industrial wastewater treatment and zero liquid discharge
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Industrial Wastewater Treatment and
Zero Liquid Discharge
Centre for Water ResearchDepartment of Civil and Environmental Engineering
National University of Singapore
How Yong NG
Zero Liquid Discharge (ZLD) – Why? Environmental compliance regulations get stricter each year
Sometimes the only viable means of meeting discharge restrictions is to eliminate discharge
Public scrutiny of the industry’s impact on the environment is growing ZLD has a real potential for improving public relations with plant neighbours and government regulatory agencies
Water use needs to be minimized to allow continued industry growth. ZLD is mainly about discharge, but a very real effect is a reduction of inlet water needs, by as much as 20 – 30%
Zero Liquid Discharge – Benefits & Costs Benefits (Mickley, 2006):
ZLD generally does not require a lengthy or tedious permitting process.
It may gain quick community acceptance.
It can be located virtually anywhere.
It represents a positive extreme in recycling, by efficiently using the water source.
Selective salt recovery is a promising consideration in approaching the goal of sustainability.
Costs: Capital and operating costs
associated with ZLD are higher than any other concentrate disposal method.
Significant Energy costs associated with the evaporation process.
High chemical costs associated with treatment following a second membrane process.
High costs associated with final brine or solids disposal.
How to Achieve ZLD? Example:Step 1: Effluent after solvent recovery
Step 5: Effluent after clarification Further reduction in TSS by using filters
Step 8: High TDS reject from RO Concentration of RO rejects by using evaporators
Step 7: Effluent after UF Recovery of low TDS permeate by using RO
Step 6: Effluent after filters Reduction in turbidity and SDI by using ultrafiltration
Step 2: Raw effluent from industry Removal of organic matter by using anaerobic digestion
Step 4: Treated effluent from ETP Clarification by using, tube settler/clariflocculator
Step 3: Anaerobically treated effluent Removal of balance organic matter by using aerobic digestion
Recovery of solvents by using distillation process
Step 9: Solids Extraction & Disposal Separation of salts from mother liquor using centrifuge/ dryer
Zero Liquid Discharge - Approaches
Examples of ZLD technologies: Recycle using Cold Lime Softening Discharging to the Plant Process Evaporation Ponds Evaporation/Crystallization of Discharge Stream Enhanced ZLD Process
Combination Thermal Process with ZLD Enhanced Membrane and Thermal ZLD Wind-Aided Intensified Evaporation (WAIV) Dewvaporation Salt Solidification and Sequestration
New Approaches
Cold Lime SofteningDischarge to the plant process
Evaporation pondEvaporation/Crystallization Process
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