This essay secured the 1st position at the INAE National Online Essay Competition 2018, organized by the Indian National Academy of Engineering (INAE), and was presented at the INAE Youth Conclave 2018 at IIT Kharagpur.

Introduction

We live in an expanding world. As the number of human inhabitants of the planet swells by the day, so does the volume of consumption necessary to ensure the survival of the entire demography. According to Adam Smith, pioneering Scottish economist, economics is the struggle of satisfying unlimited human wants through limited available resources. While it is imperative that human knowledge of science, engineering, sociology and economics must work in tandem for efficient progress of a nation, it should be kept in mind that on a planet of 7 billion people, it is not only what is “consumed” that deserves attention, but also the “waste” by-products which accompany consumption that merit a lot of thought. These wastes are not due to prodigality or profligacy of actions on our part, but form an integral part of the process of progress and cannot be avoided entirely by any means.

Urban Wastewater

According to the census carried out by the central government in 2011, 68.84% of India’s population of just over 1.2 billion people live in cities. Considering that India’s annual Gross Domestic Product (GDP) should be reaching USD 2.3 trillion by 2020, Barclays predicts that the contribution of urban India to the GDP will remain in the vicinity of 70%. Some simple mathematics thus places the annual GDP of Indian cities at USD 1.6 trillion; the waste generated in cities would be proportional to this number. These statistics are not astonishing to a moderately aware individual, but it certainly impresses upon us the fact that urban wastes are justifiably a major point of concern while considering development of urban India. Consequentially, treatment and tackling of these wastes deserve considerable engineering research and effort.

Such is the brilliance of nature that for solving even the most critical and apparently adverse problems relating to development, it provides a part of the solution by itself. Wetlands are a natural occurrence found quite commonly in various forms, and they feature across all six continents of the world excluding Antarctica. It refers to a landmass which is covered by water for a major part of the year, and plays host to a special type of ecosystem unique to wetlands only. There are more to these wetlands than what meets the eye. What is a desolate stretch of empty uninhabited inundated space to the eyes of a layman, is actually a powerhouse of reconstruction and nature’s factory for waste management. This essay deals with how natural and constructed wetlands can be used as a potent instrument for effective treatment of water-based urban waste.

Effective Treatment of Water-Based Waste

The first question that begs clarification while dealing with treatment of water-based urban wastes is that what the actual requirement for managing of urban wastes is in the first place. This enquiry can be answered on two primary grounds: firstly, to rid the environment of the harmful chemicals and contaminants which may potentially cause immense damage to human civilization and life, and secondly to detoxify the water carrying the waste and bring it back into circulation for human use. Simply put, the “waste” and the “water” of wastewater are both highly relevant.

Neutralizing solid waste

First let us consider the threat posed by the waste in wastewater to civilization. While the medium remains same, the waste content may have two broad sources of origination. They can be a by-product of human metabolic or household which are mostly organic in nature, or they can be industrial refuses containing toxic metal and organic compounds as salts or residues in the water.

The bulk of liquid household wastes come in two forms: black water and grey water. Black water is the flushed liquids contaminated with human excreta – chiefly faeces and urine. Black water is stored in underground septic tanks and ultimately transported to dumps or vats for treatment and decomposition into nature. Grey water is the wastewater which is devoid of excreta but has been used for cleaning purposes. These are composed of sink water, washing machine refuses, etc. These are most commonly contaminated with detergents or soaps, but due to their relative cleanliness in comparison to black water, they might be reused as flushing water in toilets.

Next, we also have industrial refuses originating from the manufacturing sector from industry-based cities. These wastewaters contain poisonous and contaminating metals and hydrocarbons. If metals like arsenic, lead or cadmium enter our alimentary canal, they can cause serious health disorders.

According a report carried by The Times of India in 2017, India generates over 100,000 metric tonnes of urban wastes per day, out of which 17,000 metric tonnes alone can be attributed to Mumbai and Delhi together. While this statistic is not very healthy in comparison to other developed countries of the world, these wastes still need to be treated and the environment needs to be protected from them on a very urgent basis.

