Many elements crucial for life on Earth are depleting rapidly due to disrupted biogeochemical cycles caused by human activities
If you think carbon is bad enough, other essential elements that sustain life on Earth are also crossing the planetary boundaries of sustainability, as their natural ‘biogeochemical’ cycles are broken by human activities. For about ten thousand years before the ‘green’ revolution, farmers grew crops without fertilisers by combining legume-based crop rotations and livestock farming. Legume crops and some soil microbes fixed atmospheric nitrogen, while livestock manure and urine enriched the soil with nutrients such as compounds of nitrogen (N), phosphorus (P), potassium (K), sulfur (S), carbon (C) and even micronutrients. But modern cropping in India shifted away from legume-based crop rotations and relies heavily on NPK fertilisers rather than manures, costing the Indian govt over Rs. 2 lakh crores per year in subsidy.
As livestock farming moved away from crops and intensified as peri-urban dairies, manure and urine mostly find their way to our ground and surface water bodies. The release of untreated dairy or domestic and other wastes has reduced the Sahibi River in New Delhi to a wastewater drain (Nazafgarh drain), which along with the Shahdara drain heavily pollutes the river Yamuna, apart from releasing noxious gases into the air.
The nutrient cycles have thus become cascades causing nutrient pollution, but the good news is that some pollutants are nutrients in the wrong place and can be brought back. Unfortunately, less than 30 per cent of the fertiliser nutrients supplied as fertilizers are harvested as crop yield and the remaining add to the growing pollution. In water bodies, the accumulation of these nutrients supports unwanted algal growth causing eutrophication and death of fish and other useful aquatic and marine species. This destroys the ecosystem and the livelihoods of people who depend on fishing, tourism and other ecosystem services. In our coastal areas, algal eutrophication progressively causes green tides, brown and eventually red tides and even the accumulation of poisonous species. The reversal of these trends can rebuild water economies and support the livelihoods of millions.
Nitrogenous compounds from fertilisers, manures, urine and sewage also cause air pollution as ammonia or nitrous oxide. Ammonia contributes heavily to particulate matter pollution (PM2.5 and PM5) by combining with NOx gases (nitrogen dioxide and nitric oxide) emitted from fuel or residue burning for power, transport industry, or waste disposal. Over a million deaths per year are attributed to PM2.5 alone in India, while some attribute up to 7 per cent of all deaths to PM2.5, as India has the largest number of the world’s most polluted cities in terms of PM2.5. These figures call for drastic measures to control air pollution in general and PM2.5 in particular, but it needs not only curbing pollution from fuel burning but also restoring the nutrient cycles in agriculture and waste management.
While a fraction of livestock manure is recycled for cropping in India, urine recycling is nearly nonexistent. If we recycled all the 15 kg per animal per day of manure produced by 200 million cattle, its 5 per cent NPK nutrients amount to 1,50,000 metric tons. This is much more than our average daily fertiliser consumption, which is about 1,37,000 metric tons. Add to this about 3 per cent of nutrients lost from 15-20 litres of cattle urine per animal per day totalling 1,20,000 metric tons. Technologies and best practices are available from Europe and elsewhere to maximise nutrient retention and recycling from manure and urine. We already know that at least half of the currently recommended fertiliser doses can be replaced with farmyard manure without any loss of crop yield. It not only saves a lakh crores but also reduces the environmental footprint of fertilisers, manures and agriculture itself.
Similarly, over 55,000 metric tonnes of nutrients equivalent to 40 per cent of our fertiliser consumption are lost daily from over 150 billion litres of wastewater produced per day in India. This is because of our abysmally low wastewater treatment capacity of about 27 per cent. Most sewage treatment plants (STPs) exist only in the cities and only a few of them work. Fortunately, some metropolitan cities like Delhi and Hyderabad are rapidly expanding their STP capacity to become 100 per cent wastewater treatment capable in a year or two and some other big cities in India are following suit. However, they vary in their efficiency of nutrient removal, which must be addressed immediately to ensure that the purpose of treatment is fully realised and that the treatment plants become resource plants by selling the recovered nutrients.
