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Disinfection of Aquarium Effluents by Chlorination and Uv Treatment

M.N. Islam
Department of Fisheries Technology, Bangladesh Agricultural University Mymensingh-2202, Bangladesh

M.A.R. Faruk
Department of Fisheries Technology, Bangladesh Agricultural University Mymensingh-2202, Bangladesh

V. lnglis
Institute of Aquaculture, University of Stirling. Scotland, UK

Abstract/ Executive Summary:

The study was conducted to investigate the efficacy of chlorine and UV irradiation in disinfecting aquarium effluent. A non-agglutinating, avirulent strain of Aeromonas salmonicida (NCIMB 11 02) was used as the test organism. Effluents from a fish tank were inoculated with a suspension of test organisms and subsequently treated with different concentrations of hypochlorite and UV irradiation separately and simultaneously. When used alone, 1.0 ppm hypochlorite reduced the viable cell count from 6.5 logs to 3.0 log within 20 minutes of the contact period. On the other hand, when used in combination with UV irradiation only 0.5 ppm hypochlorite exerted the same bactericidal effect within the same contact period as was observed with 1.0 ppm hypochlorite alone. This result indicated that the required dose of disinfectant for the disinfection of aquarium effluents can be considerably reduced when it is used in combination with UV irradiation.

Keywords: Disinfection, Effluent, Chlorination, UV

Location: Department of Fisheries Technology, Bangladesh Agricultural University Mymensingh, Bangladesh

Start Date:

End Date:

Program Area: Animal Health and Management

Commodity: Fish, Virus

Objectives:

To investigate the disinfection efficiency of chlorine and UV irradiation in aquarium effluent and to determine if the simultaneous application of chlorine/UV in these increased the efficacy.

Methodology:

Test organism and growth procedure A non-agglutinating, the avirulent strain of Aeromonas sa/monicida (NCIMB 11 02) was used as a model bacterium in this study because the virulent strain of this organism is highly pathogenic to salmonid fish causing septicemia and abundant in both fresh water and marine environment in the colder region. The bacteria were grown at 22°C for 3 days in tryptone soya agar (TSB, Unipath, Basingstoke). Cells were harvested by centrifugation at 2500 rpm for 10 minutes and the resultant pellet was resuspended in 0.85% sterile saline solution. The suspension was further diluted to give a concentration of approximately 108 cfu /mi. Preparation of disinfectant and neutralizing solutions Chlorine stock solutions were prepared from a sodium hypochlorite solution (14% w/v available chlorine). Appropriate volumes were added to distilled deionized water to obtain 10, 20, 30 and 40 ppm free chlorine. Stock solutions (11, 22, 33 and 44 ppm) of a neutralizing solution for hypochlorite were prepared by dissolving appropriate quantities of sodium thiosulfate in distilled water. Four separate stock solutions of hypochlorite were prepared so that when 0.5 ml was added to 9.5 ml of the test sample the required concentration range of 0.5 to 2.0 ppm was attained. Similarly, since 1 gm of active chlorine is effectively removed by 2 gm of thiosulfate (Hom 1971 ), stock solutions of sodium thiosulfate from 11 to 44 ppm were prepared so that when 1 ml was added to the 1 0 ml test sample there will be a concentration ratio of 2:1. Fish tank and UV assembly Twenty five rainbow trout (1 00-150 gm each) were introduced in a tank of 100-gallon capacity and held for several days with standard feeding and husbandry. The tank was fitted with a pipe in the middle to discharge the effluent into a sump tank (1 00 gallon plastic tank) mounted on the floor below the fish tank. The sump tank had two overflow pipes mounted near the top of the tank but below the level of the fish tank outlets. A submersible pump with an integral float switch was mounted inside the sump tank to pump water through the UV unit (Aquarium sterilizer-Model 30) and then to waste. A sidearm with a valve was also present to control the rate at which water was pumped from the sump. Water sample preparation The effluent from the fish tank was collected from the sump tank in a sterile conical flask and brought to the laboratory. The water contained dissolved and suspended organic matter from feed pellets, faecal materials and other waste. The sample was heated at 80°C for 10 min in a water bath to kill the indigenous bacteria and was subsequently cooled to 7°C. Hypochlorite treatment Heat treated and cooled water sample was inoculated with the previously prepared bacterial suspension to obtain a suspension of approximately 107 cells/mi. From this suspension 9.5 ml aliquots were taken in 4.5 em diameter sterile plastic disposable petri plates and 0.5 ml stock solutions of different concentrations of hypochlorite were added. Petri plates with the samples were immediately put in an ice bath (ice-water temperature 7°C) placed over a magnetic stirrer. After the required contact periods with stirring 1.0 ml of stock solution of different concentrations of the neutralizing solution was added to each sample. After neutralizing for 1 min samples were subjected to total viable count according to the drop count method (Miles and Misra 1938). The experimental procedure has been summarized Combined UV-hypochlorite treatment Effluent in the sump tank with indigenous and added bacterial inoculum was treated with a calculated amount of hypochlorite solution to give the desired concentration of chlorine and mixed quickly and thoroughly by vigorous agitation. After selected time intervals (1 0, 20 and 30 min) the effluent water was passed through a UV unit by using a submersible pump. UV treated water sample was collected from the discharge point and quickly dechlorinated by sodium thiosulfate and subjected to total viable count (Miles and Mirsa 1938). The temperature of the aquarium effluent was around 7°C.

Source of Information: Bangladesh J. fish. Res., 1 (1) : 01-08

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

A general trend in the loss of viability of the cells was observed with the increase of contact time as well as the concentration of chlorine. With 0.5 ppm chlorine, one log reduction was achieved within 5 minutes of the contact period, thereafter the reduction was slow and gradual. There was a more rapid and massive reduction of bacteria/ number at the 1 .0 ppm free chlorine concentration /eve/. At this concentration, two log reductions could be achieved within 5 minutes and three log reductions in 15 minutes, which is equal to a 99.9% reduction in the viable count. The rate of reduction was rapid during the first 5 minutes with 0.5 ppm and the first 15 minutes with 1 .0 ppm chlorine but after that, the slope of the curve leveled off. With 1 .5 ppm and 2.0 ppm, the number of viable cells fell below the level of detection within 5 minutes, which means the .99,9995% reduction in the cell number could be achieved in 5 minutes with 1.5 ppm chlorine under this experimental condition. This effect is identical to the effect of 1.0 ppm chlorine alone Showing that required chlorine. concentration is only 50% when it is used in combination with UV treatment. In the UV study test organisms were a mixed population because indigenous bacterial flora of the aquarium effluent was not eliminated by treatment as was done when the only hypochlorite was used. This was necessary to see the combined effect of UV and chlorine in the actual aquarium system.

Knowledge Management: Report/Proceedings