Water Reclamation Trial Projects in Drainage Services ... · This paper is intended to present the experience learned and ... (PTW) / Sewage Pumping Station (SPS): c1 - Kwun Tong

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Water Reclamation Trial Projects in

Drainage Services Department

Horace H. CHAN

Drainage Services Department, the Government of the Hong Kong Special Administrative Region

Abstract

To keep abreast of the latest membrane filtration technologies on reclaimed water and its

application to align with the Drainage Services Department (DSD)’s vision of providing

world-class wastewater and stormwater drainage services enabling the sustainable development

of Hong Kong, DSD has successfully commissioned 11 small-scale water reclamation trial plants

in September 2010 to reclaim part of the effluent having received different level of treatment at

various sewage treatment works for in-house non-potable uses. These plants were designed with

different scales, configurations and technologies, including micro-filtration, ultra-filtration,

membrane bioreactor and reverse osmosis.

The 11 trial plants have been operated under close monitoring for nearly 20 months and the

reclaimed water was mainly used for toilet flushing, plant and facility washing, make-up water

for chemical scrubbers, landscape irrigation and chemical preparation within the sewage

treatment works.

This presentation will attempt to give an overview of the performance of the different water

reclamation technologies of these trial plants.

Introduction

To have a better understanding of the latest

membrane filtration technology on reclaiming

effluent having received different level of sewage

treatment, and to align with the DSD’s vision of

providing world-class wastewater and stormwater

drainage services for enabling the sustainable

development of Hong Kong, DSD has implemented a

pilot scheme of using reclaimed water from 11

reclaimed water plants installed at its sewage

treatment facilities in 2010 for different in-house

non-potable applications. These pilot plants were

designed with different scale and configurations, as

well as technologies and membrane materials for

treating different types of effluents at DSD sewage

treatment facilities on a trial basis. This paper is

intended to present the experience learned and

performances of these different plants based on the

operational data/records collected since the trial

operation of these plants for some 20 months. It is a

short period of time as comparing with the typical

life cycles of membranes which are normally in the

range of 5 to 7 years.

Water Reclamation (WR) Processes

The WR plants in the pilot schemes adopted a

three-process treatment trains (e.g. membrane

filtration or membrane bioreactor (MBR) using

activated sludge process, reverse osmosis (RO)

membrane for salt rejection and chlorination) for

treating different effluents which had accomplished

various sewage treatment processes namely

secondary treated effluent, chemically enhanced

primary treated effluent and preliminary treated

effluent.

For non-saline effluent after receiving secondary

treatment at Sewage Treatment Works (STWs),

micro-filtration (MF) or ultra-filtration (UF) alone is

sufficient to treat the effluent for use as reclaimed

water. RO is required to further polish the permeate

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from the MF or UF system to reduce the amount of

Total Dissolved Solids (TDS), for polymer

preparation.

For saline effluent having received chemically

enhanced primary treatment or preliminary treatment,

the process of MBR can remove all of the suspended

solids, and produce the MBR permeate for

ground/facility washing and toilet flushing. The

process of RO is required to remove the dissolved

solid, in particular, salt, for landscape irrigation and

polymer preparation for wastewater treatment.

As biological matter may adhere on surfaces of tank

in case of tank storage of permeate, so in all

processes, chlorine disinfection is used to minimize

the human health risk. The schematic diagrams of

two process trains for reclaiming water from

secondary effluent and chemical enhanced primarily

treatment (CEPT) effluent are shown in Figure 1 and

Figure 2. The process train diagram for screened raw

sewage is similar to Figure 2.

