Advancing Water Treatment: The Need for Developing a Biosensor for Wastewater Monitoring
In 2021, my team and I began working with biosensors for the analysis of wastewater. A key data point that guided our research direction was the staggering fact that water scarcity affects approximately 71% of the global population at various times throughout the year. This pressing issue underscored the importance of our work and inspired us to develop innovative solutions for wastewater treatment and reuse.
As the need to conserve and reuse water continues to grow, wastewater treatment plants have become essential in purifying wastewater for reuse. A key aspect of these plants’ efficiency is measured through biochemical oxygen demand (BOD) assessments, which indicate the level of biodegradable organic pollutants in the water. Accurate and timely BOD monitoring is crucial for ensuring the effective operation of these treatment plants. However, the traditional BOD measurement method, which requires a five-day incubation period, poses significant challenges. The delay in obtaining BOD results can hinder the ability to quickly address and adjust treatment processes, potentially impacting the overall efficiency and effectiveness of wastewater purification. As industries strive for more efficient solutions, the development and implementation of faster, more reliable BOD monitoring technologies become increasingly critical.
Recognizing this need, we decided to focus our research efforts on developing a BOD biosensor. Our goal is to create a tool that not only enhances wastewater analysis but also contributes significantly to tackling global water scarcity challenges.
Microbial Fuel Cell-based Biosensors: An Innovative Solution
In the last two decades, Microbial Fuel Cell (MFC)-based biosensors have emerged as a promising alternative for real-time BOD monitoring. These biosensors utilize electroactive microorganisms that naturally form a biofilm on the anode and convert the chemical energy present in organic pollutants into electrical energy. Electroactive bacteria can be found just about everywhere, from soil and sediment to sludge, marine environments, and even within the guts of animals. For our study, we sourced these remarkable microbes from a lake right here on the University of Surrey campus! Electroactive bacteria generate more electricity as the pollutant levels in the wastewater increase. Consequently, the electrical current is proportional to the BOD concentration in the wastewater. One of the fascinating aspects of MFC-based biosensors is their ability to function without needing an external power supply. Additionally, there is no need for a transducer to convert signals into electrical output, as the output itself is already in the form of electricity.
Addressing the Research Gap: Understanding Biofilm Dynamics in MFC Biosensors for Real-World Applications
The magic behind these MFC biosensors lies in the biofilm of electroactive bacteria that acts as the main receptor. A mixed-culture electroactive biofilm is highly effective at oxidizing a wide range of pollutants but comes with its own set of challenges. MFC biosensors are particularly sensitive to environmental conditions. Factors such as temperature, pH levels, and the presence of various substances in the wastewater can significantly impact their stability.
Despite numerous advancements in recent years aimed at enhancing the performance of biosensors in terms of sensitivity, dynamic range, and response time, challenges remain. These advancements have focused on optimizing the geometry and materials of the biosensor, as well as the genetic manipulation of the bacteria at the anode. However, there has been limited understanding of how a complex mixed-culture electroactive biofilm, developed in the lab from environmental sources, responds to sudden changes in substrate. This is especially true when the substrate is real, untreated wastewater introduced directly into the MFC biosensor. Considering the high number of variables affecting the current response of the biosensor, understanding these microbial dynamics is challenging and requires novel techniques such as metataxonomics and metagenomics. These techniques help elucidate the intricate interactions of a diverse biofilm with a complex substrate, which is crucial for the practical application of MFC biosensors in real-world wastewater treatment scenarios.
Exploring the Impact of Wastewater Properties on MFC Biosensors
Our goal in this study was to see if (and why) lab-developed biosensors could maintain their performance and accuracy when used in real-world conditions, ultimately offering a practical solution for wastewater monitoring and other applications. We explored how MFC biosensors with lab-cultivated electroactive biofilms respond differently to sterile synthetic urban wastewater (SWW) and untreated real urban wastewater (RWW). We focused on factors driving changes in the biofilm’s microbial composition and how these changes influence the biosensor’s current output, robustness, and adaptability across various feedstocks.
Study Results: Robustness and Adaptability
Our study has demonstrated that MFC-based biosensors can be effectively recalibrated for different wastewater types, maintaining consistent sensitivity and detection limits. The study highlights that once recalibrated, MFC-based biosensors can maintain consistent sensitivity and detection limits across various wastewater types, including sterile synthetic and untreated real urban wastewater. This finding is significant as it suggests the potential to develop a standard biofilm for MFC biosensors that can be adapted to different wastewaters based on specific user needs.
A notable observation is that wastewater pre-treatment (e.g. sterilization, O2 removal, conductivity adjustments) is not necessary before introducing it into the biosensor. While the presence of native aerobic microorganisms in the wastewater can compete for substrate with the electroactive biofilm, reducing the current production, the signal of the biosensor still correlates linearly with the BOD of the wastewater. Moreover, native bacteria found in urban wastewater do not integrate into the electroactive biofilm in significant amounts, staying below 1% in relative abundance. This indicates that the biofilm is fairly robust regarding the main bacterial taxa that compose it. Metagenomic and taxonomic analyses reveal that the variations detected in the biofilm composition are mainly responses to the different chemical and microbiological compositions of the real urban wastewater, compared to the sterile synthetic one. Although bacterial adaptation to new substrates can cause fluctuations in current output, these variations are comparable to those seen in the standard BOD test, underscoring the biosensor’s robustness and ease of application across diverse substrates.
Conclusions and Future Directions
In conclusion, MFC-based biosensors represent an innovative technology in the field of wastewater treatment. Their ability to provide real-time, reliable BOD measurements without the need for extensive pre-treatment makes them an invaluable tool for enhancing the efficiency and sustainability of wastewater treatment plants.
Future research will focus on testing the biosensor in continuous flow operations, where wastewater flows continuously through the biosensor, allowing for ongoing monitoring of the current response. Additionally, we will test the biosensor with various real wastewater types to account for seasonal variations in urban wastewater composition. Last but not least, further studies are needed to correlate electrochemical behaviour with transcriptomic and metabolomic profiles of the mixed-culture electroactive biofilm, enhancing the understanding and optimization of biosensor performance.