There is a growing emphasis worldwide on preventing the wastage of nutrients and recycling them. The most notable among them is Target 7 of the Kunming-Montreal Global Biodiversity Framework adopted under the United Nations Convention on Biological Diversity at its 15th Conference of Parties in 2022: It seeks to “Reduce pollution risks and the negative impact of pollution from all sources by 2030, to levels that are not harmful to biodiversity and ecosystem functions and services considering cumulative effects, including (a) by reducing excess nutrients lost to the environment by at least half, including through more efficient nutrient cycling and use”.
In Europe, where extensive recycling of livestock manure and urine is already in practice, the new buzzword is the so-called RENURE (recovery of nitrogen from manure) policy of the European Commission (2024). As such proposals are debated to ensure that they contribute to overall sustainability objectives in the European context, it is important to note the policy attention that the recovery and recycling of nutrients has garnered. In the meantime, a Swedish fertiliser company, Ragn-Sells, has patented a process to recover nutrients from wastewater and convert them into industry-grade fertilisers and spun off a company easymining.se to launch it in Europe within a year. If India can set up such units attached to our STPs, they can hugely reduce the economic and environmental costs of earlier fertiliser technologies, generate green jobs.
Delhi alone produces about 3330 Million Litres per Day (MLD) of wastewater, far over the installed and operational treatment capacities of the city’s 38 STPs (CPCB, 2021). The Delhi Government has set its target to achieve 100 per cent wastewater treatment by 2025 and increase the reuse of treated wastewater from 12.5 per cent to 60 per cent with the proposed utilisation of 197 MGD, 112 MGD and 10 MGD treated sewage for drinking purposes, irrigation and rejuvenation of water bodies respectively (CPCB, 2021).
We conducted some studies on the wastewater nutrients and their recovery/recycling potential in several STPs of the national capital, aided by the University’s memorandum of understanding with the Delhi Jal Board.
They were funded by the UN Environment Programme (UNEP) under the Global Wastewater Initiative and the Global Partnership on Nutrient Management. Our studies found that the current level of removal of phosphatic nutrients in various STPs of Delhi varies between 35-74 per cent and 14-93 per cent for nitrogenous nutrients. Except for the Akshardham STP, which operated at the higher end of the range, most of the other STPs we studied were closer to the lower end of the range, indicating the huge scope to improve nutrient recovery. A similar study will be undertaken in Hyderabad soon, in association with agricultural scientists who will also test the crop performance and estimate the amount of commercial fertiliser that can be saved by recycling nutrients recovered from wastewater.
Such efforts will hugely improve the quality of treated water for various uses and also relieve the water crisis looming over India’s metropolitan cities. In Delhi, the nutrient-depleted water is also critical to expediting the rejuvenation of the water bodies of Delhi, as the quality of treated water currently used is not good enough to revive the heavily eutrophicated water bodies.
As for the recycling of nutrients removed from wastewater, currently, there are huge piles of nutrient-rich sludge in the backyard of every working STP. They need to be developed and marketed as alternatives to fertiliser by building necessary market linkages and supply chains as needed.
This is already happening to some extent in Hyderabad but needs to be scaled up further to clear the inventory. An important task is to find ways to pre-process the sludge to minimise the heavy metals, plastics and other undesirables we found coexisting with nutrients in the sludge in Delhi. Overall, on a national scale, if we recover and recycle the 84 per cent of nutrients lost in wastewater for agriculture, up to forty per cent of our national fertiliser consumption can be saved. In economic terms, these savings are equivalent to the entire R&D budget of the Government of India.
(The writer is a Professor and Head of, the Centre for Sustainable Nitrogen and Nutrient Management School of Biotechnology, Guru Gobind Singh Indraprastha University, New Delhi; views are personal)
