Hub APTA Background
Accumulation of solid residues (suspended and sedimentable solids) is one of the main problems present in culture ponds used in land-based aquaculture production systems. This problem considerably influences on production capacity of these systems, since solids accumulation causes reduction of dissolved oxygen available in water’s ponds, due to natural oxidation process of these accumulated waste. Additionally, there is an increase of compounds which are harmful and / or toxic for the species under cultivation, such as, ammonia nitrogen compounds and carbon dioxide, among others.
Generally, solid waste come mixed in the feed water or they are generated during the fish culture process, corresponding mainly to uneaten food and fish faeces.
These variations in water quality conditions can be detrimental to the development of species under cultivation, causing a sanitary risk for the cultivation and an increase of environmental impact due to effluents discarding from cultivation process.
Currently, fluid dynamic conditions are used to generate a conventional self-cleaning effect, achieving adequate levels of solids accumulate removal in circular ponds. This conventional self-cleaning effect is achieved by mean of generating circular and radial flow patterns in water’s ponds, using the control-variation of direction and rotational speed of water’s bodies inside the ponds. This type of solution generates high consumption of water and energy since it is necessary to ensure a certain filling level of the tanks and maintain a high injection flow to achieve self-cleaning effect. Additionally, high flow velocities (greater than optimal) generate unsustainable swimming conditions for fish affecting their health since they become stressed.
Technology Overview
The technology is both a system and a self-cleaning method which allows solid waste continuous removal in farming ponds by generating a vortex for concentrating and suctioning waste by means of rotary movement of water’s body at different rotational speeds. It does not require to modify the existing ponds to implement this system in aquaculture ponds. It specifically assures that self-cleaning effect is successfully achieved, even in conditions where the aspect ratio (D/h) between pond diameter (D) and useful water height (h) are too low, producing “blind spots” for the drainage. Or when the water’s injection speed is too low for solid waste removal.
The system comprises an acrylic or polycarbonate separator of the same diameter of the pond (), which is installed inside it to set a horizontal separation between the pond floor and the water body, creating an upper section and a lower section. The species under cultivation are located on the upper section, meanwhile on the lower section specific fluid-dynamic conditions are generated, creating vorticity, suction and self-cleaning of the pond, i.e., occurs solid waste’s collection and elimination.
The separator includes a divider, a central opening, radial openings, and an outer opening, where central opening and radial openings have a screening mesh to prevent the passage of crop species into lower section, but allows water transfer containing the solid waste toward lower section and where the external opening is dimensioned in such a way as to allow the entry of a water injection device, whose dimensions will depend on hydrodynamic configurations desired to be generated.
The separator has fixing means, which allow to fix and regulate its vertical position inside culture pond. These fixing means correspond to a cluster of supports located on the periphery of its lower face leaning on pond’s bottom, also, can be ropes, chains or similar elements that allow to hang the separator from pond’s upper part.
There are two water injection devices in the system, first one injects a first flow of water in upper section and the second do it in lower section (). The first flow of water produces water’s body rotation (initial rotational speed) generating at least one primary flow within the upper section. The injection device allows to regulate water flow entering the upper section, creating an adequate flow rate for development of the species in cultivation. On the other hand, the second flow of water is injected into lower section producing the mass of water rotation inside lower section with a second rotational speed. These primary and secondary flows produce a suction vortex throughout the separating disc lower surface which drags the particles from the disc upper surface downwards. The second injection device allows to control the second flow rate, hence, to control the vorticity within the lower section.
The water speed in lower section is higher than in upper section, therefore, in the interaction zones between sections, such as in central opening and radial openings of separator, a pressure difference displaces solid waste from upper section to the lower through lift and drag phenomenon.
Once transferred to lower section, the solid residues are transported by the vorticity created for primary and secondary flows to a central drain connected to a drainpipe and are transported out of culture pond toward conventional cleaning and filtration water treatment systems. In this way, this self-cleaning system allows a rapid and continuous solid waste elimination, maintaining a safe speed for the species in culture in upper section, with the benefits of culture pond self-cleaning, even when the relationship between pond diameter and its useful water height (D/h) is lower than required for conventional self-cleaning to occur.
Benefits
This technology has the following benefits:
Improves the conditions for species development.
It prevents farmed species from being exposed for a long time to sub-lethal levels of low water quality, due to residues accumulation in the pond.
It allows to adjust depth conditions and water speed suitable for the animals without affecting solids removal.
Better life quality for species in cultivation, encourages growth, and decreases stress and mortality.
Saving water end energy.
Reduces system water consumption about a 20%, by avoiding the need to fill the pond to its full height to ensure self-cleaning (Aspect ratio).
It allows to ensure ponds continuous cleaning conditions without need to put in motion the entire water mass in the pond. Lower injection flow.
Improves all recirculating aquaculture system or RAS
Crop water treatment and conditioning systems can improve their efficiency or be smaller in size, hence, use less space and less energy.
Reduces dissolved and suspended organic matter levels in the RAS, hence, there is lower CO2 & NH4 production and less consumption of oxygen by pathogens growing in non-consumed food or faeces.
Improves biofilter, UV filter, and degassing efficiency.
Decreases freshwater replacement rate.
Easy installation and operation in a RAS
Its installation and use It does not require modification or replacement of existing culture ponds.
Applications
The aquaculture pond self-cleaning system could be used in land-based RAS without any further modification because of its easy integrating to such installations.
Currently, the technology has been validated in a relevant environment (prototype test), and in the next couple of months is planned to test the system in operative conditions.
The objective of these tests:
Validate solids removal rate in real conditions.
Validate changes rate in water quality variables (O2 demand, CO2 production, and Total Ammonia Nitrogen or TAN) in real conditions.
Validate recirculating water reduction due to system action in real conditions.
Validate system effect over species growth and mortality.
Opportunity
We are currently looking for potential licensees or commercial partners.