A LOGICAL MBR

Membrane bioreactors (MBR) are becoming quite popular these days.  I designed one.  MBRs have the advantage of producing reuse quality effluent  and have a small footprint.  They have 2 BIG disadvantage:

1.  The design to peak flows are usually just 2:1
2.  They have a BIG energy demand because of the scour air needed to keep the membranes clean, and the low alpha of the fine bubble diffusers due to the high MLSS that the manufacturers tout. Additionaly, if you live in the cold weather part of the country, you will need to buy lots of extra membranes because  low temperature adversely affects the membrane flux rate

I will propose a different solutioon:  Put the membranes downstream of the secondary clarifiers. Why?

1.  You only need 1/3 of the membranes compared to an MBR
2.  The requirement for scouring air is much reduced, saving energy
3   The membranes can be bypassed, if necessary
4.  You can still eliminate disinfectioin in some states, as the membranes remove the bacteria.

This makes a lot more sense to me.

YOU CAN'T GO HOME AGAIN

Once you have been a consultant, you can never be an operator again.  You can teach operators, design plants, troubleshoot plants, write books, fill in as superintendent, run performance tests, start up equipment, win awards, but you  will never be considered to be competent to work at a plant again.

OPERATOR FOLLIES #6

A few years ago I was working at a plant and needed an operator for a "teachable moment".  I found an operator watching Oprah Winfrey, and he was very angry with me for pulling him away from his TV show.  Really now, Oprah?  Oprah?  What kind of man are you? You could at least watch ESPN.  I bet he watched the "men are pigs" channel too (lifetime).

The belt press operator had a TV in his cubicle too.

This same plant declined to interview me for an assistant plant manager position.

Unattended operation looks better all the time.

RAS RATES

I have been thinking about how to determine the optimum RAS rate for years.  Here's what I think:

The optimum RAS  rate is the one that maintains the system in equilibrium with a minimal blanket.

What RAS control methods are there?

PROPORTIONAL RAS

The proportional RAS scheme is where you select the RAS rate to be a percentage of the influent flow, and to change the RAS flow with the influent flow.  This is supposed to make sure there is sudffdicient RAS to treat the wastewater as the flow changes.

There are two big problems with this method
1.  It assumes that there ios a big inventory to be returned to the aeration tank at a moments notice. Your mixed liquor belongs in the aeration tank, not the clarifier blanket.
2   It will overload the clarifier at high flow.

RAS SS = CONCENTRATION OF SLUDGE IN THE 30 MINUTE SETTLOMETER (AKA RSC=SSC30)

In this scheme the RAS flow is adjusted to maintain the RAS SS at the same concentration as the solids in the bottom of your 30 minute settleometer.  This means that if you have a higher SVI, your RAS flow will be higher, and if your SVI is lower your RAS flow will be lower.  This temds to work pretty well, as long as you pay attention to the blankets at high RAS flow.

CONSTANT RAS FLOW

In this scheme you set the RAS flow and leave it there

This scheme can work well, although it means that you store some of your MLSS in the clarifier blanket at high flow and then return it at low flow.  Still, this works well as long as you pay attention to the blanket

CONSTANT BLANKET LEVEL

In this scheme, you adjust the RAS flow to maintain a level blanket.

This works well as long as you are willing to measure the blanket level several times a day and to keep a LOW blanket level - 2 ft or less.  a 6-inch blanket is not too low.

SUNDAY PAPERS

This is one of my favorite Joe Jackson songs.  In England all the papers are moe tabloidlike than here., Makes for some intresting reading, especially for people in Portsmouth, who havew been marryinjg cousins for far too long.  I think pop music lost its way in the 90's  I agree with the state ment that the past is a different country, but thats a topic for another day

I'll have a techniczal posting in the nest few days

1,000 PAGEVIEWS

Thank you loyal readers!

