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![San Mateo’s Recycled Water Demand
● San Mateo population: 100,023 (2012) → 104,750 (2017)
● The San Mateo Water Market Survey
○ Estimated Recycled Water Demand in 2012:
● Concluded recycling process should produce 4 mgd
Usage
Number of
Customers (Sites)
Average Annual
Demand [afy]
Estimated MDD
[mgd]
Urban Irrigation 95 1,231 2.3
Commercial/Industrial 9 31 0.04
Total 106 1,263 2.34](https://image.slidesharecdn.com/fin-181116160059/85/Fin-midterm-presentation-13-320.jpg)
![Influent Water Parameters
Mark Burke: Laboratory Analyst, City of San Mateo WWTP
● August 2017- August 2018 WWTP Effluent Values
● Salinity: 2,000 ppm (mg/L)
● TSS: 7.3 mg/L
Ammonia
[mg/L]
Total
Kjeldahl
Nitrogen
[mg/L]
Nitrate
[mg/L]
Nitrite
[mg/L]
Dissolved
Reactive
Phosphate
[mg/L]
Total
Phosphorus
[mg/L]
Nickel
[ug/L]
Copper
[ug/L]
Cyanide
[ug/L]
Mercury
[ug/L]
Average 32.68 35.58 2.34 0.90 3.72 3.45 5.03 5.95 0.74 0.00
Max 43.00 51.90 18.00 2.50 31.00 5.60 21.00 8.50 2.10 0.01](https://image.slidesharecdn.com/fin-181116160059/85/Fin-midterm-presentation-14-320.jpg)
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Fin. midterm presentation
- 1. Senior Design: Water Reusein San Mateo Biosystems Engineering Capstone Design Clemson University Elena Miyasato, Kylie Bednarick, Lillian Kome, and Amanda Dara
- 2. Outline ● Introduction ○ Background ○Problem Statement ○ Goals and Scope ○ Constraints and Considerations ● Literature Review ○ Water Recycling ○ Our partner: City of San Mateo ● Design ○ Process Overview ○ Treatment Processes and Results ○ Equations ○ Final Thoughts Hetch Hetchy Reservoir
- 3. Background Client: The Cityof San Mateo, California The Current Situation: The Opportunity: Design a recycled wastewater treatment process
- 4. Recognition of Problem ●Current water usage in California is not sustainable ○ Growing population → Increase in water demand ○ Climate change → Decrease in water security ■ Extreme droughts ■ San Mateo: Snowpack that feeds reservoir shrinking & less reliable ○ Current water practices → Inefficient water usage
- 5. Goals and Scope Goal:Design a water recycling process that can produce reusable water from the liquid effluent of the San Mateo WWTP Scope: ● Meet water quality standards ● Determine uses for recycled water ● Determine uses for by-products ● Analyze economic viability ● Promote positive perception of recycled water
- 6. Fundamentals of Sustainability Environmental ●Decrease the demand of water sourced from Hetch Hetchy ● Limit wastewater effluent into San Francisco Bay Social ● Improve the perception of wastewater reuse ● Increase confidence in water security for future generations Economic ● Cost effective water resource ● Affordable to consumer
- 7. Considered Constraints Design TeamConstraints: Producing a Design Proposal ● Time ● Modeling Resources Process Constraints: ● Water reuse requirements ● Budget for the plant & distribution ● High cost can prohibit some people from accessing water ● Space ● Logistics
- 8. Introduction to LiteratureReview Required Information ● Recycled Water Demand and Perception ● Water Treatment Process ● Regulations for Recycled Water ● Water Quality coming from San Mateo Wastewater Treatment Plant
- 9. Water Recycling Water Recycling:The process of treating wastewater to the extent that it can be reused for beneficial purposes ● Uses liquid effluent of municipal wastewater treatment ● Purple pipes used for non-potable recycled water Levels of water treatment: ● Non-potable ○ Primary treatment ○ Secondary treatment ○ Tertiary treatment ● Potable
- 10. Recycled Water Usage ●World Leader: Israel ○ Recycles over 85% of its wastewater ○ Used for agricultural irrigation ● USA Leader: Florida ○ Recycles 50% of its wastewater ○ Used for landscape & golf course irrigation ● California has been using recycled water since 1912 ○ Current top uses: ■ 40% Agricultural irrigation ■ 20% Landscape and golf course irrigation ■ 12% Groundwater recharge
