Tuesday, November 12
Technical Sessions – 1:15-5:00 PM
The ELGs are Coming! Really. FGD Treatment Alternatives
IWC Rep: Tisha Scroggin-Wicker, P.E., Burns & McDonnell, Chicago, IL
Session Chair: Thomas Higgins, P.E., Ph.D., Worley, St. Augustine, FL
Discussion Leader: Lanny Weimer, SUEZ Water Technologies & Solutions, Ormond Beach, FL
The original ELGs were based on biological treatment for FGD wastewater and physical and chemical treatment for low volume wastes. Our first presenter as a first adopter of FGD biological treatment will share the tricks they developed to make this technology work. Reliable operation depends on monitoring wastewater composition in real time. Our next paper presents results of evaluation of real time monitoring equipment. Specific FGD wastewater characteristics or local limits can make biological treatment undesirable. ZLD is sometime selected for reliable compliance, although it can be expensive. Our next paper presents experience with membrane systems for brine concentration, making thermal evaporation feasible. Our final paper presents laboratory and conceptual design studies for treating coal pile runoff to achieve low volume wastewater effluent limits.
Consider Attending: W1, W3, W4, W8, W9, W10, W11, W15, W17, W21
IWC 19-45: Utility Experience on Commissioning and Operating FGD WWT
Derek Henderson, P.E., Duke Energy, Raleigh, NC; Jared Troyer, P.E. and Ray Lidke, Duke Energy, Charlotte, NC; William Kennedy, P.E., Stantec, Charlotte, NC
New flue gas desulfurization wastewater treatment (FGD WWT) systems are being installed at coal generating facilities to facilitate compliance with the Steam Electric Power Generating Effluent Limitation Guidelines (ELGs) and local National Pollutant Discharge Elimination System (NPDES) permits. These systems are comprised of multiple treatment units that provide primary, secondary and tertiary treatment. A utility’s experience in commissioning and operating these new FGD WWT systems.
Discusser: Nelson Fonseca, SUEZ Water Technologies & Solutions, Oakville, ON Canada
IWC 19-46: Near Real-Time Detection of Mercury and Selenium in FGD Wastewaters for Process Control
Cassandra Hutson and Craig Katkic, AECOM, Austin, TX; Naomi Goodman, EPRI, Palo Alto, CA
Some coal-fired power plants have wastewater treatment (WWT) systems to reduce the concentrations of mercury, selenium, and other analytes in their flue gas desulfurization (FGD) wastewater. WWT system operators would benefit from the ability to monitor concentrations of these analytes on site and in near real-time to troubleshoot the FGD system and/or treatment processes before compliance issues arise. This paper presents results from laboratory and field evaluations of several online monitors and benchtop analyzers.
Discusser: Robert Simm, Stantec, Chandler, AZ
IWC 19-47: Vortex-Assisted Nanofiltration and Reverse Osmosis for FGD Wastewater Meets and Exceeds 2015 Effluent Limitation Guidelines to Produce Reuse-Quality Effluent: Operational Findings for Maximizing Flux and Minimizing Scaling
Jonathan Liberzon, Jonathan Chen and Tzu Lung Lin, Tomorrow Water (BKT), Anaheim, CA
The EPA’s 2015 effluent limitation guidelines (2015 ELG) mandate treatment of flue gas desulphurization wastewater (FGD-WW) to meet selenium (Se), arsenic (As), mercury (Hg) and nitrate/nitrite (NOx) limits prior to discharge. While conventional physical/chemical and biological treatment systems may succeed in meeting discharge requirements, reuse of this effluent remains difficult due to high total dissolved solids (TDS) and corrosivity. FGD-WW also contains concentrated scale-forming compounds (mainly sulfates with various divalent metals), which cause severe membrane fouling. A novel anti-fouling membrane system (AFMS), which uses rotating, vortex-generating blades, was previously tested in the treatment of FGD-WW (Liberzon et al., IWC 2018). This system was used to batch-concentrate pretreated FGD-WW over 8 months, achieving fluxes of 61 gal/ft2d (GFD) or 108 liter/m2hr (LMH) with negligible scaling. The AFMS nanofiltration (NF) membranes greatly reduced 2015 ELG regulated species, but were not able to guarantee adherence to all discharge standards without additional downstream membrane filtration, as modeled by reverse osmosis (RO) projection software.
