cso control at saco

8/8/2019 CSO Control at Saco

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CSO Control, Treatment and Disinfection at Saco Wastewater Treatment

Plant using Advanced Vortex Technologies

Robert Andoh1*

, Howard Carter2, Christopher Osterrieder

3

1 Hydro International, 94 Hutchins Drive, Portland, Maine, 0410, USA2 Saco Water Pollution Control Facility, 300 Main Street, Saco, ME 040723

Deluca-Hoffman Associates Inc, 778 Main St Ste 8, South Portland, ME 04106

*To whom correspondence should be addressed. Email:[email protected]

ABSTRACT

The use of novel CSO control, treatment and disinfection systems based on advanced vortex technologiesincluding Vortex Flow Controls (VFC) and Hydrodynamic Vortex Separator (HDVS) that enable,Screening, Grit Removal, Sedimentation and Disinfection to be accomplished in one vessel is described.The application of the technologies at the Saco Wastewater Treatment Plant involves a new generation of

HDVS and vortex flow controls that regulate wet-weather flows to control maximum flows to the existingwastewater treatment plant to avoid hydraulic overloading and the diversion of excess combined sewageflows to the new CSO treatment facility.

The wet-weather treatment facility utilizes an advanced HDVS that incorporates a non-powered, self-activating and self-cleansing CSO floatables screening system; with the captured pollutants comprisingsewer debris and solids including sediments, settleable organic solids and floatables, being returned to theheadworks at the treatment plant and the clarified, screened and disinfected overflow being discharged tothe receiving environment (Saco River), after de-chlorination.

The ability to perform several essential unit processes (i.e. Screening, Grit Removal, Sedimentation and

Disinfection) all in one vessel resulted in significant savings in the overall project scheme costs onaccount of the more compact design of the advanced HDVS system coupled with the elimination ofadditional tanks and vessels that would have been required with the conventional approach. Analyticalresults from post-construction compliance monitoring have confirmed the efficacy of the advanced vortextechnologies.

KEYWORDS: CSO, Satellite Treatment, Vortex Flow Control, Disinfection, Hydrodynamic Separators

INTRODUCTION

The Clean Water Act and subsequent amendments has mandated that communities must solve their CSOdischarge problems. Communities across the nation are coming under increasing pressure to implementschemes to deal with increased volumes of combined sewage and other wet-weather impacted flows.

Approaches to resolving CSO problems tend to be site or community specific and involve a matrix ofsolutions ranging from increasing the conveyance capacity of municipal sewer systems, either by buildingnew, separated sewers, treating CSO at satellite sites within the collection system or by significantlyexpanding end-of-the-pipe treatment plants to treat the excess wet-weather flows. These approaches,particularly where they involve tunneling schemes and significant new collection systems infrastructure,can be very expensive and in the case of separating sewers, if the separated stormwater does not receive


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water quality improvements, this may not necessarily address the problem of environmental degradationand poor water quality resulting from the discharge of untreated wet-weather flows into receiving waters.

Current estimates of the costs required to address CSO issues are on the rise. An EPA assessment in 2006noted that utilities had spent $6 billion in the preceding three years to control CSOs, reducing the annualCSO volume from 1 trillion gallons to about 850 billion gallons. The same report estimates an additional$50 billion will be needed to solve the CSO problem. This is confirmed by the Clean Watershed NeedsSurvey report to Congress (EPA, 2008) which estimates more than $54 billion in CSO needs. Private

estimates put the figure much higher, up to $100 billion.

With the reduction in available Federal Funding sources such as the Construction Grants program and theClean Water State Revolving Fund (CWSRF), communities now have to bear the brunt of the costsassociated with CSO projects. Most of these costs are passed on to residents in the form of sewer fees, butother costs are also affecting individual communities already struggling to pay for education, publicsafety, environmental clean-ups and community programs. Many sewer separation projects that windmiles through busy downtown areas run well into the tens and hundreds of millions of dollars. Separatingsewers in the busy downtown areas also extracts a cost on the community in the form of closed streets formonths on end. Communities are therefore looking for more cost-effective ways of addressing the CSOissue whilst meeting consent limits for their discharges.

The City of Saco in Maine was faced with similar challenges and embarked on the implementation of aCSO Abatement Master plan. The Master plan incorporated a series of milestone projects including sewerseparation, flow slipping and primary treatment of combined sewage at the treatment plant. This resultedin the elimination of seven of the citys eight CSO sites and implementation of a wet-weather treatmentstage at the eighth CSO site located at the wastewater treatment plant to reach the knee of the curve andsatisfy the level of abatement required under the approved CSO Master plan.

