Wednesday, November 7
Technical Sessions – 8:00 A.M.-12:00 Noon
Cooling Water – Recent Advances in Monitoring, Chemistry, and Modeling
IWC Rep: Ken Dunn, Solenis-Retired, Mashpee, MA
Session Chair: Ray Post, ChemTreat, Langhorne, PA
Discussion Leader: David Fulmer, Baker Hughes, a GE Company, Sugar Land, TX
Owners and operators of cooling systems are facing increasing challenges related to water utilization efficiency and environmental sustainability. The drive for higher cycles of concentration and zero liquid discharge amplify both scaling tendency and corrosivity. Environmental restrictions are driving the development of chemistries with better environmental profiles. The four papers in this session describe prominent advancements in meeting current cooling water challenges including real-time scale detection, copper alloy corrosion inhibition, silica deposit control, and thermodynamic and kinetic modeling of scaling tendencies.
IWC 18-61: Monitoring and Prevention of Mineral Scale Formation in Open Cooling Systems with an Inline Fouling Monitor
Shih-Hsiang Chien and Michael Bluemle, Solenis LLC., Wilmington, DE; Donald Holt, Solenis LLC., Burlington, ON, Canada; Jacob Young, Solenis LLC., Grimes, IA
Prevention of mineral scale formation is critically important to the treatment of industrial cooling systems. Inorganic scale greatly reduces heat exchanger efficiency, may lead to under deposit corrosion, and increases operational costs. Scale formation can be mitigated by many types of additives, which have varying efficiency on different scaling species. The effectiveness of the inhibitors depends on temperature, pH, and additive concentration. Constant monitoring of water composition provides an indirect indication for scale forming potential, but does not directly measure scale formation. Additionally, the potential for mineral scale deposition can be affected, often abruptly, by changes in makeup water quality, pH, hydrodynamic conditions (e.g., flow velocity), or due to weather-related events. Therefore, a real-time inorganic scale analyzer is essential to ensure system cleanliness and minimize heat transfer reduction.
This paper discusses the successful management of mineral scale formation while also optimizing chemical treatment. A patented, real-time fouling monitoring technology was utilized to investigate the formation of calcium carbonate and calcium phosphate under pilot and field conditions. A correlation between fouling factor and scale thickness and the efficacy of chemical additives were compared at heat exchanger surface temperatures of 45 to 75 °C. By directly monitoring scale growth and switching to a higher performing product, a cost savings of 40% was achieved at a North American manufacturing facility. The technology has been proven to be accurate, reliable, and responsive to chemical treatment, which equates to improved chemical management under varying water quality and operating conditions.
IWC 18-62: A Novel, Better Performing Yellow Metal Corrosion Inhibitor with Lower Toxicity and its Use for Copper Alloy Condenser at a Power Plant
Yanjiao (Andrew) Xie, Jothibasu Seetharaman, Daniel Meier, Xuejun Wang, Donald Johnson, Anand Harbindu, Deepak Rane, and Pradeep Cheruku, Nalco Water, an Ecolab Company, Naperville, IL
Copper and its alloys have been widely used in heat exchangers due to its high thermal conductivity and natural corrosion resistance. However, in acidic-to-neutral and highly halogenated environments that are common in cooling water systems these metals suffer from corrosion. This may result in failure of heat exchangers and consequently loss of production and costly replacement. In the last few decades, different triazole chemistries were used as a protective filming inhibitor for yellow metal. These chemistries have their limitations, including poor stability in halogenated environment, high consumption rate, and high aquatic toxicity. To overcome these challenges, Nalco Water has developed an innovative non-triazole based yellow metal corrosion inhibitor with improved halogen stability, as well as reduced aquatic toxicity compared to triazole compounds. The new patent-pending chemistry has been evaluated for its performance in electrochemical tests, pilot cooling tower tests and customer field trials. The results from both lab and field trial will be discussed in detail. The mechanism why the new chemistry works better than triazoles will be briefly discussed. Additionally, a handheld analyser has been developed and evaluated to precisely measure the residual of this eco-friendly, next generation non-triazole based yellow metal corrosion inhibitor.
