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High algal recovery using a Salsnes Water to Algae Treatment (SWAT) filter technology

Final Report Summary - OPERATION SWAT (High algal recovery using a Salsnes Water to Algae Treatment (SWAT) filter technology)

Executive Summary:

Microalgae has been researched and cultivated commercially for applications such as, biofuels, cosmetics, human and animal nutrition, wastewater treatment, to name a few. The most critical challenge faced by all algae growers is harvesting. Harvesting is expensive and energy intensive. Typically, harvesting costs contribute 25-30% of total costs of algal biomass. A group of European SMEs (Salsnes, NO; Asio CZ; Inwatec, PL) decided to work together to capture a part of the global algae harvesting equipment market. Today, European Union is home to 30% of the world’s algae market activity.

The overall objective of the project was to develop a universal algae harvesting technology by building on the SMEs experiences, which are currently in the wastewater market. The overall algae harvesting technology is marriage of two technologies, a flocculator (designed by Asio) and Salsnes filter (designed by Salsnes Filter, SF) and a database system for harvesting (designed by Inwatec). The harvesting technology was named, Salsnes Water to Algae Treatment (SWAT) technology and the project was called, Operation SWAT.

The technical objective was to achieve 95% algae recovery with 40% lower costs than the current harvesting equipment in the market and achieve an energy consumption of less than 0.08 kWh/m3 of algae. Two test sites were chosen, IGV, Potsdam, Germany and Aqualia, Chiclana de la Frontera, Spain. The former test site grows microalgae for animal nutrition and cosmetics applications using pure cultures while the latter grows microalgae using wastewater from an activated sludge plant for biofuel application. Both these test sites served as large enterprises (LEs) in the project.

The project had 6 work packages (WP) out of which 4 were technical. Two RTDs were involved, HERI, UK and Aquateam, NO. The technical WPs initially investigated cultivation of 5 different commercial algae species at pilot scale, particle size analysis and harvesting using bench scale SF fine mesh sieves. Different commercial dewatering polymers from six different vendors were tested using different flocculators. The results obtained on flocculation + SF during the initial testing resulted in more than 95% algae recovery for most species (different polymer dosages, sieve sizes, G-values for flocculation). The results were used for design of a pilot scale Asio flocculator (PSAF) and SF prototype unit (SF500). Later, the PSAF + SF500 were tested at IGV and Aqualia field sites for algae harvesting.

The coupling of the two technologies involved further modifications to both the SF500 unit and the overall integration. After the SF500 underwent seven versions, the final testing at Chiclana field site resulted inmore than 95% algae recovery using less than 0.03 kWh/m3 of algae. The SWAT technology was operated in a continuous mode at the field site using automatic program. A cleaning and harvesting protocol was designed and documented for Inwatec as the design manual.

Some technical results were disseminated and shown at the IWA Leading Edge Technology conference (Bordeaux, France), the World Resource Forum (Davos, Switzerland) and published as news in local newspapers. The SWAT project resulted in 23 deliverables. During the phase of the project seven different commercial algae species were investigated for harvesting.

Project Context and Objectives:

The overall objective of the Operation SWAT project was to build a universal microalgae harvesting system to achievemore than 95% algae recovery and using less than 0.08 kWh/m3 of algae. The project has six WPs, out of which, 4 are technical and 2 are management and dissemination related. Each WP has different objectives as listed below.