Figure 1 Process Train of WR Plants for Secondary

Effluent

Figure 2 Process Train of WR Plants for CEPT

Effluent

WR Pilot Plants in 3 Groups

The locations of the 11 water reclamation plants in

the territory are shown in Figure 3, classified into

three different groups in accordance with the effluent

to be treated by the plants:

Group A – for non-saline effluent of Secondary STW:

a1 – Yuen Long STW

a2 – Sai Kung STW

a3 – Stanley STW (Photo 1)

Group B – for saline effluent of Chemically

Enhanced Primarily Treated (CEPT) STW:

b1 - Stonecutters Island STW

b2 - Sham Tseng STW

b3 - Siu Ho Wan STW (Photo 2)

Group C – for screened raw saline effluent of

Preliminary Treatment Works (PTW) / Sewage

Pumping Station (SPS):

c1 - Kwun Tong PTW (Photo 3)

c2 - Chai Wan PTW

c3 - To Kwa Wan PTW

c4 - Sham Shui Po No.1 & No.2 Sewage Screening

Plants

c5 - Cheung Sha Wan Sewage Pumping Station

(Photo 4)

Figure 3 Locations of 11 Pilot WR Plants at DSD’s

Facilities in 3 Groups

Photo 1 – RO Plant at Stanley STW

Photo 2 – WR Plant at Siu Ho Wan STW

Photo 3 – RO Plant at Kwun Tong PTW

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RO Plant at Stanley STW

Siu Ho Wan STW

RO Plant at Kwun Tong PTW

Photo 4 – WR Plant at Cheung Sha Wan SPS

Water Quality Requirements

These projects, involving the reuse of treated sewage

effluent from sewage treatment facilities, are

classified as designated projects under the

Environmental Impact Assessment Ordinance

(EIAO). As such, a series of project profiles

detailing the environmental aspects of the facilities

were submitted for approval by EPD. According to

the project profiles approved by EPD

quality parameters of reclaimed water from

Secondary and CEPT STWs are summarized

Table 1. In brief, the parameters of pH,

Total Suspended Solids (TSS),

Demand (BOD5) and E.Coli are the

quality requirements to be controlled and

Total Residual Chlorine (TRC)

indication on the completeness

process and the amount of TRC would depend on the

application of the reclaimed water.

Solids (TDS) of the RO permeate

how effective the RO systems remove the dissolved

solids, e.g. salt, which shall be

than 200 mg/L for reclaimed water to be used for

polymer preparation.

The typical water samples of crude sewage

effluent and reclaimed water

Cheung Sha Wan SPS

Water Quality Requirements

These projects, involving the reuse of treated sewage

effluent from sewage treatment facilities, are

classified as designated projects under the

Environmental Impact Assessment Ordinance

. As such, a series of project profiles

detailing the environmental aspects of the facilities

were submitted for approval by EPD. According to

approved by EPD, the water

rs of reclaimed water from

CEPT STWs are summarized in

In brief, the parameters of pH, Turbidity,

olids (TSS), Biochemical Oxygen

and E.Coli are the main water

controlled and monitored.

Total Residual Chlorine (TRC) is used as an

completeness of the disinfection

process and the amount of TRC would depend on the

application of the reclaimed water. Total Dissolved

of the RO permeate is a parameter of

how effective the RO systems remove the dissolved

which shall be controlled to be less

than 200 mg/L for reclaimed water to be used for

The typical water samples of crude sewage, final

effluent and reclaimed water are shown in Figure 4.

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N.S. = Not Specified / N.D. = Not Detectable

Table 1 Water Quality Parameters of Reclaimed

Water from Secondary and CEPT STWs

Figure 4 – Typical Water Samples collected at a WR

Plant

Applications of Reclaimed Water

Reclaimed water produced in these projects is used

for the following non-potable uses inside the sewage

treatment facilities:

� ground and facilities washing (Photo 5),

� toilet flushing (Photo 6),

� make-up water for deodorizer,

� polymer preparation (Photo 7), and

� landscape irrigation.

Photo 5 – MBR permeate for ground and facilities

washing at Chai Wan PTW

Photo 6 – MBR permeate for toilet flushing at To

Kwa Wan PTW

Water Quality

Parameter

Reclaimed Water Quality from

Secondary and CEPT STWs

Make-up

Water,

Ground &

Facility

Washing,

Toilet Flushing

Polymer

Preparation

Landscape

Irrigation

pH 6-9 6.2-8.3 6-9

Colour (HU) N.S. < 20 N.S. Turbidity (NTU) ≦ 2 ≦ 2 ≦ 2

Total Suspended

Solids (TSS) (mg/L) ≦ 10 ≦ 5 ≦ 10

Biochemical

Oxygen Demand

(BOD5) (mg/L)

≦ 10

≦ 10

≦ 10

E.Coli (no./100mL) N.D. N.D. N.D.

