The past decade witnessed a steady growth in the global production of vegetable oil to meet an increased demand that reached more than 110 million metric tons produced in the 2005/06 production year. According to the U.S. Environment Protection Agency (EPA), bulk shipment and storage of non-petroleum oils (e.g. vegetable oils) can result in spills and leaks that have significant impacts on fresh water and marine environments even though such oils may be biodegradable under both aerobic and anaerobic conditions. Among all the vegetable oils commercially available in the market, canola oil is believed to have the "best fatty-acid profile of any edible oil" which makes canola oil one of the most popular oils in the market.
This research was aimed at designing and conducting experiments on five primary component triglycerides of canola oil, three liquids triolein (OOO), trilinolein (LLL), and trilinolenin(LnLnLn) and two solids tripalmitin (PPP) and tristearin (SSS), to investigate their aerobic biodegradability and their toxic byproducts during biodegradation. The rate and extent of triglycerides biodegradation were examined in respirometry flask tests, at the same time toxicity tests were performed on the fatty acid byproducts. Also, a comparative study was performed on
commercial canola oil and synthetic canola oil using the same experimental setup and methods to identify and generalize the causes of the observed biodegradability and toxicity.
The performance of the solid triglyceride experiments was largely restricted by their extremely low solubility and low polarity. When mixed with water, PPP and SSS formed irregular lumps, not the uniform and homogeneous suspension required for the lipase activity, rendering them not available for microbial attack. No substantial mineralization was observed after 30 days of reaction time. In the case of liquid triglycerides, a competition between autoxidation and biodegradation took place due to the presence of the double bonds in their fatty acid chains. The produced hydroperoxides polymerize and become non-biodegradable while the non-oxidized portions readily biodegrade and mostly mineralize.
Microtox® Toxicity was only observed at the early stages of biodegradation in the solid phase and was proven to be caused by the degraded FFA (Free Fatty Acids) products. All three unsaturated triglycerides followed the same increasing then gradually decreasing trend during the toxicity studies. Triolein was observed to have the highest toxicity among the five tested triglycerides throughout the 30-day experiment.
Higher toxicity and higher FFA were detected during the commercial canola oil experiments than during the synthetic canola oil ones, possibly due to the presence of additives in the commercial oil intended to prevent breakdown, biodegradation and peroxidation.