Category Archives: Engineering

Forced diversity of race is racist

Let me browse through some thoughts on efforts to address endemic racism. I’m not sure I’ll get anywhere, but you might as well enter the laboratory of my mind on the issue.

I’d like to begin with a line of the bible (why not?) “‘Do not pervert justice; do not show partiality to the poor or favoritism to the great, but judge your neighbor fairly.” (Lev. 19:15). This sounds good, but in college admissions, I’ve found we try to do better by showing  favoritism to the descendants of those who’ve been historically left-out. This was called affirmative action, it’s now called “diversity”.  

In 1981, when I began teaching chemical engineering at Michigan State University, our department had race-based quotas to allow easier admission to the descendants of historically-disadvantaged groups. All major universities did this at the time. The claim was that it would be temporary; it continues to this day. In our case, the target was to get 15% or so black, Hispanics and American Indians students (7 in a class of 50). We achieved this target by accepting such students with a 2.0 GPA, and not requiring a math or science background; Caucasians required 3.0 minimum, and we did require math or science. I’m not sure we helped the disadvantaged by this, either personally or professionally, but we made the administration happy. The kids seemed happy too, at least for a while. The ones we got were, by and large, bright. To make up for the lack of background we offered tutoring and adjusted grades. Some diversity students did well, others didn’t. Mostly they went into HR or management after graduation, places they could have gone without our efforts.

After some years, the Supreme court ended our quota based selection, saying it was, itself racist. They said we could still reverse-discriminate for “diversity,” though. That is, if the purpose wasn’t to address previous wrongs, but to improve the class. We changed our literature, but kept our selection methods and kept the same percentage targets as before.

This is a popular meme about racism. It makes sense to me.

This is a popular meme about racism.

The only way we monitored that we met the race-percent target was by a check-box on forms. Students reported race, and we collected this, but we didn’t check that black students look black or Hispanic students spoke Spanish. There was no check on student honesty. Anyone who checked the box got the benefits. This lack of check bread cheating at MSU and elsewhere. Senator Elizabeth Warren got easy entry into Harvard and Penn, in part by claiming to be an Indian on her forms. She has no evidence of Indian blood or culture Here’s Snopes. My sense is that our methods mostly help the crooked.

The main problem with is, I suspect, is the goal. We’ve decided to make every university department match the state’s racial breakdown. It’s a pretty goal, but it doesn’t seem like one that helps students or the state. Would it help the MSU hockey squad to force to team to racially match the state; would it help the volleyball team, or the football team?  So why assume it helps every academic department to make it’s racial makeup match the state’s. Why not let talented black students head to business or management departments before graduation. They might go further without our intervention.

This is not to say there are not racial inequalities, but I suspect that these diversity programs don’t help the students, and may actually hurt. They promote crookedness, and divert student attention from achieving excellence to maintaining victim status. Any group that isn’t loud enough in claiming victim status is robbed of the reverse-discrimination that they’ve been told they need. They’re told they can’t really compete, and many come to believe it. In several universities, we gone so far as to hire “bias referees” to protect minorities from having to defend their intellectual views in open discussion. The referee robs people of the need to think, and serves, I suspect, no one but a group of powerful politicians and administrators — people you are not supposed to criticize. On that topic, here is a video of Malcolm X talking about the danger of white liberals. Clearly he can hold his own in a debate without having a bias referee, and he makes some very good points about white liberals doing more harm than good.

Robert Buxbaum, November 5, 2017. In a related problem, black folks are arrested too often. I suggest rational drug laws. Some financial training could help too.

How Tesla invented, I think, Tesla coils and wireless chargers.

I think I know how Tesla invented his high frequency devices, and thought I’d show you, while also explaining the operation of some devices that develop from in. Even if I’m wrong in historical terms, at least you should come to understand some of his devices, and something of the invention process. Either can be the start of a great science fair project.

physics drawing of a mass on a spring, left, and of a grounded capacitor and inception coil, right.

The start of Tesla’s invention process, I think, was a visual similarity– I’m guessing he noticed that the physics symbol for a spring was the same as for an electrical, induction coil, as shown at left. A normal person would notice the similarity, and perhaps think about it for a few seconds, get no where, and think of something else. If he or she had a math background — necessary to do most any science — they might look at the relevant equations and notice that they’re different. The equation describing the force of a spring is F = -k x  (I’ll define these letters in the bottom paragraph). The equation describing the voltage in an induction coil is not very similar-looking at first glance, V = L di/dt.  But there is a key similarity that could appeal to some math aficionados: both equations are linear. A linear equation is one where, if you double one side you double the other. Thus, if you double F, you double x, and if you double V, you double dI/dt, and that’s a significant behavior; the equation z= atis not linear, see the difference?

Another linear equation is the key equation for the motion for a mass, Newton’s second law, F = ma = m d2x/dt2. This equation is quite complicated looking, since the latter term is a second-derivative, but it is linear, and a mass is the likely thing for a spring to act upon. Yet another linear equation can be used to relate current to the voltage across a capacitor: V= -1/C ∫idt. At first glance, this equation looks quite different from the others since it involves an integral. But Nicola Tesla did more than a first glance. Perhaps he knew that linear systems tend to show resonance — vibrations at a fixed frequency. Or perhaps that insight came later. 

