treatment plant using biological and physico- chemical processes - - PowerPoint PPT Presentation

Modelling a water treatment plant using biological and physico- chemical processes

Marc Laliberté Senior Process Engineer, Industrial Veolia

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Contents

• 1. Introduction
• 2. Process Development
• 3. Modelling
• 4. Conclusion

Us (Veolia) Our Client (Pretium) The permitting process

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Introduction

Veolia: We treat water

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Pretium’s Brucejack Project

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New gold mine being developed Located approximately 65 km north of Stewart in NW British Columbia. Probable mineral reserves of 6.6 million ounces of gold Currently in exploration phase Started permitting for the construction and operation phases

Permitting Process

Highly sensitive area BC government has been very proactive regarding environment Permitting is done by phase

• Exploration, Construction, Operation, Closure
• Exploration and Construction criteria are less stringent (impacts

are lower)

• Operation criteria are very stringent

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Expected Water Quality and Criteria Metal Removal Nitrogen Removal Polishing The proposed system

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Process Development

Expected Water Quality and Criteria

Parameters

• Metals, such as Ag, Cd, Co, Cu, Cr, Fe, Ni, Zn
• Anions, such as Cl, SO4 and NO3
• Nitrogen Species, such as NH3, NO2 (and NO3)
• Criteria are typically sub ppm, some are sub ppb
• Little BOD and organics, neutral pH, lot of TSS

Exact quality is not known

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Using predictions from geochemical kinetic studies

• Confirmed in lab on synthetic

water made to match predicted quality

• However there are

uncertainties...

Lorax

Metal Removal

BATEA (Best Available Technology Economically Achievable):

• Lime precipitation
• Enhanced Coagulation and Settling

pH to be optimized to get best metal removal

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HYDROCYCLONE COAG. TANK INJ. TANK MATUR. TANK SCRAPER LAMELLA SETTLING TANK RAW WATER COAGULANT POLYMER MICROSAND SLUDGE PUMP MICROSAND + SLUDGE CLARIFIED WATER

Nitrogen Removal

BATEA:

• NH3, NO2: Active Aerobic Biological Oxidation

NH4

+ + 3/2 O2 = NO2

• + 2 H+ + H2O

NO2

• + ½ O2 = NO3
• NO3: Active Anoxic Biological Reduction

2 NO3

• + 3 (CH2O)n = N2 + 3 CO2 +3 H2O
• Using Moving Bed Biofilm Reactor

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Aerobic reactor Anoxic reactor

Polishing

Removing TSS produced in Biological Reduction Also allow second stage of coagulation to remove leftover metals using complexation (adsorption) on ferric hydroxide

• Key to achieving sub ppb levels

Using same Enhanced Coagulation and Settling equipment

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Proposed System

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Metal Precipitation Reactors Actiflo Biological Reactors Polishing Reactor Actiflo

Why model, and why model using ESP? Model Set-Up Chemical Precipitation Biological Treatment Polishing and Surface Complexation

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Modelling

Why model, and why model using ESP?

Why model?

• Can we meet the discharge criteria?
• What’s the optimum pH?
• Do we need to add sulfide?

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Why model using ESP?

• ESP is the best modelling

tool on the market for electrolyte-based processes

• The interface looks

primitive, but the software is very easy to learn and is intuitive

Model Set-Up

Model : Aqueous Framework (H+ based)

• Mix-Solvent still incomplete with respect to heavy metals and

metalloids

• Concentrations are generally low, so aqueous framework should

be OK

Redox only applied when required

• Redox and nitrogen species don’t mix well, require careful

handling

• As, N, Fe, Se, S only are used
• Cr is assumed as Cr III

Require validation, kinetic of biological oxidation / reduction is unknown

Large number of species

• Require two model restarts, but this is now handled well
• Calculation times reasonable with today’s computers

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Chemical Precipitation

Easiest step No redox Simple mixers, separators

• Sludge recirculation not modelled, irrelevant for this process
• Will be physically present

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Biological Treatment

Redox used for oxidation only Oxidation done using ESP built-in equations (using O2 from air) Reduction cannot be done that way

• ESP does not recognize carbon based reducers
• Had to use a reactor, so redox turned off
• Methanol used for the purpose of the simulation
• Other reducing reactions ignored

Kinetics are not well known, but some reduction of As and Se is expected

Small oxidation step at end to remove residual methanol

• Will possibly oxidize back As and Se
• Kinetics unclear, requires validation

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Polishing and Surface Complexation

Key step Very cumbersome to actually model Solid removal modelled in ESP Complexation calculations done offline in Excel using data from Dzombac and Morel Validated using lab data

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Next steps What did we learn? What tools are we missing?

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Conclusion

Next Steps

Complete Lab Validation Prepare Permit Request Build Equipment, Install and Commission Long-term follow-up to make sure water quality is as expected

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What Did We Learn?

Chemical precipitation is better defined

• pH was optimized
• Allowed us to really understand what’s happening

Confirmed that criteria can be met Mass balance allow sizing of equipment and permitting

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What Tools Are We Missing?

Mix-Solvent vs Aqueous Framework

• Mix-Solvent is probably better but incomplete
• Until it is completed work will be done using Aqueous Framework

Biological Redox

• Require a way to have carbon species act in redox

Many, many species, how to select?

Surface Complexation

• As we go from g/L to mg/L to ug/L... this becomes an essential

part of modelling

• Current implementation is poorly documented and difficult to use

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What Tools Are We Missing?

Inputs

• Better interface with StreamAnalyzer

Results Output

• The whole interface need rethinking
• pH with mixed phases
• Elemental concentration

Currently only molar flow...

• Non Americans also use ESP

ESP output should follow Windows localization

Kinetics are ignored

• Not sure how this could be handled

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