Presentation on theme: "CEAC Presentation Friday, April 23, 2010"— Presentation transcript:
1 CEAC Presentation Friday, April 23, 2010 Chris CrockAaron LammersBrent LongAaron Raak
2 IntroductionCarabuela, Ecuador has a Flawed Wastewater Treatment SystemOverloaded Septic TankFailed Leaching FieldWorked with HCJB to Remedy the Problem
3 Project Management Thank you Brent Team Member:Christopher CrockAaron LammersBrent LongAaron RaakConsultant:Tom NewhofClient:Bruce RydbeckAdvisor:Leonard DeRooyThank you BrentFor this project our general team structure involved our client, our advisor, our industrial consultant and our team membersOur client contact was Bruce Rydbeck. Bruce is the Director of Clean Water Projects at HCJB. He brought us the project and has provided us information and insight about Carabuela.Our advisor is Professor De Rooy. He has oversaw our project throughout the design process and has given valuable insight about our structural design.Our industrial consultant is Thomas Newhof from Prein and Newhof. We have met with him twice and he has provided us advice about wastewater treatment design and construction.Our team members include myself (Aaron Lammers), Christopher Crock, Aaron Raak and Brent Long.
4 Project Management Method of Approach Decision Process Task Division Group MeetingMethod of ApproachDecision ProcessTask DivisionIndividualPartnerTeamDivide TasksIndividual ResearchGroup MeetingOur Method of Approach throughout the design process has utilized team, partner and individual work.Our general method and process for making decisions and dividing up tasks can be seen here.To start we would meet as a whole team and discuss our options whether it be options for projects or options for treatment.At the end of our meeting we would divide up tasks to individuals or partners to complete before our next scheduled meeting.We would then research our options individually or with a partner.We would then meet and each option would be presented to the rest of the team. We would discuss and come to a decisionAt the end of the meeting we would once again divide up tasks to individuals or partnersFinally we would complete our individual or partner design whether it be environmental, hydraulic or structuralThis process allowed us to work efficiently by utilizing each team members time while also keeping the rest of the team informed of progress. This process also has a series of checks by the whole group to reduce errors.Divide TasksIndividual Design
5 Design Norms/Criteria Effective TreatmentCulturally AppropriateSustainabilitySite AppropriateLow CostUser FriendlinessLife of DesignEffective TreatmentAppropriate BOD levelsReduction in TSSAppropriate pathogen removal for irrigation reuseCulturally AppropriateLocal materials used for constructionLocal construction methods and practicesProven - similar wastewater treatment casesSustainabilityNo electricityLower levels of sophisticationSite AppropriatePlan view footprintRequired equipment for constructionLow CostCost of constructionCost of maintenanceUser FriendlinessTransparencyTrustworthinessSimplicity in operationLife of DesignLong lasting design
6 Requirements Performance Requirements Water Effluent Coliform count < 1000/100 mLBOD under 2.0 mg/LHelminth eggs < 1 egg/100mL(Who standards set E. coli limit for leafy crops at 1,000/100mL; at this level of treatment other pathogens are assumed to be treated as well)Sludge Effluent1000 E. Coli/gram solids< 1 Helminth egg/ g solids(With alfalfa, requirements need to only meet Class B sludge treatment. The US EPA determined that sludge which goes through one of six processes of significant reduction of pathogens may be applied to crops)Performance Requirements- found from Ecuadorian gov’t and WHOWater Effluent- standards are met for irrigation of leafy crops (alfalfa for grazing will be irrigated)Sludge Effluent- Class B sludge can be used for fertilizer
7 Requirements Functional Requirements Handle the waste of the entire population for 20 yrs (2700 ppl. for projected population)No electricityThe system must fit in 0.5 hectaresNo chemical additivesShall not need experts outside of the village for constructionFunctional Requirements- Design Life will handle a 20 yr. population growth, no electricity, 0.5 hectares of land as a footprint, should not need chemicals for treatment, and should use locals for construction and Operations and Maintenance
8 General System Description Bar RacksScreen for large solids and objectsTwo open channels with inclined barsDewatering plate for screeningsGrit ChamberSettle out large particles (sand, grit, etc.)Two open channels acting as grit chambersVelocity control weirImhoff TankSettle out discrete organic materials and small particlesStore organics for later treatmentAnaerobic digestion of organic solidsTwo tanks and settling chambersStabilization LagoonsOne facultative pond for BOD reductionTwo maturation ponds for further BOD reduction and pathogen removalSludge Drying BedsTreat sludge from Imhoff Tank and Grit ChamberFour sludge drying beds for treatment cyclingBar Screen- remove large solids and objects in waste streamGrit Chamber- remove smaller particles like grit and sandImhoff tank- primary settling and anaerobic digestion (50% of BOD reduced)Sludge stored for six monthsStabilization Ponds- 3 ponds for secondary treatment. Further reduction of BOD and removal/inactivation of pathogensSludge treatment- 6 beds to dewater the sludge from imhoff and grit chamber
9 General System Description Bar RacksGrit ChamberImhoff TankSludge TreatmentStabilization PondsQ = 196 m3/dayBOD = 32 kg/dayTSS = 40 kg/dayBOD = kg/dayTSS = ?Solids = ?IrrigationBOD = 0.51 kg/dayMust satisfy the requirements for water and sludge quality