The application of vortex technology at Saco utilizes vortex flow regulators in the upstream diversionchambers to regulate maximum flows to the existing wastewater treatment plant in order to avoidhydraulic overloading and the diversion of excess combined sewage flows to the new CSO treatment

facility. The new facility utilizes an advanced hydrodynamic vortex separator (HDVS) that incorporates anovel non-powered, self-activating and self-cleansing CSO floatables screening system and accomplishesprimary treatment equivalency, disinfection, floatables capture and grit removal all in one vessel. Theunderflow from the CSO facility comprising sewer debris and solids including grit, sediments, settleableorganic solids and floatables, is returned to the headworks at the treatment plant and the clarified,screened and disinfected overflow is discharged to the receiving environment (Saco River) after de-chlorination.

CSO CONTROL AND TREATMENT AT SACO

The Saco CSO control and treatment scheme involved the construction of a new 24 influent line at FrontStreet to transport peak wet-weather flows to the local wastewater treatment plant and the installation of anovel CSO treatment system that utilizes advanced vortex technology for controlling and treating excesswet-weather flows. The system installed at Saco includes the Hydro International Storm King Overflowwith Swirl-Cleanse Screen, Grit King Separator and Reg-U-Flo Vortex Valve units to provideimproved handling, management and treatment of CSO and wet-weather flows to meet the MaineDepartment of Environmental Protections primary treatment equivalency for wastewater dischargestandards.

An aerial view of the site together with an overview of the flow scheme is shown in Figure 1. Thisincludes the location of the flow diversion chambers (housing the vortex flow controls), layout of existing


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treatment components and the new CSO treatment and Grit Removal systems. A vortex flow controldevice (22 Type C Reg-U-Flo Valve) installed in an upstream diversion chamber, regulates the peakwet-weather discharges that arrive at the treatment plant site through the new 24 influent line. This newsewer line follows the path depicted by the arrows labeled Raw Sewage To Treatment Plant in Figure 1and terminates in the Diversion Structure that houses the other Reg-U-Flo Vortex Valve.

Figure 1: Aerial View and Flow Scheme at Saco Wastewater Treatment Plant

This second diversion chamber which is sited at the treatment works facility, incorporates a high leveloverflow weir (see Figure 2) such that under dry weather flow conditions, the wastewater continuesunimpeded to full treatment whereas under wet-weather conditions, the vortex valve regulates themaximum amount of combined sewage entering the existing wastewater treatment facilities with excessflows being diverted over the high level weir into the new CSO treatment facility. Figure 2 shows a closeup schematic of the CSO and wet-weather treatment facility and how this has been integrated into theexisting wastewater treatment works.

The new CSO and wet-weather treatment facility utilizes an advanced hydrodynamic vortex separator(HDVS) that incorporates a novel non-powered, self-activating and self-cleansing CSO floatablesscreening system and accomplishes primary treatment equivalency, disinfection, floatables capture andgrit removal all in the one vessel (labeled Storm King with Swirl Cleanse Screen in Figure 2). Theunderflow from the CSO facility (labeled Pumped underflow from Storm King) which comprisessewer debris and solids including grit, sediments, settleable organic solids and floatables, is returned tothe headworks at the treatment plant and the clarified, screened and disinfected overflow is discharged tothe receiving environment (Saco River) following de-chlorination.

To Clarifiers

GritHandling

Dischargeto Saco River

RawSewageToTreatmentPlant

Saco River

Grit Removal

12 ft. Grit King

Diversion Structure

Reg-U-Flo Vortex Valve

CSO Treatment

22 ft. Storm King

To Clarifiers

GritHandling



Saco River

Grit Removal

12 ft. Grit King

Diversion Structure


CSO Treatment

22 ft. Storm King

Location of Upstream Diversion

Chamber Housing 22 Type CReg-U-Flo Vortex Valve

To Clarifiers

GritHandling



Saco River

Grit Removal

12 ft. Grit King

Diversion Structure


CSO Treatment

22 ft. Storm King

To Clarifiers

GritHandling



Saco River

Grit Removal

12 ft. Grit King

Diversion Structure


CSO Treatment

22 ft. Storm King

Location of Upstream Diversion

Chamber Housing 22 Type CReg-U-Flo Vortex Valve


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PROCESS COMPONENTS

Flow Control

Conventional flow control devices such as orifice plates, throttle pipes and penstocks have traditionallybeen used for controlling flows either within collection systems or at wastewater treatment works. Thefundamental equation governing the operating characteristics of most flow control devices is given byEquation 1:

