Recovery of nutrients from biogas digestate with biochar and clinoptilolite

The liquid fraction of digestate contains nutrients which makes it a valuable fertiliser in agricultural crop production systems. However, direct application of digestate may raise practical and environmental problems. Therefore, processes to concentrate nutrients have been proposed aiming not only to treat the liquid fraction of digestate to overcome the problems related to direct application, but also to recover the nutrients of which natural reserves are being depleted such as phosphorus and potassium. In this thesis, the focus was on the evaluation of the use of clinoptilolite and biochar for nutrient recovery from the liquid fraction of digestate; and to investigate the further use of these nutrient-enriched materials as fertiliser. This thesis showed that sorption with clinoptilolite and biochar can be a promising technology to recover nutrients from liquid fraction of digestate. Using biochar and clinoptilolite provides concentration of nutrients and, thereby, volume reduction which allows for savings on storage, transport and application of the voluminous liquid fraction of digestate. The end-products are digestate-enriched clinoptilolite and enriched biochar can act as N fertilisers.