Recovery of phosphate from real municipal wastewater and its application for the production of phosphoric acid

The concepts of sustainability and circular economy in wastewater treatment have recently gained momentum and they are fundamentally pursued to minimize and eliminate environmental impacts associated with wastewater. In this study, the concept of circular economy was explored in the treatment of municipal wastewater, through phosphate recovery and its use towards the production of phosphoric acid. To this end, real wastewater was treated with calcium hydroxide (hydrated lime) in batch experimental studies. Ammonia was removed (42%) thought stripping, while phosphate was practically removed through calcium phosphate synthesis and precipitation. This was then used for phosphoric acid production through the 'wet' process (sulphuric acid addition), while calcium sulphate (gypsum) was also co-produced. The results were underpinned by state-of-the-art analytical techniques, including ICP-MS, FIB-FESEM, EDS, FTIR, XRF, and XRD. It was identified that an increase in calcium phosphate dosage led to an increase in phosphate concentration (from 0 to 200 ppm) and a reduction of sulphate levels (from 70,000 ppm to 15,000 ppm). A fast reaction rate between calcium phosphate and sulphuric acid was also observed, with the optimal reaction time being 15 min. However, results suggest the need for phosphate pre-concentration in municipal wastewater, along with the need to study the effect of temperature and different stoichiometries. To improve the sustainability of the process, product water can also be reclaimed, after further treatment, e.g., for agricultural use, while the recovered phosphorous can also address, at least partly, the problem of the dwindling global phosphate rock reserves. Findings from this study highlight that wastewater reuse can be used to meet UN's sustainable development goals and create opportunities for green employment, social well-being, and ecological health, while at the same time freshwater ecosystems will be protected from eutrophication. By reclaiming or recovering valuable products that have commercial value from wastewater the running costs of this technology could be offset, thus making the process self-sustainable. As such, the proposed initiative will ensure the sustainable management of the ever-increasing municipal wastewater quantities and address problems of emerging concern, such as water scarcity and phosphate shortage.