The potential of the co-recycling of secondary biodegradable household resources including wild plants to close nutrient and carbon cycles in agriculture in Germany

Abstract

The aim of this study is to evaluate the potential for conserving natural resources (fossil resources, mineral fertilizer, fertile soil and biodiversity) with alternative circular concepts in order to contribute to the achievement of global sustainability goals. This study examines the potential contribution of substituting conventional products for three alternative circular economy concepts. This includes the household resources black water, kitchen and green waste for the production of design fertilizer, plant charcoal, biopolymers (concept 1) and biogas (concept 2), as well as the combination of household kitchen waste with wild plants for the production of biogas (concept 3). For evaluation, literature values were combined with analyzed parameters of input streams and biogas tests. The production and consumption values determined all relate to the functional unit of a person and year in Germany. Concept 1 has the highest potential for substitution in terms of the amount of recycled products. Co-recycling of organic household waste can account for 20% of NPK (nitrogen, phosphorus, potassium) mineral fertilizer, 19% of plastic consumption and 11% as a soil improving measure in soils in agriculture that are at risk of degradation. Concept 2 has the potential to contribute 12% of the final energy consumption in private households, which is an alternative solution regarding energy recovery due to the extensive practical experience. The joint recycling generates 141 kWh without, and 174 kWh with, fermentable green waste. If 75%, by weight, of fresh wild plants are added to the kitchen waste in concept 3, a wild plant area of 5 m2 is required, which could replace 41% of the biogas corn area, which is concept 3. This mix generates 193 kWh with the potential to reach 78% of corn energy production. The share of wild plants in kitchen waste of 50 or 25% by weight has the potential to achieve 115 or 104% of the corn energy yield, which is a promising concept for rural areas regarding energy recovery from an ecological point of view. The results show a considerable contribution potential of household resources in alternative cycle concepts to increase resource efficiency, and indirectly to diversify the agricultural landscape.