Vermifiltration of Dairy Wastewater for Reuse: The Earthworm Revolution
Item Type text; Electronic Thesis
Authors Patton, Catherine Marie
Publisher The University of Arizona.
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VERMIFILTRATION OF DAIRY WASTEWATER FOR REUSE:
THE EARTHWORM REVOLUTION
By
CATHERINE MARIE PATTON
______
A Thesis Submitted to The Honors College
In Partial Fulfillment of the Bachelors degree With Honors in
Chemical Engineering
THE UNIVERSITY OF ARIZONA
M A Y 2 0 1 7
Approved by:
______
Dr. Kimberly Ogden Department of Chemical and Environmental Engineering
Acknowledgements: Thank you to Manuel Vasquez, Kimberly Ogden, Jack Garrett, and Tiffany Hawks. Special thanks to Veikko Kanto for assistance and funding with experimental design; Mary Kay Amistadi for ICP-MS testing, lab supplies, and for being the best boss; and Charly Amling for cutting an unwieldy glass vessel. You all are wonderful!
Wastewater treatment is a problem of great importance to arid climates like the American Southwest, but common processes often require many treatment chemicals and high energy use. The purpose of this project was to design a process to remediate 600,000 gallons/day of wastewater from the Shamrock Dairy treatment plant in Phoenix, AZ. Vermifiltration was chosen as a chemical-free and low energy treatment process to remove BOD, COD, and TSS. A vermifiltration experiment was run confirming high contaminant removal (~85% TOC) in an 8 hour retention time. The process design included solid liquid separation, vermicomposting, cooling, and vermifiltration. A full economic and environment analysis was done, leading to the recommendation that the process be built without the solid liquid separation and vermicomposting, and that research on worm species such as the Indian Blue Worm (Perionyx excavates) be done to investigate their ability to remediate wastewater in the 25-30°C temperature range for reduced cooling requirements. With these improvements the process would be an economically sustainable and very environmentally friendly solution for remediation of dairy waste water.
The main objective of this project is to design a process to treat 600,000 gallons of dairy wastewater per day. The contaminant levels are reduced to the City of Phoenix Water and Sewer wastewater disposal standard. The treated water is clean enough to dispose without incurring fines. The contaminants of concern are biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), arsenic, lead, selenium and cadmium.
The wastewater treatment system consists of a solid liquid separator, a vermicompost bed and six vermifiltration beds. This process is based on vermicompost and vermifiltration research done by Sinha et al. and Kumar et al. using Red Wiggler worms (Eisenia fetida). Vermifiltration is used for the design because of its high contaminant removal and low energy requirements. The vermifiltration beds remove up to 98% of BOD, 90% of COD, 90-95% of TSS, and most heavy metals (Sinha et al.) The removal of contaminants is dependent on the hydraulic retention time (HRT). Experimentation shows 81% TOC removal for an 8-hour HRT and potential for 90% or higher removal at an 11-hour HRT (Appendix B). Energy requirements for this process mainly come from pumping and cooling. Cooling is the main contributor to energy requirements with a total duty of 13,480,000 kWh/year.
The proposed process has few safety hazards, with no hazards under normal operating conditions. Hazards inherent to the system result from abnormal feed conditions or equipment failure. Equipment failure is most likely due to increased solids composition of the feed stream. This could result in safety hazards associated with clogging and pressure buildup in the units.
Vermifiltration is inherently an environmentally friendly process in that it has relatively low power consumption and requires no hazardous chemicals. The main environmental impact of the process comes from the emission of carbon dioxide due to mineralization within the vermifiltration and vermicompost beds and due to power requirements for cooling.
Mineralization accounts for the release of approximately 16,000 metric tons of CO2 per year.
Energy use accounts for the release of approximately 563 metric tons of CO2 per year. The CO2 emissions due to mineralization could be greatly reduced with the use of a CO2 scrubber.
The vermifiltration system is not economically feasible as currently designed. Further research is needed to find a species of worm suitable for use in the Phoenix, AZ. This will reduce
the need for significant cooling. It is recommended that Indian Blue worms be investigated for this purpose, as they can withstand temperatures up to 35°C and have an optimum temperature range of 21-30°C. Assumptions made include the retraining of workers and that the process is added to the existing plant in its footprint. It is also assumed that the exiting storage tank and main fed line pump can be reused. Based on this model the process designed may be economically sustainable with further research.
This vermifiltration system is not viable as designed with the use of Red Wigglers, but could be with further research using different species of worms. The process should exclude the solid liquid separator and vermicompost bins for cost feasibility.
Kara Kanto Wrote GUI code for experiment Wrote control system code for experiment Designed and built circuits for experimental apparatuses Designed and built (and modified when needed) experimental apparatuses Preformed experiments and collected effluent samples Wrote Experimental Design (Appendix A) Contributed to BFD/PFD Contributed to Lab Report (Appendix B) Wrote lab notes Edited report Printed and bound report
Catherine Patton Wrote summary Contributed to Introduction Contributed to BFD and PFD 1, created PFD 2 Contributed to ASPEN simulation, specifically inlet heat exchanger modeling Wrote Description of Process Contributed to Process Rationale Heat Exchanger design, description, optimization, and safety analysis Contributed to building experimental setup Performed experiments with group Contributed to Cost Analysis Contributed to Environmental analysis Edited report
Connor Stahl Contributed to BFD Contributed to overall ASPEN simulation Cost analysis calculations Wrote economic analysis section Created stream tables Contributed to equipment table Created utility table Created CO2 emissions table and pie charts Contributed to mass balance Worked with solid-liquid separator Created Economic Analysis Appendix and Mass Balance Appendix Created Meeting Log Appendix
Calliandra Stuffle Contributed to Mass Balance Contributed to Introduction Contributed to PFD 1 Contributed to Process Rationale Contributed to building experimental setup Performed experiments with group Performed lab sample prep and analysis Data analysis Wrote Lab Report - Appendix B Vermicompost design, description, optimization, and safety analysis Contributed to Environmental Conclusion
1. Introduction ...... 2 1.1 Overall Goal ...... 2 1.2 Current Market Information...... 2 1.3 Project Premises and Assumptions ...... 2 2. Process Description, Rationale and Optimization ...... 4 2.1 Block Flow Diagrams ...... 4 2.2 Process Flow Diagrams ...... 5 2.3 Equipment Tables ...... 7 2.4 Stream Tables ...... 9 2.5 Utility Tables ...... 11 2.6 Written Description of Process ...... 11 2.7 Rationale for Process Choice ...... 12 3. Equipment Description, Rationale, and Optimization ...... 14 3.1 Solid Liquid Separator ...... 14 3.2 Heat Exchangers...... 14 3.3 Vermifiltration ...... 15 3.4 Vermicompost ...... 16 4. Safety Issues...... 17 5. Environmental Impact Statement...... 18 LCA Assessment ...... 18 Effects on Climate Change, Resource Depletion, and Ecotoxicity ...... 19 Recommendations ...... 20 6. Economic Analysis...... 21 7. Conclusions and Recommendations ...... 25 Works Cited ...... 27 Appendices ...... 29 Appendix A: Experimental Design ...... 29 Experimental Apparatus Parts and Approximate Costs ...... 29 Apparatus Building ...... 31 Apparatus Images and Diagrams ...... 37 ...... 39 ...... 41 Arduino Control and Data Acquisition...... 45 Lazarus GUI Flow Diagram ...... 48 Appendix B: Lab Report Executive Summary ...... 49 Appendix C: Economic Analysis Equations and Methods ...... 55 Appendix D: Mass Balances...... 57 Appendix E: Energy Balance...... 57 Appendix F: Minimum Energy Requirements Calculations ...... 57 Appendix G: HAZOP Reviews...... 58 Solid Liquid Separator ...... 58 Heat Exchangers ...... 58 Vermifiltration ...... 58 Vermicompost ...... 58 Appendix G: Vermifiltration Vessel and Initial Loading Calculations ...... 58 Appendix H: Emissions Calculations...... 58 Appendix I: Problem Description ...... 58 Appendix J: Meeting Information ...... 59 Appendix K: ASPEN Simulation...... 59
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1. Introduction
1.1 Overall The vermifiltration process treats 600,000 gallons of dairy wastewater to reduce contaminant levels to Phoenix wastewater disposal. Treatment of the wastewater eliminates the need for Shamrock to pay fines to dispose of its wastewater. If the water is further treated to meet EPA tap water standards in the future, its reuse will significantly cut the cost of water utilities. The vermicompost process generates castings (worm excrement) that can be sold as a byproduct.
1.2 Current Market Information The Shamrock dairy plant currently spends $38,200 per month to dispose of their wastewater. The vermifiltration process eliminates this fee. This process treats 600,000 gallons of wastewater per day to produce 500,000 – 600,000 gallons of treated water per day. Water loss is due to evaporation and reuse in vermipost beds. After treatment, the water is disposed of (Appendix I). Municipal water in Phoenix costs between $3 and $4 per unit (748 gallons) or between 0.4 and 0.5 cents per gallon, depending on the season. There is an additional environmental charge for water supplied of 28 cents per unit ("Current Specific Water & Sewer Rate Charges"). If Shamrock chooses to further treat the effluent for reuse in the future, the plant will save about $3,210 per day (assuming 600,000 gallons costing $4 per unit). Worm castings are a byproduct that can be sold for about $1.80/kg ("Wiggle Worm Earth Worm Castings - 15 Lbs"). Castings are produced in both the vermifilters and the vermicompost, but are mainly a product of the vermicompost process.
