Making dirty water clean and safe with low-cost solutions especially for rural communities is the goal of Iso Lomso fellow Ismaila Emahi of the Department of Chemical Science, University of Energy and Natural Resources, Ghana.
“We are hoping to find solutions that are applicable to everyone to address a very real problem,” said Emahi. “Looking at both low-tech, low-cost as well as high-tech, low-cost technologies to improve water quality and remove trace toxic metals.”
“Safe water is a human right,” said Emahi. “The consumption of contaminated water is a global concern, especially contamination with heavy metals. These can accumulate and at a certain threshold become very harmful with long-lasting health effects. They cannot easily be removed. Many rural poor depend on untreated water from rivers and streams containing these toxic metals for their water supply.”
Emahi explained that the sources of these metals are natural (they are found in the earth’s crust) but they also come from human activities – in particular heavy industry and mining. The World Health Organization highlights the most concerning of these as mercury, cadmium, arsenic and lead.
“Arsenic poisoning from water is estimated to be a risk in about 108 countries. At least 13 countries in Africa are affected,” said Emahi. “Even clean-looking water may not be safe – low levels of arsenic can be very dangerous.”
Indiscriminate, and often illegal, mining activities – called Galamsey in Ghana – are a major source – leading to contamination of surrounding water bodies resulting in elevated toxic metal levels.
“Affected communities depend on the polluted water for domestic and other use – they have no other options,” said Elmahi. “While the government and other stakeholders are trying to crack down on these activities, it’s up to scientists to try to minimise the effects by tracing and removing these metals.”
Traditional analytical methods for detecting and removing these toxic metals in water (including atomic absorption spectroscopy, atomic fluorescent spectroscopy and inductively coupled plasma) are expensive, require bulky equipment, infrastructure and training, and often laborious laboratory procedures, making them impractical for rapid, in situ measurements. Emahi and his collaborators are therefore searching for cheaper alternatives using simple biofiltration techniques.
All in a coconut
One of the options is biofiltration with natural adsorbents. This involves the use of lignocellulosic biomass to remove the heavy metals – basically the use of biological materials like plant waste materials containing electron-rich or negatively charged groups allow negatively charged species such as heavy metals to bind and be removed. It’s a cost-effective, environmentally friendly option. Coconut waste is a particularly good biosorbent and coconuts are abundant in the coastal areas in Ghana. Emahi explained that there is more lignin in the husk of the coconut and therefore it is used more but the shell can also be used.
“Traditionally these are also processed before use using an activated carbon preparation but this adds to the cost so we are looking at comparing the processed versus the raw, unmodified coconut shells,” he said.
“So far the work has shown that the raw shells is just as good as the activated. Raw shells were able to remove 49% of mercury and 65% of arsenic – only slightly less than activated so activating is not worth the extra costs.”
But ongoing work is needed to enhance the selectivity and sensitivity of the process to ensure you don’t also remove essential minerals like calcium and magnesium, and Emahi will work with Stellenbosch University during his STIAS fellowship to understand in more detail the chemistry of the interactions in order to optimise the process, and to try to reduce the time taken – currently an hour under laboratory conditions.
“We also need to build collaborations with industry to take this forward,” he added.
Solutions on the ground
But Emahi remains conscious of the urgent need to get a workable solution to people at the point of use – the focus of his next project.
“The need for handy, cheaper and sensitive alternatives that can be used at the point of sampling is crucial,” he said. “Biosensors have gained great attention as alternative methods for detecting toxic metals in the environment because they are easy-to-use and relatively inexpensive.”
Taking inspiration from the chameleon, Emahi and his colleagues hope to develop a DNA aptamer-based, smart biosensor, which they refer to as an ‘artificial tongue’.
Aptamers are single-stranded DNA or RNA molecules that are generated via natural in vitro selection or through SELEX (the systematic evolution of ligands by exponential enrichment). They can selectively bind to targets ranging from heavy metal ions to human cells with high degrees of affinity and specificity but they are not easy to identify, clone and sequence. Once the researchers have identified appropriate aptamers, the idea would be to develop an easy-to-operate, low-cost biosensor which can monitor exactly which metals are present in water and remove them.
Emahi is collaborating with researchers at Cambridge and Oxford Universities in the UK through the Cambridge Africa and the Africa Oxford Initiative respectively in order to start the aptamer selections. He hopes that with more funding, the goal of providing handy, cheaper and smart biosensors for toxic metal removal will be accomplished.
“The need is there,” he said. “Before 2015 only 40% of Ghanaians had access to clean water. Now it’s about 70%. But we urgently need to help the rest, especially if we want to reach the Sustainable Development Goal of achieving universal and equitable access to safe and affordable drinking water for all by 2030.”
Right now the technology is aimed at rural communities. “More conventional methods are used by governments and municipalities – but, in many countries, these are still not optimal and tap water is still not completely safe. So it’s also possible that governments would use this technology.”
Addressing the broader issue of the political economy of water and environmental pollution, he said: “This technology is for people who have no other option. The solution is unique to the people and the problem. We can’t wait for ever for legal and policy solutions. This buys time. We need many different approaches working together to address the larger problem.”
Michelle Galloway: Part-time media officer at STIAS
Photograph: Noloyiso Mtembu