Calculation of ChemicalNeeds in CombinedPhosphorus Removal andRecovery at HenriksdalWWTP, Sweden K. Stark, B. Hultman, E. Levlin, M. Löwén and A. Mossakowska* Dep. Land and
Water Resources Engineering, Royal Institute of Technology *Stockholm Water Co |
INTRODUCTION Problems with sludge disposal and expected demands to recover phosphorus have led to reconsideration of the operational scheme at Henriksdal wastewater treatment plant in Sweden. In a study simple models were developed to calculate the chemical demand for different operational schemes including use of different chemicals in chemical precipitation and different degrees of biological phosphorus removal. The calculation model is in agreement with reported studies on the phosphorus recovery systems Cambi/Krepro and BioCon. In this poster is presented the results of chemical demand of different technology systems for phosphorus recovery at present operational conditions at Henriksdal wastewater treatment plant both by calculation and compared with performed experiments. |
Figure 1 Connection between used amount acid and base at the dissolving step and recovery step by use of the systems KREPRO, Cambi/KREPRO and BioCon (Hultman et al, 2001) |
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Calculation
Model A calculation model has been
developed to predict chemical demand of acids and bases at transferation of
particle bound phosphorus to a liquid phase followed by product recovery from
the liquid phase (Hultman et al, 2001 and Stark et al, 2001). It was
applied to Henriksdal WWTP by different operation design. |
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Figure 2 Effect of weight relationship Fe/P of total
chemical demands of acid and base |
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Results from Calculation The calculation model on chemical demand for phosphorus recovery
shows that the demand for dissolving inorganic components by use of acids is
due to influent inorganic constituents that will form part of the sludge and
the inorganic sludge formed due to addition of precipitation agents. The
amount of chemicals needed for dissolution of inorganic chemicals is about
the same as the chemical needs, calculated in kg/ton dry solids, to obtain
phosphorus as a product (figure 1). With present mode of operation at
Henriksdal WWTP about 800 kg chemicals (acids and bases) are needed for
phosphorus recovery independent of chosen technology for phosphorus recovery
(figure 2). The chemical demand could be reduced to about 400 kg chemicals if
the operational mode was changed to biological phosphorus removal followed by
minor dosage of ferrous sulphate to the filters. As mentioned, BioCon and KREPRO use
approximately the same amount of chemicals. In both cases will the acid be
used to 1) solve the inorganic material in the sludge which is entering
together in the sewage 2) solve the iron from precipitation agents.
Thereafter will the chemical (approximately the same amount) to precipitate
the different inorganic component incl. Iron phosphate (KREPRO) or generating
from ion exchanger BioCon.
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Figure 3 Amount of acid used to release the phosphorus in the digested sludge ACKNOWLEDGEMENTS REFERENCES
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Comparing with Experiments
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CONCLUSION
Main conclusions from the calculation work are:
Preliminary experiments works are in good agreement with the calculations. |
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