Aquaculture net cleaning with cavitation improves biofouling removal

Abstract

The attachment of a large number of biofouling organisms on net cages has a very negative impact on the safety of cage structure and aquaculture organisms. This paper presents a new type of marine aquaculture net-cleaning system (ANCS) that adopts the power of continuous cavitating jets to remove biofouling in underwater environments. The cavitation characteristics of the nozzle, which is the key component of the ANCS, were analyzed under different conditions in a submerged cage environment, and the system's cleaning rate with different inlet pressures (P) and nozzle diameters (d) was obtained. Under the same input flow rate and increasing nozzle aperture (from 0.6 to 1.0 mm), the gas phase volume fraction of the nozzle showed a rising trend (the maximum value reached 37.5% for the 1.0 mm nozzle) and jet velocity at 40 mm away from the nozzle was reduced by 85.6%–97.0%. Net-cleaning tests showed that, with an inlet pressure of 16.42 MPa and nozzle diameter of 0.8 mm, the ANCS achieved the highest rate of biofouling removal (79.8%) and the lowest specific energy consumption of removing unit mass fouling (5.13kw). The shellfish fouling organisms mainly fell off and their shells broke under the impact of the cavitating jet produced. After the cleaning experiment, most of the residues consisted in the soft byssus plaques of shellfish, which strongly adhered to the net. The soil on the net surface was completely removed, revealing the original color of the aquaculture cage net.