Arsenic contamination in water has posed severe health problems around the world. In spite of the availability of some conventional techniques for arsenic removal from contaminated water, development ...of new laboratory based techniques along with enhancement and cost reduction of conventional techniques are essential for the benefit of common people.
This paper provides an overview of the arsenic issue in water such as modes of contamination of ground water as well as surface water by arsenic, its metabolism and health impacts, factors influencing arsenic poisoning, fundamentals of arsenic poisoning mechanism and world scenario of arsenic poisoning. It discusses and compares the conventional laboratory based techniques, like precipitation with alum, iron, Fe/Mn, lime softening, reverse osmosis, electro dialysis, ion exchanges, adsorption on activated alumina/carbon, etc., for arsenic removal from contaminated water. It also discusses the best available techniques and mentions the cost comparison among these techniques too. Recent developments in the research on the laboratory based arsenic removal techniques, like improvement of conventional techniques and advances in removal technology along with its scopes and limitations have also been reviewed.
Most heavy metals are well-known toxic and carcinogenic agents and when discharged into the wastewater represent a serious threat to the human population and the fauna and flora of the receiving ...water bodies. In the present review paper, the sources have discussed the industrial source of heavy metals contamination in water, their toxic effects on the fauna and flora and the regulatory threshold limits of these heavy metals. The various parameters of the biofiltration processes, their mechanism for heavy metals removal along with the kinetics of biofilters and its modeling aspects have been discussed. The comparison of various physico-chemical treatment and the advantages of biofiltration over other conventional processes for treatment of heavy metals contaminated wastewater have also been discussed. The applications of genetic engineering in the modification of the microorganisms for increasing the efficiency of the biofiltration process for heavy metals removal have been critically analyzed. The results show that the efficiency of the process can be increased three to six folds with the application of recombinant microbial treatment.
This paper presents the observations of the study on arsenic removal from a contaminated ground water (simulated) by adsorption onto Fe(3+) impregnated granular activated carbon (GAC-Fe). Fe(2+), ...Fe(3+) and Mn(2+) have also been considered along with arsenic species in the water sample. Similar study has also been done with untreated granular activated carbon (GAC) for comparison. The effects of adsorbent dose, particle size of adsorbent and initial arsenic concentration on the removal of As(T), As(III), As(V), Fe(2+), Fe(3+) and Mn(2+) have been discussed. Under the experimental conditions, the optimum adsorbent doses for GAC-Fe and GAC have been found to be 8 g/l and 24 g/l, respectively with an agitation time of 15 h. Particle size of the adsorbents (both GAC and GAC-Fe) has shown negligible effect on the removal of arsenic and Fe species. However, for Mn removal the effect of adsorbent particle size is comparatively more. Percentage removal of As(T), As(V) and As(III) increase with the decrease in initial arsenic concentration (As(0)). However, the increase in percentage removal of all the arsenic species with decrease in As(0) are less for higher value of As(0) (3000-500 ppb) than those of the lower value of As(0) (500-10 ppb). The % removal of As(T), As(III), As(V), Fe, and Mn were approximately 95%, 92.4%, 97.6%, 99% and 41.2%, respectively when 8 g/l GAC-Fe was used at the As(0) value of 200 ppb. However, for GAC these values were approximately 55.5%, 44%, 71%, 98% and 97%. The pH and temperature of the study were 7+/-0.1 and 30+/-1 degrees C, respectively.
In the present study, removal of methyl ethyl ketone (MEK), toluene,
n-butyl acetate and
o-xylene (MTBX) emitted from the paint industry was carried out in a coal based biotrickling filter. When the ...influent MTBX loadings were less than 120
g
m
−3
h
−1, nearly 100% removal could be achieved. A maximum elimination capacity of 184.86
g
m
−3
h
−1 was obtained at a MTBX load of 278.27
g
m
−3
h
−1 with an empty bed residence time of 42.4
s in phase V. Results showed that the condition was the most favorable for
n-butyl acetate degradation followed by MEK, toluene and then
o-xylene. The corresponding maximum removal rate,
r
max values of MTBX were calculated as 0.085, 0.033, 0.16 and 0.024
g
m
−3
h
−1, respectively. Standard deviation of error in prediction of MEK, toluene and
o-xylene removal were within limit of 10%, while in the case of
n-butyl acetate this was approximately 60%. The MTBX concentration profiles along the depth were also determined by using convection-diffusion reaction (CDR) model. It was observed that at low concentration and low flow rate, the model is in good agreement with the experimental values for MEK, toluene and
n-butyl acetate, but for
o-xylene the model results deviated from the experimental.
