Monitoring of denitrifying activities in moving bed biofilm reactors with an ex-situ manometric batch test

Sammanfattning: Emissions of reactive nitrogen to the environment is of major concern, e.g. since it is known to contribute to eutrophication and dead sea floors in water bodies. The capability to remove nitrogen from wastewater has therefore become a critical means of preserving and protecting the environment. Conventional nitrogen removal from municipal wastewaters usually includes nitrification together with denitrification. Due to more stringent legislation regarding effluent standards as well as higher loads, many wastewater treatment plants (WWTPS) in Sweden will have to be upgraded for increasing their degree of nitrogen removal. It is therefore important not only to be able to evaluate the efficacy of the existing facilities, but also to consider the implementation of new processes. The aim of this Master’s thesis was to adapt an ex-situ manometric batch test, developed for measuring anammox activity, to be used to measure denitrifying activity. The adapted test was used in order to study the activity on K1 carriers from the post-denitrification moving bed biofilm reactors at Sjölunda WWTP. Carriers from four different lines in the post-denitrification plant were analyzed. Experiments were conducted with initial nitrate concentrations in the interval 25-150 mg N/L. The specific denitrifying activity turned out to be independent of initial nitrate concentrations in range 35-150 mg N/L and dependent on nitrate concentrations below 35 mg N/L. It was also revealed that COD/N ratios of 5.3-133.3 had no effect on the denitrifying activity, given that nitrate was not limiting. A small denitrifying activity was detected when no carbon source was added to the reactor, which indicated that the bacteria could use intracellular carbon as electron donor. Experiments performed on the different lines showed varying specific denitrifying activities. However, operational results assessed over a period of four months, showed that all the lines in the post-denitrification plant had equal nitrate reduction efficacy. The operational data did not give any further information on how the capacity in the first zones differed from the capacity in the second zones. However, it was concluded by experimental assessment that the first zones had 3-4 times higher denitrifying activity than that of the second zones.