Nutrients Recovery from Municipal Wastewater Effluent using Electrochemical and Freeze Concentration Approaches

Abstract

Municipal wastewater (MWW) is now being re-evaluated as a potential multi-resource for water, energy and nutrients. Anaerobic membrane bioreactors (AnMBRs) are increasingly being investigated as a cost-effective biological option with strong potential for the recovery of energy and removal of pathogens and contaminants from MWW. However, the recovery of nutrients by AnMBRs is typically negligible. This thesis focused on the simultaneous removal of nutrients from the effluent of AnMBRs for MWW treatment. Three approaches were proposed, namely, electrodeionization (EDI), freeze concentration (FC), as well as using FC as a preconcentration step for electrodialysis(ED). Synthetic effluents from AnMBR for MWW treatment were used as feed in the EDI, FC, and integrated FC/ED studies in this thesis. In the investigation of EDI approach, the effect of the scan rates on limiting current (Ilim) determination and effects of 110% of Ilim, Ilim and 90% of Ilim were studied. At the recommended Ilim over 3 h, the removal efficiency of NH4 +-N, HxPO4 y--P, Ca2+ and Mg2+, was 74.4%, 100%, 92.3%, and 58.8%, respectively, with a specific energy consumption of 0.74 kWh/m3 of feed wastewater. The results demonstrated that the EDI process is very promising for the removal of ionic nutrients and hardness ions from wastewater similar to municipal wastewater. For FC approach, synthetic feed water containing the single impurities (HxPO4 y--P, NH4 +-N and COD causing glucose) and the multiple impurities with different concentrations were tested at various mixing conditions. The average achieved removal efficiencies of HxPO4 y--P, NH4 +-N and COD in single impurity tests were 99.9%, 96.5% and 100%, respectively. In multiple impurities tests, the average removal efficiencies of HxPO4 y--P, NH4 +-N and COD ranged 99.9% - 90.6%, 96.2% - 90.2%, and 100% - 88.2%, respectively. The experimental results indicated a potential that FC was efficient to remove nutrients from municipal wastewater effluent. An approach of using freeze concentration as a preconcentration step for electrodialysis (ED) was also investigated. The removal efficiencies of NH4 +-N, HxPO4 y--P, and Ca2+ at a current from 90% to 110% of limiting current over 3 h, ranged from 93.9% - 97.1%, 56.4% - 62.3%, and 88.6% - 94.5%, respectively. The results of experiments with synthetic MWW without freeze concentration revealed that preconcentration was prerequisite for improving the performance of ED for dilute solutions, particularly for the removal of HxPO4 y--P. Freeze concentration as a preconcentration step for ED offers a promising approach for the treatment of MWW via ED.