Rakesh Govind - Profile on Academia.edu (original) (raw)

Papers by Rakesh Govind

Overview of air biofiltration - basic technology, economics and integration with other control technologies for effective treatment of air toxics

This paper provides an overview of air biofiltration with experimental data on the performance of... more This paper provides an overview of air biofiltration with experimental data on the performance of peat/compost, pelletized packed bed and structured media biofilters. It is shown that use of high surface area per unit volume structured media results in higher contaminant treatment rates per unit biofilter volume. Peat/compost biofilters exhibit lower removal efficiencies at high (> 100 ppmv) inlet contaminant concentrations and require control of media moisture content. Increase of temperature results in increasing biodegradation rates. It is shown that use of structured ceramic media allows effective control of biomass buildup by continuous removal of biomass from the biofilter media and that the biomass removal rate depends on nutrient flowrate. An experimental system is presented which enables biofilm kinetics to be determined and a simple biofilter model is developed in this paper. A group contribution approach has been developed to estimate biokinetic parameter which allows biofiltration effectiveness to be determined for a variety of volatile organic compounds (VOCs). Finally, a procedure is presented, illustrated by an example, which is used to develop an integrated process for effective treatment of air contaminants. 22 refs., 12 figs., 4 tabs.

Grace, J.R. 91986). contacting modes and behaviour classification of gas-solid and other two-phas... more Grace, J.R. 91986). contacting modes and behaviour classification of gas-solid and other two-phase suspensions,

Proceedings of the Water Environment Federation, 2010

As this paper was being finalized, world leaders were meeting in Copenhagen to lay the ground wor... more As this paper was being finalized, world leaders were meeting in Copenhagen to lay the ground work for a global agreement on climate change. Carbon dioxide is one of the main gases that has been implicated in global climate change or global climate disruption. Methods to control the atmospheric accumulation of carbon dioxide include scrubbing with alkaline solutions, adsorption, and bioconversion using cyanobacteria and phototrophic cultures. The first two methods are energy intensive processes and produce several environmentally unfriendly waste streams. In this paper, a novel technique for biofiltration of carbon dioxide by Tetraselmis suecica is presented here. The major advantages of using Tetraselmis suecica include: (1) the inherent buffering action of the marine algae that maintains the pH at 8.5; and (2) the requirement of a limited spectrum of light by the marine algae. Gallium-Aluminum-Arsenic (GaAlAs) light emitting diodes (LED's) emit light in the range required by Tetraselmis suecica. These GaAlAs LED's were put in series on both sides of the photobioreactor in a cascading manner for maximum photosynthesis activity. Laboratory scale experiments were carried out in a bubbling photobioreactor with different liquid recycle rate and photobioreactor conditions to determine the reaction kinetics and develop a process model that can be applied for a full-scale design. For liquid residence time of about 1 second, the carbon dioxide removal efficiency was about 4% in the photobioreactor. Further, the experimental data matched closely with the model calculations. Area requirement and pressure drop calculation carried out between a sparged bioreactor and spray chamber bioreactor for the same operating condition indicated spray chamber bioreactor to be a better alternative than a sparged bioreactor. In spray chamber bioreactor, the area requirements are about a 100 fold less than that for a sparged bioreactor. Also the pressure drop is negligible across the spray chamber bioreactor in comparison to a sparged bioreactor. Based on the process model, it has been determined that for separation of 7000 million tons CO 2 /year and 95 % removal efficiency, 15 units of 25 m diameter and 52 m height will be required.

Proceedings of the Water Environment Federation, 2000

Air emissions from manufacturing operations and waste treatment plants often consist of a combina... more Air emissions from manufacturing operations and waste treatment plants often consist of a combination of odors and volatile chemicals. Odors are inorganic or organic compounds, which are present in low concentrations, typically 20 ppmv or less, which have an unpleasant odor. While several U.S. EPA and OSHA regulations govern the emission of hazardous volatile chemicals in the ambient air and in the workplace, odor emissions are often a major nuisance to the plant workers and surrounding communities. Major advantages of biological treatment are ambient temperature and pressure operation, no generation of toxic by-products requiring disposal or further treatment, and favorable economics. Disadvantages associated with biological treatment are upsets due to inactivation of active microbial cultures, and lack of adequate knowledge to operate the process at peak capacity and performance level.

