The influence of the strength of bone on the deformation of acetabular shells: a laboratory experiment in cadavers.

Concerns have been raised that deformation of acetabular shells may disrupt the assembly process of modular prostheses. In this study we aimed to examine the effect that the strength of bone has on the amount of deformation of the acetabular shell. The hypothesis was that stronger bone would result in greater deformation. A total of 17 acetabular shells were inserted into the acetabula of eight cadavers, and deformation was measured using an optical measuring system. Cores of bone from the femoral head were taken from each cadaver and compressed using a materials testing machine. The highest peak modulus and yield stress for each cadaver were used to represent the strength of the bone and compared with the values for the deformation and the surgeon's subjective assessment of the hardness of the bone. The mean deformation of the shell was 129 µm (3 to 340). No correlation was found between deformation and either the maximum peak modulus (r² = 0.011, t = 0.426, p = 0.676) or the yield stress (r² = 0.024, t = 0.614, p = 0.549) of the bone. Although no correlation was found between the strength of the bone and deformation, the values for the deformation observed could be sufficient to disrupt the assembly process of modular acetabular components.

Ozonation of endogenous residue and active biomass from a synthetic activated sludge.

Coupling the activated sludge and the ozonation processes is an efficient, although expensive, solution for sludge reduction. A better knowledge of the mechanisms involved in the degradation of various sludge fractions by ozone is needed to optimize the coupled process. The objectives of this study were to determine the biodegradability of ozone-solubilized endogenous residue, the action of ozone on the active biomass and the solubilization yield of these two main sludge fractions. Batch tests were conducted with slug input of ozone stock solution into fresh or aerobically digested synthetic sludge. Biodegradability of the solubilized endogenous residue was increased by ozonation by up to 0.27 g BOD5/g CODi. Ozone caused biomass lysis, as opposed to an increase in maintenance needs, as shown by a correlation between the decrease in microbial activity and viability. Lysis caused by ozonation was associated with a solubilization of 20% of the lyzed cell COD mass. Solubilization yields were of 9.6 and of 1.9 to 3.6 g COD/g O3 for fresh and aerobically digested sludge, respectively. Design of sludge ozonation processes should account for the variability between the solubilization yield and biodegradability of the various sludge fractions.

Enhanced nutrient removal MBR system with chemical addition for low effluent TP.

A pilot study was conducted to test an membrane bioreactor (MBR) process for combined biological and chemical P removal to achieve a very low effluent total phosphorus (TP) concentration of 0.025 mg P/L. With the data from the pilot test, a simulation study was performed to demonstrate that: (1) the pilot system behaviour (effluent quality, MLSS, etc.) can be modelled accurately with an activated sludge model combined with a chemical precipitation model; and (2) with the calibrated model, simulation scenarios can be performed to further understand the pilot MBR process, and provide information for optimizing design and operation when applied at full-scale. Results from the pilot test indicated that the system could achieve very low effluent TP concentration through biological P removal with a limited chemical addition, and chemical addition to remove P to very low level did not affect other biological processes, i.e., organic and nitrogen removal. Simulation studies indicate that the process behaviour can be modelled accurately with an activated sludge model combined with a chemical precipitation model, and the calibrated model can be used to provide information to optimize system design and operation, e.g., chemical addition control under dynamic loading conditions is important for maintaining biological P removal.

Denitrification with carbon addition--kinetic considerations.

The Blue Plains Advanced Wastewater Treatment Plant (Washington, D.C.) uses methanol as an external carbon source in a postdenitrification process, to achieve low effluent total nitrogen concentrations. This becomes more difficult in winter, at lower mixed liquor temperatures and higher flows, as a consequence of the kinetic behavior of the methanol-utilizing heterotrophs. The paper reports on an experimental batch test study conducted on Blue Plains postdenitrification sludge to investigate (1) the maximum specific growth rate of methanol-utilizing heterotrophs (Mu(METH)); (2) the temperature dependency of the growth rate; and (3) the efficacy of alternate substrates (ethanol, acetate, and sugar). A limited number of tests were conducted on sludge from two other treatment plants with methanol addition.

A biofilm model for engineering design.

