Water Filters and the History of Water Treatment
Water Treatment Through Water Filters
Human interest in the quality of drinking water dates back more than five thousand years. Due to the limited knowledge in those eras about diseases and their causes, attention was confined only to the color, taste, and odor of water. For this purpose, some treatment processes were used, albeit in a limited way during separate historical periods, such as boiling, filtration, sedimentation, and the addition of some salts. Then the eighteenth and nineteenth centuries AD witnessed many serious attempts in European countries and Russia to advance water treatment technology, where stations for treating water at the city level were established for the first time in history. The concept of water filters was not known yet.
In 1807, a water treatment plant was established in the Scottish city of Glasgow. This plant is considered one of the earliest in the world, and it marked the beginning of the idea of water filters. Water was treated there by filtration and then transported to consumers through a special pipe network. Although these contributions were considered a technical development during that period, the focus at that time was on aspects of color, taste, and odor, or what is called palatability. Sand filter treatment was the dominant feature in these plants until the beginning of the twentieth century. With the comprehensive development of science and technology since the beginning of this century and the discovery of the relationship between drinking water and some prevalent diseases, there was a rapid development in the field of treatment techniques. Many processes were added that generally aim to bring water to a high degree of purity, making it free of turbidity, colorless, tasteless, odorless, and safe from chemical and biological aspects. Table (1) shows the chemical specifications for drinking water.
Water Treatment Through Water Filters
The cholera epidemic was one of the earliest diseases discovered to be closely linked to the contamination of drinking water in the pre-development stage of water treatment techniques or even water filters. For example, about 17,000 residents of the German city of Hamburg were infected with this epidemic during the summer of 1829, resulting in the death of at least half that number. It was proven beyond doubt that the main source of the epidemic was the contamination of the city’s water source. Chlorine disinfection was one of the earliest processes used for water treatment after filtration to eliminate some microorganisms such as bacteria and viruses, leading to the reduction of the spread of many waterborne diseases such as cholera and typhoid fever. Treatment includes processes used to remove water hardness, such as softening processes, or to remove turbidity, such as coagulation processes.
Due to the industrial and technological progress witnessed in this era and the subsequent rapid increase in the consumption rates of natural, relatively pure water, without even water filters at that time, and due to the pollution of some of these sources as a result of industrial waste, sewage, and other environmental accidents, treatment processes have begun to take a new direction that differs in many applications from the path of traditional treatment. In this article, we will briefly review the traditional methods of drinking water treatment, in addition to some current and future trends in treatment technologies using water filters.
Traditional Treatment Methods
Drinking water treatment processes differ according to the sources of these waters and their quality, as well as the specifications set for them. It should be noted that the continuous change in water specifications also often leads to a change in treatment processes. Specifications are constantly updated as a result of the continuous change in the maximum concentration of some water contents and the addition of new contents to the list of specifications, whether through water filters or other methods. This comes as a result of several factors such as:
– Development in water analysis techniques and treatment technologies.
– Discovery of new contaminants that were not present in traditional waters or were present but their presence or the extent of their danger was not noticed before.
– Discovery of some problems caused by some contents originally present in the water or resulting from some traditional treatment processes. This, and traditional treatment processes used for water can be addressed based on their surface and groundwater sources, focusing on groundwater due to the kingdom’s reliance on it compared to surface water.
Surface Water Treatment:
Surface waters (flowing waters on the surface) contain a small proportion of salts compared to groundwater, which contains high proportions of them, and they are therefore soft waters (non-hard). In general, the treatment processes aim to remove suspended solids that cause high turbidity and changes in color and odor. Therefore, it can be said that most methods of treating this type of water were limited to sedimentation, filtration, and disinfection processes. Suspended solids consist of organic and clay materials and contain some microorganisms such as algae and bacteria. Due to the small size of these components and their large surface area compared to their weight, they remain suspended in the water and do not settle. In addition, their surface and chemical properties make them resistant to natural sedimentation. Coagulation processes using coagulants are the main method for treating surface waters, where some chemicals are used to disrupt the balance of suspended solids and create suitable conditions for their sedimentation and removal from settling basins. The sedimentation process is followed by a filtration process using sand filters to remove any remaining sediments and microorganisms. Well-known coagulants include aluminum sulfate and ferric chloride, and there are some auxiliary coagulants such as some organic polymers, bentonite, and activated silica. Activated carbon can also be used to remove many organic compounds that cause changes in the taste and odor of water. The sedimentation and filtration processes are followed by the disinfection process before sending the water to the consumer.