Theory of Emission of Volatile Compounds from Aeration Basins of Wastewater Treatment Plants

Proceedings of the Water Environment Federation, 2000

Computer-aided synthesis of process control systems

IEEE Transactions on Automatic Control, 1981

Development of Predictive Structure-Biodegradation Relationship Models with the Use of Respirometrically Generated Biokinetic Data

Water Science and Technology, Aug 1, 1992

Biodegradation is an important mechanism determining the fate of chemicals in the aquatic environ... more Biodegradation is an important mechanism determining the fate of chemicals in the aquatic environment. In this paper, experimental data, determined from electrolytic respirometry, for 27 compounds were analyzed using first order and Monod kinetics. Additional data from the literature were also used in our analysis. A method based on group contribution to predict first-order and Monod kinetic rate constants was developed and validated. The group contribution approach gave reasonable results for a variety of compounds. More kinetic data are required to extend the group contribution approach.

Sorption - From Fundamentals to Applications

Sorption in wastewater solids is an important removal mechanism for pollutants in biological trea... more Sorption in wastewater solids is an important removal mechanism for pollutants in biological treatment systems. It is often an overlooked mechanism, since traditionally, excess solids from biological treatment were land filled. However, with the emergence of using wastewater solids as a potential fertilizer, pollutants sorbed into the solids can re-emerge as soil pollutants, with potential uptake by crops, and even transported into groundwater. This is especially applicable for hydrophobic chemicals, like alkyl fluorinated compounds (PFAS, PFOS), which have recently received widespread attention as pollutants in water bodies across the globe. In this chapter, sorption of pollutants in wastewater solids has been presented from both a thermodynamic analysis, involving equilibrium parameters, as well as a kinetic process involving transport to the cell walls and permeation through the cell membranes. Based on experimental data and models it is shown that biodegradation in wastewater sy...

Process modeling for control system synthesis

IEEE Transactions on Automatic Control, 1977

Membrane reactor technology

Study of Biofilm Growth and Metabolic Activity Using Mpedimetry

Proceedings of the Water Environment Federation, 2010

Studies on a Swirling Circulating Fluidized Bed

Circulating Fluidized Bed Technology, 1988

ABSTRACT In this paper, a novel coal combustor termed “Swirling Circulating Fluidized Bed (SCFB)”... more ABSTRACT In this paper, a novel coal combustor termed “Swirling Circulating Fluidized Bed (SCFB)” has been studied. The SCFB is a circulating fluidized bed with tangential injection of the secondary air. Studies on hydrodynamics using cold model and combustion using a pilot plant have been conducted. The system has also been simulated and good agreement has been achieved with the experimental data. The advantages of the swirling action in the bed over the traditional circulating bed have been discussed.

Systematic generation of reaction pathways for manufacturing bulk industrial chemicals from carbon- neutral feed-stocks

Journal of Chemical Engineering & Process Technology, Oct 24, 2017

Biomass, Biorefineries and Bioeconomy, 2022

The objective of this work was to develop a systematic strategy for generating efficient, alterna... more The objective of this work was to develop a systematic strategy for generating efficient, alternate reaction paths that could be used to manufacture the top 100 industrial chemicals, currently produced from crude oil, using renewable feedstocks. Manufacturing these chemicals from oil, coal, or natural gas results in increasing carbon dioxide levels in the atmosphere, responsible for global climate change. The methodology employed here uses the existing knowledge on the conversion of carbon-neutral feedstocks, such as biomass, wood, etc., to suitable precursor raw materials. Known industrial reaction paths, currently used for manufacturing the top 100 industrial organic chemicals, are then combined with the known conversion of carbon-neutral feedstocks to systematically develop and evaluate alternate carbon-efficient reaction paths. The fractional carbon economy was determined from a comprehensive listing of industrial reactions paths, which also gives the yields and efficiencies of ...

