Scalant Removal at Acidic pH for Maximum Ammonium Recovery

Abstract

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.