IWC 18-63: Cooling Water High Cycle Silica Treatment Program Implemented at a Southwest ZLD Power Plant
Caroline Sui, Ph.D. and Jeffrey Melzer, SUEZ Water Technologies & Solutions, Trevose, PA; Timothy Eggert, SUEZ Water Technologies & Solutions, Seal Beach, CA; Joseph Grenier, SUEZ Water Technologies & Solutions, Fort Collins, CO
A Southwestern United State (US), zero-liquid discharge (ZLD) power plant faces challenges with managing its water balance during seasonal, full load operation. Extended full-load operation overloads the brine concentrator operation causing the evaporation ponds to fill to maximum capacity. This high evaporation pond level can potentially lead to power production rate reductions to prevent overflowing the evaporation ponds. The plant determined that increasing cooling water cycles of concentration would be the most cost-effective and feasible approach to reduce blowdown volume that reduces the load on the brine concentrators, therefore reducing the flow of brine concentrate to the evaporation ponds. The only source of water to the plant was from onsite wells that, due to the high concentration of silica, would with conventional treatment, limit cooling cycles well below the desired high-cycle operation necessary to manage the plant water balance.
The paper discusses comprehensive laboratory study and successful implementation of the novel silica treatment program in the plant. The program expands silica limit to 280 – 300 mg/L, increasing cycles from a conventional silica limit of seven cycles to thirteen cycles. The increased cycle operation minimizes load on the brine concentrators and reduced water consumption by up to one million gallons per day.
IWC 18-64: Scale Formation in Cooling Tower: Theoretical Approach to the Thermodynamics and Kinetics of the Water Chemistry in the Makeup and Cycled Water
Kenneth Chen, Fluor Enterprises, Inc., Aliso Viejo, CA; Americus Mitchell and Joe Guida, Fluor Enterprises, Inc., Houston, TX
As fresh water becomes scarcer due to population growth, it is imperative to reduce fresh water consumption through water chemistry adjustment, utilization of alternative source of water (i.e. seawater, gray water, etc.), revamp of existing designs, and water reuse. For power plants, in particular combined cycle plants, cooling towers represent the largest continuous water demand due to the evaporation and blowdown of the circulating water. The water chemistry dictates the blowdown rate, and as a result, it is a variable that may be controlled to reduce the amount of water consumption. To prevent the formation of scale, fouling, and corrosion issues, the blowdown rate is adjusted to maintain the water chemistry at an acceptable level based on the cycles of concentration and quality of the makeup water. This paper will review the thermodynamics and kinetics of the water chemistry in a cooling tower as it relates to major scaling issues observed in various operating combined cycle plants based on different makeup water quality (i.e. gray water, river water, and fresh water). The water chemistry will focus on the major scaling compounds such as silica, calcium, and alkalinity and their interactions with some of the more common species/chemicals in the makeup water and circulating water after chemical injection. The goal of this paper is to establish a basis to theoretically analyze the operating conditions, such as pH, ambient temperature, cycles of concentrations, makeup water quality, water chemistry, and fluid velocity, to better predict the frequency and location of scale formation that is commonly observed and documented in the cooling tower.
Consider Attending: W-1, W-2, W-5, W-8, W-10, W-12, W-18, W-19, W-20
Water Management in Power Plants
IWC Rep: Scott Quinlan, GAI Consultants, Cranberry Township, PA
Session Chair: Jeffery Preece, Electric Power Research Institute, Charlotte, NC
Discussion Leader: Jeff Easton, P.E., WesTech, Salt Lake City, UT
There are many applications of water management in power plants. Process and regulatory changes are major drivers leading to the reconsideration of existing approaches and evaluation of new techniques. The papers in this session present examples where power plants, impacted by changes in disposal of coal combustion residuals, are addressing management of bottom ash water, outage wash water, and treatment of water from impoundments.
