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  • Writer's pictureK S Deepak

Cheap and frugal ways of removing impurities from water


The list of impurities for which inexpensive ways of removal is documented in this post are:-


Arsenic

It is one of the most common pollutants found in water. There are two types of arsenic found in water namely: AS (III) and AS (V). The AS (III) is difficult to be removed than AS(V) because of its charge. If found its way to human body, it can cause serious health issues like cancer and has been recognized as group 1 carcinogens by the International Agency for Research on Cancer (IARC). A maximum arsenic concentration of 10 µg/L in drinking water has recommended by World Health Organization (WHO) and a concentration of 50 parts per billion (ppb)/ µg/L is set by the Indian government.


Below are few processes which I believe are the cheapest and effective of all other ways for removal of arsenic from water.


Arsiron Nilogon


It is a technology developed by researches of Tezpur University to remove excess arsenic present in water.

  • Process- The whole process can be divided into 2 parts.


  • Chemical part- In arsiron nilogen unit there consists of 2 plastic drums kept one above the level of other. The topmost drum is the place where chemical action takes place. The chemical action is done by virtue of three chemicals namely baking soda, potassium permanganate and ferric chloride. These chemicals act as a pH-conditioner, oxidant and coagulant, respectively to facilitate the removal.

  • Physical part- After the chemical reaction, the water is allowed to sit for an hour after which it undergoes filtration using sand gravel present in the tank below.


The Bucket Treatment Unit (BTU)

The above mentioned process is a patented technology/ setup for removal of arsenic based on the oxidation-coagulation at optimized pH (OCOP) method.


The iron-impregnated bio-char

This method is currently in its research stages. In this method Bio-char which is basically char formed by pyrolysis of wood chips is used. The bio-char acts as an effective and cheap alternative of activated carbon. This adsorbent is then soaked in iron nanoparticles. This resulting product act as a filter to screen out arsenic from water. Since It’s in its initial stages the commerciality of the product is not yet clear. But, because this novel synthesis is convenient for large-scale production, the Fe-impregnated bio-chars developed in this work has great potential for use as a low-cost sorbent material to remove arsenic from water.


Coagulation with lime


The addition of quick lime, CaO, or hydrated lime, Ca(OH)2 removes arsenic from water. These chemicals act as a sorbing flocculent for arsenic. It s to be noted that excess of lime will not dissolve, and will remain as a coagulant aid, which has to be removed along with precipitates through sedimentation or filtration process. Also, it should be kept in mind that even though its an effective means of removal it has been observed that the efficiency is relatively low, usually between 40-70 %.


Solar oxidation and precipitation of Fe(III)-oxides with adsorbed As(V)


The process used in SORAS method is divided into two stages-

1. Photochemical oxidation - the UV light facilitates oxidation of As (III) to As(V). This helps in removal of arsenic as the AS(III) is difficult because of its charge.

2. Precipitation and Filtration - here the converted arsenic is precipitated after being adsorbed on Fe(III)-oxides.


The arsenic bio-sand filter



It is a regular bio-sand filter but with iron in the diffuser plate for arsenic removal. This slow purification process can remove up to 98% of bacteria, 100% of viruses, 99% of parasites, protozoa, amoebae, and worms, 95% of heavy metals, and with a slight modification, 93% of arsenic. The filter consists of three layers:

a. Under drain gravel,

b. Separation layer of small gravel

c. The filter bed

The iron nails and iron filings present in the BSF bind to the arsenic in the water. Ideally , the iron is coated with iron (III) oxide which adsorbs As (V) from the water and facilitate its removal. The average arsenic removal rate for a BSF with iron filings was 94%.


Fluoride

It is known to have toxic properties even in low dosages. The increase of fluoride to 3 mg/l, increases the risk of dental fluorosis, and its concentration to 6 mg/l leads to irritation of bone marrow and dysfunction of a central nervous system. WHO recommends that the concentration of fluoride in the water shouldn’t exceed 1 mg/l. Below are some of the cheapest processes available for its removal.