This formula shows that in order to reduce flow rate (Q) for a given operating head (h), you either need toreduce the cross sectional area (A) of the outlet or the co-efficient of discharge (Cd) for the flow controldevice. Compared with vortex valves which have variable co-efficient(s) of discharge ranging from ~0.15to ~0.3 depending on their geometry and design, orifice plates and other conventional flow controldevices such as penstocks and float valves have a fixed co-efficient of discharge (typically ~ 0.6). This

Flow Diversion

Chamber

Grit King SeparatorStorm King with Swirl

Cleanse Screen

De-chlorination

Chamber

Flow to WwTWfrom Westside of City(New 24 Sewer)

Pumped underflowfrom Storm King

Flow to CSO Treatment

Flow to Full Treatment

Effluent from CSOTreatment to Saco River

Reg-U-FloVortex Valve

Mesh Screen

Air Brake Siphon

Weir Wall

Headworks

Flow Meter

Flow to WwTWfrom Eastside of City

Flow Diversion

Chamber

Grit King SeparatorStorm King with Swirl

Cleanse Screen

De-chlorination

Chamber

Flow to WwTWfrom Westside of City(New 24 Sewer)

Pumped underflowfrom Storm King

Flow to CSO Treatment

Flow to Full Treatment

Effluent from CSOTreatment to Saco River

Reg-U-FloVortex Valve

Mesh Screen

Air Brake Siphon

Weir Wall

Headworks

Flow Meter

Flow to WwTWfrom Eastside of City

Figure 2: Schematic of CSO Treatment Facility

Where Q = Continuation flow in m3/s

Cd = Coefficient of discharge

A = Cross-sectional area of outlet (m2)

g = Acceleration due to gravity (m/s2)

h = Differential head across flow control (m)

Equation 1ghACdQ 2=


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means that for an equivalent duty (i.e. h and Q), the conventional flow control devices require muchsmaller aperture sizes to reduce flow rates compared with vortex flow controls.

Devices such as penstocks and float valves achieve the desired control by reducing the cross-sectionalarea of the flow path by means of either a movable slide or gate. This poses a problem in that the smallerthe outlet aperture, the more prone the control device is to the risks of blockages occurring. Float valvesand other control devices with moving parts are also susceptible to fouling (e.g. ragging) particularlywhen utilized in flow environments laden with debris (e.g. wastewater and CSO). This can significantly

affect their discharge characteristics. Ideally therefore, flow control should be achieved without movingparts and with devices that have the largest possible outlet aperture thereby minimizing risks of blockage.

Vortex ValveVortex flow controls are proprietary gravity operated self-activating passive flow control devices with nomoving parts that control flows without reducing the physical cross-sectional area of the outlet aperture ofthe flow control device. These valves are typically designed with a snail, circular or conical shaped voluteand act like natural hydraulic brakes. High flows initiate a vortex within the volute of the valve, which inturn restricts the flow of water out of the device.

These devices typically have two distinct modes of operation. In the first mode termedpre-initiation, the

valve acts as a large orifice where water and debris pass directly from its inlet to its outlet unimpeded. Thepre-initiation mode tends to occur under low to moderate flow conditions and allows relatively higherflows (compared to an equivalent orifice or penstock) to be discharged at low operating heads (see Figure3). This is because the vortex valve has an outlet cross-sectional area that is typically four to six timesgreater than that of the equivalent orifice or penstock for similar duties. This has the benefit oftransporting a lot more of the first foul flush on to treatment and also reducing the amount of anyequalization storage volume required at the treatment plant.

