(PART-1)
A Multipurpose Tool For Producing High Quality Water
By Mark E. Evans
In the natural world, objects frequently have more than one purpose. For example, a Damselfish comes to a sudden stop in the water with its pelvic fins flared downward which makes it easier for the fish to slow. A Goby comes to rest on the bottom and the shape of its pelvic fins enable it to cling to a rock more securely. The pelvic fins in both examples are homologous structures but they clearly perform separate functions. Similarly, in the equipment-filled world of the aquarium hobby, the reverse osmosis (RO) filter is a tool that is also capable of performing multiple functions. The intent of this article is to provide further clarification on several of them. A reverse osmosis filter is undoubtedly a useful piece of equipment to own, but before you purchase one you first need to decide what you need it to do.
Most aquarium hobbyists have seen ads for RO filters online, in magazines or in catalogs. But what did they take away from viewing such ads other than prices and promises of purer water and a healthier aquarium? The expense alone of buying an RO filter demands that you do your homework before purchasing one. The fact is that not all filters are equal and ads alone are just too little information to go on. You need to decide which RO filter is correct for your particular application. The general design of most RO filters is basically the same but the filter cartridges and membranes that come with the various models differ greatly and these are the items that make up the majority of the price of an RO unit. So, the replacement parts are an expense you should consider prior to your purchase of an RO unit because not all the filter cartridges that come pre-installed in an RO filter unit may suit your needs. And replacing them unnecessarily or prematurely is a costly lesson that can be easily avoided with a little planning.
RO Unit Components
Before we discuss choosing a unit, a brief discussion on the various components of an RO filter may be helpful. RO units usually consist of several individual filters placed in series. Each individual filter is referred to as a "stage". The placement of the individual filter cartridges on RO units may differ according to the manufacturer but the general path of the water through the filters remains the same.
The water begins its journey at the source, for example a pipe under you kitchen sink. It is then pre-filtered through one or two cartridges that remove substances that could damage the RO membrane (which is the most expensive element of the RO unit). The first is usually a sediment cartridge that removes particulate matter that could clog the membrane. The second is a chlorine pre-filter. The chlorine or chloramines used to disinfect municipal waters damage some types of RO membranes (particularly the TFC - thin film composite type), so it is necessary to remove such chemicals prior to the water reaching the surface of the membrane. (The carbon filter also removes heavy metals and many chemical pollutants). Once the water is pre-filtered it is ready to be pushed through the membrane itself. This is accomplished through back pressure, hence the name "reverse osmosis". The pressure is created by a small part called a flow restrictor, which is connected to the waste water line.
The most common configuration of stages (in order of water flow) is sediment, carbon, carbon, RO. The presence of two carbon filters demonstrates how important it is to remove chlorine and chloramine. Drinking water units often have a final carbon filter for polishing the water and many aquarium units have a de-ionization filter for the final stage. RO membranes alone are not capable of removing 100% of the impurities from the source water, so a de-ionization cartridge is placed at the end to filter out most of the remaining traces.
The least expensive models of RO units, sometimes called "bare bones" units usually consist of 2 stages: a carbon block filter to remove sediment and chlorine, etc., and the membrane itself. [Editor's note: Some companies sell "bare-bones" units without any pre-filter at all. These units are doomed to a short life span. Choosing units with at least a single prefilter will greatly extend the life of the membrane and is cheaper in the long run.>
RO Unit Function and Performance
The back pressure produced forces some of the water through the membrane and allows the rest to pass by into the waste water line. Depending on several variables, anywhere from about 1 to 6 gallons of waste water are produced for every 1 gallon of filtered water collected. The waste water serves two important purposes in an RO filter. It flushes away the substances extracted from the source water and it produces the very back pressure that allows the filter to operate.
The primary influences on the type of RO filter unit you will want to purchase will most likely be geography and geology, because where you live invariably determines what type of water comes out of your tap. For instance, cities that receive municipal water from the Mississippi River usually have very hard tap water. Cities in Southern California have the same problem. Water is the universal solvent, so rivers pick up all kinds of substances as they travel through geologically rich areas. For the home aquarist this can be a bane. This difficulty leads many aquarists to finally buy an RO filter.
