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Environmental 2010: Situation and Perspectives for the European Union, 6-10 May 2003. Porto, Portugal

CLEANING AND DISINFECTION OF WATER SUPPLY SYSTEMS Filipa Magalhães (1), and Mário Neves (2) (1) Faculty of Engineering, University of Porto, Portugal – [email protected] (2) Faculty of Engineering, University of Porto, Portugal – [email protected]

KEYWORDS cleaning, disinfection, biofilm, water-storage facilities, water mains ABSTRACT Water for human consumption needs to be in excellent conditions, otherwise it can compromise public health. This paper shows that water-storage facilities and water mains need to be well disinfected to reduce water contamination. There are several techniques and oxidizing agents to perform disinfection procedures. In contrast with other EU countries, USA and Brazil, there is no legislation in Portugal compelling to periodic interventions, although the internal regulations of some municipal services already predict such procedures. The main conclusions of this paper are: the need to create standards or legislation compelling to periodic interventions of cleanness and disinfection; the need to include water mains and storage facilities disinfection in the municipal services procedures; although chlorine is the most widely used disinfecting agent, it is not the most efficient. Several entities developed alternative disinfecting agents: chlorine free and surface pH independents. INTRODUCTION Good quality captured water, efficient disinfection and residual chlorine concentrations maintenance during transportation, are considered to be sufficient to keep the Portuguese consumers satisfied and avoid troubles in their health. Nevertheless, water treatment is not enough to guarantee excellent quality water to consumers, because storage, transportation and distribution conditions can introduce contamination in many ways. The ma in causes for water quality deterioration in the distribution systems are: phytoplankton and zooplankton existing in water-storage facilities which support microorganisms’ proliferation; construction and pipelines internal revetment materials, as well as other instruments and defective cleaning and disinfection of storage facilities and new pipelines. Facing these concerns, entities start to pay more attention to water distribution systems maintenance and cleaning, especially pipelines and storage tanks. On a community, water quantity varies hourly, as a reflex of domestic and industrial activities. For this reason, storage tanks are an essential element in any water distribution system. A storage facility is as a tank from which water, without further treatment, is supplied directly to the distribution piping system for domestic use. Its main functions are: to provide water storage during emergency situations, equalize water operational pressure and supply an appropriate water flow during periods of great fluctuations. Between extraction and consumption, water follows a long and delayed system of pipelines and tanks that can seriously affect its quality and even turn it improper for consumption, if they are not in perfect conditions of hygiene. Water-storage facilities represent the point in the network where water remains longer time and, consequently, the possibility of any contamination is higher. The main purpose of water distribution systems is to conduct water to each consumer’s house, and it represents the final barrier against contamination of treated water. However, distribution system

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expansion projects, as well as the aging of current infrastructures, present opportunities for breaches in this barrier. When this final barrier is compromised, so is public health. On its composition, water contains dissolved substances (as calcium, iron and manganese compounds) and others in suspension (such as colloidal substances, bacteria, fungus, seaweed and protozoa). Oxidation reaction of iron (Fe2+) and manganese (Mn2+) occurs when water is in contact with air, particularly with oxygen. These deposits may still have biological origin. There are specific bacteria (autotrophic) which remove energy for its metabolism from oxidation reactions of iron and manganese. In case of iron oxidation, they are called iron bacteria , and manganese bacteria, in case of manganese oxidation. Once water is not barren, it carries microorganisms that tend to excrete compact gelatinous substances (extracellular polymeric substances – EPS), with strong trend to stick on the inner walls of reservoirs and pipes. This mucus works as a stable protective barrier, creating a micro zone where bacteria colonize and proliferate. Thus, we have what it is technically referred as Biofilm (Figure 1). Biofilm works as a bacterial shell that protects them from disinfecting agents and when there is a sporadically contamination in the water, it can be lodged and developed in the biofilm, becoming a permanent contamination of the distributed water. The dis tribution system integrity can be compromised if procedures are not followed to protect it from contamination Figure 1 – Schematic representation of biofilm formation when installing new lines and reservoirs or repairing existing ones. STANDARDS AND LEGISLATION In Portugal, cleaning and disinfection procedures of storage facilities and pipelines still have a lot of gaps. In contrast with other EU countries, USA and Brazil, there is no legislation in our country compelling to periodic interventions, although the internal regulations of some municipal services already predict these procedures. European Directive 98/83/CE of 3 November 1998 relating to the quality of water intended for human consumption is transposed for internal law through Decree nr. 234/2001 for 5 September 2001. It refers the importance of water quality in the distribution systems, once many of the problems associated with water contamination are caused by deficient disinfection in new installations, deficient cleanness and disinfection of private tanks and inefficient maintenance of domestic systems. This diploma, on 13º article, only establishes the ability of the managing entity to take the necessary measures to assure the continuous improvement of water quality, by maintenance of the existing Cleaning and Disinfection of Water Supply Systems – page 2 of 6