Figure 3: Head Discharge Characteristics of Vortex Valve and Orifice Plates

For example in Figure 3, which presents the head discharge characteristics for an eight (8) inch vortexvalve, eight (8) inch orifice and four (4) inch orifice, shows that both the four (4) inch orifice and eight (8)

0

1

2

3

4

5

6

0 500 1000 1500 2000

Flow (gpm)

Hea

d(ft)

8" Vortex Valve

8" Orifice Plate

4" Orifice Plate

Pre-initiation

Post-initiation


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inch vortex valve, are capable of controlling flows to less than 500 gpm up to six (6) feet of operatinghead whereas an eight (8) inch orifice discharges in excess of 1500 gpm at six (6) feet of operating head.In the low operating head ranges (i.e. less than say two (2) feet), the eight (8) inch vortex valve howeverdischarges significantly greater flows than the four (4) inch orifice without necessarily exceeding thedesired maximum discharge rate of 500 gpm. At one (1) foot of head the eight (8) inch vortex valvedischarges in excess of 400 gpm compared with less than 200 gpm for the four (4) inch orifice. The eight(8) inch vortex valve appears to initially operate in a similar fashion to an eight (8) inch orifice during itspre-initiation stage and when the post-initiation stage is fully developed, it operates more like a four (4)

inch orifice.

In the post-initiation mode of operation, the discharge from the vortex valve outlet is in the form of aspiraling flow with a central core of entrained air. This pattern of flow is different from the jet emittedfrom an orifice or partly closed penstock (or slide gate valve) in that it does not contain the same highenergy per unit of cross-sectional area. The vortex valve is therefore less likely to cause scour andstructural damage to downstream structures and the entrained air also provides water quality benefits byaerating the flow and helping to prevent the onset of septicity especially in foul or combined sewer flows.

Units typically have outline dimensions that range from less than eight (8) inches to over 15 feet in length.The vortex valve installed in the diversion chamber at the wastewater treatment works site is a 16 inches

type CH unit designed to allow the maximum flow of 5.2 mgd to pass onto the treatment facility.

Advanced Hydrodynamic SeparatorFlows in excess of the designed maximum flow to treatment discharge over the weir wall in the diversionstructure (see Figure 2) and are diverted to the new CSO treatment unit. This unit is a 22ft diameter StormKing with Swirl-Cleanse Screen that has been designed to provide primary treatment equivalency anddisinfection for combined sewage flows. The Storm King with Swirl-Cleanse Screen is an advancedHydrodynamic Vortex Separator (HDVS) which enables Grit Removal, Sedimentation, Screening andDisinfection to be accomplished in one vessel before the treated overflows are discharged into the SacoRiver after de-chlorination. The unit has a peak design flow of 5.6mgd though it is capable ofhydraulically coping with flows in excess of this.

This device also has no moving parts but relies on optimized geometrical arrangements of flow modifyingcomponents and baffles to produce highly stabilized rotary flow regimes conducive to high-ratesedimentation, effective macro-mixing and contacting for high-rate chemical disinfection. The systemalso incorporates a non-powered, self-activating and self-cleansing CSO floatables control mesh screeningsystem. The mesh has an aperture of 4mm (1/6) which ensures that the CSO discharges receive finescreening and that effluents are free of sewer debris and aesthetic solids greater than 4mm (1/6) in twodimensions.

HDVS are known for their effectiveness as high-rate solids liquid separation devices (Andoh et al., 2002)and their use as effective contact vessels for the disinfection of CSOs has been demonstrated at full scale

in Columbus, Georgia in the USA, where over 5 years of intensive monitoring has confirmed theirefficacy as both high rate solids liquid separators and contact vessels for chemical disinfection ofcombined sewage (Turner et al., 2000).

In common with other gravity and inertial based separation devices, HDVSs are not very effective atcapturing neutrally buoyant solids. Neutrally buoyant solids are typically the aesthetically offensivematerials such as panty liners; condoms, etc. which have a specific gravity close to that of the suspendingfluid (water in this instance). In more recent times, these devices have been further developed withimproved variants that enable additional unit processes to occur in the same vessel such as theincorporation of the Swirl-Cleanse Screen for floatables capture.


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The Swirl-Cleanse Screen utilizes a novel air-brake Siphon to effect a cyclical backwashing processwhich keeps the mesh screen clean. The incorporation of an integral self-cleansing screening system hasresulted in a CSO treatment device that captures a more complete spectrum of the Sewer Solids and otheraesthetic pollutants in combined sewage. A more comprehensive description of the technology and itsapplications can be found elsewhere (Andoh et al., 2002). Swirl-Cleanse Screens in combination withHDVSs are currently being installed at locations where water quality improvements are required inaddition to the control of floatables and other aesthetic pollutants.