THERE GOES THE NEIGHBORHOOD

I went out today tto find that the rear window in my van had beed bashed in with a brick.  It must havew been a good heave, because  found the brick up by the front seats.  Nothing was taken.  It must have been the local yoots. Maybe the ones I challenged when they walked 6 abreast in the middle of the road.  Mayve it's time to move and put the house up for section 8 housing.

One side of my car was keyed too.  I tghink a gated community would be good.  A "vibrant" neighborhood means crime.

SPORTS

I went to a local sports bar for fish dinner Friday night.  In the Toledo area we have a channel, Buckeye Cable Sports Network devoted to localsports of all sorts.  I watched Whitmer and  Toledo Central Catholic play.  I noted that the parochial schools and the non Toledo Public Schools bring  a lot more fans.  At some of the TPS games there arent enough people to start a fight, and when there are fights, its the black girls who are fighting.  My daughter went to Start HS, about 1600 students and sometimes they have fewer fans in the seats for a football game than my old school with less than 400 students.

The boys are much more athletic than in my day, but less disciplined on offense.  They are better conditioined, too, as some teams play full court press for the whole game.

I watched the highlights of the Waite and Start girls BB game.  Girls basketball today looks like the game we played when I was a yoot:  lots of passes and jump shots, and rebounds close to the basket and well below the rim

My daughter Sarah played broomball, a big girls sport here.  She was the league leading scorer and her team, the Start Chaos, were champions her senior year.  Here is a picture of her with Lauren Szyzmanski and Samatha Bauman. Sarah is on the left.  She has her mom's megawatt smile.  as she gets older she looks more like her mom.

here is one from the prom

The other girls are her best friends Ella Rywalski and Meredith Shalda

And here you thought I could only talk about poo.

GRAVITY THICKENER OPERATION

Gravity thickeneers can be a useful and easy to operate piece of equiment.  However, there are many who do not operate it properly.  This includes the engineers who wrotde the chapter on gravity thickening in the soon to be published EPA solids handling manual.  If you do not operat it properly, you will have poor performance and a smelly putrid mess.

Here is what is important:

Gravity thicvkening depends upon compressive settling. that is, you allow a sludge blanet to form so the the weight of the blanket above presses water out of the sludge on the bottom.  The sludge collectors have vertical bars, or pickets on theem to stir the blanket a bit and release watger and gas from the blanket.  If the blanket gets septic, you will have lots of gas and scum poor performance and a big stink.

How to optimize thickener operation

• Pump lots of thin fresh sludge.  Your primary clarifier should ave a ZERO blanket.  Yes, it should.  This keeps the sludge fresh and promotes fast settling in the thickener.  I taught this co9ncept to PSG at the old New Bedford MA plant and the assistant supt. said that they imrpooved primary clarifier removals by 30%.
• Your surrface overgflow rate should be 400-800 gpd/sf  sometimes you can go higher
• Use plenty of dilution water to keep the overflow rate up where it belongs.  dilution water should be secondary or final effluent
• If you arer thickening primary sludge your solids loading rate can be up to 15 Lbs/day/sf
• If you are thickening WAS it should be no more than 8 Lbs/day/sf and a rate of 4 Lbs/day/sf is better.  Even lower can be better.
• Draw sludge out on a regular basis.  Put the underflow pump on a timer.  If you have fancy monitoring equipment, you can have the underflow pump shit off when the density meter says the sludge is thin.
• Check your blanket and maintain what works best.
• If you thicken cosettled primary and WAS, treat it as WAS for the purpose of solids loading

That waswn't so difficult, was it?

OPERATOR FOLLIES #5

Many  years ago I was working on a start up when I sent into the laboratory and saw two operators smoking dope under the big air intake in the center of the room.  I said  "Jeez guys, all the places you have here to fuck off and youo choose the lab?  They were good operators, though, all of them.  One of the men liked to have a real good time and one night at a party he had a little too much and kinda dozed off.  While he was not paying attention a woman painted his nails and wrfote "I Love You" on the back of his neck.  His wife was not amused

The Fabulous Thunderbirds have a song for occasions like this, called "Amnesia"  I'll try to fnd it on You Tube.

