It is well known that urbanization and industrialization have resulted in the rapidly increasing emissions of volatile organic compounds (VOCs), which are a major contributor to the formation of secondary pollutants (e.g., tropospheric ozone, PAN (peroxyacetyl nitrate), and secondary organic aerosols) and photochemical smog. The emission of these pollutants has led to a large decline in air quality in numerous regions around the world, which has ultimately led to concerns regarding their impact on human health and general well-being. Catalytic oxidation is regarded as one of the most promising strategies for VOC removal from industrial waste streams. This Review systematically documents the progresses and developments made in the understanding and design of heterogeneous catalysts for VOC oxidation over the past two decades. It addresses in detail how catalytic performance is often drastically affected by the pollutant sources and reaction conditions. It also highlights the primary routes for catalyst deactivation and discusses protocols for their subsequent reactivation. Kinetic models and proposed oxidation mechanisms for representative VOCs are also provided. Typical catalytic reactors and oxidizers for industrial VOC destruction are further discussed. We believe that this Review will provide a great foundation and reference point for future design and development in this field.

/pdf/recent-advances-in-the-catalytic-oxidation-of-volatile-zw2c35dbg7.pdf

Recent Advances in the Catalytic Oxidation of Volatile Organic Compounds: A Review Based on Pollutant Sorts and Sources.

The transformations of nitrogenous compounds by soil bacteria have beenstudied for over a century. In terms of the global fluxes between aerial and terrestrial-aquatic systems, the simplified nitrogen cycle can be envisioned as a triangle where the only biologically reversible reaction occurs between ammonium and nitrate. The reverse reactions of dinitrogen fixation or denitrification by biological means do not occur in nature. Hence, the reductive process of denitrification, defined as the reduction of nitrate or nitrite to gaseous nitrogen (usually N2), is intimately associated with the oxidative process of nitrification.

Biochemical Ecology of Nitrification and Denitrification

Struvite formation, control and recovery

We review the state of the art in using passive sampling technology for environmental monitoring of waterborne organic and inorganic pollutants. We discuss strategies for sampler design, calibration, in situ sampling and quality-control issues, and advantages and challenges associated with passive sampling in aqueous environments. We then review typical applications of passive samplers in assessing the aquatic environment.

Passive sampling techniques for monitoring pollutants in water

The present review provides an understanding of principles of struvite crystallization and examines the techniques and processes experimented to date by researchers at laboratory, pilot, and full-scale to maximize phosphorus removal and reuse as struvite from wastewater effluents. Struvite is mainly known as a scale deposit causing concerns to wastewater companies. Indeed, struvite naturally occurs under the specific condition of pH and mixing energy in specific areas of wastewater treatment plants (e.g., pipes, heat exchangers) when concentrations of magnesium, phosphate, and ammonium approach an equimolar ratio 1:1:1. However, thanks to struvite composition and its fertilizing properties, the control of its precipitation could contribute to the reduction of phosphorus levels in effluents while simultaneously generate a valuable by-product. A number of processes such as stirred tank reactors and air-agitated and -fluidized bed reactors have been investigated as possible configurations for struvite recove...

/pdf/phosphorus-recovery-from-wastewater-by-struvite-1m5eccuyu5.pdf

Phosphorus Recovery from Wastewater by Struvite Crystallization: A Review

Predicting struvite formation in digestion

A literature study was conducted to compare the feasibility of biofilters and biotrickling filters for the treatment of complex odorous waste air containing hydrogen sulfide (H2S), organic reduced sulfur compounds, and chlorinated and nonchlorinated volatile organic compounds (VOCs). About 40 pilot-plant studies and full-scale applications at wastewater treatment plants and other facilities were reviewed. Reactor design and pollutant removal efficiencies were summarized in tables for easy reference and for a perspective on the current state of the art, and to allow comparison between different projects. The survey indicated that both biofilters and biotrickling filters are capable of combining a high H2S and odor removal efficiency with VOC removal. Apart from odor abatement, biological treatment therefore holds promise for reducing the overall toxicity and potential carcinogenicity of VOC-containing odorous waste air from wastewater treatment plants and other facilities. VOC removal efficiencies were in general lower than those of H2S and odor, although concentrations of individual VOC species were relatively low. This indicates that for effective treatment of VOC-containing odorous waste air, the design and operation should emphasize VOC removal as the rate-limiting parameter. © 2005 American Institute of Chemical Engineers Environ Prog, 2005

