5382 001R99002 DEVELOPMENT OF AND APPLICATION OF THE SWIRL AND HELICAL BEND DEVICES FOR COMBINED SEWER OVERFLOW .ABATEMENT AND RUNOFF CONTROL By Richard Field, Chief and Richard P. Traver, Staff Engineer Storm and Combined Sewer Section Municipal Environmental Research Laboratory U.S. Environmental Protection Agency Edison, New Jersey 08S17 at USEPA - Technology Transfer Seminar Series on Combined Sewer Overflow Assessment and Control Procedures Tp-piTr'---!--.—I—I'—-- * - ' -r j_ , , _ ' ' '- ' -^''ton Agency l< ;- s, ' ' , ^ . ' ' ^ Ciiict^o, I^VLIOU eOo04 ------- ------- The Combined Sewer Problem Overflow points are the built in inefficiencies of combined sewers. Untreated overflows from combined sewers are a serious and substantial u Nationwide there are roughly 15,000 to 18,000 combined sewer overflow points.- The 1977 Clean Water Act (PL95-217) critically fosters counter measures, planning and construction for combined sewer overflow pollution. In October 1978, EPA is to submit a report to Congress which in part is to es- timate 1-hp mimber of years nec.sssa-rv, assuming an annual app-mp-n' afi nn nf $5 billion to correct CSO problems. This is strong indication—thatrcorigress recognizes, and their willingness to support combined sewer overflow pollution control. Physical treatment alternatives are primarily applied for suspended solids removal and their associated pollutants from wastestreams, and are of particular importance to storm and combined sewer overflow treatment. Physical treatment systems have demonstrated a capability to handle high and variable influent concentrations and flowrates and operate independ- ent of other treatment facilities, with the exception of treatment and disposal of the sludge/solids residuals. Both the swirl and helical bend units have demonstrated good treatment potential for highly variable. combined sewer overflows. The practice in the USA of designing regulators exclusively for flowrate control or diversion of combined wastewaters to the treatment plant and overflow to receiving waters must be reconsidered. Sewer system management that emphasizes the dual function of combined sewer overflow regulator facilities for improving overflow quality by concentrat- ing wastewater solids to the sanitary interceptor' and diverting excess storm flow to the outfall will pay significant dividends. In 1971 a state-of-the-art report on regulators suggested a British device using VQrtex_flow_patterns could regulate flow and simultaneously remove solids. _This device would utilize the differences in inertia between particles and liquid as well as gravitational forces to effect solids-liquid separation. Based on this concept, studies were conducted for EPA by the American Public Works Association (for Lancaster. PA, EP_A^emp_nstration_granjt_jio_. _ S-802208) in conjunction with the LaSalle Hudrauli_c Laboratories, Quebec _ during 1972-1973 for swirl developement to suit American practice and design optimization for greater solids removal. They produced a universal design for the swirl regulator/concentrator which has been successfully demonstrated in Syracuse, NY; and a large-scale 24 foot demonstration unit in Lancaster, PA. The dual functioning swirl flow regulator/solids separator has shown outstanding potential for simultaneous quality and quantity control. ------- IntegralParts of Swirl Regulator/Concentrator Desim The swirl regulator/concentrator is of simple annular-shaped con- struction and requires no moving parts. An isometric view of the final form of the device is shown in Figure 1. Again, the swirl provides a dual-function — regulating flow by a central circular weir spillway while simultaneously treating combined wastewater by swirl action, which imparts solids/liquid separation. Dry weather flows are diverted through a cunette-like channel in the floor of the chamber into the bottom orifice or foul underflow located near the clear water down shaft to the inter- cepting sewer for subsequent treatment at the municipal plant. During higher flow storm conditions, the low-volume concentrate (3-10% total flow) is diverted via the same bottom orifice leading to the interceptor, and the excess, relatively clear, high-volume supernatant overflows the central circular weir into a downshaft for storage, treatment or discharge to the stream. This device is capable of functioning efficiently over a wide range of CSO rates and has the ability to separate settleable light weight matter and floatable solids at a small fraction of the detention time normally required for primary separation. Figure 1. Isometric view of swirl regulator/concentrator Legend: a - Inlet Ramp b - Flow Deflector c - Scum Ring • d - Overflow Weir a.