Production of  Clarias gariepinus  Fingerlings in Recirculating Systems

Oparaku Nkiruka Francisca; B.O. Mgbenka

Production of Clarias gariepinus Fingerlings in Recirculating Systems

Oparaku Nkiruka Francisca

, B.O. Mgbenka

National Centre for Energy Research and Development, Zoology Department, University of Nigeria, Nsukka, Nigeria

Author

Correspondence author
International Journal of Aquaculture, 2013, Vol. 3, No. 21 doi: 10.5376/ija.2013.03.0021
Received: 09 Jun., 2013 Accepted: 27 Jun., 2013 Published: 09 Jul., 2013

This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Preferred citation for this article:

Francisca, 2013, Production of Clarias Gariepinus Fingerlings in Recirculating Systems, International Journal of Aquaculture, Vol.3, No.21 117-125 (doi: 10.5376/ija.2013. 03.0021)

Abstract

Fingerling productions using recirculating system of fish pond, powered with electricity and solar panelsas power sources were carried out. Plumbing work was carried out for installation of pipes and accessories that helped in water circulation inside and outside the pond and treatment tank. Oxygen pump with air stones was installed and air stones placed in each pond to aerate the ponds continuously. The dimensions of treatment tank which was constructed with concrete were (3.4×1×1.5) m. There were four compartments in the water treatment tank each measuring (1×0.6×1.25) m. Procurements of biofilters that were arranged inside the treatment tank in the following order; bioblocks, biobrush, Maifan stones, coral sand, ceramic ring, activated charcoal and UV light. The results of the microbial analysis of the recirculating system water samples were (2.2×10³±200) cfu/mL, (6.8×10³±10) cfu/mL and (1.8×10³±10)cfu/mL for solar powered pump water, electric powered pump water, and UV treated waste water (outlet water) respectively. Oxygen values were 9.4±1.6, 6.2±0.20, 5.7±0.20, 7.2±0.15 for inlet, solar powered fish pond, electric powered fish pond and UV treated water respectively; dissolved oxygen was between 5.7 mg/L to 9.4 mg/L. Survival % was high for both systems.

Keywords

Recirculating system; Clarias gariepinus; Power sources

Water conservation and reuse has become a major issue in aquaculture in recent years. Concern over increased demand in aquifers, cost of operating wells, environmental impact of aquaculture effluent, and the desire to increase production efficiency continues to drive advances in technology and management practices. Several of the management strategies developed to address these issues include enhancing water circulation in ponds and developing intensive, recirculating tank systems. The combination of these two technologies is referred to as pond recirculating systems.

Pond culture is the most widely used production technology in world aquaculture. The lower stocking and feeding rates, permit of water and lower investment and production costs have contributed to the present expanse of pond production worldwide (Wheaton, 1977).

Masser et al. (1992) stated that recirculating system is biologically complex and mechanically sophisticated. It requires constant monitoring to ensure that they are functioning properly.

Major objective of water circulation is to destratify, or mix, the deeper, cooler, oxygen-deficient waters with the shallow, warmer waters rich in dissolved oxygen, reducing the risk of low dissolved oxygen due to turnovers and again water disinfection is important. In this experiment filtered water was passed through UV light to destroy any microbes causing disease that may be in the water.

One way of achieving high production intensities is through the use of recirculating aquaculture tanks systems (concrete or fibre glass). This system requires aeration and complete feeds to support the high stocking densities (Boyd, 1982). In aquatic production aeration is vital to the vigorous health and vitality of fish. Intensively cultured fish becomes stressed without enough oxygen if not aerated, Boyd (1982). Paddle wheels and surface aerators do not address these problems or correct them. Complete aeration of pond through pond bottom is achieved with recirculating systems and toxic gas removal enables oxygen-breathing micro organisms and insects to feed on the organic sediment and organic water (Boyd and Watten, 1989). Recirculating system maximizes water re-use by employing comprehensive water treatment system. Water treatment processes typically are solid removal, infiltration, gas balancing, oxygenation, and disinfection. By addressing each of the key water concern through treatment rather than flushing as is used in flow-through and the partial reuse systems, ultimate control over culture conditions and water quality is provided. Deborah and Andrew (1997) concluded that indoor recirculating aquatic systems may be used for various operations, some of which may include: the quarantine of new animals, isolation of sick fish, aquaculture, research, or as educational displays.

