Solids removal and effluent treatment - AquaCircle · 2020-02-09 · Many factors are improtant to...
Transcript of Solids removal and effluent treatment - AquaCircle · 2020-02-09 · Many factors are improtant to...
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Solids removal and effluent treatment
By Henrik Mortensen MSc, senior consultant, CMAQUA
© CM AQUA Technologies ApS 2013
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Fish feed Fish growth
Respiration(O₂;CO₂)
Excretion(ammonia)
Feces
Waste feed
Feeding animals have an impact on the environment
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However there is sometimes a contribution of waste from inlet water and erosion of fishponds
Effluents from fishfarms
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Particles are by definition above 0,45-1,0 µm
Density of feces are not more than 1,05
It is difficult to use sedimentation systems !
Effluents from fishfarms
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Normal range of concentrations of waste from fishfarms
Suspended solids mg/l
Tot –P mg/l
Tot-N mg/l
BOD5 mg/l
1-15 Less than 0,1* Less than 2* 1-10
* Will be higher in RAS as nitrate and P accumulate
Very low concentrations compared to eg municipal waste water
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Percentage of total waste in particle form
Parameter Particle bound
Tot-P Up to 90 %
Tot-N Up to 32 %
BOD5 Up to 90 %
TSS 100 %
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Normal range of efficiencies of microfiltration
Parameter % removal
Tot-P 50-80 %
Totn Up to 30 %
BOD5 30-80 %
TSS 50-90 %
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Potential for high efficiency of a mechanical filter!
The oppertunity
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What can you do to optimize your production!
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Many factors are improtant to achieve optimal filtration.
System design and management to optimize removal of particles.
What is generating particles in your system ? (feces, feed waste, biofilm, inlet water etc).
Where is larger particles formed? (feces, Bioreactors--)
Where is small particles formed/ what is destroying your particles ?
Where and how do you remove them most efficient ?
Knowledge on particle sizes in effluent water.
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Flow through fishfarms may need a coarse screen in front of drumfilters. A long outletchannel may not be a problem as long as there is no weirs to disturb the formed particles, particles after fish ponds may tend to ”agglutinate” and form larger particles.
Flow design matters
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Drumfilters
High capacity on limited installed ”footprint”
Fine filtration from 10 to 1000 µm
Independent of density of particles
Remove particles very fast:
no leaking to the water
Work by gravity so very little erosion of particles.
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Drumfilter technology
Drum filters uses screens of monofilament filtercloth: • High flow per m2 • Accurate ”cut off” for given
particle size
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Special paneldesign support the fabric and optimize the filtration process
Drumfilter technology
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Drumfilters come in many sizes and configurations
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Particle control is important in fishfarming
Inlet to fishfarms, waterquality & parasite control
Outlets, environmental aspects
RAS, control of waterquality
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Water supply to fishfarms
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Filtration of inlet water to aquaculture facilities:
Shrimp farming are facing seriuos challenges- particle control would improve performance significantly:
Reducing disease carrying zooplancton
Predating fishlarvae, crab larvae, etc
Improving chemical water parameters
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Salmon and troutfarm
Inlet filtration:
Salmonides requires clean and cold water, microscreens removes suspended solids which causes gill problems.
Removes parasites as eyefluke, ”white spot” etc.
In combination with UV-- bacteria and some virus may be reduced by at least a log 3 factor.
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Channel installed UV works well with gravitational filters.
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Recirculating aquaculture systems (RAS)
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RAS, main componenets
Selfcleaning tanks Piping/inlets/outlets Gases: oxygensupply/co2stripping Internal fishhandling/gradingsystem Bioreactors Control/alarm/feeding systems Waste handling systems Particle control(microscreens) & UV/Ozone
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Drumfilters in RAS
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Functional diagram of a drumfilter
∆P is the driving force, flow is directly proportional to the pressure and resistance in the filtercloth(R). Flow = ∆ P /R R is a combination of different forms of resistance: Rm + Rp + Rc m: Friction in the mesh p: resistance caused by particles blocking the holes c: ”cake” building
Normal operational level: 15-25 cm
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Flow and different meshsizes
Above mentioned characteristics can be summaries and used for better control of microscreens: Slow rotation for ”cake”
building. Faster rotation at peakload.
HEX PLC controlbox
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Traditional troutfarm D-ended raceway
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Propeller pump is lifting water in an energy efficient way, slow running, not eroding particles
Traditional troutfarm -upgraded-
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Just after one day of filtration turbidity improves from 0,2 to 1,0 m, once every 1,5 H all water had been filtered!
Before filtration After filtration
Mixed flow concept based on massbalances !
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Sludge handling
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Backwash water from drumfilters are still quite thin, 300-1000 mg/l TSS
Sludge handling
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Backwash water from HEX drumfilters
Suspended solids 40 micron 60 micron 90 micron
10 mg/l 1 % 0,5 % 0,4 %
15 mg/l 1,4 % 0,7 % 0,6 %
25 mg/l 2,4 % 1,2 % 1,0 %
Data based on 100 % loading on filter.
Volume of backwash water is proportional with TSS loading
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Traditional flow through fish farms, sometimes sand may interfere with coagulation & flocculations systems.
RAS, some RAS does not backwash in ”batches” (if only moving bed bioreactors), some bioreactors needs to be backwashed eg every week = flush of sludge to be contained before treatment.
Most sludge originates from microscreens.
Sludge handling
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Sludge settling after drumfilters !
Overflow from settling meets filtered water
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Pre-concentration of sludge from microscreens before flocculation.
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Beltfilter incl polymer mixertank
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Polymers for flocculation.
Longchained cationic, high molecular weight, works well, even in saltwater.
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After polymer addition, sludge is drained on a beltfilter, resulting dry matter content app 8-12 %
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Testfacility at AquaPri By Courtesy of martin vestergård
RAS
A B C D
Drumfilter
Oxygencone
UV
E
Reservoir
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Particle sizes and formation in RAS
Bioreactors 1-3, have different media, submerged bioblock or random media. The high surface random packing media retains more fine particles than bioblock.
Both types of bioreactors produce particles ≥30 micron and retains the smaller(adsorption) ≤ 30 micron
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Results of particle filtration
Different micron on drumfilter were tested, 20µ, 30µ, 40 µ & 60µ
All meshsizes had a nice cut-off, 90 % of particles bigger than opening size were retained
30 micron seems to be the best choice as the particles formed in the bioreactors were larger than 30 micron
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Improving particle filtration:
Produces optimal particle free water(thereby also less BOD) for further processing in downstream bioreactors(nitrification).
Reduces TSS in the tanks = less stress on the gills of the fish.
Reduces the ”food” for bacterial growth.
Removes a larger part of BOD = less hydrolysis and thereby less carbondioxide.
Less parasites to be circulated.
Improved turbidity = UV more efficient.
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New thinking ?
Plug flow thinking ?
Fully mixed ?
Reactor kinetics ?
Optimize component functionality, not adding functions to components eg bioreactors should not be sized as particle traps ?