Efficient digestate treatment is critical to the performance and sustainability of any biogas plant. Advanced tubular ultrafiltration (UF) membranes provide the high‑quality solid‑liquid separation necessary for managing challenging digestate streams and maintaining stable, reliable plant operation. Tubular UF systems are designed to perform under the harsh conditions typical of digestate processing. They ensure consistent filtration efficiency while minimizing downtime and maintenance.
Biogas operators can increase overall plant efficiency, improve effluent quality, and support regulatory compliance by integrating robust UF membrane-based digestate treatment technologies. These solutions also play a key role in enhancing environmental performance and enabling more effective nutrient recovery. They help biogas plants transition to more circular, resource-efficient operations.
As a sustainable alternative to fossil fuels, biogas is gaining growing attention for its role in mitigating climate change and reducing greenhouse gas emissions. Beyond its environmental benefits, biogas offers practical advantages: it can be easily stored and used on demand, and it enables decentralized, off‑grid energy production directly at the source. These features make biogas a highly flexible and resilient solution for both energy generation and waste management.
However, biogas production also generates large volumes of digestate — the nutrient‑rich residual material left after anaerobic digestion. Traditionally, this digestate has been spread directly on agricultural land as a soil conditioner. While this practice returns valuable organic matter and nutrients to the soil, it also comes with increasing constraints and drawbacks.
Regulatory limits on nitrogen application, competition for available farmland, seasonal land‑spreading restrictions, and growing concerns about nutrient leaching and environmental impact all highlight the limitations of relying solely on direct land application. As a result, advanced digestate treatment technologies are becoming essential. This shift is key to ensuring that digestate management supports — rather than limits — the future growth of biogas and biomethane and the broader circular‑economy framework.
For land spreading, with limited amount of nitrogen that can be applied per hectare.
For landfarming, only permitted during the crop‑growing season.
For land, in regions with high livestock density.
if the biogas plant is far from the agricultural fields.
By transitioning from simple land disposal to more sophisticated processing approaches, biogas plants can reduce environmental burden, comply with evolving legal requirements, lower logistics costs, and unlock new opportunities for nutrient recovery and resource valorization.
Digestate is a challenging stream to process: it contains slowly biodegradable organic matter, high suspended solids loads, and elevated nitrogen concentrations. To address these complexities, Berghof tubular UF membranes are deployed in two optimized process configurations, depending on the treatment objectives, project constraints, and the required balance between CAPEX and OPEX.
The external MBR allows removing the difficult to biodegrade organic matter and nitrogen and produces high-quality water for discharge or RO post-treatment. On the other hand, tubular UF can be used as a standalone filtration step to preserve and concentrate nutrients and produce high value biofertilizers.
Digestate treatment places high demands on biological processes, requiring technologies that can operate reliably under challenging conditions. The external MBR offers a robust solution, delivering stable bioprocess performance and excellent nitrification rates even with difficult feedstock. Berghof tubular membranes ensure consistent, trouble‑free operation, providing the reliability biogas plant operators depend on.
The external MBR integrates a biological reactor with anoxic and aerobic zones for efficient carbon and nitrogen removal, combined with Berghof tubular UF membranes for reliable biomass separation and high‑quality effluent production. Compared to conventional biological processes and submerged MBR systems, this approach offers several distinct advantages:
High Efficiency
Operating at elevated MLSS concentrations, even up to 20 g/L or higher, allows for long sludge ages, which intensify biological activity, support highly efficient nitrification, and improve the degradation of slowly biodegradable organic matter. Remarkably, this is achieved with a smaller bioreactor volume and substantially reduced excess sludge generation.
Robustness
Digestate is a challenging stream and the resulting mixed liquor is significantly less filterable than that produced from municipal or other industrial wastewater streams. Tubular membranes offer superior fouling resistance, and can reliably handle high solids concentrations, elevated viscosity, and severe fouling loads — conditions under which submerged membranes typically struggle. For these reasons, the majority of digestate‑treating MBR systems rely on external tubular membranes.
Effluent Quality
The external MBR delivers exceptionally clear, solid‑free effluent, achieving turbidity levels below 1 NTU and a SDI of less than 3. This high‑quality permeate is ideally suited for downstream polishing and can be further treated with RO systems to achieve more than 99 % removal of carbon, total solids, and nitrogen.
Compact and Modular
External MBRs are among the most compact solutions available for digestate treatment, offering a significantly reduced footprint compared to conventional systems. The UF units are fully modular, allowing easy scaling and straightforward upgrades as treatment capacity or performance requirements evolve.
Customizable
Berghof Membranes has developed B‑SMART®, a fully customizable external membrane filtration platform that can be configured with a wide range of features and functionalities to meet specific process requirements.
After mechanical separation, the liquid fraction of digestate is fed into the tubular MBR, where organic matter and nutrients are removed through a sequence of anoxic and aerobic reactors. The tubular UF modules coupled to the biological process produce a solids‑free permeate, which can be further polished using reverse osmosis. The resulting high‑quality effluent can be safely discharged in compliance with the strictest environmental regulations or reused for irrigation and various industrial applications.
Organic waste management has become one of the strongest examples of a circular economy, producing renewable energy while recovering and valorizing the nutrients contained in waste products. With a proven global track record and long‑standing partnerships with leading OEMs in digestate treatment and biogas plants engineering and operation, we are uniquely positioned to support and enhance the performance of any new or existing waste‑to‑energy project.
Berghof tubular UF membranes effectively separate particles, colloids, and macromolecules present in the digestate. Their ability to handle high concentrations of suspended solids enables high‑recovery filtration, even with complex and heavily loaded digestate streams. Particulate carbon and nutrients are partially captured in the UF reject, which is returned to the liquid/solid separation for recovery as a dry, nutrient‑rich material suitable for agricultural use. Most dissolved nutrients remain in the UF permeate, which is ideally conditioned for final treatment with RO. The RO concentrate becomes a nutrient‑dense liquor containing dissolved NPK, providing a valuable liquid fertilizer, which can be further concentrated with evaporation. Meanwhile, the RO permeate is a high‑quality treated water that meets the most stringent standards for discharge or reuse.
High tolerance to suspended solids
Berghof tubular membranes have wide channels, up to 12.7 mm diameter, which allows them to process digestate with high solids loads while maintaining stable flow conditions and minimizing the risk of clogging and plugging.
Mechanical robustness
Berghof’s dual‑layer tubular membranes are engineered for exceptional mechanical strength and high pressure resistance. Compared with ceramic membranes, they offer a significantly lower investment cost while still providing a long operational lifetime and lower energy consumption.
Ideal pre-treatment before RO or ammonia stripping
By removing virtually all solids and colloids, tubular UF delivers a highly stable, low‑turbidity permeate. This consistent quality significantly enhances the efficiency and reliability of downstream processes such as reverse osmosis or ammonia stripping, reducing fouling rates and improving overall system performance.
Tubular modules operate in direct filtration mode to separate the suspended solids and high‑molecular‑weight compounds remaining in the liquid fraction of digestate after the primary solid–liquid separation step. Most of the nutrients are preserved and recovered in the UF permeate, which is then treated in a multi‑pass, multi‑stage RO-system. The RO concentrate forms a nutrient‑rich liquor suitable for recovery and use as a high‑value fertilizer. Meanwhile, the RO permeate is a high‑quality water stream that meets even the most stringent discharge or reuse requirements.
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