1.3 Premises and Assumptions
The wastewater feed is assumed to be 32ºC and 1 atm. Contaminant compositions are listed in Table 1.1. The process is located at the dairy processing plant in Phoenix, Arizona,
USA.
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Table 1.1: Wastewater Contaminant Compositions Current Influent* Target Effluent** (mg/L) (mg/L) BOD 1341 25 COD 2030 75 TSS 128 100 Arsenic 0.0255 0.01 Lead 0.137 0.01 Selenium 0.13 0.05 Cadmium 0.13 0.003
*Appendix I*("National Primary Drinking Water Regulations.") The wastewater produced by the dairy treatment plant varies in composition throughout the day. This is due to production of a wide assortment of products. The storage tank preceding the vermifiltration process provides surge and mixing capabilities for a filtration feed stream that is consistent in flow rate and composition. It is assumed that the feed will be consistent in composition and flowrate after the surge tank for calculations. The effluent has a composition that meets or exceeds the City of Phoenix Water and Sewer wastewater disposal depending on the retention time used in the vermifiltration beds.
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Figure 1: Block Flow Diagram for Vermifiltration and Vermicomposting
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Figure 2: Process Flow Diagram 1/2 for Vermifiltration and Vermicomposting - Main Process
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Figure 3: Process Flow Diagram 2/2 for Vermifiltration and Vermicomposting - Cooling Cycles 6
Table 2.1: Equipment Table Vermifilter Bed HE E-102 E-103 E-104 E105 E-106 E-107 Type Coil Coil Coil Coil Coil Coil Area (m^2) 0.190 0.190 0.190 0.190 0.190 0.190 Temperature In (K) 278.15 278.15 278.15 278.15 278.15 278.15 Temperature Out (K) 288.15 288.15 288.15 288.15 288.15 288.15 Pressure (kPa) 101.325 101.325 101.325 101.325 101.325 101.325 Phase l l l l l l Duty (kW) 0.781 0.781 0.781 0.781 0.781 0.781
Vermifiltration Beds R-101 R-102 R-103 R-104 R-105 R-106 Temperature (K) 298.15 298.15 298.15 298.15 298.15 298.15 Pressure (kPa) 101.325 101.325 101.325 101.325 101.325 101.325 Orientation Vertical Vertical Vertical Vertical Vertical Vertical Volume (m^3) 157.85 157.85 157.85 157.85 157.85 157.85
Separator V-101 Surge Tank T-101 Vermicompost R-107 Temperature (K) 305.372 Temperature (K) 305.372 Temperature (K) 298.15 Pressure (kPa) 101.325 Pressure (kPa) 101.325 Pressure (kPa) 101.325 Orientation Vertical Orientation Vertical Orientation Vertical Area (m^2) 4.65 Volume (m^3) 2271.25 Volume (m^3) 157.85
Cooling Cycle Pumps Inlet Coils Head (m) 8.8 10.1 Flow Rate (m^3/day) 893 89.5 Temperature (K) 278.15 278.15 Pressure (kPa) 201 101.325 Phase l l Power Shaft (kW) 1.73 0.128 Inlet HE 1 Type S&T Area (m^2) 45.0 Duty (kW) 1577 Shell Temperature In (K) 278.3 Temperature Out (K) 260.9 Pressure (kPa) 201.3 Phase l,g Tube Temperature In (K) 309.8 Temperature Out (K) 295.15 Pressure (kPa) 201.3 Phase l
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Inlet Pump 1 Head (m) 10.33 Flow Rate (m^3/day) 2271 Temperature (K) 305.4 Pressure (kPa) 101.325 Phase l Power Shaft (kW) 3.245
Coolers Inlet Cooling Coil cycle Cycle Type Electric Electric Temperature In (K) 260.85 288.15 Temperature Out (K) 278.15 278.15 Pressure (kPa) 201.3 101.325 Phase g,l l Duty (kW) -1579 -4.805
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Table 2.2: Stream Table Stream Number 1 2 3 4 5 6 7 8 9 10 Temp. (C) 35 35 22 22 22 22 22 22 22 22 Press. (kPa) 101 101 101 101 101 101 101 101 101 101 Mass Flow (kg/day) 2279194 2279130 2279130 379855 379855 379855 379855 379855 379855 378551 Component Mass Flow (kg/day) Water 2271246 2271246 2271246 378541 378541 378541 378541 378541 378541 378541 BOD 3046 3046 3046 507.6 507.6 507.6 507.6 507.6 507.6 4.010 COD 4611 4611 4611 768.4 768.4 768.4 768.4 768.4 768.4 6.071 TSS 290.7 227.1 227.1 37.85 37.85 37.85 37.85 37.85 37.85 0 Arsenic 0.0579 0.0579 0.0579 0.00965 0.00965 0.00965 0.00965 0.00965 0.00965 0 Lead 0.311 0.311 0.311 0.052 0.0519 0.0519 0.0519 0.0519 0.0519 0 Selenium 0.295 0.295 0.295 0.049 0.0492 0.0492 0.0492 0.0492 0.0492 0 Cadmium 0.295 0.295 0.295 0.049 0.0492 0.0492 0.0492 0.0492 0.0492 0 Stream Number 11 12 13 14 15 16 17 18 19 20 Temp. (C) 22 22 22 22 22 22 22 22 35 25 Press. (kPa) 101 101 101 101 101 101 101 101 101 101 Mass Flow (kg/day) 378551 378551 378551 378551 378551 2271306 0.02 2271306 64 0.02 Component Mass Flow (kg/day) Water 378541 378541 378541 378541 378541 2271246 0.0200 2271246 0 0.0200 BOD 4.010 4.010 4.010 4.010 4.010 24.06 0.000 24.06 0 0 COD 6.071 6.071 6.071 6.071 6.071 36.42 0.000 36.42 0 0 TSS 0 0 0 0 0 0 0 0 63.600 0 Arsenic 0 0 0 0 0 0 0 0 0 0 Lead 0 0 0 0 0 0 0 0 0 0 Selenium 0 0 0 0 0 0 0 0 0 0 Cadmium 0 0 0 0 0 0 0 0 0 0 9
Stream Number 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 Temp. (C) -12 5.00 5.02 5.02 5.02 5.02 5.02 5.02 5.02 5.02 5.02 5.02 5.02 5.02 5.02 5.02 Press. (kPa) 203 203 203 203 203 203 203 203 203 203 203 203 203 203 203 203 Mass Flow (kg/day) 1077725 1077725 90672 15106 15106 15106 15106 15106 15106 15106 15106 15106 15106 15106 15106 90672 Component Mass Flow (kg/day) Water 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 BOD 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 COD 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 TSS 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Arsenic 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Lead 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Selenium 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Cadmium 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 HFO-1234yf 1077725 1077725 90672 15106 15106 15106 15106 15106 15106 15106 15106 15106 15106 15106 15106 90672
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Table 2.3: Utility Table Utility Stream Unit kW Inlet Cooling Pump (P-201 A/B) 3.25 Inlet Cooling Cycle Cooler (E-201) 1579 Coil Cooling Pump (P-202 A/B) 0.13 Coil Cooling Cycle Cooler (E-202) 4.80 Compost Bed Cooling 27.30 Total 1614.48
This utility table assumes that pumping already done by the plant enables the wastewater feed to flow through the solid liquid separation, surge tank, and inlet heat exchanger (i.e. P-101 is extraneous).
The process flow diagram (PFD) for the wastewater treatment process can be seen in Figures 2 and 3. The block flow diagram (BFD) for this process can be seen in Figure 1. The wastewater supply (Stream 1) is fed through a solid-liquid separator (V-101), the solids are then fed to the vermicomposting unit via Stream 19. The liquid fraction is fed to the storage tank (T- 101) by stream 2. The wastewater exits T-101 and is pumped (P-101 A/B) to a heat exchanger (E-101) to cool stream 3 from 35°C to 22°C, a temperature for optimum worm functionality (Sinha et al.). This exchanger is supplied with cooling water from stream 22 (PFD 2), which has been cooled and compressed in E-201 to a liquid at 5°C and pumped via pump P-201 A/B. This water exits the exchanger as stream 21 as a vapor at -12°C and reenters cooler E-201.
From exchanger E-101 the wastewater (Stream 3) is fed to six vermifiltration beds (streams 4-9 corresponding to beds 1-6). Each bed is cooled with a coil heat exchanger. The cooling water (stream 23) exits cooler E-202 at 5°C and is split equally into streams 24-29 to cool beds 1-6 in exchangers E-102 through E-107, respectively. These streams exit seds 1-6 in streams 30-35, respectively. They are combined into stream 36 and re-enter cooler E-202. The remediated wastewater exits the beds in streams 10-15. These streams are combined into stream 16. This stream is split into the main remediated water product (stream 18) and a side stream
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(stream 17) to provide moisture to the vermicompost bed (R-107). The vermicompost unit provides worm castings that are removed from the vermicompost unit periodically (stream 20).
