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Performance of an On-Site Wastewater Treatment System Using Reactive Filter Media and a Sequencing Batch Constructed Wetland. SUSTAINABILITY 2019. [DOI: 10.3390/su11113172] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Many on-site wastewater treatment systems, such as soil treatment systems, are not sustainable in terms of purification efficiency, nutrient recycling potential, and economics. In this case study, a sequencing batch constructed wetland (SBCW) was designed and added after a package treatment plant (PTP) using reactive filter media for phosphorus (P) removal and recycling. The treatment performance of the entire system in the start-up phase and its possible applicability in rural areas were investigated. Raw and treated effluents were sampled during a period of 25 weeks and analyzed for nitrogen, phosphorus, BOD7, and bacteria. Field measurements were made of wastewater flow, electrical conductivity, oxygen, and temperature. The entire system removed total-P and total inorganic nitrogen (TIN) by 83% and 22%, respectively. High salt concentration and very low wastewater temperature were possible reasons for these unexpectedly low P and TIN removal efficiencies. In contrast, removal rates of bacteria (Escherichia coli, enterococci) and organic matter (as BOD) were high, due to filtration in the alkaline medium Polonite® (Ecofiltration Nordic AB, Stockholm, Sweden) and the fine sand used as SBCW substrate. High pH in effluent from the PTP was efficiently reduced to below pH 9 in the SBCW, meeting recommendations by environmental authorities in Sweden. We concluded that treating cold on-site wastewater can impair treatment performance and that technical measures are needed to improve SBCW performance.
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Hobson AJ, Stewart DI, Bray AW, Mortimer RJG, Mayes WM, Riley AL, Rogerson M, Burke IT. Behaviour and fate of vanadium during the aerobic neutralisation of hyperalkaline slag leachate. THE SCIENCE OF THE TOTAL ENVIRONMENT 2018; 643:1191-1199. [PMID: 30189535 DOI: 10.1016/j.scitotenv.2018.06.272] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Revised: 06/15/2018] [Accepted: 06/22/2018] [Indexed: 06/08/2023]
Abstract
Vanadium is a toxic metal present in alkaline leachates produced during the weathering of steel slags. Slag leaching can therefore have deleterious effects on local watercourses due to metal toxicity, the effects of the high pH (9-12.5) and rapid carbonation (leading to smothering of benthic communities). We studied the fate and behaviour of V in slag leachate both through field observations of a heavily affected stream (Howden Burn, Consett UK) and in controlled laboratory experiments where slag leachates were neutralised by CO2 ingassing from air. V was found to be removed from leachates downstream from the Howden Burn source contemporaneously with a fall in pH, Ca, Al and Fe concentrations. In the neutralisation experiments pH reduced from 12 → 8, and limited quantities of V were incorporated into precipitated CaCO3. The presence of kaolinite clay (i.e. SiOH and AlOH surfaces) during neutralisation experiments had no measureable effect on V uptake in the alkaline to circumneutral pH range. XANES analysis showed that V was present in precipitates recovered from experiments as adsorbed or incorporated V(V) indicating its likely presence in leachates as the vanadate oxyanion (HVO42-). Nano-scale particles of 2-line ferrihydrite also formed in the neutralised leachates potentially providing an additional sorption surface for V uptake. Indeed, removal of V from leachates was significantly enhanced by the addition of goethite (i.e. FeOOH surfaces) to experiments. EXAFS analysis of recovered goethite samples showed HVO42- was adsorbed by the formation of strong inner-sphere complexes, facilitating V removal from solution at pH < 10. Results show that carbonate formation leads to V removal from leachates during leachate neutralisation, and the presence of both naturally occurring and neoformed Fe (oxy)hydroxides provide a potent sink for V in slag leachates, preventing the spread of V in the environment.
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Affiliation(s)
- Andrew J Hobson
- School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
| | | | - Andrew W Bray
- School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
| | - Robert J G Mortimer
- School of Animal, Rural and Environmental Sciences, Nottingham Trent University, Brackenhurst Campus, Southwell, Nottinghamshire NG25 0QF, UK
| | - William M Mayes
- School of Environmental Sciences, University of Hull, Hull HU6 7RX, UK
| | - Alex L Riley
- School of Environmental Sciences, University of Hull, Hull HU6 7RX, UK
| | - Michael Rogerson
- School of Environmental Sciences, University of Hull, Hull HU6 7RX, UK
| | - Ian T Burke
- School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK.
