condoms, and expired medications, even at the risk of causing blockages. the privacy of a toilet offers a clandestine means of removing embarrassing evidence by flushing such things as drug paraphernalia, pregnancy test kits, combined oral contraceptive pill dispensers, and the packaging for those devices. there may be reluctance to retrieve items like children's toys or toothbrushes which accidentally fall into toilets, and items of clothing may be found in sewage from prisons or other locations where occupants may be careless. trash and garbage in streets may be carried to combined sewers by stormwater runoff. micro-pollutants sewage contains environmental persistent pharmaceutical pollutants. trihalomethanes can also be present as a result of past disinfection. sewage may contain microplastics such as polyethylene and polypropylene beads, or polyester and polyamide fragments from synthetic clothing and bedding fabrics abraded by wear and laundering, or from plastic packaging and plastic-coated paper products disintegrated by lift station pumps. pharmaceuticals, endocrine disrupting compounds, and hormones may be excreted in urine or feces if not catabolized within the human body. some residential users tend to pour unwanted liquids like used cooking oil,: 228 lubricants,: 228 adhesives, paint, solvents, detergents,: 228 and disinfectants into their sewer connections. this behavior can result in problems for the treatment plant operation and is thus discouraged. typical sewage composition factors that determine composition the composition of sewage varies with climate, social and economic situation and population habits.: 28 in regions where water use is low, the strength of the sewage (or pollutant concentrations) is much higher than that in the united states where water use per person is high.: 183 household income and diet also plays a role: for example, for the case of brazil, it has been found that the higher the household income, the higher is the bod load per person and the lower is the bod concentration.: 57 concentrations and loads typical values for physical–chemical characteristics of raw sewage in developing countries have been published as follows: 180 g/person/d for total solids (or 1100 mg/l when expressed as a concentration), 50 g/person/d for bod (300 mg/l), 100 g/person/d for cod (600 mg/l), 8 g/person/d for total nitrogen (45 mg/l), 4.5 g/person/d for ammonia-n (25 mg/l) and 1.0 g/person/d for total phosphorus (7 mg/l).: 57 the typical ranges for these values are: 120–220 g/person/d for total solids (or 700–1350 mg/l when expressed as a concentration), 40–60 g/person/d for bod (250–400 mg/l), 80–120 g/person/d for cod (450–800 mg/l), 6–10 g/person/d for total nitrogen (35–60 mg/l), 3.5–6 g/person/d for ammonia-n (20–35 mg/l) and 0.7–2.5 g/person/d for total phosphorus (4–15 mg/l).: 57 for high income countries, the "per person organic matter load" has been found to be approximately 60 gram of bod per person per day. this is called the population equivalent (pe) and is also used as a comparison parameter to express the strength of industrial wastewater compared to sewage. values for households in the united states have been published as follows, whereby the estimates are based on the assumption that 25% of the homes have kitchen waste-food grinders (sewage from such households contain more waste): 95 g/person/d for total suspended solids (503 mg/l concentration), 85 g/person/d for bod (450 mg/l), 198 g/person/d for cod (1050 mg/l), 13.3 g/person/d for the sum of organic nitrogen and ammonia nitrogen (70.4 mg/l), 7.8 g/person/d for ammonia-n (41.2 mg/l) and 3.28 g/person/d for total phosphorus (17.3 mg/l). the concentration values given here are based on a flowrate of 190 l per person per day.: 183 a united states source published in 1972 estimated that the daily dry weight of solid wastes per capita in sewage is estimated as 20.5 g (0.72 oz) in feces, 43.3 g (1.53 oz) of dissolved solids in urine, 20 g (0.71 oz) of toilet paper, 86.5 g (3.05 oz) of greywater solids, 30 g (1.1 oz) of food solids (if garbage disposal units are used), and varying amounts of dissolved minerals depending upon salinity of local water supplies, volume of water use per capita, and extent of water softener use.: 234 sewage contains urine and feces. the mass of feces varies with dietary fiber intake. an average person produces 128 grams of wet feces per day, or a median dry mass of 29 g/person/day. the median urine generation rate is about 1.42 l/person/day, as was determined by a global literature review. flowrates the volume of domestic sewage produced per person (or "per capita", abbreviated as "cap") varies with the water consumption in the respective locality.: 11 a range of factors influence water consumption and hence the sewage flowrates per person. these include: water availability (the opposite of water scarcity), water supply options, climate (warmer climates may lead to greater water consumption), community size, economic level of the community, level of industrialization, metering of household consumption, water cost and water pressure.: 20 the production of sewage generally corresponds to the water consumption. however water used for landscape irrigation will not enter the sewer system, while groundwater and stormwater may enter the sewer system in addition to sewage.: 22 there are usually two peak flowrates of sewage arriving at a treatment plant per day: one peak is at the beginning of the morning and another peak is at the beginning of the evening.: 24 with regards to water consumption, a design figure that can be regarded as "world average" is 35–90 l per person per day (data from 1992).: 163 the same publication listed the water consumption in china as 80 l per person per day, africa as 15–35 l per person per day, eastern mediterranean in europe as 40–85 l per person per day and latin america and caribbean as 70–190 l per person per day.: 163 even inside a country, there may be large variations from one region to another due to the various factors that determine the water consumption as listed above. a flowrate value of 200 liters of sewage per person per day is often used as an estimate in high income countries, and is used for example in the design of sewage treatment plants. for comparison, typical sewage flowrates from urban residential sources in the united states are estimated as follows: 365 l/person/day (for one person households), 288 l/person/day (two person households), 200 l/person/day (four person households), 189 l/person/day (six person households).: 156 this means the overall range for this example would be 189–365 l (42–80 imp gal; 50–96 us gal). analytical methods general quality