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2.6 Other Technologies of Wastewater Treatment and Reuse
In Southeast Asian countries, including Hold Kong, urban and surrounding
areas are the centres of rapid expansion. The resources required to manage
municipal, industrial and agro-industrial wastes are very often severely
strained. Thus, economic growth is often accompanied by ecological damage,
as industries generate considerable amounts of both solid and liquid waste
products. Waste management is therefore an urgent environmental
consideration. Conventional freshwater augmentation technologies involve
different wastewater treatment processes such as preliminary or primary
treatment; secondary treatment; and tertiary or advanced treatment
techniques. As with any other environmental problem, new methodologies for
improved waste handling and treatment rely on advancements in related
sciences and technologies. In recent years, biological treatment of wastes
has developed rapidly because of breakthroughs in biotechnology.
Biologically-based technologies, therefore, are becoming an area of
increasing importance as a mean of water pollution abatement and
environmental rehabilitation. Nevertheless, with both conventional and bio
technological wastewater treatment techniques, waste materials, when
properly managed and treated, should not cause any appreciable
environmental damage (Whitton and Wong, 1994).
Preliminary treatment is basically screening of settleable organic and
inorganic solids by sedimentation and removal of materials. Approximately,
about 25% to 50% of the incoming BOD5, 50% to 70% of the suspended solids,
and 65% of the oil and grease is removed during the preliminary or primary
treatment process. This process largely reduces the volume to be treated
through secondary and advanced treatment processes, and, for some purposes
such as irrigation of orchards and vineyards, may be considered sufficient
treatment for reuse, depending upon the local acceptance. A bar screen
made of long, narrow, metal bars spaced at 25 mm is used for preliminary
treatment. The primary treatment process consists of grit removal.
Basically two types - horizontal flow and aerated types - of grit removal
techniques are used. Primary settling tanks are then used to remove the
readily settleable solids prior to further treatment. The treatment
process involves chemical treatment and flocculation, and passage through
second and third stage settling tanks. A study by Chen (1993) to evaluate
the effectiveness of primary treatment of municipal wastewater before
discharge into the ocean indicated that the removal of suspended solids
was always less than 50% while COD and BOD5 removals were in the range of
23% to 41% and 15% to 27%, respectively.
The main purpose of secondary treatment is to remove non-settleable
solids remaining in the wastewater stream after the preliminary and
primary treatment process. Efficiency is estimated at about 85% removal of
BOD5. This technique involves biochemical processes for the oxidative or
reductive degradation of biodegradable organic pollutants, and includes
such technologies as the anaerobic and facultative ponds as well as
aerated lagoons previously described.
Fish Farming or Aquaculture.
Fish farming has been used extensively to assist in the treatment of
wastewater. It helps to reduce the levels of suspended solids and algal
growth in the wastewater, and improves the quality of the final effluent,
which may be used subsequently for crop irrigation and other uses.
Wastewater treatment using fish ponds is a natural process that degrades
and stabilizes organic wastes, while fertilizing a fish pond with organic
wastes to stimulate the growth of natural biota, especially microorganisms
which serve as fish food (Edwards, 1985). Systems consist of both dry and
wet variants. The dry systems utilize nightsoil or faecally contaminated
surface water, applied to the pond bottoms during the dry season, for
aquacultural purposes in artificial ponds. The wet systems, which remain
water-filled throughout the year, use similar nutrient sources to drive
fish production in enclosures within ponds and natural lakes. These kinds
of systems have been widely used in several Asian countries (Edwards,
Overland Flow Systems.
Overland flow systems pass wastewater across slightly sloping grasslands
which provide both filtration and erosion control. The technology is
similar to the conventional trickling filter technology applied in
traditional secondary treatment processes. When wastewater is passed
across sloping grasslands, the contaminants are retained by filtration and
adsorption, and organic contaminants are decomposed under primarily
aerobic conditions. Intermittent feeding from parallel lanes provides
aeration to the root zones of the grasses and avoids flooding of the
treatment plots. In this process, the wastewater remains in contact with
open air. This results in a relatively high dissolved oxygen content at
the outlet of the system and helps to aerate the effluent without the need
for additional energy. The efficiency of this method largely depends on
the selection of the grass species, and is further influenced by specific
local soil and climatic conditions. Common grasses used in this technology
are paragrass (Braciera muticia), chestnut (Eleocharis dulcis),
red sprangle top (Leptochola chinensis). Studies carried out at
the Asian Institute of Technology (AIT, 1992) indicate that the overland
flow system designed with paragrass in main lane and with other two
grasses in other parallel lanes were effective in removing 80% of the
suspended solids, 47% of the BOD5, 39% of the organic nitrogen, and 19% of
the total phosphorus at the loading rate of 532 m3/week. This system is
more effective in removing suspended solids than dissolved solids, but the
research indicates that combined pond and overland flow systems can result
in an high quality effluent. Combination systems also work well where the
treatment requirements are high or the land available is insufficient.