This study builds upon previous research by operating an AFMS in conjunction with downstream high-TDS RO membranes to verify the performance of the complete treatment train on raw (not pre-treated) FGD-WW at a second large power plant. The AFMS and RO unit processed 630,082 gallons of raw FGD pond water over 3 months, producing effluent that met and exceeded the 2015 ELG standards. Combined removal rates for regulated species were at least 99% for Se, 98% for Hg, 78% for NOx, and 28% for Ar. Moreover, combined AFMS NF and RO removed 99% of sulfates and 95% of TDS, producing a low-TDS (192 mg/l) product appropriate for various reuse applications within the plant. In order to improve flux and recovery through the AFMS, several operational variables were changed from the earlier study. These included operating in single-pass (rather than batch) mode, increasing blade speed, utilizing chemical anti-scalants, and reducing the CIP frequency and chemical use. Taken together, these operational strategies achieved a 21% improvement in average flux (75 GFD or 128 LMH), despite 64% higher sulfate concentrations as compared to the earlier study. Clean water recoveries in the AFMS also increased to a maximum sustainable recovery of 85%. These results suggest that combined AFMS and RO systems can compete with conventional technologies for treating FGD wastewater while also producing reuse-quality effluent and downsizing evaporation systems in zero-liquid discharge treatment systems.
Discusser: David Pernitsky, Stantec, Calgary, AB, Canada
IWC 19-48: Coal Pile Runoff: A Management and Treatment Case Study to Find a Resourceful Solution
Chloe Grabowski, HDR, Missoula, MT; Chad McKnight and Chandler Shelton, Southern Company, Birmingham, AL
This paper will present a case study of a project at a large coal fired power plant in North America. The plant’s coal pile runoff flows to a coal pile runoff pond and is pumped to their ash surface impoundments for treatment via settling prior to discharge. Upon closure of their impoundments, treatment of the coal pile runoff will be required to meet the plant’s NPDES limits. This paper will discuss the alternatives evaluated which focused on two goals: minimize suspended solids entering the coal pile runoff pond through storm water management techniques and modify the existing coal pile runoff pond to facilitate removal of suspended solids to permit levels prior to discharge. The wastewater testing, modeling, and analysis performed as part of this study will be discussed as well as the significant cost savings, both in capital and operational costs, achieved for the plant.
In response to the Environmental Protection Agency’s (EPA) Steam Electric Effluent Limitations Guidelines (ELGs) and Coal Combustion Residual (CCR) Rules, coal fired power plants have closed or are in the process of closing their CCR-related surface impoundments. In addition to ash handling challenges, this change presents a huge wastewater management challenge as many facilities discharge their low volume wastewater streams, along with stormwater flows such as coal pile runoff, to their surface impoundments. The impoundments provide for flow equalization and treatment (solids settling) prior to discharge. As facilities work toward impoundment closure, rerouting and evaluating treatment options for the low volume wastewater flows can become a bigger task with a higher price tag than anticipated forcing the need for resourceful solutions to avoid cost overruns.
When it comes to treatment of low volume wastewater flows, coal pile runoff presents a unique challenge given the high solids and fine particle distribution. Most coal pile run-off ponds were originally designed primarily to collect, contain, and transfer the runoff volume to the CCR impoundments and not to maximize settling/removal of solids to achieve discharge limits. Therefore, facilities must find new ways to handle coal pile runoff in order to meet discharge limits with this wastewater stream.
