WO2021247975A1

WO2021247975A1 - Real time monitoring of drinking water chlorination

Info

Publication number: WO2021247975A1
Application number: PCT/US2021/035860
Authority: WO
Inventors: Dylan Morgan
Original assignee: Parker Water & Sanitation District
Priority date: 2020-06-05
Filing date: 2021-06-04
Publication date: 2021-12-09

Abstract

A drinking water disinfection system (200) includes a contact tank (202). Drinking water enters the contact tank (202) at water inlet (204) and exits the contact tank (202) at drinking water outlet (222). A circuitous water path from the water inlet (204) to the water outlet (222) is defined by partitions (218). The system (200) further includes an entry sensor system (214), a controller (216) and an exit sensor system (220). The entry sensor system (214) includes one or more sensors for sensing values indicative of a concentration of the disinfecting agent in the water. The controller (216) is operative to receive output signals from the sensor system (214) and to process such signals to assist in controlling the amount of disinfecting agent added to the water at the disinfectant inlet (208).

Description

REAL TIME MONITORING OF DRINKING WATER CHLORINATION

Field of the Invention

The present invention relates generally to disinfecting drinking water and, in particular, to a monitoring system for monitoring disinfectant levels in drinking water that enables quick corrections and closer tracking of ideal disinfectant levels.

Background of the Invention

Drinking water is usually sourced from wells, groundwater or other sources of fresh water. Before the water is distributed to drinking water consumers, the water is generally processed in a number of ways to yield drinking water that is safe to consume as well as more appealing. Such processing may involve sedimentation to remove sediment from the water, filtration to remove dissolved particles, and disinfection to remove parasites, bacteria, viruses, and other pathogens. While various methods of disinfection are possible and many disinfecting agents can be employed, the most common disinfecting agent added to drinking water is chlorine added in the form of pure chlorine (gas or liquefied chlorine gas), sodium hypochlorite, and calcium hypochlorite, among others. All of these chlorine sources, including pure chlorine, are referred to herein as chlorine-containing substances. Chlorine functions as an oxidizing agent to neutralize pathogens and has been found, over many years, to reliably yield safe drinking water.

For chlorine to function as intended, the amount of chlorine added and the resulting concentration levels must be carefully controlled. The amount of chlorine required depends on a number of factors including the throughput rate of water and the pH of the water. One important factor relates to the amount of pathogens in the water that need to be neutralized. A certain amount of chlorine is required to fully neutralize the pathogens; a level sometimes referred to as the breakpoint. This depends on the amount of pathogens in the water that need to be neutralized, or the infectant load of the water. Generally, an amount greater than this is utilized so that free chlorine remains in the drinking water as supplied to the drinking water distribution network. This additional amount ensures that the water remains clean as the water may remain for some time in the distribution network before it is consumed. However, chlorine in concentrations too high over time can pose health hazards to the public. Accordingly, regulatory bodies in various jurisdictions have promulgated chlorine ranges that are deemed safe and must be followed by municipalities, water districts, and other drinking water providers.

The effectiveness of the disinfection process is generally a function of the concentration of the disinfecting agent and the length of time that the disinfecting agent is in contact with the water. Drinking water providers typically perform disinfection in a disinfection system or contact tank. Water to be disinfected is introduced into the tank at a water inlet. Near the water inlet, a disinfecting agent is added. Depending on the disinfecting agent used, this may involve adding liquid and/or solid disinfecting agents at a disinfectant inlet. The water then moves slowly through the tank, for example, along a circuitous path, in order to provide sufficient contact time for disinfection, before exiting at a water outlet. At the water outlet, the water may be tested by water quality specialists to make sure it complies with all applicable standards for potability including the residual chlorine levels as noted above. If the chlorine levels approach the limits of acceptable ranges, the amount of chlorine added can be adjusted by the skilled specialists so that a continuous supply of high-quality water is maintained.

Summary of the Invention

It has been recognized that the conventional processes for monitoring drinking water disinfection, as described above, can be improved. In particular, it would be desirable to be able to more closely control the level of residual disinfectant in the treated water so that it is maintained at a desired level. This would not only better ensure that the levels substantially continuously stay within the required ranges as set forth by regulatory bodies but also enable control to stay closer to levels deemed ideal. In this manner, higher quality drinking water can be provided that is more healthy and appealing.

