The effect and application of treatment for wastewater of productive shrimp aquaculture by constructed wetlands combined with pond facilities

Wastewater treatment technologies with constructed wetlands and pond facilities for freshwater Litopenaeus vannamei culture were conducted and the effects were measured. The wetlands consist of free water surface (FWS) and subsurface horizontal flow (SF) wetlands. Ponds facilities contain aerators and artificial water purifying nets. During the middle and late culture period (about 60 d later), shrimp ponds’ wastewater was recirculated three times through the wetlands under hydraulic loading rate (HLR) of 1.65 m/d which effectively improved water quality in shrimp ponds and ensured a good harvest. At the same time, the outbreak of blue-green algae was controlled. -N and BOD5 at outlet were significantly removed at different levels (P<0.01 and P<0.05). The removal percentage and removal rates were 72.6%, 0.467 g/m²·d and 29.7%, 2.651 g/(m²·d). The removal percentage and removal rates of -P, TN and CODMn were 41.7%, 0.022 g/(m²·d), 26.1% , 2.619 g/(m²·d) and 15.9%, 3.738 g/(m²·d) respectively. The removal percentage of -N was only 3.6% but the removal rate was as high as 0.462 g/(m²·d). -N and -N were both significantly (P<0.01) reduced by 96.8% and 93.3% when effluents remained in the macrophytes unit for 4 d. The water chemical parameters were all maintained within a safe range during the culture period. The harvested shrimp in experimental pond had the mean body weight of 8.81 g and length of 9.36 cm. While the culture in control group had to terminate on the 60th day due to an outbreak of shrimp disease caused by microcystin and the harvested shrimp was only 3.06 g and 6.54 cm each. The results indicated that low frequency operation of the constructed wetlands under a higher HLR combined with pond facilities could effectively control water quality in shrimp pond under the conditions of no water exchange and no medicine use and then ensured a good harvest.