Efficacy of a Closed Water Depuration System with Charcoal filter on the Bacteriological quality of Villorita cyprinoides var. cochinensis (Hanley, 1866)

Bivalves are good bio-indicators of the sanitary quality of the aquatic bodies in which they survive. The sanitary quality of the shellfish harvesting areas is assessed based on the faecal coliforms/E. coli levels of the harvesting water/shellfish tissue; on exceeding the regulatory limits depuration suggested. In the present study, the efficacy of a closed water depuration system attached with a charcoal filter to depurate Indian black clams (Villorita cyprinoides var. cochinensis (Hanley, 1866) was evaluated. The depuration system consisted of a closed water holding glass tank, with a wall-hung immersion water pump which re-circulated (18 l min-1) the seawater [salinity – 10 ppt, pH -7.3, ambient temperature (29-30°C)] through a coconut shell based activated carbon (charcoal) filter. Clams were sampled at time intervals of 0, 6, 12, 24, 72, and 96 h to assess the reduction of total coliforms (TC), faecal coliforms (FC) and faecal streptococci (FS). Initial TC, FC, FS and Salmonella loads were assessed using standard microbiological methods. Salmonella was not detected in any of the clam samples. Complete removal of both FC and FS whose initial loads were 4.6 x 104 MPN 100 g-1 and 1.1 × 105 MPN 100 g-1 respectively was observed within 48 h. Maximum rate of depuration of TC, FC as well as FS were observed during the initial first 6 h. However, TC could not be fully depurated even after 96 h of depuration. The differences in the depuration rates of TC, FC and FS were found to be statistically significant (p<0.05). The FC load of the black clams selected for the study conformed only to the class C shellfish growing area of EU which could be reduced to acceptable regulatory limits of <230MPN 100 g-1 of depurated shellfish; which proved the system used is efficient. The system uses simple, cost-effective, easily available, natural, and renewable water treating agent such as coconut shellbased activated carbon and is suitable for household purposes. In India, black clams do not have much export value and is also not preferred to be eaten raw. Hence less stringent, cost-effective, and simple depuration measures as mentioned above may be sufficient enough to meet the required sanitary quality as it is consumed only after proper cooking.