Search

Vegetation filters (VFs) are on-site wastewater (WW) treatments that can be considered as a nature-based solution (NbS). They are green infrastructures that provide several environmental benefits such as non-potable water reuse, contamination reduction, biomass production, landscaping improvements and CO 2 fixation, among others. However, nutrient leaching, especially nitrate, partially exists. To overcome this limitation, operational parameters related to the irrigation water management and soil amendments were tested in a real system receiving WW from an office building operated along 4 years. The attenuation of N is improved (up to 83%) in the vadose zone by boosting biodegradation. Lower hydraulic loads and more frequent irrigation events using drippers and the incorporation of woodchips as a layer above the topsoil promote denitrification processes. Changes in organic carbon characteristics also confirm that biodegradation is enhanced. P attenuation is a result of abiotic processes, mainly driven by chemical equilibriums between the liquid and the sorbed and/or precipitated phase and, when uncontrolled changes in the WW quality occurs, removal efficiency is negatively affected. However, only 10% of the samples collected at 45 cm depth present concentrations above 2 mg/L. The woodchips application does not seem to ameliorate P removal regardless of the application method. The implemented measures allow higher soil water content, infiltration and groundwater recharge and prevents aquifer contamination. [Display omitted] • Different amendments and wastewater irrigation management has been tested in a VF. • Low irrigation loads and soil woodchip amendments enhance nutrients attenuation. • Biodegradation and phytoabsorption are the main processes in N and TOC attenuation. • Abiotic processes (sorption and precipitation) control P attenuation. • Quality of groundwater recharge improves with drip irrigation and amendments. [ABSTRACT FROM AUTHOR]

Vegetation Filters (VFs) can be a sustainable solution to treat wastewater and to recover resources such as nutrients, water and biomass from small municipalities and isolated dwellings. However, under certain conditions, the leakage of nutrients, especially of nitrate, can represent a limitation. The addition of two sustainable soil amendments, woodchips and biochar, has been tested as a strategy to improve nutrient attenuation in VFs increasing sorption sites and microbial activity. To this end, unsaturated infiltration and batch experiments have been carried out at laboratory scale. The systems for infiltration experiments contain natural soil, natural soil amended with woodchips and natural soil amended with biochar. To determine the sorption capacity of NH 4 +, batch tests were performed using an amendment/SWW ratio of 1:20 and an NH 4 + initial concentration ranging from 30 to 600 mg L−1. Results from the infiltration experiments show a high attenuation (~95%) of total phosphorous (TP) independently of the amendments. Different behaviour is observed for total nitrogen (TN). The removal of this species is obtained only in the soil amended with woodchips (>85%) whereas the natural soil alone and the soil with biochar have no impact on TN attenuation. In these two porous media, all the NH 4 + input concentration is transformed to NO 3 − that infiltrates without further reactions. According to batch experiment results, the potential role of biochar in the nutrient attenuation is limited to sorption processes (K d (NH 4 +) = 21.37–193.18 L kg−1). Woodchips act primarily as a labile source of carbon promoting biodegradation, being more effective for nutrient attenuation than the sorption capacity of biochar. Image 1088 • Two soil amendments are tested in lab to improve COD, P and N attenuation in VFs. • Woodchips incorporate biodegradable and non-biodegradable OM reducing COD removal. • P removal is high in soil and neither woodchips nor biochar improves attenuation. • N is only attenuated in soil with woodchip by denitrification thanks to extra OM. • Biochar increases sorption but it is a minor process in COD, P and N attenuation. [ABSTRACT FROM AUTHOR]

Vegetation filters, a nature based wastewater regeneration technology, have been reported as a feasible solution for small municipalities and scattered populations with limited access to sewage networks. However even when such a treatment is properly planned, the leaching of contaminants through the unsaturated zone may occur. The amendment of soil with a readily-labile source of carbon is supposed to ameliorate the removal of contaminants by stimulating microbial activity and enhancing sorption processes. In this study, lab-scale leaching column experiments were carried out to explore if the addition of woodchips to the soil could be a feasible strategy to be integrated in a vegetation filter. Two different types of arrangement of soil and woodchips layers were tested. The soil was collected from an operating vegetation filter treating wastewater of an office building characterised by a high nutrient load. Daily pulse of synthetic wastewater were applied into the columns and effluent samples were collected and analyzed for major ions, total nitrogen (N T ), total phosphorous (P T ) and chemical oxygen demand (COD). By the end of the experiment, N T , NO 3 -N and P T soil contents were also measured. Results indicate that amendments with woodchips enhance the elimination of wastewater-originated contaminants. N T removal in the columns with woodchips reaches a value of 99.4%. The main processes responsible for this elimination are NH 4 -N sorption and nitrification/denitrification. This latter fostered by the reduced redox conditions due to the enhanced microbial activity. High removal of P T (99%) is achieved independently of the woodchips presence due to retention and/or precipitation phenomena. The COD removal efficiency is not affected by the presence of the woodchips. The leaching of organic carbon occurs only during the experimental start-up period. [ABSTRACT FROM AUTHOR]