Integrated Biological Pond Systems.
The feasibility of an inexpensive wastewater treatment system based upon
the principles of aquatic biology was evaluated by Wu et al. (1993), and
an integrated biological pond system was constructed and operated for more
than 3 years to purify the wastewater from a medium-sized city in Central
China. The experiment was conducted in three phases, using different
treatment combinations for testing their purification efficiencies. The
pond system was divided into three functional regions: an influent
purification area, an effluent upgrading area, and a multi-utilization
area. These functional regions were further divided into several zones and
subzones, each representing a particular ecosystem component. Various
kinds of aquatic macrophytes, algae, microorganisms and zooplankton were
effectively cooperating in the wastewater treatment in these zones within
this integrated system. The system attained high reductions of BOD5, COD,
TSS, TN, TP and other pollutants. The purification efficiencies of this
system were higher than those of most traditional oxidation ponds or
ordinary macrophyte ponds. Mutagenic effects and numbers of bacteria and
viruses declined significantly during the process of purification, and,
after the wastewater flowed through the upgrading zone, the concentrations
of pollutants and algae evidently decreased. However, plant harvesting did
not significantly affect the levels of reductions of the main pollutants
achieved, although it did significantly affect the biomass productivity of
the macrophytes. The effluent from this system could be utilized in
irrigation and aquaculture. Some aquatic products were harvested from this
system and some biomass was utilized for food, fertilizer, fodder and
related uses. Finally, the treated wastewater discharged from the system
was reclaimed for various purposes.
Wastewater Treatment and Reuse in India
In Calcutta, India, systematic reuse of wastewater for aquaculture
started in the early 1940s. The sewage-fed fish ponds were initially
created on about 4 628 ha in an 8 000 ha wetland area. As of 1987,
about 3 000 ha of ponds remained active. The treatment process
involves screening the raw sewage prior to it entering the ponds.
After twelve days, the ponds are repeatedly netted and manually
agitated using split bamboo rods. The agitation enhances the oxidation
and mixing of the effluent, and promotes improved water quality. The
pond is stocked with fish after 25 days, and additional sewage
effluent is applied to the ponds during a 3 hour period in the
morning, 7 days/month at an estimated rate of 130 m3/day/ha. Even
though the total fish pond area has been reduced over the period of
operation, total production and yield of fish has gone up from 0.6
tones/ha in 1948 to between 4 and 9 tones/ha in 1984. (Source: FAO,
1992; Edwards, 1985, 1990; and Ghosh, 1984)
Advanced Wastewater Treatment Systems.
Some contaminants, such as inorganic substances and a sizeable portion
of microbiological populations, present in the waste stream remain in the
effluent after the preliminary and secondary treatment processes. Amongst
others, nitrates, phosphates and ammonia radicals may still be found in
high concentrations. These pollutants can be removed through advanced
treatment processes using autotrophic plants to take up nutrients and
selected heavy metals and organic substances, flocculation of colloidal
particulate matter with chemical flocculants, and removal of synthetic
organic contaminants using absorbents and the oxidizing agents.
Technologies used in advanced wastewater treatment systems include
filtration, carbon adsorption, microstraining, chemical phosphorus
removal, and biological nitrogen removal (Shah,1994).
Filtration can remove most of the residual suspended solids, BOD5, and
bacteria from the secondary effluent using multimedia or microstrainer
filters. Multimedia filters contain low density charcoal for removal of
particles with large grain sizes, medium density sand for intermediate
sizes, and a high density medium for the smallest grain sizes. These
filters can decrease the concentration of suspended solids in activate
sludge-treated effluent from 25 mg/l to approximately 10 mg/l (Shah,
1994). The carbon adsorption technique is used also to adsorb persistent
organic substances onto activated carbon, the organic removal capacity of
which depends on the surface area of the carbon particles within the
cartridge. Microstrainers can also be used to remove residual suspended
solids. These filters consist of woven steel wire or a special cloth
fabric mounted on revolving drums which capture the solids still remaining
in the wastewater.
