High Ammonium Wastewater Treatment of Stirred Tank Anammox Reactor using Polyvinyl Alcohol/Alginate Gel as Biomass Carrier

Abstract

Appropriate biomass retention in the reactor is crucial to the operation of the anaerobic ammonium oxidation (anammox) process due to the extremely slow growth rate of the bacterial population. In the present work, anammox sludge, immobilized in a poly vinyl alcohol (PVA)/sodium alginate gel, was studied to improve anammox biomass retention in the reactor. 150 ml of concentrated anammox sludge (33.3 g suspended solids l^–1) was entrapped into a PVA/alginate aqueous solution (15% w/v PVA and 2% w/v alginate) at a volumetric ratio of 1:1 that was then solidified in a solution containing 50% w/v NaNO₃ and 2% w/v CaCl₂. The anammox activity increased gradually and reached a maximum nitrogen loading rate of 9.9 kg–N m^–3 d^–1, with a removal efficiency of more than 80% even at a low hydraulic retention time of 2.67 h, after 250 days of operation when the bicarbonate concentration was increased to 1.0 g l^–1 as KHCO₃ from day 145. A porous structure in the PVA/alginate immobilized biomass beads was observed by scanning electron microscopic (SEM) analysis. This study shows the potential for the treatment of wastewaters containing high ammonium and low carbon, such as digester liquor, using PVA/alginate gels for whole cell entrapment of anammox sludge.