Physical & Chemical Treatment Chapter 9

Chemistry Review Chapter 3

Activity - Individual Is it organic or inorganic? –PCBs –Methane –Carbon dioxide –Ammonia –Lead –Pesticides

Organics

In-Class Activity Solubility Vapor pressure Diffusion coefficient Henry’s constant Organic-carbon partition coefficient Octanol-water partition coefficient Freundlich constant Bioconcentration factor Biomagnification Volatility 1.Amount of chemical passing through an area 2.Sorption of an organic to another organic 3.Increased concentration in an organism 4.Amount of solute dissolved in a solvent 5.Tendency to adsorb to a solid 6.Solubility of a gas in a liquid 7.Tendency to move from solution to gas phase 8.Pressure exerted by a vapor on a liquid at equilibrium 9.Sorption of an organic to the organic portion of soil or sediment 10.Increased concentration through the food chain

Physical/Chemical Treatment Methods Stripping Carbon adsorption Neutralization Precipitation Reduction/oxidation

Physical Treatment Carbon Adsorption (Section 9-2)

Activated Carbon

Typical Column

Flow Patterns

Design Parameters Contaminant properties –Solubility –Molecular structure –Molecular weight –Hydrocarbon saturation Contact time Carbon exhaustion

Adsorption Evaluation: Batch Test Grind GAC to pass 325-mesh screen Evaluate contact time to reach equilibrium –Mix 500 mg/L GAC with waste over 24 h –Determine degree of adsorption at various time intervals –Choose time to achieve  90% removal Evaluate GAC dosage –Mix various C with waste for 90% chosen time

Adsorption Isotherm Plot of contaminant adsorbed per unit mass of carbon (X/M) vs. equilibrium contaminant concentration in bulk fluid Mathematical forms –Langmuir: X/M = (aC e )/(1+bC e ) –Freundlich: X/M = kC e 1/n

Example: Adsorption Isotherm Each jar receives activated carbon and 100 mL of a 600-mg/L solution of xylenes and is then shaken for 48 h. Jar12345 Carbon (mg) C e (mg/L)

Example continued

Example: Adsorption Isotherm Test1234 P (kPa) X/M (kg/kg) Benzene

Example continued

Activity – Team Each jar receives activated carbon and 100 mL of a solution with 0.5% TOC and is then shaken for 48 h. Jar12345 Carbon (g) C e (mg/L)

Example: Using Reference Data Estimate the daily carbon utilization to remove chlorobenzene from 43.8 L/s of wastewater saturated with chlorobenzene. Assume a chlorobenzene concentration of 5 mg/L is acceptable for discharge to the sewer.

Freundlich Isotherms

Comparing Different Carbons

Batch vs. Column Capacity

Adsorption Zone

Bed Depth Service Time Design Bohart-Adams equation

Modified Bohart-Adams Eq.

BDST Design Determine height of adsorption zone (AZ) –Small diameter columns in series run to breakthrough –Plot breakthrough for 10% and 90% vs. cumulative depth –AZ = horizontal distance between 10% & 90% lines Determine number of columns –n = [(AZ)/d] +1, where d = depth of column –Round up to next whole number

BDST Design Continued Determine diameter of columns –Use same loading rate in full-scale units as lab units [L = Q w /A s from lab operation] –A s = Q w /L with Q w for full-scale operation –Round up to nearest size available –Typically, d:D = 3:1 - 10:1 Determine carbon usage rate –CUR = (A s )(1/a)(CUW) a = slope of 10% line = velocity of AZ CUW = carbon unit weight

Example: BDST Design A waste stream at a flow rate of m 3 /min requires treatment to reduce the organic concentration from 89 mg/L to 8.9 mg/L (90% removal). Lab studies are run in columns 2.3 m high by m diameter at a flow rate of 0.5 L/min. Assume a unit weight of carbon of 481 kg/m 3.

Example: BDST Design

Activity – Team A petrochemical washwater with a flow of 322 m 3 /d and concentration of 630 mg/L has to be treated to an effluent standard of 50 mg/L. A four-column pilot plant was operated with a carbon that had a density of 481 kg/m 3. The columns were 3 m long and loaded at a hydraulic rate of 0.20 m 3 /min/m 2. The pilot plant was operated in series. Determine the required number of columns, the time required to exhaust a column, the column diameter, the daily carbon use, and the carbon adsorption loading.

Empty Bed Contact Time

Example: Single Column Data Limited data has been obtained to evaluate whether carbon adsorption is a viable alternative to treat 1 MGD of secondary effluent containing 50 mg/L organics to a level of 5 mg/L. Carbon density is 23 lb/ft 3. Is adsorption a viable treatment option? Is the data adequate?

Example cont.

Other Design Considerations Pretreatment Fluctuations in contaminant concentration Head loss Short circuiting Air binding Regeneration and/or disposal

Carbon Regeneration Heat Steam Solvent Acid/base Oxidant

Regeneration Effects

Common Design Deficiencies Poor effluent quality due to poor carbon adsorption –Adsorption not applicable to waste –Poor regeneration –pH out of proper range –Operating temperature wrong BDST too short due to high loadings or under- designed system Head loss too high for available gravity head or pump capacity

Deficiencies continued High & ineffective backwash volume due to high influent solids content No method to determine breakthrough Carbon transfer piping plugging and no means provided to disconnect & flush lines Incorrect pumps for carbon slurries Incorrect valves for carbon slurries

Adsorber Selection 2,000-lb vessel 5 vessel exchanges/year Monthly monitoring 10,000-lb vessel 1 vessel exchange/year Quarterly monitoring