Zero Liquid Discharge

Capability, Experience, and Overview

Principal Technical Consultant

Dan Sampson
 Introductions

 Brief Overview of WorleyParsons Experience

 ZLD Overview

 Background

 Process building blocks

 Process considerations

Meeting Agenda
Dan Sampson

 Principal Technical Consultant –

Power/Water/Wastewater

 30+ Years

 ZLD experience

− Design (modeling, options evaluation, cost estimates)

− Procurement (specification, bid evaluation, equipment 

due diligence, installation)

− Operation (initial commissioning, operating procedure 

development, operating plant support)

− Maintenance (troubleshooting, cleaning)

Introductions
Water/Wastewater Capabilities

 Identifying future water needs

 Demand forecasting

 Water security

 Water assessment

 Strategic planning

 Identifying potential water supplies

 Quantifying sustainable yields from 

natural, municipal & industrial sources

 Water modeling

 Linking resources to needs

 Sustainability assessment

 Regulatory compliance

 Developing & implementing water 

strategies

 Water reuse and recycling

 Desalination

 Inter-catchment transfers

 Demand & leakage management

 Wastewater minimization/ZLD

 EcoNomicsTM

 Sustainability being the key decision and 

planning tool
Water/Wastewater Capabilities (con’t)

 Water Source(s)

 Qualifying Source Water Quality

 Quantifying Source Water Quality

 Water Purification

 Design – Conceptual, Detailed,

 Technical Support – Troubleshooting, 

Evaluation for Performance & Cost 

 Ion Exchange

 Reverse Osmosis

 Wastewater Treatment

 Design – Conceptual, Detailed

 Technical Support – Troubleshooting, 

Evaluation for Performance & Cost

 Water Reuse & Recycling

 Environmental Compliance

 ZLD system design, specification, 

commissioning, and troubleshooting
ZLD Experience
ZLD Background

 Feed water sources

 Traditional Plants - incoming water 

concentrates in cooling tower, demin 

systems, and/or process wastewater

 Oil and Gas – drilling and completion of 

wells, hydraulic fracturing, EOR, oil sands 

steam generation, oil sands hot water 

treatment, upgrading

 Environmental concerns

 High TDS discharge

 Ion-specific limits may be exceeded

 Organic contaminants

 ZLD

 Water leaves site only as a gas (steam or 

water vapor)

 Dissolved solids concentrated until only 

solid waste remains
What ZLD is Not – A Wastewater 

Treatment System

 Wastewater treatment systems

receive different streams with 

variable flow and chemistry

 Treat wastewater to provide an 

acceptable effluent

 ZLD systems MUST operate with 

constant chemistry and flow

 Do not turn up or down well

 Do not turn on or off well

 Cannot tolerate deviations from 

design chemistry

 Cannot receive waste streams 

other than those for which they 

were specifically designed

 MUST be monitored continuously
 No such thing (water would leave 

only as a vapor or steam)

 Can’t treat sanitary or cleaning 

wastes

 Can’t treat oily waste

 Chemistry and/or contaminants may 

limit concentration

 Usually nitrates or total organic carbon

 Could be anything, though

 “Bleed” often required

− Small liquid stream with highest 

concentration of contaminant

− Hauled off as liquid waste

 Lots of onsite liquid storage/handling

What ZLD is Not – Not Really 

Zero
 Conventional plant (no ZLD)

