Summary of Recent and Current Research
New Projects Under Contract Negotiations:
Reducing Taste and Odor and Other Algae-Related Problems for Surface Water Supplies in Arid Environments (A Cooperative Research and Implementation Program among ASU, SRP, CAP, and the City of Phoenix)
The goal of the proposed project is to develop a comprehensive management strategy to reduce algae-related water quality problems for drinking water supplies in arid environments. Algae can cause problems in water supply reservoirs, water distribution canals, and water treatment plants. Algae cause several types of problems:
The primary focus of the proposed project is the taste and odor problem. However, because algae also produce dissolved organic carbon (DOC), which react to form disinfection by-products (DBPs) and contribute other in-plant operational problems, these issues will also be addressed.
Funding: City of Phoenix ($1.2 Million over 1999-2002)
A ZERO-VALENT IRON (FE0) PACKED-BED TREATMENT PROCESS
Groundwater contamination by nitrate has become widespread in the U.S. (Nielsen and Lee, 1987). In the Phoenix, AZ area for example, over 60% of the production wells have nitrate levels that exceed the United States Environmental Protection Agency (USEPA) drinking water Maximum Contaminant Level (MCL) of 10 mg-N/L. Contaminated groundwater, agricultural drainage, and municipal wastewater, once considered unusable, are now being seriously considered as sources of municipal water in order to meet current and future demands (Andrews et al., 1994). Nitrate was the most frequently reported contaminant of concern in groundwater, reported by more than 40 state nationwide (Fetter, 1993; USEPA,1990). The USEPA has also recognized the health effects from oxo-anions other than nitrate (e.g., bromate, chlorate, chlorite, perchlorate).
Many communities throughout the Midwest and southwest that had shut down nitrate-contaminated wells are now finding that those wells must be re-activated to meet growing water demands (Clifford and Liu, 1993). Current methods of nitrate treatment (e.g., membrane separation, ion exchange, biological treatment) are costly, difficult to maintain, and can generate concentrated wastestreams. There is need for a low-cost, low-maintenance, but efficient method to treat nitrate contaminated groundwater.
The goal of the proposed research is to develop and test a zero-valent iron (ZVI) packed bed treatment process for electrochemically reducing problematic inorganics in groundwater. The process will be optimized for nitrate removal, and will evaluate the removal of other oxo-anions (e.g., perchlorate, bromate, chlorate). The use of elemental iron (Fe0) for in-situ, sub-surface, groundwater treatment of halogenated organics has recently received strong interest. A few studies have indicated that Fe0 can remove oxo-anions, such as nitrate. This project represents an initial step in assessing the feasibility of an above-ground water treatment process for treating problematic inorganic ions. The project has the following specific objectives and corresponding general technical approaches:
Funding Source: American Water Works Association Research Foundation ($90,000 over 1998-2001)
Mechanistic-based Disinfectant and Disinfectant By-Product Models
Principal Investigator: Paul Westerhoff; Co-Investigators David Reckhow (University of Massachusetts, Amherst) Gary Amy (University of Colorado, Boulder) Zaid Chowdhury (Malcolm Pirnie Inc.)
We will develop a mechanistic-based numerical model for chlorine decay and regulated DBP (THM and HAA) formation derived from (free) chlorination; the model framework will allow future modifications for other DBPs and chloramination. Predicted chlorine residual and DBP results will be compared against predictions from several other quasi-mechanistic models. We anticipate a significant improvement in prediction accuracy over existing empirical models. Several modeling hypotheses are proposed as a basis for a mechanistic-based model for disinfectant decay and DBP formation. The central modeling hypothesis is that a two-site reaction mechanism can be used to predict disinfectant decay in the presence of natural organic matter (NOM). It assumes that NOM contains both slow and fast disinfectant-reacting and DBP-forming sites. NOM site densities and concentrations are related to the concentration, size, structure and functionality of NOM. Our model will also include fitted rate constants that are a function of pH and temperature. A series of distribution functions, based upon the predicted ratios of free-bromine to free-chlorine, will be used to estimate each of the four trihalomethane species (THM4) and each of the nine haloacetic acid species (HAA9).
DBP experimental data from completed projects conducted by the Investigators and other researchers will be integrated into a single Unified Database. Existing empirical models and newly developed numerical models will initially be calibrated with our Unified Database. Additional experimental data will be collected since prior databases lack complete documentation of NOM characteristics before and during disinfection addition. Controlled laboratory disinfection and DBP formation studies will be conducted using water collected at several points through different water treatment plants, including raw, coagulated, softened, and pre-oxidized (ozone and/or chlorine dioxide) waters, thus the waters represent a wide range of water qualities and NOM characteristics. Experiments will investigate the affects of pH and temperature, and NOM, bromide, and free-chlorine concentrations; DBP hydrolysis studies will also be conducted.
