Short-Circuit Short circuiting the carbon and nutrient cycles between urban and rural districts by establishing three new systems for source separation, collection and composting of organic waste in the greater Copenhagen area Final report presented to the EU-Life programme May 2006(LIFE02/ENV/DK/00150)

Summary

The overall objective of the Short-Circuit project was to promote the waste recycling concept using three sub-systems, i.e. collection of vegetable residues from the box scheme business Aarstiderne A/S and composting the residues at Krogerup farm, on-farm composting of urban waste at an experimental farm belonging to KVL and a community involved combined biogas production and composting system developed by Solum A/S. Data from the optimised systems formed the basis of a Life Cycle Analysis (ecotoxicology not included) to evaluate environmental impact. This was done by KTH using the ORWARE waste management model. All systems performed very well and lived up to the specifications put down in the project application and it was demonstrated that the Short-circuit concept in many cases are superior to more conventional waste treatment systems.
Aarstiderne have developed a simple system for collecting vegetable residues from their customers. One of Aarstidernes vans was equipped for the collection system. In all 850 customers were involved for 24-76 weeks and of the 20,000 times boxes were delivered waste was collected at 6,600 occasions resulting in a participation rate of 33%. During the project period more than 10 tons of organic waste with extremely low amount of impurities was collected and subsequently composted at Krogerup farm. The waste was composted together with straw, hay, silage and horse manure and the total amount of material exceeded 100 tons. The compost was made by simple techniques using machinery normally present on a farm and the compost was of high quality.
KVL´s HI-LO (high temperature, low emission, low cost) on-farm composting system was designed to co-treat source separate household waste and farm residues. The system consists of a 20 ft. container with a roof-cover that functions as a heat exchanger trapping water vapour from the compost and thereby diminishing NH3-loss. The compost is actively aerated. During a typical composting run the temperature in the middle of the compost exceeded 70C for more than five days, and the material in this way complied with EU regulations to secure a sanitised product. The material adjacent to the surface of the container did not reach 70C, but even at this position the maximum temperature was 62C and the temperature exceeded 60C for more than 24 hours.
The third system for waste treatment consists of a high-tech combined biogas production- and composting plant, the AIKAN-plant constructed by Solum A/S. The technology utilizes biowaste (organic MSW) initially for biogas production and subsequently to produce compost with high process control and sanitation according to EU regulation. An important new feature of the plant is that biogas production and subsequent composting of the waste material takes place in the same facility. In this way, part of the waste materials energy content is utilised and at the same time the end-product is stable compost better suited for soil application than biogas residues.
The systems analysis using the ORWARE model can be summed up as follows: The Aarstiderne/Krogerup system had lower environmental impact in several categories than conventional systems – especially the energy consumption was low. For these systems good source separation and small distance for collection are important factors. The Hi-Lo on-farm composting system had a higher environmental impact compared to incineration. Optimization of the system to decrease N-emission could change that by eliminate acidification and eutrophication potential. There were only minor differences in environmental performance between the AIKAN system and a traditional incineration system even when organic waste with high amounts of impurities was treated. In-depth analysis of assumptions, system boundaries etc., demonstrated the need to consider the inherent limitations of system analysis when evaluating waste management systems.