Paper 360
Every mill management team recognizes the financial and environmental impacts their facility has, both within their community and the world. Approximately 17,000 gallons/ton of water is used for making paper;(1) after process losses, 85—90 percent of that water makes it to a wastewater treatment plant (WWTP).(2) For some perspective, this represents nine percent of the treated water released in the United States.(3)
Today’s mills are under more competitive and regulatory pressures than ever. Older facilities trying to stay competitive and newer facilities in environmentally sensitive locations all need to deliver unquestionable consistent performance. An Industrial Internet of Things (IIoT) infrastructure offers tremendous opportunity in this area.
Fig. 1: A simplified view of a paper mill’s wastewater biological ecosystem (WBE).
This article will focus on the environmental concern of wastewater handling and treatment. It is important to recognize that this includes all the mill sewers and the WWTP, all working together as a wastewater biological ecosystem (WBE).
The complexity and the large number of processes in a mill require multiple different human command structures. While production processes are the operational responsibility of a single command structure, cost centers like stores and effluent treatment are reactive centers that must respond to the needs or behaviors of their upstream customers. Historically, it required little to no effort to optimize cost and performance of an industrial site’s WBE. The WBE sewer system is typically siloed; each department handles the sewers in its operating area with the WWTP operating blindly, handling all upsets while attempting to operate within permit constraints. For this reason, most sites run in a continuous reactionary mode when responding to process variability and upsets, increasing waste and cost.
There is an unlimited number of physical mill layouts, and each will need to be addressed individually on a case-by-case basis. For the purposes of this article, we’ll use an oversimplified mill layout (Fig. 1).
One key point has been overlooked or ignored. From the initial point of the first sewer in the mill to the WWTP outfall, mills must deal with a complex and interactive biological ecosystem. Proper analysis of the microbiology is required to understand the impacts production has on the WWTP. This analysis requires microscans, nutrient analysis, and adenosine triphosphate (ATP) testing to discover vital information about the health of the microbiology.
In addition to the microbiology, integrated pulp and paper mill effluents contain a complex mixture of various classes of organic compounds, such as degradation products of carbohydrates, lignin, and extractives. The effluents contain high values of biochemical oxygen demand (BOD), chemical oxygen demand (COD), and chlorinated chemicals that are collectively termed as absorbable organic halides (AOX). The ratio of BOD to COD is a particularly useful quantity because it represents the fraction of organic compounds in the effluent that are easy to degrade. Chemical pulping processes have been reported to generate more than 40 percent of poorly biodegradable organics within the total organic matter of the effluent.(4)
When fibers are recovered from recycled papers, a wider spectrum of contaminants will be present due to the variability in the nature of the used paper materials, their contamination during paper’s use and recovery, and the additives that are used for dispersing the fibers, removing ink, and bleaching.(4)
There is now a way to implement a complete end-to-end solution using an IIoT architecture, interactive controls, microbial analysis services, and human-machine interfaces (HMIs).
CURRENT APPROACH
For far too long, wastewater treatment has been viewed as a necessary evil. It is expensive, time consuming, and regulated by the government. For many, the wastewater plant is an eyesore and a necessary part of the cost of making useful products.
Engineers measure and collect data: flows, equipment running, power consumed, BOD, COD, total suspended solids (TSS), ammonia, phosphorus, etc. In many cases, the data are incomplete. Anecdotal information suggests that 40-60 percent of operational data (pump is running, valve is open, pressure, temperature, etc.) are not connected to any system.
Maintenance crews keep all the instruments and equipment operating properly. In some cases, maintenance is tasked with monitoring the wastewater system as one of their many other tasks.
What about operations? Process operators maintain the sewers in their respective areas, ensuring that they do not plug and flow freely. What is flowing in them is someone else’s problem. Many mills do not even have certified operators supporting their WWTP operations. That job is often relegated to maintenance, for which the primary concern is to keep everything running. What does that mean? Wastewater and its treatment are considered a waste of time and money for the mill.
Where dedicated wastewater operators are available, these operators rely on experience with the system and what is known in the industry as “the art of wastewater treatment” to solve problems, either because of the lack of available data or available training.
WHAT HAS CHANGED?
