D ISSOLVED A IR F LOTATION (DAF) Skimmer pushes the Solids attach - PowerPoint PPT Presentation

D ISSOLVED A IR F LOTATION AND M EMBRANES Compared to a new energy efficient , low capital cost Alternative.... Nanoflotation

T ODAY ’ S L EADING W ATER T REATMENT T ECHNOLOGIES TO REMOVE C OLLOIDAL (S MALL ) S OLID P ARTICLES AND O RGANICS  This is a Presentation on the leading technologies to treat industrial waste water.  Treatment of industrial waste water needs to have a very high level of treatment so that the water can be reused in industrial plants or discharged to rivers or lakes  We will review the key design parameters for Dissolved Air Flotation (DAF) and Froth Flotation 1. Membranes (Polymeric and Ceramic) 2. and New Nanoflotation 3. ( a combination of DAF or Froth Flotation and Membranes)

D ISSOLVED A IR F LOTATION (DAF) Skimmer pushes the Solids attach to solids on the surface the air bubbles to a waste collection and float to the trough surface Water from the effluent is recycled back to The Recycled water with the head end of the air combines with the the plant untreated water. Air is added under pressure (6 Bar) to the recycled water

M EMBRANES Pressure +++ Water with Concentrate Membrane Material Waste water Colloidal (small) solid particles to Pressure be separated Treated Water Difference is from the water called Trans Membrane Pressure (TMP) Pressure --- Membranes are defined as a barrier or fine screen to separate colloidal (small) particles. Membranes are not a media like sand or activated carbon

M EMBRANE M ATERIAL IS ROLLED INTO T UBES Membrane tubes Submerged in Water Membrane in a tank tubes inside a casing Water to Membrane Material Concentrate be treated Waste water Clean water

N ANOFLOTATION - C OMBINATION OF F LOTATION TECHNOLOGY (S TEP 1) AND S UBMERGED M EMBRANES (S TEP 2) 1D Skim of Floating Sludge layer of solids 2A 1E Precoat Tubes (SS, 2C Sludge Ceramic or Backwash Membranes Polymeric) to when flow through Water to be Create membrane Membranes is slow 1C treated 2B Flotation of Colloidal (Raw Filter Water solid particles to the Water Sucked With Water) surface Submerged through the Membranes membranes to 1 A 1B produce Clean Addition of Addition of Water Coagulant froth or Air

N ANOFLOTATION M EMBRANE B UNDLE

N ANOFLOTATION P ILOT P LANT S TEP 1 F ROTH S EPARATION OF S OLIDS IN WATER

D ISSOLVED A IR F LOTATION – A MORE DETAILED DISCUSSION

DAF AND THE S EPARATION OF M INERALS IN M INE O PERATIONS  Most Mines such as coal mines or metal mines use DAF type technology.  Mining operations were the first to use a surfactant (detergent/soap) to coat the mineral particle which made the particle “Hydrophobic” (means that the particle does not want to be in water).  These chemicals were called “ frothers ” and the mining industry called their treatment technology using air and the frothers as “froth flotation”  Froth flotation is a key component of Nanoflotation

D ESIGN L OADING R ATES  typical designs for Clarifiers (settling tanks) or Dissolved Air Flotation tanks rely on the flow rate (M 3 per minute) for the water being treated divided by the surface area (M 2 )  “A” times “B” = (M 2 ) B of Area length A  The Rate is M / hour width

T YPICAL D ESIGN L OADING R ATES  Clarifiers / Settling Tanks -1 to 2 M /hour  In the 1960’s to 1980’s Dissolved Air Flotation (DAF) designs for Water treatment plants were based on 5 to 10 M /hour. This is why DAF became so popular.  In the 1990’s the design rate became 10 to 15 M / hour  In the last 10 years there are some new designs called High Rate DAF where the design loading rate is 20 to 30 M / hour.  For Industrial Waste Water treatment, Engineers in North America still use 5 to 10 M / hour for DAF  Froth flotation uses 20 to 30 M / hour for Industrial Waste Water treatment

A REA REQUIREMENTS FOR F ROTH F LOTATION V ERSUS DAF Froth flotation Requires 50 % less tankage than DAF for Industrial Water treatment Projects

T YPICAL A IR B UBBLE V OLUME FOR DAF R EFERENCE : E DSWALD , J AMES K.; H AARHOFF , J OHANNES ; D ISSOLVED A IR F LOTATION FOR W ATER C LARIFICATION ; A MERICAN W ATER W ORKS A SSOCIATION /M C G RAW H ILL , 2012 Typical DAF Design is 7000 to 9000 PPM = < than 1% Air Bubble Floc density in a Volume typical water Concentration treatment Parts per million application is 90 to 10000 = 1% 100 ppm. Therefore the ratio of bubbles to floc is 100 to 1 Nanoflotation is typically 3 % to 10 % Air Bubble Result: Much higher Number per M 3 number of bubbles and contact with particles

