In order to improve efficiencies of phoshorus removal at low water temperature, media-added batch activated sludge process combined with droplet method of thick iron solution as a chemical dosing was investigated in a process treating a sewage wastewater.
An thick iron solution is able to be made by heating the crystal of the iron (III) chlorid hexahydrate within one hour at 50-60°C. However, it was shown that the dilution of thick iron solution was necessary to prevent solidification of the solution due to lowering of temperature. The optimal dilution ratio (the ratio of water volume to the volume of thick iron solution) was 0.4 v/v and it was observed the diluted solution did not solidify at 2°C.
Removal efficiency of phosphorus by using the dosage of diluted thick iron solution was remarkably enhanced up to 79-82% at 10°C and it was not observed the inhibitive effect of the dosage on the nitrification and the BOD removal. These results indicate that biological process combined with the droplet method of thick iron solution improve treatment efficiency of phosphorus significantly at low water temperature.
This method could decrease the frequency of maintenance because smaller quantity of dosage is required comparing with the conventional chemical method.