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A Case Study

RO Pilot Plant - QatarIntroduction

The State of Qatar has a number of WastewaterTreatment Works (WWTW) from where treated sewageeffluent (TSE) is distributed mainly for irrigationpurposes. The Public Works Authority, Drainage Affairs(PWA DA) has identified the potential to enhance the

treatment of municipal foul sewage to improve thequality of treated sewage effluent (TSE), therebyexpanding the range of TSE re-use applications. The DAproposed that the enhanced treatment process bebased on membrane technology, which has evolved asone of the front-runners in the field of AdvancedWastewater Treatment (AWWT). Drainage Affairsexpressed their desire to investigate the viability ofmembrane technology in the State of Qatar by means ofa Pilot Plant Study.The Pilot Plant Study was to be located at the Doha West

STW, about 30km from Doha International Airport. Theoperation would test the overall feasibility of themembrane AWWT process, and the extent to which TSEcould be purified by each type of pre-treatment processunder study.

The scope of the pilot study phase included supply,installation and operation of a Pilot Plant. Depending on

the success and feasibility of the study, a second phasewould include the installation of large scale plant(s).

Scope of WorkPlant General Information

The Pilot Plant was provided in a containerized form,thus allowing flexibility of relocation to any site. Theplant consisted of four pre-treatment units operated inparallel, feeding one Reverse Osmosis (RO) train. These

Brief description of the pilot plant:

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Plant Technical Features

treatment units include Micro-filtration (MF) andUltra-filtration (UF). During normal operation of theplant, filtrate form the UF stage is collected in a break

tank and fed to the RO train. However, provisions weremade to feed the RO train using filtrate from any of thefiltration units.

Feed water from the TSE wet wel l is pumped to a buffertank by means of a submersible pump. The buffertank acts as a steady source of water to all fourpre-treatment units that are in parallel operation at thesame time. The filtrate and product are returned backto the TSE wet well. Effluent/water containinghazardous/cleaning chemicals is collected in aholding tank and is then pumped to a designatedlocation inside the works.

The Pilot Plant is PLC based, fully automated withminimum manual intervention. It is equipped with localinstruments to check operational parameters suchas flow, pressure and conductivity as well as othercritical parameters. Initia tion of operation is manual.

Each filtration unit is able to operate independently.

All operations such as start up / stop, flushing andbackwashing are automatic. All the cleaning systems areclean-in-place (CIP) type, and all units are equippedwith individual flushing/cleaning facilities.

The RO train has the capacity to treat a flow of 45m/h.Each membrane pre-treatment unit is designed toproduce sufficient water to feed the RO train and thewater needed for other services such as backwash.

Process description

The pilot plant consists of two pre-treatment unitsrunning in parallel as Duty / Standby, and one RO train.These pre-treatment units are membrane type filtrationthat includes Micro and Ultra-filtration. During normaloperation, filtrate from pretreatment is collected in theFiltered Water Tank and fed to the RO train. However,provision is made to run the RO train using filtrate from

any one of these filtration units. Each unit is able tooperate independently.

Feed water from the TSE wet well is delivered to thebuffer tank via submersible pumps. The buffer tank actsas a steady source of water to the two filtration unitsrunning in parallel. Filtrate and product water are leadback to the TSE wet well. Water containing chemicals inhigh concentration, i.e. UF and MF chemical backwashwater, is collected in a chemical waste holding tankwhere it is neutralized and sent back to the TSE wet well.

Process Flow

1stOption MF/RO :

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TSE Wet Well Pumps Pre-Chlorination DosingCoagulant Dosing MF Feed / Backwash Pump MFSelf Cleaning Filte Micro Filtration Unit Filtered WaterTank RO Feed Pump Ultraviolet Unit Cartridge Filter- Acid Dosing Antiscalant Dosing SBS Dosing ROHigh Pressure Pump Reverse Osmosis Unit DischargeWater Tank - Wet Well

2ndOption UF/RO :

TSE Wet Well Pumps Pre-Chlorination Dosing -Coagulant Dosing - UF Feed Pump - UF Self-cleaningFilter - Ultra - Filtr ation Unit - Filt ered Water Tank- RO Fee d Pump - Ultraviolet Unit - Cartridge Filter -Acid Dosing - Antiscalant Dosing - SBS Dosing - ROHigh Pressure Pump - Reverse Osmosis Unit -Discharge Water Tank - Wet Well.

Demonstrate the technical feasibility of the ReverseOsmosis Technology

Provide a working model to demonstrate thesuitability of the process

Implement a wide range of TSE analyses from theselected intake point, and subsequently test thequality of treated effluent after various stages oftreatment

Verify plant design conditions with particular reference to:

The effectiveness of the proposed

pre-treatment stages under various operatingand expected TSE conditions. This wouldinvolve evaluation of the TSE conditions as wellas the TSE feed water silt density index (SDI),cartridge filter replacement rate, fouling rate ofMicro-filtration (MF), Ultra-filtration (UF), andRO membranes and chemical dosing rates.

The effectiveness of the proposed membranesystem, in particular with respect to the productwater quality.

RO system process parameters by:

1.

2.

3.

3.1.

3.2.

3.3.

The test programme for the pilot plant was intended toachieve the following :

Testing the proposed membrane processparameters (recovery ratio and flux rate)

Testing the effectiveness of the membranecleaning procedure

Testing the correct dosage of the scaleinhibitor

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Metito was proud to be involved in this project. Onceproven, the technology would open new horizons forreuse. One of the pioneering ideas for reuse is AquiferStorage and Recovery (ASR), which PWA has beencontemplating. If applied, this will be the first of its kindnot only in the Gulf region but in all of the Middle East

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RO Pilot Plant Block Flow Diagram

and Arab World. Under this scheme, treated wateris injected in the aquifer to create strategic storagefacilities where fresh water can be withdrawn for futurepotable or other uses, thus adding to the renewablewater resources of the country.

Chemical Waste HoldingTank & Neutralization

System( Capacity: 10 m3)

Backwash Water

Main Process LineSecondary Line

Filtered WaterTank

R.O. Feed( Capacity: 20 m3)

Wet Well TSE

or

No. of Stages: 3Arrangement: 4x6 /2x6 / 1x6

Maximum Recovery: 85%MaximumFeed Flow: 40 m

3/hHPP &BoosterPumpsSupplied

with VFD

UVSystem

45 m3/h

55.6 m3/h

42.0 m3/h

35 m3/h

RO SYSTEM

FLUSHING TANK( Capacity: 10 m3)

CLEANING TANK( Capacity: 20 m3)

MF SYSTEMRecovery 94%

Maximum Filtration Flux:80 l/m2/h

Maximum Product Flow:40 m3/h

MF Feed Pump & BackwashPump Supplied with VFD

Buffer WaterTank

( Capacity: 10 m3)

mcs 014

Discharge Water Tank& Backwash Tank

( Capacity: 10 m3)

UF SYSTEMRecovey: 83 %

Maximum Filtration Flux :65 l/m3/h

Minimum Filtration Flux :48 l/m3/h

Maximum Product Flow :46 m3/h

Maximum Feed Flow :62 m3/h

UF Feed Pump & BackwashSupplied with VFD