Nutrient transport, shear strength and hydraulic characteristics of topsoils amended with mulch, compost and biosolids.

Anthropogenic disturbance of soils can disrupt soil structure, diminish fertility, alter soil chemical properties, and cause erosion. Current remediation practices involve amending degraded urban topsoils lacking in organic matter and nutrition with organic amendments (OA) to enhance vegetative growth. However, the impact of OAs on water quality and structural properties at rates that meet common topsoil organic matter specifications need to be studied and understood. This study tested three commonly available OAs: shredded wood mulch, leaf-based compost, and class A Exceptional Quality stabilized sewage sludge (or biosolids) for nutrient (nitrogen and phosphorus) water quality, soil shear strength, and hydraulic properties, through two greenhouse tub studies. Findings showed that nitrogen losses to leachate were greater in the biosolids amended topsoils compared to leaf-compost, mulch amended topsoils, and control treatments. Steady-state mean total nitrogen (N) concentrations from biosolids treatment exceeded typical highway stormwater concentrations by at least 25 times. Soil total N content combined with the carbon:nitrogen ratio were identified to be the governing properties of N leaching in soils. Study soils, irrespective of the type of amendment, reduced the applied (tap) water phosphorus (P) concentration of ∼0.3 mg-P/L throughout the experiment. Contrary to the effects on N leaching, P was successfully retained by the biosolids amendment, due to the presence of greater active iron contents. A breakthrough mechanism for P was observed in leaf compost amended soil, where the effluent concentrations of P continued to increase with each rainfall application, possibly due to an saturation of soil adsorption sites. The addition of OAs also improved the strength and hydraulic properties of soils. The effective interlocking mechanisms between the soil and OA surfaces could provide soil its required strength and stability, particularly on slopes. OAs also improved soil fertility to promote turf growth. Presence of vegetative root zones can further reinforce the soil and control erosion.

Impact of vegetation selection on nitrogen and phosphorus processing in bioretention containers.

A year-long bioretention container study in Maryland, USA, measured the relationship between three plant species (Eutrochium dubium, Iris versicolor, and Juncus effusus) and N ( NO 3 - , NO 2 - , NH 4 + , total nitrogen [TN], total dissolved nitrogen [TDN], dissolved organic nitrogen, particulate organic nitrogen [PON]) and total phosphorus (TP) removal from synthetic stormwater. Statistically significant removal was only found for NO 3 - and TP. Plant-independent NO 3 - removal occurred 9 months after planting, and then changed to removal only by the least-densely planted Juncus treatment. Removal in higher-density Juncus plantings was suspected to be limited by preferential pathways created by high root density. Juncus' low-density NO 3 - removal success correlates with its high growth rate, root mass and length, and large biomass, matching previous literature. TP removal was plant-independent. Shoot harvesting of one plant of each species after 1 year would remove 0.61 g N. Of the plant species in this study, Juncus effusus is most highly recommended for bioretention for its nutrient removal dynamics and year-round green aesthetics. PRACTITIONER POINTS: Only the one-Juncus density treatment had significant NO 3 - removal. All Juncus treatments as well as non-Juncus treatments prevented the PON, TN, or TDN export seen in the No-plants control. TP removal was plant-independent. Juncus had the greatest biomass increase and biomass N. Shoots contain the majority of biomass N for each plant species. Juncus and Iris had high survivorship. Joe Pye had low survivorship. These, and all other study results, need field-scale verification.

Evaluation of an enhanced treatment media and permeable pavement base to remove stormwater nitrogen, phosphorus, and metals under simulated rainfall.

An enhanced stormwater treatment media, developed previously by the authors, was shown to effectively retain dissolved phosphorus (DP) and total Cu and Zn under simulated rainfall. The media comprises expanded shale aggregate, aluminum-based water treatment residual (WTR), and a psyllium-based binder. A 5-cm layer of media was installed as a permeable pavement base layer in a laboratory mesocosm and subjected to rainfall simulations using synthetic stormwater. At rainfall intensity of 0.66 cm/h, effluent DP event mean concentration (EMC) fell from an average of 0.22 mg/L P to below the EPA water quality criterion of 0.037 mg/L in 8 of 9 storms. DP retention increased at lower rainfall intensity and lower pH. Effluent EMC was lowered to less than 30 µg/L for total Cu and less than 92 µg/L for total Zn, on average, relative to average influent EMCs above 61 and 255 µg/L for total Cu and Zn, respectively. Effluent total Al EMCs were below the 25 µg/L detection limit for all storm simulations, indicating Al leaching from the WTR-containing media not to be an issue. Inclusion of an internal water storage (IWS) zone resulted in a 33% total nitrogen (TN) load reduction when adequate carbon was present to advance denitrification. This study provides an evaluation and demonstrates expected treatment performance of a novel stormwater treatment media under conditions representative of urban stormwater.

