PFAS fate using lysimeters during degraded soil reclamation using biosolids.

Carbon- and nutrient-rich biosolids are used in agriculture and land reclamation. However, per- and polyfluoroalkyl substances (PFAS) typically present in biosolids raise concerns of PFAS leaching to groundwater and plant uptake. Here, we investigated PFAS persistence and leaching from biosolids applied to a site constructed artificially to mimic degraded soils. Treatments included biosolids and biosolids blended with mulch applied at different rates to attain either one and five times the agronomic N rate for vegetable crops and a control treatment with synthetic urea and triple superphosphate fertilizer. Leachates were collected for a 2-year period from 15-cm depth zero-tension drainage lysimeters. Soils were analyzed post biosolids application. PFAS were quantified using isotope-dilution, solid-phase extraction and liquid chromatography tandem mass spectrometry. Leachate profiles exemplified an initial high total PFAS concentration, followed by a sharp decline and subsequent small fluctuations attributed to pre-existing soil conditions and rainfall patterns. Quantifiable PFAS in leachate were proportional to biosolids application rates. Short-chain perfluoroalkyl acids (CF2 < 6) were dominant in leachate, while the percentage of longer chains homologues was higher in soils. A 43% biosolids blend with mulch resulted in 21% lower PFAS leachate concentrations even with the blend application rate being 1.5 times higher than biosolids due to the blend's lower N-content. The blending effect was more pronounced for long-chain perfluoroalkyl sulfonic acids that have a greater retention by soils and the air-water interface. Biosolids blending as a pragmatic strategy for reducing PFAS leachate concentrations may aid in the sustainable beneficial reuse of biosolids.

Engineered and Environmental Controls of Microbial Denitrification in Established Bioretention Cells.

Bioretention cells (BRCs) are effective tools for treating urban stormwater, but nitrogen removal by these systems is highly variable. Improvements in nitrogen removal are hampered by a lack of data directly quantifying the abundance or activity of denitrifying microorganisms in BRCs and how they are controlled by original BRC design characteristics. We analyzed denitrifiers in twenty-three BRCs of different designs across three mid-Atlantic states (MD, VA, and NC) by quantifying two bacterial denitrification genes ( nirK and nosZ) and potential enzymatic denitrification rates within the soil medium. Overall, we found that BRC design factors, rather than local environmental variables, had the greatest effects on variation in denitrifier abundance and activity. Specifically, denitrifying populations and denitrification potential increased with organic carbon and inorganic nitrogen concentrations in the soil media and decreased in BRCs planted with grass compared to other types of vegetation. Furthermore, the top layers of BRCs consistently contained greater concentrations and activity of denitrifying bacteria than bottom layers, despite longer periods of saturation and the presence of permanently saturated zones designed to promote denitrification at lower depths. These findings suggest that there is still considerable potential for design improvements when constructing BRCs that could increase denitrification and mitigate nitrogen export to receiving waters.

Assessment of selected bioretention blends for nutrient retention using mesocosm experiments.

This study compares the performance of three bioretention media blends for N and P removal from simulated urban runoff in experimental mesocosms. TerraSolve, Biofilter, and "VT Mix" (Virginia Tech) were compared with and without vegetation at varying hydraulic residence times (HRTs). Adsorption isotherm experiments were also conducted. TerraSolve and VT Mix included water treatment residuals (WTRs), Biofilter and VT Mix included yard-waste compost (YWC), and TerraSolve included a mix of coir and peat. TerraSolve removed the highest amount of total P (>95%), which is attributed to the high quantity of WTRs. Results were similar for VT Mix, likely due to WTR content. Adsorption isotherms indicate a substantial difference due to this factor. Vegetative mesocosms were found to be less effective at P removal at an HRT of 6 to 12 h but not at an HRT of 24 h. VT Mix had the highest removal of total Kjeldahl nitrogen (TKN), significantly different than the other blends. Interactive effects with vegetation were observed, generally improving TKN removal at all HRTs, with the highest at 24 h. Substantial export of nutrients when using compost was not observed. The addition of YWC appeared to increase N removal, possibly by denitrification. It is recommended that bioretention media contain <10% fines, a source of amorphous Al for P adsorption, at least 3 to 5% total organic C in the form of a low P, relatively stable compost, and a minimum concentration of plant-available nutrients for establishment of vegetation. For systems that use HRT, optimum residence time is influenced by media composition.

Chemistry and transport of metals from entrenched biosolids at a reclaimed mineral sands mining site.