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•Toxic and copious algal bloom as a promising feedstock for C. pyrenoidosa.•Acid autoclave hydrolysis showed maximum nitrogen, phosphate and carbon content.•Maximum biomass ...productivity (436mg/L/d) obtained in acid autoclave medium.•High lipid content (43%) accumulated in acid autoclave hydrolysis medium.•Acid autoclave hydrolysis had most appropriate FAME profile.
In the present investigation, toxic algal bloom, a copious and low-cost nutrient source was deployed for cultivating Chlorella pyrenoidosa. Various pre-treatment methods using combinations of acid/alkali and autoclave/microwave were tested for preparing hydrolysates and compared with minimal media (BG-11). Acid autoclave treatment resulted in maximum carbon, nitrogen and phosphorous content which substantially boosted the growth of the microalgal cells (4.36g/L) as compared to rest of the media. The microalga grown in this media also showed enhanced lipid content (43.2%) and lipid productivity (188mg/L/d) as compared to BG-11 (19.42mg/L/d). The biochemical composition showed 1.6-fold declines in protein while 1.27 folds in carbohydrate content as compared to BG-11. The fatty acid profile revealed the presence of C14-C22 with increased amount of monounsaturated fatty acids as compared to BG-11. The results obtained showed that algal bloom can be used as a potential nutrient source for microalgae.
This paper presents the observations on the bio-removal of arsenic from contaminated water by using
Ralstonia eutropha MTCC 2487 and activated carbon in a batch reactor. The effects of agitation ...time, pH, type of granular activated carbon (GAC) and initial arsenic concentration (As
o) on the % removal of arsenic have been discussed. Under the experimental conditions, optimum removal was obtained at the pH of 6–7 with agitation time of 100
h. The % removal of As(T) increased initially with the increase in As
o and after attaining the maximum removal (∼86%) at the As
o value of around 15
ppm, it started to decrease. Simultaneous adsorption bioaccumulation (SABA) was observed, when fresh GAC was used as supporting media for bacterial immobilization. In case of SABA, the % removal of As(III) was almost similar (only ∼1% more) to the additive values of individual removal of As(III) obtained by only adsorption and only bio-adsorption. However, for As(V) the % removal was less (∼8%) than the additive value of the individual % removals obtained by only adsorption and bio-adsorption. Percentage removal of Fe, Mn, Cu and Zn were 65.17%, 72.76%, 98.6% and 99.31%, respectively. Maximum regeneration (∼99.4%) of the used bio-adsorbent was achieved by the treatment with 5NH
2SO
4 followed by 1N NaOH and 30% H
2O
2 in HNO
3. The fitness of the isotherms to predict the specific uptake for bio-adsorption/accumulation process has been found to decrease in the following order: Temkin isotherm
>
Langmuir isotherm
>
Freundlich isotherm. For the adsorption process with fresh GAC the corresponding order is Freundlich isotherm
>
Langmuir isotherm
>
Temkin isotherm for As(V) and As(T). However, for As(III) it was Langmuir
>
Temkin
>
Freundlich.
This paper presents the observations of the study on arsenic removal from a contaminated ground water (simulated) by adsorption onto Fe3+ impregnated granular activated carbon (GAC-Fe). Fe2+, Fe3+ ...and Mn2+ have also been considered along with arsenic species in the water sample. Similar study has also been done with untreated granular activated carbon (GAC) for comparison. The effects of adsorbent dose, particle size of adsorbent and initial arsenic concentration on the removal of As(T), As(III), As(V), Fe2+, Fe3+ and Mn2+ have been discussed. Under the experimental conditions, the optimum adsorbent doses for GAC-Fe and GAC have been found to be 8g/l and 24g/l, respectively with an agitation time of 15h. Particle size of the adsorbents (both GAC and GAC-Fe) has shown negligible effect on the removal of arsenic and Fe species. However, for Mn removal the effect of adsorbent particle size is comparatively more. Percentage removal of As(T), As(V) and As(III) increase with the decrease in initial arsenic concentration (As0). However, the increase in percentage removal of all the arsenic species with decrease in As0 are less for higher value of As0 (3000-500ppb) than those of the lower value of As0 (500-10ppb). The % removal of As(T), As(III), As(V), Fe, and Mn were 95%, 92.4%, 97.6%, 99% and 41.2%, respectively when 8g/l GAC-Fe was used at the As0 value of 200ppb. However, for GAC these values were 55.5%, 44%, 71%, 98% and 97%. The pH and temperature of the study were 7+/-0.1 and 30+/-1 deg C, respectively.
