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Sewage and Effluent Treatment : 


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What is Sewage or Wastewater? • Liquid wastes containing a variety of pollutants in suspension and solution – Eight General Categories of Water Pollutants •Oxygen Demanding Wastes (Biodegradable Organics) •Disease Causing Agents (pathogens and parasites) •Nutrients • Synthetic Organic Compounds (SOCS) • Inorganic Compounds and minerals (IOCS) • Sediment •Radiation •Heat

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Two General Types of Sewage 1) Sanitary or “Domestic” Sewage Combination of Human and Animal excreta (feces and urine) (“black water”) and “gray water” from washing, bathing and cooking. Human excreta: 100 – 500 g wet weight feces / day 1 – 1.3 l urine / day

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Domestic Sewage Composition • Protein: (40 – 60%) • Carbohydrates: (25 – 50%) • Fats & Oils ( ~ 10% ) •High in microorganisms, High in organic materials

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2) Storm Sewage – Runoff. Carries excreta of animals, fecal matter Other organisms, organic material (leaves, detritus) as well as minerals and metals.

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Wastewater Solids: density particle size level of Volatile Suspended Solids Biochemical Oxygen Demand Temperature Ammonia Nutrient levels

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Wastewater Treatment Considerations Objective: to maintain or improve the quality of the receiving body of water Treatment stages: Preliminary Primary Secondary Tertiary

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Sewage Treatment Primary: Physical Screening or “Bar Filters” Removal of “large” materials Grinding Grinding and sedimentation of “larger” materials Removal from Grit chamber Primary Sedimentation Tanks Decrease velocity of sewage Sedimentation of “suspended solids” Biosolids (sludge) removed from bottom Low density material float (fats, oils) Removed from surface by skimmer arm

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Primary Treatment • Physical Processes • Removes 45 to 85% of solids • Removes about 25 to 50% BOD

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Primary sedimentation (bar screens)

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Secondary: Primary + Biological A) Bio solids from sedimentation and skimming Organic Compounds - Methane Complex Organic Molecules Monomers

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Flow of sewage

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• B) Liquid Effluents from Primary Sedimentation Tanks – Contains soluble organic materials • i) Trickling Filters • ii) Rotating Biological Contactors (RBC’s) •iii) Activated Sludge Processes

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Secondary – Liquid Phase • Trickling Filters –Effluent is sprayed over a bed of filter media, consisting of limestone, granite or plastic – The media develops a “biofilm” consisting of Bacteria, fungi, algae, protozoa, rotifers and various macro invertebrates

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Secondary – Liquid Phase Activated Sludge – Employs an Aeration Tank – Mix effluent with a slurry (liquor) of bacteria & water – Aerate vigorously – Produces “floc” of Biomass – > 300 strains of Bacteria

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Secondary treatment

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Secondary treatment

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Secondary / Tertiary – Liquid Phase Rotating Biological Contactors (RBC’s) Series of plastic discs mounted on a horizontal shaft that rotate slowly through liquid phase wastewater ~ 40% submerged Develop a biofilm further reduce BOD and ammonia

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Tertiary Treatment • Liquid Phase • Final Sand Filtration •Further reduces BOD upto 90%

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Tertiary treatment

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Tertiary treatment

Disposal of treated sewage : 

Disposal of treated sewage Dumped under earth Incineration: into seas Fertilizer for agriculture Reuse of treated sewage

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