Only about 20% of the phosphorus in domestic wastewater is removed
during secondary treatment. With phosphorus removal techniques, phosphorus
is removed through chemical precipitation of the phosphorus with aluminum
sulphate (alum), ferric chloride, or calcium carbonate (lime). This
process requires a reaction basin and settling tank to remove the
precipitate. Likewise, nitrogen is removed either chemically or
biologically. The chemical process is called ammonia stripping and the
biological process is called nitrification/denitrification. In the ammonia
stripping process, nitrogen is removed in two stages by first raising the
pH to convert ammonium into ammonia, and then stripping the ammonia by
passing large volume of air through the effluent. In the biological
process, secondary effluent is further aerated to convert ammonia nitrogen
to nitrate nitrogen. During the denitrification processes, nitrate
nitrogen is converted to gaseous nitrogen by bacteria under anaerobic
conditions. Using these techniques, Chen (1993) found that the addition of
polyaluminium-chloride (PAC) resulted in a 70% removal of suspended solids
at a PAC dosage rate of 30 mg/l. If polyelectrolytes are added (at a rate
of about 1 mg/l), the dosage of PAC could be reduced to around 10 mg/l
with a similar result. Air flocculation, or dissolved air flotation
filtration (DAFF), followed by sedimentation, resulted in the removal of
more than 80% of the suspended solids at an aeration rate of 0.5-1.0 Nl
air/l. This technology is more effective for smaller solids than for
larger solids in wastewater. Organic removal, with either sedimentation or
combined air flocculation and sedimentation processes, removed about 15%
to 40% of the COD or BOD5. The efficiency of organic removal from
wastewater was increased to about 60% by utilizing chemical coagulation
and sedimentation treatment.
The use of advanced treatment is only recommended where major pollutants
are not removed to a sufficient extent by the secondary treatment.
Usually, advanced treatment are very complicated and expensive, and its
use in developing countries to produce suitable effluent for aquaculture
or farm purposes is not recommended (FAO, 1993).
Reuse of Wastewater in Irrigation.
In the face of growing water scarcity, reuse of marginal quality water
is the best alternative available for agriculture. Marginal quality water,
as defined by FAO (1992), refers to water that possesses certain
characteristics (such as agricultural drainage water, municipal
wastewater, and brackish water) which have the potential to cause problems
when the water is used for purposes other than the intended use.
Converting marginal quality water to freshwater that can be used for
agricultural purposes requires less complex treatment technologies than
those required to produce a multi-purpose quality water. Further, use of
wastewater for agriculture mimics the traditional use of night soils for
agricultural purposes that has been practised in different parts of Asia
from ancient times. Sewage farming was initiated in Bombay, India, as
early as 1877, and, in Delhi, from 1913 (Shuval et al., 1986). In
modern times, the most intensive use of wastewater for irrigation has been
made in Israel. In India, modern use of sewage effluents for irrigation is
reported to be about six decades old. China's sewage irrigation systems
have developed rapidly since 1958. In Laos, effluent of sewage is used
directly for the irrigation of 400 to 500 ha fields.
Reuse of irrigation drainage water provides another important source of
water for agricultural purposes. Conventional irrigation methods, such as
flood or spray irrigation, result in excess water being applied to
agricultural fields. The runoff that results, referred to as drainage
water or return flows, may be collected and reused for irrigation purposes
downstream. This practice, which is widespread though not well documented,
can be found in many farmer-managed irrigation systems of Nepal, India and
Thailand. In western hills of Argakhachi, Nepal, five parallel canals run
across the base of the hills and successively collect drainage water from
the farming areas upslope for reuse downstream. In the Kailai Terhi-Gurgi
irrigation system, farmers have constructed parallel drainage networks to
collect drainage water in the upper portions of the system for reuse in
the lower portions of the area. The exact quantities of water reused
through this process are not known. In some cases, rules have been
formulated for the allocation of rights to reuse drainage water. In arid
zones, such as in Egypt, drainage water is collected by an extensive
network of covered and open drains and reused. The quantity of drainage
water collected and reused during the 1988/89 hydrological year was
estimated to be 2 634 million m3. The drainage water available for reuse
had a salinity content within the limit of 1.5 mS/cm (Abu-Zeid et al.,
1991), but the quantity of water available was reported to be decreasing
and the salinity increasing.
