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

The Rantox biosensor, designed for anaerobic process control and based on t he response of acetoclastic methanogenic microorganisms to periodic organic overloads, was tested under variable operating conditions at laboratory sc ale. The aim was to detect the presence of an incoming inorganic toxic comp ound before any effect was observed in a digester under control. The experi mental set-up, including the biosensor and the digester, was connected to a n automated control system developed under a Labview(R) environment (the Ra nter Virtual Instrument), and various operating conditions were tested in o rder to interface the plant with the software properly. Anaerobic sludges w ith different activities were used as active biomass in both reactors, and inhibition was simulated by different NaCl dosing procedures. The results c onfirmed 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 du e to NaCl was found to be independent of the salt addition procedure. A con centration of 15 g NaCl l(react)(-1) caused a decrease in peak biogas produ ction ranging between 26.6% and 43.1%, depending on the different biomass t ested.