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Sludge Management Programs Utilizing Geotextile Dewatering Technology

Smaller sized municipal waste treatment plants face many difficulties when developing their sludge management procedures. Limited capital availability as well as space limitations prevent these plants from utilizing mechanical sludge dewatering processes such as gravity bed filter presses or screw presses. This leaves the plant with the option of either putting in storage facilities and developing land application programs or utilizing sand drying beds to dewater the sludge. Land application is expensive and involves time consuming record keeping. Most land application programs also require costly testing of both the sludge being land applied and ground samples of the crop land after application. In many cases the application operations are held up by crop growing cycles or weather related delays. The process of continually thickening the sludge to overcome these delays can have a adverse effect of the operation of the plant.

Sand drying beds are also very dependent on weather and removal of sludge from the beds can become a difficult and labor intensive process. Mechanical removal of the dewatered sludge can become an expensive task that requires man hours that are limited in most small waste treatment plants.

Blue River Technologies offers an alternative to these options. Geotextile Dewatering Bags are polypropylene filtration bags that are used to separate solids from water. The bags are produced in a wide range of sizes and micron meshes. The utilization of these filter bags can significantly reduce the costs related to a small municipal waste treatment plants sludge management program. In addition the bags are available in small sizes that can be fit into a standard 20 or 30 yard landfill roll off container.

These bags can be placed out on existing sand drying beds. These tubes can significantly increase the capacity of a sand drying bed. Once full the bag is allowed to dewater completely. Other bags are used while the first bag is dewatering. When dewatered the bag is cut open and the sludge loaded out for land application or land fill disposal. This operation can now be done during ideal conditions. In addition the bag reduces odors and provides a solution for weather related problems. By coupling the use of the filtration bag with a standard land fill container the operator eliminates the manual labor required to load out and remove dewatered sludge to the landfill. The Geotextile Dewatering Technology offers small municipal waste treatment plants an economical alternative for the sludge management program. In addition the process requires much less manual labor than other systems.

Sludge Dewatering with Geotextile Container Bags Utilizing Geotextile Container Bags is a very efficient method for dewatering and disposing of bio-solids at a small waste treatment facility. Typical costs range from $.01 to $.04 cents per gallon depending on solids concentration. Capitol investment requirements are very low compared to other mechanical dewatering systems. The container bag fits into a standard 20 or 30 yard roll off. Sludge is pumped into the bag and the water separates from the solids and drains through the pores of the bag leaving 99% of the bio-solids in the bag. The bag pumping cycle is repeated over and over until the bag has reached its maximum capacity. This is usually around 12-15 tons of dewatered bio-solids. A flocculant is used to aid in the dewatering process and prevent “blinding” or plugging the pores of the bag. A complete Geotextile Dewatering System will include either a liquid or dry polymer mixing and injection package.

Setting up a Mobile Dewatering System Basic Components:

The Town of Mooreland, Indiana set up this Geotextile Dewatering System for their Waste Water Treatment Plant. The concrete pad is 20’ wide X 30’ in length. The pad slopes to the center where a drain returns the clean effluent back to the head works of the plant. The stand pipe at the right side of the picture comes from the digester of the plant. Another stand pipe located farther to the left allows the operator to pump from either of two lagoons as well. This plant chose to purchase a new roll off that is dedicated to their Sludge Management Program. The roll off is fitted with (4) 2” drains (two in each side). These drains help to rapidly drain the clean effluent as it flows from the bag. This also allow the operator to latch the rear door of the roll off completely shut.

The Dewatering bag is shipped as shown to the left. It is rolled in such a way as to facilitate placement into the roll off.

The drainage netting is shipped in one piece. Aluminum strips are used to securely attach the drainage netting to the sides of the container.

Slotted corrugate drain pipe is placed in the bottom of the roll off. This helps to hold the bag up and off of the steel floor of the roll off. This will allow the effluent to drain faster and more efficiently thru the bottom area of the bag.

The drainage netting will be placed over the slotted pipe and up the sides of the roll off. The netting will be secured with aluminum strips to keep the sides held up and out of the way as the bag is placed into the roll off. This will also help to keep the netting in place when the container is dumped at the landfill.