I found it.  The guitarist is JImmie Vaughn, brother of Stevie Ray

She said I went and took back my ring

I don't remember a doggone thing

ANDREW SCISSON 6 MONTH MEMORIAL

I know you are all tired of vechnaya pamyat, so here is another hymn, done in byzantine style.  The skeleton images are not orthodox but the muxic is beautiful and correct.

Thid is byzantine chant, wich is always acapella.  takes you back to Constantinople before the filthy turks overran it.

Here is a photo of Andrew and I

BIX BEIDERRBECKE AND ANDREW SCISSON

I was listening to Bix Beiderbecke's "In a Mist" last night and thought of my son.  It made mme very sad that he is not here now, and that he missed so much in life, and that the courts took him from me to be poisoned by his mother and then gave him back when I could do nothing despite all me trying.

Who is Bix Beiderbecke?  A cornet player and pianist in the 20's a seminal figure in jazz.  Mostly known as a cornet player, he also composed several very modern sounding piano pieces including "In the Dark", :Candlelight" and "Flashes".  They are all on YouTube if you wan to listen to them.  I have "In a Mist" here.  I think it sounds better played slower, but I am putting the original 78 rpm recording here

WET WEATHER OPERATION - KEEPING YOUR CLARIFIER CLEAR

I have worked at numerous plants that have big flow increases during wet weather operation and have learned by trial ,error and observation how do deal with rainy weather.

The key to good wet weather operation is simple.  YOU NEED TO KEEP THE SURFACE RISE RATE (in feet per hour) SLOWER THAN THE SLUDGE SETTLING RATE. What is the surface rise rate? Its the rate, in feet/hr that water fills the tank if it were empty and the flow is x MGD If the flow doubles, the rise rate doubles.

What is the sludge settling rate?  Take you r settleomeeter and run a settling test.  Take the readings EVERY 30 SECONDS for 10 minutes or so.  Plot the readings on graph paper or on your computer if you can stop watching that internet porn.  The part of the graph that is a straight line is you sludge settling rate.  This is the settling rate when the sludge is not hindered by other particles.

To keep your sludge in the plant durng a storm, you have to either decrease the sludge rise rate (put more tanks on line), or make the sludge settle faaster (yes you can)

I will divide this post into 2 sections:

• Physical plant additions and alterations, and
• Things the plant staff can do themselves, instead of whining about it

Plant Additions and Alterations
The keys to good settling at high flows is, in addition to a good settling sludge, are QUIESCENCE,  DILUTION OF THE MIXED LIQUOR, AND REDUCING CURRENTS/SHORT CIRCUITING

What is quiescence?
Quiescence is quietness, of a non turbulent area in the clarifier where the activated sludge floc can coagulate and begin to settle.  The best way to improve quiescence is to have better clarifiers.  The best clarifiers are peripheral feed-peripheral overflow (PFPO) clarifers.  I discussed this in a previous posting.  PFPO clarifiers have 10 times the quiescent zone that a center feed clarifier does. It is possible to convert center feed clarifiers to PFPO clarifiers.  I'd be glad to help you.
Rectangularr clarifiers also perform well at high flows, according to John Esler, clarifier expert.  The clarifers have to be built a certain way with 2 effluent launders that are parallel to the long sides, influent baffling, and co-current sludge removal (Gould Types 1 and 2).
Extra clarifiers are good insurance for that rainy day. Why is that?  BECAUSE YOU NEED TO KEEP THE SURFACE RISE RATE (in feet per hour) SLOWER THAN THE SLUDGE SETTLING RATE. 

Diluting the Mixed Liquor

Why is diluting the mixed liquor good?

