Economics anaerobic digestion

If there is a need for odour reduction on an animal husbandry farm anaerobic digestion is one of the real possibilities. The investment and running costs of the methods, mentioned in table 3, are indicated in previous chapters. An economic calculation for the feasibility of an anaerobic digestion is open for discussion. For our purpose we must valuate the nett output of biogas. 

MARCHAIM, U. Anaerobic digestion of agricultural wastes. The economic lie in the effluent uses. Int. Symposium on Anaerobic Digestion 83. Boston Ma., 1983. 

Even after anaerobic digestion the voluminous sludge contains a lot of water. It is thus necessary to decrease the amount of water in it and hence also its volume so that its transport and eventual further processing would become more economical. For this purpose various methods can be used, especially thickening, dehydration and drying, or eventually incineration (for details see Section 3.11). 

Despite the current industry attention to these systems and their potential to meet site-specific needs, industry experience indicates that the economics of the anaerobic digestion of manures are not competitive at the present time. In fact, many of the companies interviewed indicated that the refeed materials (by-products which can be fed to animals) produced by anaerobic digestion have higher economic value than the gas which is produced. 

Byproduct flexibility Byproduct credits do not significantly affect the process economics. The furfural by-product produced from hemicellulose can be easily converted to levulinic acid (via hydrogenation to furfuryl alcohol) thereby significantly increasing the yield of the main product. Formic acid can be sold, converted to derivatives or waste-treated by gasification or anaerobic digestion to recover its energy value. 

Barta, Z., Reczey, K., Zacchi, G., 2010. Techno-economic evaluation of stillage treatment with anaerobic digestion in a softwood-to-ethanol process. Biotechnology for Biofuels 3, 21-32. 

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