Wastewater Recycling in China:
Application of Conventional
Wastewater treatment and reuse in China has a long history,
beginning in 1956 in North China. Municipal wastewater is treated to
primary and secondary standards, with secondary treatment being
provided by i) conventional activated sludge processes; ii) contact
stabilization processes; and iii) pure oxygen aeration processes. In
some cases, natural biological treatment facilities such as oxidation
ponds and sewage irrigation systems are used as secondary treatment
alternatives. Presently, wastewater from cities and towns in China
amounts to about 99.6 million m3 of water.
Both activated sludge systems and fixed film systems are widely used
for treating organic industrial wastewater in China. The activated
sludge systems are both mixed systems and ontact-stabilization
systems. The fixed film systems are mainly rotating biological
contactor systems, contact aeration systems, and biological tower
systems. Efficiency is good, removing both BOD5 (95%) and COD (75%),
but diminishes in the case of colour (50%), with the efficiency of the
combined tanks being inferior to that of separate tanks in which the
aeration and settling tanks are constructed separately.
Secondary treatment plants, using technologies such as sedimentation
- dissolved air floatation - activated sludge, or tertiary treatment
plants, using technologies such as mechanical - activated sludge -
activated carbon absorption or zonation, exist in cities like
Shanghai, Nanking and Beijing.
(Source: Ku, 1982)
In Tainan, Taiwan, night soil is spread over the bottoms of
ponds which are empty during the winter, with additional night soil being
added at intervals, about 4 to 5 times during the growing season. Several
thousand hectares of ponds exist.
TABLE 8. Cost Comparison of Various Wastewater
|| Initial Cost
||Operation & Mainte
| Life Cycle Cost
|| Sludge Production
|| Effluent Quality
SP, Stabilization Ponds; AL, Aerated Lagoons; OD,
Oxidation Ditches; AS, Conventional Activated Sludge; MA, Modified
Aeration Activated Sludge or Trickling Filter Solids Contactor
Note: Flexibility and expandability are similar for all types.
Source: BMA (1990)
In Bangladesh, overhanging latrines are constructed to supplement the
water and nutrient supply to fish ponds during the dry season. The ponds,
constructed near housing units, may be dry for part of the year and are
usually filled with floodwater during the rainy season. Fish, entering the
ponds with the floodwater, grow rapidly in the nutrient-rich ponds and are
harvested prior to the ponds drying out. Similar systems can be found also
in West Java,
Wastewater Recycling in Industries: An Example from Bangkok
The Phoenix Pulp and Paper Co., the largest paper mill in the
Northeast Province of Thailand, is currently using and discharging
process water at a rate of about 30 000 m3/day. The mill, located next
to the Nam Pong River in Khon Kaen, is proposing to spend about $ 26
million to recycle its wastewater for reuse within the company
compound, instead of discharging it into the nearby river and
eucalyptus plantations. This proposal comes at a time when the Thai
government is expected to ban effluent discharges. The company also
aims to reduce its effluent to about 20 000 m3/day by using new
technologies to produce pulp products. This reduction will also reduce
the volume of effluent discharged to eucalyptus plantations under "Project
Green", and help to control seepage damage in neighbouring rice
fields, which has cost the company about $86 000 in compensation to
about 100 villagers.
Source: Bangkok Post, August 9, 1995; Mill May Use Up
Recycled Water, p.3.
Indonesia, where about 25% of fish ponds of 1 000 m2 or less in
areal extent have overhanging latrines associated with them.
Wet pond aquaculture systems have been used mainly in Calcutta, India,
and in China, where fish cultivation in wastewater is carried out in about
670 ha of ponds in 42 cities. The yields of the wastewater-fed fish ponds
were about 3 to 4 times greater, and operating costs about 50% less, that
those of conventional ponds.
In the Bangkok Metropolitan Area (BMA), Thailand, the modified aeration,
activated sludge wastewater treatment method was found to have lowest
initial cost, while stabilization ponds had the highest.
Table 8 shows the rankings of the various treatment technologies
evaluated, according to operation and maintenance costs, operational ease
and flexibility, land area required, power usage, and effluent quality.
Level of Involvement
These technologies can be implemented as both private and the
governmental initiatives, as in China, or as local or private industrial
initiatives, as in other countries. In most developing countries,
innovative approaches that would encourage the increased use of such
technologies have been hampered due to the absence of concrete regulatory
measures and enforcement mechanisms, and, possibly, by government control
of public water supply and sanitation systems.