- Spoilers f - Floatables Trap g - Foul Sewer Outlet h - Floor Gutters i - Dowrishaft . .. - j'- Overflow Weir Plate__ ------- For an essentially static device to perform efficiently under varying flowrates and suspended solids concentrations, special" attention.must be given to the various elements within the chamber. ] ' The Inlet Ramp and Transition, .Sectjpji_siip_uld be designed to introduce^ ' tne~Incommg flow at the bottom or tne chamber and allow solids to enter ; at the lowest position possible. The inflow should be nonturbulent to I prevent solids from being carried directly to the overflow weir along with' the water and the floor of the ramp should be V-shape to allow for self cleaning during periods of low flow. The Flow Deflector is a verticle free standing wall that is an exten- sion of the internal wall of the inlet ramp. It directs the flow around the chamber, setting up the swirl or 'spiral hydraulic patterns, thereby creating a longer particle path and a. greater change for solids separa- tion. The purpose of the Scum Ring^ is to prevent floating solids from over- flowing. It should be extended a minimum of 6 inches below the level of the overflow weir crest. The Overflow Weir and Weir Plate^ connects to a Central Downshaft carrying the overflow liquid to discharge. Its underside acts as a storage cap for floating solids that are directed beneath the weir plate through the Floatables Trap. The verticle element of the weir is extended below the weir plate a.minimum of 18 inches to retain and store floatables. When the liquid level in the chamber decreases after the rainfall, the floatables exit through the _foul sewer underflow._ The Spoilers are radial flow guides that extend from the downshaft to the'scum ring and are vertically mounted onjthe weir plate, which break "up the'turbulent vortex conditions that if allowed to exist would impede proper function. The Foul Sewer Outlet or Underflow is strategically located on the floor of the. ^chamber which allows dry-weather flow and concentrated storm- flow to exit via the interceptor to the municipal treatment plant. It is placed at the point of maximum settleable solids concentration and is designed to reduce the clogging problems that often incapacitate conven- tional regulators. Primary and Secondary Floor Gutters are designed for peak dry-weather flow and are semi-circular in shape to prevent shoaling and solids deposi- tion. An Emergency Side Overflow Weir Assembly is present in the current desing manuals. This allows the swirl to be overdriven to better than twice its design flowrate(QD)and still maintain effective settleable solids removal efficiencies. This is accomplished by short circuiting excess flow and lint aini ng thp intpg-Hty nf thp rham'nA-r'g «;opa-r.ati"" f 1 nw paftP-r-r)<; , . ------- Automated or Manually Actuated Flush RingAssemblies located around the upper portion of the interior wall of the swirl chamber, and beneath ' the floatables trag_ allow fpr_ea_sy jzlean^up^operations following a CSO' e-yent. . . . Swirl device hydraulic models were developed using synthetic materials simulating the particle size distribution and specific gravities of grit and organics found in domestic sewage, CSO, and erosion ladden runoff that resulted in a series of design curves relating anticipated performance to "design flow and other pertinent design parameters. A number of research reports and papers are available from the USEPA Storm and Combined Sewer Section located in Edison, New Jersey. Structurally, swirl regulator/concentrators, swirl degritters, and swirl primary separators incorporate distinctly_different features. Some of these differences are illustrated in Figure 2, The selected configur- ation for each application was a result of consideration of hydraulic principles and testing of a variety of physical models. It is hoped that full-scale demonstrations of the degritter and primary separator will be conducted and that complete technology transfer documentation on the swirl concept will be accomplished. An amendment has been added to the ongoing American Public Works Association grant for additional work to include optimization of the swirl regulator/concentrator