Venkata N. Yarlagadda

Selenium is an essential trace element needed for all living organisms. Despite its essentiality, selenium is a potential toxic element to natural ecosystems due to its bioaccumulation potential. Though selenium is found naturally in the earth's crust, especially in carbonate rocks and volcanic and sedimentary soils, about 40% of the selenium emissions to atmospheric and aquatic environments are caused by various industrial activities such as mining-related operations. In recent years, advances in water quality and pollution monitoring have shown that selenium is a contaminant of potential environmental concern. This has practical implications on industry to achieve the stringent selenium regulatory discharge limit of 5μgSeL(-1) for selenium containing wastewaters set by the United States Environmental Protection Agency. Over the last few decades, various technologies have been developed for the treatment of selenium-containing wastewaters. Biological selenium reduction has emer...

Metal-bearing solid and liquid wastes are increasingly considered as secondary sources of critical and scarce metals. Undoubtedly, microorganisms are a cost-effective resource for extracting and concentrating diffuse elements from secondary sources. Microbial biotechnology for extracting base metals from ores and treatment of metal-laden wastewaters has already been applied at full scale. By contrast, microbe-metal interactions in the recovery of scarce metals and a few critical metals have received attention, whereas the recovery of many others has been barely explored. Therefore, this article explores and details the potential application of microbial biotechnologies in the recovery of critical and scarce metals. In the past decade bioelectrochemical systems have emerged as a new technology platform for metal recovery coupled to the removal of organic matter.

A 6-L sequencing batch reactor (SBR) was operated for development of granular sludge capable of denitrification of high strength nitrates. Complete and stable denitrification of up to 5420 mg L(-1) nitrate-N (2710 mg L(-1) nitrate-N in reactor) was achieved by feeding simulated nitrate waste at a C/N ratio of 3. Compact and dense denitrifying granular sludge with relatively stable microbial community was developed during reactor operation. Accumulation of large amounts of nitrite due to incomplete denitrification occurred when the SBR was fed with 5420 mg L(-1) NO3-N at a C/N ratio of 2. Complete denitrification could not be achieved at this C/N ratio, even after one week of reactor operation as the nitrite levels continued to accumulate. In order to improve denitrification performance, the reactor was fed with nitrate concentrations of 1354 mg L(-1), while keeping C/N ratio at 2. Subsequently, nitrate concentration in the feed was increased in a step-wise manner to establish complete denitrification of 5420 mg L(-1) NO3-N at a C/N ratio of 2. The results show that substrate concentration plays an important role in denitrification of high strength nitrate by influencing nitrite accumulation. Complete denitrification of high strength nitrates can be achieved at lower substrate concentrations, by an appropriate acclimatization strategy.

The biological effect of ionic liquids (ILs) is one of the highly debated topics as they are being contemplated for various industrial applications. 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]) showed remarkable hormesis on anaerobic Clostridium sp. and aerobic Pseudomonas putida. Bacterial growth was stimulated at up to 2.5gL(-1) and inhibited at >2.5gL(-1) of [EMIM][Ac]. The growth of Clostridium sp. and P. putida were higher by 0.4 and 4-fold respectively, in the presence of 0.5gL(-1) [EMIM][Ac]. Assessment of the effect of [EMIM][Ac] under different growth conditions showed that the hormesis of [EMIM][Ac] was mediated via regulation of medium pH. Hormetic effect of [EMIM][Ac] was evident only in medium with poor buffering capacity and in the presence of a fermentable substrate as the carbon source. The hormetic effect of [EMIM][Ac] on bacterial growth is most likely associated with the buffering capacity of acetate anion. These observations have implications in ILs toxici...

