intelligent dissolved oxygen control systemfor intensive...

Scholarly Journal of Agricultural Science Vol. 4(4), pp. 188-200 April, 2014Available online at http:// www.scholarly-journals.com/SJAS

ISSN 2276-7118 © 2014 Scholarly-Journals

Full Length Research Paper

Intelligent Dissolved Oxygen Control SystemforIntensive Carp System

Wael Mohamed Elmesseryand Said El shahat Abdallah

Department of Agricultural Engineering Faculty of Agriculture, Kafrel sheikh University Kafrel sheikh 33516, Egypt

Accepted 19 February, 2014

Success in designing affordable automated control systems for aquaculture will be widely applicablebecause it will enhance water management. Intensive recirculation systems have the potential for asignificant increase in production per volume of water requiring dissolved oxygen monitoring andcontrol. An intelligent Lab View dissolved oxygen sensing unit was designed using only one oxygensensor and its transmitter for monitoring several tanks. Peristaltic pumps extracted water from eachtank without adding oxygen to the sample. Measurements were auto-calibrated and statisticallydiagnosed using the air dissolved oxygen measurements. Dissolved oxygen sensor membrane foulingfrom algal blooms, sediments or suspended water droplets that still attaching to the membrane at themoment of oxygen measurements in the air were analyzed; the system controlled membrane foulingproblems. Dissolved oxygen changes with temperature and fish feeding were analyzed from three tankshaving each carps in a different growth stage. Dissolved oxygen mass balance was studied to gain abetter understanding of events which can contribute to low dissolved oxygen concentration, such asheavy plankton blooms and high temperature.

Keywords: dissolved oxygen monitoring, system control, auto-calibration,and oxygen mass balance.

INTRODUCTION

Automation of aquaculture systems locates theproduction closer to markets, improve environmentalcontrol by minimizing effluents, reduce production costsand improve product quality. Today with the decrease ofcomputers and software cost, and off-the-shelf monitoringhardware cost it has become an alternative toaquaculture producers. The degree of monitoring neededfor recirculating aquaculture systems (RAS) andenvironmental factors depends on system design, fish lifestage and fish density. Aquaculture managers needaccurate, real time information on system status andperformance, in order to maximize their productionpotential. At high production densities, failure of acirculation pump or aeration system can result in fishsevere stress or even significant losses within minutes(Appelbaum et al., 1999).

*Corresponding author. E-mail:[email protected].

Lab View is a widely used graphical programmingenvironment which allows designing systems in anintuitive block-based manner (Pereira et al., 2008; Bart,2002); it could acquire dissolved oxygen (DO) andtemperature data, process them to control threerecirculating aquaculture systems (Elmessery, 2011).Sensors measuring critical factors can be linked to anautomatic telephone dialer for remote diagnostic andprevention of catastrophic losses (Lee, 2000). Fish growquicker with optimum temperature, achieving improvedfood conversion ratios; fish feed poorly beneath 16°C anddeath will occur beneath 12°C (Chervinski, 1982). Aftermeeting fish feed requirements, low concentration ofdissolved oxygen is the major variable that limits fishgrowth and production in intensive aquaculture andshould be kept above 5ppm. Although several dissolvedoxygen sensors are used in aquaculture applications,galvanic and luminescence sensors are now-a-dayscommonly employed. Galvanic cells avoid sulfidepoisoning,reduce anode maintenance and use a constant pH

Elmessery and Abdallah 189

Figure 1: Lateral view showing two column aerators, two fish tanks, the hydraulic head and the instrumentation system.

electrolyte solution; no external voltage polarization isrequired and it works quicker as no warm-up time isnecessary (Eutech Instruments, 2006). Bryan andCushman (1991) developed a real time on-line system formonitoring dissolved oxygen testing galvanic sensormembrane impedance and studying its response.Luminescence based devices quantify O2nondestructively as color changes with oxygen variations(Evans and Douglas, 2006). Algae blooms and fine solidparticles are identified as water foulants and affect DOmeasurements; silica and organic matter become part ofthe sensor membrane (Howe et al., 2002; Schafer et al.,2000; Lander et al., 2010). Algae produce oxygen duringphotosynthesis and consume oxygen through theprocess of respiration (Vasile, 2008; Tafangenyasha etal., 2010); fish die on warm summer nights due to algaeblooms excessive oxygen consumption (Stone andDaniels, 2006). The sensor membrane and optical pathrequire an effective cleaning system, as the ultrasonicmodule integrated to the VisoTurb ® 700 IQ(Wissenschaftllch-Technische Werkstatten, 2011). In thisstudy, dissolved oxygen was monitored and controlled.The controller was interfaced to Lab View and used onedissolved oxygen sensor and transmitter to control fourfish tanks; the system presented auto-calibration,statistically self-diagnostic and anti-fouling mechanisms.Oxygen budget in the RAS was studied generating onemodel; the automatic system can rely on in cases ofsensor failures. The choice of the system's architecturewas based on price performance considering labor,

product value, environment and vendor support.

