'Municipal wastewater source of valuable energy, nutrients'

Vast amounts of valuable energy, agricultural nutrients, and water could potentially be recovered from the world's fast-rising volume of municipal wastewater, a new study by the UN University's Canadian-based Institute for Water, Environment and Health (UNU-INWEH) said on Monday.

The volume of wastewater roughly equals the annual discharge from Ganga river in India. And by the mid-2030s, it will roughly equal the annual volume flowing through the St. Lawrence river, which drains North America's five Great Lakes.

Furthermore, the paper says, wastewater volumes are increasing quickly, with a projected rise of roughly 24 per cent by 2030, 51 per cent by 2050.

Among major nutrients, 16.6 million metric tonnes of nitrogen are embedded in waste water produced worldwide annually, together with three million metric tonnes of phosphorus and 6.3 million metric tonnes of potassium.

Theoretically, full recovery of these nutrients from wastewater could offset 13.4 per cent of global agricultural demand for them.

Beyond the economic gains of recovering these nutrients are critical environmental benefits such as minimising eutrophication the phenomenon of excess nutrients in a body of water causing dense plant growth and aquatic animal deaths due to lack of oxygen.

The energy embedded in wastewater, meanwhile, could provide electricity to 158 million households roughly the number of households in the US and Mexico combined.

The study's estimates and projections are based on theoretical amounts of water, nutrients, and energy that exist in the reported municipal wastewater produced worldwide annually.

The authors underline that information on wastewater volumes generated, available, and reused is scattered, infrequently monitored and reported, or unavailable in many countries. They also acknowledge the limitations of current resource recovery opportunities.

Nonetheless, says lead author Manzoor Qadir, Assistant Director of UNU-INWEH, in Hamilton, Canada: "This study offers important insights into the global and regional potential of wastewater as a source of water, nutrients, and energy."

"Wastewater resource recovery will need to overcome a range of constraints to achieve a high rate of return but success would significantly advance progress against the Sustainable Development Goals and others, including adaptation to climate change, anet-zero' energy processes, and a green, circular economy."

Among many findings, the study says the energy value in 380 billion m3 (cubic meters) of wastewater is estimated to be 53.2 billion m3 methane enough to provide electricity for up to 158 million households, or 474 million to 632 million people, assuming an average of three to four persons per household.

Given the foreseen wastewater increases, that number rises to 196 million households in 2030, and 239 million households in 2050.

In agriculture, the volume of water potentially recoverable from wastewater could irrigate up to 31 million hectares equal to almost 20 per cent of the farmland in the European Union (assuming two crops and a maximum 12,000 m3 of water per hectare per year).

"The reclaimed water can be used to irrigate new areas or replace valuable freshwater where crops are already irrigated," says the study.

Asia is the largest wastewater producer with an estimated 159 billion cubic meters, representing 42 per cent of urban wastewater generated globally, with expectations of that proportion rising to 44 per cent by 2030.

The paper cites prior research showing that human urine is responsible for 80 per cent of the nitrogen and 50 per cent of phosphorus entering municipal wastewater treatment plants.

"Removing these nutrients in time would not only be environmentally beneficial," the paper says, "resulting in less eutrophication, it would reduce the cost of wastewater treatment while supporting closed-loop processes".

( With inputs from IANS )