Control of disinfection by products formation potential by enhanced coagulation

Jar-test experiments were conducted to study enhanced coagulation effectiveness in removal of disinfection by products [DBPs] from Zayandehrud River at Isfahan Province-the center part of Iran- in 2004. In this study, the removal of suspended and colloidal particles and natural organic matter [NOM] at various coagulant doses and coagulation pHs was assessed through raw and treated water measurements of turbidity, UV254 absorbance, TOC, and dissolved organic carbon [DOC]. The trihalomethane formation potential [THMFP] was also determined by a mathematical relationship with TOC. Results indicated that NOM removal was a function of coagulant type, coagulant dose, and pH of coagulation. In general, TOC, DOC, and UV254 absorbance removal enhanced with increasing coagulant dose. However, further increases in coagulant dosage had little effect on disinfection by-products precursors removal. Ferric chloride was consistently more effective than alum in removing NOM. Coagulation pH was appeared to be a determining factor for maximum NOM removal and the removal of DBPs precursors by enhanced coagulation was significantly enhanced at pH 5.5 in comparison with initial pH of water. Furthermore, it is specified that preadjustment of pH with sulfuric acid reduced the coagulant dosage and thus, production of sludge. The reduction in THMFP was consistent with the trends observed for DBPs precursors removal data [i.e. UV254 and TOC data]

Evaluation of ferric chloride and alum efficiences in enhanced coagulation for toc removal and related residual metal concentrations

Although the removal of colloidal particles continues to be an important reason for using coagulation, a newer objective, the removal of natural organic matter [NOM] to reduce the formation of disinfection by-products [DBPs], is growing in importance. Enhanced coagulation is thus introduced to most water utilities treating surface water. Bench-scale experiments were conducted to compare the effectiveness of alum and ferric chloride in removing DBPs precursors from eight synthetic water samples, each representing a different element of the USEPA's 3x3 enhanced coagulation matrix. The effect of enhanced coagulation on the residual metal [aluminum/iron] concentration in the treated water was assessed as well. The removal of total organic carbon [TOC] was dependent on the coagulant type and was enhanced with increasing coagulant dose, but the latter had no further considerable effect in case of increasing to high levels. For all the treated samples coagulation with ferric chloride proved to be more effective than alum at similar doses and the mean values of treatment efficiencies were 51% and 32% for ferric chloride and alum, respectively. Ferric chloride was therefore considered the better chemical for enhancing the coagulation process. Besides, due to less production of sludge by this coagulant, it would be predicted that treatment plants would be confronted to fewer problems with respect to final sludge disposal. Measurements of residual metal in treated water indicated that iron and aluminum concentrations had been increased as expected but the quality of water concerning the residual metal deteriorated much more in cases of under-dosing. Despite expecting high residual Al and Fe concentrations under enhanced coagulation, metal concentrations were frequently remained low and were not increased appreciably