C.R.O.P. - Combined Regenerative Organic food Production: Using trickling filters for wet composting of organic waste in hydroponic greenhouse cultures

Abstract

In the past decades the upcoming shortage of mineral oil caused intense public debates and research efforts on the subject of alternative fuels and the recycling of plastics. The limited availability of environmentally compatible fertilizer for food production purposes attracted muss less public interest, but is of equal importance. C.R.O.P. is a sustainable concept for the improvement of organic wastes and wastewaters, which combines microbial trickling filters for waste processing with hydroponic plant cultivation on the basis of the resulting nutrient containing solutions. Although the trickling filters are designed as waste processing plants for closed environment systems in the first place, they are also suitable for nutrient recycling in modern hydroponic greenhouse cultures. Wet composting of plant wastes comprises two steps, the first of which is the liquefaction of the solid parts and the second the mineralization of the organic matter. These processes require the presence of several microbial species with differing environmental demands. To enable the simultaneous growth of the necessary organisms in one filter unit, the filter medium has to provide the corresponding habitats. Therefore, our trickling filters contain porous lava rock as filter medium. The small pores of the lava particle form different habitat zones under the growth of the biofilm in which the outer layers provide oxic habitats for aerobic bacteria and anoxic habitats for anaerobic bacteria. Presently, three full-scale trickling filters of the type described with special adaptations for solids processing located at AgroHort Campus Klein-Altendorf of the University of Bonn are in operation. Each filter unit consists of a tank that contains 800l of water and a filter that contains 250l of lava. The water is constantly circulated through the lava filter. Between 5 to 15 kg of shredded plant wastes were added every fortnight to the water (total amount approximately 120 kg). The waste was carried along in the flow, thus also passing the filter, and was liquefied within days. The process resulted in a clear and almost completely odour-free solution. Alter the measurement of mass concentrations of inorganic compounds by ion exchange chromatography the solution is used as stock solution for liquid fertilizer application in growth tests, which are currently in progress. To date we can state that nutrients, especially micronutrients, have to be added when the filter units are solely fed with plant wastes but the consumption of conventional fertilizer is reduced.