Neutralizing and reusing water

Let us now consider the second aspect - the need for neutralizing the water. In spite of being residents of the “blue planet” where 70% of the planet surface is covered by water, we still have very limited quantities of water available for human use, the reason being the redundancy of sea water due to its salinity. Why and how should we conserve water and save it for the future generations may be the matter for a separate discussion, but it suffices to accept the need for reusing wastewater and consequently the need for developing technology which allows us to do so - at an economically justifiable cost.

It should be borne in mind that the focus on urban wastes in particular is not due to any lack of concern towards rural environment and livelihood. Three reasons may be identified for giving higher priority to urban wastes over their rural counterparts. Firstly, urban wastes are simply much greater in volume and density, i.e. waste generated per unit landmass. Combined with very limited availability of open land in cities, waste management is a greater challenge. Secondly, rural environments are mostly equipped with some sort of natural mechanism to take care of their own wastes. Finally, village wastes consist chiefly of agricultural by-products and human refuse, which are potentially easier to tackle. But urban wastes more commonly include toxic industrial releases which are more difficult to treat.

Considering all these aspects, it can be stated with some degree of certainty that treatment of urban wastewater is indeed a major challenge for our nation and needs to be researched upon and invested in sufficiently.

Natural and Constructed Wetlands in Suburban Areas for Processing of Urban Wastes

In the year 1981, an engineer in the Urban Development Ministry of the Govt. of West Bengal by the name of Dr. Dhrubajyoti Ghosh was deputed to inspect the ecology and environment of the low lying inundated wastelands located towards the eastern limits of the city of Kolkata, the capital of West Bengal. A sanitation engineer with a degree in Civil Engineering from BE College Shibpur (presently IIEST Shibpur) in 1968, Dr. Ghosh then embarked upon a journey which went on to have an impact upon the metropolis on a scale which very few people could have ever conceived. The first foundation stones were laid for the creation and maintenance of a conserved ecosystem which would be responsible for treating over 55,000 cumecs of wastewater per day, which amounts to one-third of the wastewater generated by the sprawling city of Kolkata. The East Kolkata Wetlands (EKW), as they are known, perform the function of the “kidneys” of the metropolis. The world lost a visionary in Dr. Dhrubajyoti Ghosh when he passed away in February 2018.

Dr. Ghosh’s vision was not an isolated one across the world, because similar environmental engineering projects are being pursued in different countries for some decades. It is important to note that while any natural ecosystem is important for preservation of nature’s equilibrium, not all wetlands are significant in context of urban waste management. But considering wastewater treatment, we are no longer dependent on nature for natural occurrences of wetlands; civil engineering has enabled us to build artificial (constructed) wetlands through human endeavour. In India, the Vembanad-Kol wetlands or the Kerala backwaters lead the merit list according to the area covered. As the global awareness on wetland conservation started increasing, the Ramsar Convention was signed in Iran in 1971 by countries of the world agreeing to cooperate on the protection of wetlands over the world. The Contracting Parties of the Convention meet every three years to deliberate upon methods of wetland conservation and to maintain the list of Ramsar wetlands of international importance.

Role of a wetland

So what exactly is the role of a wetland in urban wastewater management? Answering this question would require us to enquire into the ecosystem of a wetland – natural or constructed – in greater detail. A wetland is not simply a landmass flooded with water, but it is an ecosystem which has specific characteristics of its own. Among these, the two most important ones are the possibility of anaerobic respiration processes in the soil, and the biota (collection of resident biological communities) existing in the flooded area which depends on soil salinity, pH, flooding duration and various other factors. In this essay, the focus will be on highlighting the contribution of wetland based ecosystems in three major domains: biological waste management, purification of industrial toxicants, and agriculture and pisciculture.

Biological waste

Biological wastes, as have been clarified earlier, chiefly consist of organic matter; a majority of them come from human excreta. A random sample of wastewater contains 5% human faecal material on an average. This water is allowed to pass through the natural buffers and gravel layers into the wetland medium and come in contact with the plant rhizosphere occurring beneath the water. Here, a combination of aerobic and anaerobic respiration takes place with the help of the microorganisms and bacteria. A thin microfilm is created on the root surfaces of the vegetation, where oxygen is released from the plant tissues. The rhizome layer and the roots of the plant develop a symbiotic relationship as the plants themselves become a carbon source for the microorganisms once they die. Apart from carbon, nitrogen present in ammonia and organic compounds present in the wastewater also undergoes a two-step process of nitrification and denitrification.

