1 Introduction of a drinking water treatment plant

Article Index

1.1. What is a Drinking Water Treatment Plant?

Drinking water treatment plants are used to remove particles and organisms that lead to diseases and protect the public’s welfare and supply pure drinkable water to the environment, people and living organisms. In addition, they also provide drinking water that is pleasant to the senses: taste, sight and smell and provide safe, reliable drinking water to the communities they serve.

Water treatment, as a word originally means the act or process of making water more potable or useful, as by purifying, clarifying, softening or deodorizing it.

To provide drinking water to the public is one of the most important tasks of communities and the design of water supply systems has to follow the rules of engineering sciences and also needs technical knowledge and practical experience. Water is treated differently in different communities depending on the quality of the water which enters the plant. For example; groundwater requires less treatment than water from lakes, rivers and streams. In order to analyse all these technical aspects in the drinking water treatment systems and for the supplement of a training guide on drinking water treatment plants, PURE-H2O project received a European Grant from the Turkish Agency and formed a competent partnership as follows for the realization of the project and a thorough introduction of a drinking water treatment plant system to the engineers and technicians:

ORKON INTERNATIONAL ENGINEERING TRAINING CONSULTING INC., ANKARA TURKEY (PROMOTER)

GAZI UNIVERSITY, ANKARA, TURKEY

NIGDE UNIVERSITY, NIGDE, TURKEY

PLANART, ANKARA, TURKEY

RESEARCH and DEVELOPMENT CENTER "BIOINTECH" Ltd. (BIOINTECH), SOFIA, BULGARIA

OPEN UNIVERSITY OF THE NETHERLANDS, HEERLEN, NETHERLANDS

Снимка 1: Пречиствателни станции за питейни води

Photograph 1.1. Views from Drinking Water Treatment Plants

783 million people do not have access to clean and safe water,
1 in 9 people worldwide do not have access to safe and clean drinking water.
Diarrhea caused by inadequate drinking water, sanitation, and hand hygiene kills an estimated 842,000 people every year globally, or approximately 2,300 people per day.
In developing countries, as much as 80% of illnesses are linked to poor water and sanitation conditions.
Half of the world's hospital beds are filled with people suffering from a water-related diseases.
Nearly 1 out of every 5 deaths under the age of 5 worldwide is due to a water-related diseases.
Over half of the developing world's primary schools don't have access to water and sanitation facilities.
84% of the people who don't have access to improved water, live in rural areas, where they live principally through subsistence agriculture.
Globally we use 70% of our water sources for agriculture and irrigation, and only 10% on domestic uses.
The water crisis is the #1 global risk based on impact to society (as a measure of devastation), and the #8 global risk based on likelihood (likelihood of occurring within 10 years) as announced by the World Economic Forum, January 2015.

Снимка 2. Световната карта, показваща недостига на вода

Figure 1.1. World Map showing the water scarcity Source: http://thewaterproject.org and http://water.org

Снимка 3 Графично представяне на пречиствателна станция за питейни води

Figure 1.2. Graphical representation of a drinking water treatment plant Graphic source: www.waterandhealth.org

In brief, we can define the stages of the drinking water treatment plant as follows:

Coagulation: removes dirt and other particles suspended in water. Alum and other chemicals are added to water to form tiny sticky particles called “floc” which attract the dirt particles. The combined weight of the dirt and the alum (floc) become heavy enough to sink to the bottom during sedimentation.

Sedimentation : The heavy particles (floc) settle to the bottom and the clear water moves to filtration.

Filtration : The water passes through filters, some made of layers of sand, gravel and charcoal that help remove even smaller particles.

Disinfection : A small amount of chlorine is added or some other disinfection method is used to kill any bacteria or microorganisms that may be in the water.

Storage : Water is placed in a closed tank or reservoir for disinfection to take place. The water then flows through pipes to homes and businesses in the community.

Plan view of the drinking water treatment plant in Aydın city of Turkey approved by the Republic of Turkey, General Directorate of State Hydraulic Works

Figure 1.3. Plan view of the drinking water treatment plant in Aydın city of Turkey approved by the Republic of Turkey, General Directorate of State Hydraulic Works

1.2. The Need for Drinking Water Treatment Plants

Substances that are removed during drinking water treatment process include suspended solids, bacteria, algae, viruses, fungi, minerals such as iron, manganese and sulfur, and other chemical pollutants such as fertilizers. Measures are taken to ensure that not only the water quality during the treatment process, but during its conveyance and distribution after the treatment as well. It is therefore common practice to have residual disinfectants in the treated water in order to kill any bacteriological contamination during distribution.

