The water hyacinth has been clogging waterways and causing havoc and destruction of ecosystems since the 1900s. But researchers are discovering that it can play a role in reducing carbon emissions – as well as providing raw materials for production. By Henrylito D. Tacio  

Manila, Philippines, 29 July 2019. Reports of flooding across the world are increasing, and as often as not, people will be blaming the disappearance of forest cover. But in many places, one plant is making flooding even worse: the water hyacinth. This “invasive alien plant species” was brought to the US and Australia in the 1890s as an ornamental plant, from the Amazon basin in South America. Today it is one of the world’s most serious and out of control weeds.

In tropical regions in Asia, Africa and America it threatens to choke waterways making them inaccessible to commerce. It is a serious problem in the coastal rivers of Queensland and northern New South Wales. It has also proved that it can adapt to temperate inland lagoons and rivers in New South Wales, Western Australia and along the River Murray in South Australia. Rafts of the weed interfere with irrigation and fishing, and led directly to massive and catastrophic flooding in Cotabato City, Philippines in 2011. Nearby provinces experienced their worst flooding in years as the plant infested swathes of rivers, dams, lakes and irrigation channels. It spreads like a pest on every continent except Antarctica, and costs billions of dollars every year in control costs and economic losses.

Officials blame many floods on the water hyacinth but also took some of the blame, as others cited negligence of officials that allowed the aquatic weed to grow uncontrollably. According to one report, the Cotabato flood started when about eight hectares of water hyacinth were dislodged from Liguasan Marsh – an extensive 288,000-hectare swamp region in Central Mindanao – following weeks of heavy rain.

The plants, about 3m in length with their dangling roots and soil in tow, jammed in tens of thousands into the normally open river beds. They blocked bridges and spillways along the 5m-deep river, and caused a huge flood, displacing an estimated 36,000 people that lost their homes and generated a rescue bill of some US$3.5million. That’s a very expensive weed.

But Eichornia crassipes, or the water lily as many call it can also be an agricultural blessing. It yields more than 200 tonnes of biomass per hectare per year under normal conditions, studies have shown. And on water containing high concentrations of sewage, the floating plant yields an astonishing 650-plus tonnes of biomass per hectare.  For example, in Dianchi Lake in Kunming City, the provincial capital of China’s Yunnan Province, water hyacinth has become a rapid water cleaning agent – thanks to the lake’s polluted water. “The plant grows particularly fast in polluted water,” says Dr. Zanwin Wang, associate professor at the School of Development Studies in Yunnan University.

This means there is a better way to effectively control water hyacinth in a practical manner. It can be done through biogas, to produce power. That is what Dr. Wang is doing; he wants to find out whether biogas is cost-effective to control the noxious weed, help clean up water pollution, and generate a source of renewable energy.     

“Compared with the current water hyacinth control method, the use of water hyacinth to produce biogas has two major advantages,” said Dr. Wang. “For one, the biomass of water hyacinth is used rather than disposed of as a waste. For another, the emission of landfill gas is avoided.”    

Due to this double-whammy environmental and economic approach in controlling the expansion of water hyacinth, the use of water hyacinth in biogas production “can be a potential option to respond to policies on water pollution control, renewable energy development, and carbon emission reduction,” all in one go, Wang’s study pointed out.

And there are other uses of water hyacinth that could be explored. In some parts of the world, research has been done to make water hyacinth into a profitable crop instead of a pest. In Bangladesh, researchers have been experimenting with paper production from water hyacinth and also to make rope. The fibre from the stems of the plant can be used to make rope if the stalk from the plant is shredded lengthways to expose the fibres and left to dry for several days. The finished rope is then treated with chemicals to prevent it from rotting.     

In some areas of the Philippines, water hyacinth is dried and used to make baskets and matting for domestic use. If the stalks still contain moisture this can cause the product to rot quite quickly, however, thoroughly dried stems are perfect for weaving.

But there is still a problem with clearing the plant. As it can reproduce so rapidly – estimates show that in ideal conditions the plant can grow almost 700,000 plants from around ten sprouts within a mere eight months. This not only covers any water bodies with a sea of weed, but also threatens the survival of many aquatic flora and fauna as they block sunlight’s penetration into the lower water levels. And it’s hard to get rid of that too, as well as being so prolific. In the 1990s, the world reportedly spent US$3billion a year just to control the aquatic weed, for the most part with little or no success.

To help decrease the plague of water hyacinths that clog the waterways in the country, the Philippines Department of Science and Technology (DOST) developed a machine that scoops up the plants out from the waters. Called the Water Hyacinth Harvester, it can collect and hold up to 25 kilograms of water hyacinth per load. When full, the harvester discharges the collected plants to a dumping site or an assisting barge.     

The harvester mechanically removes water hyacinths using a specially-developed conveyor system. “Mechanically removing the plant is the better alternative because chemical methods are hazardous to plants and animals,” say DOST engineers, who have also develop special machines to dry and compact the plant biomass into burnable briquettes which are up there with wood when it comes to thermal efficiency.

So the plant that has been labelled one of the worst aquatic pests globally might just have a role as a cleaning agent for highly polluted water masses, as well as an incredibly rapid growing, totally carbon neutral fuel for producing both gas, heat, and possibly power generation too.

“The water hyacinth is in fact far more productive than many of the crops that have been carefully cultivated by man under near-ideal conditions of fertilisation, irrigation, and pest control,” wrote one local researcher.

And with a list of pluses like E. crassipes can offer, maybe it’s time to reconsider the role of the humble water lily. Worldwide plague? Yes, but possibly a productive plant too.