World Water Day is an annual event that takes place on 22nd March.  It is a means of focusing attention on the importance of freshwater, as well as emphasising the need for sustainable management of global water resources.  Each year, World Water Day highlights a different aspect of freshwater, and the theme chosen for 2017, is “wastewater”, in support of Sustainable Development Goal 6.3, to improve water quality and reduce, treat and reuse wastewater.  This article, written by CABI’s Global Health and Environmental Science Editors, Wendie Norris and Stephanie Cole, examines the importance of wastewater treatment in terms of resource recovery and environmental preservation, as well as its role in protecting human health.

But what is wastewater?  There are a number of definitions, with wastewater meaning different things to different people, but taking a broad perspective, it can be defined as “a combination of one or more of:

  • Domestic effluent consisting of blackwater (excreta, urine and faecal sludge) and greywater (kitchen and bathing wastewater);
  • Water from commercial establishments and institutions, including hospitals;
  • Industrial effluent, stormwater and other urban run-off;
  • Agricultural, horticultural and aquaculture effluent, either dissolved or as suspended matter” (Corcoran et al. 2010)

Worldwide, the majority of all wastewater produced from homes, industry, cities and agriculture flows back into the environment without being treated or reused.  A growing global population, rapid urbanisation, rising fertiliser prices and increasingly scarce good quality water resources are the main driving forces behind the upward trend in the use of wastewater, creating a demand for new solutions for its reuse.  Treatment of wastewater is also important to safeguard human health, as well as to avoid the contamination of freshwater bodies, such as rivers and lakes, although industrial treatment can often be an expensive process. 

Limitations in the availability of resources are driving a change in current production systems, from residues treatment, such as wastewater treatment, toward resource recovery (Puyol et al. 2017).  Biological technologies provide an economical way to transform resources from wastewater into valuable products.  An example of this is the production of biogas, through the process of anaerobic digestion, where the transformation of biomass into methane-rich biogas provides the opportunity to reduce the organic matter content of the wastewater.  Biotreatment of wastewater using microalgae culture is another option, as it has the capability to effectively remove nutrients from wastewater, as well as providing a biomass energy source.

According to recent research from the US Department of Energy’s Pacific Northwest National Laboratory, wastewater treatment plants treat approximately 34 billion gallons of sewage every day, which it said, could produce the equivalent of up to 30 million barrels of biocrude oil each year, through the use of hydrothermal liquefaction technology, which breaks the organic matter down into simpler chemical compounds which is then pressurized and heated, causing the waste material to break down into biocrude oil.

Another process currently on trend in the wastewater industry is the recovery of nutrients such as nitrogen and phosphorus from used water and conversion into a fertiliser feedstock.  Typically, wastewater can contain a significant amount of nutrients, such as phosphorus, which can pose a threat to the environment and cause eutrophication in water bodies.  By recovering these nutrients, wastewater treatment plants can help to mitigate these issues, while improving water quality. 

While wastewater treatment is essential for the preservation of the environment, it is also extremely important for protecting public health.

There are 3 public health aspects to wastewater: the direct use of wastewater (treated to remove harmful material), the indirect use of wastewater (the user has no knowledge that the water from their reservoir or river is contaminated with untreated wastewater), and occupational health of workers handling wastewater (e.g. on the farm or at water treatment plants).

But in all aspects, the potential hazards are the same: wastewater if untreated contains pathogens and heavy metals which are detrimental to human health.

The pathogens cover all classes: bacteria, viruses, helminths and protozoa. Domestic and hospital-produced wastewater contain the highest levels for  pathogens are shed by infected people (& animals) into their faeces and excreta,  so reuse of this water will naturally cause such diseases to spread.  Examples of the diseases they cause are cholera, typhoid, hepatitis, viral gastroenteritis, amoebic dysentery, cryptosporidiosis, giardiasis and campylobacteriosis. In developing countries, in addition to these, they also have to deal with for example guineaworm, hookworm and schistosoma, which are all helminths.

In developing countries, with the pressure of urbanisation there is direct use of wastewater in projects in metropolitan centres, but still most of the wastewater goes untreated and is discharged directly into reservoirs and rivers that supply irrigation  and drinking water (indirect use).  Thus the cycle of the pathogen is maintained within the local community with the knock-on effect of reducing the overall health of the people. This works against other initiatives linked to SDG-6 (such as WASH driven programmes to provide hand-washing facilities with every toilet) that have been trying to improve population health in developing countries through sanitation and hygiene.

Outbreaks of disease due to untreated or partially treated wastewater occur in both developed and developing countries.  Hookworm has a water stage in its life cycle, the protozoa giardia and cryptosporidia can survive cold temperatures, so it’s no wonder that there are regular outbreaks of cryptosporidiosis and giardiasis in the USA and Europe from drinking water, nor that such effort has been needed to eliminate hookworm. Contaminated wastewater used to water a salad sprout crop thought to be behind the outbreak of E. coli 0104 in Germany in 2011, and currently, areas of India facing shortages of drinking water expect outbreaks of typhoid.

Emergency refugee camps, such as those now being set up in East Africa will build into their plans separation of water for drinking, bathing and sanitation and chlorination of any wastewater to prevent cholera outbreaks.

Wastewater is not just a potential source of pathogens. The heavy metals cadmium, zinc, copper and nickel are found in industrial wastewater:  food crops irrigated with it will concentrate the metals to a point that the crop is not safe for human consumption. Pesticides are found in agricultural run-off.  

 And so, the initiatives outlined earlier to reduce the organic matter in wastewater will, alongside standard treatments, contribute to the improvement in water quality and to improved human and animal health. It is no coincidence that water quality guidelines measure the number of faecal coliforms (gut bacteria) found in the drinking water supply.

Further information on wastewater and the environment is available to subscribers of the Environmental Impact database.  By using the search string "wastewater treatment" AND "water pollution" AND "water quality" AND eutrophication AND (CC=XX300 AND CC=PP600) yields 149 records.  Alternatively, (wastewater OR "wastewater treatment") AND (nitrogen OR Phosphorus) AND fertilizers AND CC=JJ700 yields 713 records and (biofuels OR biogas OR bioenergy) AND (wastewater OR "wastewater treatment") AND "anaerobic digestion" AND CC=XX300 returns 416 records.

Information on wastewater and public health can be found on the Global Health database. For instance, using the search string "wastewater treatment" and cc:(VV210 or VV220) yields 1004 records on pathogens, including drug resistance genes, in wastewater treatment plants.


Corcoran, E., Nellemann, C., Baker, E., Bos, R., Osborn, D., & Savelli, H. (eds) (2010) Sick Water? The central role of wastewater management in sustainable development. A Rapid Response Assessment. UNEP/UNHABITAT

Puyol, D., Batstone, D. J., Hülsen, T., Astals, S., Peces, M., & Krömer, J. O. (2016). Resource Recovery from Wastewater by Biological Technologies: Opportunities, Challenges, and Prospects. Frontiers in Microbiology7, 2106.

Useful links

Each year the United Nations publishes its World Water Development Report.  This year’s report, titled 'Wastewater: The untapped resource' has been purposefully aligned with the theme of World Water Day.  The report will be launched at a special World Water Day event in South Africa on 22nd March.  Reports from previous years are also available on the UN-Water website.

Sustainable Development Goal #6

UN-Water – Key Water Indicator Portal

UN-Water – Publications library

Water Sanitation and Hygiene (WASH)

WHO (2006) – Guidelines for the safe use of wastewater, excreta and greywater

WHO – Publications of Water Sanitation and Health


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