Reject water treatment performance was investigated by whole cell anammox sludge entrapped polyvinyl alcohol/sodium alginate gel in the stirred tank reactor (STR). The whole experiment was conducted through Phase 1 and Phase 2 in which synthetic wastewater and modified reject water were used as feeding medium, respectively. The anammox reactor demonstrated quick start-up after 22 days as well as stable and relatively high nitrogen removal rate of more than 8.0 kg-N m(-3) day(-1) during the two both phases even under moderately low temperature of 25 ± 0.5°C during the last 2 months of Phase 2. The matured brownish red PVA beads had good characteristics with buoyant density of 1.10 g cm(-3), settling velocity of 141 m h(-1) and diameter of 4 mm. The bacterial community was identified by 16S rDNA analysis revealing the concurrent existence of KSU-1 and new kind anammox bacterium Kumadai-I after changing influent from synthetic wastewater to reject water. It was speculated that Kumadai-I might play a role as "promotion" factor together with KSU-1 on high nitrogen removal rate. These results demonstrate the potential application of whole cell anammox entrapment by PVA/alginate gel for achieving stable and high-rate nitrogen removal from high ammonium with low C/N ratio contained wastewaters, such as reject water, digester liquor or landfill leachate.

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.