Aluminum-Based Water Treatment Residual Use in a Constructed Wetland for Capturing Urban Runoff Phosphorus: Column Study

Abstract

Aluminum-based water treatment residuals (Al-WTRs) have a strong affinity to sorb P. In a proofof-concept greenhouse column study, Al-WTR was surface-applied at rates equivalent to 0, 62, 124, and 248 Mg ha −1 to 15 cm of soil on top of 46 cm of sand;Al-WTR rates were estimated to capture 0, 10, 20, and 40 years of P from an urban watershed entering an engineered wetland in Boise, ID, USA. Creeping red fescue (Festuca rubra) was established in all columns; one set of columns received no Al-WTR or plants. After plant establishment, once per week over a 12-week period, ∼1.0 pore volumes of ∼0.20 mg P L −1 were added to each column. Infiltration rates were measured, leachate was collected and analyzed for soluble P, and fescue yield, P concentration, and uptake were determined. After plant harvest, the sand, soil, and the Al-WTR layer were collected and analyzed for Olsen P; amorphous Al, Fe, and P; P storage capacity (PSC); and soluble + Al + Fe-bound, occluded, and Ca-bound P phases. Infiltration rate increased only due to the presence of plants. Leached P decreased (50 %) with plants present; Al-WTR further reduced soluble P leaching losses (60 %). Fescue yield, P concentration, and uptake increased with increasing Al-WTR rate, due to Al-WTR sorbing and potentially making P more plant available; Olsen-extractable P increased with increasing Al-WTR rate, supporting this contention. The PSC was reduced with the 62 Mg ha −1 Al-WTR rate but maintained with greater Al-WTR rates. The 124 and 248 Mg ha −1 Al-WTR rates also contained greater P associated with the soluble + Al + Fe and occluded phases which should be stable over the long term (e.g., decadal). It was recommended to apply Al-WTR near the 124 and 248 Mg ha −1 rates in the future to capture urban runoff soluble P in the Boise, ID, engineered wetland.

Potential Alternative Reuse Pathways for Water Treatment Residuals: Remaining Barriers and Questions—a Review

“…For instance, work by Oladeji et al (2008) demonstrated that surface application of Al WTRs at 10 g kg −1 reduced the leachate P concentration by 46-54% in sandy soils amended with either poultry manure or sewage biosolids. In soil column experiments, Al WTR surface applications of 124 and 248 t ha −1 have proven to assist in the reduction of leached P from urban runoff (Ippolito 2015). Similarly, field studies found that Al WTR application at 22.4 dry t ha −1 can reduce leaching of P into shallow groundwaters ).…”

Water treatment residuals as soil amendments: Examining element extractability, soil porewater concentrations and effects on earthworm behaviour and survival

“…millions of tons) of WTRs are produced globally (Babatunde and Zhao, 2007), with the majority disposed of via landfill. However, landfill disposal is increasingly expensive and may be wasting a potentially useable material; an increasing array of potential beneficial uses of WTRs have been researched and demonstrated over the last two decades, including use in constructed reedbeds or as a soil amendment to manage phosphorus (P) mobility within catchments (Babatunde et al, 2011;Ippolito, 2015;Oliver et al, 2011), land application to increase organic matter and water holding capacity and related soil parameters (e.g. Ahmed et al, 1998;Bugbee and Frink, 1985), and most recently as a way of remediating polluted soils through immobilization of contaminants by WTRs (Garau et al, 2014;Garau et al, 2017;Wang et al, 2012).…”

Laboratory evaluation of alum, ferric and ferrous-water treatment residuals for removing phosphorous from surface water

“…pH of the WTR samples were determined using 1:1 ratio of WTR to distilled water ( Ippolito, 2015 ). Triplicate beakers containing 10 g of WTR and 10 mL of distilled water were stirred for 15 min.…”