The King's initiatives using water hyacinth to remove heavy metals and plant nutrients from wastewater through Bueng Makkasan in Bangkok, Thailand

H.M. the King of Thailand proposed Bueng Makkasan, the repair factory belonging to the Royal Railway of Thailand (RTT), as a wastewater-collection pond of Bangkok City. It covers about 40 acres, with 5-m depth. The RRT wastewater pond functions at a repair factory and is the collection site of the direct-polluted waste of homeless people living around the pond rim and also for temporary reservoir of two influent canals. The water hyacinth aquatic plants were grown well and covered almost the entire surface area of the pond.An experimental design was laid by making a floating bamboo frame 5 m × 10 m in size and spreading systematical distribution through all parts of the pond with the coverage area 30 percent of pond surface. Data collection and analysis were conducted on plant nutrients, heavy metals and toxic chemicals in wastewater (influent, storage, and effluent) sediment, leaves and roots of water hyacinth (in fresh and compost). Also, the water hyacinth growth rate in various periods of time in relation to chemical concentration in wastewater were determined from the beginning through harvesting time.The results found that water hyacinth would be the high-absorbing plants to extract the heavy metals (such as Mn, Cd, Fe, Zn, Cu, and Pb) and plant nutrients (such as N, P, K, Ca, Mg). The floating aquatic vegetables contaminated via high concentration of heavy metals were not eaten under the regulations of Ministry of Public Health. Consequently, the compost that was made by water hyacinth showed a high concentration of heavy metals. An application of such compost would only be for flowering-plants growth, with no possibility of application to edible vegetables.The study also indicated that water hyacinth on the wastewater treatment pond would be maximized at 20 percent cover. Sunshine-open space needed the intensity of visible light for phytoplankton and other algae species to support the photosynthesis in order to produce enough oxygen for the power-digesting aerobes to degrade the organic waste in wastewaters.