NO345995B1

NO345995B1 - Low energy consumption process and device for cleaning and aerating spent water from a land-based aquaculture vessel

Info

Publication number: NO345995B1
Application number: NO20181334A
Authority: NO
Inventors: Stephen Malcolm Westall
Original assignee: Aqua Harvest Solutions As
Priority date: 2018-10-18
Filing date: 2018-10-18
Publication date: 2021-12-13
Also published as: WO2020080953A1; NO20181334A1

Description

LOW ENERGY CONSUMPTION PROCESS AND DEVICE FOR CLEANING AND AERATING SPENT WATER FROM A LAND-BASED AQUACULTURE VESSEL.

Ambit of the invention

The present invention concerns a low energy consumption process and device for cleaning and aerating spent water from a land-based aquaculture vessel as defined in claim 1 and 13, for recycling, aerating, degassing and gravity feed bio-filtrating of depleted biomass stock water volumes. The process and device according to the present invention is capable of treating up to 1500 m<3>/h via a 25 kW motive energy consumption unit and Borda-Carnot design aeration head system.

Background for the invention

When cultivating aquatic organisms in land-based aquaculture vessels it is important to maintain the oxygen level in the aquaculture vessel at levels conductive to the health of the aquatic organisms and cleaning the water in the aquaculture tank for removing contaminants produced by the aquatic organisms in the tank. This is formerly done by pumping the spent water through a system for removing carbon dioxide and waste materials from the water of the tank. However, such prior systems are prone to several drawbacks and face several challenges.

Today’s Biomass pumped recycle transfer systems are subject to:

1. Reduced water flow rates, resulting in stagnant water conditions and high expenditure of pure oxygen and accumulation of metabolic products in Biomass water.

2. Biomass sea farms face new increased challenges due to environmental changes (global warming), creating consequential problems with water temperature conditions, reduced oxygen levels and increase of pesticides.

3. High polluted volumes of waste water from the Biomass Tanks or sea cages creating problems with pumping and waste receiving stations systems.

4. High maintenance of equipment and possible failures from many moving parts.

5. Complex equipment design and maintenance for non-familiarized operating personnel.

6. Large and cumbersome, non-flexible and impractical installation units.

Today’s major problem is to save energy consumption and reduce the present environmental global warming situation. One of the major problem causes associated with this issue is the high-volume size of required holding tanks and flow velocity control. The consequences resulting from these problems have created extreme adverse knock on effects in what is required, especially where the following listed illustrational examples apply:

• High Volume Transfer Rate

High volume = High volumes of water with Large equipment

• Large Equipment

Large Components = Large surface lay-down areas

= High capital Costs = High maintenance costs = High operating energy

Large Tanks = Unnecessary high volumes and Costs

• Pipe Line Flow Velocities

Such prior art devices and systems are described in GB patent 2457230 A, KR patent 100610589 B1, US patent 2015/230439 A1 and US patent 2009/152192 A1 describing airing units and systems for purifying and recirculating water in aquaculture vessels, however suffering from one or more of the drawbacks indicated supra.

General disclosure of the invention

The present invention will be better understood with reference to the enclosed figures wherein:

FIG. 1 shows a side elevation sketch drawing of a piping manifold build apparatus configuration of a preferred embodiment, employing primary & secondary gravity feed floating bed biofilter module, pump module (motive energy unit), aeration/ degassing module and UVGI intake module interfaced with biomass stock tank.

Fig. 1A shows a simplified motive energy flow path of the employed module units utilized in the simultaneous quadruple (4) process system formation, energized by the single source power unit.

Fig. 2 shows a schematic drawing of the low energy self-balancing aeration head unit utilized in aeration manifold assembly configuration displayed in Fig. 2A, employed in the UVGI intake interface module preferred apparatus, but not limited, embodiment.

Fig. 2A shows a schematic side elevation sketch of the aeration/degassing module and UVGI intake module embodiment of the floating fired ceramic bead membrane bioreactor configuration, in relationship to the gravity head flow orifices levels and internal recirculation valve control positioning.

Fig. 3 shows an enlarged schematic side elevation of one form of the solids waste recovery unit arrangement, used to extract the waste particles or alternatively, form entrained gas bubbles through the floating fired ceramic bead membrane bioreactor employed in the filtration apparatus of a preferred embodiment.