Place the Mobile dewatering bag at the front of the roll off. Pull the end of the bag up the front end of the roll off 2-3’. Roll out the bag. The fabric bag fill spout should be located in the center of the roll off. Position the bag so that the fill spout is near the center of the container and unfold the bag to it’s full size. Using the sewn in straps, tie the bag up, stopping at the middle to install the fill tube into the fabric spout.

At this point, your container should look like the one pictured above.

Insert the fill tube into the fabric bag snout. The coupling on the end of the tube is used to insure that the tube does not slip out of the bag during the fill cycle.

Pull the fabric over the 90 degree elbow of the fill tube. Wrap the fabric tightly around the fill tube and secure it with 3 heavy duty plastic cable ties. (Thomas&Betts L-28-120-0-L or Panduit PLT9H-LO ,28” Long, 120# Test) When the bag is full you will be able to cut the ties and pull the fill tube easily out of the fabric snout.

Use a 2 X 6 or 4 X 4 that is long enough to reach across your roll off to secure the fill tube up on a horizontal plane. Secure the fill tube and hose to this support and extend it out toward your mixing manifold. Tie up the remaining two straps and close the door of the container.

Your bag is now fully installed and ready to be pumped into. You can now move on to the next steps in setting up your container dewatering system.

The mixing manifold can be located as desired. The manifold shown has a duel discharge port.

The mixing manifold is constructed from Schd40 or Schd80 PVC pipe. They are available with cam lock fittings. The manifold has a slide valve at the inlet end to allow flow regulation. The polymer injection point includes a stainless steel injection quill and 1” check valve and cam lock fitting for the polymer line. The discharge end includes a 2” ball valve that is used to sample the sludge from time to time to check the flocculant conditions.

Attach the cam lock hose connections for the pump discharge line and the fill tube of the bag.

Attach the polymer injection hose to the cam lock fittings on the manifold and polymer injection pump.

This photo shows the flocculant preparation and injection system at the Mooreland Waste Water Treatment Plant. The Blue River Technologies Port-A-Poly mixing unit is located on the shelf. It will prepare a liquid polymer solution and pump it into the 300 gallon holding tank. This mixing system will make down the solution at a rate of 5gpm. It is capable of making a solution concentration level of from 0 to 1/2% (.005). This plant utilizes a sludge pump with an output of 50 gpm. The operator plans on wasting 5000 gallons of sludge per pumping session. He knows from experience that this will require 250-300 gallons of flocculant solution. He makes the liquid emulstion polymer down at a concentration of .2% (.002). He makes his polymer solution first thing in the morning and wastes in the afternoon. This allows the polymer solution to age for 2-4 hours before use and with that amount of aging time the solution has reached its maximum activity level. The injection pump (located on the pad next to the tank) will pump from 0-10 gallons per minute of prepared solution into the mixing manifold. The operator has learned from experience that a setting of 3 on the dial is a good place to begin pumping. He will adjust the pump speed to suit after the bag begins to fill.

When the sludge pump is turned on the operator switches on the flocculant injection pump. Sludge begins to fill the bag and polymer is injected into the line at the front of the mixing manifold. After about 2 minutes the operator takes a sample of the flocked sludge from the sample valve at the front of the manifold. He checks to determine the condition of the flocked sludge. The goal is to obtain large agglomerations or clumps of sludge that settle or separate from the water very quickly. There should be a minimum of fines visible in the clear water surrounding the flocked sludge. You may need to adjust the injection rate of the flocculant up or down to accommodate changing conditions of the pumped sludge. The solids content of the sludge will have the maximum impact on the requirement for polymer but other factors can also have an impact. Water temperature, hardness and pH can affect flocking conditions. Experience will allow you to quickly adjust your flock pump to obtain best results. Do not over floc as this will result in poor flocculation or residual polymer going through the bag.

The bag begins to fill, water can be sen flowing through the bag .

Clean effluent begins to flow from the side ports and out the back of the roll off. At this time check the effluent for excess polymer. A large excess may be evident by a milky white mixture mixed with the effluent. The polymer will be sticky and slick to the touch. Close your thumb and fore finger together and when separated a string of polymer may be seen. If this is evident turn the polymer pump down a little at a time. Each time you adjust the pump take a sample from the sampling valve to insure that proper flocculation is being obtained. With a little experience you will obtain good results very quickly. Use your flocculant supplier to assist you in maximizing the flocculation operation.

