Advancements in Wastewater Treatment: Screen Technologies and Grit Removal Innovations

What do headworks screens and grit systems do?

They take out what the treatment process cannot handle. CDPHE's Design Criteria for Domestic Wastewater Treatment Works, WPC-DR-1, Chapter 5, defines preliminary treatment as removing large solids, grit and debris that can harm downstream processes.

The two states set different baselines:

• Colorado requires screening, or an equivalent such as a septic tank, at every wastewater plant. It requires grit removal at every mechanical plant unless other parts of the plant handle settled grit.
• Texas requires a grit removal system only at a plant that uses anaerobic digestion, under 30 TAC §217.124. For other plants, grit removal is optional.

How fine should a small plant screen?

Fine enough for the process downstream, and no finer than you can keep clean. Both states draw the line between coarse and fine screens at a quarter inch.

Texas sets the openings in two sections:

• A mechanically cleaned coarse screen has clear openings of 0.25 to 1.0 inch, and a manually cleaned one 0.5 to 1.0 inch, under 30 TAC §217.121.
• A fine screen has openings under 0.25 inch, under 30 TAC §217.122. A coarse screen goes ahead of it when the manufacturer recommends prescreening.

Colorado allows a wider coarse range in WPC-DR-1 Section 5.2.2. Manually cleaned screens run 1 to 1.75 inches, and mechanically cleaned coarse screens more than 0.25 up to 1.75 inches.

A Colorado fine screen, 0.25 inch or less, needs a coarse screen or grinder ahead of it unless the manufacturer says otherwise. Grit removal ahead of fine screens must be considered.

The states differ on credit. Colorado grants no organic removal credit for fine screens. Texas allows BOD5 reduction credit only if enough fine screens are installed to keep the credit with the largest unit out of service.

Ask each downstream equipment maker for its screening requirement in writing. That number, not a catalog, should set the opening. Our episode on simplifying screening design gets into why fewer moving parts matter in harsh headworks conditions.

How do you size a screen for peak flow?

For the design peak hour, with a bypass that works without anyone touching it. WPC-DR-1 Section 5.2 sets the Colorado rules:

• Firm screening capacity meets design peak hour influent flow.
• A single mechanically cleaned screen is allowed only with a bypass channel holding a manually cleaned screen.
• Flow overflows to a redundant channel automatically, by gravity, if the screen fails or overloads.
• Velocity through the screen stays under 3 feet per second at design peak hour flow.
• Screens with openings under 1 inch, and screens in the main channels of plants of 0.5 mgd or more, are mechanically cleaned.
• Fine screens get screenings washing facilities.

Texas asks for an emergency overflow sized to the plant's peak flow, and a way to divert flow to it, in Section 217.121.

When does a small plant need grit removal?

Colorado requires it at a mechanical plant unless other parts remove settled grit. Texas requires it when the plant uses anaerobic digestion. Where Texas requires it, Section 217.124 calls for at least two units that can handle peak flow, plus an emergency overflow.

WPC-DR-1 Section 5.4 sets design ranges by chamber type:

• Channel chambers hold velocity between 0.8 and 1.3 feet per second across the flow range.
• Aerated chambers give at least 3 minutes of detention at design peak hour flow, with a length to width ratio of 3:1 to 8:1.
• Vortex chambers need a straight inlet channel.
• Proprietary units follow the manufacturer's velocity and detention time.

Some grit equipment now targets finer particles. In our WEFTEC episode on sludge reduction, grit removal and dryers, the guest described grit removal that captures finer particles than traditional systems, down to about 75 microns. If finer capture matters to you, ask what particle size and capture rate the performance guarantee is written to.

Where do screenings, grit and sludge go?

Screenings and grit usually go to a landfill, so they leave the plant drained and covered. The federal sludge rule does not cover them: 40 CFR 503.6(h) excludes grit and screenings from preliminary treatment.

Texas handling rules sit in 30 TAC §217.123. Storage must hold at least one day of screenings, in covered containers. The storage area drains to the headworks, and disposal follows Chapter 330, the state's municipal solid waste rules.