Literature Review of Air Pollution Control Biofilters and Biotrickling Filters for Odor and Volatile Organic Compound Removal

The kinetics of struvite (MgNH\d4PO\d4·6H\d2O) formation was studied to determine the cause of preferential accumulation at certain locations within the anaerobic digestion and postdigestion processes in wastewater treatment. Mechanisms controlling nucleation were also studied in laboratory induction time experiments. A field study of struvite accumulation on postdigestion process appurtenances was conducted to evaluate mechanisms affecting crystal growth rates. Struvite nucleation was found to be reaction-controlled, with nucleation strongly dependent on the struvite supersaturation level. Increased mixing intensity at constant supersaturation had a small effect on induction times. The crystal growth rate was found to be transport-limited, with the growth rate a function of mixing energy input. Evaluation of the effect of pH change resulting from CO/d2 evolution in high turbulence areas showed that it has a minor influence on the crystal growth rate. Preferential struvite accumulation was found to be primarily controlled by growth kinetics, which was strongly dependent on mixing energy. Preferential accumulation of struvite on selected construction materials was also studied, and experimental evidence suggested that surface roughness exerted the greatest control over preferential struviite accumulation on various materials under similar mixing and supersaturation conditions.

Kinetics Effects on Preferential Struvite Accumulation in Wastewater

1. Sources and Uses of Water. 2. Physical, Chemical, and Biological Characteristics of Water. 3. Significance of the Characteristics of Water. 4. Water Quality: Standards and Global Perspectives. 5. Stoichiometry, Reaction Kinetics, and Materials Balances. 6. Mathematical Models of Physical Systems. 7. Movement of Contaminants in the Environment. 8. Water Quality in Rivers and Estuaries and Near Ocean Outfalls. 9. Water Quality in Lakes and Reservoirs. 10. Water Quality in Groundwater Systems. 11. Introduction to Water and Wastewater Treatment. 12. Physical Treatment Methods. 13. Chemical Treatment Methods. 14. Biological Treatment Methods. 15. Synthesizing Water and Wastewater Treatment Systems.

Water quality : characteristics, modeling, modification

A laboratory-scale compost-based biofilter was operated over a six-month period to study the requirements for removal of n-hexane from air. Hexane is a relatively short chain aliphatic hydrocarbon with a high Henry's coefficient and a low water solubility. Acclimation of the biofilter was slow, but removal efficiencies around 80% were achieved after one month of operation. However, performance decreased during the next two months of operation to 50% removal efficiency. Nutrient limitation was proposed as a reason for the decrease in reactor performance. After the addition of a concentrated nitrogen solution, reactor performance increased almost immediately to >99%. Removal efficiency remained above 99% for the following two months of operation at inlet concentrations of 0.7 g/m3 (200 ppmv), at superficial bed velocities approaching 50 m/h, and empty bed residence times of about one minute. Thus, nutrient availability may well limit biofilter performance even in compost- based units. It was shown ...

Edward D. Schroeder

Papers

Predicting struvite formation in digestion

Literature Review of Air Pollution Control Biofilters and Biotrickling Filters for Odor and Volatile Organic Compound Removal

Kinetics Effects on Preferential Struvite Accumulation in Wastewater

Water quality : characteristics, modeling, modification

Nutrient Limitation in a Compost Biofilter Degrading Hexane.