(CONT. PART-2)
A Multipurpose Tool For Producing High Quality Water
By Mark E. Evans
In the natural world, objects frequently have more than one purpose. For example, a Damselfish comes to a sudden stop in the water with its pelvic fins flared downward which makes it easier for the fish to slow. A Goby comes to rest on the bottom and the shape of its pelvic fins enable it to cling to a rock more securely. The pelvic fins in both examples are homologous structures but they clearly perform separate functions. Similarly, in the equipment-filled world of the aquarium hobby, the reverse osmosis (RO) filter is a tool that is also capable of performing multiple functions. The intent of this article is to provide further clarification on several of them. A reverse osmosis filter is undoubtedly a useful piece of equipment to own, but before you purchase one you first need to decide what you need it to do.
Most aquarium hobbyists have seen ads for RO filters online, in magazines or in catalogs. But what did they take away from viewing such ads other than prices and promises of purer water and a healthier aquarium? The expense alone of buying an RO filter demands that you do your homework before purchasing one. The fact is that not all filters are equal and ads alone are just too little information to go on. You need to decide which RO filter is correct for your particular application. The general design of most RO filters is basically the same but the filter cartridges and membranes that come with the various models differ greatly and these are the items that make up the majority of the price of an RO unit. So, the replacement parts are an expense you should consider prior to your purchase of an RO unit because not all the filter cartridges that come pre-installed in an RO filter unit may suit your needs. And replacing them unnecessarily or prematurely is a costly lesson that can be easily avoided with a little planning.
RO Unit Components
Before we discuss choosing a unit, a brief discussion on the various components of an RO filter may be helpful. RO units usually consist of several individual filters placed in series. Each individual filter is referred to as a "stage". The placement of the individual filter cartridges on RO units may differ according to the manufacturer but the general path of the water through the filters remains the same.
The water begins its journey at the source, for example a pipe under you kitchen sink. It is then pre-filtered through one or two cartridges that remove substances that could damage the RO membrane (which is the most expensive element of the RO unit). The first is usually a sediment cartridge that removes particulate matter that could clog the membrane. The second is a chlorine pre-filter. The chlorine or chloramines used to disinfect municipal waters damage some types of RO membranes (particularly the TFC - thin film composite type), so it is necessary to remove such chemicals prior to the water reaching the surface of the membrane. (The carbon filter also removes heavy metals and many chemical pollutants). Once the water is pre-filtered it is ready to be pushed through the membrane itself. This is accomplished through back pressure, hence the name "reverse osmosis". The pressure is created by a small part called a flow restrictor, which is connected to the waste water line.
The most common configuration of stages (in order of water flow) is sediment, carbon, carbon, RO. The presence of two carbon filters demonstrates how important it is to remove chlorine and chloramine. Drinking water units often have a final carbon filter for polishing the water and many aquarium units have a de-ionization filter for the final stage. RO membranes alone are not capable of removing 100% of the impurities from the source water, so a de-ionization cartridge is placed at the end to filter out most of the remaining traces.
The least expensive models of RO units, sometimes called "bare bones" units usually consist of 2 stages: a carbon block filter to remove sediment and chlorine, etc., and the membrane itself. [Editor's note: Some companies sell "bare-bones" units without any pre-filter at all. These units are doomed to a short life span. Choosing units with at least a single prefilter will greatly extend the life of the membrane and is cheaper in the long run.>
RO Unit Function and Performance
The back pressure produced forces some of the water through the membrane and allows the rest to pass by into the waste water line. Depending on several variables, anywhere from about 1 to 6 gallons of waste water are produced for every 1 gallon of filtered water collected. The waste water serves two important purposes in an RO filter. It flushes away the substances extracted from the source water and it produces the very back pressure that allows the filter to operate.
The primary influences on the type of RO filter unit you will want to purchase will most likely be geography and geology, because where you live invariably determines what type of water comes out of your tap. For instance, cities that receive municipal water from the Mississippi River usually have very hard tap water. Cities in Southern California have the same problem. Water is the universal solvent, so rivers pick up all kinds of substances as they travel through geologically rich areas. For the home aquarist this can be a bane. This difficulty leads many aquarists to finally buy an RO filter.
(CONT. PART-2)