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Nanotechnology-the-answer-to-water-purification

At present, more than one billion people mostly in developing countries, lack access to safe drinking water and 2.4 billion people lack access to proper sanitation, according to the Science Daily magazine.

A third of the world's population is living in water-stressed countries, and by 2025, this is expected to rise to two-thirds.

Currently, Zimbabwe is struggling to supply clean water to residents due to different factors such as obsolete equipment, shortages of chemicals and procurement challenges. 

This has prompted experts and stakeholders to look for an affordable and long lasting solution to the water supply woes bedeviling the countries.

  Nanotechnology could be the answer to ensuring a safe supply of drinking water for regions of the world stricken by periodic droughts and water contamination.

 

Nanotechnology is the engineering of functional systems at the molecular scale.

It involves the study and building of matter and compounds at the scale of 0.1 to 100 nanometers.

To get an idea of how small a nanometer is; a strand of hair for example, measures 50,000 nanometres in diameter and a nylon fibre is 30,000 nanometres.

Nanotechnology is used in various fields such as water treatment, medicine, agriculture and many others.

In water treatment, different kinds of membranes are used depending on the water’s pollutants level.

Nanofiltration is a relatively recent membrane filtration process used mostly to remove solids including bacteria and parasites in surface and fresh groundwater. 

It is a cross flow filtration technology which ranges between ultrafiltration and reverse osmosis.

With, reverse osmosis mechanical pressure is applied to an impure solution to force pure water through a semi-permeable membrane.

According to Chemistry International July-August 2009, reverse osmosis is theoretically the most thorough method of large scale water purification available, although perfect semi-permeable membranes are difficult to create.

Reverse osmosis and nanofiltration use the cross flow filtration principle whereby, the feed is passed across the filter membrane (tangentially) at positive pressure relative to the permeate side.

 

A proportion of the material which is smaller than the membrane pore size passes through the membrane as permeate or filtrate while everything else is retained on the feed side of the membrane as retentate or waste.

 

Professor Hillary Magadza of the Zimbabwe Academy of Sciences said most of the country’s water sources like Lake Chivero and Manyame are now more polluted with high levels of phosphorous and nitrates than in the 1960s.

The two elements are rich in nutrients giving rise to the growth of menacing weeds such as the water hyacinth.

“The city council is currently doing its best as its water quality meets World Health Organization standards but consumers should also use filters to purify the water ”,he said.

He said the use of chlorine to purify heavily contaminated water may have long term effects as the chlorine can be attracted by organic matter forming chlorophenols which can lead to the development of cancer.

However, Professor Magadza added that the large scale filtration of water using nanotechnology requires huge capital injection.

“The technology is still new and a few companies are manufacturing the membranes making it an expensive venture and also membrane filters have to be changed regularly depending on the level of contaminants in the water. Further morel, the membranes are patented”, he explained.

He urged ZINWA and city councils to research further and develop the use of activated carbon, another product applicable to nanotechnology which they are currently using.

 

According to Wikipedia disinfection by chlorination can be problematic in some circumstances. Chlorine can react with naturally occurring organic compounds found in the water supply to produce dangerous compounds known as Disinfection By Products (DBPs).

The most common DBPs are trihalomethanes (THMs) and haloacetic acids which are carcinogenic.

 However, the World Health Organization has noted that the risk to health caused by chlorine treatment is almost insignificant compared to the risk caused by untreated water.

Aesthetic concerns such as its bad taste and odour are also a cause for concern.

Nanotechnology eliminates the use of chemicals in water purification currently being used in Zimbabwe.

For instance, ZINWA spends US$105,770 monthly on water treatment chemicals for small towns and growth points around the country while the City of Harare spends US$1,972,170 per month for the procurement of around ten chemicals it uses to treat its heavily contaminated waters.

The major water treatment chemical is Aluminum Sulphate, a coagulant that traps heavy pollutants in water.

Chlorine is also widely used to kill bacteria while soda ash or lime maintains the proper ph level in water.

Researchers, Peter Majewski and Chiu Ping Chan of the Ian Wark Research Institute at the University of South Australia have observed that the availability of healthy drinking water is fast becoming a major socio-economic issue across the globe, especially in the developing world.  

The Australian team suggested that nanotechnology could provide a simple answer to the problem. 

Professor Christopher Chetsanga the President of the Zimbabwe Academy of Sciences said nanotechnologies are set to make a considerable impact on the water treatment sector.

“After the terrible cholera outbreak that hit the country in previous years, it is important to look at other safer ways of treating water and nanofiltration is one of them”, he said.

Membrane filters are widely used in developed countries for filtering both drinking water and sewage for reuse.

 For drinking water, the filters can remove virtually all particles larger than 0.2 micrometers.

The membranes are an effective form of tertiary treatment when it is desired to reuse the water for industry, for limited domestic purposes, or before discharging the water into a river that is used by towns further downstream.

They are widely used in industry, particularly for beverage preparation (including bottled water).

However no filtration can remove substances that are actually dissolved in the water such as phosphorus, nitrates and heavy metal ions which are a health hazard.

For instance water with high levels of dissolved lime and magnesium classified as hard water can cause gallstones, kidney stones and urinary stones.

Borehole water usually contains high levels of these minerals.

