Simultaneous carbon-nitrogen removal in wastewater using phosphorylated PVA-immobilized microorganisms

Abstract

Acclimated sludge was immobilized by a previously developed phosphorylated polyvinyl alcohol (PVA) gel. The immobilized-cell reactor system was established in a 12-l continuous aeration vessel with a synthetic municipal wastewater as the feed substrate. In addition, a method was developed to estimate the biomass concentration of the suspended sludge and the immobilized-cell beads by detecting the microbial cell protein content. The system was operated at a HRT of 2–10 h in which the COD loading rate ranged from 0.855–4.223 g COD l −1 d −1. More than 90% of COD removed efficiency was obtained at a COD loading rate lower than 2.0 g COD l −1 d −1 accompanied by a total nitrogen removal efficiency at around 45%. The immobilized cell process has yielded highly promising results particularly in terms of maintaining a high biomass concentration to attain high efficiency and reducing production of excess sludge to decrease operation cost. The so-called aerated denitrification occurring inside the gel beads was verified experimentally by measuring the nitrate reduction activity of gel beads. Microscopic observation revealed that three kinds of bacterial species, i.e., BOD oxidizers, nitrifiers, and denitrifiers, developed a habitat segregation from the peripheral surface into the interior part of the gel bead.