Materials and methods

The work was divided in four strategic areas:

(1) Installation of equipment for DO monitoring from thefour tanks(2) Analysis and detection of different membraneantifouling problems(3) Development of an alternative energy system toassure fish survival and(4) Model for aeration requirements under some set ofconditions for the system(5). Development of a Lab View program that monitorsthe data, stores it, control the aerators and diagnosticsensor status.

Recirculation aquaculture system

The aquaculture recirculation system (Figure 1) is locatedat Tlapeaxco at the experimental camp of theUniversidad AutonomaChapingo. The system installedwithin a greenhouse consists of four circular polyethylenetanks having a diameter of 1.1m and a capacity of1100liters. The tanks were positioned within a squarearea of 10 by 10m with the monitoring and control unit atthe center. The four tanks were stocked at different time

to obtain one harvest every 37days being the harvestsize of 400grams after 5 cultivation months. The first tankwas cultivated in December, the second in January, thethird in February, and the fourth in March with mirror carpvar. Cyprinuscarpio. Carps were fed with Nutripec 3508at: 9:00, 14:00 and 19:00h. The water from each culturetank circulated through the solid waste separator beforeentering to a trickling bio filter having polyethylene bio-strata as media. A spray column aerator oxygenated thewater using fine jet sprays (mod. 130327, SURTEK,MEX); the conical water spray increased the oxygenationefficiency as a better contact area between water and airexists. The column aerator employed an air fan derivedby a 0.5hp induction motor. The photovoltaic system (PV)stored energy in the batteries, and an inverter convertedDC to AC voltage (Hahn, 2010). Batteries and solarpanels were selected considering the day having thehighest energy consumption (2076.787Wh/day). Duringthis day the aerators worked 20 continuous hoursoxygenating water for a carp biomass density of 25kg percubic meter. A line power failure of 14 continuous hoursoccurred once a month; batteries should recharge everytwo weeks and last for 14hours. A line fault was carriedout analyzing dissolved oxygen variations for 200 and400grams carps. Energy saving of the aerators wasstudied under three on-off periods: 1hr on-1h off; 1hr on-0.5h off and 1.33 h on 0.75h off. As batteries are chargedin 14days by a solar panel having six irradiance hoursover 1000Wm2/day it should provide 57.6 Ah daily; a 200W solar panel was selected (mod. ES-A-200, EvergreenSolar, USA).

DO monitoring equipment

The monitoring system was designed to measure the fourtanks DO using only one sensor and one controller. Agalvanic probe (HI 76410/4, Hanna Instruments, andUSA) was connected to a panel mounted controller (mod.HI 8410, Hanna Instruments, USA). A membranecovered the galvanic probe having a built-in thermistor fortemperature compensation; an electrolyte solution (mod.HI 7041S, Hanna Instruments, USA) refilled themembrane cap. The probe provided a 0.1mg/L O2resolution with a temperature accuracy of ±0.2ºC.Calibration is performed with HI 7040L zero oxygensolution while 100% calibration is done when the probecontacts the air. The controller 4-20mA recording outputwas connected to a USB acquisition board (mod. DAQ NIUSB 6008, National Instruments, USA) and thenintroduced to the PC computer.

Water sampling was provided by 25W at 0.356liter/minperistaltic pumps (mod. 41k25GN-AUL-ES, OrientalMotor Co. LTD, Japan). Water samples from each tankare pumped to the 5° slope hydraulic head (Figure 1)passing by the DO probe before returning to the tank.Peristaltic pump poor suction required being primed prior

Scholarly J. Agric. Sci. 190

pumping; suction hose inlets were placed below thepumping level (Figure 1). A black polyethylene U-mounted hose (internal diameter of 0.65cm) had its input30cm beneath the tank water surface. After adding a50cm hose, the input was placed 80cm beneath thewater surface. As the distance between the samplingtank and the hydraulic head varied DO measurementdelay time had to be programmed. The time required forthe water sample to arrive from the first tank (3.3m away)to the DO probe was of 23.5 or 20.1seconds accordingwhether the hose inside the tank was 80 or 30cm deep,respectively. The fourth tank (5.2m away from thehydraulic head) required 33.4 or 37seconds before thewater sample arrived to the DO probe if the hose was 30or 80cm deep, respectively. The sample taken from onedepth was programmed at the user interface by a toggleswitch named peristaltic pump automatic sampling. Theautomated monitoring system starts operating when theperistaltic pump sucks a water sample from the first tank.Maximum dissolved oxygen values of 6.4ppm (rosemarks) were measured during the first 20seconds andwithin the 100-120second interval that starts the newreading cycle (Figure 2). The galvanic probemeasurement settles down after 60seconds; thecontroller acquires thirteen values (green marks) andstores them in the Lab View data logger. The thirteenvalues are averaged and when the standard deviationexceeds 0.3ppm, a fault exists within the monitoringsystem; another thirteen measurements should be taken.When the average dissolved oxygen value is beneath agiven set point the first aerator will be turned-on; it couldbe turned-off after the next measurement but to avoidexcessive motor current peaks it will be disconnected tenminutes after. Once the peristaltic pump is turned-off, thewater remaining within the hydraulic head returns to thetank and air will fill-up the hydraulic head. This operationis repeated for each tank being each aerator controlledseparately.

