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).

Using a mathematical model, a resource recovery assessment was carried out at a pulp mill activated sludge wastewater treatment plant (WWTP) located in Uruguay. Through the evaluation of different scenarios, the potential production of methane from secondary sludge, with its inherent energy savings, and the recovery of phosphorus (P) as struvite were estimated. Considering the current WWTP configuration with a sludge retention time (SRT) of 32 days, and according to the model, which is a simplification of reality, the assessment indicates that the implementation of an anaerobic digester (AD) to treat the excess sludge can lead to a methane production of approximately 1736 m³ CH₄ d⁻¹, being a promising alternative to increase the WWTP treatment performance. Furthermore, the model predictions suggest that by shortening the SRT from 32 to 5 days, the methane production could increase by up to 5568 m³ CH₄ d⁻¹. If the methane produced is used to generate electrical energy to operate the WWTP, energy savings of about 88% can be achieved. Regarding the potential recovery of P as struvite, the addition of a struvite reactor could be an efficient option to recover approximately 1611 mg L⁻¹ of struvite (corresponding to a load of about 433 kg d⁻¹). By optimizing the process performance, these findings highlight the potential recovery of resources in pulp mill WWTP, while complying with stringent effluent discharge standards. In addition, further research activities such as pilot-test or detailed laboratory studies may be needed to validate the previous recommendations for industrial scale application.