With finite supply of combustible and natural energy sources, there is a demand for alternative energy sources. This has led to increased focus on biofuels. Now, researchers from the Department of Biotechnology and Medical Engineering at the National Institute of Technology (NIT) Rourkela, Odisha, have discovered a marine bacterial strain ( Citrobacter species) that can produce ethanol directly from fruit waste.
Tolerant strains
The Citrobacter species was isolated from the marine water near Digha and Shankarpur seashore of West Bengal. Ten strains were found to be highly tolerant to ethanol. The strains were tested with various waste materials including kitchen, paper, fruit and garden waste for their ability to produce ethanol.
“We wanted a more eco-friendly and cost-efficient method apart from the usual fermentation processes for the production of bioethanol,” says Angana Sarkar from NIT Rourkela, the corresponding author of the paper published in the journal Process Safety and Environment Protection.
Of the ten ethanol-resistant strains screened, a particular species ( Citrobacter sp. E4) was found to directly convert fruit waste into ethanol without any pretreatment.
The waste material was powdered to enhance bacterial activity and thereby reduce the time taken to produce ethanol. The powdered waste along with the bacterial strain and mineral salts required for its growth were introduced into the bioreactor. Under optimum temperature (33.2°C) and optimum pH (7.1), a maximum output of 0.30g of ethanol was obtained from 1g of fruit waste. It took over 24 hours to convert waste into ethanol.
Due to the high sugar content, fruit waste was found to be the most favourable, whereas paper waste was the least favourable due to the presence of cellulosic substances. The researchers note that this method is environment-friendly, sustainable and cost-efficient.
The species was further tested and found to be non-pathogenic and antibiotic-resistant against cephalosporin and ampicillin, to name a few.
The species could be easily cultured under laboratory conditions. “We are trying to genetically modify the species to increase the amount of ethanol produced,” adds Dr. Sarkar.