design curves to cover smaller treatment inflow capacities than now exist and to also prepare a swirl design textbook on all aspects of the device. Verification of these design curves have been, or will be made, in pilot and prototype facilities which will be discussed later. ^ Swirl cost curves shown in Figure 3 were developed on the basis . of.jCapital costs experienced at Syracuse and full-scale costs estimated by th-eAmerican Public Works Association study. It is assumed that isaintenance and repair requirements will be similar for the swirl regulator independent of size and that the person-hour requirements and associated costs will be 88 hours/year and $l,800/yearT~res^e~ctivelyT~ J ------- '3 - Inlet Ramp b • Flow Deflector c - Scum Ring d • Overflow V/eir and •,Yeir Plats a - Spoilers I - Floataoles Trap g - Foul Sawar Outlet h - Floor Gutters i - Downshart (b) SMIRl. PRIMA3Y SEPARATOR a - Inlet b - c - skirt d - Gutters • - Clear Effluent Outlet f • 3affl» g • Sludga Discharge inlet Deflector Weir and '.Yeir Plates Spoiler e - Floor f - Conical Hooper Figure 2. Isometric configurations of swirl device in three applications ------- 10- o o o o 0 o Note a o Swirl Concentrator rit Removal Swirl Concentrator 90% Grit Removal Swirl Concentrator 100% Grit Removal Swirl Concentrator 90% Grit Removal J_ 50 150 200 100 Discharge - CFS Figure 3. Estimated construction costs — swirl concentrator/regulator Helical Bend Concentrator/Regulators have been modeled and design criteria and comparative cost evaluations have been developed. Although no demonstration projects have been implemented in the United States, helical bends appear practical as in-line regulator devices commensurate with, swirl. The helical bend flow regulator is based on the concept of using the secondary helical motion imparted to fluids at bends when a total angle of approximately 60° is employed. Figure 4 illustrates the device. ------- INLET CHANNEL -OR OVERFLOW '.VE1R OUTLET TO STREAM TRANSITION SECTION 15D STRAIGHT \ SECTION 5D HELICAL BEND 60° NOTES: 1. Scum baffle is not shown. 2. Dry-weather flow shown in channel ,\\ OUTLET TO PLANT Figure 4. Isometric view of helical bend regulator ------- The polluted sewage is drawn to the inner wall. It then _____ _ passes to a_sjs:micircular chajmefTituated" at'a lowef~Tevel~l eliding to the treatment plant. The proportion of the concentrated discharge will depend on the particular design. The overflow passes over a side weir for dis- charge to the receiving waters. Surface debris collects at the end of the chamber and passes over a short flume to join the sewer conveying the flow to the treatment plant. The hydraulic model studies and the computer-mathematical simulation of the helical bend combined sewer overflow regulator indicates that this flash method of solids removal, without use of mechanical appurtenances, can produce excellent efficiencies with reasonable size units in combined sewer systems. Model studies have confirmed the pattern of solids deposition in the deeper channel portion of the helical bend, located along the inner circumference of the bend section, and the ability of dry-weather flows in this restricted deep channel to self-scour the deposited solids into the foul sewer outlet. The basic structural features of significance in the helical bend model are: the inlet from the entrance sewer section to the device; the transistion section from the inlet to the expanded cross section of the straight-run section ahead of the bend; the overflow side weir and scum board; and the foul outlet for the concentrated solids removal in the secondary flow pattern, together with the means for controlling the amount of this underflow going to the treatment works. A design manual was developed which will enable engineers to utilize the helical flow principal for solids removal from combined sewer flows and to properly regulate the overflow of clarified wastewater to receiving waters or points of retention and/or treatment. A demonstration grant has been awarded to the Boston Water and Sewer Commission to test the feasibility of using the swirl regulator/concentrator and the helical bend regulator for removing pollutant loads from a separate 'storm sewer serving an urbanized area. The comparative effectiveness of both units will be monitored by splitting storm sewer effluent into two 10 cfs influent waste streams. The foul concentrated sewer effluents for both devices will be