A tropical marine bacterium isolated from the hard coral, Symphyllia sp. was identified as Serratia marcescens on the basis of morphological, biochemical and 16S rDNA analysis. The bacterium showed antimicrobial activity towards the pathogens Candida albicans and Pseudomonas aeruginosa and the marine biofouling bacterium Bacillus pumilus. S. marcescens displayed biosurfactant activity as evidenced by drop collapse, blood hemolysis and surface tension reduction (52.0-27 mN m(-1)). The active compound was purified by solvent extraction and silicic acid chromatography. Characterization was by thin layer chromatography, gas chromatography mass spectroscopy (GC-MS), Fourier transform infrared (FTIR) spectroscopy and (1)H as well as (13)C nuclear magnetic resonance (NMR) analysis. The surfactant was found to be a glycolipid composed of glucose and palmitic acid. The glycolipid prevented adhesion of C. albicans BH, P. aeruginosa PAO1 and B. pumilus TiO1. The glycolipid also disrupted preformed biofilms of these cultures in microtitre plates. Confocal laser scanning microscopy and electron microscopy confirmed the effective removal of biofilms from glass surfaces. The glycolipid derived from S. marcescens could thus serve as a potential anti-biofilm agent.

Mixed microbial consortia in the form of aerobic microbial granules (AMG) capable of xenobiotic degradation can be developed from activated sludge or by adaptation of microbial granules pre-grown on labile carbon sources. Both of these approaches were investigated for the cultivation of AMG capable of p-nitrophenol (PNP) biodegradation. Attempts to cultivate AMG from activated sludge using PNP as the sole carbon source were not successful due to poor microbial growth and washout of the inoculated activated sludge. As part of the second approach, parallel sequencing batch reactors (SBRs) were inoculated with pre-grown AMG and operated by feeding both acetate and PNP together (RA), PNP alone (RB) or acetate alone (RC). Acetate/PNP mineralization and nitrification were monitored in the three SBRs. PNP biodegradation was quickly established in both RA and RB. PNP removal rates were found to be 47 and 55 mg g VSS(-1) h(-1) in RA and RB, respectively. PNP biodegradation during the SBR cycle consisted of distinct lag, exponential and deceleration phases. However, with higher concentrations of PNP (>50 mg l(-1)), disintegration of granules was observed in RA and RB. When PNP was the sole carbon source, it inhibited the development of aerobic granules from activated sludge and caused disintegration of pre-cultivated aerobic granules. When PNP was the co-substrate along with acetate, the structural and functional integrity (including nitrification) of the granular sludge was maintained. This report highlights the importance of a labile co-substrate for maintaining the physical and functional integrity of granular sludge, when used for toxic waste degradation.

We assessed the potential of mixed microbial consortia, in the form of granular biofilms, to reduce chromate and remove it from synthetic minimal medium. In batch experiments, acetate-fed granular biofilms incubated aerobically reduced 0.2 mM Cr(VI) from a minimal medium at 0.15 mM day −1 g −1 , with reduction of 0.17 mM day −1 g −1 under anaerobic conditions. There was negligible removal of Cr(VI) (i) without granular biofilms, (ii) with lyophilized granular biofilms, and (iii) with granules in the absence of an electron donor. Analyses by X-ray absorption near edge spectroscopy (XANES) of the granular biofilms revealed the conversion of soluble Cr(VI) to Cr(III). Extended X-ray absorption fine-structure (EXAFS) analysis of the Cr-laden granular biofilms demonstrated similarity to Cr(III) phosphate, indicating that Cr(III) was immobilized with phosphate on the biomass subsequent to microbial reduction. The sustained reduction of Cr(VI) by granular biofilms was confirmed in fed-batc...

Nitrogen and phosphorous are key pollutants in wastewater to be removed and recovered for sustainable development. Traditionally, nitrogen removal is practiced through energy intensive biological nitrification and denitrification entailing a major cost in wastewater treatment. Recent innovations in nitrogen removal aim at reducing energy requirements and recovering ammonium nitrogen. Bioelectrochemical systems (BES) are promising for recovering ammonium nitrogen from nitrogen rich waste streams (urine, digester liquor, swine liquor, and landfill leachate) profitably. Phosphorus is removed from the wastewater in the form of polyphosphate granules by polyphosphate accumulating organisms. Alternatively, phosphorous is removed/recovered as Fe-P or struvite through chemical precipitation (iron or magnesium dosing). In this article, recent advances in nutrients removal from wastewater coupled to recovery are presented by applying a waste biorefinery concept. Potential capabilities of BES ...

