Maximum Concentration Limit Research Articles

Modeling Tool for Air Stripping and Carbon Adsorbers to Remove Trace Organic Contaminants

Removal of trace organic contaminants from aqueous solutions by air strippers (AS) and fixed bed carbon adsorper (FBCA) has been studied. A trace organic treatment tool has been developed to capture and adapt the best-known design procedures and to have all regulated trace organics, their physical and chemical properties, and the corresponding maximum concentration limits. Outputs include the selected treatment method and the final design parameters of air stripper or fixed bed carbon adsorber. Running the model shows that water temperature is a very important factor in designing AS and FBA. It also shows that the best air pressure values, in AS, ranged between 150 -200 ATM. And there is a big relation between the column size and the packing material. On the other hand, it shows that FBA diameter has an obvious effect on the needed volume, and the best values ranged between 1.2 – 2.5 m.

A superstructure optimization approach for water network synthesis with membrane separation-based regenerators

This work addresses the problem of water network synthesis. We propose a superstructure with fixed topology for a water network that consists of three layers, similar to a pooling problem: sources for reuse/recycle; regenerators for contaminants removal; and sinks for acceptance of water for reuse/recycle. The superstructure encompasses multiple freshwater sources, membrane separation-based partitioning regenerators of the industrially favored ultrafiltration and reverse osmosis, and sinks for incineration and deep ocean discharge. A mixed-integer nonlinear program is formulated based on this superstructure to determine the optimal interconnections in terms of total flowrates and contaminant concentrations. The main decisions include determining the split fractions of the source flowrates, extents of regeneration, and mixing ratios of the sources and regenerated streams subject to compliance with the maximum allowable inlet contaminant concentration limits of the sinks and discharge regulations. We also develop linear models for the membrane regenerators that admit a more general expression for the retentate stream concentration based on liquid-phase recovery factors and removal ratios. Computational studies are performed using GAMS/BARON on an industrially significant case study of a petroleum refinery water system. We incorporate linear logical constraints using 0–1 variables that enforce certain design and structural specifications to tighten the model formulation and enhance solution convergence. A globally optimal water network topology is attained that promotes a 27% savings equivalent to about $218,000/year reduction in freshwater use.

Chemical and isotopic methods for management of artificial recharge in Mazraha Station (Damascus Basin, Syria)

AbstractArtificially enhancing recharge rate into groundwater aquifer at specially designed facilities is an attractive option for increasing the storage capacity of potable water in arid and semi‐arid region such as Damascus basin (Syria). Two dug wells (I and II) for water injection and 24 wells for water extraction are available in Mazraha station for artificial recharge experiment. Chemical and stable isotopes (δ2H and δ18O) were used to evaluate artificial recharge efficiency. 400 to 500*103 m3 of spring water were injected annually into the ambient shallow groundwater in Mazraha station, which is used later for drinking purpose. Ambient groundwater and injected spring water are calcium bicarbonate type with EC about 880 ± 60 μS/cm and 300 ± 50 μS/cm, respectively. The injected water is under saturated versus calcite and the ambient groundwater is over saturated, while the recovered water is near equilibrium. It was observed that the injection process formed a chemical dilution plume that improves the groundwater quality. Results demonstrate that the hydraulic conductivity of the aquifer is estimated around 6.8*10−4 m/s. The effective diameter of artificial recharge is limited to about 250 m from the injection wells. Mixing rate of 30% is required in order to reduce nitrate concentration below 50 mg/l which is considered the maximum concentration limit for potable water. Deuterium and oxygen‐18 relationship demonstrates that mixing line between injected water and ambient groundwater has a slope of 6.1. Oxygen‐18 and Cl− plot indicates that groundwater salinity origin is from mixing process, and no dissolution and evaporation were observed. These results demonstrate the efficiency of the artificial recharge experiments to restore groundwater storage capacity and to improve the water quality. Copyright © 2011 John Wiley & Sons, Ltd.

