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GUIDELINES ON THE FILTRATION

AND DISINFECTION FACILITIES FOR FISH TANK WATER


General

(1) The filtration / disinfection system shall be a closed loop system capable of providing continuous filtration and disinfection action.  The system used should be operated round the clock.

(2) Seawater from doubtful sources should not be used for keeping live seafood. With effect from 1 August 2010, the law forbids any person to extract, supply, deliver or use seawater from specified prohibited areas for keeping live fish or shell fish for human consumption in the course of food business. Prohibited areas for extracting seawater include Victoria Harbour, the shoreline of Hong Kong Island (including Ap Lei Chau), the shoreline of New Territories West (including Tsing Yi) and the 14 typhoon shelters specified in the Merchant Shipping (Local Vessels) (Typhoon Shelters) Regulation.

(3) The use of synthetic seawater is desirable. If natural seawater is used, new batch of water should preferably be stored in an empty tank fitted with an effective filtration and disinfection system.  The system should be run for at least one to two hours before being used for keeping live seafood.  Abstraction of seawater for keeping live seafood should be avoided during and after inclement weather.

(4) Live fish and shellfish should be kept separately in different tanks and at a stock density not causing overcrowding.  It is preferable to use separate sets of filtration and disinfection systems for tanks used for keeping live fish, crustaceans and shellfish.  Live bivalve mollusks should be washed free of mud with clean water before being kept in the storage tank.

(5) The filtration and disinfection facilities for fish tank water should be properly installed and regularly maintained by a company/supplier specializing in water treatment for live seafood. At present, UV radiation is the most common method used for disinfection of fish tank water. Other methods used are ozone, copper-silver ionization and photocatalytic oxidation technology with the use of UV radiation and titanium dioxide.

(6) Food and Environmental Hygiene Department (the Department) reviews the disinfection methods from time to time. An updated list of the accepted methods is kept at the district offices of the Department for public reference. A copy of the guidance note specific for each of the methods can be obtained at those offices upon request. If an operator intends to use a method other than those on the list, he/she should apply to the Department with full particulars of the proposed system. Before it is accepted, the proposed system should not be installed for disinfection of the water of the fish tanks used for keeping live seafood intended for human consumption.

(7) The operators should assign dedicated staff to take care of the cleansing and maintenance of the whole system.

(8) All records using the format as per attached to register the maintenance details, including the checking and cleansing work carried out to the systems, replacement and addition of the filter medium, replacement of the UV-light bulbs/tubes, etc. should be completed and certified by the dedicated staff/contractor. The records should be kept on the premises for at least one year. They should be readily available for inspection and for reproduction should the Health Inspector demand for them at all times.

(9) All the internal surfaces of the fish tanks should be scrubbed and thoroughly cleansed regularly, preferably at least once a week. Sand, stones and other objects laid on the fish tanks for decoration purposes should also be cleansed in the like manner. After scrubbing and cleansing, all water in the fish tanks should be drained off. The fish tanks including the sand and stones inside should be rinsed clean before refilling of the wholesome seawater.

(10) All pipes for the supply of water and air to fish tanks should be thoroughly cleansed and rinsed with clean water during cleansing of fish tanks each time. Proper and thorough cleansing of the whole set-up at regular intervals are important in upkeeping the quality of tank water.

(11) The fish tank area should be clean, well ventilated and free from any building defect.

(12) Fish net and other articles in contact with the fish tank water should always be kept clean. If not in use, the fish net should be stored in a clean bucket specially for the purpose. After business hours, fish net and the buckets should be cleansed thoroughly and rinsed with clean water.

(13) When handling fish tanks, clean rubber gloves should be worn.

(14) Fish tanks and other connected articles left unused for a period of time should be cleansed thoroughly before they are used again.

(15) Periodic changing of tank water is an effective means to remove harmful substances produced by the stock after a period of time. Periodic changing of water will also prevent turbid water from decreasing the efficacy of disinfection systems.

Synthetic Seawater

(16) The marine salts used for the preparation of synthetic seawater should be sourced from reliable suppliers.

(17) Free residual chlorine level in tap water decreases with time.  Addition of salt and aerating the water overnight effectively reduce residual chlorine to a very low level.

(18) The instructions for the use of marine salts such as the proportion of salt and water to be used are usually printed on the packages and should be followed.

Filtration System

(19) The filter materials should be cleansed at least once a week and replenished at least once a month.

(20) If spongy filter is used, more regular cleansing and replenishment of the filter materials should be carried out. In addition, more regular cleansing and replenishment of filter materials should be conducted if the water quality is poor and/or fish stock density is high.

(21) If sand filters are used, they must be cleansed periodically by backwash. Backwash should be carried out until the effluent is clear. After a long running time, the sand should be replenished.

(22) If activated carbon filter is used, it should be regularly maintained.

