Biosolids Compost Research Articles

17 β-estradiol and 17 α-ethinylestradiol mineralization in sewage sludge and biosolids

Natural steroid estrogens (e.g., 17 β-estradiol, E2), synthetic steroid estrogens (e.g., 17 α-ethinylestradiol, EE2) and pharmaceutical antibiotics (e.g., ciprofloxacin) are chemicals detected in biosolids and sewage sludges because they partition into the solids fraction during the wastewater treatment process. This research utilized a three-way factorial design (six media × two estrogens × three antibiotic treatments) to quantify cumulative E2 and EE2 mineralization over 133 d (MAX) in a range of sewage sludge and biosolid samples in the presence (4 and 40 mg kg−1) and absence of ciprofloxacin. The same three-way factorial design was utilized to quantify the impact of the six media, E2 or EE2, and ciprofloxacin on cumulative soil respiration over 133 d (RESP). Minimal ciprofloxacin mineralization was observed (<0.05% over 133 d), but despite its persistence, ciprofloxacin had no significant effect on MAX of E2 or EE2, and, in general, no significant effect on RESP. MAX ranged from 38.38% to 48.44% for E2 but from only 0.72% to 24.27% for EE2 although RESP was relatively similar, ranging from 101.00 to 866.54 mg CO2 in the presence of E2 and from 69.55 to 893.95 mg CO2 in the presence of EE2. The sorption-limited bioavailability of EE2, which is inherently resistant to biodegradation due to chemical structure, as MAX and Freundlich sorption coefficients (Kf) were negatively correlated. As such, the Kf values of EE2 were largest in composted biosolids in which EE2 was particularly resistant to microbial degradation as the MAX of EE2 was <3%. In contrast, the MAX of E2 showed a positive association with the Kf values of E2 because some steps in the E2 transformation process have been found to occur in the sorbed phase. The MAX of E2 was significantly greater in the biosolid and composted biosolid media than in any other media, whereas the MAX of E2 decreased in the following order: secondary sewage sludge > primary sewage sludge > biosolid = composted biosolid. This suggests that sewage sludges in municipal lagoons and pre-treatment holding lagoons are a more favorable media for mineralization of EE2, whereas biosolids in post-treatment storage lagoons are a more favorable media for the mineralization of E2. The presence of ciprofloxacin will have no impact on the potential E2 or EE2 mineralization rates in these cases.

Composting of Biosolids Enhanced by a Combined Pretreatment with Hydrogen Peroxide and Triton X-100

In this report, effects of oxidative pretreatment on the composting of biosolids were demonstrated. Pretreatment with 0.18 % hydrogen peroxide (H2O2) in combination with 0.1 % Triton X-100 enhanced biodegradation of biosolid composting mixtures, including that of food factory waste-activated sludge (FFWAS), rice husk and mature compost in a ratio of 75:15:10 and paper mill-cellulosic sediment sludge (PMCSS), pig manure and mature compost in a ratio of 45:45:10. The composting process was monitored on the changes of several parameters, including temperature, carbon dioxide evolution, pH, organic matter content (volatile solids, VS), carbon/nitrogen ratio and microbe populations. Organic matters in FFWAS and PMCSS composting mixtures decreased at a rate of 0.42 and 0.33 % VS reduction day−1, respectively. Both FFWAS and PMCSS composts were adequate for plant growth as shown by a maturity assay on day 20. Furthermore, initiation effect of H2O2 on the composting of biosolids was examined on FFWAS-rice husk mixture. The outcome indicated that biodegradability of organic matter increased by the combined pretreatment with Triton X-100 was affected by total amount of H2O2 applied with an optimum concentration as low as 0.18 %.

