Experimental system
The system consisted of 12 equal sized cisterns and 2 smaller ones. Each cistern had
inlet and outlet facilities connected to the bio-filter system which was located along the
east and south sides of the system. The substrates of the bio-filter consisted of
styrofoam, gravels, PVC nets and shells of mussels. The pump house was located at the
south-eastern side of the system. The pumping unit consisted of two water pumps which
ran alternatively for six hours to ensure continuous water flow and aeration.
Nine cisterns of uniform size were selected for conducting the experiment. The
cisterns had a length, width and depth of 2.06 m, 1.8 m and 0.94 m respectively. So each
cistern had an area of 3.708 m2 and a volume of 3.486 m3
• XTater level in the cisterns was
adjusted at a depth of0.76 m to maintain the water volume of 2.82 m3
• The desired level
of water in the system was maintained by continuous recirculation of water at a rate of
15 ]/min. In each cistern, water level was controlled by a PVC pipe placed at the
opening of the outlet located at the middle of the cistern. The pipe was covered by a
larger pipe (in terms of diameter and height) with four notches at the bottom which
facilitated easy removal of waste materials from the cisterns. X!ater loss from the
cisterns due to evaporation was adjusted every week by adding groundvvater. The
cemented cisterns were cleaned thoroughly with washing powder and washed with
freshwater. After complete drying they were filled with groundwater up to a level of 0.76
m which was maintained throughout the experiment. Polyester net was placed over each
cistern to prevent fish from predatory birds