Addition of a foaming agent to improve N2 gas permeability of PVA/alginate carriers for deammonification process

Long term use of anammox carriers immobilized in PVA/alginate has always faced problem due to expansion and bursting due to dense surface. The physical and morphological characteristics were investigated by adding foaming agent to 0, 0.15, 0.3, 0.6 and 1.2 w/v% to increase the gas permeability. Maximum real and bulk density, minimum specific surface area and swelling ratio were found at 0.3 w/v% foaming agent. The gas permeability increased continuously up to 1.2 w/v% foaming agent, as found in the break point test. The 0.3 w/v% foaming agent gave optimum bacteria retention capacity of 98.9%. With 0 w/v% foaming agent, non-porous outer layer was burst due to pressure of produced nitrogen gas as confirmed by morphology test. Addition of foaming agent caused porous structure and the anammox bacteria grew deep inside the carrier. Therefore, the optimum foaming agent content of 0.3% can greatly enhance process stability in the deammonification system.