IWC 18-65: Arsenic Treatability and Pilot Testing at Little Blue Run CCR Impoundment
Ronald Ruocco and Michael Keen, Civil & Environmental Consultants, Inc., Charlotte, NC; Robert Golightley, First Energy Generation, LLC, Akron, OH; Mark Orzechowski, Civil & Environmental Consultants, Inc., Pittsburgh, PA
The Little Blue Run Disposal Facility (LBR) is an unlined surface impoundment that received Coal Combustion Residuals (CCR) from the Bruce Mansfield Generating Station. With approximately 135,000,000 yd3 of capacity and covering an area of more than 950 acres, it is one of the world’s largest CCR disposal facilities. Water monitoring at two locations at LBR identified arsenic concentrations that exceeded the groundwater abatement standard under Pennsylvania’s residual waste disposal impoundment regulations. This bench and pilot study identifies treatment technologies and verifies arsenic removal from onsite water, in the event that arsenic removal would be needed to treat spring discharge prior to discharging to surface water under a NPDES permit, or in-situ treatment of groundwater would be needed to meet the groundwater abatement standard. The purpose of this study was to present to the regulatory agency a systematic approach for reliable arsenic removal from surface water or groundwater.
This bench and pilot study identifies several optimum treatment technologies, and empirically verifies arsenic removal and process performance under site-specific conditions for this specific water matrix.
This paper provides the details of the systematic procedure from initial desktop investigations, comparisons through technology screening by bench treatability testing, and confirmation by on-site pilot testing.
Bench testing identified oxidation/coagulation/agglomeration/solids separation as a robust, flexible approach to arsenic removal on this site-specific water matrix. After initial bench scale tests, the oxidant selected was sodium hypochlorite; the coagulant was ferric chloride; the agglomerating chemical additive (agglomerant) was an anionic polyelectrolyte; and solids separation was by gravity separation.
Pilot-scale testing proved that oxidation/coagulation/agglomeration/solids separation performed well and was reliable over a range of arsenic concentrations for the spring water tested. The pilot system consistently reduced arsenic concentrations to below the target limit of 10 micrograms per liter (μg/L).
Subsequent studies have shown that the cessation of CCR disposal and capping of the facility will reduce the concentrations of arsenic in groundwater to less than the groundwater abatement standard. As such, full-scale implementation of the oxidation/coagulation/agglomeration/solids separation technology is not currently warranted.
IWC 18-66: Closing the Loop in Bottom Ash Systems – Not as Easy as it Sounds
Diane Martini, Burns & McDonnell, Chicago, IL; Derek Henderson. P.E. and Jared Troyer, Duke Energy, Raleigh, NC
With the movement around the Coal Combustion Residuals rule (CCR) and the Steam Electric Power Effluent Guidelines (ELG) many power plants are installing closed loop bottom ash systems. As true closed-loop bottom ash systems had not been extensively installed and operated prior to the advent of these rules, the industry has encountered many challenges related to water management. The large ash ponds previously used for ash management provided more extensive water treatment than was previously recognized. Long hydraulic detention times (sometimes on the order of months) not only allowed particles to settle, but also allowed water quality to stabilize and equilibrate, and provided opportunities for biological treatment.
As coal fired power plants close the loop in their bottom ash systems, the industry is being faced with new challenges within these systems including pH control, dissolved solids, corrosion, and scaling.
This paper will provide background on the water balance and chemistry issues facing closed loop systems, and provide case studies of pH control and solids control strategies.
IWC 18-67: Water Management in Closed-Loop Bottom Ash Systems
Laura Reid, P.E., Jacobs Engineering, Charlotte, NC; Thomas Higgins, P.E., Jacobs Engineering, Jacksonville, FL; Dennis Fink, P.E., Jacobs Engineering, Oakland, CA; Paul Chu, EPRI, Palo Alto, CA
Recent regulations are leading many power plants to install recirculating, closed-loop systems for bottom ash transport water. Issues observed in managing a closed-loop system include water quality ones, such as carryover of fine solids, scaling, and corrosion, as well as having more water entering the system than exiting. This paper discusses management options for these issues through a study of six plants with recirculated water bottom ash systems and bench test studies.
