Opportunities For Biodegradable Watersoluble Polymers

Opportunities are the drivers for research into environmentally biodegradable polymers and for the development of laboratory testing protocols. It is opportunities that indicate the property and disposal requirements for the polymer. Disposal methods and locations identify the testing protocols that must be established for polymers in order to evaluate their environmental degradation under laboratory-simulated environmental exposure conditions. As already mentioned, the drivers for environmentally biodegradable polymers are waste management programs to avoid environmental contamination from the use for nondegradable polymers. Figure 12.2 indicates likely disposal pathways for water-soluble polymers.

Water-soluble polymers, after use, are usually in very dilute aqueous solutions and are preferably disposed of through wastewater treatment facilities or sometimes directly into the aquatic environment, as shown schematically. On entering a wastewater treatment plant, a polymer may pass straight through, remaining soluble, into streams, rivers, lakes, and other aquatic environments, or it may be adsorbed onto the suspended solids in the treatment plant. If it

Water-soluble polymers

Water-soluble polymers

Water treatment facility

Aquatic environment

Adsorption

Compo

- Landfill

Water treatment facility

Adsorption

Compo

- Landfill

Environmental fate and effects

Figure 12.2. Environmental disposal options for water-soluble polymers.

Environmental fate and effects

Figure 12.2. Environmental disposal options for water-soluble polymers.

passes straight through, it is no different from direct disposal into those aqueous environments, and both raise similar questions as to the fate and effects of the polymers involved. On the other hand, adsorption of a polymer onto sewage sludge results in the possibility of the polymer being land filled, incinerated, composted, or land applied as fertilizer or for soil amendment, depending on the local options available. However, here again, environmental fate and effects need to be addressed, it must be established how and where these polymers move in their new environmental compartments and where incineration products are ultimately deposited. Clearly, for water-soluble polymers there is a preference for complete biodegradation in wastewater treatment facilities. Polymers should be designed to be completely biodegradable and removed in the immediate disposal compartment, generally the sewage treatment facility. If biodegradation is not complete in the disposal environment, it must be assessed, often with difficulty, in subsequent compartments. Once the biodegradation of a polymer has been confirmed in any environmental compartment, no uncertainty remains as to its fate and effects. The advantage of complete biodegradation is that it is a positive result that can be established, whereas the assessment of environmental fate and effects are risk assessments and are negative results, based on limited studies with a few aquatic species. These results may not be representative of all the species that a water-soluble polymer, or its partial degradation fragments, may contact as it moves through many aqueous environment compartments.

A major difference in the waste management of water-soluble polymers and plastics using biodegradable substitutes is that there is a well-established widely available disposal infrastructure of wastewater treatment plants for the former, whereas plastics being developed for composting will require the large-scale implementation of a composting infrastructure; and this will slow their acceptance.

Hence, given the need for biodegradable water-soluble polymers to protect the environment and the ready availability of a disposal infrastructure in almost every country in the world, the opportunity is obvious and waiting a solution.

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