The process development of sludge to ethanol via biochemical pathway has been studied over the past few decades. Previous studies show that enzymatic hydrolysis of paper sludge has been inefficient in separate hydrolysis and fermentation due to the interference of large amount of ash in the sludges during enzymatic hydrolysis. According to research conducted in the group by doctoral student, Hui Chen, acid soluble ash like CaCO3 not only buffers the pH level (usually two to three units higher than the optimum pH) making pH adjustment with acid required for enzymatic hydrolysis, but also adsorbs cellulase with a higher affinity than cellulosic fiber. Acid-insoluble ash like clay also presents inactive binding with cellulase thereby decreasing enzyme digestibility of fiber in sludge. Therefore, in order to achieve higher efficiency in enzymatic hydrolysis with lower enzyme dosage, Chen conducted sludge fractionation prior to enzymatic hydrolysis to separate sludge into two streams: ash-rich and fiber-rich streams. This step not only lowers acid demand to adjust the pH in enzymatic hydrolysis but also generates an ash-rich stream for soil amendment.