Some complications in this regard relate to the nature of conventional contact tanks and how they are monitored. As noted above, disinfection depends on both the concentration of the disinfecting agent and the contact time. In order to provide adequate contact time, the contact tanks are designed so that it takes a sufficient time, e.g., 1-3 hours, for water to transit from the water inlet of the contact tank to the water outlet. Thus, there is a substantial lag time between when chlorine is added at the water inlet and when an undesired rise or fall in the free chlorine levels in the water at the water outlet is detected. It will be appreciated that the amount of chlorine required varies over time due to changes in the water sources, infectant loading, pH and other characteristics. To some extent, experienced specialists can anticipate this based on the sources being used, seasonal effects related to wet, dry, and shoulder seasons, and other factors. Nonetheless, proper chlorine levels cannot always be anticipated and specialists therefore carefully monitor the disinfectant levels in the end product emerging from the water outlet. The noted lag time sometimes means that disinfectant levels can vary substantially within the required ranges or even stray outside required ranges for certain intervals.

The present invention improves upon the conventional systems and processes by obtaining substantially real time levels of the disinfecting agent closer to the disinfectant inlet where the disinfecting agent initially contacts the water. The values measured at such a sensor, e.g., chlorine concentration levels, can be correlated to the expected disinfectant levels in the end product, i.e., disinfected drinking water supplied to the drinking water distribution network. As a result, the monitoring system can respond more quickly to detected increases or decreases in the disinfectant levels. Disinfectant levels can therefore be more tightly controlled to provide more healthy and desirable drinking water.

In accordance with one aspect of the present invention, a drinking water disinfection system is provided. The system includes a contact tank having a water inlet for receiving water to be treated, a disinfectant inlet, adjacent to the water inlet, for receiving a disinfecting agent, and a water outlet for outputting disinfected drinking water. The contact tank includes structure defining a flow path from the water inlet to the water outlet, wherein disinfection of the water is accomplished based on a concentration of the disinfecting agent and length of time of contact between the water and the disinfecting agent along the flow path. For example, barriers may be provided within the contact tank to cause the water to flow along a circuitous path from the water inlet to the water outlet.

The system further includes a sensor and a controller. The sensor is disposed in the flow path closer to the water inlet than to the water outlet relative to the flow path.

For example, the distance between the disinfectant inlet and the sensor may be less than 1/10 of the length of the flow path from the water inlet to the water outlet. The amount of time it takes for water to flow from the location of the disinfectant inlet to the location of the sensor may also be considered. Such a time measure may provide greater consistency from location to location based on the geometry of contact tanks and variable flow rates. In one implementation, the sensor is disposed less than 30 seconds, for example, about 5 seconds, from the disinfectant inlet, relative to the water flow rate. In that implementation, feedback concerning the disinfectant level is provided very close to the beginning of the transit time through the contact tank, which is generally greater than one hour. The sensor is operative for sensing a measured value in the water at the sensor and providing an electronic sensor signal indicative of the measured value. For example, the sensor may be an oxidation-reduction potential (ORP) sensor. The disinfecting agent may be any agent appropriate for disinfecting drinking water such as a chlorine -containing substance, e.g., pure chlorine, sodium hypochlorite, calcium hypochlorite, or the like. Preferably, the sensor provides a substantially real time measurement of the measured value.

The controller receives the electronic sensor signal, processes the sensor signal to obtain the measured value, and provides an output, based at least in part on the measured value, for controlling the supply of the disinfecting agent via the disinfectant inlet. In this regard, control of the supply of the disinfecting agent may be implemented manually or automated. In the latter regard, the controller may provide a control signal to a disinfectant feed mechanism, such as a valve or pump, to automatically control the supply of the disinfecting agent at the disinfectant inlet. It will be appreciated that the nature of the disinfectant feed mechanism can vary depending on a number of factors including the nature of the disinfecting agent. For example, a valve may be suitable for controlling the feed of chlorine gas whereas a pump may be used for other disinfecting agents. The controller may take into consideration one or more additional factors. These may include one or more of the following: information regarding a flow rate of water into the contact tank at the water inlet, information regarding an infectant load of the water entering the contact tank, information regarding a pH of the water, and information from a second sensor disposed downstream from the noted sensor. For example, the second sensor may provide information regarding a concentration of the disinfecting agent in the water exiting the contact tank at the water outlet.

