Water and Urban Initiative
Working Paper Series
Number 01 — April 2015

Urban Development and Water
Sustainability

Chongrak Polprasert Thammasat University, Pathumthani, Thailand

Tatchai Pussayanavin Asian Institute of Technology, Pathumthani, Thailand

Thammarat Kottatep Asian Institute of Technology, Pathumthani, Thailand

Water and Urban Initiative
This working paper series shares findings produced as part of the research activities under the Water and Urban Initiative(WUI), a research project of the United Nations University Institute for the Advanced Study of Sustainability (UNU-IAS). TheWUI aims to contribute to sustainable development, focusing on developing countries in Asia, by providing policy tools and an
information platform to assist planning and implementing policies for sustainable urban and water environment.
To find out more, please visit unu.edu/research/water-and-urban-initiative.html© 2015 United Nations University. All Rights Reserved.
The views expressed in this publication are those of the author(s) and do not necessarily reflect the views of the United Nations University.

Urban Development and Water Sustainability

ABSTRACTDue to limited access to safe drinking water and lack of adequate sanitation facilities in most developing counties, therapid population growth and urbanization have caused serious water scarcity and water pollution problems. Anotherprevalent environmental problem is global warming causedby burning of fossil fuels which has negative impacts on thehydrological cycle and consequently unfavorable changes
in water quality. The threats posed by global warming are
an additional stressor to the environmental system andwater sustainability. An ecological wastewater treatment
management such as the “closed-loop systems” should beconsidered. The closed-loop concept, using wastewater
cycles from “point-of-generation” to “point-of-production”,
could provide a better way for attaining high environmental
quality and full utilization of wastewater resource. Subsequently, some innovative sanitation technologies recently
developed such as solar septic tanks and hydrothermal carbonization for feacal sludge have been found to meet theclosed-loop concept because they were able to inactivate
the pathogens, remove the pollutants and producing valuable by-products such as biogas and hydrochar, respectively. These cost-effective technologies should be able toprotect the public health, improve quality of the canals andrivers in the urban areas, all contributing to water sustainability.

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than 80 percent of human waste in developing countries
is discharged untreated to receiving water (WWAP, 2009).
Water pollution problems are also increasing with morethan 1,500 km3 of untreated wastewater being discharged
to nearby canals and rivers (WWAP, 2003). The report of
UNEP (2000) indicated that the amount of fecal bacteria
indicators in Asia’s rivers is about 50 times higher than the
WHO (1989) guidelines.

Figure 1 (a): World, urban and rural population: (a) Population
rural and urban (Modified from United Nations, 2014)

Keywords: urban development; water sustainability;
resource recovery; environmental technology

1. INTRODUCTION
The world population is growing rapidly over the last few
decades. There are currently about 7 billion people withmore than 50 % of them, mostly in developing countries,
living in urban areas. Urbanization in many countries isgenerally due to economic growth in the past 40 years. The
United Nations (2009) reported that more than 2.5 billion
people of the world’s population, especially in Asia andAfrica, will add to the urban population, reaching up to
66% by 2050 (Figure 1). Sub-Sahara Africa and South Asia
are expected to account for half of the world population in
2100 (United Nations Water, 2009).
Hinrichsen et al. (1998) estimated the demand for freshwater to be about 64 billion m3 per year, while the global
fresh water resources is limited. A recent report of theUnited Nations (2009) found some areas of Asia and Africa
to be already in water scarcity and the percentage of theworld population affected by water-scarcity could increase
up to 47% in a mere three decades. Because the main
activity that contribute to poor water quality is wastewater
generated from human activities (blackwater and greywater), lack of access basic sanitation facilities is one of themost important concerns of global water pollution. More

Figure 1 (b): World, urban and rural population: percentage
urban and rural (Modified from United Nations, 2014)

Hinrichsen et al. (1998) estimated the demand for freshwater to be about 64 billion m3 per year, while the global
fresh water resources is limited. A recent report of theUnited Nations (2009) found some areas of Asia and Africa
to be already in water scarcity and the percentage of theworld population affected by water-scarcity could increase
up to 47% in a mere three decades. Because the main
activity that contribute to poor water quality is wastewater
generated from human activities (blackwater and greywater), lack of access basic sanitation facilities is one of themost important concerns of global water pollution. Morethan 80 percent of human waste in developing countries
is discharged untreated to receiving water (WWAP, 2009).
Water pollution problems are also increasing with morethan 1,500 km3 of untreated wastewater being discharged
to nearby canals and rivers (WWAP, 2003). The report of
UNEP (2000) indicated that the amount of fecal bacteria

Urban Development and Water Sustainability

indicators in Asia’s rivers is about 50 times higher than the
WHO (1989) guidelines.
Another prevalent environmental problem is global warming caused by burning of fossil fuels which has negative impacts on the hydrological cycle and consequently unfavorable changes in water quality. For example, the effects ofsevere drought and increased precipitation rate caused by
global warming could dramatically increase the risk of diarrheal diseases (WHO 2009; Confalonieri et al. 2007). The
threats posed by global warming are an additional stressor
to the environmental system and water sustainability.

