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Development of an Electrically Operated Aerator for Tilapia Fish

A. T. M. Ziauddin
Department of Farm Power and Machinery Bangladesh Agricultural University Mymensingh-2202

Md. Golarn Ambia Mahrnud
Department of Farm Power and Machinery Bangladesh Agricultural University Mymensingh-2202

M. Abdul Wahab
Department of Fisheries Management Bangladesh Agricultural University Mymensingh-2202

Abstract/ Executive Summary:

Due to acute shortage of dissolved oxygen at night in a pond ecosystem, the demand of surface aerator in fish ponds is increasing. Aerator of different designs and capacities are available in developed countries. However, the use of aerator in pond fishery even in commercial fish farm is absent in Bangladesh because of unavailability of a simple and cheaper aerator in local market. An attempt has been made to develop a suitable electrically operated aerator after gaining experiences with laboratory version of the aerator earlier. The impact of this type of aerator was evaluated in the field. The aerator was installed in the middle point of a pond (44 m x 19 m x 1.25 m water body) behind the Faculty of Agricultural Engineering & Technology of Bangladesh Agricultural University, Mymensingh. It was operated by an electric motor (0.4 kW). Dissolved oxygen (DO), water temperature, water PH and air velocity were recorded during day and night at an hourly interval. Data were recorded hourly basis continuously for five hours in sunny days, cloudy days and at late nights at a distance of 2 meter and 4 meters from the center of the aerator. It is well established fact that the DO level of a pond ecosystem is highly influenced by the photosynthesis activity of algae and other biotic parameters of the pond. It was observed that in a sunny day the DO concentration level had increased from 4.20mg/l to 7.53 mg/l but at cloudy day the DO concentration was increased from 4.10 mg/I to 7.18 mg/l, recorded at a distance of 2 meter from the center or the aerator. At day time without using aerator the DO concentration level was increased from 4.12mg/1 to 6.10 mg/l. In absence of photosynthesis activity of algae at night DO concentration level was increased from 5.30 mg/l to 7.12 mg/l, which is considered good for fish culture. This phenomenon was observed in the water body area 01' 450 square meters. This indicated that two aerators (0.4 kW each) are good enough to provide required amount of DO for fish in the pond of 836 sq. meter of water body where the experiment was conducted. It may be concluded that the performance of the aerator of the pond was highly satisfactory but it needs further development to stop leakage of water from its moving parts. Further study with optimization technique could help determine the required size and numbers of aerator for a specific pond size.

Keywords: Aerator, Dissolved oxygen, Pond, Fish

Location: Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh

Start Date:

End Date:

Program Area: Farm Mechanization

Commodity: Tilapia

Objectives:

1.To develop a low cost electrically operated aerator for increased dissolved oxygen in a pond eco-system.

2.To study the performance of the device in the field.

Methodology:

A sprinkler consists of two discharge nozzles was constructed in the workshop of the department of Farm Power and Machinery. Bangladesh Agricultural University (BAU), Mymensingh. It includes two nozzles, two elbows, one T-socket, one bush bearing and a raiser pipe made of G.I. pipes of 12 mm diameter and 1 meter length. Two discharge nozzles were fitted each other at an angle of 1800 in opposite direction horizontally to obtain rotating action while discharging water. The sprinkler was fitted with a water pump of 0.67 litre/second coupled with an electric motor of 0.5 hp. A suction pipe of 12 mm diameter and 1 meter long, fitted with a foot valve was incorporated with the pump. The complete unit was placed on a wooden platform bolted with a floating rubber wheel of a vehicle. The rubber wheel provides the floating action. The aerator rotates in clock wise direction. It lifts water from a depth of one meter and throws water into the atmosphere. Thus water came into contact with the atmospheric oxygen.

The transfer depends on the many variables including i) discharge rate of the pump, ii) size and shape of the aerator, iii) ability of pump to splash the water of pond, iv) oxygen concentration gradient, v) air velocity/speed, vi) amount of aquatic plant and phytoplankton in the pond water. The aerator was placed in the central location of the pond behind the Faculty of Agricultural Engineering & Technology, BAU, Mymensingh. A single-phase electric connection was given to the 0.4 kW motor and the aerator was started. The device was continued running for 5 hrs for each experiment. The dissolved oxygen in the pond water, pH, water temperature, wind speed were measured to study the aerator performances. The data were recorded hourly interval by the measuring devices. DO was measured by a DO meter, pH by a pH meter, temperature by a thermometer and wind speed by an anemometer. The experiments were conducted in various weather conditions such as sunny day with and without aerator, cloudy day with and without aerator and after mid night with and without aerator. In day time the experiment was started at 8 am (0 hr) and in night the experiment was started at 12 pm (0hr) at 0 hr the first reading was taken in each experiment. Twenty four sets of experimental data were recorded in different distances from the center of the aerator towards the edge of the pond.

Source of Information: Journal of Agricultural Engineering The Institution of Engineers, Bangladesh, Vol. 33/ AE, December, 2007

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

During daytime (sunny day), the aerator contributes the addition of oxygen by 40.54%, where as the micro algae contributes the addition of oxygen 59.46%. The total DO increment in late night was 1.82 mg/l in 5 hours operation of aerator when phytoplankton and micro algae contributed no addition of dissolved oxygen. It has observed that the aerator significantly contributed the addition of oxygen in late night when micro algae produce no oxygen. So, it may be concluded that the aerator would be more effective during night and in cloudy days. This phenomenon was observed in the water body area of 450 square meters. This indicated that two aerators are good enough to provide required amount of DO for fish in the pond of 836 sq. meter of water body where the experiment was conducted. It may be concluded that the performance of the aerator of the pond was highly satisfactory but it needs further development to stop leakage of water from its moving parts. Further study with optimization technique could help determine the required size and numbers of aerator for a specific pond size.

Knowledge Management: Journal