Biochemical oxygen demand

Biochemical oxygen demand (BOD) is the measurement of oxygen consumed by living microorganisms (primarily bacteria) while utilizing the organic matter present in a water or waste sample under conditions as close as possible to those that occur in nature. Microbial conversion of nitrate to nitrite will also contribute to BOD. Non-biodegradable (or refractory) organic compounds will not contribute to BOD.

In order to make BOD test quantitative, the samples must be protected from the air to prevent reoxygenation as the dissolved oxygen concentration diminishes. Also, high concentration wastes must be diluted to ensure that dissolved oxygen will be present throughout the test duration. It is important that the environmental conditions during the test be suitable for the living ‘ organisms. Therefore nutrients are added to the dilution water. Nutrient blanks must be included in the test to ensure that the nutrient-enriched dilution water does not contribute to BOD. For industrial wastes which may have low populations of microorganisms, seed microorganisms may be required.

The rate at which biologically medicated reactions proceed is primarily governed by the microbial population size and temperature. For this reason, BOD tests are carried out at a constant temperature of 20°C.

Complete biodegradation of the organic material in a water sample may take 14 to 20 days. However, 60 to 70% of the BOD in most domestic and industrial waste is expressed within 5 days. Therefore, in order to make BOD analyses less time-consuming (1'. e. make it possible to complete the analyses within a 5 day work week), the BOD measurement was adopted and is the basis for many' regulatory standards.

BOD can also be defined as the amount of oxygen required by bacteria while stabilizing decomposable organic matter under aerobic conditions. The quantity of oxygen required may be taken as a measure of its content of decomposable organic matter. The rate of BOD exertion is governed by the characteristics of sewage, its decomposable organic content, bacterial population, and temperature.

RS Aggarwal Aptitude Book PDF Free Download

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Limitations of Terzaghi Theory

Limitations of Terzaghi Theory The value of the coefficient of consolidation has been assumed to be constant. The distance d of the drainage path cannot be measured accurately in the field. The thickness of the deposit is generally variable, and an average value has to be estimated. There is sometimes difficulty 1n locating the drainage face, and sometimes thin previous seams that can act as good drainage faces are missed in the boring operations. The equation is based on the assumption that the consolidation is one-dimensional. In the field, the consolidation is generally 3-dimensional. The lateral drainage may have a significant effect on the time rate of consolidation. The initial consolidation and secondary consolidation have been neglected. Sometimes these form an important part of the total consolidation. In actual practice, the pressure distribution may be far from linear or uniform.

Comparison between VSI and CSI

Comparison between VSI and CSI In power electronic systems, inverters are an essential component that converts direct current (DC) into alternating current (AC). There are two main types of inverters used in power electronic systems: Voltage Source Inverters (VSI) and Current Source Inverters (CSI). Both have their own unique advantages and disadvantages, and the choice of which to use depends on the specific application and the desired outcome. Comparisons between voltage source inverters and current source inverters are as follows. In voltage source inverters, the input voltage is maintained constant and the amplitude of the output voltage does not depend on the load. However, the waveform of load current, as well as its magnitude, depends upon the nature of load impedance. In current source inverters (CSI), the input current is constant but adjustable. The amplitude of output current from CSI is freelance of the load. However, the magnitude of output voltage and its undulation outp

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