Defluoridation by plant biomass

It is probably the most cheapest and efficient way for removal of fluoride. In this method we add plant biomass to water to regulate its fluoride content. Following are names of few biomass that are commonly used:-

Tulsi/ Holy basil leaves


The leaves have to be dried and dipped in water for few hours. Tulsi is one of the best known plants with anti-oxidant properties. Researches done by Natural society has stated that addition of Tulsi leaves reduced fluoride found in the water by up to 1.1ppm. The efficiency of this process can be optimised by using these leaves in their powdered forms.

Tamarind fruits

Neem leaves

Coffee husk

Rice husk

Clove


Bone-char method

It is the charcoal formed by heating animal bones at particular temperature for a particular time and with controlled oxygen level. The bone char has efficiency of 60% even at neutral pH. The bone char act as a defluorant and screens out fluoride in water just by mixing both. It basically works on the principal of ion exchange method to remove fluoride from water. The resulting mixture after being kept for few minutes can be filtered to give water with acceptable amount of fluoride.


Nalgonda technique

It is a technique developed National environmental engineering research institute Nagpur. In this technique chemical like sodium aluminate, lime and bleaching power is added to the water. The process can be divided into following stages:-

1. Rapid mixing- in this stage the coagulant is rapidly mixed with water. It helps in formation of micro flocs and optimised used of the coagulant.

2. Flocculation- in this stage the destabilised colloids forms flocs.

3. Sedimentation- This is the pre-final stage where the flocculated particles are sedimented.

4. Filtration- in this stage the sediment flocs are separated out via porous media.


Micro-plastics

Plastics smaller and finer than 0.5 microns are termed as micro-plastics. Owing to their small size, micro-plastics are biologically available to a wide range of organisms. Ingestion has been documented in animals throughout the marine food web, including zooplankton. Plastics can act as a source of chemical contamination, containing plasticizers and additives incorporated into the plastic during manufacture. They may also be vectors for chemicals sorbed onto their surface from the marine environment.


Sediment-Micro-plastic Isolation (SMI) unit

The unit was constructed using PVC piping and ball valve, secured to a PVC plate of College of Life and Environmental Sciences: Bioscience. It is a compact, portable device that extracts micro-plastics from different sediment types in a single step, with reproducible results. The Solutions of sodium chloride (NaCl), sodium iodide (NaI) and zinc chloride (ZnCl2) were prepared by dissolving the salts to facilitate removal of micro-plastics by purging method. The advantages of manufacturing the SMI using PVC include resistance to corrosion, plus ease of construction, reduced costs, durability and weight. The SMI unit is simple in design and use, relatively cheap to produce, which allows for multiple units to be manufactured and used simultaneously ( R.L. Coppock, et.al,2017).


Adding sugar and yeast

It is another commonly used method for removal of micro-plastics but from beer and wine. In this process sugar and yeast are added to the solution. The sugar would act as a substrate which would help the yeast to grow. This culture then agglomerates the micro-plastics which can later be decanted and filtered for drinking purposes. Even though it’s a common practice, the efficiency and the credibility of this method is yet to be studied.


Munich Plastic Sediment Separator (MPSS)

This system uses density separation approach to facilitate removal of micro-plastics. It enables a reliable separation of micro-plastic particles. The MPSS is divided into three major compartments that are entirely made of stainless steel which are Sediment container, Standpipe and a Standpipe. The separation liquid is introduced into the sediment container through the inlet flange. This is where first separation of the buoyant plastic particles have from the sinking sediment takes place. After the sediment is allowed to settle down for 1–2 h, the dividing chamber is mounted on the sediment inlet flange and fresh separation fluid can be introduced using the bottom valve. This step elevates the fluid level and lifts the floating plastic particles through the open ball valve into the dividing chamber. All plastic particles are carried with the rising fluid which can be separated later on using the ball valve (imhof,et.al,2012).


Pesticides

Pesticide contamination of drinking water is very common, especially in agricultural areas because of the farming profession. Accidental or illegal spilling or dumping of pesticides can lead to contamination of drinking water, and even proper application of pesticides can lead to contamination of drinking water through leaching into groundwater or runoff into surface water bodies. They can cause health problems such as cancer, organ damage, reproductive effects, birth defects, or nervous system damage. Below are few processes that facilitate its removal.


