Explores the options available to process wastewater generated from liquid penetrant inspection.
Rinse waters containing residues from the penetrant inspection process are generated from all but Method C (solvent removal). The rinse water contains penetrants (Method A), or penetrants and emulsifier (Methods B and D), which contain oils and surfactants. The water may also contain suspended solids (e.g. from powder developers). Although generally considered to be of low toxicity, these wastes can pose problems if sewered without treatment. A number of treatment options are available.
All municipal sewer authorities or POTW’s (publicly owned treatment works) restrict the concentration of certain contaminants that industrial users can discharge into the sewer system. Although there is a large variation in these limits, most POTW’s place limits on fats, oils and grease (FOG), color, and turbidity (suspended solids). Most also limit BOD and COD (biological and chemical oxygen demand).
Most of these limits are established to reflect the added cost burden that untreated contaminants place on the POTW. The dyes present in penetrant rinses pose a unique problem, however. POTW’s rely on micro-organisms to break down domestic waste and organic material. The micro-organisms require ultra-violet radiation from sunlight to survive and reproduce. Penetrant dyes, both fluorescent and visible (red), absorb the UV rays from sunlight, resulting in a kill-off of the micro-organisms. Further, because of their distinctive color, penetrant rinses are easily observed and can be tracked back to their source.