Enhancing enzyme activity via low-intensity ultrasound for protein extraction from excess sludge

Review on ultrasonic technology enhanced biological treatment of wastewater

As a clean, sustainable and efficient technology of wastewater treatment, ultrasonic irradiation has gained special attention in wastewater treatment. It has been widely studied for degrading pollutants and enhancing biological treatment processes for wastewater treatment. This review focuses on the mechanism and updated information of ultrasonic technology to enhance biological treatment of wastewater. The mechanism involved in improving biological treatment by ultrasonic includes: 1) degradation of refractory substances and release carbon from sludges, 2) promotion of mass transfer and change of cell permeability, 3) facilitation of enzyme-catalyzed reactions and 4) influence of cell growth. Based on the above discussion, the effects of ultrasound on the enhancement of wastewater biological treatment processes can be categorized into indirect and direct ways. The indirect effect of ultrasonic waves in enhancing biological treatment is mainly achieved through the use of high-intensity ultrasonic waves. These waves can be used as a pretreatment to improve biodegradability of the wastewater. Moreover, the ultrasonic-treated sludge or its supernatant can serve as a carbon source for the treatment system. Low-intensity ultrasound is often employed to directly enhance the biological treatment of wastewater. The propose of this process is to improve activated sludge, domesticate polyphosphate-accumulating organisms, ammonia-oxidizing bacteria, and anammox bacteria, and achieve speedy start-up of partial nitrification and anammox. It has shown remarkable effects on maintaining stable operation, tolerating adverse conditions (i.e., low temperature, low C/N, etc.), resisting shock load (i.e., organic load, toxic load, etc.), and collapse recovery. These results indicate a promising future for biological wastewater treatment. Furthermore, virous ultrasonic reactor designs were presented, and their potential for engineering application was discussed.

High-Temperature Ash Melting and Fluidity Behavior upon the Cocombustion of Sewage Sludge and Coal

Wastewater treatment produces a large amount of sludge, where the minimizing of the disposed sludge is essential for environmental protection. The co-combustion of sludge with coal is a preferable method for sewage sludge disposal from the economic and environmental perspective. The co-combustion of sludge has been widely used in the industry with the advantages of large processing capacity. The melting characteristics of ash are an important criterion for the selection of the co-combustion methods and furnace types. In this study, two types of sludge and four types of coal with different ash melting points were selected, where the ash melting behavior upon co-combustion is investigated by experimental and thermodynamical approaches. Especially, the slag fluidity upon co-combustion is explored via a modified inclined plane method. It has been found that the presence of SiO2 and CaO in sludge substantially enhances its fusion temperature owing to the high content of CaO, while SiO2 acts as a solvent, facilitating the co-melting of other oxides and raising the sludge fusion temperature. Fe2O3 exhibits a specific mass fraction within the range of 10-20%. Furthermore, the presence of CaO and SiO2 prohibits the flow ability of the slag at high temperatures, and Fe2O3 promotes the flow ability for sludge at high temperatures. With increasing base/acid ratio, the sludge flow velocity increases remarkably and peaks at 1.6. The interaction between Fe-Ca and Si-AI significantly affects the fluidity significantly. The findings are expected to optimize the condition of co-combustion and desirable furnace design for the incineration of sludge.

Compound mutation by ultraviolet and diethyl sulfate of protease producing thermophilic bacteria to hydrolyze excess sludge

Excess sludge (ES), a resource-rich organic waste, can be solubilized by thermophilic enzymes to extract proteins for sludge reduction and resources recovery. To solve the problems of low hydrolysis effect of ES and low enzyme producing ability of wild thermophilic bacteria, ultraviolet and diethyl sulfate (UV-DES) were adopted to mutate thermophilic bacteria in this study. Mutation sites were detected and annotated by whole genome sequencing analysis. The results showed that UV-DES mutagenesis could effectively improve enzyme-producing capacity of thermophilic bacteria and promote the hydrolysis of ES. The protease activity of the mutant strain KT16 was 46.7 % higher than that of the original strain DC8. The protein extraction rate with enzyme produced by KT16 reached 83.3 %. The total content of proteins recycled through KT16 enzyme solution was 3539.6 mg·L-1, 18.4 % higher than that of DC8. This work provided a theoretical idea and technical guidance for the protein recovery from ES.

Sono-activation of food enzymes: From principles to practice

Over the last decade, sono-activation of enzymes as an emerging research area has received considerable attention from food researchers. This kind of relatively new application of ultrasound has demonstrated promising potential in facilitating the modern food industry by broadening the application of various food enzymes, improving relevant industrial unit operation and productivity, as well as increasing the yield of target products. This review aims to provide insight into the fundamental principles and possible industrialization strategies of the sono-activation of food enzymes to facilitate its commercialization. This review first provides an overview of ultrasound application in the activation of food protease, carbohydrase, and lipase. Then, the recent development on ultrasound activation of food enzymes is discussed on aspects including mechanisms, influencing factors, modification effects, and its applications in real food systems for free and immobilized enzymes. Despite the far fewer studies on sono-activation of immobilized enzymes compared with those on free enzymes, we endeavored to summarize the relevant aspects in three stages: ultrasound pretreatment of free enzyme/carrier, assistance in immobilization process, and modification of the already immobilized enzyme. Lastly, challenges for the scalability of ultrasound in these target areas are discussed and future research prospects are proposed.