In aquaculture biomass water holding vessel’s 1 (Fig. 1) incorporates an oxygen level sensor 1a (Fig. 1) for measuring the oxygen level content and providing a signal transmission, via an electronic control panel, for variably opening or closing control valve V6 Fig. 1. After receipt of respective low or high oxygen biomass water content level value signal, valve V6 Fig. 1 conducts a closing or opening function creating an additional bypass recycle loop via the aeration/degassing module 10 Fig. 1 back through the pipe 6A (Fig. 1) to a circulation pump module 7 (Fig. 1), creating a respective ascending or descending static head water level change in the aeration degassing module 10 (Fig. 1) in relative to the vessel 1 (Fig. 1) water surface level. Therefore, static head activity changes produces gravitational pressure levels, which constitutes a higher or lower water flow velocity via outlet orifice 13 (Fig. 1) allowing for larger or smaller volumes of water reoxidizing up to 100% oxygen saturation back to the vessel 1 (Fig. 1) according to ingress of atmospheric air volumes sucked in via Borda-Carnot design, selfbalancing, low energy aeration head unit’s 9-2 (Fig. 2), and transferred into the aeration/degassing modules expansion transition zone area 10.1 (Fig. 1) via atmospheric pressure UVGI intake module 11 (Fig. 1) , to which a pump 7 (Fig. 1) distributes the ongoing filtered water flow from primary and secondary filtration modules 3 and 5 (Fig. 1) into a piping spool 8 (Fig. 1) through either a nonmotorized centrifugal separator 14 or direct to Borda-Carnot design, self-balancing, low energy aeration head unit’s 9-1 (Fig. 2), so at the outlet opening 9-3 (Fig. 2), the encapsulated gas diffusion of gas molecules to the water or the occurs naturally in accordance with Boyle's and Charles's laws. In in the event of an over saturation of so-called "dirty" gases, such as nitrogen and C02 in the used recycled water, the light gasses will naturally diffuse away from the aeration/ degassing module’s 10 (Fig. 1) vent outlet 12 (Fig. 1), whereas oxygen, which is the under saturated, will remain in the water until a 100% oxygen saturation balance has occurred.

The invention also concerns a water process treatment method as defined in claim 1 entraining and mixing volumes of Ultraviolet Germicidal Irradiation (UVGI) atmospheric air gases into aquaculture oxygen depleted Biomass grit-silt water up to a volume range of 1500 m<3 >/hr so that all recycled water is recovered, sterilized and refurbished back to 100% gas saturation at a pH level value between 6.0 - 8.0 and used as a sterilizer.

In the process as well as in the device according to the invention the deoxygenated water stream out of a land-based aquaculture vessel 1 (Fig. 1) wherein the stream is defused back into the water based on a return plan of a new principle, derived from Borda–Carnot equation entraining high volumes Ultraviolet Germicidal Irradiation (UVGI) atmospheric air gases at low energy, for diffusing oxygen into recycled oxygen depleted Biomass water without creating high gas supersaturation levels. The oxygen depleted Biomass water is pumped into motive inlet port 9-1 (Fig. 2), via recycle pump 7 (Fig. 1), at pressures between 0.25 -1.0 bar gauge. Air inlet orifice 9-2 (Fig. 2) diameter is calculated to accept a water flow velocity of 100% value of the high gravity level flow volume. The number of air inlet orifice 9-2 (Fig. 2) are not limited, but are subject to the Biomass flow volume requirement in relationship to Biomass Tank 1 (Fig. 1) stock load and size. The oxygen depleted Biomass water is then utilized as the motive energy source of supply for entraining the atmospheric air through inlet port 9-2 (Fig. 2), based on a construction factor of 0.5 cubic meters per hour water flow entraining 23 standard cubic meters per hour of atmospheric air at 20 degrees Celsius. The actual entrained air volume is subject to the expansion transition zone area of the Aeration/Degassing Module 10 (Fig. 1) total gas pressure and outlet port 9-3 (Fig. 2). The delta pressure (Dp) construction characteristic and transition area of the liquid feature requirement has been formulated in the outlet port 9-3 (Fig. 2), for entering into the gas expansion transition zone area of the Aeration/Degassing Module 10 (Fig. 1). The construction format has been superimposed at an outlet Dp of 1333 - 2000 pascals above 99991 pascals (Barometric pressure). The entrained (UVGI) atmospheric air becomes encapsulated with the oxygen depleted Biomass water in the outlet port 9-3 (Fig 2) and forms a two-phase flow pattern, prior to expulsion into the expansion transition zone area of the Aeration/Degassing Module 10 (Fig. 1). During this cycle, the oxygen depleted Biomass flow stream becomes saturated with (UVGI) atmospheric air gases. The expulsion of water at outlet port 9-3 (Fig. 2) will always remain constant to recycled oxygen depleted Biomass flow stream. However, the entrained and expelled gas molecules will change according to their surrounding atmospheric conditions. (Reference Dalton’s and Henry’s Gas Laws of Pressure and Distribution.) The saturated gas expelled water from outlet port 9-3 (Fig. 2) is pinged onto the inner wall surface of the expansion transition zone area of the Aeration/Degassing Module 10 (Fig. 1). The velocity speed change combined with the water agitation effect produces excited gas molecules, which initiates the formation of the following three-step process for rapidly transferring oxygen into water at a balanced nitrogen ratio.

