wastewater influent is about two-thirds of its usual 300 to 450 mg/l COD value. If such a factor can be figured for a certain kind of wastewater, COD data can be used to predict BOD 5 test results that will not be known for 5 days.

TOTAL SUSPENDED SOLIDS TEST

Total suspended solids are those solids in wastewater that can be taken out with a filter having a specified pore size. Suspended solids are made up of settleable solids and nonsettleable solids. Suspended solids tests can be run with either grab or composite samples, but flow- proportional composite samples are the best for this test. Influent wastewater may have as much as 400 mg/l of suspended solids.

MIXED LIQUOR SUSPENDED SOLIDS (MLSS) TEST

The suspended solids test that is run on the aeration tank mixed liquor is called the mixed liquor suspended solids test or MLSS test. It is used as a control test to help find out whether to increase or decrease the rate of sludge return and when to waste sludge. The very high solids content of mixed liquor requires a larger diameter filter (11 centimeters instead of 2.4 centimeters) to prevent rapid clogging.

CHLORINE RESIDUAL TEST

When chlorine is used to disinfect the effluent, tests are needed to see if the chlorine residual requirement has been met. The chlorine residual test may be run using the iodometric or amperometric methods. Since grab samples are used for these tests, most states suggest that the test be run within 30 minutes after taking the sample.

FECAL COLIFORM TEST

The fecal coliform test is an indicator of harmful bacteria in the wastewater. Both the membrane filter and most probable number (MPN) can be used to run the test. If the sample is not prepared for the test on the site, it should be cooled to 4C within 30 minutes and then tested within 6 hours.

ALKALINITY

The alkalinity test can tell the operator a lot about the wastewater in the plant. A very high alkalinity in the wastewater may mean that an alkaline industrial waste has entered the system. The alkalinity test is often used to see how the anaerobic sludge digesters are working. The alkalinity in treatment lagoons usually goes down as the lagoon becomes septic. The alkalinity usually shows a 20 to 30 mg/l change before there is a change in pH.

LABORATORY RECORDS

Records can be used to find the best operating controls for a wastewater plant, problems that might arise in the plant, and the future needs of the plant. Records may also be used in court if a lawsuit is filed against the treatment plant.

The treatment plant should keep three kinds of records. These three types are physical records that describe in detail all areas of the plant itself, maintenance records that show what repair and cleaning has been done or needs to be done, and performance records that show the plant's operating data.

Physical records include operation and maintenance (O&M) manuals, actual plans and blueprints for the plant, shop drawings, O&M guides from equipment manufacturers, costs for all units, a hydraulic profile showing the height of water in all treatment units, and an equipment record. Under Public Law (PL) 92-500, consulting engineers are required to provide operation and maintenance (O&M) manuals for the treatment plants they design. These O&M manuals must meet the requirements of Considerations for Preparation of Operation and Maintenance Manuals, EPA, Washington, D.C., 1974.

Preventive maintenance in the treatment plant can reduce costly repairs and downtime on equipment. One of the key steps in a good maintenance program is keeping records. These records include the data needed to make a maintenance schedule, to estimate a maintenance budget, and to build up enough spare parts.

A record of all equipment in the plant must be made. This can be done on index cards. Each piece of equipment should be given a number based on where it is located in the plant. This number is written on an index card with the name of the equipment, where it is located in the plant, the name and address of the manufacturer or supplier, the cost, and when it was installed. The card should also have the type, model, serial, and any other code numbers, along with the capacity or size rating. The same card or another set of cards should include the type of maintenance