720 kld basic process design airlift

8/11/2019 720 KLD Basic Process Design AirLift

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Basic Process Design

720 m/day

Airlift MBR Ultra Filtration

Client GET Water solutions Pvt. Limited

Project name 720 KLD

Project No. STP MBR

Norit company X-Flow

Document statusRev. Date Description Prepared Checked Approved

0 Nov 3rd

, 2009 First issue PCGanesh

This document is property of X-Flow in Enschede. Nothing from this document may be duplicated and/or published without written

approval of the owner. 2007 X-Flow.


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X-Flow Client: GET Water Solutions Pvt. Ltd.,Know-How Centre Project: STP MBR

Basic Process Design Page 2 of 20

Revision 0, 09-91-TBA

Disclaimer

All information in this document is based on enquiry information and assumptions supplied by the

customer and not independently confirmed by X-Flow. X-Flow does not warrant the accuracy,

timeliness, completeness, adequacy or fitness of the information or the membrane design which

is based on this information and shall not be held liable to the customer or any third party with

respect to any alleged inaccuracy, incompleteness, inadequacy or lack of merchantability or

fitness for the purpose listed in this document.


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Revision History

Revision Description

0 First issue

Related documents

Doc. No. Originator Description Rev. Date

List of abbreviations

Abbreviation Description

AL Air Lift

BW Backwash

CA Citric Acid

CEB Chemical Enhanced Backwash

DC Drain

HC Hydraulic Clean

Lmh Litre/m2.h (membrane flux)

MBR Membrane Bioreactor

MLD Megalitres per day

MLSS Mixed liquor suspended solids

n.a. Not applicable

NaOCl Sodium hypochlorite

Nm3/h Airflow in normal cubic meters per hour (1bara, 20C)

TMP Trans Membrane Pressure

TSS Total suspended solids

VSD Variable Speed Drive

UF Ultra Filtration


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Contents

1 Introduction ______________________________________________________________________ 6

1.1

Project definition ______________________________________________________________ 61.2 Objective Basic Process Design __________________________________________________ 6

2 Basis of Design ___________________________________________________________________ 7

2.1 UF influent quality (mixed liquor)__________________________________________________ 7

2.2 Typical UF permeate quality _____________________________________________________ 7

2.3 Design capacity _______________________________________________________________ 7

3 Process Design ___________________________________________________________________ 8

3.1

Process summary _____________________________________________________________ 8

3.1.1 Filtration ______________________________________________________________ 9

3.1.2 Backwashing during filtration _____________________________________________ 9

3.1.3

Drain procedure ________________________________________________________ 9

3.1.4 Chemically enhanced backwash (CEB) ____________________________________ 10

3.1.5 Relaxation/ Stand-by ___________________________________________________ 11

3.2 UF plant design ______________________________________________________________ 12

3.2.1 Configuration UF plant _________________________________________________ 13

3.2.2 Main operational parameters ____________________________________________ 14

3.2.3 Chemical consumptions ________________________________________________ 16

3.2.4 Main process equipment ________________________ Error! Bookmark not defined.

4 Design Specifications _____________________________________________________________ 17

4.1 Pre-treatment _______________________________________________________________ 17

4.2

Bioreactor __________________________________________________________________ 17

4.3 Hydraulic design _____________________________________________________________ 17

4.3.1 Feed and permeate piping ______________________________________________ 17

4.3.2 Feed flow control during filtration, backwash and relaxation ____________________ 18

4.3.3 AirLift flow control _____________________________________________________ 18

4.3.4 Permeate flow control __________________________________________________ 18

4.3.5

Backwash flow control __________________________________________________ 18

4.3.6

UF skid pressures _____________________________________________________ 18

4.4

Permeate tank design _________________________________________________________ 19

4.5 Backwash strainers ___________________________________________________________ 19

4.6

Air ingress __________________________________________________________________ 19

4.7 Automatic valves _____________________________________________________________ 19

4.8 Chemical dosing for CEB ______________________________________________________ 19

4.9 Compressed air ______________________________________________________________ 19

4.10 Membrane storage ___________________________________________________________ 20

4.11 Facilities for commissioning and future operation ____________________________________ 20


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Tables

Table 2-1: UF influent quality ___________________________________________________________________ 7

