AMMONOX: Ammonia for Enhancing Biogas Yield and Reducing NOx—Analysis of Effects of Aqueous Ammonia Soaking on Manure Fibers

A Lymperatou,H N Gavala,I V Skiadas,K H Esbensen

doi:10.1007/s12649-015-9365-4

Abstract

Laboratory experiments have shown that aqueous ammonia soaking (AAS) is a promising treatment for increasing the methane yield of the solid fraction of manure (fibers). AMMONOX is a new concept based on the sustainable use of ammonia for enhancing biogas pro- duction at biogas plants digesting manure. The proposed process is based on an optimized AAS treatment of manure fibers in combination with an efficient ammonia recovery step. The enhancement of biogas production is achieved by enriching manure with AAS-treated fibers, or other ligno- cellulosic residues, while the ammonia recovered can be used for fulfilling the needs of the treatment itself. Excess of ammonia could be produced when ammonia is recov- ered from both the treated fibers and the digester effluent, which could be used for the reduction of NOx in biogas- based electricity generation by gas turbines. In this survey study, the importance of different factors affecting the performance of AAS of digested manure fibers was in- vestigated in order to conclude on which variables to op- timize. Principal component analysis of the present data was used for a preliminary analysis of effects. The tem- perature and the ammonia concentration during AAS were the most influencing variables in terms of methane yield under the conditions tested. Further experiments should be conducted in order to investigate the effect of shorter AAS duration than the ones tested (lower than 24 h) and for assessing the importance of the solid-to-liquid ratio in the treatment mixture; the follow-up campaign should be op- timized with respect to possible interactions/correlated experimental factor effects.

Highlights

Livestock manure has been pointed out as one of the most important agricultural sources of environmental pollution.Manure is rich in valuable nutrients for plant growth such as nitrogen and phosphorus, which makes its use as a crop fertilizer and soil amendment a common practice in many countries
ammonia soaking (AAS) has been recently proved to be a pretreatment of great potential for increasing CH4 yield of manure fibers
AAS pretreatment of manure fibers coupled with a successful NH3 recovery step could lead to a more sustainable biogas production allowing biogas plants to operate solely on manure

Summary

Introduction

Livestock manure has been pointed out as one of the most important agricultural sources of environmental pollution.Manure is rich in valuable nutrients for plant growth such as nitrogen and phosphorus, which makes its use as a crop fertilizer and soil amendment a common practice in many countries. Due to the large contribution of manure to ammonia, greenhouse gas emissions and water pollution, concerns about its management have increased, and many regions in Europe that have an intensive livestock production, are struggling to find solutions in order to comply with the disposal limits stipulated in environmental legislation (91/676/EEC) [2]. The digestion of solely manure is a non-feasible process due to its low content in digestible organic matter [3]. This is because the digestible part of the animal feed has already been utilized in the animal digestion; manure contains a recalcitrant lignocellulosic concentrated part [4] mixed with washing water and other lignocellulosic biomasses, such as straw, that are used for bedding materials [5]. As the demand for these extra materials increases, their availability remains very limited, presenting biogas plants with a new problem [3]

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Conclusion