Bioclogging extensively exists in porous media, such as permeable reactive barrier (PRB), constructed wetland, reverse osmosis, and biofilter systems and affects efficiency of sewage treatment. In this paper, variation in biochemical and hydraulic parameters under discontinuous flow condition during the clogging process was obtained. Hydraulic conductivity (K) first decreased sharply to 34.22 % of the original value during the initial 12th day and, finally, decreased to 13.70 %. Hydrodynamic dispersion (D) went through slow increase, fast increase, fast decrease, slow increase, and ultimately decreased to 44.25 %. Porosity (n) decreased obviously, especially during the initial 12 days, and total bacterial counts in the inlet of the column had more than one order of magnitude increase. The bioclogging process can be divided into four stages: (1) severe bioclogging occurred and aerobic microorganisms reproduced rapidly in the inlet, (2) bioclogging existed in the entire sand column and the hydrodynamic dispersion increased drastically as anaerobic microorganisms generated some gas, (3) aerobic and anaerobic microorganisms reproduced and hydrodynamic dispersion decreased rapidly, and (4) microorganisms multiplied continuously and the hydraulic parameters (hydrodynamic dispersion, hydraulic conductivity, and porosity) decreased steadily. Bioclogging then transformed into steady stage. Based on analysis of experimental data, hydraulic conductivity (K) follows the rule of negative exponent relationship, porosity (n) accords with power exponent relationship, and hydrodynamic dispersion (D) is polynomial equation under bioclogging process.

The aim of this study was to statistically compare sampling sites identified along the Berg River system to identify the major point sources of metal pollution from June 2004 to May 2005. Three sites were selected [site A—agricultural farming area, site B—Plot 8000 (close to the informal settlement), and site C—the Newton pumping station] representing different sectors which the river services. Aluminium (Al), iron (Fe), manganese (Mn), and lead (Pb) concentrations were determined using Inductively Coupled Plasma Atomic Emission Spectrometry and were statistically compared and analysed with one-way ANOVAs. For all the metals analysed, site C (industrial area) proved to be the site where the highest average metal concentrations were recorded. Generally, the concentrations recorded at site A (site furthest from the industrial area) were significantly (p < 0.05) lower than the concentrations recorded at both sites B and C. While the Al and Fe concentrations were consistently higher than any of the other metals analysed for, site C was identified as the primary source of metal contamination in the Berg River, resulting from the runoff from industrial activities at this particular site.

The feasibility of a sequentially enhanced process for the remediation of soils contaminated by mixed contaminants, specifically multiple polycyclic aromatic hydrocarbons (PAHs) and heavy metals, was investigated. This process consists of sequential flushing using two chemical agents: a surfactant and a chelate. A series of laboratory column experiments was conducted with three different sequential schemes, designated as SEQ1, SEQ2, and SEQ3, in two distinct flushing stages, to remove PAHs and heavy metals from a field-contaminated soil. The SEQ1 scheme involved flushing 0.2 M ethylenediaminetetraacetic acid (EDTA) followed by flushing 5 % Igepal. The SEQ2 scheme involved flushing 5 % Igepal followed by flushing 0.2 M EDTA. SEQ1 was investigated under a constant hydraulic gradient of 1.2, while the SEQ2 scheme was investigated under hydraulic gradients that increased from 1.2 to 4.0. The SEQ3 scheme consisted of sequential flushing of 5 % Igepal (first stage) and 0.2 M EDTA (second stage) under a constant low hydraulic gradient of 0.2. The selected sequential schemes allowed an assessment of the efficacy of sequencing the surfactant and chelating flushing for the removal of multiple heavy metals and PAHs under various hydraulic gradients. The hydraulic conductivity (or flow) was found to vary depending on the flushing agent and the sequence scheme. Under the high hydraulic gradient, the hydraulic conductivity was lower during chelant flushing stage as compared with surfactant flushing stage in both SEQ1 and SEQ2. However, under a low gradient condition (SEQ3), the hydraulic conductivity was approximately the same during both chelant and surfactant flushing stages. The contaminant removal was also significantly affected by the flushing agent and sequence and the applied hydraulic gradient. Heavy metals were removed during chelant flushing, while PAHs were removed during surfactant flushing. The total removal efficiencies of Pb, Zn, and Cu were 76 %, 63 %, and 11 % in SEQ1 and 42 %, 40 %, and 7 % in SEQ2, respectively, while the total removal efficiencies of phenanthrene, anthracene, benz(a)anthracene, and pyrene were 51 %, 35 %, 58 %, and 39 % in SEQ1 and 69 %, 50 %, 65 %, and 69 % in SEQ2, respectively. Overall, the total mass removal of heavy metals and PAHs was higher in SEQ1 as compared with SEQ2, demonstrating that SEQ1 is the effective sequence scheme. Comparison of the results of high and low gradient conditions (SEQ2 and SEQ3) reveals that the removal of contaminants, especially heavy metals, is rate-limited. Overall, this study showed that the removal of co-existing heavy metals and PAHs from soils is possible through the careful selection of the sequence under which the flushing of chelant and surfactant occurs and depends on the site-specific soil and contaminant conditions. Additional research is needed to establish the most optimal flushing scheme (sequence duration and flow velocity) to remove the mixed contaminants effectively and efficiently. © 2013 Springer Science+Business Media Dordrecht.

