Efficient Nitrogen Removal And Recovery From Real Digested Sewage Sludge Reject Water Through Electroconcentration

Reject waters from the dewatering of anaerobically digested municipal sewage sludge are nitrogen-rich (ca. 1 g(NH4-N) L-1) wastewater streams. They account for up to 25% of the total nitrogen load of wastewater treatment due to their internal recirculation within treatment plants. In this study, nitrogen was effectively removed and recovered from real reject water using a novel electrochemical setup combining electroconcentration and stripping. High nitrogen removal (<= 94 +/- 0.7%) and recovery (<= 87 +/- 8.5%) efficiencies from real reject water were obtained while simultaneously reducing the influent nitrogen concentration of 913 +/- 14 mg(NH4-N) L-1 to 57 +/- 6.7 mg(NH4-N) L-1 in the effluent. Most of the nitrogen recovery took place via electroconcentration into a liquid concentrate (<= 82 +/- 5.7%), while stripping contributed little to the removal and recovery (<= 5 +/- 2.8%). The reported removal and recovery efficiencies are the highest to date for a system utilising three-chamber elec-troconcentration. Furthermore, the concept of cation load ratio (the ratio between applied current density and cation loading rate) was introduced as a more precise parameter than the widely used and simpler NH4-N load ratio for predicting the performance of a (bio)electrochemical nutrient removal and recovery system.