Evaluation of a chemical phosphorus removal process at a pulp mill WWTP in Uruguay

In this study, the potential biological and chemical removal of phosphorus were assessed in an industrial effluent from a full-scale pulp mill wastewater treatment plant (WWTP) that had a relatively higher influent P-concentration compared to other plants from the same sector. For that purpose, the potential biological removal of phosphorus was evaluated in a lab-scale SBR under fully aerobic conditions for merely biomass synthesis. The chemical P-removal (CPR) process was studied following a co-precipitation (through the addition of coagulants to the lab-scale SBR) and a post-precipitation approach (conducting different jar-tests with the effluent from the SBR). Three coagulants (FeCl₃, Al₂(SO₄)₃, and Ca(OH)₂) were tested at different concentrations. The treatment of the pulp mill effluent by merely biological means was unable to contribute to a considerable P-removal due to the low P growth requirements of the biomass. The co-precipitation CPR approach showed to be highly effective independently of the coagulant used resulting in removal efficiencies of between 79 and 82 % and achieving final soluble P wastewater concentrations in the range of 0.28-0.34 mgP L^-1. However, it struggled to comply with the discharge standard permit limit (annual) of 60 kg TP d^-1. On the other hand, the post-precipitation approach (with the addition of Al₂(SO₄)₃ at a PO₄^3-/metal salt ratio (mol-to-mol) of 1:10 or when dosing 400 mg Ca(OH)₂ L^-1) allowed to achieve the lowest observed TP and soluble P concentrations (lower than 0.5 and 0.2 mgP L^-1, respectively).