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<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>

3.4 Reuse (Topic d)

Most of the Asia Pacific countries are tropical countries and their water resources are not very limited. As a result, most of the developing countries do not reuse wastewater except India, China and Vietnam where wastewater is being used for irrigation.

In India, studies on the productivity of crop production have found that recycling and reuse of nutrients and other valuable materials in domestic and industrial wastewater is an effective method for utilising the wastewater. General utilisation of wastewater through reuse and recycling has become very important. In fact, wastewater is a resource rather than a waste since it contains appreciable amounts of nitrogen, phosphorus and potash. Stabilisation ponds can be used for fish aquaculture and the effluent can be used for cultivation of short-term and long-term, ornamental, and commercial and fodder crops.

Wastewater treatment and reuse improves water use efficiency. Wastewater has been adopted as one of the major water resources nationwide, especially in the northern area of coastal cities in China.

Practical experience in China has shown that wastewater reuse not only reduces the demand for fresh water but also can improve environmental quality. Reuse of treated wastewater has the following benefits: make up water supply (reduces demand on good quality water); reduces the wastewater discharge thus reducing water pollution; results in economic efficiency due to lower water cost compared to transporting water from a distant source.

The main potential applications for reuse of treated wastewater in China are in the following fields:

* Agricultural use through irrigation of crops as well as for improving river amenity;
* Industrial cooling especially in the large industrial enterprises;
* Reuse in municipal public areas such as watering lawns and trees;
* Flushing toilets in hotels and residential districts;
* Reuse of the treated wastewater for urban landscape purposes.

Many municipalities set wastewater reuse as a strategy to meet the increasing water demand. To identify the alternatives of wastewater reuse as well as their feasibility and implementation, some cities where water shortage and pollution are very serious such Beijing, Tianjin, Taiyuan, Dailian and Qingtao have been selected as pilot areas for this particular purpose.

In Beijing the main purpose for reuse of treated wastewater is in agricultural production during the irrigation season and to improve river amenity. Some 487 m3/d of treated wastewater that meets the standard will be available for reuse by 2005, replacing the existing untreated effluent and providing the potential for reducing existing reliance on groundwater resources.

A project of wastewater reuse for industrial cooling purpose has been completed and will be put in to operation soon.

Treatment and reuse of wastewater of a guest house in Jinan city in Shandon Province is an example of reuse of treated wastewater for non-potable purpose in the water shortage area.

The rotating disc biological treatment followed by filtration and disinfection is used for treating the effluent from a hotel. The treated wastewater is reused for watering grasses, make up water of a lake, washing cars and flushing the toilet.

A wastewater reuse treatment plant with a capacity of 50,000 cubic meters per day was built in Tai An city, in which a part (20,000 cubic meters per day) is reused for industrial cooling and landscape purposes after reclamation by tertiary treatment.

In 2000 the municipal wastewater treatment rate will be more than 20 % of total discharged wastewater, and the reuse rate to 10% of municipal wastewater treated in the whole of China. It is forecast that the reuse rate of treated municipal wastewater in 2020 will be up 3-49% in small and medium sized cities and cities with a shortage of water (Lin 1999).

Reuse of wastewater occurs most effectively with on - site or small scale treatment systems. Thus implementation of reuse options in the local context with local community consultation must be seriously considered. Indeed many Western Australian householders are already engaged in the practice of recycling greywater. Greywater is defined as untreated household wastewater, which has not come into contact with toilet waste. It can originate from the shower, bath, bathroom, washing basin, clothes washing machine and laundry trough. The criteria associated with greywater recycling solely for irrigation, as distinct from combined black and grey water reuse, may be less stringent.

A number of greywater recycling installations are also currently in use in Western Australia such as:

Irrigation:
- Woodlots,
- Horticulture,
- Agriculture
- Urban parkland, sports grounds, golf courses etc.
Ground:
- Surface infiltration,
Private garden reuse
Industrial reuse
Disposal via constructed wetlands to surface water
Potable:
- Direct to water supply
- Indirect via groundwater

In the developing countries nightsoil has been used as fertiliser. Nightsoil from buckets and latrines is generally collected by private contractors and sold to farmers, or collected directly by the farmers. Farmers use the nightsoil as a fertiliser and soil conditioner and apply it to agricultural areas without pre-treatment. The urban public service and environmental companies frequently collect nightsoil from pubic toilets with bucket latrines, which is also sold to farmers.

This use of untreated nightsoil is illegal according to current environmental legislation, but the enforcement is overlooked. The Vietnam Wastewater Planing for Urban Areas study, reports that infestation rates of intestinal parasites are more than 95% in areas that use nightsoil in agriculture.

Exact information about the quantities of sludge and nightsoil collected and disposed of by public and private companies is not known. However, Table 3.14 gives information about the average quantities collected from each household according to each city classification. There are insignificant regional differences in sludge and nightsoil collection rates. The relatively large difference in sludge collection rate per household for the various city classes may be the result of several households sharing toilet facilities, and that the survey has not been able to differentiate between houses with own and households sharing in-house toilets. This situation is believed to be more prevalent in the larger cities with blocks of flats. Nightsoil collection rates are, on the other hand, considerably higher per household in the smaller cities, but city sample size may be too low to give an accurate estimate.

Table 3.14: Quantities of septic sludge and nightsoil collection in Vietnam
City

Septic tank sludge

Nightsoil

  l/d/hh l/d/person 1/d/hh 1/d/person
Class I 1.27 0.28 0.48 0.11
Class II 0.87 0.16 0.61 0.11
Class III 0.35 0.08 0.85 0.19
Source: Vietnam National Urban Wastewater and Sanitation Strategy Nov. 1995.

 

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