally
occurring bacteria are enriched in the activated sludge by introducing an anaerobic reactor
upstream of the aerobic reactor in an activated sludge treatment system. The specific plant
operating conditions favour PAO that have the ability to accumulate organic substrates during
anaerobic conditions, and therefore gain advantages over other heterotrophic organisms. The
bacteria also have an ability to store phosphorus during aerobic conditions, to a higher extent
than what is needed instantly, and this is the key mechanism in the EBPR process which leads
to a phosphate removal from the bulk liquid phase.
The microbiologically available organic substrates for PAO consist solely of volatile fatty
acids (VFA) (Comeau et al., 1986, Mino et al., 1987) that are fed to the anaerobic reactor by
the wastewater. VFA are stored in carbon reserves in the cell as poly-hydroxyl-alconates
(PHA) while energy and reduction equivalents are provided by the break down of
accumulated polyphosphate (poly-P) and glycogen (Seviour et al., 2003) . Subsequently,
under aerobic conditions, the stored carbon favors growth and accumulation of phosphate by
PAO, which are capable of dual poly-P and carbon storage. High phosphate removal
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