RECYCLED WATER: TECHNICAL-ECONOMIC CHALLENGES FOR ITS INTEGRATION AS A
SUSTAINABLE ALTERNATIVE RESOURCE
V. Lazarova
Lyonnaise des Eaux- CIRSEE, 38, rue du Président Wilson, 78230 Le Pecq, France
E-mail: valentina.lazarova@lyonnaise-des-eaux.fr
ABSTRACT
Growing water scarcity, population growth, rapid urbanisation and the spread of megacities,
increasing competition among users and growing concern for health and environment protection are
the main trends that may seriously challenge the water industry in this new millennium. To manage
and safeguard water resources for coming generations, integrated management of water resources is
becoming the leading strategy worldwide. In this context, wastewater reuse is becoming a key factor
for counteracting the negative quantitative and qualitative impacts between the anthropogenic and
natural water cycles, for preventing any increase in pollution of natural freshwater resources and for
providing low-cost alternative resources for human activities, and in this way integrating the two water
cycles.
The main purpose of this paper is to present and discuss the main socio-technical-economic
challenges for developing water reuse, with emphasis on the choice of treatment trains,
economics, water quality issues and the social value of recycled water.
KEYWORDS
Recycled water, wastewater reuse, treatment trains, economics, decentralised treatment,
multiquality water production, public acceptance
INTRODUCTION
The increasing scarcity and pollution of freshwater resources create a monumental new challenge for
water managers and policy makers: to satisfy increasing water demand from an ever-growing
population, while protecting the environment and public health and avoiding sectoral, regional and
international conflicts over water. In this context, wastewater reuse is becoming an essential factor for
developing sound water and environment management policies. In arid and semi-arid regions, recycled
water is a vital component, providing an alternative water resource, ensuring sustainability, reducing
environmental pollution and protecting public health. In temperate regions, wastewater reuse
contributes towards environmental protection and is an alternative resource for water crisis
management in the event of drought. The new challenges for the water industry in successful
implementation of wastewater reuse projects around the world are: innovative global water
management; increasing the cost-efficiency of water reuse systems, including treatment processes,
distribution networks and storage reservoirs; controlling water quality; educating and informing the
public; reorganising institutional structures; and developing and enforcing new policies.
Requirements for integrating wastewater reuse into the natural water cycle are appropriate
treatment technologies, stringent quality control and a better understanding of the risks
inherent to each type of reuse. These new requirements, which all concern the quality of the
reclaimed water, make it necessary to combine wastewater and potable treatment techniques.
There are now technical advances that make it possible to produce recycled wastewater of a
quality suitable for almost all types of use. However, there are still economic constraints; for
example, recycled water is not competitive compared to other resources. Water reuse will
only be able to fulfil a major role in overall water management policy once the appropriate
administrative, regulatory and financial mechanisms have been established.
A flexible water management policy can ensure the competitiveness of reuse as: (1) a lowercost, drought-proof alternative resource available near the point of use, (2) a unique and
inexpensive solution for pollution control, (3) a complementary resource for coastal areas,
where discharges into the sea are irreversible, (4) a viable alternative to transporting natural
resources over long distances, (5) a balancing factor in conflicts between different sectors'
requirement, ensuring independence in water resources, (6) an important element for
developing major urban and rural settlements, (7) a solution for restoring polluted resources
and lost wetlands.
DECENTRALISED APPROACH: AN INNOVATIVE SOLUTION TO WASTEWATER
TREATMENT AND REUSE
Decentralised wastewater management is a new and growing trend in Europe and the United States,
where it has been developed in response to the new requirements of integrated resource management
and sustainable development. The conventional centralised approach, which consists in the
construction of large sewers and centralised treatment facilities, is not only an expensive solution for
both small and large municipalities, but also has negative impacts on the environment.
By definition, the decentralised wastewater concept requires the use of appropriate treatment
and disposal technologies, taking into consideration the current and future needs of the
community. This new solution makes it possible to address the needs of both sewered and
unsewered areas in a more comprehensive, cost-effective and environmentally friendly way.