drained into a large receiving sanitary sewer having sufficient hydraulic capacity and rate of flow to adequately transport without deposition the removed solids to a treatment facility. The proposed helical bend regulator is roughly fifty-feet long. Swirls and helicals of the combined sewer overflow regulator variety can be installed on separate storm drains before discharge and the re- sultant concentrate can be stored in relatively small tanks as is shown ------- in Figure 5, since concentrate flow is only a few percent of the total flow. Stored concentrate can later be directed to the sanitary sewer for subsequent treatment during low-flow or dry-weather periods, or if capacity is available in the sanitary interceptor/treatment system, the concentrate may be diverted to it without storage. This method of storm- water control would be cheaper in many instances than building hugh holding reservoirs for untreated runoff, and offers a feasible approach to the treatment of separately sewered urban stormwater. i i! < , ( 1 l SI/ 5 i * — UJ H- < 3— a 5i7 Sil i o] r*— >•> \ ZT ! . ( \ i > < s I - L= f 1 i s > M V V ^^ § OVBR-OVf TREATMENT PLAMT ^**^*^^ ^ r *•«. ^ STORM DRAIN NETY/OKK \ SANITARY JNTEHCEPTOR ~- SMALL CONCENTRATE > TANK s S-.YIRL CHAA13EH S A" " ~ j*^ / X' \ \ ^^ \ \ , "^^ Figure 5. Swirl urban storm runoff pollution control device schematic diagram Site Selection and Design Philosophy __„„_. The development and refinement of the swirl concentrator/regulator has received major emphasis by the Storm and Combined Sewer Section. The unit serves as a compact, static device for removing solids and particulate material from combined and separate storm sewers during storm flow and for primary treatment, erosion control and grit separation. A large scale 40 cfs 24 foot diameter swirl regulator/concentrator has just been com- pleted and is on-line in Lancaster, Pennsylvania. A 10 cfs 12 foot diameter swirl regulator was constructed in Syracuse, New York in June 1974 and evaluated. The performance of the device is good and extremely economical providing the dual function of flow regulation and solids separation. At the present time, the application of the swirl is being implemented by such programs as the 108 Great Lakes Program, 201 Construction Grants Program and the 208 Areawide Waste Treatment Mana- gement Program. But what is the design application philosophy for sizing the swirl for an actual site? __In _St. _Denis, France, a lOjneter diameter swirl regulator has been constructed using' a. 10 year storm return period. In other words, the swirl unit will reach design flow once every 10 ------- years—not very economical! The second problem with the French swirl is that the pump for lifting the underflow from either a wet-weather event or dry-weather flow are incapable of handling the heavy solids loading. A reasonable design philosophy for the sizing of_aswir_l_js.to-base the design on percent of suspend'ed solids removed or percent of flow treated at a specific site over a long- duration, for example, a-.year. This means that a proposed location should have long term jqua_lity/ quantity data_j?or each overflow location. It then becomes an easy jLas arrive"at a mass "loading curvs Tor each rainfall event. By making the correct cost-benefit choice based on incremental removal versus storm flowrate and hopefully receiving water impacts, design flow, which re- lates to swirl chamber size, will readily fall out. Now, let's come back to reality and how things really are I The city engineer, consultant, or regional planning council will be lucky if they have good raingauge data for the catchment area they wish to apply swirl at, much less than quantity of overflows, or even number of overflow occurrences. A rough-cut approach, tp_ see what design flowi (QD) and resulting size swirl would be applicable for a candidate site can~be made utilizing rain- fall intensity records for the area in question.Following the determina- tion of a "ballpark" QQ, and the decision to pursue swirl construction, it is the responsibility of the consultant to make a characterization of the subject catchment utilizing quantity/quality simulation models which are available today in conjunction with some verification data. Only then can a "cost-effective" decision be made as to what will be the actual design flow. An example of this rough-cut methodology can be cited with the ~ Detroit Water and Sewerage Department. An