Workshop 4: OPTIMISING WATER USE BEYOND URBAN
BOUNDARIES
Session 2: Wastewater Management to Support River Basin Water Quality:
Improving water quality: Are centralised solutions cost effective?
Organized by Specialist Group on Sanitation and Water Management in Developing
Countries
Moderator and introduction: Dr. Markus Starkl, BOKU University, Vienna, Austria
Presentation 1: Centralised versus decentralised management options (Ir. Dorai Narayana, IndahWater Konsortium Sdn Bhd, Malaysia)
Presentation 2: River quality impact and cost assessments of different wastewater management
options in the Melana catchment, Malaysia (Prof. Zulkifli Yusop, Technical UniversityMalaysia)
Presentation 3: Potential for small and large scale solutions: costs and quality aspects (Mr. PierreFlamand, Japan Sanitation Consortium, Japan)
Panel discussion: Improving water quality: Are centralised solutions cost effective?
Ir. Dorai Narayana, Indah Water Konsortium Sdn Bhd, Malaysia
Prof. Zulkifli Yusop, Technical University Malaysia, Malaysia
Mr. Pierre Flamand, Japan Sanitation Consortium, Japan
Prof. Thammarat Koottatep, Asian Institute of Technology, Thailand

Introduction:This workshop has aimed at discussing the rational behind centralized and decentralizedsolutions for water management. The arguments for both are well known. Whereas worldwide
there is a trend towards decentralized solutions, this workshop tried to critically reflect this trend
and look at potential and limitations of both options.
Presentation 1:
Ir. Dorai highlighted that the question of centralised vs decentralised sewerage management has
been debated often. In most instances, costs, both Capital and Operational – would be cited as
the main criteria in the selection. While this is to some extent valid, the issue is far morecomplex:
Sanitation is high priority primary concern for urban areas, basically to address Public Healthissues. The focus is initially on providing toilets, and educating people to use them. The waste isusually treated in rudimentary on-site systems, often a pit or pour flush latrine. With time, theslightly more effective septic tanks began to be used. And while these were more effective inpreventing ground water pollution and also producing reasonably acceptable effluent, the septic
tanks had to be desludged periodically, leading to a septage problem. Then came piped waterborne sanitation, transporting the sewage away from the premises to a remote location. Thesetreatment facilities were usually small scale communal facilities. Issues included nuisance due toproximity to residences and also difficulties of managing them due to large numbers andlogistics. As cities grew, regionalised sewerage systems began to e built. These are capitalintensive and are expensive to build operate and maintain. Moreover building such system in anexisting city and connecting all the sewage sources is extremely challenging.
In Malaysia, all of the above systems co-exist, as remnants of the evolution of the sewerage
infrastructure in the country. Catchment Strategies are used to ascertain the best strategy for agiven urban area, considering such factors as existing systems, issues, growth rates, landavailability, Capital and Operating costs and NPV, affordability, suitability as well as other noncost considerations in deciding whether to go for regionalisation, and when to implement it.
Usually the strategies are staged, to allow for flexibility to cater changing conditions.
Presentation 2:
Prof. Yusop presented a case study from the Melana catchment located in Johor Bahru in South
Malaysia. The overall objective of this study was to assess the performance of different
wastewater management options by carrying out the following tasks:••••

calculate a design capacity based on the predicted population equivalent in the area
predict the river water quality based on the current and future development scenarios
identify feasible wastewater treatment options
assess environmental and economic impacts

The river quality was analysed for pH, temperature, dissolved oxygen (DO), biochemical oxygen
demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), Ammoniacal
nitrogen (AN), nitrate, phosphate, lead, cadmium and copper. TSS was selected as indicator ofsoil erosion and sedimentation, BOD as indicator for organic pollution, nitrate and phosphate fornutrient contents that may lead to eutrophication and the heavy metals represent industrial
sources. QUAL2E was used for modelling the river quality. The model is widely applied forevaluating river water quality and can be applied in various conditions for different parameters(Ghosh, 1996). In this analysis QUAL2E was used to simulate Melana River quality and predictthe present and future river quality over 30 years time span. Options were proposed to upgrade
the existing wastewater treatment performance. The proposed options were based on factors suchas site suitability for treatment plant, accessibility, availability of new area, consumer demand,technology and cost.
Based on the QUA2E modelling results, both the decentralised and centralized option areexpected to exhibit quite similar river quality pattern. However, the centralized option may
perform even better in the upstream because there is no discharge. The cost modelling showedthat the centralized option is cheaper by about 15% compared to the decentralized options.

Presentation 3:
Mr. Flamand discussed the aspects that would favor centralized or decentralized wastewater
treatment systems in the quest of improving water quality at river basin level, and whether

centralized systems are cost-effective solutions. In terms of treatment quality, Japan has theparticularity of having developed both centralized and decentralized technologies (so-called“johkasou”) that can achieve the same level of treatment. This is a specific and important featurethat is not found in many countries, where septic tanks and centralized wastewater treatment
systems achieve very different performances. Mr. Flamand detailed the characteristics of themajor wastewater treatment systems in Japan, and the criteria for the selection of centralized ordecentralized systems. This was emphasized by the introduction of a case study at river basin
level in Japan, including a cost comparison between different options. This gave a concrete
example on how selection is made, mainly based on population density and cost per capita.
Finally, he highlighted that the combination of both centralized and decentralized systems
enabled Japan to achieve full sanitation coverage in a relatively short period of time, and also toprotect water resources, as demonstrated by the constant quality improvement in water bodies,
especially rivers.

Panel discussion:
After the presentations the advantages and disadvantages of decentralized and centralized
solutions were discussed and questions from the audience taken up. The discussion has shownthat there is a general tendency to favor decentralized systems (a question to the audience about
their general preferences has shown that the large majority preferred decentralized systems).
However, the argument of economy of scales and capacity of operating the systems supported
centralized systems. As a conclusion, the question whether decentralized or centralized solutions
are better depends on the local contexts e.g. socio-economic conditions, user perceptions andparticipation, regulatory enforcement, etc. whereby the byproducts from either systems shall beproperly managed and/or recycled A feasibility study should compare centralized, decentralized
and mixed solutions in order to identify the most suitable one for a specific case.