In order to realize the full potential of agriculture in Africa there is an urgent need to develop and promote agriculture technologies that will intensify production through the application of renewable energy systems. Photovoltaics energy and electricity was used to power the recirculating systems. The use of recirculating systems will help to improve fingerling production, renewable energy will serve to encourage eco-friendly, economically and socially viable aquaculture. The use of electricity in Nigeria is not feasible as a result of constant power failure and unsteady electricity supply. There is need to try alternative energy sources as result of perennial problem of power in our country since recirculating system will not function properly where power is not steady. Effort was made in this work to compare electricty and photovoltaics productions.

1 The Objectives of This Project Were to

Assess the production and the growth parameters of Clarias gariepinus cultured in recirculating system; Assess the effect of the use of energy sources (photovoltaics and electricity) in recirculating system for fish production; Determine the water quality parameters of recirculating system using biofilters and UV light.

2 Results

As shown in Table 1, the results of the microbial analysis for the water samples were (2.2×10³±200) cfu/ml, (6.8×10³±10)cfu/ml and(1.8×10³±10)cfu/ml for solar powered pump water, electric powered pump water, and UV treated (outlet water) respectively. The inlet water had no aerobic mesophilic bacteria. There were no Escherichia coli in any of the water samples. The total count show the number of organisms recorded while the sensitivity tests conducted showed the type of the organism identified was non pathogenic only aerobic mesophilic bacteria were seen as shown above. Inlet water had no fungus and no aerobic mesophilic bacteria were seen in the inlet water. Water from the electric powered pump recirculating system had the highest average aerobic mesophilic bacteria of (6.81×10³±10)cfu/ml followed by solar powered pump water which had (2.2×10³±200)cfu/mlaerobic mesophilic bacteria count total. The lower microbial count for the solar powered pump water could be due to the fact that the solar powered pump is not restricted by power shortage and therefore with continous flow, the water flows freely and is recirculated unlike the electric powered which is restricted by light and might be stagnant during power shortage. Treated water had the lowest aerobic mesophilic bacteria present. This is an indication that the UV is effective in controlling the microorganism that might be in the system which might result in the disease outbreak in the system.

Table 1 Results of microbial analysis of the water samples in the recirculating system of solar and electric powered fish pond

Table 2 shows the results of the physicochemical properties for the different water sample. pH values were 6.4±0.8, 6.9±0.17, 6.2±0.01, 8.0±0.01 for inlet, solar powered pond, electric powered pond and UV treated water respectively. pH values recorded shows that the highest pH values was in UV treated water with the value 8.0±0.01, followed by 6.9±17 in solar powered fish pond, the least was 6.2±0.01 in electric powered fish pond. Oxygen values were for inlet, solar powered pond, electric powered pond and UV treated water respectively, dissolved oxygen was between 5.7 mg/L to 9.4 mg/L. and temperature was between 26.2℃~26.5℃. NH₃ (mg/L) were for inlet, solar powered pond, electric powered pond and UV treated water respectively the least was 0±0 in the inlet water. Nitrate values were for inlet, solar powered pond, electric powered pond and UV treated water respectively. NO₂(mg/L) were for inlet, solar powered pond, electric powered pond and UV treated water respectively.

Table 2 Mean values of physicochemical properties of the water samples in the recirculating system of solar and electric powered fish pond

The inlet water had the highest quantity of dissolved oxygen which is more favourable for aquatic life, followed by the UV treated water, solar powered pump water and then electric powered pump water. All the treated samples affected by the fish activities had the same concentration of calcium carbonate, nitrate and nitrite, which were higher than the concentration for that of inlet water. However the concentration of ammonia in the UV treated water was much lower than that of the solar powered pump water and then electric powered pump water. This shows that UV disinfection as stipulated by other authors is really a good method of disinfection.

Growth performance of Clarias gariepinus fry in recirculating system powered by solar photovoltaics and electricity showed that the average length and weight of fish in solar pump of recirculation system were 11.058±0.84 and 19.46±1.17, respectively after eight weeks of rearing in recirculating system while those powered with electricity were 15.7±0.30 and 20.7±10.61 (Table 3). Weight gained for solar powered recirculating system were recorded and the electricity powered ones were also recorded as well throughout the period of rearing.

