TOC based control of anaerobic reactor treating wastewater from a fruit juice packaging factory

This paper describes the application of TOC as a control variable for a full-scale expanded granular sludge bed (EGSB) reactor treating wastewater from a fruit juice packaging factory. The carbohydrate-rich wastewater shows high variations in both flow and concentration. Treatment efficiency was too low before the implementation of the TOC based control, while the design loading rate could not be achieved. The poor performance was associated with large fluctuations of the wastewater load in combination with several other factors, including: too small an equalisation tank, insufficient mixing in the equalisation tank and too course a control scheme (based on flow only), which failed to deliver a smooth enough organic loading to the EGSB reactor to secure stable performance. A control strategy based on inline wastewater TOC was developed and implemented in order to cope with the large fluctuations of the wastewater load. This paper describes the TOC based control strategy and the treatment performance obtained after its implementation. Combining TOC based control with better operation of the equalisation tank is shown to have improved the performance of the EGSB reactor. Even with a relatively small equalisation tank in combination with a fluctuating load the control strategy enables stable operation of the reactor. Among other improvements COD removal has increased from 50% to 82% despite a load increase from 1700 to 2100 kgCOD/d, equivalent to an organic loading rate of 11.3 to 14 kg/m3d.