Recuperação de fósforo e nitrogénio por precipitação de estruvita para uso como fertilizante a partir do efluente de sistemas de tratamento de esgoto

Abstract

The scarcity of phosphorus, the costly processes for obtaining nitrogen and all the environmental problems arising from the use of inefficient fertilisers alert us to the need to create alternatives that bring solutions to these aspects. The aim of this work was to study the recovery of nutrients in an aqueous matrix in the form of struvite using the precipitation technique, a fertiliser characterised by its greater efficiency and being less harmful to the environment. The work was carried out with the effluent treated at the Infulene WWTP in Maputo, where it was first characterised, followed by the process of preparing the samples and precipitating the struvite crystal. Three parameters were analysed which are some of the main parameters influencing the precipitation process. The crystallisation process occurred due to the action of an agent that promotes the precipitation of phosphorus and nitrogen, which in this case was magnesium sulphate heptahydrate (MgSO4.7H2O). When the pH was varied, better results were obtained for values of 10 and 11, where one of the implications may be related to the greater availability of PO4-3 ions. Other parameters analysed were molar ratio and stirring time. For this study, it was found that pH 11, a P:Mg molar ratio of 1:1.3 and a stirring time of 40 minutes were the values that gave the best results, with maximum average recoveries of 86% for phosphorus and 86.4% for nitrogen.