marine hatchery: TECHNICAL SYSTEMS 1. pumping procedures

A 120 micron screened filter is positioned on the creek bank to allow input of seawater at salinity of 35 parts per thousand on the flood and ebb tides (Figure 1). Pumping is avoided during heavy deluge or the presence of algal blooms in the creek (Figure 2). The three phase Onga Model OJ800 saltwater pump lies 4.4 metres at the base of a concrete well. The pump lifts water to a subset of filters before flowing into the 350 tonne storage tank. The subset consists of a 100 micron cartridge filter, then two sandfilters (Figure 3). Liquid chlorine in the form of sodium hypochlorite is added to the raw water at 20 mg.L^-1 for sterilization purposes (Figure 4). Chlorinated seawater is pumped from the settlement tank with the three phase Onga pump Model 112 and through a one micron cartridge filter to either of two 40 tonne temperature controlled tanks (Figure 5).

During periods of low rainfall, freshwater is added from the bore water tank to maintain salinity at 34-35 parts per thousand. Heating occurs overnight to 29⁰C and is regulated to the low rated tariff through thermostatically controlled switches. The seawater undergoes a neutralization process by the addition of sodium thiosulphate at 5 mg.L^-1 dissolved in a solution of freshwater. During this process pressurized air from the main blowers is released from a valve on the tank roof to enable mixing inside the tank. A screen is placed on the lid of the tank for gaseous exchange (to release chloroform and carbon tetrachloride bi-products). The process takes approximately twenty minutes. The seawater is sampled in a clear flask and a test is performed for the presence of chlorine using potassium iodide powder. If the result is a yellow discolouration, chlorine is still present. If the sample is clear, the seawater is fully neutralized and ready for dissemination.