• Transfer of oxygen in the gas to the gas-liquid interface.

• Transfer across the gas-liquid interface.

• Transfer of oxygen away from the interface into the liquid.

Other surplus gas molecules such as carbon dioxide etc. will follow the normal gas law theory and will be forced out via vaporisation through vent piping spool 12 (FIG 1). (Reference Dalton’s and Henry’s Gas Laws of Pressure and Distribution.)

In the process and device according to the invention there may be used a simultaneous quadruple Self-Balancing Aeration, Degassing, Gravity Feed Bio-Filtration Process System, utilizing one single motive energy unit for all four flow streams.

In an embodiment of the device and process according to the invention there may be used:

Flow Stream 1:

Full auto-flow control operation process system via Oxygen monitoring probe unit 1a and valve V6 changing velocity head in expansion chamber 10A.

• Recycle of biomass water from V1 to V7 (Fig. 1).

Flow Stream 2:

Expelling of entrained sterilized atmospheric air into a liquid mixing stream, via Aeration Head Unit 9, at low motive energy pressure and allowing for diffusing of all the associated gas molecules dispersion to formulate in accordance with their normal environmental temperature conditions, without creating a supersaturated gas liquid.

• Motive fluid for aeration head unit 9 (Fig. 1 & 2).

Flow Stream 3:

Implemented flow balance control valve line V6 from the expansion tank down to the pump holding module station 7 (Fig. 1), provides additional efficient mixing of aeration gases and used water, which control the correct bubble sizes and biotreatment gas load in the re-conditioned water stream being fed back to the biofilters and bio-mass tank.

• Internal aeration/degassing balance recycling system via V6 (Fig. 1) from expansion tower module 10 (Fig. 1) to the pump holding module station 7.

Flow Stream 4:

Gravity Feed Biofilter modules 3 and 5 Floating Bead design utilizes a simultaneously secondary and third reverse flow stream principle for either, or both, waste extraction or bio-balance feed treatment gas recycle line.

• Motive fluid for waste extractor device manifolds 16 and 17 (Fig. 1) via piping manifold’s 15 bio-gas recycle line valves V2, V3, V7, V8 and V9 (Fig. 1).

The invention thus comprises in one embodiment a simplified standalone high volume gravity feed, variable flow, maintenance free, bio-filter process system as defined in claim 13.

Low Energy Self-Balancing Aeration, Gravity Feed Filtration Process System for Aquaculture water treatment:

The present invention relates to a quadruple, interface manifold module, build configuration process system as defined in claim 13, for the recycling and treatment of up to 1500 m<3 >/h. volumes of depleted biomass stock water via a 25kW motive energy consumption unit. The system is configured in a unique flexible manner so that all the recycled depleted oxygen water 70% (in mg/kg) is recovered, treated and refurbished back to 100% saturation by pumping simultaneous flow streams through a self-balancing aeration, degassing, gravity feed Biofiltration, module water treatment unit, by the single source motive energy unit, without introduction of conventional associated pure or industrial produced oxygen.

The present invention introduces a new improved efficient process technological concept use of ultraviolet germicidal irradiation (UVGI) atmospheric air water mix prior to the gas diffusion into water, via an expansion transition zone area in the Aeration/Degassing Module. The transition of this (UVGI) atmospheric air water mixing is produced via a new design aeration nozzle unit manifold assembly, formulated from Borda–Carnot equation (A sudden flow expansion) shock loss equation theory, for entraining high volumes of this atmospheric air, which diffuses and mixes the oxygen and nitrogen molecules into the recycled oxygen depleted Biomass water, at low energy, without entrainment of high supersaturation gas levels. Diffusion/oxidization rate are always subject to variable pressure, temperature and salinity of the water derived by Dalton’s and Henry's gas laws of pressure and distribution.

The invention has a unique velocity head outlet flow control system that is formulated around a variable liquid level fall and rise in the Aeration/Degassing Module, allowing for activation of an operating flow control signal, to either respective delivery outlet or secondary internal recycle flow valves, from the Biomass Tank Oxygen Probe concentration level.

The system of the invention introduces a recirculating balancing Bio feed flow Solids Waste Recovery Unit, formulated from Borda–Carnot equation (A sudden flow expansion) shock loss theory, for extracting waste particle residues at low motive pressures from each respective primary and secondary gravity feed biofilter module. Also, the system incorporates a variable piping manifold interface valve system for utilizing alternative low-pressure mixing air supply needed for assisting with the Oxidation-reduction potential (ORP), balancing or removal of light density slurries. The interface valve assembly shown in the example is for a manual control valve embodiment, but activation via an automatic system is also an alternative.

What Can The Present System Do and How?

