Question 1 of 18: Five Strategies to Reduce Liquid Industrial Waste Strength

Question 1: Five Strategies to Reduce Liquid Industrial Waste Strength (5 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(1) Raw material or product substitution — replacing a high-pollution-potential input (e.g. a solvent-based process chemical) with a lower-strength alternative reduces the pollutant mass entering the wastewater before it is ever generated. (2) Process modification or equipment change — redesigning a unit operation (e.g. switching a batch dye bath to a continuous, more efficient application method) so that less raw material is lost to the wastewater stream in the first place. (3) In-process recovery, recycling and reuse — recovering a valuable by-product or process chemical (solvent distillation, metal reclamation from rinse baths, counter-current rinsing) before it becomes waste, which simultaneously reduces cost and waste strength. (4) Good housekeeping — dry clean-up of spills and process residues before wash-down, tighter inventory and batch control to reduce off-spec product, and preventive maintenance to control leaks, all keep material out of the wastewater stream that would otherwise raise its strength. (5) Waste stream segregation — keeping a small-volume, high-strength stream (e.g. a concentrated process bath) separate from large-volume, low-strength streams (cooling water, non-contact wash water) allows the high-strength stream to be recovered or treated on its own, rather than diluting it into — and having to treat the full volume of — the combined flow.