 Unrecoverable water losses (evaporation, process consumption) can’t be reclaimed

 Unrecoverable losses often the majority of plant water usage

What ZLD is Not – A Water Conservation 

System

Evaporation

to Atmosphere

All Flows in Gallons/Minute 1760

Total

Water

Usage Blowdown

Plant Makeup Water 2126.77 2030.77 Cooling Tower 270.769

Cycles of Concentration 7.5

Total Makeup = 2127

Total Waste = 314.8

Waste (%) = 14.8%

Demin Waste Offsite Disposal

96 Demineralization System 24 Wastewater 315

0.75

72

Steam Cycle, Blowdown

Combustion Turbines, Boilers, 20

Other DI Water Users

50 2

Evaporation or Loss Unrecoverable

to Atmosphere Cleaning Wastes
What ZLD is Not – A Water Conservation 

System

Evaporation

to Atmosphere

All Flows in Gallons/Minute 1760

Total

Water 239

Usage Blowdown

Plant Makeup Water 1812 1716 Cooling Tower 196

Cycles of Concentration 10.0

Total Makeup = 1812 Reclaimed Water

Total Waste = 0.479 239

Waste (%) = 0.0%

Demin Waste Offsite Disposal

96 Demineralization System 24 ZLD System 0

0.75 0.998

72

Steam Cycle, Blowdown

Combustion Turbines, Boilers, 20

Other DI Water Users

50 2

Evaporation or Loss Unrecoverable

to Atmosphere Cleaning Wastes

ZLD with maximum conservation/reclamation

 Water usage lowers from 2127 to 1812 gpm (14.8% reduction) 

Much better options to 

conserve water:

• Air-coolers (90% conservation)

• Recycled water (100% conservation)
 Combined cycle plant Operations 

Supervisor: “We run a chemical plant 

that happens to produce power.”

 ZLD is a chemical process with 

stringent chemistry and flow limits

 Designed to recover specific salts

 Cannot tolerate variation in flow or 

chemistry, so large buffer tanks required

 Chemical feed often required to balance 

chemistry (often requires thousands of 

pounds of other salts, in various forms)

 Pure water and moist salt cake are 

products

 Some liquid waste usually has to be 

hauled off-site

What ZLD is – Targeted Salt and Water

Recovery System
ZLD Process Building Blocks

 5 Basic Processes

 Initial Concentration

 Pretreatment

 Intermediate Concentration

 Thermal Concentration

 Solid Waste Production

 Processes may overlap or be eliminated entirely

 Cost of concentration generally proportional to TDS in concentrated 

streams

 Essentially free in cooling towers

 As high as $40/gal in final step

 Volume of water to be concentrated lowers with each step of the 

process

 Designs often focus on moving evaporation to the “front end” (less 

expensive)
Initial Concentration

 Occurs in processes, cooling towers, demin systems, or produced 

water

 Level of concentration obtainable depends on the incoming makeup 

water quality and its propensity to form scale or cause corrosion

 Typical makeup water can be concentrated from 3-10 times, raising 

TDS to 2500-8000 ppm

 Water high in scale-forming dissolved solids or corrosive ions can be 

concentrated only a few times prior to being removed from the 

system via blowdown. Water with low concentration of problem 

constituents may be concentrated ten or more times prior to removal 

through blowdown

 “Front-end” removal of scale-forming minerals a good option to 

maximize initial concentration (may not address corrosion issues)

 Initial concentration is least expensive and should be maximized
Pretreatment

 VERY broad topic – pretreatment depends on subsequent 

processes

 May require filtration, clarifier/softener, ion exchange, biological 

treatment, oil removal, etc.

 May not be required if initial concentration exceeds 6 cycles or 

feedwater TDS already high

 “Best” approach requires financial analysis

 IX usually economical only if water is “hardness limited” (NaZ, WAC, or 

both)

 TDS in effluent may be unchanged, higher, or lower. 

Depends on process. May generate solid and/or liquid waste

 Liquid waste generated goes to intermediate or final 

concentration

 Solid waste hauled off-site

 Goals vary, but generally

 Remove TOC, oils, and/or grease

 Remove suspended solids

 Replace less soluble species with more soluble species

 Stabilize or remove silica
Intermediate Concentration

 Utilizes RO/ED to further concentrate TDS

 Limited by level of insoluble species in RO 

reject

 RO permeate reused, reject goes to final 

concentration

 Allows smaller final concentration 

equipment

 Minimizes capital cost

 Minimizes parasitic load

 Raises TDS 

 20,000-60,000 ppm range
Thermal Concentration

 Three Options (in various combinations)

 Brine Concentrator

 Crystallizer

 Other evaporation options (ponds, dryers, etc.)