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Environmental 2010: Situation and Perspectives for the European Union, 6-10 May 2003. Porto, Portugal

systems and construction of new ones, without referring any type of relative obligation for cleanness and disinfection. In accordance with Decree nr. 236/98 for the 1 August 1998, the materials used in the supplying systems that are in contact with water for human consumption cannot provoke alterations in water quality, but it does not specify which measures should be taken to assure that this happens. In the United States of America, AWWA (American Water Works Association) has a standard that presents essential procedures for disinfecting new and repaired water mains (ANSI/AWWA C65-99, 01-Jan-1999) and a standard for disinfection of water storage facilities (ANSI/AWWA C652-92, 01Jan-1992, recently replaced by ANSI/AWWA C652-02, 01-Aug-2002). In France there is a methodology which is applied for water storage facilities and water mains disinfection, authorized by Health Ministry. In accordance with Sanitary Regulation nr 1978-40 (13Sep-1978), storage facilities with more than 1 m3 volume, must be cleaned and disinfected once a week. WATER-STORAGE FACILITIES It is necessary that storage facilities are regularly cleaned to avoid contaminations and health risks. Traditionally, there are several cleaning solutions for water storage facilities: • Use of steel brushes, to rub the walls and floor of the reservoir; • Flushing with high-pressure water jet (higher than 45 bars). However, these mechanical procedures, particularly the use of steel brushes, do not assure the biomass destruction in a general way and degrade reservoir surfaces. In a similar way, flushing with highpressure water jet tends to deteriorate storage-facilities walls. These techniques create microcracks where bacteria successfully attach and subsequently grow, speeding up the inner surfaces walls degradation. Standard ANSI/AWWA C652-92 refers the use of these traditional solutions as a cleaning measure of water storage-facilities. Nevertheless, some Portuguese and French companies use specialized products and technologies to clean reservoirs. First, they flush the surfaces with abundant water (maximum pressure: 10 bars). Following this preliminary cleaning, they pulverize all surfaces with scale remover agents in a generalized way. These products remove iron and manganese incrustations which are present in water distribution systems, removing seaweed and calcareous as well. After the cleaning operation has been completed, disinfection proceeds. Disinfection operation consists in selective destruction of all pathogenic microorganisms, which is distinguished from sterilization for the fact that this last one cause total microorganisms destruction. Disinfection depends on the following parameters: • Retention period; • Disinfection agent type and concentration; • Existing microorganisms . Chlorine compounds are the most commonly used oxidizing agents for water storage facilities disinfection and because of its high oxidizing capacity, it is extremely useful in organic substances destruction and simultaneously in the destruction of essential enzymes to microorganisms’ survival. According to ANSI/AWWA C652-92, the forms of chlorine that may be used in the disinfecting operations are: liquid chlorine (Cl2 ), sodium hypochlorite solution (NaOCl) and calcium hypochlorite granules or tablets (Ca(OCl)2 ). Despite chlorine is a good disinfecting agent for water, the same is not true for reservoir surfaces, once biofilm growth occurs, even when residual chlorine is present. This is because of the surface wall pH. To understand this fact, it is convenient to mention that chlorine aqueous solutions contain two species in equilibrium, as it is represented in equation (1) and (2): hypochlorous acid (HClO) and hypochlorite ion (ClO-). Cl2 + H2 O → HOCl + H+ + Cl-

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(1)