The controller may be operative to correlate the measured disinfectant concentration value of the entering water at the sensor to the resulting disinfectant concentration value of the exiting water at the water outlet. Such a correlation may be dependent on factors as noted above and may vary over time. In some cases, for example, where the water has undergone substantial pretreatment prior to reaching the contact tank and/or where the disinfectant load of the water is low, there may be little or substantially no difference between the concentration level measured at the sensor and the concentration level in the water exiting the contact tank at the water outlet. In other cases, the difference between the concentration measured at the sensor and the resulting concentration in the water exiting the contact tank may be substantial. A correlation component may be obtained by comparing measured values to resulting values taking into account the transit time of water from the water inlet to the water outlet. Additional factors may be considered. The correlation may be determined by an algorithm, by an experienced specialist, by heuristic logic taking into account multiple factors as noted above, or by any other processing suitable for establishing the correlation.

In accordance with another aspect of the present invention, a method is provided for sanitizing drinking water in a contact tank. As described above, the contact tank may have a water inlet, a disinfectant inlet, a water outlet, and structure defining a flow path through the contact tank from the water inlet to the water outlet. The method involves disposing a sensor within the flow path at a point closer to water inlet than to the water outlet relative to the flow path. For example, the sensor may be positioned a distance from the disinfectant inlet that is less than 1/10 of the length of the flow path from the water inlet to the water outlet. The method further involves operating the sensor to provide a measured value indicative of a concentration of a disinfecting agent in the water at the sensor and controlling introduction of the disinfecting agent into the water at the disinfectant inlet based at least in part on the measured value. The disinfecting agent may be added based on operation of a controller that takes into account the measured value and, optionally, other factors as described above. The disinfecting agent may be added manually or automatically. In this manner, the concentration of the disinfecting agent can be monitored substantially in real time to provide high quality drinking water that is more healthy and appealing. Brief Description of the Drawings

For a more complete understanding of the present invention, and further advantages thereof, reference is now made to the following detailed description, taken in conjunction with the drawings, in which:

Fig. 1 is a schematic diagram of a drinking water treatment facility in accordance with the present invention;

Fig. 2 is a schematic diagram of a drinking water disinfection system that may be implemented in connection with the facility of Fig. 1; and

Fig. 3 is a flowchart summarizing a process for disinfecting drinking water in accordance with the present invention.

Detailed Description

The present invention relates to a drinking water disinfection system and associated functionality. In the following description, the invention is set forth in the context of a municipal or other water district treatment facility for treating raw water from wells, surface water, or other sources using a chlorine containing substance as a disinfecting agent. While this is a particularly advantageous application of the present invention, it will be appreciated that the invention can be used in other contexts. Accordingly, the following description should be understood as illustrative and not by way of limitation.

Referring to Fig. 1, a drinking water treatment facility is generally identified by reference numeral 100. The illustrated facility 100 generally includes a water source 102, a pretreatment system 104, a disinfection system 105, a water storage system 116, and a distribution network 118. Each of these components will be described in more detail below.

The water source 102 may vary from facility to facility and from time to time. For example, the water source 102 may include wells, surface water sources such as streams or lakes, and/or other sources. In one implementation, the water source 102 may include multiple alluvial wells. The number of wells activated and production rates can be varied based on demand. For example, during dry months when customers may use more water for landscaping and the like, additional wells may be brought online and pumping rates may be increased. Where surface water is used, extraction rates may vary depending on demand, contracts, availability, and other factors.

The water from the source 102 may then be processed by a pretreatment system

104. The treatments implemented by the pretreatment system 104 may vary depending on the nature of the facility 100, the water sources 102, seasonal impacts and other factors. Such treatments may include, among others, some or all of the following: coagulation and flocculation, sedimentation, and filtration. Coagulation and flocculation relate to adding chemicals to the water that causes certain substances to form larger particles. Sedimentation is a process by which sediment and large particles settle such that they are removed from the water. In the filtration process, filters are used to remove dissolved particles from the water. It will be appreciated that, although the pretreatment system 104 is schematically illustrated as a single component, such pretreatment may involve a series of tanks and systems.