As the scarcity of potable water increases, recycling of treated wastewater is increasing. Small-... more As the scarcity of potable water increases, recycling of treated wastewater is increasing. Small-scale, decentralized treatment can be implemented to serve local populations by keeping water within their boundaries and within reach for reuse, particularly in less dense, non-urban communities. Availability of cellular networks and high-speed internet connectivity, along with significant reduction in cost, allows ongoing monitoring of decentralized treatment systems at a central location. In this paper a decentralized treatment system using micro nanobubble aeration, moving media and membranes is able to produce reusable water with low energy consumption, thereby allowing the use of solar energy in places with unreliable electrical supply. The treatment system, which uses no external chemicals, is able to operate una ended and deliver clear, disinfected water with non-detect suspended solids, BOD5 less than 10 mg/L and nutrients below 5 mg/L.

Development of Structure Biodegradability Relationships (SBRs) for Estimating Half-Lives of Organic Contaminants in Soil Systems

Springer eBooks, 1996

Knowledge of half-lives or biodegradation rate constants in soil is useful for estimating the nat... more Knowledge of half-lives or biodegradation rate constants in soil is useful for estimating the natural attenuation rates of contaminants due to microbial transformations and to make decisions regarding treatment action or no treatment with isolation of the contaminated site to minimize exposure to animal and human life. Half-life is defined as the time required for 50 % of the contaminant to be biodegraded. Soil treatment is time consuming and expensive, and often for large isolated contaminated sites, relying on natural attenuation may be the most cost-effective solution. In this paper, a neural network is trained to estimate the range of half-lives for organic contaminants in soil. Soil half-life data, obtained from the literature for 258 chemicals is correlated with 14 molecular fragments or indicators using a back-propagation neural network with 14 input nodes, 12 nodes in the hidden layer and 2 output nodes. A cross-validation method was used to test the neural network. The converged neural network produced less than 50 % relative error for more than 80 % of the chemicals in the training set. Using a classification scheme of fast (half-life range of 1 to 7 days), moderately fast (half-life range from 7 to 28 days), slow (half-life range from 28 to 180 days) and resistant (half-life range from 180 to 365 days), the neural network was able to correctly classify more than 95 % of the 258 chemicals in the database.

Humana Press eBooks, Nov 14, 2003

Biokinetics and bioavailability protocol for organic pollutants in soil to enhance bioremediation

Bioremediation of polluted soil requires a fundamental understanding of biodegradation kinetics a... more Bioremediation of polluted soil requires a fundamental understanding of biodegradation kinetics and the physicochemical factors that control the rate of biodegradation. A systematic multi-level protocol based on three types of bioreactor systems, was developed to determine the biokinetic parameters of the suspended and immobilized microbiota and the transport and diffusivity parameters of soil contaminants and oxygen in the soil matrix. In the soil slurry reactor, significant biodegradation occurs in the aqueous phase by the suspended and immobilized microbiota and to some extent by the soil immobilized biofilms. The soil slurry reactor data were used to derive the biokinetic parameters for the suspended and immobilized microorganisms. The wafer reactor data were used to obtain additional information on biokinetic and transport parameters with oxygen limitation. The porous tube reactor data provided quantitative determination of oxygen diffusivity. In the soil tube reactor, oxygen l...

Development of Nonlinear Group Contribution Method for Prediction of Biodegradation Kinetics from Respirometrically Derived Kinetic Data

ACS Symposium Series, 1993

... Development of Nonlinear Group Contribution Method for Prediction of Biodegradation Kinetics ... more ... Development of Nonlinear Group Contribution Method for Prediction of Biodegradation Kinetics from Respirometrically Derived Kinetic Data Henry H. Tabak1 and Rakesh Govind2 ... He also attempted correlations using the steric and lipophilic constants but failed. Vaishnav et al. ...