Total Residual

Chlorine (TRC)

(mg/L)

≧ 1 N.S. ≦ 1

Total Dissolved

Solids (TDS)

(mg/L)

N.S. < 200 N.S.

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Photo 7 – RO permeate for preparation of

polymer at Stanley STW

Technical Schedules of 3 Groups of WR Plants

The process configurations (i.e. hollow fibre

membrane, flat sheet membrane), materials (i.e. PE,

PVDF and PES etc.), pore sizes and capacities of the

11 WR plants supplied from different manufacturers

were selected based on the characteristics of influents

to be treated, required output qualities of the

reclaimed water and its applications. In these trial

projects, different combinations of configurations,

materials and capacities of systems were chosen for

the purpose of evaluation. For easy reference, the

main schedules of the plants are summarized in

Appendix 1.

Observations, Analysis and Experience Sharing

In the past 20 months of operations of these pilot

plants till March 2012, laboratory results, power and

chemical consumption, as well as operation

experience of each plant have been monitored on a

monthly basis. Based on these operating records,

this section will try to summarize some of the current

findings:

1. The water qualities (e.g. Turbidity, E.Coli, BOD5,

TSS, TDS etc.) of the reclaimed water produced

from each of the WR plants (i.e. MF/UF, MBR

and RO) could achieve full compliance with the

requirements stated in the environmental permits

issued by EPD.

2. The influent to the WR plants of Group A was

secondary treated and the influent to plants of

Group C was screened raw sewage. Membrane

filtrations are well developed technologies for

producing reclaimed water, the WR plants in

these two groups demonstrated that they could

handle these influents without significant

problems and the results were very much

expected. For the influent to the MBR systems

which had been treated by CEPT process where

polymer and chemicals (such as coagulant) were

added during the wastewater treatment process,

the systems showed that they could handle these

additional polymer and chemicals successfully

and produce quality reclaimed water.

3. In terms of quantity of reclaimed water produced,

most of the WR plants could meet the design flux

requirement, whereas the O&M issues of the

MBR plant at Stonecutters Island STW and the

RO plant at To Kwa Wan PTW hindered the

operations of the two RO plants at these two

locations and the operating data of the two plants

have been excluded in the following analysis.

4. The 11 water reclamation trial plants produced

on an average of 850 m3/day of reclaimed water

for in-house non-potable uses in 2011. Excluding

the time for servicing, maintenance and repair of

these WR plants and all these plants had been

designed without peaking factors (i.e. design

capacities are their maximum production rates),

the production quantities are reasonable though

some systems could be further stressed for an

increased output. For sustainable development,

DSD will continue to explore the opportunity of

using more reclaimed water from the treated

effluents with a view to further minimizing the

use of fresh water within the sewage treatment

facilities

5. Based on the operating data collected so far, the

O&M performance (i.e. using power and

chemical consumption as an indication whereas

labour costs, replacement of spare parts etc. are

not included) per unit of MF/UF, MBR and RO

permeate produced have been summarized in

Table 2 below. Figure 5, 6 and 7 in Appendix

2 further show the average power and chemical

consumption of WR plants of the same type

under the three different groups. The early stage

of the trials was believed to be a learning process,

the operating contractors attempted to use more

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power and/or chemicals to maintain the

operations on a rather comfortable or safe side

and they should have adjusted the systems for

optimization when they familiarized with the

operations and had confidence to use less

resources for producing quality reclaimed water.

Table 2 – Summary of Power and Chemical

Consumption of WR Plants

6. The typical characteristics of influents to the 3

groups of WR plants are shown in Table 3,

which indicate the loadings for different WR

plants and give indications for the differences on

O&M performance.

