Leaching of Arsenic from Wastes of Arsenic Removal Systems
Arsenic in groundwater was first detected in Bangladesh at Chapai Nawabgonj district in 1993. Since then arsenic contamination problem has been reported from almost every parts of the country. It is estimated that approximately 27% of the wells are contaminated with levels above 50ppb, the current drinking water standard for arsenic in Bangladesh (Kinninburg, D. G., et al., 2001). It is also estimated that about 77 million people are at risk of arsenic poisoning. A number of technologies are now available for end-of-the-pipe treatment arsenic present in groundwater. These are primarily based on coagulation and filtration. Some of the technologies use alum or ferric chloride as coagulants followed by filtration through a sand column. Other technologies are based on sedimentation and/or filtration through activated/doubly activated column/granular ferric hydroxide column. Aggressive leaching adopted in the Toxicity Characteristic Leaching Procedure (TCLP) at pH ≤ 5 when applied to the wastes collected from different arsenic removal units has not produced lechate concentrations significant enough to term the wastes toxic as per the USEPA regulatory levels. However, TCLP may not be suitable for assessment of long-term leaching of arsenic from arsenicrich waste, because such leaching may be kinetically restricted. Thus, modification of TCLP to represent the natural leaching environment comparable to real disposal conditions is necessary. Tests under modified TCLP may provide different results. The users are currently practicing a number of arsenic-sludge disposal options. The sub-aqueous disposal 162 Fate of Arsenic in the Environment and buried in mud or mixed with organic matters has been considered for studying the anaerobic leaching of arsenic from solids and multiphasic sludge. This option addresses the situation where the users dispose the sludge/waste into a nearby pond where it is mixed with mud and a small amount of domestic sewage. For both the solid wastes and the mutiphasic sludge, the leaching of arsenic into the overlying aqueous phase showed similar trend where the arsenic concentration peaked within the first week and then tapered off and disappeared after twelve weeks. Absence of residual arsenic in the solids following anaerobic leaching indicate that a significant amount of arsenic is lost through biomethylation induced by the presence of organic matters used in the leaching experiment.
A Study of Arsenic Treatment Technologies and Leaching Characteristics of Arsenic Contaminated Sludge
The arsenic crisis of Bangladesh has led to massive concerted efforts of NGOs and donor agencies in mitigating the disaster. Most of the focus has been on awareness building and the development and distribution of arsenic removal treatment systems. The disposal of arsenic concentrated sludge generated from the treatment process is one issue that has received little attention from the sponsors of the technologies and the users. This study was aimed at determining whether the present sludge disposal methods are safe and arsenic does not return to contaminate the environment. The present research investigated 15 NGO-led arsenic mitigation projects in 11 districts. Qualitative data were collected from interviews with villagers and NGOs, while soil and sludge samples were collected from the field sites. Samples were analysed at the BUET Environmental Laboratory and a toxicity characteristic leaching test was conducted to determine the quantity of mobile arsenic in the sludge samples. This study has concluded that the arsenic treatment units rendered the majority of the arsenic into a stable and non-mobile phase. No hazardous leachate was identified from the sludge produced from these units. Therefore, present arsenic-sludge disposal methods appear to be safe and not to contribute to recontamination of the environment. It is hoped that this study will lay the groundwork for informed public debate on arsenic treatment technologies and more particularly on longterm consequences of sludge disposal methods. 208 Technologies for Arsenic Removal from Drinking Water COMPARISON OF DIFFERENT TYPES OF ARSENIC TREATMENT UNITS AND TREATMENT ALTERNATIVES A comparison of the different types of arsenic treatment units in operation and treatment alternatives is provided in Table 1. The cost of each unit, treatment capacity, maintenance requirements and acceptability by users are compared. All the units, except the iron removal unit, have comparable and sufficient arsenic removal capabilities (greater than 90% arsenic removal). The possibility of arsenic leaching from the sludge/waste generated from the treatment processes is dependent on the type of removal mechanism and the ultimate sludge disposal method. These issues are covered in the next section. Table 1: Comparison of different types of arsenic treatment units and treatment alternatives Type of