Overview of air biofiltration - basic technology, economics and integration with other control technologies for effective treatment of air toxics

This paper provides an overview of air biofiltration with experimental data on the performance of... more This paper provides an overview of air biofiltration with experimental data on the performance of peat/compost, pelletized packed bed and structured media biofilters. It is shown that use of high surface area per unit volume structured media results in higher contaminant treatment rates per unit biofilter volume. Peat/compost biofilters exhibit lower removal efficiencies at high (> 100 ppmv) inlet contaminant concentrations and require control of media moisture content. Increase of temperature results in increasing biodegradation rates. It is shown that use of structured ceramic media allows effective control of biomass buildup by continuous removal of biomass from the biofilter media and that the biomass removal rate depends on nutrient flowrate. An experimental system is presented which enables biofilm kinetics to be determined and a simple biofilter model is developed in this paper. A group contribution approach has been developed to estimate biokinetic parameter which allows biofiltration effectiveness to be determined for a variety of volatile organic compounds (VOCs). Finally, a procedure is presented, illustrated by an example, which is used to develop an integrated process for effective treatment of air contaminants. 22 refs., 12 figs., 4 tabs.

Grace, J.R. 91986). contacting modes and behaviour classification of gas-solid and other two-phas... more Grace, J.R. 91986). contacting modes and behaviour classification of gas-solid and other two-phase suspensions,

Proceedings of the Water Environment Federation, 2010

As this paper was being finalized, world leaders were meeting in Copenhagen to lay the ground wor... more As this paper was being finalized, world leaders were meeting in Copenhagen to lay the ground work for a global agreement on climate change. Carbon dioxide is one of the main gases that has been implicated in global climate change or global climate disruption. Methods to control the atmospheric accumulation of carbon dioxide include scrubbing with alkaline solutions, adsorption, and bioconversion using cyanobacteria and phototrophic cultures. The first two methods are energy intensive processes and produce several environmentally unfriendly waste streams. In this paper, a novel technique for biofiltration of carbon dioxide by Tetraselmis suecica is presented here. The major advantages of using Tetraselmis suecica include: (1) the inherent buffering action of the marine algae that maintains the pH at 8.5; and (2) the requirement of a limited spectrum of light by the marine algae. Gallium-Aluminum-Arsenic (GaAlAs) light emitting diodes (LED's) emit light in the range required by Tetraselmis suecica. These GaAlAs LED's were put in series on both sides of the photobioreactor in a cascading manner for maximum photosynthesis activity. Laboratory scale experiments were carried out in a bubbling photobioreactor with different liquid recycle rate and photobioreactor conditions to determine the reaction kinetics and develop a process model that can be applied for a full-scale design. For liquid residence time of about 1 second, the carbon dioxide removal efficiency was about 4% in the photobioreactor. Further, the experimental data matched closely with the model calculations. Area requirement and pressure drop calculation carried out between a sparged bioreactor and spray chamber bioreactor for the same operating condition indicated spray chamber bioreactor to be a better alternative than a sparged bioreactor. In spray chamber bioreactor, the area requirements are about a 100 fold less than that for a sparged bioreactor. Also the pressure drop is negligible across the spray chamber bioreactor in comparison to a sparged bioreactor. Based on the process model, it has been determined that for separation of 7000 million tons CO 2 /year and 95 % removal efficiency, 15 units of 25 m diameter and 52 m height will be required.

Proceedings of the Water Environment Federation, 2000

Air emissions from manufacturing operations and waste treatment plants often consist of a combina... more Air emissions from manufacturing operations and waste treatment plants often consist of a combination of odors and volatile chemicals. Odors are inorganic or organic compounds, which are present in low concentrations, typically 20 ppmv or less, which have an unpleasant odor. While several U.S. EPA and OSHA regulations govern the emission of hazardous volatile chemicals in the ambient air and in the workplace, odor emissions are often a major nuisance to the plant workers and surrounding communities. Major advantages of biological treatment are ambient temperature and pressure operation, no generation of toxic by-products requiring disposal or further treatment, and favorable economics. Disadvantages associated with biological treatment are upsets due to inactivation of active microbial cultures, and lack of adequate knowledge to operate the process at peak capacity and performance level.