The main goal of this design is to remove high levels of BOD contaminants from the dairy wastewater in a process that is cost effective and efficient. Energy required for the treatment process is minimized while maintaining treatment standards at high volumes of wastewater. Vermifiltration and vermicomposting achieve these objectives.
Vermifiltration and vermicomposting processes use earthworms to digest contaminants. Vermifiltration is used to produce clean effluent while vermicomposting produces worm castings. The system has low energy use because it takes place at standard temperature and pressure and the worms do most of the work. The process does not require buffering chemicals or catalyst regeneration costs (see Appendix B). The worms reproduce naturally to a sustainable population for the available food and space. Earthworms can remove upwards of 98% of BOD, 90% of COD, 90-95% of TSS, and most heavy metals (Sinha et al.). Earthworms eat most of these contaminants, while microbes that live in their stomachs are passed into their excrement and remediate contaminants like as heavy metals. The castings produced by the worms are a valuable byproduct. Selling these can help to offset the cost of the process. Vermifiltration is used for this design for its high contaminant removal rates, comparatively low energy requirements and sellable byproduct.
Other treatment processes under consideration require high energy costs and do not treat all the contaminants in a single process. These include microbial fuel cell treatment and up flow anaerobic sludge blanket reactor to remediate COD and BOD, with adsorption and precipitation reactions to remediate heavy metals. While removal rates for BOD, COD, TSS, and heavy metals are relatively consistent with that of the vermifiltration process these processes were not pursued. Microbial fuel cell treatment requires longer treatment time for similar COD removal, 72 hours for 91% removal, compared to the vermifiltration removal of 90% COD in 10-hour HRT (Mardanpour et al. 2012). The combined precipitation adsorption process that was investigated uses sonication to activate clay, and can reduce heavy metal concentration by a factor of 102-103 (Myasnikov et al. 2016). This process has yet to be scaled up to handle the volume of wastewater that the plant produces, and requires additional equipment to sonicate the clay, and was thus not
12 pursued. Moreover, the treatment process would need to include a step to remove organics and then another to remove heavy metals. More equipment, space, and energy are required to treat the wastewater with a serial process treatment.
The final process design uses six vermifiltration reactors. This optimizes the tradeoff between a smaller overall footprint for fewer but larger reactor vessels and the lower initial cost and ease of maintenance of having more small reactors. This design provides the capability to shut down one of the reactors for maintenance while maintaining treatment of the full load of wastewater in the other five reactors. The final process design also includes an inlet heat exchanger (E-101) as well as a coil heat exchanger in each vermifiltration bed (E-102 to 107). These heat exchangers cool the feed to an optimized temperature for digestion of contaminants by the worms. The coil exchangers in the vermifiltration beds keep the beds cool for times when the ambient temperature is higher than the maximum operating temperature. These heat exchangers require a cooling duty of approximately 13,876,000 kWh/year. Calculations for the reactor size, flowrates, and energy use can be seen in Appendices C and F.
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A cyclone separator (V-101) is used in this process. Cyclone separators are highly efficient and can remove 99% of all 25 micron or larger particles (LAKOS 2017). The benefits of a cyclone separator include the lack of moving parts and no energy requirement for operation. The lack of moving parts also reduces maintenance costs. The design of a cyclone separator also requires minimal space, while separators can be connected in parallel to handle higher flow rates. Additionally, cyclone separators have a low pressure drop and can be designed to have no water loss (LAKOS 2017).
The process consists of an inlet heat exchanger (E-101) and six coiled heat exchangers (E-102 to E-107) in the vermifiltration beds. A shell and tube heat exchanger was chosen for the inlet heat exchanger (E-101). The wastewater is pumped through the tube side, and the cooling water is pumped through the shell side. This follows Heuristic 55 in Seiders' Product and Process Design Principles, which advises that the tube side be used for hazardous fluids while the shell side to be used for cleaner fluids. The heat exchangers in each vermifiltration bed (E-102 to E- 107) are simple cooling tubes that run through the beds in coils to provide cooling to the beds. All heat exchangers are stainless steel to prevent corrosion from the wastewater.
The required duty for the inlet heat exchanger is 13,300,000 kWh/year. This duty can be reduced to 5,270,000 kWh/year using Indian Blue worms. These worms allow a higher operating temperature of 21-30°C (Bentley). The required duty for the coil heat exchangers is 1,600 kWh/year for warm months. Cooling is required in the summer and heating could also be needed in the winter months with the use of Indian Blue worms. The total coil exchanger duty using Indian Blue worms is 62,000 kWh/year. The use of the coil heat exchangers could also possibly be eliminated with insulation of the vermifiltration beds. For more information on heat exchanger energy requirement calculations see Appendix F.
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Vermifiltration beds are the main component of the wastewater treatment process. Effluent produced at a 10 to 11-hour HRT meets or exceeds the standards of the City of Phoenix Water and Sewer. It can be disposed without incurring a fine (Appendix B, Sinha et al.). The final process design includes six vermifiltration reactors. This allows a small footprint, low cost of purchase, and easier maintenance. The total footprint for the six beds is 360 m2. The use of six reactors in parallel allows for continued operation during maintenance or in case of failure. Stainless steel vessels are used to prevent corrosion and oxidation while posing no toxicity to worms.
The wastewater is distributed over the top of the vermifiltration bed with a sprinkler system to ensure even dispersion. Each bed is divided into four layers. The top layer has soil and worms, underneath this layer is a stainless-steel mesh screen which prevents the unwanted movement of worms into lower layers. Underneath the screen is a layer of sand. Below the sand there is a layer of small gravel (1-1.2cm) then another layer of slightly larger gravel (3.5-4.5cm). Each layer is approximately equal in height. Sinha et al. recommend 25cm of larger gravel, 25cm of smaller gravel, 20cm of sand, and 10cm soil and worms for a small scale bed- i.e. a 2.5:2.5:2:1 ratio (Sinha et al., 491). Kumar et al. recommend a 1.5:1.5:1.5:2 ratio (Kumar et al., 1178). Vermifiltration requires 10kg worms/m3 soil (Sinha et al, 491). The vermifiltration beds (370m3) require a biomass of worms of 1853 kg per vermifilter bed; or 5560 kg total.
Worms double in population approximately every 60 days. This allows 25% of the required worm biomass to be purchased initially. During the startup process the worms reproduce to achieve the total required worm biomass in 120 days. The worms will reproduce to a mass sustainable in their environment, thus worm removal is not necessary.
Each vermifiltration bed contains a cooling coil within the soil layer. These coils maintain an optimum temperature range for the worms. Vermifiltration with Red Wigglers (Eisenia fetida), has an optimal temperature range of 20-25°C. Indian Blue worms (Perionyx excavates) have an optimal temperature range of 21-30°C. These worms can survive up to 35°C and down to 10°C (Bentley, Reinecke et al.). Using Indian Blue worms for filtration results in
15 large energy savings due to the expanded temperature range (See Section 3.2). For further discussion of cooling coils see sections 2.6 and 3.2.
The vermicompost beds (R–107) are used to decompose the soild fraction of the wastewater stream. There are twelve vermicompost beds. Each bed treats a five-day accumulation of solid waste over a 60-day time (Seenappa). Separation of the solids from the liquid stream allows for more rapid treatment of the water stream. It also mitigates damage to equipment due to clogging and consequential high pressures. Stainless steel vessels are used for the vermicompost beds to prevent oxidation of the equipment and contamination of the vermicompost product. Energy and mass balances can be found in Appendix D and E. Ambient heating occurs for most of the year (average temperatures are above 25°C). Temperature in the beds is optimized by having a heat exchanger with cooling water from the plant. The required footprint of the vermicompost beds is 88 m2. This assumes twelve cylindrical beds with a 0.662 m3 volume. Approximately 657 kWh is required to cool the vermicompost beds daily. Approximately 33 kg of vermicompost is produced daily. Extra worms are removed when the vermicompost is collected.
Due to space and energy requirements for the vermicompost beds, this part of the design is not recommended to be implemented. Sale of the vermicompost would bring in approximately $22,000 per year. This is negligible compared to the cost of cooling the vermicompost beds, the purchase and upkeep of the solid liquid separator and the vermicompost bed vessels, and the cost of employing workers to operate this part of the system (Wiggle).
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The proposed process has few safety hazards, none of which should occur under normal operating conditions. Hazards inherent to the system result from extremely abnormal feed conditions or from equipment failure. The main source of potential safety hazards comes from an increased solid fraction of the feed stream. This could result in safety hazards associated with clogging or pressure buildup in all the units and associated piping. The process requires no special personal protective equipment (PPE) or hazardous chemicals.
The cyclone solid-liquid separator has no moving parts and no electric input, resulting in little safety risk. If the inlet solids fraction is significantly increased the separator can be at risk for clogging or for expelling solids with the water effluent. If the water effluent contains solids, they can deposit downstream in vital pieces of equipment (e.g. heat exchanger E-101 or surge tank T-101). Due to the amount of fluid that is being treated, a clog or undesired deposition can cause the system to clog, backup, or rupture. This puts personnel and the local community in danger of contamination due to the nature of the fluid. See Appendix G for a full HAZOP analysis of the separator.
