CIVE 321 Exam 2

1. Protect people and ecosystems from toxic materials in wastewater.
2. Remove suspended solids and pollutants before the effluent returns to the environment.
3. Preserve the water quality of natural water resources such as rivers and lakes.
4. Make wastewater usable for other purposes

pre-, primary, secondary, and tertiary treatment

Bar rack, grit chamber, equalization basin, primary settling. Removes pollutants that will either settle or float.

Bar rack, grit chamber, equalization basin, primary settling, biological treatment, secondary settling. Achieved by using biological processes to break down organic pollutants and remove more than 85% of BOD and suspended solids.

Bar rack, grit chamber, equalization basin, primary settling, biological treatment, secondary settling, tertiary wastewater treatement. Used when secondary treatment is not adequate and involves chemical treatment and filtration of wastewater.

Raw sewage, bar rack, grit chamber, equalization basin, primary settling, biological treatment, secondary settling, tertiary wastewater treatment, receiving body.

(Influent) -> (Aeration Basin) -> (Secondary Clarifier) -> (Effluent, Waste Sludge, Return Sludge)

To convert soluble and colloidal pollutants to microbes (solids), gases (CO2, CH4, N2), and water

Respiration. carbon sources, energy sources

aerobic, anaerobic, obligate anaerobes, facultative, photosynthesis

organic carbon, inorganic carbon

light (photosynthesis), organic chemicals, inorganic chemicals

require O2 for cell production

use something other than O2 for cell production

require complete absense of O2 because it is toxic to them

can grow without O2 or in low O2 environments, but will use O2 for metabolism when present

Cryphilic (10-20), Mesophilic (25-40), Thermophilic (50-65) (Degrees Celsius)

Growth, use substrate (pollutants/what the bacteria is treating), die/decay

natural air flow through an underdrain system

Facultative, Aerated (Aerobic), Anaerobic, Complete Retention (or "no discharge")

Sludge is removed periodically; up to 95% BOD removed in summer, none removed in winter except sedimentation

Like a CMR; mechnaical aeration used to maintain a high oxygen content throughout the pond

Very deep, unmixed basin, usually used as pretreatment for strong industrial wastes

No discharge/outlet, avoids significant seepage from bottom, designed large to avoid overflow

1. Reduce the volume of water so that sludge behaves as a solid and not a liquid
2. Reduce the mass of the solids
3. Reduce the concentration of pathogens (wastewater sludges)

Aerobic Digestion, Anaerobic Digestion, Thickening, Dewatering

i. Hydrolysis and Fermentation
ii. Acid Formation
iii. Methane Formation

1. Land Application
2. Fertilizer and Soil Conditioner
3. Ocean Disposal
4. Disposal in Landfills
5. Incineration of sludge

Total coliform, Fecal coliform, E. Coli

a disease-causing microorganism

cholera, typhoid, polio

To coagulate particles together so that they grow in size and are less stable, and can be removed by sedimentation and filtration processes

As particle size decreases, the settling velocity decreases. So, small colloids may not be removed by sedimentation alone.

A 6 beaker test where water is mixed and flocculated with the same dose of alum and varying pHs, then holding the pH constant and varying the alum dosage. It is used to determine the efficiency of coagulants in wastewater treatment.

Adsorption-destabilization: dose-turbidity curve shows charge-reversal (steep at higher doses).
Sweep coagulation: dose-turbidity curve does not show charge reversal (relatively flat at higher doses).

Compression of Double Layer, Adsorption and Charge Neutralization, Enmeshment in a precipitate ("Sweep Floc"), Adsorption and Interparticle Bridging

Concentration of ions in solution increases, and volume surrounding the particle to balance the surface charge is reduced. This makes it easier for particles to collide and form a new larger particle.

Chemical coagulants attach themselves to the surface of particles, and if the surface has charge opposite to that of the coagulant, the charge on the surface is reduced or eliminated.

Like a snow globe; coagulant is added in large enough quantities to cause precipitate to form. Particles in the water are trapped within the precipitate as it forms or captured as floc particles settle.

Applies to coagulants that are synthetic organic polymers of large molecular weight with mutliple charges along a chain of carbon atoms. Polymers attach to surface of two or more particles to tie them together.