And Tesla saw something else, I imagine, something even less obvious, except in hindsight. If you take the derivative of the two electrical equations, you get dV/dt = L d2i/dt2, and dV/dt = -1/C i . These equations are the same as for the spring and mass, just replace F and x by dV/dt and i. That the derivative of the integral is the thing itself is something I demonstrate here. At this point it becomes clear that a capacitor-coil system will show the same sort of natural resonance effects as shown by a spring and mass system, or by a child’s swing, or by a bouncy bridge. Tesla would have known, like anyone who’s taken college-level physics, that a small input at the right, resonant frequency will excite such systems to great swings. For a mass and spring,

Basic Tesla coil. A switch set off by magnetization of the iron core insures resonant frequency operation.

Basic Tesla coil. A switch set off by magnetization of the iron core insures resonant frequency operation.

resonant frequency = (1/2π) √k/m,

Children can make a swing go quite high, just by pumping at the right frequency. Similarly, it should be possible to excite a coil-capacitor system to higher and higher voltages if you can find a way to excite long enough at the right frequency. Tesla would have looked for a way to do this with a coil capacitor system, and after a while of trying and thinking, he seems to have found the circuit shown at right, with a spark gap to impress visitors and keep the voltages from getting to far out of hand. The resonant frequency for this system is 1/(2π√LC), an equation form that is similar to the above. The voltage swings should grow until limited by resistance in the wires, or by the radiation of power into space. The fact that significant power is radiated into space will be used as the basis for wireless phone chargers, but more on that later. For now, you might wish to note that power radiation is proportional to dV/dt.

A version of the above excited by AC current. In this version, you achieve resonance by adjusting the coil, capacitor and resistance to match the forcing frequency.

A more -modern version of the above excited by AC current. In this version, you achieve resonance by adjusting the coil, capacitor and resistance to match the forcing frequency.

The device above provides an early, simple way to excite a coil -capacitor system. It’s designed for use with a battery or other DC power source. There’s an electromagnetic switch to provide resonance with any capacitor and coil pair. An alternative, more modern device is shown at left. It  achieves resonance too without the switch through the use of input AC power, but you have to match the AC frequency to the resonant frequency of the coil and capacitor. If wall current is used, 60 cps, the coil and capacitor must be chosen so that  1/(2π√LC) = 60 cps. Both versions are called Tesla coils and either can be set up to produce very large sparks (sparks make for a great science fair project — you need to put a spark gap across the capacitor, or better yet use the coil as the low-voltage part of a transformer.

power receiverAnother use of this circuit is as a transmitter of power into space. The coil becomes the transmission antenna, and you have to set up a similar device as a receiver, see picture at right. The black thing at left of the picture is the capacitor. One has to make sure that the coil-capacitor pair is tuned to the same frequency as the transmitter. One also needs to add a rectifier, the rectifier chosen here is designated 1N4007. This, fairly standard-size rectifier allows you to sip DC power to the battery, without fear that the battery will discharge on every cycle. That’s all the science you need to charge an iPhone without having to plug it in. Designing one of these is a good science fair project, especially if you can improve on the charging distance. Why should you have to put your iPhone right on top of the transmitter battery. Why not allow continuous charging anywhere in your home. Tesla was working on long-distance power transmission till the end of his life. What modifications would that require?

Symbols used above: a = acceleration = d2x/dt2, C= capacitance of the capacitor, dV/dt = the rate of change of voltage with time, F = force, i = current, k = stiffness of the spring, L= inductance of the coil, m = mass of the weight, t= time, V= voltage, x = distance of the mass from its rest point.

Robert Buxbaum, October 2, 2017.

Estimating the strength of an atom bomb

As warfare is a foundation of engineering, I thought I’d use engineering to evaluate the death-dealing power of North Korea’s atomic/hydrogen bomb, tested September 3, 2017. The key data in evaluating a big bomb is its seismic output. They shake the earth like earthquakes do, and we measure the power like earthquakes, using seismometers. I’ve seen two seismographs comparing the recent bomb to the previous. One of these, below, is from CTBTO, the Center for Test Ban Treaty Oversight, via a seismometer in western Kazakhstan (see original data and report).

Seismic output of all North Korean nuclear tests.

Seismic output, to scale, of all declared DPNK nuclear tests as observed from IMS station AS-59 in Western Kazakhstan

North Korea’s previous bomb, exploded 9 September 2016, was reported to be slightly more powerful than the ones we dropped on Hiroshima and Nagasaki, suggesting it was about 20 kilotons. According to CTBTO, it registered 5.3 on the Richter scale. The two tests before that appear somewhat less powerful, perhaps 7-10 kilotons, and the two before that appear as dismal failures — fizzles, in atomic bomb parlance. The MOAB bomb, by comparison, was 9 Tons, or 0.009 kiloTons, a virtual non-entity.

