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25 Cards in this Set
- Front
- Back
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What is the difference between MCL and MCLG? Be able to explain more than just G is for Goal.
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Maximum Contaminant Level Goals
-unenforceable -set at levels w/ no adverse health effects, plus margin of safety Maximum Contaminant Levels -enforceable -consider technological & economic feasibility |
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Why are Treatment Techniques sometimes specified?
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Measurement for contaminant may not be feasible (time, cost, difficulty), and treatment method that has been shown to achieve MCL can be used instead.
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Do primary standards consider economic or technical feasibility? More than yes or no needed.
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Yes, primary drinking water standards balance health criteria, technological & economic feasibility to meet MCL.
Want lots of people to be able to afford water. |
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Why are MCLGs for carcinogens set at zero?
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Delaney clause - federal law said there's no safe level of exposure to carcinogens (so EPA has no choice).
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Secondary standards address???
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aesthetics, e.g. taste, odor, color
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Difference between surface water and ground water?
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Surface water- more suspended solids
Ground water- more dissolved minerals |
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Difference between particle settling velocity & critical settling velocity of a basin?
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Particle must reach critical settling velocity to assure removal within sedimentation basin. It is a basin-specific characteristic.
Particle settling velocity - particle characteristic (its actual settling velocity) |
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How would reducing a basin’s hydraulic detention time affect the critical settling velocity?
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Reducing hydraulic detention time would increase critical settling velocity of that basin and possibly decrease particle removal efficiency
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What would be in the primary sludge of a surface water plant? Secondary sludge?
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Primary- grit & silt
Secondary- coagulant and colloids (i.e. flocs) |
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What is in the sludge of a lime/soda softening plant?
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CaCO3, Mg(OH)2
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Why is alum a better coagulant than NaCl?
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Al3+ is more positively charged than Na+, so it better compresses charge layer around colloidal material, leading to better flocculation.
Also, Al(OH)3 is insoluble, which contributes to flocculation & settling |
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How are rapid sand filters cleaned?
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Backwashing - pumping a high flow rate of water up through the bottom of the filter
Sand particles become suspended in upflow water, and water scours away deposited material. |
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What happens to dirty water from cleaning sand filters?
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Backwash water is sent to head of the plant where it will enter primary settling basin.
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Do sand filters remove particles that are smaller than the pores within the filter?
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Yes, quite a bit of the particle removal is due to adsorption onto the sand surface.
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How would application of Darcy’s Law help with operation of a sand filter?
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Darcy's Law establishes a relationship between flow rate & head loss. In a sand filter, as it becomes clogged, it will take more pressure (head) to achieve constant flow (or at constant head, the flow will decline). The operator can monitor flow and/or head and know when to clean the filter.
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In conventional municipal wastewater treatment what is the “unit operation” that causes the process to differ significantly from drinking water treatment?
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Biological removal of dissolved organic material is usually used in municipal wastewater treatment.
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Why is it necessary to remove BOD from water prior to discharge?
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To maintain sufficient dissolved oxygen levels in surface water
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What is the concept behind the performance advantage derived from biomass recycle?
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Biomass recycle increases the concentration of waste-degrading microbes in the biotreatment unit, which increases the rate of biodegradation and allows for construction of smaller facilities.
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How does anaerobic treatment affect the WWTP “carbon footprint” relative to the traditional aerobic activated sludge process?
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Aerating activated sludge uses a lot of electricity. Anaerobic treatment produces methane which can substitute for primary energy consumption.
The combination of not aerating & capturing methane from anaerobic process reduces its carbon footprint relative to aerobic WWTP. |
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What are the two ways a waste becomes designated as "hazardous?"
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By being listed (based on prior knowledge) or having one of the four 'characteristics'
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What are the four characteristics used to define hazardous waste? How many characteristics need to be met to achieve hazardous designation?
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Ignitible, corrosive, reactive, toxic
only 1 |
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In 1975 your firm contributed a small fraction of the total mass in a waste landfill. This landfill was declared a Superfund site in 1990. Your firm had complied with all existing regulations in 1975 and never attempted to evade any environmental responsibility. Thus, your firm is not liable, or at worst minimally liable for clean-up costs of the Superfund site. True or false? Explain.
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False.
Joint & several liability - any contribution makes you responsible. Strict & retroactive - negligence v. diligence doesn't matter, and neither does the time of action. |
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Considering CERCLA and toxic metals in a manufacturing process waste stream: what philosophy might you use to improve the manufacturing process (see Fig 6.23).
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Eliminate, reduce, recycle, and reuse!
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Look at Figure 6.26. What happens to the spent GAC?
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It must be treated or discarded in compliance with waste disposal regulations (b/c although water has been treated, another waste stream has been generated)
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Identify two processes in Table 6.11 that destroy organic hazardous waste. Can these processes be used to destroy metals?
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Chemical oxidation
Ozonation Liquid injection Incineration Rotary kilns Fluidized bed incineration Pyrolysis Molten glass None destroy metals. |