From the pretreatment system 104, the water is routed to the disinfection system

105. The system 105 will be described in more detail below. Generally, the disinfection system includes a contact tank 106. A disinfecting agent from a disinfectant tank 108 is added to the water near the water inlet of the tank 106. A monitoring system 110 may be provided adjacent to the water outlet from the tank 106 to ensure that the water meets all applicable standards. The monitoring system 110 may include one or more sensors 112 and associated instrumentation 114.

From the disinfection system 105, the water may be delivered to one or more storage tanks 116. For example, the tanks may be mounted on a water tower or located at a high elevation to provide the desired head pressure. The water can then be delivered from the storage tanks 116 via a distribution network 118 to end users or customers of the water district. The distribution network 118 may include water mains, local water lines, and a network of local branches that serve residences, businesses, and the like.

Fig. 2 is a schematic diagram of a disinfection system 200 in accordance with the present invention. The disinfection system 200 generally includes a contact tank 202. Drinking water enters the contact tank 202 at water inlet 204 and exits the contact tank 202at drinking water outlet 222. In the illustrated embodiment, a circuitous water path from the water inlet 204 to the water outlet 222 is defined by partitions 218. One function of the circuitous path is to increase the minimum contact time of the disinfecting agent with the water. As noted above, the effectiveness of disinfection is a function of the concentration of the disinfecting agent and the length of time that the disinfecting agent contacts the water. The path length through the contact tank 202 ensures that a sufficient contact time will be provided taking into consideration the flow rate through the tank 202. In the illustrated embodiment, the transit time of water from the water inlet 204 to the water outlet to 22 may be on the order of 1 to 3 hours.

The illustrated system 200 further includes a disinfectant tank 206. Although a tank is shown, it will be appreciated that different types of repositories may be provided for disinfecting agents provided in a solid form. The tank 206 may include one or more disinfecting agents and other chemicals or additives as desired (e.g., to further promote disinfection or for other purposes such as fluoridation). There are a variety of disinfecting agents that are appropriate for use in drinking water, such as ammonium sulfate, chlorine containing substances and others. Any such disinfecting agents may be utilized in accordance with the present invention, with appropriate modification of related systems such as sensors and the like. A common type of disinfecting agent used in municipal and other water district treatment facilities is chlorine containing substances such as chlorine, sodium hypochlorite, and calcium hypochlorite. Chloramines are often used because they are more stable. Generally, such chlorine containing substances function as oxidizing agents to neutralize pathogens that may be present in the water.

Disinfecting agents from the disinfectant tank 206 are added to the water at the disinfectant inlet 208. The inlet 208 may be submerged in the water or may be a port into the tank 202 above the expected water level. Where the disinfecting agent is provided in a fluid form, flow of the disinfecting agent may be controlled by a flow control device such as a valve 210 or pump. The illustrated valve 210 may be manually operated or electronically operated, e.g. solenoid valves. As will be described below, the valve 210 may be electronically controlled for fully automated or near fully automated operation of the system 200.

The illustrated system 200 further includes an inlet sensor system 214, a controller 216 and an outlet sensor system 220. The inlet sensor system 214 includes one or more sensors for sensing values indicative of a concentration of the disinfecting agent in the water. A variety of different types of sensors may be used in this regard depending, for example, on the nature of the disinfecting agent and the desired response time. In this regard, the inlet sensor system 214 may physically sample water or may obtain concentration information based on certain characteristics of the water without requiring a physical sample. In preferred implementations, the inlet sensor system 214 provides a substantially real time sensor output signal including information indicative of the concentration level of the disinfecting agent in the water at the location of the inlet sensor system 214. The illustrated inlet sensor system 214 includes at least one oxidation-reduction potential (ORP) sensor that senses an oxidation-reduction potential of the water that is indicative of a concentration of the disinfecting agent. Appropriate ORP sensors for use in this regard are manufactured by the Hach company of Loveland, Colorado.