Heterogeneously catalyzed Suzuki–Miyaura conversion of broad scope

The reaction tolerates a broad range of functional groups in the coupling partners and is usually performed in solution under homogeneous conditions at T ¢ 60 uC using 2–3 mol% catalytic amounts. The catalyst is often a Pd(0) complex with triarylphosphane ligands. 2 The catalytic cycle (Scheme 2) begins with the oxidative addition of an aryl halide to a Pd(0) species formed in situ to form an arylpalladium(II) halide intermediate. 3 Chloroarenes, especially nonactivated aryl chlorides, are notoriously less reactive due to the stability of the C–Cl bond (the relative reactivity of Ar–X is correlated to the respective bond dissociation energy: Ph–Cl: 96 kcal mol 21 ,P h–Br: 81 kcal mol 21 ,P h–I: 65 kcal mol 21 ). This, from a practical viewpoint adds cost to the products of traditional Suzuki–Miyaura reactions, because aryl chlorides are considerably less costly than iodo and bromoarenes. Another significant problem preventing widespread utilization of palladium homogeneous catalysis lies in the Pd impurities left in the reaction product since the upper limit for residual Pd levels in active pharmaceutical ingredients is typically very low (less than 5 ppb). 4 Removing residual palladium in a pharmaceutical substance to reduce its content to the maximum acceptable concentration limit requires rigorous product–catalyst separation processing (a purification process that often makes use of silica-based Pd scavengers). Intense research activities have therefore being devoted in the last decade to finding heterogeneous Pd catalysts of broad scope, capable of affording the recovery and reuse of the valued palladium while avoiding time-consuming catalyst separation and product purification steps which impact cost and worsen the environmental footprint of the reaction. 5

Leaching of trace metals from high carbon fly ash stabilized highway base layers

Fly ash produced by power plants in the United States occasionally contains significant amounts of unburned carbon due to the use of low nitrogen-oxide and sulphur-oxide burners in recent years. This ash cannot be reused in concrete production due to its reactivity with air entrainment admixtures and is largely placed in landfills. Roadways have high potential for large volume use of high carbon fly ash (HCFA). HCFA can be activated with lime kiln dust (LKD) and used as a base layer for newly paved roads. However, in such applications, the leaching of heavy metals from fly ash-stabilized base layers can be of concern. A series of batch water leach and column leach tests were conducted to investigate the leaching potential of six metals, Al, Cr, Fe, Mn, Sb and V, from the fly ash-lime kiln dust (LKD) stabilized soils. The results indicate that an increase in LKD amount, pH, and fly ash content have significant effects on leaching behavior of heavy metals from soil–fly ash–LKD mixtures. All six metals, except Al, exhibited a first flush pattern in column leach tests, and the measured concentrations quickly decreased to below EPA maximum concentration limits (MCLs) for drinking waters.

How much room for BiGa heteroantisites in GaAs1−xBix?

We addressed the issue of bismuth heteroantisite defects (BiGa) in GaAs1−xBix/GaAs epilayers by coupling x-ray absorption spectroscopy at the bismuth edge with density functional theory calculations of the defect structure. Calculations predict a large relaxation of the Bi-As interatomic distances when Bi atoms substitute Ga, however we found no experimental evidence of it. Quantitative analysis of the x-ray absorption spectra allows us to establish a maximum concentration limit for BiGa, which corresponds to about 5% of the total Bi atoms. BiGa do not account for the modifications in the spectra previously attributed to short range ordering.

Missing links in the regulatory chain controlling life cycle emissions of hazardous chemicals from articles

It is widely acknowledged that the management of risks associated with chemicals in articles, including consumer products, needs to be improved. The purpose of the present study is to empirically analyze to what extent European legislations that control emissions of hazardous chemicals from articles during different life cycle phases are coherent or not. To illustrate this, the regulation of a number of case-study chemicals, used in various consumer products and in high volumes, is scrutinized. This analysis identifies missing regulatory links between the rules that are relevant for the use phase and the rules applicable to the waste phase. With the exception of the RoHS directive, a clear connection to the rules for waste is missing in the regulatory system. Clear links are also missing between the rules regulating chemical emissions during the articles’ life cycle and maximum environmental concentration limits set for sludge, soil and surface water. The Waste Directive, the WEEE Directive, and the Water Framework Directive refer to EU environmental and waste policies. These policies state that environmental damage should be rectified at source. The lack of connection between the rules regulating different phases of an article's life cycle makes these objectives difficult to fulfill. These legislative gaps will encourage end-of-pipe solutions, rather than actions to manage the source of the problem. We argue that it is necessary to minimize the input of hazardous chemicals into articles, so that waste and other end-products can be recovered and used without harming human health or the environment.

