By Dr P. K. Jena in Bhubaneswar, October 6, 2021: The capital of India, Delhi is the most polluted city in the world. Its air, water and land are highly polluted causing a lot of harm to millions of people living in and around the city. According to World Health Organization (WHO), the quality of air in Delhi amongst 1650 world cities is considered to be the worst. The millions of vehicles using petrol and diesel and releasing colossal amount of poisonous gases, the road dust, the carbon particles and gases released during burning of organic municipal wastes and particularly stubbles of adjacent agricultural lands have resulted in high air pollution.

The air quality index (AQI) of Delhi particularly during October to December becomes very severe ranging from 400 – 500 and more. This causes a great harm to the people living in the city particularly by damaging the lungs of more than 2.2 million people including more number of children. It has been reported that, the degree of pollution due to vehicular emission, dust and industries including power plants are 41%, 21.5% and 18% respectively.

For example, in November 2017, during the great smog of Delhi, the air pollution became far beyond the acceptable levels and the levels of particulate matters (PM) rose to 999 mg per cubic meter, whereas the safe limits are 60 and 100 respectively. Besides burning of stubble, the animals, and other agricultural activities in and around Delhi also contribute significantly to air pollution of the city. Because of high atmospheric pollution, a large number of people in Delhi suffers from diseases like cancer, asthama etc. In view of this, health experts advice the residents to wear mask and stay indoors as long as possible as a general practice. However, the outdoor poor air quality has an impact in indoor air quality.

The water bodies in and around Delhi are equally polluted. The river Yamuna is the main source of water in Delhi, but the Yamuna river is at present highly polluted and some places even froths appear. About nineteen major drains in Delhi flow into the river contributing 96% of its pollution. It is estimated that, 3260 million liters of waste water is generated including 218 million liters per day (mld) from industrial sector.

Very small amounts of the total sewerage before discharging into the rivers are treated. The annual average discharge through drain into river Yamuna in the year 2003 was around 3267 mld and the average pollution load in terms of Biological oxygen demand (BOD) was 243 tons per day. In view of this water quality in Delhi is at alarming situation. It has been found that, discharge of untreated sewage is the single most important source of pollution of ground as well as the surface water. Thus, the polluted water in Delhi has become the main cause of various water borne diseases like diarrhea, dysentery etc. affecting a large number of people living in the city.

In addition to air and water pollution, the land pollution is also very severe. Delhi generates about 8,700 tons of solid wastes per day, including organic wastes, construction wastes, metal scraps, broken glasses, plastics etc. Most of these solid wastes are dumped in open areas in and around Delhi, These wastes are not segregated and it seems there are no notified municipal waste rules for proper segregation. It is reported that, 50% of these wastes are organic in nature, 30% are metal scraps, broken glasses, plastics etc. and the rest 20% are roads and building construction wastes.

In view of the present situation in mis-management of solid and liquid wastes along with heavy air pollution, It is essential that, the authorities should streamline the management of these wastes to make Delhi pollution free. In order to bring down the pollution level in the atmosphere, it is important to use renewable energy harnessed from sun, wind and biomass as well as the hydro power. In the transport system, efforts should be made to utilize as much as possible the renewable energy converted to electrical energy and also CNG in place of the polluting diesel and petrol.

Further, the biomass like organic wastes, stubbles etc. can be utilized to produce bio energy. There are two well known processes for conversion of bio mass into biofuels namely thermo chemical and bio chemical processes and both are techno economically viable. As solid organic municipal wastes, agricultural wastes including stubbles are available in large quantities; these can be subjected to either of the processes.

The thermo chemical process includes combustion, gasification and pyrolysis, whereas the bio chemical process includes anaerobic digestion and fermentation. The municipal solid organic wastes, waste sludge of sewerage water obtained after treatment and agricultural wastes are huge in quantity. These can produce large amounts of renewable energy. It may be mentioned here that, one ton of dry bio mass can produce 85 kwh of electricity or 189 liters of bio fuel.

In Delhi, the municipal solid wastes rules like segregation of wastes at the source should be mandatory. If it is done properly, at least 50% of waste which is organic in nature can be used to produce renewable energy by the above processes, 30% of the wastes which are metal scraps, plastic, glasses, waste paper etc. can be sold for recycling to the respective industries and the rest 20% which are mostly the wastes generated in roads and building repair and constructions should be used for land filling.

It is reported that, there are 30 sewerage treatment plants in Delhi with total treatment capacity of 2030 million liters per day. However, it is reported that, most of these do not perform satisfactory due to various operational problems. All over the world, the sewage treatment is carried out in three stages namely activated sludge process, chlorination and filtration. In Delhi, similar technology should be adopted to treat all the sewage. After removing the solid materials from the sewage, the treated water can either be let out to river Yamuna or used for purposes like gardening, landscape development, road washing etc.

Heavy pollution of air, water and land in and around Delhi is causing a lot of harm to the people living in the city and surrounding areas. In view of this, the following programmes should be urgently carried out to keep the city environmentally clean and making it suitable for healthy living.

1. In order to keep the air in Delhi pollution free, it is essential to have transport systems run by electricity and bio fuels as much as possible. The industries in and around the city should take measures to treat their flue gases before letting these out and also should dispose the solid wastes and waste water after proper treatment.
2. Efforts should be made to treat all the city sewage water, remove the sludge from it for producing compost and bio gas and let out the clean water to the river or utilize for gardening, road washing etc..
3. All municipal solid wastes should be processed at the source to separate the organic wastes, recyclable materials like metal scraps, broken glasses, plastics etc. and the rest wastes like rejects of building and roads construction. The organic materials should be subjected to anaerobic digestion for producing methane gas and organic compost. The recyclable materials can be sold to the respective industries and the rest of the solid wastes can be used for land filling the low lying areas.
4. At suitable sites in the outskirts of Delhi the organic municipal solid wastes, the sludge of sewage and stubble and other agricultural wastes should be subjected to anaerobic digestion to produce large amounts of fuel gas and manure. The technology being simple large scale units of these can be setup easily. One ton of dry organic wastes can produce 800 cubic meter of fuel gas and 400 kg of organic manure. The authorities can earn a lot of money by selling these two essential items to the users in and around Delhi.
5. Delhi city and nearby areas should be kept green by planting large number of trees like Neem, Karanj, mango etc. in the vacant places and roadsides in and around Delhi. The Aravali green ecological corridor along aravali range from Gujarat to Delhi connecting shivalik hill range as planned earlier should be made green by planting these trees which will help in combating air pollution to a great extent and also help to increase the ground water resource.

The above mentioned programmes should be planned scientifically and implemented seriously under the supervision of a high power expert committee as early as possible. In this way the clean capital of India will be a model for all state capitals and other cities in the country.

• Former Director General, Council of Scientific & Industrial Research, India