Study Of Chlorination Technique On High Salinity Cept Or Secondary Effluent

Fresh water shortage crisis has been a vital environmental issue that the whole world faces. Alone with population growth and urbanization level increase, the situation of fresh water resource is extremely serious. The seawater direct use is one of the most important means to relax the contradiction between fresh water supply and demand. However, the health risk arises which derived from the consequent high salinity sewage effluent containing chemical pollutants and pathogenic microorganisms. So, the current study for the purpose of controlling pathogenic microorganism counts and disinfection by-products formation becomes research hotspot. The chlorination technique is the most widely used disinfection method, which has many advantages, such as good kill effectiveness, lower treatment cost, easy to use and operation. Chlorination disinfection has great significance for increasing the bio-safety of sewage effluent.To promote R & D and practical application of seawater utilization in coastal cities, based on field experiment, a pipe loop simulator study combined with lab batch test has been conducted to explore chlorination efficiency of wastewater with high salinity; to observe the exact pattern of E. coli inactivation correlated with the final TRC (total residual chlorine) in saline sewage effluent; to assess the biofilm growth and sloughing when the effluent is subjected to chlorination; to assess the corrosion extent in ductile iron pipe when it is used to transport chlorinated saline sewage effluent. In addition to studying the effect of temperature, chlorine dosage, ammonia and bromine concentration on CBPs formation (chlorination by-products), this is the first case to explore the relationship between sludge age and CBPs formation.Diurnal/monthly change of chlorine demand in high salinity CEPT (chemically enhanced primary treatment) effluent varied greatly, no obvious changing regularity was observed. The variation could reach 8.0 mg/L at daytime, the chlorine demand was high in the morning, which lowered down a lesser degree at night, and the change tendency of monthly average chlorine demand was almost the same as daytime. Daily/hour/total variation coefficient (K_d, K_h and K_z) of chlorine demand in high salinity CEPT effluent was 1.477,1.094 and 1.616, respectively. The resistance of E. coli in CEPT effluent was low to free chlorine and high to combined chlorine, say monochloramine. The remaining E. coli level was mainly dependent upon the prevailing residual chlorine level, the contact time was non-essential parameter as long as it's over 6-8 mins.The temperature of high salinity secondary effluent had minor effect on chlorine dosage, the CBPs formation increased with increasing temperature. However, the ammonia-N level had major effect, which should be closely monitored in the real chlorination process in sewage treatment works. The more chlorine dosage and ammonia-N level, the more chloramine formed and the other products-CBPs formation relatively decreased. The sludge age in biological treatment had a major effect on CBPs formation. A longer sludge age had been found to yield a higher CBPs formation in the chlorinated saline secondary effluent. The effluent organic matters from the longer sludge age operation had a higher reactivity with chlorine, which resulted in a greater specific total CBPs/DOC (dissolved organic carbon) yield. The rich bromine ions in saline sewage shifted some CBPs to bromine-containing species, such as CHBr3 and DBAA, which represented a large fraction of the total CBPs. These was no positive relationship between Br-CBPs/DOC and SUVA (specific UV absorption) value.Simulation study of sewage conveyance system upon chlorination suggested that in carrying the saline secondary effluent, the ductile iron force main corrosion by DO (dissolved oxygen) was about 17.8 times higher than that by chlorine. When DO and chlorine residual were present together, even DO approached saturation, there appeared no synergistic corrosive action, the corrosion rate was mainly dictated by DO while chlorine played only a very insignificant role in affecting the corrosion. The corrosion rate increased when the oxidant increased, however the corresponding rate was much higher with DO increasing than chlorine. The level of biofilm growth in the pipe wall was always in a dynamic equilibrium with the organic strength of the carried flow. For conveying the saline secondary effluent with a BOD (biochemical oxygen demand) of about 10 mg/L, the biofilm thickness was approximately 200μm; for conveying the saline CEPT effluent, the biofilm thickness could reach 300-500μm. With chlorination of up to 5.0 mg/L even higher, the biofilm growth and sloughing were not adversely affected; there was no noticeable deterioration of the current effluent qualities with respect to suspended solids.This study developed a better understanding about E. coli kill profile, CBPs formation and proved up the impact degree of the chlorination on sewage conveyance system. The results obtained laid a foundation for further research, also provide technical support and theoretical basis in practical application for the other coastal cities.