Frequently Asked Questions

1. Q: What is the function of the headworks of a wastewater treatment plant?
  A: The function of a headworks is to remove floatables and other solids from the waste stream as it enters the plant. Headworks equipment is the first to treat the influent and protects sensitive downstream processes and equipment. Unwanted material removed at the headworks includes sticks, stones, rags, trash, condoms, paper, tampons, plastics, grit and sand. Equipment typically found in this area of the plant may include grinders, screens, screenings compactors, grit removal systems, pumps, gates and conveyors.

Provided by JWC Environmental

2. Q: What is the standard layout of a wastewater treatment plant headworks?
  A: There are two types of flow that enter a headworks: gravity fed and pumped flow. Gravity fed layouts must consider odor control and overflow issues. Pumped flow may require grinders ahead of the pumps to reduce large bulky solids like trash, sticks and leaves that can clog the pump’s inlet. Redundancy and bypass are important considerations in terms of the layout, because you never now what or how much is coming down the influent pipeline. For example, a plant might have three channels: two for flow and one for bypass. Selecting a layout will also be determined by the amount of headroom available. This will dictate the type of equipment that can be installed. Many medium and small plants are designing outdoor headworks without coverings, which can greatly reduce costs. A few manufacturers have developed screens that can operate outdoors, even in freezing weather, and clean discharged screenings to help eliminate odors.

Provided by JWC Environmental

3. Q: What types of wastewater screens are used in the headworks?
  A: The type of screen a facility uses is dependent on its process. Plants with heavy solids loading or combined stormwater systems need bar screens or auger screens with a grinder to turn large, bulky solids like tree branches into easy to handle chunks. On the other hand, a plant using Membrane Bioreactors need a finescreen with 3mm or smaller perforations so the high-tech treatment process can operate at maximum efficiency. A Sequencing Batch Reactor also requires a screen with small perforations, typically an auger fine screen, in part to ensure condoms and rags are removed so they do not escape into the environment. Condoms and some rags pass right through bar screens even if they have the smallest available spacing between the bars.

Provided by JWC Environmental

4. Q: How much debris will headworks screens generate?
  A: While there is a chart to determine the amount of debris a screen will generate (chart shows cubic feet of solids per mgd based on the screen’s spacing) so many large bulky solids end up in the influent pipeline that calculating and selecting a figure is difficult. Typical sewage has a 0.5% concentration of solid material in water; however, a combined system and many sanitary sewer systems can experience surges of debris that will exceed this figure. Moreover, illegal dumping of construction debris or yard waste can also enter the headworks making it important to have smart screens and equipment that can sense and adjust to changing solids loading. Look for screen manufacturers that make “smart headworks.” These headworks systems include product logic controllers that can tell the screens to speed up, turn on more screen equipment, activate conveyors or sluices or reverse a screen or channel grinder in order to clear an obstruction. This way the equipment works harder to take care of itself – instead of making you work harder. It’s also important to remember that today’s perforated plate screens have a higher capture efficiency than any other type of screen, according to a recent U.K. Water Industry Research report. The report demonstrated a bandscreen with 3mm perforations can achieve an 87% capture efficiency. Imagine the capture efficiency of a bandscreen with 2mm perforations. While fine screening creates a mountain of material in the headworks, it is more efficient to deal with the material here than later on in the process.

Provided by JWC Environmental

5. Q: How do you handle debris generated in the headworks?
  A: Today’s treatment processes demand smaller openings in both bar screens and fine screens, resulting in an increase in the amount of material pulled from the channel. Selecting or specifying a washer compactor will require consideration of how to reduce the material’s cubic volume, weight, water content, fecal content and odor. Recent studies indicate a washer-compactor with a grinder can have the greatest impact on managing discharged screenings. Results of using a compactor with a grinder have shown an 80% reduction in the cubic volume, a 50% dewatered content level and a tremendous reduction in fecal content and odors. The fecal material is broken up into tiny particles or even liquefied by the grinder, allowing organics to flow further downstream for biological processing, rather than being removed at the headworks and then sent to the landfill.

Provided by JWC Environmental