Optimization of protein recovery from sewage sludge via controlled and energy-saving ultrasonic-alkali hydrolysis

• Published in: The Science of the total environment 2023-04, Vol.870, p.162004-162004, Article 162004
• Main Authors: Yan, Yixin, Zhang, Yajing, Wan, Junfeng, Gao, Jianlei, Liu, Fan
• Format: Article
• Language: English
• Subjects: Alkalies; Energy efficient; Foaming agent; Hydrolysis; Nitrogen; Proteins; Semi-batch operation; Sewage; Sludge protein; Ultrasonic-alkaline method; Ultrasonics; Waste Disposal, Fluid - methods
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2023.162004

The abundant protein in excess sludge can be recovered to prepare high value-added products. However, this sustainable treatment method still has large challenges, such as high energy consumption. In this work, the classical batch operation (BO) and semi-batch operation (SBO) modes were adopted and compared for ultrasonic-alkali hydrolysis. The results showed that the reaction time of SBO significantly decreased to half of that of BO with the same efficiency (ca. 70 %), indicating that SBO was much more energy-efficient. Moreover, analysis of the nitrogen solubility index and trichloroacetic acid-soluble nitrogen index demonstrated that the further proteolysis of protein under SBO was limited. Furthermore, the first-order reaction model fitted the hydrolysis data well (R2 ≥ 0.91) for both modes, in which the rate constant of SBO (k = 0.44 min−1) was 2.3 times that of BO. Finally, the properties of both products met the standards of foaming extinguishers. [Display omitted] •Sludge protein obtained via ultrasonic alkaline (UA) hydrolysis was optimized.•Semi batch operation (SBO) UA hydrolysis was well modeled with a high-rate constant.•SBO mode was much more energy efficient than batch operation (BO) mode.•The production of small molecular proteins was controlled in SBO mode.•The products of protein extracted from excess sludge meet foaming standards.