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

Abstract

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 PO43−/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).