Treatment of efluent from ponds of Litopenaeus vannamei shrimp rearing through nutrients sedimentation and absortion with the macroalga Ulva fasciata
Keywords:
effluents, shrimp farming, macroalgae, sedimentationAbstract
Efficiency to remove suspended solids and dissolved nutrients from Litopenaeus vannamei marine shrimp effluent through sedimentation and absorption with macroalga (Ulva fasciata) was assessed using three settling times: 6, 12 and 24 hours. The water quality parameters analyzed were: dissolved oxygen (mg/L), salinity (‰), pH, temperature (°C), turbidity (NTU), BOD5 (mg/L), total suspended solids (mg/L), ammonia (mg/L N-NH4+), nitrite (mg/L N-NO2), nitrate (mg/L N-NO3) and orthophosphates (mg/L PO4-3). Results suggest that highest efficiency in sedimentation stage were found when effluent was left standing for 6 hours, with removal of 94.0%, 93.6%, 41.6%, 74.3%, 47.4% and 56.1% of chlorophyll a, BOD5, N-NH3, N-NO2, N-NO3 and P-PO4 , respectively. The best result to remove turbidity from raw effluent was found in the 24 hours treatment with 95.5% removal rate, when compared with rates of 93.5% for 12 hours and 78.4% for 6 hours. In the nutrient absorption stage, highest removal rates were found in the 6 hours treatment with 23.7%, 47.1%, 7.1%, 37.0% and 48.4% for BOD5, N-NH3, N-NO2, N-NO3 and P-PO4, respectively, when compared to the control tank. Finally, integrating sedimentation and absorption, all treatments showed high removal efficiency. Turbidity for the three settling times tested was of 95.8% (6 h), 96.6% (12 h) and 96.8% (24 h). In the final removal of BOD5 the best result was observed in the 6 hours treatment, with 90.7% removal rate, when compared to the 12 hours (85.6%) and the 24 hours (81.4%) treatments. In the removal of N-NH3 (57.1 í 59.8 and 57.4% for 6, 12 and 24 h), N-NO2 (64.9 í 62.2 and 59.5% for 6, 12 and 24 h), N-NO3 (37.3 í 21.0 and 41.1% for 6, 12 and 24 h), and P-PO4 (75.9 í 76.9 and 77.7% for 6, 12 and 24 h) results were similar. The present study demonstrates that the sedimentation and macroalgae absorption processes tested are efficient methods to remove nutrients from shrimp farm effluents.