People feel uneasy about the reuse of treated wastewater. Further, there
are several public health hazards associated with the reuse of wastewater,
especially associated with aquaculture systems. The risks are related to
the potential for exposure to public health hazards during the
transportation and application of night soils, and the consumption of
contaminated organisms, and to the potential for the spread of disease by
encouraging the spread disease vectors, such as mosquitos. These health
risks, along with other cultural barriers, make the widespread adaptation
of such technologies for wastewater treatment and reuse difficult.
Government Initiatives and the Future of Municipal Effluent
Reuse for Irrigation
Land application of treated wastewater is a low-energy treatment
system, providing economic returns from the reclamation of
wastewater,especially in areas with acute shortages of water and
nutrients. Research carried out at China's Beijing Agricultural
University (BEU) and the India's National Environmental Engineering
Research Institute (NEERI) concluded that, compared to other
conventional secondary treatment methods, land application was
generally better for the removal of pollutants. Because of the
potential expansion of wastewater reuse technologies, these institutes
have established a monitoring network.
In India, NEERI has conducted research on the problems arising from
sewage farming, crop and soil responses to different wastewater
treatments, the formulation of guidelines for sewage farming systems,
and direct and indirect health effects. As part of India's VIIth Plan,
a multi-locational framework is envisaged, including regional research
centres linked with Technology Transfer Centres that will implement
100 new schemes for sewage and sullage utilization in selected cities
In China, BAU has been actively carrying out an investigation of the
environmental impacts of sewage irrigation systems. Several methods to
measure the environmental quality in the study areas have been
developed. The methods include identification of the pollution
concentrations in crops irrigated with treated wastewater.
(Source: RAPA, 1985).
Further Development of the Technologies
The further development of wastewater technologies has a high potential
in many parts of Asia, especially in Thailand, India and China. With the
growing demand for water in the urban sector, more and more water suitable
for potable use will be diverted to urban areas, increasing the need to
use waters of marginal quality in aquaculture and irrigation farming. The
adoption of wastewater treatment and reuse technologies, however, will
depend on many factors. Government and planners have to develop and
facilitate such mechanisms to encourage people to adopt such technologies.
Motivating mechanisms include environmental concerns -- it is better to
use treated wastewater for economic purposes rather, than directly
discharging it to waterways and decreasing the waste assimilative capacity
of the water courses, economic concerns -- reuse of wastewater for
aquaculture and irrigation can help reduce the pressure for public
investment in large (and costly) water resources development projects; and
legal concerns -- regulatory and economic instruments can provide direct
incentives to polluters to use treated wastewater for aquaculture and farm
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Agricultural Drainage Water Re-use in Egypt. Water International,
Bangkok Metropolitan Administration 1990. Pre-feasibility Study on
Private Wastewater Treatment for BMA, Office of the Prime Minister,
Edwards, P. 1985. Aquaculture: A Component of Low Cost sanitation
Technology. World Bank Technical Paper No. 36, Integrated Resource
Recovery, The World Bank,Washington DC.
FAO (Food and Agriculture Organization of the United Nations) 1992. Wastewater
Treatment and Use in Agriculture, FAO Irrigation and Drainage Paper
47, FAO, Rome.
FAO (Food and Agriculture Organization of the United Nations) 1993. Integrated
Rural Water Management. FAO Irrigation and Drainage Paper, FAO, Rome.
Ghosh, G. and P.N. Phadtare 1990. Environmental Effects of the
Groundwater Resources of the Multiaquifer system of North Gujarat Area,
India. In: Proceedings of International Conference on
Groundwater Management, AIT, Bangkok.
Ku, H. 1982. The Status and Trend of Water Pollution Control Technology
in China. Water International, 7, 78-82.
Regional Office for the Asia and Pacific (RAPA)/FAO 1985. Organic
recycling in Asia and Pacific, RAPA Bulletin, 2/85, Bangkok.
Shah, K.L. 1994. An Overview of Physical, Biological, and Chemical
Processes for Wastewater Treatment, In: Process Engineering
for Pollution Control and Waste Minimization, D.L. Wise et al. (Eds),
Marcel Dekker, Inc. New York.
Shuval, H.I. et al. 1986. Integrated Resource Recovery: Wastewater
Irrigation in Developing Countries, World Bank Technical Paper No. 51, The
World Bank, Washington DC.