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Mårten Krogerus

NAME OF PRESENTATION 1

SUB HEADER – A SHORT DESCRIPTIVE TEXT

Marten Krogerus is presently manager and leading technology specialist at ÅF-Pöyry and has more than 35 years of experience of working with environmental assignments for the pulp and paper, and other industry both as process supplier and as technical consultant. He has a broad know-how and understanding of all the environmental issues related to the industry branch. His special area of expertise is effluent treatment in the pulp and paper industry. Along with other areas he has worked specifically with conceptual studies, mill environmental audits, and process optimisation and improvement tasks. Marten has been working in more than 20 countries worldwide.

Initially, Marten was involved in the development and implementation of the first biological treatment plants for Pulp&Paper industry in the Nordic countries in the 1980’s as a turnkey supplier. Later, as a consultant, he has worked out from Finland, Sweden and the U.S. for pulp and paper industry clients locally and abroad.

Marten is very knowledgeable in design and operation of biological treatment systems. One of his specialties is analysis of treatment plant performance and assessing corrective measures for achieving optimal results. He has developed strategies for assuring continuous good results.

Marten has also a capability to quickly evaluate design issues and bottlenecks in an existing plant and propose measures to avoid such problems.

Aerobic biologic treatment / Activated sludge


P&P EFFLUENT TREATMENT - MODULE I

Technology and control - Day 2 14:00 – 18:00

Technology and control session

General description of the activated sludge process

Technology concepts

Pretreatment requirements─ Primary sedimentation─ Cooling─ Neutralisation─ Nutrient addition

Aeration concepts─ Flow patterns, selectors, plugflow, alternative aeration concepts─ Aeration equipment─ Main aeration design principles

Sedimentation process, sludge recycling and excess sludge removal─ Sedimentation process alternatives─ Sludge recycling rate principles

Sludge dewatering─ Sludge characteristics and how this will impact on dewatering concept─ Alternative dewatering equipment


Technology and control session, cont.

Operational control

Key control parameters─ Impact of temperature─ Impact of of incoming solids─ Impact of incoming pH─ Organic loading

─ F:M ratio

─ Sludge age

─ Oxygen control principles─ Nutrient control principles

Process optimisation principles─ Pretreatment─ Aeration basin─ Sedimentation process and sludge recycling rate principles─ Sludge dewatering

Expected removal efficiencies─ Impact of operational control─ Other parameters


General description of the activated sludge process

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GENERAL DESCRIPTION OF THE ACTIVATED SLUDGE PROCESS

Activated sludge process

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pH control,Nutrients addition

Aeration Tank Sedimentation

Return Sludge Excess Sludge


Background and objectives• A biological wastewater treatment method for treatment of biodegradble

organic matter

• Process ”invented” already 100 years ago but has gradually improved over the years

• Today activated sludge is the most common biological technology for industrial wastewater treatment

•

• Efficiently remove biodegradable organic substances (BOD, COD, TOC)

• Remove specific substances

• Remove toxic substances

• Ammonium or nitrogen removal (nitrification, denitrification)

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Activated sludge• A biological treatment process where optimal conditions for high removal of

organics are created by:

Recirculation of biologically active biosludge and thus increasing the concentration of biosolids in aeration tank

Assuring that all physical and chemical conditions are optimised in incoming water and in the treatment process

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Types of activated sludge• Completely mixed systems

• Plug flow

• Selector

• Low/Minimum Biosludge Production

• Pure oxygen

• Two stage systems

• Nitrification - Denitrification

• Powdered activated carbon in activated sludge

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Prerequisites for optimal conditions in incomingwater to an activated sludge processes

• Low concentration of suspended solids

• pH within optimal range

• Sufficient levels of nutrients

• Temperature within optimal range

• Equalization if incoming water is highly variable

• Use of spill pond in emergency conditions

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Micro-organisms

• The key requisite in activated sludge process is a healty culture of micro-organisms

• The micro-organisms or microbes form the biomass or biosludge

• The biosludge must flocculate to enable separation and return ofbiosolids back to aeration tank

• The biomass in the system is a mix of different aerobic micro-organisms an ecosystem where the species interact and feed on each other

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Micro-organisms

Micro-organism

OxygenNutrients

Organic matter

Heat

Carbon DioxideWater New micro-organisms

Other compounds(degradation products)


Micro-organisms

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13

Free swimming bacteria

Floc forming bacteria

Filamentous bacteria


Micro-organisms and micro-animals

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Protozoa Rotifers

Nematods

Free living

Flagellates

Ciliates

Stalked ciliates


Bacteria

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Floc forming

Filamentous

Free living cells


Type of bacteria

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Good quality sludge Poor quality sludge