(23) If circumstances permit, use of layered multi-sand filter comprising both coarse sand and fine sand as filter materials fitted with automatic backwash self-cleansing device is desirable.

(24) The filtration system should be installed upstream of the disinfection system and not vice versa such that it can remove suspended solids or particulate matters in the fish tank water which may affect the efficacy of the disinfection system.

Guidance Note for UV Radiation Disinfection System

(1) The UV lamp used should be operating at the wavelength of UVC range (i.e. 280-100 nanometer) with peak effect at 254 nanometer. The use of a double barrel UV lamp tube and higher lamp intensity is preferred.

(2) The UV lamp should be sealed completely to avoid human exposure to the UV radiation.

(3) As the output of UV lamp declines over time, the UV lamp should be replaced preferably at 6 to 9 months interval, before its natural burnt out time.

(4) The quartz sleeve of the UV lamp should be cleansed at least monthly by trained personnel of the operator or the system supplier.

(5) The system should be regularly maintained by trained personnel of the operator or the UV lamp supplier preferably at least once every 6 months.

(6) Since the efficacy of the disinfection system is also affected by water circulation time, the water in the system should recycle at least two times per hour, i.e. water passes through the filtration and disinfection system once every 30 minutes, in order to effectively reduce the bacterial load in fish tank.

For example, for a 600-litre fish tank, the water flow rate through the filtration and disinfection system should be 20 litres/min in order to achieve an overall cycling time of 30 minutes for the whole system.

(7)The operator should work with the supplier to ensure the system in place meet the design specifications aiming to achieve optimal disinfection efficacy.

Guidance Note for Ozone System

(1) For optimal disinfection efficacy, tailor-made systems by contractors are necessary. The system should be pilot-tested and calibrated prior to installation to ensure that they are able to produce optimal ozone concentration for disinfection.

(2) Regular maintenance of the system equipment should be carried out by trained personnel or the system supplier preferably at quarterly intervals. The ozone source must be switched off during the cleansing and maintenance operations.

(3) Ambient ozone levels should be monitored and equipment shutdown and alarm device should be incorporated into the system and operating automatically when levels exceed 0.1 ppm. If there are practical difficulties for installation of the off-gas destructor, the ozone generator and the contact tank should be installed in a well ventilated area fitted with ozone leakage detector with automatic alarm and equipment shutdown device. Users should take note of the potential hazard of improperly operated ozone system.

(4) If UV radiation is used to generate ozone, the UV lamp should be regularly replaced preferably at 6 to 9 months interval, but well before its natural burnt out time.

(5) For optimal disinfection efficacy, human safety and health of the fish, the system should be installed with an ozone contact tank where ozonation is done inside the tank with sufficient contact time. The ozone contact tank should be well covered. Continuous introduction of ozone directly to the fish tank is not recommended as the direct contact of ozone can be harmful to fish and the release of ozone off-gas can be hazardous to humans in the vicinity.  Direct introduction of ozone into the tank containing the filtration facilities should also be avoided as it would adversely affect the filtration and disinfection efficacy.

(6) The operators should require the supplier to ensure that the system in place meet the design specification aiming to achieve optimal disinfection efficacy.

Guidance Note for Copper-silver Ionization Disinfection System

(1) The operators should require the suppliers to ensure that the system in place meets the design specifications aiming to achieve optimal disinfection efficacy. Measurement of residual ions levels in the fish tank water should be carried out preferably at bi-weekly interval.

(2) The operators should consult the supplier of the system on the dosage of copper / silver ions to be used to ensure its effectiveness while not producing any undesirable side effects to the live seafood.

(3) The operators should monitor the pH value of the fish tank water preferably on daily basis to ensure that the pH is within the range of 7.2 to 7.8 for optimal disinfection.

(4) The electrodes of the ionizer should preferably be replaced at yearly interval.

(5) Regular maintenance of the system should be carried out by trained personnel or the system supplier preferably at quarterly interval.

Guidance Note for Disinfection System employing Photocatalytic Oxidation Technology with the use of UV Radiation and Titanium Dioxide

(1) The UV lamp used should be operating at the wavelength that is effective to trigger the photocatalytic oxidation reaction.

(2) The UV lamp should be sealed completely to avoid human exposure to the UV radiation.

(3) As the output of UV lamp declines over time, the UV lamp should be replaced preferably at 6 to 9 months interval, before its natural burnt out time.

(4) The quartz sleeve of the UV lamp should be cleansed at least monthly by trained personnel of the operator or the system supplier.

(5) The photocatalyst should be regenerated or replaced by the system supplier preferably at least once yearly.

(6) The system should be maintained by trained personnel of the operator or the system supplier preferably at quarterly intervals.

(7) The operator should require the supplier to ensure the system in place meet the design specifications aiming to achieve optimal disinfection efficacy.

Maintenance Record on Filtration and Disinfection Facilities for Water
for Keeping Live Marine Fish and/or Shellfish ( PDF / 14 KB )

 

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