Theory of Emission of Volatile Compounds from Aeration Basins of Wastewater Treatment Plants

Proceedings of the Water Environment Federation, 2000

Computer-aided synthesis of process control systems

IEEE Transactions on Automatic Control, 1981

Development of Predictive Structure-Biodegradation Relationship Models with the Use of Respirometrically Generated Biokinetic Data

Water Science and Technology, Aug 1, 1992

Biodegradation is an important mechanism determining the fate of chemicals in the aquatic environ... more Biodegradation is an important mechanism determining the fate of chemicals in the aquatic environment. In this paper, experimental data, determined from electrolytic respirometry, for 27 compounds were analyzed using first order and Monod kinetics. Additional data from the literature were also used in our analysis. A method based on group contribution to predict first-order and Monod kinetic rate constants was developed and validated. The group contribution approach gave reasonable results for a variety of compounds. More kinetic data are required to extend the group contribution approach.

Sorption - From Fundamentals to Applications

Sorption in wastewater solids is an important removal mechanism for pollutants in biological trea... more Sorption in wastewater solids is an important removal mechanism for pollutants in biological treatment systems. It is often an overlooked mechanism, since traditionally, excess solids from biological treatment were land filled. However, with the emergence of using wastewater solids as a potential fertilizer, pollutants sorbed into the solids can re-emerge as soil pollutants, with potential uptake by crops, and even transported into groundwater. This is especially applicable for hydrophobic chemicals, like alkyl fluorinated compounds (PFAS, PFOS), which have recently received widespread attention as pollutants in water bodies across the globe. In this chapter, sorption of pollutants in wastewater solids has been presented from both a thermodynamic analysis, involving equilibrium parameters, as well as a kinetic process involving transport to the cell walls and permeation through the cell membranes. Based on experimental data and models it is shown that biodegradation in wastewater sy...

Process modeling for control system synthesis

IEEE Transactions on Automatic Control, 1977

Membrane reactor technology

Study of Biofilm Growth and Metabolic Activity Using Mpedimetry

Proceedings of the Water Environment Federation, 2010

Studies on a Swirling Circulating Fluidized Bed

Circulating Fluidized Bed Technology, 1988

ABSTRACT In this paper, a novel coal combustor termed “Swirling Circulating Fluidized Bed (SCFB)”... more ABSTRACT In this paper, a novel coal combustor termed “Swirling Circulating Fluidized Bed (SCFB)” has been studied. The SCFB is a circulating fluidized bed with tangential injection of the secondary air. Studies on hydrodynamics using cold model and combustion using a pilot plant have been conducted. The system has also been simulated and good agreement has been achieved with the experimental data. The advantages of the swirling action in the bed over the traditional circulating bed have been discussed.

Systematic generation of reaction pathways for manufacturing bulk industrial chemicals from carbon- neutral feed-stocks

Journal of Chemical Engineering & Process Technology, Oct 24, 2017

Biomass, Biorefineries and Bioeconomy, 2022

The objective of this work was to develop a systematic strategy for generating efficient, alterna... more The objective of this work was to develop a systematic strategy for generating efficient, alternate reaction paths that could be used to manufacture the top 100 industrial chemicals, currently produced from crude oil, using renewable feedstocks. Manufacturing these chemicals from oil, coal, or natural gas results in increasing carbon dioxide levels in the atmosphere, responsible for global climate change. The methodology employed here uses the existing knowledge on the conversion of carbon-neutral feedstocks, such as biomass, wood, etc., to suitable precursor raw materials. Known industrial reaction paths, currently used for manufacturing the top 100 industrial organic chemicals, are then combined with the known conversion of carbon-neutral feedstocks to systematically develop and evaluate alternate carbon-efficient reaction paths. The fractional carbon economy was determined from a comprehensive listing of industrial reactions paths, which also gives the yields and efficiencies of ...