The main advantages of this approach are as follows:
 watershed and water resource protection, avoiding transfer of wastewater on a large scale;
 greater flexibility and the ability to provide the most appropriate solution for specific site
conditions, e.g. high population density, shallow bedrock or shallow aquifers, including
the possibility to use individual septic tanks, shared or clustered treatment systems or even
centralised systems where appropriate;
 a cost-effective option for rural areas and low-density communities, avoiding the expense
of large sewerage systems and allowing for the use of low-tech extensive treatment
processes;
 environmental protection combined with a cost-effective technical solution for urban and
ecologically sensitive areas, by the use of advanced treatments in compact, covered
buildings, including odour treatment, nutrient removal and disinfection;
 favouring wastewater reuse and recycling for various purposes near the point of use.
The last two points are crucial for the development of water-scarce regions. Significant
benefits and cost saving can be achieved, especially in unsewered areas.
TECHNOLOGICAL ADVANCE AND TECHNICAL CHALLENGES FOR WATER
REUSE
There are numerous state-of-the-art technologies that can be used to make wastewater a
competitive alternative resource to replace water from the natural environment. Reliable and
effective treatments can be easily adapted to the specific needs of different uses. The inclusion
of such systems into long and medium-term water planning is an indispensable condition for
the successful development of wastewater reuse practices.
The level of treatment is chosen according
to standards, legal requirements and the
type of reuse envisaged (Fig. 1). In this
way, the same treatment objective can be
met by using either intensive technologies
or extensive technologies, which are similar
to natural treatment processes. The final
choice of process will depend on technical
and economic considerations as well as
local conditions (infrastructure, uses,
available space, plant capacity, etc.). The
concern for public health has led to the
concept of “multibarriers”, essential to the
production of ultra-pure water: each type of
pollutant is targeted by different treatment
techniques, which are carried out in
succession.
Fig. 1 Treatment levels required for the main water
reuse applications
The main technical challenges for the
successful development of wastewater
reuse projects are as follows:
1) Ensure high operational reliability, not only of treatment facilities but also of storage
reservoirs and distribution networks, to guarantee good water quality at the point of use. A
high level of sample conformity is required for all types of wastewater reuse, to minimise
health risks and bacterial regrowth.
2) Improve treatment process design and integration to meet specific water quality
requirements. Improvements are needed for greater economic efficiency and to minimise
by-products. Innovation should be promoted to identify new combinations of treatments,
including emerging advanced technologies, in order to improve operational reliability, salt
removal and disinfection efficiency. Finally, satellite treatment facilities should be
considered to improve water quality at the point of use at minimum cost.
3) Enhance water quality monitoring to demonstrate the compliance of recycled water with
existing standards. Rational monitoring programs should be developed, as well as
standardised, simple, low-cost analytical tools for monitoring pathogens. Advanced
analytical tools developed for monitoring drinking water should be applied, to determine
the occurrence of organic micropollutants and emerging pollutants (endocrine disrupters,
drugs, etc). New research is needed to assess health risks.
4) Develop best practices for wastewater reuse to guarantee public health safety, decrease
water losses and improve economic efficiency.
As regards specific treatment requirements, a high rate of removal of suspended solids is
essential to ensure that the subsequent processes are more effective. Particles are particularly
troublesome for disinfecting pathogens, which cling to solid matter and are then more
resistant to the action of disinfectants. For safe reuse of wastewater containing carbon and
nitrogen pollutants as fertiliser for irrigation purposes, effective particle removal and
disinfection are imperative.
In almost all cases, secondary treatment is required to guarantee the reliability and
effectiveness of the disinfection step. In this context, the choice biological treatment also
plays a very important role. Extended aeration, for example, produces easily-disinfected
effluents that high rate activated sludge. Membrane bioreactors are a very promising emerging
technology, producing high quality and fully-disinfected effluent.
