Line of action:

Status:

Execution date:

Design and installation of a biofilter for the purification of aquaculture water with filling of residual material from aquaculture activity, such as mussel shell, for its future implementation in a water recirculation system, with the ultimate objective of reducing water consumption in this sector.

The BIOSHELL project consists of 4 main activities, articulated to achieve the main objectives of the project:

A1. Laboratory-scale tests. Based on previous experiences based on the available scientific literature, ANFACO-CECOPESCA with the support of the University of Valladolid will carry out experiments with bioreactors with mussel shells as filler material.

A2. Sizing of the Biofilters. The University of Valladolid will be in charge of designing the biofilters on a pilot scale that will be used in the third activity. The preliminary results of the laboratory tests will be taken into account as well as the problems that arose at that stage in order to try to solve them in the pilot scale, such as obstructions, flotation, etc. A calculation will be made for the sizing of the biofilters and the number of shells needed for the pilot experiment (10-15L). From these designs, the construction stage of the equipment will begin, which must be for its possible integration into real “low cost” aquaculture plants, not only in the issue of filling, as is understood in the project when working with residual shells, but also in terms of materials and ease of integration into a recirculation system (RAS) that could be implemented in the field.

A3. Pilot-scale application. ANFACO-CECOPESCA, helped by the University of Valladolid, will work on the selection of materials that will allow the integration of a low-cost shell filling bioreactor on a pilot scale (around 15L) that will allow validating the results achieved on a laboratory scale and see how improvements in the design of the equipment allow an improvement in the process monitoring parameters such as the elimination of organic matter or nutrients from the wastewater of the inland aquaculture plant.

A4. Dissemination of the progress and results of the project. Finally, the results and conclusions of the project will be disseminated among the aquaculture sector with the aim of giving these low-cost systems an effective and sustainable alternative to RAS systems, and to promote their implementation in the production processes of companies, both through specialized media such as industry magazines and through general media. The dissemination activities will also include those of updating social networks (LinkedIn, Twitter, etc…) with the progress of the project. Also, a dissemination event will be held at the headquarters of ANFACO-CECOPESCA at the end of the project execution period where the final results of the project will be presented and other presentations on the same topic may also be made.

The beneficiary entity ANFACO-CECOPESCA has developed, together with its partner, the University of Valladolid, laboratory-scale tests that made it possible to compare and obtain results on the effectiveness of mussel shells in biofiltration systems compared to the use of plastic materials.

The data collected made it possible to calculate the sizing of the biofilters, leading to a design of the pilot system composed of two biofilters for denitrification-nitrification using mussel shell beds for the treatment of farmed water. When compared with commercial landfills, the results of the use of new sustainable landfills were positive.

In particular, two nitrification reactors were set up, one with shells and the other with commercial bioballs. In addition, a third reactor, shell denitrification, was assembled at the same time, but was started once the nitrification equipment had a steady steady state. The nitrification reactors operated for 120 days, with ammonium concentrations ranging from the initial 25 ppm to 5 ppm and with two different TRHs 1 and 0.5 days. For its part, the denitrification reactor operated for 70 days, with the exit of the nitrification reactor with mussel shells. The results show that with the bioball filters, almost 100% elimination was achieved at concentrations of 15, 10 and 5 ppm and TRH 1 day. Certain problems were recorded due to the rise in ammonium with no apparent explanation. The occasional drops in pH were compensated with bicarbonate. With the shell biofilter, an elimination of almost 100% was achieved at concentrations of 10 and 5 ppm and TRH 1 day, and at 5 ppm and 0.5 days of TRH, except in the last days, when there were increases in ammonium, no pH problems were recorded. As for denitrification, it was operated with a TRH of 1-1.5 days, feeding the outlet of the nitrification reactor with shells, but the results were not satisfactory.

As the laboratory results did not succeed in denitrifying, a system was thought of that would improve the denitrification rate by modifying the configuration of the reactor, placing the denitrification system prior to the nitrification system. The pilot system was set up at the Tres Mares Group plant in Lires. The nitrification and denitrification biofilters were filled with mussel shells, and the biofilter was inoculated with a mixture of urban WWTP sludge with aquarium nitrifying bacteria, just like in laboratory systems. The pilot system was operating for 10 weeks, measurements of pH, concentration of ammonium, nitrites and nitrates were carried out about 2-3 times a week and the elimination of organic matter in the stationary phase was monitored. Ammonium and nitrite clearance was 100% in the last 20 days, while nitrate concentration was reduced in the last few days, indicating that denitrification was adequate, contrary to what happened on a laboratory scale, where nitrate was not removed.

In short, the results show that the use of mussel shell led to greater stability in the nitrification process.

The main conclusions of the study were:

• Similar efficacy has been verified in shell filling systems compared to bioball fillings for nitrogen removal. The pilot-scale validation of the effectiveness of mussel shells as biofilter filler has resulted in 100% results in ammonium and nitrite removal, with a removal capacity of 5 ppm per day of ammonia nitrogen. In addition, the pH remained stable between 7.8 and 7.2 for most of the operation, without the need for external alkalinity sources. Total Organic Carbon (TOC) analyses in input and output samples indicated an organic matter removal of around 45-55%.
• The use of the shell allows greater stability in the pH in the biofilters, as initially envisaged.
• Scaling improved the results with respect to nitrate removal in the laboratory, although longer times were needed to reach a stable process.

The biggest problem is that very little waste is used, since biofilms do not accumulate in short periods and, therefore, there is no need to replace the shell filling, so as an aquaculture solution it is viable, but for waste management, the demand would be low.

The results have been disseminated in the journal Investigación, as well as in the Anfaco blog and in numerous press releases, in addition to their dissemination on the Twitter channel of the project’s profile and other social networks.

It can be concluded that the support and promotion of activities aimed at the use of waste from aquaculture, such as mussel shells in the case in question, through the application in biofiltration systems in aquaculture facilities or others susceptible to valuation, will favour, from a circular and sustainable economy perspective, a reduction in the impacts of human activity on the environment.