Composto orgânico com altos teores de níquel e sua biodisponibilidade no sistema solo planta

A utilização de biossólidos industriais na agricultura pode proporcionar aumento de níquel no solo, porém sua biodisponibilidade é influenciada por diversos fatores e, muitas vezes, resíduos com elevados teores de níquel não estão associados à sua alta absorção pela planta. O objetivo foi avaliar a solubilidade do níquel no solo, sua biodisponibilidade e acumulação em plantas. O experimento foi conduzido em vasos em delineamento inteiramente casualizado com seis doses de níquel: 0, 9, 18, 36, 72 e 144 mg de níquel kg-1 de solo, via fonte orgânica (biossólido compostado) e mineral (cloreto de níquel) com 4 repetições. Utilizou-se um Cambissolo Háplico como substrato e o morangueiro como planta indicadora. Avaliaram-se os teores no solo pelos extratores: ácido nítrico + clorídrico concentrado (3:1), nitrato de cálcio a 0,5 mol L-1, ácido nítrico a 1,0 mol L-1 e o pirofosfato de sódio a 0,1 mol L-1 além, ainda, dos teores de níquel na raiz, coroa, parte aérea e fruto. As maiores e menores extrações de níquel no solo foram observadas pela aplicação da fonte orgânica e extração com o ácido nítrico e clorídrico concentrado e pelo nitrato de cálcio, respectivamente. Ambas as fontes aumentaram os teores de níquel nos tecidos avaliados, com menores aumentos para fonte orgânica. Os maiores teores foram observados em raiz e os menores em coroa.

Quality of trace element contaminated soils amended with compost under fast growing tree Paulownia fortunei plantation

The use of fast growing trees could be an alternative in trace element contaminated soils to stabilize these elements and improve soil quality. In this study we investigate the effect of Paulownia fortunei growth on trace element contaminated soils amended with two organic composts under semi-field conditions for a period of 18 months. The experiment was carried out in containers filled with tree different soils, two contaminated soils (neutral AZ and acid V) and a non contaminated soil, NC. Three treatments per soil were established: two organic amendments (alperujo compost, AC, and biosolid compost, BC) and a control without amendment addition. We study parameters related with fertility and contamination in soils and plants. Paulownia growth and amendments increased pH in acid soils whereas no effect of these factors was observed in neutral soils. The plant and the amendments also increased organic matter and consequently, soil fertility. Positive results were also found in soils that were only affected by plant growth (without amendment). A general improvement of “soil biochemical quality” was detected over time and treatments, confirming the positive effect of amendments plus paulownia. Even in contaminated soils, except for Cu and Zn, trace element concentrations in leaves were in the normal range for plants. Results of this mid-term study showed that Paulownia fortunei is a promising species for phytoremediation of trace element polluted soils.

Marigold and Pepper Growth in Container Substrates Made from Biosolids Composted with Carbon-rich Organic Wastes

Composts made from organic wastes have the potential to substitute for peat and bark as components of container growth substrates. Composts for this research were produced in small-scale aerobic bins using biosolids blended with construction debris, storm debris, or horse waste in a 1:3 (v:v ratio). The composts were screened and blended 1:1 (v:v) with douglas fir (Pseudotsuga menziesii) bark to produce substrates. They were compared with a peat–perlite control substrate, a biosolids blend control substrate, and substrates made from a commercial biosolids compost mixed 1:1 with bark and from fiber from an anaerobic digester (dairy manure and food waste) mixed 1:1 with bark. Chemical and physical properties of the substrates were measured before transplanting, and growth, quality, and leaf color of ‘Little Hero Flame’ marigold (Tagetes patula) and ‘Golden California Wonder’ bell pepper (Capsicum annuum) were measured in a replicated greenhouse study comparing the substrates at two rates of nitrogen (N) application. The experimental biosolids composts-bark substrates performed similar to the peat–perlite and biosolids blend controls for growing marigold and pepper. The commercial biosolids compost mixed with bark did not perform as well as the experimental substrates or the controls. Digester fiber-bark was intermediate between commercial biosolids compost-bark and other treatments. Higher N rates improved plant growth and quality across all container substrates in pepper, but had fewer significant effects on marigold. Experimental substrates were coarser texture than the peat–perlite or biosolids blend controls, resulting in higher aeration porosity (AP) and lower water-holding capacity (WHC), but performed well nonetheless under the drip irrigation used in this study. Using locally sourced organic waste materials as container substrates can help capture value from organic wastes and contribute to the sustainability of nursery production practices.

