ANOTHER MUSICAL INTERLUDE

I dont know how many of you remember the Beach Boys song "Heroes and Villains"  It was produced in the studio with lots of separate tracks melded together.  Here is a group, the Fendertones, who do it perfectly, live, with no overdubs.  Amazing

COMMENTS

To all my loyal fans:  Feel free to leave a comment, even to say hi

COMMENTS

Visitiors, don't be shy about leaving a comment, even just to say HI!

THE COST OF HAULING WATER, PART 2

Last time I looked at the cost of hauling liquid sludge.  This time I will look at hauling cake.

The table below shows the cost of hauling cake at $25 and $20 per wet ton.

TABLE 1
THE COST OF HAULING CAKE

CAKE SOLIDS	TONS WATER/TON SOLIDS	COST/DRY TON @ $25/WET TON	COST/DRY TON@ $20/WET TON
15%	5.6	$166	$133
20%	4	$125	$100
25%	3	$100	$80
30%	2.3	$83	$67
35%	1.8	$71	$57

You can see from this table and then comparing cake vs. liquid hauling costs that:

• cake hauling is less expensive than liquid hauling until you get the liquid solids up to 6% or more
• if liquid hauling is more expensive than 3 cents/gallon, cake hauling will be cheaper at any concentration
• You save a lot of money getting the cake colilds from 15% or 20%, but not so much from 30/5 to 35%

So, what keeps you from switching over to cake solids immediately?  The cost of the dewatering equipment.   I wont't go into the actual costs herede but you will need:

• The dewatering machine
• A polymer feed system
• A building for the dewaterng maching
• A conveyor
• A cake storage pad, preferably a COVERED storage pad
• A front end loader if you don't already have one to load the cake
• Utilities to the building.
• A mechanism to get the cake to the storage pad, either a conveyor (preferred) or a dump truck ( not preferred)
• If you are DIY on sludge hauling, you will need 30 cubic yard dump trailer(s) or lots of dump trucks.

You will have to do your own arithmetic.  Cake hauling prices range from less than $15/wet ton to over $25/wet ton depending upon location and competition

What kind of dewatering device?  Thats a whole other lecture.  Centrifuges make the dryest cake but may not be the most cost effective for you.  Rotary presses do well on some sludges and have some advantages on water use, odor and noise. Belt presses are less expensive than centrifuges, but the cake is usually wetter.  For the smallest operations, simple geotubes work best.  Hire me and I'l help you figure it out.

THE COST OF HAULING WATER

If you haul sludge, liquid or cake, increasing sludge solids before hauling can save you a lot of money.  For example, one ton of sludge at 2% solids is 2000 Lbs of solids and 98,000 Lbs of WATER.  If you thicken it to 4%, now you still have 2,000 Lbs of solids, but only 48,000 pounds of water.  If you are paying by the gallon, you just cut your bill 50%.

I'll show the effect of thickening on your hauling bill here.  Assume that hauling cost $0.03/gallon

COST OF HAULING ONE DRY TON OF SLUDGE VS SLUDGE CONCENTRATION

Total Solids	Pounds Water	Gallons	Cost per Dry Ton
2%	98,000	11,990	$359
4%	48,000	5,995	$180
6%	31,333	3,996	$120
8%	23,000	2,997	$90

Hauling at 2% is pricey, isn't it?  If you land applied 200 dry tons at 6% instead of 2% you would save $48,000 in hauling cost.

How can you improve your solid concentration?  You can supernate caefully, and often to improve solids concentration.  You can have a dedicated storage tank for concentrating solids.  You can buy a thickener, and thicken the solids prior to land application.  I always wondered why consultants never recommeded small dedicated storage tanks and then a gravity belt thickener to jack the solids up to 8% solids just prior to hauling.  It make a lot of sense. 

MUSICAL INTERLUDE

Ever have songs that just go through your head?  Here is one of mine.  Here it's sung by a group called Harmony Grass. You can also find versions by the Four Freshmen, Spanky & Our Gang, and a Filipino group called the Bloomfields.  Note the dated references to Northwest Orient, DeGaulle and the Coconut Grove, and that you could get jailed in France for making fun of Degaulle.  He did have an extrordinarly large honker.

