In situ treatment of arsenic contaminated groundwater

Groundwater in a sand and gravel aquifer was contaminated by arsenic compounds. The extent and the As concentration of the polluted groundwater plume decreased from 1971 to 1975, whereas the content of free dissolved oxygen increased. High As concentrations (> 1 mg/1) occured in groundwater with typical characteristics of a “reduced” water with negative Eh values and high concentrations of dissolved iron (up to 140 mg/1 in 1971). When plotted into an As stability field diagram, the higher values (> 1 mg As/1) coincided with the fields of trivalent As species, whereas the lower values (< 0.1 mg As/1) fitted to the fields of the pentavalent arsenic species. Therefore it was concluded that an improvement of the oxygen supply should accelerate the natural precipitation processes. By injection of 29,000 kg KMnO₄ into 17 wells and piezometers the soluble As (III) species were oxidized to As (V) species, which were precipitated as FeAsO₄ or Mn₃(AsO₄)₂ or co-precipitated with Mn- and Fe-hydroxides.     

In situ oxidation of petroleum-hydrocarbon contaminated groundwater using passive ISCO system

Groundwater contamination by gasoline spill is a worldwide environmental problem. Gasoline contains methyl tertiary-butyl ether (MTBE) (a fuel oxygenates) and benzene, which are the chemicals of concerns among the gasoline components. In this study, an in situ chemical oxidation (ISCO) barrier system was developed to evaluate the feasibility of applying this passive system on the control of MTBE and benzene plume in aquifer. The developed ISCO barrier contained oxidant-releasing materials, which could release oxidants (e.g., persulfate) when contact with water for the contaminants’ oxidation in groundwater. In this study, laboratory-scale fill-and-draw experiments were conducted to determine the component ratios of the oxidant-releasing materials and evaluate the persulfate release rates. Results indicate that the average persulfate-releasing rate of 7.26 mg S₂O₈²⁻/d/g was obtained when the mass ratio of sodium persulfate/cement/sand/water was 1/1.4/0.24/0.7. The column study was conducted to evaluate the efficiency of in situ application of the developed ISCO barrier system on MTBE and benzene oxidation. Results from the column study indicate that approximately 86-92% of MTBE and 95-99% of benzene could be removed during the early persulfate-releasing stage (before 48 pore volumes of groundwater pumping). The removal efficiencies for MTBE and benzene dropped to approximately 40-56% and 85-93%, respectively, during the latter part of the releasing period due to the decreased persulfate-releasing rate. Results reveal that acetone, byproduct of MTBE, was observed and then further oxidized completely. Results suggest that the addition of ferrous ion would activate the persulfate oxidation. However, excess ferrous ion would compete with organic contaminants for persulfate, and thus, cause the decrease in contaminant oxidation rates. The proposed treatment scheme would be expected to provide a more cost-effective alternative to remediate MTBE, benzene, and other petroleum-hydrocarbon contaminated aquifers. Results from this study will be useful in designing a scale-up system for field application.     

Aerated treatment pond technology with biofilm promoting mats for the bioremediation of benzene, MTBE and ammonium contaminated groundwater

A novel aerated treatment pond for enhanced biodegradation of groundwater contaminants was tested under field conditions. Coconut fibre and polypropylene textiles were used to encourage the development of contaminant-degrading biofilms. Groundwater contaminants targeted for removal were benzene, methyl tert-butyl ether (MTBE) and ammonium. Here, we present data from the first 14 months of operation and compare contaminant removal rates, volatilization losses, and biofilm development in one pond equipped with coconut fibre to another pond with polypropylene textiles. Oxygen concentrations were constantly monitored and adjusted by automated aeration modules. A natural transition from anoxic to oxic zones was simulated to minimize the volatilization rate of volatile organic contaminants. Both ponds showed constant reductions in benzene concentrations from 20 mg/L at the inflow to about 1 μg/L at the outflow of the system. A dynamic air chamber (DAC) measurement revealed that only 1% of benzene loss was due to volatilization, and suggests that benzene loss was predominantly due to aerobic mineralization. MTBE concentration was reduced from around 4 mg/L at the inflow to 3.4-2.4 mg/L in the system effluent during the first 8 months of operation, and was further reduced to 1.2 mg/L during the subsequent 6 months of operation. Ammonium concentrations decreased only slightly from around 59 mg/L at the inflow to 56 mg/L in the outflow, indicating no significant nitrification during the first 14 months of continuous operation. Confocal laser scanning microscopy (CLSM) demonstrated that microorganisms rapidly colonized both the coconut fibre and polypropylene textiles. Microbial community structure analysis performed using denaturing gradient gel electrophoresis (DGGE) revealed little similarity between patterns from water and textile samples. Coconut textiles were shown to be more effective than polypropylene fibre textiles for promoting the recruitment and development of MTBE-degrading biofilms. Biofilms of both textiles contained high numbers of benzene metabolizing bacteria suggesting that these materials provide favourable growth conditions for benzene degrading microorganisms.     

