Everything you want to know about wastewater treatment

Aerial view recirculation solid contact clarifier sedimentation

Wastewater: why it deserves to be treated well

The world must wake up to the importance of this precious renewable resource

Every time you bathe, use the toilet, do the laundry, wash hands, clean produce, cook, and wash utensils, you generate wastewater. In the UK, for example, the average wastewater output per person per day is 150 litres. In the US, the average is 370 litres per person per day. In addition, every day around the world, industries, and businesses also generate millions of litres of wastewater. A 2021 study by the Utrecht University in The Netherlands says, “Globally, about 359 billion cubic meters of wastewater is produced each year, equivalent to 144 million Olympic-sized swimming pools.” These facts reveal that wastewater treatment is a matter of global priority.

According to the United Nations Water report, globally, 40 percent of household wastewater is not safely treated. The 2017 UN World Water Development Report,  Wastewater: The Untapped Resource says 80% of wastewater is released back into the ecosystem without being treated or reused, which endangers the lives of about 1.8 million people who use this contaminated water.

The World Water Development Report (WWDR) says it “seeks to inform decision-makers, government, civil society, and private sector, about the importance of … wastewater as an undervalued and sustainable source of water, energy, nutrients, and other recoverable by-products, rather than something to be disposed of or a nuisance to be ignored.”

These numbers are telling us a story. Its biggest lesson? We should not waste wastewater because it is one of the most significant renewables. The UN’s Sustainable Development Goal No. 6 considers wastewater a valuable resource and says its management is crucial to ensure access to water and sanitation for all by 2030.

So, how can countries tackle the issue of wastewater treatment? And what should we learn from those who are doing an excellent job in this field?

Before we answer those questions, let’s quickly understand our planet’s water resources and how wastewater fits in.

Aerial Drone view top up from clarifier sedimentation tank.

Where does water come from?

If you paid attention in your geography class, you would know that nearly 97 percent of the earth’s surface is water. But not all of it is available for us to drink or use for agriculture, industry, and leisure. Only about 2.5 percent of this water, called freshwater, is usable for these purposes. Freshwater includes surface water and groundwater, or water below the earth’s surface, which is the primary source of our water needs. About 96 percent of the freshwater is groundwater.

Groundwater is also geographically variable depending on soil moisture, porosity, et cetera, and maintaining its reserves requires sustainable practices. For example, over-extraction of groundwater can push the saltwater that lies further down to rising and contaminate groundwater. As nature intended, freshwater is a replenishable source. If we follow sustainable practices, it can be a long-lasting gift to the planet. Many of our traditional societies understood this discipline and treated water with respect until we marched into the 20th century. Then all hell broke loose as industrialization, urbanization, pollution, and deforestation went on steroids. We began to abuse the gift of water, resulting in the arrival of climate change. Today, freshwater stocks in the planet’s pantry are depleting faster than you say ‘Cheers’.

Unpredictable rainfall, floods, storms, droughts, and melting glaciers severely disrupt the planet’s water cycle. Add changes in precipitation patterns, snowfall and runoffs, pollution of freshwater bodies such as lakes, rivers, tributaries, and streams by toxins due to industrial sin, and you will see why our primary sources of water, surface and groundwater, and farmed rainwater are under threat.

This is the big picture, of which wastewater treatment is a significant part.

Aerial Drone view top up from clarifier sedimentation tank.

What is wastewater?

The residual output of any water used in homes, industries, commercial areas, agriculture, et cetera is wastewater. Wastewater can also include stormwater, rainwater, runoffs, floodwaters, even sewer overflows. But this does not mean the wastewater can be discarded and forgotten.

Why bother with wastewater treatment?

The range of toxins, chemicals, additives, and bacteria that wastewater contains poses a threat to the entire ecosystem if released back into it untreated. Therefore, we must treat wastewater.

The United Nations World Water Development Report 2017 says, “Wastewater management generally receives little social and political attention in comparison to water supply challenges, especially in the context of water scarcity. Yet, the two are intrinsically related – neglecting wastewater can have highly detrimental impacts on the sustainability of water supplies, human health, the economy, and the environment.”

The World Bank report From Waste to Resource, Shifting paradigms for smarter wastewater interventions in Latin America and the Caribbean says, “Wastewater should not be seen as a burden to governments and society, but as an economic opportunity that can be turned into a valuable resource.”

Aerial shot of a dirty polluted lake

Wastewater Treatment: The 4 Stages

Wastewater is treated in four stages, preliminary, primary, secondary, and tertiary or advanced. After the filtration or screening in the initial stage to remove large objects and any items that can potentially damage the treatment equipment, the primary stage essentially helps the water stand’ or remain stable to remove solids that sink or float.

The secondary stage involves treating dissolved solids with biological processes, which produce biosolids subjected to further processing. There are many treatment methods for tackling biosolids to eliminate their threat to the environment.

Finally, the tertiary or advanced stage uses a variety of methods, biological and chemical, to further clean up the wastewater. One interesting aspect of wastewater treatment involves reoxygenating the water through aeration. The breakdown of solids induced by biological processes, or bacteria, uses up oxygen. This depletion needs to be compensated because when the treated wastewater is re-released into the environment, it must have oxygen to sustain the animal and plant life that depend on it.

The clarified, cleaned, and reoxygenated wastewater called effluent is discharged into the local water channels for various purposes such as agricultural, industrial, fisheries, et cetera.

Globally, how much wastewater is treated?

According to the United Nations University, Institute for Water, Environment and Health, an estimated 52% of wastewater is treated globally, though treatment rates vary between high-income (74%), upper-middle-income (43%), lower-middle-income (26%), and low-income (4.3%) countries.

