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Environmental Engineering 343

Philadelphia University Faculty of Engineering Department of Civil Engineering First Semester, 2013/2014. Environmental Engineering 343. Lecture 9: Wastewater treatment 1. Some Physical and Chemical properties of wastewater 1- Inorganic substances.

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Environmental Engineering 343

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  1. Philadelphia University Faculty of Engineering Department of Civil Engineering First Semester, 2013/2014 Environmental Engineering 343 Lecture 9: Wastewater treatment 1

  2. Some Physical and Chemical properties of wastewater • 1- Inorganic substances A -Nutrients: Two nutrients are essential for the growth of organisms: • Nitrogen • Phosphorus

  3. I- Inorganic substances Nitrogen; Exist in a form of “inorganic”, and “organic nitrogen Measured by TKN “total Kjeldahl Nitrogen; is a measure of the total organic and ammonia nitrogen. Phosphorus ; Exist in a form of “inorganic”, and “organic phosphate Total phosphorus (P) Nitrogen & Phosphorusare essential for building cell

  4. DISSOLVED OXYGEN One of the most important measures of water quality is dissolved oxygen. Oxygen, although poorly soluble in water, is fundamental to aquatic life. Without free dissolved oxygen, streams and lakes become uninhabitable to aerobic organisms, including fish and most invertebrates. It is found that the concentration of DISSOLVED OXYGEN in water is SMALL Dissolved oxygen is inversely proportional to temperature, and the maximum amount of oxygen that can be dissolved in water at 0°C is 14.6 mg/L to 7.6 at 30C.

  5. Dissolved oxygen in water is consumed by the oxidation of dissolved ammonia (NH3)and ammonium ion (NH4+)to form the nitrate ion (NO3⎯). • NH3(aq) + 2O2(aq) + OH-----NO3-(aq) + 2H2O(aq) • The most common substance oxidized by oxygen in water is ORGANIC MATTER OF BIOLOGICAL ORIGIN • Such organic matter (such as dead plant material like polymerized carbohydrate below), is oxidised by dissolved oxygen. • e.g. CH2O+O2(aq) ------ CO2(g) + H2O(aq)

  6. Some Physical and Chemical properties of wastewater • II- organic substances Various parameters are used as a measure of the organic strength of wastewater: • BOD –Biochemical oxygen demand • COD –Chemical oxygen demand • TOC –Total organic carbon • VSS –Volatile suspended solid

  7. II- organic substances1- Biochemical Oxygen Demand- BOD The quantity of oxygen utilized by a mixed population of micro organisms to biologically degrade the organic matter in the wastewater under aerobic condition. BOD is the most important parameter in water pollution control. it is used a measure of organic pollution as a basis for estimating the oxygen Needed for biological processes, as and indicator of process performance Expressed in milligrams of oxygen required per liter of wastewater (mg/L).

  8. Biochemical Oxygen Demand BOD : BOD5: is the amount of dissolved oxygen used up from the water by microorganisms as they break down organic material at 20C over a 5-day periods. • BOD5 for Rivers if > 5 mg/L, they considered polluted • BOD For MWW range 150-1000mg/L

  9. II- organic substances2- chemical oxygen demand -COD - • Determine the amount of oxygen needed to oxidize the organics in a water or wastewater using a strong oxidizing chemical agent- Potassium dichromate rather than using micro-organisms as in BOD • It measures the total organic carbon with the exception of some aromatics such as benzene which are not oxidized in the reaction. • Indirectly measure amount of organic matter in the water sample • Faster determination of oxygen demand in a water sample, than BOD • It takes shorter time ( 2hrs) compared to 5 days for BOD5 • The EU upper limit of 125mg/L for treated wastewaters prior to discharge to rivers

  10. Relation between COD and BOD • COD > BOD • COD ~ ultimate BOD • COD/BOD ~ 2, biodegradable organic • COD >> BOD, non-biodegradable organic

  11. II- organic substances3-total Organic Carbon- TOC • TOC- : measures all carbon as CO2 in mg/L • Inorganic carbon ( HCO3, CO2, CO3, etc) must be removed prior test by acidifying and aerating the sample. • Theoretically the COD is 2.66 times greater than TOC

  12. Composition of WW Pathogens Biodegradable Organics Suspended Solids Soluble organics Bacteria, virus etc. Body waste, food waste rags, paper, biological cells Protein (40-60%) – amino acids Lipids (10%)- fats, oils and grease Carbohydrates 25-50% - sugars starch, cellulose Contain Carbon – exert an oxygen demand

  13. Wastewater Characteristics – Industrial Municipal If Industrial waste characteristics are similar to municipal, the waste is discharged into the municipal sewers. If not, pre-treatment is required Note: although suspended organic materials are biodegradable, In wastewater we consider biodegradable materials to be of the Soluble type. The composition of municipal waste varies seasonally as well as daily. • Wastewater Treatment Plants Note: Unit Operation – contaminants are removed via physical forces Unit Process – contaminants are removed via chemical and or biological processes

  14. Wastewater Treatment Plants Municipal treatment is divided into: Primary, Secondary and Tertiary Primary Treatment – removes solid materials from stream-Large debris may be removed by screens or reduced in size by grinding device. Inorganic solids are removed by the grit chamber Much of the organic suspended solids are removed by sedimentation Primary treatment removes 60% SS and 35% BOD This treatment is still the only treatment for used by many cities around the world

  15. Wastewater Treatment Plants • Secondary Treatment: the major goal is to remove the soluble BOD and SS that escape the primary treatment • Consist of the biological conversion of colloidal organics into biomass – this is then removed by sedimentation • Designed to speed up these natural processes so that the break down of degradable organic pollutants can be achieved in relatively short time periods • May remove > 85% BOD & SS; • Not removing N, P & heavy metals or pathogens • Contact is maintained between the MO and the organics by: • Suspending biomass in a reactor – Activated Sludge System • Passing the wastewater over a film of biomass attached to a solid - Trickling Filter

  16. Wastewater Treatment Plants

  17. Wastewater Treatment Plants • Trickling Filter • Stones are used to increase the surface area for biofilm growth. • Mature biofilms become dislodge due to friction and are washed out of the settling basin with the liquid flow. • Part of the liquid effluent may be recycled to the trickling filter for additional treatment or to maintain hydraulic flow rates

  18. Trickling Filter

  19. Wastewater Treatment Plants • Sludge Digestion • Sludge from primary treatment as well as the secondary clarifier are sent to the sludge digestion unit where it is undergoes anaerobic degradation. • The results are: • Methane – Used for power generation • CO2 • Liquid – contains high organic – recycled through the plant • Inert solids – contains high minerals – soil conditioner/ fertilizer on agricultural lands

  20. Clarifier

  21. Sludge Digester

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