Recirculating Aquaculture Systems Short Course Biofiltration- Biofiltration- Nitrification Nitrification Design Overview Design Overview James M. Ebeling, Ph.D. James M. Ebeling, Ph.D. Environmental Engineer Environmental Engineer Aquaculture Systems Technologies, LLC Aquaculture Systems Technologies, LLC New Orleans, LA New Orleans, LA
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High levels of nitrite can be produced under High levels of nitrite can be produced under conditions when there is an imbalance conditions when there is an imbalance between populations of between populations of NitrosomonasNitrosomonas and and NitrobacterNitrobacter, which can occur:, which can occur:• within the first 4-8 weeks of biofilter startupwithin the first 4-8 weeks of biofilter startup• if inadequate surface area or dissolved oxygenif inadequate surface area or dissolved oxygen• if ozone is used for an extended period and then if ozone is used for an extended period and then
Volume of media 0.6 to 0.7 kg/m3 day 1.0 to 1.5 kg/m3 day
Recirculating Aquaculture Systems Short Course
Biofilter is sized to remove a given daily TAN Biofilter is sized to remove a given daily TAN production (kg TAN/day).production (kg TAN/day). You must know or assumeYou must know or assume
daily TAN production, kg TAN/day.daily TAN production, kg TAN/day. Arial TAN removal rate, g TAN removal/day per mArial TAN removal rate, g TAN removal/day per m22
Classified according to packing Classified according to packing characteristics, i.e.,characteristics, i.e.,
• Random packing:Random packing:• aggregate sand, crushed rock, or river gravel;aggregate sand, crushed rock, or river gravel;
• plastic or ceramic beads, spheres, rings, or plastic or ceramic beads, spheres, rings, or
saddles;saddles;
• Structured packing:Structured packing:• plastic blocks of corrugated plates or tubes.plastic blocks of corrugated plates or tubes.
Recirculating Aquaculture Systems Short Course
Structured PackingStructured Packing
It is important to It is important to consider:consider:• Large void spacesLarge void spaces• Non-pluggingNon-plugging• Easy to maintainEasy to maintain
ACCUPAC
NORPAC
Recirculating Aquaculture Systems Short Course
Structured PackingStructured Packing
Courtesy of LS Enterprises (FL)
Structured packings are not limited to rectangular tower designs! – circular cut packing blocks
AccuPac CF-3000:3 cm flute,95% void ratio,102 m2/m3 ,Crossflow design
Recirculating Aquaculture Systems Short Course
Random PackingRandom PackingRandom packing below a rotary spray nozzle.Random packing below a rotary spray nozzle.
Recirculating Aquaculture Systems Short Course
Biofilter DesignBiofilter Design
To provide good performance and avoid To provide good performance and avoid solids plugging & dead zones requires solids plugging & dead zones requires proper:proper:
• media selection, media selection, • media support or retention mechanismsmedia support or retention mechanisms• flow distribution,flow distribution,• flow collection.flow collection.
Pro'sPro's Con'sCon'sVery simple design and construction Very simple design and construction requirementsrequirements
Some biofilm sheared off is large enough Some biofilm sheared off is large enough to be problematic and to be problematic and many systems many systems integrate post-biofiltration mechanical integrate post-biofiltration mechanical filtration for this reasonfiltration for this reason
Currently a very popular method of Currently a very popular method of biofiltration in the wastewater industry, biofiltration in the wastewater industry, which should improve material which should improve material availability and costavailability and cost
Filters using this media type tend to be Filters using this media type tend to be veryverylarge in high feed load coldwater large in high feed load coldwater systemssystems
Allows for passive aeration and COAllows for passive aeration and CO22
removal concurrent with biofiltrationremoval concurrent with biofiltrationMedia itself can be costly due to low Media itself can be costly due to low specific surface areaspecific surface area
Media and design assistance is Media and design assistance is currently available from reputable currently available from reputable commercial vendors facilitating the commercial vendors facilitating the design effortdesign effort
Systems using these types of filters Systems using these types of filters tend to be extremely stabletend to be extremely stable
Pro'sPro's Con'sCon'sWell developed product available Well developed product available from reputable commercial vendors. from reputable commercial vendors. Can simplify system design and Can simplify system design and constructionconstruction
Can be expensive due to relative low Can be expensive due to relative low specific surface area for large scale specific surface area for large scale facilitiesfacilities
Can be combined with other filter Can be combined with other filter types in interesting hybrid systems types in interesting hybrid systems as alternative design methodas alternative design method
Relatively high head loss across filter Relatively high head loss across filter can be an operational cost can be an operational cost considerationconsideration
Can in some cases improve fine Can in some cases improve fine particle removal rates in well particle removal rates in well designed systemsdesigned systems
Variable head loss across system can Variable head loss across system can be problematic in systems without be problematic in systems without variable speed pumpsvariable speed pumps
Amenable to modularization, which Amenable to modularization, which can be useful for development of can be useful for development of scalable facilitiesscalable facilities
Has potential to leach nutrients into Has potential to leach nutrients into system or to fuel heterotrophic system or to fuel heterotrophic bacteria growth if not installed with bacteria growth if not installed with pre-filtration systems or is pre-filtration systems or is backflushed infrequentlybackflushed infrequently
Recirculating Aquaculture Systems Short Course
Fluidized Bed BiofiltersFluidized Bed BiofiltersBiofiltrationBiofiltrationNitrificationNitrification
Pro'sPro's Con'sCon'sVery economical to build from Very economical to build from commercially available materialscommercially available materials
Can have problems with media Can have problems with media carryover (initial fines) on system start-carryover (initial fines) on system start-upup
Large amount of design effort specific Large amount of design effort specific to coldwater systems using these to coldwater systems using these types of filterstypes of filters
There are historical anecdotal reports There are historical anecdotal reports of intermittent bed motility and system of intermittent bed motility and system crashescrashes
Raw filter media has very high Raw filter media has very high specific surface area at low cost, specific surface area at low cost, which allows for very conservative which allows for very conservative design allowing for inherent capacity design allowing for inherent capacity for expansion or load fluctuationfor expansion or load fluctuation
Can have problems with restarting if Can have problems with restarting if not designed to account for bed re-not designed to account for bed re-fluidization and distribution fluidization and distribution manifold/lateral flushingmanifold/lateral flushing
Widest installed base of coldwater Widest installed base of coldwater biofilters offers large operational and biofilters offers large operational and design experience base to draw fromdesign experience base to draw from
Media density changes over time with Media density changes over time with biofilm accumulation in fine sand filters biofilm accumulation in fine sand filters typical of coldwater systems, which typical of coldwater systems, which necessitates a bed growth management necessitates a bed growth management strategystrategy
Can be field built using a variety of Can be field built using a variety of proven methods or purchased from proven methods or purchased from established and reputable vendors established and reputable vendors opening many design and opening many design and construction options for facility construction options for facility designers or operatorsdesigners or operators
Some systems can require relatively Some systems can require relatively expensive plumbing to ensure that expensive plumbing to ensure that media is not back-siphoned on pump media is not back-siphoned on pump shut-down or power failureshut-down or power failure