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Industrial Wastewater Treatment and Zero Liquid Discharge. How Yong NG. Centre for Water Research Department of Civil and Environmental Engineering National University of Singapore . Zero Liquid Discharge (ZLD) – Why?. Environmental compliance regulations get stricter each year
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Industrial Wastewater Treatment and Zero Liquid Discharge How Yong NG Centre for Water Research Department of Civil and Environmental Engineering National University of Singapore
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 • 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. • 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.
How to Achieve ZLD? Example: Step 1: Effluent after solvent recovery Recovery of solvents by using distillation process Step 2: Raw effluent from industry Removal of organic matter by using anaerobic digestion Step 3: Anaerobically treated effluent Removal of balance organic matter by using aerobic digestion Step 4: Treated effluent from ETP Clarification by using, tube settler/clariflocculator Step 5: Effluent after clarification Further reduction in TSS by using filters Step 6: Effluent after filters Reduction in turbidity and SDI by using ultrafiltration Step 7: Effluent after UF Recovery of low TDS permeate by using RO Step 8: High TDS reject from RO Concentration of RO rejects by using evaporators Step 9: Solids Extraction & Disposal Separation of salts from mother liquor using centrifuge/ dryer
Zero Liquid Discharge - Approaches Discharge to the plant process • 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 Evaporation/Crystallization Process Evaporation pond Cold Lime Softening