10 Design Decisions/Alternatives – Bar Rack Bar RacksMesh screen fitted to the inlet of grit chamberDifficult to maintainClogs easilyDamages easilyMesh cage sitting on bottom of channel to catch large objectsComplicated to makeCostly to buildInclined bars that are manually rakedEasy to maintainSimple to constructFairly cost efficientThree alternatives were researchedOf these three the manually cleaned incline bar racks were the best choiceThey were simple to construct, easy to maintain and fairly cost efficient
11 Environmental Design - Bar Rack Important to remove larger solids and particulateBar RackDesign depends mostly on clear space between barsVelocity should be within 0.3—0.6 m/sOpenings between 20—50 mmRack for dewatering screeningsRedundancy accounted forMost important in design was to remove the rags and floatables or larger objects in the waste streamThe openings in the rack would be the main factor for design for certain size objects to be removed20 mm was the choiceThe velocity had to fall with in the min and max range of 0.3—0.6 m/sWidth of the channel was the main factor in this design to allow for this velocity
12 Structural Design - Bar Rack Ultimate moment designUses minimum steel and coverTwo open channels and racks for redundancyTwo depressed steel plates for dewateringThe bar rack structure was designed for redundancy2 channels were constructed, ea. Having a bar rackMinimum reinforcing and cover was needed for the design because of the small size of the chamber
13 Design Decisions/Alternatives – Grit Chamber Vortex Grit ChamberRequires electricityCostly to buyModified Vortex Grit ChamberNot ‘proven technology’Does not require electricityCheap to makeOld Septic TankCheap to modifyToo large to settle only girtDifficult to maintainRectangular Open ChannelEasy to maintainRequires manual laborFairly cheap to construct4 alternatives for design that we researchedThe vortex grit chamber and old septic tank for grit chamber use could be marked off our choices fairly quicklyVortex required electricity to power the pumpsOld septic tank was to large to only allow grit to settle (organics would have also settled in the grit chamber)The modified grit chamber was not proven technology; therefore, we were unable to design and use this mode of treatmentRectangular open channel was the last choice and proved to be easy to maintain, require no electricity, and was fairly cheap to construct
14 Environmental Design – Grit Chamber Important to remove larger solids and particulateGrit ChamberDesign largely depends on the velocity the water (0.3 m/s)Velocity controlled by sutro weirGrit removed is treated in sludge drying bedsRedundancy accounted forVelocity was most important in this design to effectively remove only grit particles.The velocity had to be 0.3 m/sThis was achieved with a sutro weir
15 Structural Design – Grit Chamber Ultimate moment designUses minimum steel and coverTwo open channels and sutro weirs for redundancyAs with the bar racks chamber, the grit chamber was designed with minimum reinforcing and cover because of its small sizeAgain, two chambers were designed to allow for redundancy, and two sutro weirs were also designed
16 Design Decisions/Alternatives – Imhoff Tank Septic TankPros - Simple, Durable, Little SpaceCons – Low efficiency, odors, already failed systemLagoon SystemPros - Simple, Flexible, Little MaintenanceCons – Large open land, odors, mosquitoesImhoff TankPros – Durability, little space, odorless effluentCons – Less simple, regular desludgingSeptic TankThe septic tank is the most common, small scale and decentralized treatment plant, worldwide. It is compact, robust and in comparison to the cost of its construction, extremely efficient. It is basically a sedimentation tank in which settled sludge is stabilized by anaerobic digestion.The main advantages of a septic tank are that they are simple, durable, and require little space because of being underground.The main disadvantages of septic tanks are the low treatment efficiency and the effluent not being odorless.We decided to not use a septic tank because the septic tank that is currently used in Carabuela has lost all treatment ability because of the difficulty to desludge the tank and variable flows. Because of this the confidence of local residents in septic tank effectiveness has most likely been reduced to a point in which septic tanks are no longer appropriate to the location.Lagoon SystemLagoons are artificial lakes. What happens in lagoons closely represents treatment processes which take place in nature.The main advantages of lagoon systems are that they are simple in construction, flexible with respect to degree of treatment, and require little maintenance.The main disadvantages of lagoon systems are that the wastewater pond occupies open land, there is always some odor, can even be stinky, and that mosquitoes are difficult to control.We decided to not use a lagoon because of the limited land that would be available for use as a primary lagoon. We are using a lagoon system for tertiary treatment which occupies all of the available land.Imhoff TankThe Imhoff tank was invented and patented by a German engineering named Karl Imhoff in The tank combines two wastewater treatment processes, sedimentation and biological digestion, into one physical system. The tank consists of a settling compartment above the digestion chamber. Funnel-like baffle walls prevent up-flowing foul sludge particles from getting mixed with the effluent and from causing turbulence. The effluent remains fresh and odorless because the suspended and dissolved solids do not have an opportunity to get in contact with the active sludge to become sour and foul.The main advantages of an Imhoff tank are durability, require little space because of being underground, and have an odorless effluent.The main disadvantages of an Imhoff tank are that it is less simple than a septic tank and that it requires a regular desludging intervalWe decided on using an Imhoff tank because of its small space impact, its odorless effluent and the simpler desludging process as compared to a septic tank. Also our client, Bruce, encouraged us to consider using an Imhoff tank for the primary treatment.
