Active Filtration of Phosphorus on Ca-Rich Hydrated Oil Shale Ash: Does Longer Retention Time Improve the Process?

Abstract

The purpose of this research was to investigate the phosphorus binding capacity of active filtration through hydrated Ca-rich oil shale ash sediment in a laboratory-scale experiment at different retention times. Three column experiments were established with hydraulic loading rates of 12 L d(-1), 18 L d(-1), and 24 L d(-1), with residence times of 12, 8, and 6 h, respectively. The results showed good removal efficiency (up to 91% at loading of 1.66 gP m(-2) d(-1)) in the experiment with the longest retention time. The overall performance of the filters did not, however, improve with increasing retention time, and the decrease in binding capacity was 41% at longer retention times. Chemical clogging by carbonate precipitates probably reduces the availability of Ca from the dissolution of unstable ash sediment mineral phases, and the phosphate removal decreases rapidly from 91% to 49% at loading of 1.66 gP m(-2) d(-1).

Alternative filter material removes phosphorus and mitigates greenhouse gas emission in horizontal subsurface flow filters for wastewater treatment

“…High P removal with hydrated oil shale ash was also demonstrated in other studies in which various wastewater types were used (Liira et al, 2009;Vohla et al, 2011;Kõiv et al, 2012;Karabelnik et al, 2012). Several experiments indicate that the capacity of hydrated oil shale ash sediment to remove phosphorus is very high, up to 65 mg P g À1 (Kaasik et al, 2008;Liira et al, 2009). In our study, we measured a value of 17 mg P g À1 at the end of the experiment.…”

“…Estonian oil-shale is highly calcareous (calcite/dolomite content of 40-60%) and after thermal combustion a large amount of ash (45-48%) is produced . Thereafter, ash is transported to waste heaps through a pipe system in water slurry at an ash-water ratio of 1:20 (Kõiv et al, 2010;Liira et al, 2009). Approximately 280 million tons of ash has been disposed of since 1950s, and every year around 5-7 million tons of ash is added making waste plateaus up to 45 m high and the total area which is covered by plateaus is more than 20 km 2 .…”

“…Several studies have shown that hydrated oil shale ash has a high phosphorus (P) removal capacity (Kõiv et al, 2010;Liira et al, 2009) and high atmospheric CO 2 adsorption (Uibu et al, 2008(Uibu et al, , 2010. Hydrated oil shale ash consists of a high amount of calcium oxide (CaO), which has high CO 2 binding capacity in open-air conditions; hence CaCO 3 is formed (Uibu et al, 2008).…”

“…P removal by ash sediment mostly takes place through Ca-phosphate precipitation and the formation of insoluble calcium phosphate complexes (Ca 3 (PO 4 ) 2 ), while the reduction of P in well mineralized peat is caused by the sorption, sedimentation and combination of complex compounds (Kõiv et al, 2010). A number of small-scale short-term, in-and outdoor experiments have been carried out where peat and hydrated oil shale ash was used for different wastewater treatments (Liira et al, 2009;Vohla et al, 2005Vohla et al, , 2011Kõiv et al, 2012;Karabelnik et al, 2012), however, year-long investigations are missing.…”

Reuse potential of phosphorus-rich filter materials from subsurface flow wastewater treatment filters for forest soil amendment

“…The composition of the filter materials was tested before and after the water-treatment experiment at ACME Analytical Laboratories Ltd. Vancouver, Canada, where content of SiO 2 , Al 2 O 3 , Fe 2 O 3 , MgO, CaO, Na 2 O, K 2 O, TiO 2 , P 2 O 5 , MnO, Cr 2 O 3 and trace heavy metals was measured using the ICP-ES and ICP-MS techniques. For a detailed description of this wastewater treatment experiment and the performance of the filter materials, see Liira et al (2009.…”