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  • 1.
    Larsdotter, Karin
    KTH, School of Biotechnology (BIO), Bioprocess Technology.
    Microalgae for Phosphorus Removal from Wastewater in a Nordic Climate2006Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    As part of a research project aiming to develop and evaluate a hydroponic system for wastewater treatment in Sweden, extended nutrient removal by microalgae was tested. The hydroponic/microalgal wastewater treatment system was built in a greenhouse in order to improve growth conditions for plants and algae. Studies on the treatment step with microalgae showed that phosphorus removal could be successfully accomplished owing to the cmbined effect of phosphorus assimilation and biologically mediated chemical precipitation of calcium phosphates. This precipitation was mainly induced by the increased pH in the algal cultures, and the pH increase was in turn a result of the inorganic carbon assimilation by the algae. The results showed that the algal growth was mainly light limited which resulted in higher algal biomass density and also lowe residual nutrients in the water at longer hydraulic retention times (HRT). In contrast the phosphorus removal rate was load limited, i.e. shorter HRT gave higher removal rates. This load dependency was due to the chemical precipitation, whereas the phosphorus assimilation was dependent on algal growth. Furthermore, results from an intensive study during summer showed that culture depths of 17 cm gave higher removal efficiencies (78% - 92%) than cultures of 33 cm (66% - 88%). On the other hand, the removal rate per area was higher in the deeper cultures, which implies that these may be preferred if area is of concern.

    Nitrogen removal was achieved mainly by the assimilation of nitrate to algal biomass, and removal efficiencies of around 40% (nitrate) could be reached for most parts of the year although the nitrogen removal performance was quite uneven. Up to 60% - 80% could however be reached during summer in the shallow cultures. A net removal in total nitrogen of up to 40% was observed in the shallow cultures during summer, which was most probably a consequence of grazing zooplankton and subsequent urea excretion and ammonia volatilisation as a reslt of the high pH values.

    Over the year, there were large fluctuations in algal growth and removal efficiency as a result of the seasonal variations in light and tempeature. During winter, phosphorus removal efficiencies lower than 25% were observed in the shallow tanks and lower than 10% in the deep tanks. Additional illumination during winter improved the phosphorus removal in the shallow cultures but did not have a significant efect on the deep cultures. Such additional illumination increases the total energy demand of the system, and hence alternative methods for phosphorus removal during winter would probably be more economical unless the algal biomass roduced had great commercial value.

  • 2.
    Larsdotter, Karin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Finnveden, Göran
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Sustainability Assessment and Management.
    Creating change with seed funding.2018Conference paper (Other academic)
  • 3.
    Larsdotter, Karin
    et al.
    KTH, School of Biotechnology (BIO), Bioprocess Technology.
    Jansen, Jes La Cour
    Dalhammar, Gunnel
    KTH, School of Biotechnology (BIO), Environmental Microbiology.
    Biologically mediated phosphorus precipitation in wastewater treatment with microalgae2007In: Environmental technology, ISSN 0959-3330, E-ISSN 1479-487X, Vol. 28, no 9, p. 953-960Article in journal (Refereed)
    Abstract [en]

    A lab-scale continuous microalgal culture was grown on sterile-filtered wastewater in order to clarify the phosphorus removing mechanisms in a microalgal treatment step that treats residual phosphorus from a hydroponic wastewater treatment pilot plant. The phosphorus assimilation was dependent on algal biomass production, whereas the chemical precipitation was dependent on phosphorus load, i.e. an increase in average precipitation rate with decreased hydraulic retention time was observed. The chemical precipitation was mainly a result of the increased pH, which was biologically mediated by the photosynthesising algae. The precipitate was composed of a calcium phosphate with magnesium included, magnesium hydroxide and calcite. A significant nitrogen removal was also experienced, which implies that the microalgal wastewater treatment is appropriate both for phosphorus and nitrogen removal.

  • 4.
    Larsdotter, Karin
    et al.
    KTH, School of Biotechnology (BIO), Bioprocess Technology.
    Jansen, Jes La Cour
    Dalhammar, Gunnel
    KTH, School of Biotechnology (BIO), Environmental Microbiology.
    Microalgae as a phosphorus trap after hydroponic wastewater treatmentManuscript (Other academic)
  • 5.
    Larsdotter, Karin
    et al.
    KTH, School of Biotechnology (BIO), Bioprocess Technology.
    Jansen, Jes la Cour
    Dalhammar, Gunnel
    KTH, School of Biotechnology (BIO).
    Phosphorus removal from wastewater by microalgae in Sweden: a year-round perspective2010In: Environmental technology, ISSN 0959-3330, E-ISSN 1479-487X, Vol. 31, no 2, p. 117-123Article in journal (Refereed)
    Abstract [en]

    The phosphorus and nitrogen removing capacity of a microalgal treatment step in Sweden was studied during an annual cycle. The treatment step had been constructed for extended phosphorus removal in a hydroponic wastewater treatment system, which had been built in a greenhouse. Two culture depths (17 and 33 cm) were compared as well as the effect of additional illumination during winter. The results showed large fluctuations in algal biomass production and phosphorus removal as a result of season. The phosphorus removal efficiency showed a clear correlation with pH, and the shallow cultures generally had higher phosphorus removal efficiencies than the deeper cultures. The efficiencies were between 60% and 100% during summer but mostly lower than 25% during winter, except in the shallow culture with extra illumination where efficiencies of 60-80% were recorded even during winter. A nitrogen removal efficiency of around 40% was reached for most parts of the year, and efficiencies of up to 60-80% were achieved during summer in the shallow cultures. In conclusion, the results showed that a large proportion of the phosphorus could be removed on a year-round basis, hence reducing the need for chemical precipitation, and also that significant nitrogen removal is possible.

