User:Monicadonayre/Wastewater treatment

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Wastewater treatment is a process used to remove contaminants from wastewater or sewage to convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environment or is reused for various purposes (called water reclamation). The treatment process usually occurs in a wastewater treatment plant (WWTP). There are two kinds of wastewater: domestic and industrial; both types of wastewater are treated at the appropriate wastewater treatment plant. For domestic wastewater (also called municipal wastewater), the treatment plant may be called a Water Resource Recovery Facility (WRRF) or a Sewage Treatment Plant (STP). For industrial wastewater, treatment either occurs in a separate industrial wastewater treatment plant or a sewage treatment plant (usually after some form of pre-treatment).

Processes commonly used are designed to achieve phase separation, oxidation, or polishing. Types of wastewater treatment plants include sewage treatment plants, industrial wastewater treatment plants, agricultural wastewater treatment plants, and leachate treatment plants.

The treatment of wastewater is part of the overarching field of sanitation. Sanitation also includes the management of human waste and solid waste and stormwater (drainage) management. The main by-product from wastewater treatment plants is sewage sludge, usually treated at the same wastewater treatment plant or another wastewater treatment plant. Biogas can be another by-product of anaerobic treatment processes.

Processes

Oxidation

Oxidation reduces the biochemical oxygen demand of wastewater, and may reduce the toxicity of some impurities. Secondary treatment converts organic compounds into carbon dioxide, water, and biosolids through oxidation and reduction reactions. Chemical oxidation is widely used for disinfection.

Biochemical oxidation[edit]

Main article: Secondary treatment

Secondary treatment by biochemical oxidation of dissolved and colloidal organic compounds is widely used in sewage treatment and is applicable to some agricultural and industrial wastewater. Biological oxidation will preferentially remove organic compounds useful as a food supply for the treatment ecosystem. Concentration of some less digestible compounds may be reduced by co-metabolism. Removal efficiency is limited by the minimum food concentration required to sustain the treatment ecosystem.

Chemical oxidation[edit]

Main article: Redox

Chemical (including electrochemical) oxidation, also known as advanced chemical oxidation is used to remove some persistent organic pollutants and concentrations remaining after biochemical oxidation and to break down compounds into simple compounds. Disinfection by chemical oxidation kills bacteria and microbial pathogens by adding hydroxyl radicals such as ozone, chlorine or hypochlorite to wastewater. These hydroxyl radical then break down complex compounds in the organic pollutants into simple compounds such as water, carbon dioxide, and salts.

Sewage treatment plants[edit]

Main article: Sewage treatment plant

A typical municipal sewage treatment plant in an industrialized country may include primary treatment to remove solid material, secondary treatment to digest dissolved and suspended organic material as well as the nutrients nitrogen and phosphorus, and – sometimes but not always – disinfection to kill pathogenic bacteria. The sewage sludge that is produced in sewage treatment plants undergoes sludge treatment. Larger municipalities often include factories discharging industrial wastewater into the municipal sewer system. The term "sewage treatment plant" is sometimes replaced with the term "wastewater treatment plant." Sewage can also be treated by processes using "Nature-based solutions."

Disposal or reuse[edit]

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Further information: Reclaimed water

River carrying wastewater

The main purpose of wastewater treatment is for the water to be able to be disposed or reused safely. However, before it is treated, the options for disposal or reuse must be considered so he correct treatment process is used on the wastewater.

Disposal

For disposal into the ocean, environmental treaty requirements have to met. As international treaties often manage water over countries' borders, wastewater disposal is easier in bodies of water found entirely under the jurisdiction of one country.

Environmental impacts of wastewater disposal

In many developing countries, where water scarcity and water pollution is often a significant issue, wastewater treatment facilities are not apt to treat the amount of wastewater received, and it ends up being disposed in local waterways untreated. For example, in Afghanistan and Pakistan, the Kabul River receives about 1 m³/sec of untreated wastewater, and it has been proven to be a causing factor for the contamination of the river. Globally, water pollution from untreated wastewater comes from the presence of chemicals in detergents. The chemicals surfactants in detergent cannot be degraded unless they are in the presence of specific microorganisms. In more recent years, water pollution from detergent residue has become a more relevant problem.

