ON-LINE MONITORING FOR PROCESS FEEDBACK CONTROL IN WASTEWATER PLANTS

This is a preliminary investigation of a method for timely monitoring of Biochemical Oxygen Demand (BOD) in wastewater. This investigation is part of an automation project to develop online BOD monitoring for process control in wastewater treatment plants to prevent process upsets due to shock loadings or toxic events. Tests were made on the Siepmann und Teutscher GmbH (STIP) BIOX-1010 (presently a part of ISCO Inc.) which uses a bioreactor containing a previously established large population of bacteria from the wastewater to measure soluble BOD in three minutes, designated BOD-M3. Thus, although the quantity that it directly measures is soluble BOD, the calibration measurements allow the operators to establish a conversion factor kept in its computer control, so that an estimate of BOD5 is displayed. This instrument has been used in a number of applications in Europe, but has not been applied in the United States to process control. Comparisons were made to the results of the standard laboratory BOD5 procedure on primary effluent at the Terminal Island Treatment Plant (TITP) of the Bureau of Sanitation of the City of Los Angeles in 1994-95. Agreement between the two types of tests was excellent but the testing had to be halted after a few weeks because of biogrowth in the instrument and a leak. Similar results and difficulties occurred during a similar test of the Nissin Electric BOD-2000 (Iranpour, et al., 1997), an instrument that estimates BOD5 from soluble BOD measurements made during a 30 minute measurement cycle using a yeast impregnated biomembrane. Thus, the chief issues in using such instruments are ambient temperature of the instrument, wastewater pH and salinity, apparatus needed to provide samples to the instrument, durability, screening, filtering, and disinfection needed to prevent or remove clogging. Since the BIOX-1010 instrument more closely simulates the operation of secondary treatment, such designs appear preferable to the biomembrane technology. Experiments are to be resumed at Los Angeles Glendale Water Reclamation Plant. We have just installed the BOD instrument and are in the startup operations. We briefly discuss developments that appear needed for using respirometry for this application to process control. Technical and economical characteristics relevant to a choice of instrument are compared for these two devices. Additional information will be presented for LAG on the new BIOX 1010 instrument results.