 BC and Bxtal use thermal energy to evaporate 

incoming water

 Distillate recovered for reuse

 Concentrated slurry sent to solid waste production

 Focus shifts from TDS to TS (Total Solids), 

combination of TSS and TDS

 Can typically raise waste stream TS to the 150,000 

to 500,000 range
Solid Waste Production

 Transforms concentrated 

brine into a damp solid

 Requires various 

combinations of

 Solar evaporation ponds

 Filter presses

 Centrifuges

 Dryers

 Solid waste eventually 

hauled off-site
ZLD Process Considerations

 Pretreatment Systems

 Clarifiers and Clarifier/Softeners

 Filtration

 Ion Exchange

 High-TDS RO Systems

 Thermal Systems

 Complexity

 Degradation

 Sizing Criteria

 Manpower

Sanitary System Waste

1 GPM

To atmosphere

Evap Drift 1264 GPM

Concentrated

Cooling Tower Blowdown Wastewater Brine to Waste

Makeup Water 1580 GPM 316 400 GPM 20 GPM

1522 GPM GPM

Service Water Waste 1 GPM

Pretreatment System 1 GPM

320 GPM Waste 80 GPM

Drains and

Combustion Turbines Steam System Blowdown

220 GPM 20 GPM

Washwater 2 GPM

218 GPM PAG/Fog to Atmosphere

Recovered Water

380 GPM
Clarifiers and Clarifier/Softeners

 Inherently difficult to balance

 Require significant chemical addition and 

control

 Generate solid waste

 Require stable influent and effluent flow

 May require installation of extremely large 

“buffer” tanks

 Blowdown softeners especially difficult

 Must overcome cooling tower dispersant

 Cooling tower treatment chemicals “lost” 

across the unit and must be added again if 

effluent recycled to cooling tower

 Avoid if possible
 Media or membrane filtration 

required for High-TDS RO

 Large debris (mesh strainers) for 

thermal concentrators

 Filtration ahead of RO systems 

always a problem

 Filters themselves may foul (uF and 

mF)

 Filters may not remove TSS (media

filters)

 RO membrane fouling results

 Avoid intermediate concentration

Filtration
 Sodium Zeolite (NaZ) and 

Weak Acid Cation (WAC) 

most common

 Remove hardness to increase 

High-TDS RO recovery

 Generate high-TDS waste 

(spent regenerant), must be 

processed in ZLD

 Generate large volume of 

low-TDS waste 

(rinses/flushes - requires 

complex recovery systems)

 Regeneration/rinse often 

challenging and must be 

optimized.

Ion Exchange
High-TDS RO

 Most “elegant” chemistry

 Initial modeling often shows lowest cost

 Implementation extremely difficult

 Adds several pieces of support equipment

 Increased complexity reduces reliability

 Experience shows poor reliability and high 

maintenance

 Almost all sites have to haul-off water

 Actual costs much higher than predicted

 Increased operator involvement

 High maintenance

 Water haul-off

 May still have a niche, but EXTREMELY 

difficult to manage

 Avoid use if at all possible. Install 2x100% 

trains if used
 Simplest approach (avoids 

most pretreatment and all 

intermediate concentration)

 Easiest operation if ZLD is 

required

 Still have issues

 Cleaning (often and expensive)

 Corrosion (alloy selection very 

important)

 Capacity (heat transfer surface 

area and thermal input capacity 

very important)

 Small failures (seals, 

instruments, pumps, etc.) 

common and impact reliability

Thermal Systems
Complexity

 Increased 

operator 

involvement 

(two extra per 

shift required 

for complex 

designs)

 Maintenance 

costs increase

 Reliability 

decreases

 Additional 

spares required 

(2x100% trains, 

additional shelf 

spares)