For WP 1, the overall objective is to identify the commercial algal species and investigate their morphology to determine the harvesting efficiency using Salsnes Filter. The specific tasks of this work package are to:

1.1 Investigate the different commercial species (identity, morphology, growth rates andconditions)
1.2 Conduct size analysis of selected algal species
1.3 Determine harvesting efficiency by filtration without added chemicals and polymers using different mesh size
1.4 Develop a database for SWAT operations with the above results and for new species
1.5 Evaluate the risks associated or identify the new risks with the current work package

For WP 2, the overall objective is to develop and test a flocculator for algae species. The specific tasks of this work package are to:

2.1 Conduct a literature review of different dewatering polymers (including possible risks associated with flocculent presence in the final material) and study the different flocculator configurations
2.2 Evaluate jar test results with polymers and inorganic chemicals for algae flocculation and study effect of polymers on filter materials
2.3 Perform particle size analysis on algae flocs
2.4 Investigate bench scale testing of different flocculators and build, test pilot scale flocculator
2.5 Evaluate the risks associated or identify the new risks with the current work package

For WP 3, the overall objective is to modify the current Salsnes Filter for algae harvesting. The specific tasks of this work package are to:

3.1 Conduct bench scale Salsnes filtration experiments with flocculated algae from jar tests and bench scale flocculator
3.2 Develop a filter mesh and optimize the operational parameter of filter mesh operation (size, speed, etc)
3.3 Assess the cleaning cycles and energy optimization
3.4 Evaluate the risks associated or identify the new risks with the current work package

For WP 4, the overall objective is to integrate and validate the SWAT technology. The specific tasks are to:

4.1 Transport and assemble the pilot scale flocculator and salsnes filter at two different test sites (one at a time),
4.2 Evaluate the performance of SWAT to determine maximum algae recovery,
4.3 Minimize energy consumption by modifying the operational parameters,
4.4 Configure the SWAT for performance optimization, Develop a design manual and couple it to tested algae database
4.5 Evaluate the risks associated or identify the new risks with the current work package.

For WP 5, the overall objective is to conduct innovation related activities. The specific tasks are to:

5.1 Protect Intellectual Property Rights (IPR) developed in the project and develop a exploitation strategy
5.2 Disseminate SWAT performance results
5.3 Dissemination of innovation through different markets

For WP 6, the overall objective is to control and manage the work packages to ensure all the objectives are met. The specific tasks are to:

6.1 Co-ordination of knowledge and innovation related activities
6.2 Management of deliverables, milestone and cost statements
6.3 Management of legal, contractual, ethical, finance and administrative tasks and managing consortium agreement
6.4 Organise board meetings and project meetings
6.5 Submission of certificates on the financial statements (CFS), co-ordination of payments and distribution of money
6.6 Communicate between the consortium and the European Commission

Project Results:

The Operation SWAT project has six WPs, out of which 4 are scientific and technical and 2 are management and dissemination related.

Five microalgae species obtained from IGV (SWAT partner) and University of Life Sciences (UMB) at Ås, Norway were investigated for their particle size characteristics and morphology. The five species were all selected from commercial species of today. All were grown in pure cultures except one which was grown in wastewater. The five species were grown in tray photobioreactors using natural light and supplying carbon-dioxide, air and sufficient nutrients (Figures 1 and 2, attachement _1). Grab samples of 30 mL were obtained and investigated using a FlowCam device for their morphology and particle size distribution (Figure 3, attachement_1). Area based diameter was used to characterize the microalgae. Based on the particle sizes the sieve size range for direct filtration was determined.

The five microalgae species were further investigated for direct filtration using a Salsnes filter (SF) bench scale apparatus (Figure 4 attachement_1). Based on their sizes, five different filter mesh sizes were selected for filtration of each species. Fresh microalgae species were harvested from tray photobioreactors and 1 litre of the species was passed through each individual filter. Suspended solids (SS) was measured before and after filtration to investigate the filtration efficiency. High removal efficiency is classified as greater than 90%. %), No specie achieved high removal efficiency (more than 90 %) even with the smallest filter mesh size, which suggested the need of flocculation.Figure 5 attachement_1, Direct filtration.