To measure the output of the current bomb, I place a ruler on my screen and measure the maximum distance between the top to bottom wiggles. I find that this bomb’s wiggles measure 5 cm, while the previous measures 5 mm. This bomb’s wiggles are ten times bigger, and from this I determine that this explosion registered 6.3 on the Richter scale, 1.0 more than the previous — the Richter scale is the logarithmic measure of the wiggle amplitude, so ten times the shake magnitude  is an addition of 1.0 on the scale. My calculation of 6.3 exactly matches that of the US geological survey. The ratio of wiggle heights was less on the, NORSAR seismometer, Norway, see suggesting 5.8 to 5.9 on the Richter scale. The European agencies have taken to reporting 6.1, an average value, though they originally reported only the 5.8 from NORSAR, and a bomb power commensurate with that.

We calculate the bomb power from the Richter-scale measure, or the ratio of the wiggles. Bomb power is proportional to wiggle height to the 3/2 power. Using the data above, ten times the wiggle, this bomb appears to be 10^3/2 = 31.6 times as powerful as the last, or 31.6 x 20kTon = 630kTon (630,000 tons of TNT). If we used the European value of 6.1, the calculated power would be about half this, 315 kTons, and if we used the NORSAR’s original value, it would suggest the bomb had less than half this power. Each difference of 0.2 on the Richter scale is a factor of two in power. For no obvious reason we keep reporting 120 to 160 kTons.

NORSAR comparison of North Korean bomb blasts

NORSAR comparison of North Korean blasts — suggests the current bomb is smaller; still looks like hydrogen.

As it happens, death power is proportional to the kiloton power, other things being equal. The bombs we dropped on Hiroshima and Nagasaki were in the 15 to 20 kTon range and killed 90,000 each. Based on my best estimate of the bomb, 315 kTons, I estimate that it would kill 1.6 million people if used on an industrial city, like Seoul, Yokohama, or Los Angeles. In my opinion, this is about as big a bomb as any rational person has reason to make (Stalin made bigger, as did Eisenhower).

We now ask if this is an atom bomb or a hydrogen-fusion bomb. Though I don’t see any war-making difference, if it’s a hydrogen bomb that would make our recent treaty with Iran look bad, as it gave Iran nuclear fusion technology — I opposed the treaty based on that. Sorry to say, from the seismic signature it looks very much like a hydrogen bomb. The only other way to get to this sort of high-power explosion is via a double-acting fission bomb where small atom bomb sets off a second, bigger fission bomb. When looking at movies of Eisenhower-era double-acting explosions, you’ll notice that the second, bigger explosion follows the first by a second or so. I see no evidence of this secondary-delay in the seismic signature of this explosion, suggesting this was a hydrogen bomb, not a double. I expect Iran to follow the same path in 3-4 years.

As a political thought, it seems to me that the obvious way to stop North Korea would be to put pressure on China by making a military pact with Russia. Until that is done, China has little to fear from a North Korean attack to the south. Of course, to do that we’d likely have to cut our support of NATO, something that the Germans fear. This is a balance-of-power solution, the sort that works, short of total annihilation. It was achieved at the congress of Vienna, at the treaty of Ghent, and by Henry Kissinger through détente. It would work again. Without it, I see the Korean conflict turning hot again, soon.

Robert Buxbaum, September 11, 2017.

Activated sludge sewage treatment bioreactors

I ran for water commissioner of Oakland county in 2016, a county with 1.3 million people and eight sewage treatment plants. One of these plants uses the rotating disk contractor, described previously, but the others process sewage by bubbling air through it in a large tank — the so-called, activated sludge process. A description is found here in Wikipedia, but with no math, and thus, far less satisfying than it could be. I thought I might describe this process relevant mathematics, for my understanding and those interested: what happens to your stuff after you flush the toilet or turn on the garbage disposal.

Simplified sewage plant: a plug-flow reactor with a 90+% solids recycle used to maintain a high concentration of bio-catalyst material.

Simplified sewage plant: a bubbling, plug-flow bio-reactor with 90% solids recycle and a settler used to extract floc solids and bio-catalyst material.

In most of the USA, sanitary sewage, the stuff from your toilet, sink, etc. flows separately from storm water to a treatment plant. At the plant, the sewage is first screened (rough filtered) and given a quick settle to remove grit etc. then sent to a bubbling flow, plug-flow bioreactor like the one shown at right. Not all cities use this type of sludge processes, but virtually every plant I’ve seen does, and I’ve come to believe this is the main technology in use today.

The sewage flows by gravity, typically, a choice that provides reliability and saves on operating costs, but necessitates that the sewage plant is located at the lowest point in the town, typically on a river. The liquid effluent of the sewage, after bio-treatment is typically dumped in the river, a flow that is so great more than, during dry season, more than half the flow of several rivers is this liquid effluent of our plants – an interesting factoid. For pollution reasons, it is mandated that the liquid effluent leaves the plant with less than 2 ppm organics; that is, it leaves the plant purer than normal river water. After settling and screening, the incoming flow to the bio-reactor typically contains about 400 ppm of biomaterial (0.04%), half of it soluble, and half as suspended colloidal stuff (turd bits, vegetable matter, toilet paper, etc). Between the activated sludge bio-reactor and the settler following it manage to reduce this concentration to 2 ppm or less. Soluble organics, about 200 ppm, are removed by this cellular oxidation (metabolism), while the colloidal material, the other 200 ppm, is removed by adsorption on the sticky flocular material in the tank (the plug-flow tank is called an oxidation ditch, BTW). The sticky floc is a product of the cells. The rate of oxidation and of absorption processes are proportional to floc concentration, F and to organic concentration, C. Mathematically we can say that

dC/dt = -kFC

where C and F are the concentration of organic material and floc respectively; t is time, and k is a reaction constant. It’s not totally a constant, since it is proportional to oxygen concentration and somewhat temperature dependent, but I’ll consider it constant for now.

