Coagulation pH appeared to be a determining factor for maximum NOM removal.Several bench‐scale studies were conducted to evaluate the effectiveness of enhanced coagulation for controlling chlorination by‐products and to assess the impace of coaqulation pH preadjustment on total organic carbon (TOC) removal and plant operating costs. Tests were conducted on a variety of surface water sources with TOC values ranging from 2 to 1 mg/L. An iron‐based coagulant, such as ferric chloride, was consisitently more effective than alum in removing natural organic matter (NOM). Coagulation pH appeared to be a determining factor for maximum NOM removal when ferric chloride was used as a primary coagulant. Typically, preadjustment of pH at a value of 6.0 ± 0.2 increased NOM overall removal to as much as 65 percent and reduced the coagulant dose by as much as 60 precent. Enhanced coagulation led to higher overall operating costs, but preadjustment of pH with sulfuric acid reduced costs, by lowering the coagulant dosage as well as sludge production.
Considering this rapid growth in the purchasing of bottled water and home filtration devices, utilities are increasingly concerned about consumer dissatisfaction with tap water quality. This project aimed to characterize public perceptions of chlorinous flavors in drinking water, and how these impact customers' choices with respect to consumption of tap water alternatives. On-site taste tests at seven water utilities with 30 to 40 panelists at each site, were conducted using a forced-choice triangle test method (ASTM method E679-91) to measure public sensitivity to chlorine and chloramine in drinking water. The chlor(am)ine concentration increased from set to set. The best-estimate sensitivity limit for each panelist was the geometric mean of that concentration at which the last miss occurred and the next (adjacent) higher concentration. The measured sensitivity limit of average American populations to free chlorine (159 persons tested) and chloramine (93 persons tested) in tap water were 0.8 and 3.7 mg/L Cl2, respectively. These thresholds are much higher than those previously reported in the literature using trained FPA panels. No significant differences were observed between tap water users and users of tap water alternatives or between the various markets tested with respect to average sensitivity, though individual sensitivity varied widely.
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