F ROTH F LOTATION - E NERGY E FFICIENT WITH LOWER RECYCLE FLOW AND N O C OMPRESSED A IR REQUIREMENTS . DAF requires 10 to 100 % recycle flow. Froth Flotation requires 3 % to 10% because of the high bubble concentration Froth Flotation does not require compressed air

O PERATING C OSTS - F ROTH F LOTATION MORE EXPENSIVE Froth Flotation uses Surfactant Assuming Surfactant cost is $2000/ M 3 the cost per M 3 of treated water is $0.10 Dissolved Air Flotation relies on Recycle water pumping and compressed air. The total amount of energy consumption is approximately 0.05 KwH per M 3 . At $0.10 per KwH the cost per M 3 is $0.005

A IR B UBBLES ATTACHING TO S OLID P ARTICLES IN W ATER Bubble and particle behavior in water is controlled by four forces 1. Van der waal Forces 2. Electrostatic 3. Hydrophobic 4. Hydrodynamic Hydrophobic forces are the most important forces to have solid particles attach to air bubbles

Van der waal forces and electrostatic forces are important for the attachment of particles to particles Conclusion: In Nanoflotation, emphasis is placed on developing strong  Hydrophobic forces for the Flotation Step (Step 1) of Nanoflotation Followed by :  Van der Waal and Electrostatic forces for the particle contact in the Filtration/Membrane Step (Step 2) of Nano flotation

U SE OF C OAGULANTS IN F LOTATION T ECHNOLOGY  For Flotation to perform it is important for the solid particles in the water to be neutral  Particles are typically non polar (hydrophobic) but become negative charged because of Natural Organic Materials (NOM) and natural surfactants in the water.  NOM and natural surfactants coat the surface of the hydrophobic particles making them negatively charged.  To neutralize the negative charge, positive charged metal hydroxide coagulants have to be added (Alum , Ferric and Poly Aluminum Chlorides)

U SE OF C OAGULANTS IN F LOTATION T ECHNOLOGY -C ONTINUED  The neutral particles become hydrophobic again and attach to the surfactant based Hydrophilic froth bubble.  As the bubble and solid rise to the surface, the hydrophobic component attracts to more solids which are attached to more bubbles thereby creating a floating sludge layer  The air inside the bubble, once above the water is Hydrophobic and wants to attract to the open air and the solids.  The bubble collapses and the skim layer with the solids becomes concentrated with solids

B UBBLES AND S OLIDS FLOAT TO THE SURFACE AND CAUSE A S KIM LAYER

F ROTH F LOTATION T EST IN THE L ABORATORY

C OAGULANT A DDITION  Natural Organic Materials require much more positive charged coagulants to neutralize than inorganic solid particles. ( i.e. 5 to 20 times more coagulant)  The optimum coagulant addition is to neutralize the solids.  Over dosing will work in the opposite way where the particles will become positive charge and electrostatic forces will repel the solids. DO NOT OVERDOSE

N ATURAL O RGANIC M ATERIALS Eight Fractions of Organic Material are Considered as NOM Aquatic Humic matter from  Fulvic Acid decomposition of plant and  Humic Acid animal matter  Weak Hydrophobic Acids  Hydrophobic Bases From phenols ,  Hydrophobic Neutrals carbohydrates, surgars, proteins , polysaccharides,  Hydrophilic Acids amino acids and fatty acids  Hydrophilic Bases  Hydrophilic Neutrals Coagulants will separate the Aquatic Humic Matter (Negative Charged) but not the remaining fractions

I MPACT OF H ARDNESS IN W ATER AND T OTAL D ISSOLVED S OLIDS (TDS) ON C OAGULATION The Harder the water or the higher the TDS level the easier it will be to coagulate the solid particles in the water

I MPACT OF A LKALINITY IN W ATER ON C OAGULATION High Alkalinity > 120 mg/l as CaCO 3 Medium Alkalinity is 60 to 120 mg/l as CaCO 3 Low Alkalinity is < 60 mg/l as CaCO 3 The higher the Alkalinity in water the greater the buffer capacity is to keep the pH stable.  Alum provides higher positive charged particles when the pH is less than 6.5.  PACl provides higher positive charges when the waters are in the pH 7 range.

A C LOSER L OOK A T M EMBRANES

C ERAMIC M EMBRANES CAN BE INDIVIDUAL TUBE OR IN A B UNDLE (C ALLED A M ONOLITH )

S UBMERGED M EMBRANES VERSUS P RESSURE M EMBRANES  Polymeric Membranes can be Submerged Membranes or Pressure Driven  Ceramic membranes are only Pressure Driven Submerged Pressure Driven Polymeric polymeric or ceramic Membranes Membranes

P RESSURE D RIVEN M EMBRANES – T WO FORMATS PDO membranes can handle solids in the 100 to 200 µm range PDI membranes can handle solids in the 85 to 150 µm range RO Membranes are limited to solids less than 5 µm