Leaching of boron through sewage sludge amended soil: the role of clinoptilolite

A laboratory experiment was conducted to determine the release of boron from soil-sewage sludge mixtures by leaching using a clinoptilolite type natural zeolite, before land application of the sewage sludge. Soil columns were filled up with the clinoptilolite soil after mixing with sewage sludge at a rate of 30 tons ha(-1) and with two different particle sizes (0.1-0.25 and 1.0-2.0 mm) of clinoptilolite each at the concentrations of 1% and 2%. The particle size and the application rate of clinoptilolite affected both boron leaching from soil compared to the control treatment (soil and sewage sludge mixture). The total soluble boron leached from a soil column varied from 66-92% depending on the applications of clinoptilolite and reached 96% for the control treatment, following application of 80 cm depth of water in all treatments. In the cases of the 1% application rate of 0.1-0.25 and 1-2 mm sized clinoptilolite 78% and 92% of the total boron leached, respectively. While at 2% application rate of 0.1-0.25 and 1-2 mm zeolite, 66% and 87% of total soluble boron leached, respectively. Boron concentrations in the soil layers increased as application rate increased and particle size of clinoptilolite decreased because of its high adsorption capacity. Adsorption isotherms indicated that clinoptilolite had a high adsorption capacity for boron compared to the sewage sludge and soil.     

Characterization of cadmium desorption in soils and its relationship to plant uptake and cadmium leaching

Experiments on Cd desorption were conducted with a range of water-to-soil ratios to assess the desorption characteristics of Cd in soils and the availability of Cd for absorption by plant roots and leaching to groundwater, Soil samples were collected from sites contaminated by a former Pb and Zn smelter, by sewage irrigation, or with artificial additions of Cd and sewage sludge. Glasshouse pot experiments were conducted in which the yield and Cd uptake of crop plants were determined. Cadmium leached from soil columns was also studied using soil lysimeters. The soil solution Cd concentration decreased with increasing solution-to-soil ratio and followed a negative power function. Two constants obtained from logarithmic linear regression were identified. The intercept (C₁) was Cd concentration in the soil solution where the solution/soil ratio was equal to 1 and this constant was the intensity factor of the initial element supply in the soil. The slope (a) showed a decreasing trend for Cd concentration in the soil solution which was related to the soil buffering capacity. A corrected concentration (C₁/a) is proposed for expressing soil desorption ability. This combined index was significantly correlated with Cd uptake by plants and also with Cd leached from soil columns.     

Some observations on surface soil pH,base saturation and leaching of cations under three contrasting orchard soil management practices

Summary Observations from a soil management trial conducted on a previously grassed down orchard showed that after 3 years the pH of the surface soil (0–10 cm) whether measured in distilled water or 1N KCl was significantly lowered in herbicided and cultivated treatments in comparison with plots under continued grass sod. The drop in pH was accompanied by a decrease in base saturation and a consequent increase in exchange acidity. This was attributed to the leaching of Ca and also Mg from the surface soil of the non-grassed plots.In a subsequent laboratory leaching study, cubic soil blocks (16 cm³) were leached with distilled water at two weekly intervals for 24 weeks. It was found that over the experimental period, the cumulative quantity of cations leached (in milli-equivalents) per soil block from the herbicided and cultivated treatments was approximately 3.5 times that leached from the grassed treatment.     

Mobility and Distribution of Zinc,Cadmium and Lead in Calcareous Soils Receiving Spiked Sewage Sludge