As shown in the figure above, the process relies on a high recycle of floc (solids) to increase the concentration of cells, and speed the process. Because of this high recycle, we can consider the floc concentration F to be a constant, independent of position along the reactor length.

The volume of the reactor-ditch, V, is fixed -it’s a concrete ditch — but the flow rate into the ditch, Q, is not fixed. Q is high in the morning when folks take showers, and low at night. It’s also higher — typically about twice as high — during rain storms, the result of leakage and illegal connections. For any flow rate, Q, there is a residence time in the tank, τ where τ = V/Q. We can now solve the above equation assuming an incoming concentration C° = 400 ppm and an outgoing concentration Co of 2 ppm:

ln (C°/Co) = kFτ

Where τ equals the residence time in the tank. Since τ = V/Q,

ln (C°/Co) = kFV/Q.

The required volume of reactor, V, is related to the flow rate, Q, as follows for typical feed and exit concentrations:

V = Q/kF ln( 400/2) = 5.3 Q/kF.

The volume is seen to be dependent on F. In Oakland county, thank volume V is chosen to be one or two times the maximum expected value of Q. To keep the output organic content to less than 2 ppm, F is maintained so that kF≥ 5.3 per day. Thus, in Oakland county, a 2 million gallon per day sewage plant is built with a 2-4 million gallon oxidation ditch. The extra space allows for growth of the populations and for heavy rains, and insures that most of the time, the effluent contains less than 2 ppm organics.

Bob Martin by the South Lyon, MI, Activated Sludge reactor

Bob Martin chief engineer the South Lyon, MI, Activated Sludge plant, 2016. His innovation was to control the air bubblers according to measurements of the oxygen content. The O2 sensor is at bottom; the controller is at right. When I was there, some bubblers were acting up.

As you may guess, the activated sludge process requires a lot of operator control, far more than the rotating disk contractor we described. There is a need for constant monitoring and tweaking. The operator deals with some of the variations in Q by adjusting the recycle amount, with other problems by adjusting the air flow, or through the use of retention tanks upstream or downstream of the reactor, or by adding components — sticky polymer, FeCl3, etc. Finally, in have rains, the settler-bottom fraction itself is adjusted (increased). Because of all the complexity. sewer treatment engineer is a high-pay, in demand, skilled trade. If you are interested, contact me or the county. You’ll do yourself and the county a service.

I’d mentioned that the effluent water goes to the rivers in Oakland county. In some counties it goes to the fields, a good idea, I think. As for the solids, in Oakland county, the solid floc is concentrated to a goo containing about 5% solids. (The goo is called unconsolidated sludge) It is shipped free to farmer fields, or sometimes concentrated to more than 5% (consolidated sludge), and provided with additional treatment, anaerobic digestion to improve the quality and extract some energy. If you’d like to start a company to do more with our solids, that would be very welcome. In Detroit the solids are burned, a very wasteful, energy-consuming process, IMHO. In Wisconsin, the consolidated sludge is dried, pelletized, and sold as a popular fertilizer, Milorganite.

Dr. Robert Buxbaum, August 1, 2017. A colleague of mine owned (owns?) a company that consulted on sewage-treatment and manufactured a popular belt-filter. The name of his company: Consolidated Sludge. Here are some sewer jokes and my campaign song.

A rotating disk bio-reactor for sewage treatment

One of the most effective designs for sewage treatment is the rotating disk bio-reactor, shown below. It is typically used in small-throughput sewage plants, but it performs quite well in larger plants too. I’d like to present an analysis of the reactor, and an explanation of why it works so well.

A rotating disc sewage reactor.

A rotating disk sewage reactor; ∂ is the thickness of the biofilm. It’s related to W the rotation rate in radians per sec, and to D the limiting diffusivity.

As shown, the reactor is fairly simple-looking, nothing more than a train of troughs filled with sewage-water, typically 3-6 feet deep, with a stack of discs rotating within. The discs are typically 7 to 14 feet in diameter (2-4 meters) and 1 cm apart. The shaft is typically close to the water level, but slightly above, and the rotation speed is adjustable. The device works because appropriate bio-organisms attach themselves to the disk, and the rotation insures that they are fully (or reasonably) oxygenated.

How do we know the cells on the disc will be oxygenated? The key is the solubility of oxygen in water, and the fact that these discs are only used on the low biological oxygen demand part of the sewage treatment process, only where the sewage contains 40 ppm of soluble organics or less. The main reaction on the rotating disc is bio oxidation of soluble carbohydrate (sugar) in a layer of wet slime attached to the disc.

H-O-C-H + O2 –> CO2 + H2O.

