Module 10 Process Q&A
Comment of phyto/bio-remediation
There is a difficult economic/political aspect to bio- and phytoremediation.
It is generally cheap and usually slow. If it doesn't work, it will be many
years before it is clearly shown to not be working. Meanwhile, natural attenuation
- dissipation - is probably working as well. So any large costs associated with
failed phytoremediation and subsequent cleanup by traditional methods will be
years in the future. Thus the short term profitably of the PRP will not be harmed.
So PRPs will use it, if the regulators allow.
***Q. What is done with the ash of the incinerated hazardous wastes?
A. The ash from MSW incineration goes to a landfill. The benefit is known as
"volume reduction." The ash from a specific hazardous waste might
still be very hazardous. For example radioactive elements remain so. Metals
stay as metals. So that ash would still be a hazardous waste.
** Q. I found what I thought was a fair amount of information about intrinsic
[natural attenuation] remediation methods in this week's module. That is interesting
to me, and encouraging. For many contaminated sites, it seems that there is
little risk (and probably little chance for outrage!) to just let mother nature
do her thing. Some monitoring is appropriate of course, to make sure that a
desirable end is coming. There have been some huge numbers of dollars spent
on engineered approaches in the past, maybe without the highest cost benefit
ratio, so I am in favor of affording intrinsic approaches the benefit of equal
consideration.
A. Don't ever do a cost-benefit analysis of a clean up. In rational terms, it
is never warranted. On the other hand, consider how I would feel if I had a
trespasser on my 2.5 acre home property, say old Clyde pulls up in his pickup
truck, pulls out a tent, and starts to camp. I'll get angry and want him removed.
It will not impress me that old Clyde is a good person and has no record of
harming people. He even digs a pit privy and covers his droppings. The point
is not Clyde's damage to me in monetary terms. He's an invader that does not
belong there. It's not too much different if Exxon spill some oil and removes
most of it. What is left does not belong there. You and I can argue all day
that what is left is harmless, will go away in a few years, and will cost a
lot of money to clean up - money that our PR Department could use to buy Little
League uniforms. The public will demand Exxon clean it, no matter.
**Q. What are the regulations for scrubbers on smoke stacks?
A. Many hazardous chemicals are oxidized to CO2 and water. But some are not.
Incomplete incineration often makes more dangerous products. Today the permitting
for a hazardous waste incinerator is very strict.
**Q. It seems like the waste is not being treated, but it was just altered
from its original physical state.
A. Depends on the waste. A "pure" waste, such as an off-specification
chemical, might be 100% oxidized. Often however, the contaminant is mixed with
other things, like "dirty dirt." Asbestos waste is combined with building
materials, etc. Each waste would need to be considered separately.
** Q. One thing I found a bit foggy is the difference between flocculation and
coagulation. I understand that in both small contaminant particles are removed
by getting them to stick together so they can be removed from the solution but
I don't exactly understand the difference between the two. I've always thought
that the biological treatment systems are interesting. Especially when they
can be used passively so lots of resources are not required for operations and
maintenance.
A. Confusing terms. Colloidal particles tend to stay suspended because of kinetic
energy and also the particles have the same charge (usually negative in wastewater,
your mileage may differ) and repel each other. Coagulation is the process of
destabilizing the colloid. The coagulant binds and somehow causes the particles
to form "flocs" which are larger than colloids. A flocculent is a
chemical that enhances this process, i.e., helps this formation of larger particles.
That formation is called flocculation.
**Q. From the batch culture growth curve for microorganisms it seems that the
death curve is more linear than the growth curve (which looks logarithmic).
Any particular reason for this.
A. None that I know of - just the way these are drawn usually drawn. In practice
these would vary a great deal. Also, what was shown was idealized for only one
microorganism. In practice there are many types of organisms, each with different
kinetics.
**Q. One thing I was a little uncertain about was the difference between absorption and adsorption as it relates to wastewater treatment. I had to do a little digging to clarify the meanings for myself. When we talk about carbon filtration, were talking about adsorption. Adsorption is what happens when a contaminant clings to the surface of the carbon in a filter system. The carbon adsorbs the contaminant (not absorb). The following list are some of the chemicals and compounds that can be adsorbed by carbon.
A. Here's some information It is not always easy to tell whether the gas is inside the solid or merely at the surface because most practical' absorbents are very porous bodies with large internal' surfaces. It is not possible to determine the surface areas of such materials by optical or electron microscopy because of the size and complexity of the pores and channels of the materia l. (from http://itl.chem.ufl.edu/4411L_f00/ads/ads_1.html )
*Q. I understand that carbon adsorbs contaminants. But can contaminants be absorbed in the treatment process? Would flocculation/coagulation be an adsorption process or an absorption process?
A. No, flocculation/coagulation is just to make larger particles, which must then be settled or filtered. You would not describe that as adsorption.
* Q.In regards to incineration from what I read quite a bit of dioxin is released. Is this true? Also what are the differences in incineration requirements between a MSW incinerator and a certified hazardous waste incinerator? Which is safer, incineration or landfilling?
A. Remember, safety is in the eye of the beholder. “Dioxin” or 2,3,7,8-tetrachlorodibenzo[p]dioxin http://www.faculty.uaf.edu/ffrap/ENVE_652/Module02/2B_Organic/2B_3_Organic.htm is a byproduct of the incomplete combustion of chlorinated aromatics. You might make some in your barbeque by burning some fatty meat for the aromatics and burning a pvc (“paper or plastic?” ) bag together. MSW has lots of possibilities for combinations like those. However the actual amount made in MSW incineration is very small. Burning actual chlorinated aromatics, like PCBs, will make a lot of dioxin. Today there should be no chlorinated aromatics in MSW. There are hazardous waste incinerators that are authorized to burn PCBs, and they need to be closely monitored to make sure the combustion is complete.
* Q. Concerning question 7 on the quiz, the textbook states on p245 that "Membranes
are subject to fouling, which can be caused by metal oxides, precipitating salts,
colloids, and biological growth…Pretreatment prior to membrane filtration
is required to reduce heavy solids and remove free oil." This made me think
that the colloid would foul the filter, and that another method would be more
effective.
A. This is a question of which is less wrong. Charcoal filtering is wrong because
it is expensive and only used for organic chemicals, soils would just foul it.
Screening is wrong because clay is too small. Clarification is wrong because
clay settles much too slowly.
*Q. I find it incredibly interesting that it is even necessary to create all
these types of clean-up systems in the first place. I wonder how other nations
in the world handle contamination. Do they have more government money set aside
to clean up sites or is it mostly private like it seems it is in the US?
A. There is a tremendous range of options used. In general the industrialized
countries are much more wealthy than the non-industrialized. The industrialized
spend lots of money on clean-ups. In Europe, the governments and industry tend
more toward consensus; while in the US the government and industry tend towards
an adversarial mode.
* Q. I don't know if this has been attempted, but I would think that mix and
matching some of the remediation techniques would be cost effective methods
of clean-up. For example, If the standard pump and treat method were employed,
I would imagine reinforcing the removal of the contaminants by injecting microbes
into an area could increase the rate of degradation.
A. Usually the volume of water generated by pump and treat is too great for
any but physical or chemical treatment. Biological are for in situ treatment
or relativity small quantities.