 CA RW/FW 2.0 Service Water

 Aquaduct Storage Tank Users

3562 GPM 850,000 Gal 30.4 Losses to Atmosphere

3530 0.0 2.0 55.5 Makeup 0.0 106.7 2.8 CT Wash Water

Firew ater PAG Steam CT Wash Water

Reactor/ Oil/Water HRSG Steam 0.0 Combustion 2.8

47.4 Clarifier Separator HRSG Leaks and Drains Cycle BXtal Steam Turbines

Sludge (%of Infl) 0.5% 12.0 18.1 76.3

Fogging Systems

3561 16.5 16.8 0.0 Blow dow n 25.4 0.0 30.4

Oil to Off-site Disposal

Sludge 1x1 ACC

Thickener Evap Cooler 30.4

Sludge (%of Infl) 7.1% Cycles 2.0

Aux Boiler

1.2 15.4 Steam Cycle 30.4 Blow dow n

Decant

Sludge Cake Plate & Frame BXtal Steam

Lb/Day 6681 Filter Press 0.0 0.0

GPM 0.4 Sludge (%of Infl) 33.3%

18.1

0.8 Filtrate

Recycle Sump HRSG Blowdown

System

Total Flow , gpm 47.4

3561 48.2 2.7

Quenched Blow dow n

Clearwell Vent to Atmosphere

3561 Tank

50,000 Gal

Evap Drift

3428 4.4

Site Cooling

3553 Towers/WetSACs 560.8

Cycles 6.0

7.4 655.9 25.4

HRSG BD Quench

Backw ash Supply Blowdown NaZ Regen Brine Concentrator Demineralized

31.2 Storage Tank Waste Tank 105.9 Water Storate Tk 165.0

500,000 Gal 200,000 Gal Recovery (%) 90.0% 750,000 Gal

Excess

624.7 Lost to 10.6 95.3 0.0 166.3

Atmosphere Distillate Distillate

Blowdown WAC Regen Crystallizer Mixed Bed

0.0 Filters Waste Tank 18.1 Demineralizer

Backw ash Supply 300,000 Gal Recovery (%) 50.0% (Off-site Regen)

31.2 624.7 9.0 9.0 166.3

Backw ash Regen Waste Distillate

Regen Supply NaZ Units 7.4 HERO Reject Belt Filter Press Distillate to Mixed Bed

7.4 Waste Tank 7.5 95.3 Feed Tank

Regen (%) 1.2% 450,000 Gal Filtrate Recovery (%) 82.6% Demin Feed 5,000 Gal

Salt Cake

624.7 97.3 1.6 56461 456.4 71.0

Regen Waste GPM Lb/Day Excess Permeate

Regen Supply WAC Units 1.3 Decarbonator High Efficiency Demin

1.3 624.7 Reverse Osmosis 551.1 94.7 Reverse Osmosis

Regen (%) 0.2% Recovery (%) 85.0% Permeate Demin Makeup Recovery (%) 75.0%

624.7 23.7

Reject
PRE TREATMENT

 ANCILLARY TREATMENT (ALTERNATIVE)

FILTRATION

MAIN TREATMENT

Feed Water Balance 

Tank

INTERMEDIATE 

BARRIER

Dosing

• PAC

• PACl

Dosing

• H2SO4

• NaOCl

Disk Filters

HARDNESS & HEAVY 

METALS REMOVAL

Dosing

• SBS 

•AS 

•H2SO4

MAIN TREATMENT

Ion Exchange Units

SW RO System

BW RO Feed Tank

& Pump Station

REVERSE 

OSMOSIS

BW RO System

SOLIDS 

DEWATERING

Feed pump

Air 

blower

Wastewater

(out)

Ultra-filtration System RO Bypass

Dosing

• NH3

SW RO Feed Tank

& Pump Station

BRINE RECOVERY

SYSTEM

(ALTERNATIVE)

BACKWASH RECOVERY 

SYSTEM

Solids 

Disposal

Sludge Bag 

(Option)

