Archive for April, 2014

« Older Entries
Newer Entries »

BOD Incubator

April 19th, 2014

BOD incubator is the most versatile and reliable low temperature incubator which is designed to maintain at 20°C, necessary for Biological Oxygen Demand/Biochemical Oxygen Demand (BOD) determination. BOD incubators provide controlled temperature conditions for accelerated tests and exposures.  The biological oxygen demand (BOD) is an empirical test in which standardized laboratory procedures are used to determine the relative oxygen requirements of microbes in wastewaters, effluents, and polluted waters and in simple words, It is a chemical process that determines how fast biological organisms use up oxygen in a body of water or it measures the oxygen required for the biochemical degradation of organic material (carbonaceous demand) and the oxygen used to oxidize inorganic materials, such as sulfides and ferrous iron  The seeding and dilution procedures provide an estimate of the BOD at pH 6.5 to 7.5.

Overview of BOD Methodology

Biochemical oxygen demand (BOD), sometimes referred to as biological oxygen demand, is a quantitative expression of microbes ability to deplete the oxygen content of a wastewater. This depletion takes place due to the microbes consuming organic matter in the water via aerobic respiration. This type of respiration uses oxygen as an electron acceptor, and the organic material being consumed provides the energy source. This organic matter also undergoes oxidation without the aid of microbes, which can be measured using the chemical oxygen demand (COD) procedure.

The method consists of placing a sample in a full, airtight bottle and incubating the bottle under specified conditions for a specific time. Dissolved Oxygen (DO) (amount of oxygen present in water body) is measured initially and after incubation. The BOD is computed from the difference between the initial and final DO.

High levels of BOD in streams cause the dissolved oxygen (DO) content of the water to drop. It is this DO that fish, and zooplankton use to survive. If the DO drops to below a critical level the ecology of the stream could begin to die off as well. This condition can lead to an increase in anaerobic bacteria (species that can live in the absence of oxygen) that leads to the production of foul-smelling, and possibly toxic gases. These gases may include methane, hydrogen sulfide, and ammonia. If this water were to enter into groundwater sources one can imagine the potential problems with toxicity to humans.

Factors affecting the BOD

Some factors may affect the accuracy and precision of BOD measurements. Such as

  • soluble versus particulate organics,
  • settle able and float able solids,
  • oxidation of reduced iron and sulfur compounds, or
  • lack of mixing
  • Oxidation of reduced forms of nitrogen, such as ammonia and organic nitrogen, can be mediated by microorganisms and exert nitrogenous demand. Nitrogenous demand historically has been considered as an interfering factor in the determination of BOD, and the inclusion of ammonia in the dilution water contributes an external source of nitrogenous demand. The interference from nitrogenous demand can now be prevented by an inhibitory chemical (If an inhibiting chemical is not used, the oxygen demand measured is the sum of carbonaceous and nitrogenous demands).

BOD and Water Pollution

Biological Oxygen Demand (BOD) is one of the most common measures of pollutant organic material in water. BOD indicates the amount of pollutents present in water. Therefore, a low BOD is an indicator of good quality water, while a high BOD indicates polluted water. Dissolved oxygen (DO) is consumed by bacteria when large amounts of organic matter from sewage or other discharges are present in the water. DO is the actual amount of oxygen available in dissolved form in the water. When the DO drops below a certain level, the life forms in that water are unable to continue at a normal rate. The decrease in the oxygen supply in the water has a negative effect on the aquatic life.

The BOD test serves an important function in stream pollution-control activities. It is a bioassay procedure that measures the amount of oxygen consumed by living organisms while they are utilizing the organic matter present in waste, under conditions similar in nature. The other traditional tests or indicators for water quality are chemical oxygen demand (COD) and pH.

 

Applications

  • In measuring waste loadings to treatment plants and in evaluating the BOD-removal efficiency of such treatment systems.
  • It measures the molecular oxygen utilized during a specified incubation period for the biochemical degradation of organic material (carbonaceous demand) and the oxygen used to oxidize inorganic material such as sulfides and ferrous iron.
  • It measures the amount of oxygen used to oxidize reduced forms of nitrogen (nitrogenous demand) unless their oxidation is prevented by an inhibitor.

