CHAPTER 10 SEWAGE TREATMENT AND DISPOSAL

Sewage is the wastewater of community life. In composition it includes dissolved and suspended organic solids that are liable to become putrid and decay. Sewage contains countless numbers of living organisms, bacteria, and other microorganisms whose life activities cause the process of decomposition. When decay proceeds under anaerobic conditions (an absence of dissolved oxygen), offensive conditions result and odors and unsightly appearances are produced. When decay proceeds under aerobic conditions (dissolved oxygen present), offensive conditions do not result and the process is accelerated.

It is important to remove sewage and other wastes to an area away from the center of activity. It is only by such practices that the environment can be maintained in an acceptable and safe condition. Among the waste products of life are the disease-producing (pathogenic) bacteria and viruses that can be readily transferred by sewage from sick individuals to well ones. Procedures for proper disposal of sewage are necessary to protect the health and comfort of the people and to maintain the cleanliness of the environment.

The degree of treatment used for sewage depends on two main considerations: (1) health protection for individuals in the command and community and (2) prevention of water pollution. State and local authorities with statutory authority in pollution control have established standards of purity that are necessary to prevent pollution of natural waters. Accordingly, when a Navy installation discharges liquid waste into controlled waters, the standards set by state and local authorities must be maintained. As a Utilitiesman you may be involved in the installation, operation, and maintenance of systems designed to meet the above requirements. This chapter discusses the major sources of sewage along with sampling and testing procedures and monitoring of sewage disposal influents. In addition to these subjects, septic tanks, cesspools, and leaching fields are also discussed.

SOURCES OF RAW SEWAGE

The major sources of raw sewage are domestic sewage, industrial sewage, and storm water.

DOMESTIC SEWAGE

Domestic sewage consists of waste from toilets, lavatories, urinals, bathtubs, showers, home laundries, and kitchens. It also includes similar wastes from medical dispensaries and hospitals.

INDUSTRIAL SEWAGE

Industrial waste, depending upon the source, has characteristics that are different from domestic waste. Some of these wastes are dangerous to plant operators as well as to the treatment plant and collection system. Industrial waste sources include, but are not limited to, laundry and dry-cleaning plants, metal-cleaning and plating processes, paint spray booths, aircraft and vehicle cleaning racks, boiler plants, photographic processing systems, and fire-fighting activities. Most industrial waste requires pretreatment before being introduced into a collection system at their source.

Industrial wastes can also be very high or low in pH because of acids and/or bases used in their processes. You may expect intense colors in wastes from painting areas. Grit, salt, and dirt levels may be high from vehicle wash racks. Radioactive wastes must never be dumped into. regular collection systems. They must be handled separately and, in most cases, very carefully. Explosive or flammable liquids can often enter the system from fuel storage areas. These liquids also create a dangerous fire hazard in a sewage treatment plant.

STORM WATER

Storm water should be excluded from the sewage collection system as much as possible. Heavy input of storm water can disturb the operation of a treatment plant by sending it too much water, a problem called hydraulic overloading.

This situation may force diverting or bypassing effluent from the treatment plant. Bypassing is normally a violation of National Pollutant Discharge Elimination System (NPDES) permits. These permits are controlled by the Environmental Protection Agency (EPA). Bypassing can result in releasing bacteria, heavy metals, and other dangerous contaminants into receiving waters. It is to be avoided whenever possible.

Very large paved or roofed areas should not be drained into the sanitary collection system. Maintenance personnel should prevent stormwater infiltration as much as possible by ensuring manholes are sealed, pipes are not cracked or broken, and all leaking joints are repaired.

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