Because it lets you improve the settling rate

Secondary clarifiers can become solids limited - that is, you can push more solids into the clarifier than can settle.  There are  various ways of  diluting the mixed liquor, including step-feed, contct stabilization and RAS adjustment

If you have multiple aeration tanks you can convert your system to step feed or contact stabilization.  Since most plants have the influent agt one end and the clarifier at the other end, your system can be converted to 3-pass, 5-pass or 7-pass , etc.

Going to for example, a 3-pass step feed parks some the the mixed liquor in tanks one and 2, for instance and feeds some of the influent into pass 3, diluting the mixed liquor and lowering the solids loading rate to the clarifier

Step feed conversion can be done by your engineer, or you can do it yourself.  If you want some help, call me.  n Carey, OH, Doug Keller, Roy Johnson and staff did this as a DIY after I suggested it.  They had 5 tanks of 2 different sized and a problem with short circuiting and flow spliting.  They rented a concrete say and cut holes in the tanks to make them plug flow.  The also had to instaqll a submersible pump and a float switch because 2 of their tanks were detache3d from the other 3.  Total cost?  $9000 plus their labor.  The results?  Well worth the money.

Another good example of how step feed can be effective is Bowling Green.  I redesigned their system from 4, 1-pass tanks to 2. 3-pass tanks.  After the conversion, they were still having problems with clarifier performance at high flow.  They were finally persuaded to try step feed.  The results?  They went from a secondary efflulent TSS of 200 mg/L at 20 MGD to 20 mg/L at 24 MGD.  I know some of you out ther are not impressed and will keep doing it the same old way.

Here are some things that operators can do without much effort and keep playing internet poker.

Adjust the RAS Rate

Adjusting the RAS rate will change the solids loading rate and reduce clarifioer turbulence.  I leaned this lesson long ago as a Chief Operator at Bloomington IN, a 15 MGD AWT plant.  (See I did have a real supervisors job at one time).  We began there when it was a brand new plant.  Control the RAS as a fixed percentage of gthe influent flow.  When we had our firstg real big rain, we kept turning the RAS up until we turned the clarifiers into mixed liquor.  My good friend and co-worker, Bill Bardes, suggested that we reduce gthe RAS frlow since turning it up didn't work so well.  We figured out what to do by trial and error, and kept the sludge in the clarifier even at maximum flow.  This trick has worked for me at several places.

I know there are some famous consultants who poo-poo this, and say that RAS has nothng to do with the solids loading rate, but I say  I'm right, you're wrong and that's that.

Put Extra Tanks on Line

Putting extra tanks on line will give you some breathing space whille they are filling up and will dilute the MLSS

Reducing Aeration Tank Airflow

Reducing aeration tank air flow will promote good flocculation and rapid settling.  You dont need to have a DO of 10 mg/L.  Cut your air flow to the recommended minimum.


Follow these suggestions and your plant will work better.

MY DOG

I don't have a picture of my dog Taylor, but this is a good facsimilie.

How can anyone not like a dog like this?  Gary Goldberg said my traffic would increase if I put kittens on my blog:  there are limits.  So here is a lab.  Taylor has never seen food she woudn't eat except uncooked vegetables   She also eats sausage casings and butter paper and bread wrappers.  I love her.

800 PAGE VIEWS!

Thank you loyal readers.  more articles to come

NEW SERIES ON WET WEATHER OPERATION

My next series will be on how to improve your wet weather operation.  And you thought all I could was sludge.  I have lots of practical experience.  Some people are scared.

OPERATOR FOLLIES #4

Years ago a digester sludge recirculation pump quit working.  One operator said  "Don't blame me I haven't been in that room for 6 months"

Automation is looking better all the time

RUSSIANS!

I see I have a lot of page views from Russia!  Well, dobre dyen gospodin and gasperzha.  Send me an email,  I don't read cyrillic or Russian, just a little bit of Church Slavonic  because I'm pravoslavnie.  I'll be glad to talk to you.

