Resource recovery from chitosan and ragworms’ bioremediation of waste

At present, the oceans are providing approximately 14 million tonnes of whole feed fish and 4.6 million tonnes of by-product seafood processing (frames, guts, skin, etc.) on a yearly basis to produce 4.2 million tonnes of fishmeal and 900,000 tonnes of fish oil used as feed in aquaculture farming. The UN has projected a population increase to 9.7 billion people by 2050, and as a consequence, the UN Food and Agriculture Organisation has estimated aquaculture production to double in size over the next few decades to keep pace with the rising global demand for seafood . However, overfishing, mismanagement of crucial feeding grounds and unsustainable aquaculture farming methods are already threatening sources of fishmeal and fish oil used in aquaculture, fish and seafood stocks and hence, the long-term supply of seafood to market.

Furthermore, aquaculture wastewater has been found to pollute natural water resources, e.g. by causing eutrophication. Sustainable aquaculture and aquaculture wastewater treatment solutions hence need to be found in order to address several of the UN’s Sustainable Development Goals, which include Zero Hunger (Goal 3), Clean Water and Sanitation (Goal 6) and Life Below Water (Goal 14). Aquaculture is of particular relevance to Scotland, who has identified the food and drink sector as a key economic area for development. In particular, the Scottish Government has recently adopted the Scotland’s National Marine Plan (NMP) setting out a national strategy to ensure the sustainable economic growth of marine industries taking environmental protection into consideration: Scotland is the third world’s largest producer of salmon alone, with finfish and shellfish production set to increase by 25% and 100% in the next few years, respectively.

Polychaetes, a diverse group of predominantly marine annelids, are robust and widespread, with species tolerating many different conditions such as extremely polluted environments and a wide range of salinities, to name but a few. Many species of polychaetes consume detritus, with studies showing that polychaetes can bioremediate the water they naturally inhabit, as well as bioremediate aquaculture wastewater effluents by feeding and extracting valuable elements from uneaten fishfeed and faeces, including lipid and protein.

Furthermore, the large majority of species are extremely palatable to fish and crustaceans and a nutritional source of rich fatty acids, easily digested and highly valuable protein and lipid: polychaetes are rich in marine protein and omega 3 and 6 fatty acids. The use of fresh polychaete biomass is routine in Penaeid shrimp hatcheries and several finfish species, having positive impacts on production and viability of subsequent offspring. More recently, they have also found use in the pharmaceutical industry and inclusion in ornamental aquarium and pet food markets. Polychaetes are hence excellent candidates to bioremediate waste, including aquaculture wastewater, whilst concomitantly producing biomass, which is a proven fishmeal and fish oil replacement in aquaculture feed.

Polychaetes feed mainly on particulate matter and have been found to reduce total suspended solids (TSS) in aquaculture effluents by more than one third. However, part of the wastewater effluent will be composed of dissolved matter, requiring further treatment, which can be expensive and energetically consuming. One way to circumvent this would be to coagulate the dissolved matter into bigger particulate form and feeding it to the polychaetes. This could be achieved by using chitosan, a non-toxic and biodegradable polysaccharide derived from waste shellfish outer skeleton, which has been tested for coagulation of aquaculture wastewater treatment and shown promising results. Since chitosan has also shown promising results for the coagulation of contaminants in freshwater, namely algae and dissolved organic matter (DOM), this project will further assess the possibility of feeding chitosan coagulated sludge from freshwater treatment, in order to determine if this waste stream can be recovered and used to feed polychaetes and hence generate income in the Water Sector.

The Hydro Nation Scholars Programme is an open competition for PhD Scholars to undertake approved projects, hosted within Scottish Universitites and Research Institutes. Full funding is available from the Scottish Government (to host institutions via the Scottish Funding Council). The funding available will be in line with the REsearch Councils UK doctoral stipend levels and indicative fees. Fully-funded PhD studentships for four years. This includes stipend and fees (indexed on the RCUK rate).