Deep row incorporation of biosolids is an alternative land treatment method whose typically high rates may result in elevated pollutant transport. The objectives of this research were to compare the effects of entrenched biosolids stabilization type and rate on heavy metal chemistry and mobility. Two rates each of Alexandria (Virginia) Sanitation Authority anaerobically digested (213 and 426 dry Mg ha(-1)) and Blue Plains (Washington, DC) lime-stabilized (329 and 657 dry Mg ha(-1)) biosolids were placed in trenches at a mineral sands mine reclamation site in Dinwiddie County, Virginia, in summer 2006. Vertical and lateral transport of heavy metals from the biosolids seams were determined by analyzing leachate collected in zero tension lysimeters below the trenches and suction lysimeters adjacent to the trenches. Silver, Cd, Pb, and Sn did not move vertically or laterally to any significant extent. During the 15-mo period following entrenching, lime-stabilized biosolids produced higher cumulative metal mass transport for Cu (967 g ha(-1)), Ni (171 g ha(-1)), and Zn (1027 g ha(-1)) than did the anaerobically digested biosolids and control. Barium mass loss was similar for both biosolids. All metals moved primarily with particulates. MINTEQA) predicted that > 70% of Cu was bound to fulvic acids, whereas > 80% of Ba was found as Ba2+. As pH decreased with time, free ions of Zn decreased and the metal's association with fulvic acids increased. Largely insignificant transport of metals into the lysimeters demonstrated that biosolids-borne heavy metals posed little risk to groundwater even when entrenched in very coarse-textured soil.

Distribution of copper, zinc, and phosphorus in coastal plain soils receiving repeated liquid biosolids applications.

Continuous N-based application of biosolids contributes to a gradual increase of trace elements and P in soils. The objectives of this study were to assess the accumulation and vertical transport of Cu, Zn, C, N, and P within the profile of two coastal plain soils. Liquid (6-8% total solids) biosolids were applied to an Acredale silt loam (fine silty, mixed, thermic typic Ochraqualfs) and Bojac loamy sand (coarse loamy, mixed, thermic typic Hapludult) annually from 1984 to 1998. The repeated applications supplied 70, 204, and 3823 kg ha(-1) of Cu, Zn, and P, respectively, to the Acredale and 81, 225, and 4265 kg ha(-1) of Cu, Zn, and P, respectively, to the Bojac. The total C and N contents were not different than background levels in the Bojac soil and were slightly higher in the Acredale soil 7 years after cessation of biosolids application. Phosphorus, Cu and Zn are still concentrated in the top 0.25 m of the Acredale soil. Enrichment of P, Cu, and Zn were detected to the deepest soil increment in the coarse-textured Bojac soil. Approximately 20 to 40% of the Cu and Zn applied in the biosolids could not be accounted, which was likely due to a combination of leaching and incomplete extraction. Excessive Mehlich 1-P concentrations and a high degree of P saturation were found in amended soil, raising the potential for P release to runoff or leaching water.

Repeated compost application effects on phosphorus runoff in the Virginia Piedmont.

Increasing amounts of animal and municipal wastes are being composted before land application to improve handling and spreading characteristics, and to reduce odor and disease incidence. Repeated applications of composted biosolids and manure to cropland may increase the risk for P enrichment of agricultural runoff. We conducted field research in 2003 and 2004 on a Fauquier silty clay loam (Ultic Hapludalfs) to compare the effects of annual (since 1999) applications of composted and uncomposted organic residuals on P runoff characteristics. Biosolids compost (BSC), poultry litter-yard waste compost (PLC), and uncomposted poultry litter (PL) were applied based on estimated plant-available N. A commercial fertilizer treatment (CF) and an unamended control treatment (CTL) were also included. Corn (Zea mays L.) and a cereal rye (Secale cereal L.) cover crop were planted each year. We applied simulated rainfall in fall 2004 and analyzed runoff for dissolved reactive P (DRP), total dissolved P (TDP), total P (TP), total organic C (TOC), and total suspended solids (TSS). End of season soil samples were analyzed for Mehlich-3 P (M3P), EPA 3050 P (3050P), water soluble P (WSP), degree of P saturation (DPS), soil C, and bulk density. Compost treatments significantly increased soil C, decreased bulk density, and increased M3P, 3050P, WSP, and DPS. The concentration of DRP, TDP, and TP in runoff was highest in compost treatments, but the mass of DRP and TDP was not different among treatments because infiltration was higher and runoff lower in compost-amended soil. Improved soil physical properties associated with poultry litter-yard waste compost application decreased loss of TP and TSS.

Cadmium, copper, nickel, and zinc availability in a biosolids-amended piedmont soil years after application.

