Oxygen Consumption, Ammonia Excretion and Biodeposition of Ark Shell Scapharca broughtonii under Different Temperature Regimes for the Design of Recirculating Depuration System

Abstract

Oxygen consumption, ammonia excretion and biodeposition rates of ark shell Scapharca broughtonii under three different temperature regimes 15ºC, 20ºC and 25ºC, were studied to design a proper recirculating depuration system for ark shell. Oxygen consumption and ammonia excretion of the ark shell were measured in a small seawater recirculating system. The system consisted of three 2.4 L respiration chamber where 3 ark shells were placed in each chamber. The chamber were sealed with oxygen probe, water flow rate was 200 mL/min and salinity 30 PSU. Oxygen consumption and ammonia excretion was determined between inflow and outflow concentration on each chamber. Biodeposition of the ark shell was measured by placed 4 ark shell in one aquarium (5 liter), 5 aquaria for each temperature treatment. Biodeposits collected daily, freeze dried and then weighed. 100% of seawater was replaced after biodeposits collection. Oxygen consumption and ammonia excretion of the ark shell have a positive relation with temperature. At the temperatures of 15ºC, 20ºC and 25ºC, oxygen consumption were 31.85+0.65, 36.87+2.06, 42.34+2.02 mg O2 kg BW-1hr-1 respectively. For 7 days of research, oxygen consumption of the ark shell decreased. Ammonia excretion of the ark shell also has a positive relation with temperature. At the temperatures of 15ºC, 20ºC and 25ºC, ammonia excretion were 0.12+0.01, 0.18+0.01, 0.27+0.01 mg kg BW-1hr-1 respectively. For 7 days of study period, ammonia excretion was slightly increased in all temperatures but not statistically significant. Biodeposition of the ark shell has a positive relation with temperature for the first three days after stocking. At temperature 15ºC, 20ºC and 25ºC, amount of biodeposits in dry weight were 0.74+0.55, 1.84+0.68, 1.28+0.66 g kg BW-1day-1, respectively. In the last 4 days of the study period, no significantly different amount of biodeposits under different temperatures were found. Based on the results of oxygen consumption, ammonia excretion and biodeposition of the ark shell, a recirculating depuration system to accommodate 1 metric ton of ark shell was designed. The design was made based on the particular conditions and assumptions are as follows: + 70 gr weight of each ark shell, 1.5 m depth and 1 m width of settling basin dimension, Kaldnes bead biofilter media, inlet water 30 PSU of salinity, 5 mg L-1 of dissolved oxygen and 0 mg of TAN. With all of the above mentioned conditions and assumptions, required flow rate, minimum settling basin length and required biofilter volume of the depuration system for particular temperature (15ºC–25oC), can be determined using these following equations: Flow rate (m3/day) = -0.506 + 0.2 T (r2 = 0.99); Settling basin length (m) = -0.533 + 0.188 T (r2 = 0.99); Biofilter volume (m3) = -29.946 + 3.712 T (r2 = 0.99).