Clean effluent will continue to flow through the bag and out of the roll off as the bag is being pumped. A new bag will typically hold between 7500-15000 gallons depending on your pumping rate and solids content of the sludge. When the bag is pumped full you will shut down the pump and let the bag dewater before the next pumping session. The bag will deflate as the effluent drains off and after that the bag can be pumped back up again. It is obvious that as the bag is filled with solids the volume that can be pumped before the bag is full is reduced. Some plants utilize two roll offs and bags sitting next to each other. By switching back and forth between the two roll offs the plant is able to waste a larger volume in a shorter period of time. While every plant is different and results vary most plants will pump between 30,000 to 50,000 gallons of sludge into a bag before it will need to be replaced. Higher concentrations of solids in the sludge will lower the total gallons that you can put into a bag. Higher frequencies of pumping will also reduce the total gallons that a bag will dewater. A plant that only wastes 2000-3000 gallons of sludge per week will be able to obtain better dewatering rates than a plant that dewaters 5000-7500 gallons per week. Keeping your sludge concentration levels low will also produce better results with Geotextile Dewatering Bags.

This roll off is being filled with a pumping rate of 75 gpm. The clean effluent is pouring out of the back and sides of the roll off. Good flocculation procedures and chemical selection will produce excellent results.

Placing two roll offs side by side in the sand drying beds allows this plant to switch back and forth between the two bags. This gives each bag a longer period to dewater between pumping cycles and increases the efficiency of the dewatering operation.

The bag can be pumped until it is completely full. When the bag is full it will swell out and usually will extend up above the top of the roll off by a foot or two. The exterior of the bag will be drum tight and you may start to see little geysers of water start to shoot upward. This is the time to shut down the pump and allow the bag to dewater. Most dewater times should be 2-3 days to a week or more if possible. This will allow the sludge retained inside the bag to dewater until there is little or no free water left in the bag. This will free up as much space as possible in the bag for subsequent pumping cycles. When the bag is deemed full allow as many days as possible for the bag to dewater before removing the roll off to the land fill. Most land fills require the sludge in the bag to pass a standard paint filter test before dumping. This means that there will be no “free water” in the sludge. You can accelerate the dewatering cycle of the bag by adding weight to the top of the bag during the last one or two pumping cycles.

Method 9095A PAINT FILTER LIQUIDS TEST

Land fill regulations require that the bio-solids that are accepted must pass the standard “Method 9095A Paint Filter Liquids Test”. This test is used to determine the presence of free liquids in the waste contained in the Container Bag. You can perform this test easily with a minimum of equipment if you want to insure that the biosolids you are sending to the landfill will conform to the standard. Most land fill operators will not require the test be performed on every load. Once you have established your operational procedures you will not need to pull samples to be sure that you are meeting the minimum requirements of your landfill. You can obtain a sample of the dewatered sludge from the fabric fill port of the bag. After removing the fill tube, use a soil sample auger to obtain a column of sludge from the center of the bag. Remove a 100mL or 100-g representative sample and place it in the filter as shown on the picture on the right. A 1000mL glass beaker makes a very good container for this test. Allow the sample to remain in the paint filter for 5 minutes. No free liquid should be evident in the beaker after this period. The paint filters can be obtained from local paint supply houses such as Sherwin Williams or Glidden. Use the fine meshed size (Mesh number 60). If your paint supplier does not have this mesh size (the medium is more commonly found), they can order some for you.

FULL SIZE GEOTEXTILE BAGS ON SAND DRYING BEDS High volume operations many times prefer to use larger Geotextile Bags . These tubes are laid out directly on the drying bed or other prepared surface. The sludge is pumped into the bags at higher rates and in larger volumes than can be handled by the container filter bags. Pumping into these bags at 300 gallons per minute is not unusual. A 100’ long bag with a 45’ circumference can dewater up to 1/2 million gallons of sludge.

This municipal waste treatment plant is using Geotextile bags to dewater sludge. Each of the sand drying beds will hold two bags. Pumping is alternated between the two bags and as they are being pumped other bags are set up in adjacent beds. When the active bags are pumped to capacity the operation is switched over to the new bags. This gives the full bags many weeks and even months of drying time before they are opened up and loaded out. By utilizing geotextiles the plant eliminated odor problems and quadrupled the capacity of the drying beds. In addition the bags are not as sensitive to weather related issues. Land application is still the preferred option but now the operation can be done when ideal conditions exist. The bags are laid out on the drying beds over an expanded plastic drainage mat. This mat helps to hold the bag off the sand and promotes faster drainage. Some plants prefer to put a layer of coarse stone down prior to putting down the drainage mat. Since all of the solids are retained in the bag the stone overlay will remain clean. When the bag is opened the dried bio-solids are loaded out and the bag rolled up for disposal. The polypropylene bag can be removed to any landfill.

