United Stales September Environmental Protection 1986 Agency Intrachannel Clarification An Update ------- Intrachannel Clarification - An Update Introduction Intrachannel clarifiers have now been funded almost seventy times through the construction grants program, and twelve of these systems were operational as of June 1986. The geographical distribution of these facilities is shown in Table 1. The operational experiences at these facilities have shown that while construction, O&M, and energy savings can be achieved using an intrachannel clarifier, problems may also be experienced especially if proper design criteria are not utilized. An evaluation of several of the operating systems was conducted in early 1986. The evaluation identified several advantages and common problems which are highlighted herein. Many of the systems were in start-up; thus, the problems reported may not be typical of the long-term performance of the systems. The Process The intrachannel clarifier originated as a modification of the oxidation ditch process in which aeration and clarification are conducted in the same basin. A subsequent modification by several manufacturers was to place the clarifier adjacent to the oxidation ditch using common wall construction. Due to the unique means of wastewater flow into and sludge return from these common wall clarifiers, these systems are also included in the assessment of intrachannel clarifiers. The systems funded the most to date have been the United Industries BOAT CLARIFIERS™ and the Armco Environmental Enterprises-Burns and McDonnell Treatment System (BMTS™). The BOAT CLARIFIER™ is constructed of stainless steel and requires little to no modification in design for installation into a conventional oxidation ditch. The clarifier is fabricated independent of the ditch structure and can be placed directly into the channel. Independent construction also allows for surface flow around the unit which eliminates the possibility of floating debris accumulating in the channel. The mixed liquor enters through the stern of the BOAT™ where quiescent conditions exist. As the wastewater flows toward the bow of the BOAT'" the solids settle and EPA Region State II New York New Jersey III Delaware Maryland Virginia West Virginia IV Alabama Florida Kentucky Mississippi South Carolina Tennessee V Illinois Minnesota Ohio VI Arkansas Louisiana Oklahoma Texas VII Iowa Kansas Missouri VIII South Dakota IX Arizona X Idaho Total Manufacturer 1 2 3 4 5 6 7 - Armco Environmental Enterprises - United Industries - EIMCO - Lakeside Equipment Corp. - Lightnin - Innova-Tech - Envirex Manufacturer 1234567 Total 1 1 1 1 1 1 2 3 1 1 6 1 8 4121 3 1 2 2 2 7 1 2 12 2 2 2 2 2 5 2 2 1 1 38 46 2 1 2 Location Kansas City, MO Baton Rouge, LA Salt Lake City, UT Bartlett, IL Rochester, NY Valley Forge, PA Waukesha. Wl 2 4 1 2 1 1 3 4 7 9 8 3 1 2 2 2 7 3 12 4 2 2 2 7 2 1 1 2 1 92 System BMTS1" (Burns & McDonnell Treatment System) BOAT CLARIFIER" Carrousel Intraclarifier Sidewall Separator Draft Tube Channel Pumpless Integral Clarifier Side-Channel Clarifier Table 1. Location of Intrachannel Clarifier Systems in Design, Construction or Operation. ------- re-enter the ditch through sludge ports (Figure 1) The clarified effluent then ftows over a weir m the bow and is removed Irom the ditch Semi-concentrated solids are wasted Irom (he stem of the BOAT" >_ a Location of the BOAT in an Oxidation Ditch • vje Hoped • rS^Oge Return 'ON b Details of the BOAT " Figure 1 BOAT CLARlFIER'" In the BMTS '. the clanfier is constructed as pan of the ditch (Figure 2) The mixed liquor enters the clanfier through baffles in the bottom of the dander As the wastewater flows upward toward submerged orifice launderers. solids settle back down through the baffles and re-enter the ditch Solids wasting is accomplished by wasting the mixed liquor from the ditch Advantages The advantages of intrachannel clanfiers can include reduced construction and O&M costs and a reduction in land area requirements Common wall construction reduces concrete requirements Hydraulic head differences and gravity are used to force wastewater into the clanfier and return sludge back into the ditch Pumping requirements