MUSICAL INTERLUDE #10

Here is one from my misspent youth  The Fabulous Thunderbirds and "Can't Tear it up Enuff"

This reminds me of when Bob King and I would get out at lunch, go to the ice house, pick up sausage sandwiches and beer, and go to the San Antonio river below the Rillling Rd WWTP and listen to the Fabulous Thunderbirds and watch the Mexicans swim in the San Antonio River.  at that point at least 85% of the River flow was WWTP effluent.

Why is it that bosses are so uptight about having a drinkie or two at lunch these days.  The personnel department is turning bosses into neo-prohibitionists.  So come and have a beer with me.

DEWATERING FOR BIG AND SMALL

Here is my long-awaited post on dewatering.

To paraphrase Alfred P Sloan, former head of Government Motors, there are dewatering devices "for every purse and purpose"  There are dewatering devices that are useful at package plants, and others that are useful at plants as big as 1 BGD (billion gallons per day).  Lets look at some.

I have yet to receive any figures for vendors.  I will do what I can.


GEOTUBES

A geotube is a special material that passes free water and leaves the solids behind.  It is a tube (go figure) most often used to dewater silt from lagoons and as an erosion barrier, but it has sludge dewatering uses too.  The tube is closed at both ends.

Sludge is pumped to the tube.  polymer is injected just before entering the tube.  The polymer coagulates the solids and separates them from the water.  free water drains through the tube.  Sludge is pumped in until the tube is full.  Water continues to drain away.  When drainage is complete, further dewatering occurs by leaving the tube at the site for dewatering by evaporation.  At some sites geotubes are stacked together for air drying.
When it is time to remove the sludge the tube is slit and the dewatered sludge removed by a front end loader.  In some cases the tube is placed in a roll-off container prior to use and the sludge, tube and all taken away to a landfill.

The dewatered sludge can be landfilled or land applied.  Most of the material is landfilled.  Cake solids range from mid teens to mid 20s percent. 
The advantages of geotubes are that they are

• relatively inexpensive
• can be used at small, medium and large sized plants
• are easy to use

They are a bit labor intensive for sludge removal and cake solids can be limited.  Collecting all the run off water can be a problem and the EPA does not want this water flowing into the waters of the state.
My friend Doug Brookhart likes these for small and package plants and says that they have been a godsend at some places.

IMPROVED SAND DRYING BED TECHNIQUES

Although sand drying beds are severely limited by the weather, a few simple and inexpensive improvement, and a different operating technique (free) can increase greatly the number of times the bed can be cycled. These improvements and techniques are:

Stir up the Sand Before Each Pour

Drying beds remove water by percolation (drainage) and evaporation. Percolation is rapid. Evaporation is slow and absolutely not controlled by the operator. Increasing percolation greatly speeds up sludge drying.

Stirring the drying bed before pouring a bed :

• Breaks up any crusts in the sand that would blind the bed
• Fluffs up the bed. This increases air voids in the sand, which increases the filtration rate

If the maintenance man or someone at the city garage is handy, a rake that will fit on the forks or toothed bucket of a tractor or bobcat loader that will rake the sand to a depth of 1-2 feet can be made from scrap. The tines should be 2-3 inches apart

Pour Shallow Beds

Evaporation only occurs at sludge surfaces. Sludge in the middle of the pour does not dry until air reaches it when the sludge cracks. The sooner air can get to the sludge the quicker it can dry. By pouring a shallow (10 inch) bed, the bed will crack sooner and allow all the sludge to dry.

Take it Out Wet if You Must. That’s Why Those Concrete Strips are in the Bed

Today’s drying beds usually have concrete strips for the tractor or bobcat tires so the bed can be mechanically cleaned. The operator is not shoveling the wet sludge into a wheelbarrow as in the bad old days. The wet sludge can be stockpiled, and the bed fluffed up with a rake

Don’t Be Afraid to Take Out Some Sand

Some operators wait until the sludge is very dry to avoid losing sand. DRYING BED SAND COSTS $10/TON (ABOUT $27/CUBIC YARD). Get the sludge off the bed and put on some new sand. Sand is cheap.