The greatest safety risks associated with the heat exchangers result from a major increase in the temperature or solids composition in the wastewater. A major increase in temperature of the inlet stream results in incomplete cooling of the stream and feeding of high temperature wastewater to the vermifiltration beds. Prolonged high temperature wastewater prevents contaminant removal by the worms and can result in worm death. An increase in solids composition can clog the heat exchangers or piping between units. See Appendix G for a full HAZOP analysis of the heat exchangers.
The greatest safety risks associated with the vermifilters result from shutdown of the SLS process, a clogged pump or pipe, or some other issue resulting in prolonged lack of flow of greatly decreased flow to the vermifilters. Prolonged lack of flow or greatly decreased flow to the vermifilters would result in death of the worms. See Appendix G for a full HAZOP analysis of the vermifiltration beds.
The main safety issue with vermicompost treatment is related to having heat exchangers to cool the beds. The heat exchangers run cooling water from the plant in simple coils around the vermicompost beds and offset the heat from the ambient environment. Pressure build up or 17 leaking cooling water are the main hazards associated with the heat exchange system. Equipment failure can be caused by a large pressure build up. Leaking water provides a slipping hazard. Incorrect moisture content or temperature in the vermicompost beds can lead to worm death and unviable castings, but is unlikely to cause safety hazard to the equipment operators. Castings are sold as they are produced, and do not pose a storage or transportation hazard. See Appendix G for a full HAZOP analysis of the vermicompost beds.
The proposed process does not require any raw material extraction or transport beyond the initial procurement and transport of worms. In comparison to the environmental impacts of the process for wastewater treatment this impact would be negligible. The only environmental impact of the process is in carbon dioxide released due to mineralization and energy consumed. The energy balance for the process can be seen in Appendix E, and the emissions calculations can be seen in Appendix H.
Carbon dioxide is emitted from this process from two main areas: degradation and mineralization of organic contaminants in the wastewater and utilities associated with running the process. When the BOD and COD in the wastewater are mineralized, upwards of 16 million kg CO2 per year are released (see Table 5.1). Mineralization accounts for 72 percent of the total
CO2 emissions (see Figure 4). The non-mineralization emissions are almost exclusively due to the coolers associated with the heat exchangers (see Figure 5).
Table 5.1: CO2 Emissions in kg/year CO2 Emissions (kg/year) Vermifilters Mineralization 16,155,645 Inlet Cooling Cycle Pump (P-201 A/B) 12,604 Inlet Cooling Cycle Cooler (E-201) 6,123,524 Coil Cooling Pump (P-202 A/B) 504 Coil Cooling Cycle Cooler (E-202) 18,615 Compost Bed Cooling 105,872 Vermicompost Mineralization 6,686 Total 22,423,450
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Figure 4: Overall Carbon Dioxide Emissions
Figure 5: Composition of Non-Mineralization Carbon Dioxide Emissions
The release of CO2 into the atmosphere has a negative effect on climate change and global warming. The total CO2 emissions associated with this process are equivalent to the CO2 emissions of 1,367 average American people ("CO2 Emissions (metric Tons per Capita)"). As suggested in the recommendations below, the use of a CO2 scrubber can greatly reduce the total
CO2 emissions to the atmosphere.
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This process does not have negative impacts for resource depletion, and in fact contributes to resource conservation by providing graywater that can be reused. This process also eliminates the release of toxic chemicals currently used in the current process. This is mostly due to the elimination of buffering of wastewater and other chemicals.
The emissions due to mineralization can be reduced by installing a CO2 scrubber over the vermifiltration beds. Additionally, the emissions from cooling can be greatly reduced by running the process at a higher temperature. This is possible with the use of another species of worm, namely Indian Blue worms. These worms have an optimum temperature of 21-30°C (Bentley). The cooling power savings of using these worms is about 60% of the proposed process (see
Appendix F) and therefore 60% of the CO2 emissions associated with cooling could be eliminated. The cooling power required could also be greatly reduced by insulation the vermifiltration tanks. The CO2 emissions from power associated with the coolers and pumps could be also offset by use of solar power or other renewable energy to power these units. In comparison to the release of CO2 by mineralization, the emissions from power requirements is small. The use of a CO2 scrubber should therefore be strongly considered.
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The economic analysis conducted shows the proposed plant is not economically feasible as designed. The main cause for such a high cost is the cost to purchase the cooling system and the energy usage needed to cool the wastewater in the process (Table 6.1, Appendix C). As designed, the savings of the proposed process - $458,400/year in the disposal of untreated water and $240,000/year for chemicals used in the current treatment process (Appendix I and J) – is greatly outweighed by the required cost. The cost to purchase equipment (Total Bare Module Cost) is almost $5 million, putting the Total Capital Investment at $8.5 million. Electricity costs are estimated to be approximately $89,400 a year, which can be seen in Table 6.2.
Assumptions are made to simplify cost analysis calculations. The material of choice for all equipment contacting wastewater is stainless steel to help prevent oxidation and material failure. The total permanent investment (TPI) is corrected by a factor of 0.95, the TPI for the southwestern region. For the process, it is assumed that employees who currently work at the plant can be retrained for the new process, and that no new employees need to be hired. Equipment depreciation is evaluated over a 5-year period. An interest rate of 5% can be assumed. It is also assumed that the proposed process is using the existing surge tank and feed pump (Seider 2015). For more information on economic analysis calculations, refer to Appendix C.
An ASPEN model (Appendix K) determines the utilities and area of the heat exchangers. The sizing factors from this model are used for costing the equipment in the process.
21
Table 6.1: Total Capital Investment Total Capital Investment Calculation Table
Total Bare-Module Cost $4,866,710
Total Bare-Module Cost for $200,000 Spares Total Cost for Initial $223,392 Catalyst Charges Total Bare-Module Cost for $5,000 Computers Total Bare-Module TBM $5,295,10 Investment TBM 2 Cost of Site Preparation $264,755
Cost of Service Facilities -
Allocated Costs for Utility $68,438 Plants and Related Facilities Total of Direct Permanent DPI $5,628,29 Investment DPI 5 Cost of Contingencies and $1,013,09 Contractor's Fee 3 Total Depreciable Capital TDC $6,641,38 TDC 9 Cost of Land -
Cost of Royalties $332,069
Cost of Plant Startup $796,966
Total Permanent TPI $7,381,90 Investment TPI (corrected) 4 Working Capital $1,107,28 5 Total Capital Investment TCI $8,489,18 TC 9
Table 6.2: Annual Cost Cost Factor $/year Utilities Total $89,400 Operations Total $0 Maintenance Total $0 Operation Overhead Total $0 Property Taxes and Insurance $0 Depreciation $524,851 Cost of Manufacture $619,000 General Expenses $0 Total Production Cost $619,000 Cost Excluding Depreciation $89,400
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Table 6.3: Net Present Value Estimation Net Present Value Estimation for Wastewater Treatment Year fCTDC CWC Depreciation Cos Sales Net Discounte Cash Cum t Earn d Cash Flow PV 5% Flow 1 (4.24) (4.24) (4.04) (4.04)
2 (4.24) (1.11) (5.35) (4.85) (8.90)
3 1.70 0.09 0.70 (0.69) 1.01 0.87 (8.02)
4 2.72 0.09 0.70 (1.33) 1.39 1.14 (6.88)
5 1.63 0.09 0.70 (0.64) 0.99 0.77 (6.11)
6 0.98 0.09 0.70 (0.23) 0.75 0.56 (5.55)
7 0.98 0.09 0.70 (0.23) 0.75 0.53 (5.02)
8 0.49 0.09 0.70 0.08 0.56 0.38 (4.64)
9 0.00 0.09 0.70 0.38 0.38 0.25 (4.39)
10 0.00 0.09 0.70 0.38 0.38 0.24 (4.16)
11 0.00 0.09 0.70 0.38 0.38 0.22 (3.93)
12 0.00 0.09 0.70 0.38 0.38 0.21 (3.72)
13 0.00 0.09 0.70 0.38 0.38 0.20 (3.51)
14 0.00 0.09 0.70 0.38 0.38 0.19 (3.32)
15 0.00 0.09 0.70 0.38 0.38 0.18 (3.14)
16 0.00 0.09 0.70 0.38 0.38 0.18 (2.96) 17 0.00 0.09 0.70 0.38 0.38 0.17 (2.79)
Currently, the process is not profitable after 15 years, with a remaining debt of $2.79 million. The Net Present Value (NPV) at each year after installation of the process can be seen in in Table 6.3. The NPV for the recommended process – with the SLS and vermicompost beds left out of the design - can be found in Table 6.4. After 15 years, a debt of $2.56 million remains. Although this process is still not economically feasible, costs can be greatly mitigated by insulation of vermifiltration beds, using a different process to help cool the water, or using worms with higher optimum temperatures. Underground piping could be used to reduce the load on the inlet heat exchanger by letting heat dissipate, and insulation of the vermifiltration tanks could greatly reduce or eliminate the need for coil heat exchangers in the vermifiltration beds. Using a different species of worms, namely Indian Blue worms which have an optimum temperature range of 21-30°C, would also greatly help reduce energy costs due to cooling.