- 11. Water Quality Standardsin CA ● Title 22: California Code of Regulations ○ Defines 3 types of recycled water based on level of treatment ■ Disinfected Secondary-2.2 ■ Disinfected Secondary-23 ■ Disinfected Tertiary ● “Filtered and subsequently disinfected wastewater” that meets given disinfection criteria ○ Chlorine contact time and total coliform bacteria ○ Defines uses for each type of water
- 12. Disinfected Tertiary WaterUses ● Disinfected tertiary recycled water can be used for all non-potable uses in CA ○ Unrestricted irrigation ■ Food crops, pastures, golf courses, parks, school grounds, etc. ○ Industrial or commercial cooling ■ Cooling towers, evaporative condensers, etc ○ Decorative fountains & ponds ○ Flushing toilets ○ Artificial snow ○ Fire fighting and control
- 13. San Mateo’s RecycledWater Demand ● San Mateo population: 100,023 (2012) → 104,750 (2017) ● The San Mateo Water Market Survey ○ Estimated Recycled Water Demand in 2012: ● Concluded recycling process should produce 4 mgd Usage Number of Customers (Sites) Average Annual Demand [afy] Estimated MDD [mgd] Urban Irrigation 95 1,231 2.3 Commercial/Industrial 9 31 0.04 Total 106 1,263 2.34
- 14. Influent Water Parameters MarkBurke: Laboratory Analyst, City of San Mateo WWTP ● August 2017- August 2018 WWTP Effluent Values ● Salinity: 2,000 ppm (mg/L) ● TSS: 7.3 mg/L Ammonia [mg/L] Total Kjeldahl Nitrogen [mg/L] Nitrate [mg/L] Nitrite [mg/L] Dissolved Reactive Phosphate [mg/L] Total Phosphorus [mg/L] Nickel [ug/L] Copper [ug/L] Cyanide [ug/L] Mercury [ug/L] Average 32.68 35.58 2.34 0.90 3.72 3.45 5.03 5.95 0.74 0.00 Max 43.00 51.90 18.00 2.50 31.00 5.60 21.00 8.50 2.10 0.01
- 15. Overview of Process ProcessObjectives: 1. Remove suspended solids (TSS) 2. Reduce concentration of dissolved chemicals and salts 3. Disinfect effluent Our Components: 1. Granular Media Filtration (GMF) → Remove TSS; serve as pretreatment for filtration 2. Nanofiltration (NF) → Remove TDS (including salts), organics, and microorganisms 3. Chlorination → Ensure disinfection
- 16.
- 17.
- 18. 1. Media FiltrationConsiderations ● Purpose: removes suspended solids by passing water through a porous medium ○ Mechanism of retention: adsorption and straining ○ Treated effluent has low turbidity and low organics concentration ● Factors: medium, number of layers, layer depth, filtration rate, pore size ● Selection: Dual-medium GMF Anthracite coal Silica sand Gravel
- 19. 1. Granular MediaFiltration: Design Hydraulics modeling: head and water levels to conduct flow Design Parameters: ● Influent Flow Rate: 5.56 MGD ● Filtration Rate: 200 L/m2-min ● Water Loss: 4% to backwash ● Area: 74 m2 ● Anthracite depth: 7.2 cm ● Sand Depth: 3.6 cm
- 20. 1. Granular MediaFiltration: Flow SuperPro Modeling: ● General SuperPro goal ● Objective 1: remove TSS ● Undetectable bacteria levels compared to large flow rate Constituent TSS Fecal Coliform Bacteria Concentration 7.3 mg/L 36.7 MPN/100 mL Flow Rate 6.41 kg/h 3.22 x 1010 MPN/h Concentration 1.46 mg/L ~0 Flow Rate 1.28 kg/h ~0 Requirement 1-4 mg/L 2.2 MPN/100 mL InfluentEffluent
- 21. 2. Membrane FiltrationConsiderations ● Purpose: removes total dissolved solids ○ Total dissolved solids (TDS) includes minerals, salts, metals, cations, and anions ○ Drinking water: 500 mg/L TDS (EPA), Ocean water: ~35,000 mg/L TDS ● Options: Microfiltration, Ultrafiltration, Nanofiltration (spiral-wound or hollow- tube), Electrodialysis Reversal, Reverse Osmosis ● Selection: Nanofiltration
- 22. 2. Nanofiltration: Design ●Allows monovalent ions to pass, rejects larger molecules and highly charged ions ● Pore size: 1 nm ● Spiral-wound vs. Hollow tube configurations ● Applications include: ○ Softening, removing heavy metals, removing salts from brackish water
