Biological Wastewater Management
From Swikipedia
Introduction
Biological wastewater management entails purifying wastewater in a natural or emulated wetland environment. Such systems are powered mainly by sunlight and achieve purification through the combined action of living food chains, many of which are microscopic.
Brief Description
The Process
The following explains the process of biological wastewater treatment:
• Bacteria use oxygen to burn or break down organic carbons into carbon dioxide, water and energy.
• This energy is then used to fuel bacteria growth and metabolic activities.
• Oxygen being a crucial component, during the biological treatment process, air or pure oxygen is introduced into the tank.
• This process, known as aeration, is essential in fuelling the aerobic respiration of the bacteria.
Biological Treatment Plant
A biological treatment plant is made up of three parts:
• Primary Phase: In this phase, the settlement of solid waste occurs.
• Secondary Phase: Here the main biological treatment occurs.
• Tertiary Phase: In this phase, the quality of the effluent is further improved by removing any nitrates, phosphates, residual suspended solids or pathogens in the water.
The growth rate and activities of the carbonaceous bacteria found in active sludge during the Secondary Phase doubles with every 10°C increase in temperature, between the range of 0°C to 30°C. Solubility of oxygen, on the other hand, reduces as temperature increases, making optimal aeration more difficult and costly as temperature within the tank rises. Since approximately 50% of the energy cost in a normal biological treatment plant goes to aeration, this inversed relationship between the solubility of oxygen and performance of bacteria means that oxygen concentration and temperature must be carefully managed to achieve optimal performance per unit cost.
Advantages:
• Like all biological systems, operation takes place at ambient temperature. There is no need to heat or cool the water, which saves on energy consumption.
• As wastewater treatment operations take much space, they are located outdoor, and this implies that the system must be able to operate at seasonally varying temperatures. Cells come in a mix of many types, and accommodation to a temperature change is simply accomplished by self adaptation of the cell population.
References:
http://www.eutechinst.com/tips/do/08_DO_wastewater.pdf
http://engineering.dartmouth.edu/~cushman/courses/engs37/BioTreatmentTypes.pdf