Concerns over the possible increase in phytoavailability of biosolids-applied trace metals to plants have been raised based on the assumption that decomposition of applied organic matter would increase phytoavailability. The objectives of this study were to assess the effect of time on chemical extractability and concentration of Cd, Cu, Ni, and Zn in plants on plots established by a single application of biosolids with high trace metals content in 1984. Biosolids were applied to 1.5 by 2.3 m confined plots of a Davidson clay loam (clayey, kaolinitic, thermic Rhodic Kandiudults) at 0, 42, 84, 126, 168, and 210 Mg ha(-1). The highest biosolids application supplied 4.5, 760, 43, and 620 kg ha(-1) of Cd, Cu, Ni, and Zn, respectively. Radish (Raphanus sativus L.), romaine lettuce (Lactuca sativa L. var. longifolia), and barley (Hordeum vulgare L.) were planted at the site for 3 consecutive years, 17 to 19 yr after biosolids application. Extractable Cd, Cu, Ni, and Zn (as measured by DTPA, CaCl(2,) and Mehlich-1) were determined on 15-cm depth samples from each plot. The DTPA-extractable Cu and Zn decreased by 58 and 42%, respectively, 17 yr after application despite a significant reduction in organic matter content. Biosolids treatments had no significant effect on crop yield. Plant tissue metal concentrations increased with biosolids rate but were within the normal range of these crops. Trace metal concentrations in plants generally correlated well with the concentrations extracted from soil with DTPA, CaCl(2), and Mehlich-1. Metal concentrations in plant tissue exhibited a plateau response in most cases. The uptake coefficient values generated for the different crops were in agreement with the values set by the Part 503 Rule.

Recovery and distribution of biosolids-derived trace metals in a clay loam soil.

The long-term mobility of trace metals has been cited as a potential hazard by critics of EPA 503 rule governing the land application of biosolids. The objectives of this study were to assess the accumulation of Cu, Ni, Cd, and Zn within the soil profile; the distribution of exchangeable, specifically adsorbed, organic, and oxide fractions of each metal; and mass balance of Cu, Ni, and Zn 17 yr after a single biosolids application. Biosolids were applied to 1.5- x 2.3-m confined plots of a Davidson clay loam (fine, kaolinitic, thermic Rhodic Kandiudult) in 1984 at 0, 42, 84, 126, 168, and 210 Mg ha(-1). The highest biosolids application supplied 4.5, 750, 43, and 600 kg ha(-1) of Cd, Cu, Ni, and Zn, respectively. Soils were sampled to a depth of 0.9 m and sectioned into 5-cm increments after separating the Ap horizon. Total (EPA-3050B), bioavailable (Mehlich-I), sequential extraction, and dispersible clay analyses were performed on samples from the control, 126 Mg ha(-1), and 210 Mg ha(-1) treatments. Trace metals are still concentrated in the top 0.2 m with slight enrichment down to 0.3 m. More than 85% of applied Cu, Ni, and Zn are still found in the topsoil where biosolids was incorporated and 95% or more of the applied metals were accounted for with mass balance calculations. Mehlich-I results showed a slight increase in metal concentration down to 0.35 m. Biosolids application increased the concentrations of trace metals in all the extracted fractions. The major portions of Cu, Zn, and Ni are associated with the metal-oxides fraction. Dispersible clay content and water-soluble metal contents were low and except for water-soluble Zn they were not affected by biosolids application. Results from this study showed that 17 yr after biosolids application there was negligible movement of trace metals through the soil profile and consequently there is little risk of contamination of ground water at this site.

Decomposition and plant-available nitrogen in biosolids: laboratory studies, field studies, and computer simulation.

This research combines laboratory and field studies with computer simulation to characterize the amount of plant-available nitrogen (PAN) released when municipal biosolids are land-applied to agronomic crops. In the laboratory studies, biosolids were incubated in or on soil from the land application sites. Mean biosolids total C, organic N, and C to N ratio were 292 g kg(-1), 41.7 g kg(-1), and 7.5, respectively. Based on CO2 evolution at 25 degrees C and optimum soil moisture, 27 of the 37 biosolids-soil combinations had two decomposition phases. The mean rapid and slow fraction rate constants were 0.021 and 0.0015 d(-1), respectively, and the rapid fraction contained 23% of the total C assuming sequential decomposition. Where only one decomposition phase existed, the mean first order rate constant was 0.0046 d(-1). The mean rate constant for biosolids stored in lagoons for an extended time was 0.00097 d(-1). The only treatment process that was related to biosolids treatment was stabilization by storage in a lagoon. Biosolids addition rates (dry basis) ranged from 1.3 to 33.8 Mg ha(-1) with a mean value of 10.6 Mg ha(-1). A relationship between fertilizer N rate and crop response was used to estimate observed PAN at each site. Mean observed PAN during the growing season was 18.9 kg N Mg(-1) or 37% of the biosolids total N. Observed PAN was linearly related to biosolids total N. Predicted PAN using the computer model Decomposition, actual growing-season weather, actual analytical data, and laboratory decomposition kinetics compared well with observed PAN. The mean computer model prediction of growing-season PAN was 19.2 kg N Mg(-1) and the slope of the regression between predicted and observed PAN was not significantly different from unity. Predicted PAN obtained using mean decomposition kinetics was related to predicted PAN using actual decomposition kinetics suggesting that mean rate constants, actual weather, and actual analytical data could be used in estimation of PAN. There was a linear relationship between predicted N mineralization for the growing season and for the first year. For this study, the mean values for the growing season and year were 27 and 37% of the organic N, respectively.