Table 3 Growth performance of Clarias gariepinus fry in recirculating system powered with solar photovoltaic and electricity

Length and weights of solar powered systems were stated as follows: the lowest lengths from 2 weeks to 8 weeks was 1.4±0.07, and 15.7±0.30.73 was the highest; the lowest weights was 0.06±50 and the highest was 20.7±10.61. The number of fish stocked reduced from 500, 482, to 378. The lowest biomass was 30 g while the highest was 7586.46 g. Quantity of feed given (g) was as presented in the Table 1; the lowest quantity of feed given was10.5 g and the highest was 379.323 g. The lowest weight gain was 0.4 g and the highest was 13.93 g. The number of fish survived during the period was calculated and percentage recorded. Solar had the highest mean weight of 20.7±10.61 while the electric powered fish pond had the fish weight of 19.46 ±1.17. The initial number of fish was 500, at 4 weeks was 480 and in 6 weeks 375 and final number was 375. Feed ration (g) given at 5 % body weight were 1.5, 24.72 and 110.625, 364.875. Total biomass (g) were from week 2 to 8 were 30494.4, 2212.5 and 7297.5. Solar had the highest biomass of 7586.46 g while the electric powered fish pond had the total biomass of 7 297 g. Total Weight gain (g) was 0.97, 4.87 and 13.56. Survival (%), 1 009 675 (Table 3). Food conversion ratio were (FCR) for solar powered system were, 1.0, 1.34 and 1.01, while the electric powered for week 4, 6 and 8, were 1.38, 1.17 and 1.00%. FCR is one of the most important benchmarks for measuring the efficiency of an operation; FCR alone does not give a true measure of production. Survival % was high for the both system.

Conductivity of the electric and solar powered system is shown on the Table 4. For electric powered system conductivity was (35±5.00) µS/m and the solar powered was 45 µS/m, inlet water was (10±0.58) µS/m while the treated water was (85±15) µS/m.

Table 4 Conductivity and Total dissolve solids of water recirculating system

Total dissolved solids (ppm) for electric powered pump was (23.45 ± 2.55) ppm while solar powered are 30.15± 9.85. Total dissolve solids for Inlet water was (6.7 ±0.70) ppm and treated water was (56.95± 6.05) ppm. Solid wastes or particulate matter, consisted mainly of feaces and uneaten feed.

Table 5 shows the biochemical oxygen demand for recirculation system. Electric powered pump had the highest BOD which was (4.80±0.70) mg/L. The water from the solar powered pump had biochemical oxygen demand of (3.20±0.20) mg/L; the inlet water had nothing while the treated water had (1.60±0.40) mg/L.

Table 5 Biochemical oxygen demand of recirculating system

3 Discussion

In this work oxygen values were for inlet, solar powered pond, electric powered pond and UV treated water between 5.7 to 9.4 mg/L which are within the acceptable levels. Tookwinas and Charearnrid (2008) obtained dissolve oxygen range 4.0-8.0 mg/L during their experiment with recirculating system, the range which was a little difference with the range obtained in this work. Syarikat (2008) obtained dissolved oxygen 6.5 mg which was within the range in this work. Pada (2007) obtained the oxygen range of 10.5mg/L during his work with recirculating system. Dissolved oxygen supply is usually the first process applied to prepare water for further use, because dissolved oxygen is often the first water quality parameter to limit production in intensive culture systems (Colt et al., 1991). Even though the availability of dissolved oxygen could be increased by movement of water from a depth to a height as was achieved during the conduct of this experiment and the use of aerator, other fish wastes can begin to accumulate to concentrations that must be reduced to maintain a healthy fish culture environment (Colt et al., 1991). Hence several complementary water treatment processes are required to reduce waste accumulations to maintain a healthy fish culture environment. Water treatment processes are used to change the physio-chemical conditions or characteristics of the water that pass through the process. Sometimes water treatment processes can change more than one characteristic of the water. For example, water flowing through a trickling biofilter can gain dissolved oxygen and nitrate, while dissolved carbon dioxide and un-ionised ammonia are removed (Wheaton et al., 1991; Summerfelt et al., 2004).Other physicochemical parameters of the pond were pH 6.2-7, temperature 26.2℃-26.5℃ which differed with the work of Syarikat (2008). Temperature was 29℃, pH 7.7, Syarikat (2008). Tookwinas and Charearnrid (2008), obtained pH 7.5-8.3, temperature 26℃-32℃, ammonia was less than 0.02ppm, Tookwinas and Charearnrid (2008). Ammonia in this work was 0.6 ppm in the two recirculating systems but improved to 0.3ppm after passing through biofilters and activated carbon. The oxygen ranges from (5.7-9.4) mg/L indicated that the aerator system and the biofilter are technically capable of delivering sufficient oxygen and removing nitrogenonous waste that could contaminate water respectively. Critical to successful operation of RAS is the ability to remove ammonia. The biofilter system was able to keep ammonia below 0.6 mg/L in the culture tanks. Nitrate, the end product of nitrification, is relatively nontoxic except at very high concentrations (over 300 ppm). Usually nitrate does not build up to these concentrations if some daily exchange (5 to 10 percent) with fresh water is part of the management routine. In general, the project experiment went well as both systems were functioning in the environment at the facility and NH3-N levels in the system with biofilter. The more critical measurement for fish growth is the unionised ammonia. Pada (2007) recorded ammonia levels 0.005 mg/L for the system without biofilter and 0.015 mg/L for the system with filter. There was no ammonia in the inlet water from bore hole water supplying the whole campus community with drinking water. Ammonia is the principal nitrogenous waste released by fish and is mainly excreted across the gills as ammonia gas. Ammonia is a byproduct from the digestion of protein. An estimated 2.2 pounds of ammonia nitrogen are produced from each 100 pounds of feed fed. Bacteria in the biofilter convert ammonia to nitrite and nitrite to nitrate, a process called nitrification. Both ammonia and nitrite are toxic to fish and are, therefore, major management problems in recirculating systems. Ammonia in water exists as two compounds: ionized (NH⁴⁺) and un-ionized (NH₃) ammonia. Unionized ammonia is extremely toxic to fish. The amount of unionized ammonia present depends on pH and temperature of the water. Un-ionized ammonia nitrogen concentrations as low as 0.02 ppm-0.07 ppm have been shown to slow growth and cause tissue damage in several species of warm water fish (Michael et al., 1997). The removal of solid wastes, the uneaten feed and faeces by biofilter from the culture tank was efficient. However, wastes that deposit in the joints of the discharge pipe from the culture tanks to the reservoir tank need to be removed daily. The wastes that accumulate in the sedimentation tank need to be flushed out manually. RAS consists of an organised set of complementary processes that allow water leaving a fish culture tank to be reconditioned and then reused in the same fish culture tank or other fish culture tanks (Liao and Mayo, 1972; Timmons et al., 2002).

