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Removal of micro-organisms in a small-scale hydroponics wastewater treatment system
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
KTH, School of Biotechnology (BIO).
KTH, School of Biotechnology (BIO).
2005 (English)In: Letters in Applied Microbiology, ISSN 0266-8254, E-ISSN 1472-765X, Vol. 40, no 6, 443-447 p.Article in journal (Refereed) Published
Abstract [en]

Aims: To measure the microbial removal capacity of a small-scale hydroponics wastewater treatment plant. Methods and Results: Paired samples were taken from untreated, partly-treated and treated wastewater and analysed for faecal microbial indicators, i.e. coliforms, Escherichia, coli, enterococci, Clostridium perfringens spores and somatic coliphages, by culture based methods. Escherichia coli was never detected in effluent water after >5.8-log removal. Enterococci, coliforms, spores and coliphages were removed by 4.5, 4.1, 2.3 and 2.5 log respectively. Most of the removal (60-87%) took place in the latter part of the system because of settling, normal inactivation (retention time 12.7 d) and sand filtration. Time-dependent log-linear removal was shown for spores (k = -0.17 log d-1, r2 = 0.99). Conclusions: Hydroponics wastewater treatment removed micro-organisms satisfactorily. Significance and Impact of the Study: Investigations on the microbial removal capacity of hydroponics have only been performed for bacterial indicators. In this study it has been shown that virus and (oo)cyst process indicators were removed and that hydroponics can be an alternative to conventional wastewater treatment.

Place, publisher, year, edition, pages
2005. Vol. 40, no 6, 443-447 p.
Keyword [en]
Coliforms, Coliphages, Enterococci, Hydroponics, Removal, Spores, Wastewater treatment
National Category
Water Engineering
Identifiers
URN: urn:nbn:se:kth:diva-5183DOI: 10.1111/j.1472-765X.2005.01689.xISI: 000202967500009Scopus ID: 2-s2.0-20044378137OAI: oai:DiVA.org:kth-5183DiVA: diva2:7993
Note
QC 20100928Available from: 2005-05-03 Created: 2005-05-03 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Comparative analysis of pathogen occurrence in wastewater: management strategies for barrier function and microbial control
Open this publication in new window or tab >>Comparative analysis of pathogen occurrence in wastewater: management strategies for barrier function and microbial control
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This project was initiated to fill knowledge gaps on the occurrence of pathogens in different streams of wastewater, e.g. greywater and domestic wastewater. The aims were also to measure the removal of pathogens in different treatment processes, conventional and innovative, and correlate the removal to that of common microbial process indicators, such as faecal coliforms, enterococci, Cl. perfringens spores and bacteriophages. One study also assessed the correlation between the removal of microorganisms and some commonly measured physico-chemical process indicators. The results can be applied in microbial risk assessments (MRAs) of urban wastewater systems.

Indicators and parasitic (oo)cysts were enumerated with standard methods and viruses with rtPCR. High levels of Giardia cysts and enteroviruses were found in untreated wastewater (103.2 and 104.2 L-1 respectively) indicating high incidences in the society. Noroviruses were also often found in high numbers (103.3 L-1) during winter, but less frequent and in lower numbers (102.3 L-1) during the rest of the year. This temporal variation correlated to the clinical laboratory reporting of noroviruses. A temporal variation was also shown for Giardia with significantly lower cyst counts in untreated wastewater during spring. Cryptosporidium oocysts were not as numerous in untreated wastewater (5 L-1) reflecting a lower incidence in the society than for the other pathogens during the time of the study. Since temporal variation had a larger impact than spatial, site-specific measurements may not be necessary to perform screening level MRAs of wastewater discharge and reuse. Good data can be found in the literature and corrected for by recovery of the detection method, flow and incidence in the society. Removal of microorganisms in wastewater treatments varied from 0 to >5.8 log due to process combination and organism in question. Treatment in integrated hydroponics removed microorganism more efficiently than did secondary conventional treatment, though having longer hydraulic retention time. Tertiary treatment and treatment in a membrane bioreactor (MBR) showed better removal potential than treatment in upflow anaerobic sludge blankets (UASB) in a pilot plant. Human virus genomes were less removed and Giardia cysts more removed than all of the studied indicators. Enumeration with PCR, however, may underestimate infectious virion removal. Spores of sulphite-reducing anaerobes and somatic coliphages were significantly less removed than E. coli and enterococci in all the studied processes. Bacterial indicator and spore removals correlated to enterovirus genome removal (p<0.05), but the predictive values were low (R<0.4). Removals between microbial indicators and NH4-N, Kjeldal-N, COD and TOC correlated stronger (10-18<p<0.02; 0.43<R<0.90).

To manage the risk with reuse and discharge of wastewater, treatment performance targets have been calculated as a step in a hazard analysis and critical control point (HACCP) approach. These targets varied from 0 to 10.4 log removal due to water (grey or wastewater), organism (rotavirus, Campylobacter or parasitic (oo)cysts) and exposure (drinking water, surface water, aerosols, irrigation of crops or public parks). Faecal contamination in greywater was measured by coprostanol and was shown to be 980 times lower than in wastewater, corresponding to 2.9 log removal in treatment. Somatic coliphages were suggested to function as an index of virus removal in wastewater treatment processes as well as to be included in the monitoring of bathing water. The guideline level was suggested to be 300 PFU 100 mL-1 based on MRA of enteroviruses. This level in a water sample would equal a probability of infection of 0.3% (95th percentile 4%). The risk is overestimated if animal sources dominate the faecal pollution. Development in methods to track sources of faecal pollution showed that if somatic coliphages are enumerated together with phages infecting Bacteroides strain GA17, discriminating human from animal faecal pollution is possible based on the ratio between the phages

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. ix, 67 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1021
Keyword
bacteria, parasites, treatment
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-233 (URN)91-7178-059-9 (ISBN)
Public defence
2005-06-02, Sal V2, Teknikringen 72, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101013Available from: 2005-05-03 Created: 2005-05-03 Last updated: 2010-10-13Bibliographically approved
2. 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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