Corrugating International, October 2000
Conversion Magazine, Feb 2001
MARI Magazine, May 2001
Zero Discharge Programs
in a Corrugated Box Plant
Cassie Rothstrom and Peter A. Snyder
Many boxplants and sheet feeders struggle to keep pace with the changing rules and regulations involving the discharge of industrial wastewater. Industrial wastewater includes flexo wash up water, corrugator run off water, and boiler blow down that could be released from a corrugated facility into the local sewer system, The challenges that box plants face include:
- Reducing the amount of wastewater generated each day.
- Successfully treating the wastewater in a cost-effective manner.
- Re-using the wastewater in a safe and non-destructive manner.
There are several strategies currently in play in the United States. Corrugating plants in the United States follow one or more of the following techniques:
Allowing the wastewater to flow into the drain for treatment by the local municipal water treatment center. In the face of increasing concern for the ecology this is tolerated in very few locations. Most corrugated plants are pursuing ways to avoid this practice in anticipation of large fines for violation of future federal, state, or local regulations.
Collecting the wastewater in large storage tanks for treatment by an on-site waste treatment system. The treated wastewater is then allowed to flow into the drain for further treatment by the local municipal treatment or used as a portion of the water-based corrugating adhesive. It is surprising that even the most effective waste treatment systems available cannot always clean dirty water up to the expectations of local regulations. Therefore, using the treated water in corrugating adhesive is an option under consideration by many factories.
Collecting the wastewater in large storage tanks and using this untreated water as the base for the necessary corrugating adhesive used in the corrugated container plant. Obviously this is a very attractive option since it appears that there would only be a minor investment necessary for storage tank(s), pumps, and piping. Compared to the need to install a complete waste treatment system, this alternative is very inexpensive to consider but can be very difficult to successfully implement. This is due to the chemistry of the wastewater and the specific properties of corrugating adhesive. An example of such a system is shown in Figure 1. Many box plants are using untreated wastewater in their corrugating adhesive with great success.
The Corrugated Container Division (CCD) of the Technical Association of the Pulp and Paper Industry (TAPPI) has taken a leadership role in the successful management of industrial wastewater produced by the corrugating plants. These efforts have included technical committee members reviewing possible options and preparing Technical Information papers (TIPs) for use by the industry at large. TIP sheet number 0304-44 is entitled "Using Washwater as the Vehicle in Corrugating Adhesive" and is available by calling TAPPI at 1-800-332-8686 (U.S.), 1-800-446-9431 (Canada), or +1-770-446-1400 (international).
Another very successful effort by TAPPI to assist box plants manage their wastewater was the wastewater Workshop presented during the 1997 TAPPI Corrugated Containers Conference in Milwaukee, WI. The workshop presented information from suppliers of waste treatment equipment regarding the mechanical and chemical nature of water treatment. Also presented were case histories from several box plants that have successfully treated wastewater and/or have begun to use some form of wastewater in their starch adhesive. One of the clear messages from this workshop was that many box plants are managing wastewater in a safe, cost effective, and efficient manner. Proceedings from this conference are available by calling TAPPI's Service Line at 1-800-332-8686 (U.S.), 1-800-446-9431 (Canada), or +1-770-446-1400 (international).
WASTEWATER TREATMENT SYSTEMS
For many years, the treatment of wastewater was presented as a topic too difficult to understand due to the technical nature of the various treatment processes. Many of the popular processes had not changed for years and, in fact, had not kept up with the advances in polymer chemistry.
The basic principle of treating wastewater is to create a chemical environment within the water being treated that is "unfriendly" to the waste portion of the dirty water. Many of us are familiar with the chemical concept of pH, which is the relative measure of the acidity of water. We measure pH on a scale that runs from 0 to 14, with 1 being very acidic and 14 being very alkaline. Pure water has a pH of 7, the midway point of the scale.
Many waste treatment systems work by effecting a wide pH change to the wastewater to begin the process. Once the pH change has occurred, this "unfriendly" chemical environment works together with other chemicals, including liquid polymers, to cause the suspended waste material to form large particles, which are then removed from the solution by a series of processes that could include a settlement tank and/or a filter press. While the chemistry available from each supplier may be proprietary, and very difficult, the end result is to eliminate as much of the waste as possible from the water. The old style was often very slow and labor intensive. This, fortunately, is changing.
