Since the days of the original Clean Water Act, operations and maintenance personnel have struggled with problems in wastewater treatment plants caused by flaws in design. The problems include safety hazards, difficulty sampling and monitoring streams, problems getting to equipment for maintenance or repair, and more.
Most such problems can be prevented during design if operators and engineers work together. It’s not just a matter of engineers coming down from their ivory towers to live in the real world. It’s also a matter of plant managers, supervisors and operators going to engineers with their issues and desires early in the process of a new plant design or upgrade.
In our years on both sides of the engineer-operator divide, we have seen what operators experience, heard their opinions, learned lessons, and developed approaches that help lead to the design of efficient, flexible, operator-friendly treatment plants. Here’s a look at a few kinds of problems that can be avoided if engineers and operators talk to one another.
Safety
Safety is the most important concern in operating a wastewater treatment plant. The facility should be designed safe, yet cost-efficient. One common hazard to be avoided whenever possible is confined-space entry. Figure 1 shows a return activated sludge flow meter hidden in a vault, and later relocated above the vault for easier access.
In addition, physical hazards should be designed out where possible. Figure 2 shows trip hazards in the form of conduits in walkways, and a slip hazard where spill containment with proper drainage should have been included.
Communication
Communication between engineers and operators enhances understanding of problems and leads to better designs. On one project, operators noticed that the digesters were achieving lower-than-normal volatile solids destruction. The engineers, acting on “textbook” information, decided to add mixers and heating to increase digestion performance. Because they looked at only a small fraction of the available data from the site, they failed to identify the true cause of the low performance.
After the “upgrade,” the digesters began foaming, and the digestion complex electrical consumption increased by a factor of four, without a significant increase in performance. To handle those side effects, the plant staff had to reduce the operating level and gas pressure of the digesters. The effort to solve a problem created a bigger one.
In another case, fractured communication led to a fractured structure. Figure 3 shows cracked masonry caused by direct contact between the steel support structure and the split-face cinder block. The engineers, making this modification under a change order, failed to recognize that the problem would occur. Insight from the operations staff might have prevented the problem.
Equipment accessibility
A recurrent error in treatment plant design is providing inadequate access to equipment. Easy access to panels, valves, actuators and other devices is essential. Engineers and operators should discuss up front which devices need to be read, monitored, adjusted and serviced, and make sure the design leaves operators ample space to do what must be done.
Figure 4 shows exposed conduits in front of a control panel — a clear impediment to access. Another common mistake is to install valves and actuators out of reach for an average person (Figure 5).
Automatic versus manual
Operators also deal with problems caused by too much or too little automation. Figure 6 shows an example of too little: A bar screen that requires manual cleaning when automated systems are available. Besides being a distasteful job, manual bar screen cleaning can be dangerous during rain events when operators will be exposed to high flows and lightning.
On the other hand, automated processes are sometimes installed without a manual mode that can be easily activated in case the automation should fail.
Eliminating “Hindsight is 20/20”
It is important to communicate during all phases of design, especially during the preliminary stage. Proper planning empowers engineers to design structures with an overall perspective of the system operation. In addition, when operators understand the scope of work, engineers are better able to prioritize needs versus wants and avoid missing critical design elements.
Figure 7 shows the lack of a drain in a chlorination basin. The absence of a drain requires the plant staff to spend many man-hours and move many truckloads in cleaning this basin.
Putting value to work
Operators know everything written in the plant log and on the computer monitoring screens. Most important, they know their plant in ways an engineer never can. Their experience, gained from working around the clock, can help engineers minimize failures and hold down costs. Before that can happen, operators must be empowered to express opinions and suggestions in all stages of treatment plant design and construction — and must take the initiative to do so. Keys to better treatment plant designs include:
• Fostering clear communication between operators and engineers.
• Trusting operators’ experience and knowledge.
• Identifying problems early and solving them collaboratively.
• Confirming the plant layout and making sure designers understand plant operations.
• Using three-dimensional drawings to identify conflicts.
• Using common sense when locating equipment.
• Including all maintenance crafts during the early phases of design review.
• Researching site-specific issues before trying to solve problems.
• Determining the optimum level of equipment automation and providing manual backup modes that are easy to deploy.
ABOUT THE AUTHORS
Contributors to this article are Ana Julia Pena-Tijerina, project engineer, Carollo Engineers; Raymond Perez, Jr., and Roberto Macias, plant managers, San Antonio Water System; Sterling Lee, plant superintendent, San Antonio River Authority; Rajendra P. Bhattarai, manager, Environmental and Regulatory Services Division, City of Austin; and Orren West, Jr., division manager, wastewater treatment plants, City of Austin.