Reverse osmosis

They are the most effective and cheapest way of removing pesticides from drinking water. In this method, the contaminated water is made to go through a porous medium. It is done n a direction opposite to normal flow direction. To facilitate this, the hydrostatic pressure is kept greater than the osmotic pressure. This flow of solution through the porous medium causes large molecules to get screened out whereas the smaller water molecules pass by the medium. But the disadvantage of using this system is that it is a slow process and since RO membrane removes dissolved solids that contribute to taste along with contaminants the treated water has a flat taste. It can remove 97-99% of all pesticides, insecticides and herbicides from drinking water.


Heavy metals

Effluents from large number of industries viz., electroplating, leather, tannery, textile, pigment & dyes, paint, wood processing, petroleum refining, photographic film production etc., contains significant amount of heavy metals in their wastewater. The heavy metals, if absorbed above the permissible levels, could lead to serious health disorders. The conventional methods for heavy metal removal from water includes chemical precipitation, chemical oxidation, ion exchange, membrane separation, reverse osmosis, electro dialysis etc. Below I have mentioned the cheapest way to remove heavy metals from water.


Bio-sand filters

A bio-sand filter is a water treatment system adapted from traditional slow fine sand filters. A 3-step bio-sand filtration with a layer of bio-film is generally constructed. At the top of the filter, fine sand column below the sand column, a layer of charcoal and below the charcoal column, a layer of gravel was placed. Each layer was separated by using plastic mesh that prevents sand particles entering into the charcoal column and charcoal particles into gravel layer. The bio-film layer is present below the standing water layer which is the man component of the filter. It is responsible for removal of pathogens and other contaminants from water. the processes applied include:

a. Mechanical trapping- Suspended solids and pathogens are physically trapped in the spaces between the sand grains.

b. Predation- Pathogens are consumed by other microorganisms in the bio-layer.

c. Adsorption- The suspended solids in the water and the sand grains become attached to each other.

d. Natural death- Pathogens finish their life cycle or die because of shortage of food or oxygen for them to survive.


Peat moss

It is abundant in nature and has a very high organic content. Its large surface area and high porosity makes it an effective agent for heavy metal removal from wastewater. It was observed that peat moss plays an important role in treatment of heavy metals such as Cu2+, Cd2+, Zn2+ and Ni2+ .The benefit of using this adsorbent in treatment is the easiness of the system, low cost, and the capability to acknowledge a wide variation of effluent composition.


Chitin

It is a long-chain polymer of a derivative of glucose. It is the main component of the cell walls of fungi, the exoskeletons of insects. It has been used for removal of several heavy metals in the past because of its chelating property. It has shown ability for the treatment of Hg2+, Cu2+, Ni2+, Zn2+, Cr6+, Cd2+ and Pb2+.

There is another prominent method for removal of heavy metals from water which is by the help of adsorbents. The problem with adsorbents is that some are costly and therefore, several other materials could be used as a low cost adsorbent like coffee husks, Areca waste, tea factory waste, sugar beet pulp, olive oil factory waste, battery industry waste, waste biogas residual slurry and grape stalk wastes. They have been utilized as low-cost adsorbents for the removal of toxic heavy metals from wastewater.


Dissolved solids and total dissolved solids

Total dissolved solids (TDS) refers to any compound left in the water after normal filtration and treatment. Total Dissolved Solids (TDS) is a measure of the combined content of all inorganic and organic substances contained in a liquid in molecular, ionized or micro-granular (colloidal sol) suspended form. Usually these are ions such as calcium, sodium, potassium and magnesium. There are several methods available for removal of TDS and colour from Textile effluent such as, ion exchange, coagulation and flocculation, biological decolourization, adsorption etc.


Addition of lime and soda ash

The addition of these substances into water precipitates the carbonates, bi-carbonates and sulphates of calcium and magnesium which are responsible for the hardness of the water. Thus providing water with low TDS. The method used is referred to as Clark’s method.


Bark and peel of plantain plant (banana)

The traditional view of many plants is that they are invasive weeds that require strict control. However, the increased pollution in the world's rivers and lakes has led to the discovery of plants that can be used as a tool for extracting unwanted solids from water. The banana plant is the largest herbaceous flowering plant. It should be noted that, banana peel and banana plant bark was considered as adsorbent. It removes pollutants by directly assimilating them into their tissue, and by providing a suitable environment for microorganisms to transform pollutants and reduce their concentrations.


