Building, Civil and Environmental Engineering

– The purpose of this study is to design a passive controller on the hydrofoil, CAV 2003, to decrease and control the size of the cavitating bubble around the hydrofoil forming of the pressure drop in a specific area near the hydrofoil surface. For the purpose, a novel idea is presented here by a numerical simulation. In this idea, an appendage is located on the hydrofoil wall to decrease the size of the bubble. The location of this appendage is important to make a good condition to decrease the bubble size. Secondly, the size and height of the appendage have a significant effect on the flow around the hydrofoil and consequently select a wrong size and height can have an adverse effect. The characteristics of the numerical method, based on the cavitating bubble behaviour, are time dependent, pressure based, and finite volume. The set of Navier Stokes equations are supposed to be incompressible. Additionally, to capture the turbulent boundary layer near the hydrofoil surface, RNG k-ε model is used. The first part of this paper is allocated to verification the accuracy of the numerical simulation. The second part is the presentation on the effects of the passive controller, including the shape of the appendage and its location.

The increasing concentration of carbon dioxide (CO 2 )the most dominant component of greenhouse gases-in the atmosphere has been of growing concern for many years. Many methods focus on CO 2 capture and storage and there is always the risk of CO 2 release to the environment. In this study, a new method to convert CO 2 to biogas with a high content of methane (CH 4 ) in an anaerobic system with a lab-scale upflow anaerobic sludge blanket reactor at 35°C was developed. In a series of experiments, the reactor was run with and without CO 2saturated solutions including volatile fatty acids (VFAs) as sources of hydrogen. The concentration of dissolved CO 2 in the influent solutions was 2.2-6.1 g/L, with corresponding chemical oxygen demand (COD) values of 2.6 -8.4 g/L for the solutions. Overall CO 2 removal values of 2.7-20 g/day (49 -88% conversion) were obtained for the organic loading rates (OLR) and CO 2 loading rates of 8 -36 gCOD/L ⅐ day and 6 -26 gCO 2 /L ⅐ day, respectively with CH 4 purity of above 70%. Also, VFA and COD removal were in the range of 79 -95% and 75-90%, respectively. Methanogenic activities of the cultures with the concentrations measured as volatile suspended solids (VSSs) were 0.12-0.40 L CH 4 /gVSS ⅐ d with the highest value for the system containing acetic acid. This anaerobic method can be applied to reduce CO 2 emitted to the atmosphere from a wide variety of industrial point sources with a valueadded product, CH 4 . IMPLICATIONS CO 2 is the major contributor to the greenhouse gas effect and global warming. In this study a new approach was developed to convert CO 2 to CH 4 , which in addition to reducing its emission provides CH 4 as a clean source of energy. Air and energy management sections would benefit from the application of this method and in the long term, it could have a major impact on reduction of atmospheric levels of this greenhouse gas. Figure 12. Biomass particles from (a) the cheese water treatment plant and (b) in system 1 (magnification, ϫ50).

A computational model was developed to study the hydrodynamic characteristics of a new multienvironment air-lift bioreactor. This model study considerably expands on the laboratory experiments by exploring the hydrodynamic characteristics of multiple combinations of geometries and operating conditions and by providing a visual illustration of the liquid-phase flow patterns. The model was first tested against preliminary laboratory results to ensure its validity. This included comparing two simplified geometries for the three-disc prototype air sparger assembly to determine which led to results closer to laboratory measurements. A torus geometry was found to better represent the prototype than a single disc. The model was modified to evaluate the hydrodynamic characteristics of alternative operating conditions and physical geometries beyond what would be possible in the laboratory. The flow pattern in the outer clarifier zone was shown to be very sensitive to the geometry of the bioreactor wall separating the clarifier from the inner microaerophilic zone. Establishing a smooth, upward flow pattern in the clarifier was shown to be possible only when the clarifier was sufficiently shielded from the circulation in the anoxic cone below. Further research is needed to quantify the effect of hydrodynamic characteristics on contaminant removal efficiency.

Greenhouse gas (GHG) emission in wastewater treatment plants of the pulp-and-paper industry was estimated by using a dynamic mathematical model. Significant variations were shown in the magnitude of GHG generation in response to variations in operating parameters, demonstrating the limited capacity of steady-state models in predicting the time-dependent emissions of these harmful gases. The examined treatment systems used aerobic, anaerobic, and hybrid-anaerobic/aerobic-biological processes along with chemical coagulation/flocculation, anaerobic digester, nitrification and denitrification processes, and biogas recovery. The pertinent operating parameters included the influent substrate concentration, influent flow rate, and temperature. Although the average predictions by the dynamic model were only 10 % different from those of steady-state model during 140 days of operation of the examined systems, the daily variations of GHG emissions were different up to ±30, ±19, and ±17 % in the aerobic, anaerobic, and hybrid systems, respectively. The variations of process variables caused fluctuations in energy generation from biogas recovery by ±16, ±17, and ±14 % in the three examined systems, respectively. The lowest variations were observed in the hybrid system, showing the stability of this particular process design.

Pulp-and-paper mills produce various types of contaminants and a significant amount of wastewater depending on the type of processes used in the plant. Since the generated wastewaters can be potentially polluting and very dangerous, they should be treated in wastewater treatment plants before being released to the environment. This paper reviews different wastewater treatment processes used in the pulp-and-paper industry and compares them with respect to their contaminant removal efficiencies and the extent of greenhouse gas (GHG) emission. It also evaluates the impact of operating parameters on the performance of different treatment processes. Two mathematical models were used to estimate GHG emission in common biological treatment processes used in the pulp-and-paper industry. Nutrient removal processes and sludge treatment are discussed and their associated GHG emissions are calculated. Although both aerobic and anaerobic biological processes are appropriate for wastewater treatment, their combination known as hybrid processes showed a better contaminant removal capacity at higher efficiencies under optimized operating conditions with reduced GHG emission and energy costs.