How Well Does It Work?

These small improvements work quite well, At a small plant in northeast Indiana aerobically digested sludge at about 1.5% TS is poured onto a prepared bed about 10” deep. The sludge will crack within 4 days if the weather is dry.

WEDGEWIRE BEDS

Wedgewire beds are made of plastic tiles with small slotted openings (figure 1). Sludge, conditioned with polymer is poured onto the beds. The polymer binds the sludge solids together, releasing free water, which drains through the tiles. When the bed is full, the sludge is left to set for a few days to continue dewatering. The dried sludge is taken off the tiles with a small tractor and taken to a stockpile. The cake solids depend on the sludge, but range from 15-22% TS.

The beds can be loaded at 2 lbs/sq.ft. for aerobically digested sludge, and 4 lbs/sq. ft. for anaerobically digested sludge.

The drying beds come as a package and include the tiles, a lightweight building to cover the beds (sometimes the building is translucent to speed drying), and a polymer makeup and dosing system. The beds are priced at $50-55/square foot, plus $7500 for the polymer feed system.

The advantages of wedgewire beds are:

• Simple technology. Not much can go wrong.
• Easy to size, price and engineer
• Fair to good solids capture.
• Relatively inexpensive to build. NOTE: the cost depends upon how often the beds are to be cleaned. For example, if the beds are sized to be used twice/week, the cost is about half that of beds sized to be cleaned once/week
• Cake that can be handled with a tractor and a bucket. NOTE: bobcat loaders are not recommended, as the steering system of braking the back wheels is too stressful for the tiles and tends to pop them out

The disadvantages of the wedgewire beds are:

Polymer costs may be high

• Labor intensive. The superintendent at Ada Ohio estimates that is takes 8 man-hours to pour and clean a 70’ x 20’ bed that dewaters 20,000 gallons of sludge for each pour. (But at Upper Sandusky, OH, it only takes 4 hours).

LIGHT DUTY BELT PRESS

The light duty belt press is a one-belt press with an extended gravity zone and one or two nip rollers to provide the pressure for dewatering (figure 3). The units are generally sold skid mounted and ready to operate with a polymer system, flocculation tank, sludge feed pump, washwater pump, sludge conveyor or cake pump and a control panel. 

The press will produce cake solids at 14-21% TS depending upon the type of sludge dewatered. Anaerobically digested sludge generally dewaters to higher cake solids content, but may not be as easy to handle in the field.

The advantages of a light-duty belt press are:

• Comes ready to use. No assembly required except connection to sludge, water and power
• Modest capital cost ($80,000 for 1.5 meter unit and 33 gpm capacity)
• Easy to use. NOT labor intensive
• Compact: Can fit in a space of a 1-car garage.
• Good cake solids: 13-21% depending upon the sludge
• Good solids capture
• Fair polymer consumption

The disadvantages of a light-duty belt press are:

• Higher capital cost, especially when the building cost is added in
• Noisy
• Lower cake solids that a 2-belt filter press
• Low output: about 33 gpm for 1.5-meter unit (One manufacturer has a unit with a drum pre-thickener ahead of the gravity drainage zone who claims an output of 100 gpm, but there are not many of these units sold).

REGULAR (2 BELT) BELT PRESSES

A regular belt press has 2 belts and come in widths ranging from 0.5 mdters to 3 meters.  It is possible to get these machines skid mounted, with the machine, polymer system, control panel and sludge feed pump on one skid.  The most common size is the 2.2 meter width.  Machine throughput ranges from 50 gpm to 300 gpm through these size ranges.  Throughput for the common 2.2 meter machine can range from 50 gpm to 180 gpm depending upon sludge type, condition and operator philosophy.

