On the roof of the John Deere tractor factory in Mannheim, Germany, there is an ingenious plant-based wastewater treatment system – or constructed wetland – that produces clean water. Lilies, reeds and rushes purify wastewater from the factory’s production processes before returning it to the public water system. As part of his MBA studies at Steinbeis University Berlin, Hartmut Bauer developed this eco-friendly system while looking for a cost-effective solution for wastewater disposal.
Conventional constructed wetlands usually require a relatively large area, which in this case was not available due to the location of the John Deere plant in central Mannheim. This inspired Hartmut Bauer to design a treatment system which would fit on a flat roof. To avoid the need for structural changes to the roof, the new wetland was not allowed to exceed its maximum load. This meant that it had to be able to purify industrial water without using a conventional soil layer. Instead, the wetland uses special phytolytic plants which grow in the wastewater.
Each day at John Deere, up to ten cubic meters of wastewater are flushed into the rooftop constructed wetland via a heated pipe. “The water to be treated contains a high proportion of phosphates and mineral oil hydrocarbons. Micro-organisms like algae, fungi and bacteria, which mostly live at the plants’ roots, play a major role in removing contaminants,” explains Hartmut Bauer. These micro-organisms absorb and metabolize substances in the wastewater. In particular, the ability of the common water plantain (a marsh plant) to remove contaminants exceeded all expectations. There are minor fluctuations in contaminant removal rates depending on the type of plant, the season and the time of day. Wastewater purification involves several stages: an initial purification tank, a mixing zone for industrial wastewater and sanitary sewage, a storage tank, the main purification tank, and finally a drainage area.
The results of Bauer’s project are impressive across the board. Not only is this unique wastewater treatment system environmentally friendly, it’s also economical – costing up to 60% less than conventional chemical wastewater treatment. What’s more, capital investment is relatively low and the system is economical to operate and low on maintenance. Also, buildings with constructed wetlands on their roofs need less air conditioning. However, the system does require a relatively large area.
The constructed wetland is environmentally friendly in a variety of ways. Up to 30% of wastewater evaporates during treatment; fine particulates are filtered out of the air; CO2 is converted to oxygen; and treated water can be reused. Starting in 2012, the purified wastewater will be used at John Deere for toilet flushing, pre-treatment of industrial materials, and watering gardens. The goal for 2015: a wastewater free factory.