Inhibition of Methanogenesis from Acetate in Granular Sludge by Long-Chain Fatty Acids

Abstract

The effect of four saturated long-chain fatty acids (caprylic, capric, lauric, and myristic) and one unsaturated long-chain fatty acid (oleic) on the microbial formation of methane from acetate was investigated in batch anaerobic toxicity assays. The tests were carried out with granular sludge from an upflow anaerobic sludge bed reactor. In this sludge, Methanothrix spp. are the predominant acetoclastic methanogens. Lauric acid appeared to be the most versatile inhibitor: inhibition started at 1.6 mM, and at 4.3 mM the maximum specific acetoclastic methanogenic activity had been reduced to 50%. Caprylic acid appeared to be only slightly inhibitory. Oleic acid was almost as inhibitory as lauric acid. Although adsorption of the inhibitor on the cell wall might play an important role in the mechanism of inhibition, the inhibition was found to be correlated with concentration rather than with the amount per unit of biomass. In practical situations, as in anaerobic waste treatment processes, synergism can be expected to enhance the inhibition of methanogenesis. In the present research a background concentration of lauric acid below its MIC strongly enhanced the toxicity of capric acid and (to an even greater extent) myristic acid.

Antimicrobial activity of shredded carrot extracts on food‐borne bacteria and yeast

“…Dodecanoic acid, methyl esters of dodecanoic acid and methyl esters of pentadecanoic acid, identified by gas chromatography and mass spectrometry in the PVP-treated extract but not in the extract filtered through C, , Sep Pack column, could be responsible for the antimicrobial activity. An antimicrobial activity of saturated fatty acids has been demonstrated, with CIz compounds being the most active (Kabara et al 1972(Kabara et al , 1977Nunez de Kairuz et al 1983, Hogan et al 1987Koster and Cramer 1987;Kabara 1987). For instance, minimum inhibitory concentrations reported for dodecanoic acid were (in pg ml-'): 1000 for C. albtcans; 31-500 for a range of Gram-positive bacteria (Kabara et al 1977); 100 for Clostrtdzum botulznum (Dymicky and Tenchard 1982); and minimum bactericidal concentrations of 10-20 p g ml -'…”

Biodegradability of Nonionic Surfactant Used in the Remediation of Groundwaters Polluted with PCE

“…In another work, Lalman and Bagley (2001) observed that methanogenesis started to be inhibited at 10 mg L À1 of oleic acid. Koster and Cramer (1987) indicated that either 300 mg L À1 of myristic, lauric, or capric acid were inhibitory to methanogenic cultures in batch reactors. Moreover, typical values of half maximal inhibitory concentration (IC50), of oleic acid to methanogenesis were 345 and 133 mg/L for granular and flocculent anaerobic sludges (Pereira et al, 2002).…”

Influence of co-substrates on structure of microbial aggregates in long-chain fatty acid-fed anaerobic digesters

“…Left column, Granules fed by oleate and glucose; middle column, granules fed by oleate and cysteine; right column, granules fed by oleate, cysteine and glucose. Bars ¼ 500 lm Rinzema 1988;Koster and Cramer 1986). The results indicated that the addition of glucose and cysteine together with oleate not only decreases the inhibition of oleate on methanogenic activity but also improves formation of granular biomass.…”

“…The first step in the degradation of lipids is the hydrolysis of lipids to long-chain fatty acids (LCFA) and glycerol. It has been shown that LCFA and lipids inhibit the formation of granules (Koster and Cramer 1986;Rinzema 1988;Sam-soon et al 1991) and that the adsorption of LCFA onto the granules can result in its flotation and washout (Hwu et al 1997). Sam-soon et al (1991) found that a digester fed with oleate could not produce granular sludge and that the degradation of oleate was very poor.…”