2. Water sustainability concept
The above water problems especially in urban areas giverise to concern about appropriate wastewater management practices. In this respect, an ecological wastewater
treatment management such as the “closed-loop systems”
should be considered. The closed-loop concept, using
wastewater cycles from “point-of-generation” to “pointof-production”, could provide a better way for attaining
high environmental quality and full utilization of wastewater
resource (Jhansi and Mishra, 2013).

2.1 Ecological wastewater treatment
The development of ecological wastewater treatment
systems will provide a better solution for the managementof valuable wastewater resources and the reduction ofpathogens in the receiving water. These systems employ
the natural reactions of plants, microorganisms and sunlightto biodegrade organic wastes from the point-of-generation
with the production of valuable products such as protein
biomass for uses as animal feeds or human foods (pointof-production). Examples of these ecological wastewater
treatment systems are described below.

High rate algae pond
Algae are diverse group of microorganisms that can perform photosynthesis. Solar energy is the primary source ofenergy for all life. This energy is utilized by phytoplankton
during photosynthesis and synthesis of new cell occurs.
With respect to algal mass culture in wastewater, efforts
have been directed towards single cell protein production for potential human and animal consumption (Figure2a). The desirable properties of algal single cell protein
are high growth rate, resistance to environmental fluctuations, high nutritive value, high protein content and ability
to grow in wastewater. Algal cells have high protein value,and subsequent harvesting of algae for human and animal
consumption will be the financial incentive to wastewater
treatment. The average production of algae is reported as
70 tons/(ha-yr) or 35 tons/(ha-yr) algal protein; comparing
with the productivity of conventional crops, wheat 3.0 (360kg protein), rice 5.0 (600 kg protein) and potato 40 (800 kg

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protein) tons/(ha-yr) (Becker, 1981). However, the existing
technologies of algal harvesting are normally complex and
expensive. Pathogen destruction occurs in algal ponds due
to adverse environment such as: diurnal variation of pH due
to photosynthesis, algal toxins excreted by algae cells, andmost importantly, solar radiation (UV light). At present, themain attractiveness of algal mass cultures is that they havegreat versatility to be integrated into multi-use systems for
simultaneously solving several environmental problems.

Aquaculture fish pond
The culture of phytoplankton-feeding (herbivorous) fish
(Figure 2b) to graze on the algae is attractive in order toproduce the fish protein biomass which is easily harvestable for animal (or human) feed. Waste treatment is theprimary objective of any waste recycling scheme and theinclusion of fish production recovers nutrients in the waste,such as N, P and K. Addition of waste or its by-products
such as biogas slurry and compost to fish ponds resulted
in increased fish yields (Polprasert et al. 1982). Fish is acold blooded animal and, unlike other farm animals such as
cattle or poultry, does not have to spend a lot of energy for
movement because friction is less in water. Thus fish havea better food conversion ratio than any other farm animals.
Fish culture does not require highly skilled manpower for its
operation (Polprasert, 2007). Fish production from wastes
might have some limitations such as land requirement andexistence of a waste collection system, availability of suitable fish fry, marketing and public acceptance

Aquatic weed
Using aquatic weeds in waste recovery and recycling will
result in waste stabilization and nutrient removal, andconversion of the harvested weeds into productive uses.
Aquatic weeds provide a medium for bacteria to be attached and grow at their roots and stems, to stabilize thewaste (Figure 2c). The presence of weeds in the aquatic
medium and subsequent harvesting enable the nutrient
removal from the wastewater. Even though stabilizationof waste is a slow process in aquatic systems, the removal
efficiency is high and can produce an effluent superior orcomparable to that of any other treatment systems (Polprasert, 2007). Aquatic weeds can be used, directly orafter processing, as soil additives, mulch, fertilizer, green
manure, pulp and fiber for paper making, animal feed, andhuman food, organic malts for biogas production and forcomposting.

