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Waste in Wastewater: Looking for the Green

Posted on Friday, March 22, 2019

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As my grandfather would tell you, “There’s nothing wrong with skim milk that a little half and half won’t fix.” A point made in a joke, that a little of the right chemistry can go a long way.

In the manufacturing world the focus is constantly on production and the speed with which parts are processed and sold. The primary goal, to get parts out the door efficiently while reducing both the time to market and the cost of manufacturing, rarely considers the waste treatment process. This makes waste treatment a fertile source of improvements in efficiencies that can simultaneously increase both the bottom line and environmental impact. This article will touch on several ways that your waste treatment process can benefit from a review and update in technology to first, reduce the process inputs, including time commitment, chemical consumption, monetary spend and oversight. And second, provide the added benefit of reducing the amount of sludge and regulated effluents on the output side.

Minimizing the Impact

Waste streams are often complicated mixtures from multiple sources. Coming from the desire to get a better powder coating through phosphating and cleaning, as well as associated processes like stamping and metal removal, the waste stream has a high degree of variability that requires a capable and robust system to address the inputs from manufacturing and meet the outputs required by municipalities.

When it comes to the treated waste, there is both a liquid and a solid portion that can be optimized.

For solids - By reviewing the waste treatment process and updating technologies, savings in terms of the amount of sludge the process creates are possible. While this may seem like a minor impact in the overall scheme of manufacturing, the maintenance of press filters and the transport of sludge to dumpsters take man hours that can be better applied to getting parts through the production line and maintenance of manufacturing equipment.

For liquids – The primary driver is meeting the levels prescribed by the regulating authority. While this defines the end, the means to that end is quite variable. Newer polymer technologies introduced in coagulation have been demonstrated to reduce the overall chemical usage and therefore, expense. Equipment designed for processing and delivering treatments can improve process efficiencies and reduce chemical consumption.

The waste treatment process is governed by risk and a desire to keep the company protected from bad PR as well as non- compliance fines.

Sludge Reduction

Often sludge in waste treatment is considered a good thing. You do, of course, want to remove the contaminants. The production of sludge demonstrates that something is happening, and that waste is being removed from the solution. This view takes away from the end goal of removing contaminants from the water to meet the requirements as efficiently as possible.

For example, one manufacturer of cabs for agriculture equipment had a long-standing process of treating their waste water with calcium chloride and an anionic polymer to treat the waste from their pretreatment and e-coat process. The discharge met the city’s requirements for water pollutants. It also was quite turbid and produced a large amount of sludge that plugged up the filter press quite regularly. As is common in manufacturing, the situation was endured for years in order to produce parts. In fact, the situation went on so long that the routine of monitoring and cleaning the filter press became part of standard operations.

Updating technology can not only lead to cost savings, it can result in process improvements and more time for productive activities like making parts. In this case a review of the process and effluent indicated that by upgrading the technology from the classic calcium chloride and anionic chemistries to the newer polyelectrolyte-flocculant and a high performing polymerized coagulant, the process could deliver three advantages. One benefit was environmental, an increase in clarity. The second benefit was a 35 percent reduction in sludge created at the filter press. The third benefit was achieved by introducing a polymer blending system reducing the amount of chemicals needed for the process.

Gaining Compliance: The Value of Process Review

Perhaps you have not been paying much attention to your waste treatment process and are unaware of the state in which it is currently operating. Such was the case for an agricultural equipment supplier. It was observed that waste was lacking clarity and the optimal pH for neutralization was not being maintained. The process implemented traditional calcium chloride technology and was being dosed excessively to meet effluent requirements.

Testing for flocculation
Testing for flocculation, the process by which fine particulates are caused to clump together.

After a process review and testing was complete, the company converted to a new polyelectrolyte and liquid alum-polymer technology, which enabled them to achieve the required clarity. In addition, the excessive use of calcium chloride was eliminated, reducing sludge by 50 percent.

This case study clearly illustrates the value of process review and its potential results in terms of reduced man-hours invested in treating the waste as well as the amount of waste going to the landfill. It is important to keep in mind that if you look solely at the numbers related to chemical costs, you may be overlooking potential savings in time, waste disposal costs and avoiding fines by complying with regulations.