Effectiveness of Low‐Cost Planting Techniques for Improving Water Availability toOlea europaeaSeedlings in Degraded Drylands

AbstractReforestation projects in semiarid lands often yield poor results. Water scarcity, poor soil fertility, and structure strongly limit the survival and growth of planted seedlings in these areas. At two experimental semiarid sites, we evaluated a variety of low‐cost planting techniques in order to increase water availability to plants. Treatments included various combinations of traditional planting holes; water‐harvesting microcatchments; stone or plastic mulches; small waterproof sheets to increase water harvesting; dry wells; buried clay pots; and deep irrigation. Some of these treatments were also combined with addition of composted biosolids. Waterproof sheets significantly enhanced water harvesting (43%) and soil moisture in the planting hole (40%), especially for low‐intensity rainfall events. Treatment effects on the survival and growth ofOlea europaeaseedlings varied between experimental sites. At the most water‐limited site, clay pots, and dry wells improved seedling survival, while no treatment enhanced seedling growth. At the least water‐stressed site, the application of composted sludge significantly improved seedling growth. We conclude that nutrient‐mediated stress is subordinate to water stress in arid and semiarid environments, and we suggest modifications on the microsite scale to address these limiting conditions in Mediterranean drylands.

Commercial Amendments for Sand-based Root Zones: Review and Interpretation

Amendments used in sand-based root zones are typically native peats, composts, or inorganic materials of diverse mineralogy. Literature-based guidelines for amendment inclusion include root zone capillary porosity (CP) values exceeding 0.2 m3·m−3 or soil surface water contents exceeding 0.1 m3·m−3. It is also suggested that the cation exchange capacity (CEC) need not exceed 4 cmolc·kg−1. Summarizing published data, native peat added to a U.S. Golf Association (USGA) guideline sand yielding organic matter (OM) content values of ≈15 g·kg−1 would typically yield benchmark values of CP = 0.2 m3·m−3, surface water content = 0.1 m3·m−3, and CEC values between 3 and 4 cmolc·kg−1. This OM content is roughly equivalent to 15% by volume of a fibric sphagnum or 7.5% by volume of a hemic reed-sedge. By comparison 15% by volume of an inorganic amendment would likely result in CP and surface water content values less than the benchmark values, and CEC values between 1.5 and 4 cmolc·kg−1. However, the CP benchmark measured at 30 cm of soil water suction should be re-evaluated because it may bias against the use of biosolids compost and inorganic amendments that reduce the thickness of the capillary fringe and create a broader pore size distribution. Also a weak relationship has been observed between longer-term turfgrass quality and 30-cm CP values. Measurement of CP at 40-cm suction would be a better indication of water retention in sand-based root zones for all amendment types. Lastly, inorganic amendments produce a drier root zone that may be preferred for both playability and long-term agronomic concerns.

Effect of organic amendment on soil fertility and plant nutrients in a post-fire Mediterranean ecosystem

Backgrounds and aims In Mediterranean frequently burnt areas, the decrease of soil fertility leads to regressive vegetation dynamics. Organic amendments could help to accelerate post-fire ecosystem resilience, by improving soil properties and plant nutrition. This study was conducted to assess the potential of a composted biosolid to restore an early post-fire shrubland.

