Using plants to treat wastewater

Posted on 22 April 2014.

The new generation of greenhouses

Take a plant, any plant, local or exotic, as long as it has a highly-developed root system. Add some micro-organisms – bacteria, worms, or even mussels, snails and small crabs – and you’ve got everything you need to partially treat wastewater.

The natural era

“This new system is used in several regions of the world”

For the last 15 years or so, this new approach, which is based on an artificial ecosystem, has started to catch on in Hungary, Austria, Poland, China, and even France, where it’s being used in the northwestern town of Le Lude.
Each treatment plant uses the same system: a buffer tank and two greenhouses – one for treating the water and the other for drying the sludge. After the wastewater is screened and the sand is removed, it passes through the buffer tank and enters the greenhouses, where it goes through the different stages of treatment: degassing, phosphorus removal, denitrification, and carbon pollution removal. Although this process takes several days, it requires very little equipment, and a lot of input from “nature,” because the plants and micro-organisms feed on the effluents, removing them in the process. That’s what makes this system so clever: the roots give bacteria a larger surface area – three times bigger, in fact – to hold on to, making it easier to take in nutrients. And they recycle the sludge by mineralizing it! After decantation, the clean water, which is harmless to nature, is drained away for reuse, and solar energy is used to dry the sludge for use on farms.

Diagram of the wastewater treatment system
Diagram of the wastewater treatment system

1/ Wastewater
2/ Pre-treatment: fine screening, desanding, detention basin
3/ ANOXIC/ANAEROBIC reactor: removal of organic pollution and nitrification
4/ AEROBIC reactor: removal of organic pollution and nitrification
5/ EFFLUENT: The treated water complies with the strictest of environmental regulations.
6/ Degassing tank

This water treatment plant is also twice as compact as a traditional plant, as well as more stable and cost-efficient. And it enhances its surroundings, as the rise in the number of visitors to Le Lude shows. So the next time you see two horticultural greenhouses side by side, you might actually be looking at a water treatment plant.