Promoted from the Ricochet Member Feed by Editors Created with Sketch. What Your Wastewater Treatment Specialist Wants You to Know

 

Wastewater-Treatment-Plant-300x225I’ve seen that there is an unofficial series of sorts on Ricochet, where members write posts explaining what they do in their day jobs. I work for a company that does wastewater treatment (for industries, so my perspective is a little different from your local municipal wastewater treatment plant). This post is my contribution.

The motivation for treating wastewater is to avoid or mitigate negative impacts on the river, lake, ocean, or other area into which it flows. Common negative impacts include filling waterways with debris or sediment, causing fish kills or dead zones by depleting oxygen levels, promoting algae blooms, and spreading pathogens that can harm other people who use that water. In some cases, there may also be concerns related to specific heavy metals or other chemicals. I’ll focus on oxygen depletion, but feel free to ask about other impacts in the comments.

When organic matter (and there is plenty of that in wastewater) gets discharged into the environment, it gets degraded by microorganisms. These decay processes consume oxygen, which dissolves fairly poorly in water. If the amount of organic matter is high enough, the rate of decay can exceed the rate at which more oxygen can dissolve into the water, and the level of oxygen can drop to the point that fish and other things living in the water start to die.

Wastewater treatment systems take these same natural degradation processes and accelerate them in engineered environments. Then, when the treated effluent is discharged, it is low in organic matter and negative impacts can be avoided. This idea of providing engineered environments for biological processes will be familiar to anyone who has ever done home-brewing: You add a starter culture, maintain suitable temperatures, manage the release of gases, and so on, but the bulk of the work is done by microorganisms.

One of the keys to the engineered environments in wastewater treatment plants is maintaining a suitable oxygen level. Oxygen does not dissolve that easily in water, so wastewater treatment plants use prodigious amounts of energy (on air compressors or blowers, surface agitators, etc.) to add air to the water at a sufficient rate. At other times, air is deliberately excluded to promote modes of decay that happen in the absence of oxygen, or anaerobic processes.* In contrast to the energy expended to add oxygen to water, anaerobic processes actually yield energy because biogas (comprising methane and other gases) is the end product of decay under those conditions.

Another important aspect to biological wastewater treatment is keeping the microorganisms that do the work around long enough and in sufficient quantities. To accomplish this, wastewater treatment processes incorporate some form of solid-liquid separation (which has the added benefit of keeping discharges of debris and sediment low). Traditionally, this was achieved in settling tanks, with the sludge that settled to the bottom pumped back to the main part of the treatment system. Known as “activated sludge,” this process is now a century old. In a growing number of modern facilities, solid-liquid separation is achieved with membrane technology, in which water is drawn through a thin layer of polymer or ceramic by a pressure difference while particles (and even some dissolved constituents) are retained. This is a more efficient and reliable separation process than settling, at the cost of requiring more energy and maintenance for operating.

Aside from understanding a little bit about how wastewater treatment plants work, there are a couple of other things I think you should know:

1. Household water use (and wastewater generation) is only a small slice of a large pie that includes agriculture, industry, electricity generation, oil, and gas. In discussions of the drought in California, for example, it often seems people are not aware of the relative scales.

2. There is a growing trend to see wastewater not as a problem to get rid of, but as a potential resource. As alluded to above, anaerobic processes can be used to recover some energy from wastewater (particularly with some industrial wastewaters). It is also possible to treat wastewater to the point that the purified effluent can be reused.** Recovering nutrients to use as fertilizers is another interesting application.

Feel free to ask any questions in the comments below or in a private message! I enjoy talking about this, um, “stuff.”

*There is also an in-between condition known as “anoxic” where free oxygen is not present but there is nitrate, which is a weak oxidant and can partially act as a substitute. Anoxic processes produce nitrogen gas, not biogas.

**At a conference I attended last week, I had a chance to sample a beer that was brewed with recycled effluent.

There are 38 comments.

  1. Jules PA Member

    very interesting. thanks for sharing.

    • #1
    • October 7, 2015, at 6:19 PM PST
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  2. Seawriter Member

    When I lived in Palestine, TX the water was horrible. Tasted like something had died in it.

