Influence of carbon-to-nitrogen ratio on the mixed-acid fermentation of wastewater sludge and pretreated bagasse

• Published in: Bioresource technology 2012-05, Vol.112, p.91-97
• Main Authors: Rughoonundun, Hema, Mohee, Romeela, Holtzapple, Mark T.
• Format: Article
• Language: English
• Subjects: acetic acid; Bagasse; Bioreactors; Butyric acid; carbon; Carbon - analysis; Carbon-to-nitrogen ratio; Carboxylic acid; Carboxylic acids; Carboxylic Acids - metabolism; Cellulose - chemistry; Drying; Fermentation; Methane; methane production; Mixed-acid fermentation; nitrogen; Nitrogen - analysis; protein degradation; Sewage - chemistry; Sludge; valeric acid; Waste Disposal, Fluid; Waste water; wastewater; Wastewater sludge
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2012.02.081

► Co-digestion of wastewater sludge and bagasse enhances mixed acids yield. ► Highest conversion occurred at a C/N ratio of 30, and the highest yield occurred at 13.2–25g C/g N. ► Yield was mostly affected at the extreme C/N ratios. ► Yield was on average about 0.42g Aceq/g VS fed for mixtures S30 to S100. ► Protein from sludge enhance i-butyric, valeric and i-valeric acids production. In mixed-acid fermentation, carbon and nitrogen are critical nutrients for cell synthesis, growth, and metabolism. To study the effect of C/N ratio on the yield of carboxylic acids, wastewater sludge was co-digested with pretreated bagasse; the amount of sludge was varied from 0% to 100% (dry weight basis). Fermentation was performed at 55°C at a solids concentration of 50g dry solids/L, and Iodoform was used to inhibit methane formation. It was observed that C/N ratio significantly affects yield, especially at extreme ratios. The highest carboxylic acid yield (0.36g acids/g VS fed) was obtained for C/N ratios ranging from 13 to 25g C/g N. C/N ratio also affected the composition profile of carboxylic acids. In all mixtures, acetic acid was the major fraction, followed by butyric acid. However, i-butyric, valeric acid, and i-valeric acid increased with increasing sludge content, which likely resulted from protein degradation.