are fhereoy reduced Control over sludge return is eliminated, and sludge age ts easily controlled by wasting mixed liquor from the ditch or from the mtrachannel clanfier Figure 2 BMTS" intracharwei Barrier Start-up Operational Difficulties As of March 1986, many of the systems listed n Table 1 had only recently begun operation The operational problems reported may thus be more representative of start-up problems rather than tang-term design deficiencies At several systems, problems have been encountered with obtaining adequate (low velocity in the oxidation ditch Proper operation o» the danfier is dependent upon adequate wastewater flow velocity around the ditch Several faaktes have reported thai inadequate velocity has caused solids settling in the ditch, resulting in sludge bulking and excess scum accumulation Changes m mixer design or mixing systems have smce corrected velocity problems at some facilities nsuffoent aeration has also occurred n several systems in general, aerator systems when have performed well in conventional oxidation ditch systems provide adequate aeration m mtracnanne* clanfier systems Structura'. prob'ems with submerged propeler mocers have also occurred The ongmal support masts were not strong enough to withstand the vexation of the mixer and masi failure resulted The use of masts has corrected this problem ------- Undersizing of the sludge handling facilities is the final common problem reported. Several systems are experiencing difficulty in wasting sufficient solids to keep the mixed liquor suspended solids (MLSS) concentration and the sludge age at desirable levels. The design of the solids dewatering and removal facilities should take into account the consistency and settleability of the sludge associated with the specific intrachannel system being considered. Design Keys Based upon the operational problems discussed above, it is important to provide: • Adequate mixing and aeration capacity • Scum removal systems where flow barriers occur • Adequate sludge handling capacity • Adequate structural support for the mixing and aeration systems In addition, one manufacturer recommends not using an intrachannel clarifier if the peak-to-average flow ratio exceeds 2.5. Finally before selecting or designing a system, it is recommended that operating systems be contacted. Effluent Quality When adequate flow velocity, aeration, and sludge handling facilities are available, secondary effluent quality is achieved. An effluent quality of 20 to 30 mg/L of BOD and TSS is reasonable to expect. Better effluent qualities have been attained at some systems; however, sufficient data are not available to determine if such treatment levels can be maintained continuously. References A brief review of the systems currently available is presented in the following references: 1, Intrachannel Clarification - State of the Art, by John Zirschky. Presented at the Field Evaluations of I/A Technologies, Technology Transfer Seminar Available from EPA-OMPC. 2. U.S.EPA. 1983. Intrachannel Clarification - A Project Assessment. DMPC-WH595; 401 M Street, SW; Washington, DC 20460,2 page brochure. 3. Anon. 1986. Emerging Technologies with Roots in the Past. Water Engineering and Management. March, 1986. pp.28-31. ------- Mention of trade names or commercial products does not constitute endorsement Prepared by Environmental Resources Management, Inc For additional information on intrachannel clarifiers, the manufacturers listed in Table 1 or EPA regional offices, listed below, may be contacted. EPA-OMP«WH-SM) EPA-WEHL («9| 401 M Shunt SW 26 Wnsl SI Clan Sireat Washington DC 20460 Cincinnati. OH 45268 |3CZt382 736fr7369 (513)569-7931 EPA Region f EPA Region 6 John F Kennedy Fedeisl Baiting 1201 Elm Streel Boston. MA 02203 Daias IK 75270 EPA R«glon 2 EPA Region 7 26 Federal Puza 726 Minnesota Avcnoo New York. NY 10278 Kansas City KS 66101 EPA Roglon J EPA Roglon 8 641 ChWBW. Sb«ot 999 teih Stj«gt Ph,iadftip*wi PA 19107 Denver CO B0202 EPA Region 4 EPA Hogton 9 345 Coixltand Si/cot. NE 21S Frenvxn Sl'egl Ailantii. GA 30365 San Francisco, CA 9410S EPA Xeglon 5 EPA Roglon 10 230 Sculh Oeaitnm Strmt 1200 Wi Avenue Cheapo. 'L £0604 Soattle WA 98101 ------- |