In this paper, preliminary investigation was conducted to evaluate the potential ecological risk of heavy metals contamination in cemetery soils. Necrosol samples were collected from within and around the vicinity of the largest mass grave in Rwanda and analyzed for heavy metal concentrations using total digestion–inductively coupled plasma mass spectrometry and instrumental neutron activation analysis. Based on the concentrations of As, Cu, Cr, Pb, and Zn, the overall contamination degree (C dₑg) and potential ecological risks status (RI) of the necrosols were determined. The preliminary results revealed that the associated cemetery soils are only contaminated to a low degree. On the other hand, assessment of the potential ecological risk index (RI) revealed that cumulative heavy metal content of the soil do not pose any significant ecological risks. These findings, therefore, suggest that, while cemetery soils may be toxic due to the accumulation of certain heavy metals, their overall ecological risks may be minimal and insignificant.

Understanding denitrification rates in groundwater ecosystems can help predict where agricultural reactive nitrogen (N) contributes to environmental degradation. In situ groundwater denitrification rates were determined in subsoil, at the bedrock interface and in bedrock at two sites, grassland and arable, using an in situ 'push-pull' method with 15N-labelled nitrate (NO3 --N). Measured groundwater denitrification rates ranged from 1.3 to 469.5 μg N kg-1 day-1. Exceptionally high denitrification rates observed at the bedrock interface at grassland site (470 ± 152 μg N kg-1 day-1; SE, standard error) suggest that deep groundwater can serve as substantial hotspots for NO 3 --N removal. However, denitrification rates at the other locations were low and may not substantially reduce NO3 --N delivery to surface waters. Denitrification rates were negatively correlated with ambient dissolved oxygen, redox potential, k s and NO3 - (all p values, p < 0.01) and positively correlated with SO4 2- (p < 0.05). Higher mean N 2O/(N2O + N2) ratios at an arable (0.28) site than the grassland (0.10) revealed that the arable site has higher potential to indirect N2O emissions. Identification of areas with high and low denitrification and related site parameters can be a tool to manage agricultural N to safeguard the environment. © 2013 Springer Science+Business Media Dordrecht.

An electrokinetic technique was used to remediate As-, Cu-, and Pb-contaminated paddy soil in a real field on a pilot scale. A hexagonal electrode placement with one anode at the center and six cathodes at the vertices of the hexagon was installed in the field. After operation for 4 weeks, the average removal of Pb was 64.9 % in the top layer (0–0.4 m), 81.2 % in the middle layer (0.4–0.8 m), and 66.9 % in the bottom layer (0.8–1.2 m). The removal of As was 28.2 % in the top layer, 43.2 % in the middle layer, and 24.5 % in the bottom layer. The removal of Cu was 17.7 % in the middle layer and was not observed in the other layers. The relatively high removal of Pb might come from the more labile fraction of Pb in soil compared to As and Cu. However, the circulation of anolyte using an alkaline solution to enhance removal of As failed because the electrolyte leaked between the anode and surrounding soil. Effective circulation might enhance the performance of the electrokinetic process.

