Anammox Bacteria Immobilization Using Polyvinyl Alcohol/Sodium Alginate Crosslinked with Sodium Sulfate

Abstract

For immobilizing Anammox biomass, different materials have been studied such as sodium alginate (SA), polyvinyl alcohol (PVA), and so on. PVA-SA is one of the most popular materials because of various advantages of when compared with others. In this study, boric acid and sodium sulfate were applied to make PVA-SA gel beads, which is a new method of immobilization technology. This type of gel bead is less toxic, more stable in water, and more biologically active than gel beads made by other methods. First, two types of seed sludge were used to make gel beads that were introduced in two different continuous stirred tank reactors (CSTR). Only Reactor 1 used the seed sludge having Anammox biomass. By observing the difference in nitrogen performances, Reactor 2 was applied as evidence to detect the start-up of the Anammox process in Reactor 1. After 20 days, relying on the stoichiometric ratios, NO2−─N and NH4+─N removal efficiency and NO3−─N concentration, the Anammox process was detected in Reactor 1 while the results of Reactor 2 revealed that aerobic oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were dominant in PVA-SA gel beads. Subsequently, after 180 days, the nitrogen removal performance reached nearly 70%, whereas the nitrogen loading rate (NLR) grew from 0.1 to 0.3 kg·N/m3/day. Furthermore, fluorescence in situ hybridization (FISH) analysis also confirmed the presence of Anammox bacteria inside the PVA-SA gel beads. Based on these results, using Anammox bacteria immobilized in PVA-SA gel beads crosslinked with sodium sulfate is suitable for starting the Anammox process.