E. coli Response on Chlorine Dose in Saline CEPT Effluent

摘要

A 1.7-km ocean outfall has been used to transport saline CEPT (chemically enhanced primary treatment) effluent which was not chlorinated to the receiving water body. Now the effluent is being considered for chlorine disinfection using existing outfall as the chlorine contact chamber to achieve a 2-3 log reduction in E. coli counts. As no purposely built sampling locations after outfall system, a simulator study coupled with batch tests has been conducted with a pipe loop which provides a similar contact time and hydraulic regime as that existing in the field to provide valuable information to correlate the E. coli kill with the final TRC after the chlorine contact, and show the exact pattern of E. coli disinfection in saline sewage. Experimental results indicate the chlorine demand of CEPT effluent is mostly satisfied within the first 10 minutes of contact, any longer contact will only increase the demand by around 3.5% and not lead to any substantial increase in the E. coli kill The remaining E. coli levels are mainly dependent upon the prevalent TRC levels while their contact times play only a relatively insignificant role. The comprehensive E. coli-TRC correlation curve, coupled with the observed diurnal/monthly chlorine demand variations, apparently suggests that in order to comply with a promulgated E. coli limit, a certain final TRC level must be maintained at the end of the contact. Results from this study can be used as a reference to allow the operator to determine the needed chlorine dosing level in order to meet discharge water quality standards in future full-scale chlorination operation.