Madhumita B. Ray

Degradation of paracetamol in aqueous solutions by TiO2 photocatalysis

In this study, photo/photocatalytic oxidation of common analgesic and antipyretic drug, paracetamol (acetaminophen), was investigated to determine the optimal operating conditions for degradation in water. UVA (365 nm) radiation alone degraded negligible amount of paracetamol, whereas paracetamol concentration decreased substantially under an irradiation of UVC (254 nm) with marginal changes in total organic carbon (TOC). In the presence of TiO2, much faster photodegradation of paracetamol and effective mineralization occurred; more than 95% of 2.0mM paracetamol was degraded within 80 min. The degradation rate constant decreased with an increase in the initial concentration of paracetamol, while it increased with light intensity and oxygen concentration. The degradation rate also increased with TiO2 loading until a concentration of 0.8 g L(-1). The degradation rate slowly increased between pH 3.5 and 9.5, but significantly decreased with increasing pH between 9.5 and 11.0. Based on the experimental data, a kinetic equation describing paracetamol photocatalytic degradation with various process parameters is obtained.

Advanced Oxidation Processes

Since the early 1970s, advanced oxidation processes (AOPs) have been used considerably to remove both low and high concentrations of organic compounds from diverse sources such as groundwater, municipal and industrial wastewater, sludge destruction, and volatile organic compound (VOC) control. These processes, although often having high capital and operating costs, are the only viable treatment methods for effluents containing refractory, toxic, and non-biodegradable materials. In the AOP, the organic compounds can be completely mineralized to carbon dioxide and water mostly by hydroxyl radicals, the second most powerful oxidizing agent generated in situ in the reaction environment. The rate constant values of oxidation of the organics with hydroxyl radicals range from 108 to 1011 M−1s−1

Techno-economic evaluation of ultrasound and thermal pretreatments for enhanced anaerobic digestion of municipal waste activated sludge

To enhance the anaerobic digestion of municipal waste-activated sludge (WAS), ultrasound, thermal, and ultrasound+thermal (combined) pretreatments were conducted using three ultrasound specific energy inputs (1000, 5000, and 10,000 kJ/kg TSS) and three thermal pretreatment temperatures (50, 70 and 90°C). Prior to anaerobic digestion, combined pretreatments significantly improved volatile suspended solid (VSS) reduction by 29-38%. The largest increase in methane production (30%) was observed after 30 min of 90°C pretreatment followed by 10,000 kJ/kg TSS ultrasound pretreatment. Combined pretreatments improved the dimethyl sulfide (DMS) removal efficiency by 42-72% but did not show any further improvement in hydrogen sulfide (H(2)S) removal when compared with ultrasound and thermal pretreatments alone. Economic analysis showed that combined pretreatments with 1000 kJ/kg TSS specific energy and differing thermal pretreatments (50-90°C) can reduce operating costs by

Application of Computational Fluid Dynamics for Simulation of Drying Processes: A Review

44-66/ton dry solid when compared to conventional anaerobic digestion without pretreatments.

Impact of ultrasonication of hog manure on anaerobic digestability

In recent years, computational fluid dynamics (CFD) has been used increasingly to improve process design capabilities in many industrial applications, including industrial drying processes. Drying of food and beverage products, industrial and municipal wastewater sludge, and other manufacturing and environmental products is done regularly in order to enhance the quality and life span of these products and to facilitate their use, storage, and transportation. With recent advancements in mathematical techniques and computer hardware, CFD has been found to be successful in predicting the drying phenomenon in various types of industrial dryers, which utilize all forms of drying operations including spray, freeze, and thermal drying techniques. The CFD solutions are being used to optimize and develop equipment and processing strategies in the drying industry, replacing expensive and time-consuming experimentations. However, a comprehensive review on the application of CFD for the design, study, and evaluation of industrial dryers is not yet available. A comprehensive review of the current literature on the use of CFD models in both industrial and lab-scale drying applications is presented in this article. The use of Eulerian-Eulerian and Eulerian-Lagrangian models in the study of the drying kinetics for gas–solid multiphase flow systems is fully discussed. Merits and disadvantages of using various CFD models in the design of industrial dryers are illustrated and the scope of their applicability is also discussed.

Pretreatment of municipal waste activated sludge for volatile sulfur compounds control in anaerobic digestion.