Detections of Eleven Organophosphorus Insecticides and One Herbicide Threatening Pacific Salmonids, Oncorhynchus spp., in California, 1991–2010

California's surface water monitoring results from 1991 through 2010 were analyzed to determine whether 12 organophosphorus insecticides and herbicides (i.e., azinphos methyl, bensulide, dimethoate, disulfoton, ethoprop, fenamiphos, methamidophos, methidathion, methyl parathion, naled, phorate, and phosmet) and their degradates have been detected above maximum concentration limits (MCLs) in Pacific salmonid habitats. Methidathion, methyl parathion, phorate, phosmet, and the oxygen analogue of naled (DDVP) detections exceeded MCLs. Methyl parathion detections may be accounted for by monthly use trends, while methidathion detections may be explained by yearly use trends. There were inadequate phorate, phosmet, or DDVP data to evaluate for correlations with use.

Leaching Behaviour of Heavy Metals from the Class C Fly Ash-Based Geopolymers

In this paper, leaching behavior of heavy metals from the class C fly ash (CFA)-based geopolymers were studied. The CFA-based geopolymers were prepared from CFA, flue gas desulfurization gypsum (FGDG), and water treatment residual (WTR). The extraction-leaching concentrations of heavy metals from CFA-based geopolymers were lower than their maximum concentration limits according to the U.S. environmental protection law. And the encapsulated and fixed ratios of heavy metals by the CFA-based geopolymers were 96.02~99.88 %. The dynamic real-time leaching concentration of Pb (II) were less than 1.1 µg / L, Cr (VI) less than 3.25 mg / L while Hg (II) less than 4.0 µg / L. Additionally, dynamic accumulated leaching concentrations were increased at the beginning of leaching process then kept stable. The leaching results indicated that the security of heavy metals in CFA-based geopolymer was safe.

Impacts of alum residues from Morton Jaffray Water Works on water quality and fish, Harare, Zimbabwe

Metal pollution of freshwater due to human activities is a major problem confronting most urban centres in developing countries. This study determined the extent to which aluminium in the residues from Morton Jaffray Water Works in Harare were affecting the water quality of Manyame River and Lake Manyame. The study also measured aluminium bioaccumulation in Nile Tilapia (Oreochromis niloticus) which is of importance to the commercial fisheries industry in Zimbabwe. Depth integrated water, and sediment grab samples and adult fish were collected per site in January and March, 2010. A total of six sites were selected on the Manyame River and in Lake Manyame. The levels of Total Aluminium (Al) were determined in sediments, water and fish tissues (liver, kidney, gill and muscle). Total solids, total dissolved solids, conductivity, pH, dissolved oxygen and temperature were also determined in water and residues. The texture of the sediments was also assessed. Aluminium concentration in water ranged from 2.19mg/L to 68.93mg/L during both sampling campaigns surpassing permissible maximum concentration limits of 0.087 to 0.75mg/L suggested by the Environmental Protection Agency and African Union. The site upstream of the discharge point of the residues always had the lowest levels though it was higher than acceptable levels indicated above, thus suggesting the existence of other sources of aluminium in the catchment besides Morton Jaffray Water Works. However, there was a 10-fold and 100-fold increase in levels of aluminium in water and sediments, respectively, at the site 100m downstream of the discharge point on the Manyame River. Mean aluminium concentrations in water and sediments at this site averaged 68.93±61.74mg/L and 38.18±21.54mg/L in water and 103.79±55.96mg/L and 131.84±16.48mg/L in sediments in sampling campaigns 1 and 2, respectively. These levels were significantly higher than levels obtained from all the other sites during both sampling campaigns (ANOVA: p<0.05). This also indicated that the contribution of aluminium pollution from the water works residues was higher than all the other sources in the catchment. Aluminium levels were generally in the order of; sediments>fish>water. Bioaccumulation occurred in the fish and the order of bioconcentration was; kidney>liver>gill>muscle. The amounts of aluminium in the fish tissues investigated were significantly higher (maximum=2.92mg/g) than was reported in other studies reviewed (maximum=0.18mg/g). Thus, the water treatment plant residues are greatly increasing the concentrations of aluminium in the water system downstream of the plant thus creating a great risk of aluminium toxicity for fish. Treatment of the residues before discharge, substitution of alum with other coagulants, and re-use of the residues in buffer strips, agricultural lands and in sewage works should be considered.

