Studies on the Electrolytic Conditions for the Electrochemical Elution of Iron as Applied to Phosphorus Removal Technology

Abstract

Phosphorus removal from small-scale domestic wastewater treatment systems by means of an electrolytic bath using of iron electrodes was examined.
We discovered, however, that an iron oxide layer forms on the surface of the iron electrodes, leading to a decreased phosphorus removal ratio.
To solve this problem, we discovered that specific electrolytic conditions can inhibit the formation of this iron oxide layer (FeOOH, Fe₃O₄) on the iron electrodes. One condition is the Fe:P ratio. An Fe/P ratio exceeding 1.5 inhibits the formation of this iron oxide layer. Another condition is the concentration of nitrate ions and nitrite ions. We have shown that the iron oxide layer forms when the nitrate nitrogen concentration is 60mg · l^-1 or the nitrite nitrogen concentration is 10mg · l^-1. However, a polarity reversal period of 24 hours inhibits the formation of the iron oxide layer when the nitrate nitrogen concentration is 60mg · l^-1 and the iron oxide produced by nitrate ions and nitrite ions is broken down by the chloride ion at a concentration exceeding 60mg · l^-1.