Discusser: John Peichel, SUEZ Water Technologies & Solutions, Minnetonka, MN
Concentrate Management
IWC Rep: Jane Kucera, Nalco Water, an Ecolab Company, Naperville, IL
Session Chair: Wayne Bates, Hydranautics, Rockton, IL
Discussion Leader: Matthew Flannigan, Nalco Water, an Ecolab Company, Naperville, IL
MLD and ZLD systems are becoming more popular as the industry is being asked to maximize water recovery and minimize the volume of liquid concentrate (brine) that requires disposal. This session reviews current concentrate disposal methods with an emphasis on the use of membrane technologies upstream of evaporators/crystallizers. We consider these processes to be MLD (Minimum Liquid Discharge) since recoveries can be limited to 90-97% of the feed and not 100% as expected for a ZLD process.
Consider Attending: W1, W3, W8, W10, W11, W15, W16, W17, W21, W22
IWC 19-49: Brine Management: A Review of Options and Technologies
John Korpiel, P.E. and Kurt Blohm, Veolia Water Technologies, Moon Township, PA; Corey Skadahl, Veolia Water Technologies, Plainfield, IL
The brine byproduct from an industrial desalination process typically has high salinity, high scaling/fouling potential, is highly corrosive, and contains concentrated chemical contaminants. As a result, brine can be harmful to the environment, especially aquatic life, if not properly treated and disposed. This paper reviews the options and technologies available for brine management, including surface water discharge, deep well injection, land application, beneficial reuse, evaporation ponds, and treatment via membrane-based and thermal technologies for minimization or zero liquid discharge.
IWC 19-50: Achieving Minimal Liquid Discharge (MLD) with Advanced Membrane Systems for Maximized Volume Reduction: 5X, 20X, 40X, and 70X!
Malcolm Man, Benjamin Sparrow, Anisa Maruschak and Geer Qile, Saltworks Technologies Inc., Richmond, BC, Canada
This paper presents novel options, pilot test results, and economics for water plant designers. Readers will learn how to concentrate brines to 130,000 mg/L total dissolved solids (TDS) with reverse osmosis membrane technology while avoiding scaling and fouling. The work is intended to inform on the widening use of membrane-based brine concentration systems in order to offset more expensive evaporative or disposal methods. Pilot results are presented for a real industrial project on scale saturated cooling tower blowdown brine at 1,800 mg/L TDS. The authors pilot tested ways to achieve multiple volume reduction factors (recovery): 5X (80%), 10X (90%), 20X (95%), 40X (97.5%), and 70X (99%). Each jump in volume reduction adds plant complexity and cost. Each step will be explained and mapped so water plant designers can learn about the technology and investment required to take incremental steps in recovery improvements. Two new technologies were trialed and will be reviewed. First, a robotized chemical softening system designed for use with variable water chemistry. This system includes a novel real-time calcium sensor and precipitation management system. Second, results from new ultra high pressure reverse osmosis membranes 1800 psi (120 bar) will also be disclosed, including tips to reliably implement these next generation of reverse osmosis membranes.
Discusser: Brandon Yallaly, P.E., Carollo Engineers, Inc., Boise, ID
IWC 19-51: Overcoming the Challenges of Concentrate Recovery Using Autonomous, Data-Driven RO
Michael Boyd, Desalitech, Newton, MA; Han Gu, Ph.D. and Megan Plumlee, Ph.D, P.E., Orange County Water District, Fountain Valley, CA; Jim Lozier, P.E., Jacobs, Tempe, AZ; Michael Hwang, P.E., Jacobs, Irvine, CA; Ran Nadav, P.E., Desalitech, Kefar-Sava, Israel
In Southern California, there are two traditional sources of potable water: imported surface water and local groundwater. These supplies are finite, and in some cases over allocated (Colorado River) or over-drafted (Tulare Basin), so additional water must be obtained from non-traditional sources including wastewater effluent and seawater. Seawater is attractive because it is plentiful; however is both capital and energy intensive to desalinate to potable quality and has perceived environmental challenges associated with its abstraction and the discharge of brine produced as a byproduct of the desalination process. In contrast, the treatment and purification of municipal wastewater, either through indirect or direct potable reuse, represents a lower cost and more environmentally sustainable process that has gained increasing acceptance and adoption in Southern California to meet water demands.
