Control and monitoring of a full-scale biogas plant treating the highly polluted wastewater from the cleaning of tank cars transporting food and fodder

In 2017 a 1200 m
³
biogas plant was build and commissioned treating highly polluted wastewater from the cleaning of tank cars transporting food and fodder in Fahrbinde, Germany. The biogas plant is single stage, mesophilic, intermittently mixed and automatically operated with remote control. Due to the softened water used in the cleaning of the tank cars, the cleaning wastewater is low in buffer capacity. A physicochemical model was developed for controlling the digestion process of this wastewater. The model shows that 2.4 kgNaHCO
₃
has to be added in order to maintain and control the digester pH in the optimal range of pH = 7.2 and the alkalinity in the range of = 3.2 gCaCO
₃
/L. The experimental data is well in accordance with the physicochemical calculations. The full-scale biogas plant is working stable. Volatile organic acid (VOA)/alkalinity ratio is less than 0.3. The VOA and alkalinity are measured with an analyser using Nordmann tritration method. The analyzer is verified with physicochemical calculations and measurements with synthetic digestate and digestate that is spiked with acetic acid and NaHCO3. The results confirmed that the analyzer had a good performance measuring VOA and alkalinity. The operators of the biogas plant are trained to use the analyzer in order to control and monitor the digestion process of the biogas plant.