Experimental Study On Treatment Of Protein Solution From Activated Sludge Hydrolysis With Membrane Technology

Protein solution from hydrolysis (PSH) is made by activated sludge hydrolysis in sewage treatment plant, and need to be concentrated further before being used. But this technology is limited because of the higher cost which is required by heating concentration. It is necessary to concentrate the PSH at lower cost.In this paper, the quality of PSH was analyzed. Based on the results of water quality analysis, the Mechanical filtration-MF (UF)-RO integrated membrane systems were adopted to treat PSH. The concentration polarization model was built and the operating parameters were determined.Microfiltration (MF) was used to remove the suspended particles, solid particles and colloids in the PSH. The membrane performance of MF was investigated and appropriate operation mode was explored. The experimental results show that this mode (production: 120 minutes; backwash 1 minute; flush 3 minutes.) could maintain the membrane performance of rejection and permeability. The product turbidity of MOF503 membrane is below 0.2 NTU and silt density index (SDI) is less than 3, which could meet the requirements of reverse osmosis (RO) feed. The normal water fluxes of the MOF503 MF membrane is 32L/ (m2.h) at pressure of 0.06MPa. When water flush is inefficient because of heavy pollution, sodium hydroxide solution could be used as cleaning reagents to remove those fouling effectively.The UPIS503 UF membrane can reject only a little protein, and the protein concentration (PC) of the permeated solution is almost equal to the PC in the feed. As a result, in the scope of this experiment, we think it is improper to concentrate the PSH by UF.The products of MF were treated by RE1812-50 and ULP1812-75 RO membrane modules. The results show that RO total protein rejection is efficient by both of them, and the RO total protein rejection is all more than 99%. When the operating pressure is 0.9MPa and the operating cycle is 120 minutes (flush 1 minute), the water fluxes of ULP1812-75 are about 162.6L/m2.min, and the RO total protein rejection is more than 99.9%. The PC of the permeated solution is less than 0.006%.The operation can be sustained, because the water fluxes recoverable rate is 86.7%. But the alkaline fluxes recovery rate is only 91.3%, so it should be improved.The concentration polarization model (CPM) was built according to the effect to the membranes caused by the operating pressure. The model explained the phenomenon of the concentration polarization during the RO process, and the level of the concentration polarization was analyzed according to the CPM during the concentration of the PSH by the RO membranes.On the basis of the above experiments, it is feasible to concentrate the PSH by the Mechanical filtration-MF -RO integrated membrane systems.