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Decentralisation describes the transfer of central government powers, competences and resources to the local government, closer to the people and/citizen. The concept can also be applied to infrastructures (e.g. decentralised wastewater treatments).

Decentralised Treatment System

A small-scale system used to collect, treat, discharge, and/or reclaim wastewater from a small community or service area. The treatment unit of DEWATS includes generally sedimentation and floatation (e.g. in septic tanks or biogas settlers); anaerobic treatment (e.g. in upflow baffled reactors or anaerobic filters); aerobic treatment (in sub-surface flow constructed wetlands or unplanted sand- or gravel filters); and a final aerobic treatment in maturation ponds.

Decentralised supply systems offer the possibility to provide safe drinking water where centralised supply systems are not feasible for economic or political reasons (e.g. in rural communities or informal settlements). Decentralised water supply refers to the small-scale purification and distribution o water. The decentralised treatment systems fall into three main categories: point-of-use systems (POU), point-of-entry systems (POE), and small-scale systems (SSS). POU and POE systems are designed for individual households while SSS can provide for community water supply, for emergency water supply in camps, or to purify water for sale in water kiosks. The choice of decentralised supply system depends on the local context and includes such factors as ease of use, maintenance needs, dependence on other utilities (e.g. electricity, fuel supply), and cost.

Decentralized Treatment System

Deciding with the community presents various approaches and tools that facilitate participatory decision making.

Decision making tools are approaches to take mutually-accepted decisions that benefit as many stakeholders as possible.

The ability to make decisions quickly and effectively.

Decomposition is the transformation of dead organic material (plants, animals, etc.) into more basic compounds and elements by biological and biochemical reactions.

Deep dug wells are dug wells over 20 metres in depth, thus, unlikely to get contaminated but costly to construct.

Deep shafts are enhanced biological wastewater treatment systems. They are based on the process of activated sludge systems but particularly adapted where land is in short supply. Oxygen is injected into a return sewage stream, which is injected into the base of a deep columnar tank buried in the ground. As the sewage rises the oxygen forced into solution by the pressure at the base of the shaft breaks out as molecular oxygen providing a highly efficient source of oxygen for the microorganisms contained in the activated sludge. The rising oxygen and injected return sludge provide the physical mechanism for mixing. Mixed sludge and wastewater is decanted at the surface, the sludge is again enriched in oxygen while the supernatant continuously flows out of the system. The efficiency of deep shaft treatment can be high but they require high skilled labour for both, construction and operation and maintenance and large amount of energy.

A deep well is a hand-dug water well ranging more than 7m in depth and about 1.5m in diameter.

Setting clear boundaries is an important step in the development of any project. It makes it possible to stay focused on a specific area.

When faeces are stored in the absence of moisture (i.e., urine), they dehydrate into a crumbly, white-beige coarse, flaky material or powder. The moisture naturally present in the faeces evaporates and/or is absorbed by the drying material (e.g., ash, sawdust, lime) that is added to them. Dehydration by adding dry organic material and long-term storage at high ambient temperature is the simplest treatment in order to transform faeces into a product that is safe for reuse as soil conditioner or disposal.

Dehydration vaults are used to collect, store and dry (dehydrate) faeces. Faeces will only dehydrate when the vaults are well ventilated, watertight to prevent external moisture from entering, and when urine and anal cleansing water are diverted away from the vaults. See also dehydration of faeces.

Creating demand is essential to achieve that newly developed approaches and technologies actually come in to use.

Creating demand is essential to achieve that newly developed approaches and technologies actually come in to use.

This is the coupling of denitrification and Anammox processes in one single reactor.

DNA is a nucleic acid present in nearly all living organisms as the main constituent of chromosomes. It is self-replicating and contains the genetic instructions used in the development and functioning of the cells.

Department for Housing and Infrastructure Development

Department for International Development

Department for Water Affairs

Department of Infrastructure and Support Services

The quality of being trustworthy and reliable.

The process of removing the accumulated sludge from a sanitation storage or treatment facility (e.g. pit toilet, septic tank).

Detailed Project Report

Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH changed its name to The Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH on 1 January 2011.

The process of reducing the water content of a sludge or slurry. Dewatered sludge may still have significant moisture content, but it typically is dry enough to be conveyed as a solid (e.g., shovelled).

Diammonium Phosphate (DAP) is a common fertiliser with the chemical formula (NH4)2HPO4.

Diarrhoea is the passage of loose or liquid stools more frequently than is normal for the individual. It is primarily a symptom of gastrointestinal infection. Depending on the type of infection, the diarrhoea may be watery (for example in cholera) or passed with blood (in dysentery, for example). Diarrhoea is caused by a variety of microorganisms including viruses, bacteria and protozoan.

Consists of both a diesel engine (converts chemical energy to mechanical energy) and a generator (converts mechanical energy to electrical energy).

