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/