    Well, it had. An explosion of beavers had created an explosion of beaver dams which impounded water. Which created algae blooms. Which died. Which sucked up the oxygen. Which killed the fish and other lake life. Which rotted. Which released molecules that tasted yucky, but were too small to be trapped by standard water treatment filters.

    It was horrible. We called it beaver tea.

    Seawriter

    • #2
    • October 7, 2015, at 6:40 PM PST
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  3. Belt Member

    Out here in the heartland, we’ve got reasonably good water supplies, though I have my concerns about the Ogallala aquifer. My home town sewage system does its bit to keep the water clean.

    The big issue is what to do about confinement yards. In particular, a big hog confinement will produce as much waste as a small town. There are regulations that oversee proper management and disposal of waste, of course. And now that the beans are out, I can smell the heady scent of liquid manure being knifed into the stubble ground. Every so often, a waste pond will collapse and run into a local river, killing off scads of fish. Alas, for the Mighty Floyd!

    Have you any experience with this sort of situation? How serious an issue is agricultural waste? Is it okay to treat it differently than we do residential or industrial waste? I’m assuming the answer is yes; we see it as a resource here in Iowa, but that doesn’t mean it’s not tricky to deal with…

    • #3
    • October 7, 2015, at 6:48 PM PST
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  4. Tenacious D Inactive
    Tenacious D Post author

    Seawriter: Well, it had. An explosion of beavers had created an explosion of beaver dams which impounded water. Which created algae blooms. Which died. Which sucked up the oxygen. Which killed the fish and other lake life. Which rotted. Which released molecules that tasted yucky, but were too small to be trapped by standard water treatment filters.

    At least it only tasted bad (small comfort, I know). Some types of algae can release some pretty nasty toxins.

    • #4
    • October 7, 2015, at 6:57 PM PST
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  5. The Reticulator Member

    What about trickling filters? Where do they fit into this? (When in graduate school in the 70s I took a course in the biology of wastewater treatment, mainly because it was one that my advisor taught.)

    Right next to the college campus, on the edge of the Mississippi River, there was a treatment plant that used trickling filters of the kind where wastewater was sprayed over rocks. The rock piles were back-flushed occasionally. Are those still used?

    The most interesting part that I remember was using microscopes to study and identify some of the larger (non-bacteria) organisms from the rocks.

    • #5
    • October 7, 2015, at 6:57 PM PST
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  6. Midget Faded Rattlesnake Contributor

    How serious are the worries about residues of pharmaceutical drugs in treated wastewater? Mostly overblown?

    If and when some of these drugs would need removal, how would you remove/degrade them?

    • #6
    • October 7, 2015, at 7:01 PM PST
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  7. Tenacious D Inactive
    Tenacious D Post author

    Belt: Have you any experience with this sort of situation? How serious an issue is agricultural waste? Is it okay to treat it differently than we do residential or industrial waste? I’m assuming the answer is yes; we see it as a resource here in Iowa, but that doesn’t mean it’s not tricky to deal with…

    I don’t deal with agricultural waste, but know a little bit about it. You’re right that it is tricky to deal with: unlike effluent from a city or factory, agricultural run-off doesn’t collect to a single point–where treatment could conveniently be installed–for discharge. Thus the term non-point source pollution. It is a big deal around Lake Erie at present. The main “pollutant” is nutrients, which is a dilemma because they are desirable on fields (thus the spreading of manure) but cause problems when they enter waterways in excessive quantities. Best management practices for fertilizer can mitigate things to a degree. Around the Chesapeake Bay, there is a program for wastewater treatment plants to get credits toward their own discharge limits by sponsoring reductions in non-point source discharges.

    • #7
    • October 7, 2015, at 7:07 PM PST
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  8. Tenacious D Inactive
    Tenacious D Post author

    The Reticulator: What about trickling filters? Where do they fit into this? (When in graduate school in the 70s I took a course in the biology of wastewater treatment, mainly because it was one that my advisor taught.)

    I’ve been to one trickling filter plant that is still in operation. They have lots of surface area for air to get in and the bacteria grow attached to the rocks so they don’t need to be captured by settling tanks or membranes.