A unified look at phosphorus treatment using bioretention.

Phosphorus (P) is a water pollutant of significant concern as it limits the productivity of most freshwater systems, which can undergo eutrophication under heavy phosphorus inputs. Bioretention has shown great potential for stormwater quantity and quality control. However, phosphorus removal has been inconsistent in bioretention systems, with phosphorus leaching observed in some systems. This paper examines P removal mechanisms and performance in bioretention systems through published data. A temporal concept of P fate for different time-scales is proposed. A model is developed to predict effluent P concentrations (Ce) based on a media equilibrium concentration (Ceq) assumption, which is suitable for both short and long-term simulation. Ceq is well correlated with Ce for P data for different time-scales. Ceq varies less in media containing Al and Fe than in typical bioretention soil media. Although significant change in Ceq may occur during an event and long-term, Ceq variation in short-term is small. During the event and short terms, for high-P containing media, the concentration relationship is Ceq > Ce > C0 (influent P concentrations); for low-P containing media, Ceq < Ce < C0. During long-term, as media equilibrates with the influent runoff, Ceq ≈ Ce ≈ C0. The model explains concentration changes of P with depth. With proper selection of media and amendments, Ceq can be driven towards zero for P in bioretention media.

Performance of a 'Transitioned' Infiltration Basin Part 2: Nitrogen and Phosphorus Removals.

Infiltration basins have been widely used for stormwater runoff management. However, their longevity could be compromised over time, up to the point of operational failure. This research study showed that a 'failed' infiltration basin can 'transition' into a wetpond/wetland-like practice and provide water quality benefits. Performance evaluation over three years showed that the transitioned infiltration basin reduced the discharge event mean concentrations of total phosphorus (TP), dissolved phosphorus (DP), particulate phosphorus (PP), NOx-N (nitrate+nitrite), total Kjeldahl nitrogen (TKN), organic-N (ON), and total nitrogen (TN) during most storm events. Exports of TP, DP, ON, and TKN masses were observed only during the coldest periods. The cumulative mass removals were 61% TP, 53% DP, 63% PP, 79% NOx-N, 51% TKN, 45% ON, and 64% TN. The dry-weather nutrient concentrations combined with the environmental conditions at the transitioned basin indicated that sedimentation, adsorption, denitrification, and volume reduction were the removal mechanisms.

Growth and Cadmium Phytoextraction by Swiss Chard, Maize, Rice, Noccaea caerulescens, and Alyssum murale in Ph Adjusted Biosolids Amended Soils.

Past applications of biosolids to soils at some locations added higher Cd levels than presently permitted. Cadmium phytoextraction would alleviate current land use constraints. Unamended farm soil, and biosolids amended farm and mine soils were obtained from a Fulton Co., IL biosolids management facility. Soils contained 0.16, 22.8, 45.3 mg Cd kg(-1) and 43.1, 482, 812 mg Zn kg(-1) respectively with initial pH 6.0, 6.1, 6.4. In greenhouse studies, Swiss chard (Beta vulgaris var. cicla), a Cd-accumulator maize (inbred B37 Zea mays) and a southern France Cd-hyperaccumulator genotype of Noccaea caerulescens were tested for Cd accumulation and phytoextraction. Soil pH was adjusted from ∼5.5-7.0. Additionally 100 rice (Oryza sativa) genotypes and the Ni-hyperaccumulator Alyssum murale were screened for potential phytoextraction use. Chard suffered phytotoxicity at low pH and accumulated up to 90 mg Cd kg(-1) on the biosolids amended mine soil. The maize inbred accumulated up to 45 mg Cd kg(-1) with only mild phytotoxicity symptoms during early growth at pH>6.0. N. caerulescens did not exhibit phytotoxicity symptoms at any pH, and accumulated up to 235 mg Cd kg(-1) in 3 months. Reharvested N. caerulescens accumulated up to 900 mg Cd kg(-1) after 10 months. Neither Alyssum nor 90% of rice genotypes survived acceptably. Both N. caerulescens and B37 maize show promise for Cd phytoextraction in IL and require field evaluation; both plants could be utilized for nearly continuous Cd removal. Other maize inbreds may offer higher Cd phytoextraction at lower pH, and mono-cross hybrids higher shoot biomass yields. Further, maize grown only for biomass Cd maximum removal could be double-cropped.

Phosphorus speciation and treatment using enhanced phosphorus removal bioretention.

