Efficient dewatering and heavy-metal removal in municipal sewage using oxidants

Significance 

Municipal sewage sludge has become an environmental problem globally. With the rapidly growing urban population and continued construction of large-scale sewerage facilities, the development of effective sludge treatment, disposal, and management strategies are highly desirable. Municipal sewage sludge, for instance, has been widely used in agriculture to increase soil fertility. However, the environmental issues associated with sludge disposal are complicated, considering that sludge contains heavy metals, toxic organics substances, and pathogens that can significantly affect the environment, plants, and human health at large. Moreover, lack of effective sludge treatment policies and high operating costs have remained the main factors hindering the treatment of municipal sewage sludge. Despite the extensive research on several oxidation processes for efficient dewatering sludge, i.e., the use of Fenton’s reagent, peracetic acid, little has been reported for removal of heavy metals from sludge about the use of oxidants including CaO2.

To this note, a team of researchers at Hunan Agricultural University: Jing Yuan (Ph.D. Student), Weining Zhang (M.S. Student), Professor Zhihua Xiao, Ms. Xihong Zhou, and Professor Qingru Zeng investigated the feasibility of three oxidants, namely, Fenton’s reagent, CaO2 and potassium sulfate in treating sludge. Their main objective was to evaluate the performances of the three oxidants in sludge dewatering and heavy metal removal. Their research work is currently published in the Chemical Engineering Journal.

In their approach, the research team started their experiment work by treating the municipal sewage sludge with the three oxidants. Next, heavy metals in the supernatant were separated via the addition of CaO. CaO was particularly preferred because it is a simple and cost-effective process for recycling the treated sludge. Lastly, the authors presented an in-depth insight on the contents of the heavy metals and the changes in the supernatant water quality before and after CaO treatment.

The authors observed that all of the three oxidants could effectively remove the moisture content of the sludge besides significantly reducing the SRF value used in the characterization of the sludge filtration performance. Treatment with Fenton’s reagent and potassium sulfate proved more effective for removing Pb, Zn, Cu, and Cd heavy metals, especially Cd. On the other hand, the metal removal performance of CaO2 was not satisfactory. Nonetheless, the addition of CaO to sludge treatment allowed the effective separation of metals in the supernatant. Consequently, the oxidants exhibited excellent dewatering performance for municipal sewage sludge. The water content was reduced from 99.08% to 66.5% for CaO2,74.7% for potassium sulfate, and 76.1% for Fenton’s reagent. Furthermore, the authors reported that the treated sludge was easy to transport and safe for agricultural use as per the set standards.

In summary, the study presented the use of oxidants for efficient dewatering and removal of heavy metals in municipal sewage sludge. Results showed that Fenton’s regent and potassium sulfate oxidants are more suitable for dewatering and removal of Pb, Zn, Cu, and Cd. Besides, the addition of CaO to the supernatant allowed easy separation of metals in the supernatant. Most importantly, the treated sludge was safe for agricultural use. In a statement to Advances in Engineering, the team leader, Professor Qingru Zeng, stated that the newly presented method is viable for efficient and cost-effective municipal sewage sludge treatment for agricultural application.

Efficient dewatering and heavy-metal removal in municipal sewage using oxidants - Advances in Engineering
Fig.1 Process flow diagram

About the author

Dr. Qingru Zeng currently holds a professorship position at Hunan Agricultural University, Changsha, Hunan, China. He received Ph.D. degree from Research Center for Eco-Environmental Science, Chinese Academy of Science in 2006. Now, he is the deputy director of the Hunan Provincial Key Laboratory of Rural Ecosystem Health in Dongting Lake District.

His research interests are in the areas of heavy metal pollution remediation. He hopes to elucidate chemical speciation variation of heavy metal in liquid and solid phase, and use biological and chemical process to contamination remediation of water and soil. He has over 200 publications across journals, conference contributions. He also holds over 20 patents. Some of his research results have been actually applied and popularized.

College of Resources and Environment, Hunan Agricultural University, Changsha 410128, China.

Email: [email protected].

About the author

Ms. Jing Yuan is currently studying for a Ph.D. in South China University of Technology. She received a B.S. degree from Hunan Agricultural University in 2016 and a M.S. degree from Hunan Agricultural University in 2019. Her current research direction is enhanced biological phosphorus removal. Her main research results are about phytoremediation, removal of heavy metals in seed meal.

E-mail: [email protected].

About the author

Mr. Weining Zhang is an engineer of Beijing Enterprises Water Group. He received a B.S. degree from Hunan Agricultural University in 2014 and a M.S. degree from Hunan Agricultural University in 2017. His research interests are in treatment of municipal sewage sludge, especially for removal or stabilization of heavy metals from these solid wastes.

E-mail:[email protected].

About the author

Dr. Zhihua Xiao is a professor in College of Resources and Environment, Hunan Agricultural University. He received a B.S. degree in China Agricultural University in 2010 and a Ph.D. degree in Hunan University in 2016. His primary scientific and applied research interests are focused on treatment of municipal sewage sludge, livestock and poultry manure, crop straw and forestry waste, especially for removal or stabilization of heavy metals from these solid wastes; meanwhile, the remediation of soil is another research interest.

E-mail: [email protected].

About the author

Ms. Xihong Zhou is a Senior Laboratory Technician in College of Resources and Environment, Hunan Agricultural University. She received a B.S. degree from Central South University in 2002 and a M.S. degree from Hunan Agricultural University in 2006. Her scientific research interests are focused on analysis of trace elements in environment. She has over 60 publications across journals, conference contributions.

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Reference

Yuan, J., Zhang, W., Xiao, Z., Zhou, X., & Zeng, Q. (2020). Efficient dewatering and heavy-metal removal in municipal sewage using oxidants. Chemical Engineering Journal, 388, 124298.

Go To Chemical Engineering Journal

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