Starch/polyvinyl alcohol blended materials used as solid carbon source for tertiary denitrification of secondary effluent

Starch/polyvinyl alcohol (PVA) blended materials for using as a solid carbon source (SCS) were prepared by blending PVA and gelatinized starch in an aqueous solution system, in which PVA served as framework material and starch as carbon source. The optimization of starch content and temperature effects were investigated. It was indicated that higher denitrification efficiency could be achieved with more starch in the materials. The average specific denitrification rates were 0.93, 0.66, 0.37 and 0.36 mg/(g·day) corresponding to starch content of 70%, 60%, 40% and 30% respectively at 37°C. The denitrification rates increased when operating temperature was raised from 23°C to 30°C and then 37°C. The mechanism of carbon release was analyzed incorporating the experimental results of abiotic release in deionized water. The organic carbon was mainly hydrolyzed by microbes, and the biological release efficiencies were at the range of 89.2% to 96.0%. A long-term experiment with a continuous flow reactor with SCS material containing 70% starch was conducted to gain some experience for practical application. When the influent nitrate concentration was in the range of 35.2 to 39.1 mg/L, hydraulic retention time of 4 hr, and operating temperature of 30°C, a nitrogen removal efficiency up to 94.6% and denitrification rate of 0.217 kg/(m³·day) was achieved. The starch-based materials developed in this study can be used as a solid carbon source for tertiary nitrogen removal from secondary effluent.