This field research investigated the water quality performance of a traditional bioretention cell retrofitted with 5% (by mass) water treatment residual (WTR) for enhanced phosphorus removal. Results indicate that WTR incorporation into the bioretention media does not negatively influence the infiltration mechanism of the bioretention system. Total suspended solids (TSS), total phosphorus (TP), and particulate phosphorus (PP) concentrations in runoff inflow were significantly reduced compared to outflow due to filtration of particulate matter. TP concentrations were significantly reduced by the bioretention cell; before WTR retrofit TP export occurred. Although net removal of soluble reactive phosphorus (SRP) and dissolved organic phosphorus (DOP) from incoming runoff was not found, leaching of dissolved phosphorus (DP) was prevented not only from incoming runoff, but also from the media and captured PP. Near constant outflow SRP and DOP concentrations suggest an equilibrium adsorption treatment mechanism. Both event mean concentrations and mass loads were reduced for TSS and all P species. Pollutant mass removals were higher than the event mean concentration removals due to the attenuation of volume by the bioretention media.

Assessing performance of manufactured treatment devices for the removal of phosphorus from urban stormwater.

Nutrients such as nitrogen and phosphorus in urban runoff can be controlled through a variety of nonstructural and structural controls commonly known as best management practices (BMPs). Manufactured treatment devices (MTDs) are structural BMPs that may be used in portions of a site, often when space is limited. MTDs use a variety of technologies to achieve potentially greater treatment efficiency while reducing spatial requirements. However, verifying the performance of MTDs is difficult because of the variability of runoff water quality, the variability in treatment technologies, and the lack of standardized protocols for field testing. Performance testing of MTDs has focused almost exclusively upon removal of sediment; however MTDs are now being applied to the task of removing other constituents of concern, including nutrients such as phosphorus. This paper reviews current methods of assessing treatment performance of MTDs and introduces the Virginia Technology Assessment Protocol (VTAP), a program developed to evaluate the removal of phosphorus by MTDs. The competing goals of various stakeholders were considered when developing the VTAP. A conceptual framework of the tradeoffs considered is presented; these tradeoffs require compromise among the competing interests in order that innovation proceeds and benefits accrue. The key strengths of VTAP are also presented and compared with other existing programs.

Bioretention column studies of phosphorus removal from urban stormwater runoff.

This study investigated the effectiveness of bioretention as a stormwater management practice using repetitive bioretention columns for phosphorus removal. Bioretention media, with a higher short-term phosphorus sorption capacity, retained more phosphorus from infiltrating runoff after 3 mg/L phosphorus loading. A surface mulch layer prevented clogging after repetitive total suspended solids input. Evidence suggests that long-term phosphorus reactions will regenerate active short-term phosphorus adsorption sites. A high hydraulic conductivity media overlaying one with low hydraulic conductivity resulted in a higher runoff infiltration rate, from 0.51 to 0.16 cm/min at a fixed 15-cm head, and was more efficient in phosphorus removal (85% mass removal) than a profile with low conductivity media over high (63% mass removal). Media extractions suggest that most of the retained phosphorus in the media layers is available for vegetative uptake and that environmental risk thresholds were not exceeded.

Water quality improvement through bioretention media: nitrogen and phosphorus removal.

High nutrient inputs and eutrophication continue to be one of the highest priority water quality problems. Bioretention is a low-impact development technology that has been advocated for use in urban and other developed areas. This work provides an in-depth analysis on removal of nutrients from a synthetic stormwater runoff by bioretention. Results have indicated good removal of phosphorus (70 to 85%) and total Kjeldahl nitrogen (55 to 65%). Nitrate reduction was poor (< 20%) and, in several cases, nitrate production was noted. Variations in flowrate (intensity) and duration had a moderate affect on nutrient removal. Mass balances demonstrate the importance of water attenuation in the facility in reducing mass nutrient loads. Captured nitrogen can be converted to nitrate between storm events and subsequently washed from the system. Analysis on the fate of nutrients in bioretention suggests that accumulation of phosphorus and nitrogen may be controlled by carefully managing growing and harvesting of vegetation.

Sustainable oil and grease removal from synthetic stormwater runoff using bench-scale bioretention studies.

One of the principal components of the contaminant load in urban stormwater runoff is oil and grease (O&G) pollution, resulting from vehicle emissions. A mulch layer was used as a contaminant trap to remove O&G (dissolved and particulate-associated naphthalene, dissolved toluene, and dissolved motor oil hydrocarbons) from a synthetic runoff during a bench-scale infiltration study. Approximately 80 to 95% removal of all contaminants from synthetic runoff was found via sorption and filtration. Subsequently, approximately 90% of the sorbed naphthalene, toluene, oil, and particulate-associated naphthalene was biodegraded within approximately 3, 4, 8, and 2 days after the event, respectively, based on decreases in contaminant concentrations coupled with increases of microbial populations. These results indicate the effectiveness and sustainability of placing a thin layer of mulch on the surface of a bioretention facility for reducing O&G pollution from urban stormwater runoff.