The present invention relates to a quadruple, interface manifold module, build configuration process and system as defined in claim 1 and 13, for the recycling and treatment of up to 1500 m3/h. volumes of depleted biomass stock water via a 25 kW motive energy consumption unit. The system of the invention is in one embodiment configured in a unique flexible manner so that all the recycled depleted oxygen water 70% (in mg/kg) is recovered, treated and refurbished back to 100% saturation by pumping simultaneous flow streams through a self-balancing aeration, degassing, gravity feed Biofiltration, module water treatment unit, by the single source motive energy unit, without introduction of conventional associated pure or industrial produced oxygen system.

The present invention introduces the use of ultraviolet germicidal irradiation (UVGI) atmospheric air water mix prior to the gas diffusion into water, via an expansion transition zone area in the Aeration/Degassing Module.

The transition of this (UVGI) atmospheric air water mixing is produced via an aeration nozzle unit manifold assembly, formulated from Borda–Carnot equation (a sudden flow expansion) shock loss equation theory, for entraining high volumes of this atmospheric air, which diffuses and mixes the oxygen and nitrogen molecules into the recycled oxygen depleted Biomass water, at low energy, without entrainment of high supersaturation gas levels. (Diffusion/oxidization rate are always subject to variable pressure, temperature and salinity of the water derived by Dalton’s and Henry's gas laws of pressure and distribution.)

The system of the invention has a unique velocity head outlet flow control system that is formulated around a variable liquid level fall and rise in the Aeration/Degassing Module, allowing for activation of an operating flow control signal, to either respective delivery outlet or secondary internal recycle flow valves, from the Biomass Tank Oxygen Probe concentration level.

The system of the invention introduces a recirculating balancing Bio feed flow Solids Waste Recovery Unit, formulated from Borda–Carnot equation (a sudden flow expansion) shock loss theory, for extracting waste particle residues at low motive pressures from each respective primary and secondary gravity feed biofilter module. Also, the unit construction incorporates a variable piping manifold interface valve system for utilizing alternative low-pressure mixing air supply needed for assisting with the Oxidation reduction potential (ORP), balancing or removal of light density slurries. The interface valve assembly shown in the example is for a manual control valve construction, but activation via an automatic system is also an alternative.

Other objectives and advantages of the present invention will here in-after appear and, for purpose of illustration but not of limitation, embodiments of the present invention are shown on the accompanying drawings.

Technical Description

In one embodiment the present invention comprises a Low Energy Self-Balancing Aeration, Gravity Feed Biofiltration Recirculation Process System for Aquaculture water treatment, where depleted oxygenated and grit-silt water is extracted from the Biomass Tank, 100% re-oxygenated, up to 98% foreign particle freed and recycled back to the Biomass Tank.

The embodiment of the invention illustrated on FIG 1 and 1A comprises a Low Energy Self-Balancing Aeration Gravity Feed Biofiltration Recirculation Water Treatment Unit, configured with piping manifold spools 2, 3B, 4, 5B, 6, 8, 9, 10B, 13, 15 and 18, interface link arrangement with module units 3, 5, 7, 10, 11 and devices 11A, 14, 16 & 17, for producing a simultaneously quadruple high flow recirculation process system, driven by a single source low energy unit. The total recirculation process concept can be interfaced with any existing or new multiple Biomass Tanks 1 via respective valve supply and return V1 and V7 located on respective piping manifold spools 2 and 10B allowing for the gravity feed, depleted oxygenated grit-silt water from the Biomass Tank or Tanks 1, to be 80% particle separated < 20 microns via the process flow alternative formulated in Primary and Secondary Biofiltration Module(s) 3 and 5 respective Floating Fired Ceramic Bio-Stone Screens 3A & 5A (illustrated in Fig. 1), and transferred out of respective integrated primary flow link piping spool manifolds 3B, 4, 5B and 6 into the pump holding station module 7, where the final secondary module’s 5 biofiltered depleted oxygenated water is low pressure recirculated, via Pump 7A (Motive Energy Unit) located in Module 7 through delivery piping manifold spool 8 directly to the Low Energy Self-Balancing Aeration Head manifold 9, formulated from Borda–Carnot equation, located in the expansion transition zone area of the Aeration/Degassing Module 10.1 (illustrated in Fig. 2A). This recirculated primary process stream is then utilized, as the motive energy supply flow to inlet ports 9-1 (illustrated in Fig. 2), for entraining atmospheric air through UVGI sterilization module 11 and 11A, to form a sterilized agent flow through respective (air/gas) orifice inlet ports 9-2, for creating a two-phased flow disbursement of depleted oxygenated recycled water out through respective orifice outlet path area 9-3 of the Low Energy Self-Balancing Aeration Head Unit’s 9, Fig. 2. The diverted two-phase outlet flow transferred into the expansion zone area of the Aeration/Degassing Module 10.1 (illustrated in Fig. 2A), along with the associated water and air temperature pressure level, will allow for the gas molecule levels to diffuse into water accordingly with Dalton’s and Henry’s Gas Laws of Pressure and Distribution. The total gases capsulated in the Aeration/ Degassing Module’s 10 Fig. 1, water volume flow will expand according to the variable molecule diffusion rate, therefore, allowing for the relevant heavy gases (oxygen and nitrogen) molecules to vaporize back into the lower water volume area of the Aeration/Degassing Module 10.2, Fig. 2A, at the normal formulated gas diffusion rate of solubility. The other accumulated lightweight surplus gases (such as carbon dioxide etc.) capsulated in the expansion transition zone area of the Aeration/Degassing Module 10.1 Fig. 2A, are vented out through piping spool 6A and 12, or utilized for the primary feed cycle of the biological filtering process.

