Wastewater management in cities

Wastewater management – the blessing in the curse

Nowadays, cities seem to be the places to be for more and more people. For one, they can get access to better services, like water and sewage. In fact, the United Nations says that, between 1998 and 2008 alone, 1 052 million people accessed better drinking water in cities. A whopping 813 million accessed better sanitation, and the numbers are set to grow. Of the 39% of the global population (2.9 billion people) that use safe sanitation, most live in cities; as much as three out of every five people. Two out of five people in rural areas across the planet have access to piped water, while four out of every five people in urban areas enjoy this privilege.

The trend is unlikely to turn. Under the umbrella of the Sustainable Development Goals, countries, cities and industries have committed themselves to a future with access to safe water and suitable sanitation to all.

Yet, all of this comes at a price. The more water we use, the more water we make dirty. Wastewater management today is a enormous part of managing a city. And, as much as water can give people better quality of life, as big is the price that we pay for it.

The flipside of safe water and sanitation

The water that we use must come from somewhere. The more people that access water, the more needs to be taken from nature to feed the system. At the same time, as the amount of water used by people increases, so does the amount of dirty water we produce in the process.

Over and above that, examples of places where safe water is getting harder to come by are common. And, as this is happening, it’s become clear that the dirty water we flush away, is a valuable opportunity washed down the drain.

It’s a broken circle. We take clean water, dirty it, and then send it back to pollute the system where we take our water from. At the same time, we already don’t have enough clean water.

To change this, some say that our perception of dirty water must change. In fact, an entire rethink of the traditional wastewater treatment model is necessary. In this picture, ‘dirtied’ water is not a problem to be managed, but rather an opportunity to solve many of problems inherent to wastewater management.

What is this dirty water?

Let’s take South Africa as example. Here, about 23% of the freshwater in the country is used by municipalities. This water is the oil that keeps the machinery of households running, though it mostly only passes through. The water enters the house clean enough to drink. Then, it swiftly exits the property again after it has been used for stuff like washing dishes, laundry and people, and flushing toilets. However, now the water is seen to be dirty and even dangerous to our health.

Lots of water is also used outside for gardens, although this water does not leave the property as waste. Rather, it goes back into natural system. Some water evaporates or infiltrates back into the groundwater table. A small amount of water could also run into the stormwater system; when water runs down paving after washing cars or from over-watering gardens.

For our purposes, we’re interested in that water that does not enter the natural or stormwater systems after it has been put to work. That’s the so-called wastewater, and that’s what’s being eyed as a new ‘tap’ of water to be developed.

Of course, what wastewater can be used for, depends on how dirty it is.

Not all dirty water is equal

In general, the wastewater produced in homes is divided into greywater and blackwater. Blackwater is from toilets and is commonly collected via sewer systems. This water has high concentrations of stuff that can possibly make you sick, like disease-causing microorganisms, organic loads (bits of animals and plants) and nutrients. This water is usually dark in colour and smells.

Still, although controversial, the reuse of treated blackwater is becoming more common. In Windhoek, for example, they’ve been depending in this water for decades.

Greywater is mostly untreated wastewater from all household uses except for toilets. Water from kitchen sinks and dishwashers is sometimes excluded too. Also called greywater, sullage and light wastewater, it contains some nutrients and microorganisms but usually at a much lower levels than blackwater.

What makes dirty water so attractive

Firstly, if we were to use wastewater, we would have more water available to us. Cities use vast amounts of water and as a result, generate ginormous amounts of wastewater. If wastewater instead of freshwater can be used for some stuff, the natural sources that the freshwater is taken from will also get a break. It has been reported that residents of developments that make use of wastewater can save up to 50% of drinking-standard water compared with those that don’t.

The lovely Padysha-Ata, a small transboundary river in Kyrgyzstan.

Not only will using wastewater help build security in our water reserves, but it can also result in better overall water quality. This is because the dirty water will be prevented from entering the environment again.

Plus, the stuff in the wastewater can be put to good use elsewhere. The energy, organics, phosphates, nitrogen and cellulose can be mined and, in turn, lead to financial gains. This could perhaps cover some of the operations and maintenance costs to run the process.

Using wastewater instead of getting rid of it, thus opens up many opportunities to create places that are more water secure, healthy and clean, while creating business opportunities.

But its not all smooth sailing ahead with wastewater. Dirty water comes with as many risks as opportunities.

What can we do with our dirty water?

Because of this potential risk to people’s health, recycled and treated wastewater, in South Africa at least, has mostly been used to water open grounds like sports fields, parks or plants not meant to be eaten. In rare cases this water is used irrigate fodder, but this is strictly regulated.

However, its a different ball game when drought hits. When few other options are available, greywater is often used for gardening, especially in middle to upper income suburbs. In lower income, informal and peri-urban areas, people tend to use it to also water vegetable and fruit gardens, though this is not done without health concerns.

The different uses of greywater, and its quality, also depends on the environment where it is created. Not only do people living in formal urban areas tend to use greywater for different functions than residents in informal areas, but the quality of the greywater produced from these areas differ greatly.

