Decarbonisation Technology May 2026 Issue

release the salts during anaerobic digestion. Mechanical removal is labour-intensive and time-consuming. Kurita has developed special crystallisation inhibitors that exhibit a threshold effect by changing the crystal structure. Such additives are biodegradable, do not contain ethylenediaminetetraacetic acid (EDTA), and keep the salts stable in solution for three to four days (under laboratory conditions), whereas without treatment, the struvite salts quickly precipitate. Case study: reduction of nitrogen during fermentation At a municipal biogas plant in Germany, where approximately 32 tons per day of organic household waste are processed, a significant increase in ammonium nitrogen (NH 4 + - N) was observed. The results were 4.3-5.3 g/l, whereas the target should be 3.0-3.5 g/l. The biogas plant is operated continuously and fed with approximately one tonne of additional biowaste every 30-60 minutes. An additive from the Kurita ACF Technology series was temporarily dosed to reduce the NH 4 + - N concentration. ACF is a very strong organic liquid base that displaces NH3 from ammonium salts, forming a pH-neutral water- soluble ACF salt. By releasing ammonia gas (NH 3 ), the NH 4 + - N content in the digester was reduced to 3.6 g/l, while the feed input quantity was increased to 38 tons per day. Bioethanol Bioethanol can be produced from organic matter such as maize, corn, wheat, sorghum and agricultural waste. It is used directly as an engine fuel, as a blend in various liquid fuels, or as a feedstock for sustainable aviation fuels (SAF). In Europe, the most common bioethanol blend is E5, where 5% bioethanol is mixed in gasoline. The market share for E10 (10% bioethanol in gasoline) is growing as a result of efforts to lower the GHG footprint of road fuels over the last few decades ( ePure, 2025 ). Bioethanol is considered ‘carbon neutral’ as the CO 2 released from combustion is offset by the CO 2 captured through photosynthesis during the growth phase of crops of any type. Furthermore, most bioethanol is generated locally for the regional market, significantly

Electricity

Organic substrate

Combined heat and power unit (CHP)

Heat / cold

Electricity

Bio- methane

Digester

Fuel

Digested solids

Heat / cold

Biogas upgrading

Figure 1 Biogas concept

biogas generation and less solids discharged after digestion. Most biogas plants are small- scale units owned by private individuals or families (primarily farmers). The produced biogas can be used for electricity generation without upgrading. Higher-capacity biogas plants are usually operated by cities, municipalities, or waste-processing companies. The biogas can be upgraded and make a vital contribution to energy supply security. There are four steps in the digestion of carbohydrates, lipids (fats), or proteins to produce biogas:  Hydrolysis : Breakdown of complex organic matter.  Acidogenesis : Formation of volatile fatty acids.  Acetogenesis : Conversion to acetic acid, CO 2 , and hydrogen.  Methanogenesis : Final conversion to CH 4 and CO 2 . Production problems can be caused by salt fouling in pipes or by disruptions during the digestion process. The formation of hard, stone- like salt layers is observed in many biogas plants. Precipitation usually occurs in areas where there are changes in flow, pressure drops, or turbulence (such as pumps, centrifuges, pipe bends, and heat exchangers). These deposits are mostly struvite salts, which precipitate as magnesium ammonium phosphate (MgNH 4 PO 4 . 6H 2 O) under alkaline conditions when Mg 2+ , NH 4 + , and PO 4 3- are present in a ratio of approximately 1:1:1. Operational risks include pressure increases with leaks or damage, as well as blocked filtration and separation equipment, which degrade the quality of fermentation residues. Organic materials such as slurry, manure, or biowaste are substrate sources that