Rajeshwar Dayal Tyagi

Laccases for removal of recalcitrant and emerging pollutants

Bioremediation of wastewater can be enhanced by the use of lignolytic enzymes such as laccases. Laccases oxidize, polymerize or transform phenolic or anthropogenic compounds to less toxic derivatives. Laccase substrates are diverse, and include phenols, dyes, pesticides, endocrine disrupters and polycyclic aromatic hydrocarbons, some of which can be oxidized by extracellular fungal or bacterial laccase. Despite their enormous potential, the use of laccases for decontamination has so far usually been limited to the laboratory scale due to high enzyme production costs. The use of lignocellulosic waste material and/or wastewater as culture media for the growth of microorganisms producing laccase is gaining popularity, but is still low profile due to the ever-present challenges of this approach. The last two decades have seen the publication of numerous reviews on laccases; however, information on laccase properties and production parameters remains sketchy. Hence, a global overview of parameters affecting the biocatalysis of pollutants by laccases, particularly with regard to the economical production of these enzymes using synthetic media and waste materials, is timely.

Nitrification, denitrification and phosphorus removal in sequential batch reactors

Abstract A study was conducted to evaluate the biological nutrient removal performance of three full-scale sequential batch reactor (SBR) plants. The plants were designed to handle an average flow of 0.023, 0.025, 0.001 m 3 /s, respectively. These SBR systems were designed to achieve nitrification, denitrification and biological phosphorus removal. Influent and effluent samples were analyzed for CBOD 5 , TSS, ammonia nitrogen, nitrate nitrogen, total phosphorus, pH and temperature. The SBR performance data show that typical SBR designs can meet effluent CBOD 5 and TSS concentrations of less than 10 mg/l. With some additional design modifications, SBRs can successfully nitrify to limits of 1–2 mg/l NH 3 -N. They also appear to achieve phosphorus removal, if desired, without chemicals addition to less than 1.0 mg/l.

Nanotechnologies for water environment applications.

This book is useful to undergraduate and graduate students in engineering and practicing engineers, as well as educators, scientists, government officials, policymakers, and industrial process managers.

Assessment of toxicity reduction after metal removal in bioleached sewage sludge

Sewage sludge can be applied to land to supply and recycle organic matter and nutrients. Trace elements in sludge, however, may accumulate in the soil with repeated sludge applications. Reducing metal content may therefore reduce the adverse effects of sludge application. The objective of this study was to evaluate the efficiency of bioleaching technology in reducing metal content and toxicity as measured by a battery of terrestrial and liquid-phase bioassays. Sludge-soil mixtures simulating the application of sludge to land were tested by means of terrestrial bioassays, barley (Hordeum vulgare L.) seed germination (5 d) and sprout growth (14 d), lettuce (Lactuca sativa) seed germination (5 d), and worm (Eisenia andrei) mortality (14 d). Liquid-phase bioassays, Microtox (Vibrio fischeri, 15 min), lettuce root elongation (L. sativa, 5 d), cladoceran mortality (Daphnia magna, 48 h), and SOS Chromotest (Escherichia coli) were used after elutriation of the sludge. Comparison of the bioassay results (except for D. magna) before and after treatment demonstrated that this bioleaching process reduced both sludge toxicity and metal content. In addition, lower Cu and Zn concentrations found in barley sprouts following treatment supported the assumption that the bioleaching process, by decreasing metal content and bioavailability, reduced sewage sludge toxicity. This study also emphasized the interest of using ecotoxicological bioassays for testing biosolids. In particular, the terrestrial bioassays after simulation of land application and the Microtox test after sludge elutriation proved to be the most appropriate procedures.

Contaminants of emerging environmental concern.

This book is a must-have for both undergraduate and graduate students in environmental engineering and resources; teachers; researchers; and practicing environmental engineers.

Bioenergy and biofuel from biowastes and biomass.

This book attempts to provide an in-depth compilation of relevant technical information on several aspects of biofuel and bioenergy production ... it can serve as a useful quick reference for consulting engineers. It is also a good introductory resources for advanced students, researchers, instructors, decision makers, and professionals in the biofuel and bioenergy field. Recommended. —A.C. Sheth, emeritus, University of Tennessee Space Institute, Choice: Current Reviews for Academic Libraries, December 2010.

