Thermal Alkali Hydrolysis Pretreatment Of Dewatered Sludge For Protein Extraction At Low Temperature

Protein recovery from wasted sludge has become hot research. This work provided a new approach with protein extraction for dewatered sludge by the thermal alkali hydrolysis (TAH) at low temperatures (<100 degrees C). Effects of alkali addition, temperature, and time on extraction effect were investigated. The protein extraction rate of 33.07% and concentration of 4,702.37 mg L-1 were achieved under the optimal conditions (alkali amount at 30 g kg(-1) dewatered sludge, at 80 degrees C and 5 h). Mechanism for protein extraction was investigated via X-ray photoelectron spectroscopy (XPS), three-dimensional excitation emission (3D-EEM), and Fourier-transform infrared spectroscopy (FTIR). The results of XPS indicated that the protein extraction from flocculent sludge to liquid phase might be related to the significant protein-N conversion that occurred at the optimal treatment conditions which gave the highest dominant protein. 3D-EEM showed the tryptophan-like protein predominance, which has the potential to be feed additives. FTIR showed that the protein structure has undergone first breaking the chain and then oxidizing. Based on Pearson's correlation and principal component analysis (PCA), the protein extraction was correlated with the release of organic compounds, suggesting that proteins in the flocculent sludge entered the liquid phase with treatments. The alkali amount and time were the key factors of protein extraction. The concentration of protein obtained from sludge treated with thermal alkali was four times that of sludge treated by pure alkali.