Groundwater Treatment:
Well waters are considered one of the purest natural water sources that many people around the world rely on. However, some well waters, especially deep ones, may require advanced and costly treatment processes that go beyond the scope of traditional treatment. In addition to the chlorine addition for water disinfection and then pumping it into the distribution network, the disinfection process is the only treatment for some very pure well waters that meet all water specifications. However, this type of water is the least available at present. Therefore, in addition to the disinfection process, most groundwater needs physical and chemical treatment, either to remove some dissolved gases such as carbon dioxide and hydrogen sulfide, or to remove some minerals such as iron, manganese, and minerals that cause water hardness. Dissolved gases are removed using the aeration process, which also removes part of the iron and manganese through oxidation. The purpose of aeration may be just cooling, as is the case with some deep well waters that have high temperatures, necessitating cooling to maintain the efficiency of other treatment processes. The removal of iron and manganese minerals is efficiently achieved in chemical oxidation processes using chlorine or potassium permanganate.
The general nature of groundwater treatment is the removal of hardness by precipitation. Water hardness is mainly composed of dissolved calcium and magnesium compounds in water. The concern with water hardness stems from its negative impact on the effectiveness of soap and other cleaning agents, in addition to the formation of some deposits in boilers and water pipes. The sequence of operations in a conventional plant treating groundwater containing high levels of water hardness is illustrated.
The Kingdom relies heavily on groundwater for various purposes, which has contributed to the proliferation of groundwater treatment plants in its various regions. The following is a brief overview of the different processes for groundwater in this type of plant.
A- Softening (Hardness Removal) by Precipitation
The water softening process involves removing calcium and magnesium compounds that cause hardness through chemical precipitation. This process is carried out in water plants by adding slaked lime (calcium hydroxide) to the water in limited quantities, where certain chemical reactions occur, forming precipitates of calcium carbonate and magnesium hydroxide. In many cases, it may be necessary to add soda ash (sodium carbonate) along with lime to deal with some forms of hardness. The softening process includes a relatively small basin where chemicals are added and mixed rapidly with the incoming water for uniform distribution. The water is then transferred to a larger basin to allow sufficient time for completing the chemical reactions and precipitate formation, where the water is mixed slowly, just enough to agglomerate and condition the precipitate particles for sedimentation in the next stage.
B- Sedimentation
The process of water softening involves removing calcium and magnesium compounds that cause hardness through chemical precipitation. This process is carried out at water treatment plants by adding limited amounts of slaked lime (calcium hydroxide) to the water, where certain chemical reactions occur forming precipitates of calcium carbonate and magnesium hydroxide. Often, soda ash (sodium carbonate) is added along with lime to deal with some forms of hardness. The softening process includes a relatively small basin where the chemical additives are mixed rapidly with the incoming water for uniform distribution, then the water is transferred to a larger basin and allowed sufficient time for the chemical reactions to complete and precipitates to form, with gentle agitation just enough to agglomerate and condition the precipitate particles for settling in the next stage.
C- Sedimentation
Sedimentation is one of the earliest processes used by humans for water treatment. It is used to remove suspended and settleable solids or to remove precipitates resulting from chemical treatment processes like softening and coagulation. Simple sedimentation basins rely on gravity, where solids settle under their weight.
Sedimentation basins are usually circular or rectangular concrete basins with inlet and outlet for water flow, designed to remove the maximum possible amount of solids, taking into account the hydraulic characteristics of water flow inside the basin. A key feature is a sludge collection and removal system at the basin floor, from where settled sludge is pumped out. The figure shows a section of a circular sedimentation basin. Chemical addition, slow mixing and sedimentation can be combined in a single unit called the up flow solids contact clarifier.
D- Stabilization (Re-carbonation):
Since the water exiting the softening process is usually supersaturated with calcium carbonate precipitates, and some of these precipitates remain suspended after sedimentation basins, potentially depositing in filters or distribution pipes causing clogging or reduced efficiency, re-carbonation is performed to stabilize the water. A common stabilization method is adding controlled amounts of carbon dioxide to convert the remaining calcium carbonate to the soluble bicarbonate form.
