Introduction to Environmental Engineering Code No. (PE389) Lec. 6

Wastewater Treatment

WASTEWATER CHARACTERISTICS Discharges into a sanitary sewerage system consist of domestic wastewater (sewage), industrial discharge. Industrial discharges vary widely with the size and type of industry and the amount of treatment applied before discharge into sewers.

Characteristics of Domestic Wastewater

Basic Criteria of Wastewater Disposal Systems The following basic criteria should be satisfied in the design and operation of any wastewater disposal system: 1. prevention of microbiological, chemical, and physical pollution of water supplies and contamination of fish and shellfish intended for human consumption; 2. prevention of pollution of bathing and recreational (activity) areas; 3. prevention of unpleasant odors; 4. prevention of human wastes and toxic chemicals from coming into contact with humans, animals, wildlife, and food chain crops or being exposed on the ground surface accessible to children and pets; and 5. strict adherence to standards for groundwater and surface-water protection and compliance with federal, state, and local regulations governing wastewater disposal and water pollution control.

CENTRAL WASTEWATER TREATMENT For any given wastewater in a specific location, the degree and type of treatment are variables that require engineering decisions. Often the degree of treatment depends on the capacity of the receiving water. DO sag curves can indicate how much BOD must be removed from wastewater so that the DO of the receiving water is not depressed too far. The amount of BOD that must be removed is an effluent standard and dictates in large part the type of wastewater treatment required.

Effluent standards "typical wastewater“ The effluent from this wastewater treatment must meet the following effluent standard:

Types of Treatment Systems 1. Primary treatment physical processes that remove non homogenuous solids and homogenize the remaining effluent. 2. Secondary treatment biological processes that remove most of the biochemical demand for oxygen. 3. Tertiary treatment physical, biological, and chemical processes to remove nutrients like phosphorus and inorganic pollutants, to deodorize and decolorize effluent water, and to carry out further oxidation.

PRIMARY TREATMENT screening were the first step in wastewater treatment because the most objectionable aspect of discharging raw sewage into watercourses is the floating material. A screen in a modern treatment plant removes materials that might damage equipment or hinder further treatment. In some older treatment plants screens are cleaned by hand, but mechanical cleaning equipment is used in almost all new plants. The second treatment step is the removal of grit or sand from the wastewater. (Grit and sand can damage equipment like pumps and flow meters and must be removed.)

PRIMARY TREATMENT The most common grit chamber is a wide place in the channel where the flow is slowed enough to allow the dense grit to settle out. Sand is about 2.5 times denser than most organic solids and thus settles much faster. The objective of a grit chamber is to remove sand and grit without removing organic material. Organic material must be treated further in the plant, but the separated sand may be used as fill without additional treatment. Most wastewater treatment plants have a settling tank after the grit chamber, to settle out as much solid material as possible. Settling tanks are also called sedimentation tanks or clarifiers.

PRIMARY TREATMENT The settling tank that immediately follows screening and grit removal is called the primary clarifier. The solids that drop to the bottom of a primary clarifier are removed as primary sludge. Primary sludge generally has a powerfully unpleasant odor, is full of pathogenic organisms, and is wet,

Primary Treatment

PRIMARY TREATMENT The objective of primary treatment is the removal of solids, although some BOD is removed as a consequence of the removal of decomposable solids. The wastewater described earlier might now have these characteristics: After primary treatment the wastewater may move on to secondary treatment.

Assignment # 6 Mention three important parameters should be recognized in order to caterorize wastewater. Draw a simplified flow diagram for primary treatment stages Explain all the processes involved within the primary treatment

Self- Study topics TYPES AND SOURCES OF GASEOUS AIR POLLUTANTS nongaseous air pollutants GLOBAL AND ATMOSPHERIC CLIMATE CHANGE HEALTH EFFECTS