Unit Removal Mechanism Daily Capacity Cost (Taka) Complaints by Users 3-Pitcher Filter Adsorption by iron chips and sand 25-40 L One Family 250-300 Clogging of pitcher Chari Filter Adsorption by iron chips and sand 25-40 L One Family 300-400 No complaints Tubewell Sand Filter Adsorption by iron chips and sand 20 Families 5,000 No complaints 3-Pitcher Brick Filter Adsorption by brick and sand 25-40 L One Family 300 No complaints Bucket Treatment Unit (BTU) Oxidation and coagulation followed by settling 20 L One Family 300-400 Leaking of buckets, Lack of chemical Fill and Draw Same as BTU 20 Families or 1 School 10,000 No complaints HYBRID Coagulation with lime and alum, followed by settling 25 L One Family 550 No complaints SIDKO Adsorption by granular Fe(OH)3 200 Families 2,00,000 Too expensive and difficult Maintenance Iron Removal Plant Aeration, sedimentation and rapid filtration 10 Families 8,000 Partial removal of arsenic only Eriksen-Hamel and Zinia : Arsenic Treatment and Leaching Characteristics of Sludge 209 SLUDGE DISPOSAL METHODS An evaluation of sludge disposal methods was undertaken to determine whether the present methods lead to recontamination of the environment. Results of leaching test of sludge or soil samples would indicate whether the arsenic is bound to the adsorbent material or whether it leaches back into the environment. It was decided that direct observation of disposal practices in the field would be necessary. Both quantitative and qualitative data were collected during field visits. The method for obtaining data and the testing procedure followed are summarised below. Methodology and Testing At the start of each field visit an interview took place with the NGO project coordinators. During this interview data were collected about the project size, extent of problem, number of units in place, and removal methods for each unit. Questions were also asked about the sludge disposal methods suggested by the NGO to the users. Visits were then made to the users and further questions were asked. The interviews with the users provided information about the method of use, ease of use of the unit and the maintenance of the unit. Information regarding location, frequency and method of sludge disposal were also collected. It was found, except for a few exceptions, that the users followed the method of disposal suggested by the NGOs. This information was used to determine whether a sludge sample should be collected for analysis. A sample of the sludge or left-over residuals was collected from each type of unit at least once and from each NGO. The location and methodology of collecting the sample varied depending on the situation. Ideally, the collection method should have remained the same but differences in disposal methods, lack of available sludge and sludge collection systems made the sampling procedure vary. There were four types of sampling methods; (I) collecting the absorbent media from the treatment unit, (II) collecting the absorbent media from the disposal site, (III) collecting the material on which the sludge was disposed (in the case of liquid sludge), (IV) collecting absorbent media from a sludge storage system. In all cases, a predominately solid phase sample of approximately 100g was collected into a plastic-sampling jar with a scoop or by hand. No sample preservation techniques were used when transporting samples from the field to the laboratory. The time between sample collection and sample testing averaged about one week. During this time samples remained in storage containers. The types of materials collected by sampling method I was sand, brick, and iron chips. These were collected directly from the units primarily because there 210 Technologies for Arsenic Removal from Drinking Water had not been any recent disposal of material or the location of disposal was too arbitrary to be precise. Sampling method II was used when the location of disposed adsorbent media (usually sand) could be found. This sampling procedure provides the best opportunity to examine of whether there is leaching of the arsenic out of the adsorbent media into the ground. Sampling procedure III is similar to procedure II except that it was used when a liquid sludge had been disposed of. Cow-dung and soil samples, on which the liquid sludge was poured onto, were collected. A leaching test of these samples would indicate whether the liquid sludge binds to the cowdung/soil particles or leaches into the environment. In two cases, NGOs had developed a sludge collection system. The sludge was collected in pitchers or buckets and stored for further remediation. To date the NGOs have not developed a remediation process although credit should be given to them for taking steps to control indiscriminate sludge disposal. Sampling procedure IV collected the saturated sand from 3pitcher unit from the spent pitchers in these storage areas. The leaching test that was determined to be appropriate