As it happens, the solubility of pure oxygen in water is about 40 ppm at 1 atm. As air contains 21% oxygen, we expect an 8 ppm concentration of oxygen on the slime surface: 21% of 40 ppm = 8 ppm. Given the reaction above and the fact that oxygen will diffuse five times more readily than sugar at least, we expect that one disc rotation will easily provide enough oxygen to remove 40 ppm sugar in the slime at every speed of rotation so long as the wheel is in the air at least half of the time, as shown above.

Let’s now pick a rotation speed of 1/3 rpm (3 minutes per rotation) and see where that gets us in terms of speed of organic removal. Since the disc is always in an area of low organic concentration, it becomes covered mostly with “rotifers”, a fungus that does well in low nutrient (low BOD) sewage. Let’s now assume that mass transfer (diffusion) of sugar in the rotifer slime determines the thickness of the rotifera layer, and thus the rate of organic removal. We can calculate the diffusion depth of sugar, ∂ via the following equation, derived in my PhD thesis.

∂ = √πDt

Here, D is the diffusivity (cm2/s) for sugar in the rotifera slime attached to the disk, π = 3.1415.. and t is the contact time, 90 seconds in the above assumption. My expectation is that D in the rotifer slime will be similar to the diffusivity sugar in water, about 3 x 10-6 cm2/s. Based on the above, we find the rotifer thickness will be ∂ = √.00085 cm2 = .03 cm, and the oxygen depth will be about 2.5 times that, 0.07 cm. If the discs are 1 cm apart, we find that, about 14% of the fluid volume of the reactor will be filled with slime, with 2/5 of this rotifer-filled. This is as much as 1000 times more rotifers than you would get in an ordinary constantly stirred tank reactor, a CSTR to use a common acronym. We might now imagine that the volume of this sewage-treatment reactor can be as small as 1000 gallons, 1/1000 the size of a CSTR. Unfortunately it is not so; we’ll have to consider another limiting effect, diffusion of nutrients.

Consider the diffusive mass transfer of sugar from a 1,000,000 gal/day flow (43 liters/sec). Assume that at some point in the extraction you have a concentration C(g/cc) of sugar in the liquid where C is between 40 ppm and 1 ppm. Let’s pick a volume of the reactor that is 1/20 the normal size for this flow (not 1/1000 the size, you’ll see why). That is to say a trough whose volume is 50,000 gallons (200,000 liters, 200 m3). If the discs are 1 cm apart, this trough (or section of a trough) will have about  4×10^8 cm2 of submerged surface, and about 9×10^8 total surface including wetted disc in the air. The mass of organic that enters this section of trough is 44,000 C g/second, but this mass of sugar can only reach the rotifers by diffusion through a water-like diffusion layer of about .06 cm thickness, twice the thickness calculated above. The thickness is twice that calculated above because it includes the supernatant liquid beyond the slime layer. We now calculate the rate of mass diffusing into the disc: AxDxc/z = 8×10^8 x 3×10-6 x C/.06 cm = 40,000 C g/sec, and find that, for this tank size and rotation speed, the transfer rate of organic to the discs is 2/3 as much as needed to absorb the incoming sugar. This is to say that a 50,000 gallon section is too small to reduce the concentration to ln (1) at this speed of disc rotation.

Based on the above calculation, I’m inclined to increase the speed of rotation to .75 rpm. At this speed, the rotifer-slime layer will be 2/3 as thin 0.2 mm, and we expect an equally thinner diffusion barrier in the supernatant. At this faster speed, there is now 3/2 as much diffusion transfer per area because the thinner diffusion barrier, and we can expect a 50,000 liter reactor section to reduce the initial concentration by a fraction of 1/2.718 or C/e. Note that the mass transfer rate to the discs is always proportional to C. If we find that 50,000 gallons of tank reduces the concentration to 1/e, we find that we need 150,000 gallons of reactor to reduce the concentration of sugar from 40 ppm to 2 ppm, the legal target, ln (40/2) = 3. This 150,000 gallons is a remarkably small volume to reduce the sBOD concentration from 40 ppm to 2 ppm (sBOD = soluble biological oxygen demand), and the energy use is small too if the disc bearings are good.

The Holly sewage treatment plant is the only one in Oakland county, MI using the rotating disc contacted technology. It has a flow of 1,000,000 gallons per day, and has a contactor trough that is 215,000 gallons, about what we’d expect though their speed is somewhat higher, over 1 rpm and their input concentration is likely lower than 40 ppm. For the first stage of sewage treatment, the Holly plant use a vertical-draft, trickle-bed reactor. That is they drizzle the sewage-liquids over a slime-coated packing to reduce the sBOD concentration from 200 ppm to before feeding the flow to the rotating discs. My sense of the reason they don’t do the entire extraction with a trickle bed is that the discs use far less energy.

I should also add that the back-part of the disc isn’t totally useless oxygen storage, as it seems from my analysis. Some non-sugar reactions take place in the relatively anoxic environment there and in the liquid at the bottom of the trough. In these regions, iron reacts with phosphate, and nitrate removal takes place. These are other important requirements of sewage treatment.