One objective of the present invention is to facilitate rapid detection of undesired increases or decreases in the concentration of the disinfecting agent in the water. In order to facilitate such rapid detection, it is desirable to position the inlet sensor system 214 closer to the water inlet 204 than to the water outlet 222 relative to the flow path of water through the tank 202. That is, because there is a substantial transit time for water through the tank 202 from the inlet 204 to the outlet 222, lag times can be reduced by measuring concentration close to the water inlet 204. Preferably, the inlet sensor system 214 is located a distance, d, from the disinfectant inlet 208 that is less than 1/10 of the length of the water flow path from the inlet 204 to the outlet 222. In one implementation, the distance, d, is no more than about 10 meters, for example, about 1.54 meters. This corresponds to a water travel time of no more than about 30 seconds, for example, about 5 seconds, from the disinfectant inlet 208 to the inlet sensor system 214.

It will be appreciated that multiple sensors may be utilized. Such sensors may be distributed relative to a cross-section of the flow path (e.g., to account for mixing anomalies) and/or distributed over a length of the flow path (e.g., to account for time/positi on-based gradients). Moreover, readings may be averaged or filtered over time to avoid responding to transient spikes or anomalies.

The outlet sensor system 220 is used to ensure that the drinking water exiting the tank 202 meets all relevant standards, including concentration levels for the disinfectant. For example, where chlorine is used as the disinfecting agent, typical regulations may require free chlorine in the drinking water within a range of about 1.0-5.0 mg/L. Narrower regulations may require that concentrations be maintained between about 1.0- 2.0 mg/L. As discussed above, some free chlorine is desired to ensure that the water remains clean throughout the drinking water distribution network, but excessive levels are undesirable and may entail health concerns over time. The specific outlet sensor system 220 utilized in this regard may be manual or automatic and may require regulatory approval. In the context of the present invention, it is useful to obtain exit concentration levels that can be used by the controller 216. In this regard, the outlet sensor system 220 may include an electronic sensor such as an ORP sensor as described above. Alternatively, the water may be sampled and manually tested. In such a case, the resulting concentration level together with a measurement time may be manually provided to the controller 216. The outlet sensor system 220 is preferably located near the outlet 222, for example, within the tank 202 or outside the tank 202.

The controller 216 is operative to receive output signals from the inlet sensor system 214 and to process such signals to assist in controlling the amount of disinfecting agent added to the water at the disinfectant inlet 208. In a simple example, a target concentration level may be established for the inlet sensor system 214. This concentration level may be the same as or different than the target concentration level at the outlet sensor system 220. In any event, in this simple example, the controller 216 can receive the output signal from the inlet sensor system 214 and extract or calculate a measured concentration level based on the signal. The rate of feed of the disinfecting agent at the disinfectant inlet 208 may then be increased or decreased depending on whether the measured concentration level is greater or less than the target concentration level. Thus, even in this simple example, a feedback mechanism is provided for substantially real time control of the feed rate of the disinfecting agent.

A more sophisticated methodology may involve correlating the measured concentration level of the inlet sensor system 214 to the measured concentration level of the outlet sensor system 220. There are a number of reasons why the measured concentration levels at the sensor systems 214 and 220 may be different. First, as noted above, the concentration of free chlorine may decrease from the inlet sensor system 214 to the outlet sensor system 220 as the disinfecting agent is used to neutralize pathogens in between. In addition, measured concentration levels at the inlet sensor system 214 may be affected due to incomplete dissemination of the disinfecting agent throughout the water supply. Such effects may be experienced in a predictable fashion that can be accounted for by appropriate correlation factors. Additional factors may be reflected in differences between the measured concentrations at the detector systems 214 and 220. Some of these may be modeled even if they are not fully understood. A number of additional factors or parameters may be considered by the controller 216. These include water parameters that are expected to impact the required rate of disinfecting agent that is supplied to the water. For example, such water parameters may include input water flow rates and associated seasonal variations, changes in water sources such as activating or deactivating wells or otherwise changing the mix as between multiple water sources, the water quality of the water entering at the inlet 204 as measured or expected, the pH of the water, and other factors. Such information may be manually entered to the controller 216 or provided via sensor signals. In some cases, water quality information may be obtained in connection with pretreatment processes. Other inputs to the controller 216 may include historical information, weather and environmental conditions, and anything else that may impact the operation of the disinfection system 200. Such information may be entered manually or supplied to or accessed by the controller 216 electronically.