Leaching column experiments were conducted to determine the degree of mobility and the distribution of zinc (Zn), cadmium (Cd), and lead (Pb) because of an application of spiked sewage sludge in calcareous soils. A total of 20 leaching columns were set up for four calcareous soils. Each column was leached with one of these inflows: sewage sludge (only for two soils), spiked sewage sludge, or artificial well water (control). The columns were irrigated with spiked sewage sludge containing 8.5 mg Zn l^?1, 8.5 mg Cd l^?1, and 170 mg Pb l^?1 and then allowed to equilibrate for 30 days. At the end of leaching experiments, soil samples from each column were divided into 18 layers, each being 1 cm down to 6 cm and 2 cm below that, and analyzed for total and extractable Zn, Cd and Pb. The fractionation of the heavy metals in the top three layers of the surface soil samples was investigated by the sequential extraction method. Spiked sewage sludge had little effect on metal mobility. In all soils, the surface soil layers (0-1 cm) of the columns receiving spiked sewage sludge had significantly higher concentrations of total Zn, Cd and Pb than control soils. Concentration of the heavy metals declined significantly with depth. The mobility of Zn was usually greater than Cd and Pb. The proportion of exchangeable heavy metals in soils receiving spiked sewage sludge was significantly higher than that found in the control columns. Sequential extraction results showed that in native soils the major proportion of Zn and Pb was associated with residual (RES) and organic matter (OM) fractions and major proportion of Cd was associated with carbonate (CARB) fraction, whereas after leaching with spiked sewage sludge, the major proportion of Zn and Pb was associated with Fe-oxcide (FEO), RES, and CARB fractions and major proportion of Cd was associated with CARB, RES and exchangeable (EXCH) fractions. Based on relative percent, Cd in the EXCH fraction was higher than Zn and Pb in soils leached with spiked sewage sludge.     

Metal Transport and Bioavailability in Soil Contaminated with CCA-Treated Wood Leachates

A laboratory study was conducted to investigate metal transport and accumulation within soils contaminated with As, Cr, and Cu from CCA-treated wood leachates. New blocks of CCA-treated wood were leached using synthetic rainwater. Soil columns were constructed and filled with three different soils, including a sandy soil, an organic soil and a clay soil. The leachate was applied intermittently until 80 pore volumes were eluted through each column. Metal concentrations (Cu, Cr, and As) were measured in the leachate before passage through the columns as well as in each elutriate fraction collected. Chemical analysis was complemented with toxicity testing using Ceriodaphnia dubia, Selenastrum capricornutum, and MetPLATE?. Following application of 80 pore volumes of leachate, the columns were dissected and the profile of the metal concentrations within each column was determined. A comparison of the arsenic, chromium and copper leaching patterns found arsenic to be the most mobile, with copper the most retained in the soil columns (As < Cr < Cu). Transport patterns of As differed in the three soil types, with observed mobility highest in the sandy soil and lowest in the clay soil. The three metals accumulated in the top layer of soil. Arsenic posed the greatest risk when soil concentrations were compared to risk-based target levels. Although metals were detected in soil elutriates, no toxicity was detected in any of the soil column elutriates using any of the three toxicity assays.     

Influence of dolomitic lime on DOC and DON leaching in a forest soil

The influence of liming on leaching and distribution of dissolved organic carbon (DOC) and nitrogen (DON) in mineral soil was investigated in a leaching experiment with soil columns. Soil samples from separate horizons (O, A and B horizons) were collected from control and limed plots in a field liming experiment in a spruce forest in southern Sweden. The field liming (0.88 kg m^-2) had been carried out 8 years before sampling. To minimize the variation among replicates, soil profiles were reconstructed in the laboratory so that the dry weight was the same for each individual soil horizon regardless of treatment. Two soil column types were used with either the O+A horizons or the O+A+B horizons. One Norway spruce seedling (Picea abies (L.) Karst) was planted in each soil column. Average pH in the leachate water was greater in the limed treatment than in the control treatment (5.0 versus 4.0 for O+A columns and 4.3 versus 3.8 for O+A+B columns). After reaching an approximate steady state, the leaching of DOC was 3--4 times greater from the limed O+A and O+A+B columns than from the corresponding control columns but the leaching of DON increased (3.5 times) only in the limed O+A columns. There was a significant correlation between DOC and DON in the leachates from all columns except for the control O+A+B columns, which indicated a decoupling of DOC and DON retention in the B horizon in the control treatment. This might be explained by a selective adsorption of nitrogen poor hydrophobic compounds (C/N ratio: 32--77) while there was a lower retention of nitrogen rich hydrophilic compounds (C/N ratio: 14--20). Proportionally more hydrophobic compounds were leached from the limed soil compared to the unlimed soil. These hydrophobic compounds also became more enriched in nitrogen after liming so in the limed treatment nitrogen might be adsorbed at nearly the same proportion as carbon, which might explain the fact that there was no decoupling of leached DOC and DON from the B horizon after liming.     

