Tomatoes have long since ceased to be a seasonal vegetable. They can be eaten all year round thanks to cultivation in plastic tents or greenhouses. Cultivated on an industrial scale, they grow in gutters filled with coconut fibre and an aqueous solution of all nutrients to ensure rapid growth, good taste and good appearance, and there's nothing wrong with that, just one problem ....
Plants must have a constant supply of nutrient solution. This, however, becomes waste after the growing cycle ends. One hectare of tomato cultivation in a greenhouse produces 14-15 thousand m3 of sewage. What can be done with it?
It would seem that there is nothing easier than to use it for watering tomatoes.
“But this cannot be done," explains Dr Artur Mielcarek, of the Department of Environmental Engineering at the Faculty of Environmental Sciences of the University of Warmia and Mazury. Why? “Because it’s no longer a nutrient solution. Plants have taken up the substances they need for life from it, so the composition is different. Besides, there’s a great risk that this waste nutrient solution may be infected with some kind of disease. It can infect the entire tomato plantation and destroy it. In addition, it can’t be poured out into fields, meadows or pastures, as it is forbidden by environmental regulations. So gardeners must dispose of it, and this generates costs”, explains Dr Mielcarek.
However, scientists in Kortowo have found a way of dealing with this problem.
The team led by Prof. Wojciech Janczukowicz and Dr hab. Joanna Rodziewicz, professor at UWM, developed a laboratory method for the precise treatment of wastewater from soilless tomato cultivation, which employs an electrobiological hybrid reactor. The reactor uses biological and electrochemical processes in which the bacteria that purify wastewater are fed not only with the substances present in it, but also with ... hydrogen produced by electrolysis of the wastewater. Dr Mielcarek was also a member of this team. Now he moves on a step further.
Together with Dr Tomasz Jóźwiak of the same department and Artur Dobrowolski, MSc, a doctoral student at the Faculty of Environmental Management and Agriculture, he is working on transforming the laboratory method into an industrial technology for the precise treatment of sewage from soilless tomato cultivation using a hybrid electrobiological reactor. He has just received a grant for this purpose of about PLN 1.5 million from the National Centre for Research and Development in the Lider 10 competition. The grant starts on 1 January 2020 and will last for three years. It is to be completed with a patent application.
However, environmental protection is not Dr Mielcarek’s only motivation.
“We know from numerous studies and scientific reports that the resources of phosphorus, the main component of fertilizers, will be exhausted on Earth in about 50 years. We need to think now about how to save or recover it. These 14-15 thousand m3 of wastewater from 1 ha of tomato cultivation contains between 0.5 and 2 tons of phosphorus. We cannot allow it to be released directly to the environment and we cannot let it be wasted. Our method allows for recovering it, so it can become a valuable fertilizer”, adds Dr Artur Mielcarek.