The handling and disposal of hot tarry liquid residues can be problematic in industry, in this case, a phthalic anhydride plant using naphthalene as feed stock. The residue from the plant contains an appreciable amount of phthalic anhydride which desublimates from the residue during draining, resulting in an unsafe working environment. In addition, the residue is a hot liquid that solidifies upon cooling, causing additional risks to personnel during handling and various problems associated with disposal. Research was conducted into finding a treatment method to reduce or eliminate the desublimation of phthalic anhydride from the residue and addressing the hot liquid residue, making the residue safer to handle and easy to dispose of. Laboratory experiments showed that the addition of Dicalite 4151 (a filter aid) in a concentration of 0,3 kg Dicalite 4151 per kg phthalic anhydride residue, resulted in the formation of a powdered residue. This was confirmed during plant trials where using the same concentration proved that a powdered residue could be obtained, while at the same time desublimation of the phthalic anhydride from the residue was negated by distilling the product from the residue mixture. An opportunity exists to test the use of filter aid in other residue producing industries to determine if the same results can be achieved. / Dissertation (MEng (Environmental Engineering))--University of Pretoria, 2005. / Chemical Engineering / unrestricted