This paper will discuss managing closed-loop bottom ash systems, including drivers that necessitate purges, and treating the purge for discharge or for reuse in the power plant. Information will be provided to assist plants with determining what conditions need to be considered to design and operate a closed-loop system for their ash transport wastewater. Bottom ash dewatering systems from six coal-fired power plants were visited to collect insights on design and operations, and to sample and analyze associated water and solids. These plants recirculated a majority of their water for reuse in ash sluicing and other processes internal to the bottom ash system, with intermittent or minimal discharge of water. Bench-scale testing was done to assess chemical addition and filtration required for reuse of water purged from the closed-loop.
Presentation of work findings will include:
• Considerations in how to balance water flows into and out of the bottom ash systems.
• Addition of other materials combined with bottom ash, specifically economizer ash, may negatively impact water quality of the recirculated water supply.
• Half the plants reported having to implement regular maintenance or treatment modifications to address fine solids accumulation in piping and sumps, due to carryover of solids through the dewatering systems into the recirculated water.
• Two plants reported scaling, primarily calcium precipitates, in the recirculated water supply. Scaling was minimized through sulfuric acid addition to control the pH.
• Two systems required control measures to prevent corrosion. One plant controlled acidity to help prevent corrosion through addition of caustic and the other modified hopper flushing and dewatering operations.
IWC 18-68: Outage Wash Wastewater Treatment Alternatives at Coal Fired Power Plants
Julie Horan, P.E., HDR, Inc., St. Louis, MO; Josh Prusakiewicz, P.E., HDR, Ann Arbor, MI
In compliance with the Coal Combustion Residuals (CCR) rule, many power plants are faced with closing their ash ponds and finding other alternatives to treat and dispose of the many other non-CCR plant wastewater streams that once were simply pumped to the ash pond. Non-chemical cleaning outage wash wastewaters, such as boiler fireside wash, economizer wash, air preheater wash, or precipitator wash; which have typically been discharged to the ash ponds in the past, create a special challenge for many facilities. Not only are these wastewater streams large in volume and highly intermittent, they also usually contain significant suspended solids and heavy metals loading. As such, these wastewater streams normally exceed typical NPDES permit limits and will require treatment prior to discharge through a permitted outfall.
This paper will present case studies of several coal fired power plants and explore the non-chemical cleaning outage wash wastewater treatment alternatives that were considered at these sites. The discussion will include an investigation of permanent treatment options, rental equipment treatment options, and options to repurpose existing water treatment equipment. It will focus on identifying a solution that is cost effective, provides adequate treatment to ensure continuous compliance, provides operational flexibility to handle both planned and forced outages, is suitable for a constrained project site, and is achievable in a compressed project schedule.
IWC 18-Reserve: Brine Encapsulation as an Integral Step in Power Plant Wastewater Treatment
Ben Clegg and Clark Harrison, Purestream Services, Salt Lake City, UT
IWC 18-Reserve: Ash Transport Water Quality
Corey Kipp, EIT and Diane Martini, Burns & McDonnell, Kansas City, MO
Consider Attending: W-1, W-2, W-5, W-10, W-12, W-16
Evolving Membrane Technologies and Applications
IWC Rep: Jane Kucera, Nalco Water, an Ecolab Company, Naperville, IL
Session Chair: Lyndsey Wiles, MICRODYN-NADIR, Goleta, CA
Discussion Leader: Adhiraj Joshi, Aquatech International, LLC, Cannonsburg, PA
From humble beginnings within the last century, modern membrane technologies have developed to include a wide variety of chemistries and formats that offer solutions for an ever-increasing range of applications. Modern membrane technologies include reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) chemistries in a multitude of formats, such as spiral-wound elements, tubular and capillary modules, hollow-fiber modules, plate and frame designs, and more. This session focuses on these evolving membrane technologies and the expanse of applications that they are being used for. In terms of RO, the session will discuss both a new type of RO format and a new system design that will allow the membrane industry to handle new applications. The session will also discuss a new option for dechlorination ahead of membranes and how a UF hollow fiber membrane brings a plant a new water source. All in all, the variety of papers in this session truly represents modern membrane technologies and the expanding array of applications that they provide solutions for.