application:.is being pre- pared for submission to the Region V 108 Great Lakes Program for the construction of a swirl regulator/concentrator. Five good years of raingauge data are available for the Schoolcraft Street catchment area. 402 events were recorded of which 115 were discounted as hayinp — flows too small to trigger an overflow. This leaves us with 28f7 ev.eni-s _ over a 5 year period. Utilizing the simplistic equation Q=Cia, flow- rates were determined for each rainfall intensity range and a tabulation of those reoccurring events were tallied. With the desire to treat approximately 70 percent of the overflow events, the rough-cut size was determined to be 40 foot diameter based on a design flow of 100 cfs. This results in having 41 out of 57 events per year at or below QQ. However, with the ability to overdrive the swirl to at least twice its design capacity or 200 cfs, and still effect a reasonable removal efficiency, only 5 events per year are beyond the capabilities of the "rough-cut" swirl treatment capacity. This particular case had an approximate rainfall_intensity of .45 inch/hour and an approximate runoff coefficient of .50. _Again,'this approach is only good enough to get a handle on ------- what size facility would be needed. It is the consultant's responsibility to make the decision on a final Qry after examining sufficient quantity/ quality data for the proposed site. The following section will deal with brief descriptions of existing installations which are utilizing the swirl as a regulator concentrator, degritter, primary separator and erosion control device. Syracuse, New York^ (Prototype Swirl Regulator/Concentrator) A 12 foot diameter swirl combined sewer overlfow regulator was installed at the West Newell Street outfall in Syracuse, New York. Design flood flow to the swirl device was based on maximum carrying capacity of the 24 inch diameter combined, .sewer inlet r .8.9 mgd - and_a_design flow for quality control_(in accordance with scale model investigations) of 6.8 mgd. As mentioned earlier, tests indicate that the device is capable of functioning efficiently over a wide range (10:1) of combined sewer overflow rates, and can effectively separate suspended matter at a small fraction of the detention time required for conventional sedi- mentation or flotation [seconds to minutes as opposed to hours by conventional tanks), At least_50 percent removal of suspended solids and BODg were obtained. ~~ Table__l_ further details suspended solids mass removal and concentration reduction. The capital cost of the 6.8 mgd Syracuse prototype was $55,000 or $8,100/mgd and $1,Odd/acre. Table~ 11 Suspended solids removal Storm No. 2-1974 3-1974 7-1974 10-1974 14-1374 1-1975 2-197.5 6-1973 12-1975 14-1975 15-1975 Swirl Concentrator [Conv. Reau later Mass Loading ka Inf. Eff. fen.5 374 179 52 69 34 51 93 51 34 256 134 48 99 57 42 103" 24 77 463 1 67 64 112 62 45 250 163 33 83 43 42 117 21 82 Average SS oer storm, ma/1 00 b Inf. Err. Rem. 535 245 36 132 141 23 110 90 13 230 164 29 159 1 23 23 374 167 55 342 202 41 342 259 24 291 232 20 121 81 33 115 55 52 Mass Loading ka (V a ' Inf. Underflow Rem. 374 101 27 69 33 48 93 20 22 • 255 49 19 99 26 26 . 103 66 64 i 463 170 34- 112 31 27 250 48 19 83 14 17 117 72 61 L apor the conventional regulator removal calculation, it is assumed that the SS concentration of the foul underflow equals the SS concentration of the inflow. bQata reflecting negative SS removals at tail end of storms not included. ------- However, it should be indicated 'at this point that the Syracuse design closely matched full-pipe flood conditions and could be overly safe for-pollution control; especially for larger outfalls. It is entirely possible to further reduce capital costs to: $l,000/mgd and $200 to $500/acre; in lieu of the thousands of dollars per mgd and acre usually considered for combined sewer overflow control. Denver, Colorado [Pilot Swirl Degritter} A large 6 foot pilot swirl device designed as a grit_remoyal faci1ity. was tested by the Metropolitan Denver Sanitary District.; Figure 6 exhibits a suggested swirl degritter layout for above-the-ground in- stallations. GS1T CHAM8S INLET /— WASH WATEH / OVBROW V»HR SECTION A-A Figure 6. Suggested Swirl Degritter Layout for Above-(he-Ground ' Installation with Inclined Screw Co ------- It was found under testing performed on domestic sanitary waste- water, at times spiked with 0.25mm dry blasting sand to simulate