General...

Wastewater is the flow of used water from a community. The characteristics of the wastewater discharges will vary from location to location depending upon the population and industrial sector served, land uses, groundwater levels, and degree of separation between storm water and sanitary wastes. Domestic wastewater includes typical wastes from the kitchen, bathroom, and laundry, as well as any other wastes that people may accidentally or intentionally pour down the drain. Sanitary wastewater consist of domestic wastewater as well as those discharged from commercial, institutional, and similar facilities. In general, the volume of sanitary wastewater generated is about 400 liters per capita. However, the range of flow usually varies from a minimum of about 20 % to a maximum of about 400 % of the average dry weather flow for small communities and about 200% for larger communities. Industrial wastes will be as varied as the industries that generate the wastes. The quantities of storm water that combines with the domestic wastewater will vary with the degree of separation that exists between the storm sewers and the sanitary sewers. Most new sewerage systems are separate, collect sanitary wastewater and storm wastes, whereas older combined systems collect both sanitary wastewater and storm water.

Physically, wastewater is usually characterized by a grey colour, musty odour, a solids content of about 0.1 %, and a 99.9 % water content. The solids can be suspended (about 30 %) as well as dissolved (about 70 %). Dissolved solids can be precipitated by chemical and biological processes. From a physical point of view the suspended solids can lead to the development of sludge deposits and anaerobic conditions when discharged into the receiving environment.

Chemically, wastewater is composed of organic and inorganic compounds as well as various gases. Organic components may consist of carbohydrates, proteins, fats and greases, surfactants, oils, pesticides, phenols, etc. Inorganic components may consist of heavy metals, nitrogen, phosphorus, pH, sulfur, chlorides, alkalinity, toxic compounds, etc. In domestic wastewater, the organic and inorganic portion is approximately 50 % respectively. However, since wastewater contains a higher portion of dissolved solids than suspended, about 85 to 90 % of the total inorganic component is dissolved and about 55 to 60 % of the total organic component is dissolved. Gases commonly dissolved in wastewater are hydrogen sulfide, methane, ammonia, oxygen, carbon dioxide and nitrogen. The first three gases result from the decomposition of organic matter present in the wastewater.

Biologically, wastewater contains various microorganisms but the ones that are of concern are those classified as protista, plants, and animals. The category of protista includes bacteria, fungi, protozoa, and algae. Plants include ferns, mosses, seed plants and liverworts. Invertebrates and vertebrates are included in the animal category. In terms of wastewater treatment, the most important category are the protista, especially the bacteria, algae, and protozoa. Also, wastewater contains many pathogenic organisms which generally originate from humans who are infected with disease or who are carriers of a particular disease. Since the identification of pathogenic organisms in water and wastewater is very time consuming and difficult, the coliform group of organisms which are more numerous and more easily tested for, is used as an indicator of the presence of pathogenic organisms. However, this test does not accurately reflect the presence or absence of all pathogens that may be found in the treated effluent, i.e. viruses. Typically, the concentration of fecal coliforms found in raw wastewater is about several hundred thousand to tens of million per 100 mL of sample.

Municipal Water Use...

If field measurements of wastewater flowrates are not possible and actual wastewater flowrate data are not available, water supply records can often be used as an aid to estimate wastewater flowrates. Municipal water use is generally divided into four categories ; (1) domestic (water used for sanitary and general purposes), (2) industrial (nondomestic purposes), (3) public service (water used for fire fighting, municipal landscape irrigation) and (4) unaccounted for system losses and leakage

In Türkiye, Iller Bank is responsible for design and control of infrastructure projects. Iller Bank has been establishing technical and administrative regulations related to water distribution networks, sewer systems, and stormwater drainage systems since early 1950s. Typical per capita values for aforementioned uses, stated at the Directions No.3 are shown below.

"Domestic Water Use in Türkiye"...

System losses and leakage vary widely from one city to another depending on the age of drinking water distribution network, soil characteristics, and construction quality. For example, network loss for the Metropolitan City of Izmir varies between 40 % and 80 %. For a relatively new network, unaccounted losses and leakage vary within the range of 30 to 120 L/capita.day.

The water used by commercial facilities for sanitary purposes vary widely depending on the type of activity. Typical water - use values for various types of commercial facilities are shown below. For large commercial water - using facilities such as laundries and car washes, careful estimates of actual water use should be made.

"Commercial Water Use"...

Variations in Wastewater Flowrates...

Because wastewater consists primarily of used water, the portion of the water supplied that reaches the collection system must be estimated. A considerable portion of the water produced does not reach the sanitary sewer system and includes ; (1) product water used by manufacturing establishments, (2) water used for landscape irrigation, system maintenance, and extinguishing fires, (3) water used by consumers whose facilities are not connected to sewers and (4) leakage from water mains and service pipes. As a mean value of 80 % of the per capita consumption of water becomes wastewater. In some cases, excessive infiltration, roof water, and water used by industries that is obtained from privately owned water supplies (e.g. well) make the quantity of wastewater larger than the water consumption from the public supply. If a community has well - constructed sewers and if stormwater is excluded and there is no substantial change in the industrial uses, the variation from year to year in the ratio of wastewater to water supply will not be great.

"Hourly Variations in Wastewater Flowrates - 1"...

Wastewater flowrates reflect short - term, seasonal, and industrial variations. With short - term variation, minimum flows occur during the early morning hours when water consumption is lowest and when the base flow consists of infiltration and small quantities of sanitary wastewater. Seasonal variations of domestic wastewater flows are commonly observed at resort areas, in small communities with college campuses, and in communities with seasonal commercial and industrial activities. Industrial variation is mainly caused by daily cleanup and shutdown. On the other hand, some industries, such as cannery, have a production portfolio which includes too many products (e.g. bean, peach, pear, fruit, jam). Typical hourly variation in domestic wastewater flowrates are shown below.

"Hourly Variations in Wastewater Flowrates - 2"...

Infiltration...

The presence of high groundwater results in leakage into sewers and in an increase in the quantity of wastewater and the expense of disposing of it. The amount of flow that can enter a sewer from groundwater, or infiltration, may vary between ;

• 200 - 28,000 L / ha.day
• 8,600 - 24,000 L / km.day
• 9.4 - 940 L / mm.km.day

Flowrates for Design...

Average Daily Flow : The average flowrate occuring over a 24 - hour period based on total annual flowrate data. It is used in evaulating treatment plant capacity and in developing flowrate ratios used in design. Maximum Daily Flow : The maximum flowrate that occurs over a 24 - hour period based on annual operating data. It is important particularly in the design of facilities involving retention time such as equalization basins and chlorine-contact tanks. Peak Hourly Flow : The peak sustained hourly flowrate occuring a 24 - hour period based on annual operating data. It is needed for the design of collection and interceptor sewers, pumping stations, flow - meters, grit chambers, sedimentation tanks, chlorine - contact tanks, and conduits or channels in the treatment plant. Minimum Daily Flow : The minimum flowrate that occurs over a 24 - hour period based on annual operating data. It is important in the sizing of conduits where solids deposition might occur at low flowrates. Minimum Hourly Flow : The minimum sustained hourly flowrate occuring over a 24 - hour period based on annual operating data. It is needed for sizing of flow - meters and chemical dosing systems. It is also important for trickling filters and pumping stations. Sustained Flow : The flowrate value sustained or exceeded for a specified number of consecutive days based on annual operating data. It is used in sizing equalization basins and other plant hydraulic components.