Phosphorus Removal in a Sequencing Batch Reactor Activated Sludge

Abstract

The purpose of this experiment was to develop a method of economical phosphorus removal from rural sewage. In the experiment, ferric chloride solution was added into an activated sludge reactor.
The experiment was done at a rural sewage facility which has a capacity to treat the wastewater of 940 people. The facility consists of two parallel treatment processes, which use the same sequencing batch reactor (SBR) activated sludge process.
The results are as follows:
1. T-P concentration of the treated water of the SBR which had ferric chloride solution added into it was 0.5 mg/l or less. T-P concentration of the treated water of the SBR without addition of ferric chloride solution was 1.7mg/l on average.
2. The phosphorus removed by ferric chloride solution was assumed by the next equation (1). “rc·Pin” in the equation (1) means the assumption of phosphorus removed by activated sludge.
ΔP_Fe=ΔP-γ_c·P_in(1)
3. The relationship between Fe of added ferric chloride solution and phosphorus removed by ferric chloride solution is approximated by the following equation (2).
F_e/ΔP_Fe=a·F_e/P_in+b(2)
4. Based on the equation (2), the ferric chloride solution for phosphorus removal can be estimated by the equation (3).
V_c=b·P_in·ΔP_Fe/C_Fe·(P_in-a·ΔP_Fe)(3)
V_c= the volume of ferric chloride solution necessary for phosphorus removal (l)
ΔP_Fe= the phosphorus removed by ferric chloride solution (g)
ΔP= the phosphorus removed at the SBR with ferric chloride solution (g)
r_c= the phosphorus removal rate of the SBR without ferric chloride solution (-)
P_in= the phosphorus loading of the SBR with ferric chloride solution (g)
Fe= iron in added ferric chloride solution (g)
a, b= the constants calculated by the least squares method, 4.19 and 1.81, respectively
C_Fe=Fe concentration of ferric chloride solution (g Fe/l)