In situ disinfection of sewage contaminated shallow groundwater: a feasibility study

Sewage-contaminated shallow groundwater is a potential cause of beach closures and water quality impairment in marine coastal communities. In this study we set out to evaluate the feasibility of several strategies for disinfecting sewage-contaminated shallow groundwater before it reaches the coastline. The disinfection rates of Escherichia coli (EC) and enterococci bacteria (ENT) were measured in mixtures of raw sewage and brackish shallow groundwater collected from a coastal community in southern California. Different disinfection strategies were explored, ranging from benign (aeration alone, and aeration with addition of brine) to aggressive (chemical disinfectants peracetic acid (PAA) or peroxymonosulfate (Oxone)). Aeration alone and aeration with brine did not significantly reduce the concentration of EC and ENT after 6 h of exposure, while 4-5 mg L⁻¹ of PAA or Oxone achieved >3 log reduction after 15 min of exposure. Oxone disinfection was more rapid at higher salinities, most likely due to the formation of secondary oxidants (e.g., bromine and chlorine) that make this disinfectant inappropriate for marine applications. Using a Lagrangian modeling framework, we identify several factors that could influence the performance of in-situ disinfection with PAA, including the potential for bacterial regrowth, and the non-linear dependence of disinfection rate upon the residence time of water in the shallow groundwater. The data and analysis presented in this paper provide a framework for evaluating the feasibility of in-situ disinfection of shallow groundwater, and elucidate several topics that warrant further investigation.     

复合污染地下水的两级处理工艺中试研究

开展了石英砂+生物活性炭的两级处理工艺净化复合污染地下水的中试研究。结果表明,当石英砂滤料未成熟时,单级过滤对铁、锰的去除效果较好,但是对氨氮及CODMn的去除效果不理想;二级过滤工艺可以明显提高水中氨氮和CODMn的去除效果;滤料成熟后系统对铁、锰、氨氮及CODMn的平均去除率分别达到99.5%,99.9%,93.7%和34.5%。该处理工艺出水水质较好,抗水质冲击负荷能力强,且运行稳定性高。     

Aerobic VS. anaerobic biological treatment of organically contaminated groundwater

This paper describes laboratory scale results of aerobic and anaerobic biological treatment studies conducted to evaluate the feasibility of treating ground water contaminated with an organic solvent consisting of an equal weight‐mixture of methylethylketone and cyclohexanone. For this purpose, three alternatives were considered, namely a single‐stage anaerobic baffled reactor, an activated sludge system, and an aerated lagoon. The study focused on determining and comparing the treatment efficiency of each of the three treatment processes under similar operating conditions. Aerobic processes proved to be more effective in treating the organically contaminated groundwater.     

An application of permeable reactive barrier technology to petroleum hydrocarbon contaminated groundwater.

A funnel and gate permeable reactive barrier was designed and built to treat groundwater contaminated with dissolved phase toluene. ethyl benzene. and xylene and n-alkanes in the C6-C36 fraction range. Removal efficienicies for the funnel and gate system varied from 63% to 96% for the monocyclic aromatic hydrocarbons. Average removal efficiencies for C6-C9, C10-C14, and C15-C28 fraction ranges were 69.2%, 77.6% and 79.5%. respectively. The lowest average removal efficiencies were 54% for the C29-C36 n-alkane fraction. The overall average removal efficiency for the funnel and gate system towards petroleum hydrocarbons present in the groundwater was 72% during the 10 month period over which the data were collected, and has allowed relevant water quality objectives to be met.     

