In freshwater, plants growing partially submerged, such as water hyacinth and cattail, have been identified as promising feedstock for energy applications. Water hyacinth, which is native to South America, is a free-floating herb which forms dense mats on the surface of the water. Introduced intentionally or by accident in most tropical and subtropical parts of the world, it has become a floating nightmare for the affected countries. In Africa it infests every major river and almost every lake. In the United States, it flourishes in countless bodies of water throughout the South, from California to Virginia (Fig. 12.9). Dense and rapidly expanding growth of water hyacinth can clog canals and water intakes, restrict navigation along rivers and lakes, and exclude native vegetation. In some areas it must be continually cleared from vital waterways. It has a very high annual productivity of 30-80 tonnes dry biomass per hectare.
Cattail (Fig. 12.10), which thrives in marshland and lakes throughout the planet, is also viewed as a good candidate for energy production, because it can
yield annually up to 40 tonnes of biomass per hectare. Once collected, the water hyacinth, cattail or any other suitable water plant could be processed by anaerobic conversion to form methane and subsequently methanol.
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Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.