The fact that every mill is part of an overall global economy puts more pressure on reducing the overall cost of doing business. Bad practices, which in the past had only a marginal effect on the bottom line, are now becoming more significant. With heightened emphasis on greenhouse gas emissions, global warming, carbon footprints, and water quality, environmental citizenship is becoming more important in everyone’s mind.
An added tool is the introduction of IIoT. Going back to the 1970s movie and television series The Six Million Dollar Man, the phrase “we now have the technology” takes on new meaning.
An IIoT infrastructure offers platforms, tools, and strategies that will enable a step change in process performance. This infrastructure provides a holistic view of the mill’s effluent sources and treatment systems and identifies upstream process issues that will impair the treatment biological system performance.
OBSTACLES AND OPPORTUNITIES
Microbiology never lies, but it also doesn’t tell the whole story. Wastewater treatment relies on microbiology to treat biodegradable materials, taking soluble materials and creating suspended biosolids that can then be removed from the wastewater through physical separation.
What can be measured? Everything—but to be effective, the system must monitor, at a minimum, these points:
- BOD
- COD
- AOX—a specific parameter used to monitor pollution
- Total organic carbon (TOC)
- Total dissolved and settleable solids (TDS and TSS, respectively)
- Nutrient levels, such as nitrogen and phosphorus
- Sludge depths in clarifiers or lagoons
- Dissolved oxygen
- Power consumption
- Pump running time
THE PATH FORWARD
Many mill strategies today attempt to solve problems one section at a time: the pulp mill sewer, the paper mill sewer, the clarifier, the pond, etc. (Fig. 2). The challenge to this disjointed approach is that there is no clear overview of all the conditions, suspended solids, metals, chemicals, and microbiology that eventually affect the sewers, clarifiers, pond, and outfall.
In addition, the data required for such an overview are not centralized. Some of these data reside in the DCS system; some reside in individual localized control systems. Some of the data are local only measurements on gages and/or local measurement devices. Some of the data reside in the manufacturing execution system (MES). Some of the data are not continuously measured. The step change in performance is achieved through the:
- Integration of manufacturing and treatment process expertise,
- Implementation of an environmental server supporting IIoT mesh technology,
- Collection of disparate data from existing control and MES systems,
- Addition of non-integrated measurements,
- Use of multivariate analytical tools,
- Integration of new age graphical displays,
- Addition of a stability application.
The stability application is an analytical comparison for complex assets using visual trend group representations. The application provides a real-time comparison to a historical simulation of an ideal operation. Its user-friendly interface helps engineers and operators optimize asset performance by highlighting operational parameters that are currently deviating from the targeted performance.
Pulp and paper facilities have complex interactive processes that suffer from upsets and downtime due to many different issues. Many of these adverse conditions have an impact on the WWTP system and may lead to an environmental issue. The stability application’s goal, when focused on the effluent system, is to help operators and engineers understand where their current real-time operation is affecting the effluent process and causing it to deviate from the ideal situation. With this knowledge, teams can adjust the process operation to mitigate the upset before it becomes a compliance issue. The vision for the stability application is to provide a fully integrated tool that provides real-time, short-term, and long-term input and value creation opportunities. It can:
- Identify the historical optimum demonstrated process operating points through the effluent system for each grade,
- Identify and communicate intentional or unintentional deviation from these historically successful operating points,
- Highlight repetitive process swings,
- Highlight deviation from primary quality targets that would lead to compliance issues,
- Advise proper process settings to augment younger operators.
RESULTS
Using IIoT as the architectural backbone provides a cost-effective way to bring all these data together in one place, (or multiple places: PI, cloud, MES, etc.) resulting in a new holistic view into the overall mill effluent system operation.
Not only does IIoT provide a look at how the various areas of the mill are performing individually, but how the various areas of the mill are interacting with each other. Looking at a 24- to 48-hour trend provides a quick visualization of the process interaction and the effect on the final outfall conditions. It also provides early warning as to what needs to be done to achieve permit requirements at the outfall.
Over time, operators and engineers will begin to recognize how individual areas of the mill ecosystem should react based upon the operations of other areas of the mill. New information concerning the various metals, chemicals, and fiber levels entering the WWTP will allow for preemptive actions to ultimately meet the permit requirements at the outfall.
In the future, machine learning tools can be applied to provide alerts and recommendations to further automate responses to mill upsets that affect the environmental ecosystem.