Acquisition system and Lab View interface

A multifunction DAQ NI-USB 6008 acquisition boardacquired the DO values from the controller and itsconfiguration is shown in Table 1. Port 0 turns-on eachperistaltic pump and every aerator fan. The dissolvedoxygen analyzer HI 8410 provided a 4-20 mA outputcurrent connected in single-ended mode betweenterminals 1 and 2. A digital terminal P1.2 monitors theelectrical voltage status in the system 163 and P1.3activates the inverter of the alternative photovoltaicenergy during faulty line situations.

The Lab View data logger was programmed by the userto control when monitoring start for each tank due tovariable distance to the galvanic probe at the hydraulichead. Data from each tank was saved in a different Excelfile and every new reading was appended. The user


Figure 2: Dissolved oxygen measurements of the first three tanks being AM (air measurement) and WM (water measurement

Table 1: Port configuration.

Port configurationDigital P0.0 P0.1 P0.2 P0.3 P0.4 P0.5 P0.6 P0.7

Signal

Terminal 17 18 19 20 21 22 23 24

Define 1st 2nd 3rd 4th 1st 2nd 3rd aerator 4thperistaltic peristaltic peristaltic peristaltic aerator aerator aeratorpump pump pump pump

Signal GND AI 0 P1.0 P1.1 P1.2 P1.3 GND AI1

Terminal 1 2 25 26 27 28 4 5

Single-Ended Mode Digital Single-Ended Mode

DO sensor ThermopareDefine Analog Analog Water Vibrator Electrical Photo- Analog Analog

current current spray Motor voltage voltaic voltage voltage

input -ve input +ve Pump state system

interface acknowledges which peristaltic pump isoperating and recognizes which fish culture tank is beingsampled. Maximum and minimum dissolved oxygen setpoints are introduced at the user interface to controlaerator turn-on; leds indicate aerator operation (Figure 3).

After plotting daily DO values sensor operation can be

diagnosed. P1.0 and P1.1 controlled sensor cleaningduring autocalibration when sensor fouling problemswere encountered. After diagnosing a sensor problem,cross sampling between different tanks verified that theproblem exists. The program automatically codified errormessages in the Lab View Front panel-User Interface.


Figure 3: Front panel-User Interface with dissolved oxygen control.

Table 2: Aeration required for different fish stocking densities (kg biomass) per cubic meter of water at different watertemperatures.

Kg biomass Aeration in hours for different water temperatures, °Cper m3 water 17 18 19 20 21 22 23 24

2 1.83 1.94 2.12 2.25 2.38 2.51 2.63 2.766 5.00 5.30 5.77 6.11 6.51 6.90 7.20 7.6010 7.68 8.16 8.85 9.33 10.00 10.64 11.06 11.7314 9.87 10.52 11.36 11.92 12.85 13.75 14.21 15.1518 11.56 12.38 13.30 13.86 15.06 16.22 16.65 17.8522 12.75 13.75 14.68 15.17 16.63 18.04 18.39 19.85

24 13.15 14.25 15.15 15.58 17.18 18.72 18.99 20.58

The code is generated after that the problem subsistsafter water jet injection or vibration and sent by phone toa desired cellular. Lab View was programmed to executean alternative program as a fixed timer under emergencysituations when the monitoring system failed. Undergiven water temperature and biomass density theprogram calculates the required aeration time per tank tomaintain the dissolved oxygen within 4 and 5ppm, basedon the dissolved oxygen model created in this studyTable 2. When an intermediate biomass is present,interpolation was used to determine the required aerationtime; for example, a biomass of 12kg at 19°C per m3 willrequire 10.1h of aeration.

