Phosphorus Retention of a Permeable Reactive Barrier Surpassed by an Unvegetated Artificial Pond

An artificial pond bisected by a phosphorus (P) retentive permeable reactive barrier (PRB) alongside Forrest Highway, Coolup, Western Australia was designed to remove P from farmland runoff. The pond bed was made of subsoil and road construction materials likely to have a relatively high P sorption capacity, and there was no vegetation in the bed of the pond. Flow through the pond was intercepted by the PRB, constructed from a mixture of sand, coarse crushed limestone, and bauxite residue (with 10% phospho-gypsum). The effectiveness of P removal and the impact of the PRB was measured by comparing the concentration of contaminants immediately either side of the PRB with established standards, and against background levels in runoff from surrounding farmland. Using coarse limestone to increase flow through the PRB failed where permeability was insufficient to avoid overtopping of the PRB and the wall had to be lowered to allow by-pass and avoid collapse. The PRB was effective in removing total P (TP); however, the influent TP concentration was low (mean 0.19 mg L -1 ) because most P entering from farmland was retained in the shallow pond upstream of the PRB. Despite this, TP removal by the PRB was 53% (2009–2012). Occasionally, in spring when the pond was stagnant and anaerobic, P was released from the PRB. This minor P release coincided with a minor release of iron, consistent with anaerobic conditions found in the PRB. Although not designed to do so, the shallow pond upstream of the PRB reduced the TP concentration from farmland by 85% (mean 1.26 mg L -1 down to 0.19 mg L -1 ), mainly by reducing filterable reactive P concentration. Some elements (arsenic, cobalt, conductivity, fluoride, manganese, molybdenum, pH, selenium, uranium and vanadium) were increased by flow through the PRB, but were low relative to surrounding waters and environmental standards

Reuse of industrial residues/wastes as a sustainable solution for landfill leachate contaminated groundwater

In order to increase the reuse of wastes and residues, as required by the Waste Framework Directive, the potential use of waste, residue and natural minerals as low-cost permeable reactive barrier (PRB) materials was investigated. The performance of a kitchen waste compost, sepiolite and steel slag was compared with that of volcanic slag, pumice and activated carbon in removing specific contaminants from landfill leachate. The experiments represented that the activated carbon removed 27% of the ammonium (NH4+), 75% of the chemical oxygen demand (COD) and 100% of the phosphate (PO43–), zinc (Zn2+) and nickel (Ni2+) from the landfill leachate. Volcanic slag exhibited removal efficiencies of 50% COD and 100% PO43– and pumice exhibited removal efficiencies of 20% NH4+, 27% Zn2+, 65% COD and 100% PO43–. The reactive materials were also checked for their potential in releasing unwanted constituents and represented different levels of the solute (e.g., PO43–, SO42–, NH4+) release. Among the reactives, sepiolite was found to be the reactive material reflecting a minor release (e.g., Zn2+, Cd2+ and Ni2+), but also delivering removal efficiencies of 40, 50, 65, 95, 97, 98, 98 and 100% for Ni2+, COD, Zn2+, SO42–, Cl–, F–, NH4+ and PO43–, respectively. The results show that the studied materials have the potential as reactives for PRB systems treating high strength contaminant plumes.

Remediation of Benzene and 1,2-Dichloroethylene in Groundwater by Funnel and Gate Permeable Reactive Barrier (FGPRB): A Case Study

Funnel and gate permeable reactive barrier (FGPRB) is an effective method to treat groundwater pollution. In order to clarify the impact of FGPRB on groundwater dynamic conditions, this study takes a site pilot test as the research object and establishes an FGPRB downstream of a petrochemical industry. The results show that the concentrations of 1,2-dichloroethylene and benzene in the downstream groundwater, after setting FGPRB, are lower than the detection limit. The numerical simulation results show that after setting FGPRB, both point source and area source pollution can achieve a good delay effect, extending from about 27 d to about 65 d of response time, but changing the thickness and permeability coefficient has no obvious effect on the delay effect. The tracer test shows the average permeability coefficient of the medium from the injection well to the monitoring well after the construction of FGPRB decreases from 77.0 m/d to 31.2 m/d after the construction of FGPRB. The average seepage velocity from the injection well to the monitoring well decreased from 0.19 m/d to 0.078 m/d after the construction of FGPRB. At the same time, when the FGPRB is not built, the maximum concentration time from the injection well to the monitoring well is about 10 d. After the FGPRB is constructed, the maximum concentration time of the tracer received by the monitoring well is about 27 days. These results confirm that the establishment of FGPRB will change the hydrodynamic conditions of groundwater and delay the response time of pollutants in the monitoring well.

Study on the Mechanical and Leaching Characteristics of Permeable Reactive Barrier Waste Solidified by Cement-Based Materials

The durability against wet-dry (w-d) cycles is an important parameter for the service life design of solidified permeable reactive barrier (PRB) waste. This study introduces the potential use of cement, fly ash, and carbide slag (CFC) for the stabilization/solidification (S/S) of PRB waste. In this study, solidified PRB waste was subjected to different w-d cycles ranging in times from 0 to 10. By analyzing the mass loss, the unconfined compressive strength (UCS), initial resistivity (IR), and the leaching concentration under different durability conditions, the results demonstrate that these variables increased and then tended to decrease with the number of w-d cycles. The UCS of contaminated soil is significantly correlated with IR. Moreover, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analyses indicate that the hydration products calcium silicate hydrate (C-S-H) and ettringite (AFt) are the main reasons for the enhancement of the UCS. However, the increase in concentration leads to a decrease in hydration products and the compactness of solidified soil, which has negative effects for the UCS and the leaching ion concentration. In general, the durability exhibited by the PRB waste treated with S/S in this paper was satisfactory. This study can provide theoretical guidance for practical engineering applications.

Cd(II) removal from aqueous solutions by pomelo peel derived biochar in a permeable reactive barrier: Modelling, optimization and mechanism

Biochar can have multiple benefits, such as solid waste recycling, water pollution treatment, carbon fixation and sustainability. The present study aimed to investigate Cd(II) removal from aqueous solutions using pomelo peel derived biochar combined with a permeable reactive barrier (PRB). The results show that there were slight changes in the structure of the pomelo peel derived biochar before and after activation, while the variation was not significant. The specific surface areas of the not activated and activated pomelo peel derived biochars were 3.207 m2/g and 6.855 m2/g, respectively. The pore diameter of the former was 4.165 nm and that of the latter was 4.425 nm, indicating that the two materials are mainly mesoporous. BP-GA was more suitable than RSM for optimizing the removal conditions of Cd(II) using the prepared materials combined with PRB. The maximum removal efficiency of Cd(II) was 90.31% at biochar dosage = 4.84, reaction time = 53.75 min, initial Cd(II) concentration = 19.36 mg/L and initial pH = 6.07. The verification experiment was 88.74% under these experimental conditions, and the absolute error was 1.57%. The saturated adsorption capacity of quartz sand for Cd(II) is approximately 0.08 mg/g when reaching equilibrium. The saturated adsorption capacity of biochar for Cd(II) is approximately 29.76 mg/g. Pseudo second order kinetics and Langmuir isotherm adsorption were more suitable for describing the Cd(II) adsorbed from an aqueous solution by activated pomelo peel derived biochar. The adsorption process of Cd(II) by the prepared biochar was spontaneous, endothermic and entropy driven. Our results suggest that the modified biochar can be regenerated within the fourth cycle and that it has application prospects as a useful adsorbent for water treatment in PRB systems. This finding provides a reference for relieving Cd pollution and for its large scale removal from wastewater when combined with a PRB system.