Removing oily impurities from electroplating effluents: Which method is normally not used for routine removal of oily or greasy impurities from electroplating wastewater at typical plant scales?

Introduction / Context:
Electroplating facilities may discharge wastewater containing oils and greases from cleaning and surface-prep steps. Selecting practical, cost-effective unit operations for oil removal is essential before metal precipitation and polishing treatment stages.

Given Data / Assumptions:

• Plant handles continuous or batch wastewater flows of modest to large volume.
• Oils may be free, dispersed, or partially emulsified.
• We seek what is “normally not” used in routine practice due to cost/complexity.

Concept / Approach:
Common front-end oil removal methods include gravity separation (API separators), dissolved air flotation with skimming, coalescers, and chemical coagulation to break emulsions. Ultrafiltration is also widely applied for stable emulsions in metal finishing. Centrifugation can separate immiscible liquids but is uncommon for bulk wastewater oil removal because of high energy use, maintenance, and poor economics at large flow rates.

Step-by-Step Solution:
List standard practices: gravity separation, DAF, skimming, chemical emulsion breaking.Note advanced membrane options: ultrafiltration is viable for emulsified oil streams.Identify the atypical choice for routine wastewater service: centrifugation.

Verification / Alternative check:
Industry guidelines favor DAF/coalescers over centrifuges for economy and robustness; ultrafiltration is a recognized technology for oily wastewater when emulsions resist gravity methods.

Why Other Options Are Wrong:
Chemical coagulation: standard to destabilize emulsions.Flotation & skimming: a mainstay for oil removal.Ultrafiltration: commonly applied for stable emulsions in metal finishing.Gravity separation: basic primary step, not the “not used” option.

Common Pitfalls:
Assuming any mechanical separator is practical; overlooking lifecycle cost and scaling issues associated with centrifuges.

Final Answer:
Centrifugation