Waste excretion characteristics of Manila clams (Tapes philippinarum) under different temperature conditions

Water recirculating systems have been used in the shellfish industry for depuration and wet-storage. Knowledge of shellfish excretion characteristics is critical to recirculating system design. In this study, the excretion rate of total ammonia nitrogen (TAN), total Kjeldahl nitrogen (TKN), and 5-day biochemical oxygen demand (BOD,) from Manila clams (Tapes philippinarum) were investigated under both laboratory and commercial conditions. The laboratory tests were conducted under temperatures ranging from 3 to 30 degrees C. The experimental results showed that temperature was a key factor in determining the excretion rate of all the above parameters. The relationship between TAN excretion rate (R-TAN) and temperature (T) can be represented by an exponential function (R-TAN = 0.57 x 1.25(T)). For the temperature range between 3 and 20 degrees C, the daily mean excretion rates of TAN, TKN and BOD, ranged between 1.5-46.1, 4.8-131.0 and 57.4-219.4 mg per kilogram of the clams (wet weight with shell on), respectively. There were linear correlations between TAN, TKN and BOD, production rates. The data presented in this paper can be used to estimate waste generation from a given shellfish processing operation and to size the waste treatment components for a recirculating depuration (or wet-storage) system. (C) 1999 Elsevier Science B.V. All rights reserved.