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Mechanical Filtration Hugh S. Hammer, PhD GSCC Ron Malone, PhD LSU Joe Fox, PhD Texas A&M.

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Presentation on theme: "Mechanical Filtration Hugh S. Hammer, PhD GSCC Ron Malone, PhD LSU Joe Fox, PhD Texas A&M."— Presentation transcript:

1 Mechanical Filtration Hugh S. Hammer, PhD GSCC Ron Malone, PhD LSU Joe Fox, PhD Texas A&M

2 Total Solids The amount of solid material left in a container after the water has evaporated. The amount of solid material left in a container after the water has evaporated. Total Solids = Total Suspended Solids (TSS) + Total Dissolved Solids (TDS) Total Solids = Total Suspended Solids (TSS) + Total Dissolved Solids (TDS) Total Suspended Solids (TSS) are solids that can be trapped by a filter. Examples: silt, decaying organic material, industrial wastes, sewage Total Suspended Solids (TSS) are solids that can be trapped by a filter. Examples: silt, decaying organic material, industrial wastes, sewage Total Dissolved Solids (TDS) are solids that pass through a filter (0.45 microns). Examples: carbonates, bicarbonate, chloride, sulfate, phosphate, nitrate, calcium, magnesium, sodium and other ions. Total Dissolved Solids (TDS) are solids that pass through a filter (0.45 microns). Examples: carbonates, bicarbonate, chloride, sulfate, phosphate, nitrate, calcium, magnesium, sodium and other ions. TOTAL SOLIDS ARE INDICATORS OF POLLUTION TOTAL SOLIDS ARE INDICATORS OF POLLUTION

3 Sources of Total Suspended Solids High flow rates from fast moving water, silt, sand, clay, organics High flow rates from fast moving water, silt, sand, clay, organics Soil erosion (non-point source) Soil erosion (non-point source) Urban runoff (non-point source) Urban runoff (non-point source) Waste water and septic effluent Waste water and septic effluent Decaying organic matter Decaying organic matter Fish that stir up sediments (carps) Fish that stir up sediments (carps)

4 Problems with TSS Increased biotic and abiotic turbidity Increased biotic and abiotic turbidity –Reduced light transmittance and photosynthesis –Unstable dissolved oxygen –Increase water temperature –Abiotic sources can clog gills and increase disease –Smother eggs, filter feeding animals, and aquatic insects –High TSS is often an indicator of other types of pollutants and toxins (mercury and PCB)

5 Testing TSS A water sample is filtered through a pre- weighed filter (0.45 microns) A water sample is filtered through a pre- weighed filter (0.45 microns) The residue retained in the filter is dried in an oven at 103 to 105 C The residue retained in the filter is dried in an oven at 103 to 105 C The sample is dried to constant weight and the weight is recorded The sample is dried to constant weight and the weight is recorded Reported as grams per liter (ppt) Reported as grams per liter (ppt)

6 Total Dissolved Solids The water sample is passed through a 0.45 micron filter The water sample is passed through a 0.45 micron filter The water that passes through the filter is dried in a pre-weighed dish at 180 C The water that passes through the filter is dried in a pre-weighed dish at 180 C The sample is dried to constant weight The sample is dried to constant weight TDS is reported as milligrams per liter (ppm) TDS is reported as milligrams per liter (ppm) This is directly related to the conductance of water (dissolved ions) This is directly related to the conductance of water (dissolved ions) EPA standard of 500 ppm for drinking water EPA standard of 500 ppm for drinking water

7 Sources of TDS Geology and sediment composition Geology and sediment composition Fertilizer run-off Fertilizer run-off Waste-water and septic effluent Waste-water and septic effluent Soil erosion Soil erosion Urban run-off Urban run-off *** The TDS frequently includes phosphorous, nitrate, and other nutrients

8 Aquaculture Solids FEED FECESUneaten Feed

9 Mechanical Filtration Solids removal employs systems from the wastewater treatment industry Solids removal employs systems from the wastewater treatment industry Screening, gravity separation (sedimentation, centrifuging, hydrocycloning) or adsorption between particulate beds Screening, gravity separation (sedimentation, centrifuging, hydrocycloning) or adsorption between particulate beds Processes designations for RAS Processes designations for RAS –Primary: one or more gravity methods –Secondary: biological filtration –Tertiary: ion exchange, reverse osmosis, foam fractionation, carbon adsorption, sometimes disinfection

10 Solids Characterization Three means of classification: Three means of classification: Solid materials are further classified as being either settleable, suspended, dissolved or colloidal Solid materials are further classified as being either settleable, suspended, dissolved or colloidal Difference between settleable and suspended solids is a matter of practicality Difference between settleable and suspended solids is a matter of practicality Most settleable: > 10 µM (settle in an Imhoff cone in less than 1 hr) Most settleable: > 10 µM (settle in an Imhoff cone in less than 1 hr) Particles passing through a 1.2 µM membrane filter are dissolved, suspended are trapped Particles passing through a 1.2 µM membrane filter are dissolved, suspended are trapped Dissolved particles consist of some organic and inorganic ions and molecules present in solution Dissolved particles consist of some organic and inorganic ions and molecules present in solution

