NU12 – Week 11 - REPLACEMENT - DUENAS

Edwin T. Dueñas                                                                                              NU12 – Week 11 - REPLACEMENT

NU12 Idea:  Water lettuce as a Heavy metal (Toxic) Remover

The major river systems in the Metro Manila and Bulacan are the Marilao-Meycauayan river system, Pasig-Marikina River, the Malabon-Tullahan River and the Paranaque-Zapote Rivers which flow into Manila Bay and Laguna Lake. The rivers are so highly polluted from the discharge of domestic and industrial wastewater that they can be termed as being biologically dead except for the upstream portion of the Marikina River.

As an example, the river systems of Marilao and Meycauayan City in Bulacan have been rated by an international environmental group as among the dirtiest places on earth. The New York-based Blacksmith Institute has included the two places on its "Dirty Thirty" list of the World's Worst Polluted Places for 2007. The study was based on the group's monitoring of pollution levels in different parts of the globe, Marilao and Meycauayan are the only South East Asian areas on Blacksmith's list.

The group noted that in Meycauayan, Marilao there were presence of heavy metals, chemicals, and other forms of waste in the river system. The river system is extremely polluted due to waste received from tanneries, gold and precious metals refineries, the largest lead smelter in the Philippines, and numerous municipal dumpsites. It added that substantial contamination also results from small-scale lead recycling facilities along the river at Marilao and from the many tanneries that dump untreated hexa­valent chromium wastewater into the river. Despite being the source of food, drinking and irrigation water for some 250,000 residents, the river system is contaminated with haphazardly dumped industrial waste.

Therefore due to the increased number of pollutants like heavy metals, these major river systems in Metro Manila and Bulacan are greatly in need of a wastewater treatment. If not treated, this can lead to harm to the aquatic life and can pose health problems and even death to humans. There are many methods but most of them are costly. The wastewater treatment must be effective and must have a low cost considering that the Philippines is a third world country and has a tight budget on environmental issues.  

                Water lettuce is very rampant in bodies of water in the Philippines and considers having metal hyper-accumulating properties. Water lettuce were undertaken for this project since they are potentially hyper-accumulators of metals as they have extensive roots and provide large surface area for the biofilms formation and thus enhance the microbial activities. This can reduce the levels of heavy metals in polluted waters.

Heavy metals are very dangerous and are considered to be carcinogens. An example of this is Hexavalent Chromium, Cr(VI). It is one of the most commonly occurring toxic pollutants present in wastewaters discharged from electroplating, dye and pigment manufacturing, wood preserving and leather tanning industries. In addition to being highly toxic Cr (VI) is mobile, and has a long residence time in surface water and groundwater; it poses health risk to humans and animals and impairs the development and growth of plants.

The process involves rising of plants hydroponically and transplanting them into metal-polluted waters where plants absorb and concentrate the metals in their roots and shoots. As they become saturated with the metal contaminants, roots or whole plants are harvested for disposal in landfills. The heavy metals accumulated by the plants are then naturally converted to a non toxic metal and can be disposed in landfills. Water Lettuce can also be included in a waste water treatment facility allowing the water to pass by a tank full of water lettuce. In this way, it can decrease the levels of heavy metals in the effluent.  Water lilies does this well.  4