The Orange County Water District (OCWD) Groundwater Replenishment System (GWRS) is the world’s largest potable reuse plant, treating secondary effluent to produce purified water for groundwater recharge as a drinking water supply augmentation and for injection into coastal wells that form a barrier to prevent seawater intrusion. When expanded to its full capacity of 130 MGD, the concentrate flow from GRWS’ existing 3-stage, 85% recovery RO will increase to 23 MGD. In an attempt to recover a portion of the RO concentrate and increase GWRS purified water production, OCWD has been piloting the Closed Circuit Reverse Osmosis (CCRO) process to determine how much of the concentrate can be recovered in a reliable and cost efficient manner.
There are significant challenges when treating a ‘waste’ stream containing up to 50 mg/L of total organic carbon (TOC) and supersaturated levels of several sparingly soluble salts. In addition, minor changes in the feed water quality to the full-scale RO system can translate into major impacts on the operation of a concentrate treatment system. This paper will review the steps taken to adapt to the real-time variable GWRS feed water quality, magnified by a greater than six-fold concentration through the 3-stage conventional RO system. Thus far, the system has been operated for 15 months to determine the ideal flux, cross-flow velocity, recovery and cleaning interval to optimize CCRO operation on the variable feed water quality. The pilot recently met the project goal to complete two consecutive 2-month intervals between CIPs, pushing the overall RO recovery up to 90.6%.
Discusser: Jason Bailey, Avista Technologies, Inc. Winston-Salem, NC
IWC 19-52: Pressure Retarded Osmosis: A Potential Technology for Desalination Energy Recovery and Concentrate Management
Joshua Benjamin, Qiong Zhang, and Mauricio Arias, University of South Florida, Tampa, FL
Reverse osmosis (RO) is a treatment process widely implemented in desalination and advanced water reclamation facilities. Currently, a significant challenge with RO is reducing the energy consumption of the process and the potential environmental impacts from brine disposal. Elevated levels of energy consumption cause RO product water to be much more expensive than other conventional water sources and can prevent implementation of this crucial technology in areas under severe water stress. Pressure retarded osmosis (PRO) has been suggested as a potential technology to mitigate these issues. PRO works by extracting usable energy from the high osmotic pressure difference that exists when a highly concentrated draw solution (such as RO concentrate) is placed on the opposite side of a semipermeable membrane from a dilute feed solution (such as treated wastewater). If an external hydraulic pressure is applied to the concentrated draw side that is lower than this osmotic pressure, water will flow from the dilute feed side to the concentrated draw side which created an excess of pressurized diluted concentrate on the draw side. This excess can then be divided into two streams and used for both power generation in a hydropower turbine and for pressurizing incoming concentrate using an in-line pressure exchanger, which can then be sent back into the draw side of the membrane chamber to continue the generation cycle. Acquisition of a proper dilute solution can pose challenges, as there exists both an energetic and financial cost in transporting and pretreating the solution before it can undergo PRO.
In this paper, we developed a Python-based process model that simulates how a PRO system could function in preexisting utilities in terms of energy density, energy generation, effluent concentration, cost, and net present value, with a specific focus on plants in the Tampa Bay area and the Caribbean. The advantages and limitations of implementing this technology are discussed in detail, and multi-criteria comparisons involving cost and environmental impact are made with other energy generation and brine management technologies. Future studies will focus on developing a computational fluid dynamics-based membrane model and constructing a pilot-scale system to verify and improve the model’s results and fully test the effect of membrane fouling on long-term system performance.