- 23. 2. Nanofiltration: Flow ●Assumed TDS is equivalent to salinity ○ Salinity of 2,000 ppm (mg/L) represents TDS ○ Sodium Chloride will be tracked in SuperPro Constituent Salinity Ammonia Phosphorus Concentration (mg/L) 2,000 32.68 3.45 Flow Rate (kg/h) 1,698.10 27.75 2.93 Concentration (mg/L) 139.70 2.29 0.24 Flow Rate (kg/h) 118.47 1.94 0.20 Waste Flow Rate (kg/h) 1,579.63 25.81 2.72 Requirement (mg/L) ~ 450 - - InfluentEffluent
- 24. 3. Disinfection Considerations ●Purpose: Ensure water disinfection quality is met ○ Goal: Maximize contact time between agent and wastewater ● Disinfection Options: ultraviolet radiation (UV), chlorination, ozone ○ Chlorine options: chlorine (Cl2), sodium hypochlorite (NaOCl), chlorine dioxide (ClO2) ● Selection: Chlorine (NaOCl) Characteristic Chlorine Gas Sodium Hypochlorite Ozone UV Radiation Use as disinfectant Common Common Occasional Increasing rapidly Safety concern High Moderate to low Moderate Low Effectiveness as disinfectant Excellent Excellent Excellent Good Increases TDS Yes Yes No No Byproduct formation Yes Yes Yes No
- 25. 3. Sodium Hypochlorite ●Earlier handling & less corrosive than chlorine gas ● High particle penetration Chlorine Design Parameters: ● Cl Consumption Reaction Rate: .0074 hr-1 ● Dose: 7 mg/L/day Wastewater Characteristic Effect on Chlorine Consumption Ammonia Forms chloramines Nitrate Reduces Effectiveness, Produces Trihalomethanes pH Affects hypochlorous acid equilibrium
- 26. 3. Plug FlowChlorine Contact Basin Structural Design Parameters: ● Flow Rate: 4 MGD ● Retention time: 90 mins Calculated: ● Total Volume: 946,250 L ● Length: 25 m ● Width of Channels: 2.1 m ● Depth: 5 m
- 27. Process Effectiveness Summary Influent:5.56 mgd of treated wastewater → Effluent: 4 mgd of disinfected tertiary water Constituent Influent Effluent Target (Max) Fecal Coliform Bacteria 36.7 MPN/100 mL ~ 0 mg/L 2.2 MPN/100 mL Salinity 2000 mg/L 139.7 mg/L (pre-chlor.) 450 mg/L - 960 mg/L TSS 7.3 mg/L ~ 0 mg/L 1 - 4 mg/L Ammonia 32.68 mg/L 1.94 mg/L ~ Phosphorous 3.45 0.20 1-5 mg/L
- 28. Equations ● Granular MediaFiltration ● Nanofiltration ● Chlorination ● Dechlorination
- 29. Looking Forward ● Completehand calculations for comparison with models ● Create promotional material on water reuse ● Refine SuperPro and Stella models ● Economic analysis ● By-product use ● Distribution
- 30. References Asano, T., F.L.Burton, H.L. Leverenz, R. Tsuchihashi, G. Tchobanoglous. (2007). Water Reuse: Issues, Technologies, and Applications. McGraw-Hill, New York. EPA. (2012). Guidelines for Water Reuse. U.S. Environmental Protection Agency,Office of Wastewater Management, Washington, D.C. National Risk Management Research Laboratory, Office of Research and Development, Cincinnati, Ohio. U. S. Agency for International Development, Washington, D.C. Hoeft, M., Propersi, M. (2013). San Mateo Recycled Water Market Survey Project. Technical Memorandum 0196-011. Retrieved from: https://www.cityofsanmateo.org/DocumentCenter/View/43625/Recycled-Water-FS---City-of-San-Mateo-Recycled-Water-Market-Survey?bidId= Neethling, J.B. PhD, Kennedy, H. (2018). Nutrient Reduction Study Report. Bay Area Clean Water Agencies. San Mateo. (2015). City of San Mateo Climate Action Plan. City of San Mateo California. https://www.cityofsanmateo.org/DocumentCenter/View/48812/San-Mateo-CAP--- Adopted?bidId. Accessed 28 September 2018. Sheikh, B., EBMUD Office of Water Recycling. (2000). WateRuse Association of California. Recycled Water Uses Allowed in California. Available at: www.watereuse.org/h2o. Takashi, A., Burton, F., Leverenz, H., Tsuchihashi, R., Tchobanoglous, G. (2006). Ch6-11. Water Reuse: Issues, Technologies, and Applications. Metcalf & Eddy.