The larger geotextile bags have a specific recommended height that they will be pumped to. Standard practice is to install a line or wire across the bag to use as a gage. When the bag is pumped up to the gage line, pumping is switched over to the next bag. The first bag is then allowed to dewater before pumping is returned to it.

Utilizing the geotextile de-watering bag in an existing sand drying bed will greatly increase the capacity of the bed. In addition the de-watering process is not affected by weather conditions. De-watering operations can be performed in wet or freezing weather and disposal can be done at a time that is suitable to your plant operation.

Full bags are allowed to de-water for several weeks. When ready the bag can be opened and the bio-solids loaded out with a loader for land application or land fill disposal.

Municipal bio-solids will consolidate and de-water from 12% to 16% by weight in a matter of weeks. Some plants will let bags dry for months to allow the solids to reach levels of over 20% solids by weight.

When loading out the bio-solids the bag is cut open and the top and sides removed. The bottom of the bag makes cleaning out the bed a snap. After the solids are removed the remaining bag material is rolled up and thrown away. The drainage mat under the bag is reused and a new bag laid down.

MIXING AND INJECTING POLYMERS FOR FLOCCULATION

Conditioning of the sludge as it is pumped into the bag is an essential part of a successful Geotextile Dewatering operation. By adding a flocculant to the sludge and gently agitating, the fines of the sludge will bind together forming large agglomerations. The free water will pass though the bag and the pores of the bag will remain open to facilitate the dewatering process. This process is known as “Flocculation”. The jars above show the condition of the sludge as pumped from the digester, after flocking, and the clear effluent as it filters through the bag. To meet these conditions you must inject a flocculant into the waste stream as it is being pumped into the bag. In addition you must also mix this chemical to obtain the agglomerations of fine particles as shown in the middle jar. The sludge in the jar at the left will pass through the pores of the bag and in doing so will eventually build up and blind off the pores. The free water in the sludge will not be allowed to flow out of the bag and the sludge will not pass the paint filter test as required by the land fill. Obtaining proper flocculation of the sludge is dependent on several conditions. First the proper chemical must be selected to cause the particles of sludge to bind together to form the agglomerations. Second the chemical must be properly converted into a liquid solution that can be mixed with the sludge. Thirdly, the correct amount of this chemical must be injected into the sludge at a point before the sludge enters the bag. And finally, a mechanical agitation or mixing of the chemical with the sludge must occur to insure that all of the sludge gets the proper dosage of chemical. This sounds very technical and difficult but in reality after you have selected the proper chemical and mixing equipment the flocculation operation is not difficult and good results can be easily obtained. Polymer is added to the sludge as it is pumped onto the belt of a gravity bed filter press in a Municipal Waste Treatment plant. The flocculation process induces the sludge to form large clumps of solids and the water rapidly drains away . The flocking operation significantly improves the dewatering process.

The sludge in this beaker is not showing any results from the flocculant. This sludge will blind the pores of the geotextile bag. The de-watering process will be very slow and inefficient.

This beaker contains a sludge that is beginning to floc. The flocculant is causing the sludge to form agglomerations but there is still a large quantity of fines in the slurry. These fines will also blind the bag. The sludge is not as bad as the sample shown above but is not an acceptable sample.

This beaker contains a sludge that has been properly dosed with the chemical flocculant. Nearly all of the fines have formed into the agglomerations that you see in the beaker. The water surrounding the agglomerations is clear. This sludge will not blind the bag and the de-watering operation will be efficient.

Lagoon Clean out with the Geotube® Many muncipal waste plants have lagoons that are used for overflow situations or storage purposes. These lagoons from time to time need to be cleaned to remove the buildup of anaerobic sludge. Geotextiles can be used to reduce the cost of this operation. The costly alternatives such as mobile belt filter presses or screw presses can significantly impact a plants yearly budget when this operation becomes necessary. Placing Geotextile bags around the perimeter of the lagoon allow the plant to pump the sludge into the bag, allow it to dewater back to the lagoon and then remove the contents of the bag when dry.