IWC 18-69: Counterflow Reverse Osmosis – New Membrane Technology for Ultra-High Salinity Desalination
Richard Stover, Ph.D. and Simon Choong, Ph.D., Gradiant Osmotics, Woburn, MA; Aaron U and Prakash Govindan, Ph. D., Gradiant Corporation
Water scarcity is driving the development of alternative water resources such as desalination and water reuse. Reverse osmosis (RO), the most widely-applied treatment method, generates a substantial stream of brine concentrate. Typically, additional concentration of this brine is not possible with RO equipment due to the required pressures which exceed equipment limitations. Existing brine concentration technologies use heat, require high capital costs and consume significant amounts of energy. The CounterFlow Reverse Osmosis (CFRO) process is a non-evaporative, membrane-based method for dewatering water with total dissolved solids (TDS) concentrations of up to 250,000 ppm. The CFRO process uses hydraulic pressure to drive water across a semi-permeable membrane against the osmotic pressure difference between the feed and permeate. A permeate-side saline sweep is applied to maintain this osmotic pressure difference below the burst pressure of the membrane (typically 1,200 psi or 83 bar). Multiple CFRO stages are connected in a cascade, producing a highly concentrated brine and a purified water stream for discharge or reuse.
This paper presents system and membrane performance data from the first field-ready full-scale CFRO system. Data from the concentration of a 70,000 ppm feed stream to a 210,000 ppm final brine stream at pressures of less than 1,000 psi are given, representing a breakthrough in high-salinity RO performance. The specific energy required is 13-16 kWh/m3 or 50-60 kWh/1000gallons of feed water, corresponding to a 50% decrease in energy consumption relative to mechanical vapor compression (MVC), the state-of-the-art evaporator-based brine treatment process. These results demonstrate that CFRO is a cost-effective and energy-efficient brine concentration method, meeting or exceeding the limits of thermal options. The achievement has potential significance for multiple industrial sectors including mining, power, oil and gas, electronics, pharmaceuticals and food and beverage.
IWC 18-70: Using Membranes to Produce River Water Cooling System for Large Chemical Plant
Jake Moen and Sundeep Ramachandran, The Dow Chemical Company, Minneapolis, MN; Caitlin Burns, The Dow Chemical Company, Freeport, TX; Michael Bourke, Wigen Water Technologies, Chaska, MN
The Clarified River Water (CRW) system is part of The Dow Chemical Company’s Freeport Site located in Texas, United States. The Freeport Site is the largest integrated chemical manufacturing complex in the Western Hemisphere. With physical space limited and the seasonal fluctuations of the Brazos River, the design of the plant focused on the benefits membranes can provide over traditional technology. Additional details of UF skid design and operation will be focused in this paper along with detailed operating data since startup in 2017.
This paper will examine the water quality, system design, and reliability essential to produce the cooling and utility water at the plant. The CRW system uses Dow IntegraFlux SFD-2880XP Ultrafiltration (UF) Modules to process water sourced from the oftentimes difficult Brazos River (50-125 NTU). With the use of 888 Ultrafiltration modules, the CRW system has a rated capacity of 23 MGD. Complete plant operation will be discussed which includes flash mixers, sedimentation basin, self-cleaning filters, UF membranes, and even the storage tanks implemented at the site. Additional insights surrounding the Ultrafiltration operation will be discussed.
IWC 18-71: Closed Circuit Reverse Osmosis, the New Standard for Industrial Desalination
Michael Boyd, Desalitech, Newton, MA
Reverse osmosis (RO) represents the primary technology used for the desalination of water and wastewater. In traditional RO systems, recovery, flux and crossflow are coupled, so performance becomes a balancing act. The systems are either reliable, but inefficient or the systems are efficient, but unreliable. There are ways to optimize this balancing act using hybrid-staging, concentrate recycle or inter-stage booster pumps, however this all comes at the sacrifice of operational flexibility. While the industry has made significant advancements to individual aspects of the RO process, none of these advancements have been contributed to optimization of the fundamental design.
