Dear Hans The aquatic ...

Dear Hans

The aquatic environment must meet the needs of the farmed organism, both in respect of water quality and physical properties. Particles are the undissolved fraction of the feed input to the system. These particles are normally measured as suspended solids (SS). In a recirculated fish farm, particles originate from waste feed and feces. In a farm with intake from surface waters, organic and inorganic particles will also constitute a portion of the particle distribution. As stated in the section on tanks and ponds, self-cleaning properties are very important for down stream filtration systems, particles must be transported quickly and removed gently from the system. Micro screens can be installed at fish farm outlets for reduction of solids loading on downstream rivers. Sometimes filters are employed at inlets to increase intake water quality.

Potentially harmful substances-e.g. pesticides, heavy metals and hydrocarbons-are often released into the aquatic environment. When large quantities of pollutants are released there may be an immediate impact as measured by large-scale sudden mortalities of aquatic organisms, e.g. fish kills resulting from contamination of waterways with agricultural pesticides.

Following filters can be used for fish farming.

1. Disc filters
2.  Drum filters
3. Belt filters

Drum filter is a mechanical and self-cleaning filter 

Function of Drum- and Disc filters:

1. Water to be filtered enters the inside of the drum.
2.  The water is filtered through the drum’s filter elements. The difference in water level inside/outside the drum is the driving force for the sieving.
3. Solids are trapped on the filter elements and lifted to the back-wash area by the rotation of the drum. The drum rotation is intermittent or continuous depending on type of control.
4. Water from rinse nozzles is sprayed from the outside of the f lter elements. The rejected material is washed out of the filter elements into the sludge tray.
5.  Rejected sludge flows together with water by gravity out of the filter.

The benefits of micro screen filtration are as follows:

1. Reduction of organic loading on bioflter(s).
2.   Improving turbidity of water.
3.  Reduction of larvae and eggs of some parasites.
4.   Improving conditions for nitrification
5.   Stabilising function of bio filters.

 

BIOLOGICAL FILTRATION

Some of the waste from fish and feed will be dissolved and has to be degraded or transformed into harmless substances. Again you have to consider organic material and nitrogen containing substances, (Phosphorous is an inert substance, with no toxic effect).The Bio filters can be used for that.

 

Fluidised bed filters:

Bio filters must be designed to operate as nitrification filters

At less than 5 PPM BOD, heterotrophe bacteria will be limited in growth by lack of substrate, conditions will be in favour of nitrifi cation i.e. nitrosomonas and nitrobacter will have a higher growth rate. This can only be achieved by a combination of feed management, sizing of surface area and microfi ltration before biofi lters.

Carbon dioxide

Production of CO2 is related to oxygen consumption in fish and degradation of organic material in biological filters. With CO2 the PH of water will come down and to be maintained by following

Neutralisation by Ca(OH)2 :

Neutralisation by NaHCO3 :

UV water purification –

 The best answer for aquariums, ponds and fish farms

A UV-lamp water purification system typically employs a light with a wavelength of 254 nanometres. Aquarium water pumped through the UV chamber is exposed to this light and irradiated. Free-floating microorganisms are affected by the UV light and are no longer able to multiply. Through continual use, UV-lamp purification can help manage water quality issues such as bacteria, algae, and parasites.

Regards,

Prem Baboo