swirl regulator foul concentrate concentration, that the swirl unit performed well. The efficiency of removing grit particles was equal to that of conventional grit removal devices. Scaled up detention times for full size swirl units having volumes one tenth that of conventional tanks, were as low as 20 seconds, whereas detention times of one minute and greater are normal for conventional grit chambers. The small size, high efficiency and absence of moving parts in the basic swirl degritter unit offers economical and operational advantages over conventional grit removal systems. Toronto, Canada (Pilot Swirl Primary Separator) A model study was conducted to determine if the swirl concentrator principle could be used to provide primary treatment to sanitary sewage, combined sewer overflow, and stormwater. In comparison, the swirl regulator/concentrator provides a coarser pre-treatment. The design was then tested on a pilot 12 foot diameter installation with real sewage at Metropolitan Toronto's Humber wastewater treatment plant. The studies provided proof of the applicability of the swirl principle to the function of primary clarifications and verification the design that was based on hydraulic model optimization. In a short detention period solids are deposited by inertial and gravity action and agglomeration mechanisms. Importantly, in storm flow treatment application, suspended solids will be heavier due to high sewer transport velocities and, there- fore, will tend to separate more readily which favors swirl separation over sedimentation. The basic advantages of the swirl clarification principle are that it requires: (1) less land than conventional sedimentation, and (2) no mechanical sludge collection of settled solids in the sludge hopper. The latter advantage is partially achieved by providing a deep conical hopper over the entire flood area, thus imposing an increase in costs. ------- Annual operation_aiidjna,intenance_^:osts are_estimated to be less witH~Ene swirl unit, about $5,000 TeTs for 5 mgd. In urban areas where land is expensive the fact that swirl requires one-half or less the surface area (according to overflow rates) could make it highly competitive. The engineer must consider the costs of construction, operation and maintenance, and land in a cost comparison figure. In the locations where land is at a premium it is advisable to compare the costs of smaller parallel swirl units with their lower operation and maintenance costs against those of conventional tanks. . L 'R6cHester,'New York (Pilot Swirl Primary Separator and Swirl Degritter) Pilot plant treatability studies were undertaken to delineate the treatment alternatives available for control of combined sewer overflow quality under the Monroe County, Division of Pure Waters, Rochester, New York. A major emphasis of the study was development of cost/benefit comparisons of processes that would allow primary-level treatment efficien- cies. These processes were compared relative to their response to treating variable Duality confained sewer overflows. Treatment of the highly con- centrated first-flush overflow was of particular importance. The pilot facilities included a. swirl degritter^ and a swirl primary- separator connected in series as shown in Figure 7, The swirl degritter was 3 feet in diameter and approximately 4 feet in total depth. During normal operations, the overflow from the degritter became the influent for the swirl primary separator. Provisions were also made, however, to allow the influent to bypass the degritter and go directly into the swirl primary separator. The swirl primary separator was 6 feet in diameter and approximately 6 feet in total depth including hopper. Sflim. PRIMARY SEPARATOR CSQ 1NR.QV! ErRUBJT Figure 7. .Schematic Diagram of Swirl Pilot Facility in Rochester, NY ------- The swirl devices were tested at flowrates ranging from 15 to 70 gpm. Using Froude Law scaling relationships, these translate to flows of 0.2 and 1.0 mgd for a 15 foot diameter swirl primary separator and nominal overflow rates of 1,245 to 5,705 gpd/ft, respectively. Mathematical performance models were developed for each system relating suspended solids removal rates to influent flcwrate [scaled by Froude number) and influent concentration. These performance equations were compared to the design curves of the earlier development studies_for swirl devices. Taking differences of particle size distributions'into account, the