Water hyacinth

It is commonly used for wastewater treatment in tropical and subtropical climates. Because it floats on the water's surface, it is not rooted and it is easy to harvest. It is found that it has ability to remove large amounts of nitrogen and phosphorus from water. Its roots also can absorb sulphur, calcium, magnesium, potassium, iron, zinc and manganese.


Herbal mixture of Neem leaves, Vettiver root, Tulsi leaves and Lemon peel

Neem leaves, Vettiver root, Tulsi leaves and Lemon peel are used to reduce the TDS of the domestic waste water. Most of the plant materials are available throughout the year at low or no cost. To remove TDS a mixture of all these herbs are made in a powdered form. Then the water to be treated is mixed with this mixture. The reduction of TDS by using herbal plant parts are effective and can be implemented in the field of water purification systems. The herbal mixture is used in reducing the dissolved solids effectively in the waste water. Time is also an important factor in removal of TDS. The increase in helps in removing excess dissolved solids from the waste water.


Soluble dyes

Dyes are colored compounds which are widely used in textiles, printing, rubber and leather industries to color their products results in generating a large amount of colored wastewater. Mainly dyes are classified into anionic, cationic, and non-ionic dyes. water effluents from dyeing industries contain synthetic dyes which cause a potential hazard to the environment hence these dyes need to remove from the water bodies. Dye removal techniques are classified into Chemical, Physical, and Biological methods.


Dye removal by adsorption

Adsorption is used as the best treatment procedures for the removal of dissolved pollutants like dyes from waste water. Adsorption is defined as concentration of materials on the surface of solid bodies. While searching for cheap and existed low cost adsorbents that could be used for the removal of dyes from waste water. Adsorbents prepared from waste resources used include the following:-

1. Rice husk- Activated rice husk can be used as a cheap adsorbent for dye removal.

2. Sawdust and Wood-shaving bottom ash- They can be used for the separation of azo reactive and red reactive dyes from water. These adsorbents are made by treating Wood-shaving bottom ash with H2SO4 and water, which increase the adsorption capacity.

3. Coconut shell

4. Chitosan- It is a biodegradable cationic amino polysaccharide derived from chitin. It can be used as a cheap alternative for adsorbents.

5. Red mud- is another industrial by-product. It can play an important role as an adsorbent for the removal of methylene blue, basic dye, and from waste water.

6. Fertilizer wastes

7. Clays- They are cheaply available and clay mineral works as effective adsorbents because of their layered structure. They Due to these properties are known as hosting materials for adsorbents and counter ions.

8. Fly ash- It is a residue that results from the combustion of coal in thermal power plants. The major components of fly ash are alumina, silica, iron oxide, calcium oxide, magnesium oxide and residual carbon.

9. Sugar industry wastes- Bagasse pith is a waste product produced from sugar refining industry. It is the name given to the residual cane pulp remaining after sugar has been extracted.

10. Blast furnace slag

11. Seaweed and algae

12. Peat moss

13. Scrap tyres

14. Fruit wastes- orange peel, banana peel etc.

15. Agricultural waste- Coir pith, rice husk, straw, date pit, oil palm trunk fibre, leaf powder ,almond ,pommel peels, peanut hull, water melon peels etc.

The fruit and agricultural waste material have abundant availability. They are usually discarded after eating. These materials not only create sanitation problems and causes odour to environment if discarded simply in environment. Thus, they can be very valuable if used for some useful purpose, i.e., adsorption, before discarding.

Various researches are going on to find new and cheaper options of adsorbents that could absorb the soluble dyes in water. The removal of these components are important because if taken inside can cause serious health issues like gastrointestinal diseases.


Improvised Bio-sand filters

In this method we first add a mixture of sodium carbonate and sodium hydroxide (NaOH) to the wastewater which has been collected in a tank. To this magnesium sulphate (MgSO4) is added after about six to eight hours. The tank is then left undisturbed to allow chemical reaction for 24 hours. After that, suspended particles and colloids float on the surface in the form of floc, which can be removed. The solution is then transferred to another tank. Then, sulphuric acid is added to balance its pH level and finally the solution is passed through a bio-sand filter where the remaining impurities get attached to sand grains.


