| Activated Carbon |
Activated carbon is
produced by heating organic materials (e.g. coconut shells) in the absence of
oxygen to a very high temperature (above 450 oC). The carbon that is
produced has active surfaces; the latter can remove many pollutants from water. |
| Activated sludge |
Activated sludge is
the assemblage of micro-organisms, dead and alive, together with adsorbed
organic and inert materials present in aerated wastewater. |
| Activated sludge process |
In an activated
sludge process settled wastewater is contacted with recirculated activated
sludge in an aerated chamber. In this way a substantial amount of
micro-organisms is kept in the treatment process to consume the organic
materials in the wastewater. Excess sludge is removed after sedimenting the
aerated mixture. |
| Aerobic |
With or in the presence of air (oxygen) |
| Aerobic lagoon |
Wastewater treatment
lagoon that has a high dissolved oxygen level. This is usually a result of a
combination of low organic waste input and sufficient oxygen transfer from the
air, and occurs in the last few in a series of lagoons. See Lagoon. |
| Alkaninity |
A measure of the
amount of acid that a given volume of water can absorb without substantially
changing its pH. |
| Anaerobic |
Without air (oxygen) |
| Anaerobic digestion |
Decomposition of
organic substances in the sludge by micro-organisms under anaerobic conditions. |
| Anaerobic lagoon |
Wastewater lagoon
which has very little dissolved oxygen. This condition is the result of oxygen
uptake by micro-organisms in the lagoon exceeding oxygen transfer from the air,
and occurs in the first lagoon in a series of lagoons. See Lagoon. |
| Anoxic |
Without oxygen but
with the presence of nitrate (chemically bound oxygen) |
| Aquaculture (wastewater fed) |
Rearing of fish in
ponds relying on the nutrients (nitrogen and phosphorus) contained in
wastewater. Guidelines for wastewater fed aquaculture should be followed to
ensure protection of public health. |
| Attached growth system |
An attached growth
system retains micro-organisms on the surfaces of solids (e.g. a bed of gravel
or coarse sand) for the purpose of treating wastewater. As wastewater flows
through the surfaces of the solids organic materials are consumed by the
micro-organisms. See Trickling Filter. |
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|
| Biochemical oxygen demand (BOD) |
A measure of the
strength or concentration of wastewater. This is so because micro-organisms
consume the organic substances in the wastewater for energy and growth. In the
process of microbial respiration dissolved oxygen is taken up from the water by
the micro-organisms. Because the oxygen uptake is measured over a period of 5
days, it is also denoted as BOD5 |
| Biofilter |
A biofilter is used
for the treatment of wastewater by passing the wastewater through a bed of
gravel, coarse sand or other solid surfaces. Organic substances are removed by
micro-organisms attached to the solids surfaces (See Attached Growth system). |
| Biofilter for odour |
A biofilter used for
the treatment of odorous gases consists of a bed of mature compost. As the
odorous gas passes through the moist compost bed the odorous substances are
adsorbed to the compost and degraded by compost micro-organisms. |
| Biogas |
Biogas is the gases
that are produced from the anaerobic decomposition of organic materials (e.g.
sewage sludge). The gases are mainly methane and carbondioxide, and hence have
energy value from its methane content. |
| Biogeochemical cycles |
Natural cycles of
elements which constitute living materials of plants and animals. These
elements (e.g. carbon, nitrogen, phosphorus) occur in various forms in the
living organisms, in the dead organisms, in the soil and atmosphere and when
they are taken up again by organisms. |
| Biological filter |
See Trickling Filter |
| Biological nutrient removal (BNR) |
Nutrients in
wastewater (nitrogen and phosphorus) can be removed by the use of specific
groups of micro-organisms by providing suitable conditions for their growth.