    Microscopes are fun!

    • #8
    • October 7, 2015, at 7:13 PM PST
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  9. Tenacious D Inactive
    Tenacious D Post author

    Midget Faded Rattlesnake: If and when some of these drugs would need removal, how would you remove/degrade them?

    In the context of water and wastewater treatment, pharmaceuticals (and similar bioactive chemicals such as pesticides) are known as micropollutants or emerging contaminants. I haven’t really kept up with research in this area (and it’s definitely still more an area of research than of practice) in the past few years, but I know that not much can get past reverse osmosis. Specific compounds may also be susceptible to removal by adsorption or reaction with strong oxidants.

    I really don’t know how serious any worries are. I have heard of some evidence of gender-bending fish around effluent outfalls…

    • #9
    • October 7, 2015, at 7:30 PM PST
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  10. Aaron Miller Member

    Tenacious D:When organic matter (and there is plenty of that in wastewater) gets discharged into the environment, it gets degraded by microorganisms. These decay processes consume oxygen, which dissolves fairly poorly in water. If the amount of organic matter is high enough, the rate of decay can exceed the rate at which more oxygen can dissolve into the water and the level of oxygen can drop to the point that fish and other things living in the water start to die.

    So… a crapstorm?

    I’m no longer disappointed I didn’t pack my own bucket of fish for eating after the jubilee I saw years ago.

    • #10
    • October 7, 2015, at 7:36 PM PST
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  11. Seawriter Member

    Tenacious D: At least it only tasted bad (small comfort, I know)

    That’s what I would tell my kids. They did not buy it. (Kids today . . . too smart for their dad’s good.)

    Seawriter

    • #11
    • October 7, 2015, at 7:38 PM PST
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  12. Aaron Miller Member

    On another note

    • #12
    • October 7, 2015, at 7:40 PM PST
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  13. Tenacious D Inactive
    Tenacious D Post author

    Aaron Miller: So… a crapstorm?

    Even molasses will do the trick.

    • #13
    • October 7, 2015, at 7:41 PM PST
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  14. Seawriter Member

    Tenacious D: Even molasses will do the trick.

    Molasses can be just as dangerous for humans, witness the Molasses Flood of 1919. Talk about a sticky end.

    Seawriter

    • #14
    • October 8, 2015, at 1:26 AM PST
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  15. Chris Johnson Inactive

    Thanks, TD, for addressing one of my favorite topics. You skimmed past the metals, an area I believe is typically skimped on even in sanitary wastewater treatment; perhaps in IWW as well. What does get done about them in IWW treatment? Chelation, screening out with RO?

    As to Aaron Miller’s crapstorm, I believe he is referring to the apparent feedback system that develops: Nutrient loading leads to an algal bloom, the algae eventually absorb the nutrients then die, the decay of the dead algae sucks the oxygen from the water which kills the fish, the decay of the algae and fish releases the nutrients bound up within plus sucks the oxygen out of the water, the nutrients released lead to another algal bloom and aquatic life continues to suffer from reduced oxygen. The only way I know of to really deal with this crapstorm is to get into the water body and harvest out as much vegetation as possible, thus removing the bound-up nutrients. The trick is to haul that rotting vegetation far from the waterbody so that the nutrients released do not flow right back into the waterbody. In a residential area, this is best accompanied by a community composting program that encourages residents to reduce fertilizer application and substitute with the compost. This doesn’t lower the amount of nutrients within the watershed that eventually make it to the waterbody, but it can reduce the amount of nutrients that are added to the watershed, via fertilizer.

    • #15
    • October 8, 2015, at 5:31 AM PST
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  16. Chris Johnson Inactive

    As to Belt’s questions regarding agricultural run-off, that’s a tough subject. Bear in mind a couple of regulatory issues: First, many agricultural operations, especially older “grandfathered” ones, are exempt from regulation under the Clean Water Act. Second, there are two principal phases for managing pollutant impacts to water, from those substances and sources that are regulated, within what is called the National Pollutant Discharge Elimination System (NPDES). NPDES Phase I addressed point sources, picture a pipe as a fine example; that program was considered effectively implemented as of the early 2000s, and we began to implement NPDES Phase II, for non-point sources, in the past decade. Initial focus has been on municipalities above 50,000 people, with lots of programs such as treated wastewater recycling, implementation of best management practices for storm water runoff, and many others.

