Cofermentation of whey permate and starchy waste for ethanol and biomass production

ABSTRACT

Whey permeate was supplemented as a liquid portion of potato starchy waste which was enzymatically hydrolyzed by a fungal alpha-amylase/ glucoamylase filtrate culture of Aspergillus niger grown by solid state fermentation to increase the ethanol content and make the process more economically viable. Glucose-maltose lactose mash was fermented using a mixed yeast inoculum of Kluyveromyces fragilis and Schizosaccharomyces pombe. Simultaneous and staggered inoculation procedures were studied. The staggered inoculation process had an advantage for sugars utilization, ethanol and biomass production. A staggered inoculation procedure was accomplished using K. fragilis followed by S. pombe after 18 hr in an attempt to optimize the culture conditions. Fermentation time up to 60 hr, inoculum size of both two strains [0.5-5.0% v/v], initial pH value [30 to 6.5], temperature [20-40C], urea amount [0.5 to 5.0 g/l] and phosphorus source and amount [potassium dihydrogen phosphate, calcium phosphate and orthophosphoric acid] were investigated. The maximum alcohol riches in fermentation mash [8.6% v/v] and biomass [16.5 g dry cells with 37.2% crude protein/l] were achieved after 36 hr fermentation at 30C using the staggered inoculation procedure. The mash mixture used was composed of 40% whey ultra filtrate and 60% starch hydrolysate containing 18.78 total sugars [58.86% glucose, 32.85% maltose and 8.47% lactose] with an initial pH of 6.0 and fortified with urea, 0.2%, potassium dihydrogen phosphate 100 mg/l and initial inoculum size 4% [v/v] K. fragilis and 1% [v/v] S. pombe added after 18 hr of the beginning of the fermentation. Under the above fermentation condition, the total uptake of sugars was 98.4%