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Theoretical energy requirements for hydroponic wastewater treatment
KTH, Superseded Departments.
KTH, Superseded Departments.
KTH, Superseded Departments.
2004 (English)In: Vatten, ISSN 0042-2886, Vol. 60, 187-191 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
2004. Vol. 60, 187-191 p.
National Category
Industrial Biotechnology
Identifiers
URN: urn:nbn:se:kth:diva-5525OAI: oai:DiVA.org:kth-5525DiVA: diva2:9919
Note
QC 20100907Available from: 2006-04-03 Created: 2006-04-03 Last updated: 2010-09-08Bibliographically 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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