Advanced monitoring of an anaerobic pilot plant treating high strength wastewaters

The operation of an industrial pilot scale treating wastewater from a fibre board-processing factory was monitored by an advanced system. The plant, an anaerobic hybrid UASB-UAF bioreactor (Upflow Anaerobic Sludge Blanket-Upfl ow Anaerobic Filter), was equipped with the following measurement devices: biogas flow-meter, feed and recycling flow-meters, thermometer Pt-100, biog as analyser (CH4 and CO), Hydrogen analyser and pH-meter. Other parameters such as alkalinity, Chemical Oxygen Demand (COD) and Volatile Fatty Acids ( VFA) were determined off-line. All the on-line sensor measurements were mon itored, through a PLC (Programmable Logic Controller), which indicated abou t the plant failures, including the measuring devices (giving messages or a larms to the operator) and provided the set points for the PLC. The pilot plant was started-up at an initial Organic Loading Rate (OLR) of 2 kg COD/m(3).d (Hydraulic Retention Time (HRT) 5 days and 10 kg COD/m(3)), this value increasing up to 10 kg COD/m3.d by decreasing HRT to 1 day. The behaviour of the bioreactor during start-up and steady state operation was studied. After that, an experiment was performed to analyse the response o f the bioreactor to an organic overload. From the results, different variab les were evaluated as useful control parameters. Monitoring of CO concentra tion did not permit the prediction of destabilisation of the bioreactor. Ho wever, Hz concentration is quite a sensitive variable, which must be analys ed together with other parameters such as methane composition or gas flow-r ate. Besides, alkalinity is easy to measure and provides immediate informat ion about the state of the plant, as was shown through the off-line measure ments. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved .