Journal - The Institution of Engineers, Malaysia (Vol. 67, No.

1, March 2006) 57
SYSTEMATIC DESIGN OFA MAXIMUM WATER
RECOVERY NETWORK FOR AN URBAN SYSTEM BASED
ON PINCH ANALYSIS
S. R. Wan Alwi, Z. A. Manan and Z. Ujang
Department of Chemical Engineering, Universiti Teknologi Malaysia 81310 UTM, Skudai, Johor
E-mail: zain@fkkksa.utm.my
1.0 INTRODUCTION
Water demands are growing every year as the result of the
booming world population. Apopulation report on environment
and water issues had estimated that more than 2.8 billion people
in 48 countries will lack access to adequate water supplies by
2025 [1]. The Middle-Eastern countries have long relied on non-
conventional water supplies due to water scarcity. For example,
four Gulf states; Bahrain, Kuwait, Saudi Arabia, and the United
Arab Emirates have so little fresh water available that they resort
to desalination, a costly process of converting sea water into
fresh water. Saudi Arabia now must mine fossil groundwater to
fulfill three-quarters of its water needs. Jordan and Yemen
withdraw 30% more water from groundwater aquifers every
year than the replenishment rate, Israel's annual water usage
already exceeds 15% of its renewable supply [2].
Huge investments have been spent to expand water supply to
increasing number of consumers in industry and housing estates
world-wide. Rapid increase in water tariff has spurred water
conservation efforts particularly in industrial sector. It has been
reported that industrial water used in some developed countries
has been falling as a result of greater water efficiency through
reuse, recycling or regeneration of water. For example, industrial
water use in England and Wales has fallen by 900 million m
3
since year 1998 [3]. While industries and commercial enterprises
have made significant progress in water efficiency, the reduction
of water usage among the general public have been extremely
poor, thereby resulting in a steady increase of urban water
demand [4]. This discrepancy can be attributed to the low water-
tariff and wide availability of potable water in urban areas.
Consequently, the general public, particularly the urban
population, has little consciousness on water savings and hence,
the energy savings associated with water used.
The urban sector contributes a significant percentage of
water consumption particularly in developed countries with
warmer climates. In Malaysia for example, the domestic sector
contributes 68% of the total water consumption compared to
other sectors [5]. The need for efficient water management in
urban sector is getting more crucial as a result of the sharp
increment of fresh water price. This trend is likely to continue
in the near future due to the predicted shortage of fresh water,
and hence, the possibilities of resorting to wastewater
treatment, desalination, groundwater extraction and, interstate
water purchase as well as water transfer. Compared to the
extensive amount of work conducted on water minimisation in
industry, there has been much less efforts towards water
conservation in urban sector.
The majority of works on urban water conservation have
focussed on reuse of greywater with and without treatment and
rainwater harvesting. Apart from the conventional approaches
of water recycling/reuse and rainwater harvesting for lower
grade water usages such as for toilet flushing and irrigation,
there has been noteworthy efforts towards maximising water
recovery through the design of closed-loop water system as
well as water cascading.
ABSTRACT
Pinch Analysis has been an established systematic technique for optimal design and retrofit of heat, mass and water recovery
networks in industry to achieve maximum energy as well as mass efficiency. Until today, the application of Pinch Analysis is
perceived to exclusively belong to the domain of process industry. This work represents a shift in the current process engineering
paradigm to allow Pinch Analysis application to be extended beyond the frontiers of process industry. Two key developments
related to the extension of Pinch Analysis technique to the urban sector has been presented. One is as per the establishment of
the minimum water targets using the new water cascade analysis technique; and two, the adaptation of the source-sink mapping
technique for the design of a maximum water recovery network to an urban system to achieve the water targets.
Application of these techniques on Sultan Ismail Mosque in Universiti Teknologi Malaysia yields potential maximum reductions
of 85.5% fresh water and 67.7% wastewater.
Keywords: Pinch Analysis, Regeneration, Urban Systems, Water Cascade Analysis
Figure 1: Aclosed water loop for a residential building [6]
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Journal - The Institution of Engineers, Malaysia (Vol. 67, No. 1, March 2006)
S.R. WAN ALWI, et al.
58
Closed loop water system aims towards a total re-use of
all components in the wastewater. Bakir [6] has documented
the concept of closed loop in water demand management for
a residential building. The main idea is to match water quality
with the appropriate water usage as shown in Figure 1. This
closed-loop method can also be applied for household,
neighbourhood, community, industry, or institution scale.
After water is used, the generated wastewater is segregated
into greywater and blackwater streams. The wastewater
streams are treated accordingly before being reused or
recycled for other applications.
The basic principle of water cascading system is water
quality cascade where water sources are matched with end uses
in terms of the required water quality as shown in Table 1.
According to [7], water conservation can be maximised through
integration of the whole suite of water conservation measures
such as rainwater capture, installation of water efficient fixtures,
effluent reuse and evaporation as well as productive reuse of
treated effluent in roof gardens. Two case studies, a 4-storey
commercial green building in Melbourne and a typical
commercial high-rise building have shown a reduction up to
approximately 80% of freshwater consumption and 80% of
wastewater discharge achievable via this technique.
Toilet flushing contributes between 30 to 60 percent of water
uses in urban areas [8]. As toilet flushing activity is one of the
highest water demands in urban system and it does not involve
human contacts, hence the reuse of greywater after treatment or
rainwater for toilet flushing is a viable option with minimum health
risk [8, 9, 10, 11, 12]. Several researchers have reported significant
savings in reusing greywater and rainwater for toilet flushing. For
example, [13] had stated that theoretically rain or greywater can
replace all drinking water for toilet flushing. This can constitute up
to 34% of the total water consumption. Burkhard et al.[13] has also
reported that [14] study has managed to achieve a savings of 39%
and sayers [15] has reported a reduction between 5.2 to 30.6%.
Aside from water reuse or recycle for toilet flushing, its use for
irrigation is also an alternative. CSBE [16] reported that greywater
from ablution in the King Abdullah Mosque in Jordan was
collected, filtered and reused for irrigation. The system has resulted
in significant savings on the mosques water bills such that the
capital cost for installation of the system was recovered within the
first year of operation.
In a water distribution system, it is possible to determine
the maximum water reuse/recycle flowrate through appropriate
water cascading. Note that the maximum water reuse and
recycling corresponds to the minimum fresh water
consumption. The first key step towards maximising water
recovery and minimising fresh water consumption as well as
wastewater generation is to establish the baseline minimum
water targets prior to the design of a water recovery network to
achieve the minimum water targets, or the maximum water
recovery (MWR) network.
The available works on water targeting and MWR
network design are almost exclusively focused on industrial
applications, in line with the advent of Water Pinch Analysis
(WPA) technique [17, 18, 19, 21, 22, 23, 24]. Water pinch
analysis is a systematic technique for implementing
strategies to maximise water reuse and recycling through
integration of water-using activities or processes. Typical
WPA solution comprises of two steps, i.e., setting the
baseline water targets followed by network design to achieve
the baseline targets. Wan Alwi et al. [25] had recently made
the first attempt to establish the baseline water targets for an
urban water system using a new technique known as Water
Cascade Analysis (WCA).
From the preceding review, it can be concluded that even
though water conservation techniques involving reuse,
recycling and regeneration have been implemented for urban
system, the concepts of baseline minimum water targets,
maximum water recovery design, stream mixing and process
modifications to achieve the minimum water targets are
unknown for urban sector. The objective of this study is to
extend the WPA methodology beyond the frontiers of
process industry for sustainability of water resources. In this
work, the WPA technique will be used to design a maximum
water recovery network for the urban sector. Breakthrough
of WPA technique into the urban sector will significantly
contribute towards the global effort for efficient
conservation of water resources.
2.0 METHODOLOGY
Water management hierarchy consists of five levels, namely
(1) source elimination, (2) source reduction, (3) direct reuse/
outsourcing of external water, (4) regeneration, and (5) use
of fresh water [26]. Water Pinch Analysis (WPA) is
concerned with maximising water reuse and regeneration-
reuse/recycling down the third and fourth level of the water
management hierarchy. This will minimise fresh water
consumption as well as wastewater generation. In section
4.1 to 4.5, this study presents the implementation of WPA
into the urban system in five key steps. The first step is to
Table 1: Water Quality Cascade with End Uses [7]
Figure 2: ZM Hierarchy of Water Management (Priority)
057-064systematic design 6/22/06 4:44 PM Page 58
audit the existing or the base case water network in terms of
quantity (flowrate) as well as quality (contaminant
concentration). The second step is to identify and isolate the
relevant water sources and water demands having potential
for integration. The third step is to establish the minimum
water and wastewater targets using the water cascade
analysis technique (WCA). The fourth step is to design a
water recovery network to realise the minimum water
targets. The final step is to consider process changes like
regeneration and to evaluate the economics of the newly
designed or retrofitted network. A case study involving
Sultan Ismail Mosque in Universiti Teknologi Malaysia
(UTM) was used to illustrate the procedure for implementing
Water Pinch Analysis on an urban system.
3.0 RESULTS AND DISCUSSION
3.1 Audit of the existing Sultan Ismail Mosque
(SIM) water network
Sultan Ismail Mosque (SIM) located in Universiti Teknologi
Malaysia (UTM) was chosen as the case study for this work to
illustrate the MWR network design method for urban system.
The four-storey mosque is mainly used by 3500 Muslim UTM
community for prayer and educational activities. The
estimated total fresh water consumption for SIM is 11550 m
3
/yr
[27]. Of this value, 9178 m
3
/yr is used for ablution and the rest
is for toilet flushing, irrigation, mosque cleaning, wash-basin
and toilet pipes [27]. The total water consumption varies
throughout the year during semesters and holidays. During the
semester, the amount of water consumed for ablution is about
60 m
3
/day on Friday but only 25 m
3
/day on other days. For this
study, daily water consumption calculations will be based on
normal semester days [27]. Figure 3 shows the water using
processes in terms of total flowrate and limiting maximum
contaminant data. The initial freshwater consumption for the
mosque is 29.10 te/day.
3.2 Data extraction
The maximum limiting contaminant concentration data for
water demands for SIM was based on USA-EPA standards for
water reuse [28]. USA-EPA specifies for the BOD level to be
reduced to at least 10 ppm for non-potable domestic water
recycle. Non-potable water refers to water that is not used for
human consumption, such as for drinking. Since all the water
usages after the distribution tank in SIM was non-potable, a
maximum BOD limit of 10 ppm was set for the water demands.
A BOD value of 0 ppm was set for kitchen water demand.
Fresh water, greywater, rainwater, snow and treated wastewater
are all potential water sources. The limiting contaminant
concentration for these water sources can be obtained via water
quality test or from literature data. "Blackwater" from toilet
flushing and toilet pipes were not considered as water source
since it was highly contaminated with urine and faeces while
water from irrigation was assumed to be completely absorbed
by soil.
The limiting data for water sources were based on the data
provided [16] as well as from [8]. CSBE [16] performed
quality tests on ablution greywater collected from King
Abdullah Mosque. In this work, it was assumed that wash
basin greywater and ablution greywater were of similar quality,
i.e. 23 ppm. Surendran and Wheatley [8] conducted research
on the average pollutant concentration in greywater from a hall
residence. The BOD data for sources like showering, kitchen
and mosque cleaning for SIM were based on these data. The
BOD for mosque cleaning was assumed to be similar to that of
a washing machine since they both contained detergent. The
limiting data for the water demands and sources are
summarised in Table 2 and 3 respectively.
3.3 Targeting the minimum utility using Water
Cascade Analysis technique (WCA)
One of the latest and widely used water targeting
techniques known as water surplus diagram [22] is limited in
its ability to estimate the minimum water targets as it
implements a graphical approach that involves time-
consuming trial-an-error steps. This limitation has inspired the
development of a numerical technique known as Water
Cascade Analysis (WCA) that eliminates the trial-an-error
approach [29]. The main objective of the WCA is to establish
the minimum water targets, i.e. the overall fresh water
requirement and wastewater generation for a process after
looking at the possibility of using the available water sources
within a process to meet its water demands.
Manan et al. [29] provides a detailed description of how
WCAwas used to established the baseline water targets for the
Journal - The Institution of Engineers, Malaysia (Vol. 67, No. 1, March 2006)
SYSTEMATIC DESIGN OFA MAXIMUM WATER RECOVERY NETWORK FOR AN URBAN SYSTEM BASED ON PINCH ANALYSIS
59
Figure 3: Water distribution network for Sultan Ismail Mosque
Table 2: Summary of the water demands for Sultan Ismail Mosque
Table 3: Summary of the water sources available in
Sultan Ismail Mosque
057-064systematic design 6/22/06 4:44 PM Page 59
Sultan Ismail Mosque. The targets generated via WCApredict
a significant potential reduction in terms of fresh water and
wastewater, far beyond the water network revamp proposed
earlier. Table 4 shows the WCA targets for fresh water
consumption and wastewater generation for the mosque at
10.16 te/day and 17.83 te/day respectively. These targets
represent 65.1% fresh water savings and 51.5% of wastewater
reduction. Note that the pinch point for the mosque water
network exists at the third purity level (P = 0.999977) where
there is zero cumulative pure water surplus.
Results of the study show that setting the minimum fresh water
and wastewater targets prior to design allow a designer to rapidly
pinpoint the options for water recovery network design that satisfy
the minimum water targets, thereby saving considerable amount of
resources in detailed evaluation and screening of numerous inferior
design options. Next, a systematic procedure for the design of a
maximum water recovery (MWR) network is carried out to
achieve the baseline water targets established.
3.4 Design of a maximum water recovery
network
3.4.1 Network design
The network that achieved maximum water recovery, and
hence, the minimum water targets without regeneration was
generated using the source-sink mapping diagram (Figure 4)
which were based on three key design heuristics presented in
this section. Table 4 shows the minimum fresh water target for
SIM at 10.16 te/day and the pinch concentration at 23 ppm. In
order to achieve the water targets, it was necessary to observe
the pinch division by designing the water networks above and
below the pinch separately according to heuristic 1:
Heuristic 1: Do not feed water sources above the pinch
(including fresh water) to demands below the pinch and vice
versa [22].
Heuristic 1 forbids water sources above the pinch
(including fresh water) from being mixed with demands below
the pinch concentration. On the other hand, it also disallows
mixing of demands above the pinch with sources below the
pinch. For the SIM case study, source S1 (10 ppm) above the
pinch should not be fed to any demand below the pinch
concentration. However, since all demands in this case were
above the pinch, all water sources above the pinch could be
matched with any of the demands. Sources S4 (216 ppm), S5
(472 ppm) and S6 (536 ppm), which existed below the pinch
should not be fed to demands above the pinch according to
heuristic 1. Since there were only sources and no demands
below the pinch, all sources there could not be reused and was
discharged as wastewater.
Note that the source at the pinch concentration partly
belongs to the region above the pinch and partly below the
pinch. The exact distribution of the source stream at the pinch
concentration is shown in column F
c
of the water cascade table.
Table 4 shows that 7.8 te/day of water source at 23 ppm
belongs to the region above the pinch while 17.37 te/day
belongs to the region below the pinch.
Heuristic 2 serves as a guide in finding the right match
between the various source and demand streams that exist in the
region above as well as below the pinch. Following heuristic 2,
the demand at the lowest contaminant concentration was first
matched with the source at the lowest contaminant concentration.
Heuristic 2: Start the source-demand matching process with
the demand at the lowest contaminant concentration [31].
For the SIM case study, demands D2 to D8 existed at the
same concentration of 10 ppm. Thus, the source at the lowest
concentration could be matched with any of these demands.
Table 4 shows that two sources can be selected to satisfy D2.
Source S1 at 10 ppm had the lowest contaminant concentration
and was first selected to be matched with demand D2
according to heuristic 2.
This study have proposed heuristic 3 as a corollary to
heuristic 2 for the systematic mapping of the available source
streams as well as fresh water to the individual demands.
Heuristic 3 and Equation (1) were used to determine the exact
contaminant load and flowrate of sources S1 and S2 to satisfy
demand D2.
Heuristic 3: Map the available sources one after another, and
fresh water as required, to each demand according to heuristic
2 until all demands have been satisfied in terms of both quality
(contaminant load) and quantity (flowrate) .
The contaminant load of a source S or a demand D, (m
S/D
)
was calculated using Equation (1).
(1)
Hence, the contaminant load of D2 (m
D2
) was obtained using
Equation (1) by multiplying its flowrate (F
D2
) by its
contaminant concentration (C
D2
).
Recall that S1 was selected to satisfy D2 according to
heuristic 2. The contaminant load of S1 was 0.11 kg/day. This
was less than the contaminant load required by D2. Hence, all
11.14 te/day of S1 flowrate was used to satisfy D2.
m
S, i / D, j
=
F
S/D
xC
S/D
1000
Journal - The Institution of Engineers, Malaysia (Vol. 67, No. 1, March 2006)
S.R. WAN ALWI, et al.
60
Table 4: Water Cascade Table (WCT) for Sultan Ismail Mosque
case study
m
D2
=
F
D2
xC
D2
1000
m
D2
=
25.03te/dayx10ppm
1000
= 0.25kg/day
m
S1
=
F
S1
xC
S1
1000
m
S1
=
11.14te/dayx10ppm
1000
= 0.11kg/day
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Journal - The Institution of Engineers, Malaysia (Vol. 67, No. 1, March 2006)
SYSTEMATIC DESIGN OFA MAXIMUM WATER RECOVERY NETWORK FOR AN URBAN SYSTEM BASED ON PINCH ANALYSIS
61
The balance of D2 contaminant mass load was found to be
0.14 kg/day
m
D2
= m
S1
+ m
S2
+ m
FW
m
S2
= 0.25kg / day - 0.11kg / day - 0kg / day = 0.14kg / day
The remaining contaminant load of 0.14 kg/day for D2 was
satisfied using source S2 at the next highest contaminant
concentration. The required flowrate of S2, determined using
Equation (2), was 6.04 te/day.
(2)
However, Equation (3) shows that the total quantity
required by D2 was still short by 7.85 te/day even though its
contaminant load had been satisfied. The deficit of 7.85 te/day
was satisfied using fresh water according to heuristic 3.
F
D2
= F
S1
+ F
S2
+ F
FW
F
FW
= 25.03te/day - 11.14te/day - 6.04te/day = 7.85te/day (3)
The remaining quantity of 18.99 te/day from the total flow
of 25.03 te/day for source S2 was used to satisfy the demand at
the next highest contaminant concentration.
F
S2
= F
S2, D2
+ F
S2, left
F
S2, left
= 25.03te/day - 60.4te/day = 18.99te/day (4)
3.4.2 Network Modifications
It is emphasised that Figure 4 is only one of the possible
network designs for this case study. Other possible matches,
including mixing of streams, may also yield the maximum
water savings. Even though WPAhad proposed a guideline for
design to achieve the maximum water savings, the decision to
strictly implement the design ultimately rests with the designer.
For safety or layout reasons, a designer may influence the
network design by imposing forbidden or forced connections
[22]. Adhering to these constraints may however incur penalty
in terms of the fresh water flowrate.
In the case of SIM, accepting the proposed network in
Figure 4 will require rather extensive modifications to the
original network in terms of new pipeworks, storage tanks and
control system. The inconsistent ablution water flowrate would
have to be supplied to seven water demands. For each demand,
different freshwater flowrate needed to be added in order to
satisfy the contaminant balance. This may be uneconomical
and difficult to implement. Alternatively, instead of piping
fresh water to all these demands, the rainwater (S1) and
ablution wastewater (S2) may be mixed with freshwater in a
distribution tank to produce a new water source at 10 ppm as
required. With this modification, SIM was still able to achieve
maximum water savings. The source and sink diagram for this
modified design and the flow diagram for the final water
network is shown in Figures 5 and 6 respectively. Note that the
water demands (D1 to D8) are ordered at the top according to
increasing contaminant concentration from left to right while
the water sources (S1 to S6) are aligned vertically on the left
hand side according to increasing contaminant concentration
from top to bottom.
3.4.3 Water Regeneration Network Design
Making appropriate changes to a process has been widely
accepted as an effective measure to further reduce utility
targets in heat and mass integration [18, 32]. The same
principle applies to WPA. Two possible scopes for process
changes to further reduce the water targets, and hence, water
F
S2
=
m
S2
C
S2
F
S2
=
0.14kg.day
23ppm
x1000 = 6.04te/day
x1000
Figure 4: One possible water network design that achieved the
targets for SIM case (without regeneration)
Figure 5: Water network design that achieved the targets for SIM
case without regeneration (after modifications)
Figure 6: Final water network for SIM without regeneration
(freshwater savings: 65.1% and wastewater reductions: 51.5%)
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Journal - The Institution of Engineers, Malaysia (Vol. 67, No. 1, March 2006)
S.R. WAN ALWI, et al.
62
consumption, include water regeneration and equipment
(hardware) modifications. Water regeneration involves the
partial or total upgrading of water purity using purification
techniques such as wastewater treatment like microfiltration,
greenhouse filter, sand filter with reeds, multi media filter and
biofilter. The regenerated water can either be reused in other
water-using processes or recycled to the same process to
further reduce water consumption and wastewater generation.
The main problem of dealing with process changes is that,
assessment of the impact of changes involves repetitive
calculations to revise the utility targets and relocate the pinch.
Such tasks can be quite cumbersome in the absence of an
efficient targeting tool. The WCA has managed to overcome
this problem through the introduction of the Water Cascade
Table (WCT) that is very amenable to computer programming.
Recall that the pinch concentration for SIM case study was
23 ppm (before regeneration). One possible option of
regenerating the water source is to treat the ablution water to a
concentration above the pinch. It was suggested that 7.27
ton/day of ablution water at 23 ppm be regenerated to 10 ppm
using sand filter with activated carbon. Table 5 from the WCT
shows the new pinch purity at 0.999977 (23 ppm), and the
fresh water and wastewater flowrates reduced to 6.06 ton/day
and 13.73 ton/day respectively. This contributed to 79.2%
freshwater savings and 62.7% wastewater reduction. The
network design technique described previously also applies to
the case involving water regeneration. The final flow diagram
for water network with regeneration that achieves the new
water targets is shown in Figure 7.
3.4.4 Water Network Scheme for Sultan Ismail
Mosque Proposed by IEWRM
The Institute of Environmental and Water Resource
Management (IEWRM), UTM, had proposed a water-
recycling scheme aimed at minimising fresh water
consumption for SIM. The retrofitted network design proposed
by IEWRM is shown in Figure 8. IEWRM proposed the idea
of reusing treated ablution water and rainwater for the entire
mosque except for kitchen services. The ablution water or
rainwater were to be filtered for solid particles like hair, stones
and dirts before going through a series of treatment using
activated carbon and sand filter processes. The treatment
process was to ensure that water being recycled to the
distribution tank was at an acceptable purity for uses which
involve body contact.
The amount of ablution water reclaimed and rainwater
collected was limited by the existing distribution tank. Treated
ablution water will only be sent to the last distribution tank.
Since the water output was approximately 29.07 ton/day for the
four distribution tanks, only 7.27 ton/day of treated water can
be fed into the last distribution tank. The flowrate of 7.27
ton/day represented the limiting point or bottleneck for this
system. During the rainy season, rainwater was collected
instead and the spent ablution water was diverted to the sewer.
This design allowed an estimated fresh water savings and
wastewater reductions up to 25% and 20%, respectively.
3.5 Economic Analysis
The system proposed by IEWRM predicted fresh water
savings of 25% and wastewater reductions of 19.8% (Figure 8).
The system suggested by WPA predicted savings of 79.2%
freshwater and 62.7% of wastewater reduction after
regeneration (Figure 7).
Table 6 provides a preliminary comparison of the
economics between the solution proposed by IEWRM and
WPA involving partial water regeneration. Both IEWRM and
water pinch method used a UV disinfection unit and sand filter
with activated carbon treatment to regenerate about the same
amount of wastewater. Sand filter equipped with activated
carbon that has a maximum flow rate flow of 7.27 m
3
/day costs
RM1170 per unit [33] and a UV system with 11 m
3
/day flow
rate cost RM1900 per unit [34]. The UV system has an
operating cost of RM483 per year [34] for 10 hours in
operation per day per unit. IEWRM uses one unit of sand filter
and UV system for their new water network solution while the
WPA solution uses one unit of sand filter for regeneration
(secondary treatment) purposes and two unit of UV system for
Table 5: WCT for process involving partial regeneration of
ablution water
Figure 7: Final water network for SIM after partial regeneration
(freshwater savings: 79.2% and wastewater reductions: 62.7%)
Figure 8: Retrofitted water network for SIM proposed by IWERM
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Journal - The Institution of Engineers, Malaysia (Vol. 67, No. 1, March 2006)
SYSTEMATIC DESIGN OFA MAXIMUM WATER RECOVERY NETWORK FOR AN URBAN SYSTEM BASED ON PINCH ANALYSIS
63
primary treatment purposes. The freshwater tariff in Johor for
the year 2004 is RM2.13 per m
3
(SAJ water bill, [35]). This
gives the treatment investment cost and annual freshwater
savings as stated in Table 6.
Preliminary economic evaluation on these schemes indicated
the payback period for IEWRM and WPA at 7.4 months and 4
months, respectively. The payback period using WPA was
shorter due to much higher potential fresh water savings as
compared to the IEWRM solution. Note however, that the
current analysis, which considered only the cost of regeneration
units was adequate as a preliminary economic comparison and
design screening. To implement the selected design, a more
detailed economic evaluation, which also considers pipework
and storage tank costs should be performed.
4.0 CONCLUSION
A systematic procedure for design of a maximum water
recovery network for an urban system based on WPAhas been
proposed. Sultan Ismail Mosque was selected as a case study
to demonstrate the impact of the technique. The conventional
solution proposed by IEWRM predicted fresh water savings of
25% and wastewater reductions of 19.8%. However, WPA
method predicted savings of 65.1% fresh water savings and
51.5% of wastewater reduction for SIM without regeneration
and 79.2% fresh water and 62.7% of wastewater reduction for
SIM with regeneration. WPA enabled the minimum utility
targets to be established prior to network design and provided
systematic guidelines for the design of an MWR network to
achieve the established utility targets.
I
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PROFILES
Zainuddin bin Abdul Manan
Chemical Engineering Department,
Universiti Teknologi Malaysia,
81310 Skudai, Johor, Malaysia.
NOMENCLATURE
Symbols
C = contaminant concentration, ppm
F = flowrate of water demand or source, kg/s or t/hr
n = number of purity intervals
N = number of water demands or sources
P = purity
= difference
= summation
m = contaminant load
Subscripts
C = cumulative
D = water demands
FW = fresh water
S = water sources
WW = wastewater
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