Unlocking Extra Capacity and Managing Ammonia from Digestate

Anaerobic digestion (AD) plants generate energy from organic waste, but face inhibition from ammonia for certain nitrogen-rich feedstocks. This also results in their post-digestion reject waters being highly nitrogen-rich and difficult to treat. High ammonia loads can limit treatment capacity, requiring prior removal or dilution of ammonia to continue operation. Feed dilution lowers the overall treatment capacity, while biological removal of ammonia removes the feedstock itself to degrade ammonia and lower its concentration, both of which resulting in loss of revenue from biogas output. Aquature enhances AD sites with modular BASE polishing units that remove ammonia while recovering additional energy and green byproducts at minimal use of feedstock - the most efficient way to unlock additional AD output capacity without expanding the digester installation.

An AD operator was using up to equal amounts of dilution water to decrease the concentration of ammonia in their feedstock coming from a highly nitrogen rich source, such as manure, while removing much of the carbon within in the process during nitrification/denitrification of the dilution water. This limited the treatment capacity of the digester and incurred additional installation, operational and maintenance costs. Aquature offered a circular solution by efficiently removing the nitrogen directly from the feedstock instead.

At a Glance

The Challenge

• Ammonia-rich digester feed and digestate need decrease in ammonia concentration
• Conventional nitrification/denitrification steps are energy- and chemical-intensive, require extensive process control and consume 5-10x the amount of organic carbon per ammonia removed
• High nitrogen loads can cap plant throughput and limit acceptance of new feedstocks

For many AD operators, ammonia management in feedstock and reject water has become a bottleneck for growth, not just a side issue.

Aquature’s Solution

Aquature deploys a BASE polishing unit downstream of the AD process:

• Treat nitrogen-rich reject water by efficient, targeted ammonia removal and recovery, reducing the nitrogen load on existing polishing steps
• Recover additional energy and green byproducts from residual organics
• Implement in a compact, modular skid, minimising civil works and retrofitting complexity

The system was configured to operate continuously alongside the existing AD plant, with flexible control to match varying digestate flows.

Results

• >70 t/year of ammonia removed
  Significant reduction in nitrogen load to downstream treatment or discharge.
• 40-80% effective treatment capacity
  By relieving ammonia constraints, the plant can process more feedstock or higher-strength inputs without building new digesters.
• 1.6 GWh/year
  Recovered as hydrogen to supplement biogas energy, improving overall plant efficiency.
• Lower chemical, energy and feedstock demand
  Reduced reliance on intensive nitrification/denitrification or advanced chemical polishing.

Business Impact

For AD operators, integrating Aquature’s BASE polishing:

• Unlocks new capacity without the CAPEX of building more digesters
• Reduces OPEX and compliance risk associated with nitrogen-rich reject water
• Strengthens the business case for accepting higher-value, higher-strength feedstocks

By turning reject water from a hidden liability into a managed and partially valorised stream, Aquature helps AD plants operate more profitably, flexibly and sustainably.