A biofilm model is presented for process engineering purposes--wastewater treatment plant design, upgrade and optimisation. The model belongs in the 1D dynamic layered biofilm model category, with modifications that allow it to be used with one parameter set for a large range of process situations. The biofilm model is integrated with a general activated sludge/anaerobic digestion model combined with a chemical equilibrium, precipitation and pH module. This allows the model to simulate the complex interactions that occur in the aerobic, anoxic and anaerobic layers of the biofilm. The model has been tested and is shown to match a variety of design guidelines, as well as experimental results from batch testing and full-scale plant operation. Both moving bed bioreactors (MBBR) and integrated fixed film activated sludge (IFAS) systems were simulated using the same model and parameter set. A new steady-state solver generates fast solutions and allows interactive design work with the complex model.

Examining the influence of substrates and temperature on maximum specific growth rate of denitrifiers.

Facilities across North America are designing plants to meet stringent limits of technology (LOT) treatment for nitrogen removal (3-5 mg/L total effluent nitrogen). The anoxic capacity requirements for meeting LOT treatment are dependent on the growth rates of the denitrifying organisms. The Blue Plains Advanced Wastewater Treatment Plant (AWTP) is one of many facilities in the Chesapeake Bay region that is evaluating its ability to meet LOT treatment capability. The plant uses methanol as an external carbon source in a post-denitrification process. The process is very sensitive to denitrification in the winter. One approach to improve anoxic capacity utilization is to use an alternative substrate for denitrification in the winter to promote the growth of organisms that denitrify at higher rates. The aim of this study was to evaluate denitrification maximum specific growth rates for three substrates, acetate, corn syrup and methanol, at two temperatures (13 degrees C and 19 degrees C). These temperatures approximately reflect the minimum monthly and average annual wastewater temperature at the Blue Plains AWTP. The results suggest that the maximum specific growth rate (mu(max)) for corn syrup (1.3 d(-1)) and acetate (1.2 d(-1)) are higher than that for methanol (0.5d(-1)) at low temperature of 13 degrees C. A similar trend was observed at 19 degrees C.

Nitrification parameter measurement for plant design: experience and experimental issues with new methods.

Nitrification kinetics are important for process design, optimization, and capacity rating of activated sludge wastewater treatment plants. A Water Environment Research Foundation (WERF) project on Methods for Wastewater Characterization in Activated Sludge Modeling (WERF, 2003) focused significantly on the development of procedures for measuring the nitrifier maximum specific growth rate, micro(AUT). In addition, the importance of (and lack of data for) the nitrifier decay rate, b(AUT), was identified. This paper describes three bench-scale methods for measuring micro(AUT): the Low F/M SBR, Washout and High F/M methods. During the WERF project, the importance of pH and temperature control was investigated briefly; this paper summarizes further experimental work performed to address these issues. A summary of micro(AUT) measurements in a number of locations and using the different measurement techniques is provided.

Importance and measurement of decay rate when assessing nitrification kinetics.

Nitrification kinetics are important for process design, optimization and capacity rating of activated sludge wastewater treatment plants. Assessment of nitrification behaviour historically has focused on measuring the nitrifier maximum specific growth rate, micro(AUT). Very little attention has been directed at the of nitrifier organism rate has been assumed negligible. However, incorrect assessment of decay rate leads to errors in the micro(AUT) estimate; the magnitude of the error depends on the micro(AUT) measurement method employed. This paper illustrates why decay rate is important when measuring micro(AUT), and that the decay rate is significant. The paper also explains why measurement methods for nitrifier decay may have underestimated the decay rate. Results from an experiment incorporating improvements to previously suggested methods and data analysis are presented.

Feasibility studies and pre-design simulation of Warsaw's new wastewater treatment plant.

The proposed transfer of wastewater from the western part of Warsaw, across the Wisla (Vistula) River for joint treatment at the existing eastern side "Czajka" wastewater treatment plant (WWTP) will result in combined winter flows of approx. 580,000 m3 d(-1). One-year of pilot-scale studies defined the COD characteristics and kinetics of nitrogen removal and VFA production from primary sludge. BioWin simulation was used to size and price the optional processes and pointed to the Westbank process as the most cost-effective. The process consists of a sequence of a RAS pre-denitrification zone followed by an anaerobic, anoxic and aerobic zone. Some 100-150 t d(-1) of 10% methanol would be needed to remove 2-4 mg l(-1) of NO3-N above the recommended effluent level TN = 10 mg l(-1). Applying the principle of annual average 80% TN removal, and allowing for use of daily composite samples (rather than grab) could annually save the municipality over 1.5 million Euro on external carbon source.