The solid and/or liquid material remaining after undergoing anaerobic digestion.

Dioxins are a class of chemical contaminants that are formed during combustion processes such as waste incineration, forest fires, and backyard trash burning, as well as during some industrial processes such as paper pulp bleaching and herbicide manufacturing. The most toxic chemical in the class is 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD). The highest environmental concentrations of dioxin are usually found in soil and sediment, with much lower levels found in air and water. Humans are primarily exposed to dioxins by eating food contaminated by these chemicals.

Sales agents that usually use door-to-door techniques to directly sell products or services at the customer’s doorstep. Brings additional value in terms of convenience and aspiration to the customer.

In direct groundwater recharge water moves from storage above-ground (e.g. a spreading basin or ditch) to the aquifer via soil percolation. Most of the existing large-scale artificial recharge schemes in Western countries make use of this technique. In general direct surface recharge systems based on percolation have relatively low construction costs and are easy to operate and maintain.

The elimination of (pathogenic) microorganisms by inactivation (using chemical agents, radiation or heat) or by physical separation processes (e.g., membranes). The process is used for water purification or for advanced or tertiary wastewater treatment.

The use of chemical disinfectants in water treatment usually results in the formation of chemical by-products, some of which are potentially hazardous. If chlorination is practised, the trihalomethanes, of which chloroform is the major component, are likely to be the main disinfection by-products, together with the chlorinated acetic acids in some instances. However, the risks to health from these by-products are extremely small in comparison with the risks associated with inadequate disinfection, and it is important that disinfection should not be compromised in attempting to control such by-products.

The concentration of oxygen dissolved in water, expressed in mg/l or as percent saturation, where saturation is the maximum amount of oxygen that can theoretically be dissolved in water at a given altitude and temperature.

Distributed energy resource (DER) systems are small-scale power generation technologies (typically in the range of 3 kWe to 10000 kWe) used to provide an alternative to or an enhancement of the traditional electric power system.

District Water, Sanitation and Health Education Committees

Double Entry Accrual Accounting System

Double pit latrines are latrines with several pits used in alternation. By constructing twin pits, it is possible to dig out a filled pit only after it has stood for a while (approximately one year) allowing the faecal matter to degrade while the other pit is put in use. Thus smell and the health risk during excavation will be reduced.

The double VIP has almost the same design as the single VIP with the added advantage of a second pit that allows it to be used continuously and permits safer and easier emptying.

Dried Faeces are Faeces that have been dehydrated until they become a dry, crumbly material. Dehydration takes place by storing Faeces in a dry environment with good ventilation, high temperatures and/or the presence of absorbent material. Very little degradation occurs during dehydration and this means that the Dried Faeces are still rich in organic matter. However, Faeces reduce by around 75% in volume during dehydration and most pathogens die off. There is a small risk that some pathogenic organisms can be reactivatedunder the right conditions, particularly, in humid environments.

Drilled Well

The addition of particular substances, e.g. natural clay, bentonite, organic polymers, air, foam, fibres, fresh cow-dung, to drilling water increases viscosity and hence improves removal of cuttings and stabilises the borehole.

Freshwater that is chemically and biologically safe for human consumption, naturally or by purification.

In drip irrigation, water flows through a filter into special drip pipes, with emitters located at different spacing. Water is discharged through the emitters directly into the soil near the plants through a special slow-release device. If properly designed, installed, and managed, drip irrigation may help achieve water conservation by reducing evaporation and deep drainage as compared to other types of irrigation such as flood or overhead sprinklers since water can be more precisely applied to the plant roots.

Dry Cleansing Materials are solid materials used to cleanse one-self after defecating and/or urinating(e.g., paper, leaves, corncobs, rags or stones). Depending on the system, Dry Cleansing Materials may be collected and separately disposed of. Although extremely important, a separate menstrual hygiene products like sanitary napkins and tampons is often forgotten. In general (though not always), they should be treated along with the solid waste generated in the household.

Low-rate anaerobic digestion systems are classified according to the percentage of total solids (TS) in the waste stream. Dry digestion means that the TS content is higher than 20 %.

A dry toilet is a toilet that operates without flushwater. The dry toilet may be a raised pedestal on which the user can sit, or a squat pan over which the user squats. In both cases, excreta (both urine and faeces) fall through a drop hole.

Drying beds are either planted or unplanted sealed shallow ponds filled with several drainage layers and designed for the separation of the solid from the liquid fraction of (faecal) sludge from latrines, septic tanks, biogas reactors, trickling filters, etc. Sludge is dried naturally by a combination of percolation and evaporation and evapotranspiration. When drying beds are covered with plants, evaporation is enhanced by transpiration (evapotranspiration). See also planted drying beds and unplanted drying bed.

A dual-flush toilet is a variation of the flush toilet designed to save water by using two buttons or handles to flush different levels of water.