for this project was the Toxicity Characteristic Leaching Procedure (TCLP, USEPA method 1311). The TCLP is designed to determine the mobility of both organic and inorganic analytes present in liquid, solid and multi-phase wastes (USEPA, 1992). The Bangladesh University of Engineering and Technology (BUET) Environmental Engineering Laboratory was contracted to perform the leaching tests. Three initial samples were tested at a private laboratory, Intronics Technology Centre (ITC). However, BUET was chosen to perform the rest of the tests because of its good reputation and better laboratory facilities. Typically, the TCLP test removes the mobile component of any analyte present in the solid phase. The solid phase sample is extracted with an amount of extraction fluid equal to 20 times the weight of the solid phase. The extraction fluid employed is a function of the alkalinity of the solid phase of the waste (USEPA, 1992). The resultant extract from the TCLP test is the leachate. This leachate was analysed by atomic absorption spectrophotometer. The lower detection limit for this test is 0.001 mg/L. The reported concentration of arsenic in the leachate is precise to ± 10%. RESULTS AND DISCUSSION The results from the TCLP tests are presented in Table 2. The type of material tested, the arsenic concentration in the leachate, the sampling procedure, treatment unit of origin and the sponsoring agencies are also indicated in the table. The types of adsorbent media tested have been grouped together for better comparison. Eriksen-Hamel and Zinia : Arsenic Treatment and Leaching Characteristics of Sludge 211 Table 2: Results of TCLP tests performed on sludge/soil generated from arsenic removal units Sample No. Sample Type Arsenic Concentration in TCLP Extraction Fluid (mg/L) Sampling Procedure Arsenic Treatment Unit Name of the sponsoring agencies and Location 1 Iron Chips <0.001 I TWSF DCH, Pabna 2 Iron Chips <0.001 I Chari Filter DCH, Pabna 3 Sand 0.002 I TWSF DCH, Pabna 4 Sand 0.001 I Chari Filter DCH, Pabna 5 Sand 0.002 II Pitcher Filter AFV, Rajshahi 6 Sand <0.001 I Chari Filter DCH, Pabna 7 Coarse Sand <0.001 IV Pitcher Filter BRAC, Jhikargachha 8 Fine Sand 0.003 IV Pitcher Filter BRAC, Jhikargachha 9 Brick 0.005 I Brick Pitcher Filter Grameen, Kachua 10 Cow Dung 0.002 III BTU NGOForum, Manikganj 11 Soil 0.006 III BTU VERC, Nawabganj 12 Soil 0.012 III Fill &Draw Danida, Maijdi 13 Cow Dung 0.007 III BTU Danida, Maijdi 14 Soil 0.003 III BTU NGO Forum, Sylhet 15 Cowdung 0.001 III Hybrid Filter Hybrid, Singair 16 Soil 0.013 III Brick Pitcher Filter (Wash Water) Grameen, Kachua 17 Soil 0.043 III Alum Settling MCC, 
Pharmacokinetics of Mivacurium Isomers and Their Metabolites in Healthy Volunteers after Intravenous Bolus Administration
Background Previous studies report the pharmacokinetics of mivacurium isomers after an infusion using venous blood sampling. Although the extent of the mivacurium arterial‐venous gradient is not known, the sampling site is likely to influence mivacurium pharmacokinetic parameters because the drug is rapidly metabolized as it traverses the circulation. The objectives of this study were (1) to determine the pharmacokinetics of mivacurium isomers in healthy persons after intravenous bolus administration using intensive arterial blood sampling, and (2) to characterize the formation and elimination of mivacurium metabolites in human plasma. Methods Eight persons classified as American Society of Anesthesiologists physical status 1 or 2 who were scheduled to undergo elective surgery under balanced anesthesia received 0.15 mg/kg mivacurium chloride as an intravenous bolus. Arterial blood samples were collected every 10 s during the first 2 min and at frequent intervals for 4 h thereafter. Plasma concentrations of mivacurium isomers and their metabolites were determined by two stereoselective high‐performance liquid chromatographic methods coupled with fluorometric detection and noncompartmental pharmacokinetic parameters. Results Mean elimination half‐lives of the trans‐trans, cis‐trans, and cis‐cis isomers were 2.4, 2, and 28.5 min, respectively, with corresponding mean plasma clearances of 29.2, 45.7, and 6.7 ml [center dot] min‐1 [center dot] kg‐1. The volumes of distribution at steady state of the trans‐trans, cis‐trans, and cis‐cis isomers were 0.047, 0.054, and 0.189 l/kg, respectively. Plasma concentrations of monoester and alcohol metabolites peaked 25 s (median) after mivacurium injection, with half‐lives in the range of 90 min, except for the cis alcohol metabolite, which was only negligibly and transiently formed. Conclusions Substantial hydrolysis of mivacurium isomers by cholinesterases was confirmed by the rapid appearance of mivacurium metabolites in plasma. The intensive arterial sampling proved to be critical for the trans‐trans and cis‐trans isomers because the area under the curve between 0 and 2 min accounted for 75% and 86% of the total, respectively.