Table 2-2: UF permeate quality _________________________________________________________________ 7

Table 2-3:

UF capacity assumptions ______________________________________________________________Table 3-1: Configuration UF plant ________________________________________________________________

Table 3-2: Main operational parameters per skid(filtration, backwash, drain and CEB)

Table 3-3: Typical chemical consumptions per skid __________________________________________________

Table 3-4: Main process equipment UF plant ________________________________________________________


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1 Introduction

1.1 Project definitionThis document outlines the design for an Airlift MBR to be installed at projected site for the

purification of municipal waste water. The Airlift MBR process consists of an activated sludge

process combined with a side stream Ultra Filtration membrane system for the separation of

activated sludge (mixed liquor) from treated effluent. As an out of basin solution (not being

submerged in the reactor), maintenance and cleanability are simple, safe and allow full

automation. The UF membrane system is 100% efficient at separating mixed liquor from treated

effluent. Only the UF part is described in this document. The engineering of the pre-treatment

and bioreactor is the responsibility of Prakruti.

The overall process consists of the following treatment steps:

Pre-treatment

Pre- screen *)

Oil and grease removal *)

Sand removal *)

Fine- screen *)

Bioreactor

AirLift UF unit

Post chlorination

The UF stage comprises the following units and equipment:

UF mixed liquor recirculation pumps

UF air supply for airlift

UF skids

UF permeate extraction

UF permeate tank

UF drain tank and pumps

UF backwash pumps (incl. manual UF backwash strainer)

Chemical dosing units

Air compressor (instrument air)

*) to be optimised

1.2 Objective Basic Process Design

The Basic Process Design document provides the basic process design information of the UF

plant. The following items are described:

Basis of design

Process design

Design specifications


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2 Basis of Design

2.1 UF influent quality (mixed liquor)The influent quality design envelope for the UF plant is presented in Table 2-1.

Table 2-1: UF influent quality

Parameter Units Min Avg Max Comment Note

Temperature C 20 - 40 1)

pH - 6 - 8.5 1)

Oil & grease [mg/l] n.p. n.p. n.p. n.p.: not present 3)

MLSS [g/l] g/l 8 10 14 Range between 8 14 g/l 2)

Filterability ml > 15 - -Filterability is based on filtered amount

through C5- paper during 5 minutes

2)

1) X-Flow assumption of UF feed water quality;

2) Based on UF feed water quality data according to enquiry document (see related documents);

3) Oil& grease must be emulsified. Higher concentrations will have impact on cleaning frequency and plant capacity.

Free O&G is not allowed, since this can irreversibly foul the membranes. Soluble O&G will pass the membranes.

2.2 Typical UF permeate quality

The typical UF permeate quality for the UF plant is presented in Table 2-2.

Table 2-2: UF permeate quality

Parameter Units Min Avg Max Comment Note

Temperature C 20 - 40 Same as UF feed water quality.

pH - 6 - 9

TSS mg/l - - 0.5 95%ile on daily composite sample 1)

Turbidity NTU - - 0.5 95%ile on daily composite sample 1)

SDI - - 3 1)

1) X-Flow specification of permeate quality, based on historical data. No warranty figures.

2.3 Design capacity

The membrane system with the proposed amount of membrane modules is designed to

accommodate the capacity assumptions as presented in Table 2-3 at the feed water conditions

as specified in Table 2-1.

Table 2-3: UF capacity assumptions

Parameter Units Design Comment

Average flow operation flow m3/h 31 UF design is based on maximum flow

Average flow duration h/d 24

Maximum operation flow m3/h 31

Maximum flow duration h/d 4

Daily throughput m3/d 739


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3 Process Design

3.1 Process summaryThe AirLift UF membrane system is a part of the MBR process and is applied to separate the

mixed liquor from treated effluent. The UF membrane system is fed with the mixed liquor from the

bioreactor by means of a recirculation pump. This recirculation pump is also used to maintain a

relatively constant flow of mixed liquor from the bottom to the top side of the vertically positioned

UF membranes. The three meter high membrane elements comprise tubular membranes with a

typical diameter of 5.2 mm. with a total of 33 m2of membrane area. These membrane tubes are

operated inside-out, i.e. mixed liquor is introduced at the lumen of the tubular membranes and

extracted as permeate at the shell side. The bottom side as well as the top side of the membrane

element are covered by an end cap. The bottom end cap is equipped with an air distribution

system (aerator). See below figure for a schematic layout of the AirLift MBR system.

