Struvite scaling is a common but often underestimated constraint in biogas processes. It does not cause immediate failure, but gradually reduces efficiency by impairing heat transfer, restricting flow, and increasing maintenance frequency.
At one Ductor plant in Germany, this led to near-daily cleaning cycles. This article takes a closer look at how Ductor implemented Altum’s power-ultrasound solution to tackle that challenge, and the results that followed.
Ductor processes high-nitrogen feedstocks such as chicken manure using anaerobic digestion, mechanical dewatering, ammonia stripping, and nutrient recovery. This type of process creates near-ideal conditions for struvite to form.
Operational Impact of Scaling – What This Looked Like in Practice
Before intervention, the plant experienced significant buildup across pipelines, plate heat exchangers, and pumps.
This resulted in:
- up to 10 mm thick deposits inside pipelines
- reducedheat transfer efficiency
- increasing pressure losses and flow restrictions
To maintain operation, the plant relied on frequent clean-in-place (CIP) cycles:
- cleaning every one to two days
- approximately two hours of downtime per cycle
- roughly 335 cleaning events per year
- substantial citric acid consumption
This results a continuous loop of fouling, and all the cleaning, chemical handling, and manual labor that comes with it.
The Solution: Ultrasound, Applied from the Outside
Instead of removing deposits after they form, the approach focused on influencing how particles form and behave in the liquid.
High-power ultrasound was installed externally on pipelines upstream of critical heat exchange equipment, without process modifications or production interruptions.
The ultrasonic field changes particle formation so that solids remain suspended in the liquid rather than attaching to surfaces. As a result, hard deposits do not build up on heat exchangers and pipelines.
Results
Following implementation:
- cleaning downtime decreased from approximately two hours per day to two hours per month
- annual cleaning cycles were reduced from 335 to 12
- citric acid consumption decreased by more than six tons per year
- associated CO₂ emissions were reduced by over seven tons per year
After several weeks of operation, previously fouled pipelines remained largely clean, with only minimal residue observed. At the same time, process stability improved, particularly in ammonia stripping and overall system reliability.
If you’re cleaning every week – or every day
In processes with ammonia stripping or high-nitrogen feedstocks, struvite isn’t an isolated problem, it’s a predictable outcome of the process conditions. And if stable operation depends on frequent CIP, there’s a good chance you’re solving the wrong problem. It’s a sign that particle formation isn’t being controlled.
Frequent CIP is often accepted as part of the process, even when it’s quietly driving real costs: lost production time, excess chemical use, and avoidable wear on equipment. That’s reactive maintenance in practice, waiting for fouling to accumulate, then fighting it with chemicals, labor, and downtime. In most cases it can be reduced dramatically without changing the core process.
Struvite isn’t equally severe at every biogas plant, but it’s widely recognized across the industry. The plants carrying the highest risk tend to share one or both of the same characteristics: they incorporate ammonia stripping, or they process high-nitrogen feedstocks, such as manure from animal farms, wastewater treatment sludge, food-based organic waste, or slaughterhouse waste. If your plant falls into either category, struvite management isn’t a peripheral concern.
The potential doesn’t stop at fouling prevention either. Ultrasound can also be used to homogenize feedstock prior to digestion breaking down cell walls to improve fermentation efficiency and solid-liquid separation. It’s an area still being explored, but it points to a broader role for ultrasound technology across the biogas value chain.
If you want a direct view on whether this applies to your plant, we can review your process setup and identify where fouling is likely forming, and what can be done to prevent it.
Contact our team to discuss your process.