Flocculation is slow mixing (stirring) to encourage floc formation during coagulation to grow larger in size to create larger solids that can easily settle or be filtered. It is typically applied at a treatment in basins with large paddles that mix slowly.

1. Duration of Mixing (hydraulic residence time in flocculation tank)
2. Intensity of Mixing (G)

A process where "heavy" solids are removed by gravity settling

Sedimentation basin, settling basin, clarifier

For Type I Design:
1. Plug-flow reactor
2. Particle introduced at top of reactor (tank)
3. Particle settling velocity such that particle just hits the bottom at the end of the tank

Particles tend to have a surface charge that attracts ions of opposite charge, forming an electrical double layer. The diffuse layers of particles repel as they get close to one another, preventing coagulation. But, Van der Waals forces cause attraction at very close distances, so it is important that particles collide in order to coagulate for removal.

Relative humidity is lower, so evaporation is faster, making the size of particles smaller.

Solids are separated from the water by passing the water through a porous bed that retains the solids. Particles attach onto other particles in media. Particles are not typically removed by straining in granular gravity filtration because particples must get stuck in the pore space between media in order to be strained.

Colloids become trapped in the media and pore spaces between media become smaller, increasing the change of particple contact with media or other particles. Water flows through filters until solids accumulation is large. The filter is then backwashed to remove the accumulated solids if filtrate quality is not good enough or is head loss is too great.

Ripening is the period of time that shows a spike in the number of particles once particles first begin to start to adhere to the filter after a backwash cycle.

Multiple media sizes are used because these are able to remove a wider range of particle sizes and types.

Straining (particles get stuck in pore space), Sedimentation (settle out of water onto media), Interception (hits media and sticks while moving through filter), Brownian Motion (random motion of small particles)

1. Must deactivate the pathogens in the water
2. Meet possible fluctations in composition and concentration in the water
3. Are neither toxic to humans and domestic animals nor unpalatable or objectionable in required concentrations
4. Must be dispensable at a reasonable cost and safe/easy to store, transport, handle, and apply
5. Strength and concentration must be determined easily in treated water.
6. Must persist within disinfected water with sufficient concentration to provide protection against recontamination.

Disinfection by-products; organic chemicals formed during disinfection using chlorine.

Chloramines, Ozone, or Ultraviolet Radiation

UV disinfection causes the DNA of pathogenic organisms to over-absorb ultraviolet light (between 200-300 nanometers), which renders the organisms incapable of reproducing. Pros: smaller footprint, minimized pollution from airborne material, minimal personnel exposure to UV during drinking water treatment, modular design makes installation simple. Cons: no residual, dark repair of microbial DNA.

An anion is a negatively charged ion, and a canion is a positively charged ion.

The carbonate system is a natural buffer against large pH changes produced by carbon dioxide (CO2) via the chemical equation:

CO2 + H2O --> H2CO3 --> H(+) + HCO3(-) --> 2H(+) + CO3(2-)

When CO3(2-) reacts with Ca(2+), which occurs naturally as limestone, it creates a calcium carbonate precipitate (CaCO3). This is the fundamental reaction used in water softening.
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Hard water is water that does not lather well, causes scum in bath tubs, and leaves scale deposits on water heaters and pots. It is characterized by the amount of calcium, Ca(2+), and magnesium, Mg(2+), dissolved in water.

Carbonate hardness: Lesser of total hardness or approximate alkalinity, often Conc. of HCO3(-) as CaCO3 + 2•Conc. of CO3(2-) as CaCO3
Non-carbonate hardness: Total hardness - carbonate hardness, Conc. of Ca(2+) as CaCO3 + Conc. of Mg(2+) as CaCO3 - [Conc. of HCO3(-) as CaCO3 + 2•Conc. of CO3(2-) as CaCO3]

Softening is the process of removing Ca(+2) and Mg(+2) from water.

Chemical precipitation: Using a base, often lime - Ca(OH)2, to form a precipitate containing hardness ions
Ca(OH)2 + Ca(HCO3(-)) --> 2 CaCO3 + H2O
Ca(OH)2 + Mg(HCO3(-)) --> 2 CaCO3 + Mg(OH)2 + H2O

Ion exchange: Using an ion exchange resin to exchange Ca(+2) & Mg(+2) for ions of similar charge, often Na(+), attached to the resin surface
CaCl2 + R-(Na)2 --> R-Ca + 2 NaCl