E- Filtration:
This is the process of removing suspended solids (turbidity) by passing the water through a porous medium like sand. It occurs naturally when river water percolates through soil strata, which is why groundwater has very little or no turbidity compared to surface waters. Filtration is also used to remove residual precipitates after sedimentation in chemical treatment.
Removing suspended solids from drinking water is essential for public health protection and to prevent operational issues in distribution systems. The solids can shield microorganisms from disinfectants, react with disinfectants reducing their effectiveness, deposit in pipes causing bacterial growth, taste, odor and color issues.
The filter consists of three main components: the filter box, under-drains, and filter media. The filter box is the concrete structure containing the filter media and under-drains. The under-drains are a system of pipes and channels to collect filtered water and distribute backwash water during filter cleaning. The filter media is typically a layer of silica sand, sometimes crushed coal or garnet sand is used. As water passes through the media, suspended particles get trapped on the surface of the media grains. With time, the voids in the media get clogged, reducing filter efficiency, at which point backwashing is performed by reversing the flow and using high pressures to expand and agitate the media to dislodge trapped solids which get carried away in the waste backwash water.
F- Disinfection:
This process aims to kill pathogenic microorganisms using heat (thermal treatment), ultraviolet radiation, or chemicals like bromine, iodine, ozone or chlorine at concentrations safe for humans and animals. Boiling was one of the earliest disinfection methods, still suitable for small emergency water quantities but impractical for large-scale treatment due to cost. While UV radiation, bromine and iodine are costly, ozone and chlorine became widely used for disinfecting drinking water, with ozone favored in Europe and chlorine in America initially. However, due to potential health effects of chlorination byproducts, many US plants have shifted to ozone despite its chemical instability and higher cost.
Chlorine reacts with water forming hypochlorous acid and hypochlorite ions, some of which further react with ammonia present to form chloramines (combined residual chlorine), while the remaining hypochlorous acid and hypochlorite ions constitute the free residual chlorine. These compounds provide the disinfecting action, so plants typically add enough chlorine to maintain a free chlorine residual through the distribution system to continuously disinfect against potential contamination.
G- Residuals Treatment:
The main residuals from water treatment are the sludge from sedimentation basins and backwash water from filter cleaning, which require treatment before disposal to protect the environment. Backwash water is typically sent to a thickening basin where a polymer is added to aid settling of suspended solids, with the clarified water recycled back to the plant inlet. The thickened sludge then undergoes dewatering using mechanical methods like centrifugation or filter presses, producing a solid cake that can be disposed of in drying beds or landfills. Some chemical recovery from the residuals is also possible.
New Challenges
Recent years have seen major shifts in treatment technologies, often driven by severe water scarcity in many countries or source water contamination issues in industrialized nations. This has led to exploiting new non-conventional sources like seawater and brackish groundwater desalination using energy-intensive processes like multi-stage flash distillation and reverse osmosis, in addition to other advanced treatment processes to remove emerging contaminants.
Naturally occurring radioactive elements like uranium, radium and radon in some sources are another challenge, prompting research into their removal using adsorption processes with activated carbon or silica, and reverse osmosis membranes.
There has also been a drive to find alternatives to chlorine disinfection due to its potential to react with organic matter forming disinfection byproducts with suspected health impacts, though recent findings indicate that alternatives like ozone, chloramines and chlorine dioxide may also produce their own byproduct issues.
Biological treatment using microorganisms, long applied to wastewater, is gaining interest for drinking water treatment due to its potential for removing organic compounds, micro-pollutants, nitrates, iron and manganese, though current applications are still largely experimental.
Overall, implementation of advanced treatment technologies may necessitate major upgrades to conventional plants and new design approaches, significantly increasing treatment costs, which could be mitigated through water conservation and pollution prevention programs.
The sedimentation process is one of the earliest processes used by humans in water treatment. This process is used to remove suspended and settleable solids or to remove precipitates resulting from chemical treatment processes such as softening and coagulation. Sedimentation basins rely on the action of gravity, where precipitates are removed under the influence of their weight.
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