Closed Circuit Reverse Osmosis (CCRO) represents the first major breakthrough in reverse osmosis since its inception. The simple solution combines the strengths of dead-end filtration with the strengths of crossflow filtration. Using standard components configured in an elegant single-stage design, recovery, flux and crossflow are uncoupled with standard triggers to purge concentrate based on volumetric recovery, pressure and/or conductivity. This flexibility provides a level of efficiency and reliability that can only be achieved with CCRO.
The presentation will go through the technical differences between traditional RO and CCRO in terms of recovery, fouling and scaling, CIP frequency, membrane life, energy consumption, chemical consumption, required operator engagement and overall system flexibility. These metrics will then be quantified in the form of case studies to understand the performance and specific value CCRO provided in each application.
The first case study will discuss how a beverage company reduced its volume of wastewater by 80% by replacing their traditional RO with a CCRO. The second case study will discuss how a paper mill reduced water footprint, while simultaneously extending CIP frequency by 500% and reducing antiscalant consumption by 63% after replacing their traditional RO with a CCRO. The third case study will discuss how a food processing company utilizes CCRO to automatically adapt to seasonal feed water conditions in order to meet stringent ingredient water specifications. The fourth case study will discuss how a power company saved 44 million gallons of water per year, while increasing reliability and reducing annual water operating costs by over $1 million at each of its five peaking plants. The project received Power Magazine’s 2017 Water Award for the company’s pioneering efforts with water purification systems.
Join us to learn how a single decision can boost your financial, environmental and operational competitiveness, positioning your company for a long and prosperous future.
IWC 18-72: Evaluation of Long-Term Membrane Performance with Continuous Use of Hydro-Optic UV Dechlorination at Plant Bowen
Dennis Bitter, Atlantium Technologies, Inc., Sarasota, FL; Ytzhak Rozenberg, Atlantium Technologies, Israel
In 2014 Plant Bowen, a 3,160 megawatt coal-fired power station, in Cartersville, Georgia evaluated and installed a non-chemical dechlorination process, the Hydro-Optic™ (HOD) UV water treatment technology, to improve the overall quality of reverse osmosis (RO) feed water. New membrane elements were installed in March 2014. As a non-chemical approach to decompose the free chlorine oxidant and protect the RO membranes, the technology provided the facility with the opportunity to reduce or eliminate the use of sodium metabisulfite (SMBS) and reduce maintenance and associated costs. Data for the membrane system’s differential pressure, normalized salt passage and rejection, permeate flow, and normalized permeate flow under the use of the technology was analyzed for a 940 day period from August 2014 to February 2017.
After three years of operation, the RO membranes are operating at the same level as new elements. The membranes are only up to 34 psi differential pressure from the original 28 psi when they were put into service; indicating a longevity of the membrane elements that did not exist without the use of the technology. Comparatively, the pre-2014 membrane elements were running at a 50 psi differential pressure after three years of operation.
These operational efficiencies have resulted in considerable savings, providing a two-year return on investment. Since the installation of the technology the facility has reduced the use of SMBS (75% reduction; from 44.3 gallon/month to 7.6 gallon/month, 2014-2017 savings of $15K) and also minimized the frequency of micron filter replacement (reduction from 6 times/year to 2 times/year, 2014-2017 savings of $240K).
Since the installation of the technology Plant Bowen has been able to maintain the integrity of their feed water for the boiler and steam cycle, ensuring production and quality levels necessary for the facility to operate efficiently. This presentation will detail the long-term membrane performance with the continuous use of the technology at Plant Bowen.
IWC 18-Reserve: Real Time Continuous Membrane Integrity Monitoring in Wastewater Reuse for Potable Purposes
Seong Hoon Yoon, Ph.D., P.E., Ritika Singh, Jason Fuse, Nalco, An Ecolab Company, Naperville, IL
Consider Attending: W-1, W-2, W-3, W-5, W-10, W-12, W-15
From the Bench to Full-scale – Optimization of Wastewater Treatment Systems
IWC Rep: Tom Lawry, McKim and Creed, Sewickley, PA
Session Chair: Mike Bluemle, Solenis LLC, Wilmington, DE
Discussion Leader: Andrew Erikson, Burns & McDonnell, Kansas City, MO
Due to the often complex nature of industrial wastewater, development of effective treatment strategies typically require bench-scale testing to augment design calculations and confirm innovative treatment approaches. Additionally, varying process conditions and water quality drive the necessity for continued monitoring and refinement to maximize the efficiency of plant operations. Papers in this session discuss the implementation of bench-scale testing to improve full-scale applications and theoretical and practical enhancements to dissolved air flotation (DAF) unit operations.