Settleable solids, detritus (including fecal solids, food debris etc.), grit and sewer sediments (and theirassociated pollutants) are captured in the underflow within the sump region of the device. The unitinstalled at Saco incorporates an integral underflow pump which conveys the captured pollutants in arelatively small underflow (typically less than 10% of the peak design flow) to the head works (inlet) ofthe existing wastewater treatment facility where a new 12ft diameter in-situ Grit King advanced vortexhydrodynamic separator unit separates the grit from the flows to full treatment (see Figure 2).

DISINFECTION AND REGULATORY COMPLIANCE

An important aspect of the Saco scheme was the need to demonstrate the effectiveness of the technologynot just for high-rate solids liquid separation but also for high-rate chemical disinfection. Earlier work at

Liverpool John Moores University in the UK had demonstrated that the macro flow regime in the HDVSbehaves like that of a number of tanks in series which means that the device has very little short circuitingand can be described as a plug-flow mixing reactor. This work further demonstrated that effectiveinactivation of microorganisms can be achieved in the HDVS using a chemical disinfectant (Alkhaddar etal., 2000).

A Water Environment Research Foundation report which describes results of long-term (more than 5years) monitoring of a full-scale implementation of an HDVS (Storm King) for CSO treatment atColumbus, Georgia, concluded that effective high-rate chemical disinfection can be achieved with aminimum contact time of 3-mintes (WERF, 2003). This observation would appear to be corroborated byresearch work undertaken at Cardiff University in the UK utilizing Computational Fluid Dynamics

(CFD).

Computational Fluid Dynamics (CFD)

Advances in Computational Fluid Dynamic (CFD) modeling have resulted in a significant increase in theability to predict the performance of hydraulic structures and different tank/vessel configurations. CFDcan be used to provide predictions of the flow patterns, solids separation performance and residence timedistributions of sewer ancillary structures including CSO chambers (Harwood and Saul, 1996; Faram andAndoh, 2000; Stovin and Saul, 2000;Jarman et al., 2008). There are now many general purpose CFDpackages that are capable of modeling fluid flow and chemical reactions and are usually based on finitevolume or finite difference methods to solve the governing fluid flow equations.

Figure 4 shows an example of a CFD output for an advanced HDVS highlighting the fact that the macro-mixing flow regime in the active region is fully developed after around 192 seconds (i.e. less than 5minutes); (Egarr, 2005a). This suggests that the hydrodynamic flow regime in an HDVS results inrelatively long internal flow paths.

CFD modeling has also been undertaken for the assessment of full-scale HDVSs for which RTDcharacterizations have previously been obtained for a range of laboratory conditions (Egarr et al., 2005b).The CFD outputs were validated against the experimental results, with good correspondence being found.This work has subsequently been extended further using the results from the CFD modeling and batchinactivation results from the disinfection of secondary treated wastewater, to ascertain the theoreticalperformance of a HDVS as a contact vessel for disinfection (Egarr et al., 2005c).


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Figure 4: CFD outputs showing evolution of mixing regime in an advanced HDVS (Egarr, 2005a)

One benefit of using CFD compared to physical experimental techniques is that it provides detailedinsights into the mechanics of a systems operation. Work undertaken by Egarr and other demonstrates

the usefulness of CFD as a tool to provide insights and the potential for predicting the disinfectionperformance of different HDVS configurations when they are utilized as continuous flow systems appliedto disinfection of wastewater.

Disinfection in the Advanced Hydrodynamic SeparatorThe effectiveness of the flow regime as a macro-mixing contact chamber, conducive to high-rate chemicaldisinfection achievable in less than 5-minutes compared with the often applied rule of thumb designvalue of 15-minutes, has been demonstrated after more than six years of full-scale monitoring atColumbus, Georgia in the USA (Boner et al., 1993; Turner et al., 2000 and WEF, 2003).

Results from the WERF study coupled with CFD simulations were utilized to demonstrate to the

regulatory authorities that in addition to its proven solids control efficacy, effective high-rate disinfectioncould be achieved in less than 5-minutes contact time compared with the norm of 15-minutes.

This resulted in significant savings in the size of vessel required for chemical disinfection and meant therewas no need to provide a separate chamber or vessel on site for chemical disinfection leading to furthercost savings. The Storm King with Swirl-Cleanse unit at Saco has an effective theoretical retentiontime of 8-minutes at the design flow.