Gases (especially methane)

Several dissolved gases like oxygen, carbon dioxide, methane and hydrogen sulphide concern the water treatment industry. Methane is a colourless, odourless, tasteless, and combustible gas. Methane may occur in a water well due to natural conditions or it may enter a well due to human activities including coal mining, gas well drilling, pipeline leaks and from landfills. Methane can be flammable and explosive when mixed with air, and it can displace oxygen if released into a confined space, resulting in asphyxiation.


Well vents

Since methane is lighter than air, any gas entering the water well will quickly rise and accumulate at the top of the well under the well cap. Adding a vent tube to the water well cap can release the methane trapped in the water well and ultimately, lowering the concentration of dissolved methane in the water.


Gas shroud

A gas shroud is a pipe or tube which is inserted over a submersible pump. It is kept open above the pump and sealed at the bottom to the pump. Methane or other gas problems can sometimes be reduced or eliminated in a well by installing a gas shroud. These gases rise through the water column in the well, leaving methane-reduced water in the shroud.


Microbes

Removing or inactivating bacteria in the water we drink is essential to protect the health of any person drinking the water. It can be done in a variety of ways, depending on the water source, level of bacteria and inorganic matter, and resources available.

Viruses are difficult to eliminate in drinking water using current methods because they are far smaller than bacteria, highly mobile, and resistant to chlorination, which is the main disinfection method used all over the globe.


Elemental or zero-valent iron (Fe) in filtration

The elemental or “zero-valent” iron (Fe) used in the technology is widely available as a by-product of iron and steel production and hence is inexpensive. Researchers of University of Delaware have developed this inexpensive and non-chlorine based technology that can remove harmful microorganisms, including viruses, from drinking water. By using elemental iron in the filtration process, they were able to remove viral agents from drinking water at very high efficiencies.


Bio-sand filters

The main feature of the filter is the biological zone or the bio-film which naturally forms on the sand surface. This layer consumes harmful bacteria and pathogens. As the water passes through the sand layer these contaminants gets adsorbed to the particles of sand. Then, in the lower layers of the filter oxygen levels diminish and the organisms die a natural death.


The Drinkable Book

It is a patented technology developed by Dankovich, a phD student. It is an inexpensive, simple and easily transportable nanotechnology-based method to purify drinking water has just been developed. She had added nanoparticles which have disinfectant properties to paper. One just have to use this paper as a filter. Each page can be removed from the book and slid into a special holding device in which water is poured through and filtered .The researcher has claimed that a page can clean up to 100 litres of drinking water. This means, that a book can filter one person's water needs for four years.


Chlorination

It is the most widely used method for disinfecting water supplies in the world. The near universal adoption of this method can be attributed to its convenience and to its highly satisfactory performance as a disinfectant, which has been established by decades of use. When chlorine is added to water two species are formed: hypochlorous acid, which is electrically neutral, and hypo-chlorite ion, which is electrically negative. Optimum inactivation occurs when the disinfectant is distributed uniformly throughout the water. To disperse the chemical disinfectant when it is added to the water, it must be mixed effectively to assure that all of the water, however small the volume, receives its proportionate share of the chemical.


Regulate pH

Water, in general has a neutral pH i.e. 7.0, which means it's neither alkaline nor acidic. The pH level of water is largely affected by the source and the type of minerals found locally in rock. Pollution and acid rain can also affect tap water pH.Following are the cheapest ways to regulate Ph of water. Also, it is important to know whether water is alkaline or acidic so to have better regulating options.


Addition of soda ash

Soda ash, also known as sodium carbonate, raises the pH levels of overly acidic water when added to a water system.


Addition of acetic acid

Acetic acid found in vinegar, citric acid or alum, can be used to bring the pH value closer to 7of alkaline water. That’s why, it is first important to know the pH of the water before neutralising it.


Addition of Fresh lemons

A fresh lemon added to the drinking water will eventually, make the water more alkaline. It is because adding an acidic lemon to the drinking water could ultimately produce an alkaline result, it's important to remember that fresh lemons are also anionic. It is important to note that one must use fresh lemons that haven't been exposed to air for more than 30 minutes and not any lemon juice purchased at the store or lemons that have been cut up and sitting out in the open all day.


Suggested reads

For arsenic

For fluoride

For micro-plastics

For Pesticides

For Heavy minerals

For TDS

For Dye removal

For gases

For microbes

For pH

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