Applying sheet iron to enhance the treatment efficiency of digested effluent with continuous flow and the...

Because of the unstable wastewater quantity and quality, the biological treatment efficiency of digested effluent was not as expected. A convenient and effective way was eagerly required to improve the efficiency of biological treatment. By sheet iron addition (R₁), the COD and TN removal efficiencies under continuous flow condition increased by 59% and 37% respectively. The bulk pH maintained at around 7.5 which benefited most bacteria, while in the control (R₀, without sheet iron addition) the pH decreased to 5.0. Both chemical and bio-removal of COD existed in R₁, but the chemical removal dominated (63.71%). The enhanced COD removal efficiency came from the chemical oxidation by Fe³⁺ (47.43%) and Fe⁰ (10.86%). For the TN removal, the enhancement mainly came from the improvement of anammox activity by Fe³⁺ (14.87%), the bio-oxidation of ammonium with Fe³⁺ as electron acceptor (8.78%), and the bio-reduction of nitrate/nitrite with Fe²⁺ and H₂ as electron donor (35.76%). By the first-order kinetic fitting analysis, the COD and TN removal rate in R₁ was higher than that in R₀. Thus, for a quick and high COD and TN removal from digested effluent, the addition of Fe⁰/Fe²⁺/Fe³⁺ was suggested, and the best form should be Fe⁰ (e.g., sheet iron). The addition of sheet iron reduces the cost of nitrogen removal and improves the efficiency of COD and TN removal. Comparing with the combined processes, this novel approach has potential advantages with simple operation and high efficiency. It endows the biological process much broader application in digested effluent treatment.