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Table 6.4: Net Present Value Estimation (Recommended) Net Present Value Estimation for Wastewater Treatment (Recommended) Year fCTDC CWC Depreciation Cost Sales Net Discounted Cash Cum Earn Cash Flow Flow PV 5% 1 (4.06) (4.06) (3.87) (3.87) 2 (4.06) (1.11 (5.17) (4.69) (8.56) ) 3 1.63 0.09 0.70 (0.64 0.99 0.85 (7.71) ) 4 2.60 0.09 0.70 (1.26 1.35 1.11 (6.60) ) 5 1.56 0.09 0.70 (0.60 0.96 0.75 (5.85) ) 6 0.94 0.09 0.70 (0.21 0.73 0.54 (5.31) ) 7 0.94 0.09 0.70 (0.21 0.73 0.52 (4.79) ) 8 0.47 0.09 0.70 0.09 0.56 0.38 (4.41) 9 0.00 0.09 0.70 0.38 0.38 0.25 (4.16) 10 0.00 0.09 0.70 0.38 0.38 0.24 (3.93) 11 0.00 0.09 0.70 0.38 0.38 0.22 (3.70) 12 0.00 0.09 0.70 0.38 0.38 0.21 (3.49) 13 0.00 0.09 0.70 0.38 0.38 0.20 (3.29) 14 0.00 0.09 0.70 0.38 0.38 0.19 (3.09) 15 0.00 0.09 0.70 0.38 0.38 0.18 (2.91) 16 0.00 0.09 0.70 0.38 0.38 0.18 (2.73) 17 0.00 0.09 0.70 0.38 0.38 0.17 (2.56)
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Ultimately, the goal of this process is to efficiently treat wastewater from a dairy processing plant to meet EPA tap water standards. This allows wastewater to be reused in the plant, saving money and resources. The preliminary goal achieved by this process is remediating wastewater to meet standards for City of Phoenix Water and Sewer disposal. This eliminates additional fees currently incurred to dispose of the wastewater. Vermifiltration is the selected process for remediation due to the low energy requirements, small equipment footprint, no catalyst recharge costs (worms reproduce naturally), no use of chemicals, and the ability to process wastewater with one treatment. The initially designed process includes a solid liquid separator, an inlet heat exchanger, six vermifilters with in-situ temperature control, and a set of twelve vermicompost beds for treating solid waste. The optimized process includes vermifilters with in-situ cooling and an inlet heat exchanger. This optimized process is suggested to be implemented if worms can be found that will treat the wastewater to the required standard at higher temperatures (30-35°C). Vermifiltration remediates solids in the wastewater stream. Excluding the solid liquid separator and vermicompost beds reduces the footprint by 20% while reducing energy requirements by approximately 120,000 kWh/year. The inlet heat exchanger is designed to reduce the wastewater feed temperature from 35°C to 25°C, where the wastewater then enters the vermifilters. In-situ coils in the vermifilters run cooling water to offset heating from the ambient environment for the seven months of the year when ambient temperature is greater than 25°C. Additional temperature control can be gained by insulating the vermifilter beds. Based on the level of treatment desired by Shamrock, the effluent leaves the system either ready for disposal or for reuse as grey water. This water can be reused if it undergoes additional treatment to reach tap water standards. Red Wiggler worms (Eisenia fetida) remediate wastewater effectively at 25°C. The wastewater feed requires cooling from 35°C to 22°C, which has an energy duty of 1579 kW. Keeping the vermifilters at 22°C requires an energy duty of about 18 kW on an average day in
Phoenix (24°C). Overall 6,261,000 kg of CO2 are released per year due to energy used in this process. However, 16,160,000 kg of CO2 are released each year from the mineralization of organic contaminants from the wastewater. This significantly outweighs CO2 released from
25 energy generation. Another environmental issue related to this process is resource depletion. If further treatment of the effluent is implemented, the plant can greatly reduce water consumption. There are minimal safety hazards associated with the vermifiltration process. No special personal protective equipment is required to operate this process. The main safety hazards are associated with solids clogging the equipment, resulting in pressure increase and potential equipment failure. The vermifiltration process is not economically viable, even with the optimized design. The cost of purchase of the equipment makes this process unfeasible if using Red Wiggler worms (Eisenia fetida). This is due to the large cooling duty required of the heat exchangers. If Indian Blue worms (Perionyx excavates) are used, the cooling duty is reduced by 60% and smaller heat exchangers could be used. With this change in the design, it is theorized that the process could be economically viable. Shamrock previously has been paying approximately $460,000 per year in fees due to disposal of water and $240,000 to purchase chemicals for water treatment. With the fee-free disposal of water and no need to purchase chemicals, this cost is almost completely diminished. The worms reproduce and do not need to be purchased again after the initial purchase. It is recommended that vermifiltration with Indian Blue worms be tested. If they, or another type of worm, can be implemented to remediate the wastewater at sustainable temperatures, the optimized process should be used. The Indian Blue worm’s optimal temperature range is 21-30°C. Energy requirements associated with cooling the water are greatly reduced with the use of Indian Blue worms, also decreasing the size of heat exchangers and pumps needed. The geology of the rocks, gravel, and sand used in the vermifiltration beds needs to be further investigated so minerals and metals are not introduced into the effluent. The organic contaminants that are remediated are mineralized and release CO2 into the atmosphere. It is recommended that a CO2 scrubber be installed over the vermifiltration unit to mitigate the environmental consequences.
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Bentley. "Blue Worms vs Red Worms & Euros." Red Worm Composting. N.p., 30 July 2015. Web. 21 Apr. 2017. "CO2 Emissions (metric Tons per Capita)." The World Bank. The World Bank Group, n.d. Web. 24 Apr. 2017.
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Seider, Warren D., Daniel R. Lewin, J. D. Seader, Soemantri Widagdo, R. Gani, and Ka Ming Ng. Product and Process Design Principles: Synthesis, Analysis and Evaluation. New York: John Wiley & Sons, 2016. Print.
Sinha, R. K., G. Bharambe, and P. Bapst. "Removal of High BOD and COD Loadings of Primary Liquid Waste Products from Dairy Industry by Vermi-filtration Technology Using Earthworms." Indian Journal of Environmental Protection 27.6 (2007): 486-501. Print. "Water - Thermodynamic Properties." The Engineering ToolBox. N.p., n.d. Web. 21 Apr. 2017.
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The goal of our experiment was to find how well the worms could remediate the dairy wastewater, collect temperature, pH, and tank height data during the experiment. Two HRTs were tested in the experiment. Untreated and effluent samples were also taken to compare values of TOC and heavy metals.
Table A1: Apparatus Parts and Costs System Part Cost Sub Total Rasberry Pi Computer Canakit Pi3 and Supply $41.99
3ft HDMI Cable $4.96
Logitech K360 Keyboard $21.95
32G micro SD Card $13.95
Computer Monitor $69.99
$152.84 Aruduino Controller KeyeStudio Uno R3 $11.99
3x Gikfun Protoshield $11.88
9x 0.1uF capacitors $0
4x 100K 1/8W resistors $0
1x 12V 1A Supply $6.99
Dosing peristaltic pump $13.99
IRF1310N MOSFET $0
1 ohm metal oxide 2W $0
3 - 1K 1/8W resistors $0
74HC4066 analog mux $0
14-pin socket $0.95
2x pin screw jack $0
2x Analog pH Meter Kits $78
pH calibration solution $22
1.5x2" proto board $0
$145.80 Reactor Glass carboy $0
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Glass shop cut of vessel $0 Fiberglass screen $7.05 Worms $25 Vermipost $9 Aggregate $0 Red cellophane wrap $3.99 Scrap wood $0 Screws $0 ¼” PVC sheet $0
$45.04 Inlet and Effluent Tanks 2 x 5 gal measure right $9.36 buckets 2 x screw on lids $14.56
1/4"OD 1/8" ID poly tubing $8.94
1/4"OD 3/16” ID poly tubing $3.77
Quick Fit coupler $3.29
2x Quick Fit 1/8-27NPT $6.98
Drip 1/8 T-coupler $0
1/4" x 36" Brass Rod $8.25
1/2"x48" Aluminum Channel $5.39
Double Sided Tape $0
Resistor Film $0
BeCu wiper $0
4x 1/4"x1/2" Nylon Spacers $1.60
1/2" Poly Rod $0
Silver Epoxy $11.99
3x Food Containers (floats) $3.99
Poly flat stock 1/2" $0
5 x thermistor w/ Teflon wire $8.99 *0 cost indicates materials on hand or free of charge $87.11 Total Cost $430.79
30
Parts: 12 L glass carboy, sand, large aggregate (10-12 mm), medium aggregate (6-8 mm), fiberglass screen, scrap wood, screws, wood glue, clear tape, vermipost, hot glue, carbon filter, red cellophane, stainless steel screen
Tools: Table saw, orbital sander, power drill, jigsaw, tape measure, calipers, clamps, scissors, lathe, CNC Mill, plastic bin, hot glue gun
PPE: Close-toed shoes, pants, ear plugs, safety glasses, N95 woodworking and sanding painted surfaces respirator mask
1. The glass carboy was taken to the UA glass cutting shop and the bottom of the vessel was removed. 2. Height, width, and diameter measurements of the vessel were made and recorded. 3. Scrap plywood was cut down with the table saw to create two 12”x 13” pieces, three 12”x8.5” pieces, two 12”x1” pieces, four 5”x5” pieces, and four 3”x1” pieces. 4. Circles slightly larger than the diameter of the vessel were cut out using a jig saw in the middle of the two 12”x13” boards. 5. A jig saw was used to cut a radius, in the four 5”x5” pieces, to fit the outlet of the reactor vessel. 6. The stand was assembled using wood glue and ¾” wood screws. 7. The reactor vessel was placed in the stand to check for fit. 8. A rectangle of red cellophane was cut to the circumference and height of the reactor vessel. 9. The cellophane was taped to the reactor vessel and the vessel was placed back in the stand.
