Filter bed systems treating domestic wastewater in the Nordic countries – Performance and reuse of filter media

Abstract

a b s t r a c tNine filter beds have been constructed in the Nordic countries, Denmark, Finland, Norway and Sweden. Filter beds consist of a septic tank followed by an aerobic pre-treatment biofilter and a subsequent saturated flow grass-covered filter. Thus, filter beds are similar to subsurface flow constructed wetlands with pre-treatment biofilters, but do not have wetland plants with roots submerged into the saturated filter. All saturated filters contain Filtralite ® P, a light-weight expanded clay aggregate possessing high phosphorus sorption capacity. The filter bed systems showed stable and consistent performance during the testing period of 3 years. Removal of organic matter measured as biochemical oxygen demand (BOD) was >80%, total phosphorus (TP) >94% and total nitrogen (TN) ranged from 32 to 66%. Effluent concentrations of fecal indicator bacteria met the European bathing water quality criteria in all systems. One system was investigated for virus removal and somatic viruses were not detected in the effluent. The investigations revealed that the majority of the BOD and nitrogen removal occurred in the pre-treatment filters and the phosphorus and bacteria removal was more prominent in the saturated filters. The saturated filters could be built substantially smaller than the current design guidelines without sacrificing treatment performance. The used filter material met the Norwegian regulations for reuse in agriculture with respect to heavy metals, bacteria and parasites. When saturated with phosphorus, the light-weight aggregate, Filtralite ® P used in the saturated bed is a suitable phosphorus fertilizer and additionally has a liming effect.

Effect of hydraulic loading rate on pollutant removal efficiency in subsurface infiltration system under intermittent operation and micro-power aeration

“…was generally satisfactory at low hydraulic loading rate (HLR) of 0.01-0.10 m 3 /m 2 d (Hatt et al, 2007;Jenssen et al, 2010;Li et al, 2012;Llorens et al, 2011), but it declined significantly under high HLR (0.125 m 3 /m 2 d) due to lack of oxygen in the filter media (Li et al, 2012). Moreover, unlike the excellent organic removal, nitrogen removal efficiency varies from 10% to 90% according to wastewater compositions, environmental conditions and operating conditions in SWIS (Pan et al, 2015;Wang et al, 2010).…”

Performance of six multi-stage hybrid wetland systems for treating high-content wastewater in the cold climate of Hokkaido, Japan

“…Moreover, hybrid systems have been in use since the 1980s (Vymazal 2011). Several important studies about the selection of filter media, the treatment performance at low temperature, and the recirculation effect have been conducted in cold climates (Poldvere et al 2009(Poldvere et al , 2010Jenssen et al 2005Jenssen et al , 2010Speer et al 2012). However, issues of clogging and freezing for treating high-content wastewater in cold climates still remain.…”

Mechanisms of removal of three widespread pharmaceuticals by two clay materials

“…light expanded clay aggregates (LECA), expanded shale, expanded slate and exfoliated vermiculite) [19,20,[25][26][27][28]. Among thermally processed clay materials, LECA and exfoliated vermiculite have been increasingly used over the latest years for water and wastewater treatment, performing several possible roles, such as filters or as support matrix in constructed wetlands systems [19,[29][30][31][32][33][34][35][36][37][38]. Both materials have exhibited good adsorbent qualities for the removal of several organic pollutants [25,28,39,40].…”