Solids Loading Rate, ppd/sf
Average Annual (50% return), 12 Peak Hour (100% return), 47
Number, 8 Surface Area, 0.44
The wastewater enters the plant through the headworks where it passes through a bar screen, comminutor and Parshal flume. Following the headworks, the wastewater enters the aeration basin where floating surface aerator aerate and mix the sewage. Biological growth in an aeration basin is carried with the effluent to secondary sedimentation. Here the growth settles to the bottom of the tank. It is raked to the center of the tank by rotating arms and flows to the return activated sludge pump station. The clarifier effluent flows by gravity to the infiltration basins where it seeps into the ground. The sludge from the return activated sludge pump station is pumped back into the aeration basin on the anoxic zone side. The return sludge seeds the incoming waste water and increases the BOD removal capacity. Excess sludge is removed from the clarifier of the aeration basin by the waste activated sludge pump. The excess sludge is disposed by spraying on an adjacent forest land with a permanent spray irrigation system. Based on the above information, do the following exercises:
(a) Develop a list of any terms that you are not familiar with and not covered in detail in this volume. Obtain the definitions and an understanding of those terms as they apply to this design case.
(b) Develop a detailed process flowsheet for the plant. Show flow rates and mass flows for major process streams on your system diagram.
(c) Develop an inventory list of the chemicals needed for water conditioning in this plant.
(d) Develop an estimate for the horsepower requirements needed for the return sludge pumps.
(e) Develop a plot plan layout for the plant based on the information given above. Roughly determine the amount of plot area needed for this plant.
(f) Work with your design team to develop a estimate for the cost of installing such a plant. Include in your estimates engineering, site preparation, start-up, and training costs.
(g) Based on the cost estimate you develop, discuss with your team options for financing such an investment.
15. A large settling lagoon (approximately 0.5 ac in area and 75 ft deep) is used to separate a solid waste product whose particle density is roughly 1,700 kg/m3. The density of the dilute slurry is roughly 1,300 kg/m3 and its viscosity is 3.2 cp. The particles are spherical in nature with a 50 wt% size of 210 ^m. If the lagoon is filled to 90% capacity with a solids concentration of 40%, how long will it take to achieve an 85 % separation of sludge from the slurry? First analyze this problem by ignoring any evaporation losses. Next, analyze the problem considering evaporation losses. Assume that pan evaporation data from a local weather station show a yearly average of 53 in./yr. (Note - a standard evaporation pan is about 2 ft in diameter and 36 in. deep).
16. The lagoon described in the above question operates in the summer months at a mean temperature of 65° F. The mean ambient air temperature between the months of June and September is about 75° F. Assuming an average wind velocity of 5 m/s, determine the following: (a) estimated losses due to evaporation; and (b) the concentration of the dilute slurry at then end of four months.
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