11 Particle Size Distribution (microns) DissolvedColloidalSuspended Settleable

12 Foam Fractionation Granular Filter Microscreen Tube Settler Cartridge Filter Coarse Screens Plain Sedimentation Particle Size, microns SOLIDS REMOVAL PROCESSES AND PARTICLE SIZES

13 Impact of Solids on Recirculating Systems Increased BOD: causes oxygen availability problems with animals and biofilters Increased BOD: causes oxygen availability problems with animals and biofilters Organic wastes (feces) build up increasing ammonia and nitrite levels (toxic) Organic wastes (feces) build up increasing ammonia and nitrite levels (toxic) Increased system turbidity, decreased water clarity (fine particles) Increased system turbidity, decreased water clarity (fine particles) Gill damage in fish (fine particles) can create opportunities for diseases Gill damage in fish (fine particles) can create opportunities for diseases

14 Waste Solids Become Chemical Problems Both uneaten feed and fecal material become toxic ammonia through the action of decomposing bacteria. Both uneaten feed and fecal material become toxic ammonia through the action of decomposing bacteria. Uneaten FeedFeces Heterotrophic Bacteria Ammonia NH 3 /NH 4

15 Increased Biochemical Oxygen Demand (BOD) Oxygen

16 No Fine Solids Capture Tilapia

17 Tiger Barbs

18 Settleable Solids Removal If screens arent used, wastewater is first treated by simple sedimentation (primary treatment) If screens arent used, wastewater is first treated by simple sedimentation (primary treatment) Separation is via gravity settling Separation is via gravity settling As with ponds, the principle design criteria are the basins cross-sectional area, detention time, depth and overflow rate (refer to previous notes) As with ponds, the principle design criteria are the basins cross-sectional area, detention time, depth and overflow rate (refer to previous notes) Ideal sedimentation basins dont exist in the real world due to a variety of particle sizes, composition, etc. Ideal sedimentation basins dont exist in the real world due to a variety of particle sizes, composition, etc. Once settling velocity is known, basic dimensions can be estimated Once settling velocity is known, basic dimensions can be estimated

19 Sedimentation Advantages: Advantages: –Inexpensive –Works by gravity and doesnt require energy Disadvantages: Disadvantages: –Only gets largest solids –Takes a lot of space –Labor intensive to clean

20 INFLO W OUTFLOW Inlet Zone Outlet Zone VsVs VhVh Sludge Zone Settling Zone (V s > Overflow Rate to settle) SEDIMENTATION

21 Sedimentation Tanks and Basins

22 Sedimentation Tank

23 P late and Tube Separators Also work on principle of gravity Also work on principle of gravity Actually enhance settling capacity of basins Actually enhance settling capacity of basins Typically shallow settling devices consisting of modules of flat parallel plates or inclined tubes of various geometric design Typically shallow settling devices consisting of modules of flat parallel plates or inclined tubes of various geometric design Used in primary thru tertiary treatment Used in primary thru tertiary treatment Limited success Limited success

24 C entrifuges and cyclonic separators Increase gravitational force on particles via spinning motion (i.e., settling rate increases) Increase gravitational force on particles via spinning motion (i.e., settling rate increases) Many devices rated at different g forces Many devices rated at different g forces Work best on freshwater systems due to many particles having similar densities to that of seawater Work best on freshwater systems due to many particles having similar densities to that of seawater Most practical are hydrocyclones or cyclonic separators Most practical are hydrocyclones or cyclonic separators Heavy particles are moved by higher outside velocity to outside and downward Heavy particles are moved by higher outside velocity to outside and downward Underflow exiting unit is very small and high density, cleaner water exits top Underflow exiting unit is very small and high density, cleaner water exits top

25 Under-gravel Filters Advantages: Advantages: –Easy to build and operate –Inexpensive –Does both mechanical and biological filtration Disadvantages: Disadvantages: –Needs to be vacuumed regularly (lots of maintenance) –Clog easily –Cant handle big loads (mainly for aquariums and not practical for aquaculture production)

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28 Airlifts Perform Several Functions –Circulation –Aeration –C02 stripping –Foam control

29 Circulation Options Pump Circulation

30 Screens Simplest, oldest method, pre-treatment prior to primary treatment Simplest, oldest method, pre-treatment prior to primary treatment Placed across flow path of RAS water Placed across flow path of RAS water Coarse screens handle raw effluent, biofloc; fine screens for tertiary treatment Coarse screens handle raw effluent, biofloc; fine screens for tertiary treatment Many materials: fibers to A/C filters; cost increases with decreased mesh size Many materials: fibers to A/C filters; cost increases with decreased mesh size Static vs. rotary screens (0.25 to 1.5 mm; about 4-16 gpm flow per square inch of screen; removal efficiency around 5-25% Static vs. rotary screens (0.25 to 1.5 mm; about 4-16 gpm flow per square inch of screen; removal efficiency around 5-25% Rotary screens for fine solids removal are 50-70% efficient; µM Rotary screens for fine solids removal are 50-70% efficient; µM