A computer package that evaluates DBP formation in Water Treatment Plants is know available as version 2.1 of the EPA WTP Simulation model. Both files must be in the same directory for the model to run. Click on the files to download ~ 1.5 MB files (WTP model and secondary bitmap file).
Funding source: USEPA ORD/NCERQA STAR GRANTS PROGRAM ($330,000 over 1999-2001)
Kinetic-Based Models for Bromate Formation in Natural Waters
Ozone (O3) is an effective disinfectant, but it can form by-products (e.g., bromate). Bromate forms via oxidation of naturally occurring bromide through a series of steps (Figure 1). There is a need to develop tools to understand and predict bromate (BrO3-) formation while still achieving high levels of microbial disinfection. The central hypothesis is that a kinetic-based understanding of natural organic matter (NOM) reactions with hydroxyl (HO) radicals and aqueous bromine (HOBr/OBr-) over a range of temperatures is necessary to develop mechanistic-based models for bromate formation in bulk waters. Objectives include:
Develop a comprehensive database of BrO3-, O3, and HO radical concentrations;
Determine rates of reaction between HOBr and OBr- and NOM;
Calibrate and verify a BrO3- formation mechanistic-based model that includes NOM;
Simulate BrO3- control measures necessary to meet proposed and future MCLs;
Link the numerical BrO3-formation model with hydraulic and CT disinfection models.
A mechanistic-based, numerical, kinetic BrO3- formation program will be developed (Figure 2). The program links an oxidant module for predicting O3 and HO radical concentrations with a BrO3- formation module. The model employs a set of bromide oxidation reactions that have been previously developed by the Investigator, and calibrated against bromine and BrO3- formation in NOM-free water; NOM reactions will now be incorporated. The oxidant module will be calibrated against experimental O3 decay data (e.g., simple first-order decay) and HO radical concentrations (calculated from the disappearance of a HO radical probe compound during ozonation). Predicted BrO3- levels will be calibrated and verified against an internal database, that accounts for synergistic effects of key parameters (bromide, pH, ozone dose, temperature, inorganic carbon, and ammonia) on ozone decay, HO radical concentrations, and BrO3- formation, and an external USEPA database.
Funding source: USEPA ORD/NCERQA STAR GRANTS PROGRAM ($90,000 over 1999-2001)
Soil Aquifer Treatment & Sustainable Water Supply
The National Center for Sustainable Water Supply (http://www.eas.asu.edu/~civil/ncsws/NCSWS.html ) has been created at Arizona State University. The NCSWS is a collaborative effort between Arizona State University, the University of Arizona, Stanford University and the University of Colorado-Boulder. The Center will address fundamental problems with the sustainability of present and proposed water reuse and management practices. NCSWS is funded by the United States Environment Protection Agency and the American Water Works Association Research Foundation (AWWARF). The role of two PhD students working with me is to (1) develop fluorescence spectroscopy techniques to quantify DOC of wastewater origin, (2) develop techniques to isolate and characterize DOC, and (3) compare the performance of reverse osmosis treatment to soil aquifer treatment (SAT).
Funding source: USEPA/AWWARF for multiple years
Preparing for Regional Changes in Groundwater Quality Due to GRUSP and Other Recharge Projects
The purpose for this project was to better understand localized and regional impact of groundwater recharged by SRP and other entities on the groundwater quality that will serve future water users throughout the Metropolitan area. Key issues regarding metals contamination are regulated by ADEQ, but other water quality constituents are typically not regulated and not measured (e.g., salts, organic carbon). SRP currently recharges up to 200,000 ac-ft per year of primarily Salt and Verde River water at the Granite Reef Underground Storage Project (GRUSP). SRP is also in the process of demonstrating direct groundwater recharge using existing wells along its canal system as dual-use (recharge-recovery) wells. In addition to SRP, there are nearly 30 other recharge projects that vary in magnitude around the Valley, and many more are planned. SRP should consider assessing the current state of un-impacted groundwaters, understanding the impact of current groundwater recharge practices, and be capable of monitoring and predicting future changes in groundwater quality.This project provides SRP with information and tools that can be used to assess the impact of recharge on SRP customers. Along with the water resources expertise obtained by GRUSP and the Rio Salado Town Lake Project, this project will allow SRP to establish itself as an expert in large-scale recharge projects. The project was designed to address the following key questions:
Funding Source: Salt River Project ($35,000 over 1998-1999)
Application of Photosynthetic Algal Culture Technology for Carbon Dioxide Emission Control and Nitrate Reduction
Raising worldwide atmospheric carbon dioxide (CO2) levels may be responsible for global warming. Industrial gas emissions have been recognized as a major input of CO2 into the atmosphere. Many industries that produce carbon dioxide have been controlling their emissions, but will continue to produce carbon dioxide as long as fossil fuels are used as an energy source. To this end, industries are purchasing CO2 credits. One such CO2 credit strategy includes purchasing stands of trees; photosynthetic plants fix atmospheric CO2 and convert it to organic matter through solar energy. Over the past twenty years, other applications of photosynthesis for CO2 removal have been considered and are now emerging as viable technologies that have multiple benefits. One such application is to use the natural photosynthetic process in microalgae (including green algae and cyanobacteria) to remove CO2 from atmospheric gases or power-plant off-gases, while producing biomass that has an economic benefit (e.g., fuel source, food source, etc.). Microalgal photosynthesis in engineered photobioreactors has much higher CO2 uptake rates and efficiencies than higher plant photosynthesis (e.g., trees, water hyacinth).
