Enhancing biological phosphorus removal from municipal wastewater with partial simultaneous precipitation

Pilot-scale tests to enhance phosphorus removal with ferrous sulphate in a biological phosphorus and nitrogen removal process (modified UCT) for treating municipal wastewater were performed. The results indicated that Fe(II) competes with the BioP organisms and will inhibit the biological phosphorus removal process completely at doses exceeding 9 g m⁻³ of Fe(II). The goal of an effluent P level of 0.5 mg l⁻¹ can be attained with 5 g m⁻³ of Fe(II). A consistent effluent concentration of 0.3 mg l⁻¹ could not be achieved with this method. A centrifugation method to evaluate the dewatering properties of sludge was developed. Comparison of the settling and dewatering properties between activated sludge from the pilot plant and a full-scale simultaneous precipitation process indicated no consistent differences between them. The poor settling properties are due to the long sludge retention time needed by nitrification and not to the biological phosphorus removal process.