Sewage

Some of the Primary Constituents of Sewage from a City 

Oxygen-demanding substances Mostly organic materials, particularly human feces and urine Consume dissolved oxygen 

Refractory organics Industrial wastes, household products Toxic to aquatic life 

Viruses Human wastes Cause disease (possibly cancer) major deterrent to sewage recycle through water systems 

Detergents Household detergents Esthetics, prevent grease and oil removal, toxic to aquatic life 

Per capita flow varies from 378 L/d (2) for a residential community to 1134 L/d for highly industrialized areas. The concept of population equivalent is used for evaluating industrial waste contributions to sewage. It is appHed when planning for hydraulic and BOD loadings. 

Because of large equipment and land requirements, capital costs for wastewater-treatment plants are high. A collection system that conveys both sanitary and storm flows must be designed to deal with high peak flows at the treatment plant detention basins are usually provided in order to smooth the flow into the plant and reduce the sudden peak flow. In the absence of such precautions, it may be necessary to by-pass a portion of the flow. 

Some materials, such as gasoline and heavy metals, may damage the collection system, cause explosions, or upset the treatment processes. 

Therefore, they cannot be discharged directly into the system. These prohibitions are governed by sewer ordinances. 

Small Communities. Small communities and recent subdivision additions to larger communities, which have not yet been connected to municipal collection systems, must have a means of waste disposal. Septic tanks are a possibiHty, but require periodic servicing and cleaning. Furthermore, the soil is not always suitable for accepting the effluent. An alternative is the package plant. These units are commercially produced to serve small areas. They furnish primary treatment and some secondary treatment, and require only minimal operating supervision. Capacity can be varied as needs dictate. In general, pubHc health authorities prefer such installations instead of septic tanks. 

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If the composition of the waste stream is known, then the theoretical oxygen demand can be calculated from the appropriate stoichiometric equations. As a first level of approximation, we can assume that this theoretical oxygen demand would be equal to the COD. Then, experience with domestic sewage indicates that the average ratio of COD to BOD will be on the order 1.5 to 2. The following example will help to clarify these relationships. 

Enzymes are used in baking, cheese manufacture, wine-making, brewing and distillation, pharmaceuticals, leather tanning, paper manufacture, adhesives, sewage disposal, animal feeds and in detergents. 

Sewage gases Sewage methane Sewage treatment... 

Water, sewage Water softeners Water softening... 

Most aquaculture faciUties release water constandy or periodically into the environment without passing it through a municipal sewage treatment plant. The effects of those efduents on natural systems have become a subject of intense scmtiny in recent years and have, in some instances, resulted in opposition to further development of aquaculture faciUties in some locales. There have even been demands that some existing operations should be shut down. 

Under the pressure of progressively more stringent government regulations with regard to permissible levels of residual NH and urea content in wastewaters, the fertilizer industry made an effort to improve wastewater treatment (see also Water, sewage). 

The xylenes are mildly toxic. They ate mild skin irritants, and skin protection and the cannister-type masks are recommended. The oral LD q value for rats is 4300 ppm. The STEL for humans is 150 ppm. Xylenes show only mild toxicity to fish, and the threshold limit for crop damage is 800—2400 ppm. Biodegradation with activated seed is slow, and sewage digestion is impaired by 0.1% concentrations. In the event of a spih, oil-skimming equipment, adsorbent foam, and charcoal maybe used for cleanup. 

Dissolved matter lowers oxygen solubihty. At 20°C and 101.3 kPa (1 atm), the equihbrium concentration of dissolved oxygen in seawater is 7.42 mg/L. It is 9.09 mg/L in chloride-free water and 9.17 mg/L in clean water. This lessening of oxygen solubihty is of importance to wastewater treatment. The solubihty of atmospheric oxygen in a domestic sewage is much less than in distilled water (12). 

Filtration is the separation of two phases, particulate form, ie, soHd particles or Hquid droplets, and continuous, ie, Hquid or gas, from a mixture by passing the mixture through a porous medium. This article discusses the more predominant separation of soHds from Hquids. Filtration of soHd particles or Hquid droplets from gases is dealt with elsewhere (see Airpollution controlmethods). The oldest recorded appHcations of filtration are the purifications of wine and water practiced by the ancient Greeks and Romans. Cake filters, such as the rotary vacuum filter and the filter press, were developed much later from the necessity to filter sewage. 

Multicompartment dmm filters range in size from about 1 m to over 100 m they are widely used in mineral and chemical processing, in the pulp and paper industry, and in sewage and waste materials treatment. 

Washing and dewatering by air displacement of cakes are possible. AppHcations are in the treatment of minerals, in the sugar industry, and in the treatment of municipal sewage sludge and fillers like talc, clay, whiting, etc. 

The ECLP tube press was originally developed for the filtration of china clay but has been used with many other slurries such as those in mining, Ti02, cement, sewage sludge, etc. The typical cycle time is about four minutes or more. 

The vertical recessed plate automatic press, shown schematically in Figure 15 and described previously, is another example of a horizontal belt pressure filter. Cycle times ate short, typically between 10 and 30 minutes, and the operation is fully automated. The maximum cake thickness is about 35 mm washing and dewatering (by air displacement) of cakes is possible. Apphcations include treatment of mineral slurries, sugar, sewage sludge, and fillers like talc, clay, and whiting. 

Originally designed for the continuous filtration of conditioned sewage sludges, as were most of the filter belt presses available, the Manor Tower press is increa singly used for the treatment of paper mill sludge, coal, or flocculated clay slurries. 

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