Algal treatment of membrane rejects: a unique approach towards zero liquid discharge

Abstract

A major concern in membrane-based water purification system is generation of huge concentrate stream and wastage of water. A typical Reverse osmosis (RO) or Nanofiltration (NF) system generates 20–25% reject containing high amount of dissolved salts and other contaminants. Contrary to popular belief, this reject water cannot be used without removing the contaminants or cannot be discharged anywhere. Main goal of this project is to find a cheapest and green way for treatment of RO/NF reject. Algal evaporation technique was explored in laboratory scale, to find its suitability for treatment of chloride-rich membrane reject in actual scenario and based on the results obtained, a pilot plant of 48KL was established on Hooghly Met Coke division (HMC), Tata Steel. Particular species of microalgae was selected, to take up minerals from reject water. There are several types of bacteria and symbiotic algae associated with selected micro algae survive in high TDS. A unique slope roof system, connected with algae growth tank, helps in efficient evaporation of water ensuring a Zero discharge. A markedly improved performance was achieved when algal evaporation followed solar evaporation. A total evaporation of 11 L/m²/day was observed, which was almost five times faster than Solar evaporation.

Graphical abstract

Novelty statement

• Algae based evaporation technology was explored to find its suitability for treatment of high chloride-based membrane reject. Specific Species of microalgae, which can take up minerals from reject water was selected.

• Based on algal evaporation, a pilot plant of 48 KL was established on Hooghly Met Coke division (HMC), Tata Steel India site.

• Rate of evaporation 11 L/m²/day was observed, which was almost five times faster than solar evaporation.

Keywords:

• Membrane reject
• coke quenching water
• algal evaporation
• micronutrient
• zero discharge

Acknowledgements

The authors are thankful to Phycospectrum Environmental Research Centre (PERC) Laboratory, Chennai, India for their support in Screening and developing the algae culture in laboratory. Authors are gratefully acknowledged R&D division of Tata Steel Ltd, Jamshedpur for providing infrastructural and all the required facilities.

Disclosure statement

No potential conflict of interest was reported by the author(s).