Where you live changes the wastewater you make

In a formally developed area, water enters the home, is used and is taken away again. During drought, some wastewater (greywater) might be collected with a bucket from the shower or bathtub and used to flush the toilet or water the garden.

In comparison, the journey of water in an informal settlement is very different. First, the basic infrastructure to remove used water from the household is often non-existent. Still, the household might have access to some means to bring water into the house, like a communal tap or a river.

In informal settlements water thus often needs to be collected away from the home and carried back. This is hard work and takes time, so water is used multiple times. When there is no infrastructure to remove the used water, the wastewater is generally thrown outside of the house. Here it can mix with other forms of waste.

Especially where settlements are densely populated, a lot of dirty water accumulates in streets and other areas used by people. This leads to a myriad of potential harmful impacts on people’s health, the direct environment that they live in, and the broader environment that the water flows towards.

Because this water is so seriously polluted, some refer to the greywater generated from unsewered, informal settlements as dark greywater. This water is often more like blackwater than greywater, and is hazardous.

Wastewater management in informal settlements

It’s not possible to reuse this water without extensive treatment. In general, the consensus is that this water should really only be diverted to a sewer, to be managed in the same way as blackwater. In informal settlements the challenge is not how to make better use of wastewater. Rather, the challenges is how to tackle wastewater management so it does not endanger the health of people and the environment.

The most ideal places for wastewater use

At least locally (in South Africa), the most promising source of greywater to add to the country’s water security is at low-density, high-income areas. Here more greywater is produced and there are fewer health concerns.

Especially promising is large buildings such as office blocks, public buildings and hostels. At these places, greywater can be collected and treated for reuse under proper supervision.

How to tackle better wastewater management

General consensus is that as a starting point, the aim of managing wastewater is to improve health, conserve water and protect the environment. Then, where possible, wastewater can be recycled and reused.

In South Africa, the recycling of water for any purposes, whether it is domestic, agricultural or industrial is strictly regulated. By and large, our laws are not aimed at regulating reuse of wastewater. Mostly, they aim to protect and conserve the country’s natural water resources.

At the moment the goal is thus largely to return treated wastewater to the natural water environment. Ideally, we want to recover as much of the volume of water originally extracted. Then, we want to ensure that the reclaimed water does not harm the natural ecological status of the environment to which it is returned.

There is a lot of work to be done before the benefits of wastewater can become reality. This depends as much on technology and management intervention, as it is on shifting perspectives and new thinking.

What needs to change for better wastewater management?

The linear model of traditional water treatment, in which water is extracted from the source, treated and used before the wastewater is treated and disposed of, needs to change. A new, circular model is called for. In this plan, less water is extracted by reducing the water used and consumed. Water is recycled and reused for different purposes depending on the quality of the water, allowing the water resources to recover.

In order to see this become a reality, a number of things need to change. For one, the purpose of wastewater treatment plants need to be re-imagined as a place where water and other resources are recovered.

Planning should also move from focusing on individual wastewater plants for individual municipalities to bigger scale thinking that considers the basin.

To do this, regulation, policies and incentives across sectors must be aligned. At the same time, the institutions that ensure that such laws and policies are applied, must have clear and enforceable sanctions.

While it’s a long haul ahead, there are examples of places that have chosen to go down this road. Singapore, for example, sees wastewater as one of the central pillars of its future water security. In San Francisco, again, the country’s first legislation to allow for alternative water sources to be used in buildings has been written. Even in South Africa, there are great examples. Wastewater has been part of the mix of water supply to Atlantis in the Western Cape for decades.

Some would say that wastewater is our greatest untapped water resource. From this point of view, one of the biggest curses of the development of cities, can be seen as a potential blessing, helping people that move to cities to live their best lives, along the way.

Notes

Sources

  • A Review of the Applicability of the South African Guide for the Permissible Utilisation and Disposal of Treated Sewage Effluent in Agriculture and Aquaculture, by P Jagals & M Steyn (WRC Report No. 1039/1/02)
  • Sustainable Use of Greywater in Small-Scale Agriculture and Gardens in South Africa, by Nicola Rodda, Kirsty Carden, Neil Armitage (WRC Report No. 1639/1/10)
  • The reuse opportunity – IWA Wastewater Report 2018
  • Understanding the use and disposal of greywater in the nonsewered areas in South Africa, by Kirsty Carden, Neil Armitage, Kevin Winter, Owen Sichone and Ulrike Rivett (WRC Project 112 WRC GLOBAL SERIES: WATER RESILIENT CITIES K5/1524 final report)
  • Wastewater? Shifting Paradigms: From Waste to Resource, Preliminary Insights for the Latin America and Caribbean Region for the World Water Forum 2018, accessed at www.worldbank. org
  • Wastewater treatment: A critical component of a circular economy by Diego Rodriguez for the World Bank
  • www.unwater.org
  • www.watersensitivecities.org.au

Leave a Reply

Your email address will not be published. Required fields are marked *