The solution to Problem is a process flow diagram for a surface water treatment plant, and...

The solution to Problem is a process flow diagram for a surface water treatment plant, and the solution to Problem is a process flow diagram for a water-softening plant. Expand each diagram to include a scheme to process the sludge from sedimentation and the wash water from filtration. The wastes must be thickened and dewatered for hauling to land disposal, since sufficient land area at the plant sites is not available for lagoons or drying beds. (Refer to Sections 13.5 and 13.3.)

Problem 1:

Sketch a preliminary process flow diagram for a water treatment plant to clarify and disinfect a turbid surface water at a design flow of 50 mgd. Use two identical, parallel, and separate processing lines with rapid mixing, flocculation, sedimentation, filtration, and clear-well storage. The flocculation and sedimentation processes for each line are in the same large rectangular concrete tank with paddle flocculators in baffled compartments ahead of the sedimentation section, and effluent “finger” channels extending into the tank from the outlet end (Figures 10.6 and 10.8a). For each line, use four gravity dual-media coal-sand filters with deep filter boxes to prevent “air binding” and flow control by influent flow splitting for constant-rate filtration (Figure 10.24). The preferred filter bottom is the plastic dual-lateral block underdrain illustrated in Figure 10.20.

On the flow diagram, show the chemicals to be added with alternate points of application. The raw water has a turbidity ranging from 10 to 40 NTU, and in the spring the water contains natural organic matter that creates bad taste and odor and forms trihalomethanes with prechlorination. The fluoride concentration is less than optimum. The treatment plant must meet the EPA rule for surface water disinfection as discussed in .Section 11.28. Sketch a longitudinal cross-sectional view of the flocculation-sedimentation tank. List the design criteria for sizing the flocculation section and specifying paddle flocculators, sizing the sedimentation section and effluent channels, and sizing the fillers. Sketch a plan view of the clear well to ensure compliance with the EPA disinfection rule.

Problem 2:

Sketch a preliminary process flow diagram for a split-treatment lime-soda ash water treatment plant to soften a design flow of 60 mgd. Use six equal-sized flocculator-clarifiers (Figure 10.10). The first-stage flow for excess-lime treatment is expected to be 110 greater than 50% of the raw water. Use eight gravity dual-media coal-sand filters with traditional flow control using rate-of-flow controllers (Figure 10.22). The preferred backwashing system is air scouring prior to water backwash. The clear-well capacity is 6.0 mil gal. The raw water has a hardness of approximately 230 mg/l, iron in the range of 0.2-0.3 mg/l, and a less than optimum concentration of fluoride. On the flow diagram, show the chemicals being added and their points of application. Sketch a cross-sectional view of the filter box showing the wash-water troughs, filler media, and underdrain system. List the design criteria for sizing the flocculator-clarifiers and filters.