Growth of micro-organism cultures

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Amount ofBOD / Sludge

Time

High loadedAS

ConventionalAS

Extendedaeration

Logarithmicgrowth

Declininggrowth

Endogenousphase

Biosludge

BOD


Growth of micro-organisms

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Time Weight0 1 kg20 min 2 kg40 min 4 kg1 h 8 kg2 h 64 kg3 h 512 kg4 h 4096 kg

• Generation time is 20 min for some bacteria

• Microbe culture is constantly changing – part of the culture dies and become food for others

Technology concepts

Pretreatment requirements

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TECHNOLOGY CONCEPTS – PRETREATMENT REQUIREMENTS

Primary sedimentation

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Objectives

• There are two primary objectives why goodprimary sedimentation is required:1. To reduce COD load related to solids entering

biological process 2. To avoid accumulation of inactive deadload in the

biological system

• By achieving good suspended solids removalhigher sludge age can be achieved



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Principles

• Primary sedimentation may be carried out on total incoming flow or only the fiber-containing flows

• Primary clarifiers must have capacity to allow settling of settleablesolids• The clarifiers are principally design based on surface load (m3/m2, h)

• Primary clarifiers must have volume to allow some buffering of the settled solids • The clarifiers must be designed deep enough

• Primary clarifiers may be circular or rectangular• Circular clarifiers are ofter preferred based on operation and cost



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Principles

• Solids transport and removal must be designed sufficient

• Surface solids skimming systems

• Sufficient controls on solids amount and consistency in clarifier


Cooling

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Objectives

• Assure optimal temperature conditions for microbes• Too high temperatures will kill the microbes• Low temperatures reduce biological activity and

degradation rates

• Optimal temperature for mesofilic microbes is about 37 C

• Cooling is typically carried out using heat exchangers or cooling tower or both


Cooling

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Principles

• Cooling can be carried out using• Spray cooling in ponds• Direct cooling in cooling tower• Indirect cooling using heat exchangers and own cooling

loop with cooling tower • Indirect cooling using heat exchangers and common

cooling water

• Cooling towers and heat exchangers are generally sensitive to suspended solids• Different design available to avoid clogging

• Redundancy recommended


Direct cooling

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Advantages:• Proven technology most commonly used in

P&P industry• Simple technology• Maintenance (cleaning) relatively easy • Low investment cost

Drawbacks:

• In case, the effluent includes unstripped condensate, the cooling tower will drive it off and create a significant odour problem. With no cooling tower a part of the odour would still be released in aeration tank. Consequently, to assure no odorous emissions to atmosphere, odorous condensate should never be directed to the effluent.


Indirect cooling with cooling water

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Advantages:

• No odorous emissions

• Small footprint

Drawbacks:

• Permitting issues related to withdrawal and discharge of cooling water

• High risk for scaling and plugging of HXs

• High operation cost due to maintenance


Indirect cooling with cooling tower

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Advantages:

• No odorous emissions

• Closed cooling loop with make-up water only

Drawbacks:

• Significant risk for high maintenance (cleaning)

• High risk for scaling and plugging of HXs

• High operation cost due to maintenance

• High investment cost (increased cooling tower and HX sizing)


Neutralisation

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Objectives:

• Wastewaters from pulp and paper production aretypically not close to normal

• Wastewater pH will impact on the health ofmicrobes

• Each specie has a optimum pH range


Neutralisation

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Design

• Wastewaters are neutralised with acids and alkali• Sulfuric acid• Hydrochloric acid• Sodium hydroxide• Lime (CaO or Ca (OH)2)

• The retention time has to be properly chosen depending on neutralization chemical and temperature

• The required amount of chemicals should be confirmed with lab tests (titration)

• Add the chemicals to the most acid/alkaline effluent

Potential operation problems

• Odour gases

• Foam


Nutrient addition

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Objectives

• Nutrients deficiency are often a primary reason for poor performance• Nutrients – nitrogen and phosphorus• Micronutrients – trace elements

• Required to optimise microbial growth• Minimum requirement, but excess will not improve performance

Principles

• Nutrients are typically added as:• Urea• Ammonia water• Nitrate salts

• Phosphoric acid• Phosphate salts

Technology concepts

Aeration concepts

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TECHNOLOGY CONCEPTS – AERATION CONCEPTS

Tank configuration

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Tank dimensions

• Rectangular

• Circular

• Compartments/Divison walls

• Water depth from 4 m to 12 m

Construction

• Earth basins

• Concrete tanks

• Blasted in bedrock


Flow patterns

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Total mixed tanks

• Wastewater is mixed with total aeration volume

• Less costly investment

• Disadvantage is risk for filament formation

Plug flow tanks

• Plug flow

• Compartmented flow


Selectors

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Objectives

• To select bacteria/microbes which have a goodsettling characteristics and will enable the process to maintain a high sludge concentration

Principles

• Natural selection

• Takes place in a small initial volume (0,5 h-1 h retention)

