GLOSSARY
Backpulse or backwash: 1) Backwash is a procedure in which periodically the flow direction is reversed through the membrane for a short period of time in order to remove particulates accumulated at the membrane surface. 2) Backwash also refers to the waste water produced as a result of the backwash procedure.
Breach or integrity breach: A breach refers to leakage in the membrane module to due a broken fiber, leaking seal or other leak that can allow microbes and particulates to bypass the membrane and pass directly into the finished water.
Cartridge filtration: Cartridge filtration uses disposable filter elements. The pore sizes can be the same as typical microfiltration membranes and the units could meet the definition of a membrane filter under the LT2ESWTR but often the pore sizes are much larger.
Challenge testing: Challenge tests are conducted to determine the efficiency of removal of target particulates such as a microbe or a surrogate in order to calculate the log removal value of the membrane module.
Clean-in-place (CIP) or in-situ chemical cleaning: Clean-in-place is a procedure performed periodically to clean a membrane more thoroughly than backwashing can achieve in order to restore the permeability of the membrane towards baseline levels. The process uses chemicals such as citric acid and chlorine or others to remove accumulated foulants on the membrane.
Coagulant aids: Coagulant aids are often polymers used to assist primary coagulants such as alum or ferric salts in order to achieve better settling or better filtering flocs.
Concentrate: Concentrate refers to the waste stream created in reverse osmosis and nanofiltration systems or any membrane system in which not all the feed water passes through the membrane. The water that does not pass through the membrane will have a much higher concentration of dissolved solids and/or particulates.
Control limit (CL): A control limit in membrane systems refers to a response from an integrity test, for example exceeding a maximum allowable rate of pressure loss, that triggers a response by the operators such as searching for breaches.
Conventional treatment: Conventional treatment refers to older established water treatment process such as coagulation, flocculation, and rapid sand filters.
Cryptosporidium: According to the U.S. Center for Disease Control, Cryptosporidium is a microscopic parasite that causes the diarrheal disease cryptosporidiosis. Both the parasite and the disease are commonly known as "Crypto." There are many species of Cryptosporidium that infect humans and animals. The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very tolerant to chlorine disinfection.
While this parasite can be spread in several different ways, water (drinking water and recreational water) is the most common method of transmission. Cryptosporidium is one of the most frequent causes of waterborne disease among humans in the United States.
Cross-flow configuration: A cross-flow configuration is the application of water at high velocity tangential to the surface of a membrane to maintain contaminants in suspension.
Cross-connection: A cross-connection occurs when untreated or non-potable water can enter the treated water system. In membrane systems, cross-connections must be prevented with the clean-in-place chemical system although there may be other potential cross-connections as well.
Daltons: A Dalton is a unit of mass equal to 1/12th the mass of a carbon-12 atom (i.e., one atomic mass unit. (amu)).
Dead-end configuration: Dead end filtration refers to a hydraulic configuration in membrane systems in which all the feed water passes through the membrane and no concentrate is produced.
Direct integrity test: A direct integrity test refers to the process usually performed daily to detect breaches in the membrane system. Integrity tests are pressure-based or marker-based.
Disinfection-by-products (DBP's): Disinfection-by-products are typically organic molecules such as trihalomethanes or haloacetic acids that are formed from the reaction of the disinfectant with organic materials in the water. Several such DBP's are regulated and have maximum contaminant levels. A major consideration in selecting treatment processes and operation for many utilities is to minimize the formation of DBP's.
Enhanced flux maintenance: Enhanced flux maintenance is a proprietary term used by Pall. It is the same thing as a “Maintenance Clean” which is a more generic term.
Feed water: The feed water is the water stream applied to the membrane unit.
Filtrate: Filtrate is the water that has passed through the membrane.
Flux: Flux is the flow rate of water applied per unit area of the membrane and has units of volume/unit area/time.