The controller 216 can use all of this information to control the supply of the disinfecting agent 206. For example, various values obtained from such information may be employed in an algorithm to determine the required input rate for the disinfecting agent. Alternatively, the controller 216 may present this information, or a processed or annotated collection of information based on the input information, to a skilled specialist who then determines the input rate for the disinfecting agent. As a further example, such input information may be fed into a processing module that employs machine learning or heuristic logic to determine a feed rate for the disinfecting agent. The resulting feed rate may then be executed manually using the valve 210 or pump to control the supply of disinfecting agent, or the feed rate may be controlled automatically, for example, by control signals provided by the controller 216 to one or more feed control mechanisms such as valves 210 or pumps to set the feed rate at the level determined by the controller 216.

Fig. 3 is a flowchart summarizing a process 304 disinfecting drinking water in accordance with the present invention. The process 300 is initiated by obtaining (302) flow rate information for water entering the contact tank. Such flow rate information may be obtained manually or may be obtained from a flow rate sensor positioned at the tank inlet or in a supply pipeline. Additionally or alternatively, such flow rate information may be determined or supplemented with seasonal demand information or historical demand information. The system may also obtain (304) water characteristic information. Such information may relate to an infectant load of the water, a pH of the water, or any other information that may impact the amount of disinfecting agent that will be required.

Based on this information, and initial disinfectant feed rate may be set (306). Such a feed rate may be expressed, for example, in terms of the volume or weight of the disinfecting agent or disinfecting agent solution per unit time fed into the contact tank at the disinfectant inlet. A disinfectant feed mechanism such as one or more valves may then be operated (308) to provide the desired feed rate.

An inlet disinfectant concentration may then be measured (310). As discussed above, such a measurement is preferably obtained by a sensor system disposed close to the water inlet of the contact tank. In certain implementations, real time measurements may be obtained and output sensor signals may be provided to a controller. For example, an ORP sensor may be employed. In such cases, ORP measurements in the range of 500- 800 millivolts (mV) may be expected. These inlet disinfectant concentration levels may then be correlated (312) to outlet disinfectant concentration levels. In some cases, little or no difference may be expected between the inlet concentration levels and outlet concentration levels. In other cases, a simple correlation such as a linear use factor may accurately correlate the inlet concentration to the outlet concentration. In other cases, more complicated algorithms or logic may be employed taking into account a number of factors. In any event, exiting concentrations may be measured (314) and used in such correlations or to scale correlation factors.

In any event, the controller may thereby determine (316) whether an adjustment to the disinfectant feed rate is required. If so, a new disinfectant feed rate may be set (306). For example, this may be executed by controlling a feed rate mechanism such as one or more valves or pumps from a disinfecting agent tank. If no adjustment is required, the process 300 may nonetheless be repeated (318) periodically to ensure that the concentration levels of the disinfecting agent in the drinking water supplied to the distribution network remains within required ranges.

The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.

Claims

What is claimed:

1. A drinking water disinfection system, comprising: a contact tank having a water inlet for receiving water to be treated, a disinfectant inlet, adjacent to said water inlet, for receiving a disinfecting agent, and a water outlet for outputting disinfected drinking water, said contact tank including structure defining a flow path through said contact tank from said water inlet to said water outlet, wherein disinfection of said water is accomplished based on a concentration of said disinfecting agent and a length of time of contact between said water and said disinfecting agent along said flow path of said contact tank; a sensor, disposed in said flow path closer to said water inlet than to said water outlet relative to said flow path, for sensing a measured value in said water at said sensor and providing an electronic sensor signal indicative of said measured value; and a controller for receiving said electronic sensor signal, processing said sensor signal to obtain said measured value, and providing an output, based at least in part on said measured value, for controlling the supply of said disinfecting agent via said disinfectant inlet.

2. The drinking water disinfection system of claim 1, wherein said disinfecting agent is an oxidizing agent.

3. The drinking water disinfection system of claim 1, wherein said disinfecting agent comprises a chlorine-containing substance.

4. The drinking water disinfection system of claim 1, wherein said sensor provides a substantially real time measurement of said measured value.