Robert E. Buxbaum, July 18, 2017. As an exercise, find the volume necessary for a plug flow reactor or a stirred tank reactor (CSTR) to reduce the concentration of sugar from 40 ppm to 2 ppm. Assume 1,000,000 gal per day, an excess of oxygen in these reactors, and a first order reaction with a rate constant of dC/dt = -(0.4/hr)C. At some point in the future I plan to analyze these options, and the trickle bed reactor, too.

If the wall with Mexico were covered in solar cells

As a good estimate, it will take about 130,000 acres of solar cells to deliver the power of a typical nuclear facility, 26 TWhr/year. Since Donald Trump has proposed covering his wall with Mexico with solar cells, I came to wonder how much power these cells would produce, and how much this wall might cost. Here goes.

Lets assume that Trump’s building a double wall on a strip of land one chain (66 feet) wide, with a 2 lane road between. Many US roads are designed in chain widths, and a typical, 2 lane road is 1/2 chain wide, 33 feet, including its shoulders. I imagine that each wall is slanted 50° as is typical with solar cells, and that each is 15 to 18 feet high for a good mix of power and security. Since there are 10 square chains to an acre, and 80 chains to a mile we find that it would take 16,250 miles of this to produce 26 TWhr/year. The proposed wall is only about 1/10 this long, 1,600 miles or so, so the output will be only about 1/10 as much, 2.6 TWhr/year, or 600 MW per average daylight hour. That’s not insignificant power — similar to a good-size coal plant. If we aim for an attractive wall, we might come to use Elon Musk’s silica-coated solar cells. These cost $5/Watt or $3 Billion total. Other cells are cheaper, but don’t look as nice or seem as durable. Obama’s, Ivanpah solar farm, a project with durability problems, covers half this area, is rated at 370 MW, and cost $2.2 Billion. It’s thus rated to produce slightly over half the power of the wall, at a somewhat higher price, $5.95/Watt.

Elon Musk with his silica solar panels.

Elon Musk with his, silica-coated, solar wall panels. They don’t look half bad and should be durable.

It’s possible that the space devoted to the wall will be wider than 66 feet, or that the length will be less than 1600 miles, or that we will use different cells that cost more or less, but the above provides a good estimate of design, price, and electric output. I see nothing here to object to, politically or scientifically. And, if we sell Mexico the electricity at 11¢/kWhr, we’ll be repaid $286 M/year, and after 12 years or so, Republicans will be able to say that Mexico paid for the wall. And the wall is likely to look better than the Ivanpah site, or a 20-year-old wind farm.

As a few more design thoughts, I imagine an 8 foot, chain-link fence on the Mexican side of the wall, and imagine that many of the lower solar shingles will be replaced by glass so drivers will be able to see the scenery. I’ve posited that secure borders make a country. Without them, you’re a tribal hoard. I’ve also argued that there is a pollution advantage to controlling imports, and an economic advantage as well, at least for some. For comparison, recent measurement of the Great Wall of China shows it to be 13,170 miles long, 8 times the length of Trump’s wall with China.

Dr. Robert E. Buxbaum, June 14, 2017.

Sewage jokes, limericks, and a song.

I ran for water commissioner (sewer commissioner) of Oakland county, Michigan last year, lost, but enjoyed my run. It’s a post that has a certain amount of humor built-in. If you can’t joke about yourself, you’ve got no place in the sewer. So here are some sewage jokes, and poems, beginning with an old favorite; one I used often in my campaign:3b37b9cab2d27693de2aa7004a3d90ef

Why was Piglet staring into the toilet?
He was looking for Poo.

Last week someone broke into the police station and stole all the toilets. The cops are still searching. So far, they have nothing to go on.paperwork

On administration: In life as on the toilet, the job isn’t done until the paperwork is finished.

Speaking of toilet paper: do you know why Star Trek is like toilet paper? They both go past Uranus and capture Klingons. I wrote an essay on Toilet paper — really. 

Here’s my campaign song and video. It’s sung by Art Carney (I’ve no rights, but figure they’ve expired). The pictures are of me, my daughter, and various people we met visiting sewage treatment plants around the county. Great men and a few great women who don’t mind getting their hands dirty. 


The Turd Burglar, We’re No.1 in the No. 2 business. What a motto!

And now for sewage Limericks:

There once was a man named McBride.
Who fell in the sewer and died.
The same day his brother
Fell in another,
And they were interred side by side.

There is a double intent in that Limerick, in case you missed it

By the sewer she lived, by the sewer she died. Some said t’was disease, but I say, Suicide

sewage treatment

sewage treatment plant in Pontiac, MI — the county’s largest.

How do you describe a jocular sewage joker? pun gent.

Life is like a sewer, what you get out of it is what you put into it (Tom Lehrer). And sometimes it stinks.

Robert E. Buxbaum, June 4, 2017. There is just one more sewage joke I know, but I thought I’d leave it out. It concerns the sewage backup at the prom. Unfortunately, the punchline stinks.

