Pre-sedimentation tank effects on water treatment unit operation

Abstract

Understanding the effect of any unit of water treatment plant (WTP) on the performance of the other units is very important in optimal design of a WTP. In some of the WTP a Primary settling is done in the unit of pre-sedimentation tank (PST) in entrance of raw water to the WTP. In some WTP, the unit of PST is used only in flood condition. Regarding the high-cast of equipment and maintenance of PST, more studies are needed for evaluation of the role and performance of the PST on the other units of the WTP .This study was done in Salman Farsi WTP.  The removal efficiency of turbidity for PST, clarifier, filters and backwash interval time in filters in flood and non-flood conditions and use and non-use of PST were examined and evaluated. Coagulant and chlorine consumption were also compared in the presence and absence of pre-sedimentation basin during non-flood condition. The results showed that in non- flood condition and using from PST, the PST didn’t play significant role in decreasing the turbidity and coagulant consumption increased compared to none use of PST. In this condition, consumption of gaseous chlorine of 900 kilograms in one month is more than in none-use of PST condition. In flood condition and non-use of PST filtration, efficiency is considerably reduced and filters backwash interval time is decreased more than 3 times and rate of water treatment is reduced by 20 percent. Overall, the results showed if PST is absent in low turbidity, Total costs will reduce; Instead, in the absence of PST in flood condition the rate of water production reduces, and quickly clogging of the filters is happened