Process Comparisons of PhaSE Separation in Anaerobic Digestion of Complex Organic Substrates

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The Two phase anaerobic digestion has been considered to be an advantageous process to improve the methane production efficiency. It remains still to be investigated for the anaerobic digestion mechanisms of each compornent of organic materials. For instance, it is expected that there should be some differences in the anaerobic degradation processes among carbohydrates, proteins and lipids.Two different substrates skimmed milk and baby milk were used to analyse these effects. The major components of skimmed milk are carbohydrates and proteins which makes up 87.4% of it whereas 93.7% of baby milk is carbohydrates and lipids. As carbohydrates are easily biodegradable the study will compare the effects of presence of proteins and lipids. Substrate differences have differences in the pattern of changes in the process, but less variations in the overall efficiencies. The reason for less percentages of volatile acids in the case baby milk can be found as baby milk has only 47% of easily biodegradable carbohydrates and proteins.Phase separation effects for carborhydrates has no clear merits and a little advantage for protein (Hanaki, 1986) but hydrolysing lipids and breaking into long-chain fatty acids inhibits methanogenous organisms activity (Tanaka, 1985). Therefore comparing the single phase and two phase operations the reasons for little different in skimmed milk and better stabilization for baby milk by two phase operation by avoiding this inhibition are clearly understood. Generally speaking two phase operations are reccommended for all the type of substrates, but especially highly reccommended for substrates like baby milk with high contents of lipids.