Decolourisation of a pulp mill effluent using commercial activated carbons

Abstract

The decolourisation of industry effluents is a challenging and fundamental task related to pollution control, mainly in pulp mill and textile industries. The dark colour of the pulp mill effluent, depending on the river characteristics, can lead to the reduction of the light penetration into the aquatic environment with the consequent decrease of photosynthesis and aquatic life destruction. Also, the lignocelulosic material deposited on the margins and river bed can lead to a large depletion of the dissolved oxygen with the creation of anaerobic conditions that can give rise to the death of aquatic organisms (Ali, 2001). The chemical composition of the pulp mill effluent (referred as effluent) is very complex. Nevertheless, we can say that the lignin and tannin compounds are the main causes for the effluent´s dark brown colour. Among these compounds we can find hidroxyphenyl, siringyl and guaiacyl complexes (Mohan, 1997). These compounds are chemically stable, resistant to biodegradation and extremely difficult to separate by most methods in cost effective processes, such as membrane adsorption (Mutlu, 2002), cationic coagulants, ultrafiltration (Mutlu, 2002) and chemical oxidation (Malik, 2004). One of the most promising methods is the use of activated carbons for the removal of the effluent colour. In this work the use of 5 commercial activated samples with different shapes, origins and characteristics were tested for the decolourisation of a pulp mill effluent collected directly on the effluent discharge of a plant situated in Setúbal, Portugal, property of Portucel. The colour adsorption was done using batch and dynamic trials.