MONITORING RESULTS

The CSO treatment facility at Saco has been subjected to compliance monitoring as part of its consent


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requirements; this monitoring has included a period in the spring of 2007 when a series of storm eventscaused widespread flooding in a number of New England States. Figure 5 shows the observed daily flowsduring events when overflows occurred from the CSO treatment facility. Also shown in Figure 5 is theperiod in April 2007 when overflows occurred for five (5) successive days. The highest daily flowobserved was close to 4 mgd which would mean the likelihood of the unit seeing instantaneous peakflows well in excess of 4 mgd.

Figure 5: Measured Flow to CSO Treatment Facility at Saco

Figure 6: Measured BOD at Saco CSO Treatment Facility

5 successive days of

Overflow events

0

1

2

3

4

5

1/8/2007

2/8/2007

3/8/2007

4/8/2007

5/8/2007

6/8/2007

7/8/2007

8/8/2007

9/8/2007

10/8/2007

11/8/2007

Date

Flow

(mgd)

Daily Flow (mgd)

0

5

10

15

20

25

30

35

4/15/2007

4/16/2007

4/17/2007

4/18/2007

4/19/2007

Date

Concen

tra

tion

(mg

/l)

0

1

2

3

4

5

Flow

(mg

d)

Daily Flow (mgd)

5 successive days of

Overflow events

0

1

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3

4

5

1/8/2007

2/8/2007

3/8/2007

4/8/2007

5/8/2007

6/8/2007

7/8/2007

8/8/2007

9/8/2007

10/8/2007

11/8/2007

Date

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(mgd)

Daily Flow (mgd)

0

5

10

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20

25

30

35

4/15/2007

4/16/2007

4/17/2007

4/18/2007

4/19/2007

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(mg

/l)

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(mg

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1/1/2007

1/31/2007

3/2/2007

4/1/2007

5/1/2007

5/31/2007

6/30/2007

7/30/2007

8/29/2007

9/28/2007

10/28/2007

11/27/2007

12/27/2007

1/26/2008

Date

Concen

tration

(mg

/l)

Influent BODEffluent BOD

0

20

40

60

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100

120140

160

4/15/2007

4/16/2007

4/17/2007

4/18/2007

4/19/2007

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tra

tion

(mg

/l)

0

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3

4

5

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(mg

d)

Influent BOD

Effluent BOD

Daily Flow (mgd)

0

50

100

150

200

250

1/1/2007

1/31/2007

3/2/2007

4/1/2007

5/1/2007

5/31/2007

6/30/2007

7/30/2007

8/29/2007

9/28/2007

10/28/2007

11/27/2007

12/27/2007

1/26/2008

Date

Concen

tration

(mg

/l)

Influent BODEffluent BOD

0

20

40

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100

120140

160

4/15/2007

4/16/2007

4/17/2007

4/18/2007

4/19/2007

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tra

tion

(mg

/l)

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5

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(mg

d)

Influent BOD

Effluent BOD

Daily Flow (mgd)


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In addition to the flow monitoring, samples of the influent to; and effluent from the advanced HDVS wereanalyzed for a number of parameters including the Total BOD and Total Suspended Solids (TSS). Resultsfor these are shown in Figure 6 and 7 for BOD and TSS respectively. The observed influent and effluentconcentrations for the period in April (when there were five successive days of overflow) are alsohighlighted in Figures 6 and 7.

Solids removals as measured by TSS and BOD have been observed to be consistently high even duringthe period of successive overflows in April. An interesting characteristic of the HDVS is its ability toproduce a fairly consistent effluent quality from a variable influent feed. As would be anticipated, there isa general reduction in influent solids concentration during the April events which would indicate adilution effect with the prolonged period of wet-weather flows. Details for the April 2007 events arepresented in Table 1 and include the overflow duration. This shows a three day period (16th to 18th April2007) where the unit operated continuously without cessation in overflows. This represents an unusualperiod of sustained loading.

Table 1: Data for the five successive days of overflows in April 2007.

Date Influent

BOD

(mg/l)

Effluent

BOD

(mg/l)

BOD

Removal

(%)

Influent

TSS

(mg/l)

Effluent

TSS

(mg/l)

TSS

Removal

(%)

Daily

Flow

(mgd)

Duration

(Hrs)

4/15/2007 138 24 83 183 53 72 0.2663 4

4/16/2007 83 18 78 110 49 56 3.889 24

4/17/2007 66 16 76 91 55 40 3.134 24

4/18/2007 52 17 67 78 27 65 2.93 24

4/19/2007 70 31 56 93 35 62 1.031 21

The average influent TSS and BOD observed during the April events are 111.0 mg/l and 81.8 mg/lrespectively with corresponding average effluent TSS and BOD of43.8 mg/l and 21.2 mg/l respectively.

