By Robert L Bryant. President, Chemtrac Systems, Inc., Atlanta, Ga.
The most critical time in the water treatment process usually occurs within the first two minutes after the raw water enters the plant. What the operator does. or doesn't do, in this short time span afects everything in the system—to the household tap.
The results of coagulation control problems are well known, i.e., poor finished water quality, high chemical costs, short filter runs and high backwash costs, excessive sludge, increased pumping costs (raw and finished), soluble aluminum at tap, post precipitation and fouling of distribution systems, and passage of parasitic organisms into he water system. Articles on the last three problems were published in recent issues of the AWWA Journal (''The Occurrence of Aluminum in Drinking Water," Jan, 1984; "Postprecipitation in Distribution Systems," Nov, 1984: "Giardisis: The New Waterborne Disease." Feb, 1985).
Every water plant operator wants to maintain good finished water quality. When everything is going smoothly. the plant pretty much runs itself. The operator's lob has been described as one of many quiet days, interrupted occasionally by a few hours of mass panic. This panic is usually caused by such things as: (1) coagulant pump failures, (2) heavy rain- storms causing wildly swinging raw turbidities, (3) instrument and controller malfunctions, etc. These upsets can cause any or all of the problems described above.