Simultaneous removal of selenite and ammonium by aerobic granular sludge was investigated to develop an improved biological treatment process for selenium rich wastewaters. Aerobic granules not previously exposed to selenite were able to remove selenite by converting it to elemental selenium (Se(0)) and simultaneously remove ammonium under different conditions in batch experiments. To achieve sustainable selenite and ammonium removal, an aerobic granular sludge reactor was operated in fill-and-draw mode with a cycle of anaerobic (8 h) and aeration (15 h) phases. Almost complete removal of different initial concentrations of selenite up to 100 μM was achieved in the anaerobic phase. Ammonium removal was severely inhibited when the granules were initially exposed to 1.27 mg L−1 selenite, but ammonium and total nitrogen removal efficiencies gradually improved to 100 and 98%, respectively, under selenite-reducing conditions. Selenite loading shifted ammonium removal occurring mainly dur...

A 6-L sequencing batch reactor (SBR) was operated for development of granular sludge capable of denitrification of high strength nitrates. Complete and stable denitrification of up to 5420 mg L L1 nitrate-N (2710 mg L L1 nitrate-N in reactor) was achieved by feeding simulated nitrate waste at a C/N ratio of 3. Compact and dense denitrifying granular sludge with relatively stable microbial community was developed during reactor operation. Accumulation of large amounts of nitrite due to incomplete denitrification occurred when the SBR was fed with 5420 mg L L1 NO 3 eN at a C/N ratio of 2. Complete denitrification could not be achieved at this C/N ratio, even after one week of reactor operation as the nitrite levels continued to accumulate. In order to improve denitrification performance, the reactor was fed with nitrate concentrations of 1354 mg L L1 , while keeping C/N ratio at 2. Subsequently, nitrate concentration in the feed was increased in a step-wise manner to establish complete denitrification of 5420 mg L L1 NO 3 eN at a C/N ratio of 2. The results show that substrate concentration plays an important role in denitrification of high strength nitrate by influencing nitrite accumulation. Complete denitrification of high strength nitrates can be achieved at lower substrate concentrations, by an appropriate acclimatization strategy.

Nitrogen and phosphorous are key pollutants in wastewater to be removed and recovered for sustainable development. Traditionally, nitrogen removal is practiced through energy intensive biological nitrification and denitrification entailing a major cost in wastewater treatment. Recent innovations in nitrogen removal aim at reducing energy requirements and recovering ammonium nitrogen. Bioelectrochemical systems (BES) are promising for recovering ammonium nitrogen from nitrogen rich waste streams (urine, digester liquor, swine liquor, and landfill leachate) profitably. Phosphorus is removed from the wastewater in the form of polyphosphate granules by polyphosphate accumulating organisms. Alternatively, phosphorous is removed/recovered as Fe-P or struvite through chemical precipitation (iron or magnesium dosing). In this article, recent advances in nutrients removal from wastewater coupled to recovery are presented by applying a waste biorefinery concept. Potential capabilities of BES in recovering nitrogen and phosphorous are reviewed to spur future investigations towards development of nutrient recovery biotechnologies.

Tributyl phosphate (TBP) is commercially used in large volumes for reprocessing of spent nuclear fuel. TBP is a very stable compound and persistent in natural environments and it is not removed in conventional wastewater treatment plants. In this study, cultivation of aerobic granular biofilms in a sequencing batch reactor was investigated for efficient biodegradation of TBP. Enrichment of TBP-degrading strains resulted in efficient degradation of TBP as sole carbon or along with acetate. Complete biodegradation of 2mM of TBP was achieved within 5h with a degradation rate of 0.4 μmol mL(-1) h(-1). TBP biodegradation was accompanied by release of inorganic phosphate in stoichiometric amounts. n-Butanol, hydrolysed product of TBP was rapidly biodegraded. But, dibutyl phosphate, a putative intermediate of TBP degradation was only partially degraded pointing to an alternative degradation pathway. Phosphatase activity was 22- and 7.5-fold higher in TBP-degrading biofilms as compared to bioflocs and acetate-fed aerobic granules. Community analysis by terminal restriction length polymorphism revealed presence of 30 different bacterial strains. Seven bacterial stains, including Sphingobium sp. a known TBP degrader were isolated. The results show that aerobic granular biofilms are promising for treatment of TBP-bearing wastes or ex situ bioremediation of TBP-contaminated sites.