0

50

100

150

200

250

300

350

1/1/2007

1/31/2007

3/2/2007

4/1/2007

5/1/2007

5/31/2007

6/30/2007

7/30/2007

8/29/2007

9/28/2007

10/28/2007

11/27/2007

12/27/2007

1/26/2008

Date

Concentration(mg/l)

Influent TSS

Effluent TSS

020406080

100120140160180200

4/15/2007

4/16/2007

4/17/2007

4/18/2007

4/19/2007

Date

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tra

tion

(mg

/l)

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(mg

d)

Influent TSS

Effluent TSS

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350

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1/31/2007

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7/30/2007

8/29/2007

9/28/2007

10/28/2007

11/27/2007

12/27/2007

1/26/2008

Date

Concentration(mg/l)

Influent TSS

Effluent TSS

020406080

100120140160180200

4/15/2007

4/16/2007

4/17/2007

4/18/2007

4/19/2007

Date

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tra

tion

(mg

/l)

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(mg

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Effluent TSS

Daily Flow (mgd)

Figure 7: Measured TSS at Saco CSO Treatment Facility


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Monitoring results for the entire sample sets for overflow events occurring in 2007 give overall averageinfluent TSS and BOD of130.3 mg/l and 86.3 mg/l respectively with corresponding average effluent TSSand BOD of48.8 mg/l and 29.4 mg/l respectively. Table 2 provides annual summaries up to date (i.e. upuntil the first week in April 2010).

Table 2: Data summaries from January 2007 to April 2010.

Year Number

of CSOEvents

Avg.

InfluentBOD

(mg/l)

Avg.

EffluentBOD

(mg/l)

BOD

Removal(%)

Avg.

InfluentTSS

(mg/l)

Avg.

EffluentTSS

(mg/l)

TSS

Removal(%)

Avg.

FecalCount

Total

Precipitation(inches)

2007 19 86.3 29.4 66 130.3 48.8 63 110 22.2

2008 21 84.5 30.1 64 110.2 34.8 68 51 28.6

2009 21 51.0 34.2 33 93.2 47.5 49 129 29.5

2010* 15 43 28.3 34 67.3 27.3 59 74 17.5

*Note: 2010 is not a full years worth of data.

These results show average removals in excess of those anticipated for primary treatment equivalency ofcombined sewage, particularly for the BOD. It is surmised that the higher BOD removals observed maybe a function of the additional effects of the fine screen mesh (see Figure 8). The fecal numbers are also

below the consent requirements for the site.

These results prove the device is performing very well in conformance with its consent requirements evenunder a notable period of sustained loading.

Figure 8: View of Storm King

with Swirl Cleanse Screen and Integral

Pump Sump

Inflow to CSO Treatment Unit

Clarified, Screened and

Disinfected Overflow

Novel Screening System

(Swirl-Cleanse Screen)

Integral Sump with Underflow Pump

Inflow to CSO Treatment Unit

Clarified, Screened and

Disinfected Overflow

Novel Screening System

(Swirl-Cleanse Screen)

Integral Sump with Underflow Pump


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SUMMARY

Faced with the challenge of addressing Combined Sewer Overflow (CSO) issues, the City of Saco,Maine, adopted an approach which involved improving the transport and management of excess wet-weather flows by implementing a scheme that applied advanced vortex technologies for both flow controland water quality improvement.

The flow control technology implemented utilized vortex valves, which operate by converting upstream

water energy into rotary motion within the device and when the vortex flow pattern is fully established,this has the effect of creating a back pressure which opposes the through flow. This throttling effectresults in the device behaving like an orifice or penstock with a significantly smaller opening than that ofthe physical size of the outlet of the vortex valve (typically less than ) meaning that the cross-sectionalarea of the outlet aperture for a vortex valve can normally be greater than four (4) times that of theequivalent conventional flow control.

A novel system for CSO treatment based around advanced vortex technology implemented at the Sacowastewater treatment plant has proven to be very effective for the control and treatment of combinedsewage and wet-weather related flows. The core of the system in use at Saco (see Figure 8) is a furtherdevelopment and enhancement of hydrodynamic vortex separation technology that incorporates a novel

self-cleansing screening system for floatables capture, an integral pump sump for returning capturedsolids to the wastewater treatment plant and utilization of the same vessel for high-rate chemicaldisinfection.