Sensor calibration and fault analysis

The sensor presents auto-calibration using a suitable

scale equation for the sensor signal at saturation state(6.3ppm at20°C) at an altitude of 2400 m above sealevel; Hanna zero oxygen solution HI 7040 is used once amonth. The scale equation used for calibration dependson the current I given in mA:

DO = 2533.1 − 9.6621In recirculation aquaculture systems 194 (RAS) dissolvedoxygen sensors encounter periodic problems during carpgrowth. Solid particle accumulation at the sensormembrane is encountered for very fine particles below40m. Algae blooms also accumulate on the membraneand affect sensor readings; blooming dinoflagellatesranging between 10 and 50m in size pass through inletscreens. Sometimes, after evacuating the water samplefrom the hydraulic head, water droplets remainsuspended on the membrane affecting sensor


Figure 4: Backwash mechanism.

measurements. Another common measurement erroroccurs after exchanging the electrolyte or the sensormembrane as air bubbles remain within the electrolyte ifnot properly installed. The effect of DO variations undermembrane sediment accumulation was studied. DO wasmeasured at air saturation and then 100ml of distillatedwater were sprayed to the sensor head storing the waterwith particles and measuring its turbidity (DRT-15CE, HFScientific Inc., Ft. Myers, FL). Three different algaeblooms (Scenedesmus sp., Chlorella sp. and filamentousmicroalgae) were reproduced over the galvanic sensormembrane measuring DO values under air saturationprior to cleaning the sensor with distillated water toquantify them with the turbidity sensor. The hydraulicsensor head was equipped with an automated waterspray to clean the sensor membrane. A 100Wsubmergible pump (mod. 2480, Kairui Electrochemical,China) produced a working pressure and flow of 15kPaand 500cm3/min, respectively; the water spray resultedfrom passing the water through a nozzle having adiameter of 1.7mm. The water spray operated for5seconds to remove algae and suspended solidsadhered to the membrane. A vibrating motor (mod. 30827CRA212-ND, Cramer Co.Digi-Key, USA) with aneccentric disc removed the droplets; the 18W at 12 VDCmotor rotated at 60rpm. The motor turns ten revolutionsevery five days offering maintenance to the sensor

membrane. Another antifouling hydraulic head wasdesigned for cleaning the sensor membrane on lineinstead of using a spray nozzle. This system is based onbackwash solid removal of irrigation system filters (Buckset al., 1979; Gilbert et al., 1981). Three orthogonal watersample inlets coming from different tanks entered thehydraulic head and left through the fourth hole afterpassing through the DO probe (Figure 4). Algae bloomswere grown over the membrane and backwash removalwas analyzed. Similarly, the membrane was covered withfine particles to observe its removal by this method.

Aeration requirements model

A basic task of fish tank management is the maintenanceof dissolved oxygen for fish survival and growth. Themanagers can monitor dissolved oxygen level at a givenpoint in time, predicting potential critical periods of lowconcentration. Dissolved oxygen concentrations, aregiven by chemical, physical and biological reactions. Inorder to gain a better understanding of events which cancontribute to low dissolved oxygen concentration, such asheavy phytoplankton blooms and high temperature. Theparameters under-studies participating to the oxygenbudget in the recirculating aquaculture system arePhytoplankton, Cultivating Fish, Nitrifying bacteria, and


Table 3: Oxygen mass balance equations in RAS.

Inlet variables Equation R2

Algae oxygen production AOP 4.5795ln(NTU) 3.0793 0.894Algae oxygen consumption AOC 0.0286ln(NTU) 17.306 0.978Carp oxygen consumption FOC AW 2 BW C Table 4Nitrobacter NBOC (0.1936(W) 2.0174) (Vm) 0.885Sediments SOC 1279.62(Vsed) 0.812

Sediments as shown in Table 3.

DOD AOP AOC FOC NBOC SOC2 Eqn. 2

Where AOP is accumulated oxygen production per day,AOC is accumulated oxygen consumption per day, NTUis water turbidity in NTU units, W is carp mean mass ingrams, Vm is the biofilter media bulk volume in m3, FOCis carp oxygen consumption, NBOC is Nitrobacter oxygenconsumption, SOC is sediments oxygen consumption.

Results and Discussion

Sampling with peristaltic pumps and dissolved oxygendata management worked as planned; it could workproperly for measuring several tanks at different depths.Peristaltic pumps as pressurized equipment are notefficient but for sampling without gaining oxygen areuseful. Pneumatic bladder, submergible pumps orperistaltic pumps are well suited for low flow purging andsampling. Low stress purging and sampling is atechnique being used in wells where the flow rate ofwater being extracted is less than the one entering thewell. However, peristaltic pumps are not suitable for usein wells containing contaminants or suspended solids.Assuming a static lift of 2m, the pump suction lift will be5m, resulting in a maximum hose length of about 50m(Van Rijn, 1979). Hoses were fixed within the culturetanks in one extreme in order that fishes didn’t move itsposition; total length from the largest hose used was10.5m. Lab View was easy to use, having a simplehardware software interaction; for example when thesensor fails the aerator timing table gives enormousflexibility to the system. Output pressure is always anassay on peristaltic pump applications, although someare used only for sampling. Under different outputpressure of two peristaltic pumps the volume metered perpump revolution remained almost constant, Way et al,1990. Temperature was not a factor within the blackhoses avoiding algae formation. Dissolved oxygen at thewater kept within the hose at the middle of the day variedby 3% as water temperature increased by 2ºC. It isrecommended to clean the hoses with a pressurizedpump every two weeks to avoid solid deposition insidethem. A future design should consider a multi-pumpmodule (mod. MD4, DASGIP AG, Jülich, Germany)