The biological effect of ionic liquids (ILs) is one of the highly debated topics as they are being contemplated for various industrial applications. 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]) showed remarkable hormesis on anaerobic Clostridium sp. and aerobic Pseudomonas putida. Bacterial growth was stimulated at up to 2.5 g L(-1) and inhibited at >2.5 g L(-1) of [EMIM][Ac]. The growth of Clostridium sp. and P. putida were higher by 0.4 and 4-fold respectively, in the presence of 0.5 g L(-1) [EMIM][Ac]. Assessment of the effect of [EMIM][Ac] under different growth conditions showed that the hormesis of [EMIM][Ac] was mediated via regulation of medium pH. Hormetic effect of [EMIM][Ac] was evident only in medium with poor buffering capacity and in the presence of a fermentable substrate as the carbon source. The hormetic effect of [EMIM][Ac] on bacterial growth is most likely associated with the buffering capacity of acetate anion. These observations have implications in ILs toxicity studies and ecological risk assessment.

Metal-bearing solid and liquid wastes are increasingly considered as secondary sources of critical and scarce metals. Undoubtedly, microorganisms are a cost-effective resource for extracting and concentrating diffuse elements from secondary sources. Microbial biotechnology for extracting base metals from ores and treatment of metal-laden wastewaters has already been applied at full scale. By contrast, microbe–metal interactions in the recovery of scarce metals and a few critical metals have received attention, whereas the recovery of many others has been barely explored. Therefore, this article explores and details the potential application of microbial biotechnologies in the recovery of critical and scarce metals. In the past decade bioelectrochemical systems have emerged as a new technology platform for metal recovery coupled to the removal of organic matter. Precious Pollutants Contamination of natural resources with metal ions is increasingly reported worldwide. Although both natural and anthropogenic activities contribute to metal mobilization, the extent of metal contamination through the anthropogenic route is of concern [1]. Wastewaters containing metal ions are generated in various anthropogenic activities (mining, metallurgical operations, burning fossil fuels, cement production, electroplating, leather tanning) and products (manufacturing plastics, fertilizers, pesticides, anticorrosive agents, Ni-Cd batteries, paints, pigments, dyes, photovoltaic devices) [2]. Metal contamination is a serious concern because metals are (i) not biodegradable, unlike organic pollutants; (ii) toxic and metal ions can undergo transformations to potentially toxic and carcinogenic compounds; and (iii) transfer across the trophic levels of the food-chain, reaching higher trophic levels and bioaccumulating in living organisms. Therefore, metal(loid)s such as silver (Ag), arsenic (As), beryllium (Be), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), antimony (Sb), selenium (Se), thallium (Tl), and zinc (Zn) are included in the US priority pollutants list [3], and stringent limits are in place for regulating discharge of various metals in industrial wastewaters to minimize contamination of natural resources. Aside from pollution, metals are precious raw materials to the economy of a country and need to be secured for sustainable production of key components of various products such as low-carbon energy technologies, automobiles, and electronic and biomedical devices [4]. Low-carbon energy technologies, catalytic processes, and electronic gadgets require large amounts of critical and scarce metals including platinum group metals (PGMs), rare earth elements (REEs), cobalt, selenium, and tellurium [5]. The availability and supply of critical metals (see Glossary) greatly influence the economy of a country by affecting manufacturing, export, and job creation [6]. Most of the critical and scarce metals are currently obtained through mining of