With the increased concern for public health and environment protection, the choice of
disinfection technologies is one of the critical steps in a treatment scheme. It must be stressed
that treatment quality upstream of disinfection has a major impact on the dosage required to
achieve a given disinfection level. If a stringent regulation must be met, disinfection cannot
cope with water from a less efficient upstream treatment and often has to be coupled with
tertiary filtration or some other advanced treatment process such as ultrafiltration or
microfiltration. The increasing use of UV technologies in wastewater reuse schemes is largely
attributable to low costs, as well as the absence of toxic by-products (Lazarova et al., 1999).
Compared to chlorination, the other main advantages of UV technology are low maintenance
requirements, ease of use, suitability for automation, and small foot print. Ozonation, and in
particular the recent progress in ozone generation and other equipment, are not well known
among technical experts and consultants because large scale experience has so far been
limited. However, several recent studies described in the literature and R&D experimental
results point to some applications when ozonation should also be considered as a promising
treatment, would compete well with UV irradiation, and bring several other advantages
(Lazarova et al., 1999).
Membrane treatment is an efficient and reliable solution for producing high-quality recycled
water (Adham et al., 1998). As a new application, the use of low-pressure membranes as a
pretreatment to reverse osmosis is being investigated and implemented for indirect potable
reuse in California, USA.
MULTIQUALITY RECYCLED WATER PRODUCTION: THE WEST BASIN
EXPERIENCE
Another new concept developed for successful implementation of integrated resource
management in urban and protected areas is the production of multiquality recycled water for
different reuse purposes. With this approach, wastewater treatment costs are optimised by
producing alternative water resources of different qualities for different reuse purposes. One
of the largest water reclamation facilities in existence, in West Basin, California (in operation
since 1995, final design capacity of 340,000 m3 d-1), is a good example.
The West Basin Water Recycling Plant (WBWRP), located in El Segundo, California, is owned by
West Basin Municipal Water District (WBMWD), a public agency providing wholesale water to local
water utility companies and municipal water departments (17 cities and unincorporated areas of
Southwest Los Angeles County). WBMWD has implemented a water recycling program that so far
includes a pump station that pumps secondary effluent through a 4.5 km long force main to the
Recycling Plant. Advanced tertiary and quaternary treatment (Fig. 2) is carried out to produce high
quality recycled water. Reliable plant operation and guaranteed water quality are ensured by means of
a private/public partnership with United Water Services, a subsidiary of Lyonnaise des Eaux.
The WBWRP treats secondary effluent from the City of Los Angeles’ Hyperion WWTP and produces
four types of recycled water. The first type meets Title 22 standards, referring to the California Code
of Regulations for wastewater reuse. This type of recycled water is typically used for landscape
irrigation and industries such as dye works and oil refineries. The processes used to treat the secondary
effluent to Title 22 standards include coagulation, flocculation, filtration and chlorine disinfection. The
water is further treated to a second type of water quality  ammonia-free Title 22 effluent  at two
satellite nitrification plants, for use in refinery cooling towers
Fig. 2. Multiquality recycled water production: main treatment train and reuse purpose in
West Basin Water Recycling Plant, California
The third type of water produced at the plant is distributed to the West Coast Basin Barrier, a
series of wells that inject a blend of potable and recycled water into the groundwater basin to
protect it from seawater intrusion. Barrier water must meet all drinking water standards.
Reverse osmosis (RO) is used as a final treatment process after two types of pretreatment by
conventional lime clarification and microfiltration (MF).
Table 1. Annual average water quality data of the West Basin Reclamation plant
Parameter
Unit
Turbidity
PH
TOC
TSS
BOD
TDS
NTU
pH units
mg/L
mg/L
mg/L
mg/L
Influent
Permitted
Measured
5.4
6.7
20
10.6
30
14
30
27
-
Title 22 Water
Permitted
Measured
2
1.8
6.9
20
1.2
1
1000
789
Barrier Water
Permitted
Measured
2
0.39
8
2
0.7
0.1
124
The fourth type of ultra-pure recycled water is MF/RO effluent, produced in a new satellite
treatment plant for use as boiler water in the petroleum industry.
Table 1 presents the average annual data for the influent and the final effluent water quality
for the Title 22 and barrier treatment trains. The data clearly show the differences in water
quality: the low TDS, TOC and turbidity values of the RO advanced treatment train are
indicative of its high treatment efficiency.