Polybrominated Diphenyl Ether (PBDE) Accumulation by Earthworms (Eisenia fetida) Exposed to Biosolids-, Polyurethane Foam Microparticle-, and Penta-BDE-Amended Soils

Polybrominated diphenyl ether (PBDE) flame retardants have been used in consumer polymers at up to percent levels. While long viewed as biologically inaccessible therein, PBDEs may become bioaccessible following volatilization or polymer deterioration. PBDEs may then enter soils via polymer fragmentation or following land application of sewage sludge-derived biosolids. Studies of direct PBDE uptake from these materials by soil organisms are scarce. We thus exposed earthworms ( Eisenia fetida ) to artificial soil amended with a Class B anaerobically digested biosolid (ADB), an exceptional quality composted biosolid (CB), PBDE-containing polyurethane foam (PUF) microparticles, and Penta-BDE-spiked artificial soil (SAS). Worms accumulated mg/kg (lipid) ∑Penta-PBDE burdens from all substrates. Biota-soil accumulation factors (BSAFs) for worms exposed to ADB- and CB-amended soils were comparable after 28 d. BSAFs generally decreased with increasing congener KOW and substrate dosage. Biosolids-associated PBDE bioavailability was lower than spiked PBDEs. BSAFs for worms exposed to PUF microparticles ranged from 3.9 to 33.4, with ∑Penta-PBDE tissue burdens reaching 3740 mg/kg lipid. Congener accumulation patterns were similar in worms and polyethylene passive sampling devices immersed in ADB-amended soil coincident with exposed worms. However, passive sampler accumulation factors were lower than BSAFs. Our results demonstrate that PBDEs may accumulate in organisms ingesting soils containing biosolids or waste plastics. Such organisms may then transfer their burdens to predators or translocate them from the site of application/disposal.

Characterizing Water Holding Capacity and Runoff during Composting of Greenwaste and Biosolids

ABSTRACT Most composters in the United States use open-windrows. During high intensity precipitation events, uncontained water running off of the surface of the compost piles can potentially contaminate surface waters with nutrients and metals. Water that is absorbed poses no runoff concern but may threaten groundwater quality. To gain insight into these processes, stormwater runoff fractions and water holding capacity of compost piles have been characterized for greenwaste (GW) and biosolids (BS) materials. Laboratory scale experiments were conducted using days 1, 7, and 14 materials representing three different stages of composting. This study also evaluated sloped and flat-top as different pile geometries and surfactant use for promoting infiltration. Results indicate that fresh materials were most hydrophobic and the infiltration rates increased with increased composting times. The water storage capacity of the compost pile increased with the age of the compost pile. Compost water storage capacities could not be reliably estimated as the difference between field capacity and as-received water contents.

Can we build better compost? Use of waste drywall to enhance plant growth on reclamation sites

Compost is a readily available source of organic matter and nutrients and is produced large scale in many jurisdictions. Novel advancements in composting include addition of construction waste, such as drywall, to address its disposal while potentially improving compost quality for use in land reclamation. Varying compositions (15–30% by weight) of coarse and ground waste drywall were added to manure and biosolids during composting. Six composts were applied at four rates (0, 50, 100, 200 Mg ha−1) to three reclamation soils (agricultural, urban clean fill, oil sands tailings). Response to composts was assessed in the greenhouse with three plant species (Hordeum vulgare L. (barley), Agropyron trachycaulum (Link) Malte (slender wheat grass) and Festuca saximontana Rydb. (rocky mountain fescue). Drywall added to biosolids or manure during composting had no detrimental effects on vegetation; any negative effects of compost occurred with and without drywall. In agricultural soil and clean fill, biosolids composts with 15% coarse and 18% ground drywall improved native grass response, particularly biomass, relative to biosolids compost without drywall. Drywall manure composts reduced native grass response relative to manure compost without drywall. Only low quality tailings sand was improved by 30% coarse drywall. Compost rate significantly affected above and below ground biomass in agricultural soil and reduced performance of native species at highest rates, suggesting a threshold beyond which conditions will not be suitable for reclamation. Grinding drywall did not significantly improve plant performance and use of coarse drywall would eliminate the need for specialized equipment and resources. This initial research demonstrates that drywall composts are appropriate soil amendments for establishment of native and non native plant species on reclamation sites with consideration of substrate properties and plant species tolerances to dictate which additional feed stocks should be used.

