Removal of arsenic by Acidothiobacillus ferrooxidans bacteria in bench scale fixed-bed bioreactor system

In the present study arsenic contaminated simulated water and groundwater was treated by the combination of biological oxidation of tri-valent arsenite [As (III)] to penta-valent arsenate [As (V)] in presence of Acidothiobacillus ferrooxidans bacteria and its removal by adsorptive filtration in a bioreactor system. This method includes the immobilisation of A.ferrooxidans on Granulated Activated Carbon (GAC) capable of oxidising ferrous [Fe (II)] to ferric [Fe (III)]. The Fe (III) significantly converts the As (III) to As (V) and ultimately removed greater than 95% by the bed of GAC, limestone, and sand. The significant influence of Fe (II) concentration (0.1–1.5?gL^?1), flowrate (0.06–0.18?Lh^?1), and initial As (III) concentration (100–1000?µgL^?1) on the arsenic removal efficiency was investigated. The simulated water sample containing the different concentration of As (III) and other ions was used in the study. The removal of other co-existing ions present in contaminated water was also investigated in column study. The concentration of arsenic was found to be <10?µgL^?1 which is below Maximum Contaminant Level (MCL) as per WHO in treated water. The results confirmed that the present system including adsorptive-filtration was successfully used for the treatment of contaminated water containing As (III) ions.     

Recovery of hydrogen and removal of nitrate from water by electrocoagulation process

The present study provides an optimization of electrocoagulation process for the recovery of hydrogen and removal of nitrate from water. In doing so, the thermodynamic, adsorption isotherm, and kinetic studies were also carried out. Aluminum alloy of size 2 dm² was used as anode and as cathode. To optimize the maximum removal efficiency, different parameters like effect of initial concentration, effect of temperature, pH, and effect of current density were studied. The results show that a significant amount of hydrogen can be generated by this process during the removal of nitrate from water. The energy yield calculated from the hydrogen generated is 3.3778 kWh/m³. The results also showed that the maximum removal efficiency of 95.9 % was achieved at a current density of 0.25 A/dm², at a pH of 7.0. The adsorption process followed second-order kinetics model. The adsorption of NO ₃ ^? preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules. Thermodynamic studies showed that adsorption was exothermic and spontaneous in nature. The energy yield of generated hydrogen was ~54 % of the electrical energy demand of the electrocoagulation process. With the reduction of the net energy demand, electrocoagulation may become a useful technology to treat water associated with power production. The aluminum hydroxide generated in the cell removes the nitrate present in the water and reduced it to a permissible level making the water drinkable.     

Enhanced degradation of organic contaminants using catalytic activity of carbonaceous structures: A strategy for the reuse of exhausted sorbents

Generation of hydroxyl radicals (?OH) is the basis of advanced oxidation process (AOP). This study investigates the catalytic activity of microporous carbonaceous structure for in-situ generation of ?OH radicals. Biochar (BC) was selected as a representative of carbon materials with a graphitic structure. The work aims at assessing the impact of BC structure on the activation of H₂O₂, the reinforcement of the persistent free radicals (PFRs) in BC using heavy metal complexes, and the subsequent AOP. Accordingly, three different biochars (raw, chemically- and physiochemically-activated BCs) were used for adsorption of two metal ions (nickel and lead) and the degradation of phenol (100 mg/L) through AOP. The results demonstrated four outcomes: (1) The structure of carbon material, the identity and the quantity of the metal complexes in the structure play the key roles in the AOP process. (2) the quantity of PFRs on BC significantly increased (by 200%) with structural activation and metal loading. (3) Though the Pb-loaded BC contained a larger quantity of PFRs, Ni-loaded BC exhibited a higher catalytic activity. (4) The degradation efficiency values for phenol by modified biochar in the presence of H₂O₂ was 80.3%, while the removal efficiency was found to be 17% and 22% in the two control tests, with H₂O₂ (no BC) and with BC (no H₂O₂), respectively. Overall, the work proposes a new approach for dual applications of carbonaceous structures; adsorption of metal ions and treatment of organic contaminants through in-situ chemical oxidation (ISCO).     

A COMPARISON OF MODELS PREDICTING GROUND WATER LEVELS ON HILLSIDE SLOPES1

ABSTRACT: A comparative study of ground water level predictions on hillside slopes using two models is presented. The models are a simplified mass balance model that has components for evapotran-spiration, recharge, and drainage; and a two-dimensional finite difference model that employs kriging to estimate soil parameters and accounts for non-uniform thickness of the soil layer. These models are representative of a wide range of modeling capabilities and are used to illustrate the sensitivity of ground water level predictions to the sophistication of the modeling techniques. The drainage and recharge components of the two models are evaluated and the importance of unsaturated flow in recharge computations is underscored. Piezometric observations in a small drainage depression on the slope of Kennel Creek Valley in Tongass National Forest, Alaska, were used to evaluate the two models. The results show that, although the predictions differ from the field observations, the simple physically-based mass balance model predicts the ground water levels as well as the two-dimensional model. It is suggested that caution should be exercised in using complex models to validate simpler models.     

Studies of some biochemical changes in the tissues of Catla catla (Hamilton), Labeo rohita (Hamilton) and Cirrhinus mrigala (Hamilton) exposed to NH3-N,NO2-N and NO3-N

Biochemical changes, total proteins, glycogen, aspartate and alanine (AAT and ALAT) amino transferases were studied with exposure of sublethal concentrations of NH3-N, NO2-N and NO3-N to the freshwater fish Catla catla (Hamilton), Labeo rohita (Hamilton) and Cirrhinus mrigala (Hamilton). Depletion in the food reserves and enzyme activity was observed in all the three fish species exposed to these toxicants. Hence, the concentrations of NH3, NO2 and NO3 in water need to be monitored in water quality in aquaculture practices.     

Trends of surface water quality of the Krishna River,India during the urbanization process

In the present study, Amaravati, the proposed city of India is considered to assess the impacts of urbanization on water quality of the Krishna River in the vicinity. Long-term surface water quality data of various parameters of Krishna River are obtained from Central Water Commission (CWC). Trends of various parameters are analyzed using a modified version of Mann-Kendall (M-K) test; bootstrapped M-K trend test with optional bias corrected pre-whitening and R programming are used affecting water quality prior to and at the commencement of urbanization. During the onset of urbanization, minimum BOD is decreased from 0.49 to 0.2 mg/L, while the maximum BOD is increased by 67.7%. Dissolved oxygen's (DO) minimum value is decreased by 29.33% while maximum DO value is decreased by 4.47% at the beginning of urbanization. During the process of urbanization, total coliform's minimum count is increased to 330 from 2 MPN/100 ml while the maximum count of total coliforms is increased to 16,000 from 2400 MPN/100 ml. Faecal coilform's minimum count is increased from 2 to 80 MPN/100 ml while maximum count is increased to 16,000 from 800 MPN/100 ml during urbanization. It is found that due to urbanization, pH, DO values exceed the allowable limit.     

Remediation and toxicity of endocrine disruptors: a review

Environmental Chemistry Letters - Endocrine disruptors are hazardous chemicals with chronic health effects for most living organisms, inducing homeostasis, hormonal imbalances, cancer, reproductive...