Figure 3-1: Schematic representation of the AirLift MBR concept.

An AirLift membrane system is a modification of the conventional cross-flow membrane system

design in which the membrane modules are horizontally positioned. In an AirLift membrane

system the membrane modules are vertically positioned. This vertical orientation of the

membrane modules allows using air injection in the bottom end cap to maintain a gentle cross

flow through the membrane module. Due to this principle the mixed liquor is transported via an

Air-Lift pump through the membrane modules. In addition the injected air causes a very high

turbulence at the membrane surface and this ensures a continuous cleaning action and

subsequent constant system flux at a very low trans membrane pressure. While using the reliable

and proven technology of cross-flow tubular membranes the benefit of this AirLift system design

is that the energy consumption is significantly lower than the cross-flow system.

Back wash

Feed flow

De aeration

Air Lift

Drain

Permeate control

Chemical dosing

Bio reactor


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The filtrate (permeate) production of the AirLift system is measured by a flow transmitter and

controlled by an automatic control valve and/or permeate pump to meet the set-point production

flow. A part of the produced permeate is used for backwashing and cleaning operations of the UF

membrane elements in the system. For this purpose the system is equipped with a backwash

pump and dosing pumps.

3.1.1 Filtration

During production (filtration) operation of the plant, mixed liquor is pumped from the bioreactor

into the UF system by the recirculation pump. The recirculation pump ensures that a relatively

constant flow of mixed liquor from the bottom to the top of the membrane modules is established.

Air is injected via the bottom end cap air distribution system. The mixed liquor will be transported

upwards by air bubbles. In addition, each tubular membrane is scrubbed by the rising air bubbles

under turbulent conditions. The permeate production is controlled by an automatic control valve

and/or a permeate extraction pump to reach a constant permeate flow out of the AirLift system.

3.1.2 Backwashing during filtration

During operation (filtration) solids are retained by the membrane and some accumulate on the

membrane surface (inside) of the tubular membranes. These solids must be periodically removed

via backwashing to maintain system performance. For backwashing the flow direction through

the membranes is reversed. UF permeate is pumped into the membrane modules from outside to

inside of the tubular membranes by means of a variable speed backwash pump at a constant

preset flow. During this backwash the mixed liquor recirculation pump and air injection are kept

running to enhance solids removal and cleaning performance. Backwash waste is returned to the

bioreactor.

When using multiple skids, each skid is backwashed in a stream backwash. This means that

each skid in a section of skids is backwashed consecutively. A stream backwash is initiated after

a pre-set filtration time.

3.1.3 Drain procedure

The drain procedure is vital for proper operation of an Airlift MBR plant. It is also a feature that

makes the system unique because it ensures that no solids build-up (e.g. hairs) occurs at the

membranes. During the drain procedure the UF membrane skid is completely drained followed

by a automatic backwash. This sequence on the empty module is very effective; all material that

may have accumulated on the membrane surface and at the inlet (bottom side) of the membrane

module is drained and flushed out by this procedure. The subsequent backwash is very effective

because there is no re-circulation flow, the membrane feed side is empty. In addition, the air

distribution system in the bottom end cap and the air supply line to the distribution system is

flushed with UF permeate to prevent clogging. This drain procedure is typically executed 4 to 6

times a day. The collected mixed liquor from the drain procedure is routed back to the inlet


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strainer of the bioreactor, where any large particulate matter that may have formed in front of the

modules is removed from the system.

The drain sequence is also performed as:

Pre-step for chemical cleaning

After certain alarms or emergency stops

Pre-step before idle mode.

3.1.4 Chemically enhanced backwash (CEB)

Not all retained material can easily be removed by backwashes and drain procedures. Through

accumulation of absorbed substances onto the membrane surface, the pressure drop across the

membrane may increase gradually over the course of weeks or months. To remove these

substances and to restore the membrane performance a chemical enhanced backwash (CEB) is

required. The fully automatic CEB program is typically performed once per 1 to 3 months and if

possible during low flow hours, most likely at night, when full capacity is not required. Each skid

is cleaned separately while the other skids remain in production (filtration).

