Ligy Philip

Groundwater quality in the towns of Namakkal and Erumaipatti in India was studied to understand the nexus between surface sanitation and groundwater quality in hard rock regions. In total, 32 wells, both shallow open and deep bore wells, were monitored over a two-year period. The presence of fecal coliforms (FCs) up to 600 CFU/100 mL in wells as deep as 100 m showed that bacteriological contamination had reached deep aquifers through fractures and fissures. Statistical analyses showed that bore wells located in Namakkal were bacteriologically more contaminated than those in Erumaipatti (p = 0.017 for FC) because of urbanization, the type of top soil and the shallow groundwater table. Wells in densely toileted areas of Namakkal were more contaminated than those located in open defecation areas. After replacing a soak pit with a septic tank, concentrations of FC and chemical oxygen demand (COD) in the leachate at a depth of 2.1 m reduced from 2,500 to 1,000 CFU/100 mL and from 200 to 50 mg/L, respectively, after 150 days of the construction of septic tanks. To improve the hygiene and sanitation, the provision of toilets along with on-site waste management systems, capable of achieving required effluent quality, are essential.

Pilot scale studies were carried out to evaluate the suitability of bioremediation of Cr(VI) contaminated aquifers using bio-barrier and reactive zone technologies, employing chromium reducing bacteria. Experimental results showed that a 10. cm thick bio-barrier with an initial biomass concentration of 0.44. mg/g of soil was able to completely contain a Cr(VI) plume of 50. mg/L concentration, when the Darcy velocity was 0.0196. cm/h. In the case of reactive zone technology, a system with four injection wells was effective even when Cr(VI) concentration in the plume was as high as 250. mg/L, when 150. g (wet weight) of bacteria were injected into each injection well. A mathematical model was proposed for simulating the bioremediation process. Though the model could predict the over all trends observed in the experiments, it is limited by the assumption of homogeneous conditions. © 2010 Elsevier B.V.

In the present study, an attempt was made to evaluate the performance of a solar and wind aided cross-flow evaporator prototype as an alternative to conventional evaporators for concentrating reverse osmosis (RO) rejects. The performance of the solar and wind aided cross-flow evaporator was evaluated for different operating conditions such as (i) wind velocity, (ii) relative humidity in the ambient air, (iii) temperature of inlet water, (iv) trickling rate and (v) different packing geometries. Empirical correlations for evaporation loss were developed, as a function of the above variables. Among the various synthetic and natural media tried, plastic flexi ring was the most effective. Solar and wind aided cross-flow evaporator with random packing performed better than that with structured packing, as long as the air flow is not blocked by the packing. Studies revealed that the exposed surface area and depth of packing in the direction of wind are the important dimensions of the natural evaporator. It was also found that solar pre heating significantly increased the evaporation rate. Evaporation rate decreased as the concentration of salt in the water increased. © 2013 Elsevier B.V.

Volatile Organic Carbon (VOC) emissions from industries typically consist of a mixture of compounds of different chemical properties. The biodegradation kinetics of individual VOCs often get affected in the presence of other VOC species. In the present study, biodegradation kinetics of different multiple substrate mixtures of common industrial ketones viz. methyl ethyl ketone (M) and methyl iso-butyl ketone (B); and mono-aromatic VOCs such as toluene (T), ethyl benzene (EB) and o-xylene (X) were studied. Acclimatized aerobic bacterial consortium was used for the biodegradation study. A general mixed-substrate biodegradation model was developed which can describe the biodegradation kinetics of common industrial VOCs when present as a mixture, incorporating biokinetic parameters obtained from single substrate biodegradation studies. This model also employs a parameter for interaction effect, which may be obtained from biodegradation studies with binary mixtures. Three types of basic inhibitions, possible in the biodegradation of any mixture i.e. (i) self-substrate inhibition, (ii) interactive inhibition among VOCs of similar chemical nature and (iii) inhibition due to dissimilar VOC species, are considered in the general model. The performance of the proposed model was evaluated using the experimental data obtained from a previously published work, as well as from relevant data reported in the literature. High E-values obtained consistently for the simulations indicated good performance of the proposed model. This general model can be used for simulating the biodegradation of mixtures of similar/dissimilar VOCs and may be helpful in the optimal design of biological systems treating multiple VOCs. © 2013 Elsevier B.V.

In this study, the performance of a biotrickling filter (BTF) treating complex mixtures of VOCs from pharmaceutical industries was evaluated. Effects of inlet loading rate (ILR) and empty bed residence time (EBRT) on elimination capacity (EC) and removal efficiency (RE) were evaluated. Methanol, ethanol, acetone and toluene were taken as model pollutants. The net inlet concentration was varied from 1 to 4g/m3 to achieve an ILR variation from 52 to 419g/m3/h, while the EBRT was varied from 25 to 69s. The BTF was able to completely degrade the VOCs up to an ILR of 240g/m3/h, while treating mixed pollutants. On the other hand, 100% RE was achieved for ILRs up to 320g/m3/h in case of single pollutants and the corresponding maximum elimination capacity (ECmax) for ethanol and acetone was 380g/m3/h. However, the ECmax was only 320g/m3/h for the BTF treating mixed pollutants. Competitive interactions between different pollutants resulted in significantly lower ECmax for individual pollutants in a mixed pollutant system than those in a single pollutant system. Toluene was the most resistant to degradation, followed by acetone, among the four pollutants studied. It was found that much of the degradation of ethanol and methanol occurred in the first 30cm of BTF. It was also observed that the ILR and nature of the pollutants significantly affected the RE achieved at different EBRTs. Results from this study help in selecting the operational parameters for optimal performance of a BTF treating complex mixtures of VOCs emitted from pharmaceutical industries. © 2012 Elsevier B.V.