New Technology for the treatment of wastewater is now available from several of the suppliers featured in this article. The benefits of the new technology include a treatment process that is faster, less expensive, easier for operators to learn and requires less equipment. Another benefit is that the process does not require the addition of harsh chemicals to drastically change the pH. Not only is this a safer process, it is often much more effective.
The implementation of a zero discharge program in a box plant will involve the use of some or all of the wastewater in the starch-based corrugating adhesive. Despite the obvious basic similarities in corrugated plants, each has a unique process that will generate a particular volume and quality of wastewater. It is important to understand that wastewater comes in a variety of consistencies:
- Raw wastewater in industrial wastewater from any source that is untreated.
- Treated Wastewater is the result of a water treatment process designed to remove ink solids and other impurities.
The original source of the wastewater in a corrugated plant will include:
- The flexo department: ink pigments, which are the primary source of adhesive problems; detergents; vehicles; fillers.
- The corrugator department: diluted starch adhesive, including caustic and borax; gelled starch; paper debris.
- The boiler room: high salt content in blowdown water, including calcium and magnesium; boiler scale inhibitor chemicals.
When a box plant considers the use of any form of wastewater in starch adhesive, it is important to understand that the "water" ingredient is the largest single component in the formula. The use of an alternate form of water will have some impact on the behavior of the adhesive in regard to many aspects of its performance, including actual runnability, water-holdout, gel point, film properties, set back, and viscosity control. A box plant will need to keep this new raw material as consistent as possible.
RAW WASTEWATER OR TREATED WASTEWATER USED IN STARCH ADHESIVE
The storage tank for these water sources should be kept free of any settled material. Box plants that have used such a tank for any amount of time should get this tank cleaned out for a fresh start. The sludge removed should be tested for the presence of dangerous or controlled chemicals.
The raw and treated wastewater should be tested for pH, percent solids, heavy metals, VOCs (Volatile organic Compounds), and any other regulated materials.
The storage tank contents contain suspended solids that will fall out of solution and form a sludge on the bottom of the tank if there is no agitation. Continuous mechanical agitation works the best.
Use the alternate water source in the starch adhesive will require a pumping system and, if possible, a metering system.
Monitoring the pH of this water will provide excellent information for your starch adhesive formulator to use for adhesive fine-tuning. If the raw or treated wastewater experiences wide pH swings, there will be problems formulating consistent adhesive.
Use of either wastewater source is possible in the slurry portion and the carrier portion of the adhesive. It is important to note that if the raw wastewater is used in the carrier portion and it contains a variable amount of starch, then this ingredient will cause changes in the desired viscosity. (This is often the reason why raw wastewater is not used in the carrier portion.)
Plan the use of this raw material in phases and keep experienced talent on hand during the transition. Your starch adhesive technician should be involved with this process as well as any local experts, including all corrugator crews.
SPECIAL CONSIDERATIONS FOR TREATED WATER USE
Treated wastewater may contain a variable amount of flocculant and/or coagulant polymers. These ingredients will have a negative impact on the properties of starch adhesive. The treatment process will need to be evaluated and fine-tuned to avoid excessive treatment chemical use.
Some treatment processes involve the use of lime (calcium hydroxide) for pH control and to provide a surface on which floc will form. This may cause a potentially large increase in the water hardness of the treated water. High calcium content of water used in the starch adhesive may lead to calcium carbonate salts building up on the adhesive mixers, storage tanks, and adhesive applicator systems. Since there are alternative chemicals available for many treatment processes, these new choices should be considered for treated water to be used in starch adhesive.
BIOLOGICAL CONSIDERATIONS IN WASTEWATER USE
Starch adhesive is susceptible to biological attack due to the dissolved nature of the carrier portion.
Starch is a polymer composed of long chain carbohydrate molecules, which in turn are composed of individual sugar molecules. Microbes can use these molecules as a food source in spite of the presence of caustic soda, borax, and other ingredients that create a harsh pH environment.
The microbes that can cause problems include bacteria, mold, and yeast.
Wastewater typically is stored in an uncontrolled manner. This will eventually lead to a large population of microbes capable of creating significant adhesive-related problems.