IWC 18-73: The “Ins/Outs” and “Dos/Don’ts” of Bench Scale Treatment Studies
Chloe Grabowski, HDR, Inc., Missoula, MT
This paper will focus on the planning, execution, and data evaluation phases of bench scale treatment studies. It will discuss potential pit falls to avoid in the planning and execution processes through review of lessons learned during several real-world studies conducted at industrial facilities. The paper will provide tips for optimizing bench scale treatment studies as well as an understanding of the benefits and limitations of these types of studies.
IWC 18-74: Zeta Potential for Optimizing Coagulation at Industrial Water Treatment Plants
David Pernitsky, Ph.D., P.Eng., Stantec, Calgary, AB, Canada; Gabe Maul, Stantec, West Palm Beach, FL; Keri Seeley, Babcock and Wilcox, West Palm Beach, FL; Basil Perdicakis, Adrian Revington, and Anita Selinger, Suncor, Calgary, AB, Canada
Sedimentation, flotation, and granular media filtration processes are at the heart of many industrial water and wastewater treatment plants, including pretreatment for boiler feed water systems and sedimentation in ash-management facilities. Determining the appropriate coagulant dose is essential to making these processes work effectively. Although the theory of these processes is well known to researchers, practical application of this theory in operating water treatment plants is not common. Rather, coagulant doses are determined using jar tests, visual observations, and trial and error.
This paper summarizes the author’s twenty-five years of experience to illustrate the use of bench-scale zeta potential measurements for coagulation optimization. The paper begins with an overview of the fundamentals of coagulation and how particle surface charge affects sedimentation/flotation and media filtration. The chemistry of raw water particles, dissolved organics (humics), and metal-salt and polymeric coagulants is summarized. The critical importance of pH and temperature are stressed. The fundamental basis of using zeta potential for directly measuring particle charge is then reviewed.
The paper will then present several case studies illustrating bench-scale zeta potential use. The first case study discusses zeta potential use at a waste to energy facility to select coagulant type and dose to enhance the settling of fly ash and bottom ash wastewaters. Data showing the relationship between zeta potential and good settling will be presented.
The results from several clarification-filtration troubleshooting exercises will then be presented. Jar testing is typically adequate for selecting coagulation conditions for clarifier performance, but often falls short for determining the doses needed to ensure long, reliable granular media filter runs. Data will be presented illustrating the selection of polymer type and dose based on achieving near-neutral zeta potential.
Additional case study data will be presented in the paper on how changes in Total Organic Carbon (TOC) in a plant’s source water influence coagulant doses, and how routine measurements of raw water TOC and/or UV absorbance can be used to avoid upsets.
IWC 18-75: Tiny Bubbles Float Floc — Optimizing Dissolved Air Flotation Operations
Mikel Goldblatt, P.E., Solenis, LLC, Wilmington, DE
Factors determining efficacy of dissolved air flotation (DAF) unit operations include i) solids loading, oil & grease loading and float sludge removal; ii) hydraulic loading, dwell time and rise rate; iii) air injection in the air dissolution tank, and evolution in the flotation tank. This paper focuses on optimization of air injection and evolution as embodied in the air-to-solids (A:S) ratio calculations. Examples of improvements in industrial wastewater DAFs based on enhancing A:S ratios are given.
A generic dissolved air flotation (DAF) unit consists of a flotation tank with a skimmer for float sludge removal, baffling to segregate and capture clear underflow effluent, a pumped pressurized recycle and air saturation system, a pressure let-down valve at the recycle stream entrance to the flotation tank, and associated auxiliary tanks and chemical treatment systems. Figure 1 shows the flotation tank and recycle air pressurization and letdown system.