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10. The10-12 mm aggregate was placed into a plastic bin and washed thoroughly with water. 11. A piece of the fiberglass screen was placed at the bottom of the vessel to keep the aggregate inside the reactor. The 10-12mm aggregate was then placed into the bottom of the vessel. (approximately 8 cm high). 12. The 6-8mm aggregate was placed into the plastic bin and washed thoroughly with water. 13. The 6-8mm aggregate was then placed on top of the 10-12mm aggregate in the vessel (approximately 8 cm high). 14. The sand could not be washed in the bin, so approximately 8 cm of sand was placed on top of the 6-8mm aggregate. The reactor was then flushed with water until the effluent ran clear. 15. The fiberglass screen and stainless steel mesh were cut into two circles with the same inside diameter of the reactor vessel. The two pieces were adhered to each other using a hot glue gun, and the edges were coated in a layer of hot glue to prevent any sharp edges. 16. The screen filter was placed on top of the sand layer. It was checked to ensure it covered the entire area. 17. A layer of vermipost was added on top the screen (approximately 9 cm). 18. A piece of ¼” PVC sheet was used to create the top for the reactor. It was cut using the saber saw and sanded until the diameter was about ½” wider than the top of the reactor vessel. 19. The CNC mill was then used to cut a 7-1/2” hole in a second piece of PVC sheet. It was glued to the top to create a cap for the vessel top. 20. Lid holes were cut using the mill for the inlet stream tubing, carbon air filter and the temperature sensor.
**See Fig. A3, A7, A9, A13 for reference**
Parts: 2 x 5 gal. buckets, 2 x screw on lids
Tools:
32
Power dill
1. One 1/2” hole was drilled in the center of each lid for the potentiometer float shaft to fit through. 2. One 5/16” hole was drilled approximately 2” from the edge of the lid for the inlet/outlet tube. 3. Inlet tank only: one 5/16” hole was drilled for the temperature sensor and one 5/8” hole for pH sensor cable.
**See Fig. A6, A8, A12 for reference**
Parts: 5 x thermistor cable assembly (100K Ω at 25ºC), solder, ¼” OD 1/8” ID poly tubing, 5 x 2-pin female socket (came with Arduino proto board)
Tools: Hot glue gun, wire strippers, soldering iron
1. Cut poly tubing to length adequate to prevent water damage (for inlet tank, reactor, ambient, and effluent temperature sensors). 2. Threaded cable assembly through tubing and left end of thermistor and approx. ¼” of cable exposed. 3. Thermistor was encased with hot glue and excess cable was pulled into tube to completely seal the assembly. 4. The other end of the tubing was then hot glued to seal the wires. 5. The ends of the wires were stripped and then soldered to the 2-pin female sockets.
**See Fig. A1, A3, A7, A12, A13, A15 for reference**
Parts: 33
¼” OD 3/16” ID poly tubing, 3 x 1/8” drip t-connectors
Tools: wire strippers, drill press, 1/16” drill bit
1. Cut two 7” and two 1.5” lengths of poly tubing. 2. Drill approx. 1” spaced holes in tubing. 3. Connect two 7” lengths of tubing with two t-connectors to create a circle. 4. Add 1.5” tube to center of each t-connector. 5. Attach last t-connector between the 1.5” tubes inside ring.
**See Fig. A4 for reference**
Parts: 2 x ½” aluminum u-channel (14” length), 2 x ¼” brass rod (18” length), 2 x strips resistive film (1/4” wide by 9” length), 2-part silver epoxy, double-sided tape, nylon spacers, 2x BeCu wipers, ½” scrap plywood, wire-wrap wire, solder, tie wraps, 2 x 8-80 screw, ½” polyethylene sheet, 2 x ½” polyethylene rod, 2 x Ziploc food storage containers, DI water, 2 x 5-gallon bucket, 2 x screw on lids
Tools: Hot glue gun, soldering iron, screw driver, wire strippers, CNC mill, ¼” drill bit, ½” drill bit
1. Attached double-sided tape to bottom of aluminum u-channel. 2. Attached resistive film to center of tape. 3. Mixed two-part silver epoxy and made ¼” long termination on ends of each resistor element. 4. Attached stripped wire-wrap wire to terminations with silver epoxy. 5. Milled and drilled poly sheet to create wiper slider. 6. Soldered wire to BeCu wiper.
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7. Attached wiper with 8-80 screw to wiper slider. 8. Slid wiper assembly onto brass rod. 9. Placed nylon spacer on each end of brass rod. 10. Attached spacers to aluminum u-channel with tie wraps. 11. Drilled ¼” hole into end of poly rod. 12. Drilled ½” holes in three 1”x4” poly blocks and one 1”x8” poly block. 13. Drilled second ½” hole into 1”x8” poly block ¼” from end. (for pH sensor in inlet tank) 14. Hot glued one 1”x4” block to bottom of each food storage container. 15. Hot glued remaining poly blocks to top of each container. 16. Drilled hole through tops of containers at existing hole in poly blocks. 17. Placed undrilled end of ½” poly rod through hole in food containers. Hot glued rod into place. 18. Attached potentiometer assembly to plywood form (from scrap plywood) and attached plywood to lid using screws. 19. Attached float assembly to bottom of brass rod with screw. 20. Placed float assembly (food container) into 5-gal. bucket. 21. Soldered three-wire cable to end terminations and wiper. 22. Soldered three-pin cable connector to other end of cable. 23. Strain relief wires of potentiometer. (hot glue) 24. Added enough DI water to 5-gal bucket to until float lifted potentiometer wiper.
**See Fig. A6, A8, A12, A14 for reference**
Parts: Ziploc food container, poly block, ¼” quick connect fitting, ¼” OD 3/6” ID tubing, screws
Tools: Drill, hot glue gun, ½” drill bit, ¼” drill bit, 3” hole cutter, screw driver
1. Drilled 3” hole into top of food container (at an edge).
35
2. Drilled ½” and ¼” holes in top of food container and poly block (for sensors). 3. Drilled ½” hole into a side of food container approx. 1” above bottom (for outlet drain). 4. Hot glued quick connect fitting into ½” hole on side of food container. 5. Attached ¼” tubing to fitting. 6. Attached poly block to reactor base with screws.
**See Fig. A3, A13 for reference**
Parts: 2 x analog pH sensor, screws, plywood board
Tools: Screw driver
1. Attached pre-amp boards to plywood board. 2. Placed one pH sensor into end hole of inlet tank float. 3. Routed cable through hole in tank lid. 4. Placed second pH sensor in poly block holder at secondary effluent tank. 5. Connected coaxial cables to pre-amps.
**See Fig. A3, A10, A12, A13, A16 for reference**
36
Figure A1: Multiplexor and Thermistor Circuit Figure A2: Pump Motor Circuit
37 Figure A3: Reactor and Secondary Effluent Tank Figure A4: Dispersion Mechanism
Figure A5: Control GUI
Figure A6: Inlet Tank and Potentiometer Figure A7: Reactor and Secondary Effluent Tank 38
Figure A8: Effluent Tank and Potentiometer Figure A9: Reactor Top and Carbon Air Filter
Figure A10: Mounted Circuit Boards and pH Preamps
39
Figure A11: Dosing Pump
potentiometer
5 gal tank Inlet tube
pH meter temperature meter float
Figure A12: Schematic of Inlet and Effluent Tanks
40
Figure A13: Schematic of Vermifilter Reactor
41
Figure A14: Tank Height Potentiometer Assembly
Thermistor Circuits for Temperature Monitoring +12V
1 M
IN4001 0.1µF
1K IRF1310 12
Figure A15: Thermistor Circuits for Temperature Monitoring Schematic
42
2 k n a T
2 1 3
r e V p 5 i + w F µ 1 . 0 1 k n
a T
2 3 1
s r e r t e V e p i 5 + w M
F H µ p 1
. r 0 o f g V n 5 s i 1 + r 1 A 8 n 1 o o s i t n i e d S n
t o h 6 C 6
g l i 0 4 a e n H g i k S n
a d T n 0 0 9
1 A a d r n o a x e l p i t l u M g F o l µ 1 a . F 0 n µ A 1 . 0 4 1 9 N I 4 1 9
N
I K 1 V
t
5 u
+ o K 1 2 H p t 5 u V + o 1 H
p
Figure A16: Analog Multiplexor and Signal Conditioning for pH Meters and Tank Tank and Meters pH for Conditioning Signal and Multiplexor Analog A16: Figure Height Sensors Schematic Sensors Height
43
Thermistor Circuits for Temperature Monitoring
+12V
1 M
IN4001 0.1µF
1K IRF1310 12
Figure A17: Thermistor Circuits for Temperature Monitoring Schematic
44
The goal of Arduino code was to collect and record temperature data for the inlet tank, reactor, effluent tank and ambient; pH data for the inlet tank and secondary effluent tank; height changes in the inlet and effluent tanks; and to control the flow rate of the dosing pump. Data is collected every 10 seconds. The data can be seen in the memo pad in Fig. A5 (upper right hand corner). When new data is collected, the old data is appended to an invisible memo pad. This memo pad is saved every hour as a new file.