Assessment of in situ degradation of chlorinated ethenes and bacterial community structure in a complex contaminated groundwater system

The occurrence of in situ degradation of chlorinated ethenes was investigated using an integrated approach in a complex groundwater system consisting of several geological units. The assessment of hydrogeochemistry and chlorinated ethenes distribution using principal component analysis (PCA) in combination with carbon stable isotope analysis revealed that chlorinated ethenes were subjected to substantial biodegradation. Shifts in isotopic values up to 20.4 per thousand, 13.9 per thousand, 20.1 per thousand and 31.4 per thousand were observed between geological units for tetrachloroethene (PCE), trichloroethene (TCE), cis-dichloroethene (cDCE) and vinyl chloride (VC), respectively. The use of specific biomarkers (16S rRNA gene) indicated the presence of Dehalococcoides sp. DNA in 20 of the 33 evaluated samples. In parallel, the analysis of changes in the bacterial community composition in the aquifers using canonical correspondence analysis (CCA) indicated the predominant influence of the chlorinated ethene concentrations (56.3% of the variance, P=0.005). The integrated approach may open new prospects for the assessment of spatial and temporal functioning of bioattenuation in contaminated groundwater systems.     

Microcosms-experiments to assess the potential for natural attenuation of contaminated groundwater

Groundwater samples from six wells of a former gas plant site were characterised using chemical, microbial and ecotoxicological methods. Degradation studies were performed in batch-culture under aerobic conditions with the groundwater samples containing their autochthonous microflora and original contaminant mixture. The highest O2-consumption (3 mmol 100 ml-1), combined with BTEX (8.3 mg l-1) and naphthalene (171.3 mg l-1) degradation, as well as formation of organic acids was found after N- and P-supplementation with the highest contaminated groundwater sample. The other highly polluted groundwater sample showed no activity obviously because of the toxicity of some compounds. The major part of the PAHs and BTEX was eliminated in the assays with the low contaminated groundwater samples. The results indicate that the microbial degradation capacity and thereby the natural attenuation capacity in each groundwater differ and cannot be assessed simply by chemical, microbial and toxicological data. Additionally activity tests with authentic groundwater samples with and without nutrient supplementation are recommended.     

A review of the impact of climate change on future nitrate concentrations in groundwater of the UK

This paper reviews the potential impacts of climate change on nitrate concentrations in groundwater of the UK using a Source-Pathway-Receptor framework. Changes in temperature, precipitation quantity and distribution, and atmospheric carbon dioxide concentrations will affect the agricultural nitrate source term through changes in both soil processes and agricultural productivity. Non-agricultural source terms, such as urban areas and atmospheric deposition, are also expected to be affected. The implications for the rate of nitrate leaching to groundwater as a result of these changes are not yet fully understood but predictions suggest that leaching rate may increase under future climate scenarios. Climate change will affect the hydrological cycle with changes to recharge, groundwater levels and resources and flow processes. These changes will impact on concentrations of nitrate in abstracted water and other receptors, such as surface water and groundwater-fed wetlands. The implications for nitrate leaching to groundwater as a result of climate changes are not yet well enough understood to be able to make useful predictions without more site-specific data. The few studies which address the whole cycle show likely changes in nitrate leaching ranging from limited increases to a possible doubling of aquifer concentrations by 2100. These changes may be masked by nitrate reductions from improved agricultural practices, but a range of adaption measures need to be identified. Future impact may also be driven by economic responses to climate change.     

Amendments for the in situ remediation of contaminated sediments: Evaluation of potential environmental impacts

Active sediment caps represent a comparatively new technology for remediating contaminated sediments. They are made by applying chemically active amendments that reduce contaminant mobility and bioavailability to the sediment surface. The objective of this study was to determine if active cap amendments including organoclay, apatite, and biopolymers have the potential to harm benthic organisms. Methods included laboratory bioassays of amendment toxicity and field evaluations of amendment impacts on organisms held in cages placed within pilot-scale active caps located in Steel Creek, a South Carolina (USA) stream. Test organisms included Hyalella azteca, Leptocheirus plumulosus, Lumbriculus variegatus, and Corbicula fluminea to represent a range of feeding modes, burrowing behaviors, and both fresh and saltwater organisms. In addition to the laboratory and field assays, chemical extractions were performed to determine if the amendments contained harmful impurities that could leach into the ambient environment. Laboratory bioassays indicated that 100% apatite had minimal effects on Hyalella in freshwater and up to 25% organoclay was nontoxic to Leptocheirus in brackish water. Field evaluations indicated that pilot-scale caps composed of up to 50% apatite and 25% organoclay did not harm Hyalella, Lumbriculus, or Corbicula. In contrast, organisms in caps containing biopolymers died because of physical entrapment and/or suffocation by the viscous biopolymers. The extractions showed that the amendments did not release harmful concentrations of metals. These studies indicated that apatite and organoclay are nontoxic at concentrations (up to 50% and 25% by weight, respectively) needed for the construction of active caps that are useful for the remediation of metals and organic contaminants in sediments.     