Inlet Water

500 micron 

Screen

Reject Neutralized Waste to Drain/Sewer

Drain/ Recirculation Pump

Air Scour Blower

NaOH Sodium

Optional for Neutralization

Permeate to product water tank

Permeate/ Backpulse Pump

Backpulse Tank

NaOCl Citric Acid

Membrane Tank

Bisulphite

CIP Tank

Submerged UF

Services Tank

To Irrigation 

Pond

Dosing

• NaOH

To 

Pond

Brine 

Auburndale – Calpine

Zero Liquid Discharge System

Complexity
Degradation and Redundancy

 Design Margin

 Developers may not perform detailed risk analysis

 May buy cheapest system with nameplate capacity to handle the 

required flow

 Feed water analysis often uncertain – any deviation from design 

causes additional loss of capacity

 System almost never meets nameplate

 Best Case

 Expect 75-95% mechanical reliability

 Expect 20% degradation between cleanings (80% of nameplate flow 

capacity)

 Effective ZLD capability = 80% x 80% = 64%

 That’s BEST CASE – more complex designs much worse (more to 

go wrong)

 So, a 500 GPM ZLD system can reliably handle about 300 GPM
Sizing Criteria and Spares

 Sizing Criteria – NO exceptions

 Based on max peak flow

 “Simple” designs (thermal only) – 2x60% trains (prefer 2x75%)

 “Complex” designs (WWRO, intermediate concentration) – 2x100% 

trains (completely independent)

 Provides effective capacity of 90-150% of nameplate

 “Thermal” only most reliable, so lower redundancy requirement

 Increasing complexity = decreased reliability, more redundancy 

(additional design margin) required

 Spares

 Perform single-point failure analysis

 Purchase additional shelf or installed spares (regardless of design)

 Risk assessment must be part of initial plant design – cost 

analysis should include redundancy
Manpower

 Common mistake – assume that ZLD can be operated with same staff 

as a typical water plant

 ZLD Vendor: “The system uses a PLC, so it basically runs itself.” – not 

accurate.

 ZLD systems much more complex, increased manpower required

 Additional manpower depends on complexity

 “Simple” ZLD designs require 7-9 extra EXPERIENCED people

 One operator 24/7 (dedicated to ZLD system)

 1⁄2 mechanic, 1⁄2 I&C

 Manager (plant chemist or ZLD O&M manager)

 “Complex” ZLD designs require 12-14 extra people

 Two operators (24/7)

 Full time mechanic, full time I&C

 Manager (plant chemist or ZLD O&M manager)

 No ZLD plant “runs itself” – vendor sales pitches create wrong 

impression

 Need at least one experienced person constantly watching the PLC and 

running chemistry – no other duties

 At least one other person available to combat problems
Critical Issues

 ALWAYS get references:

 Talk to others actually operating the equipment you intend to buy

 No references = no sale

 “Emerging” or “new” technology = extreme process risk (pilot test)

 AVOID use of intermediate concentration

 Looks good on paper, very challenging in the real world

 Pretreatment too complex and unpredictable

 Intermediate concentration technologies also unreliable

 Simplify pretreatment

 Avoid pretreatment

 Simple filtration only preferred

 Focus on redundancy and capacity

 Brine Concentrator/Crystallizer Sizing: at least 2-60% (based on max peak 

flow) trains

 Complex systems: at least 2x100% completely independent trains

 NO exceptions

 Manpower

 Factor into cost analysis

 Include in plant staffing plan

 Dedicated staff provide best reliability

 Spares

 Perform single-point failure analysis

 Purchase shelf spares
Conclusions

 ZLD is LAST resort. Discharge to others if 

possible. A basic 500 gpm ZLD system will cost 

about $50 million in NPV over 20 years

 Avoid use of intermediate concentration. Minimize 

processes that require chemical feed.

 Minimize complexity. Simple thermal systems least 

efficient, but easiest to operate.

 Move concentration as far back in the system as 

possible. Concentration in the cooling tower costs 

nothing and should be maximized.

 Regardless of vendor claims, ZLD systems are 

MUCH harder to operate than they claim or you 

may think.
32

KEY CONTACTS

Power/Water/Wastewater: 

Dan Sampson, Principal Technical Consultant, 

dan.sampson@worleyparsons.com; (707) 643-2834 / Mobile: (925) 570-0842