OPERATOR FOLLIES

A nice plant in  Ohio got their DC motor sludge feed pump motors wet after a storm.  The pump stateion had a poser outage and the sump pumps did not work, allowing water for the extensive basement to flow to the lowest point in the building.  The storm was on Friday.  The wet pumps were discovered on Monday morning.  The plant is staffed 24/7 by operators, including weekends.  I do not know the work schedule, but I assume that the operator makes rounds twice an 8-hour shift.  How could such a thing happen? At least 3 different men have to not go to the basement over the course of 7 shifts.

Automation sounds like a good idea..

PERIPHERAL FEED VS. CENTER FEED CLARIFIERS

You may know that I have been a big fan of peripheral feed clarifiers for many years.  Why?  Can you say 10 mg/L TSS at an SOR of 2000 gpd/sf?  Thats double the 10 states standards flow limits.

How do peripheral feed and center feed differ?   Let’s look at a cutaway of a center feed clarifier.  

 (Image from Westech)

At peak flows under 10 states standards, the MLSS and RAS flows upward in the column at abougt 3 fr/sec (fps).   It exits the ports at about the same velocity.  The velocity in the flocculation chamber is about 0.19 fps, and the detention time is about 1.1 minutes.

When the flow exits the center column, it hits the flocculation basin walls and has nowhere to go but DOWN, creating a current called the waterfall effect.   The waterfall can disrupt the sludge blanket.  The current then flows along the bottom till it gets close to the weirs, where it rises,  This current will pull solids along with it and degrade clarifier performance.

Now lets look at a peripheral feed clarifier 

(Figure taken from SIEMENS, thanks)

Mixed lliquor enters the tank through an outer raceway (1), which circles the tank.  Flow drops through the floor through a tube .  The velocity through this tube at peak 10 state standards flow is 0.50 fps.  The area just below the raceways has a target baffle (8) and a skirt baffle (9).  The target baffle breaks up the current from the drop pipe.  The skirt baffle provides a large flocculation zone that is an analogue to the center feed flocculation basin.  The sludge velocity behind the skirt baffle is 0.018 fps, or 1/10 that of the center feed tank. The detention time is 83 minutes as opposed to 1.1 minute

After leaving the flocculation zone, the current pushes the sludge to the center of the tank, the clarified water loops back and leave the tank by the effluent raceway adjacent the influent raceway

There are 3 keys as to why peripheral feed tanks are better:

1. They provide less turbulent conditions.  Good gravity settling means getting rid of turbulence, and allowing the flow to form.  Violent conditions shear the floc and slow down settling
2. The long flow path essentially doubles the water’s travel path from inlet to outlet, reducing short circuiting and providing more settling time.
3. The flow path takes the sludge blanket away from the effluent launder and towards the center of the tank.  This is the reason why these tanks perform s well at high flows; the blanket is being pushed AWAY from the launder, not TOWARDS it.

OTHER GOOD THINGS ABOUT PFPO CLARIFIERS

Head loss and flow splitting

PFPO clarifiers have a significant advantage in headloss due to the lack of the center feed pipe.  The reduction in head loss has advantages in elevation. flow capacity and gives youhead to burn for good flow splitting.

Next, flow splitting.  With the peripheral feed, mixed liquor can flow from the aeration tank to the clarifier through an open channel, wheich can be an advantage.  If you are using a diamond shaped flow splitter for 4 tanks, the splitter can be made simpler and closer to the tanks.  Another advantage is with tanks in a line.  I remember she Ohio EPA "SWAT" team using their fancy fluorometer (which my employers would never buy me) to demonstrate problems with flow spitting in recgtagular tanks in a line.  They were able to improve flow splitting by using  (I swear to God) pieces of shingles to add headloss to the clarifie inlets to improve flow splitting,  With a PFPO clarifier, you can put in a weir or a flume and measure the flow, and add an up-to-close weir gates to adjust flow to each tank.  WARNING! Do not allow too many people the ability to adjust the flow to individual clarifiers, or write a computer program to do it, because overadjustment leads to instability and poor performance.  The ability to adjust the gates can lead to "fingeritis", a sin of which the Author (that's me) has been guilty in the past.  It's best to adjust the gates so the flow splits are pretty good most of the time rather than seek perfection.

OTHER ADVANTAGES

Other advantages of the PFPO clarifier are reduced construction costs, and the sheer elegance of the design.  Whats's wrong with elegance?

I have never figured out why more engineers don’t build these tanks.  The Chinese have standardized on them.  After all, one billion chinese can't be wrong.

I want to thank ED ROGOZINSKI for the data on center feed clarifiers.  May god bless you and your sons.  and now, for Ed  a little musical interlude.