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  • 1.
    Grönlund, Erik
    et al.
    Water Direct Secretariat, Östersund.
    Hanaeus, Jörgen
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Johansson, Erica
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Falk, Stefan
    Mittuniversitetet, Department of Natural and Environmental Science.
    Performance of an experimental wastewater treatment high-rate algal pond in subarctic climate2010In: Water environment research, ISSN 1061-4303, E-ISSN 1554-7531, Vol. 82, no 9, p. 830-839Article in journal (Refereed)
    Abstract [en]

    A pilot-scale experimental high-rate algal pond (HRAP) was investigated in the subarctic mid-Sweden region, at latitude 63 degrees N. During autumn 2002, conditions included temperatures below 10 degrees uC and photosynthetic active radiation below 200 mu E/m(2).s. Biochemical oxygen demand was reduced by approximately 90% (approximately 40 g/m(3)), chemical oxygen demand by 65% (approximately 80 g/m(3)), total phosphorus by 20% (approximately 1 g/m(3)), and total nitrogen by 46% (approximately 15 g/m(3)), at a retention time of approximately 2.5 days. During autumn 2003, the performance of the HRAP appeared better with a more dense microalgae culture; however, as a result of poor settling of the microalgae, the reduction was considerably lower. A major difference between the years was the microalgae composition. In 2002, the large green algae Coelastrum dominated with Chlamydomonas, Scenedesmus, Lagerheimia, and the Cryptophyte Rhodomonas. In 2003, there was a total dominance of the very small green algae Chlorella, known to be difficult to settle. In batch growth experiments during spring 2002, doubling times of 4 to 6 days were achieved. The period of temperatures above 10 degrees C and an insolation of more than approximately 270 uE/m(2).s (125 Langleys), which is well-documented as appropriate for HRAP function (Oswald, 1988a, 1988c), were measured to last for 4 to 4.5 months from early May to late September. However, the growth and treatment performance experiments indicated that a longer season may be possible-6.5 to 7 months, at best-from early April to late October.

  • 2.
    Hellström, Daniel
    Luleå tekniska universitet.
    An exergy analysis for a wastewater treatment plant: an estimation of the consumption of physical resources1997In: Water environment research, ISSN 1061-4303, E-ISSN 1554-7531, Vol. 69, no 1, p. 44-51Article in journal (Refereed)
    Abstract [en]

    The objective of this article is to exemplify how an exergy analysis could be used to estimate the consumption of physical resources at a wastewater treatment plant (WWTP). The exergy analysis has been performed for Luleå WWTP in Northern Sweden. About 60 000 population equivalents are connected to the WWTP, which has mechanical and chemical treatment. Flows included in the analysis are the wastewater heat, precipitants and other chemicals, organic matter and nutrients in the wastewater and biosolids, and electricity used for operation and maintenance. One conclusion is that the value of the heat is overestimated in a conventional energy analysis. Also, the organic matter probably represents the largest technical exergy flow. It is not clear how the exergy value of nutrients should be estimated.

  • 3.
    Hellström, Daniel
    Luleå tekniska universitet.
    Exergy analysis: a comparison of source separation systems and conventional treatment systems1999In: Water environment research, ISSN 1061-4303, E-ISSN 1554-7531, Vol. 71, no 7, p. 1354-1363Article in journal (Refereed)
    Abstract [en]

    Exergy analysis and material balances are useful to describe resource use in different systems. In this study, three different sewerage systems are analyzed: a conventional system with biological nitrogen removal, a conventional system in combination with source separation of urine, and a treatment system with source separation of urine and feces. The influence of factors such as the size of the system, access to farmland, and concentration of collected urine is studied. The study shows that total exergy consumption is least for the system with source separation of urine and feces and greatest for the conventional wastewater treatment system. The primary difference results from the amount of methane gas that is produced by each alternative. Another conclusion is that a significant portion of exergy consumption in the source separation system is the transport and spreading of urine.

  • 4.
    Rostmark, Susanne
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Colombo, Manuel
    University of British Columbia, Vancouver.
    Knutsson, Sven
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Öberg, Gunilla
    University of British Columbia, Vancouver.
    Removal and Re-use of Tar-contaminated Sediment by Freeze-dredging at a Coking Plant Luleå, Sweden2016In: Water environment research, ISSN 1061-4303, E-ISSN 1554-7531, Vol. 88, no 9, p. 847-851Article in journal (Refereed)
    Abstract [en]

    Submerged tar-contaminated sediments are generally very loose, which makes remediation challenging. We tested if a modified version of freeze-dredging could be used to remove and dewater such sediments in a canal down-stream a coking plant. PVC hoses carrying a heat medium were placed horizontally in the submerged sediments. Five days of freezing allowed straightforward removal of most of the sediments. Flat freeze cells were placed side by side in the canal to remove the rest. The freeze-thaw process increased the dry substance (DS) content from approximately 50 to 80%. Outdoors storage under rainy conditions did not re-wet the dried sediments. The material was successfully used as feed-stock in the coking plant, with the double cost-benefit of avoided transportation to deposit and reduced use of coal. The study demonstrates that freeze-dredging can facilitate removal, storage and beneficial re-use of submerged tar-contaminated sediments.

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