Marine environments anaerobic biodegradation

It has become clear over the past ten years that the 1980s demonstration of anaerobic microbial dechlorination of PCBs is probably the most important discovery in the field of PCB biotransformations since Ahmed and Focht first demonstrated in 1973 that PCBs were biodegradable. Many new anaerobic microbial activities have been enriched and characterized from anaerobic fresh water and marine environments and heavily polluted industrial sediments. These anaerobic cultures are capable ofdechlorinating PCBs, thereby transforming highly chlorinated Aroclors to lower-chlorinated mixtures. This natural attenuation process is an important contributor to PCB degradation and detoxification in the environment and can form the basis for intrinsic remediation of many PCB-contaminated sites. 

Biodegradability - Metabolix PHA offer hydrolytic stability under normal service conditions but when exposed to microbial organisms naturally present they break down enzymatically in soil, composting, waste treatment processes, river water and marine environments. They also rapidly decompose to carbon dioxide and water and will degrade in anaerobic environments, unlike some other biodegradable polymers. 

The bacterially produced poly(lydroxyalkanoates) (PHAs) are fully biodegradable in both anaerobic and aerobic conditions, and also at a slower rate in marine environments. 

This chapter describes the worldwide biodegradation standards for biodegradable plastics, including starch-based plastics, in common disposal environments, including compost, marine, anaerobic digestion, soil, and landfill. Compost environments include aerobic conditions within hot industrial compost environments. Marine environments include cold aerobic conditions. Landfill disposal environments include aerobic and anaerobic conditions. Anaerobic-digestion environments include hot anaerobic conditions. 

Biodegradation standards are provided in the following sections. The standards are organized based on disposal environment. Thus, the biodegradation standards from different worldwide standards organizations are presented in an industrial compost section, marine environment section, an anaerobic-digestion section, landfill section, and home compost section. 

Summary This American specification establishes the performance requirements for biodegradation of plastic materials and products, including packaging, films, and coatings. The marine environment includes conditions of aerobic marine waters or anaerobic marine sediments, or both. This specification establishes the requirements for biodegradation of plastic materials that have rates that are similar to known compostable materials. The specification also specifies that the degradation of the plastic materials will not cause any harm to sea life or habitat. 

Discussing the biodegradation of plastics in a liquid environment usually means natural degradation in freshwater (lakes, rivers), in a marine environment, or in aerobic and anaerobic sludges (wastewater treatment). However, many degradation... 

ASTM D7081 covers biodegradation of plastic materials (including packaging materials and coatings) in marine environments (aerobic sea water and/or anaerobic marine sediments. The standard allows for shallow and deep saltwater as well as brackwater as possible environments. Currently, there is no comparable ISO standard. 

The D20.96 Committee of the American Society of Testing and Materials (ASTM) worked intensively on test methods for water-insoluble polymers and plastic materials [38,39]. Since 1993, five standards for biodegradation of plastic materials in various conditions have been published (Table 2), and other test methods with different environments are nearing completion [39], i.e., anaerobic high-solid digestor and anaerobic accelerated landfill to simulate the fate of a material during solid waste management. Other experimental methods need to be developed for freshwater and simulated marine conditions. 

Chitin that occurs in the exoskeleton of invertebrates (such as mollusks and arthropods) is composed of N-acetyl-D-glucosamine residues linked by 1,4 /3-Iinkages. A partially deacetylated chitin also occurs naturally as chit-osan. Microbial species responsible for the breakdown of chitin and chitosan have not been comprehensively studied. Micro-organisms found in a variety of environments (for instance, in fresh water [29], marine sediment [30], garden soil [31], and even anaerobic environments [32]) are known to produce chitinases and/or chitosanases. Table 56.1 shows a listing of some reported species of bacteria and fungi that yield these enzymes and are therefore, able to biodegrade these polysaccharides. 

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