Effects of programmed maintenance shutdowns on effluent quality of a bleached kraft pulp mill

Abstract Routinely, the mills perform programmed maintenance shutdowns (PMS) that can affect the characteristics of the effluents and the performance of the effluent treatment plant (ETP). A careful planning of the PMS, along with the use of industrial process sectorial spill control and the use of the emergency spill lagoon have considerably minimized these effects. The Suzano pulp mill located in Aracruz (Brazil) has three production lines and carry out, on average, PMS of each production line separately, every 15 months of operation. The purpose of the study was to evaluate the effects of the PMS on the effluent characteristics and performance of the ETP compared to the periods of normal operation. The results showed that during the PMS, the physicochemical characteristics of the raw and treated effluents were like those found during normal operation. The lower organic loads found in the effluents during the PMS periods were associated with the decrease of the flow rates and the increase of the hydraulic retention time of the ETP, causing a better performance of COD, BOD, TSS and AOX removal. A proper planning of the PMS improved the performance of the ETP and the treated effluent quality remained similar to those during the normal operating period.