Long-term phosphorus sorption and leaching in sand filters for onsite treatment systems

Rajabu Hamisi; Agnieszka Renman; Gunno Renman; Anders Wörman; Roger Thunvik

doi:10.1016/j.scitotenv.2022.155254

Long-term phosphorus sorption and leaching in sand filters for onsite treatment systems

Sci Total Environ. 2022 Aug 10:833:155254. doi: 10.1016/j.scitotenv.2022.155254. Epub 2022 Apr 13.

Authors

Rajabu Hamisi¹, Agnieszka Renman², Gunno Renman², Anders Wörman², Roger Thunvik²

Affiliations

¹ Department of Sustainable Development, Environmental Science & Engineering, Division of Water and Environmental Engineering, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden. Electronic address: rajabuhm@kth.se.
² Department of Sustainable Development, Environmental Science & Engineering, Division of Water and Environmental Engineering, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.

PMID: 35429567
DOI: 10.1016/j.scitotenv.2022.155254

Abstract

The sorption capacities of sand filters used for onsite wastewater treatment and their associated risks of phosphorus (P) leaching on contact with rainwater were investigated in column experiments and with modelling tool for over 300 days. Columns packed with sand were exposed to real domestic wastewater of different characteristics and hydraulic loading modes. The wastewater fed into the columns was effluent collected from three different treatment units in the field: a septic tank (ST), biofiltration tank (BF) and Polonite® filter bag (PO). The risk of P leaching to groundwater and surface water was also assessed, by exposing the same sand columns to natural rainwater. Overall results indicated that sand soils can exhibit different adsorption and desorption capacities for electrical conductivity (EC), Total-P, phosphate-P and total suspended solids, depending on the characteristics of influent wastewater, loading rate and total operation time. The removal efficiencies of the sand columns increased in the order ST (98.16%) > PO (93.36%) > BF (81.57%) for PO4-P and slightly decreased ST (97.11%) > PO (92.06%) > BF (76.76%) for Total-P columns. All sand columns loaded with actual wastewater solutions from septic tanks and biofiltration tank have demonstrated high risks of phosphorus leaching (>99.99%) to the groundwater. The modelling was successful captured behavior of EC tracer and adsorption of PO₄-P with acceptable prediction uncertainty in the PO < 8% columns. The modelling results indicated that the decrease of loading rate from 83.3 mL d-1 to 20.83 mL d-1 led to an average increase of removal efficiency and prolong operational lifetime and mass of adsorbed Total-P in the sand soil. This study concludes that sand is a valuable filter medium at low loading rate for phosphorus removal in full-scale operations of onsite treatment systems, however very vulnerable for leaching P when in contact with rainwater.

Keywords: Adsorption; Constructed wetlands; Leaching; Phosphorus; Sand column.

MeSH terms

Filtration
Phosphorus*
Soil
Waste Disposal, Fluid / methods
Wastewater
Water Purification* / methods

Substances

Soil
Waste Water
Phosphorus