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Potential Impact of Waste
 Water on Starch Adhesive

Cassie Rothstrom & John Kohl


With the heightened compliance regulations of many city and county municipalities on the discharging of wastewater from a corrugated facility, many box plants are now being forced to re-use this wastewater back into their starch adhesive. Since the starch adhesive is the single largest consumer of water, most box plants are looking to use the wastewater here. So the potential impact of this wastewater on the starch adhesive has become of paramount interest.

A proper implementation process will assure success with this wastewater back into the starch adhesive. Begin by verifying where all of the waste water is being generated from -- the finishing side, corrugator, and/or boiler? Calculate the amount of waste water that can be consumed daily and compare this amount to what you are actually producing daily to determine whether or not you need to put your facility on a water diet. And finally have the treated or untreated wastewater tested.

Testing your wastewater on a Monday and a Wednesday is the most important component of the implementation process. It provides a snap shot or x-ray, if you will, of what is in the water. In turn, this information is used as a map to guide your starch manufacturer as they begin the reformulation process to adequately handle the addition of the wastewater back into the starch adhesive batch.

Things to look for on your wastewater test results include: water hardness, Sulfur as Sulfate, B.O.D. and C.O.D. levels, Boron, suspended solids, and pH. Other things found in this waste water that will not show up directly on a waste water test that need to be taken into consideration when reformulating include: flexo ink and waste water treatment chemicals.

Hard Water

Hard water can be very difficult to formulate with. The sources for hard water can be boiler blow down, well water, city water, and/or treated wastewater. This hard water can make it difficult for the carrier portion of the starch adhesive batch to cook out properly causing viscosity variations, and it may cause an increased gel point. Possible solutions include the elimination of Ferric Chloride from the waste treatment chemical process, the installation of a water softener (very expensive), and/or the possible inclusion of a scale inhibitor during the starch making process.

Sulfur as Sulfate

Sulfur as Sulfate is found as a by-product in many flexo cleaners. Its potential impact on the starch adhesive batch is rapid viscosity loss. A possible solution includes a review and possible product change to a more starch friendly flexo cleaner.

B.O.D.’s, C.O.D.’s, and Bacteria

Biological Oxygen Demand, Chemical Oxygen Demand, and bacteria are often tested for when sampling of your wastewater is done. When the water is tested for B.O.D. levels, they are testing the water for the amount of oxygen found in the water. This tells you how much potential bacteria you have. Bacteria use oxygen as food. So if you have a low level of oxygen, then you likely have a high content of bacteria. When the water is tested for C.O.D. levels, they are looking for different chemicals that bacteria uses as a food source like phosphorus. If they find a high level of C.O.D.’s then it is likely that the bacteria levels will also be high.

Affects of bacteria on starch adhesive can include any or all of the following: loss of viscosity over time, increases in gel points, poor bonding at the corrugator, a build up of solids in the storage tank over time, and a loss of carrier solids. Possible solutions include the elimination of as much of the bacteria’s food source as possible, the incorporation of a short-term kill biocide in every batch of starch adhesive that is made with wastewater, and not letting your wastewater sit too long.

Boron

The most common source of Boron found in the wastewater stream is residual starch adhesive from corrugator wash downs, and scrapped batches of adhesive. The possible affects of Boron on the starch adhesive batch are increases in gel temperatures and viscosities. Possible solutions include limiting the amount of starch adhesive that is discharged into the wastewater stream, and if a brittle bond is seen, you may actually have an imbalance of caustic to borax in the formula that may call for reformulation by your starch adhesive manufacturer.

Suspended Solids

Suspended solids in the wastewater are primarily due to using untreated wastewater in the adhesive. The flexo inks all have fillers to give the inks higher viscosity to aid in ink transfer and coverage on the substrates to be printed. These suspended solids displace some of the starch solids, forcing the plant to run an adhesive lower in starch solids and can cause viscosity swings from the percent of suspended solids varying in the wastewater supply.

Possible solutions include using a water treatment or filter system to remove the solids or keeping the untreated wastewater constantly agitated so the percent of suspended solids in each batch is more consistent.

PH

Creating a consistent wastewater stream is key to successful reuse of wastewater back into the starch adhesive. Things that can cause inconsistent pH within the box plant include large spills of any material, heavy clean ups on one particular day of the week, holding the wastewater in storage too long, and changing chemicals used in the plant. Affects of inconsistent pH include viscosity and gel point fluctuations. If the pH of the water is too high or too low, it will require some reformulation of the starch adhesive batch. And it may require the installation of a pH meter.

Flexo Inks

The obvious source for flexo ink is the finishing side. Since flexo wash up water is the largest percentage of the wastewater to be used back into the starch adhesive, it can have tremendous impact on the finished adhesive. The affects can include increased viscosity, increased tack resulting in more starch adhesive being applied to the flute tips causing starch consumption to go up, and a slightly elevated gel point. The only possible solution is reformulation by the starch adhesive manufacturer. There will probably be a need to back off a little on the borax and cut back on the glue gap settings.

Waste Treatment Chemicals

Many facilities have opted to treat their wastewater before using back into the starch adhesive making process. This can create trouble for the starch adhesive batch if proper use of the waste treatment chemicals is not facilitated. Using too much flocculent to treat your wastewater will result in residual flocculent in the treated water. This floc has a purpose: to drop the solids out of the wastewater. But if there is residual floc left in the water used to make starch adhesive, the impact on the finished adhesive can be disastrous. The floc will drop the solids out of the starch adhesive batch causing rapid viscosity loss. The solution to this is a simple one – your wastewater treatment goals must change. Do not over floc your wastewater. It is better to have some residual color and material left in the treated wastewater, than to have the water clear and risk that there may be residual treatment chemicals (floc) left in the water to be used to make starch adhesive with.

Using treated or untreated wastewater back into the starch adhesive is the future of the corrugated industry. A track record of success is already present in this industry as many of the large integrated’s have begun to mandate Zero Discharge to all of their box plants. The key to successfully reusing this wastewater back into the starch adhesive is the implementation process, and the involvement of key individuals like your starch adhesive manufacturer, chemical supplier, and waste treatment manufacturer.

With a well-constructed implementation process, along with a complete buy in by management, and training of your plant personnel, the impact of wastewater on your starch adhesive should be minimal.


Cassie Rothstrom - Walla Walla Environmental Inc. & John Kohl - Harper/Love Adhesives Inc.