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A comparative study of six hydroponic wastewater treatment plants.
KTH, School of Biotechnology (BIO).
2005 (English)In: Vatten, ISSN 0042-2886, no 2, 95-104 p.Article in journal (Other academic) Published
Abstract [en]

During the last two decades, wastewater treatment in systems combining conventional biological processes andhydroponics has been tried at several locations. In this article, six different systems are described and theirtreatment results compared. Five systems were found in literature, and the sixth system was constructed andoperated by the microbiology group at KTH. These systems can be divided into three subgroups: i) demonstrationsystems with small inflow and long hydraulic retention time (HRT), ii) pilot systems with small to moderateinflow and moderate HRT, iii) full scale systems with large inflow and short HRT. In general, removalof organic matter seems to be most efficient in systems resembling an active sludge process. Systems with longHRT appears over-dimensioned as long as the volume is not simultaneously used for treatment and production.Nitrogen was efficiently removed through conventional biological processes, whereas phosphorus removalthrough mainly sedimentation and adsorption in the systems was not very efficient. Nutrient removal bymeans of up-take through plant growth has not contributed significantly in any of the described treatmentsystems. None of the treatment plants have had the primary objective of biomass production. Hence, potentialremoval and recycling of nutrients through a productive system still remains to be answered.

Place, publisher, year, edition, pages
2005. no 2, 95-104 p.
Keyword [en]
wastewater treatment, hydroponics, BOD, nitrogen, phosphorus, greenhouse
National Category
Microbiology in the medical area
Identifiers
URN: urn:nbn:se:kth:diva-25259OAI: oai:DiVA.org:kth-25259DiVA: diva2:356848
Note
QC 20101014Available from: 2010-10-14 Created: 2010-10-14 Last updated: 2010-10-14Bibliographically approved
In thesis
1. Treatment of domestic wastewater using microbiological processes and hydroponics in Sweden
Open this publication in new window or tab >>Treatment of domestic wastewater using microbiological processes and hydroponics in Sweden
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Conventional end-of-pipe solutions for wastewater treatment have been criticized from a sustainable view-point, in particular regarding recycling of nutrients. The integration of hydroponic cultivation into a wastewater treatment system has been proposed as an ecological alternative, where nutrients can be removed from the wastewater through plant uptake; however, cultivation of plants in a temperate climate, such as Sweden, implies that additional energy is needed during the colder and darker period. Thus, treatment capacity, additional energy usage and potential value of products are important aspects considering the applicability of hydroponic wastewater treatment in Sweden.

To enable the investigation of hydroponic wastewater treatment, a pilot plant was constructed in a greenhouse located at Överjärva gård, Solna, Sweden. The pilot plant consisted of several steps, including conventional biological processes, hydroponics, algal treatment and sand filters. The system treated around 0.56-0.85 m3 domestic wastewater from the Överjärva gård area per day. The experimental protocol, performed in an average of twice per week over a period of three years, included analysis and measurements of water quality and physical parameters. In addition, two studies were performed when daily samples were analysed during a period of two-three weeks. Furthermore, the removal of pathogens in the system, and the microbial composition in the first hydroponic tank were investigated.

Inflow concentrations were in an average of around 475 mg COD/L, 100 mg Tot-N/L and 12 mg Tot-P/L. The results show that 85-90% of COD was removed in the system. Complete nitrification was achieved in the hydroponic tanks. Denitrification, by means of pre-denitrification, occurred in the first anoxic tank. With a recycle ratio of 2.26, the achieved nitrogen removal in the system was around 72%. Approximately 4% of the removed amount of nitrogen was credited to plant uptake during the active growth period. Phosphorus was removed by adsorption in the anoxic tank and sand filters, natural chemical precipitation in the algal step induced by the high pH, and assimilation in plants, bacteria and algae. The main removal occurred in the algal step. In total, 47% of the amount of phosphorus was removed. Significant recycling of nitrogen and phosphorus through harvested biomass has not been shown. The indicators analysed for pathogen removal showed an achieved effluent quality comparable to, or better than, for conventional secondary treatment. The microbial composition was comparable to other nitrifying biological systems. The most abundant phyla were Betaproteobacteria and Planctomycetes.

In Sweden, a hydroponic system is restricted to greenhouse applications, and the necessary amount of additional energy is related to geographic location. In conclusion, hydroponic systems are not recommended too far north, unless products are identified that will justify the increased energy usage. The potential for hydroponic treatment systems in Sweden lies in small decentralized systems where the greenness of the system and the possible products are considered as advantages for the users.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. iv, 56 p.
Keyword
Microbiology, biological, hydroponics, microbial composition, nitrogen, organic matter, phosphorus, small scale, theoretical energy requirements, wastewater treatment., Mikrobiologi
National Category
Microbiology
Identifiers
urn:nbn:se:kth:diva-183 (URN)91-7178-030-0 (ISBN)
Public defence
2005-05-18, Oskar Kleins auditorium, AlbaNova, Roslagstullsbacken 21, Stockholm, 14:00
Opponent
Supervisors
Note
QC 20101014Available from: 2005-04-28 Created: 2005-04-28 Last updated: 2010-10-14Bibliographically approved

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