NEW CHALLENGES FOR RECYCLED WATER QUALITY
The water quality issue has high impact on water reuse projects because of public perception,
liability and public health concerns. Both conservative wastewater reuse standards and
inadequately low legislative requirements can affect wastewater reuse development.
Guidelines taking account of recent advances in scientific research rather than conservative
standards would also need to take cultural and social habits, existing infrastructure and local
conditions into consideration. Moreover, the development, application and enforcement of
best reuse practices could be the critical step for rational use of recycled water and successful
health and environment protection.
In some cases and countries, wastewater reuse quality issues, especially for potable reuse
purposes, are becoming a major national problem and a subject of controversy. However,
unplanned, indirect potable reuse occurs in many European countries and parts of the United
States, with less oversight, whenever discharged wastewater quality is subsequently lower and
the wastewater percentage is higher. Moreover, in many emerging countries, natural resources
used for water supply are heavily polluted with raw, untreated wastewater. The rational
solution for wastewater reuse to augment potable water supply is to employ appropriate
treatment lines and appropriate monitoring procedures developed for and applied to water
resources and drinking water. Among the most important parameters are pathogens, trace
organics and endocrine disrupters.
High-purity recycled water with efficient removal of trace organics can be produced using the
combination of low-pressure membrane pre-treatment (ultrafiltration or microfiltration)
followed by reverse osmosis. This advanced treatment is applied in the West Basin Recycling
Plant to produce recycled water for aquifer recharge. A number of R&D studies have
demonstrated that with this membrane combination, up to 90% of trace organics can be
removed from secondary effluents (Levine et al., 2000). The first stage of UF or MF
treatment removes all the larger compounds from the influent and the RO unit remove the
smaller compounds, such as base neutral organics and salts.
ECONOMIC AND FINANCIAL CONSTRAINTS
A critical factor for the success of any water reclamation project is its affordability and
financial viability. In general, lack of funding is the major impediment to adopting wastewater
reuse. For this reason, the majority of water reuse projects have been developed with the help
of subsidies and grants. Public/private partnerships would be another solution to establish
appropriate financial plans, cut public sector deficits, promote investments and ensure better
water resource management with efficient wastewater reuse. As a rule, wastewater reuse
projects are under-valued and significant opportunities for beneficial reuse are lost. The main
reason for this is that wastewater reuse is not considered an element in integrated water
management that brings numerous monetary and non-monetary benefits compared to other
solutions.
The cost of wastewater reuse usually includes only the marginal cost of additional treatment,
storage and distribution, excluding the cost of wastewater collection and treatment. The
distribution of capital and O&M costs varies from one project to another and depends on the
type of treatment train. These costs are also heavily influenced by local constraints: price of
building land, distance between production site and consumers, need to install a dual
distribution system or retrofitting. The latter two constraints are important, since in many
projects the main capital investment concerns the distribution system and can amount to 70%
of the overall cost depending on site-specific conditions. New systems involve less expense
than retrofitting existing networks. Reported values range from 0.06 US$/m3 in Jubail, Saudi
Arabia (Al-A’ama and Nakhla, 1995) to 0.14 and 0.36 US$/m3 in Israel, in the Dan Region
and Jerusalem respectively (Shelef, 1991).
Capital costs for tertiary filtration and disinfection or even for full Title 22 treatment
(coagulation/flocculation, filtration and disinfection) do not exceed 30-40% of the investment
for secondary treatment. Significantly higher costs are incurred for activated carbon filters
(GAC) and reverse osmosis (RO) to produce high-purity water for urban, potable or industrial
purposes. On the basis of experience in the USA, Israel and the Middle East, the life cycle
cost for the treatment of raw sewage to produce recycled water suitable for unrestricted
irrigation varies from 0.43 to 1.10 US$/m3 (Al-A’ama and Nakhla, 1995; Richard et al., 1995;
Shelef, 1991). The additional life costs of Title 22 treatment, lime clarification/RO and
MF/RO, based of the US experience, range between 0.23 and 0.75 US$/m3. The use of MF as
a pretreatment before RO leads to a saving of 45% in life costs.
