Scalant Removal at Acidic pH for Maximum Ammonium Recovery

One option for new nitrogen sources is industrial liquid side streams containing ammonium nitrogen (NH₄-N). Unfortunately, NH₄-N often exists in low concentrations in large water volumes. In order to achieve a highly concentrated NH₄-Nsolution, scalant removal is needed. In this study, scalant removal by precipitation was investigated. At alkali pH, sodium carbonate (Na₂CO₃) was used as a precipitation chemical while at acidic pH, the chemical used was oxalic acid (C₂H₂O₄). At alkali pH, high Na₂CO₃ dose was needed to achieve low content of calcium, which, with sulphate, formed the main scalant in the studied mine water. NH₄-N at alkali pH was in the form of gaseous ammonia but it stayed well in the solution during pre-treatment for nanofiltration (NF) and reverse osmosis (RO). However, it was not rejected sufficiently, even via LG SW seawater RO membrane. At acidic pH with CaC₂O₄ precipitation, NF90 was able to be used for NH₄-N concentration up to the volume reduction factor of 25. Then, NH₄-N concentration increased from 0.17 g/L to 3 g/L. NF270 produced the best fluxes for acid pre-treated mine water, but NH₄-N rejection was not adequate. NF90 membrane with mine water pre-treated using acid was successfully verified on a larger scale using the NF90-2540 spiral wound element.

Wastewater Purification with Nutrient and Carbon Recovery in a Mobile Resource Container

Water reuse from wastewater treatment plants can significantly reduce freshwater demand. Additionally municipal sewage and some industrial wastewaters could be used as sources of nutrients and carbon more effectively than they are used today. Biological treatments have attracted the most attention in wastewater purification, whereas, so far, only a little attention has been paid to the physico-chemical technologies. These technologies could, however, have great potential to recover nutrients when purifying wastewater. In this study, the main emphasis was to study the possibilities to utilize existing physico-chemical unit operations for wastewater purification and nutrients as well as carbon recovery. Unit operations were selected so that they could produce exploitable circular economy products from wastewaters and be assembled in a mobile container for carrying out recovery anywhere that is suitable. The results showed that in a mobile container, solids could be successfully separated from the studied wastewaters by flocculation-assisted solid/liquid separation and then processed into hydrochar by hydrothermal carbonization. Phosphate was precipitated using lime milk as calcium phosphate, and ammonium nitrogen was captured from the wastewater using membrane contactor technology resulting in ammonium sulphate for fertilizer use. Additionally, reverse osmosis retained residual impurities well, producing good quality water for reuse. The techno-economic feasibility seems promising.