where the speed of each peristaltic pump can becontrolled electronically and adjusted individually. Thebuilt-in microprocessor and the serial interface allowstraightforward PC support and can be easily managedby the Lab View interface. If the MD4 is fixed at thehydraulic head the variable distances from the tanksbecome irrelevant for timing the DO acquisition routine;this operation is possible as each pump can work at adifferent speed using the same delay for the four tanks.Energy consumption by the peristaltic pumps, re-circulating pumps and the aerator was 16.8, 907 and1,153Wh, respectively. Energy of 807.2W was consumedper day when the aerator turned-on for periods of 1.33hin order to oxygenate the tank with 400g carps. A bank offive 12V at 250 Ah rechargeable LiFePO4 batteries(Model OPT-200, Optimum Battery Co., Ltd, China) wasused together with a current battery charger. A 375 W,12V DC - 120V AC inverter (mod PV-375, Tripp Lite,USA) was selected to provide AC energy to the aeratorand re-circulating pumps. During lack of energy dissolvedoxygen decreased from 5 to 2.3ppm for carps weighting400grams in tank 1. At 21:45h, batteries were turned onfor 1.33hour increasing DO to 4.93ppm. Dissolvedoxygen oscillated between 2.3 and 5ppm until 9:25AMconsuming energy for 8hours. In tank 2, dissolvedoxygen in the water presented oscillations rangingbetween 3.33 and 5.2ppm for 400g carps; batteryconsumption was of 8hours. For lower size carps(200grams), dissolved oxygen varied between 3 and5ppm being battery energy consumed in 6hours (Figure5).

DO probe fouling

DO measurement varies as the probe oxidizes (Figure6a) affecting its response speed; although anodecorrosion there is enough anode material for many yearsof use. Measurement errors are found during algae(Figure 6c) and colloid (Figure 6d) fouling.As theelectrolyte gets consumed, low level measurements with1.2ppm peaks are obtained (Figure 7) requiring theaddition of the electrolyte solution (Smith et al., 2007).Membrane is normally replaced twice a year and whendamaged a DO saturation value of 4ppm is measuredfollowed by a peak which decrements its value to zero;afterwards, the DO value returns immediately to the


Figure 5: Dissolved oxygen control with the alternative 545 program for three differentaeration periods during the night.

Figure 6: Probe with (a) oxidized anode, (b) clean membrane, (c) algae fouling, (D) colloids fouling(E) and suspended water droplets.

Figure 7: Dissolved oxygen measurement under membrane damage or faulty electrolyte.


Figure 8: Dissolved oxygen measurements for different sensing anomalies.

saturation value, as shown in Figure 7 by the violet line.The user should gently tap the membrane to guaranteethat no air bubbles remain trapped.

Proper DO saturation values (purple marks) rangebetween 6.1 and 6.5 when the probe is in contact with air(Figure 8). Sediment accumulation (SA) over themembrane presented during DO saturation peakscentered at 5±0.2ppm. Once the sediments wereremoved with distilled water a turbidity of 50 NTU wasencountered. When the membrane is cleaned (TSA) withthe water jet, a DO saturation value of 6.2ppm isobtained. Algae accumulation (AA) around the membraneproduces oxygen increasing its DO value to 7.5ppm.Analysis of water samples under super-saturation byWoodbury (1941) showed excess DO values rangingfrom 17.74ppm to 23.14ppm. Fish reactions to DOexcess were swimming at an angle and then floating upat surface in a helpless manner. When a biofilm of algaecovers the sensor membrane oxygen diffusion drops-offdecreasing DO measurements. After spraying water(TAA) the probe measured correctly again, and the algaedissolved in water provided a turbidity of 166 NTU.Suspended water droplets (SWD) on the membranedecreased DO values; measurements returned to normalwhen the vibrator motor (TSWD) removed the droplets.

Antifouling mechanisms

Self-backwash and nozzle spray for membrane anti-

fouling was extremely better than leaving the probewithout any treatment. Dissolved oxygen saturationmeasurements decreased to 5.3ppm after five weeks ofoperation when no anti-fouling treatment was employed.The spray nozzle was the most reliable mechanism dueto the reduced peristaltic pump pressure applied to themembrane. A high water flow of 27l/min (velocity=14m/s)was applied to remove the solids accumulated over thesensor membrane. In continuous backwash operation,solids and algae were removed from the membranesurface and dissolved oxygen saturation measurementsremained within 6-6.5ppm range, Figure 9. It isrecommended that under backwash treatment a highpressure treatment is applied every six weeks. Airbubbles within the electrolyte were removed by the usermeanwhile vibration gets rid of suspended water droplets.

