Prabirkumar Saha

Biodegradation of phenol and m-cresol in a batch and fed batch operated internal loop airlift bioreactor by indigenous mixed microbial culture predominantly Pseudomonas sp.

An internal loop airlift reactor (ILALR) is developed and studied for biodegradation of phenol/m-cresol as single and dual substrate systems under batch and fed batch operation using an indigenous mixed microbial strain, predominantly Pseudomonas sp. The results showed that the culture could degrade phenol/m-cresol completely at a maximum concentration of 600mgl(-1) and 400mgl(-1), respectively. Batch ILALR study has revealed that phenol has been preferentially degraded by the microbial culture rather than m-cresol probably owing to the toxic effect of the later. Sum kinetic model evaluated the interaction between the phenol/m-cresol in dual substrate system, which resulted in a high coefficient of determination (R(2)) value >0.98). The fed batch results showed that the strain was able to degrade phenol/m-cresol with maximum individual concentrations 600mgl(-1) each in 26h and 37h, respectively. Moreover for fed batch operation, degradation rates increased with increase in feed concentration without any lag in the degradation profile.

Batch growth kinetics of an indigenous mixed microbial culture utilizing m-cresol as the sole carbon source

An indigenous mixed microbial culture, isolated from a sewage treatment plant located in Guwahati was used to study biodegradation of m-cresol in batch shake flasks. m-Cresol concentration in the growth media was varied from 100mg/L to 900mg/L. The degradation kinetics was found to follow a three-half-order model at all initial m-cresol concentrations with regression values greater than 0.97. A maximum observed specific degradation rate of 0.585h(-1) was observed at 200mg/L m-cresol concentration in the medium. In the range of m-cresol concentrations used in the study, specific growth rate of the culture and specific degradation rates were observed to follow substrate inhibition kinetics. These two rates were fitted to kinetic models of Edward, Haldane, Luong, Han-Levenspiel, and Yano-Koga that are used to explain substrate inhibition on growth of microbial culture. Out of these models Luong and Han-Levenspiel models fitted the experimental data best with lowest root mean square error values. Biokinetic constants estimated from these two models showed good potential of the indigenous mixed culture in degrading m-cresol in wastewaters.

Kinetics of phenol and m-cresol biodegradation by an indigenous mixed microbial culture isolated from a sewage treatment plant

An acclimatized mixed microbial culture, predominantly Pseudomonas sp., was enriched from a sewage treatment plant, and its potential to simultaneously degrade mixtures of phenol and m-cresol was investigated during its growth in batch shake flasks. A 2(2) full factorial design with the two substrates at two different levels and different initial concentration ranges (low and high), was employed to carry out the biodegradation experiments. The substrates phenol and m-cresol were completely utilized within 21 h when present at low concentrations of 100 mg/L for each, and at high concentration of 600 mg/L for each, a maximum time of 187 h was observed for their removal. The biodegradation results also showed that the presence of phenol in low concentration range (100-300 mg/L) did not inhibit m-cresol biodegradation. Whereas the presence of m-cresol inhibited phenol biodegradation by the culture. Moreover, irrespective of the concentrations used, phenol was degraded preferentially and earlier than m-cresol. A sum kinetics model was used to describe the variation in the substrate specific degradation rates, which gave a high coefficient of determination value (R2 > 0.98) at the low concentration range of the substrates. From the estimated interaction parameter values obtained from this model, the inhibitory effect of phenol on m-cresol degradation by the culture was found to be more pronounced compared to that of m-cresol on phenol. This study showed a good potential of the indigenous mixed culture in degrading mixed substrate of phenolics.

Treatment of phenolics containing synthetic wastewater in an internal loop airlift bioreactor (ILALR) using indigenous mixed strain of Pseudomonas sp. under continuous mode of operation

The scope of this study is to evaluate the performance of internal loop airlift bioreactor (ILALR) in treating synthetic wastewater containing phenol and m-cresol, in single and multi component systems. The microbe utilized in the process was an indigenous mixed strain of Pseudomonas sp. isolated from a wastewater treatment plant. The reactor was operated at both lower and higher hydraulic retention times (HRTs) i.e., 4.1 and 8.3 h, respectively, by providing an inlet feed flow rate of 5 and 10 mL/min. Shock loading experiments were also performed up to a maximum concentration of 800 mg/L for phenol at 8.3 h HRT and 500 mg/L for m-cresol at 4.1 h HRT. The study showed complete degradation of both phenol and m-cresol, when they were degraded individually at a HRT of 8.3 h. Experiments with both phenol and m-cresol present as mixtures were performed based on the 2(2) full factorial design of experiments.

