Homes and sewage

Human homes, and particularly those in urban areas, produce a broad range of materials that impact on the marine environment, including sewage, solid waste, toxic pollutants and greenhouse gases.

Pollution from domestic sewage is one of the most serious forms of ocean contamination. It affects every region of the world. In Chile for example, it is estimated 82 percent of all domestic sewage finishes up in the sea, transported there by 27 river basins. In the Mediterranean over 50% of wastewater, or over 3.2 billion cubic metres per year, are discharged untreated. Untreated sewage contains very high levels of nutrients which can lead to eutrophication. It is also responsible for introducing suspended solids, biological contaminants, and chemical waste, including persistent pollutants and toxins. In its raw form sewage can also contain significant amounts of solid waste and litter.

The complex nature of sewage requires a range of treatments to neutralise all of the damaging compounds. Preliminary treatment such as filtration removes some of the solid waste, primary treatment can remove some of the suspended sediments. Secondary treatment, typically involves bacterial introduction to remove the soluble components, while tertiary treatment attempts to disinfect the remaining liquids. Significant levels of nutrients may remain, even in well treated sewage. Pathogenic micro- organisms are only thoroughly scoured in tertiary treatments and many persistant toxins may remain even in such highly treated sewage. In some cases disinfection methods, such as chlorination, can further add to pollution. Domestic homes are major source of solid waste, including plastics, which escape into the oceans. A number of countries deliberately dump their solid waste at sea, and others incinerate their waste at sea, but with considerable losses of solid waste during this process. Homes are also major energy consumers, fuelling the greenhouse effect with CO2 emissions, particularly associated with temperature regulation through heating or air conditioning.