Saturated and unsaturated sand and soil column experiments were conducted to study the complex interaction between the effects of biological and hydrological factors on the transport of bacteria through a porous medium. These experiments were conducted with continuous input of bacteria and substrate at the inlet to reflect the groundwater contamination caused by leaking septic tanks and leach pits. Experiments were conducted with metabolically active and inactive Escherichia coli. Cell surface characteristics and batch experimental data for bacterial attachment were correlated with the transport behaviour in continuous column studies. Normalized breakthrough concentration for metabolically inactive cells (C/C0 = 0.74 in sand) was higher than that for active cells (C/C0 = 0.68 in sand) owing to change in cell surface characteristics. A similar trend was observed in the case of transport through soil columns. There was an increase of 29.5% in the peak C/C0 value at the outlet when the flow velocity was increased from 0.0535 cm/h (C/C0 = 0.61) to 0.214 cm/h (C/C0 = 0.79) in case of sand columns. However, this difference was only 20% in case of soil columns. Peak normalized concentrations at the outlet were less in soil column as compared to those in sand column because of lesser grain size. Unlike the earlier studies with pulse input, present experiments with continuous input of metabolically active bacteria along with substrate indicated that the normalized concentration at the outlet increased with increased concentration at the inlet. It was found that unsaturated conditions led to more retention of bacteria in both sand and soil columns. In case of sand columns, the normalized concentration at the exit reduced to as much as 0.46. It was also found that the existing mathematical models based on macroscopic advection–dispersion–filtration equations could satisfactorily simulate the bacterial transport except in a case where the substrate was added to the bacteria in the column studies.

Present study focused on the degradation of a mixture of phenol, cresol, xylenol, quinoline, and indole along with cyanide, commonly found in coke oven wastewater, using aerobic mixed culture. It was found that xylenol and indole were difficult to degrade, when the concentrations were above 250. mg/L. It was observed that free cyanide (2.5. mg/L and above) has the potency to holdup the oxidation of organics (250. mg/L) until the cyanide concentration drops to a minimum level. Final TOC in the mixed pollutant system was less than 4. mg/L, indicating the absence of other organic byproducts. Experimental results highlight effect of free cyanide on removal of organics and the combined toxic influence of cyanide and organics on the microbes treating coking wastewater. The proposed mathematical model was able to predict the biodegradation of mixed pollutant system satisfactorily. © 2012 Elsevier Ltd.

At present, mechanical evaporators are being used by the textile and dyeing units in Tirupur, South India, to further concentrate the discharge from Reverse Osmosis (RO) units. A large amount of wood is burnt as fuel, leading to air pollution and destruction of the natural habitat. To circumvent this problem, the evaporation of water in a cross flow tower configuration has been experimentally studied recently [L. Philip, Reddy, K. S., B. Kumar, B. S. Murty, A. Kannan, Performance evaluation of a solar and wind aided cross-flow evaporator for RO reject management, Desalination 317 (2013) 1-10]. A rigorous mathematical modeling and process simulation approach is now demonstrated for performance analysis and design of wind aided evaporators. Experimental conditions involving different packing configurations including sticks sourced from natural vegetation were simulated. The simulation predictions were fitted to the experimental results and the Number of Transfer Units (NTU) was identified. Under conditions of low relative humidity and high water inlet temperature, significant evaporation rates could be achieved. In drier places, the proposed concept offers considerable promise. Numerical simulation enables quick design and performance evaluation of wind aided evaporation schemes that may be incorporated in different industries facing RO reject management problems. © 2014 Elsevier B.V.

Trench-type biobarrier is one of the commonly used in situ systems for bioremediation of contaminated aquifers. Design variables for such a system are the length of the biobarrier, L, initial microbial concentration, M0, and inlet substrate concentration, S0. In this work, a procedure, based on a simple mathematical model, was developed for obtaining the interrelationship between these design variables for containing Cr(VI) in contaminated confined aquifers. The microbial characteristics used in this study were obtained by batch and bench scale column studies. A simulation-optimization model is presented for obtaining the screening level optimal solutions, corresponding to a minimal cost. Variation of values of design variables are presented as a function of a nondimensional parameter π1, which represents the relative magnitude of microbial growth rate and aquifer flow conditions. As π1 increases, the optimal length of the biobarrier and, hence, the cost of the treatment system is reduced. The screening level design procedure presented here can be the starting point for design using more sophisticated mathematical models. © 2007 ASCE.

The present study investigated the use of a novel clay composite adsorbent in simultaneous removal of hydrophilic and hydrophobic pharmaceuticals in a fixed bed column. The potential of a biologically active clay composite adsorbent in removing the pharmaceuticals was examined in detail. The mechanism of adsorption was elucidated based on an equilibrium sorption and mass transfer approach. The effects of dispersion, mass transfer zone, empty bed contact time, and an interfering substance such as humic acid on column operation were investigated in detail. It was observed that adsorption was the dominating mechanism of removal in the biologically active adsorbent column, and the amount of biodegradation gradually increased with an increase in contact time. Breakthrough behaviors of pharmaceuticals were numerically simulated using an equilibrium sorption approach as well as a mass transfer approach. Although both the equilibrium sorption model (EQM) and linear driving force (LDF) model predicted breakthrough behaviors satisfactorily, tailing of the breakthrough curve was better predicted by the LDF model. On the basis of the LDF model, surface diffusion coefficients for atenolol, ciprofloxacin, and gemfibrozil were estimated to be 6.5 × 10-4, 9.4 × 10-4, and 1.2 × 10-3 cm/h, respectively.