A pad is prepared along side the lagoon that is level and situated in such a way as to allow the clean effluent to return to the lagoon by gravity or by pump. In this case straw was laid down over the clay pad and a plastic drainage mat laid over the straw. The bag is spread out over the mat. The operator then attaches the fill tube and hoses to the fabric snout of the bag.

A tractor mounted agitator/pump is used to agitate the water and sludge in the lagoon. When the sludge is mixed with the pond water in the area where the pump is situated the mixture is pumped into the bag. Polymer is added and a manifold used to obtain proper flocculation. A different type and grade of polymer will be needed for anaerobic sludge than is required for aerobic sludge that might be pumped from a digester. Polymer tests are needed to determine proper polymer selection.

Clean effluent flowing from the bag can be diverted back into the pond. In some cases where ponds are being closed a temporary discharge permit may be obtained to discharge the effluent. This would require some pilot tests to evaluate the quality of the effluent coming from the bag. Once the pond has been completed the bags can be left on the bank to dewater. In general this will take from several weeks to months for the sludge to dry to a point where the bags can be cut open and the contents removed for land application or disposal at a landfill.

POLYMER SELECTION Selecting the correct chemical to obtain good flocculation is very important. The most common flocculate used in small to medium size waste water treatment plants will be either a “Liquid Emulsion Polymer” or a “Dry Polymer”. These two polyelectrolytes are produced and sold by several large chemical companies. They are also distributed and sold by a large number of small chemical supply houses. Regardless of your choice of a liquid or a dry polymer you will need to mix the chemical to place it into a state of solution. Liquid emulsions are shipped semihydrated in an oil carrier. They must be mixed with water before use. Dry polymers are shipped dry and they also must be mixed with water to put them in their active state. Polymers are supplied with a wide variety of grades. The polymer has a specific molecular weight and this molecular weight has a direct impact on its ability to work with your specific sludge. The polymer also has a specific charge and again this also effects the ability of the polymer to perform correctly. A polymer is a large molecule built up by a chain of chemical units called monomers. This chain may be a singular chain or it can have multiple branches but in any case when the polymer is in its solution state and fully extended as a chain it is very fragile. Over mixing or agitation can cause “shearing” or a break down of the chain and this will reduce the effectiveness of the polymer. The selection of the proper chemical is very important to the success of your Sludge Management Program. You should rely on your supplier to advise you of the pros and cons of using either a Liquid or a Dry polymer. In general the following are the basic considerations that you should know about.

Emulsion Polymer Emulsion polymers were developed over 30 years ago and are very popular with small plants. They are obtained in 5 gallon containers, 55 gallon drums and 1000 lb totes. Most small plants will purchase these chemicals in 5 gallon or 55 gallon containers. These polymers are available in a wide variety of grades but the most common grade found in waste treatment plants will be a mid to high molecular weight cationic polymer. The shelf life of most emulsion polymers is 6 months. Emulsion polymers are manufactured with divergent degrees of active polymer. The percentage of active polymer in most cationic polymers ranges from 40% to 60%. Emulsion polymers are manufactured to include a stabilizing agent to extend the shelf life of the product and a oil carrier to maintain the liquid state of the product and kick start the inversion process. To prepare the emulsion polymer for injection you must invert the product from a neat product to a solution. You do this by mixing the neat product (the raw liquid polymer) with water with a high degree of energy. This begins the uncoiling process where the polymer molecules build up their chain and obtain the active state which causes the flocculation to occur with the solids in the sludge. The solution produced by mixing water with the neat product can be “made down” to different levels of concentration. Many polymers work best when the percentage of neat product to the added water is around 1/4% or .0025. This means that 1 gallon of neat product will make down 400 gallons of solution. If the solution concentration is said to be .5% (1/2%) 1 gallon of neat polymer will make down 200 gallons of solution. Equipment required to mix the neat polymer with water will be discussed later. After the water and neat polymer are mixed together a period of time is required for the polymer to obtain its maximum level of activity. The “uncoiling” process takes a little time and this is generally referred to as the “aging” time. This is usually from 30 minutes to 1 hour depending on the polymer. The polymer solution will build viscosity as this aging time occurs and as a general rule when the solution has reached its maximum viscosity it will also have reached its maximum activity level. After the proper aging time the mixture is said to be “In Solution”. The polymer solution should be used or injected into the sludge line within a day or two of being made down. After 24 hours the solution begins to break down and its activity level decreases. Unused polymer solution should be discarded if you are not able to use it within a 2 day period.

