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Grab Sampling vs. Continuous Monitoring: Put The Odds In Your Favor

With relatively predictable flow patterns, municipal wastewater treatment plants (WWTPs) are conditioned to respond to the ebb and flow of demands with a series of small tweaks. While industrial wastewater processing does not always enjoy the same advantage of predictability, continuous monitoring of processes and wastewater output does offer opportunities for more responsive, more precise control.

With continuous monitoring collect data anytime, day or night.

 


 

Grab vs. Monitor

Even if both ultimately produce similar readings, the differences between continuous monitoring and grab sampling come down to the relative degree of timely process control, efficiency, and responsiveness they offer. That is because, in the world of industrial wastewater, there are multiple triggers for suddenly changing variables:

  • daily or seasonal changes to cooling water quality caused by a sudden slug of organics in surface water sources,
  • the potential for sudden process leaks that can dilute profitability and undermine the reuse of cooling water, and
  • instances where a process waste stream is combined with sanitary sewer system output.
Real-time continuous TOC monitoring is now considered by many to be a more cost-effective, accurate, and timely approach to wastewater testing than alternate parameters.

Figure 1. Real-time continuous TOC monitoring is now considered by many to be a more cost-effective, accurate, and timely approach to wastewater testing than alternate parameters.

A grab sample reading is essentially a snapshot frozen in time. At best, it is an indication of what conditions were 10 or more minutes ago when the sample was originally drawn. While a single grab sample can provide a precise numerical reading, it does so without context of whether that reading represents a stable, rising, or falling trend and no indication in rate-of-change. The only way to get trending information is to take multiple labor-intensive grab samples in sequence.

By contrast, continuous monitoring provides a steady stream of real-time process conditions — total organic carbon (TOC), pH, turbidity, etc. — for process optimization decisions (Figure 1). That makes it easier to identify changing wastewater flows in time to minimize upset conditions, costly product loss, or cooling water contamination.

 

The Motivations Behind Continuous Monitoring

While the value of automation has been widely recognized in larger applications, not every industrial application believes that the potential return is worth the investment. The only way to calculate that is to take a closer look at the cost and the benefits.

In industrial wastewater, grab sampling might be more acceptable for rare nutrient-monitoring applications than for organics sampling applications that can impact effluent compliance issues. Here are multiple attributes to consider when comparing continuous monitoring payback benefits:

  • Timely. Automated continuous monitoring can identify upset conditions or product leaks in time to minimize negative impacts.
  • Proactive. Continuous monitoring input signals can be used to adjust treatment processes automatically, using real-time control systems.
  • Error Reduction. No matter how well-trained or how careful an operator is, any manual grab sample process has the potential to introduce error — in the timing of the reading, handling of the sample, or recording of the result. Continuous monitoring minimizes such concerns, providing a continuous stream of data for follow-up analysis of specific events or overriding trends.
  • Cost vs. Payback. Whether the cost of real-time monitoring is considered an expense or an investment in future savings depends on how it is planned and implemented. In applications large and small, a careful evaluation of continuous monitoring can pay for itself based on rewards in labor savings, eliminating data gaps in grab-sample monitoring, or reducing the risk or frequency of non-compliance. Common benefits from continuous monitoring of industrial wastewater include:
    • Improving Efficiency, Avoiding Fines. TOC analyzers with certified 99.86-percent uptime for monitoring pollutants across a variety of industrial applications (Figure 2) enable users to maximize wastewater treatment efficiency and avoid costly penalties for non-compliant effluent.
    • Protecting Against Product Loss. Depending on the value of the product and the potential for leaks, continuous monitoring can generate significant payback in terms of identifying breakthrough events.
    • Protecting Treated Boiler Water And Cooling Water Investments. Application-specific water monitoring panels underscore the value of maintaining clean process water for steam/condensate water and cooling water. The expense of conditioning water used for these applications often justifies the value of continuous monitoring in terms of reduced chemical consumption.
    Numerous industries are able to meet their unique pollutant challenges with continuous TOC monitoring.

    Figure 2. Numerous industries are able to meet their unique pollutant challenges with continuous TOC monitoring.

 

The Ongoing Rewards Of Continuous Monitoring

  • Adapt To Normal Fluctuations Easily. By their very nature, some processes are prone to changing wastewater treatment demands quickly — with or without ample warning. Continuous TOC monitoring with real time control (RTC) makes it easier to cope with sudden spikes in dissolved oxygen (DO) demand and avoid process upset conditions.
  • Identify Potential Problems Quickly. The more frequently that upset conditions occur in an industrial process or the more costly their outcomes, the greater the benefits of continuous monitoring.
  • Reduce Latency And Human Variables To A Minimum. Timing issues related to sample handling or conditioning can affect reading quality. The more critical the impact of a particular reading — TOC, pH, turbidity, etc. — the greater the value of getting accurate results quickly.
  • Trim Cost And Waste To A Minimum. The intersection between continuous monitoring and real-time control maps the path to optimum efficiency through decreased chemical dosing costs, reduced manual sampling costs, and minimized product losses.
  • Support Low Total Cost Of Ownership (TCO). With the right features, real-time TOC monitoring solutions can minimize the need for operator intervention and reduce labor.
    • Self-cleaning designs minimize maintenance to just a few part replacements per year.
    • Two-stage oxidation technology offers up to 40 percent greater effectiveness than legacy technologies.
    • Continuous operation assures timely and accurate results while minimizing labor demands during overnight, weekend, or holiday periods.
    • Task-specific continuous TOC monitoring designs can be tailored to a wide range of applications — industrial ultrapure water, reverse osmosis, cooling water, industrial boiler water, stormwater, discharge control, carbon bed adsorber processes, wastewater effluent, and more.

 

Here’s What You Can Achieve

The green band in this chart documents the 15-percent cost saving opportunity and improved ammonia removal (AT2 Effluent) from wastewater at DO levels (AT2 DO) controlled through continuous TCO monitoring, as opposed to running at a typical fixed DO setpoint (AT1 DO).

Figure 3. The green band in this chart documents the 15-percent cost saving opportunity and improved ammonia removal (AT2 Effluent) from wastewater at DO levels (AT2 DO) controlled through continuous TCO monitoring, as opposed to running at a typical fixed DO setpoint (AT1 DO).

Every application is unique, but here are several case study examples of how wastewater operations have leveraged their way to outstanding operational and financial advantages by switching to continuous monitoring:

  • Controlling DO at a Grand Rapids WWTP yielded a 15-percent ($57,000) reduction in aeration energy costs (Figure 3).
  • The El Dorado Irrigation District used continuous real-time monitoring and control to experience a 50-percent reduction in aeration power consumption, while meeting permitted effluent levels.
  • A Minnesota municipal WWTP handling more industrial wastewater than residential wastewater switched to real-time monitoring and control to deal with shock loads of orthophosphates, cut treatment costs, and paid back its investment in less than one year.