Belt press cake solids depend upon the type of sludge dewatered.  Aerobically digested sludges will range from 14-22%  Anaerobically digested sludge ranges from 18 to 30%, and raw sludge ranges from 20 to 32%

The advantages of a belt press are:

• Moderate price and fair ot good cake solids
• lower polymer dose
• easy to clean
• the operator can watch the sludge on the machine and make adjustments based on his observations
• relatively low maintenance requirements and costs
• low power costs

The disadvantages of the belt press are:

•  Odors, especially with anaerobically digested sludge and raw sludge.  Sometimes the machine is completely enclosed due to odors.
• Cake solids are not as high as a centrifuge
• High water rrequirements 
• Operators tend to turn down the sludge flow and turn up the polymer so they don't have to do as much work I have over 20 years experience observing this so don't complain that I am a meanie

SCREW PRESSES

A screw press is usually an auger inside a taperd screen.  sludge mixed iwth polymer is fed into the machine.  As the sludge passes thru the machinewater drains out through the screen.  The screen's taper provides osme pressure to aid dewatering.  This type of machine is very common for dewatering cow manure, both raw and digested, and works well bacause there is much undigested vegetable matter to provide structure and prevent solids from leading out through the screen.  New polymers called cross linked polymers have allowed these machines to be used for municipal sludges.

The advantages of these machines are

• Moderate equipment cost
• Low operator attention
• cake solids comparable to a belt press
• no washwater required
• less odor than a belt press
• Low power requirements

The disadvantgages are:

• lower throughputs than some othr methods
• higher polymer cost than a belt press, about double the cost

North Baltimore has a type of screw press if you want to go look at one


ROTARY PRESS

Rotary presses are interesting to my feeble mind.  They are sort of a cross bwtween a hose pump and a screw press and a geotube.The press is hose that allows water to pass.  The hose is wrapped in a u-shape sround a cam.  Sludge and polymer are pumped into the machine.  The can revolves slowly, pressing sludge into the hose, and flushing water out of the sludge and moving it through the hose, where it is discharged at the end

Photo Thanks to Fournier

These presses are getting popular, especially beause the manufaturers have convinced owners that they can be run unattended 24 hrs/day

The advantages of this machine are

• Fair to great cake solds.   great for ATAD and primary sludge, about like a belt press fro WAS and aerobically digested sludge
• Low power requirements
• quiet
• Low maintenance
• Medium polymer requirements
• Can be run round the clock without attention

the disadvantages are

• Low throughput/dollar cost
• Each channel can dewater about 50 gpm For large plants the presses canbe ganged, but the equipment costs are high

CENTRIFUGES

A centrifuge is a spinning cylindrical bowl that uses centrifugal force to separate water and solids.  Sludege mixed with polymer is injected into the bowl.  The solids migrate to the outside, where they are removes by a screw called a scroll.  The liquid passes through a weir and leave the bowl.

The centrifuge is the machine to have if maximum cake solids is important.  Centrifuge cake solids will be 5-10% drier than a belt press. The centrifuge has several advantages over other mahcines, including

• The driest cake solids
• No odors or aerosols
• unattended operation,including start-up and shutdown
• vey good solids capture, up to 99.5% (this may require and excessive polymer dose)

And of course some disadvantages

• Higher capital cost
• Polymer dose 150-200% of a belt press, but equal to some other forms of dewatering
• Noise - the machines rotate at 2000+ rpm
• Very high wear when dewatering gritty sludge
• For some applications, like lime stabilization and multiple hearth furnace operation, it is possible to get the sludge too dry unless the operator watches the process.

CONCLUSION

I suppose I should make up a table  I'llge tto that later

Which type of dewatering device is best for you?  It all depends upon the type of sludge you have, how much money you  have and how dry you deen it to be and how often you have to (want to) dewater.

Musical interlude #9

My dewatering post is delayed due to vendors who promised to send me images did not.  Go figure.  The post will be on line Monday.  Meanwhile, some more music from The Band.  This will be a favorite of the men. 

