8-14. Logging-computer technology is described in the thirdparagraph under the heading High Efficiency Plumbing Fixtures inSection 8-5. The average decrease in indoor water use ofsingle-family homes in the Tampa Study was 49.6 percent.
9-11. Table 9-2, for normal domestic values BOD = 0.75 850 +0.25 200 = 690 mg/l N = 0.75 30 + 0.25 35 = 31 mg/l P = 0.75 0 +0.25 7 = 1.75 mg/l BOD/N/P = 690/31/1.75 = 100/4.5/0.25 No, thegenerally accepted BOD/N/P = 100/5/1. N may be ok, but wastewateris show on P
Water And Wastewater Technology Hammer.pdf
9-12. From the table, 1500/30/0 = 100/2/0. The waste isinadequate in both N and P. Adding Raw wastewater is 100/17/2 / 3 =33/5.7/1. The total is 133/7.7/1 or 100/5.8/0.8. The wastewaterremains short of P.
9-16. The presence of inhibiting or toxic substances, resultingfrom industrial wastewaters, is often indicated by increasing BODvalues with increasing dilution, lag periods at the beginning ofproperly seeded tests, and erratic test results. Wastewater flow,day of the week, weather and rainfall, and abnormal wastewaterdischarges caused, for example, by the breakdown of pretreatmentfacilities at a major industry are essential for futureinterpretation of recorded testing data.
Very few industrial wastewaters have sufficient biologicalpopulations to perform BOD testing without providing an acclimatedseed. Industrial wastes frequently have high strengths that make itdifficult, or even impossible, to pipette accurately the smallquantity desired for a single test bottle. Wastewaters high insuspended solids may be difficult to mix with water; onealternative is to homogenize the sample in a blender to aiddispersion in the dilution water.
10-1. Combined sewers convey surface runoff from rainfall,domestic wastewater, and industrial discharges in one pipecollection system. Storm sewers are those pipes in a dual networkthat carry only storm runoff and unpolluted water, such asfoundation drainage and cooling water from air conditioning andrefrigeration units. Separate sanitary sewers allow collection ofdomestic and industrial wastewaters for treatment prior todischarge. Combined wastewater flows often exceed treatmentcapacities during rain storms resulting in by-passing untreatedwastewaters to surface watercourses.
10-5. The average sanitary wastewater produced is between 80 and120 gpcd, which includes reasonable infiltration, peak(instantaneous) discharges from residential areas are many timesgreater. Hydraulic design is based on a maximum flow up to 4 timesgreater than the average or by detailed calculation of infiltrationand inflow and wastewater peak flow.
10-11. Figure 10-5 shows three manhole types. The first is astandard manhole used for access for inspection and cleaning. Theyare placed at changes in sewer grade, pipe size or alignment, wherelines intersect, at the end of lines, and at regular intervals notexceeding the length of cleaning tools. Drop manholes are necessaryto lower the elevation of a sewer in a manhole. They are used toprotect workers from the flowing wastewater when entering a manholeand to eliminate nuisance created by solids from splashingwastewater adhering to the walls of the manhole. Drop manholes areused when the vertical separation at the sewers are greater than24. Vortex sewers reduce the water fall, odors, and are typicalwhen separation is greater than six ft.
10-13. The Palmer-Bowlus flume is preferred for measuringwastewater flow in a manhole because it can be installed fortemporary use in a half section of a sewer pipe. A Parshall flumecannot be fitted into a sewer pipe, and weirs are difficult toinstall and collect stringy solids. Correct installation of aPalmer-Bowlus flume produces a smooth upstream flow and swift flowdownstream to indicate free discharge (Section 10-3). Flowmeasurement is made using an ultrasonic sensor mounted above themeasuring location, which is upstream a distance of one-half thediameter of the pipe for the flume (Figure 10-8). A submerged probeis mounted under the flowing water on the bottom of the channel atthe measuring location. A bubbler is attached to a rigid tube withthe outlet end submerged in the flow channel.
10-14. Sewer pipes may be corroded by electrochemical andchemical reactions with the surrounding soil and with chemicals inthe wastewater. Biological activity in the wastewater produceshydrogen sulfide, which when released from solution, is convertedto sulfuric acid at the crown of the pipe. The most commoncorrosion resistant material is VCP and PVC. Protective coatingsinclude coatings of coal tar, vinyl, or epoxy.
10-32. The common types of pumping stations are the submersibleand self-priming as shown in Figure 10-21. In the case of thesubmersible, the pumps are in the wet well. To work on the pumps,they must be lifted to the surface. The self-priming pump islocated at the ground and draws the wastewater up and out of thewet well.
11-1. Wastewater treatment can be viewed as a thickening processsince each unit operation concentrates the remaining solids into asmaller volume of wastewater until the dewatered sludge is a cake.The volume of the raw wastewater of 120 gpcd with less than 0.1%solids is reduced to a filter cake of less than 0.5 pint per capitaper day with 30% solids.
Screening is to remove large solids protecting pumps and othertreatment units; a shredder can perform the same function in smallplants. Pumping is required to lift the wastewater. Grit removal toremove sand and other heavy particulate matter that can causeabrasive wear on mechanical equipment and settle in tanks andpipes. Flow measuring to monitor wastewater flow. Typicalarrangements of preliminary units are illustrated in Figure 11-4.Preliminary treatment does not impact flow, BOD, or suspendedsolids. Primary treatment is to remove settable solids such aspaper, food waste, and the heavy fraction of suspended solids.Primary treatment is intended to remove what suspended solids willsettle under quiescent conditions. A portion of the BOD isassociated and removed with those solids reducing the load onsecondary treatment. A small portion of plant flow is removed withthe solids. Secondary treatment contains processes to biologicallyremove BOD and suspended solids. BOD reduction can be reduced infixed film or suspended growth processes. BOD and suspended solidsare reduced sufficiently for discharge. Solids settled in theSecondary Clarifier are removed with a small portion of the plantflow. 2ff7e9595c
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