Efficacy of Spent Lime as a Soil Amendment for Nutrient Retention in Bioretention Green Stormwater Infrastructure

Abstract

The composition of bioretention soil media (BSM) is among the most critical design attributes contributing to the water quality performance of bioretention systems, as various amendments may increase the capacity for chemical sorption of certain nutrient pollutants. We investigated the spent lime (a calcium-based water treatment residual) as BSM amendments for nutrient retention. The study was conducted in two parts: the first was a field-based mesocosm experiment in which we assessed the effect of spent lime amendments on leachate nutrient concentration for treatments receiving different levels of phosphorus and nitrogen loading (simulated by different levels of compost added to the substrate). The second was a laboratory study comparing various levels of spent lime and coir on leachate nutrient concentration at two different simulated loading rates. Effluent water was collected and analyzed for PO43−, NH4+ and NO3− concentrations in the field and lab. Spent lime significantly reduced leachate PO43− concentrations (upwards of 50%) in both the field and lab mesocosm studies compared to treatments without spent lime. Reductions in NH4+ concentrations were also observed due to spent lime but with variable significance across the different compost levels, whereas NO3− concentrations were higher in plots with spent lime than plots without spent lime. In the lab, columns with coir had significantly higher leachate PO43− concentrations compared to spent lime-treated columns, however, leachate NH4+ and NO3− concentrations did not significantly differ between treatments at the same compost levels. This study shows that spent lime, which is a waste product, is effective in significantly reducing leachate PO43− concentrations from BSM, while be a cost-effective substitute to engineered proprietary media that is expensive to acquire; however, future studies must also evaluate its potential for clogging.

Field Application of Spent Lime Water Treatment Residual for the Removal of Phosphorus and other Pollutants in Urban Stormwater Runoff

“…These P sorption materials can enhance P removal through a variety of mechanisms. It has been proposed that lime-and Ca-based filters rely primarily on chemical precipitation to remove P [26,30]. However, the findings of this study suggested that chemical precipitation (i.e., surface precipitation) may have only played a minor role as a P removal mechanism.…”

“…Spent lime DWTR, which is the sludge byproduct of water softening at a water treatment plant (WTP), is a promising P sorbent due to its high concentration of Ca and magnesium (Mg) [26] and has been previously studied in the laboratory as a P removal filter material [27]. Similar lime-based materials have been used in other stormwater treatment approaches, including sequential biofiltration systems [28], a riparian buffer [29], lime-sand filters [30], and as a substrate in rain gardens [26]. Furthermore, other Ca-rich materials have been studied for use in P removal structures, including steel slag [31], acid mine drainage residue [32], burnt lime [30], and limestone [33].…”

Nitrogen removal performance in roadside stormwater bioretention cells amended with drinking water treatment residuals

“…Additionally, DWTRs can have a high organic matter content (Keeley et al, 2014), which could serve as a carbon source for denitrifying bacteria. The high cation exchange capacity of DWTRs also offers the potential for ammonium (NH 4 + ) removal via adsorption (Shrestha et al, 2019). Conversely, DWTRs also have the potential to act as a source of N. DWTRs can release weakly bound NH 4 + via desorption from ligand exchange sites/surface complexes in the presence of an ionic solution (Wang et al, 2018(Wang et al, , 2019.…”

“…DWTRs are promising amendments for bioretention media due to their high concentrations of metal (hydr)oxides and associated P sorption capacity (Marvin et al., 2020). A growing body of research exists investigating DWTRs as a means for enhancing P sorption in bioretention and other soil systems (Agyin‐Birikorang et al., 2007; Ament et al., 2021; Babatunde et al., 2009; Liu & Davis, 2014; Makris et al., 2004; Shrestha et al., 2019). However, to our best knowledge, there are currently no studies that explicitly investigate the effects of DWTR amendment on N removal performance in field‐scale bioretention systems.…”

Urban stormwater characterization, control, and treatment

“…For a larger event with twice the concentration of nutrients in the inflow, removals were 70%, 82%, and 82%, for TN, TKN, and TP, respectively. The role of spent lime as an amendment to bioretention soil media was tested by Shrestha et al (2019) in a two‐part study comprising field and laboratory components. Phosphate concentration effluent from media without spent lime was shown to be 50% more than media with spent lime, for both field and laboratory testing.…”