http://cct.seas.ucla.edu/cct.ww.html -- Lawrence F. London, Jr. mailto:london@sunSITE.unc.edu http://sunSITE.unc.edu/InterGardenTitle: CCT Water and Wastewater Treatment
This program is rooted in the treatment waters which contain small quantities of hazardous substances in a matrix of non-hazardous contaminants. These wastewaters are especially challenging to treat; small quantities of hazardous substances may preclude release to conventional wastewater treatment plants, yet the generally large volume and dilute concentrations make for poor candidates for reuse or thermal treatment (incineration). One early goal was to develop a modified biological treatment process that could biodegrade the hazardous compounds while at the same time degrading the large matrix of conventional pollutants. The two reactor, "enricher reactor" process, shown schematically below, was developed for use with existing biological wastewater treatment facilities as well as new applications.
Over the last several years, the program has broadened to include other types of wastewater treatment, water treatment, and associated areas such as analytical chemistry and water reclamation. The overall goals of this research are to develop improved, more economical, water and wastewater treatment processes and plants. CCT investigators are seeking better process optimization, improved process content, and greater efficiency through more a thorough understanding of microbiology, chemistry and kinetics.
The following links will take you directly to a brief project report within this document:
Treatment of Low Strength Wastewaters Containing High Explosives
The U.S. Departments of Defense and Energy (DOD, DOE) face a large problem disposing of weapons, especially the nuclear weapons containing some form of high explosive, such as TNT, RDX or HMX. Many nuclear weapons use RDX or HMX to implode the plutonium sphere. When such a weapon is decommissioned, the high explosive (HE) must first be removed from the sphere by water cutting. This cutting process produces bulk quantities of HE as well as wastewaters contaminated with 5 to 40 mg/L of RDX and HMX.
Center researchers have developed a two-step process to treat the wastewaters. The volume of wastewater is first treated by adsorbing the HE onto granular activated carbon, which must be regenerated or destroyed as a hazardous waste/high explosive. Destruction, however, is expensive and conventional regeneration techniques cannot be used due to the risk of explosion. Therefore, CCT investigators have developed two alternative regeneration techniques. The first makes use of a solvent at slightly elevated temperatures, such as 60-80 C; the solvent, such as ethanol, has high solubility for the HE and can reverse the carbon isotherm. The solvent is treated in a biological process, and acts as the substrate for anoxic organisms which gratuitously biotransform RDX and HMX to non-explosive byproducts.
A pilot plant recently began operation at the Pantex Plant in Amarillo, Texas. Early results show it is possible to transform RDX and HMX to concentrations below analytical detection limits. Pilot-scale carbon regeneration research is underway and also appears promising. The second technique used in this project is alkaline hydrolysis. In this process, dissolved or particulate HE is exposed to high pH (10-13) solutions of sodium hydroxide at elevated temperatures (60-90 C). The HE, in the form of both RDX and HMX, undergoes decomposition to non-explosive end products and follows second-order kinetics. The process has recently been evaluated for regenerating granular activated carbon at lab scale. The initial results, through five adsorption/regeneration cycles, are encouraging.
Follow this link to read a newsletter article on this novel treatment for high explosives, which was originally published in the Center's Spring 1993 newsletter.
PCE Conversion in Anaerobic Digesters
PCE is widely used and is an important industrial solvent. Pollution prevention measures are underway to find environmentally safer substitutes, but until they are found, PCE containing wastewaters must be treated. PCE is also found in many remediation sites. PCE can be dechlorinated to TCE by anaerobic organisms, but no aerobic organisms are known to effect this conversion. TCE can be transformed to DCE and vinyl chlorine by both aerobic and anaerobic organisms.
The feasibility of a commercial process which anaerobically transforms and degrades PCE to less harmful byproducts, such as ethylene, has never been demonstrated. The Center's 2-year long investigation shows that PCE can be successively transformed at very high concentrations to TCE, DCE, vinyl chloride and ethylene in ordinary anaerobic digesters, such as those found at wastewater treatment plants. Activated carbon can be used in conjunction with the anaerobic process to increase stability and the maximum transformable concentrations.