Nitrate contamination of groundwater, and its remediation, also poses a significant challenge for SRP customers and users of groundwater worldwide. Nitrate is a predominant contaminant of drinking well water in many urban areas. Wastewater, fertilizers, and livestock farming are major sources of nitrate (Hem, 1992), and nitrate contamination is widespread throughout the world. Nitrate poses a potential risk to public health, particularly to infants (Gangolli et al., 1994). In the USA, the Environmental Protection Agency has maximum contaminant concentration (MCL) for nitrate in drinking water of 10 mg-N/l (0.71 mM). Canada has set the same maximum acceptable level as the US, while the European Community established a MCL of 50 mg-NO3/L (0.80 mM) and a recommended level of 25 mg-NO3/L (0.40 mM) (European Community, 1980). In many agricultural areas, the amount of nitrate in well water is 3-7 fold higher than the allowed upper limit. Removal of relatively low concentrations of nitrate by biological (denitrification), physical (reverse osmosis, electrodialysis), or chemical (ion exchange, catalytic denitrification) means is expensive (see review by Kapoor and Viraraghavan, 1997).
One very attractive and environmentally friendly alternative to remove nitrate from well water is to utilize photosynthetic microalgae such as cyanobacteria that require mostly nitrate and light for growth. Light is used as an energy source for carbon fixation as well as a source for generation of ATP and reducing power, and nitrate is used as the main source of fixed nitrogen. Other compounds that are required in smaller amounts include phosphate and trace minerals, but these are also present in water from most wells. Therefore, we have started to explore the concept of utilization of cyanobacteria for nitrate removal from ground water, and the preliminary data are very encouraging. Figure 1 presents a graph of removal of nitrate from ground water samples by different strains of cyanobacteria, and proves the concept that such nitrate removal is efficient and relatively fast. Within a day the nitrate level has dropped below the 10 mg-N/l level.
Warm temperatures and frequent sunny days in Arizona offer an opportunity to apply natural photosynthetic processes in a state-of-the-art setting for controlling CO2 emissions. This project would represent a continuation of a first year of funding through the SRP/ASU cooperative research program. During this first year of study, and research on related projects, the following key milestones were reached:
Funding source: Salt River Project ($70,000 over 1998-2000)
Other Projects:
"Isolation and characterization of organic carbon from CAP water" (Malcolm Pirnie, Inc.) for $2,051 (sole PI in 1997).
"Chemical analysis at Gilbert Water Reclamation Site" (Town of Gilbert) for $7,294 (Sole PI in 1997/98).
"Algae-related Water Quality Issues in the Verde River Reservoirs" (Salt River Project) for $48,731 (Second PI of 3-investigators in 1997/99)
"Source and transport of aquatic organic material in arid systems" (WEAL/ASU) for $9,600 (first PI of 3-investigators in 1996).
"Development of a photosynthetic bioreactor and UV-oxidation system for remediating inorganic and organic pollutants" (Project Ingenhousz/ASU) for $70,050 (first PI of 2-investigators in 1997/98/99).
"Investigating the effects of metal-salt addition to lime/soda ash softening processes for improved hardness control, cost reduction, and sludge quality at the Coronado Generating Station, St. Johns, AZ" (Salt River Project) for $26,000 (sole PI in 1997/98).
"Low-cost strategy for treating wastewater" (USEPA/SCERP) for $135,000 (Second PI of 5-investigators in 1996/97).
"Low-cost strategy for treating wastewater" (USEPA/SCERP) for $87,990 (Second PI of 5-investigators in 1997/98).
"Linking nitrate models to existing SRP canal hydraulic models to predict water quality impacts of well pumping" for $25,358 (Salt River Project) (first PI of 3-investigators in 1996/97).
"Evaluation of Physical-chemical processes in removing chemically distinct fractions of NOM" (ASU) for $6,000 (sole PI in 1996).
"Predicting DBPs in the Paris-Area Water Treatment Plants and Distribution System" (confidential client) (Co-PI in 1995/96/97).