The five microalgae species grown in open air tray photobioreactors were further investigated for flocculation for algae harvesting. Seventeen different dewatering polymers and two chemicals (PAX XL60 and chitosan) were requested from commercial suppliers and further investigated on each of the microalgae species. On screening of the 17 polymers and 2 chemicals, the best result polymer and chemical were chosen for dosage optimisation. For species where poor removal of algae from water phase was obtained, a combination of polymer and chemical dosages were investigated. The optimum dose for each microalgae species was reported as mg of polymer/g SS of algae in the water phase. The results also extrapolated some information for Asio, a SME in the project, for design of flocculators.

Five microalgae species were investigated for floc size analysis after jar test flocculation using optimised polymer/chemical dosage. Floc size was measured using a FlowCam device where in, flocs were drawn in at the end of slow mixing period using a peristaltic pump placed on the outlet of the 1000 micron flow cell.

Changes in pH on addition of polymers and chemicals were also investigated and reported. G values were estimated and reported for optimised speed settings for 1L jar tests and later scaled up to carry out flocculation at bench scale using 20 L flocculator using commercial stirrer for each of the five microalgae species.

At the IGV site in Germany, microalgae specie was investigated for bench and pilot scale flocculation using a tank flocculator provided by Asio. Experimental G values at varying speeds were estimated based on power inputs and using standard equations. Rapid mixing was carried out at the highest setting and slow mixing was carried out at the lowest setting both for bench and pilot scale set up.

At this point, six microalgae species were investigated for harvesting using the SWAT technology. A new microalgae specie was tested at the IGV site in addition to the other 5 commercial species (UMB, Ås, Norway). Three flocculators were investigated (1L, 20L and bench scale Asio flocculator, BSAF) (Figure 6 attachement_1). One litre of flocculated algae was examined for % suspended solids removal using bench scale Salsnes filter set-up. Different sieve sizes were investigated for % TSS removal and ease of dislodging the algae cake from the mesh using compressed air and water. This was done to mimic the air knife and water knife on pilot scale.

Based on criteria selected for algae harvesting (high % TSS removal) and ease of cleaning the mesh, the mesh sizes for each of the microalgae species vere ideintified for the different flocculators tested. Only one specific mesh material was tested. New materials would have a different effect on removal rates since the polymer may react with the mesh and this is beyond the scope of this present study, though the risks needs to be evaluated if this data is used to make decisions on algae harvesting.

Flocculation of microalgae species (type of flocculator, G values) and polymer dosages are two other variables which should be considered for algae harvesting. Higher the polymer dosage, the higher mesh opening one can use, however, cleaning of mesh and costs of polymer may be a bigger factor for this decision. Hence, cleaning of mesh was taken into account for this study. The results really are the range of mesh sizes based on polymer dosage and the flocculation parameter which needs investigation at a pilot stage (Salsnes prototype machine).

The SWAT technology consists of two process steps, flocculation and filtration. Flocculation is carried out in tank flocculators provided by Asio (SME) and filtration is carried out in rotating belt sieves (SF500) provided by Salsnes Filter (SME) in the SWAT project. These two units, i.e. the tank flocculator and the SF500, are coupled together to form the SWAT technology.

Two sites which presently grow algae for research and commercial scale were chosen for testing of the SWAT technology. The two sites are Test site 1: IGV, Potsdam, Germany (OTH) and Test site 2: Aqualia, Chiclana, Spain (OTH). Two prototypes of SF500 were provided. A pilot scale flocculator was provided by Asio. Both the flocculator and the SF500 were coupled and tested for algae harvesting. At Test Site 1, SF500v1 was tested. All tests done were batch tests due to limited availability of algae. The SF500v1 needed further modification and trouble shooting and the SME rectified these problems and came with a new prototype to be tested at Test Site 2. This version was called SF500v2.

Since the microalgae specie at Test Site 2 was new, all tests such as particle size analysis, direct filtration, determining the polymer, dosage, speed optimisation and filtration had to be conducted. The algae at test site 2 was also partly attached to other biosolids in the wastewater.

