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.
Highlights
Green stormwater infrastructure (GSI) has become a national stormwater focus and is commonly being implemented in cities as part of their stormwater management strategy [1]
Water 2019, 11, 1575 act as nutrient “sinks” on the landscape but existing studies have shown that a significant amount of P and N is being leached and exported to the effluent from the soil media used in these systems [3,4,5,6,7,8,9] While implementation of bioretention is happening at a rapid pace, not enough attention is paid to the different design attributes of a bioretention, especially, the soil media composition which plays a critical role in the removal capacity of pollutants
In the field-based mesocosm experiment, we assessed the effect of spent lime amendments on leachate nutrient concentration for treatments receiving different levels of P and N loading
Summary
Green stormwater infrastructure (GSI) has become a national stormwater focus and is commonly being implemented in cities as part of their stormwater management strategy [1]. Among the various kinds of waste materials that have been identified with adsorptive properties [14,15,16,17,18,19], water treatment residuals (WTR), rich in Al, Fe or Ca, have received growing attention for its potential use as a bioretention soil amendment for P sorption [20,21,22,23,24] Such studies have focused almost exclusively on WTR that is predominantly Al-based and few have described WTR properties in their study, so less is known about the efficacy of other forms, such as Ca-based WTR ( known as spent lime), in retaining nutrients. Because composition of WTR varies widely across time spans and regions
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