DRY POLYMERS The first polymers to be used for flocculation were produced as a dry powder. The dry polymers used today are in a bead form and are more easily mixed and handled than the older dry powders. Dry polymer has a longer shelf life than emulsion polymers. Most dry products can be stored for 2 to 3 years with no negative effect on activity level of the product. Dry products are 100% active and thus are sometimes considered more effective than the neat or emulsion polymers. This is not always true but the liquid product will generally require more chemical than will a comparable grade of dry polymer. In addition the cost of the dry product will normally not be as high as the emulsion product. The dry product requires a longer and more extensive mixing process to prepare it for injection. In addition the dry product is very hydroscopic in nature. This means that if you leave the bag or container open to the atmosphere it will soak up water out of the air and become lumpy and extremely slippery. An open bag of dry polymer can become unusable in 1 day. As with the neat or emulsion polymer, dry polymer must be mixed with water and made down into a solution before injecting the product into the sludge line. Making down a dry polymer will generally take longer than making down the neat product. It also will require more energy and care to prevent the forming of agglomerations in the made down solution. These agglomerations are sometimes referred to as “fisheyes”. They are lumps of dry polymer stuck together and usually are about the size of a grape or pea. In some extreme cases they can be large masses of floating gel. The center is sometimes dry and the outside a thick gelatinous mass. These fisheyes can plug up lines and pumps and at the very least are wasted product. A mixing process that does not produce these fisheyes is desirable. As with the liquid you make down a dry product at a solution concentration of from 1/4% (.0025) to 1/2% (.005). This is done by weight with the dry product. Water weighs 8.34 pounds per gallon. A tank of 200 gallons of water will weigh 1668 pounds. To make down a 200 gallon batch of polymer solution with a concentration of 1/4% you will need 4.17 pounds of dry polymer. (1668 X .0025 = 4.17) As with neat polymer you will need to “age” the dry polymer mixture after you have mixed it with water. With the dry product you will also have to continue to agitate the mixture until the aging process is complete. If you do not agitate the mixture, the un-hydrated particles will settle to the bottom of the tank and form a gel like mass at the bottom of the tank. If you agitate the mixture too long, you will shear the product. The molecular chains will be broken down and the polymer activity level reduced. More solution will be required to accomplish the flocculation of the sludge and your costs will increase. It can be seen that controlling the mixing and injection process of both the liquid polymer and the dry polymer is a critical part of your sludge management program. It is not difficult or expensive to control this process but it is important to the overall success of the flocculation process.

FLOCCULATION EQUIPMENT Preparing and injecting the flocculating chemicals requires specialized equipment. The type of equipment you select will depend on your selection of a dry or liquid polymer and the amount of chemical that you will need to use. Chemical make down equipment is usually sized in gallons per hour or gallons per day. When using the Geotextiles to dewater sludge your pumping rate into the bag will determine the volume of polymer solution you will need in gallons per hour. Typical application rates for the polymer solution will be from 30 to 300 ppm depending on the solids concentration of your sludge. As you can see this is a large range so the best way to determine your needs is to perform a jar test on your particular sludge. From the jar test your polymer supplier can determine the proper chemical to use and the amount that you will need to obtain proper flocculation of your sludge. The jar test is a simple test but it is best performed by your chemical supplier. He will have available a wide choice of polymers and will find the one that performs best at your plant. Once this is done you will need to purchase and install the proper mixing, and injection equipment for your particular needs. Blue River Technologies can provide any type or size of polymer make down and injection systems. In addition we also offer a wide variety of polymers from several different manufacturers.

The polymer solution is mixed with the sludge with a static mixer. This mixing manifold has a cam lock fitting at the far left end for the sludge line. A slide valve allows the operator to adjust the flow of sludge into the bag as desired. Next to the slide valve is an injection point for the polymer solution. The cam lock fitting allows the operator to quickly connect the solution line to the manifold. A check valve prevents sludge from back flowing into the solution line. The S.S. paddles inside the mixer gently mix the polymer solution with the sludge before it is pumped into the bag. A sampling valve at the end of the manifold allows the operator to check the flocculated sludge from time to time to insure proper opera-