Direct filtration yielded a highest removal of 76% TSS and hence flocculation was needed. Two flocculators were provided by Asio, a pipe flocculator and pilot scale tank Asio flocculator (PSAF). The pipe flocculator was designed for higher flows, and due to the limited availability of algae only bench scale Salsnes filtration was performed. Jar test flocculation and Salsnes filtration yielded 96% removal using very fine meshes. PSAF and Salsnes filtration showed a maximum removal of 90% both under batch and continuous mode operation.

The SF500v2 was tested with different meshes. Due to large leakage problem only three experiments were conducted. Suggestions and recommendations to improve the prototype were made at this stage. The SF500v2 underwent several tests in Oslo, Norway. It was modified significantly, in the form of different “Versions” up to SF500v7 up till now (Figure 7 Attachement_1).

After observations and results gathered in the initial manual testing period, the SF500 v3 was modified several times over a two week period. The modifications that were attempted included (but have not all been kept for the final iteration):

- New devices and combination of devices for mesh cleaning.
- Details that prevents solids from entering the effluent channel.
- Positioning of devices for mesh cleaning
- Influent location and design

The SF500 v 4, 5 and 6 was investigated in the ‘automatic mode.’ Percentage total suspended solids removal (TSS), total solids recovered (TS) and energy consumption was measured or estimated. Two different mesh sizes were investigated, and the results are documented. A cleaning protocol with the water knife in automatic mode has been suggested and discussions on energy efficiency calculations have been noted.

The design manual gives a strategy or step by step instructions to operate the Salsnes Water to Algae Treatment (SWAT) technology for microalgae harvesting. Several deliverables have been written on each of the steps, the overall strategy is framed here. This report can be used as a Manual to harvest microalgae from the water phase. The SWAT database has recorded the key findings from the Deliverables in the SWAT project, which can be made use of when a client request is received.

The manual is valid for the SWAT technology using the Salsnes v6 model, which was last tested in Oslo and in Chiclana, Spain. Modifications in the machine will require future changes in this design manual. However, the strategy to harvest microalgae with SWAT technology will remain the same.

After several more modifications to the SF500 unit, a final prototype (SF500 v7) was tested at the Chiclana site in Spain. Many changes were made to the control panel unit to include all SWAT equipment (filter, control panel, flocculators, dosing pumps) into the power consumption metering, as well as adding an automatic washing function. It was concluded that addition of polymer alone was not viable due to filter clogging issues, so the same coagulation and flocculation chemicals used for the DAF unit at Chiclana was tested. The initial testing of the effluent shows a 96.7% suspended solids removal, which is higher than the goal of 95% using about 0.03 kWh/m3 power consumption.

Figure 8 Attachement_1. Performance of SWAT Technology for algae harvesting at Chiclana, Spain

Potential Impact:

The impact of this new technology is that the Operation SWAT partners have succeded in designing a competitive solution for alge harvesting, with the largest potential in the biofuel and energy market.

The companies involved with the products, Salsnes, Asio and Inwatec will start marketing the product to the global algea market for fuel and energy, mid 2014. We expect the first orders at the end of 2014, gradually increasing to be a substancial part of Salsnes and Asio manufacturing the coming years.

As this has brought new knowledge into our companies and will continue to do so, we also expect and need to enforce our staff within this area.

The partners expect a growth in employees by 10% in 2015 and growing and from the turnover perspective we expect a similar growt for 2016 at 10%, after that increasing by 5% annually.

Salsnes, Asio and Inwatec will participate in the main algea trade shows and conferences globally and also bring this into the wastewater market by attending with papers and presentations and products at the next years main conferences, Weftec in USA, IFAT and Aquatech in Europe and Singapore waterweek in Asia.

List of Websites:


Contact details:

Salsnes Filter; Ivar Solvi, Asio; Marek Holba, Inwatec; Michal Pietrowski, Aquateam; Bjørn Rusten, Heri; Kangala Chipasa, Aqualia; Frank Rogalla, IGV; Uwe Hager.