5. The drinking water disinfection system of claim 1, wherein said measured value relates to an oxidation or reduction potential of said water.

6. The drinking water disinfection system of claim 1, wherein said sensor comprises and oxidation-reduction potential sensor.

7. The drinking water disinfection system of claim 1, wherein said sensor is disposed within a first distance from said disinfectant inlet, said distance being less than 1/10 of a length of said flow path from said water inlet to said water outlet.

8. The drinking water disinfection system of claim 1, wherein a transit time between said disinfectant inlet and said sensor is no more than about 30 seconds.

9. The drinking water disinfection system of claim 1, wherein said controller comprises an input module for receiving information regarding a flow rate of water into said contact tank at said water inlet.

10. The drinking water disinfection system of claim 9, wherein said input module is further operative for receiving information regarding an infectant load of said water entering said contact tank at said water inlet.

11. The drinking water disinfection system of claim 9, wherein said input module is further operative for receiving information regarding a pH of said water entering said contact tank at said water inlet.

12. The drinking water disinfection system of claim 9, wherein said input module is further operative for receiving information from a second sensor disposed in said flow path downstream from said sensor.

13. The drinking water disinfection system of claim 1, wherein said input module is further operative for receiving information regarding a concentration of said disinfecting agent in said water exiting said contact tank at said water outlet.

14. The drinking water disinfection system of claim 1, further comprising a disinfectant feed mechanism for controlling a feed rate of said disinfecting agent at said disinfectant inlet, wherein said controller is operatively associated with said disinfectant feed mechanism such that said output from said controller controls said feed rate of said disinfectant feed mechanism.

15. A method for sanitizing drinking water in a contact tank, said contact tank having a water inlet for receiving water to be treated, a disinfectant inlet, adjacent to said water inlet, for receiving a disinfecting agent, and a water outlet for outputting disinfected drinking water, said contact tank including structure defining a flow path through said contact tank from said water inlet to said water outlet, wherein disinfection of said water is accomplished based on a concentration of said disinfecting agent and a length of time of contact between said water and said disinfecting agent along said flow path of said contact tank, said method comprising: disposing a sensor within said flow path closer to said water inlet than to said water outlet relative to said flow path; operating said sensor to provide a measured value indicative of a concentration of said disinfecting agent in said water at said sensor and generate an electronic sensor signal indicative of said measured value; and controlling introduction of said disinfecting agent into said water at said disinfectant inlet based at least in part on said measured value.

16. The method of claim 15, wherein said disinfecting agent is an oxidizing agent.

17. The method of claim 15, wherein said disinfecting agent comprises a chlorine - containing substance.

18. The method of claim 15, wherein said step of operating said sensor comprises providing a substantially real time measurement of said measured value.

19. The method of claim 15, wherein said measured value relates to an oxidation or reduction potential of said water.

20. The method of claim 15, wherein said step of disposing a sensor comprises disposing said sensor within a first distance from said disinfectant inlet, said distance being less than 1/10 of a length of said flow path from said water inlet to said water outlet.

21. The method of claim 15, wherein said step of disposing a sensor comprises positioning said sensor such that a transit time between said disinfectant inlet and said sensor is no more than about 30 seconds.

22. The method of claim 15, wherein said step of controlling comprises operating a controller for receiving said electronic sensor signal and providing an output for controlling the supply of said disinfecting agent via said disinfectant inlet.

23. The method of claim 22, further comprising operating said controller for receiving information regarding a flow rate of water into said contact tank at said water inlet.

24. The method of claim 22, further comprising operating said controller for receiving information regarding an infectant load of said water entering said contact tank at said water inlet.

25. The method of claim 22, further comprising operating said controller for receiving information regarding a pH of said water entering said contact tank at said water inlet.

26. The method of claim 22, further comprising operating said controller receiving information from a second sensor disposed in said flow path downstream from said sensor.

27. The method of claim 22, further comprising operating said controller for receiving information regarding a concentration of said disinfectant agent in said water exiting said contact tank at said water outlet.

28. The method of claim 22, further comprising operating said controller for controlling a feed rate of a disinfectant feed mechanism for feeding said disinfecting agent into said water at said disinfectant inlet.