Effects of organic matter on virus transport in unsaturated flow.

The effects of natural humic material and sewage sludge organic matter (SSOM) derived from primary treated sewage sludge on virus transport by unsaturated flow through soil columns were evaluated. Bacteriophage MS-2 was applied to loamy fine sand columns 0.052 m in diameter and 1.05 m long. Virus concentrations in the influent and effluent were measured daily for 7 to 9 days. In the first experiment, virus transport through two fresh soil columns was compared with that through a column previously leached with more than four pore volumes (T) of well water. The soil water organic matter concentrations in the leachate of the fresh soil declined with time. Relative virus concentrations (C/Co) from one fresh soil column reached 0.82 in 0.9 T and then declined to 0.51 by 2.1 T. The other fresh soil column reached and maintained a steady-state relative virus concentration [(C/Co)s] of 0.47 from 1.5 to 2.5 T. The leached column reached and maintained a (C/Co)s of 0.05. Concentrations measured at 0.2-, 0.4-, 0.8-, and 1.05-m depths indicated that most virus particles were removed in the surface 0.2 m. In the second experiment, one leached column was pretreated with SSOM derived from primary treated sewage sludge and the other leached column was untreated. SSOM concentrations declined with depth. A suspension of virus and SSOM in well water was applied to both columns. Although the (C/Co)s values were similar (0.41 for the pretreated column and 0.47 for the untreated column), breakthrough was delayed for the untreated column. Both natural humic material and sewage sludge-derived SSOM increased the unsaturated-flow transport of MS-2.     

Effects of organic matter on virus transport in unsaturated flow.

The effects of natural humic material and sewage sludge organic matter (SSOM) derived from primary treated sewage sludge on virus transport by unsaturated flow through soil columns were evaluated. Bacteriophage MS-2 was applied to loamy fine sand columns 0.052 m in diameter and 1.05 m long. Virus concentrations in the influent and effluent were measured daily for 7 to 9 days. In the first experiment, virus transport through two fresh soil columns was compared with that through a column previously leached with more than four pore volumes (T) of well water. The soil water organic matter concentrations in the leachate of the fresh soil declined with time. Relative virus concentrations (C/Co) from one fresh soil column reached 0.82 in 0.9 T and then declined to 0.51 by 2.1 T. The other fresh soil column reached and maintained a steady-state relative virus concentration [(C/Co)s] of 0.47 from 1.5 to 2.5 T. The leached column reached and maintained a (C/Co)s of 0.05. Concentrations measured at 0.2-, 0.4-, 0.8-, and 1.05-m depths indicated that most virus particles were removed in the surface 0.2 m. In the second experiment, one leached column was pretreated with SSOM derived from primary treated sewage sludge and the other leached column was untreated. SSOM concentrations declined with depth. A suspension of virus and SSOM in well water was applied to both columns. Although the (C/Co)s values were similar (0.41 for the pretreated column and 0.47 for the untreated column), breakthrough was delayed for the untreated column. Both natural humic material and sewage sludge-derived SSOM increased the unsaturated-flow transport of MS-2.     