Edward Jones, a Ph.D. researcher at Utrecht University and lead author of the Utrecht study, provides figures of approximately 63% and 52% of globally produced wastewater collected and treated, respectively, with about 84% of collected wastewater undergoing a treatment process.

According to this study, “Wastewater collection and treatment rates are highest in Western Europe (88 % and 86 %, respectively) and lowest in South Asia (31% and 16 %, respectively) and sub-Saharan Africa (23% and 16%, respectively).”

The study’s authors also point to relatively high wastewater collection (74%) in the Middle East and Africa region (MEA), driven by the need for renewable water supplies.

A significant reason for this skew is that the three main aspects of wastewater treatment – output, collection, and treatment – are unevenly matched. For example, a country with high wastewater production may lack the infrastructure to collect and treat it. This results in untreated wastewater making its way back into the water reuse channels, leading to potential health and environmental problems. The Utrecht study says that wastewater treatment is substantially lower than wastewater collection in Latin America, Caribbean, and South Asia, “potentially indicative of high rates of untreated-wastewater reuse in these regions.”

On the other hand, a country may have adequate collection facilities but inadequate or less effective treatment systems. Any imbalance in the three factors can skew the wastewater treatment outcome.

Another vital factor in wastewater treatment is its qualitative condition. If wastewater is inadequately treated and released back into use, it can pose many dangers to the environment and the ecosystem’s health. From the contamination of drinking water – a leading cause of diseases in humans – to harming aquaculture, wildlife and disrupting the balance of micro-organisms, the pollutants in poorly treated wastewater can cause plenty of damage.

The UN Progress on Wastewater Update 2021 says, ‘Globally, 56 percent of household wastewater flows were safely treated in 2020 (extrapolated from data from 128 countries representing 80 percent of the global population). Wide disparities among the regional proportions of household wastewater safely treated were discovered (ranging from 25 percent to 80 percent by SDG region), indicating that progress remains uneven across the globe.”

Aerial view recirculation sedimentation tank, water treatment plant for big city from water management

What are the challenges in wastewater treatment?

There are many. As populations rise, for example, in developing countries, wastewater output increases, ramping up the need for more treatment to contain its damage to the environment.

Let us look at some of the obstacles in wastewater treatment expansion:

Putting up wastewater treatment plants and the ancillary infrastructure costs money. Many countries, especially in the developing world, do not have the funds to invest in these facilities. As a result, they release the untreated water back into the environment. According to this report, “on an average, high-income countries treat about 70% of the municipal and industrial wastewater they generate. That ratio drops to 38% in upper-middle-income countries and 28% in lower-middle-income countries. In low-income countries, only 8% undergoes treatment of any kind.”

  • In England alone, water companies discharged untreated sewage waters more than 400,000 times in 2020, according to the UK’s Environment Agency as reported by the BBC. Globally, hundreds of such statistics point to the dangers of untreated wastewater recirculating in the system.
  • Wastewater treatment plants use up a lot of energy to do their job, which strains the country’s energy grid. Apart from energy requirements, treating wastewater creates organic byproducts that must be further processed to shrink the carbon impact. This can potentially slow down the expansion of these treatment plants if the country’s resources cannot create a balance between energy investment and its wastewater treatment needs. (In the next section, we will read about how some entities are resolving this issue).

What are the solutions?

Integrated, circular economy strategies are gaining traction in many countries to turn wastewater into a renewable resource. The World Bank report offers many examples of how governments and municipal bodies are coming together to tackle the issue.

In Nagpur, India, one of the country’s most populated cities, the burgeoning population led to increased output in wastewater even as the need for power generation rose.  The latter required more water supply to generate thermal power. The result was a synchronized effort by the city’s municipal body and state’s electricity board to convert the wastewater into a reclaimed resource for the thermal power station. This outcome was an all-around pay-off for the city. The municipality reclaimed the wastewater and generated additional power to make the residents’ lives easy.

Durban, South Africa: Local government and industrial entities collaborated on a wastewater treatment and usage project that now saves potable water for 400,000 people. It is an excellent example of how a city “converted a challenge into an opportunity,” says the report.

Ridgewood, New Jersey, USA: This village set an early example of tackling carbon neutrality through intelligent planning and PPP (Public-Private Partnerships). Its existing wastewater treatment plant needed high power consumption to run, which produced a byproduct, methane. So, the village’s civic body signed a partnership with a private firm to convert the biogas into power for the wastewater treatment plant. This circular approach resulted in reduced power costs for the plant, prevented the biogas from being burned, neutralizing the carbon footprint, and enhanced treated water output for the village,

Aerial view recirculation sedimentation tank, water treatment plant for big city from water management

Policies, planning, and regulations

Governments must actively plan and implement innovative strategies to ease the burden of status quo approaches. The examples above prove that out-of-the-box thinking can lead to success. The World Bank report suggests a strategic shift from the status quo to viewing wastewater management as water resource recovery facilities. This fundamental change in attitude to wastewater will lead to more sustainable, impactful outcomes. “These resources can generate revenue streams for the utility, which would potentially transform the sanitation sector from a heavily subsidized one to one that generates revenue and is self-sustainable,” says the report.

Other recommendations in the report include better infrastructure design and the incorporation of circular economy principles.

How can you help?

As a global citizen, you are at the center of the waste management cycle. Be responsible about how much water you use. Remember, the more you generate wastewater, the more it needs to be treated to reclaim it.

Now that you know how significant the issue of wastewater management is, be a water ambassador and educate others – family, friends, colleagues.

Malavika Kamaraju

Malavika Kamaraju

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