As the scarcity of potable water increases, recycling of treated wastewater is increasing. Small-... more As the scarcity of potable water increases, recycling of treated wastewater is increasing. Small-scale, decentralized treatment can be implemented to serve local populations by keeping water within their boundaries and within reach for reuse, particularly in less dense, non-urban communities. Availability of cellular networks and high-speed internet connectivity, along with significant reduction in cost, allows ongoing monitoring of decentralized treatment systems at a central location. In this paper a decentralized treatment system using micro nanobubble aeration, moving media and membranes is able to produce reusable water with low energy consumption, thereby allowing the use of solar energy in places with unreliable electrical supply. The treatment system, which uses no external chemicals, is able to operate una ended and deliver clear, disinfected water with non-detect suspended solids, BOD5 less than 10 mg/L and nutrients below 5 mg/L.

Development of Structure Biodegradability Relationships (SBRs) for Estimating Half-Lives of Organic Contaminants in Soil Systems

Springer eBooks, 1996

Knowledge of half-lives or biodegradation rate constants in soil is useful for estimating the nat... more Knowledge of half-lives or biodegradation rate constants in soil is useful for estimating the natural attenuation rates of contaminants due to microbial transformations and to make decisions regarding treatment action or no treatment with isolation of the contaminated site to minimize exposure to animal and human life. Half-life is defined as the time required for 50 % of the contaminant to be biodegraded. Soil treatment is time consuming and expensive, and often for large isolated contaminated sites, relying on natural attenuation may be the most cost-effective solution. In this paper, a neural network is trained to estimate the range of half-lives for organic contaminants in soil. Soil half-life data, obtained from the literature for 258 chemicals is correlated with 14 molecular fragments or indicators using a back-propagation neural network with 14 input nodes, 12 nodes in the hidden layer and 2 output nodes. A cross-validation method was used to test the neural network. The converged neural network produced less than 50 % relative error for more than 80 % of the chemicals in the training set. Using a classification scheme of fast (half-life range of 1 to 7 days), moderately fast (half-life range from 7 to 28 days), slow (half-life range from 28 to 180 days) and resistant (half-life range from 180 to 365 days), the neural network was able to correctly classify more than 95 % of the 258 chemicals in the database.

Humana Press eBooks, Nov 14, 2003

Biokinetics and bioavailability protocol for organic pollutants in soil to enhance bioremediation

Bioremediation of polluted soil requires a fundamental understanding of biodegradation kinetics a... more Bioremediation of polluted soil requires a fundamental understanding of biodegradation kinetics and the physicochemical factors that control the rate of biodegradation. A systematic multi-level protocol based on three types of bioreactor systems, was developed to determine the biokinetic parameters of the suspended and immobilized microbiota and the transport and diffusivity parameters of soil contaminants and oxygen in the soil matrix. In the soil slurry reactor, significant biodegradation occurs in the aqueous phase by the suspended and immobilized microbiota and to some extent by the soil immobilized biofilms. The soil slurry reactor data were used to derive the biokinetic parameters for the suspended and immobilized microorganisms. The wafer reactor data were used to obtain additional information on biokinetic and transport parameters with oxygen limitation. The porous tube reactor data provided quantitative determination of oxygen diffusivity. In the soil tube reactor, oxygen l...

Development of Nonlinear Group Contribution Method for Prediction of Biodegradation Kinetics from Respirometrically Derived Kinetic Data

ACS Symposium Series, 1993

... Development of Nonlinear Group Contribution Method for Prediction of Biodegradation Kinetics ... more ... Development of Nonlinear Group Contribution Method for Prediction of Biodegradation Kinetics from Respirometrically Derived Kinetic Data Henry H. Tabak1 and Rakesh Govind2 ... He also attempted correlations using the steric and lipophilic constants but failed. Vaishnav et al. ...