    Even Phase II does not regulate operations that were grandfathered in, such as agricultural runoff that can impact waterbodies over wide areas, not merely through pipes. To use a very simple example, cows would poop over vast acreage, historically. How is this managed under modern conditions where vast dairy herds may be confined to small areas? The short term answer has been the implementation of “lagoons”, fetid pools that capture the waste. Within the lagoons, some treatment naturally occurs with microbial breakdown, plus products from the lagoons are spread back onto fields. However, the lagoon treatment does not begin to approach that described by TD for Industrial Waste Water.

    • #16
    • October 8, 2015, at 5:49 AM PST
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  17. Tenacious D Inactive
    Tenacious D Post author

    Seawriter: Molasses can be just as dangerous for humans, witness the Molasses Flood of 1919. Talk about a sticky end.

    What an awful way to go.

    • #17
    • October 8, 2015, at 6:08 AM PST
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  18. Chris Johnson Inactive

    The treatment of agricultural waste water in lagoon systems doesn’t approach the level described by TD for IWW, and the lagoons don’t equate to the engineered systems he describes. The lagoons are typically just ponds that are dug out, with the removed soil compacted into “berms” surrounding the lagoons. These systems can and do fail, especially during periods of heavy rains. The data we will see coming out of South Carolina after Joaquin will be extraordinary, with respect to algal blooms and fish kills.

    The treatment of agricultural runoff is a tricky issue, especially for conservatives. Do we want to empower the government to exert greater authority in this area? In my experience, farmers don’t want to pollute their neighboring waterbodies. Furthermore, one man’s pollutant is another (or the same) man’s vital and expensive product. Fertilizer costs money, as do pesticides and herbicides. These become management expenses when they leave the operation, but every bit of them must be brought in by train or truck, accompanied by hefty bills.

    Politically, this subject could take on the dimensions of an entirely separate post, perhaps moderated by Richard Epstein! Something that we should find a way to encourage, at the local level: Tail Water Recycling. Find a way to make it cost effective for our local, small farmers that are adjacent to water bodies to install “perforated pipe” along their downstream boundaries, to collect their water and pollutants, then pump them back onto the fields.

    • #18
    • October 8, 2015, at 6:15 AM PST
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  19. Tenacious D Inactive
    Tenacious D Post author

    Chris:

    Thanks for the informative comments about managing agricultural runoff!

    I haven’t dealt too much with metals; my post focused on biological treatment since that’s what I spend my time on. Most metals would be removed with physical-chemical processes, although there are some redox reactions that can be biologically mediated for some metals…

    • #19
    • October 8, 2015, at 6:23 AM PST
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  20. PHCheese Member

    Thanks for comparing beer and wine with the local polishing pond. I think all go on the wagon.

    • #20
    • October 8, 2015, at 7:10 AM PST
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  21. OmegaPaladin Moderator

    As I am on the hazardous waste side, I’ve been interested in drain disposal for minute quantities of chemicals (such as wash water from cleaning beakers. Dichloromethane is notable for one of the few chlorinated solvents (like dry cleaner solvent or old-school paint thinner) that bacteria can break down. Not easily, though – if you aren’t careful, you’ll send the oxygen demand through the roof and ruin Tenacious D’s day.

    Now, heavy metals another kettle of fish, because those could kill the helpful bacteria, and metals don’t go away. (People panic over uranium or plutonium being around for a billion years – the RCRA 8 are forever!) I tell the lab staff to dump the first rinse in the waste container.

    • #21
    • October 8, 2015, at 7:15 AM PST
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  22. The Question Inactive

    I’ve teach biology and environmental science, so I should know the answer to the following question, but I don’t so I’m asking it here:

    Why do algal blooms suck oxygen out of lakes? Algae is photosynthetic. Shouldn’t it be producing more oxygen than it is consuming?