31 Screens Disadvantages: Disadvantages: –May be difficult to remove and clean –Labor intensive to clean –Auto wash micro-screen filters use a lot of water –Some Units very expensive ($10,000) –Get mainly large solids and clog quickly Advantages: Advantages: –Simple concept –Can be inexpensive and simple to build (socks, panti- hose, furnace filters, mesh bags)

32 Micro-screen Filters

33

34 Over-Drain Flow

35 Captured Solids

36 Microscreen Cleaning Jets

37 Granular Media Filters Commonly referred to as sand or bead filters Commonly referred to as sand or bead filters Two types slow and rapid filters Two types slow and rapid filters Advantages: Advantages: –Less labor is required (typically only to backwash) –Gets a wide variety of solid sizes (down to 20 microns) –Require less water than some units –Mechanical and Biological filters (depending on the media) –Best all-around mechanical filters –Capable of handling large loads (production aquaculture) Disadvantages: Disadvantages: –Requires a lot of pressure for some (pumps) –Expensive –Can be more complex to operate –Can clog quickly depending on the media

38 Slow Sand Filters Usually custom-built, open to atm Usually custom-built, open to atm Loading rates are slow, lps/m 2 Loading rates are slow, lps/m 2 Particle size: 30 µM max Particle size: 30 µM max For this reason require more floor space For this reason require more floor space Used in gravity flow situations Used in gravity flow situations Downside: cleaning Downside: cleaning

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40 Rapid Sand Filters Typically closed, pressurized units Typically closed, pressurized units Handle high flow rates: 20 gpm/ft 2 Handle high flow rates: 20 gpm/ft 2 Downside: very high head loss (30-90 ft) Downside: very high head loss (30-90 ft) Only really good for low solids process streams with some sort of pre-trt Only really good for low solids process streams with some sort of pre-trt Backwashing can be made automatic Backwashing can be made automatic

41 Granular Filters

42 Important Point Sand filters can be used in series to filter out different size particles so that they dont clog quickly. Sand filters can be used in series to filter out different size particles so that they dont clog quickly. –Large gravel Small gravel sand filter –This is frequently used for facilities that bring in natural water (such as seawater)

43 (a) Propeller-washed (b) Bubble-washed BEAD FILTERS

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46 Propeller-washed Floating Bead Filters

47 Sludge Return Bypass Pressure Gauge Sludge View Port Anti-siphon valve Intake Broodstock

48 6/12/2014 ADM System Prop-Washed Bead Filters Motor and Backwash Propeller Pump

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50 Air Bleed Builds Charge Settled Backwash Waters returned to system Filter ModeDrop Filters : Low Water Loss Floating Bead Bioclarifiers

51 Internal Sludge Capture Drop Filters : Low Water Loss Floating Bead Bioclarifiers Released Air Washes Beads Backwash mode

52 Airlift Inlet Circulation Aeration Degassing Solids Capture Biofiltration

53 Cartridge Filters Consist of cannister and replaceable cartridge Consist of cannister and replaceable cartridge Advantages: Advantages: –Removes very small particles –Max particle retention is 0.01 µM ( mm) –Very high water clarity –Great for aquariums Disadvantages: Disadvantages: –Can be expensive –Can clog quickly –Cant handle large volumes –Not practical for production aquaculture

54 Sock and Canister Filters

55 Diatomaceous Earth (DE) Filters Granular material composed of diatom skeletons (frustules) Granular material composed of diatom skeletons (frustules) Can serve as replacement for cartridge filters, but require pre-filtration Can serve as replacement for cartridge filters, but require pre-filtration Fine grade DE can filter down to 0.1 µM Fine grade DE can filter down to 0.1 µM

56 Factors to Consider Particle size to be removed Particle size to be removed Amount of energy required to operate Amount of energy required to operate Labor and maintenance Labor and maintenance Amount of bio-load the filter can handle (pounds of fish and pounds of feed) Amount of bio-load the filter can handle (pounds of fish and pounds of feed)

57 Separate Units Strategy Partitions water treatment into a series of individually steps Partitions water treatment into a series of individually steps Optimizes each step to meet the narrow objective Optimizes each step to meet the narrow objective Integrates steps to develop a treatment train Integrates steps to develop a treatment train

58 Consolidation Strategy Utilize multi-functioning components to: Utilize multi-functioning components to: Minimize the number of components Minimize the number of components Improve the stability Improve the stability Reduce costs of components and energy Reduce costs of components and energy Smaller footprint (less space) Smaller footprint (less space) Disadvantage is that neither process is optimized Disadvantage is that neither process is optimized If you have space and money the separate units strategy is better If you have space and money the separate units strategy is better


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