Mechanism of inhibition caused by long‐chain fatty acids in anaerobic digestion process

Abstract The inhibitory effect of long‐chain fatty acids on the anaerobic digestion process was examined in batch experiments using synthetic substrates. The addition of long‐chain fatty acids caused the appearance of the appearance of the lag period in the methane production from acetate and in the degradation of both long‐chain fatty acids and n ‐butyrate. Methane production from hydrogen proceeded without lag period although its rate was lowered. Fermentation of glucose was not inhibited. Neutral fat in the whole milk was easily hydrolyzed to long‐chain fatty acids, which brought about the inhibition. The addition of calcium chloride reduced the inhibitory effect of long‐chain fatty but it did not do so after the culture had been exposed to long‐chain fatty acids for more than several hours. The addition of calcium carbonate could not reduce the inhibition because of its insolubility.