Rochester data generally supports the design presented by the earlier work. Lancaster, Pennsylvania (Prototype Swirl Regulator/Concentrator with Prototype Degritter in Series for Foul Concentrate)^ The original swirl regulator/concentrator and degritter hydraulic model studies were conducted for the Lancaster, Pennsylvania prototypes. The prototype system as shown in Figure_8 is being supported by an EPA demonstration grant. It is comprised of a 40 cfs, 24 foot main diameter swirl combined sewer overflow regulator/concentrator with a smaller 2 cfs, 8 foot diameter swirl degritter in series to degrit the swirl regulator foul underflow concentrate prior to its entry to the pumps feeding the sanitary interceptor. Upstream gTit^ removal will prevent downstream pump- ing problems, sewer siltation and deposition, and treatment pjroblems in the Lancaster sewerage system. The relatively clear swirl regulator/coricentaT-~ tor overflow will receive disinfection and go directly to the Conestoga River. This swirl system will serve a. drainage area of 215 acres. Figure 8. DemonstTation System Flow Diagram Lancaster, PA ------- The contractor's construction cost proposed for this system, which also contains degritter and control housing, a pilot dicostrainer and various appurtenances and research instrumentation is $669,000. The capital cost of the swirl regulator alone was $50,200 or $l,946/mgd or $233/acre. The Swirl Concentrator as an Erosion Control Device Erosion-sedimentation causes the stripping of land, filling of surface waters, and water pollution. Urbanization caused accelerated erosion rais- ing sediment yields two to three orders of magnitude from 100 - 1000 • ton/mi2/yr to 10,000 - 100,000 ton/mi /yr. At the present national rate of urbanisation, i.e., 4,000 acre/day, erosion/sedimentation must be recog- nized as a major environmental problem. The swirl concentrator has also been adapted for the reduction of erosion runoff sediment and other fine grained debris that results from modern construction activities. Final design specifications are in manual form. In conjunction with a. demonstration near Columbia, South Carolina that tested the effectiveness of various soil stabilizers for erosion control, a. swirl concentrator has been built, place in a highway runoff channel and prepared for field testing. A swirl concentrator with a 6 foot diameter was chosen for the test for its practicality in installation. Both its size and weight were con- sidered reansonable for manipulation by a 4-man team on the steep highway .backs lopes_in the test area. Such a _swirl deviceican_jDe rapidly and ecpnQmi.gaj.ly^ installed at points of erosion runoff by use of ""a" conventional ""cattle watering tank_fitted and equipped with a suitable inlet line, " circuTar overflow weir, a foul sewer outlet and necessary interior appurtenances. The total cost for the South Carolina 5.8 cfs unit was $800 or a cost of $381/acre. This chamber can be readily disassembled, moved to another site, and reinstalled for the treatment of erosion runoff flows. If a permanent structure is desired, it can be fabricated out of concrete. The de-silted, or clarified effluent could be discharge to drainage facilities and disposed of into receiving waters or other points of disposal or use. The collected solids could be discharged through the foul sewer outlet and entrained or collected at suitable points of erosion or for use for other predetermined.purposes. Closing Remarks The swirl principal may be employed anywhere it is desirable to remove solid particles from liquid flows. In the field' of water pollution control this principle could relate to the degritting of sanitary and storm flows and to primary separation, sludge thickening, and the final clarification process. Because the swirl creates a defined mixing pattern it appears feasible to apply a form of the swirl for the simultaneous enhancement of chemical coagulation and disinfection while clarification of raw water for _.pgt_ab_le useage or wastewater is taking p_lace_. The day has now dawned_upon us where jvuge process, multimillion dollar, high structurally intensive ------- recommendations for the treatment of our stormwater, combined sewer over- flows and urban runoff can no longer be made. The swirl is one of the low structurally cost-effective alternatives that is now available to be.broueh±_. into our fight to protect and restore the Nation's receiving waters. ^_ f ------- |