indicators this section is an excerpt from wastewater quality indicators. wastewater quality indicators are laboratory test methodologies to assess suitability of wastewater for disposal, treatment or reuse. the main parameters in sewage that are measured to assess the sewage strength or quality as well as treatment options include: solids, indicators of organic matter, nitrogen, phosphorus, indicators of fecal contamination.: 33 tests selected vary with the intended use or discharge location. tests can measure physical, chemical, and biological characteristics of the wastewater. physical characteristics include temperature and solids. chemical characteristics include ph value, dissolved oxygen concentrations, biochemical oxygen demand (bod) and chemical oxygen demand (cod), nitrogen, phosphorus, chlorine. biological characteristics are determined with bioassays and aquatic toxicology tests. specific organisms and substances sewage can be monitored for both disease-causing and benign organisms with a variety of techniques. traditional techniques involve filtering, staining, and examining samples under a microscope. much more sensitive and specific testing can be accomplished with dna sequencing, such as when looking for rare organisms, attempting eradication, testing specifically for drug-resistant strains, or discovering new species. sequencing dna from an environmental sample is known as metagenomics. sewage has also been analyzed to determine relative rates of use of prescription and illegal drugs among municipal populations. general socioeconomic demographics may be inferred as well. collection lack of maintenance causing sewage to overflow from a manhole into the street of an informal settlement near cape town, south africa sewage is commonly collected and transported in gravity sewers, either in a sanitary sewer or in a combined sewer. the latter also conveys urban runoff (stormwater) which means the sewage gets diluted during rain events.: 9 sanitary sewer this section is an excerpt from sanitary sewer. a sanitary sewer is an underground pipe or tunnel system for transporting sewage from houses and commercial buildings (but not stormwater) to a sewage treatment plant or disposal. sanitary sewers are a type of gravity sewer and are part of an overall system called a "sewage system" or sewerage. sanitary sewers serving industrial areas may also carry industrial wastewater. in municipalities served by sanitary sewers, separate storm drains may convey surface runoff directly to surface waters. an advantage of sanitary sewer systems is that they avoid combined sewer overflows. sanitary sewers are typically much smaller in diameter than combined sewers which also transport urban runoff. backups of raw sewage can occur if excessive stormwater inflow or groundwater infiltration occurs due to leaking joints, defective pipes etc. in aging infrastructure. combined sewer this section is an excerpt from combined sewer. a combined sewer is a type of gravity sewer with a system of pipes, tunnels, pump stations etc. to transport sewage and urban runoff together to a sewage treatment plant or disposal site. this means that during rain events, the sewage gets diluted, resulting in higher flowrates at the treatment site. uncontaminated stormwater simply dilutes sewage, but runoff may dissolve or suspend virtually anything it contacts on roofs, streets, and storage yards.: 296 as rainfall travels over roofs and the ground, it may pick up various contaminants including soil particles and other sediment, heavy metals, organic compounds, animal waste, and oil and grease. combined sewers may also receive dry weather drainage from landscape irrigation, construction dewatering, and washing buildings and sidewalks. dilution in the sewer infiltration of groundwater into the sewerage system infiltration is groundwater entering sewer pipes through defective pipes, connections, joints or manholes.: 26 : 164 contaminated or saline groundwater may introduce additional pollutants to the sewage. the amount of such infiltrated water depends on several parameters, such as the length of the collection network, pipeline diameters, drainage area, soil type, water table depth, topography and number of connections per unit area.: 26 infiltration is increased by poor construction procedures, and tends to increase with the age of the sewer. the amount of infiltration varies with the depth of the sewer in comparison to the local groundwater table.: 9–1, 9–9 older sewer systems that are in need of rehabilitation may also exfiltrate sewage into groundwater from the leaking sewer joints and service connections.: 167 this can lead to groundwater pollution. stormwater combined sewers are designed to transport sewage and stormwater together. this means that sewage becomes diluted during rain events. there are other types of inflow that also dilute sewage, e.g. "water discharged from cellar and foundation drains, cooling-water discharges, and any direct stormwater runoff connections to the sanitary collection system".: 163 the "direct inflows" can result in peak sewage flowrates similar to combined sewers during wet weather events.: 165 industrial wastewater main article: industrial wastewater treatment sewage from communities with industrial facilities may include some industrial wastewater, generated by industrial processes such as the production or manufacture of goods. volumes of industrial wastewater vary widely with the type of industry.: 27 industrial wastewater may contain very different pollutants at much higher concentrations than what is typically found in sewage.: 188 pollutants may be toxic or non-biodegradable waste including pharmaceuticals, biocides, heavy metals, radionuclides, or thermal pollution. an industry may treat its wastewater and discharge it into the environment (or even use the treated wastewater for specific applications), or, in case it is located in the urban area, it may discharge the wastewater into the public sewerage system. in the latter case, industrial wastewater may receive pre-treatment at the factories to reduce the pollutant load.: 27 mixing industrial wastewater with sewage does nothing to reduce the mass of pollutants to be treated, but the volume of sewage lowers the concentration of pollutants unique to industrial wastewater, and the volume of industrial wastewater lowers the concentration of pollutants unique to sewage. disposal and dilution ocean outfall pipes in cape may, new jersey, united states – pipes exposed after the sand was removed by severe storm further information: sewage treatment § disposal or treatment options assimilative capacity of receiving water bodies or land when wastewater is discharged into a