Biofiltration of air stream containing mixture of benzene, toluene, ethyl benzene and
o-xylene (BTEX) has been studied in a lab-scale biofilter packed with a mixture of compost, sugar cane bagasse ...and granulated activated carbon (GAC) in the ratio 55:30:15 by weight. Microbial acclimation was achieved in 30 days by exposing the system to average BTEX inlet concentration of 0.4194
g
m
−3 at an empty bed residence time (EBRT) of 2.3
min. Biofilter achieved maximum removal efficiency more than 99% of all four compounds for throughout its operation at an EBRT of 2.3
min for an inlet concentration of 0.681
g
m
−3, which is quite significance than the values reported in the literature. The results indicate that when the influent BTEX loadings were less than 68
g
m
−3
h
−1 in the biofilter, nearly 100% removal could be achieved. A maximum elimination capacity (EC) of 83.65
g
m
−3
h
−1 of the biofilter was obtained at inlet BTEX load of 126.5
g
m
−3
h
−1 in phase IV. Elimination capacities of BTEX increased with the increase in influent VOC loading, but an opposite trend was observed for the removal efficiency. The production of CO
2 in each phase (g
m
−3
h
−1) was also observed at steady state (i.e. at maximum removal efficiency). Moreover, the high concentrations of nitrogen in the nutrient solution may adversely affect the microbial activity possibly due to the presence of high salt concentrations. Furthermore, an attempt was also made to isolate the most profusely grown BTEX-degrading strain. A Gram-positive strain had a high BTEX-degrading activity and was identified as
Bacillus sphaericus by taxonomical analysis, biochemical tests and 16S rDNA gene analysis methods.
In the present study, a thorough investigation has been done on the removal efficiency of both As(III) and As (V) from synthetic wastewater by phycoremediation of Botryococcus braunii algal biomass. ...Artificial neural networks (ANNs) are practised for predicting % phycoremediation efficiency of both As(III) and As(V) ions. The influence of several parameters for example initial pH, inoculum size, contact time and initial arsenic concentration (either As(III) or As(V)) was examined systematically. The maximum phycoremediation of As(III) and As(V) was found to be 85.22% and 88.15% at pH9.0, equilibrium time of 144h by using algal inoculum size of 10% (v/v) and initial arsenic concentration of 50mg/L. The data acquired from laboratory scale experimental set up was utilized for training a three-layer feed-forward back propagation (BP) with Levenberg–Marquardt (LM) training algorithm having 4:5:1 architecture. A comparison between the experimental data and model outputs provided a high correlation coefficient (R2all_ANN equal to 0.9998) and exhibited that the model was capable for predicting the phycoremediation of both As(III) and As(V) from wastewater. The network topology was optimized by changing number of neurons in hidden layers. ANNs are efficient to model and simulate highly non–liner multivariable relationships. Absolute error and Standard deviation (SD) with respect to experimental output were calculated for ANN model outputs. The comparison of phycoremediation efficiencies of both As(III) and As(V) between experimental results and ANN model outputs exhibited that ANN model can determine the behaviour of As(III) and As(V) elimination process under various circumstances.
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•Optimization of phycoremediation process parameters using Bortycoccus braunii was done.•ANN model was developed for predicting phycoremediation efficiency.•CSCF technique was used to increase data points.•Three-layer feed-forward back propagation learning algorithm was used.
Recent technological advances in the area of wide-area measurement systems (WAMS) has enabled the use of a combination of measured signals from remote locations for centralized control purpose. The ...transmitted signals can be used for multiple swing mode damping using a single controller. However, there is an unavoidable delay involved before these signals are received at the controller site. To ensure satisfactory performance, this delay needs to be taken into account in the control design stage. This paper focuses on damping control design taking into account a delayed arrival of feedback signals. A predictor-based H/sub /spl infin// control design strategy is discussed for such time-delayed systems. The concept is utilized to design a WAMS-based damping controller for a prototype power system using a static var compensator. The controller performance is evaluated for a range of operating conditions.
