Purification characteristics of constructed wetland under different hydraulic loads after treatment of marine aquaculture tailwater

Abstract:

One of the main problems faced by the aquaculture industry is the discharge of marine aquaculture tailwater. Constructed wetlands may work as a comprehensive water treatment technology, effectively removing pollutants such as nitrogen and phosphorus in aquaculture tail water. For the proper implementation of constructed wetland technology, hydraulic load conditions must be optimized. The treatment effect of vertical flow constructed wetland system on the tail water of Paralichthys olivaceus was studied under three hydraulic loads (V1=0.50 m/d, V2=0.19 m/d, V3=0.10 m/d). The treatment effect of the system for the main pollutants in the aquaculture tailwater was significantly different under three hydraulic loading conditions. When the concentration of chemical oxygen demand (COD) in the influent water was relatively low, the removal rate was also low, with a peak removal rate of only 36.25%. The effect of hydraulic loading on the removal rate of COD was not obvious. When the hydraulic load was 0.50 m/d, the removal rate of total nitrogen (TN) was only 49.50%; however, when the hydraulic load was 0.10 m/d, the TN removal rate was 85.90%. The removal rate of active phosphate (PO43–-P) was less affected by hydraulic load, showing a removal rate of more than 77%. Hydraulic load affects the removal effect of nitrogen and phosphorus in the system; for example, in the downstream unit the removal rate of nitrogen pollutants was more than 80%, whereas in the upstream unit, nitrate nitrogen (NO3–-N) or nitrite nitrogen (NO2–-N) accumulated under high hydraulic loads. The adsorption and conversion of PO43–-P mainly occurred in the upper and middle layers of the downstream unit; the larger the hydraulic load, the closer the adsorption and conversion of PO43–-P was to the rear of the system.