In order to get rid of them, there is need to electrodeionize the water using ion exchange membranes to completely remove the ions after the reverse osmosis process.

Water is passed between a positive electrode and a negative electrode. Ion exchange membranes allow only positive ions to migrate from the treated water towards the negative electrode and only negative ions towards the positive electrode.

Complete removal of ions from water is called electrodialysis.

The Environment Management Agency (EMA), through its National Water Quality Control arm, monitors the various water pollutants in the country and recommends solutions to water treatment.

EMA checks on the sewer system as most of the domestic and industrial effluent contains different pollutants that contaminate the country’s water bodies.

The agency has observed that the sewer system is mostly polluted with domestic and industrial effluent which has high levels of suspended solids, partially and totally dissolved solids which leave the system with low levels of oxygen and high levels of phosphates and nitrates.

EMA’s Water Quality Manager, Mrs Sylvia Yomisi said although new technologies would be appreciated, reality on the ground has to be taken into consideration.

“It is good to use modern technology, but it all depends on the costs and scale of the operations”, she said.

She said the processes used in monitoring water quality in the country include on-site and laboratory tests, including bio-monitoring, which assesses bio-diversity in the water.

For example, some live species thrive or die under certain conditions in water bodies, and some tests can be done on or off site.

Mrs Yomisi urged industries to choose the best inputs with less contaminants and try to treat effluent on site before releasing it into the main streams.

Dr Zivayi Chiguvare, a physicist and renewable energy specialist based in South Africa, said nanotechnology is the main theme of the future.

“It is important for the country to formulate a national nanotechnology policy and strive to implement it for us not to lag behind other countries”, he said.

 Nanotechnology has been practiced in the country for a long time through the use of activated carbon and other products without calling the practice by its present day name.

For instance activated carbon has been in use in the country for a long time especially in the purification of brown sugar to white sugar.

“So, if you add the activated carbon in dirty water it will take away the colour and the odour”, he said

Dr Chiguvare said there is need to establish plants which process activated carbon since the product is being imported.

“There is need to research on the kind of kiln which can be used to make the product as we have vast resources of timber wastes in Manicaland and also jatropha hasks which can be used as feedstock to manufacture this activated carbon”, he said

 Activated carbon is a natural material derived from bituminous coal, lignite, wood, coconut shell and other material, activated by steam and other means. 

Each carbon source has different adsorption properties.

 For example bituminous carbon has high chlorine reduction capacity.

Some manufacturers use various blends of carbon to achieve specific water quality and contaminants reduction. 

For example coconut shell carbon can be used to produce a sweet taste. 

Activated carbon surface properties are both hydrophobic and oleophilic; that is, they “hate” water but “love” oil. 

 When flow conditions are suitable, dissolved chemicals in water flowing over the carbon surface “stick” to the carbon in a thin film while the water passes on. 

According to the TWAS journal, South Africa has developed its nanotechnology strategy since the collapse of the Apartheid era in 1990.

The University of Western Cape, the University of Stellenbosch and North West University together with the South Africa’s Water Research Commission have engaged on research on water treatment with projects on developing nanofiltration membranes.

Professor Cloete Eugene, head of the Microbiology Department at the University of Pretoria in South Africa, in one of his articles published in Feb 2008 said the potential impact areas for nanotechnology are divided into three categories, namely, treatment and remediation, sensing and detection as well as pollution prevention.

“Within the category of treatment and remediation, nanotechnology has the potential to contribute to long term water quality  availability and viability of water resources such as through the use of advanced filtration materials that enable greater water reuse, recycling and desalination.

With sensing and detection, of particular interest is the development of new and enhanced sensors to detect biological and chemical contaminants at very low concentration levels in the environment, including water,” he said.

Although nanotechnology appears to be the technology of the future it has its own challenges.

Scientists say unless the membranes are well-maintained, algae and other life forms can colonize them.

Furthermore, in studies carried out in South Africa on water purified by reverse osmosis, it was observed that nearly all the dissolved mineral salts needed by the body are removed in the process.   

The water is void of any essential nutrients such as calcium, magnesium ions, and others, thereby placing the nutrient levels below that of the required World Health Organization standards. 

It is therefore necessary to add nutrients to bring solute levels to the standard levels required for drinking water.  

Recommendations for magnesium have been put at a minimum of 10 milligrams per litre (mg/L) with 20 to 30 mg/L optimum; for calcium 20 mg/L minimum and 40–80 mg/L optimum, and a total water hardness achieved by adding magnesium and calcium at 2 to 4 millimol per litre.

However The World Health Organisation notes that the body’s need for minerals is largely met through foods and not drinking water.   

Another setback in nanotechnology is that membranes are subject to fouling and have a limited life span, so there is need to replace them periodically.

Meanwhile  Professor Magadza urged city councils to put nanotechnology in their future plans as an alternative means of water purification. 

“In planning, municipalities should think of incorporating nanotechnology in their water purification but right now they should work on upgrading the water treatment plants.

Industries should also reduce the strain on city councils by pre-treating their effluent before disposing it into the main water channels to save costs on water treatment chemicals,” he emphasized.

Zimbabwe needs a strategic plan on nanotechnology, to augment its endevours to meet the Millennium Development Goals and to avert loss of life through water borne diseases such as cholera and dysentery.

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