Lightning in water: how High Voltage Pulse fragmentation works

How does the High Voltage Pulse technology actually work? It's one of the questions we get most often. This is the longer answer.

A discharge that travels through, not around

The visible part of what we do at Centro Uno is industrial. Bottom ash from waste-to-energy plants enters one end of the process, and recovered metals come out the other. The interesting question is what happens in between.

The core process is called High Voltage Pulse fragmentation, or HVP for short. In academic literature it goes by electrodynamic fragmentation.

The principle: pulses of around 200,000 volts travel through a water bath in which the bottom ash is suspended. At those voltages and rise times of a few hundred nanoseconds, water behaves counter-intuitively. It insulates better than the solid material it surrounds. The electrical discharge therefore takes the path of least resistance, which is through the bottom ash, not around it.

That discharge generates internal shockwaves. Those shockwaves split the material along its natural grain boundaries.

Why "along grain boundaries" matters

A mechanical crusher reduces material by force. It crushes everything roughly equally, regardless of internal structure. A piece of copper trapped inside a mineral matrix gets pulverised together with the mineral.

HVP does something different. By splitting along grain boundaries, it separates what is already separable. A copper inclusion comes out as recoverable copper. A mineral fraction stays as a mineral fraction. An iron particle keeps its useful properties.

The result is that downstream sorting works on cleanly separated material instead of a homogenised mix. Magnets pick up iron. Eddy currents pick up non-ferrous metals. Density sorting handles the mineral fraction.

That clean separation is what makes industrial-scale metal recovery from bottom ash economically and technically viable.

From mining to waste-to-value

The technology did not start with bottom ash. It was originally developed in mining, where it was used to recover high-purity silicon from ore while preserving crystal structure. Selfrag took the underlying physics and built an industrial-scale process around a different input stream: incinerator bottom ash from Swiss waste-to-energy plants.

Centro Uno in Full-Reuenthal has been running commercially since 2024. Centro Due in Kerzers is under construction. Patents protect the industrial application. The water-based closed-loop design, the staged sorting that follows fragmentation, and the integration with Swiss waste-to-energy infrastructure are all proprietary.

What comes out

Per tonne of bottom ash that enters the process, the typical recovered fractions are iron, aluminium, copper, brass, and stainless steel, plus a clean mineral fraction. The metals re-enter the steel and aluminium cycles, where they replace virgin material. The mineral fraction goes to the cement industry. As a rule of thumb, around half the input mass leaves the process as recovered material with somewhere to go.

An older technology, a newer methodology

HVP is the engine. It has been recovering metals at industrial scale for years, before this work was being turned into verifiable carbon credits.

What got added on top is everything that turns those avoided emissions into a credit a serious buyer can pay for. Mass-balance audits. Emissions accounting against the right industry baselines. Mineralogical traceability. Independent academic and technical review. That is a separate, four-year piece of work that lives on top of the technology, not the other way around.

The technology answers the question of what is physically possible. The methodology answers the question of what a serious 2026 buyer can defensibly pay for. Both are needed. Neither, alone, is enough.