Microstructure and gas-sensing properties of nanocrystalline NiFe2O4 prepared by spray pyrolysis

Nanocrystalline nickel ferrite with a crystallite size from 3 to 40 nm has been prepared by spray pyrolysis. The 57Fe Mossbauer spectrum of NiFe2O4 samples has been found to vary systematically with crystallite size. The sensing response of the nanocrystalline nickel ferrite to 50 ppm NH3 has been studied using in situ conductance measurements. NiFe2O4 offers a strong sensing response to ammonia at the level of its maximum concentration limit. The optimum nickel ferrite crystallite size and temperature for ammonia detection are determined.

New biosensors for assessment of environmental toxicity based on marine luminescent bacteria

Sixteen strains of luminescent bacteria of Vibrio and Photobacterium genera were isolated from water of the Azov and Black seas. Two strains prospective for biotesting were genetically identified as Vibrio fisher Ve-9579 and Vibrio fisheri Ve-9580 according to Russian Industrial Microorganism Collection (VKMP) classification and accepted for depositing. The isolated luminescent strains exhibited high individual sensitivity to oil derived products, heavy metal salts, sodium dodecyl sulfate (SDS) and phenol (up to the maximum concentration limit for fishery impoundments). According to EC50, they are ten times more sensitive to heavy metal salts and potassium dichromate and 2-6 times more sensitive to SDSand phenol compared to P. phosphoreum (Cohn) Ford and Escherichia coli C600 (pPLS-5) strains. Using Vibrio fisheri VKMP Ve-9579 and Vibrio fisheri VKMP Ve-9580 as biosensors, we have shown their high sensitivity and efficacy to marine ecosystem toxicity assessment.

E-SovTox: An Online Database of the Main Publicly-available Sources of Toxicity Data concerning REACH-relevant Chemicals Published in the Russian Language

A new open-access online database, E-SovTox, is presented. E-SovTox provides toxicological data for substances relevant to the EU Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) system, from publicly-available Russian language data sources. The database contains information selected mainly from scientific journals published during the Soviet Union era. The main information source for this database - the journal, Gigiena Truda i Professional'nye Zabolevania [Industrial Hygiene and Occupational Diseases], published between 1957 and 1992 - features acute, but also chronic, toxicity data for numerous industrial chemicals, e.g. for rats, mice, guinea-pigs and rabbits. The main goal of the abovementioned toxicity studies was to derive the maximum allowable concentration limits for industrial chemicals in the occupational health settings of the former Soviet Union. Thus, articles featured in the database include mostly data on LD50 values, skin and eye irritation, skin sensitisation and cumulative properties. Currently, the E-SovTox database contains toxicity data selected from more than 500 papers covering more than 600 chemicals. The user is provided with the main toxicity information, as well as abstracts of these papers in Russian and in English (given as provided in the original publication). The search engine allows cross-searching of the database by the name or CAS number of the compound, and the author of the paper. The E-SovTox database can be used as a decision-support tool by researchers and regulators for the hazard assessment of chemical substances.

Mass transport in laser surface nitriding involving the effect of high temperature gradient: Simulation and experiment