Table 1.1. Some common water contaminants found in the water treatment plant and treatment option:

Contaminant	Treatment Options
Arsenic	Co-precipitation/Adsorption
Copper	Corrosion Control
Iron	Oxidation/Filtration
Lead	Corrosion Control
Nitrate	Ion Exchange/Reverse Osmosis
Manganese	Oxidation/Filtration/Adsorption
Turbidity	Filtration

The treatment of water to make it potable is a multi-tiered process that often includes chemical, physical and biological methods.

The chemical processes include oxidation, coagulation and disinfection. The physical processes consist of flocculation, sedimentation, filtration, adsorption and disinfection with the use of ultraviolet light. The biological activated carbon (BAC) and sand filtration comprise of the biological processes.

The types of treatment depend on the source and size of the water system. For example, if the water source is from the surface, it is more exposed to direct wet weather runoff and to the atmosphere, therefore, these sources (such as lakes, rivers, reservoirs, etc.) are more easily contaminated and will require additional treatment in order to make the water more potable. Whereas ground water sources are more likely to require minimal treatment as it is not as exposed to the elements and goes through the natural sedimentation process of purifying the water through the soil.

A combination of the following processes is just some of the processes used for municipal drinking water treatment worldwide:

There is no single solution/process regarding the purifying of water, especially when water is derived from different sources. In addition, treatability studies must be carried out during different seasons in order to arrive at the most suitable processes.

Technologies for potable water treatment are well developed, and generalized designs are available that are used by many water utilities (public or private). In addition, a number of private companies provide patented technological solutions. Automation of water and waste-water treatment is common in the developed world. Capital costs, operating costs available quality monitoring technologies, locally available skills typically dictate the level of automation adopted.

High quality, safe and sufficient drinking water is essential for our daily life, for drinking and food preparation. We also use it for many other purposes, such as washing, cleaning, hygiene or watering our plants.

The European Union has a long history of drinking water policy. This policy ensures that water intended for human consumption can be consumed safely on a life-long basis, and this represents a high level of health protection. The main pillars of the policy are to:

Ensure that drinking water quality is controlled through standards based on the latest scientific evidence;
Secure an efficient and effective monitoring, assessment and enforcement of drinking water quality;
Provide the consumers with adequate, timely and appropriately information;
Contribute to the broader EU water and health policy.

1.3. Evolution of Water Treatment Technology

In ancient Greek and India writings dating back to 2000 BC, water treatment methods were recommended. People back than knew that heating water might purify it, and they were also educated in sand and gravel filtration, boiling, and straining. The major motive for water purification was better tasting drinking water, because people could not yet distinguish between foul and clean water. Turbidity was the main driving force between the earliest water treatments. Not much was known about micro organisms, or chemical contaminants.

After 1500 BC, the Egyptians first discovered the principle of coagulation. They applied the chemical alum for suspended particle settlement. After 500 BC, Hippocrates discovered the healing powers of water. In 300-200 BC, Rome built its first aqueducts. Archimedes invented his water screw. During the Middle Ages (500-1500 AD), water supply was no longer as sophisticated as before. These centuries where also known as the Dark Ages, because of a lack of scientific innovations and experiments. Then, in 1627 the water treatment history continued as Sir Francis Bacon started experimenting with seawater desalination. He attempted to remove salt particles by means of an unsophisticated form of sand filtration.

In 1676, Van Leeuwenhoek first observed water micro organisms by the invention of the microscope by Antonie van Leeuwenhoek in the 1670s. In the 1700s the first water filters for domestic application were applied. In 1804 the first actual municipal water treatment plant designed by Robert Thom, was built in Scotland. In 1854 it was discovered that a cholera epidemic spread through water. British scientist John Snow found that the direct cause of the outbreak was water pump contamination by sewage water. He applied chlorine to purify the water, and this paved the way for water disinfection. Since the water in the pump had tasted and smelled normal, the conclusion was finally drawn that good taste and smell alone do not guarantee safe drinking water. This discovery led to governments starting to install municipal water filters (sand filters and chlorination), and hence the first government regulation of public water.

In the 1890s America started building large sand filters to protect public health. These turned out to be a success. Instead of slow sand filtration, rapid sand filtration was now applied. Filter capacity was improved by cleaning it with powerful jet steam. Subsequently, Dr. Fuller found that rapid sand filtration worked much better when it was preceded by coagulation and sedimentation techniques. Meanwhile, such waterborne illnesses as cholera and typhoid became less and less common as water chlorination won terrain throughout the world.

But the victory obtained by the invention of chlorination did not last long. After some time the negative effects of this element were discovered. Chlorine vaporizes much faster than water, and it was linked to the aggravation and cause of respiratory disease. Water experts started looking for alternative water disinfectants. In 1902 calcium hypo chlorite and ferric chloride were mixed in a drinking water supply in Belgium, resulting in both coagulation and disinfection. In 1906 ozone was first applied as a disinfectant in France. Additionally, people started installing home water filters and shower filters to prevent negative effects of chlorine in water.

