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179 TREATMENT OF PAINT WASTEWATER USING INORGANIC COAGULANTS a
a
Oupa Ntwampe , Linda L. Jewell , David Glasser a
b
School of Chemical & Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of
Witwatersrand, Johannesburg, 2050, RSA. b
Centre of Material and Process Synthesis, University of Witwatersrand, Johannesburg, 2050, RSA.
Abstract Wastewater effluent discharge poses a detrimental impact on the river ecosystem and groundwater. Paint wastewater contains chemicals such as organic matter, sulphates, other salts and suspended solids. Re-use can be economical and also contribute to environmental conservation. Processes involved in wastewater treatment include coagulation and flocculation. Coagulation involves colloidal destabilisation and the latter is the formation of larger flocs that leads to settling. Effective settling depends on the type of coagulant(s), mixing rate, mixing duration, structure of the clarifier and operating practice.
Key words: Coagulation, destabilization, coagulation, flocculation, flocs, settling.
1.0 Introduction In the paint manufacturing industries, water is used as a solvent and for rinsing. Washwater requires extensive treatment in order to be re-used in the processes or discharged back to the watercourse. The manufacturing of paint is conducted in batches that differ from one another, e.g. silk, matt, tex, solvent-based or water based. The paint is then stored in tanks or vessels from where it is pumped through the filling lines to storage containers and distributors. Equipment and pipelines are rinsed with water after every batch has been manufactured. Water is used for rinsing because it is a common cheap solvent. It is very important to ensure that extensive rinsing takes place to avoid possible contamination between batches. This washwater requires internal treatment before it can be discharged as it does not comply with statutory effluent discharge requirements, see Table 1.1. After treatment the effluent contains less dissolved substances and can be discharged to the designated as shown in Fig. 1.1.
Water-intake Raw materials
Plant Process (paint manufacturing)
Paints as product Figure 1.1: Simplified diagram in paint manufacturing.
Washwater/effluent
Parameter
Reclaimed water
Paint washwater
pH
6.5 – 9.5
6.5 – 9.5
Iron