Immobilization of Leachable Toxic Soil Pollutants by Using Oxidative Enzymes

Screening of leachable toxic chemicals in a horseradish peroxidase-H₂O₂ immobilization system established that immobilization was promising for most phenolic pollutants but not for benzoic acid, 2,6-dinitrocresol, or dibutyl phthalate. The treatment did not mobilize inherently nonmobile pollutants such as anilines and benzo[a]pyrene. In a separate study, an extracellular laccase in the culture filtrate of Geotrichum candidum was selected from five fungal enzymes evaluated as a cost-effective substitute for horseradish peroxidase. This enzyme was used in demonstrating the immobilization and subsequent fate of ¹⁴C-labeled 4-methylphenol and 2,4-dichlorophenol in soil columns. When applied to Lakewood sand, 98.1% of 4-methylphenol was leached through with distilled water. Two days after immobilization treatment with the G. candidum culture filtrate, only 9.1% of the added 4-methylphenol was leached with the same volume of water. Of the more refractory test pollutant 2,4-dichlorophenol, 91.6% had leached at time zero and 48.5% had leached 1 day after the immobilization treatment. However, 2 weeks after immobilization, only 12.0% of the 2,4-dichlorophenol was leached compared with 61.7% from the control column that received no immobilization treatment. No remobilization of the bound pollutants was detected during 3- and 4-week incubation periods. Enzymatic immobilization of phenolic contaminants in soil appears to be a promising technique for the reduction of groundwater pollution by such substances.     

Leaching of nitrogen from subtropical soils as affected by nitrification potential and base cations

A soil column method was used to determine the effect of nitrification on leaching of nitrate and ammonium from three acid subtropical soils after application of ammonium bicarbonate. Three soils, designated QF, GB and SU, derived from Quaternary red earth, granite and tertiary red sandstone, were collected from forest land, brush land and upland field, ranged in nitrification potential and cation exchange capacity. The results indicated that nitrate leaching increased with the soil nitrification potential. The soils with higher nitrification potential had a higher nitrate peak concentration and required a shorter time to reach it. In soils QF and GB with low cation exchange capacity, and a low content of exchangeable base cations, there were not sufficient base cations to accompany the nitrate leached with the result that ammonium and hydrogen ions were leached from the soil, and pH changes occurred in different layers of the soil column.     

Effectiveness of low-temperature biochar in controlling the release and leaching of herbicides in soil

Aims

Biochars, being good sorbents of organic compounds, can reduce the mobility of pesticides in soil and subsequent pollution to groundwater, but may also impact on the efficacy of soil-applied herbicides. The aim of this study is to seek a potential solution to this problem.

Methods

We prepared a wood biochar at a relatively low heat treatment temperature (350 °C), and used it as an adsorptive carrier for incorporating the herbicides 2,4-D and acetochlor, and also as a soil amendment. Release experiment through a thin soil layer and leaching experiment through a soil column were used to evaluate the effectiveness of the biochar for controlling the release and leaching of herbicides in soil.

Results

The release experiments demonstrated that the low-temperature biochar could control the release of herbicides in soil, and the leaching experiments showed that this biochar significantly reduced the leached amount of herbicides by 1/2?~?3/4, depending on the depth (5?~?15 cm) of biochar-amended topsoil. High retention of herbicides in the biochar-amended topsoil was observed.

Conclusions

The results suggest that the low temperature biochar, if applied properly in soil, may be useful for extending the efficacy of herbicides while controlling their potential pollution.     

Column Leaching Using Dry Soil to Estimate Solid-Solution Partitioning Observed in Zero-Tension Lysimeters. 1. Method Development

In order to understand the reactions taking place between the soil solid phase and the soil solution, we require knowledge of the chemistry of the soil solution as it occurs in the field. This knowledge allows us to conduct experiments with environmentally relevant concentrations of macro and microelements in solution. Zero-tension lysimeters directly sample the mobile fraction of soil solutions. Unfortunately, they are expensive to sample and require long equilibration periods. Other solution extraction methods do not provide solutions similar in concentration to lysimeters, either because they sample a different fraction of the soil solution or due to the impacts of the sampling process. The processes that produce lysimeter solutions cannot be emulated; however, to estimate lysimeter solution chemistry, we developed a standard protocol to produce solutions that resemble lysimeter solutions from podzolic soils using air-dried samples. We washed air-dried soil columns sequentially with de-ionized water until the electrical conductivity (EC) of the leachates stabilized and then leached the columns using an environmentally relevant concentration of a weak salt solution. We hypothesize that the stabilization point of the EC of the soil solution is indicative of the point at which soluble salts and organic material precipitated during sampling and storage are removed from the soil surface. Solutions produced by leaching, once the EC of wash solutions had stabilized, were comparable to lysimeter solutions from the area where samples were collected with respect to the concentrations of divalent cations, pH, EC and DOC.     

