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Analysis • Overdesign of the instrument or the instrumentation system — if there are too many instruments, they won't get maintained. Presuming the right instrument has been installed and has been checked, the next thing is to operate and maintain it — surely something that the water industry is very used to. However, a system needs to be in place, especially where multiple people look after multiple things at different times. The instrument needs to be captured, tasks need to be put in place, and the right people with the right training need to do the right things. If instruments aren't maintained or the structure they are installed in kept clean, errors creep in and trust is lost. Ultimately, the instrument is lost, and the system fails — or, more dangerously, the instrument and its data are believed, and designs are prepared on the basis of erroneous data. So What Happens When It Goes Right? The chances and opportunities are actually endless. The old, often-quoted adage is, "You can't manage what you don't measure." It's especially true in the water industry. A more-or-less continuous measurement is required by the water industry. Instrumentation is the best means to control aspects of the treatment plant and to give operators the right information to manage the plant. It empowers the operators of treatment plant to make informed decisions about how a plant is operating. This is all very well in theory, but what about the fact? At the most basic level, dissolved oxygen probes have proved over the years that they are well worth the investment. The modern optical probes are relatively cheap, and with a simple control system and PLC can be used to control the dissolved oxygen in an activated sludge treatment facility at a (near-) constant fixed setpoint. This is technology that has been in existence for years. The less commonly used methodology of wastewater instrumentation and control is the simple mixed liquor monitor. It can be used to measure the solids in the lanes to tell an operator if levels are going up on a daily basis (with trend analysis via the PLC/ SCADA) or down (allowing decisions to made about wasting rates). At the very least, this gives a more efficient mode of operation, saving time and money in activated sludge process (ASP) control. Done in an automated way, which is the next step, this can control levels with operator supervision only and give a more consistent product in terms of liquid effluent and sludge consistency. The most modern techniques involve the use of instrumentation for advanced process control, with the data from instrumentation used to drive models that control treatment. Instrumentation is becoming more and more important in the global water industry as a means to reach the production mindset that the industry is seeking. It also allows for efficiencies in both environmental and financial terms, which seems to be the ultimate goal that the industry is being driven towards. Oliver Grievson is currently the flow compliance & regulatory efficiency manager for the U.K. water company Anglian Water. He also runs the "Water Industry Process Automation & Control Group" (WIPAC) on LinkedIn and is a member of the Wastewater Committee of the Foundation for Water Research. His career has stretched from working in a water laboratory to managing water and wastewater facilities around the world. CASE STUDY 2: THE RESISTANCE TO THE EFFECTIVE USE OF INSTRUMENTATION Exhibit A: There are a plethora of instruments at a treatment plant in the U.K. – all different, all measuring different things, all needing different maintenance. The question for the operator is, "What am I looking at? How do I maintain it?" The answer is that it's too complicated … the system fails. Exhibit B: A single treatment plant has over 50 dissolved oxygen probes in combination with three activated sludge streams. The task for the operator is to maintain all the dissolved 26 wateronline.com ■ oxygen probes and keep the instruments working effectively. He can't – there are just too many instruments … the system fails. Exhibit C: A probe is installed in such a way that the operator can't maintain the instrument safely. It's not safe … the system fails. All three examples lead to a lack of trust in instrumentation. The result: a resistance to instrumentation. Water Online The Magazine