The effect of regulating-controlling water quality by constructed wetlands at intermittent operation for Macrobrachium rosenbergii culture and the prawn growth characteristic

Abstract:

A constructed wetlands ecosystem was developed with intermittent operation combined with microvesicle aerators and water purification nets to circularly treat culture wastewater for the purpose of studying the effect of regulating-controlling water quality for Macrobrachium rosenbergii culture and the prawn growth characteristic.The FWS-SF wetlands ecosystem used in this study consisted of a free water surface flow (FWS) wetland and a subsurface flow (SF) wetland.The whole area of FWS-SF wetlands was 582.2 m², including three units: the slope unit, the macrophyte unit, and the reservoir unit.The experiment was conducted during a 117 day period with no water exchange and medicine use.Since the 31th day, the constructed wetlands ecosystem was intermittently operated at a hydraulic loading rate (HLR) of 1.03 m/d during the culture period, and significantly removed NO₃^--N, COD_Mn, TAN by 66.4%, 39.6% (P≤0.01), and 45.0% (P≤0.05) respectively, the removal percentage of NO₂^--N was 33.3% and keep in very low concentration (0.006±0.005 mg/L).The main aquatic chemical parameters of experimental ponds were all maintained within a suitable and safe range for prawn growth, and blue-green algae bloom was effectively inhibited.At the end of the experiment, because of blue-green algae toxic effect, average adult prawn size and yield of the control pond (8.70 g, 0.32 kg/m²) were smaller or lower than that in the experimental pond (9.51-10.72 g, 0.38-0.41 kg/m²).The study presented three groups of growth equations of the relationship between body weight and body length, body weight and culture days, body length and culture days，respectively, it can provide a scientific basis for designing the culture production plan, adjusting the production measures and estimating yield of Macrobrachium rosenbergii.This experiment shows that constructed wetlands ecosystem at intermittent operation and combined with pond simple facilities could effectively control water quality in prawn pond under the conditions of no water exchange and no medicine use and then ensured a good harvest.