Studies on the stability of a supported liquid membrane and its cleaning protocol

This paper is a logical continuation of the previous work published by Manna et al. in RSC Adv., 2014, 4, 26247. The referenced paper established a technique for the separation and recovery of trace amounts of bioactive catechins from tea extract and their subsequent iron complexation through a Flat Sheet Supported Liquid Membrane (FS-SLM). However the technique suffers problems such as instability and fouling of the membrane support. In this work, the issues related to the instability and fouling of the SLM have been investigated. The components of the process such as the solvent, aqueous phases, membrane support, electrolyte, surfactant etc. were extensively studied to detect the best operating condition that would yield a better stability. Critical displacement pressure differentials (ΔPc) for the liquid membrane were determined. Thermodynamic aspects of emulsion formation were investigated with the addition of surfactants. Under the best conditions, the membrane was found to be stable for 120 hours with a flux (of catechin) of 23.34 × 10−8 kg m−2 s−1. The best conditions for the FS-SLM were re-employed in a similar experiment using a hollow fiber supported liquid membrane (HF-SLM) module. An experimentally evolved membrane cleaning protocol is reported.s

Iron complexation of pharmaceutical catechins through selective separation

Catechins, natural polyphenols from tea leaves are important building blocks in pharmaceutical industries due to their chemoprotective and cardioprotective effects. The concept of metal complexation of catechins is integrated with liquid membrane based selective separation technique for recovery of pharmaceutical catechins from natural bio-sources. This is first ever approach to amalgamate the complexation chemistry with engineering approach which is green and energy efficient.

Separation of toxic heavy metals from its aqueous solution using environmentally benign vegetable oil as liquid membrane

This paper presents an experimental investigation of simultaneous extraction and recovery of harmful heavy metals from the industrial wastewater through Bulk Liquid Membrane (BLM) based technology. The selective extraction and stripping are achieved through the transportation of two such heavy metals viz., lead and cadmium. The environmentally benign coconut oil is selected as solvent of the Liquid Membrane (LM) through two phase equilibrium studies. Same studies are performed to optimize various physico-chemical parameters, such as pH of feed phase, concentrations of feed and strip phases, temperature, speed of stirring of feed phase, run time (duration of extraction), concentration of carrier etc., on the extraction of cadmium. The performance of LM is enhanced with respect to run time by the use of a suitable extracting agent i.e. carrier. Three phase transportation studies are thereby conducted through BLM at the same optimized operating parameters obtained in two phase studies. The extraction and recovery are found to be 72% and 64%, respectively. Further experimentations through BLM were conducted for transportation of lead with the same set of operating parameters. Both the extraction (82%) and recovery (77%) are found comparatively higher for lead as opposed to that of cadmium.

Chapter Five – Liquid – Membrane Filters

This chapter introduces the basic concept of liquid membrane (LM) technology; theoretical background on the transport of a solute through LM; the underlying mechanisms of transport like passive and active transports; types of transport of solute like cationic, anionic, neutral and switchable transport; various types of LM configurations like bulk liquid membrane, emulsion liquid membrane and supported liquid membrane with merits and demerits of each configurations; types and role of carriers and solvents; selection of carrier and solvent; applicability potential of various environmentally benign solvents and stability aspects of various LM configurations. It then takes up some case studies based on literature reported information, which has been divided into three major categories such as transport of organic solute, inorganic solute and bioactive compounds. One example for each case has been discussed in detail. The cases considered are separation of lignosulphonate, mercury (II), and catechin. Optimization of solvent–carrier combination, extraction and stripping conditions, selection of support material, etc., have been suitably discusses. Performances of the various LM configurations are highlighted and discussed based on percentage extraction and recovery of the solutes.

Hydrodynamics and batch biodegradation of phenol in an Internal Loop Airlift Reactor

Determination of Residence Time Distribution (RTD), oxygen volumetric mass transfer coefficient (kLa) and mixing pattern in an Internal Loop Airlift Reactor (ILALR) for both living and nonliving systems have been investigated in this paper. Optimal operating condition is found at a gas flow rate of 2 l min−1. The estimated kLa values for nonliving and living system at 27°C are 0.004 s−1 and 0.017 s−1 respectively. Batch biodegradation of phenol with an initial concentration of 300 mg l−1 by the mixed microbial culture occurs at a very high degradation rate (0.16 mg l−1 h−1).

Modeling and Control of a Complex Interacting Process

In this paper, two efficient control algorithms are discussed viz., Linear Quadratic Regulator (LQR) and Dynamic Matrix Controller (DMC) and their applicability has been demonstrated through case study with a complex interacting process viz., a laboratory based four tank liquid storage system. The process has Two Input Two Output (TITO) structure and is available for experimental study. A mathematical model of the process has been developed using first principles. Model parameters have been estimated through the experimentation results. The performance of the controllers (LQR and DMC) has been compared to that of industrially more accepted PID controller.