700 PAGE VIEWS

Thanks, loyal readers.  guess I better finish that dewatering series.  I'm having trouboe finding jpeg images.  If you want you can send me some at jscisson@aol.com

COMING UP

A new posting on dewatering.  Meanwhile read my existing articles

600 PAGE VIEWS

My traffic is picking up.  Thank you, loyal readers!

MUSICAL INTERLUDE #8

This song has been a favorite of mine for over 35 years.  I hope you like it too.  The horn section really makes it good.  It's ovedue on this site

If my heart was made of glass, you could surely see......

THE DOG ATE MY HOMEWORK

W while back I interviewed for a job with a private operating company around Bedford OH.  They made the owner's ancestral home into an office, lab and storage space.  Pretty neat.

We talked and then they asked me to fill out an application, but hey, they didn't have an appllication, so they were going to mail it to me.  It never arrived.  What a scummy trick.  I'll have to remember that one for when I become a manager.

500 PAGE VIEWS

I am now over 500 page views.  Thank you mty loyal readers and keep  reading!

A SELECTION NOT A BID

Engineers and their customers often get hung up on bidding everything, and are suspicious of sole sources (selections) as being unethical, or unfair, or something.  I will show you today that in the case of blowers, the energy considerations are so great that you should almost always select the most efficient blower.

Back in 2007 I was redesigning the aeration system for Monroe MI.  They had 3, 1000-hp blowers with synchronous motors, and were using 700-some horsepower to run the system.  They had canvas sock diffusers (aka elephant prophylactics).  they even had a washing machine with which to clean them.  I redesigned the sysgtem with efficient fine bubble diffusers and new, smaller blowers,  I simulated the variations in air flow for a typical day, and asked blower manufacturers to give me shaft horsepower at the various points.  I then calculated the energy use and cost of the year 2007 and the year 2027.  The results are below. 

COST COMPARISION OF VARIOUS BLOWERS, $/YEAR PER SIMULATION

	Spencer 6000	Spencer 7000	Hoffman 7000	Hoffman 8000	National Turbine	Turblex KA10 single point 7500	Turblex KA10 dual point	Turblex 8550 KA10 single pt
2007	108424	108424	98418	104491	111112	82040	74572	79321
2027	123010	129183	108026	115891	127739	96726	89999	94126
delta from lowest
Year 2007	-29103	-29103	-19097	-25170	-31791	-2719	4749	0
Year 2027	-28884	-35057	-13900	-21765	-33613	-2600	4127	0
Average	-28994	-32080	-16499	-23468	-32702	-2659	4438	0
mulltistage only 2007	-10006	-10006	0	-6073	-12694
2027	-14984	-21157	0	-7865	-19713
average	-12495	-15582	0	-6969	-16204

shows that there is a considerable difference in energy cost between the most efficient and least efficient machines.  The single impeller machnes were more efficient.  I selected the second most efficient blower, because the outlet diffusers and the computer algorithm needed to operate them cost an additional $43,000/machine, which pushed the payback for the additional cost from 5 years to  15 years or so, and I thought that was too long (Private industry always wants a payback in 1 year).  The difference between the most and least efficient machin was over $30,000/year, or $600,000 in 2007 dollars and no increase in the cost of electricity. Vendors, don't complain because these are the data you gave to me.  Even among the multistage machines, there was a considerable difference in energy costs over a 20 or 30 year equipment life, would far outstrip the diffence in machine costs at bid time.

The lesson is:  You, the engineer or customer, should give the manufacturer a typical daily air flow variation  at your plant, and ask him to give you shaft horsepower at each flow point, and then select the most or 2nd most efficient machine and have it sole-sourced. You will save a lot of money for the customer.

How did the job work out?  Monroe reduced it electric bills by $50,000/month.

This same exersize works for diffusers, too.  You are better off to buy more diffusers and use less air than to cheap out with the least expensive diffuser layout.  I'll try to make a presentation on that later.

Now, If I can do this calculation, some of you superintendents should be able to do it too.  After all, superintendents in Wood and Lucas counties feel that I am too dumb to be an operator it can't be alll that diffucult.