CHEE 370 Waste Treatment Processes Lecture #5-Wastewater Treatment Process.
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Transcript of CHEE 370 Waste Treatment Processes Lecture #5-Wastewater Treatment Process.
CHEE 370Waste Treatment
Processes
Lecture #5-Wastewater Treatment Process
Review:
WW Characterization Solids content
TS, TSS, TDS, VS (organic), FS (inorganic) Organic content
BOD, COD, TOC, ThOD Micro-organisms
Total coliform, fecal coliform Toxicity
Acute toxicity (LC50), Chronic toxicity Nutrients
TKN, NH3, TP, ortho-phosphate Flowrates
Hydraulic flowrates (peak and min), Loadings
Municipal WW Effluent (MWWE) Guidelines and Regulations
http://www.ec.gc.ca/water
Management of MWWE
More than 3500 WWTP in Canada No real “standard” Treatment strategies range from no treatment to
state of the art In many systems, during wet weather the
combined sewer outflow (CSO) of the sewer system and storm water system often exceeds total hydraulic capacity of the plant Kingston has this particular problem!!!
Problems with aging infrastructure
http://www.ec.gc.ca/soer-ree/English/soer/MWWE1.cfm
http://www.ec.gc.ca/soer-ree/English/soer/MWWE1.cfm
http://www.ec.gc.ca/soer-ree/English/soer/MWWE1.cfm
Data for 1999
Legislation
Municipalities are responsible for WW management
Provincial governments are responsible for regulating the operation of WWTP
There is currently no federal legislation on municipal WW effluent Fisheries Act Canadian Environmental Protection Act, 1999
Proposed Canada-wide Strategy for the Management of MWWE
Drafted Oct. 2007
Facility Size Categories
Flow (Q) [m3/d]
Very Small Q ≤ 500
Small 500 < Q ≤ 2500
Medium 2500 < Q ≤ 17500
Large 17500 < Q ≤ 50000
Very Large
Q > 50000
National Performance Standards
Effluent from all treatment plants must satisfy: CBOD5 ≤ 25 mg/L TSS ≤ 25 mg/L Total Residual Chlorine (TRC) ≤ 0.02 mg/L Ammonia: Based on acute and chronic toxicity
TSS and CBOD5 values can be averaged:
Very Small - Medium WWTP: Quarterly Large or Very Large WWTP: Monthly
Consider changes in TSS and BOD5 as a function of time of day and season!
Review:
Toxicity Testing - Bioassays
LC50:
Median lethal concentration for 50% of the organisms The diluted concentration of the wastewater that will kill 50% of
the test population in a fixed time period
NOEC: No Observed Effect Concentration The highest concentration of diluted wastewater that has no
observable effect on the test organisms
ACUTE TOXICITY
CHRONIC TOXICITY
Acute Testing Requirement
Rainbow Trout Test Swim-up fry or fingerling (0.3 - 2.5 g) 96-h single concentration test (100% and control) 10 fish/test Three replicates=> To accommodate death arising from
natural causes!
Daphnia Magna Test “Water flea” - small freshwater crustacean 48-h single concentration test (100% and control) 30 daphnids/test Three replicates
http://www.etc-cte.ec.gc.ca/organization/bmd/bmd_publist_e.html
Daphnid
Acute Toxicity Testing
Failure = when the effluent at 100% concentration kills more than 50% of the test organisms in the specified time period
LC50 = 100%
Acute Toxicity Testing
What happens if a test fails?
“Toxicity Reduction Evaluation” (TRE)
Try to identify the source of the toxicity
Calculate the LC50 using a dilution series of the effluent within 5 days of a failed test Minimum 5 test concentrations plus a control Typical range: 100x (full strength) down to 1x
(dilute) of the effluent
Acute Toxicity Units (TUA)
TUA = 100/LC50
“Effluent Discharge Objectives” (EDO)
EDO = 1 TUA
Measured “At the end of the pipe”
LC50 = 100%
Chronic Toxicity
Testing considers the local environment
Requirements are influenced by site-specific factors Type of waterway (river, stream, lake, etc.) Spawning location, recreational facilities etc.
Effects on growth, reproduction, and swimming Fathead minnow larvae and Ceriodaphnia dubia 7-day test is typical
Chronic Toxicity
TUC = 100/NOEC
EDO = 1TUC for diluted sample
Measured at “the end of the mixing zone” Not at wastewater discharge point from plant!
Dilution factor based on the type of receiving waterway Rivers and streams - Max 1:100 Dilution Lakes, reservoirs, enclosed bays - Max 1:10 Dilution
NOEC = 100%for diluted sample
Monitoring Frequencies
Facility Size
CBOD5, TSS,
Coliform, TKN, TP, NH3
TRC Acute Toxicity
Chronic Toxicity
Very Small Monthly Daily n/a n/a
Small Monthly Daily Quarterly Quarterly
Medium Every 2 weeks Daily Quarterly Quarterly
Large Weekly 2x / day Monthly Monthly
Very Large Daily (5-7 days/week)
3x / day Monthly Monthly
Flowrates also monitored throughout the day
Guidelines and Regulations:Other Contaminants
Federal Discharge Guidelines Fecal Coliforms: 100 colonies per 100 mL Total Coliforms: 1000 colonies per 100 mL TP: 1.0 mg-P/L Ammonia: 1 mg/L Nitrate: 10 mg/L pH: 6 to 9 Temperature - not to alter the ambient water
temperature by more than 1 ºC
Federal Discharge Guidelines
Cadmium: 0.005 mg/mL Copper: 0.2 mg/mL Lead: 0 mg/mL (detection limit) Mercury: 0 mg/mL (detection limit) Nickel: 0.3 mg/mL Zinc: 0.5 mg/mL PCBs and dioxins: 0 mg/mL (detection limit)
PCBs are serious carcinogens!
http://toxics.usgs.gov/highlights/tracing_wastewater.html
Overview of Unit Operations in WW Treatment
Typical Municipal WW
TSS: 220 mg/L VSS: 165 mg/L BOD5: 220 mg/L COD: 500 mg/L TKN: 40 mg-N/L Ammonia: 25 mg-N/L TP: 8 mg-P/L Ortho-phosphate: 5 mg-P/L
http://www.ec.gc.ca/water/
Types of Reactors Used in WW Treatment
Batch Continuously stirred tank reactor (CSTR) CSTR with recycle Plug flow Plug flow with recycle CSTR in series Fluidized-bed Packed-bed
http://www.city.saskatoon.sk.ca/