The integrated return suction piping spool 6A located in Aeration/Degassing Module 10 acts as a foam fractionation scum waste removal and a continuous or intermittent high velocity secondary gravity recycle flow outlet system controlled from respective valve V6 and V7 located on respective piping manifold spools 6A and 13 (illustrated in Fig. 1 and 2A). The other acclaimed feature of this secondary gravity recycle flow outlet system control is that when being used for a multi Biomass Tank installation the excess aerated water reblending process, with the primary concentrated grit-silt and other foreign particle depleted oxygenated water, is evaluated from each respective Biomass Tank’s Oxygen monitoring probe unit 1a.

This process function minimizes excessive flow volumes to the other associated Biomass Tanks connected into the system.

Respective gravity outlet flow control valve V7 is activated by a linear signal level collated from the oxygen/water concentration value measured by the respective Biomass Tank’s Oxygen monitoring probe unit 1a.

The required pre-calculated atmospheric air ingress volumes into respective inlet ports 9-2 (illustrated in Fig. 2) in this system unit is provided from an atmospheric pressure UVGI Intake Module 11 (illustrated in Fig. 2A).

The embodiment of the invention illustrated on Fig. 1 concentrates on the configuration of the total system’s process concept. The embodiment of the process according to the invention illustrated on Fig. 2 comprises of a method, derived from Borda–Carnot equation (a sudden flow expansion) shock loss theory, for entraining high volumes of atmospheric air, at low energy, for diffusing oxygen into recycled oxygen depleted Biomass water without creating high gas supersaturation levels. The oxygen depleted Biomass water is pumped into aeration head’s motive inlet port 9-1 Fig. 2, via recycle pump 7, at pressures between 0.25 - 1.0 bar gauge. Nozzle outlet port 9-3 Fig. 2 diameter is calculated to accept a water flow velocity of 100% value of the high gravity level flow volume. The number of air inlet port 9-2 Fig. 2 and nozzle outlet port 9-3 Fig. 2 in the aeration head Fig.1 are subject to the Biomass flow volume requirement which is related to Biomass Tank 1 stock load and size. The oxygen depleted Biomass water is then utilized as the motive fluid energy source of supply for entraining the atmospheric air through inlet port 9-2 Fig. 2, based on a factor of 0.5 cubic meters per hour water flow entraining 23 standard cubic meters per hour of atmospheric air at 20 degrees Celsius. The actual entrained air volume is subject to the expansion transition zone area of the Aeration/Degassing Module 10 total gas pressure and outlet port 9-3 Fig. 2. The delta pressure (Dp) characteristic and transition area of the liquid feature requirement has been formulated in the outlet port 9-3 Fig. 2 when entering the gas expansion transition zone area of the Aeration/Degassing Module 10. The construction format has been superimposed at an outlet Dp of 1333 - 2000 pascals above 99991 pascals Barometric pressure. The entrained air becomes encapsulated with the oxygen depleted Biomass water in the outlet port 9-3 Fig. 2 prior to expulsion into the expansion transition zone area of the Aeration/Degassing Module 10. During this cycle the oxygen depleted Biomass flow stream becomes saturated with atmospheric air gases. The expulsion of water at outlet port 9-3 Fig. 2 will always remain constant to recycled oxygen depleted Biomass flow stream.

However, the entrained and expelled gas molecules will change according to their surrounding atmospheric conditions. (Reference Dalton’s and Henry’s Gas Laws of Pressure and Distribution.) The saturated gas expelled water from outlet port 9-3 Fig. 2 is pinged onto the inner wall surface of the expansion transition zone area of the Aeration/ Degassing Module 10. The velocity speed change combined with the water agitation effect produces excited gas molecules, which initiates the formation of the following three-step process for rapidly transferring oxygen into water at a balanced nitrogen ratio.

• Transfer of oxygen in the gas to the gas-liquid interface

• Transfer across the gas-liquid interface

• Transfer of oxygen away from the interface into the liquid.

Other surplus gas molecules such as carbon dioxide etc. will follow the normal gas law theory and will be forced out via vaporization through vent piping spool 12.

