Abs: Chitosan acetate has been used in water treatment for more than three decades. Chitosan-based water treatment has been used extensively in various industrial and municipal applications and commercial aquarium clarification. Chitosan also removes oil and grease from water via its ability to form insoluble emulsions that may be separated from water gravimetrically or by filtration. Chitosan is also known to chelate (form electrostatic bonds with) some heavy metals including copper, zinc, arsenic and several other regulated toxic heavy metals.
Introduction:
Chitosan is part of a class of large (macro) molecules called polymers; which are composed of repeating structural units linked end to end. Although the word “polymer” in popular usage may be suggestive of plastics, the term actually refers to a class of both natural and synthetic materials with a variety of properties. Since chitosan is derived from a naturally occurring polymer, it is known as a biopolymer. The repeating (or monomeric) unit of chitosan is glucosamine. Glucosamine is a familiar dietary supplement used primarily to enhance mobility of the joints (usually knees and elbows), because it plays a role in cartilage repair and maintenance. Glucosamine is a sugar (or saccharide) and therefore chitosan is in a specific group called polysaccharides within the biopolymer family.
The parent biopolymer of chitosan is the second most abundant polymer on earth, next to cellulose, and is known as chitin. Chitin was first discovered around 1811 by Braconnot, who pioneered much of the early work done on cellulose derivatives. Chitosan is a naturally occurring product of the chitin degradation process. Chitin is quite ubiquitous, and is found in sources such as: the cell walls of fungi, insect exoskeletons, and certain shellfish. ChitoVan™ chitosan products are made from recycled shrimp and crab shells.
Chitosan as a polysaccharide is unique because the glucosamine monomer contains what is known as an amino (nitrogen) group. Liquid ChitoVan acetate is a solution of chitosan and dilute acetic acid (vinegar). The acid causes the amino group to become positively charged, or cationic, thus allowing chitosan to become water soluble. It is the cationic nature of dissolved chitosan that gives it the ability to flocculate small sediment particles. Since sediment particles are usually negatively charged, or anionic, the opposite charges attract each other. ChitoVan chitosan is a very large molecule, and it binds with many small sediment particles to form an agglomerate of particles that are large enough to fall out of solution (or flocculate).
Chitosan acetate has been used in water treatment for more than three decades. Chitosan-based water treatment has been used extensively in various industrial and municipal applications and commercial aquarium clarification. Chitosan also removes oil and grease from water via its ability to form insoluble emulsions that may be separated from water gravimetrically or by filtration. Chitosan is also known to chelate (form electrostatic bonds with) some heavy metals including copper, zinc, arsenic and several other regulated toxic heavy metals. In addition to the broad applications in water treatment, chitosan has also been used in some of the following areas: hemostasis, agriculture, textiles, dietary supplements and drug delivery.
Passive Treatment
This is by far the most cost effective method for the treatment of turbid stormwater. True passive treatment requires no external energy and very little equipment. It is generally the easiest system to install and maintain. The necessary treatment elements are already available on many construction sites. These include: moving water, a settling basin and vegetative filtration. For these sites one only needs to install the chitosan lactate cartridge in the appropriate location and monitor its performance.
With a little planning this method is capable of consistently reducing the turbidity by greater than 90%.
It is best suited for sites that have concentrated flow, adequately sized settling ponds and a natural vegetated area for filtration.
Semi-Passive Treatment
Semi-passive treatment is usually grouped together with purely passive treatment, but technically the difference is that semi-passive treatment utilizes some external energy to move water. Similar to passive treatment, semi-passive treatment is very inexpensive, and easy to install and maintain. Semi-passive treatment is accomplished with a pump, interconnecting plumbing, chitosan lactate cartridge, cartridge applicator, settling basin and filtration.
The chitosan lactate cartridge is typically installed in a lay-flat hose, y-pipe or bag filter housing for easy access and containment.
Compared with purely passive treatment, this method is suited for a wider range of projects because it can be accomplished with a smaller footprint and allows more versatility.
With a little planning and correct installation this method is capable of consistently reducing the turbidity by greater than 95%.
Active Treatment
This is a more aggressive treatment approach which also utilizes chitosan (typically in the liquid chitosan acetate form) to flocculate suspended solids. The floc is separated from water by gravity settling and pressurized sand filtration. It is highly effective at removing suspended solids from turbid stormwater and typically achieves a turbidity reduction of greater than 99 percent.
In comparison with passive treatment, this technique requires significantly more equipment. The key equipment required for CESF treatment includes:
- Stormwater retention structure(s)
- Interconnecting plumbing
- Fittings
- Pumps
- Control/containment unit
- Chitosan delivery system
- Monitoring equipment
- Sand filter
- Power source
Often times chitosan lactate is used in conjunction with active treatment as a pretreatment step instead of liquid chitosan acetate. The advantage of using a dry chitosan lactate flake is that it is easier to transport, frees up chemical storage space, has a longer shelf life and does not require expensive metering pumps.