A self-consistent diffusion model has been employed to simulate the atomic nitrogen transport in titanium alloy with the coupling effect of both initial activated nitrogen concentration and high temperature gradient. Transport equations are solved through coupling the transient heat transfer equation and incorporating the surface physical phenomena in the governing equations as boundary conditions. For comparisons, laser gas nitriding of Ti6Al4V alloy has been performed by means of a pulsed Nd:YAG laser irradiation in a controlled nitrogen chamber. Results indicate that the simulated nitriding molten pool geometry and nitrogen concentration profiles are broadly consistent with the experimental results for various laser intensities and nitrogen pressures. Due to the combined driving of both concentration and temperature gradient, a rapid increase of nitrogen concentration profile during the heating stage is observed. While in the cooling stage, the redistribution of nitrogen in substrate and the local maximum of nitrogen close to the surface are mainly caused by the transient temperature gradient which is confirmed by both the experimental and simulated results. In addition, the influence of laser intensity on nitrogen transport is strongly related to the initial nitrogen concentration at surface. Especially, when the initial nitrogen concentration at surface approaches to the maximum concentration limit of nitrogen in titanium nitrided layer, slight drops of nitrogen concentration in molten zone are observed with the increase of laser intensity. This indicates that the earlier formed diffusion barrier due to the maximum concentration limit will impede the further penetration of atomic nitrogen and thus lead to the relatively lower concentration.

Análise técnica dos novos padrões brasileiros para amônia em efluentes e corpos d'água

Este trabalho discute os padrões estabelecidos pelas resoluções Conama 357/2005 e 397/2008 para os compostos de amônia em efluentes e corpos d'água. Os padrões estabelecidos pelas referidas resoluções são confrontados com os estabelecidos pela revogada Resolução Conama 20/1986 e com os padrões norte-americanos. As discussões permitem concluir que a Resolução Conama 357/2005 apresenta avanços em relação aos padrões anteriormente estabelecidos, incorporando a influência do pH sobre distribuição e toxicidade dos compostos amoniacais e alterando a concentração máxima aceitável para a amônia total nos efluentes. A Resolução Conama 397/2008 permite a eliminação do limite para efluentes sanitários. No entanto, as referidas resoluções não consideram a influência da temperatura sobre o comportamento dos compostos de amônia.

Preparation of highly concentrated nanostructured dispersions of controlled size

This article presents the use of a shearing procedure for the preparation of stable nanostructured dispersions of lipid mesophases. This new application of the shearing technique is compared with the well-established ultrasonication method for the emulsification of these mesophases in water in terms of particle size, particle size distribution and available concentration range. With a laboratory-built shear device based on a Couette cell, it was possible to produce high quantities of internally self-assembled emulsion particles of controlled size at concentrated hydrophobic phase contents ( ϕ o ) of up to 70 wt%. The concentration limit of 70 wt% could be reached however, the maximum attainable concentration depended on the internal structure type of the particles. The limit was thus easily attained for emulsified microemulsions (EME) as well as for the emulsified inverse hexagonal phase ( H 2 ), whereas it was found to be lower for emulsified discontinuous ( Fd3m) and bicontinuous ( Pn3m) cubic phases. Moreover, by shearing, it was possible to keep the size of the particles relatively constant when increasing ϕ o , whereas the particle size significantly increased with ϕ o when ultrasonication was employed. By means of ultrasonication, the hydrodynamic radius of the particles could be tuned linearly between 85 to 180 nm as a function of ϕ o up to a maximum of 20 to 30 wt%. Below the maximum concentration limit, particles displayed a well-controlled size.

Preparation of polymer-supported hydrated ferric oxide based on Donnan membrane effect and its application for arsenic removal

In the present study a novel technique was proposed to prepare a polymer-supported hydrated ferric oxide (D201-HFO) based on Donnan membrane effect by using a strongly basic anion exchanger D201 as the host material and FeCl3-HCl-NaCl solution as the reaction environment. D201-HFO was found to exhibit higher capacity for arsenic removal than a commercial sorbent Purolite ArsenX. Furthermore, it presents favorable adsorption selectivity for arsenic removal from aqueous solution, as well as satisfactory kinetics. Fixed-bed column experiments showed that arsenic sorption on D201-HFO could result in concentration of this toxic metalloid element below 10 μg/L, which was the new maximum concentration limit set recently by the European Commission and imposed by the US EPA and China. Also, the spent D201-HFO is amenable to efficient regeneration by NaOH-NaCl solution.