• Flocforming bacteria have better possibility thanfilamentous to uptake substrate at highconcentrations


Minimum Biosludge Production

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Objectives

• To create conditions where sludge generation is minimised

Principles

• Aerated without sludge return

• Creates free-swimming micro-organisms whichreduces some organics

• Main aeration will feed on free-swimming

• Total sludge generation may be as low as 0,15 kg TSS/kg COD rem


Aeration equipment

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Aeration equipment alternatives

• Surface aeration• Fixed aerators• Floating aerators

• Bottom aeration• Perforated piping• Bottom turbines• Diffusers, fixed• Diffusers liftable• Jet aeration

• Blowers• Rotary displacement blowers• Centrifugal blowers (Turbo)• Helical screw blowers


Surface aeration

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Principles

• Floating surface aerators • are low cost equipment• Can be located at any position• Aerates through splashing up water in air

• Fixed surface aerators • Fixed at bridges etc.• Larger power of motors possible• Aerates through splashing up water in air

• Limitation is mixing capacity. Typically limited to about 5-6 m and relatively low sludge concentrations

• Surface aerators have low aeration efficiencytypically 0,5-1,5 kg O2/kWh


Bottom aeration

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Principles

• Perforated piping• Low risk of clogging, low maintenance demand• Lower aeration efficiency than other bottom aeration

• Diffusers, fixed or liftable• Good aeration efficiency• Liftable can be lifted up for maintenance if required

• Diffuser aerators have good aerationefficiency typically 3-4 kg O2/kWh


Bottom aeration

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Principles

• Bottom turbines (OKI aeration)• A main maintenance issue is motor located under

water• Requires blower for air supply

• Jet aeration (MTS or Flygt)• With air suction or blower feed

Mass Transfer Systems bi-directional jet aerators


Blowers

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Objective

• Provide air to bottom aeration equipment

Principles

• Positive displacement blower• Typically for smaller air flows

• Centrifugal blowers• Single or multistage• For larger air volumes• Up to 12 mwc pressure


Aeration equipment

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Main aeration design principles

• Aeration design shall be based on actual or future COD or BOD loads

• Aearation design shall be based on expected conditions in the aeration process (Variability, sludge age and residual DO in all parts of aeration tank).

• Max month and max day conditions shall be design basis not annual average

• In selecting equipment the main criteria is:• Aearation efficiency of equipment (including blowers) , kg O2/kWh in

standard conditions• Maintenance of equipment• Sufficient redundancy installed to handle unexpected conditions

Technology concepts

Sedimentation process, sludge recycling and excess sludge removal

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TECHNOLOGY CONCEPTS – SEDIMENTATION

Sedimentation processes

Objectives

• Separate biosolids from treated water

Principles

• Circular or rectangular clarifiers• Circular gives more even return sludge

concentration

• Scraper type, plates or suction pipes• Suction type have shorter retention time in

clarifier

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TECHNOLOGY CONCEPTS – SEDIMENTATION

Sedimentation process

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• Location and type of overflow weirs• Periferal overflow in circular• Midway overflow• The main issue is to assure the proper flow patterns

• Clarifier sizing• Over 80 m in diamater clarifiers have been designed• Wind effect to be considered

Technology concepts

Sludge dewatering

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TECHNOLOGY CONCEPTS – SLUDGE DEWATERING

Principles in handling ofsludges

• Collection of various sludges

• Mixing or separate handling

• Conditioning

• Thickening

• Dewatering

• Disposal of dewatered sludges

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Factors impacting on equipment an anticipatedresult

• Amount and quality of fiber sludge and biosludge

• Ratio Biosludge to Fibersludge

• Targeted dryness (final disposal alternative)

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Sludge conditioningObjective

• Improved dewatering characteristics of sludge

• Improve degree of solids retention in sludge dewatering

Methods

• Chemical• Coagulants (Alum, Fe-salts)• Polyelectrolytes• Mixing and flocculation important

• Thermal

• Biological

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Sludge ThickeningObjective

• Initial dewatering step

• Increase dryness from 0.5 ==> 3…10 %

Principles

• Directly in sedimentation basins

• Gravitation thickening• Thickening basins• Centrifuge

• Flotation thickening

• Screen thickening• Gravity table• Drum screen 49


Sludge DewateringObjective

• Final dewatering step

• Increase dryness from 3...10 ==> 20…50 %

Principles

• Belt presses

• Screw presses

• Chamber filter presses

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Operational control

Key control parameters

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TECHNOLOGY CONCEPTS – OPERATIONAL CONTROL

Key control parameters

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• In order to assure the best operational result in an activated sludge plantthe key control parameters must be monitored continuously and measurestaken to correct characteristics if needed

• The key control parameters include both• Incoming wastewater (parameters that can be controlled)• Process conditions

• In addition all pertinent operational parameters and analysyes must be monitored and follow-up.