Environmental 2010: Situation and Perspectives for the European Union 6-10 May 2003. Porto, Portugal

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HOCl ↔ H+ + OCl-

(2)

Hypochlorous acid and hypochlorite ion are both strong oxidizing agents, but HOCl should be the strongest from these two. The relative amount of the two species strongly depends on pH, as it is shown in Figure 2. Hypochlorous acid is the predominant species between pH 1 and pH 7, the species are at equal concentrations at a pH of 7.5 and hypochlorite ion is predominant at high pH values. Considering pH 8.5 as a reasonable approach to pH of a concrete wall, the chlorine solution will have a mere superficial action, because the abundant species is hypochlorite ion. Another alternative disinfection agent is potassium permanganate (KMnO4 ), which has a highly oxidative power and act as a microfauna and microflora biocide. In accordance with the thermodynamics potential, KMnO4 is capable to oxidize organic compounds and the majority of inorganic pollutants, such as iron and manganese. Unfortunately, potassium permanganate solutions have several Figure 2 –Hypochlorous acid inconvenient: its coloration is difficult to remove, it is moderately and hypochlorite ion toxic, it demands high retention time and it does not have residual distribution in water, for action. different pH values As an alternative, some entities propose the use of a liquid disinfectant with bactericidal and fungicide activity and chlorine free. It is a solution based on 50% of peroxide hydrogen (H2 O2 ) in acid conditions and a silver salt. H2 O2 is the oxidizing agent and the silver salt has a double effect: (a) oligodynamic – even in small doses is toxic for microorganisms, and (b) catalytic – accelerates oxidation reaction. Three methods of chlorinating storage facilities are described in standard ANSI/AWWA C652-92: (1) chlorination of the full storage facility so that, at the end of the appropriate retention period, the water will have a free residual chlorine of not less than 10 mg/L; (2) spraying or painting of all storage facility water-contact surfaces with a solution of 200 mg/L available chlorine; and (3) chlorination of full storage facility having free chlorine residual of 2 mg/L after 24 hours. Cleanness and disinfection advised regularity is once a year and whenever there are bacteriological quality problems. WATER MAINS The objective of water mains disinfection is to eliminate all kind of contamination that can occur during construction or even during pipes, accessories and joints storage. These contaminations have greater impact whenever pipes extremities are not well plugged. Reducing the sources of contamination in the new or repaired pipe will enhance the effectiveness of the disinfection process. The first step of the installation procedure to reduce contamination sources is to keep the pipe as clean as possible before it is installed and placed into service. No disinfectant agent can be efficient when pipes possess sediments that serve as microorganisms’ habitat, favoring its growth, so they need to be properly cleaned before disinfection. In accordance with standard ANSI/AWWA C651-99, related to water mains disinfection, there are three forms of chlorine that may be used in the disinfecting operations: liquid chlorine (Cl2 ), sodium hypochlorite solution (NaOCl) and calcium hypochlorite granules or tablets (Ca(OCl)2 ). Potassium permanganate can also be used as a disinfecting agent for distribution networks, because of its high oxidizing capacity. Another possible disinfecting agent that can be used in some situations, in which Cleaning and Disinfection of Water Supply Systems – page 4 of 6

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Environmental 2010: Situation and Perspectives for the European Union, 6-10 May 2003. Porto, Portugal

