Wastewater biofilm initial formation process monitoring using ultrasonic reflectometry


Environmental pollution control is widely encouraged and practiced today to ensure protection and conservation of the environment. Domestic and industrial wastewater comprises one of the leading environmental pollutants. Such wastewater can be treated through biofilm process. Biofilms comprise aquatic organisms such as algae, non-living organic complex structures, and inorganic matter. They are capable of removing contaminants due to their high biodiversity, long food chain, long surviving organisms, being beneficial to the cultivation of certain microorganism and high adsorption capacity thus making biofilms processes useful technique for controlling environmental pollution. The process for biofilm formation involves various steps such as preconditioning of the adhesive surface after which the planktonic cells will get attached to the surface. Microbial multiplication then takes place followed by extracellular polymeric substances (EPS) production, biofilm maturation, and finally detachment.

Although a lot has been discovered about biofilms maturation and detachment processes, there is still limited information about the initial process for the biofilm formation, which is a crucial consideration in the wastewater biofilm process. Since the optimum combination of the bio-carriers and wastewater results to a shorter biofilm formation process, there is a great need for an efficient tool for characterizing the various biofilm characteristics such as thickness, density, and morphology.

Researchers led by professor Hongqiang Ren from the State Key Laboratory of Pollution Control and Resource Reuse at Nanjing University in China in collaboration with Professor Jianxin Li from Tianjin Polytechnic University developed ultrasonic time domain reflectometry (UTDR) for evaluating the initial biofilms formation process on bio-carriers. Their research work is published in Chemical Engineering Journal.

Briefly, the bio samples used in the experiment were obtained from practical industrial and municipal wastewaters. UTDR technique was employed for observation and evaluation of the biofilm formation process on slices through 2D and 3D wavelet analysis. The choice of UTDR was due to its ability to enable online growth monitoring of the process including biofouling caused by bacteria of the membrane surface, can provide accurate micro-level resolution and also its non-destructive nature during testing and imaging. Generally, it works on the principle of propagation of mechanical waves where interference between two media results to the reflection of waves with a given amplitude of the reflected signal.

The authors successfully distinguished the initial adherence as well as the reversible and irreversible adhesion during the initial stages of biofilms formation through the UTDR measurements. Consequently, biofilms thickness and dense degree of biofilm were also observed simultaneously during the initial development process. The accuracy of the UTDR tool was validated by comparing the obtained UTDR responses to the results obtained from the atomic force microscope (used for the offline measurements of the biofilm thickness) of which the two results correlated well.

The study is the first to evaluate the initial biofilm development on bio-carriers and will, therefore, advance the wastewater treatment processes. It brings the new approach in the biofilms development process which is very crucial in wastewater treatment such as its ability to be used for the analysis of a predefined biofilm formation area. UTDR also enables finding of the suitable bio-carriers for various kinds of wastewater in a short time hence time-saving.

Wastewater biofilm initial formation process monitoring using ultrasonic reflectometry. Advances in Engineering

About the author

Jinfeng Wang obtained his Ph.D. in Environmental Engineering (2018) from Nanjing University (Nanjing, China). Currently, he is research associate at the State Key Laboratory of Pollution Control and Resource Reuse (Nanjing, China). Dr. Jinfeng Wang research interests are focused on on-line monitoring and regulation of the biofilm formation process in wastewater treatment plants.

About the author

Hongqiang Ren obtained his Ph.D. in Fermentation Engineering (2000) from Wuxi University of Light Industry (Wuxi, China). For more than 10 years, he was full professor of Environmental Engineering at Nanjing University (Nanjing, China). His research interests are focused on biological wastewater treatment. He has published more than 200 peer-reviewed papers.


Jinfeng Wang, Hongqiang Ren, Xianhui Li, Jianxin Li, Lili Ding, Jinju Geng, Ke Xu, Hui Huang, Haidong Hu. (2018). In situ monitoring of wastewater biofilm formation process via ultrasonic time domain reflectometry (UTDR).Chemical Engineering Journal,334, 2134-2141.

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