Characterisation of phosphorous forms in wastewater treatment plants.

The removal of different forms of phosphorous (namely total phosphorous, soluble phosphorous, particulate phosphorous and total phosphate) has been studied in two municipal wastewater treatment plants (WWTP) with different characteristics, but without any specific implemented strategy for phosphorous removal. The results obtained for the different forms of phosphorus can be summarised as follows: (1) complete removal of particulate phosphorous is achieved in either primary or secondary clarifiers; (2) total phosphorous concentration in the effluent is mostly soluble phosphorous and this is mainly phosphate; (3) a small amount of soluble phosphorous is removed by biomass growth and/or biosorption; (4) both WWTPs presented a high-buffered behaviour in response to high inlet loading of phosphorous, showing a constant pattern at the outlet of the WWTP; (5) removal of total phosphorous was approximately 60-70% for both WWTPs; and (6) recirculation streams such as supernatant from centrifuge sludge dehydration operation can have a significant contribution to the inlet amount of phosphorous. The results presented in this paper provide a basis to develop prospects for phosphorous removal, which may be adapted to the particular configurations of the WWTP studied.