Improved wastewater treatment reduces diarrhoeal mortality rate

Diarrhoea is the second global cause of death of children below the age of five and causes the death of many adults. The victims are infected by pathogens in contaminated surface water. Wageningen University & Research scientists are mapping the scope of the problem. What are the most important solutions? Much more wastewater treatment and ‘dry’ toilets.

A few weeks ago, a swim through Amsterdam’s canals was cancelled because the water contained too-high counts of pathogens. Heavy rainfall had caused the sewers to overflow and discharge a large volume of contaminated water into the canals.

Intestines

Pathogens are present in the faeces of sick persons and animals. As bacteria and pathogens multiply in the intestines, persons who become infected develop diarrhoea, which results in the further dispersion of the pathogens.

The fact that a swim in the Netherlands had to be cancelled due to water contaminated with faecal matter made the news (in Dutch). However, less well-known is the fact that every day Europeans die from diarrhoea caused by contaminated and unsafe drinking water – and that the problem is much, much worse in Africa and Asia. Diarrhoea caused by large numbers of pathogens in surface water is one of the most important causes of child mortality and every year more adults die from diarrhoea than from other infections such as malaria. Diarrhoea also results in many days illness and days lost from school and work.

“Constructing sewers is only a solution if you subsequently purify the wastewater.”

Nynke Hofstra, lecturer in the Wageningen University & Research Environmental Systems Analysis Chair Group

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Nature and scope of the problem

The species of microorganisms and the precise numbers are still largely unknown and the manner in which pathogens enter the water is only generally clear. For this reason, WUR scientists have developed a method to use existing data to improve the mapping of the nature and scope of the problem needed to bring solutions closer within reach. The scientists are cooperating with organisations including the KWR Watercycle Research Institute.

Nynke Hofstra, a WUR modeller, carries out a great deal of research into pathogens in surface water. Nynke collects the necessary input by combining data on parameters including population pressure, livestock numbers, disease incidence, sanitary facilities, water treatment, land use and water management. ‘Estimates are available, for example, of the numbers of pathogens excreted by sick persons. Counts of pathogens in sewage can be used to calculate the percentage of sick persons in the population and, in combination with the effect of wastewater treatment, determine the residual numbers that enter surface water.’

Sustainable Development Goals

The most important problems are the lack of adequate wastewater treatment and defecating in public, outdoors and without protection. Both are referred to explicitly in the Sustainable Development Goals, in SDG 6: by 2030, half of all waste water must be treated before discharge. ‘And that’s a lot, because at present less than 20 per cent of the world’s waste water is treated before discharge to surface water,’ WUR’s Nynke Hofstra explains. Moreover, this contamination is increased by the pathogens from animal manure that are carried by rainwater flowing into surface water.

A study of rotaviruses, an important cause of child mortality due to diarrhoea, reveals that the greatest problems are in India and Bangladesh, megacities in Latin America, China and Africa, in particular in Nigeria. ‘These are all locations with high population pressure. Defecating in public also plays an important role in Nigeria.’

However, constructing sewers does not necessarily solve the problem: although most of the Latin American population is connected to sewers, the subsequent wastewater treatment is inadequate. Nynke Hofstra explains that ‘constructing sewers without wastewater treatment facilities actually makes the problem worse, as this increases the dispersion of the pathogens in surface water.’

Pit latrine

Hygienic pit latrines would be a better idea. A latrine is a ‘dry’ toilet, a hole in the ground which is covered over when it is full. This has been used widely in the Netherlands: the toilet bowl empties into a septic pit in the ground (and not, as was also the case, into canals). Leaving faeces undisturbed in a septic pit for several years results in the death of the majority of the pathogens. However, there is often insufficient space for septic pits and tanks – and certainly in the cities – and the contents are often ultimately discharged into the surface water. These discharges contaminate the same water that the population drinks from and uses to wash themselves, their clothes and irrigate their crops – which, consequently, results in further infections.

Climate change can only exacerbate the problem: for example, extreme rainfall can cause flooding that results in a wide range of particles in the soil being carried to surface water. Nynke Hofstra notes ‘This is why combating defecating in public is so important.’

“We are developing an app for Uganda, which can be used by policymakers to compare the effects of different solutions on water quality.”

Nynke Hofstra, lecturer in the Wageningen University & Research Environmental Systems Analysis Chair Group

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App for safe sanitary facilities

A model study based on E. coli carried out in Bangladesh and Pakistan reveals that socio-economic progress, which results in improved wastewater treatment and reduced defecating in public, plays an important role in the reduction of the problem. WUR is also involved in a study in Uganda which is examining the best policy for the provision of information about the most important measures to be taken to protect the population’s health. Only 10 per cent of the inhabitants of the capital city of Kampala, for example, are connected to the sewers. The researchers are working on approaches such as the development of an app for mobile phones. This app can be used by policymakers to analyze and compare the effects of different solutions (eg water purification) on water quality. This study is financed by the Bill and Melinda Gates Foundation.

Nynke Hofstra’s other work includes a study, for example, of the Cryptosporidium family of small parasites that can cause extremely severe diarrhoea. The best method to destroy Cryptosporidium in water is a treatment with UV light, which the Netherlands uses solely in the treatment for drinking water. ‘However, many countries don’t even have wastewater treatment facilities.’ The study revealed that the contamination of surface water with Cryptosporidium is expected, for example, be very high in England, especially in London. ‘This is because England uses less intensive wastewater treatments than the Netherlands and because London is an extremely densely populated city.’

Nynke Hofstra says that the Netherlands’ wastewater treatment is much better than in many other countries. ‘Nevertheless, even the Dutch wastewater treatment plants don’t remove all the pathogens from the waste water before its discharge.’ This means that even in the Netherlands swimming in open waters can be risky.

Water Conference

Nynke Hofstra was also one of the speakers at the international ‘Water Science for Impact’ Conference held in Wageningen on Tuesday, 16 October.

Read more:

• International conference ‘Water science for impact’
• Sustainable Water Management Programme
• Study of the Global Occurence and Emission of Rotaviruses to Surface Waters
• Study of the Quantifying the impact of climate change on enteric waterborne pathogen concentrations in surface water
• Study of the Modelling the impact of future socio-economic and climate change scenarios on river microbial water quality
• Read this item in Dutch