Large scale deployment of renewable power sources like wind and solar require energy storage because of their intermittent nature. The Hydrogen-Bromine (H2-Br2) fuel cell system is considered to be a suitable electrical energy storage system because of its high energy capacity, high round-trip conversion efficiency and low cost. While no precious metals are needed to catalyze the bromine reactions, the hydrogen (HER/HOR) reactions require a catalyst that is highly active, to keep the performance high and the cost low, and stable and durable in the highly corrosive HBr/Br 2 environment of the cell as required by the extended life of this application. Platinum, while having very high catalytic activity for the HER/HOR reactions, is not stable in the HBr/Br2 environment. An alternative catalyst is needed. This paper discusses the performance and stability of various HER/HOR catalysts that we have evaluated for this fuel cell system.

Comparison of Acid and Alkaline Hydrogen-Bromine Fuel Cell Systems Trung Van Nguyena*, Venkata Yarlagaddaa, Guangyu Linb, Guoming Wengc, Vanessa Lic, and Kwong-Yu Chanc aDepartment of Chemical & Petroleum Engineering The University of Kansas Lawrence, KS, USA bTVN Systems, Inc. Lawrence, KS, USA cDepartment of Chemistry The University of Hong Kong Hong Kong SAR, China *Corresponding Author: cptvn@ku.edu Abstract The hydrogen bromine (H2-Br2) fuel cell system is an attractive system for electrical energy storage because of its high round-trip conversion efficiency, high power density capability, and anticipated low costs. The hydrogen-bromine fuel cell system can be operated in the acid or alkaline modes. The charge and discharge electrode reactions in an acid H2-Br2 fuel cell system are as follows: Bromine Electrode: Br2 (aq) + 2e- ↔ 2Br-(aq), Eo = +1.09 V Hydrogen Electrode: H2 (g) ↔ 2H+ (aq) + 2e-, Eo = +0.0 V The H+ ions migrate from the hydrogen side across a proton conducting m...

ABSTRACT Intermittent renewable energy sources like wind and solar require energy storage to be fully exploited. The H-2-Br-2 flow battery has been identified as a great candidate for this application because of its high energy conversion efficiency and power density capability. To evaluate the performance of this system a fuel cell with a membrane electrode assembly made of a Nafion 212 membrane and electrodes with 0.55 mg Pt/cm(2) loading was tested at 22 degrees C under the H-2-H-2, H-2-O-2, H-2-Br-2 modes to compare the performance between these systems. The exchange current density of the Br-/Br-2 reactions on platinum was found to be about a quarter of that of the hydrogen reactions on the same substrate (0.3 mA/cm(2) Pt versus 1.2 mA/cm(2) Pt). Peak power density during discharge was 0.30 W/cm(2) at a voltage efficiency of 70% for the H-2-Br-2 mode versus 0.17 W/cm(2) at 40% for the H-2-O-2 mode under similar conditions. The performance of the H-2-Br-2 fuel cell is determined mainly by the ohmic and mass transport resistances in the cell, which could be improved by using higher reactant concentrations, higher operating temperatures, more conductive membranes, and electrode and cell designs that enhance transport.

ABSTRACT Hydrogen-Bromine (H-2-Br-2) fuel cells are considered to be one of the viable systems for large scale energy storage because of their high energy conversion efficiency, flexible operation and low capital cost. A 1D mathematical model is developed to serve as a theoretical guiding tool for the experimental studies. The impact of convective and diffusive transport and kinetic rate on the performance of a H-2-Br-2 fuel cell is shown in this study. Of the two flow designs (flow-by and flow-through) incorporated in this study, the flow-through design demonstrated better performance, which can be attributed to the dominant convective transport inside the porous electrode. Both experimental and simulated results validate that for the electrode properties and operating conditions selected, increasing the thickness of the Br-2 electrode beyond a certain value does not have any effect on the discharge performance of the fuel cell. The reactant concentration available inside the Br-2 electrode is greatly increased by operating the fuel cell at higher feed flow rates. Finally, the fuel cell configuration involving a thinner Br-2 electrode with higher specific active surface area is found to be the optimal choice for generating high performance.