Scalant Removal at Acidic pH for Maximum Ammonium Recovery.

One option for new nitrogen sources is industrial liquid side streams containing ammonium nitrogen (NH 4 -N). Unfortunately, NH 4 -N often exists in low concentrations in large water volumes. In order to achieve a highly concentrated NH 4 -Nsolution, scalant removal is needed. In this study, scalant removal by precipitation was investigated. At alkali pH, sodium carbonate (Na 2 CO 3 ) was used as a precipitation chemical while at acidic pH, the chemical used was oxalic acid (C 2 H 2 O 4 ). At alkali pH, high Na 2 CO 3 dose was needed to achieve low content of calcium, which, with sulphate, formed the main scalant in the studied mine water. NH 4 -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 CaC 2 O 4 precipitation, NF90 was able to be used for NH 4 -N concentration up to the volume reduction factor of 25. Then, NH 4 -N concentration increased from 0.17 g/L to 3 g/L. NF270 produced the best fluxes for acid pre-treated mine water, but NH 4 -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.