- 31.
Editor's Notes
- #3 Amanda Today we’ll be introducing our project to you, going through our literature review, and presenting our preliminary designs.
- #4 Elena: The City of San Mateo has created a Clean Water Program out of their public works department in order to update and improve their aging sewer water collection and treatment infrastructure. They have hired Jacobs Engineering group to help manage this program. I had the opportunity to work on the Clean Water Program over the summer and was introduced to the program’s interest in diving deeper into the feasibility of water reuse implementation for the city. Currently, water is collected from the Hetch Hetchy Reservoir in the sierra nevada mountains and is sold to Cal water from the SFPUC. Cal Water distributes this water to the people of San Mateo. Their waste is then sent to the San Mateo Wastewater treatment facility and is treated to meet regulations required to dump the water back into the SF bay. So the opportunity for us is to design a treatment process that produces water that can be recycled. A few of the components that were discussed for San Mateo specifically is the lack of intense agriculture in the area, the disposal of salts in the waste stream of this treatment process and people’s perception toward recycled water. (The City of San Mateo is currently in the process of designing a new liquid treatment facility though because we do not know the effluent values of that process we scoped our process to follow the current liquids process since those were the parameters we were able to access.)
- #5 Lillian Notes: “The Sustainability Advisory Committee is concerned about water supply and recognizes that less snowpack in the Sierras, a predicted effect from global warming, will result in a decreased water supply and necessitate changes in the consumption patterns of all stakeholders.” -CA just came out of a historic 5 year drought from 2012-2017. -The hetch-hetchy reservoir is fed by a snowpack in the Sierra Nevada Mts. Due to a climate-change induced lack of snowfall, the snowpack is decreasing is size and reliability. -Over the next 80 years, the snow-water equivalence (the amount of water contained in a snowpack) is expected to decrease by ½. -current water practices include over-use of rivers & other water sources Open loops→ closed loops
- #6 Lillian: The main objective of this project is to design a process that will produce reusable water from the liquid effluent of the San Mateo WWTP. A detailed process will be designed, with consideration for the required water quality parameters of recycled water. The design will focus on key pollutants such as nutrients and salts. -Determining uses includes determining the demand. -Overall, this project aims to determine the effectiveness of a water recycling process and the viability of water reuse in San Mateo, California MAKE SURE TO ADDRESS DELIVERABLES
- #7 Kylie: Throughout our proect, we have focused on 3 aspects of sustainability. Envenvironmentally, the team is looking to decrease the demand of water from hetchy and lower the amount of waste being released into the san Francisco bay. Some of our water may end up going to the bay, but it will be of a higher quality and won’t negatively impact that ecosystem. Socially, we wanted to address any misconceptions there are about using recycled wastewater and promote the practicality and overall safety of this process. In addition to this, we know there are a finite number of resources on this earth, and they’re only going to start running out with population growth, so we wanted to showcase a sustainable method for water resource management that can be used by future generations and for the benefit of future generations. For the economics side, we need this process to economically feasible and competitive with already existing sources for irrigation. No matter how sustainable the process, no one will buy water if it’s too expensive.