Wastewater Reclamation at Lake Arrowhead
In 1991, we began a project to demonstrate the feasibility of using reverse osmosis to reclaim wastewater at Lake Arrowhead, CA, a resort community located in the San Bernadino Mountains. The Lake has important recreational value and is the only water source for a community of approximately 10,000 people. The goal of the pilot plant demonstration project is to show feasibility and provide sufficient information for the community to develop a full-scale proposal and acquire funding.
A 15 GPM pilot plant was constructed to treat fully nitrified, secondary effluent from the Grass Valley Treatment Plant, which has trickling filters. The plant is composed of denitrification, coagulation/precipitation, filtration, ozonation, activated carbon biofilitration, nano-filtration, reverse osmosis and disinfection processes. The plant must aim to release water which will exceed the quality of the lake's pristine water. Target levels for phosphorous, total nitrogen are less than 0.1 mg/L, while total organic carbon targets are less than 3 mg/L. Results obtained in 1994 show that all these goals can be easily met. Research is continuing to collect economic parameters and demonstrate reliability.
Non-Point Sources of Water Contamination to Santa Monica Bay
Non-point sources of contaminated water discharged to Santa Monica Bay have become a focal point of environmental concern for the Los Angeles community. In a few years, after all the wastewater treatment plants achieve secondary standards (~2002), stormwater will be the largest pollution source to the Bay. Center investigators have participated in several projects in conjunction with the Santa Monica Bay Restoration Project. The first, conducted with Woodward Clyde Consultants, Inc., defined the watershed's characteristics, which included land use and catchment areas, and compiled all available data on wet and dry weather discharges to the Bay. The second project assessed dry weather runoff characteristics and toxicity. A third project will assess wet weather runoff characteristics and toxicity. Other related projects include management practices for auto salvage yards, development of synthetic oil filters for parking lot runoff, and evaluation of highway runoff treatment technologies.
Industrial Activities and Stormwater Runoff
This project seeks to identify sources of pollutants in storm water that originate with industrial activities, and to recommend practices that industrial facilities may implement to control or eliminate those pollutants. The research focuses particularly on the transportation-related industries (trucking, bus maintenance, municipal vehicle maintenance) where it is expected that everyday activities generally lead to pollutants which are transported by storm water runoff into the large urban storm drainage systems of the Los Angeles region and then into surface waters where they adversely affect water quality. The research goals include: identifying routine activities in the transportation industry which can lead to pollutants in storm water; identifying effective practices that facility operators can use to reduce pollutants found in storm water as a result of everyday industrial activities; and evaluating the industrial awareness of recent storm water regulations. Early results suggest that dischargers are not fully aware of the regulations and that additional education will be required.
Inorganic Contaminants in Waste Sediments and Sludges: Evaluation of the Potential for Remobilization and Toxicity
Trace metals are introduced as contaminants into soil and sediment environments through a variety of human activities, including industrial processing and waste disposal. The mobility of trace metals in soils and sediments is of particular concern because of the potential for bioaccumulation, food-chain magnification, and deleterious ecosystem and human health effects. The sorption of metals onto biological materials is an important phenomenon in: (i) biological treatment of metal-contaminated wastewaters, (ii) immobilization of metals in contaminated soils and sediments, and (iii) uptake and incorporation of metals into living biomass. Metal biosorption, defined here as the physico-chemical association of a metal with the surface of living or non-living biomass, is one of the processes by which metals may be incorporated into biological materials from solution. Other processes include the precipitation of metals as oxide-, carbonate-, sulfide-, or other solids at the surface of organisms, passive diffusion of metals into organisms, and active up-take (i.e., up-take coupled with metabolic activity) of metals by organisms. Current work focuses on the development of a database for metal biosorption. Biosorption data are obtained from the published literature and expressed in consistent units. Parameters describing the extent of biosorption are extracted with a uniform model; the comparison of the model parameters allows the assessment of various factors, such as pH, influencing biosorption.
