Figure 10-1. - Illustrations of laboratory apparatus - Continued.

manufacturer's instructions for the proper maintenance procedures for each piece of equipment. Table 10-11 gives some basic guidelines for the maintenance and use of various types of laboratory equipment.

Safety should be vital to all personnel conducting sewage tests. Good housekeeping is essential in a laboratory to prevent mishaps and damage to expensive equipment. Each piece of equipment should be cleaned and returned to its proper place after being used.

When conducting sewage tests, it is always wise for the operator to avoid actual contact of the hands with the sewage samples or other filth. Hands must be kept out of the nose, mouth, and eyes. It is particularly important to use gloves when the hands are chapped, or burned, or the skin is broken from any wound. Operators should thoroughly wash their hands with plenty of soap and hot water before eating.

DISSOLVED OXYGEN TEST

The DO test finds the milligrams per liter (mg/l) of oxygen that is dissolved in water or wastewater. Oxygen exists as a gas and can dissolve in water in only a limited amount. Pure water at 20C at sea level can hold a maximum of 9.17 mg/l of DO. Raising the temperature, salt content, or altitude will lower the DO level in the water. An important thing to remember is that this test should be run as soon as possible after the sample is taken. It must always be run as a grab sample. It is best to test several samples taken at different times during the day because the DO content of wastewater may vary. If incoming wastewater has no DO, it is septic. Most wastewater treatment plants are not built to treat septic wastewater. A great deal of plant and animal life that lives in water and wastewater, including necessary microorganisms, needs DO just as we need oxygen from the air. If the DO is used up, aerobic organisms will die and the water will become anaerobic or septic and foul