Giardia: According to the U.S. Center for Disease Control, Giardia is a microscopic parasite that causes the diarrheal illness known as giardiasis. Giardia (also known as Giardia intestinalis, Giardia lamblia, or Giardia duodenalis) is found on surfaces or in soil, food, or water that has been contaminated with feces from infected humans or animals. Giardia is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it tolerant to chlorine disinfection. While the parasite can be spread in different ways, water (drinking water and recreational water) is the most common method of transmission.
Ground water under the direct influence of surface water (GWUDI): Many groundwaters especially those in karst areas are recharged with significant amounts of surface water that does not pass through soil with its consequent filtering action but rather pass through sink holes directly into the groundwater. A groundwater with significant amounts of insects, macroorganisms, algae, or microbials or sees rapid changes in turbidity, temperature or quality would most likely be considered a ground water under the direct influence of surface water.
Hollow-fibers: In hollow-fiber membranes, the membrane consists of a long spaghetti like tube with a hollow core. The fibers are bundled together with the open ends encased in a resin. Flow can pass through the membrane either from the outside into the hollow membrane center or from the inside to the outside. Hollow fibers are typically used in microfiltration (MF) and ultrafiltration (UF) membrane processes.
Hydrophobicity: Hydrophobicity is the property of being water-repellent. In contrast, hydrophilicity is the property of having a strong affinity for water. The hydrophilic and hydrophobic properties of a membrane material are related to the surface tension of the material. The higher the surface tension value of the material, the more hydrophilic the material is. The degree of hydrophilicity or hydrophobicity influences the wettability and applied pressure requirements for water flow through the membrane. Hydrophilic membranes require less operating pressure than hydrophobic membranes.
Integrity breach: A breach refers to leakage in the membrane module due to a broken fiber, leaking seal or other leak that can allow microbes and particulates to bypass the membrane and pass directly into the finished water.
Indirect integrity monitoring: Indirect integrity monitoring consists of measuring some water quality parameter of the filtrate, e.g., turbidity or particle concentration, as an indicator of treatment effectiveness.
Life-cycle costs: Life-cycle costs include all the costs associated with an asset, i.e., cradle to grave costs including initial purchase/construction costs, operation and maintenance costs and final disposal/demolition costs.
Log removal value (LRV) or log reduction credit: The log removal value or log removal credit is the filtration removal efficiency for a target organism, particulate, or surrogate expressed as log10(feed concentration) – log10(filtrate concentration).
LT2ESWTR: The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) is an EPA regulation targeting control of Cryptosporidium and other microbial contaminants. It mandates treatment efficiency, i.e., log removal values, and gives credit to various treatment technologies to achieve the needed treatment efficiency.
Macromolecules: Macromolecules are typically large molecular weight organic molecules, e.g., polymers and humic materials. They occur naturally but many are also manmade with defined chemical and size properties.
Membrane fouling: Membrane fouling in microfiltration and ultrafiltration is the accumulation of particulates on the membrane surface or within the membrane that inhibits the flow of water through the membrane and leads to a higher transmembrane pressure or reduction in flux.
Membrane Warranty Criteria: Membrane Warranty Criteria should include requirements for material durability as well as performance requirements, such as guaranteeing a certain flux rate based on a specified number of cleans per year. Warranties can get complex and are difficult to enforce.
MGD: MGD stands for Million Gallons per Day and is a unit of flow measure.
Microfiltration (MF) membranes: Microfiltration membranes are typically hollow-fibers with a pore size range of approximately 0.1 – 0.2 μm (nominally 0.1 μm).
Nanofiltration (NF): Nanofiltration is a pressure driven membrane process that uses reverse osmosis to remove dissolved materials. Nanofiltration applications are typically for softening or organics removal.
NTU: NTU stands for nephelometric turbidity unit and is a measure of turbidity, i.e., the cloudiness of a water, and is a gross measure of the amount of suspended solids in a water.
Pathogens: Pathogens are disease causing microorganisms. Two of the most important pathogens driving interest in membrane systems are Giardia and Cryptosporidium.
