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A rapid fluorescence-based bioassay and a real-time microfluidics-based biosensor for biotoxicity in anaerobic digestion
1  Department of Biology and Chemistry City University of Hong Kong


Anaerobic digestion is sensitive to a wide range of toxicants, and when they are present in inhibitory concentrations in wastewater, digester upset or failure can occur. Although many off-line monitoring of toxicants have been developed and widely used, measurement delays result in slow responses to these shocks. Such delayed feedback responses can lead to difficulties in preventing anaerobic digestion system failure. Microfluidic droplet reactors have many potential uses, from analytical to synthesis. In our project, a real-time biosensor based on microfluidic was fabricated to monitor the biotoxicity in anaerobic digestion.

Firstly, a rapid fluorescence-based assay was developed and applied for the detection of toxicants/inhibitors to anaerobic digestion metabolism. The technique revealed PCP’s toxicity to Enterococcus faecalis at a concentration of only 0.05 mg/L in 8 minutes. By extending this technique to a mixed anaerobic sludge, not only could the effect of 0.05-100 mg/L PCP be determined on anaerobic digestion metabolism within 10 minutes, but also its rate of biogas production. Using this bioassay, and based on its change in rate over time, we evaluated inhibition/stimulatory effect nickel (II), and cobalt (II), and their mixture, in just 6 hours.

Secondly, we introduced the developed bioassay into a Poly (methyl Methacrylate) (PMMA) microfluidics whose surface was modified by silica nanoparticle (SiNP) and dodecyltrichlorosilane (DTS) layers to enhance its wetting properties. Without surfactant addition, this SiNP-DTS modified chip has been used to monitor bacterial viability with a resazurin reduction bioassay. The whole process involving sequential reagents injection, and multiplexed droplet fluorescence intensity monitoring is carried out on chip. Metabolic inhibition of the anaerobe Enterococcus faecalis by 30 mg L-1 of NiCl2 was detected in 5 minutes.