Sustainable Biosolids Management


Historically biosolids have been an “invisible” issue in sea cage farming as they simply drop through the cage and are dealt with by the natural ecosystem. Clearly undesirable both in terms of pollution and wasted resources. Pollution aside; paying for feed and then throwing away the resultant manure and uneaten portion is wasteful. On land things are different and resource recovery opportunities exist. Onland pollution is also far more visible and easier to regulate and audit. The most recent Aquaculture Stewardship Council Standards for RAS farming state “Discharge of sludge is not allowed” and that accreditation requires “Evidence of implementation of biosolids (sludge) best management practices (BMP)” RASTECH have years of practical experience of designing and running RAS without biosolids discharge. 


The Easy One: Freshwater Aquaculture

Biosolids in a freshwater matrix are an acceptable feedstock for traditional Anaerobic Digestion Plants with little or no modifications and residues are suitable for application to land as a fertiliser. 

The Hard One: Saltwater Aquaculture

In a freshwater environment salt acts as a persistent bio-inhibitor, practically this means that saltwater aquaculture biosolids cannot be used as a significant feedstock in traditional Anaerobic Digestion.

RASTECH has developed a saltwater tolerant Anaerobic Digestion system using a unique microbiota. We also have the ability to harvest “waste” heat from the bio digestion tanks and also from the biogas powered generators. Having built the UK’s first AD plant powered shrimp farm for Great British Prawns we have unique and proven practical experience.