The A:S parameter is a useful monitoring and trending tool in that it quantifies the solids flotation capability. While some literature gives desirable A:S ranges of 0.01-0.20 lbs of air per lb of floatable solids, each system will have a more narrow range that works for that particular system’s design and conditions.
Two ways to calculate A:S are presented.
1. A rotameter measures air flow for the numerator, “A.” The denominator “S” represents calculated influent total suspended solids (TSS). The problem with relying only on this calculation is that excess undissolved air in the recycle stream may be vented, or can propagate through the air saturation tank into the flotation tank. The undissolved air does virtually no good for flotation and can break up formed float sludge owing to turbulence generated by large, fast-rising bubbles.
2. The second calculation uses thermodynamic principles to determine maximum solubility of air in the recycle stream at a given temperature and pressure, then applies an efficiency of dissolution factor. Upon pressure letdown at the entrance to the flotation tank, tiny bubbles form as air solubility in water decreases. These tiny bubbles attach to solids or chemically enhanced floc particles, causing buoyancy, separation and flotation of these solids, leaving a clear effluent underflow.
Tiny bubbles formed from dissolved air are what make the dissolved air flotation process work.
This paper will present the two A:S calculations in detail. Examples from industrial wastewater optimization projects with improvements to increase air-to-solids ratios and enhance DAF capacity are cited.
IWC 18-76: Hydrogen Peroxide for Supplemental Dissolved Oxygen for Refinery Wastewater Treatment
Rick Fuller and Michael Cole, USP Technologies, Atlanta, GA
Hunt Refining Company in Tuscaloosa, AL is a 72,000 barrel per day refinery that produces asphalt, gasoline, kerosene, jet fuel, and diesel. The refinery operates two wastewater treatment systems in parallel identified simply as the No. 1 and No. 2 plants. The focus of this paper is on the use of hydrogen peroxide (H2O2) to supplement dissolved oxygen in the aeration basin of the No. 2 wastewater plant.
During the summer of 2017, Hunt Refining Company partnered with USP Technologies to provide supplemental dissolved oxygen (DO) to the aeration basin through the addition of hydrogen peroxide (H2O2). The use of hydrogen peroxide as a source of supplemental dissolved oxygen (DO) in activated sludge treatment systems is well documented and has been practiced for decades.
The H2O2 was fed into the DAF overflow which discharges directly into the aeration basin. This discussion provides a detailed analysis of operating conditions during the 62 days preceding the start of H2O2 addition compared to operating conditions during the 81 days that H2O2 was being fed, representing a 143 day “study” from June 1, 2017 through October 21, 2017.
The wastewater temperature in the aeration basin during the study period averaged 88.6°F (31.4°C) and reached a maximum of 96.9°F (36.1°C). Given the high wastewater temperature and associated decrease in oxygen solubility, maintaining a sufficient DO concentration (≥ 2.0 mg/L) was the primary objective of the H2O2 addition. A mean hydrogen peroxide dose of 147 ppm increased the average DO to 2.4 mg/L, a significant increase of 26.3%. This increase in DO occurred during a period when the refinery increased the slip stream feed rate by 131 percent. This is significant in that the slip stream contains off-spec material including complex, refractory organics known to decrease the DO concentration.
Hunt Refining Company wastewater operators collect a daily sample of the mixed liquor suspended solids (MLSS) and measure the nitrate (and nitrite) concentration in the supernatant from this sample. In terms of nitrification and oxidation of ammonia to nitrate, the nitrate concentration increased 81.6% during H2O2 treatment.
Hunt Refining’s NPDES permit limit for total ammonia nitrogen is 180 pounds per day (lb/d) for the monthly average and 270 lb/d for a daily maximum. During the period of H2O2 addition, the influent ammonia loading decreased 60% while the effluent ammonia loading from the wastewater plant decreased 74.6% from 138 lb/d to 35 lb/d, on average.
Consider Attending: W-1, W-2, W-5, W-6, W-9, W-10, W-12, W-13, W-16