Waste Treatment Process Comparision
By reviewing the waste treatment process and updating technologies, savings in terms of the amount of sludge the process creates are possible

Lowering your Costs

Sustainability has become quite a buzzword and as such, the costs of sustainability are often overlooked or muted. In manufacturing, sustainability must also be consistent with your business model. If it isn’t, you run the risk of having a very sustainable operation from an environmental perspective, but not a business perspective because it fails to provide the required cash flow. Such was the case for a manufacturer of net to near-net shaped formed and extruded components, which drove them to entertain the thought of improving their waste treatment process.

The process had already advanced from the classic calcium chloride and anionic coagulant to a more sophisticated polymer coagulation- neutralize-clarification process with a modest chemical spend of $300,000 annually.

The primary sources of waste fluid are a phosphate line and some process cleaning baths. A review of the sources revealed that there was potential to introduce an additional polymer in the coagulation process. At what cost, you might ask, and for what purpose? The cost of the polymer was estimated at $5,000 annually. However, this additional cost would reduce the coagulant usage by over $100,000!

As technology continues to advance, so do opportunities for improvement. The “we have always done it this way” mentality certainly has great ability to sustain a business, and the tendency to not fix something that is not broken can carry a lot of weight. Still, as opportunities for improvement present themselves, revisiting an old process can lead to significant improvements.

Wate Reduction System Setup
A typical waste reduction system setup.

Adding Manufacturing Capabilities

It is obvious that a change to your manufacturing process will change your waste stream and waste treatment. Perhaps you are considering upgrading your capabilities to include e-coat and powder coating applications. Let’s take a look at a retail equipment manufacturer who upgraded their capabilities from electroplating only, adding e-coat and powder coating.

Making this upgrade results in a situation where acidic and anionic wastewater comingle with the chrome wastewater, interfering with the reduction of chrome and the precipitation of the chrome, nickel and zinc. When the waste stream changes from electroplating to powder and e-coat, the increased anionic waste requires slug dosing of calcium chloride. While the waste is still predominantly the result of electroplating, the variability can go from one extreme to another depending on manufacturing needs.

Normal flow ratio [of total]:
Electroplating wastewater 70%
Powder/E-Coat wastewater 30%
Variance in Flow:
Electroplating wastewater 60-80% peak 100%
Powder/E-Coat wastewater 20-40% peak 100%

Supplemental calcium chloride dosing provided some assistance; however, the periodic waste source changes made the calcium demand erratic and essentially impossible to control on a consistent basis. The soluble and suspended solids excursion events caused the sand filter to plug routinely with zinc, nickel, and chrome hydroxide-based suspended solids.

It is clear to see that the new variability of the waste needed a more tailored and robust solution. Testing revealed that the surfactants in the powder/e-coat were the primary cause of the suspension. By designing the waste treatment chemistry to address the swings to 100 percent of either the electroplating waste or the powder/e-coat waste, at a modest treatment rate of 200 ppm the metal hydroxides were adequately formed and coagulated. After pH adjustment, a dose of 2.5 ppm polymer was successful at flocculating the waste.

A consistent solids conditioning and neutralization of all wastewater sources, in both net anionic and cationic charge differentials, was obtained. A sludge reduction of approximately 15 percent was achieved by the application of the mixed chloride coagulant at a dosage of 200 ppm versus the previous periodic slug dosing of calcium chloride. The sand filter continuous backwash procedure maintained a clean media surface and the sand filter media did not foul with carbonate salts. Ongoing regulatory compliance for zinc, nickel, and chrome was realized with no reported excursions.

Existing Treatment Technology Flow Chart

The Upgrades You Need

The waste stream is often overlooked in the effort to quickly produce parts. We all need a strong focus on delivering what the customer wants in order to stay relevant and marketable. From proper equipment utilization to updated chemistries, partnering with a knowledgeable and reputable supplier for an evaluation of waste treatment processes can put your mind at ease about reducing waste, leaving you free to focus on the manufacturing process.

Mark Fretz is product manager – metalworking and water treatment at Chemetall, a BASF company.

Author: PCT Editor