Water Pollution Continuous Monitoring Technology in Japan
Maintenance of Analyzers for Water Pollution Continuous Monitoring
Contamination of sampling pipe and control tank may affect the data collected; they should always be kept clean. Clogging of sampling pump prevents sample water from being properly fed into analyzers and results in measurement missing. Therefore, sampling pump must be cleaned and checked for any abnormality once every week. Additional cleaning and inspection of sampling system should be performed if river water is significantly contaminated after heavy rain, etc.
In addition to the maintenance of analyzers and sampling system, the indoor environment of monitoring stations must be properly maintained. For example, air conditioning and ventilation are necessary in order to prevent measurement equipment from being affected by high temperature and humidity in summer.
(1) Sampling channel
It is recommended to install 2 sampling channels for alternative operation. This can prevent measurement missing even when a pump trouble and/or clogging of sample water intake occurs to either channel.
Sampling pipes and pump are equipped with automatic cleaning functions. The automatic cleaning function should be set to turn on at a proper interval according to the water pollution level of the target river.
(a) Sampling pump
A submerged pump is often used for sample water collection due to the higher reliability, ease of repetitive operation and the availability of automatic cleaning function.
The main trouble of sampling pumps installed in a river is clogging of intake port (strainer). To prevent the clogging of strainer, automatic cleaning of strainer on a periodic basis is often used. The automatic cleaning method generally used is "Inverse flow cleaning". This method requires installation of a pump specifically used for cleaning. The cleaning pump feeds pressurized water (tap water) to the sampling pump to flush out the contaminants accumulated at the intake of the sampling pump.
In addition to the automatic cleaning, it is necessary to take the sampling pump out of water and clean the contaminants (plastic substances, weeds and algae, etc.) which were not removed by automatic cleaning, using brushes.
Placing the intake of sampling pump in a basket made of stainless steel net as shown in Fig.7.2.2 is effective to prevent intake port clogging.
A sampling pump with sufficient margin of capacity should be selected to avoid water quality fluctuation (water temperature, DO and turbidity, etc.) in the process of sample collection. For example, a 200V-750W pump is recommended for a case where the length of sampling pipe is less than 50 meters and the pump head is approximately 5 meters. Sampling pumps made of stainless steel is recommended due to the lightweight and anti-corrosive feature.
(b) Sampling pipe
Steel pipes with inner surface coated with vinyl chloride or pipes made of hard vinyl chloride are generally used. Inner diameter of these pipes is normally 45 to 50 mm.
Several meters of thick flexible vinyl hose is used for the connection of sampling pipe and submerged pump for ease of pump lifting for cleaning, etc. Although sampling pipes made of steel has semi-permanent service life due to the strong endurance against corrosion, flexible tubes at the connection must be replaced once a year.
The measurement results are affected by contamination of the sampling pipes and it is very important to keep them clean. If sampling system is not equipped with automatic cleaning function, it is necessary to disassemble and clean the pipes with a brush, etc. on a periodic basis. Therefore, sampling pipes should be designed to allow disassembling at the flange portion. Fig.7.2.3 illustrates an example of the sampling pipe design allowing disassembly and the cleaning method.
When distributing sampling pipes, the distance between the sampling pump and monitoring station must be minimized. The shorter the distance, the less the sample water quality fluctuation. Maintenance is also easily performed. In order to prevent sample water quality change and deterioration of pipes, the sampling pipes should be installed in a U-shaped duct and the top of the duct should be covered to prevent exposure to direct sun light.
(c) Control tank
Sample water collected by sampling pump passes through rough and fine screens for removal of non-dissolved contaminants and is fed into analyzers. The screens are automatically flushed out with tap water once every few hours (it is normally cleaned simultaneously with the automatic cleaning of sampling pipe).
Contaminants on inner walls of control tank and screens and sediments on the bottom may not be removed by automatic cleaning and it is necessary to clean them once every week. In particular, accumulation of a large amount of sand and dirt is expected after a heavy rain, and cleaning of each part should be carefully performed.
Automatic cleaning cannot be available for some portions of piping system. Therefore, piping distribution should be designed so that the disassembly and cleaning are easily performed. Valves in the piping should be minimized to prevent troubles due to valve clogging. If a use of valve is unavoidable, use a ball cock instead of normal valve.