Water is the catch. Under 40 CFR 258.28, a municipal solid waste landfill cannot take bulk waste with free liquids, as measured by the Paint Filter Liquids Test. That is why washing, pressing and compaction are worth their space.

Sludge follows its own path. Under 40 CFR 503.4, sludge placed in a landfill that meets Part 258 complies with the federal sludge requirements. The equipment discussed on the episode cuts the volume first:

• a sludge screen, sometimes called a strain press, pulls fibers and plastics that slipped past the headworks;
• a screw press dewaters sludge to cut the volume hauled;
• a solar dryer dries sludge in sunny climates;
• a belt thermal dryer turns sludge into a dry product that can be used as fertilizer.

Heat drying counts as a process to further reduce pathogens when sludge reaches 10 percent moisture or less, with particle or wet bulb temperature above 80 °C, under Appendix B to Part 503.

To be bagged and sold or given away free of the Part 503 land application requirements, the product must also meet the pollutant limits, Class A pathogen requirements and a vector attraction option in 40 CFR 503.10(g).

Which option wins usually comes down to climate, landfill rules and haul distance. That is a site decision, not a catalog one.

Is your headworks plan ready for design?

Answer each question yes or no. Any no is a gap to close before equipment is selected.

1. Do you know your design peak hour flow, initial and future?
2. Do you have each downstream manufacturer's screening requirement in writing?
3. Does every screen and grit unit have an automatic bypass or redundant channel?
4. Do you know whether your state requires grit removal for your process?
5. Has your landfill confirmed it will take your screenings and grit?
6. Do you know where your sludge goes and how far it travels?

Then ask your engineer: What does the downstream process need from the headworks? What happens at peak hour with one unit down?

A note on limits: this is general education on CDPHE's WPC-DR-1 (effective June 7, 2022), 30 TAC Chapter 217 and federal rules as of October 2026. It is vendor-neutral and does not rate any product. Confirm the current rules and your landfill's terms before design.

Frequently asked questions

What is the difference between a coarse screen and a fine screen?

The opening size. A fine screen has openings under a quarter inch in Texas, and a quarter inch or less in Colorado. Coarse screens have larger openings and often protect the fine screen behind them.

Is grit removal required for a small wastewater plant?

It depends on the state. Colorado requires it at mechanical plants unless other components handle settled grit. Texas requires it only where the plant uses anaerobic digestion.

I'm a developer building a package plant for a Texas subdivision. What happens to the screenings it collects?

They go into covered containers that hold at least a day's worth, in a storage area that drains back to the headworks. Disposal follows TCEQ's municipal solid waste rules, and the landfill will not take them with free liquids, so plan for drained, compacted screenings.

I run a small Colorado wastewater plant and our sludge travels a long way to the landfill. When is a dryer worth studying?

When haul and landfill charges keep climbing, or a dried product could be used instead of landfilled. Solar drying suits sunny sites. A dried product sold or given away must still meet the federal Part 503 tests, and Colorado's own biosolids rules apply.

Related resources

• Colorado Biosolids Management Regulations: How CDPHE Land Application Rules Differ from Texas for Private Plant Operators
• Sewage Sludge and Biosolids Land Application Permits in Texas: Rules, Fees, and Common Mistakes
• Package WWTP vs. Custom-Designed Plant: Which One Fits Your Project?
• Knowing When Your Wastewater Treatment Plant (WWTP) Needs to be Upgraded: A Guide for Rural Communities

Planning the headworks for a small wastewater plant?

MES designs small wastewater plants in Texas and Colorado around their real peak flows, from the headworks through solids handling.

We specialize in:

• Wastewater treatment plant design and upgrades
• Package wastewater treatment plant design
• Collection system and lift station design
• Site feasibility and wastewater due diligence
• Construction administration

Modern Engineering Solutions, McKinney, Texas. Contact: (214) 833-6748 or mod-eng.com