Introduction
The definitions, sources, flow rates, and fluctuations of sewage in wastewater management. Learn about domestic sewage, dry and wet weather flows, wastewater flow rates, and the relation of sewage to water consumption. Discover the characteristics of sewage, including physical and chemical aspects.
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Presentation Transcript
Definitions: Domestic sewage: it is that liquid which originates from dwellings, business buildings and institutions. Dry weather flow: Domestic + industrial + infiltration. Wet weather flow: Domestic +Industrial + Infiltration + Rain.
Domestic water flow source: Domestic dry weather flow is composed of the waste from sinks, baths, showers, toilets and other sources. Domestic device L/C.day % Cloth washing 34.2 14 Sink 26.5 11 Lavatory faucet 11.4 5 Shower 75.7 31 Toilets 94.6 39 242.3 100%
Wastewater flow rate: Typical discharge are reported in table below Source unit Flow (L/ unit . day) Range Typical Hospital Bed 500-950 650 School student 20-65 40 Cafeteria customer 4-10 6 Hotel Person 150-240 200 Typical home Person 180 -360 280
Sewage relation to water consumption: Sewage is obviously derived from water supplied. The proportion of water consumed which will reach the sewer varies according to the ways the water is consumed. For example: water used for steam boiler or gardens may or may not reach the sewer, on the other hand many industrial plants may have their own supplies but discharge their wastes into the sewers. Usually, sewage may vary from 70 130 % of water consumed.
Fluctuation in sewage flow: 1. Short term variation: The variation in wastewater flow tends to follow a somewhat diurnal pattern as shown in figure below.
Min. flow occur during early morning hours when water consumption is lowest. The first peak flow generally occur in the late morning when wastewater from peak morning water use reach the treatment plant. 2. Seasonal variation: This variation is common in communities with seasonal commercial and industrial activities such as food processing, in resorts communities and in small communities with college or university campuses.
Characteristics of sewage: 1. Physical characteristics: deals with color, odor, temperature. 2. Chemical Characteristics: a. Inorganic constituents: Its concentrations depend on water use. Inorganic constituent may be not removed by treatment such as chlorides, sulfur, heavy metals .etc. b. Organic constituents: include those present in sewage such as fats, proteins, carbohydrate, etc. c. Gases: Hydrogen sulfide, methane, oxygen, NH3, CO2, N2. 3. Biological constituents : Viruses, plants, worms, protozoans.
Biochemical Oxygen Demand (BOD): Bacterial placed in contact with organic material will utilize it as a food source. In the utilization process, the organic matter will eventually be oxidized to stable end products such as CO2and water. The amount of oxygen used in this process is called the Biochemical Oxygen Demand and is considered to be a measure of the organic content of the waste water. The BOD determination has been standarized to measure the amount of oxygen utilized by microorganisms in the stabilization of wastewater for 5 days at 200C . For domestic sewage, the 5 day value or BOD5represents approximately 2/3 of the demand which would be exerted if all the biologically oxidizable material were in fact oxidized.
Chemical Oxygen demand (COD): The COD test is used to measure the content of organic matter in wastewater that contains compounds that are toxic to biological life. No clear correlation exists between BOD and COD in general but at a specific treatment plant a correlation is possible. For untreated domestic waste BOD5/ COD ratio varies from (0.4) (0.8) and COD value varies from 250 1000 mg/L.
Total organic Carbon (TOC): The sample injected into a furnace where it is oxidized. The CO2 produced is measured by infrared analysis and converted instrumentally to organic carbon content. TOC for domestic sewage is = 80 290 mg/L. The major obstacle to widespread use of this test is the cost of the equipment and the skill necessary in its operation.