Once that proper maintenance is given to the galvanicprobe it sensed accurately with a good speed response.A galvanic probe let in a pond without care accumulatesalgae or solids over the membrane; erroneousmeasurements are obtained as oxygen diffusion throughthe membrane disappears. As a result, the response timeis unaffected, but dissolved oxygen magnitude changes.Very fine particles below 40m (Glasspool and Atkinson,1998) are difficult to extract and accumulate at thesensor. Adhesion forces attract fine solid particles to thesensor membrane, and after long accumulation time,nitrification bacteria grow on the membrane affectingmeasurement readouts (Whelan and Regan, 2006).Calcium appears to form a bridge between the


Figure 9: DO saturation measurements with nozzle jet spray, backwash and without any antifouling treatment.

Table 4: Parameter definitions for carp oxygen consumption calculation.

Water temperature, A B C R2

°C18 -0.00001 0.0447 0.4306 0.9920 -0.0001 0.0506 0.5103 0.9922 -0.0001 0.058 0.523 0.9724 -0.0001 0.0635 0.6812 0.96

membrane surface and the organic foulants (Ahn et al.,2008). Algae blooms can accumulate over the sensormembrane and affect sensor readings; bloomingdinoflagellates in a size ranging between 10 and 50mpass through the inlet screens. Their neutral buoyancyand ability to swim make them a settling material (Pierceet al., 2004). As algal bloom life cycle peaks and decays,a significant amount of organic material is released uponcell death (Whipple et al., 2005). Bacteria feed on thedecaying material and release their own extracellularpolymeric substance (EPS) that has the potential to foulpretreatment and RO membranes (Asatekin et al., 2006;Rosenberger et al., 2006). It is possible that the materialfrom decomposition fouls the membrane more than thealgal cells themselves. Self-contained air blast cleaningsystems clean 360 automatically DO sensors membraneswith a pressurized air jet of 300kPa (GLI, 2008). Oxyferm,Oxygold and Clark model 5500 DO probes (GLI, 2008)withstand maximum pressures of 400, 1200 and1000kPa, respectively. The backwash cleaner wasefficient maintaining a constant value during five weeks. Ifa non-maintenance equipment is requested the vibratingmotor and the pressure jet should be applied. Lab Viewhas become a very useful instrumentation tool, beingable to acquire, analyze, control and activate different

fans and pumps. Its application in aquaculture as anintelligent DO sensor fault detector, can advise theproducer when a failure is present meanwhile it can stilloxygenate the tanks. In case that a power failure exists, itis necessary to optimize the energy saved in the PVbatteries; the LabView interface indicates the amount ofenergy being available. Two power failures were presentone of 5 hours and another of twelve hours one permonth and the carps survived with the alternative energy.During line loss energy an alternative PV system wasused and dissolved oxygen was maintained between setlevels allowing fish survival under optimum energyconsumption. For the experiment with longest turn-ontime (ton: 1.33h, toff: 0.75h and 400g carps) only 40% ofthe time dissolved oxygen was below 3.5ppm, being itsminimum value 2.3ppm. At this time carps were at the topsearching for air in the atmosphere. One of the mostcommon sensor errors occurred during membraneexchange when the user did not take care of air bubbleformation within the electrolyte; high peaks were detectedby the Lab View program sending a 2-0041 messagecode, Table 4. Three additional codes informed about thebattery remaining charge to the producer. As thealternative energy system works, battery gets dischargedby 30, 60 or 90% generating and transmitting 2-0071, 2-


Figure 10: The hourly oxygen consumption expected and measured according to the diurnal change intemperature at carp mean mass of 70grams.

Table 5: Lab View interface message codes.

Error source Values when contacts Behavior Cleaning Lab Viewair action codes

Algae Higher values during Higher peaks Water-Jet 2-0011day (super-saturation)

Solids Lower value than 5.5 Smooth peaks Water-Jet 2-0021Electrolyte Lower value than 1.3 High Change 2-0031

ppm frequencymembrane Values arriving zero Low signal Change 2-0051

withnegative peaks

Air Bubbles Values above 15ppm higher Remove air 2-0041frequency bubblespeaks

Suspended Values lower than the Smooth peaks Motor 2-0062droplets

saturation (in air

0081 and 2-0091 codes, respectively.

Model expectations

The empirical model predicts the diurnal change in

overall oxygen demand for the carp recirculating systemFigure 10 under different algae densities and watertemperatures, the model response to diurnal changes inwater temperatures was observed. Based on the overalloxygen demand in the system the aeration requirementscan be determined meeting the amount of oxygen


Table 6: Overall oxygen requirement for carp recirculating system at algae absence.