During the process function of the former motive flow to the respective aeration head manifold 9 and module 10 the low-pressure recirculating flow simultaneously, provides a third and fourth (percentage) parallel motive flow stream, via piping manifold spools 15 and 18 to either or all respective devices, Centrifuge Separator 14, Solids Waste Recovery 16 and 17, formulated from Borda–Carnot equation (illustrated in Fig. 3), which is employed by opening respective valves V2, V3 V5, V5, V7, V8 and V9. to produce a continuous or intermittent bio-feed medium balance of grit-silt water from respective Primary and Secondary Filtration Modules 3 and 5 to either one of these flow path options for formulating an “enhanced” high performance biofiltration process enbodiment in respective Floating Fired Ceramic Bio-Stone Screens 3A and 5A (illustrated in Fig. 1). When not employed for the biofiltration balanced feed process requirement respective valves V10 and V11 located on respective device manifold spools 16 and 17 can be set for a continuous or intermittent flow opening forming a bottom solids waste extraction outlet flow from respective Biofiltration Modules 3 and 5, allowing for re-directing the waste either to a secondary waste cycle station or a waste transportation vehicle.

Auxiliary interface valve V8 located on piping spool 15 is for injecting additional plant air (if or when required) to create a two-phase booster flow for removing light solids in suspension or providing additional bio-loads to respective biofiltration modules 3 and 5, if required. Delivery piping spool’s 8 respective valve V4 will be closed and opened subject to process flow path options chosen.

The aeration and filtration unit and process according to the present invention may be used for any aquaculture purposes, e.g. for cultivating trout, rainbow trout, salmon, bass, Silurojeda, crawfish, oysters, clams as well as salt-water organisms.

In fluid dynamics the Borda–Carnot equation is an empirical description of the mechanical energy losses of the fluid due to a (sudden) flow expansion. It describes how the total head reduces due to the losses. This is in contrast with Bernoulli's principle for dissipationless flow (without irreversible losses), where the total head is a constant along a streamline. The equation is named after Jean Charles de Borda (1733–1799) and Lazare Carnot (1753–1823). This equation is used both for open channel flow as well as in pipe flows. In parts of the flow where the irreversible energy losses are negligible, Bernoulli's principle can be used.

The Borda–Carnot equation is

where

ΔE is the fluid's mechanical energy loss,

ξ is an empirical loss coefficient, which is dimensionless and has a value between zero and one, 0 ≤ ξ ≤ 1,

ρ is the fluid density,

v1 and v2 are the mean flow velocities before and after the expansion.

In case of an abrupt and wide expansion the loss coefficient is equal to one. In other instances, the loss coefficient has to be determined by other means, most often from empirical formulae (based on data obtained by experiments). The Borda–Carnot loss equation is only valid for decreasing velocity, v1 > v2, otherwise the loss ΔE is zero – without mechanical work by additional external forces there cannot be a gain in mechanical energy of the fluid.

The loss coefficient ξ can be influenced by streamlining. For example, in case of a pipe expansion, the use of a gradual expanding diffuser can reduce the mechanical energy losses.

Relation to the total head and Bernoulli's principle

The Borda–Carnot equation gives the decrease in the constant of the Bernoulli equation. For an incompressible flow the result is – for two locations labelled 1 and 2, with location 2 downstream to 1 – along a streamline

with

p1 and p2 the pressure at location 1 and 2,

z1 and z2 the vertical elevation – above some reference level – of the fluid particle, and

g the gravitational acceleration.

The first three terms, on either side of the equal sign are respectively the pressure, the kinetic energy density of the fluid and the potential energy density due to gravity. As can be seen, pressure acts effectively as a form of potential energy.

In case of high-pressure pipe flows, when gravitational effects can be neglected, ΔE is equal to the loss Δ(p+1⁄2ρv<2>):

For open channel flows, ΔE is related to the total head loss ΔH as:

where h is the hydraulic head – the free surface elevation above a reference datum: h = z p/(ρg).

Sudden Expansion of a Pipe

The Borda–Carnot equation is applied to the flow through a sudden expansion of a horizontal pipe. At cross section 1, the mean flow velocity is equal to v1, the pressure is p1 and the cross-sectional area is A1. The corresponding flow quantities at cross section 2 – well behind the expansion (and regions of separated flow) – are v2, p2 and A2, respectively. At the expansion, the flow separates and there are turbulent recirculating flow zones with mechanical energy losses. The loss coefficient ξ for this sudden expansion is approximately equal to one: ξ ≈ 1.0. Due to mass conservation, assuming a constant fluid density ρ, the volumetric flow rate through both cross sections 1 and 2 has to be equal:

Consequently – according to the Borda–Carnot equation – the mechanical energy loss in this sudden expansion is:

The corresponding loss of total head ΔH is:

For this case with ξ = 1, the total change in kinetic energy between the two cross sections is dissipated. As a result, the pressure change between both cross sections is (for this horizontal pipe without gravity effects):

and the change in hydraulic head h = z p/(ρg):

The minus signs, in front of the right-hand sides, mean that the pressure (and hydraulic head) are larger after the pipe expansion. That this change in the pressures (and hydraulic heads), just before and after the pipe expansion, corresponds with an energy loss becomes clear when comparing with the results of Bernoulli's principle. According to this dissipationless principle, a reduction in flow speed is associated with a much larger increase in pressure than found in the present case with mechanical energy losses.