In case of artificial or constructed wetlands, the mechanism of decomposition remains identical but the setup is different. The construct may be of subsurface, surface or floating type, depending upon features of construction and exposure to the atmosphere. The wastewater is first treated in septic tanks and dumps to remove the solid content and then passed through the dense mat-like network of plant roots containing the periphyton community. Ultimately under the effect of sunlight and in the presence of oxygen and symbiotic microbes, the human waste content in the water may be reduced to less that 0.01% through physical, chemical and biological processes without explicit human intervention.

Industrial waste

The next part of the solution deals with the toxic industrial wastes that are mixed with grey water and are released into the wetlands. It is a part of the wetlands ecosystem where certain species of plants like the water hyacinth (Eichhornia crassipes), water poppies (Hydrocleys nymphoides), bulrushes (Typha latifolia) etc. are capable of absorbing heavy metals and their derivatives from the water through their roots. Waterweed (Elodea Canadensis) and related species are special types of underwater submerged water-purifying plant with very high effectivity.

Economic feasibility

The final aspect under consideration is certainly not the least important one, because this facet of wetland engineering is what lends to this scheme high economic feasibility. Like every engineering blueprint, wetlands also have their share of disadvantages. Land prices in and around suburban locations are skyrocketing in India, so a wetland comes with the high opportunity cost of real estate. Practice of extensive wetland-based agriculture and pisciculture is a method for retrieving some of these costs.

A functioning wetland, natural or constructed, can benefit potential agriculture practiced there in a multitude of ways. The availability of clean water for irrigation or livestock feeding is in plenty. Wetland vegetations can reduce erosion, make the soil fertile with nutrients and control the pH and salinity levels of soil. Drought resilience, especially in localities near big cities, is another bonus for agriculture. It is favourable to practice small-scale vegetable production in wetlands. Pisciculture also thrives in wetlands due to steady flow of purified fresh water. The relationship is symbiotic as well; the sewage water contains potential nutrients for fish and algae, so their ingestion causes natural conversion of waste material to animal protein. It also reduces the cost of fish-meal. The EKW is supposed to produce 7 metric tonnes of Carp (Cyprinus carpio) and Tilapia (Oreochromis niloticus) per hectare of wetland area, which provides healthy protein nourishment to the economically backward populations in Kolkata.

Conclusion

A United Nations survey says that over 40% of India’s population will be living in her cities by 2030. We need to be prepared to face such a massive influx of population and creation of new cities. Considering that our manufacturing sector is growing at a rate of around 7% per year, it will not suffice to simply ensure food, accommodation and employment for 550 million people in the cities; there also has to be an infrastructure equally strong to manage the waste generated by such a substantial population and its factories and industries.

With most of the developed Indian metropolises already saturating, planned cities are the need of the hour. Greater Noida, Navi Mumbai, Durgapur, Madurai etc. are showing the way for the future. But along with planning cities the government also needs to plan for constructed wetland creation near and around the cities. Specially allocated areas will not only help the civic health and economy, but also help prevent occurrences like the Chennai floods of 2017, an event which was not unrelated to reclamation and filling of 95% of the wetlands around the Tamil capital, resulting in tremendous soil erosion and loss to human lives and property.

With the Government of India looking to emulate the country’s dream of living in a Swachh Bharat, it is not wise to turn our eyes away from the stubborn and cumbersome problem of urban waste management. It also is not sufficient to have isolated islands of proactiveness in this regard. In a country with not enough qualified environmental engineers, more interest and awareness needs to be generated regarding this problem and forward-thinking legislations need to be passed on wetland conservation and implementation of related engineering schemes. As we celebrate Mahatma Gandhi’s 150th birth anniversary in 2019, a country with a highly efficient system of urban wastewater management would be a suitable way to pay our respects towards the Father of our Nation.