Ultimate Effluent Treatment Allows for ever Larger Pulp Mill - - PowerPoint PPT Presentation

Ultimate Effluent Treatment Allows for ever Larger Pulp Mill Capacities

7th ICEP, 29th May 2015, Vitória, ES Alexis Métais Ivan Zhu Jean-Christophe Hostachy

Environmental Impact

Pulp mill effluent quality is mostly characterized today by its COD load. Environmental impact of modern pulps mill is assessed according to the COD discharge and the capacity of receiving waters to sustain it.

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Achievements

Environmental impact of modern pulps mill has been drastically improved since the 1990s thanks to implementation of:

• oxygen delignification allowing filtrate recovery
• secondary effluent treatments

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Specific COD discharge decreased by 69% per produced ton since 1992.

Better Environmental Impact – Case of Finland

4 Source: http://www2.forestindustries.fi/statistics/60-Environment

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Better Specific or Overall Environmental Impact?

However fiberline capacities have been increasing:

• 500,000 adt/y at Alberta-Pacific (Canada) in 1993
• 1 million adt/y at Hainan Jinhai (China) in 2004
• 1.5 million adt/y at Eldorado Três Lagoas (Brazil) in

2012 Despite specific COD discharge was divided by 3 since 1992, it is balanced by the threefold increase of fiberline capacity. Actually COD discharge at one single point is potentially the same as 20 years ago.

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Alternatives

It is possible to keep increasing pulp mill capacities without increasing COD discharge by:

• further

circulating bleaching filtrates to the recovery if lowering the use of chlorine dioxide

• implementing tertiary effluent treatments allowing

fulfilling with discharge limits or even reuse of treated effluent in the process.

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Tertiary Treatment Techniques

Tertiary treatment target is already in some sensitive locations to divide by half the COD at the outlet of the secondary treatment plant. Coagulation / Flocculation is the traditional tertiary effluent process. It has proved successful but results in high amounts

• f sludge which are difficult and costly to handle.

Conventional Tertiary Effluent Treatment: Dissolved Air Flotation (Coagulation/Flocculation)

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Raw Water

Major Coagulant Injection Together with a Reducing Reagent

Oxidant Injection Alternative Oxidant Injection Point

Filtration

Treated Water

COD load is precipitated and transferred to a solid phase (sludge).

Clean Tertiary Effluent Treatment: Ozone & Biofiltration Combination

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COD is destroyed in-situ through chemical and biological oxidation

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Experimental

A pulp mill producing bleached eucalyptus kraft pulp was requesting a new solution to reduce at the outlet

• f the existing ETP.

A pilot system combining ozone, biofiltration (BAFF) and Coagulation/Flocculation (DAF) was installed after their secondary biological treatment

Day 1 2 3 4 5 6 7 Average Inlet COD mg/L 147 126 132 101 116 144 147 130 Inlet color Pt-Co Units 207 169 209 135 148 192 207 181

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Objective

The main objective of the piloting is to compare the three following alternatives

• DAF (Coagulation & Flocculation)
• Ozone + BAFF (Biofiltration)
• Ozone + DAF

Results are given for a COD removal of 40% and 60%, and economic calculation is carried for a 50,000 m3/d effluent flow with 130 mg/L COD (outlet of the existing secondary treatment).

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DAF Results

CODoutlet = CODinlet – PACl dose in mg/L x 0.2 DAF treatment would require:

• (130 - 78) / 0.2 = 260 mg/L PACl for 40% removal
• (130 - 52) / 0.2 = 390 mg/L PACl for 60% removal

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O3 + BAFF Results

CODoutlet = CODinlet – ozone dose in mg/L – 20 mg/L Combined ozone and BAFF treatment would require (130 – 78 – 20) x 1 = 32 mg/L ozone for 40% removal.

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O3 + DAF Results

CODoutlet = CODinlet – ozone dose in mg/L – PACl dose in mg/L x 0.26 Changing hydrophilic behavior of macromolecules,

• zone strongly helps PACl action during DAF

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O3 + DAF Results

Increasing the ozone dose has no significant impact

• n the O3 + DAF treatment.

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O3 + DAF Results

Combined ozone and DAF treatment would require 10 mg/l ozone +

• (130 - 78 – 10) / 0.26 = 162 mg/L PACl for 40% removal
• (130 - 52 – 10) / 0.26 = 262 mg/L PACl for 60% removal

Compared to DAF alone, the PACl dosage is reduced by

• ne third thanks to ozone.

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Economics

To build an OPEX/CAPEX comparison, the following costs are considered:

• 100 $/MWh
• 100 $/ton of oxygen
• 300 $/ton of PACl
• 50 $/ton for tertiary sludge disposal

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OPEX for 40% COD Removal

Tertiary Treatment DAF O3+DAF O3+BAFF PACl dose, mg/L 260 162 Daily PACl costs, $/day 3,900 2,423 Sludge production, ton/day 3.6 2.2 0.0 Daily sludge disposal costs, $/day 179 111 Ozone dose, mg/L 10 32 Daily ozone costs, $ 915 2,928 OPEX, $/day 4,079 3,449 2,928

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OPEX for 60% COD Removal

Tertiary Treatment DAF O3+DAF PACl dose, mg/L 390 262 Daily PACl costs, $/day 5,850 3,930 Sludge production, ton/day 5.4 3.6 Daily sludge disposal costs, $/day 268 180 Ozone dose, mg/L 10 Daily ozone costs, $ 915 Daily OPEX, $/day 6,118 5,025

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Conclusions

It is possible to efficiently reduce by half COD discharge at the outlet of an existing ETP. The combination O3 + BAFF allows for

• Lower tertiary treatment operating costs
• “Real” elimination of COD through oxidation.
• No sludge generation

The combination of O3 + DAF is possible in existing DAF installations, resulting in significant decrease of PACl dose and corresponding sludge volume.

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Conclusions

Economics show that OPEX are drastically reduced. Compared to conventional DAF, payback of O3 + BAFF is lower than 5 years with a 40% COD removal target. Introducing an ozone treatment ahead of an existing DAF treatment has a payback of:

• 4 years with a 40% COD removal target
• 2 years with a 60% COD removal target

But each situation is a specific case!

Sustainable development is your ambition… Ozone bleaching is our solution!

Fibria Jacarei, Brazil

Thank you for your attention!

22 Confidential