Sand & Grit removal at Dairy RNG

Sand and grit are persistent in many dairy manure RNG facilities. Inert sand and grit enter the handling and digestion process with bedding, windblown grit, or co-substrates. Once in the system, the sand settles. As a result, this material plugs fiber removal equipment, reduces effective digester volume, accelerates abrasion, and forces costly tank cleanouts.

At one large dairy RNG project, this challenge showed up in the manure pit, fiber separation equipment, and overall solids handling train. The site needed a solution that could run continuously, seemlessly integrate into an existing operational plant, and avoid removal of volatile solids that produce valuable biogas.

Grit buildup drives maintenance and downtime

This site operates four CSTR digesters with a total working volume of about 9 million gallons. Feed manure slurry was managed around 8.1–8.5% total solids to maintain ability to pump.

Despite operational controls, inert solids remained a major burden:

6–8 feet of sand buildup in the manure feed pit
Fiber separation plugging occurring weekly or biweekly
15-20% of operational volume of digesters replaced by sand, reducing effective working volume
Frequent third-party de-sanding, reported at a cost of $1.2M per year
Cleaning events that could take days to weeks, depending on the unit and location

However, the real impacts were not limited to not labor and contractor cost, but also capacity loss and wear on downstream equipment. Therefore, the site focused on removing heavy inerts before they became a shutdown driver or diminished capacity.

Download the Paques BIOCYCLONE^™ industry paper.

Facts and figures

Process before:

Site: Dairy RNG facility in the USA
Scale: ~15,000 milking cows
Digesters: 4 × CSTR, total ~9,000,000 gal
HRT: ~15 days (site-reported)
Feed: 8.1–8.5% TS Integration

Performance output:

Sidestream flow: 400 GPM
Sand removal: ~1 ton/day
Clarified output: 7.9% TS (from 8.1% TS feed). Grit out, organics stay.
Waste grit: ~40–60% TS
Estimated inert removal: 95–98% (sidestream basis)
Payback: <5 months (site-calculated)

Benefits:

Cleanings reduced from 4/month to 1/month
Estimated savings $90k–$150k monthly
Reduced plugging and fewer reactive interventions.
Lower abrasive wear risk downstream
Minimal VS loss to protect gas yield

Paques BIOCYCLONE^™ as a retrofit “dialysis loop”

A cyclone principle, engineered for manure and digestate slurries

Paques BIOCYCLONE^™ uses the same separation physics operators know from hydrocyclones. Using centrifugal force, inert solids separate through differences in specific gravity and particle size.

However, Paques BIOCYCLONE^™ is designed for high-solids slurry variability and selective removal of heavy inerts.

What’s different versus a generic hydrocyclone

In many hydrocyclone configurations, the underflow discharges through the apex to an open outlet, often near atmospheric conditions. That “free discharge” is a common benchmark, but it limits how precisely you can control underflow behavior on changing digestate and resulting solids discharge liquid portion as well as the sizing of hydrocylones.

Paques BIOCYCLONE^™ controls solid discharge, using:

A heavy-duty discharge valve to manage the bottom outlet
Proprietary internals to stabilize the flow field and enhance separation
VFD speed control plus timers to tune how often, and how long, underflow is discharged

As a result removing sand and grit while also minimizing volatile solids loss.

Small footprint, low-disruption integration

For this dairy RNG facility, Paques BIOCYCLONE^™ was installed as a sidestream “tank dialysis” unit:

Pull from the manure pit via a high-solids feed pump
Separate heavy inerts in the BIOCYCLONE^™ vessel
Return clarified manure back to the pit
Discharge concentrated grit on a controlled cycle

This approach avoided rerouting the full plant influent and reduced integration scope demonstrating ability to retrofit into operating facilities where uptime matters.

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Let's connect for a short RNG farm assessment

Measurable savings, fast payback, simpler operations

Performance outcomes, site-reported (Fall 2024 install, 12+ months operation)

Paques BIOCYCLONE^™ delivered high solids underflow and stable clarification:

Sand removal:	~1 ton/day
Flow rate:	~400 GPM sidestream
Average feed vs Clarified output:	In: 8.1% TS - Out: 7.9% TS. Only a 0.2% TS drop. Grit out, organics stay.
Waste grit:	40–60% TS, with minimal VS loss
Estimated inert removal:	95–98% of incoming inorganic fraction in the sidestream
Simple payback:	<5 months (capital + installation, site-calculated)

Operational impact

Before Paques BIOCYCLONE^™	After Paques BIOCYCLONE^™
Sand buildup in pits and recurring plugging events Cleaning cycles frequency as many as 4 per month Increased wear risk on rotating and downstream equipment Material handling interruptions, and lost production potential	Cleanings reduced to 1 per month Estimated savings of $90k–$150k per month in maintenance and cleaning-related costs Lower grit load reaching downstream equipment and digesters Less operational disruption, and improved stability

Because wasting is controlled and underflow is thickened, the site also reduced water burden over approaches that rely on heavy dilution.

“The key advantage with the Paques BIOCYCLONE^™ is control. By managing controlled solid discharges, we concentrated grit up to 60% total solids while keeping volatile solids in the process. That control helped the site cut cleaning frequency and stabilize operations.”

Timur Dunaev,
Managing Director/CEO, Paques US

Ready to assess Paques BIOCYCLONE^™ on your RNG farm?

If you are dealing with bedding sand, grit, or recurring cleanouts, a short assessment can clarify fit and timing. Contact Paques experts to discuss:

Where grit enters and settles on your site
Expected installation scope and set-up time
The business case, based on avoided cleanouts and reduced wear

Let's connect for a RNG farm assessment

PAQUES CASE

Reducing livestock manure digester cleanout costs with Paques BIOCYCLONE™

The perfect solution for tackling sand and grit accumulation in manure digesters. Paques BIOCYCLONE™ combines efficient, controlled solids separation with proprietary internals, ensuring thickened discharge of inorganic solids, increased energy yield, and reduced maintenance downtime. Discover how BIOCYCLONE™ can enhance your biogas production process and deliver significant operational savings. Download the industry paper now.

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