CONTENTS-
Abstract
Introduction
Composition of Wastewater
Organic Matter in Waste
Reuse of Municipal Wasewater in Agricultural Irrigation
Advantages of Municipal Wastewater Reuse for Agriculture
Reuse for Industrial Purpose
Conclusion

Water is the basic element of social and economic infrastructure and is essential for healthy society and sustainable development. About 97 % of water on the earth   is found in the oceans, more than 2% remains frozen in the polar region and glaciers. The rest of less than 1% is found in streams, rivers, and lakes and as groundwater.

Consequences of the rapid increase in density of population, fast urbanisation, industrialisation and agricultural use, the demand   for water is increasing day by day. The scarcity of fresh water puts the people to trap groundwater; ultimately it results in the depletion of groundwater resource. To overcome the demand, the reuse of treated municipal wastewater as a source of supply for non-potable uses is being explored.

The reuse application includes landscape and agricultural irrigation, industrial use, water for construction activities, vehicle washing, toilet flushing and fire fighting. The big challenge is to establish guidelines and standards for non-potable and indirect potable reuse, which will provide highest level of safety and reliability to the public. Eventually, we conclude in this paper how the treated municipal water can be used for household purpose and how it is analysed.

The rapid increase in the density of population, fast urbanisation, industrialisation and agricultural use increase the demand for water day-by-day. Due to the scarcity of fresh water in surface reservoirs, the continuous extraction of ground water results in a decline in groundwater level at the rate of 40-50 cm annually.Over the next two decades, water will be an increasingly crucial resource for the survival of arid and semi-arid countries.

Municipal wastewater:

It means wastewater from:

•  Single and Multiple dwellings

•  Apartments

•  Stores

•  Restaurants

•  Markets

•  Office Buildings

•  Hostels

•  Institutions

•  Small industries, etc.

The quantity of wastewater generated depend upon

•  Season

•  Life-style of people

•  Geographical location of the area

•  Industrial operation, etc.

In India, the consumption of water and hence the amount of waste-water generated is more in summer and less in winter.

Quantity of wastewater = Quantity of water supplied (+) additions a (-) subtractions b

Ill-Effects of Wastewater:

•  The rapid urbanisation trends have aggravated the wastewater disposal problems in many developing countries.

•  The waste-water contains decomposable organic matter that exerts a demand on the oxygen resources of the receiving waters.

•  The uncontrolled disposal of waste-water causes soil pollution

•  It contains variety of micro-organisms some of which may be pathogenic.

•  Presence of heavy metal leads to bio-accumulation

•  Disposal itself becomes a big-problem due to the economy.

The reuse of wastewater in various fields

•  Agricultural irrigation

•  Industrial use

•  Construction activities

•  Replenishing the ground water

•  Recycling for household purposes (non-potable)

•  Fisheries

•  Fire-fighting, etc.

The composition of waste-water depends on industrialisation and urbanisation of the area from where the wastewater is generated.

In India the composition is

The concentration of N, P and K micro-nutrients, heavy metals are specific and zone-specific.

Availability of N, P and K in waste-water in big cities (approximately)

The organic matter of untreated waste-water is primarily carbohydrates, proteins and fats

The amount of organic matter in untreated wastewater becomes soluble exceeds the amount that remains insoluble over a period of time.

Technology for treating the wastewater

Physical Method

•  Screening

•  Grit removal

•  Sedimentation, etc.

Chemical Method using

•  Alum

•  Lime, etc.

Biological Method Using

•  Microbial species

•  Plant Species

The type of treatment to be given to the wastewater depends upon the purpose of reuse or disposal.

India is pre-dominantly an agricultural country with the food grain production around 200 million tones and aiming to the production level of 246 million tones by the year 2012.

The nutrient supply is the major constraint in the development of Indian agriculture as there is excess mining of nutrients through removal of N, P and K by crop is more than the replenishment with fertilisers.

In future, this problem will aggravate as more food has to be produced due to the continuously increasing population

Therefore, the application of nutrients needs to keep the soil fertile and to make agriculture sustainable.

But the cost of inorganic fertilizer is increasing day by day.

This calls for use of alternate sources of nutrients in agriculture in consideration with wastewater application to agriculture, horticulture and forestry.

Municipal wastewater irrigation in Coimbatore, Tamil Nadu

The sewage farm in Coimbatore corporation was established in 1956 and taken into use by 1960.

The total area of the farm is 114.49 acres

88.4 acres of the total land is leased to farmers in which

•  fodder grass

•  water grass

•  guinea

•  napier are cultivated.

The remaining 26.09 acres of land are cultivated by the corporation

The fodder grass from these fields feed 300 animals

The eucalyptus trees are also planted in the field, which yields good result in growth.

Crops suitable for wastewater amended fields :

The application of organic material improves soil structure thus reducing soil erosion

It replaces and conserves mineral fertiliser that would otherwise be introduced   into the biosphere

Naturally available but limited supplies of nutrient sources such as rock phosphate are consequently conserved.

Economically advantageous, even the primary treated wastewater can be irrigated for most crops

Applying the wastewater to sewage farm reduces the treatment cost of the same.

In developed countries, the municipal wastewater is effectively reused for the purpose of

Cooling of boilers

Cleaning

Hydroelectric power generation

Dilution etc.

The reuse of municipal wastewater is currently low

But many industries recycle their treated wastewater for various purposes.

Depending upon the purpose of reuse of wastewater, it can be treated for required level by the available treatment techniques and used.

•  By formulating “The guidelines for wastewater reuse”, the wastewater can be reused effectively

•  Where the fresh water supply is limited in quantity and/or quality, the reuse application will be attractive.

•  The reuse application will be economical where new water supply of satisfactory quality can only be developed at high cost because of distance and/or treatment.

•  Agricultural country like India, the reuse of wastewater for irrigation will be the best option, since the municipal waste water contains lot of micro and macro-nutrients, which will meet out the nutrient requirement by the crop.

•  For most of the crops, the preliminary treated wastewater itself be sufficient.

•  Environmental problem of wastewater disposal will be reduced by reuse applications.

•  Overall it improves the economy of the country.

Environmental Engineering,
Government College of Technology,
Coimbatore – 641 013, Tamil Nadu, India.
Phone: 0422 - 453192.
E-mail: Sam_rb@rediffmail.com