Alfalfa is more than a protein-rich feed for livestock; it may also be an excellent source of biogas. This mixture of methane and other gases is produced when plants (or any organic matter) undergo anaerobic digestion.
This week in mSphere, researchers in China report on a new recipe for improving biogas production from alfalfa. Adding fruit waste and an anaerobic microbe to the mix first leads to co-fermentation, then produces methane.
The group’s findings suggest that the additions boost biogas production from alfalfa and reduce the cost of the process. The added ingredients also increased the nutritional content of the remaining plant matter, which can be used as feed.
“The process offers an attractive opportunity to increase methane production from fruit waste,” said microbiologist Qiming Cheng, Ph.D, at the Guizhou University College of Animal Science. Fruit and plant biomass, noted Cheng, may serve as an inexpensive, stable source of clean energy, and an alternative to fossil fuels.
The first added ingredient was a paste-like pomace of rose hip (Rosa roxburghi), a fruit cultivated widely in the southwest region of Guizhou and often processed into juice. Fermenting the rose hip pomace, left behind after juicing, offers an appealing way to dispose of the rose hip remains. “The local treatment of its waste can reduce the cost of raw material transportation and promote the implementation of rural biogas projects,” Cheng said.
The second ingredient is Lactobacillus acidophilus, an anaerobic microbe often used as a probiotic. The researchers compared samples of alfalfa, harvested from the region, that had been treated with both the pomace and L. acidophilus to samples untreated, and to samples treated with each additive individually. At various intervals over 50 days, they analyzed the chemical composition of treated and untreated samples, and monitored the pH and other fermentation process.
The combined fruit waste and L. acidophilus had a synergistic effect and stimulated anaerobic fermentation, the researchers reported. The samples that included both materials showed a 33% increase in methane production after 3 days, compared to the untreated samples.
During fermentation, the samples became more acidic, with the fastest decrease in pH occurring in the samples treated with the pomace and probiotic. The combined treatment also promoted the development of lactic acid bacteria, which enriched the biomass.
The researchers found an increased relative abundance of Lactiplantibacillus plantarum, and a decrease in the relative abundance of Lactococcus lactis, Kosakonia cowanii, and Enterococcus mundtii in the treated samples. Those changes in the bacterial composition of the treated alfalfa samples, after anaerobic fermentation, helped set the stage for generating methane, Cheng said.
