Our last blog highlighted the benefits of adding headworks screening to your lagoon facility. This article will review the main types of lagoon screens and their pros and cons to help you to determine which is the best fit for your lagoon system. Watch our latest episode of LDIB-TV, Types of Lagoon Screens, and read below for highlights.
Lagoon Screens: Criteria to Consider
The best lagoon screening option meets the following criteria:
- Low Maintenance: One primary benefit of a lagoon-based system for wastewater is its low operational demand, so the best option will not require much oversight or maintenance
- Weather resistant and robust: Can be installed outside without the need for a building to protect it
- Ability to handle peak flows
- Capture efficiency: Keeps nonbiodegradable materials out of the lagoon
Types of Lagoon Screens
Manual Bar Screen
Manual bar screens have been used with lagoon systems for years. The manual bar screen fits into a channel in front of the lagoon at a 45–75° angle. The bars are typically about 1/2″ thick and 1″ wide, with a spacing ranging from 0.75 to 2″. The screen is raked daily and the solids deposited into a basket for disposal. Before so-called “flushable” wipes, they did an adequate job of collecting nonbiodegradable solids that made their way through the pipes: cloth, toys, hundred-dollar bills. Nowadays, however, even daily raking can be inadequate to keep the screen from clogging.
- No mechanical parts
- Fits in channel
- Captures larger solids
- Requires daily manual cleaning
- Relatively low capture efficiency of 20–30%
Mechanical Bar Screen
The mechanical bar screen fits in a channel or directly on the influent pipe, mounted vertically or at an angle. The bars are spaced 0.6 to 1.5″ apart. It automatically cleans itself based on a sensor reading and deposits the screenings into a trash can.
- Cleans itself automatically
- Single drive motor
- Higher capture efficiency than a manual bar screen
- Several parts will require maintenance
- Lower capture efficiency compared to a perforated plate
Perforated Plate Screens
Boasting the highest capture efficiency, perforated plate screens have pores of about 1/4″ in size. Typically in lagoon installations, a perforated plate screen is installed in the influent channel and may be preceded by a grinder to grind the rags into smaller particles. The screen automatically cleans itself based on a sensor reading and dumps the solids into a trash can. Some designs even compact the screenings to squeeze out water.
While perforated plate screens work exceptionally well, they have significant drawbacks, primarily the operational and maintenance demands of having continuously running motors and multiple mechanical parts.
Their higher capture efficiency also makes them more prone to clogging than a mechanical bar screen.
- Self-cleans automatically
- Highest capture efficiency
- Wear and tear from continuously running motors
- Several parts require regular maintenance
- Smaller openings are more prone to clogging
Lagoon Screens: Our Recommendation
For most lagoon applications, we recommend a mechanical bar screen. Screens are not process critical, so we weight reliability and low maintenance more heavily than capture efficiency.
While a perforated plate screen has a higher capture efficiency, it isn’t necessary to screen out everything. After all, lagoons are designed to store solids and break them down over time. Keeping wipes out of the lagoon will protect aerators from ragging and prevent sludge buildup.
We don’t manufacture lagoon screens, but we do recommend them because they help a lagoon system Do It Better, which is our mission. Adding headworks screening improves treatment and will pay for itself over time by reducing sludge removal costs.