Bisphenol A degradation in water by ligninolytic enzymes

Many endocrine disruptor compounds, such as bisphenol A (BPA) are used today and released into the environment at low doses but they are barely degraded in wastewater treatment plants. One of the potential alternatives to effectively degrade endocrine disruptor compounds is based on the use of the oxidative action of extracellular fungal enzymes. The aim of this work is to study the ability of free and encapsulated enzymes (manganese peroxidase, lignin peroxidase and laccase) to degrade BPA. Higher degradation of BPA (90%) by ligninolytic enzymes encapsulated on polyacrylamide hydrogel and pectin after 8h was obtained. The degradation of BPA while using the free enzyme (26%) was lower than the value obtained with encapsulated enzymes. The presence of pectin in the formulation significantly (p>0.05) enhanced the activity of enzymes. Kinetics of BPA degradation showed an increase in Vm, while Km remained constant when enzymes were encapsulated. Hence, encapsulation protected the enzymes from non-competitive inhibition.

Process engineering studies on continuous ethanol production by immobilized S. cerevisiae.

Abstract Saccharomyces cerevisiae cells were immobilized on three supports—calcium alginate beads, raw and hexamethylene diamine treated bagasse—for their comparative assesment in terms of cell retention on to the carrier and metabolic and physiological activities of the immobilized cells. The chosen carrier-activated bagasse adsorbed 0.41 g of cells per g of carrier (on a dry weight basis). The Gibbs free energy and activation energy for immobilization for the first and second stages was computed to be 3272.45, 14624.27 and 6336.34 J g mol −1 , respectively. The immobilized cells were used in a packed bed reactor for the continuous bioconversion of sucrose to ethanol and the packing density of the carrier and the height to diameter ratio of the packed bed bioreactor were optimized to be 50 g l t-1 and 2.5, respectively. The maximum productivity obtained was 31.8 g l t-1 h t-1 at a feed sugar concentration of 200 g l t-1 and space velocity of 0.53 h -1 . The system was operationally stable in terms of productivity for 76 days. The system then could be reactivated by intermittent air sparging for further operation.

Photocatalytic degradation of carbamazepine in wastewater by using a new class of whey-stabilized nanocrystalline TiO2 and ZnO.

Nanoscale photocatalysts have attracted much attention due to their high surface area to volume ratios. However, due to extremely high reactivity, TiO2 and ZnO nanoparticles prepared using different methods tend to either react with surrounding media or agglomerate, resulting in the formation of much larger flocs and significant loss in reactivity. This work investigates the photocatalytic degradation of carbamazepine (CBZ), a persistent pharmaceutical compound from wastewater (WW) using TiO2 and ZnO nanoparticles prepared in the presence of a water-soluble whey powder as stabilizer. The TiO2 and ZnO nanoparticles prepared in the presence of whey stabilizer displayed much less agglomeration and greater degradation power than those prepared without a stabilizer. Higher photocatalytic degradation of carbamazepine was observed (100%) by using whey stabilized TiO2 nanoparticles with 55 min irradiation time as compared to ZnO nanoparticles (92%). The higher degradation of CBZ in wastewater by using TiO2 nanoparticles as compared to ZnO nanoparticles was due to formation of higher photo-generated holes with high oxidizing power of TiO2. The photocatalytic capacity of ZnO anticipated as similar to that of TiO2 as it has the same band gap energy (3.2 eV) as TiO2. However, in the case of ZnO, photocorrosion frequently occurs with the illumination of UV light and this phenomenon is considered as one of the main reasons for the decrease of ZnO photocatalytic activity in aqueous solutions. Further, the estrogenic activity of photocatalyzed WW sample with CBZ and its by-products was carried out by yeast estrogen screen (YES) assay method. Based upon the YES test results, none of the samples showed estrogenic activity.

Encapsulation of ligninolytic enzymes and its application in clarification of juice.

The thermal stability, physico-chemical properties and effect on juice clarification of hydrogel formulations of ligninolytic enzymes from Phanerochaete chrysosporium were evaluated. The results showed that enzyme entrapment increase significantly (P<0.05) the thermal stability of enzymes at 4 and 75 °C. At 75 °C, maximum activity decreased to non detectable values of 7.9% for free laccase, manganese peroxidase (MnP), lignin peroxidase (LiP), respectively; to 94%, 97%, 93% for laccase, MnP and LiP entrapped into Polyacrylamide/pectin, 94%, 98%, 88% for laccase, MnP and LiP encapsulated respectively into polyacrylamide/ gelatine and to 87%, 91%, 87% for laccase, MnP and LiP entrapped, respectively into polyacrylamide/carboxymethylcellulose (CMC). When particle size and viscosity of the formulation increased, enzyme stability increased. The polyphenolic reduction and clarity amelioration in mixed juice of berry and pomegranate was more significant (p>0.05) using encapsulated enzymes treatment than free enzymes. This suggested that enzymatic treatment was efficient for the juice clarification.