Sudden contraction of a pipe

In case of a sudden reduction of pipe diameter, without streamlining, the flow is not able to follow the sharp bend into the narrower pipe. As a result, there is flow separation, creating recirculating separation zones at the entrance of the narrower pipe. The main flow is contracted between the separated flow areas, and later on expands again to cover the full pipe area.

There is not much head loss between cross section 1, before the contraction, and cross section 3, the vena contracta at which the main flow is contracted most. But there are substantial losses in the flow expansion from cross section 3 to 2. These head losses can be expressed by using the Borda–Carnot equation, through the use of the coefficient of contraction μ:

with A3 the cross-sectional area at the location of strongest main flow contraction 3, and A2 the cross-sectional area of the narrower part of the pipe. Since A3 ≤ A2, the coefficient of contraction is less than one: μ ≤ 1. Again there is conservation of mass, so the volume fluxes in the three cross sections are a constant (for constant fluid density ρ):

with v1, v2 and v3 the mean flow velocity in the associated cross sections. Then, according to the Borda–Carnot equation (with loss coefficient ξ=1), the energy loss ΔE per unit of fluid volume and due to the pipe contraction is:

The corresponding loss of total head ΔH can be computed as ΔH = ΔE/(ρg).

According to measurements by Weisbach, the contraction coefficient for a sharpedged contraction is approximately:

Derivation from the momentum balance for a sudden expansion

For a sudden expansion in a pipe, see the figure above, the Borda–Carnot equation can be derived from mass and momentum conservation of the flow. The momentum flux S (i.e. for the fluid momentum component parallel to the pipe axis) through a cross section of area A is – according to the Euler equations:

Consider the conservation of mass and momentum for a control volume bounded by cross section 1 just upstream of the expansion, cross section 2 downstream of where the flow reattaches again to the pipe wall (after the flow separation at the expansion), and the pipe wall. There is the control volume's gain of momentum S1 at the inflow and loss S2 at the outflow. Besides, there is also the contribution of the force F by the pressure on the fluid exerted by the expansion's wall (perpendicular to the pipe axis):

where it has been assumed that the pressure is equal to the close-by upstream pressure p1.

Adding contributions, the momentum balance for the control volume between cross sections 1 and 2 gives:

Consequently, since by mass conservation ρ A1 v1 = ρ A2 v2:

in agreement with the pressure drop Δp in the example above.

The mechanical energy loss ΔE is:

which is the Borda–Carnot equation (with ξ = 1).

Claims

C l a i m s

1. Low energy consumption process for cleaning and aerating spent water from a land-based aquaculture vessel (1), said land-based aquaculture vessel (1) containing a water mass, said low energy consumption process comprising leading spent water from the land-based vessel (1) to at least one filtration module (3,5) for removing contaminating substances from said spent water by filtration (3A,5A) and by the action of microorganisms,

c h a r a c t e r i z e d i n that the water emerging from the filtration modules (3,5) being further pumped via at least one pump (7,7A) to an aerating head with an expansion chamber (10a) including aeration nozzles forming an aeration unit (9) being controlled by a full-auto control operation system via an oxygen monitoring probe unit (1a) and valve (V6) changing velocity head in the expansion chamber (10a), forming an inspection unit for monitoring the amount of air assimilated by the water and replacing carbon dioxide in the spent water while recycling the aerated water through a control valve (V6) functioning in a way that when more aerated water is recycled the water pressure at the aeration nozzles is reduced and both the cleaned and aerated water from the aeration (V5) and the amount of air added to the water in the nozzles are reduced, and when less aerated water is recycled the water pressure at aeration nozzles is increased and both the cleaned and aerated water from the aeration (V5) and the amount of air added to the water in the nozzles are increased, said water cleaning system optionally additionally including a degassing module (10) and a vent (12).

2. Low energy consumption water cleaning process according to claim 1, c h a r a c t e r i z e d i n that the control of the aeration nozzles and aeration head (9) is automatically governed by a measurement of the oxygen level in the aquaculture vessel (1).

3. Low energy consumption water cleaning process according to claim 1 or 2, c h a r a c t e r i z e d i n that the aerated water is passed to a degassing step (10) by the aeration nozzles in the aeration head unit (9).

4. Low energy consumption water cleaning process according to claim 1 - 3, c h a r a c t e r i z e d i n that the aeration nozzles in the aeration head unit (9) passes the aerated water to a degassing step (10).

