Concerns about potential risks posed by discharge from small-scale wastewater treatment (SWT) systems to receiving water bodies have prompted robust enforcement of national discharge quality standards in rural areas of most developed countries. Consequently, communities in such places are in need of effective technologies with which to achieve compliance. Currently, reactive filter (RF) media are increasingly preferred over advanced alternatives, due mainly to their simplicity, affordability and proven potential. However, many of the field-tested filters are commercial products which are costly and scarce but also only capable of removing few contaminants they are engineered to target hence often requiring to be coupled with other treatment units to achieve full treatment. In the preliminary findings of this study, biochar (BC) was identified and thus suggested basing on existing literature, as a versatile ubiquitous low-cost material for treating wastewater. Its effectiveness in fortifying sand (Sa) and gas concrete (GC)-based SWT facilities was later demonstrated in long-term experiments using laboratory packed bed reactors and field constructed filter beds. The efficacy of SaBC and GCBC systems in reducing turbidity (&gt;95%), DOC (60%; p&lt;0.05) and PO43- (40-90%; p&lt;0.05) was significantly higher than for their reference counterparts. Further, sorbed P was more leachable from Sa (11.2 mgkg-1) and SaBC (20.5 mgkg-1) filters but more extractable and hence plant-available in GC (65-91 mgkg-1). Therefore, the study concluded that fortification of soil-based systems with biochar filters may be a promising solution in enhancing performances of soil-based wastewater treatment systems, while P-rich RF media can act as a nutrient source for plants if recycled to agriculture. / <p>NB: Research Funder was: Botswana International University of Science and Technology, Botswana. QC 20170524</p>

The increasing highway traffic is leading to higher and higher levels of pollutants in the stormwater, such as suspended solids, metals, oils, nutrients and PAH. This runoff water causes the degradation of water bodies quality, leading to increased interest in the treatment of highway runoff for the removal of contaminants. Traditional treatments mostly consist of sedimentation, aimed primarily at the removal of suspended solids and particlebound contaminants. Recently the concern has shifted to the dissolved and colloidal fractions of contaminants as well, metals in particular, which makes reactive media filters a potentially interesting technology for runoff water treatment. However, very little research has been carried out on this technology so far, mostly in batch laboratory experiments with synthetic runoff water. This study aims at investigating the performance of four reactive media filters (Petrit T, Polonite, D-Rainclean and Filtralite-P) and a defined filter sand used for water processing at removing dissolved and particulate-bound metals. To achieve the goal, a pilot plant has been constructed in Gröndal, south of Stockholm, inside the existing Gröndalsmagasin, a full-scale stormwater treatment plant. The catchment area is located mostly on the E4 and Essingeleden, the highest trafficked motorway in Sweden with an AADT of 140 000 vehicles. A pump feeds the pilot plant from the Gröndalsmagasin outlet, after the stormwater has been treated with flocculation and sedimentation, and collects such water in a collection vessel. The five filter media columns are fed during runoff events with a flow scaled proportionally to the influent in the Gröndalsmagasin to mimic real conditions of flow and pollutant concentrations. Field measurements of pH, turbidity and conductivity, have been carried out during the trial. Samples have also been collected with flow proportional samplers connected to the collection vessel and the outlet of the five columns, as well as in the form of grab samples from sample ports at different depths in the columns. These samples have been sent to ALS Scandinavia AB to perform lab analysis. The pH in the effluent of the reactive filter media increased to values between 10 and 13, and slowly decreased during the trial. No difference was found between the pH in Filtersand outlet and the influent water. All materials showed excellent performance at removal of dissolved and particulate-bound Zn as well as particulate-bound Cu. Dissolved Cu was removed effectively by reactive media, and to a minor extent by Filtersand. Leaching of metals was observed from three materials: Filtersand released Mn during April, Polonite released Cr, with a very good correlation with the Chloride content and Petrit-T released Ba during the entire trials. / Den ökande vägtrafiken leder till allt högre halter av föroreningar i dagvattnet, till exampel suspenderade ämnen, metaller, oljor, närings ämnen och PAH. Detta dagvatten försämrar degradering av vattenförekomsternas kvalitet, vilket har lett till ett ökat intresse för rening av dagvatten fr ̊ån motorvägar för att avlägsna föroreningar. Traditionella behandlingar består oftast av sedimentering, som främst syftar till att reducera suspenderade ämnen och partikelbundna föroreningar. På senaste tiden har intresset förskjutits till att även omfatta lösta och kolloidala fraktioner av föroreningar, speciellt metaller, vilket gör reaktiva filtermaterial till en potentiellt intressant teknik f ̈or behandling av dagvatten. Mycket lite forskning har dock gjorts om denna teknik hittills, då oftast i laboratorieexperiment med syntetiskt dagvatten. Denna studie syftar till att undersöka hur fyra reaktiva mediafilter (Petrit T, Polonite, D-Rainclean och Filtralite-P) och en typ av sandfilter fungerar när det gäller att avlägsna lösta och partikelbundna metaller. F ̈or att uppnå målet har en pilotanläggning byggts i Gröndal, söder om Stockholm, inuti det existerande Gröndalsmagasinet, ett dagvattenreningsverk i full skala. Avrinningsområdet ligger vid E4 och Essingeleden, den mest trafikerade motorvägen i Sverige med en ÅDT på 140 000 fordon. En pump matar pilotanläggningen fr ̊ån Gröndalsmagasinets utlopp, efter att dagvattnet har behandlats med flockning och sedimentering, och samlas upp detta vatten i ett uppsamlingskärl. De fem filtreringskolonnerna matas under avrinningshändelserna med ett flöde som är proportionellt till inflödet till Gröndalsmagasinet för att imitera verkliga förhållanden av flöde och föroreningskoncentrationer. Mätningar av pH, turbiditet och konduktivitet har utförts under försöket. Prover har också samlats in med flödesproportionella provtagare som är kopplade till uppsamlingskärlet och utloppet fr ̊an de fem kolonnerna, samt i form av grabbprover fr ̊an provtagningsöppningar på olika djup i kolonnerna. Dessa prover har skickats till ALS Scandinavia AB för laboratorieanalys. pH-värdet i utflödet fr ̊ån det reaktiva filtermediet ökade till värden mellan 10 och 13 och sjönk långsamt under försöket. Ingen skillnad hittades mellan pH-värdet i filtrets utlopp och inflödesvattnet. Alla material visade mycket goda resultat när det gäller avlägsnande av löst och partikulät bundet Zn samt partikulärt bundet Cu. Lösta Cu avlägsnades mycket effektivt av reaktiva medier och i mindre utsträckning av Filtersand. Läckage av metaller observerades fr ̊ån tre material: Filtersand släppte ut Mn under April, Polonite släppte ut Cr, med en mycket god korrelation med kloridhalten och Petrit-T släppte ut Ba under hela försöket.