Sugarcane Molasses: A Cheap Carbon Source for Calcite Production in Different Class of Soils using Stimulation of Indigenous Urease-producing Bacteria

Abstract

In this research, we investigated the abilities of three different concentration of sugarcane molasses as a carbon source to stimulate indigenous bacterial growth in different classes of soil, namely poorly graded sand (SP), silty sand (SM), and clayey sand (SC) (according to the Unified classification system). A total of 7, 10, and 15 days after the treatment, direct shear tests were performed on the untreated and treated samples. The calcite content on all direct shear samples was determined to further correlate it with the strength gains in the treated samples. The scanning electron microscopy (SEM) images, EDX analysis, and X-ray diffraction (XRD) patterns were taken before and after treatment for all samples to analyze the microbial-induced calcite precipitation (MICP) process. The SP soil samples showed the highest strength gains and also highest calcite content as compared with other two soil type. The peak cohesion intercept for SP-treated samples increased by 2.7–5.5 times as compared to the untreated samples for molasses concentration of 1–3?g/L, respectively. The treated samples became more dilative with the increase in molasses concentration. The sample with highest molasses concentration showed stiffer behavior in shear than the samples with lower concentration.     

Effect of simple and complex carbon sources,low temperature culture and complex carbon feeding policies on poly-3-hydroxybutyric acid (PHB) content and molecular weight (Mw) from Azotobacter chroococcum 6B

The molecular weight (M _w) of poly-3-hydroxybutyrate (PHB), produced by shake-flask culture of Azotobacter chroococcum showed little variation with increasing glucose concentration as carbon source (being in the range of 400–500 kDa), while M _w increased from 300–400 to 640 kDa when grown with increasing concentration of sugar cane molasses. Molecular weight increased nearly 30% from 48 to 72 h culture time when 5% molasses as carbon source was used, while with glucose the highest M _w was reached at 48 h. Under fermentor cultivation A. chroococcum produced PHB with a relatively high M _w of 1590 kDa at 53 h culture time when grown in modified Burk's medium with glucose as carbon source at an initial C/N ratio (molar basis) of 69 under fermentor cultivation. A batch glucose-grown ammonium-limited fermentor culture was repeatedly fed with sugar cane molasses (initial C/N ratio 69) and it was observed that PHB content curve decreased at a slower rate than in the fed-batch culture in which glucose and sucrose were not consumed in the culture medium after the feed.