Dry digestion of source-separated biowaste : quality requirements for digestates in agricultural use, case Nokia

Tampere Regional Solid Waste Management Ltd opens a new biowaste treatment plant in autumn 2020. After 20 years of aerobic composting, the treatment technology changes to anaerobic digestion. The technology can offer new competitive advantage, when waste can be turned into marketable products. The purpose of this study was to help the new plant to produce not just biogas for transportation use, but also digestates for fertilisation purposes. This study concentrates on utilisation of the digestates from the dry digestion line of source-separated biowaste and garden waste. The aim was to find the requirements and expectations towards these recycled fertilisers. The relevant European and national regulations concerning waste, fertiliser products and some agricultural practices were studied. Guaranteeing good quality digestate suitable for agricultural use, the feedstock of the process is of essential importance. In this study, the known feedstock values and estimated digestate quality were compared with the data found in literature. The challenges and the possibilities in the markets were identified through results of earlier interviews with producers and users of products in Finland and in Europe. It became apparent that there are many regulations one needs to comply with, both from waste and agriculture section, and both from the producer’s and the end user’s point of view. The legislation has recently been renewed, and the changes need active follow-up. The quality of the digestate can be estimated, but the variations can be big. The solid digestate after composting proved to be a good soil improver, and the liquid digestate a decent fertiliser. There is a demand for these fertiliser products in Tampere region, but the market value is measured by solving the quality, storage and price issues. To comply with the requirements of legislation and the customers, special attention should be paid to the quality of the digestates. Requirements in storage and application of digestates together with the need of knowledge of farming practices and marketing fertiliser products suggest incorporating a third party to share part of the work. At least in the beginning of operation, that would give time to learn to run the plant and produce biogas and good quality digestate, especially in the liquid form. Using a quality assurance system could help in marketing the fertiliser products, and that way, also the profitability of the plant.Key words: biowaste, dry digestion, digestate, organic fertiliser product, qualit