Incoming wastewater key control parameters

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TemperatureIssue

• Incoming temperature is too high. Wastewater temperaturewill directly impact on the system temperature and thusbiological activity

Target

• Temperatures in the aeration tank above 37 C for periods longer than 24 h should be avoided

Control/Mitigation measure

• Increase cooling capacity to reduce system to targetedtemperature.

• If capacity is not sufficient, install additional capacity



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pHIssue

• Incoming pH is outside targeted range of 6,5 to 8,0

Target

• Incoming wastewater pH 6,5 -8,0 as daily average


• Check neutralisation process to assure proper functionality




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Suspended solidsIssue

• Incoming TSS higher than target

Target

• Incoming wastewater 100-150 mg/l as daily average. (target may depend on the type of production).


• Check primary settling process to assess reason for increaseand assure proper functionality for sludge removal, hydraulicload

• Perform sludge settling tests



Process condition key control parameters

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Nutrient availabilityIssue

• Are the available nutrient levels suffient in the process?

Target

• Nitrogen minimum 3 mg/l as dissolved total nitrogen in treated effluent

• Phosphorus 0,3 mg/l as dissolved total phosphorus in treated effluent


• Correct dosage stepwise to control residual levels towards target




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Organic loading – Sludge ageIssue

• To maintain stable and optimal biodegradation conditions in the process

Target

• Maintain a sludge age at 15 days +- 3 days calculated as gliding 7 days average(The target days may be different depending on original design)


• Correct excess sludge wasting stepwise to control sludge age towards target




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Dissolved oxygen concentrationIssue

• To maintain stable and optimal biodegradation conditions in the process

Target

• Maintain the following levels in the aeration tank (on 6 hour basis)• Selector 0,5-2 mg/l• Beginning aeration tank 1,5-2,5 mg/l• End of aeration tank 2 -3 mg/l


• Correct air supply or aeration energy to control DO towards target


Operational control

Optimisation principles

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• General• Follow-up performance regulary and continuously• Act on trends and occasions when exceeding target ranges• Regular visual inspections

• Pretreatment (primary clarifier, cooling , neutralisation, nutrients)• Perform settling tests on incoming wastewater to compare with primary clarifier data• Calculate regular nutrient balances to compare with measured data• Make sure no anoxic activity occurs in the basin. In that case reduce sludge retention time.• Use of polymer in specfic cases may be warranted

• Aeration process• Calculate daily, sludge age (7 d avg), and SVI, and make visual microscopic analysis• In case of filament growth, increase nutrient levels above target and maintain high removal of excess sludge.

Gradually return then to normal.

• Sedimentation process and sludge recycling• Check functionality of suction pipes• Maintain stable return sludge flo back to aeration. Target 80-120% of average inflow rate



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• Sedimentation process and sludge recycling• Make sure no anoxic activity occurs in the basin. In that case increase sludge recycling rate .• Check functionality of suction pipes• In general maintain stable return sludge flo back to aeration. Target 80-120% of average inflow

rate

• Sludge thickening dewatering• Ensure stable an even mix of sludges to sludge dewatering• Use sufficient amount of polymer for flocculation. Sample regularly filtrate TSS

quality and calculate sludge retention percentage. Target >95-98%.

Operational control

Expected removal efficiencies

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Expected removal efficiences

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• Conditions of incoming wastewater and treatment process will affect the removal efficienciesand treated wastewater quality

• A direct connection is often difficult to pinpoint from monitoring results

• The best way of assuring highest possible removal rates is to maintain that all key controlparameters are with given ranges

• Most important is to monitor key operational parameters on a daily basis and make the rightconclusions from the data

• Many of the upsets that happen in activatred sludge plant can often be observed long beforethe results are deteriorating clearly.


Some basic rules

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Increased TSS concentration in treated effluent can be either a result of

a. TSS losses as flocs/sludge overflow• Too low sludge age• Poor sludge quality (High SVI)• Too low sludge recycling rate• Secondary clarifier problems (suction pipes, flow pattern)

b. TSS losses as dispersed growth (not as clear flocs)• Too high sludge age• Too high temperature• pH out of range• Too low nutrient levels• High internal TSS load due to poor sludge retention in dewatering• Too low DO

Increasing SVI in aeration can be a result of • Too low sludge age• Too high temperature• pH out of range• Too low nutrient levels


Some basic rules

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Increased dissolved COD concentration in treated effluent can be an indication of • Too low high sludge age• Too low DO• High temperature• pH out of range• Too low nutrient levels

Increased dissolved phosphorus concentration in treated effluent can be an indicationof

• Too low high sludge age• Too low DO• Nitrogen deficiency• High temperature• pH out of range• Too high dosage of phosphorus

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