  • 6.
    Larsdotter, Karin
    et al.
    KTH, Superseded Departments.
    Norström, Anna
    KTH, Superseded Departments.
    Dalhammar, Gunnel
    KTH, Superseded Departments.
    Theoretical energy requirements for hydroponic wastewater treatment2004In: Vatten, ISSN 0042-2886, Vol. 60, p. 187-191Article in journal (Refereed)
    Abstract [en]

    Hydroponic wastewater treatment takes advantage of the nutrient removing capacity of green plants. In addition to the nutrient assimilation, the roots provide a growth substrate for microorganisms involved in the biological treatment processes. However, to maintain year-round performance by the plants, additional energy must be provided at higher latitudes, even if the hydroponics are situated in a greenhouse. To evaluate the energy demand by hydroponics in Sweden, two theoretical operational conditions have been compared. These conditions were based on A: requirements by winter resting plants, 10°C and 400 lux 16 h day-1, and B: good growth, 20°C and 2000 lux 16 h day-1. Further, five Swedish cities at different latitudes and their respective demands to reach the two conditions were compared. These cities were Lund (55°72' N), Visby (57°38' N), Stockholm (59°35' N), Östersund (63°20' N) and Kiruna (67°83' N). The calculations showed that under Swedish conditions, the extra heat demand always exceeds the light demand on a yearly basis except for the high temperature and light standard in Lund. The yearly light requirements are similar for the five cities, whereas the heat energy displays strong latitude dependence, e.g. the yearly heat demand in Kiruna is almost seven times higher than in Lund to reach an average indoor temperature of 10°C.

  • 7.
    Larsdotter, Karin
    et al.
    KTH, Superseded Departments.
    Norström, Anna
    KTH, Superseded Departments.
    Gumaelius, Lena
    KTH, Superseded Departments.
    Jansen, Jes La Cour
    Dalhammar, Gunnel
    KTH, Superseded Departments.
    A small scale hydroponics wastewater treatment system under Swedish conditions2003In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 48, no 11, p. 161-167Article in journal (Refereed)
    Abstract [en]

    A treatment plant using conventional biological treatment combined with hydroponics and microalgae is constructed in a greenhouse in the area of Stockholm, Sweden. The treatment plant is built for research purposes and presently treats 0.559 m(3) of domestic wastewater from the surrounding area per day. The system uses anoxic pre-denitrification followed by aerobic tanks for nitrification and plant growth. A microalgal step further reduces phosphorus, and a final sand filter polishes the water. During a three week period in July 2002 the treatment capacity of this system was evaluated with respect to removal of organic matter, phosphorus and nitrogen. 90% COD removal was obtained early in the system. Nitrification and denitrification was well established with total nitrogen reduction of 72%. Phosphorus was removed by 47% in the process. However, higher phosphorus removal values are expected as the microalgal step will be further developed. The results show that acceptable treatment can be achieved using this kind of system. Further optimisation of the system will lead to clean water as well as valuable plants to be harvested from the nutrient rich wastewater.

  • 8.
    Larsdottter, Karin
    et al.
    KTH, Superseded Departments.
    Söderbäck, E.
    Dalhammar, Gunnel
    KTH, Superseded Departments.
    Phosphorus removal from wastewater by microalgae in a greenhouse in Sweden.2004In: Water Environ. Manag. Ser., Vol. 3, p. 183-188Article in journal (Refereed)
  • 9.
    Norström, Anna
    et al.
    KTH, Superseded Departments, Biotechnology.
    Larsdotter, Karin
    KTH, Superseded Departments, Biotechnology.
    Dalhammar, Gunnel
    KTH, Superseded Departments, Biotechnology.
    Theoretical energy requirements for maintenance of green plants in hydroponic wastewater treatment.2004In: Vatten, ISSN 0042-2886, no 3, p. 187-191Article in journal (Other academic)
    Abstract [en]

    Hydroponic wastewater treatment takes advantage of the nutrient removing capacity of green plants. In addition to the nutrient assimilation, the roots provide a growth substrate for microorganisms involved in the biological treatment processes. However, to maintain year-round performance by the plants, additional energy muse be provided at higher latitudes, even if the hydroponics are situated in a greenhouse. To evaluate the energy demand by hydroponics in Sweden, two theoretical operational conditions have been compared. These conditions were based on A: requirements by winter resting plants, 10°C and 400 lux 16 h day-1, and B: good growth. 20°C and 2000 lux 16 h day-1. Further, five Swedish cities at different latitudes and their respective demands to reach the two conditions were compared. These cities were Lund (55°72' N), Visbv (57°38' N) Stockholm (59°35’ N), Ostersund (63°20’ N) and Kiruna (67°83’ N). The calculations showed that under Swedish conditions, the extra heat demand always exceeds the light demand on a yearlv basis except for the high temperature and light standard in Lund. The yearly light requirements are similar for the five cities, whereas the heat energy displays strong latitude dependence, e.g. the yearly heat demand in Kiruna is almost seven times higher than in Lund to reach an average indoor temperature of 10°C.

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