Date Weight Biofilter oxygen Fish oxygen demand TOD (gO2/h)demand (gO2/h) (gO2/h)

1:00pm – 1:00am – 1:00pm – 1:00am – 1:00pm – 1:00am –1:00am 1:00pm 1:00am 1:00pm 1:00am 1:00pm

23-Dec. 20 0.30 0.24 0.95 0.80 1.24 1.0430-Dec. 22 0.36 0.29 1.04 0.88 1.40 1.176-Jan. 25 0.45 0.37 1.17 0.99 1.62 1.3613-Jan. 28 0.54 0.44 1.30 1.10 1.85 1.5420-Jan. 33 0.70 0.57 1.52 1.28 2.22 1.8527-Jan. 40 0.92 0.74 1.82 1.53 2.74 2.2703-Feb. 47 1.13 0.92 1.98 1.35 3.11 2.2710-Feb. 54 1.35 1.10 2.25 1.53 3.60 2.6317-Feb. 62 1.60 1.30 2.54 1.73 4.14 3.0324-Feb. 70 1.85 1.50 2.82 1.92 4.67 3.42

required at each period during the day.= 3

Where AR is aeration requirements in hours, OD isoverall oxygen demand (gO2) and OR is oxygen transferrate by aerator (gO2/h).

The effect of algae turbidity on overall oxygen demand,can be noted for carps weighting 250grams 167.049,167.2294, 167.4094, 167.5894 and 167.7694gO2/day for100, 200, 300, 400, 500 NTU, respectively where thecarps consume 170.155gO2/day at blooms absenceTable 6, mean that the algae blooms reduce the overalloxygen demand due to the oxygen realized during light.The model can predict the effect of water temperatureson hourly carp oxygen consumption, as watertemperature increases from 18 to 24°C, carp oxygenconsumption consequently increases from 5.68 to8.248gO2/h.An empirical model created to protect theRAS units from critical oxygen deficit caused by algae atnight and predict overall oxygen demand under differentalgae densities and water temperatures.

CONCLUSION

Dissolved oxygen in fish production systems should bemonitored and controlled as it is a vital factor for fishproduction and survival. One galvanic sensor and itscontroller were used for managing four culture tanks. Thesensor was checked previous to each measurementwhen it was in contact with the air. An intelligentinstrumentation system monitored the tanks, predictedoxygen sensor failures, sending codes to the producer,controlled the aerators and introduced a PV alternativesystem in case of a power line interruption. The systemwas capable of detecting 394 algae or solids adhered to

the membrane and could remove them using a water jetor by means of backwashing. The latter one worked aswell as the water jet during one month, but consumedless energy. The system proposes an alternative timingroutine based on biomass and water temperature to turnon the aerators in case of a sensor failure

REFERENCES

Ahn, W.Y., Kalinichev A.G. and Clark, M. (2008). Effects of backgroundcations on the fouling of polyethersulfone membranes by naturalorganic matter: Experimental and molecular modeling study. J.Membrane Sci. 309: 128-140.

Appelbaum, S., Parilutsky, A. and Birkan, V. (1999).An emergencyaeration system for use in aquaculture.Aquacult. Eng. 20: 17-20.

Asatekin, A., Menniti, A., Kang, S.T., Elimelech, M., Morgenroth, E. andMays, M. (2006). Antifouling nanofiltration membranes for membranebioreactors from self-assembling graft copolymers. J. Membrane Sci.285(1-2): 81-89.

Bart, Q.J. (2002). An investigation into using fuzzy logic techniques tocontrol a real world application.PeninsulaTechnikon.Theses andDissertations.

Brett, J.R. and Groves, T.D.D. (1979).Physiological energetics. In: Hoar,W.S., Randall D.J., Brett, J.R. (eds.) Fish Physiology, Vol. 8,Academic Press, New York, pp. 279-352.

Bryan, A. and Cushman, M. (1992).Dissolved oxygen sensorcalibration, monitoring and reporting system. United States PatentNo. 5,098,547. Mar 24, 1992.

Bucks, D.A., Nakayama, F.S. and Gilbert, R.G. (1979). Trickle irrigationwater quality and preventive maintenance. Agric. Water Manage..2(2): 149-162.

Carlson, A.R., Blocher, J. and Herman, L.J. (1980). Growth and survivalof channel catfish and yellow perch exposed to lowered constant anddiurnally fluctuating dissolved oxygen concentrations. Progress FishCulturist. 42: 73-78.

Chervinski, J. (1982). Environmental physiology of tilapias. In: Pullin,R.S.V., Lowe-McConnell, R.H. (Eds.), the Biology and Culture ofTilapias. ICLARM.Conference Proceedings 7, International Center forLiving Aquatic Resources Management, Manila, Philippines, pp.119–128.

Elmessery, W.M. (2011). Design of automatic food dosing andoxygenation for a carp recirculating aquaculture system (RAS).Ph. D.Theses and dissertation, Chapingo University, Mexico.

Eutech Instruments (2006).Solutions for water analysis. Catalogue,Singapore. pp 44-46.