Table 3 – Typical Characteristics of Influent to WR

Plants

� In the aspect of RO permeate, salinity or

TDS of influent determined the design of

RO system and hence the system power

consumption. For instance, seawater type

membrane had been used instead of

brackish type for RO plants in Group B &

C which required a higher feed pressure for

operation. This explains that the power

consumption for the processes of these two

groups in producing RO permeate should

be higher than the process of Group A, as

indicated by figures in Table 2.

� The total consumption of chemicals to

control and maintain the operation for

quality output did not only depend on the

quantity of influent to be handled, but also

on the quality of influent. Though the WR

plants had different operating capacities,

the difference in consumption of chemicals

was relatively not significant as comparing

with the power consumption of the plants in

these small-scale of pilot plants. However

for a large WR plant, there could be a

significant saving in chemical consumption

if the process system could be optimized,

e.g. accommodate a slight higher pH value

for preventing fouling and/or clogging of

the RO membranes.

7. As a general observation, we noticed that the

design of WR plant with hollow fiber (HF) type

membrane would occupy less footprint in

comparison with flat sheet (FS) type membrane.

The area saving in an MBR tank using HF could

allow the use of fine bubble air diffusers with a

higher oxygen transfer efficiency (OTE) for the

activated sludge process in combination with

coarse air bubbles primarily for membrane

scouring, which should be more energy efficient.

For this difference in OTE, the overall aeration

energy consumption using HF could be less in

comparison to FS.

8. As experiences shared by DSD’s frontline

operators, their suggestions for improvement in

design and operation are consolidated as follows:

� There is a pre-treatment or screening

process for each WR plant, and it is

basically consisting of either disc filters or

fine screen at the inlet to the plant. In

some cases, operators need to take few

hours to manually clean the filters every

day. For a full scale WR plant design,

automatic backwash system for these filters

should be equipped to facilitate the daily

operation / cleaning.

� In MBR system, air blowers are the major

process equipment and consume most of

the system electricity. For the sake of

monitoring and effective control as well as

improving the efficiency and cost

effectiveness of system operation, meters

for measuring the power consumption and

air flow rates of air blowers should be

installed. Subject to the operational needs

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or loading of MBR systems, instead of

continuous operation of air blowers,

intermittent running and/or running the

blowers at a lower capacity could be an

effective energy saving measure.

However, membrane fouling would be a

problem when there is not enough air

scouring for cleaning the membrane in time.

Therefore, there should be a balance on

energy saving, process control and cleaning

of membrane by air and/or combination of

other means, e.g. use and alter the

frequency of maintenance wash and

recovery wash of membranes. In fact, the

operation of MBR system in a cost effective

and competitive way is always a research

topic with various areas and directions for

further explorations.

� In RO system, there is a suggestion for

recovering the energy from the rejected

high pressure RO concentrate for using it to

boost up the low-pressure incoming feed

influent into the RO system. This

suggestion was adopted as a trial for

evaluation in DSD’s new designed WR

plants.

� Though MBR/RO plants are highly

automated, which still require well trained

and competent staff to operate and maintain

them. For instance, the staff should

familiarize with the wastewater treatment

processes, the membrane technologies and

monitoring and control systems of the

plants and hence he/she can response and

adjust the system parameters (e.g.

mixed-liquor suspended solids (MLSS),

dissolved oxygen, pH, TRC etc.) promptly

and correctly, particularly in emergency

cases, to rescue the plants from abnormal

operating conditions.

Summary

Based on DSD’s operating experience on reclaiming

its effluents having received different level of

treatment at its various sewage treatment works using

different membrane separation technologies,

including micro/ultra-filtration membrane, membrane

bioreactor and reverse osmosis in a period of about

20 months, this Paper focuses the attention on

analysis and comparison of the power and chemical

consumption among the 11 different pilot water

reclamation plants. Though the O&M issues hindered

the performance of two RO plants and the contractors

took time during the early learning stage to optimize

the operations of both the MF/UF, MBR and RO

plants, most of the plants have been operated in good

shape and they have produced 850 m3/day reclaimed

water for in-house non-potable uses.

