Separation Of Protein From Excess Sludge And Analysis Of The Protein Properties

To study the process of protein extraction from excess sludge, the characteristics among different protein extraction and separation methods, the properties of isolated proteins, and protein resources methods, the following work was done based on the excess sludge from Jizhuangzi wastewater plant.The protein dissolution mechanism from sludge was researched. The dynamic model, with thirteen parameters and four factors including sludge concentration, temperature, acid or alkali concentration and operating time, was built by using the principle of microbial cell wall hydrolysis, sludge adsorption / desorption mechanism and the theory of protein hydrolysis, which took the characteristics of the main bacteria structural, sludge particle and protein structure into consideration. A certain amount of the protein concentration data was collected by experiments. The parameters of kinetic model were obtained through nonlinear optimization techniques and could be used to investigate the effects of various factors on the protein concentration. The results confirmed the dynamic model and concluded that appropriate increase of sludge concentration, temperature and concentration of acid or alkali could facilitate the process of protein extraction.The protein extraction method in sludge, protein crystallization process and protein products nature analysis were carried out. Inorganic sludge dissolution by hydrochloric acid, protein extraction process characteristics and phenomena using hydrochloric acid or sodium hydroxide, and protein products analysis including ultraviolet (UV) spectroscopy, protein content analysis, fourier transform infrared (FTIR) analysis, and X-ray fluorescence analysis were investigated. The results showed that: hydrochloric acid pretreatment could reduce the inorganic content of the sludge, and it could help improve the organic content. Alkali method possessed many problems such as Maillard reaction, the difficulty of solid-liquid separation and poor quality of extract. Hydrochloric acid extraction method under high temperature could not only promote the protein extraction, but also benefit the solid-liquid separation, when the extract viscosity was small, and the color could be better. After precipitation of metal ions from the extracted hydrochloric acid at high-temperature, two times volume of ethanol was added into solution at isoelectric point. The protein yield and protein content were 78.5% and 103.8% respectively, while the five heavy metals limited in "feed hygiene standards" (GB 13078-2001) was not detected in the products. Proteins products need to be dried under 40℃, otherwise protein would be easily denatured and its solubility would be poor. Fourier transform infrared (FTIR) data proved that the obtained protein was mainly ?- helices whether using alkaline or acid extraction method.The sludge protein shows the potential possibility to be used as feed by studying the mechanism of sludge protein extraction, protein crystallization methods and protein products properties. The work could provide kinetic model guidance for the protein extraction from sludge by hydrochloric acid or sodium hydroxide under heating conditions and could have certain reference value in proteins separation and purification, which is also conducive to promoting studies on the protein resource from the excess sludge in China.