The geochemical and isotopic composition of ground waters in West Bengal: tracing ground-surface water interaction and its role in arsenic release

AbstractIn many areas of south and south-eastern Asia, concentrations of As in ground water have been found to exceed the WHO maximum concentration limit of 10 μg/l. This is adversely affecting the health of millions of people and has grave current and future health implications. It has recently been suggested that extensive abstraction of ground water in these areas may accelerate the release of As to ground water. This study uses geochemical and isotopic data to assess this hypothesis. The area investigated in this study is in the Chakdaha block of the Nadia District, West Bengal. The ground water is predominantly of the Ca-Mg-HCO3 type, although some samples were found to contain elevated concentrations of Na, Cl and SO4. This is thought to reflect a greater degree of water-rock interaction at the locations of these particular samples. Arsenic concentrations exceeded the national limit of 50 μg/l in 13 of the 22 samples collected. Four of the 13 samples with high As were recovered from tubewells with depths of 60 m or more. Shallow ground water samples were found to have a stable isotopic composition which falls subparallel to the Global Meteoric Water Line. This probably represents a contribution of evaporated surface water to the ground water, possibly from surface ponds or re-infiltrating irrigation water. Deep ground water, conversely, was shown to have a composition that closely reflects that of meteoric water. The data presented in this study suggest that, whilst the drawdown of surface waters may drive As release in shallow ground waters, it is not responsible for driving As release in deep ground water. However, local abstraction may have resulted in changes in the ground water flow regime of the area, with contaminated shallow ground waters being drawn into previously uncontaminated deep aquifers.

Chlorine: Is it really so bad and what are the alternatives?

Chlorine disinfection has been practised for over a century and has been credited with saving a significant number of lives worldwide on a daily basis, but it has received a great deal of negative publicity over the past few decades. The discovery in the 1970\'s that chlorination of water could result in the formation of potentially harmful trihalomethanes (THMs) caused concern amongst the water treatment fraternity and resulted in authorities reviewing chlorination practices in order to minimise THM formation and the United States Environmental Protection Agency (USEPA) setting maximum concentration limits for THMs in potable water. Many of the manufacturers and suppliers of water “purifiers” and alternative disinfectants exploit this information to their own advantage, misinforming the public regarding the dangers of chlorine, but even in the water treatment industry, chlorine is often misunderstood. Based on their experience in both water and wastewater disinfection and on the findings of a Water Research Commission (WRC) sponsored project into alternative disinfectants, the authors discuss the benefits and disadvantages of chlorine disinfection and compare this to the more promising alternative disinfectants. One of the main perceived advantages is the property of chlorine to maintain a residual and although THM formation can occur under these conditions, the compounds produced are perceptibly less toxic than those produced by some of the alternatives. A number of alternatives, including ozone, UV, peracetic acid, bromine and advanced oxidation are compared to chlorine in terms of their disinfectant abilities, residual effect, by-product formation, cost and ease of use. Water SA Vol. 30 (5) 2002: pp.18-24

Calculated Reduction of the Residual Adsorbent Mass Requiring Long-Term Storage in Radioactive Waste Processing by Magnetic Separation

This paper describes the uptake of plutonium, 238Pu, by an adsorbent consisting of Brimac 216 natural carbon, a type of bone char. A strongly magnetic Brimac 216 fine powder produced by Lidzey has been shown to be an excellent adsorbent for many radionuclides. After the adsorption of the radionuclides has taken place, from solution onto the magnetic Brimac 216 powder, the powder, together with the adsorbed radionuclides, can be rapidly removed from suspension, as a concentrate, using high gradient magnetic separation (HGMS). A comparison is drawn between experimental results using the conventional column filter, with bone char as the adsorbent medium, and calculations for the HGMS process to treat 3.22 m3 of solution containing 8 mg·l-1 of 238Pu and to remove the 238Pu from the suspension to reduce the effluent to less than the maximum concentration limit (MCL) for 238Pu, which is 0.74 Bq·l-1; however, the minimum concentration value used here is less than the MCL and is 0.0444 Bq·l-1 (7.006 · 10-14 g·l-1 of 238Pu) and is denoted as the lower concentration level. Calculations indicate that HGMS is considerably faster than the column filtration method. This leads to a significant reduction in the time required to process the solution, even though the HGMS process is repeated a number of times. Also, the mass of adsorbent requiring long-term storage is much smaller for HGMS than for the column filtration method.