A consequence of eutrophication in the Baltic Sea is growth of algae that accumulates in the coastal areas and beaches. Dense algal mats may cause anoxia or hypoxia and greatly reduce the recreational value of the area. Algae also functions as hyper accumulators of heavy metals and their metal levels may become toxic to higher trophic levels. The project Wetlands, Algae and Biogas (WAB) aims at removing algal beach cast for commercial use in biogas production and further use of the fermentation residues as fertilizer. Collection of algae would remove both nutrients and heavy metals from the Baltic Sea but leave us with large amounts of algae containing heavy metals. A concern for the biogas production based on these Baltic algae is the effects from the heavy metals, during fermentation, in the residues and the use of them as fertilizer. A literature review shows that the levels of heavy metals should not inhibit the biogas production but during the fermentation there is a loss of (48%) biological material and the metals are concentrated in the residues. Samples of algae from Trelleborg (SE) show higher concentrations of cadmium (Cd) than algae from Poland (PL). The Swedish residues border or surpass the legislative amount of heavy metals that are allowed to be applied to arable land in Sweden. This is both due to the higher concentrations of heavy metals and the differences between European and Swedish legislation. To use the residues as fertilizer detoxification is required, mainly for Cd in Sweden. There are effective methods, chemicals and ion exchangers (70-80%), for removing heavy metals from organic leachate. But these methods lack testing on a large scale, the costs and the environmental aspect of these methods on tons of algae per year are unknown. Co-fermentation with a suitable substrate would dilute the heavy metal concentration and could reduce possible problems such as hydrogen sulfide accumulation in the biogas. Another possible pathway for dealing with the heavy metal rich residues is as fertilizer for non-food crops such as the biofuel species willow (Salix). Willow is a fast growing tree that is a known accumulator of heavy metals and can be used as a remediation for contaminated soil. Based on the metal concentrations and respective legislation, estimations of 20 000 ha of willow for Trelleborg and 400 ha for Sopot beach (PL) is needed to process harvested algae. / Wetlands, Algae and Biogas (WAB)
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:lnu-20843 |
| Date | January 2012 |
| Creators | Bergström, Kristofer |
| Publisher | Linnéuniversitetet, Institutionen för naturvetenskap, NV |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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