Transcript Tertiary Treatment: Nutrient Removal, Filtration,and

Tertiary Treatment:
Nutrient Removal, Solids Removal, and Disinfection
Treated Wastewater Effluent Contains…
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BOD
(biochemical oxygen demand)
• Carbon matter, depletes O2, causes biomat growth
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TSS
(total suspended solids)
• Depletes O2
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NH3
(ammonia)
• Toxic to fish, depletes O2, a nutrient that promotes biol. growth
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NO3
(nitrate)
• Toxic to babies, drinking water regulated, a nutrient
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TP
(total phosphorus)
• A nutrient
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Pathogens
(bacteria/viruses)
• Disease causing
First, We Must Understand
Wastewater Assimilation
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A site’s ability to handle the amount of liquid or the
amount of pollutants without causing a public health
or environmental health concern
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In-ground or In-stream discharge
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Sometimes, high-quality effluent is necessary
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Protection of sensitive waterbodies, nearby…
• Low BOD
• Low fecal coliform
• Low nutrients (Nitrogen and Phosphorus)
• Or drinking water supplies (groundwater & wells)
“Discharge” Permits
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In-ground dispersal
• ADEM for flows of 10,000 gpd +
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UIC Permit (underground injection control)
• Specifies a certain effluent quantity and quality
• BOD, TSS and groundwater monitoring for NO3
ADPH for smaller systems
Surface dispersal
• Stream Discharge
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NPDES Permit (specifies BOD, TSS, NH3, NO3, TP, etc.)
Disinfection Required
• Spray Irrigation
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NPDES Permit
7-10 day holding pond required
Disinfection Required
Why is tertiary treatment needed?
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To better protect public health and
environment
To provide additional treatment when soils or
receiving waters cannot
Biological Nitrogen Removal
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Uptake into biological cell mass
Nitrification (conversion to Nitrate)
Denitrification (conversion to N2 gas)
Biological Nitrification
Conversion of Ammonia to Nitrite (Nitrosomonas)
NH4+ + 2 O2    NO2- + 2 H+ + H2O
Conversion of Nitrite to Nitrate (Nitrobacter)
NO2- + 0.5 O2    NO3-
Nitrification (cont.)
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For each mg of NH4+ converted…
3.96 mg of O2 are utilized (Need Oxygen)
0.31 mg of new cells are formed
7.01 mg of alkalinity are removed
Nitrification (cont.)
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Nitrifying bacteria are sensitive and
susceptible to a variety of conditions.
The following factors affect nitrification:
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Conc of NH4+ and NO2BOD/TKN ratio (BOD should be gone/removed)
Dissolved oxygen conc (need oxygen)
Temperature
pH (7.5 to 8.6)
Nitrification Processes
Suspended Growth Separate Stage Nitrification
Single State Nitrification
Nitrification Processes
Attached Growth
Attached Growth Nitrification following Act. Sludge
Biological Denitrification
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A modification of aerobic pathways (no oxygen)
• Same bacteria that consume carbon material aerobically
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Denitrifying bacteria obtain energy from the
conversion of NO3- to N2 gas, but
require a carbon source
NO3- + CH3OH + H2CO3   C5H7O2N + N2 + H2O + HCO3Organic matter
Cell mass
Denitrification
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Need low (no) oxygen (< 1 mg/L)
Need carbon source (BOD in Wastewater)
Neutral pH (pH 7)
Conc of nitrate
Denitrification (cont.)
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Separate denitrification reactor
or
Combined Carbon Oxidationnitrification-denitrification reactor
• A series of alternating aerobic and anoxic stages
• Reduces the amount of air needed
• No need for supplemental carbon source
Combined Nitrification/Denitrification
(note alternating regions of aerobic and anoxic)
Phosphorus Removal
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Chemical Precipitation
• Calcium (lime) addition at high pH (>10)
 Reacts with alkalinity
• Alum (Aluminum Sulfate) precipitation
• Iron precipitation
Disinfection
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Selective destruction of diseasecausing organisms
1. Chlorine
2. UV Light
3. Ozone (gas)
Chlorine Disinfection
Liquid chlorine
2. Sodium hypochlorite (tablets)
1.
Note: not allowed to discharge chlorine
(it must be removed after disinfection)
* chlorine removed with either…
a. sulfur dioxide
b. sodium bisulfite
Tablet Chlorinator
(Calcium Hypochlorite)
Chlorine Disinfection
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To be effective…
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Chlorine concentration
Contact time
Proper mixing
Temperature
Number and type of organisms
Chlorine Dose
UV Disinfection
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UV Light
• Specific wavelengths have biocidal
properties (~254 nm)
• Quartz, mercury-vapor lamps
• Cleaning required
• No residual
UV Disinfection
a specific wavelength of light
UV Disinfection
Ozone Disinfection
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O3 a gas, must be generated on-site
Bubbled into a basin
effluent
(or pipeline)
with treated
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Great disinfectant!
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No residual…ozone degrades to oxygen, O2
 Costs More, Need equipment and electricity
Ozone Disinfection
Flow Diagram
Ozone Generation