Before starting the CEB program the drain sequence is performed. After this drain sequence the

backwash pump is started at low flow, pumping UF permeate back into the membrane module.

At the same time cleaning chemicals (typically sodium hypochlorite or citric acid) are dosed in the

backwash line and transported into the membrane modules. After the membrane modules of the

skid are filled the backwash pump is stopped and the soak timer is started, typically between 30to 240 minutes. After the soak timer has elapsed the membrane modules are drained. The

drained chemical solution is typically fed back to the bioreactor because the activity of the

chemicals is strongly reduced after the soak period and the total volume is relatively small in

respect of the bioreactor volume.

The CEB program is performed with two chemicals consecutively, sodium hypochlorite and citric

acid. CEB1 is typically performed with sodium hypochlorite at a concentration of 200 to 400 mg/l .

CEB 2 is typically performed using citric acid to pH ca. 3 to remove foulants and scaling.

Figure 3-2 shows an example of the change in Trans Membrane Pressure (TMP), during theprocess. Stretches A depict the filtration, stretches B the backwashes or drain and stretch C

a Chemically Enhanced Backwash (CEB).


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Figure 3-2: Trans Membrane Pressure change during operation.

0,00

0,04

0,08

0,12

0,16

0,20

0,0 5,0 10,0 15,0 20,0 25,0 30,0Time

Transmem

branePressure(Bar)

A B A

B

Production

period

(2-10 wks)

C

A AB B

A

3.1.5 Relaxation/ Stand-by

The total membrane system might consist of more than one membrane skid. During low feed flow

periods, skids are taken off line in order to reduce the energy consumption of the total plant.

Taking a skid off line means that the skid goes into relaxation mode. The recirculation pump and

air supply are kept running as for normal filtration, however the permeate abstraction (via control

valve or permeate pump) is de-activated. This means that all the feed water fed to the membrane

modules is returned to the bioreactor. Due to this fact there is no driving force across the

membrane surface (as the permeate production is stopped), hence the recirculation flow will

clean the membrane surface due to the shear force in combination with air scrubbing. During this

relaxation program the skid can be taken on-line at any moment. When a skid has been inrelaxation for a certain period of time (i.e. its capacity is not required by the process) the skid will

be drained and filled with permeate after which it will be waiting in stand-by mode.


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3.2 UF plant design

The UF plant consists of one or more sections. Each section comprises several membrane skids

with one dedicated backwash pump serving all the skids in that one section. See below Figure

3-3 for a graphical presentation of a section with membrane skids.

Figure 3-3: UF section

Each membrane skid comprises a fixed amount of membrane positions, not all of whom are

necessarily filled with membrane modules. See Figure 3-4 for a picture of one membrane skid.

Figure 3-4: UF skid (example with 10, 20 & 30 modules)

Each membrane skid is controlled individually, i.e. all operating programs such as filtration,

backwash, drain procedure and CEB are performed on a skid level. All the membrane skids in

one section are backwashed consecutively, i.e. in a so called stream backwash.

Sectioncomprises ten

membrane skids

Skidwith membrane

modules


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3.2.1 Configuration UF plant

Table 3-1: Configuration UF units

Parameter Units Design Actual Comment

No. of sections - 1 -

No. of skids per section - 1 -

No. modules per skid - 30 23 7 spare modules per unit

Membrane area per module m2 33 -

Total membrane area m2 990 759

Reference is made to the UF projections; see section related documents. Typically two

situations apply:

1. Scenario for Design: UF design values based on full skids. UF equipment is always sized to

accommodate full skids (i.e. skids with all modules installed).

2. Scenario for Actual: UF design based on 19 modules installed in one skid, to reflect actual

operating parameters.

In the paragraphs below the projection data is presented in tables including additional information

such as assumptions and conditions.

Note: All UF projections are based on a 24 hours daily operation and are theoretical values at skid flange

level. To select equipment safety margins have to be included!


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3.2.2 Main operational parameters

In Table 3-2, the operational settings per skid for each of the programs are presented.

