Conversion Of Paper Sludge To Ethanol By Separate Hydrolysis And Fermentation

The purpose of the present work was to evaluate the possibility of converting paper sludge to ethanol fuels by separate hydrolysis and fermentation in our country. The approach used was based on the enzymatic conversion of major sludge components (glucan and xylan) by commercial enzymes mixtures, and sequential fermentation of the resulting sugars to ethanol using the fusant or Saccharomyces cerevisiae as the ethanologenic strain. The optimal conditions for enzymatic hydrolysis and ethanol fermentation were investigated, and the xylose utilization by the fusant was studied.The chemical components of paper sludges from three local pulp and paper mills representing two pulping processes (sulfite and deinking) were analyzed. The results indicate that the paper sludges examined exhibited a wide range of ash, glucan and xylan contents mainly determined by the pulping process used. Deinking sludges are low in carbohydrate (34%) and high in ash contents (44%). Sulfite sludge (PS3) has low ash (13%) and high carbohydrate compositions (71%).Spezyme CP supplemented with Novozyme 188 was used for enzymatic hydrolysis of the paper sludges. The results showed that PS2 and PS3 from the sulfite mill were highly susceptible to enzymatic hydrolysis. Under the same conditions, the degree of saccharification obtained from sulfite paper sludge(PS2,PS3) is 57 percent higher than that of deinking sludges(PS1).The optimal conditions for enzymatic hydrolysis of paper sludge (PS) are pH5, 40℃, cellulase on a dosage of 15 FPU/g cellulose plus 30U/g cellulose Novozyms 188 with respect to degree of saccharification(DS). Under the above conditions, PS2 on 2% substrate consistency was incubated with the filter-sterilised enzyme solution for 72 h without any pretreatment, a degree of saccharification of 99.65% was obtained. While the initial substrate concentration was increased to 6.0% (w/v) and the hydrolysis time was extended to 144 h, the resulting sugars raised 2.7 times, and final glucose concentration of 48.58g/L and xylose concentration of 10.74g/L were obtained, but the degree of saccharification decreased to 89.92%.Fed-batch hydrolysis can improve the degree of saccharification by 7.5%, reduce the amount of enzyme loading from 25FPU/g to 15FPU/g , and shorten the hydrolysis time from 144h to 120h compared to those of batch hydrolysis under the substrate concentration of 6.0%.Hydrolysate obtained from PS3 on 6% consistency can be fermented directly, with no detoxification and nutrient supplementation, to produce ethanol using the fusant SHY07-1/ Saccharomyces cerevisiae SHY08-3. The optimal conditions for fermentation of paper sludge (PS)-hydrolysate by the fusant SHY07-1/ Saccharomyces cerevisiae SHY08-3 are much the same: pH 5.5 and 35°C with respect to overall fermentation yield and rate. The maximal ethanol concentration (34.72g/L) obtained by the fusant SHY07-1 was somewhat higher than Saccharomyces cerevisiae SHY08-3(29.29 g/L) after 72h cultivation. While the ratio of the fusant and Saccharomyces cerevisiae for inoculum is 2:1, fermentation of paper sludge hydrolysate, gave maximum ethanol (33.47 g/L) with yield (0.45 g/g) and productivity (0.46 g/L/h) after 72 h.