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CTC 450 Review

WW Systems Operations

Last Homework

Will replace your lowest homework grade

http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html

http://www.ipcc.ch/

How significant are wastewater treatment plants in contributing to greenhouse gasses?

Due next Monday

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Objectives

Understand the basics with respect to advanced WW treatment

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Two systems

Advanced (tertiary and ww reclamation) Remove phosphorous Convert ammonia to nitrate (nitrification) Convert nitrate to nitrogen (denitrification) Inactivate pathogens Remove heavy metals Remove organic chemicals Remove inorganic salts Eliminate all pathogens

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Limitations-Biological Treatment

Doesn’t remove phosphorous or ammonia Incomplete disinfection Doesn’t remove all toxins Doesn’t remove non-biodegradable soluble

chemicals

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Excess Phosphorous

“Fertilizes” receiving waters Causes algal blooms

Depletes DO Reduces water transparency Releases foul odors Can lose “finer” fish species

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Excess Nitrogen

Ammonia can be toxic to fish/aquatic animals Can increase eutrophication (but usually

phosphorous is limiting)

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Pathogens

Conventional biological treatment Up to 99.9% removal With disinfection up to 99.99% Protozoal cysts and helminth eggs are

resistant

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SS Removal-Advanced

Granular-Media filters (similar to water treatment)

Cloth Media filters Membrane filters

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Pathogen Removal-Advanced

Remove solids first via filtration (pathogens can be protected in the solids)

Chlorination (similar to water treatment)

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Toxic Substance Removal

Toxic-Hazardous to aquatic life or human health

Priority toxic water pollutants-over 100 Evaluating toxicity

Test influent/effluent for specific substances Biomonitor-fathead minnows, water fleas

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Phosphorous Removal

Soluble or organic (organically bound) Conventional treatment removes 20-40% of

phosphorus Example 13-1 Advanced treatments

Chemical-biological Reverse osmosis

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Example 13-1 (Where is the PO43-)

Given the following, trace the inorganic, organic and total phosphorus through a conventional activated-sludge treatment plan.

Assume: Primary clarifier removal of 35% BOD Primary clarifier removal of 50% solids w/ 0.9%

phosphorous Activated sludge

F/M ratio of 0.40 & 2% phosphorus in the sludge Filtrate recycles 5% of the influent phosphorus

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Example 13-1

Parameter Raw After Primary After Secondary

SS 240 120 30

BOD 200 130 30

Inorganic N 22 22 24

Organic N 13 8 2

Total N 35 30 26

Inorganic P 4 4 3

Organic P 3 2 2

Total P 7 6 5

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Example 13-1 (Refer to Figure 13-11)Plant Influent / Primary Influent Total P is 7 mg/l into the plant (100%)

Primary influent is not the same as plant influent because of recycle of dewatered sludge filtrate

Recycled P=5% so influent P=105%

Total P is 7.35 mg/l into the primary

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Example 13-1 (Refer to Figure 13-11)Primary Effluent (2 routes) Sludge (15%)

0.9%*120 mg/l = 1.1 mg/l 1.1/7 = 15%

Effluent (90%); 7.35-1.1=6.25 mg/l total Pi=4.35 (see table; no change in inorganic P) Po=1.90 (6.25-4.35) 6.25/7 = 90%

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Example 13-1 (Refer to Figure 13-11)Secondary Effluent (2 routes) Sludge (20%)

From Fig 11-45 (pg 415) k=0.5 Biological sludge solids=0.5*130 mg/l=65mg/l 2% of 65 mg/l = 1.3 mg/l 1.3/7 = 20%

Effluent (70%); 7.35-1.1=6.25 mg/l total Pi=3.05 (see table; inorganic P is removed)

(6.25-1.3-1.9) Po=1.90 (see table; organic P is not removed) 4.95/7 = 70%

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Example 13-1 (Refer to Figure 13-11)

70% of P remains in the treated WW 30% of P removed in sludge solids

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Chemical-Biological

Chemicals used Alum Iron Salts

Chemical-Biological Chemicals added in primary clarifiers Chemicals added before secondary Chemicals added before final clarifier

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Example 13-2 (Refer to Figure 13-12)Add alum to remove P Alum applied to primary tank

18% of P remains in the treated WW 82% of P removed in sludge solids

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Nitrogen-Atmospheric

Atmospheric Nitrogen to Organic Molecules Nitrogen-fixing bacteria (rhizobia) Live in root nodules of plants (symbiotic relationship) Legumes (beans, clover, peas, peanuts,…)

Plants get nitrogen in a usable form Animals get nitrogen from eating plants Animals excrete nitrogen as a waste product,

usually in the form of ammonia

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Nitrogen

Organic Excreted or Decomposed to ammonia

Ammonia Nitrosomonas oxidize ammonia to nitrite

Nitrite Nitrobacter oxidize nitrite to nitrate

Nitrate Under anaerobic conditions via facultative

heterotrophs, nitrates are converted to nitrogen gas (which escapes into the atmosphere)

Nitrogen gas

New Type of Microbe

Ammonia to nitrogen directly NH4

+ + NO2− → N2 + 2H2O

Anammox (anaerobic ammonium oxidation) Advantage: No oxygen needed Strangeness: anammox bugs also produce

hydrazine (rocket fuel) Bugs store the hydrazine in a dense

membrane structure of fused carbon rings Ref: The Invisible Kingdom, Idan Ben-Barak

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Nitrogen in WW

40% ammonia; 60% is bound in organic matter

Usually not enough oxygen is available to convert to nitrites or nitrates

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Nitrogen Removal-Conventional

Primary sedimentation (15% removal) Biological treatment (another 10%) Remainder is mainly in the form of ammonia

unless oxidation occurs (activated sludge at low BOD loading)

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Nitrogen Removal-Advanced

After biological treatment: Aeration Final settling

Alkalinity is reduced when nitrification takes place; lime or soda ash is added to maintain alkalinity

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Nitrate removal

Nitrate can pollute groundwater Denitrification converts nitrates to nitrogen

gas Process is anaerobic or anoxic Process requires an organic carbon source

(methanol or raw ww) Via recycle, denitrification can be placed

ahead of nitrification

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EBPR-Enhanced Biological Phosphorous Removal Anoxic zone (0.5 to 3 hours detention time)

followed by aerobic zone (6-24 hrs) Helps remove both N and P