Ammonium removal from digested sludge liquors using ion exchange

Liquors arising from the dewatering of digested sludge typically contain ammonium levels in the range 200–700 mg l−1 NH4+-N. These liquors are frequently recycled to the head of the wastewater treatment works (WwTW) untreated and can constitute >25% of the total nitrogen load entering the works at inlet. This paper investigates the use of a clay-based material, MesoLite, as an ion exchange medium for ammonium removal from recycle streams. Pilot-scale studies performed at Didcot WwTW, part of the Thames Water wastewater treatment network, indicate that MesoLite is highly selective for the ammonium ion. Results show that >95% of ammonium was removed from belt press liquors with an initial ammonium nitrogen concentration >600 mg l−1, with an overall ion exchange capacity >51 g NH4+-N kg−1 medium and this resulted in an operating capacity in the range 27–36 g NH4+-N kg−1.