This paper describes a validation procedure applied for an on-line titrimetric analyzer (AnaSense®-Anaerobic Control Analyzer) prototype designed to detect of volatile fatty acids (VFA) and alkalinity (bicarbonate). The AnaSense® analyzer was recently developed under the framework of the TELEMAC European Project. A pilot-scale evaluation of the analyzer was carried out in an anaerobic wastewater treatment plant, in a hybrid Upflow Sludge Bed Filter (USBF) reactor with an overall volume of 1.15 m3. The sensor uses two methods, both based on two-point titrimetric analyses, for determining VFA and alkalinity concentration. AnaSense® performed on-line monitoring of VFA (13–4,900 mg · L−1) and bicarbonate (2.5–49.5 mEq · L−1), and demonstrated sufficient accuracy for both VFA and bicarbonate detection. Intermediate Alkalinity/Total Alkalinity (IA/TA) and Intermediate Alkalinity/Partial Alkalinity (IA/PA) ratios were also evaluated to test the suitability of the sensor for anaerobic digestion process control.