RESUMO
Background: this research studied the feasibility of a simple method for extracting gold from central processing units [CPUs] of computer circuit boards without solvent
Methods: ceramic and composite CPUs of computer circuit boards were used. Gold was extracted using a hydrometallurgical method in six stages: grinding of CPUs, leaching in nitric acid, leaching in aqua regia, removing the excess nitric acid, extracting the gold, washing and purifying the gold deposits. Measurements of extracted precious metals were carried out by inductively coupled plasma [ICP]
Results: the results indicated that mean concentrations of gold in the first and second stages of leaching were 0.138 and 31.16 mg/L, respectively. Following the washing stage, the concentration of gold in the final deposit was 25 mg/L. The purity rate of the final deposit was 83.9%, and the final gold recovery yielded 82.3%
Conclusion: the results of this study indicated there is a potential for extracting a high percentage of precious metals from e-wastes without solvent
RESUMO
Background: Aminoglycoside antibiotics are widely used in medical centers, particularly to treat infections. The resistance developed against these agents is a huge concern in health care. A number of researchers have reported that hospital and municipal wastewaters are among the most important dissemination sources of these agent into the environment. Some, however, do not agree with this opinion. In the present study, the prevalence of aminoglycoside resistance genes was investigated in raw and effluent wastewater from hospital and municipal wastewater treatment plants
Methods: To conduct this descriptive-analytical study, 30 samples were taken according to sampling principles and cold cycle and transferred to the molecular laboratory. DNA was extracted by the freeze-thaw method using a kit [Promega]. The genes aac[3]-IIa and aac[6']-Ib which code aminoglycoside resistance were examined in this study
Results: The results indicated that the studied genes are present in 35% of urban and hospital wastewaters, and their frequency percentage is higher in hospital wastewater [52%] than urban wastewater [48%]. The studied genes were identified in 61% of raw hospital wastewater samples; however, they were not detected in the output wastewater from the studied treatment plants
Conclusion: Although, the studied genes were not detected in the final effluent, there is a high potential for their release into the environment. The current study demonstrated that the coding genes of aminoglycoside antibiotic resistance are present in raw urban and hospital wastewaters. In the case of improper exploitation of wastewater treatment plants, the output water can contaminate other environmental sections, such as soil and water resources, and result in the emission of these contaminants
RESUMO
Background: Human exposure to antibiotic resistant bacteria [ARB] is a public health concern which could occur in a number of ways. Wastewaters seem to play an important role in the dissemination of bacteria and antibiotic resistant genes [ARGs] in our environment. The aim of this study was to evaluate the occurrence of three groups of ARB and their resistance genes in hospital and municipal wastewaters [MWs] as possible sources
Methods: A total of 66 samples were collected from raw MWs and hospital wastewaters [HWs] and final effluents of related wastewater treatment plants [WWTPs]. Samples were analyzed for the detection of three groups of ARB including gentamicin [GM], chloramphenicol [CHL] and ceftazidime resistant bacteria and their ARGs [aac [3]-1, cmlA1 and ctx-m-32, respectively]
Results: The mean concentration of GM, CHL and ceftazidime resistant bacteria in raw wastewater samples was 1.24 × 10[7], 3.29 × 10[7] and 5.54 × 10[7] colony forming unit/100 ml, respectively. There is a variation in prevalence of different groups of ARB in MWs and HWs. All WWTPs decreased the concentration of ARB. However, high concentration of ARB was found in the final effluent of WWTPs. Similar to ARB, different groups of ARGs were found frequently in both MWs and HWs. All genes also detected with a relative high frequency in effluent samples of MWs WWTPs
Conclusions: Discharge of final effluent from conventional WWTPs is a potential route for dissemination of ARB and ARGs into the natural environment and poses a hazard to environmental and public health