Table 3-2: Main operational parameters per skid (filtration, backwash and drain)

Parameter Units Design Actual Comment

Gross permeate flow m3/h t.b.d. 38 Current flow during filtration

Net permeate flow m3/h t.b.d. 31

Feed (recirculation) flow m3/h 684 (1) 525 (2)

AirLift flow nm3/h 300 (1) 230 (2)

AirLift pressure bar 0.6 0.6 To be applied at skid connections

Filtration period min n.a. 7-10

Typical TMP during filtration bar 0.03-0.5 0.1-0.3 Operational TMP range forfiltration, based on extendedhistorical operational data.

Backwash flow per skid m3/h 297 228 Flux: 300 lmh (max 1bar!)

Backwash duration per skid sec n.a. 7-10 At full capacity

Trans Membrane Pressure (TMP)during backwash

bar 0.5-1 0.5-1Operational TMP range forbackwash, based on extendedhistorical operational data.

Drain procedure interval hr. 3 t.b.d.

Expected program time sec 60 40-60 T.b.d. during commissioning

Backwash flow per skid m3/h 297 228 Flux : 300 lmh

CEB1 chemical - NaOCl - For concentration andconsumption, see Table 3-3.

CEB2 chemical- Citric Acid -

For concentration andconsumption, see Table 3-3.

CEB 1+2 interval per skid days 24 30-120

Typical duration CEB 1 min 60 -

Typical duration CEB 2min

>240-

When possible overnight soakingis advised

Backwash flow CEBs m3/h 149 114 Flux :150 lmh


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Table 3-4: Main process equipment UF plant

Equipment No. Size Design basis

(Note 1) (Note 1)

UF recirculation pump 1

684 m3/h,

Head

t.b.d. by

client

UF feed supply at max. gross flux (see Table 3 2)based on max. UF unit configuration (see Table 3 1).

Required head is max. UF unit pressure drop during

filtration (see Table 3 2) plus max. additional system

pressure drop (piping, strainer, static height

difference between suction and discharge, etc).

UF AirLift Blower 1

300

Nm3/h per

section,

Head

t.b.d. by

client

UF Airlift supply at max. gross flux (see Table 3 2)

based on max. UF unit configuration (see Table 3 1).

Required head is max. UF unit pressure drop (see

Table 3 2) plus max. additional system pressure drop

(piping, flow transmitter, etc). Maximum air

temperature at skid flange: 60 C.

UF permeate pump 1

50 m3/h,

Head

t.b.d. by

client

UF permeate based on max. UF unit configuration

(see Table 3 1). Required head is max. UF unit

pressure drop during filtration (see Table 3 2) plus

max. additional system pressure drop (piping, static

height difference between suction and discharge,

etc).

BW pump 1

297m3/h,

Head

t.b.d. by

client

UF BW supply at BW flux (see Table 3 2). Capacity

based on max. UF unit configuration (see Table 3 1).

Required head is max. UF unit pressure drop during

BW (see Table 3 2) plus max. additional system

pressure drop (piping, strainer, static height

difference between suction and discharge, etc).

BW Strainer 1

297 m3/h,

max.

screen 2

mm

Manual basket filter.

CEB NaOCl dosing pump 1

591 ltr/h

@ min. 3

bar

Achieving required CEB working concentration (see

Table 3 7) at BW flux during chemical dosing (see

Table 3 4). Capacity based on max UF unit

configuration (see Table 3 1) and 50% safety margin.

CEB CA dosing pump 1

3588 ltr/h

@ min. 3

bar

Achieving required CEB working concentration (see

Table 3 7) at BW flux during chemical dosing (seeTable 3 4). Capacity based on max UF unit

configuration (see Table 3 1) and 50% safety margin.

UF Permeate tank 1 18 m3 (2)

Minimum hold-up volume required to perform CEB

1+2 for one skid per section during the low flow

periods. Additional permeate storage volume is not

included.

UF Drain tank 1 14 m3 (2)

Buffer to control the drain unit, based on 2 times a

drain volume per skid, per section (incl. permeate

consumption).


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UF Drain pump 1

5 m3/h,

Head

t.b.d. by

client (1)

Based on minimal drain frequency per skid and 100%

safety margin.

3.2.3 Chemical consumptions

Table 3-3: Typical chemical consumptions per skid

Chemical Stock Working

conc. conc. Projectionl/CEB

% Design Actual

NaOCl (typical) 12.5 400 mg/l 12 9

All consumptions based on operational parameters as per Table 3-2 without any design margin.