Discusser: Tony Fuhrman, LG Water Solutions, Torrance, CA
Water Projects: Overcoming the Hurdles
IWC Rep: Michael Soller, P.E., CPC, DBIA, Bowen Engineering Corporation, Indianapolis, IN
Session Chair: Russell Huffmyer, McKim & Creed, Sewickley, PA
Discussion Leader: Sam Fackrell, Bowen Engineering Corporation, Glen Burnie, MD
Water projects have different hurdles depending upon the design, procurement, and construction phases. These hurdles can pertain to unique treatment challenges, defining the roles and responsibilities of the project teams, and the need to conform to moving environmental and business constraints. This session covers how different methods and procedures can be used for the successful delivery of water treatment projects.
Consider Attending: W1, W3, W8, W10, W11, W15, W17, W21
IWC 19-53: Treatment of Aerospace Machining and Inspection Wastewater
Chris Stanfill, P.E., Arcadis, Atlanta, GA; Michael Soller, P.E., CPC, DBIA, Bowen Engineering Corporation, Indianapolis, IN
Aerospace wastewater generated by machining and inspection presents unique treatment challenges. The wastewater can contain a blend of machining oil, dissolved and particulate metals, surfactants, and fluorescent penetrant inspection (FPI) emulsifier and developer. The combination of the machining and inspection water tends to emulsify the oils in the wastewater, making them difficult to remove. Additionally, the oils can hinder the metals removal processes. Further, the FPI materials often require a thorough material compatibility review for process piping and equipment due to their negative life cycle impacts on certain pipe types. Depending on the other processes performed at the facility, the wastewater may also have to meet federal categorical treatment standards for metals finishing promulgated under 40 CFR 433 as well as local sewer use ordinance limits.
This paper will describe the unique challenges to permit and treat aerospace wastewater. Specific design considerations and the qualities of typical treatment equipment used for treatment will be described. Two case studies will be used to illustrate the design considerations and lessons learned for this unique wastewater.
Discusser: Mark Owens, P.E., SUEZ Water Technologies & Solutions, Richmond, VA
IWC 19-54: Secrets to a Successful Implementation of a Water Treatment Project
Dennis McBride, Burns & McDonnell, Kansas City, MO
There really are no “secrets” to a successful implementation of a water treatment project. The success may be boiled down to primarily good teamwork amongst all the parties involved with a joint understanding of the basis of the design decisions. Also, information provided to support the design should be accurate, reliable, and cover as many of the variations as possible.
Discusser: Brian Stater, Bowen Engineering Corporation, Indianapolis, IN
IWC 19-55: Water Management and Efficiency Study for Automotive Manufacturing Complex in a Water-Stressed Region
Brian Moore, Ph.D., Arcadis, Clifton Park, NY
The Saltillo South Complex in Saltillo, Coahuila, Mexico comprises one of the larger manufacturing centers for a large automobile manufacturer, including two assembly plants and an engine plant. The three plants share water resources and are supplied by four existing groundwater wells that draw from the local aquifer. The Coahuila region is home to a high density of manufacturing operations and is highly water stressed. Furthermore, production capacity at the complex is projected to increase in the future, which would push water demand close to or in excess of the complex’s authorized allocation.
The objectives of the project were to assess water usage and availability at the complex and identify a recommended approach to ensuring adequate water supply to support future manufacturing demand. Two main paths were identified towards mitigating potential limitations on water resources. The first was to take steps to increase the available water supply. The second was to evaluate water conservation and reuse opportunities within the complex in order to reduce current consumption. Arcadis performed several evaluations to determine the viability of each approach and craft a holistic approach to water management at the facility.