Erratum: The Effects of Long-term Application of Organic Amendments on Soil Organic Carbon Accumulation

Application of organic amendments (e.g., biosolids[BS], composts) to soil may provide an effective method for accumulating considerable amounts of C, but the long term stability of such C is not well known. We investigated study sites in Virginia to determine the amounts of C remaining in soils 7 to 27 yr following amending with biosolids and composts. The first study employed a Fauquier silty clay loam (fine, mixed, active, mesic Ultic Hapludalf) to which four treatments (control, poultry litter-yard waste compost, biosolids compost, and poultry litter) were continuously applied during 2000–2004. The second study was conducted on a Davidson clay loam (fine, kaolinitic, thermic, Rhodic Kandiudult) to which six rates of aerobically digested biosolids (0, 42, 84, 126, 168, and 210 Mg ha–¹) were applied in 1984. The third study was on a Pamunkey sandy loam (fine-loamy, mixed, semiactive, thermic Ultic Hapludalfs) to which five rates of anaerobically digested biosolids (0, 14, 42, 70, and 98 Mg ha–¹), with and without sawdust, were applied in 1996. Total soil organic C concentration and bulk density were measured to calculate C accumulation. The organic amendment-treated soils increased C in the surface soil depth (<15 cm), ranging from 2 to 12% of C across all three sites. Soil C movement was limited to a depth of 15 cm. Evidence of C saturation was revealed in the third study site. These results demonstrate that organic amendments applied over a long time remain in soil and may contribute to C sequestration in the Mid-Atlantic region.

Biomass production and soil nutrients in organic and inorganic fertilized willow biomass production systems

The use of organic waste materials as nutrient sources for willow biomass production is an attractive means to decrease fertilization costs, increase biomass production and reduce greenhouse gas emissions associated with the system. In this study, changes in soil nutrients and biomass production of two willow varieties (Salix miyabeana–SX64 and Salix purpurea–9882-34) in organic and synthetic fertilized systems were compared at three locations in Northeastern U.S.A: Middlebury VT (MID), Delhi NY (DEL) and Fredonia NY (FRE). A 150 and 200 kg available N ha−1 of urea as commercial fertilizer (CF), biosolid compost (BC) and digested dairy manure (DM) and a control (CT0) treatments were applied in June 2008 to the willow which was re-sprouting after coppice. There was no significant difference (p > 0.05) in biomass production among the fertilization treatments at any of the three sites and for either of the varieties. First rotation biomass production of 9882-34 ranged from 9.0 to 11.6 Mg ha−1 yr−1 at DEL, 3.4–8.8 Mg ha−1 yr−1 at MID and 3.5–7.7 Mg ha−1 yr−1 at FRE. For SX64, biomass production ranged from 13.2 to 19.0 Mg ha−1 yr−1 at DEL, 9.0–15.0 Mg ha−1 yr−1 at Mid and 5.5–9.3 Mg ha−1 yr−1 at FRE. SX64 deployed small numbers of large stems and produced more biomass than 9882-34 which deployed large numbers of small stems. Application of BC significantly increased soil N and P levels at MID in both 2008 and 2009 (p < 0.05). At DEL, BC and DM treatments increased soil N, Ca, Mg and OM levels in both 2008 and 2009 (p < 0.05). The fertilization treatments had no significant effect on any soil nutrients at FRE. This study indicates that willow biomass can be produced without fertilizer additions in the first rotation across this range of sites due to the nutrient status of these sites and high internal nutrient cycling in these systems.

