Michael Bo Rasmussen

Bioenergy potential of Ulva lactuca: Biomass yield, methane production and combustion

The biomass production potential at temperate latitudes (56°N), and the quality of the biomass for energy production (anaerobic digestion to methane and direct combustion) were investigated for the green macroalgae, Ulva lactuca. The algae were cultivated in a land based facility demonstrating a production potential of 45T (TS) ha(-1) y(-1). Biogas production from fresh and macerated U. lactuca yielded up to 271 ml CH(4) g(-1) VS, which is in the range of the methane production from cattle manure and land based energy crops, such as grass-clover. Drying of the biomass resulted in a 5-9-fold increase in weight specific methane production compared to wet biomass. Ash and alkali contents are the main challenges in the use of U. lactuca for direct combustion. Application of a bio-refinery concept could increase the economical value of the U. lactuca biomass as well as improve its suitability for production of bioenergy.

Possible causes of temporal fluctuations in primary production of the microphytobenthos in the Danish Wadden Sea

Short-term changes of the benthic primary production on a tidal sandflat were investigated during low tide and correlated with fluctuations in environmental parameters (light, temperature, salinity and pH) and the possible causal relations were tested in laboratory experiments. There was an almost linear relationship between temperature and photosynthetic rate up to the optimum temperature (20°C in May and 30°C in September). Maximum photosyn-thesis occurred at salinities between 15 and 30‰ S and decreased to 37% at a salinity of 50‰ S. Increase in temperature (18.7° to 22.6°C in May, 8.2° to 18.3°C in September) correlated with photosynthesis during the first h of the low tide period (in May and September), whereas increased salinity (30 to 50‰ S in May and 30 to 48‰ S in September) and possibly also high pH values (up to pH 9.3) correlated negatively with photosynthetic rate during the last part of the period.

Bioremediation of reject water from anaerobically digested waste water sludge with macroalgae (Ulva lactuca, Chlorophyta)☆

Phosphorus and biologically active nitrogen are valuable nutrient resources. Bioremediation with macroalgae is a potential means for recovering nutrients from waste streams. In this study, reject water from anaerobically digested sewage sludge was successfully tested as nutrient source for cultivation of the green macroalgae Ulva lactuca. Maximal growth rates of 54.57±2.16% FW d(-1) were achieved at reject water concentrations equivalent to 50 μM NH4(+). Based on the results, the growth and nutrient removal was parameterised as function of NH4(+) concentration a tool for optimisation of any similar phycoremediation system. Maximal nutrient removal rates of 22.7 mg N g DW(-1) d(-1) and 2.7 mg P g DW(-1) d(-1) were achieved at reject water concentrations equivalent to 80 and 89 μM NH4(+), respectively. A combined and integrated use of the produced biomass in a biorefinery is thought to improve the feasibility of using Ulva for bioremediation of reject water.

The effect of light and nutrient availability on growth, nitrogen, and pigment contents of Saccharina latissima (Phaeophyceae) grown in outdoor tanks, under natural variation of sunlight and temperature, during autumn and early winter in Denmark

Late summer harvest of cultivated Saccharina latissima, prior to seasonally determined negative length growth, is considered advantageous in North Atlantic waters to optimize biomass yields. We hypothesized that seasonal increase in tissue protein and pigments over autumn and early winter would counterbalance the loss of biomass, and increase the absolute harvestable amount of protein and pigments. The hypothesis was tested in a land-based, factorial-designed, pilot-scale experiment using whole algae individuals exposed to naturally relevant high or low availability of nutrients and light. The experiment was conducted during fall/early winter in Grenaa, Denmark, in outdoor tanks, exposed to ambient light and temperature variations. With high nutrient availability, the absolute harvestable amounts of nitrogen, fucoxanthin, and chlorophyll a increased by 50.1–60.1, 21.7–53.7, and 47.0–73.5 %, respectively, despite a loss of biomass of 16.2–18.7 %. Under low nutrient availability, there was a net loss of biomass (8.1–9.5 %), tissue nitrogen (10.7–44.1 %), and fucoxanthin (7.1–17.2 %), and a minor increase in chlorophyll a (2.5–22.8 %). Nutrient availability had a significant negative impact on the biomass growth, but a positive control on the tissue concentration of nitrogen, chlorophyll a, and fucoxanthin. Our results, from a land-based experiment, indicate that early winter harvest of S. latissima biomass grown under high nutrient availability in Denmark, fulfills a higher degree of nutrient bioremediation, and has an improved biomass quality in regards of increased concentrations of pigments and nitrogen rich compounds.

The distribution and interconversion of ammonium and nitrate in the Skallingen salt marsh (Denmark) and their exchange with the adjacent coastal water

The potential nitrogen sources for the primary production in the intertidal area are nitrogen compounds obtained from mineralization in the sediment and the water column, nitrogen fixation, outflow from rivers and groundwater seeping from the mainland.

Effect of Light Quality and Nitrogen Availability on the Biomass Production and Pigment Content of Palmaria Palmata (rhodophyta)

Macroalgae constitute a huge underexploited resource for compounds of interest to the health industry. External factors strongly influence the concentration of these compounds in the algal tissue. This implies a potential for optimizing the growth conditions for cultivated macro algae in order to promote production of valuable compounds. The objective of this study was to determine the influence of light spectral composition (red, blue, and white) and nutrient treatment (30 and 440 µM NO3 - ) on chlorophyll a and carotenoid concentration as well as growth rate of the red algae Palmaria palmata. The results show that the nitrogen load has a larger effect on the pigment concentration and growth rate in the algae, than the light treatments. Experiments with different light spectral composition showed the highest pigment content with white and blue light while red light was less effective. In addition, samples cultivated under white light had higher growth rates compared to red and blue light. Therefore, to increase the concentration of nutritionally valuable pigments cultivation strategies in marine production should be to use blue or white light and use high NO3 concentrations.