In 1903 water softening was invented as a technique for water desalination. Eventually, starting 1914 drinking water standards were implemented for drinking water supplies in public traffic, based on coliform growth. It would take until the 1940s before drinking water standards applied to municipal drinking water. In 1972, the Clean Water Act was passed in the United States. In 1974 the Safe Drinking Water Act (SDWA) was formulated. The general principle in the developed world now was that every person had the right to safe drinking water.

Starting in 1970, public health concerns shifted from waterborne illnesses caused by disease-causing micro organisms, to anthropogenic water pollution such as pesticide residues and industrial sludge and organic chemicals. Regulation now focused on industrial waste and industrial water contamination, and water treatment plants were adapted. Techniques such as aeration, flocculation, and active carbon adsorption were applied. In the 1980s, membrane development for reverse osmosis was added to the list. Risk assessments were enabled after 1990.

Water treatment experimentation today mainly focuses on disinfection by-products. An example is trihalomethane (THM) formation from chlorine disinfection. These organics were linked to cancer. Lead also became a concern after it was discovered to corrode from water pipes. The high pH level of disinfected water enabled corrosion. Today, other materials have replaced many lead water pipes.

1.4. European Directives and Legislations

1.4.1. The Directive Overview

The Drinking Water Directive (Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for human consumption) concerns the quality of water intended for human consumption. Its objective is to protect human health from adverse effects of any contamination of water intended for human consumption by ensuring that it is wholesome and clean.

The Drinking Water Directive applies to:

All distribution systems serving more than 50 people or supplying more than 10 cubic meter per day, but also distribution systems serving less than 50 people/supplying less than 10 cubic meter per day if the water is supplied as a part of an economic activity;

drinking water from tankers;
drinking water in bottles or containers;
water used in the food-processing industry, unless the competent national authorities are satisfied that the quality of the water cannot affect the wholesomeness of the foodstuff in its finished form.

The Drinking Water Directive doesn't apply to:

Natural mineral waters recognised as such by the competent national authorities, in accordance with Council Directive 80/777/EEC of 15 July 1980 on the approximation of the laws of the Member States relating to the exploitation and marketing of natural mineral waters and repealed by Directive 2009/54/EC of 18 June 2009 on the exploitation and marketing of natural mineral waters.

Waters which are medicinal products within the meaning of Council Directive 65/65/EEC of 26 January 1965 on the approximation of provisions laid down by law, regulation or administrative action relating to medicinal products and repealed by Directive 2001/83/EC on the Community code relating to medicinal products for human use.

The Directive laid down the essential quality standards at EU level. A total of 48 microbiological, chemical and indicator parameters must be monitored and tested regularly. In general, World Health Organization's guidelines for drinking water and the opinion of the Commission's Scientific Advisory Committee are used as the scientific basis for the quality standards in the drinking water.

When translating the Drinking Water Directive into their own national legislation, Member States of the European Union can include additional requirements e.g. regulate additional substances that are relevant within their territory or set higher standards. Member States are not allowed, nevertheless, to set lower standards as the level of protection of human health should be the same within the whole European Union.

Member States may, for a limited time depart from chemical quality standards specified in the Directive. This process is called "derogation". Derogations can be granted, provided it does not constitute a potential danger to human health and provided that the supply of water intended for human consumption in the area concerned cannot be maintained by any other reasonable means.

The Directive also requires providing regular information to consumers. In addition, drinking water quality has to be reported to the European Commission every three years. The scope of reporting is set out in the Directive. The Commission assesses the results of water quality monitoring against the standards in the Drinking Water Directive and after each reporting cycle produces a synthesis report, which summarizes the quality of drinking water and its improvement at a European level.

Photograph 1.2. Chlorinisation and pompage units in a drinking water treatment plant

1.4.2. Water Supply

Drinking water supply in the EU is organised by supply zones, i.e. geographically defined areas within which water intended for human consumption comes from one or more sources and within which water quality may be considered as being approximately uniform. The Directive makes a distinction between large and small supplies. Minimum water quality requirements are equal for both large and small supplies. However, monitoring requirements differ and Member States do not need to report on the small supplies. About 65 million people are served by small water suppliers. Sources of Raw Water In the EU, water supply is mainly fed by groundwater and by surface water, including artificial reservoirs. Water sources vary considerably between Member States. Overviews have been provided in earlier reports, and are collected by Eurostat. There are significant differences in the percentage between large and small supplies with much higher rates of groundwater sources for small supplies (84%). Groundwater contamination, in particular by substances difficult to detect like pesticides, and surface water contamination, increasingly influenced by climate change (floods, extreme rainfalls, rain overflow) can pose problems that are passed onto drinking water. A coordinated monitoring of groundwater and drinking water, along with putting in place climate change adaptation and mitigation measures would be beneficial for safe drinking water.