Safety Guidelines

  • Do not cover the shelves of the incubator with aluminum foil. It may cause temperature control malfunction or an obstruction of air circulation.
  • Control the temperature of incubator regularly to avoid any error.
  • While performing test BOD bottles should be closed in BOD incubator.
  • BOD incubators are not designed to store eating and drinking materials and cosmetics too.
  • Flammable substances are not permitted to be stored.

Comments Off on BOD Incubator »

Posted in BOD Incubator

Tags:

Ball mill – Working and Its Advantages

April 17th, 2014

Ball mill works on impact principle that is size reduction is done by the impact. It contains a hollow cylinder shell that rotates around its axis and is partially filled with the balls. The ball mill may be operated in a batch or continuous fashion and wet or dry.

In case of continuously operated ball mill, the material to be ground is fed from the left through a 60 degree cone and the product is discharged through a 30 degree cone to the right. As the shell rotates, the balls are lifted up on the rising side of the shell and then they cascade down from near to the top of the shell. In doing so, the solid particles in between the balls are ground and reduced in size by impact.

The ball mill contains the balls of various sizes. As the shell rotates, the large balls segregate near the feed end and small balls segregate near the end product that is going to be discharge. The initial breaking of the feed particles, therefore, is done by the largest balls dropping the largest distance and the small particles are ground by small balls dropping from much smaller distances. If the rate of the feed is increased, coarser product will be obtain and if the speed of the rotation is increased (that should be less than critical speed), the fineness for a given capacity increases.

During grinding the balls themselves wear and are constantly replaced by new ones so that the ball mill contains balls of various ages and of various sizes. In case of batch operated ball mills, a measured quantity of solid to be ground is charged into the ball mill through the opening in the shell. The opening is then closed and the ball mill is rotated for several hours. It is then stopped and the product is discharged.

In case of wet grinding, there is low power consumption, increased capacity, reduction in the formation of fines, facilitates the removal of product and no dust formation.

Advantages of Ball Mill

  • The cost of installation is low.
  • The cost of power required is low.
  • It is suitable for materials of all degree of hardness.
  • It is suitable for batch as well as continues operations.
  • The grinding medium is cheap.

Comments Off on Ball mill – Working and Its Advantages »

Posted in Ball mill

Tags:

Ball mill- factors influencing the size of product

April 17th, 2014

Ball mill that works on the principle of impact is an efficient technique of size reduction through grinding. The size reduction is an important factor for many industrial applications as this process is carried out to increase the surface area, to intimate mixing and to improve dissolution rate, solubility, binding strength and dispersion properties. Therefore it is important to maintain the size of products there are many factors that influence the size of product, some of these factors are;

Feed rate – With a high feed rate, less size reduction is effected since in this case the material is present in the mill for a shorter time.

Properties of the feed material – with a hard material, a smaller size reduction is achieved.

Weight of balls – With a heavy charge of balls, there is production of fine product. One can increase the weight of the charge by increasing the number of balls or by using a ball material of high density. Optimum grinding conditions are obtained when the volume of the balls is equal to 50 percent that of the ball mill. So the variation in the weight of balls is done by using materials of different densities.

Speed of rotation of mill – At low speeds, the balls simply roll over one another and little grinding is obtained while at very high speeds, the balls are simply carried along the walls of the shells and little or no grinding takes place, so for an effective grinding, the ball mill should be operated at a speed that is optimum speed equal to 50 to 75 percent of the critical speed (the minimum speed at which centrifuging occurs is called the critical speed of the ball mill, and under these conditions, centrifugal force will be exactly balanced by the weight of the ball, little or no grinding takes place when mill is centrifuging, therefore to operate practically the mill, the operating speed must be less than the critical speed).

Comments Off on Ball mill- factors influencing the size of product »

Posted in Ball mill

Tags: