Effects of temperature and carbon-to-nitrogen ratio on the growth rate of Candida tropicalis and Candida utilis in a furfural-based wastewater
Batch tests were used to determine the effects of temperature and carbon-to-nitrogen ratio (C/N) on the maximum specific growth rate of two species of yeast: Candida tropicalis and Candida utilis. Raw wastewater was obtained from the effluent stream of the furfural production facility at the Quaker Oats Company in Cedar Rapids, Iowa. The first set of batch tests varied temperatures from 270C to 450C; however, no growth was observed at 450C, so the effective temperature range was from 270C to 400C. During the first set of batch tests, the C/N ratio was held constant at 10:1. The second set of batch tests varied the carbon-to-nitrogen ratio between 10:1 and 1000:1 compared to the raw wastewater ratio of approximately 2575:1. During the second set of batch tests, the temperature was held constant at 350C. Samples periodically taken from the batch tests were analyzed for total suspended solids (TSS), volatile suspended solids (VSS), and chemical oxygen demand (COD). A 4th order Runge-Kutta method was employed to solve two differential equations relating substrate removal to biomass growth over time. Experimental results indicate that the maximum specific growth rate ([mu][subscript max]) for both yeast increased as the batch temperature neared 350C and 330C for C. tropicalis and C. utilis, respectively. The values of [mu][subscript max] for the aforementioned temperatures were 0.42 h−1 for C. tropicalis and 0.38 h−1 for C. utilis and [mu][subscript max] decreased as the batch temperatures deviated from the aforementioned optimum temperatures. The results from varying the C/N ratio indicate that [mu][subscript max] is significantly increased for C/N ratios less than 25:1. Between the ranges of 25:1 and 10:1, [mu][subscript max] increases from 0.18 to 0.41 h−1 and from 0.20 to 0.42 h−1 for C. tropicalis and C. utilis, respectively. The [mu][subscript max] for C. tropicalis and C. utilis is sensitive to both temperature and C/N ratio and optimizing these two operating parameters would entail further laboratory research or a pilot study.