Typical drain volumes

Program Step Volume (m3) Comment

Drain volume per skid

Drain 4.1

BW 2.9

Total 7.0 Based on 23 modules per skid

Drain volume total installation

Drain incl.

BW

2.1 Based on minimal drain frequency, see Table 3-3

at full capacity.

Typical permeate consumptions per skid per program.

Program Volume (m3) Comment

BW 0.8 Based on 30 modules per skid

Drain 2.2 Based on 30 modules per skid

CEB 1+2 13.2 Based on 30 modules per skid

Drain-Fill 6.3 Based on 30 modules per skid, before IDLE status

1 Numbers and capacities are based on duty only. Redundancy is not incorporated and should be addressed as per

customer redundancy philosophy

2 All tank sizes indicated above are net working volumes, i.e. volume between high and low level. For gross tank sizes,

additional volume to be included for low-low and high-high level, inlet and outlet piping, pump suction (avoiding vortex),

level switches, tank over flow, etc


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4 Design Specifications

Apart from the process design as described in the previous chapter, the following UF plant

design specifications apply which are described in subsequent sections. In addition, a shortdescription about membrane storage and commissioning and possibly future expansion of the UF

plant is given.

4.1 Pre-treatment

Although the Airlift system is much less susceptible to large particulate matter in the feed, the

final pretreatment step before the bioreactor shall consist of a reliable screen with a mesh no

larger than 800 m (typical a drum screen is used).

4.2 Bioreactor

The performance of the UF installation is directly related to the stability/ quality of the biomass in

the bioreactor. This requires a proper bioreactor design. For example the following points are

highlighted:

- Equal mixing

- Proper biomass control

- Proper Oxygen control

- Type of anti-foam (if used, it needs to be checked by X-Flow)

- Covering (if necessary for e.g. leaves and other dirts)

4.3 Hydraulic design

For safe and proper operation of the UF plant, serious attention shall be paid to the hydraulic

design of the UF plant during detailed engineering. In the subsequent sections important points

of attention are highlighted. Final responsibility for hydraulic UF plant design is with the customer.

However, as part of detailed engineering services, X-Flow can perform a review of the UF plant

layout drawings and advise on any potential required modifications or improvements.

4.3.1 Feed and permeate piping

The maximum pressure drop across the individual UF skid during filtration and backwash (flange

to flange, provided the maximum flow velocities are met) are specified in Table 3-2 of this

document. The acceptable velocities in the pipes associated with skids are as follow:

Water:

Feed/permeate piping (feed pump pressure side) : < 2 m/s

Backwash/concentrate piping (backwash pressure side) : < 3 m/s

Feed & backwash pump suction side : 0.5- 1 m/s


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Air:

Blower pressure side: < 20 m/s

Note:The above specified velocities are not a guarantee for an equal flow distribution to the individual UF skids. It is

Important to choose a proper pipe size for the central header of a section in relation to each individual skid. An equal

air distribution to the UF skids is the responsibility of the costumer.

4.3.2 Feed flow control during filtration, backwash and relaxation

Each individual UF skid requires a feed flow control device with flow transmitter. Preferably this is

a dedicated centrifugal feed pump with variable speed drive (VSD) per UF skid. Accepted pump

speed is < 1000 rpm.

4.3.3 AirLift flow control

The air supply for the AirLift must be supplied by a frequency controlled blower, since the flow of

air will vary with required plant capacity. The air flow is measured in the central air supply line by

a flow transmitter. An equal flow distribution of the air to the individual skids is the responsibility

of the customer.

4.3.4 Permeate flow control

The permeate flow is controlled at each skid individually by means of an automatic flow control

valve and flow transmitter per skid. A frequency controlled permeate pump is/maybe required per

section of skids.

4.3.5 Backwash flow control

Each section of the total UF plant shall be equipped with a centrifugal frequency controlled

backwash pump. The frequency control on the pump motors is required for smooth ramping-up

(max ramp up time < 8 sec) and ramp down to the different flow setpoints for backwash and

CEB. Moreover, the frequency control is required for maintaining the required backwash flux

during the (short duration) backwash period. Since the membrane modules require backwashing

at a fixed flux a flow transmitter is required for backwash flow measurement.

4.3.6 UF skid pressures

The backwash pressure at the UF skid inlet flange shall be kept below max 1 bar.