This study investigated how forest soil acidification is affected by edge proximity. We measured pH(KCl) and exchangeable K, Ca, Mg and Al concentrations of the mineral topsoil (0–30 cm) from the exposed edge to the interior (128 m from the edge) of three deciduous and four coniferous forest stands. From the front edge to the interior of the deciduous stands, the pH(KCl) values decreased at 0–5 cm soil depth (from 3.07 to 2.98) but increased at 5–10 cm (from 3.26 to 3.32) and 10–30 cm (from 3.48 to 3.75) depth. In the coniferous stands, pH(KCl) values declined from edge to interior at all soil depths, i.e. from 3.10 to 2.89, from 3.26 to 3.06 and from 3.54 to 3.31 at 0–5, 5–10 and 10–30 cm, respectively. The concentrations of exchangeable cations decreased from edge to interior, with larger differences in the coniferous (of up to 265 %) than in the deciduous stands (up to 99 %). At forest edges, enhanced soil acidification due to higher potentially acidifying deposition could be counteracted in the upper mineral soil by higher base cation throughfall and litterfall, faster litter decomposition, higher soil organic matter content, lower nitrate leaching from the soil and/or lime fertiliser drift. Nonetheless, deeper in the soil of the deciduous stands, these buffer processes seem unable to counteract soil acidification due to potentially acidifying deposition at the edges. Edge effects on soil acidity are important since they can translate into effects on plant communities, soil biota, nitrogen cycling and carbon sequestration.

The present study analyzes the acute and behavioral toxicity of two commercial formulations of endosulfan and atrazine (Gesaprim 90 WDG® and Zebra Ciagro®, respectively) on the cyclopoid copepod Mesocyclops longisetus. The studied behavior was the “escape ability” because of its ecological importance in natural predator–prey interactions. This was investigated using two experimental designs: (1) a simulated predator (applying a hydraulic device) and (2) a real one (the zooplanktophagous fish Cnesterodon decemmaculatus). Both pesticides resulted highly toxic to adults and nauplii at even relatively low concentrations and similar to those found in field studies. Copepods’ survival was not only directly affected but also indirectly through altering their escape behavior, which may have increased their vulnerability to predation. The escape ability, measured with the simulated predator was stimulated early (up to 6 h of exposition) but inhibited later (after 24 h of exposition). The predation experiments with the real predator were in accordance with these results. The comparison of both experimental designs corroborates the effectiveness of the hydraulic mechanism as a testing method.

Anaerobic digestion is one of the most effective means for the stabilisation of sludge. However, it has a very slow rate-limiting hydrolysis phase which is attributed to the low biodegradability of cell walls and the presence of extracellular biopolymers. This study aims at investigating the effect of ultrasonic, microwave and combined microwave–ultrasonic treatment on biogas production, solids removal and dewaterability of anaerobically digested sludge. A comparison was made between the three pretreatment techniques conducting the digestion tests under similar conditions on the same synthetic sludge sample inoculated by digested sewage sludge. The experimental results depict that the combined microwave–ultrasonic treatment (2,450-MHz, 800-W and 3-min microwave treatment followed by 0.4-W/ml and 10-min ultrasonication) resulted in better digester performance than ultrasonic or microwave treatment. Mesophilic digestion of combined microwave–ultrasonic-pretreated sludge produced a significantly higher amount of methane (147 ml) after a sludge retention time of 17 days, whereas the ultrasonic- and microwave-treated sludge samples produced 30 and 16 ml of methane, respectively. The combined microwave–ultrasonic treatment resulted in total solids reduction of 56.8 % and volatile solid removal of 66.8 %. Furthermore, this combined treatment improved dewaterability of the digested sludge by reducing the capillary suction time (CST) down to 92 s, as compared to CST of 331 s for microwave-treated and 285 s for ultrasonically treated digested sludge samples. Optimisation tests were also carried out to determine the best combination.