Water hyacinths, considered to be one of the world’s most destructive weed can be harnessed for environmental benefit and renewable energy production, according to a latest study by the Economy and Environment Program for Southeast Asia (EEPSEA).
Increasing temperatures due to climate change have created favorable growing conditions for water hyacinths across China. It also grows fast in polluted water clogging rivers, lakes, blocking water transport and hampering fisheries and endangering the livelihood of millions of people. A mat of medium-sized plants may contain two million plants per hectare that weigh 270 to 400 tonnes while the biomass of water hyacinth can double every five days.
However, according to an EEPSEA study conducted by Zanxin Wang and Jin Wan from the School of Development Studies at Yunnan University in China, this weed can be used for the production of biogas. The researchers undertook a cost-benefit analysis of a proposed biogas plant that would be fuelled by water hyacinth from Dianchi Lake in Yunnan Province.
“ Due to the rapid development of the region’s economy, the lake has been severely polluted for several decades. It is currently one of the most severely polluted lakes in China and on e of the three lakes given national priority treatment,” the researchers noted.
In the Dinachi watershed, the annual average growth of water hyacinth is around 250,000 tonnes in fresh weigh, the study added. Over the past five years, a total of 820,000 tonnes of water hyacinth has been removed and disposed of as landfill. At present, there are eight working units designated by the Kunming municipal government to water hyacinth removal and disposal.
The proposed biogas project costing about 13.52 million Yuan, would have an annual output of biogas of around 245,438 litres, with an estimated value of 602, 941 Yuan. It would also produce organic fertilizer with an estimated value of 210,000 Yuan a year, as well as solar thermal water system. The biogas plant would consume a total of 11,004.2 tonnes of water hyacinth every year.
Biogas contains methane, carbon dioxide, sulphur and dust and can be processed to be used as electricity and as cooking gas.
The study said, the production of biogas from water hyacinth would be a potential Clean Development Mechanism (CDM) project that could result in a reduction of 3,922 tonnes of carbon dioxide a year.
“ Despite these benefits, the plant would still cost more to run than it would generate in direct returns to its operators. However, if the wider benefits to society are taken into account, then the biogas plant would make good economic sense. The local government would also spend less money on the control of water hyacinth if they were to implement the proposed project,” the EEPSEA study pointed out.
Without the biogas gas project and water hyacinth continues to be removed at the current average rate of 164,000 tonnes a year, the cost to society would be 21.16 million Yuan over 15 years.
The study recommends that the proposed biogas project is a better alternative to the current approach as methane emissions could be avoided and that the biomass of water hyacinth is used rather than being simply disposed of as waste.
“ Biogas could provide a way for local governments to respond to China’s national policies on water pollution control, renewable energy development, energy saving, and emission reductions. It needs institutional arrangements for coordination, finance and drive the development of a network of such biogas plants,” the researchers stressed.
See the full research report here:
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