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Hobson AJ, Stewart DI, Mortimer RJG, Mayes WM, Rogerson M, Burke IT. Leaching behaviour of co-disposed steel making wastes: Effects of aeration on leachate chemistry and vanadium mobilisation. WASTE MANAGEMENT (NEW YORK, N.Y.) 2018; 81:1-10. [PMID: 30527025 DOI: 10.1016/j.wasman.2018.09.046] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2018] [Revised: 08/24/2018] [Accepted: 09/28/2018] [Indexed: 06/09/2023]
Abstract
Steelmaking wastes stored in landfill, such as slag and spent refractory liners, are often enriched in toxic trace metals (including V). These may become mobile in highly alkaline leachate generated during weathering. Fresh steelmaking waste was characterised using XRD, XRF, and SEM-EDX. Batch leaching tests were performed under aerated, air-excluded and acidified conditions to determine the impact of atmospheric CO2 and acid addition on leachate chemistry. Phases commonly associated with slag including dicalcium silicate, dicalcium aluminoferrite, a wüstite-like solid solution and free lime were identified, as well as a second group of phases including periclase, corundum and graphite which are representative of refractory liners. During air-excluded leaching, dissolution of free lime and dicalcium silicate results in a high pH, high Ca leachate in which the V concentration is low due to the constraint imposed by Ca3(VO4)2 solubility limits. Under aerated conditions, carbonation lowers the leachate pH and provides a sink for aqueous Ca, allowing higher concentrations of V to accumulate. Below pH 10, leachate is dominated by periclase dissolution and secondary phases including monohydrocalcite and dolomite are precipitated. Storage of waste under saturated conditions that exclude atmospheric CO2 would therefore provide the optimal environment to minimise V leaching during weathering.
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Affiliation(s)
- Andrew J Hobson
- School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
| | | | - Robert J G Mortimer
- School of Animal, Rural and Environmental Sciences, Nottingham Trent University, Brackenhurst Campus, Southwell, Nottinghamshire NG25 0QF, UK
| | - William M Mayes
- School of Environmental Sciences, University of Hull, Hull HU6 7RX, UK
| | - Mike Rogerson
- School of Environmental Sciences, University of Hull, Hull HU6 7RX, UK
| | - Ian T Burke
- School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK.
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Higgins D, Curtin T, Burke I, Courtney R. The potential for constructed wetland mechanisms to treat alkaline bauxite residue leachate: carbonation and precipitate characterisation. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2018; 25:29451-29458. [PMID: 30128976 DOI: 10.1007/s11356-018-2983-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2018] [Accepted: 08/15/2018] [Indexed: 05/27/2023]
Abstract
Leachates emanating from bauxite residue disposal areas are alkaline and require neutralisation prior to discharge. The use of passive technologies such as constructed wetlands has received increasing interest as possible treatments for alkaline leachates, including bauxite residues. Mechanisms proposed for wetland effectiveness have included calcite precipitation but it is not clear if such a pathway is feasible in the relatively low Ca residue leachates. Carbonation of Ca-spiked residue leachate treatments was conducted to observe rates of pH decrease and precipitate formation. For all treatments, carbonation effectively decreased pH to ca. 10.5 which remained stable following aeration. Decreases in Al content of 83-93% were also observed. Precipitates retrieved from carbonation experiments and from a constructed wetland trial were characterised using XRD, SEM, XPS and EDX. Calcium carbonates formed in Ca-spiked treatments and dawsonite precipitation occur in the absence of Ca. Rinsing of precipitates removes surface calcium indicating soluble forms adsorbed on precipitates. The results demonstrate that carbonation of bauxite residue leachate is an important component of passive treatments and neutralisation.
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Affiliation(s)
- Derek Higgins
- Department of Biological Sciences, University of Limerick, Castletroy, Co., Limerick, Ireland
- The Bernal Institute, University of Limerick, Castletroy, Co., Limerick, Ireland
| | - Teresa Curtin
- The Bernal Institute, University of Limerick, Castletroy, Co., Limerick, Ireland
- Department of Chemical Sciences, University of Limerick, Castletroy, Co., Limerick, Ireland
| | - Ian Burke
- School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
| | - Ronan Courtney
- Department of Biological Sciences, University of Limerick, Castletroy, Co., Limerick, Ireland.
- The Bernal Institute, University of Limerick, Castletroy, Co., Limerick, Ireland.
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Mayes WM, Riley AL, Gomes HI, Brabham P, Hamlyn J, Pullin H, Renforth P. Atmospheric CO 2 Sequestration in Iron and Steel Slag: Consett, County Durham, United Kingdom. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2018; 52:7892-7900. [PMID: 29894185 DOI: 10.1021/acs.est.8b01883] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Carbonate formation in waste from the steel industry could constitute a nontrivial proportion of the global requirements for removing carbon dioxide from the atmosphere at a potentially low cost. To utilize this potential, we examined atmospheric carbon dioxide sequestration in a >20 million ton legacy slag deposit in northern England, United Kingdom. Carbonates formed from the drainage water of the heap had stable carbon and oxygen isotope values between -12 and -25 ‰ and -5 and -18 ‰ for δ13C and δ18O, respectively, suggesting atmospheric carbon dioxide sequestration in high-pH solutions. From the analyses of solution saturation states, we estimate that between 280 and 2900 tons of CO2 have precipitated from the drainage waters. However, by combining a 37 year long data set of the drainage water chemistry with geospatial analysis, we estimate that <1% of the maximum carbon-capture potential of the deposit may have been realized. This implies that uncontrolled deposition of slag is insufficient to maximize carbon sequestration, and there may be considerable quantities of unreacted legacy deposits available for atmospheric carbon sequestration.
