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This research report evaluates the fouling and flux decline performance of membranes after the source water is pretreated with coagulation, and identifies the conditions under which coagulation can improve membrane performance as well as the mechanisms that cause natural waters to foul membranes. Conducted at the University of Illinois, the experiments involved collecting raw water from lakes and rivers, coagulating the water in the laboratory, characterizing the physical and chemical composition of the water before and after coagulation, measuring flux decline as the water was filtered through MF and UF membranes, and examining the fouled membranes with scanning electron microscopy. No index is provided. Annotation copyrighted by Book News, Inc., Portland, OR
It is essential to find separation and purification methods that have the potential of producing water that will comply with the more stringent regulations that are being enacted. One such purification technique is membrane filtration, which is a treatment process that removes a wide majority of pathogens, water pollutants, and organic carbon. However, there are two major concerns associated with the use of membranes: one is the efficiency of the membrane (water flux and removal rate of impurities), and the other is membrane fouling, which often make this technology unfeasible, especially, for small systems. Small water systems are those that serve fewer than 3,300 people and very small water systems serve fewer than 500 people. These systems make up slightly more than 86% of the 58,908 community water systems in the United States. Small systems are the most frequent violators of federal regulations. The majority of cases against them are microbiological violations and failure to report and monitor. Bringing small systems into compliance will require technologies, operator ability, financial resources, and institutional arrangements. Membrane filtration is a relatively new technology that offers small systems a high efficiency, easy-to-operate alternative to improve the finished water quality and the biological stability of the finished water. However, the economic use of membrane filtration in small systems is often hindered by fouling, which increases applied pressure drops and cleaning frequencies, and the associated decrease in removal efficiency as the pressure drop increases. Coupling membrane filtration with pretreatment processes to decrease fouling is often avoided by small systems since it incurs additional construction costs and complicates operation. The objective of this work was to test different coagulation pre-treatment techniques to improve membrane filtration, namely ultrafiltration (UF). These four techniques were 1) conventional coagulation, 2) coagulant slurry on the membrane surface, 3) forming a dynamic coagulant-based layer on the membrane, and 4) injecting the coagulant into the feed line so that it runs inline with the raw water across the membrane. Results showed that the slurry and dynamic membrane's mode of operation achieved similar steady state flux values as UF alone and higher flux values than conventional coagulation pretreatment ahead of UF, while in-line coagulation displayed the worse flux decline. UF alone was ineffective in removing solids and dissolved organic carbon (DOC), while conventional coagulation, slurry, and dynamic UF modes rejected solids and DOC at similar rates. Through membrane autopsies, irreversible fouling measurements for the slurry and dynamic membrane modes were significantly lower than for the conventional coagulation mode.
This book provides an up-to-date overview on the membrane technology for the drinking water treatment. The applications of PVDF-TiO2 nanowire hybrid ultrafiltration membrane, nanofiltration membrane, forward osmosis membrane, etc. in water treatment are discussed in detail. With abundant practical examples, the book is an essential reference for scientists, students and engineers in municipal engineering, environmental engineering, chemical engineering, environmental chemistry and material science.
carbon (DOC), surrogates of disinfection by-products (DBPs), were reduced by 60 and 30 percent, respectively. With coagulant pretreatment, DBP concentrations were effectively reduced below their maximum contaminant levels. Optimized coagulation pretreatment with ferric chloride reduced the rate of membrane fouling by approximately 92 percent. Removals of surrogates of DBPs were approximately 20 to 30 percent higher than for the control (no coagulation) experiment. Attempts to optimize the system with aluminum chlorohydrate (ACH) were unsuccessful. In some cases an increase in the rate membrane fouling was observed as a result of the addition of ACH.The overall results demonstrated that both aluminum sulfate and ferric chloride can potentially be used for the coagulation pretreatment of ceramic membrane systems. However, aluminum sulfate was found to be more flexible and consistent at controlling the rate of membrane fouling. Under optimized coagulation conditions, current drinking water standards can be met, typically at coagulant dosages lower than those required for a conventional treatment process.
This study investigates the role of coagulation in enhancing hydraulic performance and permeate quality of UF membranes and provides insight into options for minimizing or ideally eliminating coagulation from UF pre-treatment to SWRO. Results show that coagulation improves UF hydraulic performance mainly by reducing non-backwashable fouling of the membranes. This can be achieved at very low coagulant dose (~ 0.5 mg Fe/L) by coating the membranes with sub-micron particles. Additionally, the work highlights the applicability of UF membranes with low molecular weight cut-off as the coagulant free future of SWRO pre-treatment. Major benefits in terms of reduced environmental impact is expected when applying membranes with low molecular weight cut-off, as the need for coagulation is eliminated while ensuring longevity of downstream SWRO membranes. In general terms, the research indicates that coagulant consumption can be significantly reduced in UF pre-treatment of SWRO by optimizing operational parameters and applying alternative solutions.
With global demand for water in the 20th century expected to increase ten-fold, this work focuses on the membrane filtration issues for drinking water.
Coagulation and Flocculation in Water and Wastewater Treatment provides a comprehensive account of coagulation and flocculation techniques and technologies in a single volume covering theoretical principles to practical applications. Thoroughly revised and updated since the 1st Edition it has been progressively modified and increased in scope to cater for the requirements of practitioners involved with water and wastewater treatment. A thorough gamut of treatment scenarios is attempted, including turbidity, color and organics removal, including the technical aspects of enhanced coagulation. The effects of temperature and ionic content are described as well as the removal of specific substances such as arsenic and phosphorus. Chemical phosphorus removal is dealt with in detail, Rapid mixing for efficient coagulant utilization, and flocculation are dealt with in specific chapters. Water treatment plant waste sludge disposal is dealt with in considerable detail, in an Appendix devoted to this subject. Invaluble for water scientists, engineers and students of this field, Coagulation and Flocculation in Water and Wastewater Treatment is a convenient reference handbook in the form of numerous examples and appended information.