This research was performed by using raw water from treated industrial estate wastewater of the Northern Region Industrial estate, Thailand. Coagulation in jar-test experiments were carried out under the variations of alum and ferric chloride dosages rangedfrom 10 to 80 mg/L at the conditions of uncontrolled and controlled pH between 5 and 6.5 Trihalomethane formation potential (THMFP) and other natural organic matter (NOM) surrogates were determined so as to study its correlation and its reduction. The obtained results appeared that turbidity could be effectively removed to the level of as low as about 3 NTU by coagulation at the alum and ferric chloride dosages of approximately 10 mg/L without controlled pH. TOC and THMFP showed the best correlation comparing to those of between other surrogates and THMFP. The correlation between TOC and THMFP were established with a Pearson Correlation factor of 0.91 (R2=0.866). The equation could be used to express such correlation was THMFP = 238.552 + 33.886 (TOC). Regarding TOC reduction by alum and ferric chloride coagulation, it was found that at controlled pH between 5.5 and 6.5 TOC were gradually reduced from the average value of about 6.12 mg/L to the level of about 4.0 mg/L by alum and ferric chloride dosages of approximately 40 mg/L. Chloroform of approximately 65 and 60 percent of total THMFP were found as the predominant THMFP species in treated industrial estate wastewater and in reclaimed water, respectively in comparison with dichlorobromoform, dibromochloroform and bromoform species. With reference to percent removal of total THMFP by coagulation, the percent removal of 25.53 and 27.71 by using alum and ferric chloride dosages of about 80 mg/L at pH 5.5 and 5 were obtained, respectively.