    • #22
    • October 8, 2015, at 7:23 AM PST
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  23. Emerson Member

    Michael Sanregret:I’ve teach biology and environmental science, so I should know the answer to the following question, but I don’t so I’m asking it here:

    Why do algal blooms suck oxygen out of lakes? Algae is photosynthetic. Shouldn’t it be producing more oxygen than it is consuming?

    The algae die once they have consumed all the nutrients, and it is the decay process that consumes oxygen.

    -E

    • #23
    • October 8, 2015, at 7:31 AM PST
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  24. Tuck Inactive

    Tenacious D: …At a conference I attended last week, I had a chance to sample a beer that was brewed with recycled effluent.

    All beers are brewed with recycled effluent. How it’s recycled varies.

    As I explained to my daughters early on, “Everything you eat is made of poop, and everything you drink is made of pee.”

    While I don’t know exactly what percentage of water on the planet has passed through a living creature and been expelled as waste, I think it’s a safe bet that every glass of water contains a bunch of molecules that have made this journey.

    The Circle of Life! :)

    • #24
    • October 8, 2015, at 7:50 AM PST
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  25. iWe Reagan
    iWe

    Fascinating, thanks!

    I know there are bacteria for basically everything – plastics get gobbled, as does petroleum that leaks. Heard last week about a worm that likes to eat styrofoam, rendering it biodegradable. Most of these bacteria, for one reason or another, are not easily managed (bioremediation of Superfund sites was not a big success, AFAIK).

    So it is helpful to realize that wastewater is a great example of where we manage biological systems with superb results.

    • #25
    • October 8, 2015, at 7:57 AM PST
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  26. MarciN Member

    Michael Sanregret:I’ve teach biology and environmental science, so I should know the answer to the following question, but I don’t so I’m asking it here:

    Why do algal blooms suck oxygen out of lakes? Algae is photosynthetic. Shouldn’t it be producing more oxygen than it is consuming?

    Algae grow in layers. The more nitrogen in the water, the thicker the layers. The layers of algae on the bottom die quickly for lack of air and light. Furthermore, as the algae layers grow, eventually the algae bloom blocks the light from reaching the bottom of the water, thus interfering with healthy photosynthesis for the other plants in the water system.

    In addition, the decomposition process consumes great quantities of oxygen, thus the oxygen depletion.

    What happens is therefore a death spiral. The more rotting material present, the less oxygen, the faster the decomposition proceeds.

    It can kill a fresh water system, and this usually surprises people, but it can be a problem in salt water as well where there is poor circulation of the water such as in bays and inlets.

    The good news is that it doesn’t take long to restore the health of a compromised water system. :)

    • #26
    • October 8, 2015, at 8:25 AM PST
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  27. Aaron Miller Member

    Chris Johnson: As to Aaron Miller’s crapstorm, I believe he is referring to the apparent feedback system that develops….

    I hadn’t considered it until now, but I suppose people are unwittingly helping the ecosystem recover when a jubilee occurs and we fill up our buckets with dead fish and crabs. The fish are stealing oxygen from the water as well. And a bunch of corpses would flood the water with other gases resulting from decay.

    The jubilee I saw was in Fairhope, Alabama. I don’t know how often they happen there. But when one does occur, word spreads like wildfire and a crowd quickly descends to gather up the bounty of fresh seafood.

    Sea gulls clean up the rest. There must have been hundreds of them squawking.

    • #27
    • October 8, 2015, at 8:27 AM PST
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  28. Aaron Miller Member

    • #28
    • October 8, 2015, at 8:28 AM PST
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  29. Misthiocracy grudgingly Member

    This post is nothing but a load of excrement.

    ;-)

    • #29
    • October 8, 2015, at 8:52 AM PST
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  30. Tenacious D Inactive
    Tenacious D Post author

    Chris Johnson: Politically, this subject could take on the dimensions of an entirely separate post, perhaps moderated by Richard Epstein!

    That would be cool. Maybe invite some guests to participate like someone from PERC, Ron Bailey, etc.

    • #30
    • October 8, 2015, at 9:13 AM PST
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