Techno-economic assessment at full scale of a biogas refinery plant receiving nitrogen rich feedstock and producing renewable energy and biobased fertilisers

C Brienza,I Sigurnjak,T Meier,E Michels,F Adani,O Schoumans,C Vaneeckhaute,E Meers

doi:10.1016/j.jclepro.2021.127408

Abstract

Anaerobic digestion of nitrogen (N) rich substrates might be hindered when ammonia (NH3) formation reaches toxic levels for methanogenic microorganisms. One possible strategy to avoid inhibiting conditions is the removal of NH3 from digestate by stripping and scrubbing technology and by recirculating N depleted digestate back to the digester. This study aimed to i) monitor the performance (mass and energy balances) of a full scale digestate processing cascade that includes an innovative vacuum side stream NH3stripping and scrubbing system, ii) assess the production cost of ammonium sulphate (AS) solution and iii) evaluate its fertiliser quality. The use of gypsum to recover NH3 in the scrubbing unit, instead of the more common sulphuric acid, results in the generation of AS and a fertilising liming substrate. Mass and nutrient balances indicated that 57% and 7.5% of ammonium N contained in digestate was recovered in the form of a 22% AS and liming substrate, respectively. The energy balance showed that about 3.8 kWhel and 59 kWhth were necessary to recover 1 kg of N in the form of AS. Furthermore, the production cost of AS, including both capital and operational costs, resulted to be 5.8 € t−1 of digestate processed. According to the fertiliser quality assessment, this technology allows for the recovery of NH3in the form of salt solutions that can be utilised as a substitute for synthetic mineral nitrogen fertilisers.

Highlights

Interest in renewable energy is growing in the European Union (EU), resulting in the Renewable Energy Directive EU 2001/2018 (REDII), 2018
Anaerobic digestion (AD) is a promising technology as it combines the production of biogas and the recycling of nutrients in the form of an organic fertiliser known as digestate
Chicken manure fed to co-AD system from January until April 2019 was characterised for TN, Total phosphorus (TP) and TK

Summary

Introduction

Interest in renewable energy is growing in the European Union (EU), resulting in the Renewable Energy Directive EU 2001/2018 (REDII), 2018. Anaerobic digestion (AD) is a promising technology as it combines the production of biogas and the recycling of nutrients in the form of an organic fertiliser known as digestate. In some European countries, the biogas production has remarkably increased in the last decade, due to the introduction of conspicuous incentives for the production of biogas from renewable biomass. In Germany, for example, the Renewable En ergy Sources Act (EEG, 2000) has boosted the expansion of biogas plants and since 2010, Germany covers 50% of the European biogas produc tion, mainly from silage maize (Meyer et al, 2018). Following the amendments of the Renewable Energy Sources Act, a dedicated bonus for biogas plants using at least 30% of manure as feedstock was intro duced in 2009. Anaerobic co-digestion (co-AD) of silage maize and manure is an interesting option for biogas plants

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