- #8 Elena: In this design process we must consider many constraints. In terms of our deliverables we quickly came to the understanding of the limitations our design team were going to have in regards to our scope. The breadth of the project meant that we must consider the time, resources and expertise of our team. This meant that this process design would correspond to what the industry might consider a Design Proposal or 20% design. In industry, revision following each design phase would review and refine the working design till a 100% or final design is perfected. Regarding our process- our design constraints include the process effectiveness, economics of making the process and how it affects the consumers, the space needed, and operational logistics.
- #9 Elena: Because this design would take place in California, we had our research cut out for us. The most important information we needed to find regarded the demand and perception of recycled water: is this even something that consumers would want? There is not much agriculture in the limits of San Mateo so where else would the recycled water be used? The Water treatment process it self: what needs to be done to get the influent water quality to meet standards to be recycled and what processes there are that are able to achieve such. The regulations for recycled water: what restrictions there are and how to match up the process to achieve a specific water quality with an application that actually would be used in San Mateo. And the background on the San Mateo water effluent that would serve as our influent parameters and decidedly affect the treatments we would need to use to meet the water quality standards.
- #10 Lillian: Water recycling is also called water reclamation or water reuse Can also use stormwater USA: Purple pipes and typically purple signs (picture) are used to indicate non-potable recycled water The picture (which is fair use) in from Sunnyvale, CA Official Color for piping is Pantone #512C or #522C
- #11 Lillian: People use it this way/why; tie into evidence it works for us, etc -the 80% makes up about 25% of their water supply -Other places with water scarcity such as arizona & australia also use water recycling, as well as place with good water supplies- Delaware has irrigated cropland with recycled water since 1970’s. -Diagram is the percentage of it’s wastewater that it recycles (vs. % of its water supply that recycled water makes)
- #12 Lilian: Division 4, Chapter 3, titled Water Recycling Criteria, defines in Article 1 three different levels of recycling treatment Note that the definitions/regulations pertain to disinfection levels; a regulation for nutrients or salt levels is not given by Title 22
- #13 Lillian - We chose to focus on tertiary water because it can be used for the largest selection of uses, & is generally the level of treatment achieved in water recycling facilities At end of slide: So from this list of uses, we had to investigate which would be an available and viable option in San Mateo specifically NOTE: Talk about benefits of recycled water on this and previous slide (write list)
- #14 Elena: In order to justify creating a water reuse facility is was important to know that there was demand for the final recycled effluent. In 2013 San Mateo hired a consulting firm to conduct a water market survey to estimate where recycled water effluent could be used within the city. The results of this study showed that there were 106 estimated potential recycled water customers, with total Maximum Daily Demand of 2.34 MGD. A majority of the water is used in urban irrigation, which in San Mateo’s case, has little to do with agriculture and rather is water applied for landscaping and golf courses. The primary commercial/ industrial recycled water use if for cooling towers so is significantly less (though this is the area for most potential growth as the population increases and the infrastructure for distribution is put in place.) For the purpose of our design, the team projected that a magnitude of 4 MGD recycled water would sufficiently supply enough water to both the projected recycled water consumers and encourage new recycled water consumers to enter the market.
- #15 Elena:
- #16 Kylie Moving on to the process section of our project, we had three objectives we wanted to accomplish. These are as follows: remove tss, reduce tds, and disinfect the water. To address each of these objectives, we developed three unit operations: GMF, Nanofiltration, and chlorination. Our justification for each of these unit ops will be explained as we move forward.
- #17 Kylie So this is our design laid out to give a better picture of what each unit op will look like and where it is in the process. The water from the wwtp will come in and go through granular media filtration to lower tss, and then it will move through nanofiltration which will decrease the salinity, next it will undergo chlorination or disinfection, and finally it will be dechlorinated to remove residual chlorine.
- #18 Amanda And this is the entire SuperPro design, which is basically a more complicated version of the diagram we just saw. In this next portion of our presentation, we will be going into the design of each of these 3 steps. You can see our 3 unit operations: GMF to remove TSS, NF to remove TDS, and chlorination to disinfect. There is also a dechlorination step at the end, which is vital because high concentrations of chlorine are harmful to human and plant health.