Model experiments on the microbial removal of chromium from contaminated groundwater

A bacterial consortium with representatives of sulfate-reducing and denitrifying bacteria was selectively enriched. Model experiments under microaerobic conditions showed that it precipitated chromium from Cr (VI)-containing waters (area of a former electroplating factory, Leipzig, Germany) by two different mechanisms: by sulfate reduction and precipitation as sulfide, and by some direct reduction. Sulfate reduction needed fatty acids as organic substrates and resulted at the first stage in no sulfide accumulation. In the absence of the fatty acids but with straw as organic substrate, the direct reduction of chromium was observed without sulfate reduction. In this case Cr (VI)-reduction rate correlated with that of the denitrification.     

Elevated nitrate levels in the groundwater of the Gaza Strip: distribution and sources

Seven years of monitoring groundwater in the Gaza Strip has shown that nitrate was and still is a major groundwater pollutant. The objectives of this research were to study the distribution of NO(3)(-) in the groundwater of the Gaza Strip and to identify the sources of NO(3)(-) in the Gaza aquifer system by assessing nitrogen and oxygen isotopes. The most recent samples collected in 2007 showed 90% of the wells having NO(3)(-) concentrations that are several times higher than the WHO standards of 50 mg/L. Potential NO(3)(-) source materials in Gaza are animal manure N, synthetic NH(4) based fertilizers, and wastewater/sludge. The average concentrations of N in the sludge, manure and soil of Gaza were 2.9%, 1% and 0.08%, respectively. The range in delta(15)N of solid manure samples was +7.5 to +11.9 per thousand. The range in delta(15)N of sludge samples was +4.6 to +7.4 per thousand, while four brands of synthetic fertilizers commonly used in Gaza had delta(15)N ranging from +0.2 to +1.0 per thousand. Sludge amended soil had delta(15)N ranging from +2.0 to +7.3 per thousand. For both delta(18)O and delta(15)N, the ranges of groundwater NO(3)(-) were -0.1 to +9.3 per thousand and +3.2 to 12.8 per thousand, respectively. No significant bacterial denitrification is taking place in the Gaza Strip aquifer. Nitrate was predominantly derived from manure and, provided delta(15)N of sludge represents the maximum delta(15)N of human waste, to a lesser extent from septic effluents/sludge. Synthetic fertilizers were a minor source.     

天然水中硝酸盐氮氧同位素测试技术研究进展

水环境的硝酸盐污染是一个全球性环境问题。识别水环境中硝酸盐的来源及其转化,对更好地管理水质是十分重要的。硝酸盐的稳定氮氧同位素组成可有效识别水环境中NO 3-来源及其转化。本文总结了典型的测定硝酸盐中稳定氮氧同位素组成的方法:石墨燃烧法、AgNO3-离子交换法、细菌反硝化法、亚硝酸盐去除联合细菌反硝化法、两步化学还原法、连续选择性细菌还原法,同时对这些方法的优缺点进行了评述。最后分析了检测技术中存在的共同问题及其发展方向:δ18O精确度仍有提高的潜力;把NO 3-从水中独立提取出来进行三氧同位素的测试方法还需改进和提高;水样的采集、保存有待进一步改进。     

相图理论在硝盐联产技术中的应用

水盐体系相图的知识广泛应用在无机盐、化学肥料以及三废处理等化工领域,硝盐联产作为地下卤水为原料生产无水硫酸钠和氯化钠的生产分离技术。水盐体系相图在其实际应用中具有重要意义。本文简要介绍相图理论在硝盐联产生产中的理论过程分析,为生产调节、管理进行理论指导。     

Dynamics of arsenic in agricultural soils irrigated with arsenic contaminated groundwater in Bangladesh