Leaching and transformation of urea in dry and wet soils as affected by irrigation water

Summary The leaching losses of urea in dry and wet soils as affected by the irrigation water, were studied in 90 cm long and 5 cm diameter plexiglass columns. In dry sandy loam soil urea leached with irrigation water and peaks of urea were observed with water front but in sandy soil the wetting front moved faster leaving the urea peak behind. In initially wet soils the urea peak did not coincide the wetting front, following infiltration and after redistribution for 24 hours of infiltration. More urea was recovered in sandy soil than in sandy loam soil following infiltration and redistribution for 24 hours. Urea leached only upto 30 cm with 5 and 7.5 cm irrigation water whereas with 10 and 15 cm irrigation water profiles urea penetrated to deeper layers. The sub-surface application of urea did not change the leaching behaviour of urea. Urea behaves as a non-reacting ion like Cl with respect to its movement with soil-water before it is hydrolysed.     

Effect of Phosphate Treatment on Pb Leachability in Contaminated Shooting Range Soils

A cost-effective way to reduce lead released into the environment is through immobilization with readily available soil amendments. Leaching of Pb from four shooting range soils treated with two phosphate sources was evaluated in soil columns. Phosphate was applied at a P/Pb molar ratio of 4:1 with two-thirds of the P supplied from phosphate rock (PR) and one-third from phosphoric acid (PA). The soils were incubated for 18 hr and leached with toxicity characterization leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) fluids, respectively. PR/PA treatment reduced Pb in TCLP leachate to below regulatory limit of 5 mg/L after 18 hr of incubation. Reduction of Pb leached was more dependent on clay content than total Fe. PR/PA treatment had no effect on pH of TCLP leached soils, while it led to a drastic lowering of pH that mobilized Pb in SPLP leached soils. However, leaching of Pb reduced with time in SPLP leached soils because pH increased gradually. PR/PA treatment was more effective in SPLP leached soils with low total soil Pb because they received lower amounts of PA. PR/PA treatment may be more efficient when applied as split applications in soils with a low to medium Pb loading and a high buffering capacity.     

外加氮源对杉木叶凋落物分解及土壤养分淋失的影响

采用原位（Ｉｎ ｓｉｔｕ）模拟实验方法研究了外加Ｎ源对杉木叶凋落物分解及土壤养分淋失的影响,结果表明,施加ＮＨ＾＋４－Ｎ时,杉木叶凋落物的失重率与对照（未加任何Ｎ的处理）相比,没有差异：而施加ＮＯ＾－１－Ｎ时,使杉木叶凋落物分解速率显著提高（ｐ＝０．０５,达１０％以上,与施加ＮＨ＾＋４－Ｎ相比,施加ＮＯ＾－３－Ｎ明显促进了杉木叶凋落物的分解（ｐ＝０．０５）。施加ＮＨ＾＋４－Ｎ和ＮＯ３＾－－Ｎ会产生     

Transport of Cryptosporidium parvum Oocysts in Soil Columns following Applications of Raw and Separated Liquid Slurries

The potential for the transport of viable Cryptosporidium parvum oocysts through soil to land drains and groundwater was studied using simulated rainfall and intact soil columns which were applied raw slurry or separated liquid slurry. Following irrigation and weekly samplings over a 4-week period, C. parvum oocysts were detected from all soil columns regardless of slurry type and application method, although recovery rates were low (<1%). Soil columns with injected liquid slurry leached 73 and 90% more oocysts compared to columns with injected and surface-applied raw slurries, respectively. Among leachate samples containing oocysts, 44/72 samples yielded viable oocysts as determined by a dye permeability assay (DAPI [4',6'-diamidino-2-phenylindole]/propidium iodide) with the majority (41%) of viable oocysts found in leachate from soil columns with added liquid slurry. The number of viable oocysts was positively correlated (r = 0.63) with the total number of oocysts found. Destructively sampling of the soil columns showed that type of slurry and irrigation played a role in the vertical distribution of oocysts, with more oocysts recovered from soil columns added liquid slurry irrespective of the irrigation status. Further studies are needed to determine the effectiveness of different slurry separation technologies to remove oocysts and other pathogens, as well as whether the application of separated liquid slurry to agricultural land may represent higher risks for groundwater contamination compared to application of raw slurry.     

