Abstract
Efficient and sustainable biochemical production using low-cost waste assumes considerable industrial and ecological importance. Solid organic wastes (SOWs) are inexpensive, abundantly available resources and their bioconversion to volatile fatty acids, especially acetate, aids in relieving the requirements of pure sugars for microbial biochemical productions in industries. Acetate production from SOW that utilizes the organic carbon of these wastes is used as an efficient solid waste reduction strategy if the environmental factors are optimized. This study screens and optimizes influential factors (physical and chemical) for acetate production by a thermophilic acetogenic consortium using two SOWs—cafeteria wastes and corn stover. The screening experiment revealed significant effects of temperature, bromoethane sulfonate, and shaking on acetate production. Temperature, medium pH, and C:N ratio were further optimized using statistical optimization with response surface methodology. The maximum acetate concentration of 8061 mg L−1 (>200% improvement) was achieved at temperature, pH, and C:N ratio of 60 °C, 6, 25, respectively, and acetate accounted for more than 85% of metabolites. This study also demonstrated the feasibility of using acetate-rich fermentate (obtained from SOWs) as a substrate for the growth of industrially relevant yeast Yarrowia lipolytica, which can convert acetate into higher-value biochemicals.
Highlights
The need for sustainable energy generation in recent years has increased interest in microbial processes for the production of fuels and value-added products
The cellulose, hemicellulose, and lignin content of the corn stover used in this study was 39.4%, 32.1%, and 12.8%, respectively
Sub-culturing the inoculum with the same wastes as used for the experimental batch runs allowed for acclimatization of the thermophilic microbial consortium which is favorable for achieving higher acetate production [46,47,48,49]
Summary
The need for sustainable energy generation in recent years has increased interest in microbial processes for the production of fuels and value-added products. Solid organic wastes (SOWs) such as food and paper waste, and agricultural wastes (such as corn stover) produced by anthropogenic activities, are abundant substrates that can be converted to intermediate or end-use bioproducts using microbial metabolism [2,3]. Hydrolytic enzymes produced by microbes convert the complex substrates into simpler sugars and organic acids. These intermediate organic acids often called as volatile fatty acids (VFAs) can be further utilized for microbial production of higher-value chemicals and can replace sugar substrates in industrial fermentations. Acetic acid or acetate is the most desirable VFA as it can serve as an alternate and sole source of carbon for microorganisms and can be used at comparatively higher concentrations to replace sugar substrates. In the United States, the price of acetate ($350−$450 per ton) is lower than the price of glucose ($500 per ton) [8]; it is possible to obtain high titers of acetate inexpensively using renewable, and abundant feedstocks such as SOWs
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