Environmental Engineering Reference
In-Depth Information
in humans subjects [1, 9-14]. In agriculture, CR biodegradable polymers and waxes
are used for insecticide, fungicide and pesticide applications [3, 4, 6, 7]. Despite
extensive medical and agricultural research for controlled release systems using
environmentally benign and biodegradable polymers, few studies have investigated
implementing these methods for environmental engineering applications. Several
researchers have developed controlled release systems for soil and water remedi-
ation using clay, waxes, gels, and waxy polymers. Examples include slow release
oxygen polymers for bioremediation, phosphate buffer encapsulation for polymers
for pH control during denitrification of groundwater and sediment, alginate gel for
Fenton photochemical oxidation, and encapsulation of bacterial cells [15-19].
Exploring the ability to use biodegradable polymers featuring controlled release
capabilities for environmental remediation and treatment is an emerging concept.
Like medical and agricultural systems, many environmental engineering treatments
rely on mass transfer and delivery of chemicals. Fundamental research of CR
applications for environmental protection, decontamination, and remediation there-
fore merits investigation. CR technologies can extend treatment methods for soil
and water remediation. The existing body of literature for biodegradable polymers
focuses on seeking affordable replacements for non-degradable, synthetic plastics
and methods to increase physical properties such as tensile strength for the pack-
aging industry [2,20,21]. For environmental engineering applications, however, the
benefit of using polymers which naturally degrade to deliver treatment chemicals
provides a method for in-situ remediation that would not need to be removed after
treatment is completed.
Using the advantageous characteristics of biodegradable polymers and controlled
release capabilities to improve mass transfer, delivery, and longevity of chemical
and biological treatments in environmental remediation is an intriguing approach.
A variety of biodegradable polymers serve as potential candidates for developing
controlled release structures. The broad classifications for non-toxic, biodegrad-
able polymer groups include poly(esters), poly(orthoesters), poly(anhydrides),
poly(amides), and poly(saccharides) [2, 12, 14, 22]. Biodegradable polymers can
be classified based on the mechanism for polymer breakdown. These mechanisms
include: water-soluble polymers made from hydrolytically unstable cross links
(type 1); linear polymers which are solubilized by hydrolysis ionization or proto-
nation but without backbone cleavage (type 2); or water insoluble polymers which
breakdown into smaller soluble products by backbone cleavage (type 3) [23].
Based on the environmental media, the type of contaminants present in the
target treatment system, and physical conditions, biodegradable polymers can be
selected or designed with specific physicochemical properties. Criteria for polymer
selection include compatibility with the selected delivery chemical and the abil-
ity for the polymer to erode or dissolve at a slower rate than the target delivery
chemical. Therefore, multiple combinations of biodegradable polymers and types
of chemicals are possible for controlled release design. Table 2.1 provides exam-
ples of five groups of non-toxic, biodegradable polymers that represent candidates
for controlled release development for environmental remediation. These general
polymer groups offer different physical and chemical attributes that can be used
to construct CR structures with polymer erosion, diffusion controlled chemical