The Effects of Long‐term Application of Organic Amendments on Soil Organic Carbon Accumulation

Application of organic amendments (e.g., biosolids[BS], composts) to soil may provide an effective method for accumulating considerable amounts of C, but the long term stability of such C is not well known. We investigated study sites in Virginia to determine the amounts of C remaining in soils 7 to 27 yr following amending with biosolids and composts. The first study employed a Fauquier silty clay loam (fine, mixed, active, mesic Ultic Hapludalf) to which four treatments (control, poultry litter‐yard waste compost, biosolids compost, and poultry litter) were continuously applied during 2000–2004. The second study was conducted on a Davidson clay loam (fine, kaolinitic, thermic, Rhodic Kandiudult) to which six rates of aerobically digested biosolids (0, 42, 84, 126, 168, and 210 Mg ha–1) were applied in 1984. The third study was on a Pamunkey sandy loam (fine‐loamy, mixed, semiactive, thermic Ultic Hapludalfs) to which five rates of anaerobically digested biosolids (0, 14, 42, 70, and 98 Mg ha–1), with and without sawdust, were applied in 1996. Total soil organic C concentration and bulk density were measured to calculate C accumulation. The organic amendment‐treated soils increased C in the surface soil depth (&lt;15 cm), ranging from 2 to 12% of C across all three sites. Soil C movement was limited to a depth of 15 cm. Evidence of C saturation was revealed in the third study site. These results demonstrate that organic amendments applied over a long time remain in soil and may contribute to C sequestration in the Mid‐Atlantic region.

Vermiremoval of heavy metal in sewage sludge by utilising Lumbricus rubellus

Experiments were conducted to remove heavy metals (Cr, Cd, Pb, Cu and Zn) from urban sewage sludge (SS) amended with spent mushroom compost (SMC) using worms, Lumbricus rubellus, for 105 days, after 21 days of pre-composting. Five combinations of SS/SMC treatments were prepared in triplicate along with a control for each treatment in microcosms. Analysis of the earthworms' multiplication and growth and laboratory analysis were conducted during the tenth and fifteenth week of vermicomposting. Our result showed that the final biomass of earthworms (mg) and final number of earthworms showed significant differences between treatments i.e. F=554.70, P=0.00 and F=729.10, P=0.00 respectively. The heavy metals Cr, Cd and Pb contained in vermicompost were lower than initial concentrations, with 90–98.7percent removal on week ten. However, concentrations of Cu and Zn, that are considered as micronutrients, were higher than initial concentrations, but they were 10–200-fold lower than the EU and USA biosolid compost limits and Malaysian Recommended Site Screening Levels for Contaminated Land (SSLs). An increment of heavy metals were recorded in vermicompost for all treatments on week fifteen compared to week ten, while concentration of heavy metals in earthworms' tissue were lower compared to vermicompost. Hence, it is suggested that earthworms begin to discharge heavy metals into their surroundings and it was evident that the earthworms' heavy metals excretion period was within the interval of ten to fifteen weeks.

Sanitary Assurance at Biosolids Composting Facilities: Development of a Temperature Contact Time Test Protocol

Sanitary Assurance at Biosolids Composting Facilities: Development of a Temperature Contact Time Test Protocol

Composting provides a sustainable solution to the biosolids issues in Shenyang, China

Shenyang Biosolids Composting Plant is a one-of-a-kind facility that is designed to handle and treat up to 1,000 tonnes of 80% moisture content wet biosolids per day from four municipal wastewater treatment plants (WWTPs) that have a combined capacity of 1,600 MLD in Shenyang City, Liaoning Province, China. The composting plant covers an area of approximately 130,000 m2. The moisture content of biosolids will be reduced to 35% by biodrying. The main facilities in the plant include the materials handling and mixing system (for wet sludge, raw material and compost), the agitated composting bed system, the ventilation and odor control system, the truck scale unit, the storerooms (for raw material and product), and the other auxiliary facilities. The design has incorporated the necessary environmental considerations for the protection of workers’ health and safety as well as the potential impacts on the neighboring communities. The finished compost product will be sold as soil amendment and/or auxiliary fuel. In comparison with other technologies, this plant is favored for the low capital cost (0.279 million RMB per wet tonne of sludge), the low operating cost (173.13 RMB per wet tonne sludge) and the low energy consumption/carbon footprint. The plant is currently under construction. The installation works of No.3 composting train is scheduled to be carried out in June 2012. When the plant is commissioned in September 2012, it will become a sustainable solution to the sludge problem in Shenyang City.