Permeate: Permeate is synonymous with filtrate but is typically used with reverse osmosis and nanofiltration systems.
Pilot testing: Pilot testing is the use of treatment units significantly smaller than the full scale plant but which would mimic the treatment of the full scale plant in order to determine design and operational factors.
Post-treatment: Post treatment for microfiltration and ultrafiltration water treatment systems is essentially the same as for conventional treatment and typically consists of disinfection, fluoridation, and corrosion control.
Pressure system: A pressure membrane system applies a pressure to the feed water side of the membrane in order to force the water through the membrane.
Pretreatment: In membrane treatment systems, pretreatment encompasses all treatment processes prior to the membrane, e.g., strainers, flocculation, and sedimentation.
Residuals: Residuals refers to all waste streams from a treatment process. For membrane systems it could include the backwash wastewater, clean-in-place wastewaters, rinse waters, and concentrates.
Resistance: Resistance or membrane resistance is a measure of the difficulty of passing water through a membrane due to the nature of the membrane itself or to foulants accumulated on the membrane surface.
Reverse osmosis (RO): Reverse osmosis is the reverse of the natural osmosis process, i.e., the passage of a water through a semi-permeable membrane from a solution of higher concentration of dissolved solids to a solution of lower concentration. Reverse osmosis applies a high pressure on the higher concentration side of the membrane to drive water through the membrane against the concentration gradient, in order to produce a water with a lower concentration of dissolved solids.
Rinsing: Rinsing refers to the process performed at the end of a backwash or a clean-in-place in which clean water is passed through the membrane in order purge any non-potable water that could mix with the treated water.
SCADA: SCADA is an acronym of Supervisory Control and Data Acquistion. The term refers to computer systems including programmable logic controllers (PLCs) used to monitor and control water treatment processes and distribution systems including storing data and displaying the status of systems and historical trends.
Spiral-wound: Spiral wound membranes is a configuration in which sheets of a semi-permeable membrane, a porous support matrix, and a spacer are wrapped around a central filtrate collector tube. They are typically associated with nanofiltration (NF) and reverse osmosis (RO) membrane processes.
Supernatant: Supernatant is the relatively clearer water that forms at the top of a water in a clarifier or sedimentation tank.
Surfactant: Surfactants are essentially soaps or detergents that lower the surface tension of water to allow particulates to be more easily removed from surfaces.
TOC: TOC stands for total organic carbon in a water.
Transmembrane pressure (TMP): The transmembrane pressure is the difference in pressure between the feed water side and filtrate side of a membrane.
TSS: TSS stands for total suspended solids and is a measure of the amount of particulate material in a water. It is usually determined by measuring the mass of particulates captured in the laboratory on a membrane filter, e.g., a 0.45 μm membrane filter.
Turbidity: Turbidity is a measure of the cloudiness of a water as well as a gross measure of the amount of suspended solids in a water.
Ultrafiltration (UF) membranes: Ultrafiltration membranes are typically hollow-fibers with a pore size range of approximately 0.01 – 0.05 μm (nominally 0.01 μm).
UV-254: UV-254 is a test that measures the amount of ultraviolet light absorbance at a wavelength of 254 nm. It is a gross measure of the organic material in a water that can form disinfection-by-products.
Vacuum systems: Vacuum membrane systems are microfiltration or ultrafiltration systems in which the membranes are immersed in a tank of water and a vacuum applied to pull the water through the membrane.
Variable speed pumps: Variable speed pumps can adjust their rpm's in order to match the pumping rate with demands.
Viscosity: Viscosity is a measure of the internal resistance of fluids to flow, e.g., honey has a much higher viscosity than water. The viscosity of water will control how much pressure or head loss is needed to force it through a membrane. The viscosity of water will increase with decreasing temperature and thus winter operation will see higher transmembrane pressures to maintain the same flux.
µm: A µm stands for one micrometer (or micron) which is a unit of length equal to one millionth of a meter.