The presentation of this study at IWC 2019, will cover the following elements:
• Background on regional water stress conditions and site water demands
• Approaches considered for increasing the water access rights, including a discussion of the challenges/barriers that would be encountered in getting additional water rights or allowances
• Development of water balance and a look at the water balance and major water users
• Description of the water efficiency evaluation methodology used
• Sharing of an array of example water efficiency opportunities identified in the study that may be of interest from a learning or implementation perspective for audience members. These will all be projects that provide good water savings as well as having favorable financial payback
• Demonstration that water conservation can be financially attractive; sharing of projected water and cost savings, as well as financial return through water conservation
• Demonstration of how water use at the site would change through the implementation of recommended projects
Discusser: Ronald Ruocco, P.E., Civil & Environmental Consultants, Inc., Charlotte, NC
IWC 19-56: Cogeneration – Opportunities to Improve Heat Recovery and Power Generation while Saving Water and Reducing Chemical Costs
Diane Martini and Robert Wright, Burns & McDonnell, Chicago, IL
Co-generation of heat and power is not a new concept, but as technology advances there can be real benefits to upgrading existing co-generation facilities. In many cases, projects that were not considered cost-effective in the past may become viable in areas where utility electricity prices have increased or existing equipment deteriorates. In other cases, off gases from industrial processes, landfill gas, or digester gas can be harnessed via Reciprocating Engines or Combustion Turbines (CTs) combined with Heat Recovery Steam Generators (HRSGs) to generate both heat and power.
Existing co-generation facilities can see real improvements in output and efficiency, with reductions in consumables use through upgrades. For example, replacing hot lime softening with RO saves chemical costs while conserving water and energy.
This paper will provide examples of the environmental and economic advantages of installing co-generation capability or upgrading a co-generation facility.
Discusser: Daniel Sampson, HDR, Walnut Creek, CA
The Many Faces of Industrial Wastewater Treatment
IWC Rep: Jonathan Shimko, McKim & Creed, Sewickley, PA
Session Chair: Mike Preston, Black & Veatch, Overland Park, KS
Discussion Leader: Ed Greenwood, P.Eng., BCEE, Wood Environment and Infrastructure Solutions, Cambridge, ON, Canada
One of the exciting aspects of industrial wastewater treatment is that there are an endless variety of challenges to keep one engaged and learning. In our session, we have four papers representing four different challenges and multiple industries. Everything from metals reduction to high strength biological challenges, from refining, to mining, to pharmaceuticals, and from physical treatment to biological treatment. It will be an interesting session that represent a good sampling of the issues encountered in industry and will, no doubt, keep you engaged.
Consider Attending: W1, W3, W5, W6, W8, W10, W11, W12, W13, W15, W17, W21
IWC 19-57: How Hot is Too Hot? Reviewing the Treatment Performance of Refinery WWTP Biological Treatment Systems Operating at High Temperatures
Mark Knight and Nicolas Hameon-Denis, SUEZ Water Technologies & Solutions, Oakville, ON, Canada; Shane Lund, SUEZ Water Technologies & Solutions, Trevose, PA; Jordan Schmidt, Brad McIlwain and Shawn Watkins, LuminUltra Technologies Ltd., Fredericton, NB, Canada
This study reviews the treatment performance and microbial ecology of two North American refinery WWTP biological treatment systems which continuously operate between 38°C to 52°C. Results from both refinery WWTP’s show that biological treatment systems can effectively remove organic compounds and nitrify ammonia above 35°C which can provide certain advantages when optimizing an industrial WWTP, upgrading upstream processes or building a new green field plant.
Discusser: Ivan X Zhu, Evoqua Water Technologies, Pittsburgh, PA
IWC 19-58: New Water Treatment Technology Targets High-Strength and Toxic Wastewaters-While Producing Methane for Fuel
Bryan Kumfer and Chad Felch, Siemens Water Solutions, Rothschild, WI
Many industries use complex production processes that result in high-strength, hard-to-treat wastewaters. Examples include oil and gas refining, petrochemicals, and pharmaceuticals. Their wastewaters may vary in composition, but they typically have at least one of these problematic characteristics: high levels of biorefractory compounds; toxic compounds; halogenated organics; and aromatic or aliphatic hydrocarbons.