Land treatment
Land treatment is defined as the controlled application ofwastes on to the land surface to achieve a specified degreeof treatment through natural physical, chemical and biological processes within the plant-soil-water matrix (Figure 2d).
Land treatment systems are less energy intensive than such

Urban Development and Water Sustainability

conventional systems as: activate sludge, trickling filters
and aerated lagoons. However, energy is needed in land
treatment for transportation and application of wastewater
to the land. Since less mechanical equipments are needed
for land treatment process when compared with other conventional treatment processes, the maintenance of the land
treatment system is easy and less expensive.

Constructed wetlands for wastewater treatment andrecycling
Constructed wetlands are a wastewater treatment system consisting of shallow ponds or channels plantedwith emerging aquatic plants (Figure 2e). The processes
by which wastewater is treated include a wide range ofinteracting biological, physical and chemical mechanisms.

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Constructed wetlands process are the symbiotic reactions
between aquatic plants and bacteria similar to the algal
photosynthesis. The aquatic plants perform photosynthesis
under sunlight and the produced O2 is transferred fromleaves to the root zones where bacteria will utilize it todecompose the organic matter (Polprasert, 2007). Other
reactions occurring in a constructed wetland system suchas adsorption and plant uptake will, respectively, result inbetter removal of SS and nutrients (such as N and P). BOD5
matter is degraded by the bacteria attached on the surfaceof the constructed wetland media and plant roots using
O2 photosynthetically produced by the plant leaves that istransferred to the soil-water matrix. N and P are removedby plant uptake and sedimentation while, due to long retention time, most suspended solids would settle down inthe constructed wetland beds and some could be removed
by filtration and adsorption.

Figure 2: Ecological wastewater treatment systems (clockwise from upper left): High rate of algae pond; aquaculture fish pond;
aquatic weed; land treatment; constructed wetlands for wastewater treatment and recycling

Urban Development and Water Sustainability

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2.2 Innovative sanitation technology
Some innovative sanitation technologies recently developed such as solar septic tanks and hydrothermal carbonization of feacal sludge (Figure 3) can meet the closed-loop
concept because they effectively inactivate the pathogens,remove the pollutants and producing valuable by-products
such as biogas and hydrochar, respectively. These technologies which are cost-effective should be able to protect
the public health, improve quality of the canals and rivers in
the urban areas, all contributing to water sustainability.
A modified conventional septic tank with solar-heatedwater is considered to be an effective on-site sanitation
technology. Operating a septic tank at temperatures higher
than ambient condition could enhance pathogen die-offs,
increase biodegradation of organic matters and reducing sludge accumulation. Koottatep et al. (2013) reported
the TCOD and BOD5 removal efficiencies of septic tanks
operating at temperatures of 40-70 oC to be more than
80 %, while E.coli reduction was 4-6 logs. Rates of sludge
accumulation and amount of CH4 production in the solar
septic tank operating at a temperature of 40 oC were
found to be about 50 % lower and higher, respectively,
than those in the conventional septic tank (Pussayanavin etal, 2014). Hydrothermal carbonization is an alternative technology that can be used to treat and convert feacal sludge
into valuable solid product called hydrochar. The energy
content and yield of the produced hydrochar were found to
be about 20MJ/kg and 70%, respectively.

3. Common barriers and major concerns of water
sustainability
Although awareness of water sustainability is increasing,
due to globalization and industrialization, many developing
countries still do not consider wastewater management asa priority. The common barriers for moving towards water
sustainability consist of such issues as: government’s priorities, legal status and regulation, national budgeting, availability of appropriate technology and technology transfer,and lack of awareness among local people. Moreover,restricted local budgets or funding can be one of barriers
that decrease affordability for water sustainability approach, especially in many small and isolated villages.

4. Summary
Because of limited water resources, water pollution andglobal warming, many developing countries are facing
water scarcity and water contamination. The application of
the ecological wastewater treatments as presented in thispaper are some of the technologies, which have proveneffective in the pollution control and resource recovery.
These systems are environmentally friendly and socially

Figure 3: Innovative sanitation technology (top to bottom): Solar
septic tank; hydrothermal carbonization of feacal sludge

acceptable which should contribute to urban sustainability.
The innovative sanitation technologies are new trends ofon-site technologies which could be effective in wastewater treatment and sludge stabilization including the
production of value-added products. Implementation ofthese technologies could create a platform towards global
sustainability, but common barriers such as policies, regulatory procedures and budget planning need to be tackledconcurrently.

Urban Development and Water Sustainability

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