CONCLUSIONS

The application of advanced vortex technology for optimal CSO control and treatment at Saco utilizesvortex flow controls in diversion chambers to regulate maximum flows to the existing wastewatertreatment plant to avoid hydraulic overloading and the diversion of excess combined sewage and wet-weather flows to the new CSO treatment facility where disinfection and solids removals to meet primarytreatment equivalency standards are accomplished.

The ability to perform several essential unit processes (i.e. Grit Removal, Sedimentation, Screening andDisinfection) all in one vessel resulted in significant savings in the overall project scheme costs onaccount of the more compact design of the advanced HDVS system coupled with the elimination ofadditional tanks and vessels that would have been required with the conventional approach.

Results of compliance monitoring over several years has confirmed the efficacy of the advanced vortextechnologies and their ability to consistently achieve disinfection and primary treatment equivalencystandards even under stress loading conditions.

The technologies deployed at Saco provide CSO communities with an option to achieve compliance with

their CSO abatement commitments in a cost efficient manner.

REFERENCES

Alkhaddar, R. M., Higgins, P. R. and Phipps, D. A. 2000, Characterisation for in situ disinfection of ahydrodynamic vortex separator (HDVS).Proceedings of the1stWorld Congress of theInternational Water Association, Paris, 3-7 July.

Andoh, R.Y.G., Hides, S.P. and Saul, A.J., 2002, Improving Water Quality using Hydrodynamic VortexSeparators, 9ICUD Conference, Portland, Oregon, USA.


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Boner, M.C., Hides, S.P., Turner, B.G. (1993). High rate treatment of Combined Sewer Overflows inColumbus, Georgia.Proceedings of the Sixth International Conference on Urban Storm Drainage,12-16 September, pp 1671-1676.

Egarr, D.A. (2005a) Studies of fluidic systems for environmental applications. PhD Thesis, University ofWales, Cardiff School of Engineering, UK.

Egarr, D.A., Faram, M.G., ODoherty, T., Phipps, D.A. and Syred, N. (2005b). Computational fluid

dynamic prediction of the residence time distribution of a prototype hydrodynamic vortexseparator operating with a base flow component, Journal of Process Mechanical Engineering,Proc. Instn. Mech. Engrs, Vol 219, Part E, pp 53-67.

Egarr, D.A., Faram, M.G., Guymer, I., ODoherty, T. and Syred, N. (2005c). Use of Computational FluidDynamics to assess the disinfection performance of a Combined Sewer Overflow treatmentchamber. 10th Int. Conf. on Urban Drainage, Copenhagen, Denmark, 21-26 August.

Faram, M.G. and Andoh, R.Y.G., 2000, Application of Simulation and Predictive Techniques for theEvaluation of Hydrodynamic Separators, Wastewater Treatment: Standards and Technologies toMeet the Challenges of the 21st Century, CIWEM/AETT Millennium Conf., Leeds, UK, 4-6 April,

pp 223-230.

EPA, 2008, Clean Watersheds Needs Survey 2004 Report to Congress

Harwood, R. and Saul, A.J. (1996). CFD and novel technology in combined sewer overflow. 7th Int.Conf. on Urban Storm Drainage, Hannover, Germany.

Jarman, D.S, Faram, M.G., Butler, D., Tabor, G., Stovin, V.R., Burt, D. and Throp, E. (2008).Computational fluid dynamics as a tool for urban drainage system analysis: A review ofapplications and best practice. 11th Int. Conf. on Urban Drainage, Edinburgh, UK, 31 August 5September.

Stovin, V.R. and Saul, A.J. (2000). Computational fluid dynamics and the design of sewage storagechambers. Journal of the Chartered Institution of Water and Environment Management14(2):103-110.

Turner B. G., Arnett, C.J., and Boner M. 2000, Performance Testing of combined SewerOverflow Control Technologies Demonstrates Chemical and Non-Chemical DisinfectionAlternatives and Satisfies EPA CSO PolicyDisinfection 2000: Disinfection of Wastes in the NewMillennium, WEF, March 2000, USA.

WERF, 2003,Peer Review: Wet Weather Demonstration Project in Columbus, Georgia, Co published:

Water Environment Research Foundation, Alexander, VA, and IWA Publishing, London, UK,2003.

cso control at saco

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