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Affiliation(s)
- William Matthew Mayes
- School of Environmental Sciences , University of Hull , Hull HU6 7RX , United Kingdom
| | - Alex L Riley
- School of Environmental Sciences , University of Hull , Hull HU6 7RX , United Kingdom
- Chemical and Biological Engineering , University of Sheffield , Sheffield S10 2TN , United Kingdom
| | - Helena I Gomes
- School of Environmental Sciences , University of Hull , Hull HU6 7RX , United Kingdom
- Food, Water, Waste Research Group, Faculty of Engineering , University of Nottingham , University Park, , Nottingham NG7 2RD , United Kingdom
| | - Peter Brabham
- School of Earth and Ocean Sciences , Cardiff University , Cardiff CF10 3AT , United Kingdom
| | - Joanna Hamlyn
- School of Earth and Ocean Sciences , Cardiff University , Cardiff CF10 3AT , United Kingdom
- TerraDat UK Limited , Penarth Road , Llandough, Cardiff CF11 8TQ , United Kingdom
| | - Huw Pullin
- School of Earth and Ocean Sciences , Cardiff University , Cardiff CF10 3AT , United Kingdom
| | - Phil Renforth
- School of Earth and Ocean Sciences , Cardiff University , Cardiff CF10 3AT , United Kingdom
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Stewart DI, Bray AW, Udoma G, Hobson AJ, Mayes WM, Rogerson M, Burke IT. Hydration of dicalcium silicate and diffusion through neo-formed calcium-silicate-hydrates at weathered surfaces control the long-term leaching behaviour of basic oxygen furnace (BOF) steelmaking slag. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2018; 25:9861-9872. [PMID: 29372528 PMCID: PMC5891564 DOI: 10.1007/s11356-018-1260-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Accepted: 01/11/2018] [Indexed: 06/07/2023]
Abstract
Alkalinity generation and toxic trace metal (such as vanadium) leaching from basic oxygen furnace (BOF) steel slag particles must be properly understood and managed by pre-conditioning if beneficial reuse of slag is to be maximised. Water leaching under aerated conditions was investigated using fresh BOF slag at three different particle sizes (0.5-1.0, 2-5 and 10 × 10 × 20 mm blocks) and a 6-month pre-weathered block. There were several distinct leaching stages observed over time associated with different phases controlling the solution chemistry: (1) free-lime (CaO) dissolution (days 0-2); (2) dicalcium silicate (Ca2SiO4) dissolution (days 2-14) and (3) Ca-Si-H and CaCO3 formation and subsequent dissolution (days 14-73). Experiments with the smallest size fraction resulted in the highest Ca, Si and V concentrations, highlighting the role of surface area in controlling initial leaching. After ~2 weeks, the solution Ca/Si ratio (0.7-0.9) evolved to equal those found within a Ca-Si-H phase that replaced dicalcium silicate and free-lime phases in a 30- to 150-μm altered surface region. V release was a two-stage process; initially, V was released by dicalcium silicate dissolution, but V also isomorphically substituted for Si into the neo-formed Ca-Si-H in the alteration zone. Therefore, on longer timescales, the release of V to solution was primarily controlled by considerably slower Ca-Si-H dissolution rates, which decreased the rate of V release by an order of magnitude. Overall, the results indicate that the BOF slag leaching mechanism evolves from a situation initially dominated by rapid hydration and dissolution of primary dicalcium silicate/free-lime phases, to a slow diffusion limited process controlled by the solubility of secondary Ca-Si-H and CaCO3 phases that replace and cover more reactive primary slag phases at particle surfaces.
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Affiliation(s)
- Douglas I Stewart
- School of Civil Engineering, University of Leeds, Leeds, LS2 9JT, UK.
| | - Andrew W Bray
- School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
| | - Gideon Udoma
- School of Civil Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - Andrew J Hobson
- School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
| | - William M Mayes
- School of Environmental Sciences, University of Hull, Cottingham Road, Hull, HU6 7RX, UK
| | - Mike Rogerson
- School of Environmental Sciences, University of Hull, Cottingham Road, Hull, HU6 7RX, UK
| | - Ian T Burke
- School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
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