Evans, R.C. and Douglas, P. (2006).Controlling 426 the color spaceresponse of colorimetric luminescent oxygen sensors. AnalyticalChemistry 78(16): 5645-5652.

Gilbert, R.G., Nakayama, F.S., Bucks, D.A., French, O.F. andAdamson, K.C. (1981). Trickle irrigation: Emitter clogging and otherflow problems. Agric. Water Manage. 3(3): 159-178.

Glasspool W. and Atkinson, J.K. (1998). A screen-printed amperometricdissolved oxygen sensor utilising an immobilised electrolyte gel andmembrane. Sens. Actuators B. 48: 308-317.

GLI (2008).Model 5500-series Clark Technology Membrane DissolvedOxygen Sensor.Datashheet 5500, GLI International, Wisconsin, USA.

Hahn, F. (2010). Self-Powered Instrumentation Equipment andMachinery using Solar Panels, In: Ochieng, R.M. (ed.), Solarcollectors andpanels, Theory and Applications. Sciyo International,Vienna, Austria. pp: 293-314.

Hahn, F. (2011). On-line detector sorts four types of coconut waterefficiently. Biosystems Engineering (IN PRESS)

Howe, K.J., Ishida, K.P. and Clark, M.M. (2002).Use of ATR/FTIRspectrometry to study fouling of microfiltration membranes by naturalwaters. Desalination 147: 251-255.

Kramer, D.L. (1987). Dissolved oxygen and fish behavior.Environmental Biology of Fishes 18 (2), 81-92.

Lander, D.A., Vardon, D.R., Clark, M.M. 2010.Effects of shear onmicrofiltration and ultrafiltration fouling by marine bloom-formingalgae. J. Membrane Sci. 356: 33-43.

Lee, P.G. (2000). Process control and artificial intelligence software foraquaculture.Aquacultural Engineering. 23: 13-36.

Pereira, D.G., Tonso, A. and Kilikian, B.V. (2008).Effect of dissolvedoxygen concentration on red pigment and citrinin production byMonascuspurpureus ATCC 36928.Brazilian J. Chem. Engine. 25(2):247 - 253.

Pierce, R.H., Henery, M.S., Higham, C.J., Blum, P., Sengco, M.R. andAnderson, D.M. (2004). Removal of harmful algal cells(Kareniabrevis) and toxins from seawater culture by clay flocculation.Harmful Algae 3(2): 141-148.

Rijn, L.C. van.(1979). Pump Filter Sampler. Delft Hydraulics Laboratory,Report S404, the Netherlands.

Rosenberger, S., Laabs, C., Lesjean, B., Gnirss, R., Amy, G., Jekel,M.andSchrotter, J.C.(2006). Impact of colloidal and soluble organicmaterial on membrane performance in membrane bioreactors formunicipal wastewater treatment. Water Res. 40(4):710-720.


Schafer, A.I., Schwicker U., Fischer M.M., Fane, A.G. and Waite, T.D.(2000).Microfiltration of colloids and natural organic matter. J.Membrane Sci. 171(2): 151-172.

Smith, M.J., Kerr, A., Cowling, M.J. 2007.Effects of marine biofouling ongas sensor membrane materials. Journal of EnvironmentalMonitoring 9, 1378–1386.

Stone, N. and Daniels, M. (2006). Algal Blooms, Scums and Mats inPonds. Report No. FSA9094. University of Arkansas.

Tafangenyasha, C., Marshall, B.E. and Dube, L.T. (2010).The diurnalvariation of the physico-chemical parameters of a lowland river flow ina semi-arid landscape with human interferences in Zimbabwe. Int. J.Water Res. Environ. Engine. 2(6): 148-163.

Vasile, A. (2008). The implications of water chemical properties from thebreeding nursery pond on the fish pathological state.InnovativeRomanian Food Biotechnol. 2: 25 – 29.

Way, T.R., Bashford, L.L., VonBargen, K. and Grisso, R.D. (1990).Peristaltic pump accuracy in metering herbicides. Appl. Engine. Agric.6(3): 273- 276.

Whelan, A. and Regan, F. (2006).Antifouling strategies for marine andriverine sensors. J. Environ. Monitoring. 8: 880–886.

Whipple, S.J., Patten, B.C. and Verity, P.G. (2005). Life cycle of themarine alga Phaeocystis: A conceptual model to summarize literatureand guide research. J. Mar. Syst. 57: 83-110.

Wissenschaftllch-Technische Werkstatten GmbH (WTW) (2011).Onlineinstrumentation. Catalogue 32-37, Germany.

Woodbury, L.A. (1941). A sudden mortality of fishes accompanying asupersaturation of oxygen in lake Waubesa, Wisconsin.Tans. Amer.Fish. Soc. 71: 112-117.

YSI. (2009). The Dissolved Oxygen Handbook. YSI Incorporated, p: 76.

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