The average total power and chemical consumption

of MF/UF/MBR permeate and RO permeate of the

11 trial small-scale Group A, B and C plants are

found to be in line with the quality of influents to be

handled by the plants. For a larger plant size, a more

optimized process and taking the suggestions shared

by the operators in this Paper, the operation of a

full-scale WR plant shall be able to produce high

quality reclaimed water in a more efficient way.

The knowledge and experience gained from the

operation of these 11 water reclamation trial plants

would provide DSD with valuable information in the

future design, operation and maintenance of WR

plants.

Acknowledgement

The author wishes to express his gratitude to the

Drainage Services Department of the Hong Kong

Special Administrative Region for permission on

using the data collected from the respective projects

to publish this Paper. Special thanks are given to the

management and colleagues of the E&M Branch and

the operating contractors of the WR plants for their

guidance, assistance and experience shared for

preparation of the tables, figures and the Paper.

References

Principle and Applications of Membrane &

Bioreactors in Water & Wastewater, short course by

Prof Simon Judd, Centre for Water Science Cranfield

University, May 2010.

Project Profiles (Type A, Type B and Type C) of

Water Reclamation Facilities for Environmental

Permit Applications

Water Reuse – Issues, Technologies and Applications,

Metcalf & Eddy

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Water Quality and Treatment, American Water Works

Association, Raymond D. Letterman

Handbook of Water and Wastewater Treatment

Technologies, Nicholas P. Cheremisinoff, Ph.D. N&P

Limited

Industrial Waste Treatment Handbook, Woodard &

Curran, Inc.

The NALCO Water Handbook, Frank N. Kemmer

Membrane Case Studies, Past, Present and Future,

J.S. Taylor, S.J. Duranceau

A Pilot Study for Wastewater Reclamation and Reuse

with MBR/RO and MF/RO Systems, ScienceDirect,

L.S. Tam, T.W. Tang, G.N. Lau, K.R. Sharma, G.H.

Chen

Demonstration Studies in Singapore of Membrane

Bioreactor for Wastewater Reclamation, Takanori

Itonaga, Yasuo Oda, Toshiyuki Kawashima, C.B.

Chidambara RAJ, Craig Bartels

Model-based Energy Optimisation of a Small-scale

Decentralised Membrane Bioreactor for Urban Reuse,

ScienceDirect, Bart Verrecht, Thomas Maere,

Lorenzo Benedetti, Ingmar Nopens, Simon Judd

Integration of MBR with RO for Water Reuse, Dr

Dirk Herold, Christoph Kullmann, Tony van

Loggenburg

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Appendix 1 - Technical Schedules of 3 Groups of WR Plants

Plants of Group A (MF/UF + RO) Characteristics of MF / UF Plant

Description a1 – MF at Yuen Long STW a2 – UF at Sai Kung STW a3 – UF at Stanley STW

Configuration Hollow Fibre, outside-in Hollow Fibre, inside-out Hollow Fibre, outside-in

Material Polyacrylnitrile (PAN) Polyethersulfone (PES) Polytetrafluorethylene (PVDF)

Pore Size 0.1 micron 0.02 micron 0.04 micron

Flux Rate 700 L/m2/d 1600 L/m2/d 840 L/m2/d

Design Capacity 200 m3/d 97 m3/d 127 m3/d

Membrane Area 290 m2 80 m2 150 m2

Characteristics of RO Plant Description a1 – MF at Yuen Long STW a2 – UF at Sai Kung STW a3 – UF at Stanley STW

Configuration Brackish Water Brackish Water Brackish Water

Material Composite Polyamide Composite Polyamide Composite Polyamide

No. of Pass Single Pass, 10 - 15 bar Single Pass, 10 - 15 bar Single Pass (2 Stages)


Recovery Ratio 75% 75% 75%


Plants of Group B (MBR + RO) Characteristics of MBR Plant

Description b1 – MBR at

Stonecutters Island STW

b2 – MBR at

Sham Tseng STW

b3 – MBR at

Siu Ho Wan STW

Configuration Flat Sheet Hollow Fibre, outside-in Flat Sheet

Material Chlorinated Polyethylene (PE) Polyethersulfone (PES) Polyethersulfone (PES)