Microbial analysis in the ponds were 2.2×10³ cfu/mL³, 6.8×10³ cfu/mL³, 1.8×10³ cfu/mL³ for solar powered, electric powered and UV treatred water. The lowered microbial count could be due to the fact that the solar powered were never stagnated as a result of power failure because there was availability of power all through the duration of the experiment. The electricity powered pond suffered from power outages for between 2 hours-5 hours two times a week. The pumping of treated water from under ground treated water to the fish ponds helped in improving dissolved oxygen in the fish ponds coupled with the fact that the water was aerated continuously during the period all these enhanced the dissolved oxygen in the pond and prevented the organisms from exposure to the dangerous low level of oxygen. Khleifat et al. (2006) noted that ultraviolet radiation could eliminate microorganisms when it is expose to ultra violet radiation. Eccleston (1998) reported that the UV is harmful to microorganism and it could improve water qualities. The UV system has distinct advantages where waterborne pathogens are a problem (Gadgil and Shown, 1995).The challenge to designers of recirculating systems is to maximize production capacity of capital invested through employing the use of efficient energy sources to power the systems. Components should be designed and integrated into the complete system or existing fish ponds to reduce cost while maintaining or even improving reliability. There are many alternative technologies for each process and operation. The selection of a particular technology depends upon the species being reared, production site infrastructure, production management expertise, and other factors. Prospective users of recirculating aquaculture production systems need to know about the required water treatment processes, the components available for each process, and the technology behind each component. A recirculating system maintains an excellent cultural environment while providing adequate feed for optimal growth.

Most recirculating systems are designed to replace 5% to 10% of the system volume each day with new water, in this work 10% of water was exchanged every day, it is not compulsory but is by choice since water was available during the course of this project. This amount of exchange prevented the build-up of nitrates and soluble organic matter that would eventually cause problems. In some situations, sufficient water may not be available for these high exchange rates. A complete water exchange should be done after each production cycle to reduce the build-up of nitrate and dissolved organics. For emergency situations it is recommended that the system have an auxiliary water reservoir equal to one complete water exchange (flush). The reservoir should be maintained

