Monitoring the inhibitory effect of NaCl on anaerobic wastewater treatment processes by the Rantox biosensor

The Rantox biosensor, designed for anaerobic process control and based on the response of acetoclastic methanogenic microorganisms to periodic organic overloads, was tested under variable operating conditions at laboratory scale. The aim was to detect the presence of an incoming inorganic toxic compound before any effect was observed in a digester under control. The experimental set-up, including the biosensor and the digester, was connected to an automated control system developed under a Labview(R) environment (the Ranter Virtual Instrument), and various operating conditions were tested in order to interface the plant with the software properly. Anaerobic sludges with different activities were used as active biomass in both reactors, and inhibition was simulated by different NaCl dosing procedures. The results confirmed the sensitivity and rapid response of the biosensor to unexpected inhibitors in the feed, and demonstrated the suitability of this instrument for continuous or semicontinuous monitoring of the influent to a digester in order to prevent intoxication of its biomass. Furthermore, inhibition due to NaCl was found to be independent of the salt addition procedure. A concentration of 15 g NaCl l(react)(-1) caused a decrease in peak biogas production ranging between 26.6% and 43.1%, depending on the different biomass tested.