Flow rate, and therefore retention time, is adjusted by inputting the seconds for the pump to be on in the Pump on sec of the GUI (Fig. A5), and how often the pump should turn on in the Pump interval Min section (see Fig. A5).
Offset in the pH sensors can also be adjusted in the GUI. For our experiment, pH1 needed an offset of -6 to be calibrated correctly; pH2 needed no adjustment.
The GUI also shows a real-time graph of the pH, temperature sensors, and the relative tank heights (see Fig. A5). Temperature bounds were chosen to be between 15ºC and 35 ºC since the ambient temperature the experiments took place in was well controlled. pH bounds were set from 4 to 10 since no extreme changes in pH were expected, and tank height bounds were set from 0 to 8 in accordance with the bounds of the potentiometer build. Basic controls and logic for the system are as follows: setup() serial port 9600 baud pins 8-13 set as digital outputs 8-11 are for CD4066 analog mux and 12 is for pump motor control pin 7 set as digital input for future use
45
Table A2: Analog Multiplexor Mapping Command Arduino Instrument 8 9 10 11 Analog In Analog In acd0000 A0 pH-1 1 0 - - acd0001 A0 pH-2 0 1 - - acd0002 A1 Tank-1 “ - - 1 0 acd0003 A1 Tank-2 “ - - 0 1 acd0004 A2 Temp-1 C - - - - acd0005 A3 Temp-2 C - - - - acd0006 A4 Temp-3 C - - - - acd0007 A5 Temp-4 C - - - -
*-no affect; Pin 8 = Pin 9 = 1 is an invalid state; Pin 10 = Pin 11 = 1 is and invalid state
Main loop()
If current time(ms) > marked time(ms), turn off pump motor
If a serial character is available Save it in the character array If it was the @ character, reset the array pointer to zero After three command characters are received Read up to four additional integer characters Execute a command search after four integers, a
Command Search fndcmd()
Look for match of first three characters to a command string If a match is found, execute the command using the integer value as an input variable
‘adc’ Sets the CD4066 mux bits and Arduino analog input according to the variable 0-7, reads the ADC and returns the integer value with a letter prefix A-H for the channel
46
‘pmp’ Turns on the pump motor, multiplies the variable by 1000 = delay(ms) marked time(ms) = current time(ms) + delay(ms). Returns the input value
‘led’ The variable = 0 turns off the LED and = 1 turns the LED on and it is the returned value
‘din’ Returns the level of pin 7 as a 0 or 1
47
An image of the GUI can be seen in Fig. A5.
TimerChkStatus() ReadComByte() Interval = 1ms Get Serial Data Memo1() Memo Pad Strings
Timer7() Pumpdata[1:512,0:8] PumpTime[1:511] Interval = 5001ms Single Float Array Date Time Array Parse Commands pH1, pH2, tank1, tank2, Get Return Values temp1, temp2, temp3, Scale Values and Save temp4, pumptime Update Chart and Labels Send Command String DumpData.Click() Shift Data in Array TimerPoll() Mark Time Send Command String Interval = 10s Send Arduino commands to Request Arduino Data read all ADC channels Update Web Files At 1 hr intervals, save 360 values from array data Form1 Values Canvas Graphics Plot Pump repeat interval 1 to 1440 min Text Labels Button Controls Pump run interval seconds Spin Controls
TimerPumpInterval() Interval = 1 to 1440 min Send Arduino Pump Command
Figure A18: Lazarus GUI Logic
48
Appendix B: Lab Report
Vermifiltration was used to filter dairy wastewater to investigate the transient behavior of contaminant removal, measured by total organic carbon, arsenic, cadmium, lead, and selenium concentration. Two hydraulic retention times were tested, 8 hour and 11 hour, and produced a decrease in organic carbon by 51-81% and 56-79% respectively. Heavy metals were not remediated, instead they were added by the materials of the system. The 10-hour HRT treatment produced effluent that met EPA standards for arsenic, cadmium, lead, and selenium. The 8-hour HRT treatment produced effluent that met the heavy metal standards, other than arsenic, which exceeded standards by approximately 1 ppb.
Introduction
Vermifiltration is used to effectively and efficiently remediate wastewater. Vermifiltration can reduce contaminant levels to acceptable concentrations for water reuse, particularly the biological oxygen demand, the chemical oxygen demand, total suspended solids, and heavy metal concentrations (Sinha et al. 2007). The level of remediation depends on the hydraulic retention time through the vermifiltration vessel, and the level of contamination of the influent wastewater. The vermifiltration unit consisted of a wastewater distribution system, a packed bed reactor with segments of rock, gravel, sand, and compost with red wiggler worms, and an effluent collection vessel.
Hydraulic retention times were calculated by using the void volume of the vermifiltration vessel and the flow rate of wastewater influent. Organic degradation was measured by analyzing total organic carbon (TOC) concentration, and heavy metal remediation was measured by analyzing samples for their metal concentration using ICP-MS.
Experimental
A detailed description of the experimental setup can be found in Appendix A. The system consists of a wastewater feed system, a vessel with segmented 4" layers of pre-washed – rock (10-12mm), gravel (6-8 mm), sand, and compost with worms – and an effluent collection vessel, with temperature and pH monitoring at the inlet and outlet. Two different hydraulic retention times were tested in the system, 8-hour HRT and 11- hour HRT, by varying the set flowrate. There was insufficient wastewater to allow the system to 49 come to steady state (assumed to be 5 bed volumes of wastewater, 5 time constants) for either of the tested hydraulic retention times. However, data was collected to show the transient behavior of the system. Effluent water samples were collected at documented times throughout the experimental trials. Samples were collected in metal free tubes. Temperature and pH were monitored to ensure the system was at optimum conditions for the worms to remediate the wastewater, approximately 25 °C and within 2 pH units of neutral. The pH data can be seen in Fig. 3 and 4. The fluctuation in Experiment 2 seen at about 250,000 min was due to sensor error. The voltage leak was fixed and the experiment continued.
In the lab, samples were prepared for analysis by filtering with 0.45 µm nylon filters and diluting by a factor of 10. Sample aliquots for TOC testing were diluted with MilliQ water (18.2 MΩ-cm resistivity), and sample aliquots for heavy metal testing were diluted with 1% nitric acid. TOC was analyzed using the Shimadzu TOC-L (catalytic oxidation), and heavy metal concentration was analyzed using the Agilent 7700 Inductively-coupled mass spectrometer. Results
Figure 1: TOC(ppm) vs. Time of Wastewater Samples
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Figure 2: Mean Heavy Metal Concentration (ppb) of Wastewater Samples
pH vs Time (Experiment 1) 8.5 8 7.5 7
pH 6.5 pH1 6 pH2 5.5 5 0 500 1000 1500 2000 2500 time (min)
Figure 3: pH vs Time for Experiment 1
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pH vs Time (Experiment 2) 9 8.5 8 7.5 7 pH pH1 6.5 pH2 6 5.5 5 0 1000000 2000000 3000000 4000000 time (min)
Figure 4: pH vs Time for Experiment 2
Total organic carbon concentration for each treatment is plotted against the time in Figure 1. The untreated sample had a constant concentration of 360 ppm organic carbon. For the 8-hour hydraulic retention time treatment, TOC was relatively constant at about 150 ppm until approximately 18 hours into the experiment trial. TOC then dropped to 68 ppm. The curve for the 11-hour HRT treatment vs time has an initial drop at the beginning of the treatment before rising to 160 ppm and steadily decreasing to 76 ppm organic carbon. Figure 2 displays the mean heavy metal concentration (based on each species) versus the treatment type, alongside the EPA limit for drinking water. The untreated sample had the lowest metal concentration for each species of metal, while the 8-hour hydraulic retention time had the highest metal concentration for each species. The mean arsenic concentration of the samples from the 8-hour HRT was the only metal concentration that exceeds EPA drinking water standards, and does so by approximately 1 ppb.
Discussion
The untreated sample had the highest organic carbon concentration, as expected. The organic carbon concentration of the 8-hour HRT effluent was relatively constant at 150 ppm before beginning to decline after 18 hours, or just less than two bed volumes of water, three bed
52 volumes shy of reaching steady state. As the system approached steady state, more organic carbon was removed. The samples ranged from 51-81% removal of organic carbon. The 11-hour HRT was the first trial that was run, and the vermifiltration bed had to be pre-wetted before introducing the wastewater. It is believed that some of the water that was used to wet the system and wash the materials may have been sampled at the beginning of the run. If this dip in organic carbon concentration can be explained as thus, then the data makes sense. The organic carbon concentration further decreased the longer the system had been running, as it approached steady state. The removal of organic carbon ranged from 56-79%. The sample with the highest removal of organic carbon was collected 23 hours into the trial, or after approximately two bed volumes of water had passed through the filter. The similar removal rates for the 8-hour HRT at 3 time constants, and the 10-hour HRT at 2 time constants implies that the 11-hour HRT treatment is more effective at removing organic carbon. As the system approached steady state in both trials, organic carbon was further removed; the 8-hour HRT trial was closer to steady state than the 10-hour HRT trial was. The untreated sample had the lowest heavy metal concentration for all species investigated. This was an unexpected result. Heavy metals were introduced into the wastewater by the experimental setup. The gravel, rocks, and sand were acquired from a Tucson business that has materials from local sources (soils and rocks around Tucson are known to have naturally high arsenic concentrations). When designing the experimental setup, the geology of the materials was not taken into close enough consideration. Tubing and the plastic feed tank almost definitely introduced metals to the system as well. The levels of all investigated heavy metals were lower in the 11-hour HRT samples than in those of the 8-hour HRT. Although a higher retention time allows for more time for metals to leach into the water, the water had more time to be in contact with the microbes from the worm castings that remediate heavy metals. Another possible explanation could be that metals sorbed to the soil and rocks in the first experimental trial, the 1- hour HRT treatment, and these sites were occupied and unable to sorb the metals in the succeeding trial, the 8-hour HRT treatment. However, the metals were remediated more effectively with a longer retention time in this experiment.