When the microbes attack starch adhesive, it is the carrier portion that is the most vulnerable. As the carrier portion is digested, the adhesive loses a portion of this very necessary ingredient. Contaminated adhesive often will a rapid viscosity loss as a result of this biological action.
As starch digestion occurs in wastewater, oxygen is consumed. A measure of this is known as biological (or biochemical) oxygen demand (BOD), This is formally described as a laboratory test that measures the ability of common bacteria to digest the organic matter in a test water sample, usually in a five-day incubation period of 20 oC, by analyzing the depletion of oxygen from a fully aerated starting point. It is expressed as O2 in mg/L. If wastewater has a high BOD content -- over 250 mg/L, for example -- the concentration of microbes may lead to poor adhesive performance when similar water is used for starch adhesive.
In virtually every case of wastewater use in starch-based corrugating adhesive, the use of a biocide product is recommended. There are several different ways to incorporate a biocide. Some box plants treat the wastewater holding tank. Other use a short-term kill and/or a long-term kill biocide in each batch of starch adhesive.
WATER SAVING TECHNIQUES
In order to be successful at obtaining zero discharge, you must do the numbers. You must produce less flexo wash up, corrugator run off, and boiler blow down water (if intended for reuse) than you can consume throughout your box plant. To determine this number, calculate how much wastewater the box plant currently generates on a daily or weekly basis. Then calculate how much wastewater can be consumed by the box plant in the secondary portion of the starch adhesive batch daily or weekly. Once you have these two number, simply subtract the amount of wastewater generated from the amount of wastewater that can be consumed. If the box plant is generating more than it can consume, then water-saving techniques need to be implemented.
The following list addresses some water-saving techniques that, when applied at the box plant level, will effectively bring down the total amount of water produced.
1. Conduct crew trainings. These seem to be best done by an outside source. Things to discuss include:
|a.||Why the facility is going to start using wastewater in the starch adhesive.|
|b.||What impact, if any, this wastewater may have on the starch adhesive.|
|c.||What impact, if any, the wastewater will have on the finished product and consumers using this finished product.|
|d.||Discuss with them the various water-saving techniques that the facility is planning to implement.|
|e.||Elicit suggestions from the crews on other places to save on water usage.|
|f.||Create a general comfort level among the crews with this process and make sure that they are on board.|
2. Install water saver nozzles on every water hose in the plant. Follow this with a message to all personnel from management about the need to leave these nozzles on every hose.
3. Install water meters with electric valves on every incoming line to the finishing side machines.
|a.||Determine how long you want the valve with the meter to run each time the knob is turned.|
|b.||Have the machine operators log in their water meter start number and log out their water meter finish number.|
|c.||The shift supervisor will then need either to load these numbers into a spreadsheet or at least compare each machine's total water usage during that shift to ensure that each employee is not overusing water during cleanup.|
|d.||Begin posting the amount of wastewater generated by shift daily. The key is to keep reminding the crews to save water!|
4. Replumb the water jackets so that the water is recirculated.
Many corrugating box plants are using machinery that requires a water jacket for cooling certain parts of the process. In many cases, this results in a single pass of cold city or well water through the "cooling jacket", which can lead to incredibly high water usage rates. In the United States, it is not uncommon to use up to 10,000 gal of water per day. In many cases, this water is sent down the drain to be "treated" as dirty water when in fact it is actually very clean when it is done with its job of cooling the glue pans. Unfortunately, when the water runs down the drain, it mixes with actual dirty water and then may need to be treated before being released to the local sewer system or used in adhesive. An inexpensive alternative for this is to install a water chiller that continuously circulates water to and from the "cooling jackets" while cooling it down in the process. Box plants that install such devices have experienced savings of up to 90,000 gal of water per month that does not have to be purchased, treated, or released back to the local waste treatment sewer system. The payback period for water chillers will depend upon local environmental rules, but it is normally less than six months.
Rothstrom is chief operating officer with Walla Walla Environmental, formerly known as Enviro-Chem, Inc., P. O. Box 1298, 4 West Rees, Walla Walla, WA 99362; Snyder is a 20-year corrugating industry veteran with a background in research & development, technical service, and corporate sales. He currently is the national accounts manager at Harper/Love adhesive Corp., 11101 West Lake Drive, Charlotte, NC 28273.