Hydraulic shocks and pressure/flow surges must be avoided at all times. Hence, an appropriate

hydraulic profile shall be established for the UF plant during detailed engineering. During

commissioning, valve opening and closing times and pump ramp-up and ramp-down times have

to be carefully set and monitored. For large and complex UF plants, a hydraulic surge analysis is

advised.


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4.4 Permeate tank design

The permeate tank has to be constructed from non-corroding materials that will not leach

contaminants into the water. The water in the permeate tank has to be protected from directsunlight in order to minimize bacterial and/or algae growth.

4.5 Backwash strainers

To avoid any potential damage to the UF membranes, entrance of foreign harmful matter must

be avoided at all times. For this purpose the backwash water to the UF skids shall be pre-filtered

by strainers with a screen size of maximum 2 mm.

4.6 Air ingress

During start-up, and every time the UF plant has been opened for maintenance activities,

attention shall be paid to proper filling and venting of the pipe work, the UF skids and other

process equipment involved.

4.7 Automatic valves

Each skid is equipped with automatic valves. The valve opening and closing times are directly

related to the efficiency of the UF installation. Thats why quick acting valves are strongly advised

(e.g. pneumatic valves).

4.8 Chemical dosing for CEB

During CEB, the chemicals are dosed proportionally to the backwash flow into the backwash

pipe. Thus the chemicals are diluted to the correct CEB working concentration to be applied for

the membranes. For this purpose, a static in-line mixer shall be installed for proper and effective

mixing of the chemicals into the backwash flow.

Check the X-Flow data sheet for the specific chemical resistance of the membrane.

4.9 Compressed air

During UF plant operation, compressed air is required as instrument air (e.g. pneumatic valve

operations) and for the AirLift principle as explained in previous sections. Compressed air shall

meet the following specifications:

Instrument air:

ISO 8573-1, class 2/3/2 (oil/water/particles) @ 6 bar g minimum pressure

AirLift:

ISO 8573-1, class 1/3/1 (oil/water/particles)


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Revision 0 09 91 TBA

4.10 Membrane storage

New membrane modules can be stored as supplied in a dry, ventilated place, away from sources

of heat, ignition and direct sunlight. Store between 0C and 40C and prevent freezingtemperatures at all times.

After unpacking the UF membranes (i.e. removal of the original plastic vacuum bag), the

membranes require to be stored under wet conditions at all times.

To avoid biological growth during shutdowns or storage, wet membranes shall be treated with a

compatible biocide. The membrane is compatible with many common disinfecting agents or

biocidal preservatives. For short-term shutdowns, a daily flush with permeate quality water

containing up to 2.0 ppm free chlorine is adequate for bacteria control. In case of long-term

storage, membranes should be chemically cleaned (CEB) before the disinfection step is carried

out. For disinfection, a 1% sodium metabisulfite solution can be used. In either situation, modulesshall be stored filled with this solution (wet condition).

4.11 Facilities for commissioning and future operation

For commissioning purposes and future operational flexibility, attention shall be paid to

(temporary) facilities consisting of but not limited to the following:

To avoid any potential damage to the UF membranes, entrance of external harmful matter

must be avoided at all times. For this purpose the feed flow (mixed liquor) must be free of

particles > 2mm at the start of the installation and in future operation.

Commissioning connections for membrane flushing:

Prior to start-up, the membranes have to be flushed with drinking water quality to flush out the

preservation chemicals to waste (sodium bisulphite and glycerine = BOD). For this purpose,

drinking water supply to the UF feed tank and/or permeate/backwash shall be available.

Connections/facilities/space for future extensions:

In case future extension of the UF plant is considered, it is advised to reflect upon the

consequences for the overall UF plant design as early as possible. To avoid future

inconvenience and to limit overall investment costs, some measures may already be taken

into account during the initial UF plant design, e.g.

Increase UF unit size by providing space for future installation of additional membranes

Increase BW pump and CEB chemical dosing pumps for future extension of the number

of UF units

Increase pipe work sizes for future increase of capacity

Provide (building) space for future installation of additional UF units

Provide (building) space for future installation of additional feed and/or backwash pumps

Provide (building) space for future installation of an additional CEB dosing unit

Increase size of permeate tank for future increase of capacity.

720 kld basic process design airlift

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