A clever, sorption-based, hydrogen pump

Hydrogen-power ed fuel cells provide a lot of advantages over batteries, e.g. for drones and extended range vehicles, but part of the challenge is compressing the hydrogen. On solution I’d proposed is a larger version of this steam-powered compressor, another is a membrane reactor hydrogen generator, and a few weeks ago, I wrote about an other clever innovative solutions: an electrochemical hydrogen pump. It was a fuel cell operating backwards, pumping was very efficient and compact, but the pressure was borne by the fuel cell membranes, so the pump is only suitable at low pressure differentials. I’d now like to describe a different, very clever hydrogen pump, one that operates by metallic hydride sorption and provides very high pressure.

Hydride sorption -desorption pressures vs temperature.

Hydride sorption -desorption pressures vs temperature, from Dhinesh et al.

The basic metal hydride reaction is M + nH2 <–> MH2n. Where M is a metal or metallic alloy. While most metals will undergo this reaction at some appropriate temperature and pressure, the materials of interest are exothermic hydrides that undergo a nearly stoichiometric absorption or desorption reaction at temperatures near 1 atm, temperatures near room temperature. The plot at right presents the plateau pressure for hydrogen absorption/ desorption in several, common metal hydrides. The slope is proportionals to the heat of sorption. There is a red box shown for the candidates that sorb or desorb between 1 and 10 atmospheres and 25 and 100 °C. Sorbants whose lines pass through that box are good candidates for pump use. The ones with a high slope (high heat of sorption) in particular, if you want a convenient source of very high pressure.

To me, NaAlH4 is among the best of the materials, and certainly serves as a good example for how the pump works. The basic reaction, in this case is:

NaAl + 2H2 <–> NaAlH4

The line for this reaction crosses the 1 atm red line at about 30°C suggesting that each mol of NaAl material will absorb 2 mols of hydrogen at 1 am and normal room temperatures: 20-30°C. Assume the pump contains 100 g of NaAl (2.0 mols). We can expect it will 4 mols of hydrogen gas, about 90 liters at this temperature. If this material in now heated to 250°C, it will desorb most of the hydrogen (80% perhaps, 72 liters) at 100 atm, or 1500 psi. This is a remarkably high pressure boost; 1500 psi hydrogen is suitable for use filling the high pressure tank of a hydrogen-based, fuel cell car.

But there is a problem: it will take 2-3 hours to cycle the sober; the absorb hydrogen at low pressure, heat, desorb and cycle back to low temperature. If you only can pump 72 liters in 2-3 hours, this will not be an effective pump for automobiles. Even with several cells operating in parallel, it will be hard to fill the fuel tank of a fuel-cell car. The output is enough for electric generators, or for the small gas tank of a fuel cell drone, or for augmenting the mpg of gasoline automobiles. If one is interested in these materials, my company, REB Research will supply them in research quantities.

Properties of Metal Hydride materials; Dhanesh Chandra,* Wen-Ming Chien and Anjali Talekar, Material Matters, Volume 6 Article 2

Properties of Metal Hydride materials; Dhanesh Chandra,* Wen-Ming Chien and Anjali Talekar, Material Matters, Volume 6 Article 2

At this point, I can imagine you saying that there is a simple way to make up for the low output of a pump with 100g of sorbent: use more, perhaps 10 kg distributed over 100 cells. The alloys don’t cost much in bulk, see chart above (they’re a lot more expensive in small quantities). With 100 times more sorbent, you’ll pump 100 times faster, enough for a fairly large hydrogen generator, like this one from REB. This will work, but you don’t get economies of scale. With standard, mechanical pumps give you a decent economy of scale — it costs 3-4 times as much for each 10 times increase in output. For this reason, the hydride sorption pump, though clever appears to be destined for low volume applications. Though low volume might involve hundreds of kg of sorbent, at some larger value, you’re going to want to use a mechanical pump.

Other uses of these materials include hydrogen storageremoval of hydrogen from a volume, e.g. so it does not mess up electronics, or for vacuum pumping from a futon reactor. I have sold niobium screws for hydrogen sorption in electronic packages, and my company provides chemical sorbers for hydrogen removal from air. For more of our products, visit

Robert Buxbaum, May 26, 2017. 

Future airplane catapults may not be electric

President Trump got into Hot Water with the Navy this week for his suggestion that they should go “back to god-damn steam” for their airplane catapults as a cure for cost over-runs and delays with the Navy’s aircraft carriers. The Navy had chosen to go to a more modern catapult called EMALS (electromagnetic, aircraft launch system) based on a traveling coil and electromagnetic pulses. This EMAL system has cost $5 Billion in cost over-runs, has added 3 years to the program, and still doesn’t work well. In response to the president’s suggestion (explosion), the Navy did what the rest of Washington has done: blame Trump’s ignorance, e.g. here, in the Navy Times. Still, for what it’s worth, I think Trump’s idea has merit, especially if I can modify it a bit to suggest high pressure air (pneumatics) instead of high pressure steam.

Tests of the navy EMALS, notice that some launches go further than others; the problem is electronics, supposedly.