The feed conversion ratio (FCR) is estimated at 2.2:1 (2.2 pounds of feed will produce 1 pound of fish) using a 32 percent floating catfish pellet (Carole and Nathan, 2002). FCR of 1.3 to 1.5 was obtained during experimental trials. This is a little higher than what was obtained in this work, food conversion ratio (FCR) for solar powered system was 1.0 to 1.34 while the electric powered pond was from 1.00 to 1.38. Carole and Nathan (2002) noted that FCR could be used as benchmarks for measuring the efficiency of an operation; an artificially low FCR can be created by underfeeding, so it is important to consider the growth rate. Survival is estimated to be 70 percent. The survival rate was high in the photovoltaic’s and generator powered system because sorting was conducted every three days initially and later every two weeks so as to prevent cannibalism. Cannibalism is the main problem with fry rearing as well as competition for feed de Graaf et al. (1995) reported in his work that cannibalism were the major factors affecting the pond nursing of C. gariepinus. Effort was made to prevent cannibalism, they were fed properly and adequate water quality maintained as the water was aerated and circulated throughout the period of rearing, resulted in the high survival rate of the fingerlings. Toxic metabolic products (e.g. ammonia) in water can be decomposed effectively by a close contact of ammonia with oxygen on the large surface area of plastic substrates in the biofilters tank. In the conventional method, toxic metabolic products such as ammonia have been oxidized by blowing air into the water or zeolite and activated carbons have been used to absorb unwanted products but which absorbents are required to be cleared frequently to remove clogged materials or be replaced.

4 Conclusion

Recirculating water systems should be designed for simplicity of operation and economic feasibility. Sufficient time must be allowed for conditioning of the biofilter prior to introducing fish. Ammonia and nitrite concentrations must be checked frequently and biological filtration using media to remove waste ammonia and nitrite should be practiced. Biological filtration to remove waste ammonia and nitrite. These processes can be achieved by a simple composite unit such as an aquarium filter and UV which reduced disease outbreak as was accomplished in this work.

5 Materials and Method

5.1 Installation of Recirculating System

5.1.1 Construction of pond and stocking of fish pond

Pond was constructed and dimensions are (1.55×2.88×1.2) m = 5.208 m³ which had the capacity of containing 1000 litres of water (Figure 1 for details and also diagrams 37 and 38). Plumbing work was carried out for installation of pipes (Figure 2) and accessories that will help in water circulation inside and outside the pond and treatment tank. Oxygen pump with air stones was installed and air stones placed in each pond to aerate the ponds continuously. The oxygen pump was mounted on the roof very close to the pond.

Figure 1 Recirculating system connections and Solar module for powering recirculating system

Figure 2 Pipes connection in recirculating system

Three weeks old fry were stocked at a high density stocking rate of 101 larvae/m². That is 500 larvae per pond. Fry was fed with feed (ground artemia) containing 64 % protein three days after hatching at 5% body weight for one month, Feed containing 56 % protein (0.3-0.5mm in size) was fed at 5% body weight till the end of rearing, fish was fed twice daily, at 8.00 am and 4pm. Growth of the fish was monitored by measurement of length and weight measured with ruler and weighing balance respectively, every two weeks. At the end of two months it was harvested and growth was evaluatedusing the following methods;

Total weight gain= W₂-W₁

(W₁- initial weight, W₂- final weight)

Average daily weight gain, ADG (g / day) =W₂-W₁

Food Conversion ration (FCR)=Total dry feed/weight gain.

5.1.2 Treatment tank construction

The dimensions of treatment tank which was constructed with concrete are (3.4×1×1.5) m. There were four compartments in the water treatment tank each measuring (1×0.6×1. 25) m (Figure 3).

Figure 3 Plain view of fish pond and treatment tank

Procured biofilters namely bioblocks, biobrush, Maifan stones, coral sand, ceramic ring, activated charcoal and UV light were used for this study. They were arranged inside the treatment tank in the following order. Biobrush, bioblock, Maifan stones, coral sands, ceramic ring, activated charcoal and UV light.There were four compartments in the water treatment tank each measuring (1×0.6×1.25) m. The first compartment contains the biobrush, the second had bioblocks, the third contained maifan stones, coral sands, ceramic ring and activated charcoal, finally the last chamber housed the UV fluorescent tube which was placed at close proximity to the water surface but was not immersed in the water. Two pumps, Interdab electropome Jet 100 M 1horse power pump and Grundfos KPBasic 300A submersible pump were procured at Onitsha and Lagos respectively and used in the study. Interdab electropome Jet 100 M used electricity power while Grundfos submerssible pump was powered by solar modules (photovoltaic) which was installed by Energy Research Centre technicians to ensure constant power supply and to serve as comparative studies between electric and solar energy. The quantity of water pumped by both pumps used for the recirculating system was 50 litres per min at the depth of 1.25 m. Air stone aerator supplied oxygen constantly to the ponds. Ceramic rings - surface area 1200 m²/L and weighing 10 kilograms, bamboo carbon (activated carbon) - surface area 1200m²/L and weighing 10 kilograms were purchased at Kingdom Aquarium and Fisheries Ltd. Lagos, Nigeria and used in the study. Two overhead plastic tanks, volume 1000 litres each were procured at Onitsha for water storage. (Figure 4).

