Ask the Experts: Tapping into wastewater for World Toilet Day


Today is World Toilet Day, a global initiative to inspire and mobilize action to tackle the sanitation crisis. This year’s theme is wastewater. More than 80% of global wastewater is released into the environment without treatment, but far from being something to dispose of, wastewater has huge potential as a valuable resource. Microbiology could play a transformative role in the sustainable reuse and treatment of wastewater. To find out more, we asked an expert panel to share their views on how to take the ‘waste’ out of wastewater. 

Kate Medlicott | Bruce Gordon

Team leader for WHO Sanitation and Wastewater | Coordinator of WHO Water Sanitation Hygiene and Health Unit  

“The 2030 Sustainable Development Goals (SDG) explicitly call for a “substantial increasing safe reuse of wastewater” under target 6.3. This is the first time the topic has received such high level attention and recognition of the role safe wastewater use play in achieving other targets on health, nutrition, agriculture, sustainable cities and economic productivity. In fact, direct or indirect use of untreated wastewater in agriculture and aquaculture is a common practice in many parts of the world. The challenge is often not increasing reuse per se, but increasing the proportion that is safely reused.

This is where microbiologists have an important role to play by ensuring the negative impacts on health are minimized while maximizing benefits for nutrition and food security. Microbiological risk assessment and management underpins WHO Guidelines on Safe Use of Wastewater and Sanitation Safety Planning and needs to be scaled up globally to help achieve SDG 6.3. Wastewater is also increasingly recognized as a driver of antimicrobial resistance (AMR). Microbiologists can help enormously by addressing key research questions in this area. Coincidentally, World Toilet Day is at the same time as World Antibiotic Awareness Week, so it’s a great opportunity to highlight the links between sanitation, wastewater and AMR.”

Birguy Lamizana

Programme Officer for UN Environment on behalf of the UN-Water Task Force

“Globally, 80% of the wastewater generated by society flows back into the ecosystem without being treated or reused. In most countries facing water scarcity, safe reuse of water is becoming part of the solution to alleviate water scarcity. Therefore, the use of wastewater will be more and more a common practice. Indeed, to achieve Sustainable Development Goal 6, we need everyone’s poo to be contained, transported, treated and disposed of in a safe and sustainable way. In addition to the profound impact this will have on health and living conditions, safely-managed wastewater has massive potential as an affordable and sustainable source of  water, energy, nutrients and by-products.

Dealing with our poo properly is not only about averting danger, it’s also about seizing an opportunity. Safely processed poo can become a valuable and sustainable source of nutrients, energy and water. For example, the effluent volume from Schiphol Airport in Amsterdam is comparable to that of a small city with a population of 45,000. About half of the wastewater originates from passengers and businesses at the airport, 25% is discharged by aircraft and catering, and the remaining volume is produced by other aviation-related businesses. The on-site wastewater treatment plant biologically purifies water to a quality fit for discharge into local waterways. In this context, microbiology will have to play an active role to ensure the safety of the use of wastewater, particularly when it comes to helping identify and remove pathogens, pharmaceutical and or endocrine disruptors.”

Rémi Kaupp

Urban Sanitation and Resilience Programme Advisor at WaterAid

“To solve the sanitation crisis, we need to look at the whole sanitation chain, from toilets to transport and treatment to final disposal or reuse, as otherwise wastewater can contaminate the environment again and create further health problems. WaterAid’s priority is addressing the most pressing health issues, especially those felt by the most excluded people, and therefore consider toilets and containment and transport of wastewater and sludge first. Reuse is however useful to reduce some of the costs associated with managing the sanitation chain; to reduce freshwater consumption, especially for agriculture near cities.

There are useful guidelines for the reuse of wastewater that already exist from the World Health Organization (WHO), but they are seldom applied for a variety of reasons: where there are toilets and sewers, systems were often designed without reuse in mind and a big effort has to be made to allow for it; and where good toilets don’t exist yet, a lot of efforts are going into improving them and making sure we can empty toilet pits and manage the sludge afterwards.

I would suggest that the future isn’t necessarily in wastewater but in faecal sludge, i.e. the contents of pit toilets, which are much less studied, but represent more than half of the world’s toilets. We still don’t have good ways of emptying pits (apart from some experimental pumps like the Gulper) and treating sludge (apart from drying beds and some experiments). Microbiology has a big role to play in helping us understand the processes happening in pits and during sludge treatment, and to find efficient ways to treat and reuse sludge.”

Read WaterAid’s new report highlighting where in the world it is hardest for women to find a toilet.

Mark van Loosdrecht

Professor in Environmental Technology at Delft University of Technology

“I think microbiology plays a major role for the reuse of wastewater. First by developing treatment technology that is simple and with minimal use of mechanical equipment – the aerobic granular sludge process is such an example. South Africa and Brazil are the early adopters of this technology outside The Netherlands. The capacity of bacteria to make granules instead of flocs makes this technology possible. The exopolymers produced by the bacteria form a very interesting new resource based on which interesting materials can be made. But the polymer has also interest for the local economy.

Currently we are looking at how these polymers can be used in the strengthening of the material used in construction of loam based houses. For World Toilet Day, I hope that based on the wastewater produced in cities, new products are developed. Especially products that fit in the local economy, which will help to integrate wastewater handling better in the local economy and make it become less dependent on development aid, large foreign investments and complicated tax systems.”

Jack Sim

Founder of World Toilet Organization and World Toilet Day

“I think we have a global culture of ‘flush and forget’ in the developed world and another culture of open defecation and untreated excreta entering and contaminating the water ways. These problems lead to the spread of disease with high mortality and morbidity rates. We need now to focus on making sure that all poo is treated and recycled into nutrients or energy or at least made safe. There is also a peak phosphorous problem somewhere on the horizon. If we don’t recycle urine which is phosphorous-rich, we might run out of fertilizers for crops in future.

What we don’t discuss, we can’t improve. I want people to feel comfortable talking about poo so that they can be safe from its harm and able to use it as a resource. We have a very intimate life partnership with our toilets. We can’t live without them. Like all relationships there must be love, care, dialogue and maintenance. I want everyone to think of the ecological cycle of food from input to output to recycling into the soil to produce more food again. A human produces enough poo to fertilize enough grains for him to eat a whole lifetime. Food and poop is a continuous sustainable cycle – it is not a waste, but is a resource.”

Mariska Ronteltap|Eric van Hullebusch

Senior Lecturer in Sanitary Engineering at UNESCO-IHE Delft | Professor of Environmental Science and Technology at UNESCO-IHE Delft

“In a recent publication from the United Nations World Water Assessment Programme (WWAP 2017), it was reported that the overall demand for water rises while the quantity of wastewater produced and its overall pollution load are also increasing worldwide. More than 80% of the world’s wastewater – and more than 95% in low and middle income countries – is discharged into the environment without proper treatment. In the current trend of resource recovery from wastewater for a circular economy, there is room for developing and implementing technologies aiming at the use of wastewater as a sustainable source of water, energy (biofuels such as biogas, biohydrogen and biodiesel), nutrients (N, P and others), metals and other recoverable by-products (bioplastics and proteins). Puyol et al. (2017) recently published a promising overview of the different biotechnological options where different microbial groups can play a role – individually or in synergy – including Archaea, Bacteria and Eucarya such as fungi and microalgae.”

To learn more about wastewater as an untapped resource, explore a range of articles from our journals and collaborating water journals in our World Toilet Day Twitter special collection.

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