Poliovirus removal from primary and secondary sewage effluent by soil filtration.

Adsorption of poliovirus from primary sewage effluent was similar to that from secondary sewage effluent in both batch soil studies and experiments with soil columns 240 cm long. Virus desorption by distilled water was also similar in a soil column that had been flooded with either primary or secondary effluent seeded with virus. These results indicated that absorption of poliovirus from primary effluent and virus movement through the soil were not affected by the higher organic content of primary sewage effluent.     

Poliovirus removal from primary and secondary sewage effluent by soil filtration.

Adsorption of poliovirus from primary sewage effluent was similar to that from secondary sewage effluent in both batch soil studies and experiments with soil columns 240 cm long. Virus desorption by distilled water was also similar in a soil column that had been flooded with either primary or secondary effluent seeded with virus. These results indicated that absorption of poliovirus from primary effluent and virus movement through the soil were not affected by the higher organic content of primary sewage effluent.     

Stability of Prussian Blue in Soils of a Former Manufactured Gas Plant Site

Soil contamination with iron-cyanide complexes is a common problem at former manufactured gas plant (MGP) sites. Dissolution of the cyanide, from Prussian Blue (ferric ferrocyanide), creates an environmental hazard, whereas the risk of groundwater contamination depends on the stability of dissolved iron–cyanide complexes. Lack of a standard leaching method to determine the water-soluble (plant-available) cyanide fraction generates potential limitations for implementing remediation strategies like phytoremediation. Applicability of neutral solution extraction to determine the water-soluble cyanide fraction and the stability of Prussian Blue in surface and near-surface soils of an MGP site in Cottbus, undersaturated and unsaturated water conditions, was studied in column leaching and batch extraction experiments. MGP soils used in the long-term tests varied according to the pH (5.0–7.7) and the total cyanide content (40–1718 mg kg^?1). Column leaching, after four months of percolation, still yielded effluent concentrations exceeding the German drinking water limit (> 50 μg L^?1) and the solubility of Prussian Blue reported in the literature (< 1 mg L^?1) from both alkaline and acidic soils. Long-term (1344 h) extraction of MGP soils with distilled water was sufficient to dissolve 97% of the total cyanide from the slightly alkaline soils and up to 78% from the acidic soils. Both experiments revealed that dissolution of ferric ferrocyanide under circum-neutral pH and oxic water conditions is a function of time, where the released amount is dependent on the soil pH and total cyanide content. Unexpectedly high and continuous solubility of Prussian Blue, both in acidic and slightly alkaline MGP soils, implies the need to introduce an additional cyanide fraction (“readily soluble fraction”) to improve and specify cyanide leaching methods. Long-term extraction of cyanide-contaminated soil in neutral solution seems to be a promising approach to evaluate the potential hazard of groundwater pollution at the MGP sites.     

Leaching of subterranean clover-derived N from a loam soil

The leaching of subterranean clover-derived N (¹⁵N) was investigated in a laboratory and a field experiment. In both experiments 30 cm i.d. ×50cm soil columns were used. In the laboratory experiment the clover material was buried in the soil in mesh bags, and leaching of clover-derived N was compared to leaching of added NH ₄ ⁺ −N and NO ₃ ⁻ −N over a period of 75 days at 20°C. During that time 75% of the clover-N was released from the mesh bags and 17% of the clover-N, 50% of the NH ₄ ⁺ −N and 70% of the NO ₃ ⁻ −N was leached through the soil column. In the field experiment 6 lysimeters and 7 control microplots were constructed. The clover material was buried in soil (to the soil of two control microplots within mesh bags) in October. During one year 2% of the added clover-N was leached. This was despite a release of 65% of the N from the mesh bag contents and despite a 26% loss of the clover-derived N in total from the controls.