Advocating circular economy in wastewater treatment: Struvite formation and drinking water reclamation from real municipal effluents

Abstract

In this pilot study, the circular economy concept in wastewater treatment was examined, through a zero liquid discharge (ZLD) process where struvite was recovered and drinking water was reclaimed. A stage wise approach was used for struvite formation and the subsequent reclamation of drinking water. Specifically, the early stages of treatment entail the synthesis of struvite via the chemical precipitation of nutrients (phosphate and ammonia), using thermally activated cryptocrystalline magnesite. Thence, reverse osmosis (RO) was employed for drinking water reclamation. With this dual approach, 3.5 m 3 of municipal wastewater were successfully treated at a pilot plant in South Africa, producing ~52.5 kg of struvite and ~3.4 m 3 of drinking water. The operating parameters were 30 min of residence time, 0.5 g : 500 mL solid to liquid (S/L) ratio, using ambient temperature and pH. X-ray diffraction (XRD) and High Resolution Scanning Electron Microscopy (HR-SEM) coupled with electron dispersion spectroscopy (EDS) confirmed the synthesis of struvite and the presence of notable Mg/P ratios. Fourier Transform Infrared Spectrometer (FTIR) further ascertained the obtained results. Moreover, it was identified that the reclaimed water meets the South African National Standard (SANS) 241 and the world health organisation (WHO) standards for drinking water. An economic analysis revealed the viability of the process, suggesting that the system could be self-sustainable. Therefore, the results of this work indicate that introducing the concept of circular economy in wastewater treatment can promote the sustainable management of the ever-increasing quantities of municipal wastewater and at the same time address problems of emerging concern, such as water scarcity and phosphate shortage.

Impact of Magnesium Sources for Phosphate Recovery and/or Removal from Waste

“…Desalination processes to produce potable water produce reject brine, which is also considered a viable source of magnesium [29,30]. Sacrificial magnesium anodes [31,32], magnesium oxides [33], as well as cryptocrystalline magnesite [34], are also considered viable sources for magnesium. The efficiencies of all the mentioned sources have been compared to the commonly used expensive magnesium sources, such as magnesium chloride in this study.…”

Techno-Economic Analysis of the Reclamation of Drinking Water and Valuable Minerals from Acid Mine Drainage

“…Activated magnesite was reported to be constituted of C, O, Mg, Ca and Si (Figure 4a). These elements will play a significant role in increasing the pH and attenuation of anions from the aquasphere [3]. The product sludge was observed to comprise C, O, Mg, Ca and Si from the mother magnesite and the addition of Fe, S, Al, and Mn (Figure 4b).…”

“…The quest to minimise ecological footprints of wastewater treatment has been ameliorated by the emergence of circular economy in wastewater treatment [1,2]. This concept includes the treatment, beneficiation, and valorisation of wastewater prior to them being discharged to different receiving environments [2][3][4][5]. In light of that, research studies seek prudent ways to address the issue of mineral recovery from wastewater although the quest is still ongoing [2].…”

Effect of phosphate and ammonium concentrations, total suspended solids and alkalinity on lignin-induced struvite precipitation

“…However, phosphate rocks are a limited and non-renewable resource 4 , and their reservation is being depleted 5 , 6 . A great amount of effort has been made in searching for more sustainable sources to substitute phosphate rocks 7 , 8 . Meanwhile, significant levels of phosphates are released into wastewater contributing to eutrophication 9 – 11 .…”