5. Low energy consumption water cleaning process according to claim 4, c h a r a c t e r i z e d i n unwanted constituents and pollutants in the water, e.g. carbon dioxide, being gassed off before the aerated water is returned to the aquaculture vessel (1) through the water inlet valve (V5) or is recycled through the control valve (V6).

6. Low energy consumption water cleaning process according to claim 4 or 5, c h a r a c t e r i z e d i n the agitation of the recycled aerated water in the pump (7,7A) also causing the release of unwanted constituents and pollutants, e.g. carbon dioxide, from the water.

7. Low energy consumption water cleaning process according to any of the preceding claims, wherein the removal of the contaminating substances is performed by filtration modules including at least one primary and at least one secondary filtration modules (3,5),

c h a r a c t e r i z e d i n the recycled aerated water (V6) furthermore oxidizing and breaking down the organic solids caught in the primary and secondary filtration modules (3,5) to where it is passed via the pump (7,7A) and a non-motorized centrifugal separator (14).

8. Low energy consumption process according to any of the preceding claims, c h a r a c t e r i z e d i n the aeration being conducted by using an Ultra Violet Germicidal Irradiation (UVGI) intake module (11).

9. The process according to claim 8, wherein,

c h a r a c t e r i z e d i n the recycled aerated water containing an excess of socalled “dirty gasses”, such as nitrogen and carbon dioxide, such “dirty gasses” being eventually diffused away by the repeated and intimate contacting with air in the nozzles of the aeration head unit (9) and the degassing module (10), and being disposed of through the vent (12), while the said repeated and intimate contacting with air in the nozzles keeps the oxygen level in the cleaned and aerated water returned to the aquaculture vessel (13 ,V5) at 100% saturation.

10. Low energy consumption water cleaning process according to any of the preceding claims,

c h a r a c t e r i z e d i n said filter module(s) (3,5) comprising a high-volume flow, low maintenance filter system, aided by the recycled aerated water.

11. Low energy consumption water cleaning process according to any of the preceding claims,

c h a r a c t e r i z e d i n the aerating system including a Ultra Violet Germicidal Irradiation (UVGI) intake module (11).

12. The process according to claim 11,

c h a r a c t e r i z e d i n that, in the event of the recycled aerated water containing an excess of so-called “dirty gasses”, such as nitrogen and carbon dioxide, such “dirty gasses” are eventually diffused away by the repeated and intimate contacting with air in the nozzles of the aeration head unit (9-1) and the degassing module (10) and disposed of through the vent (12), while the said repeated and intimate contacting with air in the nozzles keeps the oxygen level in the cleaned and aerated water returned to the aquaculture vessel (13 ,V5) at 100% saturation.

13. Low energy consumption system for conducting the process according to any of the claims 1 – 12, the system comprising a land-based aquaculture vessel (1) containing a water mass with a water surface level, said low energy consumption system comprising a water inlet (V5) for cleaned and aerated water from the low energy consumption cleaning system and an outlet for spent water (V1), said system comprising at last one pump (7,7A) for transporting said water, and at least one filtration module (3,5),

c h a r a c t e r i z e d i n that the system further comprises a number of aeration nozzles (9) in an aeration unit (10) including an expansion chamber (10a) being controlled by a full-auto control operation system via an oxygen monitoring probe unit (1a) and a control valve (V6) changing velocity head in the expansion chamber (10a) forming an inspection unit for monitoring the amount of air assimilated by the water replacing carbon dioxide in the spent water and recycling the aerated water through control valve (V6), the system further comprising a return conduit (13) for transporting the aerated water from the aeration unit (9,10) to the aquaculture vessel (1).

14. Low energy consumption system according to claim 13,

c h a r a c t e r i z e d i n said water cleaning system additionally including a degassing module of the aeration unit (10) and a vent (12).

15. Low energy consumption water cleaning system according to claim 13 or 14, c h a r a c t e r i z e d i n said system comprises at least one Ultra Violet Germicidal Irradiation (UVGI) unit for inhibiting the growth of microorganisms.

16. Low energy consumption water cleaning system according to any of the claims 13 - 15,

c h a r a c t e r i z e d i n that the filtration modules includes at least one primary and at least one secondary filtration modules (3,5), wherein the recycled aerated water (V6) furthermore oxidizes and breaks down the organic solids caught in the primary and secondary filtration modules (3,5) to where it goes via the pump and a non-motorized centrifugal separator (14).

17. Low energy consumption water cleaning system according to any of the claims 13 - 16,

c h a r a c t e r i z e d i n that said pump (7) is the only consumer of energy and source of transporting the water in the process.

18. Low energy consumption water cleaning system according to any of the claims 13 - 17,

c h a r a c t e r i z e d i n that said filter module(s) (3,5) comprise(s) a highvolume flow, low maintenance filter system, aided by the recycled aerated water.