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Phosphorus removal from wastewater by microalgae in Sweden: a year-round perspective
KTH, School of Biotechnology (BIO), Bioprocess Technology.
KTH, School of Biotechnology (BIO).
2010 (English)In: Environmental technology, ISSN 0959-3330, E-ISSN 1479-487X, Vol. 31, no 2, 117-123 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
2010. Vol. 31, no 2, 117-123 p.
Keyword [en]
microalgae, wastewater treatment, phosphorus, assimilation, precipitation, precipitation, system, ponds
National Category
Industrial Biotechnology
Identifiers
URN: urn:nbn:se:kth:diva-19289DOI: 10.1080/09593330903382815ISI: 000275282800001Scopus ID: 2-s2.0-77649324535OAI: oai:DiVA.org:kth-19289DiVA: diva2:337336
Note
Tidigare titel: Phosphorus removal from wastewater by microalgae in a Nordic climate – a year‐round perspective. QC 20100907Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Microalgae for Phosphorus Removal from Wastewater in a Nordic Climate
Open this publication in new window or tab >>Microalgae for Phosphorus Removal from Wastewater in a Nordic Climate
2006 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. vi, 44 p.
Keyword
assimilation,  hydroponics,  light,  microalgae,  nitrogen,  phosphorus,  plants,  precipitation,  wastewater treatment 
National Category
Industrial Biotechnology
Identifiers
urn:nbn:se:kth:diva-3896 (URN)91-7178-288-5 (ISBN)
Public defence
2006-04-12, Oskar Kleins auditorium, AlbaNova, Roslagstullsbacken, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100907Available from: 2006-04-03 Created: 2006-04-03 Last updated: 2011-01-21Bibliographically approved

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