17 Environmental Design – Imhoff Tank Two tanks in one structure for redundancySedimentationBased off Design guides and rules of thumbOverflow Rate of 600 gal/ft2 day (Tchobanoglous)Retention Time of 2 hours (DEWATS)Clearance, overlap, other recommended dimensionsDigestionBased on case study of Imhoff tank in HondurasSludge storage for 1.87 ft3 per resident (3,370 ft3)Up to 6 months of sludge storageThe Environmental design of the Imhoff tank was based off of design guides, case studies and rules of thumb based on experience.The Imhoff tank is designed as two separate tanks in one structure to allow for redundancy and for maintenance. The tank has also been designed to allow for reversal of flow to encourage equal depositing of settled materialsThe design was broken into two main components: Sedimentation and DigestionSedimentationThe sedimentation chamber was designed from design guides and rules of thumb from experience.The overflow rate for each tank was chosen to be 600 gal/ft^2 day to determine the required plan view area for sedimentation.The retention time in each tank was chosen to be 2 hours based on experience from the Decentralized Wastewater Treatment Systems manual. This is to reduce the possibility of the clean water to foul from contact with water from the digestion zone.Clearance, overlap, gas vent areas and freeboard were based on recommendations from various design guides.DigestionThe digestion chamber was designed based on a case study of an Imhoff tank in Honduras. The digestion zone has storage for a sludge volume of 1.87 cubic feet per resident or about 3,370 cubic feet total. This storage was designed for a desludging interval of about 6 months.
18 Structural Design – Imhoff Tank Analysis of forces and moments in tankFinite Element Analysis for Sedimentation wallsStructural analysis for primary load bearing walls and beamsDesigned steel and concrete to hold for highest loadsACI 318M-05 –Metric Building Code and CommentaryMinimum reinforcingMinimum/maximum spacingMinimum coverVertical and horizontal reinforcing based on analysisSimilar to case study tank in HondurasThe structural design of the Imhoff tank was designed using both finite element analysis and structural analysis. These were completed to define the maximum forces and moments that could occur in the tank. Finite Element Analysis was done on the sedimentation chamber walls while a structural analysis was done on the primary load bearing walls and the supporting beams.American Concrete Institute 318M-05 guide was used to determine minimum steel reinforcing, minimum/maximum steel spacing, and minimum concrete cover.Structural Analysis was used to determine the vertical and horizontal reinforcing required to resist the flexural and shear forces on the tank.The design was also generally based on the Imhoff tank in Honduras.Now I’ll pass it off to Brent to talk about lagoons.
20 Environmental Design – Lagoons Used Kinetics, Temperature Factors, and Hydraulic Residence Times to Size LagoonsLoading RatesBOD: 100mg/LHelminth Eggs: 1000 Eggs/LE-Coli: 2e7 Coliforms/100mLReduced RatesBOD: 2.7mg/LHelminth Eggs: 0.10 Eggs/LE-Coli: 915 Coliforms/100mL
21 Structural Design – Lagoons Pond System1 Facultative Ponds2 Maturation PondsDimensions21 meters x 21 metersDepths of 1.5 meters and 0.5 metersRedundancy
22 Design Decisions/Alternatives – Sludge Treatment Open sand drying bedsCovered sand drying bedsDrying lagoonDecision: Open bedsLower costEffective treatment
23 Environmental Design – Sludge Treatment Must hold sludge for several weeks to dewaterMust hold sludge for longer to make it safe for fertilizerDesigned to hold 1 year’s worth of sludge for Imhoff tankArea: 960 m2
24 Structural Design – Sludge Treatment Beds have a layers of sand and gravelShear gates to control sludge flowLow walls of earth or concreteUnderdrain system of PVC pipe
25 Hydraulics Townspeople connect roof drains to sewers A large rainfall event could flush the systemModel showed 15x increase in flow during 10-year eventWill require an overflow weir to prevent flushing
27 Grant Proposal Estimated cost of construction = $25,000 Probably too much for residentsWe are applying to HCJB for a grant to cover the cost of constructionMaintenance costs to be covered by CarabuelaEstimated $14,000/year
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