Treatment of shrimp effluent by sedimentation and oyster filtration using Crassostrea gigas and C. rhizophorae

Abstract

Efficiency in removing particulate matter from Litopenaeus vannamei shrimp culture effluent was assessed in laboratory scale employing sedimentation and oysters Crassostrea gigas and C. rhizophorae filtration processes. Cylindroconical tanks (100 L) were used in duplicate for sedimentation and 50-L in triplicate for oyster filtration. Fifteen oysters of each species weighing 76-80 g were stocked in each of the filtration treatment experimental units (biomass of 1065 - 1174 g oyster per unit). The control treatment was a tank similar to those used in the filtration treatment but with empty oyster shells. Hydraulic retention time of the effluent was of 6 hours in each treatment. First, effluent went through sedimentation, and then the supernatant went through the filtration tanks. Temperature, pH, dissolved oxygen, salinity, turbidity, total suspended solids, total volatile solids, chlorophyll a and BOD5 were evaluated. During sedimentation and filtration, temperature, pH, salinity and dissolved oxygen concentration remained stable. Sedimentation removed 18, 5.6, 27.5, 45.40 and 23.2% of turbidity, total suspended solids, total volatile solids, chlorophyll a and BOD5, respectively. Chlorophyll a and BOD5 after sedimentation presented significant difference (P<0.05) from the farm crude effluent. For the filtration treatment, C. rhizophorae was more efficient removing 62.1, 70.6, 36.1, 100 and 17.2% of turbidity, total suspended solids, total volatile solids, chlorophyll a and BOD5, respectively, whereas C. gigas removed 56.3, 41.2, 27.8, 51.4 and 8.0% of the same parameters. Statistically comparing C. rhizophorae and C. gigas performances, there were differences (P<0.05) in removing total suspended solids, total volatile solids and chlorophyll a.