Abstract
In anaerobic digestion (AD), long-chain fatty acids (LCFAs) produced by hydrolysis of lipids, exhibit toxicity against microorganisms when their concentration exceeds several millimolar. An absorption detection system using a quartz crystal microbalance (QCM) was developed to monitor the LCFA concentration during an anaerobic digester’s operation treating oily organic waste. The dissociation of the LCFAs considerably improved the sensor response and, moreover, enabled it to specifically detect LCFA from the mixture of LCFA and triglyceride. Under alkaline conditions, the frequency-shift rates of the QCM sensor linearly increased in accordance with palmitic acid concentration in the range of 0–100 mg/L. Frequency changes caused by anaerobic digestate samples were successfully measured after removing suspended solids and adjusting the pH to 10.7. Finally, the QCM measurements for digestate samples demonstrated that frequency-shift rates are highly correlated with LCFA concentrations, which confirmed that the newly developed QCM sensor is helpful for LCFA monitoring in terms of rapidness and usability.
Highlights
Waste oil has great potential in renewable energy production because of its high energy density and the large amount generated as a result of human activities
The quartz crystal was coated with a polyvinyl butyral (PVB)-based coating reagent (AY-302, Sunhayato, Tokyo, Japan) to reduce the interference caused by the electrolyte in anaerobic digestate, and coated again with a copolymer of styrene-divinylbenzene (PS-DVB) gel (PLS-2 for AQUA, GL Science, Tokyo, Japan) by random immobilization
The low response to acetate is likely due to its hydrophilic nature. These results indicate that pH adjustment and dissociation of fatty acids can contribute to the selectivity of the quartz crystal microbalance (QCM) sensor
Summary
Waste oil has great potential in renewable energy production because of its high energy density and the large amount generated as a result of human activities. Oil, and grease (FOG) in waste streams produced from restaurant kitchens and food industries is a major problem in the sewer systems of urban areas. FOG deposits formed on pipe walls lead to clogging, which can cause flooding, pollution, and other public health problems. Since direct discharge of FOG into sewer lines is no longer permitted, grease traps are generally installed in commercial facilities to remove FOG before it enters sewer lines. The accumulated oily organic waste, including FOG and food scraps, has a high energy potential. Major forms of energy from those oily organic wastes are biodiesel fuel and biogas
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