Arsenic (As) concentrations in the soil layers of 12 rice fields located in four As affected areas and two unaffected areas in Bangladesh were monitored during 2003. In the unaffected areas, where irrigation water contained little As (<1 microg/L), As concentrations of rice field soils ranged from 1.5 to 3.0 mg/kg and did not vary significantly with either depth or sampling time throughout the irrigation period. In the As affected areas where the irrigation water contained elevated As (79 to 436 microg/L), As concentrations of rice field soils were much higher compared to those in the unaffected areas and varied significantly with both depth and sampling time. For the top 0 to 150 mm of the soil, the As concentration increased significantly at the end of the irrigation season (May-June 2003). About 71% of the As that is applied to the rice field with irrigation water accumulates in the top 0 to 75 mm soil layer by the end of the irrigation season. After the wet season during which the rice fields were inundated with flood/rain water, the As concentrations in the soil layer decreased significantly and were reduced to levels comparable to those found in soil samples collected at the beginning of the irrigation period. The long-term As accumulation in agricultural soil appears to be counteracted by biogeochemical pathways leading to As removal from soil.     

Remediation of bromate-contaminated groundwater in an ex situ fixed-film bioreactor

Use of a pilot-scale fixed-film bioreactor was investigated for remediation of bromate contamination within groundwater. Bromate reduction with stoichiometric production of bromide was observed, providing supporting evidence for complete reduction of bromate with no production of stable intermediates. Reduction of 87-90% bromate from an influent concentration of 1.1 mg L(-1) was observed with retention times of 40-80 h. Lower retention times led to decreases in bromate reduction capability, with 11.5% removal at a 10 h retention time. Nitrate reduction of 76-99% from a 30.7 mg L(-1) as NO(3)(-) influent was observed at retention times of 10-80 h, although an increase in nitrite production to 2.7 mg L(-1) occurred with a 10 h retention time. Backwashing was not required, with the large plastic packing media able to accommodate biomass accumulation without decreases in operational efficiency. This study has provided proof of concept and demonstrated the potential of biological bromate reduction by fixed-film processes for remediation of a bromate contaminated groundwater source.     

Sources of nitrate and ammonium contamination in groundwater under developing Asian megacities

The status of nitrate (NO(3)(-)), nitrite (NO(2)(-)) and ammonium (NH(4)(+)) contamination in the water systems, and the mechanisms controlling their sources, pathways, and distributions were investigated for the Southeast Asian cities of Metro Manila, Bangkok, and Jakarta. GIS-based monitoring and dual isotope approach (nitrate delta(15)N and delta(18)O) suggested that human waste via severe sewer leakage was the major source of nutrient contaminants in Metro Manila and Jakarta urban areas. Furthermore, the characteristics of the nutrient contamination differed depending on the agricultural land use pattern in the suburban areas: high nitrate contamination was observed in Jakarta (dry fields), and relatively lower nutrients consisting mainly of ammonium were detected in Bangkok (paddy fields). The exponential increase in NO(3)(-)-delta(15)N along with the NO(3)(-) reduction and clear delta(18)O/delta(15)N slopes of NO(3)(-) ( approximately 0.5) indicated the occurrence of denitrification. An anoxic subsurface system associated with the natural geological setting (e.g., the old tidal plain at Bangkok) and artificial pavement coverage served to buffer NO(3)(-) contamination via active denitrification and reduced nitrification. Our results showed that NO(3)(-) and NH(4)(+) contamination of the aquifers in Metro Manila, Bangkok, and Jakarta was not excessive, suggesting low risk of drinking groundwater to human health, at present. However, the increased nitrogen load and increased per capita gross domestic product (GDP) in these developing cities may increase this contamination in the very near future. Continuous monitoring and management of the groundwater system is needed to minimize groundwater pollution in these areas, and this information should be shared among adjacent countries with similar geographic and cultural settings.     

Use of iron-based technologies in contaminated land and groundwater remediation: a review

Reactions involving iron play a major role in the environmental cycling of a wide range of important organic, inorganic and radioactive contaminants. Consequently, a range of environmental clean-up technologies have been proposed or developed which utilise iron chemistry to remediate contaminated land and surface and subsurface waters, e.g. the use of injected zero zero-valent iron nanoparticles to remediate organic contaminant plumes; the generation of iron oxyhydroxide-based substrates for arsenic removal from contaminated waters; etc. This paper reviews some of the latest iron-based technologies in contaminated land and groundwater remediation, their current state of development, and their potential applications and limitations.