In addition, their chemical oxygen demand (COD) levels can range widely, and up to 300,000 mg/l. On top of that, some process waters/wastewaters have high salt levels, especially chlorides, requiring expensive materials of construction, making cost-effective treatment especially challenging.
Existing treatment solutions for these high-salt wastewater streams are typically incineration or gasification. The former combusts the wastewater completely in the presence of excess oxygen at 1,100°C (2,012°F), producing carbon dioxide, water, and salts. The latter burns the wastewater using stoichiometric oxygen to produce carbon monoxide and lesser amounts of hydrogen. In turn, these gases can be processed into more useful fuel gases. Unfortunately, both processes are expensive, especially their energy costs. Also, high temperature processes can be expensive to maintain, requiring backup units that consume capital, operating expenses, labor, and space.
Given these challenges, this paper will focus on catalytic gasification (or hydrolysis) to handle wastewaters that cannot be economically treated with other oxidation technologies. It uses a heterogeneous catalyst to spur reactions similar to those that typically occur in steam reforming and gasification. These reactions occur in aqueous phase, so temperatures are much lower than what gas-phase gasification processes require. This paper will provide data on treatment for: organics and chlorides; propylene oxide/styrene monomer (PO/SM) wastewaters; produced waters containing kinetic hydrate inhibitors (KHI); and propylene glycol wastewaters.
The benefits of catalytic gasification will be explained. They include fuel gas production, providing data of gas composition for different types of compounds treated; high COD destruction rates, helping reduce downstream treatment costs; capital and energy savings, due to a lower-temperature process; and saving space, relative to other oxidation treatment approaches.
Discusser: Chris Hertle, M.Phil, GHD, Irvine, CA
IWC 19-59: Zinc – Boiling Down the Options
Christopher Huth, P.E., Pittsburgh, PA
Zinc, often overlooked as an inconsequential component of industrial wastewater, can cause serious environmental implications at high concentrations. High concentrations can occur during upset conditions that are typically not considered during normal design and therefore not included in the wastewater treatment system design. Although many viable options regarding removal of dissolved zinc exist, this paper will assess technologies currently being used or evaluated for use in the industry including sorbents, chemical precipitation, ultrafiltration, membrane filtration and biological methods.
Discusser: Joseph Guida, P.E., Fluor, Houston, TX
IWC 19-60: Evaluation of Alternate Process Chemistries for Removal of Arsenic and Fluoride from Industrial
Ryan Ames, P.E., Dewberry, Raleigh, NC
Arsenic and fluoride contamination can be byproducts of phosphorus mining and processing operations. A former mining and processing facility currently treats between 300 and 400 million gallons of wastewater for arsenic and fluoride annually. Wastewater is treated with a single lime system with addition of ferric chloride for coagulation and carbon dioxide for final pH adjustment. However the lime and carbon dioxide systems are complex and labor intensive. The facility was interested in identifying opportunities to optimize or modify the current process to reduce operating costs.
Arsenic must be converted to arsenate prior to precipitation. This can be accomplished by adjusting pH or changing the redox potential. A series of tests were conducted to evaluate process chemistries utilizing an oxidizer in combination with various coagulants for arsenic removal. Utilizing an oxidizer to create arsenate meant that lime, and subsequently carbon dioxide, could be eliminated from the existing process. However eliminating lime also eliminates the source of calcium for fluoride treatment. Therefore alternate fluoride removal chemistries were tested, including alternate calcium salts and alum.
Bench testing results indicate that it may be feasible to meet effluent permit limits with a system of sodium hypochlorite, aluminum sulfate, and ferric chloride. Results indicate that this system could reduce the annual operation cost of the treatment system by 30% or more. A full scale field test was performed to evaluate the performance of this system and to collect samples for toxicity testing.
This paper will describe the existing treatment process, process improvement goals, bench testing protocols and results, cost analysis of the alternate process chemistries, full scale trial protocol and results, and the results of toxicity testing.
Discusser: Paul Pigeon, P.E., Golder Associates, Inc., Lakewood, CO