Minimizing brine discharge in a combined biophysical system for nitrate removal from inland groundwater

Spent regenerant was first treated in a sequential batch denitrification bioreactor followed by ozonation for polishing. The SBR unit achieved complete nitrate removal in 8 h with nitrate removal rates of 2.6 ± 0.4 g N/Lreactor/d and a low average ethanol to nitrate mass ratio of 1.68 ± 0.18. An ozone dose of 3-5 mg/L brine allowed for efficient recycling of the denitrified regenerant by removing suspended solids by foam fractionation. In spite of the low brine blow-down, DOC in the recycled regenerant brine after more than a year of continuous operation was maintained at relatively low levels of 61.0 ± 11.6 mg/L.