(2) Drain system
Waste water is discharged either by "natural flow" or "forcible drainage" depending on the location of the automatic monitoring station. The natural flow uses the height difference between the monitoring station and river, whereas the forcible drainage is used when the waste water cannot be discharged naturally.
In either case, the waste water from a monitoring station must be discharged to the river at the downstream of the sampling point to avoid the discharged waste water from being mixed with the water collected as the sample.
When waste water is discharged by means of natural flow, the diameter of discharge pipe should be large enough to prevent clogging due to mud, sand and/or algae. Pipes with an inner diameter of approx. 100mm are generally used.
In the case of forcible discharge, it is necessary to install a waste water pit of about 2 square meters and a drainage pump with a capacity equivalent to or greater than that of sampling pump should to be used. As the measures against pump failure, the drainage pump should be designed to automatically shut off upon receiving an alarm signal indicating that the upper water level limit of the waste water pit is reached.
The pump's intake port and water level sensor are easily contaminated and frequent cleaning is necessary. Periodic removal of sediment on the bottom of the drain pit is also necessary.
(3) Recorder
At the time of maintenance and inspection of monitoring stations, the values on the recording charts are compared with the previous values to check the difference of measurement results from those of previous measurement. When any abnormality is found in the data collected to the Central Station, the data on the recording chart is used for the confirmation of the abnormality. The recording chart is also useful as the data backup.
Maintenance and inspection works if recorder include the weekly confirmation of data recording conditions, checking and replacement of recording paper (monthly), confirmation and adjustment of recording time and replenishment of ink or cartridge replacement. Data output should be checked once every year.
Paper feed trouble, including paper jamming, results in missing of measured data and/or damage to the recorder due to an excessive load. Recording paper should be leafed up before loading (Fig.7.2.4).
(4) Maintenance of measurement stations and peripheral facilities
A water pollution monitoring station should be designed not only for protection of analyzers from rain and wind, but also to assure proper measurement environment and ease of maintenance. Ventilation and air conditioning equipment would be necessary. Refrigerator for storage of calibration solution and reagents, experiment table and sink for preparation of reagents and shelves and containers for storage of chemicals and mechanical spare parts should be installed.
In order to attain smooth operation of automatic monitoring stations, maintenance of peripheral facilities such as water supply, power supply and drainage treatment is indispensable in addition to the maintenance of analyzers.
The containers for storage of chemicals and monitoring station building should be locked for security. Further security of station building and sampling location should be assured by means of locks and fences.
(a) Layout inside a station building
There should be a space for maintenance work in front of the analyzers. Behind the analyzers, a space for cleaning work of sample water pipe should be secured.
-The ceiling height should be approx. 3m because the adjustment tank is installed at an elevated position.
-The floor should be designed for water-proof for ease of cleaning and dust prevention.
-The lighting equipment should be installed at a proper location, taking into account the brightness necessary for various works.
-When a window is installed, proper measures for security and prevention of direct light exposure should be taken.
-A parking space for maintenance work should be secured.
(b) Tap water facility maintenance
-Tap water facility is necessary for maintenance.
-At weekly inspection, the amount of water used after the previous inspection should be checked by reading the water gauge to check for leakage.
-The faucets should be installed for ease of access for cleaning of analyzer tanks.
(c) Electric facility and power consumption
-The power panel supplies 100V and 200V power and has circuit breakers. The power consumption by the station is checked on a weekly basis to check for any abnormality.
-Since automatic analyzers are easily affected by noise, power distribution to equipment with heavy load fluctuation should be separated from the line to analyzers.
-Each power line should be provided with a circuit breaker and must be grounded.
-A power panel should be provided with proper margin to cope with the increase of power needs in the future.
(d) Management of chemicals
-Chemicals must be stored in a proper cabinet and the inventory must be checked at the time of periodic inspection.
-Chemicals include toxic or harmful substances and the cabinet of these chemical must be locked for security purpose.
-Emptied chemical containers and bottles must be cleaned with water 2 to 3 times before disposal.
(e) Waste liquid treatment
-Waste liquid after manual analysis and calibration should be safely stored in a drainage container and treated properly before discharge to public water area or sent to designated waste water treatment contractor for treatment.