Figure 4 Isometric view of water recirculating system

5.1.3 Treatment Process

Water from the overhead tank (inlet water) entered the pond where fishes are kept and then flowed into the treatment tank as waste water. As waste water flowed through biobrush, bioblocks, maifan stone, coral sand, ceramic ring and activated carbon it is filtered. Solar powered pump water and electric powered pump water were then collected. Water lastly flowed into the UV light compartment where it was disinfected (UV treated water). After the waste water had passed through the treatment tank, the treated water was air lifted into the culture tank for use by the fish and recirculated back again into the filter again for purification.

5.2 Sample collection

Three critical points of sample collection were focused on incoming and outgoing points of the fish culture tank and outlet of the filter tank. The outlet is important because it indicates the effectiveness of UV light, specifically the ability to disinfect the water so that pathogenic bacteria is killed by ultra violet rays after the water has been conditioned. One sample each was collected from the incoming and outgoing points of the fish culture tank while 2 samples were collected from the outlet of the filter tank i.e. from the solar powered pump and electric powered pump. They were collected into already properly washed two litres plastic containers. The containers were labeled and stored in the laboratory refrigerator prior to analysis. The water samples for biochemical oxygen demand were collected in properly washed glass bottles of 120ml capacity with glass stoppers labeled and stored in the laboratory refrigerator prior to analysis.

5.3 Determination of Relevant Parameters for Recirculating System

Temperature was determined using mercury-in-glass thermometer (British standard BS593). pH was determined using a ATC pH meter, Calcium carbonate (CaCO₃), nitrate, nitrite, and ammonia were determined by using water Analysis Kit by Hague made in Canada (ASTM, 2008),dissolved oxygenwere determined in situ using Labtec oxygen meter.

Microbial analysis was carried out using the MaConkey agar plate method as described below. Four water samples were cultured using nutrient agar: Petri dishes were used for the culturing. Water samples were diluted ten times from 10^-1 to 10^-10. 50 mL of diluted samples spread on the plate and incubated. Colony count was done on plates after incubation and total CFU calculated. Isolation was carried out using the Mac Conkey agar plate; 50μC≥0.05ml was used. Average micro agar/ml was counted and colony forming unit (CFU) recorded (Monica, 1984).

Biochemical oxygen demand determination was carried out using 250 ml of the sample was measured into BOD bottle. 1 cm³of MnSO_4.H₂O to the sample already measured. 1 cm³ sodium hydroxide and potassium Iodide were added. Then the sample was stoppered and shaken thoroughly by inverting several times and later allowed to settle for observation of precipitate of magnesium hydroxide. 1.5 cm³of concentrated H₂SO₄ was added then restoppered and mixed thoroughly to dissolve theprecipitate. 25 mL was withdrawn from the solution into a titrating flask. 1ml potassium iodide and concentrated H₂SO₄ less than 1ml were added into the solution. A little quantity of starch indicator was added into the solution and titrated against sodium thiosulphate (Na₂S₂O₃.5H₂O). The colour changed from blue to colourless. Sample was kept at 20℃ in the dark with test tube stoppered to prevent photosynthesis(and thereby the addition of oxygen) for five days, and the dissolved oxygen was measured again. The difference between the final DO and initial DO is the BOD. This was done for five days intervals (Lenore et al., 1999). In calculating, 1 cm³of 0.1M Na thiosulphate is equal to 0.4 mg of oxygen. The value would be multiplied by 0.4 mg out of 250 mls if used 25ml then multiply by 40 (Monica, 1984).

Acknowledgements

Authors are thankful to the former Director of Energy Research Centre, Prof. O. U. Oparaku for his assistance in providing solar panels, inverter and technical supports. Also, I thank Mr. D. O. Aneke and Mr. Christian Eze of the National Centre for Energy Research, UNN for their help in installation of solar energy devices and Mr. Chinedu Nzelu for supplying all the materials needed for the recirculating system during this work.

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