If you want to launch a 50,000 lb jet fighter at 5 g acceleration, you need to apply 250,000 lbs of force uniformly throughout the launch. For pneumatics, all that takes is 250 psi steam or air, and a 1000 square inch piston, about 3 feet in diameter. This is a very modest pressure and a quite modest size piston. A 50,000 lb object accelerated this way, will reach launch speed (130 mph) in 1.2 seconds. It’s very hard to get such fast or uniform acceleration with an electromagnetic coil since the motion of the coil always produces a back voltage. The electromagnetic pulses can be adjusted to counter this, but it’s not all that easy, as the Navy tests show. You have to know the speed and position of the airplane precisely to get it right, and have to adjust the firing of the pushing coils accordingly. There is no guarantee of smooth acceleration like you get with a piston, and the EMALS control circuit will always be vulnerable to electromagnetic and cyber attack. As things stand, the control system is thought to be the problem.

A piston is invulnerable to EM and cyber attack since, if worse comes to worse, the valves can be operated manually, as was done with steam-catapults throughout WWII. And pistons are very robust — far more robust than solenoid coils — because they are far less complex. As much force as you put on the plane, has to be put on the coil or piston. Thus, for 5 g acceleration, the coil or piston has to experience 250,000 lbs of horizontal force. That’s 3 million Newtons for those who like SI units (here’s a joke about SI units). A solid piston will have no problem withstanding 250,000 lbs for years. Piston steamships from the 50s are still in operation. Coils are far more delicate, and the life-span is likely to be short, at least for current designs. 

The reason I suggest compressed air, pneumatics, instead of steam is that air is not as hot and corrosive as steam. Also an air compressor can be located close to the flight deck, connected to the power center by electric wires. Steam requires long runs of steam pipes, a more difficult proposition. As a possible design, one could use a multi-stage, inter-cooled air compressor connected to a ballast tank, perhaps 5 feet in diameter x 100 feet long to guarantee uniform pressure. The ballast tank would provide the uniform pressure while allowing the use of a relatively small compressor, drawing less power than the EMALS. Those who’ve had freshman physics will be able to show that 5 g acceleration will get the plane to 130 mph in only 125 feet of runway. This is far less runway than the EMALS requires. For lighter planes or greater efficiency, one could shut off the input air before 120 feet and allow the remainder of the air to expand for 200 feet of the piston.

The same pistons could be used for capturing an airplane. It could start at 250 psi, dead-ended to the cylinder top. The captured airplane would push air back into the ballast tank, or the valve could be closed allowing pressure to build. Operated that way, the cylinder could stop the plane in 60 feet. You can’t do that with an EMAL. I should also mention that the efficiency of the piston catapult can be near 100%, but the efficiency of the EMALS will be near zero at the beginning of acceleration. Low efficiency at low speed is a problem found in all electromagnetic actuators: lots of electromagnetic power is needed to get things moving, but the output work,  ∫F dx, is near zero at low velocity. With EM, efficiency is high at only at one speed determined by the size of the moving coil; with pistons it’s high at all speeds. I suggest the Navy keep their EMALS, but only as a secondary system, perhaps used to launch drones until they get sea experience and demonstrate a real advantage over pneumatics.

Robert Buxbaum, May 19, 2017. The USS Princeton was the fanciest ship in the US fleet, with super high-tech cannons. When they mis-fired, it killed most of the cabinet of President Tyler. Slow and steady wins the arms race.

Nestle pays 1/4,000 what you pay for water

When you turn on your tap or water your lawn, you are billed about 1.5¢ for every gallon of water you use. In south-east Michigan, this is water that comes from the Detroit river, chlorinated to remove bacteria, e.g. from sewage, and delivered to you by pipe. When Nestle’s Absopure division buys water, it pays about 1/4000 as much — $200/ year for 218 gallons per minute, and they get their water from a purer source, a pure glacial aquifer that has no sewage and needs no chlorine. They get a far better deal than you do, in part because they provide the pipes, but it’s mostly because they have the financial clout to negotiate the deal. They sell the Michigan water at an average price around $1/gallon, netting roughly $100,000,000 per year (gross). This allows them to buy politicians — something you and I can not afford.

Absopure advertises that I t will match case-for-case water donations to Flint. Isn't that white of them.

Absopure advertises that I t will match case-for-case water donations to Flint. That’s awfully white of them.

We in Michigan are among the better customers for the Absopure water. We like the flavor, and that it’s local. Several charities purchase it for the folks of nearby Flint because their water is near undrinkable, and because the Absopure folks have been matching the charitable purchases bottle-for bottle. It’s a good deal for Nestle, even at 50¢/gallon, but not so-much for us, and I think we should renegotiate to do better. Nestle has asked to double their pumping rate, so this might be a good time to ask to increase our payback per gallon. So far, our state legislators have neither said yes or no to the proposal to pump more, but are “researching the matter.” I take this to mean they’re asking Nestle for campaign donations — the time-honored Tammany method. Here’s a Detroit Free Press article.

I strongly suspect we should use this opportunity to raise the price by a factor of 400 to 4000, to 0.15¢ to 1.5¢ per gallon, and I would like to require Absopure to supply a free 1 million gallons per year. We’d raise $300,000 to $3,000,000 per year and the folks of Flint would have clean water (some other cities need too). And Nestle’s Absopure would still make $200,000,000 off of Michigan’s, clean, glacial water.

Robert Buxbaum, May 15, 2017. I ran for water commissioner, 2016, and have occasionally blogged about water, E.g. fluoridationhidden rivers, and how you would drain a swamp, literally.