Photograph 1.3. A view from a water supply dam

1.4.3. Drinking Water Quality

In order to ensure that drinking water is safe for human consumption, the Drinking Water Directive sets out minimum water quality requirements. It identifies microbiological and chemical parameters that could pose a risk to human health when concentrations exceed certain thresholds. For each of the parameters, the Directive sets maximum concentration values that must be complied with. In addition to the microbiological and chemical parameters, the Directive identifies indicator parameters for the purpose of indicating a possible risk for human health and which requires remedial action only if further investigation confirms the human health risk. Reported data on these parameters show that drinking water quality in the EU is in general very good. The overall trend is also positive. For the large supplies, the vast majority of Member States show compliance rates for microbiological and chemical parameters of between 99% and 100%. For the few Member States showing compliance rates lower than 99%, reinforced action will be required to ensure that all citizens served by the large supplies concerned can safely use drinking water.

Monitoring and Information; The Directive requires Member States to ensure that regular monitoring of the quality of water intended for human consumption is carried out. However, monitoring approaches differ between Member States and even between different water supply zones within individual Member States, resulting in different levels and availability of monitoring data. This does not necessarily amount to a failure in meeting the legal requirements as the Directive allows for adapted monitoring programmes depending on the specific characteristics of the water supply zone. The analysis suggests, however, the need to review and better streamline the current monitoring approaches, considering in particular the WHO's risk assessment and risk management water safety plan approach. To address Member States’ monitoring and performance, the Commission is working on a so called "Structured Implementation and Information Framework" (SIIF), establishing systems at national level which actively disseminate information about how EU environment legislation is being implemented. This information is then brought together to provide an EU-wide overview. The Directive's requirement that up-to-date information on drinking water quality is made available to consumers could also be linked to such an information framework and be improved in this context. Drinking water data could also be more clearly linked to the Water Information System for Europe (WISE) which comprises a wide range of data and information collected by the EU institutions.

1.4.4. Derogations

The Directive allows derogations from the drinking water quality standards under very strict conditions and limited in time. Such derogations may not constitute a potential danger for human health and may only be established if the supply of drinking water in the area concerned cannot otherwise be maintained by any other reasonable means. A derogation may not exceed a period of three years. However, where a Member State considers that a longer derogation period is required, it may grant a second derogation for a maximum period of three years and it must communicate the grounds for this decision to the Commission. In exceptional cases, a Member State may request a third derogation from the Commission. The Commission will in this case carefully assess the request and may either refuse the request or grant the derogation for a maximum period of three years.

The Commission considers that no new derogations to the drinking water quality standards should be granted for existing water supplies with the exception of situations of new unforeseen pollution sources or following the introduction of standards for new parameters or reinforced drinking water quality standards of existing parameters. For new supplies, derogations could be considered under strict conditions if the pollution sources can be remediated within an acceptable timeframe and in case no alternative to the new supply is possible.

Challenges EU policy on drinking water has led to the development of high drinking water quality across the EU over the past decades. However, in order to keep these high quality standards and address specific remaining challenges, there may be a need to further adapt the EU legal framework.

Specific action may be required as well to reduce leakages in the distribution networks. In about half of the Member States, more than 20% of clean drinking water is lost in the distribution network before it reaches consumers’ taps, while for some Member States the proportion is as high as 60%.

1.4.5. Conclusions

The analysis confirms that the Drinking Water Directive contributed to high quality drinking water across the EU, as demonstrated by the high compliance levels with the drinking water quality standards. Although enforcement is satisfactory and progress has been made in many areas, the following issues and challenges have been identified:

The supply of high-quality water, in particular in remote and rural areas, should be improved. Small water supplies in these areas require specific risk-based management approaches and the role of the Drinking Water Directive in this context should be explored.
Risk-based approaches to the management of big water supplies would allow for more cost effective monitoring and parameter analysis in relation to identified risks and provide better guarantees for the protection of human health, Methodologies for monitoring and analysis should reflect the latest scientific and technological developments.
New scientific information about chemical and other parameters in relation to the drinking water parameter list should be considered in line with the ongoing revision of the WHO drinking-water guidelines, including emerging pollutants.
Modern information technology and easier access to environmental information should be used to provide more up-to-date information for consumers, and to explore how to link different monitoring data with reporting and consumer information.
Implementation timescales and derogation mechanisms are out- of-date and would benefit from a general update and overhaul.

An EU-wide public consultation will be a first step towards a further in-depth assessment of the above mentioned challenges and how they could be best addressed. It may also identify additional issues to be tackled in order to ensure and further improve high drinking water quality standards across the EU.