Anaerobic biodegradation of vegetable oil and its metabolic intermediates in oil-enriched freshwater sediments

Abstract

Anaerobic biodegradation of vegetable oil in freshwater sediments is strongly inhibited by high concentrations of oil, but the presence of ferric hydroxide relieves the inhibition. The effect of ferric hydroxide is not due to physical or chemical interactions with long-chain fatty acids (LCFAs) that are produced as intermediates during metabolism of vegetable-oil triglycerides. The anaerobic biodegradation of canola oil and mixtures of acetic and oleic acids, two important intermediates of vegetable-oil metabolism, were investigated using sediments enriched on canola oil under methanogenic and iron-reducing conditions to determine whether the effect of ferric hydroxide has a biological basis. Sediments enriched under both conditions rapidly and completely converted canola oil to methane when the initial oil concentration was relatively low (1.9 g oil/kg sediments), but the biotransformation was strongly inhibited in sediments enriched under methanogenic conditions when the initial concentration was 19 g/kg (< 30% of the oil-derived electron equivalents were transferred to methane in a 420-day incubation period). Sediments enriched under iron-reducing conditions, however, completely transformed canola oil to methane in about 250 days at this initial oil concentration. The anaerobic biotransformation of mixtures of acetate and oleic acid followed a similar pattern: the rate and extent of conversion of these electron-donor substrates to methane was always higher in sediments enriched under iron-reducing than under methanogenic conditions. These results suggest that enrichment on canola oil in the presence of ferric hydroxide selects a microbial community that is less sensitive to inhibition by LCFAs than the community that develops during enrichment under methanogenic conditions.

Assessment of sediment toxicity during anaerobic biodegradation of vegetable oil using Microtox® and Hyalella azteca bioassays

“…Although it is biodegradable, anaerobic metabolism of vegetable oil may produce intermediates that are inhibitory to aceticlastic methanogens and hydrogen-producing acetogens (Hanaki et al, 1981;Koster and Cramer, 1987;Hwu et al, 1996;Lalman and Bagley, 2001). Such inhibition was observed during anaerobic degradation of vegetable oil in freshwater sediments (Li et al, 2001(Li et al, , 2005. Vegetable oils and animal fats have been reported to be phytotoxic (Forster, 1992;Sampedro et al, 2005) and to exert other toxic effects on fish (Pustowka et al, 2000) in aquatic ecosystems.…”

“…It has already been shown that floating vegetable oil spills can be effectively removed from surface waters by sedimentation with clay minerals (Wincele et al, 2004), and the oil can be efficiently mineralized under anaerobic conditions in freshwater sediments (Li et al, 2001(Li et al, , 2005Li and Wrenn, 2004). The objective of this study was to evaluate the toxicity of sediments contaminated by the concentrations of vegetable oil that can be produced by sedimentation of floating vegetable oil spills by clay and other dense minerals.…”

“…Previous work has demonstrated the feasibility of removing floating vegetable oil from the water surface by using clay to promote sedimentation as dense oil-mineral-aggregates (Wincele et al, 2004). In addition, the anaerobic biodegradability of vegetable oil has been demonstrated in freshwater sediments (Li et al, 2001(Li et al, , 2005Li and Wrenn, 2004).…”

Effects of Vegetable Oil Pollution on Aquatic Macroinvertebrate Assemblage in a Freshwater Wetland and Its Use as a Remediation Tool

“…After that, the anaerobic biodegradation of vegetable oil in sediments began (Li et al 2001(Li et al , 2005Li and Wrenn 2004), explaining the drop in oil concentration in sediments over time (see Table 1). Although clay can effectively transfer vegetable oil from the water to sediments where anaerobic degradation of vegetable oil can occur, the metabolic intermediates of degradation may be toxic to microorganisms (Cherrington et al 1991), mussels (Mudge 1995) and amphipods (Li et al 2007).…”

Effects of Ferric Hydroxide on Methanogenesis from Lipids and Long‐Chain Fatty Acids in Anaerobic Digestion

“…In freshwater sediments, however, the addition of calcium chloride and clay reduced the rate of methanogenesis from canola oil, whereas the addition of ferric hydroxide stimulated the rate of its conversion to methane ( Li and Wrenn, 2004 ). Furthermore, enrichment of freshwater sediments by growth on vegetable oil in the presence of ferric hydroxide stimulated the rate of methanogenesis from vegetable oil relative to sediments that were enriched in its absence ( Li et al, 2005 ). Unlike calcium and clay, ferric hydroxide can also serve as an alternative electron acceptor in the anaerobic degradation of lipids and long‐chain fatty acids (Figure 1).…”