The efficiency of ultrasonication as a pretreatment method for hog manure prior to anaerobic digestion is evaluated at specific energies of 250-30,000 kJ/kgTS. This study confirmed that COD(solubilisation) from particulates correlated well with the more labor and time intensive degree of disintegration test. The particle size distribution for hog manure was bimodal (0.6-2500 μm), while ultrasonication primarily impacting particles in the 0.6-60 μm range. Hog manure was found to be more amenable to ultrasonication than waste activated sludge, as it took only 3000 kJ/kgTS to cause 15% more solubilization as compared to 25,000 kJ/kgTS for waste activated sludge. Bound protein degradation during sonication was 13.5% at 5000 kJ/kgTS and remained constant thereafter for higher energy input. It was noted that biomass cell rupture occurred at specific energy of 500 kJ/kgTS. An economic evaluation indicated that only a specific energy of 500 kJ/kgTS was economical, with a net energy output valued at

Photocatalytic Inactivation of Bioaerosols by TiO2 Coated Membrane

4.1/ton of dry solids, due to a 28% increase in methane production.

Degradation of estrone in water and wastewater by various advanced oxidation processes

The effect of combination of mechanical and chemical pretreatment of municipal waste activated sludge (WAS) prior to anaerobic digestion was studied using a laboratory scale system with an objective to decrease volatile sulfur compounds in biogas and digested sludge. Mechanical pretreatment was conducted using depressurization of WAS through a valve from a batch pretreatment reactor pressurized at 75 ± 1 psi, while combined pretreatments were conducted using six different dosages of hydrogen peroxide (H(2)O(2)) and ferrous chloride (FeCl(2)) along with mechanical pretreatment. About 37-46% removal of H(2)S in biogas occurred for different combined pretreatment conditions. Sludge solubilization achieved due to the mechanical pretreatment increased total cumulative methane production by 8-10% after 30 days during the biochemical methane potential (BMP) test. The pretreatment also improved dewaterability in terms of time to filter (TTF), and decreased methyl mercaptan generation potential of the digested sludge.

Drying of Sludge in a Pneumatic Dryer Using Computational Fluid Dynamics

Indoor air pollution by microbial contaminants is increasingly receiving attention as a public health problem. Under a suitable environment, such as in heating, ventilation and air conditioning (HVAC) system, airborne bacteria are able to proliferate and grow causing various allergies and illnesses. This can be particularly serious in tropical regions due to high relative humidity and warm temperatures all round the year. Application of photocatalysis using UV-A and TiO2 to inactivate air-borne bacteria is relatively new and systematic parametric study is required for the engineering design of a process based on this technology. This study investigates the effects of TiO2 mediated inactivation of various bacterial species in batch and continuous systems using different TiO2 loadings and radiation intensities. Gram-negative bacteria, E. coli and two Gram-positive bacteria, Microbacterium sp. and Bacillus subtilis were used for the inactivation studies. In both systems, inactivation rates of Gram-negative E. coli are higher than the Gram-positive Bacillus subtilis and Microbacterium sp. and the inactivation rates increased in presence of TiO2 for all bacteria. Depending on the type of bacteria, TiO2 loading and light intensity, an increase of 1.3-5.8 times in the inactivation rates was obtained from those in the absence of TiO2. The inactivation rates in the batch and continuous systems were reasonably comparable. Inactivation rates in the continuous system are somewhat higher than those in the batch system due to the unaccounted loss of bacteria via adsorption and settling on the reactor walls in the flow system. The study demonstrates an approach that can be used for the designing of large scale systems for the treatment of bioaerosol.

The Drying of Sludge in a Cyclone Dryer Using Computational Fluid Dynamics

A comprehensive study was conducted to determine the relative efficacy of various advanced oxidation processes such as O3, H2O2, UV, and combinations of UV/O3, UV/H2O2 for the removal of estrone (E1) from pure water and secondary effluent. In addition to the parent compound (E1) removal, performance of the advanced oxidation processes was characterized using removal of total organic carbon (TOC), and estrogenicity of the effluent. Although E1 removal was high for all the AOPs, intermediates formed were more difficult to degrade leading to slow TOC removal. Energy calculations and cost analysis indicated that, although UV processes have low electricity cost, ozonation is the least cost option (