Pore Size 0.4 micron 0.05 micron 0.2 micron



Membrane Area 360 m2 250 m2 630 m2

Characteristics of RO Plant

Description b1 – MBR at

Stonecutters Island STW

b2 – MBR at

Sham Tseng STW

b3 – MBR at

Siu Ho Wan STW

Configuration Brackish 1st Seawater, 2nd Brackish Brackish

Material Composite Polyamide Composite Polyamide Composite Polyamide

No. of Pass 2 Pass, 1st 12 bar, 2nd 9 bar 2 Pass, 1st 16 bar, 2nd 10 bar 2 Pass, 1st 35 bar, 2nd 15 bar

Flux Rate 1st 450 L/m2/d, 2nd 860 L/m2/d 320 L/m2/d 900 L/m2/d

Recovery Ratio 67 – 75% 55-70% 50%


Plants of Group C (MBR + RO) Characteristics of MBR Plant

Description c1 – MBR at

Kwun Tong PTW

c2 – MBR at

Chai Wan PTW

c3 – MBR at

To Kwa Wan PTW

c4 – MBR at

Sham Shui Po SSP

c5 – MBR at

Cheung Sha Wan

SPS

Configuration Hollow Fibre,

outside-in

Hollow Fibre,

outside-in

Flat Sheet Hollow Fibre,

outside-in

Flat Sheet

Material Polyethylene (PE) Polytetrafluorethylen

e (PVDF)

Polytetrafluorethylen

e (PVDF)

Polytetrafluorethylen

e (PVDF)

Chlorinated

Polyethylene (PE)

Pore Size 0.4 micron 0.4 micron 0.08 micron 0.2 micron 0.4 micron

Flux Rate 250 L/m2/d 700 L/m2/d 510 L/m2/d 240 L/m2/d 560 L/m2/d

Design Capacity 45 m3/d 45 m3/d 55 m3/d 45 m3/d 45 m3/d

Membrane Area 210 m2 75 m2 140 m2 200 m2 80 m2

Screening 2 mm Bar Screen 2 mm Bar Screen 2 mm Bar Screen 2 mm Bar Screen 2 mm Bar Screen

Characteristics of RO Plant

Description c1 – MBR at

Kwun Tong PTW

c2 – MBR at

Chai Wan PTW

c3 – MBR at

To Kwa Wan PTW

c4 – MBR at

Sham Shui Po SSP

c5 – MBR at

Cheung Sha Wan

SPS

Configuration 1st Seawater,

2nd Brackish

1st Seawater,

2nd Brackish

Brackish 1st Seawater,

2nd Brackish

1st Seawater,

2nd Brackish

Material Composite

Polyamide

Composite

Polyamide

Composite

Polyamide

Composite

Polyamide

Composite

Polyamide

No. of Pass 2 Pass, 1st 35 bar,

2nd 15 bar

2 Pass, 1st 35 bar,

2nd 15 bar

2 Pass, 1st 23 bar,

2nd 8 bar

2 Pass, 1st 35 bar,

2nd 15 bar

2 Pass, 1st 36 bar,

2nd 10 bar

Flux Rate 1st 650 L/m2/d,

2nd 1200 L/m2/d

1st 800 L/m2/d,

2nd 1300 L/m2/d

200 L/m2/d 1st 650 L/m2/d,

2nd 1100 L/m2/d

280 L/m2/d

Recovery Ratio 50% 50% 50% 50% 50-55%

Design Capacity 12 m3/d 12 m3/d 12 m3/d 12 m3/d 12 m3/d

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Appendix 2 - Average Electricity & Chemical Consumption of WR Plants in 3 Groups

Figure 5 – Average Electricity & Chemical Consumption of Group A WR Plants

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Figure 6 – Average Electricity & Chemical Consumption of Group B WR Plants

Figure 7 – Average Electricity & Chemical Consumption of Group C WR Plants

Documents

Water Reclamation Trial Projects in Drainage Services ... · This paper is intended to present the experience learned and ... (PTW) / Sewage Pumping Station (SPS): c1 - Kwun Tong