Reuse

Reuse of wastewater is a good solution to reduce water stress in cities, promote consciousness, and reduce pollutants into water bodies. Reused water can be used for multiple purposes such as “reclaimed and reused for crop and landscape irrigation, groundwater recharge, or recreational purposes.” There are two ways of wastewater reuse: direct and indirect reuse. Direct reuse entails using treated wastewater as it is, and indirect reused is diluting treated wastewater with another water source before further use.

Global situation

At the global level, an estimated 52% of wastewater is treated. However, wastewater treatment rates are highly unequal around the world. For example, while high-income countries treat approximately 74% of their wastewater, low-income countries treat an average of just 4.2%. Improving wastewater treatment across the globe is crucial for reducing our pollution to the environment and achieve water quality improvements. For this reason, Sustainable Development Goal 6 has a Target 6.3 which is formulated as follows: "By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated wastewater and substantially increasing recycling and safe reuse globally." The corresponding Indicator 6.3.1 is the "proportion of wastewater safely treated" (see map on the right for 2018). For example, Algeria, Senegal, Niger, Libya, Uganda, Somalia, and Iraq do not treat domestic wastewater safely yet. The World Health Organization reported that inadequate water, sanitation and hygiene conditions were responsible for 829,000 deaths from diarrhea in the world in 2016. Water and sanitation are a world problem, resulting from rapid global urbanization, and finding solutions in large cities is particularly urgent. Additionally there is the worsening water crisis in several regions of the world, as well as the evident ecological crisis, disasters and associated risks, such as the global warming in addition to the presence of polluting industries and technologies and their effects on water, soil, air and food, reducing the biodiversity and destroying ecosystems.

Country examples

Brazil

In Brazil, countrywide, 19.1% of households are connected to septic tanks but they are not connected to the general network. Approximately 9 million households (12.6%) had a ditch, rudimentary cesspit, river, lake or sea, in addition to other forms of waste disposal. The relevance of sanitation infrastructure in the health-disease process was highlighted in a study on hospitalizations due waterborne diseases. Overall, in 2015, diarrhea was estimated to be one of the main causes of death in all age groups (1.31 million). In terms of coverage, around 40% of the sewage generated in Brazil is treated, with an estimated number of treatment plants in the order of 2,800. National responsibility for wastewater and sewage treatment lies in the hands of the ministry of cities in Brazil. The ministry of cities consists of different ministries that each contribute to water supply and sanitation including wastewater and sewage treatment.

European Union[edit]

This section is an excerpt from Urban Waste Water Treatment Directive § Description[edit]

The Urban Waste Water Treatment Directive (full title "Council Directive 91/271/EEC of 21 May 1991 concerning urban waste-water treatment") is a European Union directive regarding urban wastewater collection, wastewater treatment and its discharge, as well as the treatment and discharge of "waste water from certain industrial sectors" and was adopted on 21 May 1991. It aims "to protect the environment from the adverse effects of urban waste water discharges and discharges from certain industrial sectors" by mandating waste water collection and treatment in urban agglomerations with a population equivalent of over 2000, and more advanced treatment in places with a population equivalent above 10,000 in sensitive areas.

Japan

In Japan, wastewater treatment is managed by both the national government and local governments and municipalities. The governmental organizations that contribute to wastewater treatment policies at a national level in Japan are the Ministry of Health, Labor and Welfare,the Ministry of Land, Infrastructure, Transport and Tourism, and the Ministry of the Environment. Currently, Japan's methods of wastewater treatment include rural community sewers, wastewater facilities, and on-site treatment systems such as the Johkasou system to treat domestic wastewater. Larger wastewater facilities and sewer systems are generally used to treat wastewater in more urban areas with a larger population. Rural sewage systems are used to treat wastewater at smaller domestic wastewater treatment plants for a smaller population. Johkasou systems are on-site wastewater treatment systems tanks. They are used to treat the wastewater of a single household or to treat the wastewater of a small number of buildings in a more decentralized manner than a sewer system.

This image is a wastewater treatment plant in Oulu.