Chemical and toxicological assessment of a full‐scale biosolid compost

The impact of a full-scale biosolid composting plant on the fate of a broad range of priority organic pollutants was investigated. Chemical analysis was performed at different steps of the process during two seasons. Simultaneously, the toxicological quality was assessed using estrogen α-, dioxin-, and pregnane X-receptor reporter cell lines. Mass-balance calculation highlighted the removal of easily degradable pollutants during composting. The important variations observed for each compound and for the two seasons might be explained by pollutant-fate dependency on process parameters like temperature. The final compost displayed low pregnane X activity but high estrogenic activity. The dioxin-like activity stayed constant through the process. The chemical and toxicological results highlight the importance of combining both approaches to accurately assess the compost quality. Such compilation of data on full-scale processes may be also very helpful for the environmental risk assessment of new organic waste disposal practices.

Effect of citric acid on metals mobility in pruning wastes and biosolids compost and metals uptake in Atriplex halimus and Rosmarinus officinalis

To assess metal mobility in pruning waste and biosolids compost (pH 6.9 and total concentration of metals in milligram per kilogram of Cd 1.9, Cu 132, Fe 8,513, Mn 192, Pb 81, and Zn 313), shrubs species Atriplex halimus and Rosmarinus officinalis were transplanted in this substrate and irrigated with citric acid (4 g L(-1), pH 2.9) and nutrient solution daily for 60 days. Citric acid significantly increased the concentrations of soluble Mn and Fe in the nutrient substrate solution measured by suction probes, while other metals did not vary in concentration (Cu and Zn) or were not observed at detectable levels (Cd and Pb). In plants, citric acid significantly increased the concentrations of Cu (2.7 ± 0.1-3.3 ± 0.1 mg kg(-1)), Fe (49.2 ± 5.2-76.8 ± 6.8 mg kg(-1)), and Mn (7.2 ± 1.1-11.4 ± 0.7 mg kg(-1)) in leaves of R. officinalis, whereas the concentration of only Mn (25.4 ± 0.3-42.2 ± 2.9 mg kg(-1)) was increased in A. halimus. Increasing Fe and Mn solubility by citric acid addition indicates the possibility of using it to improve plant nutrition. The mobility of metals in this substrate was influenced for the concentration of the metal, the degree of humification of organic matter and its high Fe content.

High‐Iron Biosolids Compost–Induced Changes in Lead and Arsenic Speciation and Bioaccessibility in Co‐contaminated Soils

The safety of urban farming has been questioned due to the potential for contamination in urban soils. A laboratory incubation, a field trial, and a second laboratory incubation were conducted to test the ability of high-Fe biosolids-based composts to reduce the bioaccessibility of soil Pb and As in situ. Lead and As bioaccessibility were evaluated using an in vitro assay. Changes in Pb, As, and Fe speciation were determined on select samples after the second laboratory incubation using μ-X-ray fluorescence mapping followed by μ-X-ray absorption near-edge structure (XANES). A compost with Fe added to wastewater treatment residuals (Fe WTR compost) added to soils at 100 g kg decreased Pb bioaccessibility in both laboratory incubations. Mixed results were observed for As. Composts tested in the field trial (Fe added as Fe powder or FeCl) did not reduce bioaccessible Pb, and limited reductions were observed in bioaccessible As. These composts had no effect on Pb bioaccessibility during the second laboratory incubation. Bulk XANES showed association of Pb with sulfates and carbonates in the control soil. μ-XANES for three points in the Fe WTR amended soil showed Pb present as Fe-sorbed Pb (88 and 100% of two points) and pyromorphite (12 and 53% of two points). Bulk XANES of the Fe WTR compost showed 97% of total Fe present as Fe. The results of this study indicate that addition of high-Fe biosolids compost is an effective means to reduce Pb accessibility only for certain types of Fe-rich materials.