Study on total residual oxidant decay in long-distance seawater intake pipeline of cooling system

Electrochlorination is often used for biofouling control along the water intake pipeline of seawater cooling system, but with the increasing of pipeline length, this process needs to be further improved. In this study, the dynamic circulation and field pilot test were used to simulate the long-distance seawater intake pipeline, investigating total residual oxidant (TRO) decay and its influencing factors by comparing the bench test. The results showed that intermediate dosing could increase terminal TRO, but also reduce the CT value, resulting in decline of local inactivation effect. The initial concentration of dynamic cycle test was higher than that of bench test under the same terminal TRO, and the difference value between the two was affected by holding time. When the initial concentration was greater than 8.5 mg L^-1, TRO decay rate was proportional to the seawater flow rate and inversely proportional to the initial concentration. The initial concentration of 8.5-10 mg L^-1 could meet TRO decay requirement under 3 h holding time, and the dosing concentration could be reduced to 6 mg L^-1 when the temperature was low. The results provided important guidance for the actual operation of biofouling control in long-distance water intake pipelines of cooling system.