Evaluation on aeration performance of movable solar aerator

Abstract: In pond aquaculture, it is usually necessary in sunny noon that running aerator stirs pond water, so that the supersaturated dissolved oxygen (DO) from phytoplankton's photosynthesis in upper water can be transferred into the relatively anoxic bottom, reducing the "oxygen debt" of bottom water and preventing fish hypoxia at the next early morning. However, this approach consumes a lot of electric energy and has low efficiency. To improve the ecological state of aquaculture ponds and save electric energy, a movable solar aerator was designed and developed. This machine is solar-powered and can move upon the water, and mainly consists of a photovoltaic power system, a water walking device, and a wave aerator. The photovoltaic power system provides power for the entire machine, while the water walking device drives the whole equipment, moving back and forth along a steel rope. The wave aerator can rotate itself and around the main part of the equipment (the photovoltaic power system and water walking device), affecting large areas of the pond. The rotation of the wave aerator makes the formation of water waves and promotes pond water convection between the surface and the bottom. The purpose of this study was to evaluate the performance of the movable solar aerator on mechanical aeration and water exchange between the surface and the bottom, and also on its practical effect in ponds, by 3 tests of aeration efficiency, water pumping capacity, and aeration effect in ponds, respectively. For standardizing the test, a battery providing the same voltage (24 V) was used instead of the photovoltaic power system in the tests of mechanical aeration efficiency and water pumping capacity. The values of performance obtained from this method of using a battery are the maximum values for the equipment. The obtained results showed that the machine increased the DO in the water of a pool (54.8 m3) from 0.84 to 7.88 mg/L within 36 minutes. The maximum mechanical aeration capacity was 1.24 kg/h, with a power efficiency of 2.59 kg/(kW·h), maximum pumping water capacity of 1 254.4 m3/h, and pumping dynamic efficiency of 2613.3 m3/(kW·h). The test of practical application effect in ponds was conducted from 07:00 a.m. on September 12, 2013 to 05:00 a.m. on September 13, 2013 at the pond ecological engineering research center of Chinese academy of fishery sciences (Shanghai), with the maximum sunlight intensity of 57 200 lx. The pond selected was 70 m in length and 25 m in width, with a depth of 1.6 m. The aerator ran automatically from 07:00 to 16:00, with a total running time of 9 hours. The DO concentrations of 0.2, 0.5, 1.0 and 1.5 m pond water were recorded with an interval of 2 hours. The results showed that the DO values of the bottom water (1.5 m) in control were maintained at 3.1-3.8 mg/L, whereas the values in the test pond were substantially increased with the maximum of 7.8 mg/L, due to the good performance of the movable solar aerator on mechanical aeration and water exchange. The DO uniformity of the test pond was maintained at 72%-84%. The DO environment in the bottom pond was improved greatly. These results revealed that the movable solar aerator has good performance on mechanical aeration and water exchange, thus, effectively improving the DO level in the bottom water of ponds and increasing DO uniformity. The present study provides a data basis for further popularization and application of the movable solar aerator developed newly.