Improving the Anaerobic Digestion of Swine Manure through an Optimized Ammonia Treatment: Process Performance, Digestate and Techno-Economic Aspects

Anna Lymperatou,Niels B Rasmussen,Hariklia N Gavala,Ioannis V Skiadas

doi:10.3390/en14030787

Anna Lymperatou, Niels B Rasmussen + Show 2 more

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https://doi.org/10.3390/en14030787

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Abstract

Swine manure mono-digestion results in relatively low methane productivity due to the low degradation rate of its solid fraction (manure fibers), and due to the high ammonia and water content. The aqueous ammonia soaking (AAS) pretreatment of manure fibers has been proposed for overcoming these limitations. In this study, continuous anaerobic digestion (AD) of manure mixed with optimally AAS-treated manure fibers was compared to the AD of manure mixed with untreated manure fibers. Due to lab-scale pumping restrictions, the ratio of AAS-optimally treated manure fibers to manure was only 1/3 on a total solids (TS) basis. However, the biogas productivity and methane yield were improved by 17% and 38%, respectively, also confirming the predictions from a simplified 1st order hydrolysis model based on batch experiments. Furthermore, an improved reduction efficiency of major organic components was observed for the digester processing AAS-treated manure fibers compared to the non-treated one (e.g., 42% increased reduction for cellulose fraction). A preliminary techno-economic analysis of the proposed process showed that mixing raw manure with AAS manure fibers in large-scale digesters could result in a 72% increase of revenue compared to the AD of manure mixed with untreated fibers and 135% increase compared to that of solely manure.

Highlights

Swine manure is a major source of environmental pollution, contributing significantly to atmospheric, soil, and waterbodies contamination
The swine manure presented an average content of organic matter, volatile solids (VS) (68% total solids (TS)), as compared to values found in literature (60–77% TS) [25,26,27,28,29]
The organic fraction of the NP manure fibers was of the same magnitude as in swine manure; they were significantly richer in carbohydrates

Summary

Introduction

Swine manure is a major source of environmental pollution, contributing significantly to atmospheric, soil, and waterbodies contamination. In presence of the available nutrients, the inherent microorganisms of manure degrade the organic matter remaining after animal digestion, resulting in a series of degradation products, among them CH4 and CO2. The controlled microbial degradation of manure through the anaerobic digestion (AD) process is a commonly applied technology, during which the emissions are captured and can be used in the form of biogas as a renewable energy source. The dry matter content of liquid manure is lower than 10%. This fact, in combination with the low degradation rate of the solid fraction (fiber) of manure and the high ammonia content, results in a poor biogas production and in economically non-feasible AD processes [2,3,4]

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