BOD = [(D1-D2)-(B1-B2) f]/P. Where D1 is dissolved oxygen of diluted sample right after preparation. D2 is Dissolved Oxygen of sample after incubation.B1 is Dissolved oxygen of control before incubation. B2 is dissolved oxygen of control after incubation. F is fraction of diluted water in sample to dilution of water in control. P is fraction of waste water sample volume to total combined volume.

The gain of a control valve should never be lesser than 0.5. Gain is defined as ratio between differences in flow to differences in stoke or travel. In case value is lesser than 0.5 n re would be a problem in controlling valve.

There are different types of nitrogen present in wastewater. Basically, our types of nitrogen are present. They are organic nitrogen, ammonia nitrogen, nitrate nitrogen and nitrite nitrogen.

Piston actuators are preferred when high and fast stroking speed is required. This type of actuator utilises air pressure upto 150psig. This eliminates need for a pressure regulator.

Centrifugal blowers are used for fluid bed reactors. These are used for dust controlling systems also. These are used for aeration systems in water or waste water treatment plant.

Industries need aestically pleasant water with low turbidity, colour, taste and odour, absence of macro-organisms. The water should be free from organisms harmful to health.

Hardness is in between 50-100 ppm in case of moderately hard water. In case of soft water it is less than 50 ppm. In case of hard water, it is in between 100-150 ppm. In case of very hard water it is greater than 150 ppm.

The curve between control valve capacity and valve stem travel is known as inherent flow characteristics. This curve is obtained at a constant pressure drop. The relationship between control valve capacity and valve stem travel is known as flow characteristic of control valve.

Size of opening plays a major role in controlling flow rate but in globe valves, flow rate is controlled by lift of valve plug and not by size of opening in valve seat.

Pasteur invented hot air oven. Charles Chamberland invented autoclave. Arnold O. Beckman invented pH meter. Antonie van Leeuwenhoek is considered as far of microbiology.