Wastewater Toxicity Reduction for Petrochemical Complex

Client: Confidential


Calcitrant hydrocarbons were resisting traditional biological treatment and contributing to whole effluent toxicity (WET) in wastewater originating at a petrochemical, natural gas liquids (NGL) and refining complex. The chemical plant manufactured organosulfur chemicals, high-purity hydrocarbons, solvents, performance fuels, reference fuels and mining chemicals. Our team designed the wastewater improvements necessary to reduce effluent toxicity.

One treatment train was constructed and an existing one was retrofitted. The most significant process modification was adding powdered activated carbon (PAC) to the biological unit process. 
We designed and provided construction support for wastewater infrastructure necessary to remove contaminants. The fast-track project required the use of two general contractors while keeping the treatment plant operational. The project was completed on schedule in seven months and met National Pollution Discharge Elimination System (NPDES) permit requirements at startup. 

Effluent quality results:

  • Chemical oxygen demand (COD) went from 65% removal to 90% removal
  • Ammonia went from 80% removal to 95% removal
  • Toxicity went from 40% survival to 100% survival
  • Tertiary filter backwash went from every 24 hours to every 36 to 48 hours


  • Front-end planning
  • Detailed design
  • Procurement and construction support


  • New 2.5 MGD treatment train
  • PAC treatment system
Featured improvements to the 5-MGD industrial wastewater plant included:
  • Splitter structure
  • Two biological unit processes
  • Two PAC silos
  • Two clarifiers
  • Two return activated sludge (RAS)/waste activated sludge (WAS) pump stations
  • Filter feed pump station
  • Polymer system
  • Disinfection system
  • Solids handling process
  • Non-potable water system