7 WWTP Design Ideas That Operators Will Love

Posted by Eric Moore on Monday, July 26, 2021

Our Roundtable Series brings together our engineers and operators with our industry friends for candid discussions about the wastewater industry. Last month we delved into the struggles operators have with the Operations and Maintenance (O&M) of their plants, and how some of these issues could be prevented at the design phase. As an Operator and a PE, I know first-hand how these issues can have a significant effect on an operator’s day-to-day work and the upkeep of a plant. Our roundtable had limited time to discuss these points, so I crafted this supplemental list of critical design elements for operators and engineers to consider during the design or upgrade of wastewater treatment plants.

These are just some issues to keep in mind – check out the roundtable for more! And please share any key design tips you’ve learned over the years.

1. Flexibility in Operations

Designing more than the bare minimum provides flexibility during use. So consider adding:

• Dissolved oxygen (DO) sensors to prevent over-aeration (saving on energy), provide DO trending over time (critical when trouble-shooting treatment system performance), and allow the operator to adjust the system based on actual conditions.
• Multiple chemical feed points, based on operator input.
• Interconnections between treatment trains to allow individual processes to be taken off-line for maintenance. This can be a challenge for smaller package plants.
• Additional capacity in wet wells to provide time to respond before an overflow can occur.
• Potable water back-up to utility water for critical system processes.
• Sequencing Batch Reactor (SBR) Tanks: SBR tanks should be drained, cleaned and inspected annually, so you’ll need a place to put your valuable bugs. That means either putting them in the digester (this may require more sludge pressing than normal, and more utility water!), or putting them in another SBR tank. But how will it get there? If you send it back to the headworks via the tank drain, it can overwhelm the influent structures and equipment, so be careful where it comes into the process. If there are flow limits, it will take forever to drain a tank.

2. Availability of Utility Water

Processing dirty water requires a lot of clean water, so be sure there is an adequate volume of utility water to handle all the plant’s major functions (i.e. influent screen, belt filter press, chemical feed motive water) plus hydrant flow for cleaning. Locate hydrants in convenient locations for tank cleaning, and design with adequate pressure for cleaning (70 psi for a 1.5” hose).

3. Site Layout

Remember that all pieces of equipment that go in will need to come back out some day! That means designing more space than you need for construction so there is adequate room later for operations, maintenance, and replacement, like:

• Configure buildings and pavement with ample turning radiuses and clearances. Don’t forget the swing-arc for cranes and lifting devices in these clearances.
• Watch the placement of vaults and other structures. Sometimes they are positioned after the building placement, without consideration of clearance space for turning and navigating equipment. Fully buried vaults may need their lids/hatches designed to stand up to the weight of vehicles and equipment (cranes, excavators, and heavy trucks) during major O&M activities.
• Even the little stuff is heavier than you think, so make sure motors, valves, fittings, etc. can be removed and placed onto a cart or truck, and be sure heavy items like pipe spools, valves, fittings, and meters can be moved within a valve vault.
• Provide access for a hand truck (or preferably, a forklift!) where barrels of chemicals need to be moved.

4. Access for Maintenance

A simple rule of thumb is if it can’t be reached, it won’t be maintained! Also be wary of:

• Head-Bangers and Nut-Busters, which are areas with a lot of piping at… uh… delicate heights. While it’s tough to route piping without having some at less-than-ideal elevations, always remember someone must step over, under, or around these pipes. Better to need a ladder for access than to repeatedly bash your skull on a low-hanging pipe.
• Provide stairs for access over low pipes to protect those folks with shorter inseams. Finally, remember that the average age of most operators is 50+, so design access that would make your mom and dad happy.
• Critical valves require quick, easy, and clear access, so your personnel can get to them in a hurry during an emergency.
• Instrumentation, which will be read by operators of varying heights. Make sure meters, dials, and readouts can be read by all, not just the tall people.
• Spacing at bolted joints, since sometimes a lot of persuasion is required to remove bolts. Account for wrench handle extensions when setting clearances between fittings and other knuckle-bashing items like walls, other pipe and fittings, and delicate instrumentation.

5. Lab Space

During use, owners and operators often find there’s never enough counter space or storage space, so don’t overlook these critical elements during the design stage. As time and technology marches onward, more testing and testing equipment is almost a certainty.

6. Vactor Truck Dump Location

Sanitary sewer cleaning requires a vactor truck to suck out sewer main contents, then takes them to a disposal site at the plant. During transport, the contents separate into a liquid on top and goopy sludge on the bottom, so disposal can lead to a huge mess when the waste comes flying out of the vactor. Thoughtful design of the dump location can make you a hero!

If a vactor dumps without removing the liquid first, it makes a huge messy splash! Don't believe me? See for yourself. Decanting the liquid before dumping reduces the splash, so provide an extra section of hose with a quick disconnect that remains at the dump pad site, along with hooks to hang and store it. Provide a decant manhole or a pipe connection plumbed directly to the pad drainpipe for the hose to dump into directly.

The dump pad is typically a concrete slab sloped down to a grated drain surrounded by three low side-walls to contain the waste. If the waste is mostly liquid, the “splash zone” may be significantly bigger than you think! So be sure it’s contained with the right size pad and sidewall height. Bonus Tip: include a low, wide bump at the entry to the pad for the rear wheels of the vactor to drive over before dumping, since trucks will still dribble after dumping, and that too can make a mess.

7. Hydrogen Sulfide Control

Just assume it will be a problem at the influent to the plant… because it will! Even if hydrogen sulfide concentrations are not particularly high, over the long-term corrosion of concrete can still occur. Protect your concrete, use corrosion resistant materials for stairs and platforms, ensure adequate ventilation, and consider odor impacts from the ventilation.

 

Categories: Municipal Infrastructure

Tagged: Wastewater