- #19 Kylie The first step in our process is media filtration, the purpose of this is to remove suspended solids. For our design, we chose a dual medium granular media filter consisting of a layer of anthracite, sand, and support layer of gravel, and how this works is the water will pass through the filter and any particulate matter that is too big to pass through the filter will be trapped within the layers. The factors we needed to take into consideration were the medium type, the pore size of the medium, number of layers and depth of each, and filtration rate of the chosen media. Picture1 link: http://wgbis.ces.iisc.ernet.in/energy/water/paper/drinkingwater/simplemethods/filtration.html Picture 2 link: http://napier-reid.com/products/gravity-filtration-systems/
- #20 Kylie 5.6 MGD = 883262.7 L/h influent→ calculated in order to achieve effluent of 4 mgd More into the actual design and function of the filter. Water will come in through the top and filter through the layer via gravity, exiting at the bottom where it continues to the next step of the reuse process. As time progresses, there will be bwaste build up within the filter layers and at a certain point, this buildup will impact the effectiveness of the system. Once this happens, wastewater inflow to the filter will be shut off and backwashing will occur, which is when high velocity water is forced back up through the filter layers to carry out all the particulate waste and cleaning the filter. In order to prevent bottlenecking and ensure continuous water processing, two gmfs will operated in parallel so one will be cleaned while another is filtering water, and vice versa.
- #21 Amanda To finish out GMF, I’ll talk about the SuperPro model. - Our goal with SuperPro was to get projected values of the water quality after each unit operation. In the coming weeks, we’ll be comparing the SuperPro values to our hand calculations. -In this table, you can see the reduction in TSS and bacteria. The effluent values from superpro are below the requirements, which accomplishes our first objective. These reqs were taken from Title 22 standards and literature. -In reality, the bacteria would not be completely eliminated in this step. We think this happened because the water flow rate was so large in comparison to the bacteria levels, that superpro just calculated it to be 0. will look into running systems in parallel or having storage basin, weir, so water column above filtration isn’t so high. Realistically, bacteria wouldn’t be 0 after GMF, but it was 0 in SuperPro bc of the huge flow rate of water compared to the tiny flow rate of bacteria.
- #22 Amanda -Now we’ll move on to our 2nd treatment step. -Remember that our second objective is to remove TDS, which includes dissolved salts, metals, and ions. For some perspective...(This is because high salinity can harm plants.) - Membrane filtration reduces TDS. -The semipermeable membrane allows for separation of contaminants and water when the system is pressurized. (the water passes through the membrane and the contaminants are held back, or rejected) - Look at the picture, and you can see our different options for membrane filtration, including MF, UF, NF, and RO. You can see that as pore size decreases, more contaminants are rejected. RO has the smallest pore size and therefore has the highest quality water. RO is often used for potable reuse and is expensive, so our selection for this project is NF. We still wanted a small pore size to remove the salts. Might use EDR to desalinate ocean water, might use RO to produce potable water. Examples of TDS: calcium, magnesium, potassium, sodium, carbonates, chlorides, fluoride, sulfates)
- #23 Amanda -Now that we’ve selected NF, I’ll go into its structure. -Pore size, mono/di ions (NF pores are small than those of micro/ultra filtration, but larger than those of RO.) -2 configurations (spiral wound has lower pressure drop than hollow-tube and higher surface-to-volume ratio) -The picture shows the flow of water through the filter. Imagine a stack of paper, and roll it up into a spiral. And put that roll into paper towel tube. That’s the structure of NF. The layers of paper are semi-permeable membranes. The clean water flows down the middle of the tube, and the contaminants are trapped in the layers. Picture link: https://emis.vito.be/en/techniekfiche/nanofiltration
- #24 Amanda -In SuperPro, we want to track the removal of TDS. We’re representing TDS as salinity. In reality, TDS is more than just dissolved salts, but equating the 2 is commonly done in industry. -Our influent TDS is 2000 mg/L. Think back to the reference values I gave (500 for drinking water and 35k for ocean). -The table shows SuperPro’s calculations. The TDS concentration went from 2000 mg/L to ~140 mg/L, which meets the requirement of 450 mg/L (according to Water Market Survey). - We also wanted to track nutrient reduction. The ammonia removal is important because in the next treatment step, ammonia reacts with chlorine, and we want to minimize that. -(Tailored SuperPro to fit the needs of the project. (Used microfiltration instead of nanofiltration and increased rejection coefficient to mimic smaller pore size). Mention that removing salinity is important because salts can harm plants. Picture link: http://excelwater.co.uk/systems/nano-filtration-systems/
- #25 Amanda -Goal -The disinfection options are… -Look at the table. UV is increasing rapidly but is expensive. Chlorine is common, has a low cost, and chlorine residuals ensure disinfection from plant to consumer. Therefore our selection is chlorine. -Chlorine in general is toxic and corrosive, but chlorine gas and liquid is esp. dangerous. There are many safety regulations on the handling/storage of chlorine gas. For this reason, many plants are switching from gas to sodium hypochlorite, so that is what we chose. Talk about our hesitation we’ve had since choosing chlorine (potentially increasing dissolved solids to the point where it negates the treatment we’ve done) UV requires pretreatment so that the rays can penetrate (disadvantage), but UV takes less contact time (advantage).