The production of multiquality recycled water for various reuse purposes, and in particular the
production of high-quality water for industrial purposes and aquifer recharge, contributes to
faster payback from wastewater recycling facilities. In general, the sale price of recycled
water for industries and urban users is higher than that charged to farmers; agricultural
irrigation involves higher water demand and lower economic value, which is usually
subsidised by local or national governments with only partial recovery of treatment and
distribution costs.
PUBLIC ACCEPTANCE AND EDUCATION
The development of sustainable water recycling schemes must include an understanding of the social
and cultural aspects of water reuse. The long-term objective is to promote expertise in ways to close
the water cycle in local scale, and this in internationally different economic, social and cultural
contexts. To accomplish this, it is necessary to extend traditional design and management activities to
include:
1) Assessment of cross-cultural factor that facilitate or hinder water recycling schemes.
2) Dissemination of information to the public, by organising forums with local agencies,
municipalities, water utilities and legislative officials from the earliest stage of any
wastewater reuse program. This means developing descriptions of the proposed
technologies, their performances, associated risks, costs and benefits to catchment-scale
water conservation and sustainable development.
3) Development of public education programs (newsletters, school education programs, open
houses and tours, meetings with stakeholders). The public’s knowledge and understanding
of the safety and proper use of recycled water is a key component of any successful water
reclamation program.
4) Establishment of new marketing approaches that treat recycled water as a new product for
sale.
Demonstrating the social value of wastewater reuse is an important challenge for the
development of wastewater reuse projects in all countries:
 The main aims of wastewater reuse for developing countries are to ensure a vital or in
some cases alternative resource for food production, and for health and environment
protection. The last point is important. Poverty contributes very considerably to
environmental degradation. In poverty-stricken areas, survival prevails over environmental
protection, while the poor are the first victims of environmental degradation.
 For developed countries, wastewater reuse saves on the cost of mobilising new water
resources, including desalination, and of wastewater treatment, which is in any case needed
for social and environmental reasons.
In some cases, the real problems arise from the political interpretation of water quality issues.
According to several recent water quality studies, the recycled water produced in the United
States from urban secondary effluents is better in terms of water quality than many natural
surface waters. Moreover, epidemiological studies indicate no microbiological or
toxicological risks in recycling treated wastewaters. Yet despite the rigorous scientific
arguments, two new projects under development in Tampa, Florida and San Diego,
California, have been stopped owing to strong opposition from politicians. The slogan they
used, without regard to scientific results or cost/environment analysis, was “From toilet to
tap”  and it was very effective.
Marketing is another key to the success of any water reuse project. Recycled water, after
appropriate treatment, is a new marketable product. The first step towards developing a
recycled water marketing strategy is to review the existing state-of-the-art terminology. The
definitions of wastewater reuse, wastewater reclamation and wastewater recycling cause real
confusion among potential consumers. Well-treated wastewater should no longer be
considered as wastewater but as a new alternative water resource. This new resource could be
named recycled water; it is safer and cleaner than many contaminated natural water resources.
Finally, the successful development of multiquality reuse practices requires a pro-active
marketing approach to convince potential consumers and win their willing participation.
Compared to the existing water supply and wastewater treatment situation, the marketing
challenges for wastewater reuse call for the latest innovative techniques in this area.
CONCLUSIONS
Water recycling is becoming the driving force in global water management. Numerous stateof-the-art technologies now exist that can make wastewater a comparable resource to water
from the natural environment by the use of reliable, effective treatments that can be easily
adapted to the specific needs of different uses. The inclusion of such systems in long- and
medium-term water planning is an essential condition for the balance of the natural cycle and
resource conservation in this new millennium. However, successful implementation of
wastewater reuse systems requires the development of new concepts, tools and approaches to
public education and the marketing of recycled water as a new product. Institutional
reorganisation, new policies and new regulations are also required. Future studies are
necessary to improve process operation and identify the most efficient and cost-competitive
treatment line for each reuse purpose.
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