If procedures that simulate treatment plant conditions are followed, jar testing can produce important information quickly and economically, and the data are directly applicable to plant design, modification, and operation. The procedure offers greater flexibility and economy than the traditional pilot plant test for pretreatment. It has shown excellent scale-up correlations with plant operating records.Experience has shown that the jar test procedure has many uses other than coagulant dosage control. Beyond the use of the jar test technique for control of coagulant dosage, other uses include but are not limited to: (I) determining the strength of floe, (2) predicting filtered water quality, (3) determining the optimum coagulant pH, (4) determining the optimum mixing intensity, (5) evaluating the optimum mixing intensity taper, (6) evaluating rapid mix duration and intensity, (7) evaluating the effect of lag time between rapid mixing and flocculation, 218 RESEARCH AND TECHNOLOGY (8) evaluating optimum coagulant aid dosages, (9) evaluating the sequence of coagulant and coagulant aid dosages, (10) establishing which coagulant is most suitable, (11) evaluating the effects of sludge recycling and concentrations of sludge for recycling, (12) predicting the effects of short circuiting, (13) predicting sludge deposit configuration, (14) predicting design criteria for in-plant settling, (15) establishing design criteria for tube and tray settlers, and (16) evaluating direct filtration possibilities and coagulant dosages.JOURNAL AWWA

Effective mixing and flocculation is of critical importance for the efficient functioning of sedimentation basins and filters. This article describes and evaluates certain factors that are involved in the design and operation of pretreatment, and illustrates the effects of these factors on filtered‐water quality, using data assembled by field testing and compiled from operating records of nine water clarification plants.

This article discusses a mathematical relation that describes the kinetics of flocculation. It takes into account flocculating time and intensity, coagulant dose, and volume and solids content of the floc. This relation indicates that the entrapment of suspended matter by floc is influenced by the volume of floc produced rather than by the size or appearance of floc particles. Jar test data confirm the hypothesis that floc volume is proportional to the coagulant dosage used and further indicate that floc can be made ten times more compact by extended agitation dose, and volume and solids content of the floc. This relation indicates that the entrapment of suspended matter by floc is influenced by the volume of floc produced rather than by the size or appearance of floc particles. Jar test data confirm the hypothesis that floc volume is proportional to the coagulant dosage used and further indicate that floc can be made ten times more compact by extended agitation (Gt = 200,000) than by limited agitation (Gt = 10,000), without impairing its settling characteristics.

During a study to determine mixing intensity, four groups of jars-test systems were utilized and mean velocity gradient, turbulent gross drag coefficient, and Reynolds and Power numbers were calculated. It was concluded that the same G, or mean velocity gradient, values could be produced by impellers of different shapes as long as projected areas were the same.The jar-test procedure is widely used to simulate the water-pretreatment process in the laboratory to produce data for process control, yet few carefully controlled jar-test techniques are found in related literature. Jar-testing has depended upon the approach of each investigator. 1 "3 However, the interpretation of jar-test data must be founded on unvarying and well-calibrated techniques if they are to be quantitatively meaningful. One of the important variables in the procedure is the mixing intensity, which is related to the rotational speed and the configuration of the agitator as well as the geometry of the mixing vessel.The purpose of this study was to determine the mixing intensity, expressed as the mean velocity gradient "G," throughout the applicable speed range, using various jar-test configurations. The resulting data should prove useful for appli- OCTOBER 1975 cation of laboratory data to water-treatment-plant design.Camp' has called attention to the facts that (1) the fluid condition in full-scale plant mixing and flocculation basins is always turbulent, even when G values are relatively low; and (2) at speeds commonly used in jar-test machines, laminar flow conditions may occur. One object of this study was to evaluate the minimum threshold speeds above which turbulence always occurs in jar-testing.Camp and Stein5 applied Stokes' theory" to relate the total energy input to what they called a root-mean-square velocity gradient G (Stokes' theory states that the velocity gradient equals the square root of energy dissipation at a point, divided by the absolute viscosity of the fluid):,where W = dissipation function = power loss per unit volume of fluid ju = absolute viscosity of the fluid The value of W depends upon the geometry of the stators, rotors, and containers and upon the speed of the rotors. Accurate values of W can be determined best by measurement of the torque input to the liquid at various speeds and temperature:in which j is the measured rotor speed in rps, T is the measured torque input, and V is the liquid volume. Once the torque is determined, the value of W can be calculated.By extensive experiments with hydrous ferric oxide floe, Camp 7 demonstrated that the floe size and volume concentration may be R. J. LAI ET AL 553

Improvements in analytical methods have created a wide range between the ideal water and the quality acceptable under the U.S. Public Health Service (USPHS) Drinking Water Standards, which define the borderline between a tolerable water and one that is unacceptable. Within this range certain water treatment plants consistently produce water of superior quality, but others barely meet the minimum levels. This article examines the reasons for the characteristic differences in results obtained, and explores their relation to viral disease incidence. The article includes a discussion by Richard L. Woodward of the Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio. He makes the point that, far from quarreling with Hudson's principal thesis, much more information and careful study are needed before the significance of water in endemic infectious hepatitis can be determined.