- #26 Elena: Sodium Hypochlorite was the chlorine chemical chosen due to its relative ease of handling and its high particle penetration. Chlorine has complex chemical reactions with treated water based on a variety of inputs and for the purpose of our design will be an area of further study. ways in which chlorine will be consumed within the contact basin and reduce the available chlorine for disinfection include producing chloramines and THMs from ammonia and nitrate. The ph of the water also influences the equilibrium of hypochlorous acid which is important because hypochlorous acid is much more effective in disinfection than hypochlorite. We are building a working stella model that will demonstrate the change in chlorine. These are our initial parameters for modeling however will be updated as we obtain more parameters from previous unit operations. In the field, the chlorine dose often fluctuates based on real time and the exact dose would be normalized using pilot run effluent. Trihalomethanes
- #27 Elena: For our process we decide to design a chlorine contact basin that was rectangular in form since this was one of the most widely used methods. The water coming from the nanofiltration will enter the retention basin in the upper left corner and mix with an influent of Chlorine then wind its way through in order to reach a retention time of 90 mins. This was the retention time recommended for the chlorine to properly kill any coliforms. Using this parameter and the flow rate of 4 MGD, the dimensions of the contact basin could be calculated and are modeled as shown. At the end of the contact basin will be a wier into the final dechlorination basin. The final effluent shown leaving on the bottom left corner is proper tertiary treated wastewater effluent that eventually can be sent to a water distribution company (CAL water in this case) in order to service San Mateo’s landscaping needs. Measurements in Meters. The depth is 5.00 m in order to have a total volume of 946,250 L and a retention time of 90 mins if the flow rate is 4 MGD. FIX arrows.
- #28 Lillian: Tell amanda you’ll talk about the targets & the components effects on this slide (instead of hers) Can we tract nitrates later? 1-4 mg/l of TSS is what is expected after depth filtration- idk what we want after everything NA: below 50 mg/L; Cl: above 100 for most plants https://extension.psu.edu/interpreting-irrigation-water-tests 1.For chlorine disinfection, that criteria is that a contact time of “not less than 450 milligram-minutes per liter... with a modal contact time of at least 90 minutes, based on peak dry weather design flow” is required. In this case, contact time is defined as “the product of total chlorine residual and modal contact time measured at the same point.” 2.applies regardless of the disinfection process: the median concentration of total coliform bacteria in the treated effluent may not exceed “an MPN of 2.2 per 100 milliliters utilizing the bacteriological results of the last seven days for which analyses have been completed.” In addition, # of total coliform bacteria may not exceed “an MPN of 23 per 100 milliliters in more than one sample in any 30 day period,” and no single sample may exceed “an MPN of 240 total coliform bacteria per 100 milliliters” at any time.
- #29 Kylie: These are the calculations that we will use to compare to SuperPro. We also need to insert a table of the parameters we used (Darnault’s request)- but maybe not here? I would say we should do it at the beginning of the process part
- #30 Amanda That is the end of our design portion. I want to close us Calculate time btwn backwash