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Conclusions The vermifiltration of wastewater produced cleaner effluent as the system approached steady state. Although steady state was not reached, both the 11-hour and 8-hour hydraulic retention time treatments produced effluent where the total organic carbon concentration had been reduced by approximately 80%. The system added heavy metals to the water effluent, but the longer hydraulic retention time produced cleaner effluent, so it is presumed that the microbes in the worm castings helped to remediate the added metals. If this experiment were to be rerun, the system would be allowed to come to steady state for each hydraulic retention time tested. Based on the observed trends, it is expected that the reported literature removal rates of 98% biological oxygen demand could be replicated (Sinha et al. 2007). Total organic carbon was measured instead of BOD due to unavailability to test BOD, and is considered an analogous analysis for this level of the experiment. In addition, the geology of the rocks, gravel, and sand would be taken into consideration to avoid adding any heavy metals to the system.
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Heat Exchangers
2 (1) 퐶퐵 = 푒푥푝(11.667 − 0.8709 ln(퐴) + 0.09005ln(퐴) )………Fixed head heat exchanger 푏 (2) 퐹 = 푎 + ( 퐴 ) ……………………………………………………..……..Material factor 푀 100 (3) 퐶푃 = 퐹푃퐹푀퐹퐿퐶퐵………………………………………………...….Cost of heat exchanger 2 (4) 퐶퐵 = 푒푥푝(11.967 − 0.8709 ln(퐴) + 0.09005ln(퐴) )………………….Kettle vaporizer Pumps and Motors
푄퐻휌 (5) 푃퐵 = ……………………………………………………..Pump break horse power 33,000휂푃 2 (6) 퐶퐵 = 푒푥푝(7.8103 + 0.26986 ln(푃퐵) + 0.06718ln(푃퐵) )…Reciprocating plunger pump (7) 퐶푃,푝푢푚푝 = 퐹푀퐶퐵…………………………………...…………………………Cost of pump 2 (8) 휂푀 = 0.80 + 0.0319 ln(푃퐵) − 0.00182ln(푃퐵) 푃퐵 (9) 푃퐶 = …………………………...……………………………Motor power consumption 휂푀 2 3 (10) 퐶퐵 = exp(5.8259 + 0.1314 ln(푃퐶) + 0.053255 ln(푃퐶) + 0.028628 ln(푃퐶) − 4 0.0035549 ln(푃퐶) )………………………………………………………..…Pump motor (11) 퐶푃,푚표푡표푟 = 퐹푇퐶퐵……………………………………………………..Cost of motor (12) 퐶푃 = 퐶푃,푝푢푚푝 + 퐶푃,푚표푡표푟 ……………………………..………..Total cost of pump Reactor and Storage Vessels
0.72 (13) 퐶푃 = 18푉 ……………………………...………Cost for reactor/storage vessels Separator
0.58 (14) 퐶푃 = 3,050퐴 …………………………………………………Cost for separator Bare-Module Cost
(15) 퐶퐵푀 = 퐶퐼 ∗ 퐹퐵푀퐶푃………………………………………………Bare-Module cost
All equations obtained from Seider’s ‘Product and Process Design Principles’ 3rd edition, chapter 22.
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TCI Calculation Table
Total Bare-Module Cost Cost of Equipment (CBM) 1 Total Bare-Module Cost of Spares Flat Fee Estimation 2 Total Cost for Initial Catalyst Charges Flat Fee Based on Calculations 3 Total Bare-Module Cost for Computers Flat Fee Estimation 4 Total Bare-Module Investment (TBM) TBM Sum 1,2,3,&4 5 Cost of Site Preparation 5% of TBM 6 Allocated Costs for Utility Plants and Related Estimation Based on Cooling 7 Facilities Total of Direct Permanent Investment (DPI) DPI Sum 5,6,&7 8 Cost of Contingencies and Contractor’s Fee 18% of DPI 9 Total Depreciable Capital (TDC) TDC Sum 8&9 10 Cost of Land 2% of TDC 11 Cost of Royalties 5% of TDC 12 Cost of Plant Startup 12% of TDC 13 Total Permanent Investment (TPI) TPI Sum 10,11,12,&13 14 TPI Corrected for Southwest Region TPIc 95% of TPI 15 Working Capital 15% of TC 16 Total Capital Investment (TC) TC 115% of TPIc 17
The annual costs table was generated using Table 23.1 in Seider ‘Product and Process Design Principles’ 3rd edition, chapter 23.
More in-depth calculations can be seen in the excel file titled “Cost Calcs FINAL.xlsx”.
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Shamrock Target Process Theoretical In Out % Out % (kg/day) (kg/day) Removed (kg/day) Removed BOD 3,046 56.8 98.1 24.1 99.21 COD 4,611 170 96.3 36.4 99.21 TSS 291 227 21.9 0 100 Arsenic 0.058 0.023 60.8 0 100 Lead 0.311 0.023 92.7 0 100 Selenium 0.295 0.114 61.5 0 100 Cadmium 0.295 0.007 97.7 0 100 Water 2,271,246 2,271,246 0.0 2,271,246 0 Total 2,279,194 2,271,700 0.329 2,271,306 0.346
Values calculated based on given target levels from Shamrock (Appendix I) and literature values (Sinha).
The overall energy balance for this process is as follows: Inlet Stream Energy + Ambient Heating/Cooling + Heating/Cooling of Exchangers = Outlet Stream Energy
푚푖푛퐻|푇푖푛 + ℎ퐴(푇푎 − 푇) + 퐸퐻퐸 = 푚표푢푡퐻|푇표푢푡 The following example is evaluated at an ambient temperature of 35°C, an average summer temperature for Phoenix, AZ, and a 22°C operation temperature, which is the maximum optimum operating temperature.
푚푖푛퐻|푇푖푛 ℎ퐴(푇푎 − 푇) 퐸퐻퐸 푚표푢푡퐻|푇표푢푡 2,279,194 kg/day * 5 W/m2K * 1295m2 * -(71.94 kJ/day + 2,279,194 kg/day * 146.7 kJ/kg (308.15K - 295.15K) 123,969,920 92.2 kJ/kg kJ/day) 334,357,760 kJ/day 84.18 kJ/day -123,970,004 210,141,687 kJ/day kJ/day 210,387,840 kJ/day 210,141,687 kJ/day This example balances given rounding errors in specific enthalpy ("Water - Thermodynamic Properties").
See the Excel sheet titled “Heat Removal Calculations Final.xlsx”.
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See the HAZOP document titled “HAZOPFormConnorStahlCHEE443.docx”
See the HAZOP document titled “HAZOPForm Catherine.docx”
See the HAZOP document titled “Kara_Kanto_vermifilter_HAZOP.docx”
See the HAZOP document titled “HAZOPForm_Calliandra Stuffle.docx”
See the Excel sheet titled "Vessel Calculations.xlsx".
See the Excel sheet titled "Emissions calculations.xlsx".
Wastewater Treatment from a Dairy Processing Plant Project Overview: A dairy processing plant in Phoenix, Arizona generates 600,000 gallons of wastewater per day which is currently channeled into a municipal drain for disposal. Between sewage fees and water replenishment costs, the plant spends $38,200 per month to discard the wastewater. It is believed this cost can be lowered by treating and reusing the water across the facility. The aim of the project is to design an addition to the plant that can clean the wastewater by reducing the contaminants listed in Table 1 from their current state to concentrations that fall within EPA guidelines. Description Current Influent (mg/L) Target Effluent (mg/L) Biological Oxygen Demand (BOD) 1341 25 Chemical Oxygen Demand (COD) 2030 75 Total Suspended Solids (TSS) 128 100 Metal Description Arsenic 0.0255 0.01 Lead 0.137 0.015 Selenium 0.13 0.05 Cadmium 0.13 0.005
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Meeting/ Phone Log
Date: 2-27-17
Contact Information Name: Jack Garrett Company: Shamrock Phone number: N/A
Team Members Present: Kara Kanto, Catherine Patton, Connor Stahl, and Calliandra Stuffle
Summary of Information, that pertains to the report (costs, flow rates, sizes, assumptions). The dairy processing plant produces 600,000 gallons of waste water per day. The temperature the water leaves the plant is approximately 90°F. They use about $20,000 in chemicals per month to treat the water.
See the Aspen file titled “443 Waste Treatment FINAL.apw”
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