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Project

A biorefinery approach to exploit digestate as key feedstock in the energy – nutrient nexus

Anaerobic digestion (AD) comprises the microbial conversion of organic matter into (i) a methane-rich biogas (50-75% CH4, 25-50% CO2), which can be used for co-generation of heat and electricity, and (ii) digestate as output streams. In 2019, 19668 anaerobic digestion plants were in operation in the EU processing bio-waste (e.g., sewage sludge, agricultural residues, animal manure) corresponding to a total estimated green energy generation of 167 TWh (biogas) and 36 TWh (biomethane). Furthermore, it is estimated that per TWh, 775 to 1050 jobs are created in the biogas sector. Although biogas plays a major role in reaching the EU’s renewable energy and sustainability objectives, the Flemish and Turkish biogas sectors are burdened with economic problems associated with (i) negative gate-fees for streams with high methane potential, (ii) limited disposal routes and hence high disposal costs for the digestate and (iii) large reductions in government subsidies.

To address this pressing problem, the BioDEN project aims to create extra revenues for the biogas sector via developing a technology cascade approach for an integrated enhanced biogas production and efficient recovery of nutrients (N, P, K) as (novel) bio-fertilisers from digestate. Indeed, besides its energy potential, animal manure is rich in nutrients, which remain in the digestate after AD. By efficiently extracting these nutrients on the biogas plant premises, they can be, in a next phase, marketed as full-fledged substitutes of petrochemical-based mineral fertilisers, hereby creating new business cases and revenues for the sector, and decrease our dependency on natural gas or rock phosphate for securing mineral N and P needs. Our main elements of focus are: (i) biogas production via anaerobic digestion (AD), (ii) ammonia recovery via stripping and scrubbing, (iii) phosphorus recovery via precipitation and adsorption and (iv) integrated value chain assessment, including pot trials and scenario analyses. Although some of the processes already receive attention in research and in industry, effective linking of the processes to obtain a successful cascade is still missing.  Concretely, the BioDEN-project will result in (i) 10-20% more biogas (at constant input) compared to standard current practice, due to reduced ammonia inhibition, release of bio-available organic matter and high organic loading rates, (ii) a, increase in CH4 content of the biogas by 3-5% due to CO2-stripping, (iii) optimised processes for the recovery of nutrients into novel (ammonium citrate, ammonium bicarbonate) and known (ammonium sulphate, struvite, calcium phosphate) bio-fertilisers.

The BioDEN consortium is composed of 6 partners carefully selected by the project coordinator, Biogas-E (BE). It involves a balanced expertise composition of 3 RTOs and 3 Association Organisations (AO) from Flanders (BE) and Turkey. Biogas-E will be the main responsible of the project management, dissemination and communication activities with the support of OSTIM ENERJIK, an AO that has close collaboration with biogas sector in Turkey. Innovation and research activities will be carried out by KU Leuven (BE), UGent (BE) and UMARMARA (TR) Universities, each specialised in different aspects of the full BioDEN concept. AO VCM (BE) will provide essential expertise for the technical, economic and ecological impact assessments of the final technologies and products.

Date:1 Jan 2022 →  31 Dec 2023
Keywords:Quality assessment, Anaerobic digestion, Ammonia stripping, Phosphate recovery, Fertilizer production, Pilot-scale testing, Animal manure, CO2 emission reduction
Disciplines:Biological energy, General chemical and biochemical engineering not elsewhere classified, (Bio)chemical reactors, Chemical process design, Recycling, Agrochemistry and fertilisers