o Objective: Asses the feasibility of achieving the disinfection requirement of the primary

effluent overflow during wet weather events through the existing Rouge River Outfall (RRO)

o Methodology: High rate disinfection approach

• Application of high-rate mixing (G value between 500 and 1,000 s-1) in combination with a chemical disinfectant

• Contact/detention time of less than 15 minutes Flow rerouting schemes during wet weather events

Evaluate disinfection alternatives use a Triple Bottom Line (TBL) approach• Peracetic Acid (PAA)• Ultraviolet Irradiation (UV)• Bromine based• Guanidine based• Chlorine/Sodium Hypochlorite

Existing Flow Scheme Proposed Flow Scheme

Balancing Environmental Stewardship and Cost in the Disinfection of Wet Weather Flows in

Water Resource Recovery FacilitiesIsaiah Shapiro, EIT Dimitri Katehis PhD, PE Lin Liang, PE

Overview

Methodology

Bench Scale TestingRecommendatio

no Detroit Sewerage and Water

Department (DWSD)o Largest single-site wastewater

treatment facility Primary Capacity = 1,800 MGD Secondary Capacity = 1,100 to 1,400 MGD Primary Overflow during Wet Weather:

• 400 to 700 MGD o Largest single-site wastewater

treatment facility

o Permit requirement for both secondary effluent and primary effluent overflow:

Fecal Coliform 7-day: 400 cfu/100 mL Fecal Coliform 7-day: 200 cfu/100 mL

o Proposed Rouge River Outfall 2 (RRO-2) to provided 30 minutes of contact time.

o Based on the Triple Bottom Line (TBL) evaluation concluded that chlorination is the most viable option

o Hence, bench scale was conducted to validate the disfection efficiency at a contact time of less than 15 minutes for both secondary effluent and primary effluent under wet weather conditions

o Three scenarios were considered at vary level of chlorine dose: Chlorination of Primary Effluent Chlorination of Chemically Enhance Primary Treatment (CEPT) Chlorination of Secondary Effluent

Results

Primary Effluent Chemically Enhanced Primary Treatment Secondary Effluent

Sample Dose Contact Time

Primary Effluent Up to 20 mg/L <15 minChemically Enhance Primary Treatment (CEPT)

5 mg/L < 15 min

10 mg/L < 10 min

Secondary Effluent 5 mg/L < 10 min

10 mg/L < 5 min

Findings

ExistingFlow Scheme

ProposedFlow Scheme

o Primary Effluent : Bench testing results show that the target f. coli level was not achieved at chlorine doses of 5

or 10 mg/L even at a contact time of 30 minutes. Although, adequate disinfection can be achieved within 10-15 minutes at the highest chlorine dose applied of 20 mg/L.

o Chemically Enhance Primary Treatment: Test results indicate that the f. coli target level can be achieved at between 2 and 15 minutes

depending on the chlorine dose. At doses of 10 mg/L and greater, less than 10 minutes of contact time are adequate to meet disinfection targets.

o Secondary Effluent: Results show that adequate disinfection of secondary effluent occurs between 2 and 10

minutes depending on the chlorine dose. At a dose of 5 mg/L up to 10 minutes of contact time is required to achieve the disinfection target; however at doses of 10 and 20 mg/L, less than 5 minutes of contact time is required.

Table: Results of the bench testing in terms of contact time required to achieve a f. coli count of 200 MPN/100 mL for a given chlorine dose

Outcome

o Based bench scale results and hydraulic modeling analysis, this study concluded that high rate disinfection with chlorine in conjunction with the proposed flow rerouting scheme during wet weather conditions is a viable alternative to the construction of the Rouge River Outfall 2 (RRO-2).

o This approach was recommended to the Detroit Sewerage and Water Department (DWSD)

o Michigan Department of Environmental Quality (MDEQ) has approved disinfection of the secondary effluent through the existing RRO and the excess primary effluent through DRO during wet weather events.

o Averted $70-90 million capital project to construct RRO-2o Estimated capital cost to allow for the flow modifications is $10-15 million

Acknowledgments:

Dan Schechter – DWSD

Nicole Spieles – Greeley and Hansen

Jared Buzo – Greeley and Hansen