conventional agents are inadequate, is copper sulphate (CuSO4 ). This agent is known as being toxic for bacteria and the most usual concentration to remove Coliforms vary between 5 and 30 mg/l, with a retention period between 1 and 3 days. However, copper sulphate is also toxic for human beings and its application has to follow a rigorous procedure of final cleanness of the pipe before entering in service. As an alternative, some countries, such as Portugal and France, found a solution based on a disinfecting agent free of chlorine, whose disinfecting capacity does not depend on the surface pH and, like chlorine, possess residual capacity. This product is a 50% peroxide hydrogen solution and silver salt (previously cited). The basic disinfection procedure consists of: I – Inspecting all materials to be used to ensure its integrity; II – Preventing contaminating materials from entering the water main during storage, construction, or repairs and noting potential contamination at the construction site; III – Removing, by flushing or other means, those materials that may have entered the water main; IV – Chlorinating any residual contamination that may remain, and flushing the chlorinated water from the main; V – Protecting the existing distribution system from backflow caused by hydrostatic pressure test and disinfection procedures; VI – Documenting that an adequate level of chlorine contacted each pipe to provide disinfection; VII – Determining the bacteriological quality by laboratory test after disinfection; VIII – Final connection of the approved new water main to the active distribution system. The disinfection and cleanness procedures for new pipelines typically cannot be used when repairing existing water lines, because of the need to minimize the disruption of service to customers. Leaks or breaks that can be fixed with a repair clamp, while the main is in use under normal operating pressure pose little danger of contamination and require no disinfection of the line. The repair clamp should be sprayed or swabbed with a chlorinated solution to clean it before installation to avoid any kind of contamination. Whenever it is not possible to repair the leak under normal operating pressure, workers should sprinkle the area with sodium or calcium hypochlorite to reduce the danger of contamination from possible nearby sewer. The section where the leak is located should be isolated and immediately repaired. After repairing the line, the section should be cleaned and disinfected in accordance with procedures described in AWWA standard C651-99. The line should then be flushed until all chlorinated water is eliminated. Whenever it’s possible, a bacteriological test should be made to assure that there is no contamination. Since sodium and calcium hypochlorite (granular or tablet forms of chlorine) may dissolve slowly, their use may not always be appropriated, because main repairs should be done as quickly as possible. As we have seen, cleanness and disinfection of repaired water lines is more difficult than for newly constructed mains but equally important. All measures should be taken to minimize water mains contamination by sprinkling disinfection agent in the area surrounding the main break and all materials used in the operation. Cleanness and disinfection advised regularity is once a year and whenever there are bacteriological quality problems. BACTERIOLOGICAL TESTS Before the connection of water main or water storage facility to the distribution system, water should be tested for bacteriological (chemical and physical) quality in accordance with Standard Methods for the Examination of Water and Wastewater, show the absence of Coliform organisms and, if required, the presence of a chlorine residual.

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COSTS FOR WATER TANKS AND WATER MAINS CLEANNESS AND DISINFECTION Table 1 refers an estimate of costs for cleanness and disinfection processes, obtained from a market consultation. Small and large facilities have been considered. Table 1 – Costs for cleanness and disinfection processes. Applications Ductile cast iron adductor pipe (D1000, L = 5000 m) PVC distribution network (D 90, L = 2000 m) Water- tank of 10 000 m3 Water- tank of 100 m3

Costs (Euros) 10 000 750 4 000 500

D – diameter L – length

CONCLUSIONS A distribution system should have maintenance procedures to minimize potential introduction of contaminants into water and reduce risks to public health. Regular disinfection is the primary barrier against contamination in the distribution system. Water main and storage facilities installation and repairs are activities that have not been historically well controlled with respect to water quality and good sanitary practices. It is urgent to create procedures or standards compelling to periodic interventions of cleanness and disinfection to avoid water contamination. Efficient water disinfection and residual chlorine concentrations are not enough to reduce treated water contamination. It is also important to consider water mains and storage facilities disinfection. Although chlorine is the most widely used disinfecting agent, it is not the most efficient for water mains and storage facility disinfection because its action depends on the surface pH. Several entities developed alternative disinfecting agents: chlorine free and surface pH independents. ACKNOWLEDGMENTS The authors would like to thank the support offered by FCT, Fundação para a Ciência e a Tecnologia. REFERENCES ANSI/AWWA C652-92 (1992). “Disinfection of Water-Storage Facilities”, USA, American Water Works Association. ANSI/AWWA C651-99 (1999). “Disinfecting Water Mains”, USA, American Water Works Association. European Commission (1998). Directive 98/83/CE for the 3 November 1998 relating to the quality of water intended for human consumption Geldreich, E. E. (1996) “Microbial Quality of Water Supply in Distribution Systems”, USA, Lewis Publishers, pp 30-31, 238-245. Pontius, F. W. (1990) – “Water Quality and Treatment – A Handbook of Community Water Supplies”, USA, American Water Works Association, 4th edition, Mc Graw Hill.

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