| 1. |
- Hellström, Daniel, et al.
(författare)
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Natural sludge dewatering. I : Combination of freezing, thawing, and drying as dewatering methods
- 1997
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Ingår i: Journal of cold regions engineering. - 0887-381X .- 1943-5495. ; 11:1, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- A Swedish full-scale pilot plant employing all-year-round natural sewage sludge dewatering is presented in this paper. The treatment includes three different types of outdoor ditches: a freezing ditch for the winter months, a drying ditch for the early summer months, and a combined drying-freezing-thawing-drying (DFTD) ditch for sludge produced in late summer and early autumn. The test period included two consecutive winters. Complete freezing of the sludge was achieved in the first winter in contrast to the second when incomplete freezing of the sludge occurred due to an unusually warm winter. The dry matter content for the freezing ditch was, at the harvest in August, 30–70 of the first test year. The second test year yielded a sludge with a dry matter content of 20–40 in the freezing ditch. The final dry matter result for the DFTD ditch was 20–40. The summers included were similar to the extent that both late summers were unusually warm, helping to produce sludge of high final dry matter content. The first summer, being somewhat warmer and with a lower sludge loading, yielded a sludge of 60–90 dry matter in the drying ditch. The second summer, when the sludge load was approximately double the preceding year, resulted in a sludge of 20–60 dry matter.
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| 2. |
- Kvarnström, Elisabeth, et al.
(författare)
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Reusing Phosphorus : Engineering Possibilities and Economic Realities
- 1999
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Ingår i: Journal of Economic Issues. - : Informa UK Limited. - 0021-3624 .- 1946-326X. ; 33:2, s. 393-402
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Tidskriftsartikel (refereegranskat)abstract
- Recycling is becoming increasingly important in rich societies both in a physical sense and in the perceptions about desirable changes of economic activity and behavior. In both respects, the significance of recycling is greatest for the raw materials of agricultural, forest, and mineral origins. Recycling of phosphorus, secondary phosphorus originating from wastewater is discussed in this paper. The recycling of phosphorus from wastewater currently involves the reuse of sewage sludge in agriculture. In Sweden, 84 percent of the population is connected to wastewater treatment plants where phosphorus is removed from the wastewater, hence producing sludge containing high levels of phosphorus. The phosphorus content is 6,000 metric tons per year in Swedish wastewater treatment plant sludge. This represents approximately 30 percent of the commercial phosphorus fertilizer used yearly in Sweden. The use of sewage sludge in agriculture has been discussed widely in Sweden during the 1990s. Far from resolving several important issues, such as the content of pollutants in the sludge and whether the content of phosphorus in sludge can be used by plants, the debate is still raging.
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