Removal of Arsenic from Drinking Water
Recent epidemiological studies on the carcinogenicity of arsenic have increased concern over the levels of arsenic in drinking water and a reevaluation of the current maximum contaminant level (MCL) of 50 µg/L. A decrease in the MCL to between 20 and 0.5 µg/L is presently under consideration by the U.S. Environmental Protection Agency. Elevated arsenic concentrations in groundwater are common throughout the western U.S.; the highest concentrations occur in nonthermal water draining mineralized (i.e., mining) areas and in geothermal waters. Both the concentration and chemical speciation of arsenic in source waters will determine whether newly-mandated levels of arsenic in drinking water can be achieved by various treatment technologies.
The goal of the current project is to examine systematically the effects of the chemical composition of source waters on arsenic removal by enhanced coagulation and membrane processes. Factors such as the arsenic oxidation state, the pH, and the presence of co-occurring inorganic solutes, humic substances, and background particles on the efficiency of arsenic removal are being studied in bench-scale experiments. The applicability of models for the adsorption of solutes on oxide surfaces and for solute rejection by reverse osmosis membranes for predicting the efficiency of arsenic removal from source waters of varying composition are being evaluated.
Metal-Organic Interactions in Sorption of Metals and Organic Compounds on Mineral Surfaces
Once introduced into the environment, contaminants may undergo chemical reactions, be re-distributed among environmental compartments, and accumulate in the biota. In studies of environmental contaminants, the behavior of trace metals and organic compounds is usually considered separately and possible interactions between them disregarded. This approach may be reasonable for hydrophobic organic compounds, but for metals and organic compounds that interact specifically with metals (i.e., organic ligands), reactivity, transport, and toxicological effects may be markedly influenced by metal-organic interactions.
Expert Systems for Improved Control of Chevron's El Segundo Effluent Treatment Plant
Activated sludge processes, especially those for treating industrial wastewaters, often have a poor record of reliability. Upsets are frequent, and while they do not always result in permit violations, can be expensive to control. One method of improving reliability and overall treatment plan efficiency is to improve process control. This can be done two ways: by improving the knowledge and skills of the personnel who operate the plant, and by improving our understanding of the process microbiology, kinetics, and dynamics, so that better control strategies can be developed. CCT Investigators have developed an expert systems process simulator using an advanced expert system, process control and simulation package (G2) which runs on Unix workstations. The package includes an operator interface which simplifies data entry through a graphical interface. The package analyzes the data and performs a variety of functions, such as charting trends, comparing with mean values, checking for implausible values, and other statistical analysis. Current research is on the development of process diagnostic tools. A version of the program is undergoing evaluation at a local refinery.
Zeta Potential of Reverse Osmosis Membranes: Implication for Membrane Performance
It has long been recognized that membrane fouling is a major problem in efficient operation of RO plants. Colloidal particles are considered to be the principal cause of membrane fouling, resulting in a rapid decline of product water flux. Colloidal fouling of RO membranes places a large economic restriction on membrane plant operation. A key to this problem lies in the fundamental understanding of the physico-chemical mechanisms of colloidal fouling. The interaction of colloidal particles with membrane surfaces in aqueous media is dependent on, among other variables, the zeta (electrokinetic) potentials of both the membrane surface and suspended particles. These, in turn, are controlled by the surface chemistry of the membranes and colloidal particles, as well as by the chemistry of the solution. Hence, the determination of the zeta potential of reverse osmosis membranes at various solution chemistries is of paramount importance. In this project we (i) develop a methodology to measure zeta potentials of RO membranes by a streaming potential analyzer; (ii) investigate the zeta potential of different commercial RO membranes at various solution chemistries; (iii) delineate the mechanisms of surface charge acquisition by RO membranes in aqueous solutions; and (iv) evaluate the implications of the results for minimizing colloidal fouling and for optimizing pretreatment of feed waters. A novel streaming potential analyzer is used in this research to determine the zeta potential of commercial reverse osmosis membranes. Cellulose acetate and thin film composite membranes of different surface chemistries are tested. The measurements are conducted at various solution chemistries, typical to natural and waste waters that might be treated by RO membranes.
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