Systems that are designed and operated to achieve this purpose are called BNR
systems. |
| Biosolids |
The term used for
sludge removed from the treatment of sewage that has undergone processing and
with the intention of reusing the sludge. |
| Blackwater |
Waste from the toilet. See Greywater. |
| Bucket latrine |
Latrine where faeces
and urine are collected in a bucket. See Night Soil. |
| |
|
| Carbon cycle |
See Biogeochemical cycle. |
| Catchment (basin) |
Area of land from
which stormwater run-off flows to a common stream or river. |
| Central(ised) systems |
Centralised systems
are systems where wastewater and/or stormwater are collected from individual
houses and brought to a central treatment plant. A system of pipes (sewer) is
used for this purpose. Gravity is relied upon for flow, but pumping may be
required. |
| Centrifuge (sludge) |
Mechanical equipment
used to remove moisture from sludge by giving the sludge a rotating motion in a
drum forcing the mixture of water and solids towards the cylindrical surface of
the drum where a filter medium is placed. Water passes through while the solids
are retained on the filter medium. |
| Chamber soakway |
A chamber where
stormwater run-off is directed to. Water percolates through the sides and
bottom of the chamber into the surrounding soil to groundwater. |
| Chlorination |
The use of chlorine
for the purpose of disinfection of water. Chlorine is available in the form of
chlorine gas or solid (calcium hypochlorite, e.g. powder or tablet) or liquid
(sodium hypochlorite). |
| Clarifier |
A clarifier separates
solids from wastewater by settling the solids out in a settling pond or tank,
and in this way the wastewater is clarified. |
| Coliforms |
Bacteria which are
abundant in the blood of warm blooded animals including people. They are used
as an indicator of faecal contamination of water. |
| Combined sewer |
Combined sewer
carries both wastewater and stormwater. Separate sewers collect only wastewater
or stromwater. |
| Combined sewer overflow (CSO) |
Combined sewer (see
above) invariably results in an overflow during heavy rain storm. This overflow
is the volume that exceeds the capacity of the treatment plant and is termed
combined sewer overflow. |
| Composting |
Composting is the
process that converts organic materials into humus. This process is carried out
by micro-organisms under aerobic conditions. |
| Composting toilet |
A composting toilet
collects human excreta in an aerated chamber for the purpose of producing humus
by composting. Air is drawn from the toilet chamber into the collection chamber
and out through a vent, thus odour is controlled. |
| Conditioning (sludge) |
Sludge may need to be
conditioned to assist the process to reduce its moisture. This is usually done
by adding chemicals that help coagulate or flocculate the particles in the
sludge. |
| Condominium sewerage |
Pipes which collect
wastewater in a condominium sewer pass through neighbouring properties. This
saves pipes compared to conventional sewer where pipes from each property are
connected to mains running in front of the properties. See Simplified Sewerage. |
| Constructed wetlands |
See Wetlands |
| Conventional sewerage |
In conventional
sewerage pipes are laid relatively deep in the ground to prevent interference
from traffic, and allowance is made for self-cleansing flow in the pipes on a
daily basis. As a result pipes are larger in size and are laid deeper compared
to shallow sewerage. Costs are correspondingly higher. |
| Cross-cutting issues |
Cross-cutting issues
in the implementation of environmentally sound technology refers to the broader
issues of planning, involvement of the community, methods for cost-recovery for
capital cost and for operating cost, and other social and political factors to
ensure successful and long term sustainability of the technology. |
| |
|
| Dechlorination |
The removal of excess
chlorine once the objective of chlorination (disinfection) has been achieved. |
| Denitrifiers |
Bacteria which carry
out the denitrification process. |
| Denitrification |
The conversion of
nitrate into nitrogen gas. This process is carried out by denitrifiers and
requires an organic carbon source and anaerobic conditions. |
| Digestion (aerobic, anaerobic) |
Digestion is the
process of biodegradation of organic materials by micro-organisms. It can take
place under aerobic conditions (in the presence of air) or anaerobic conditions
(in the absence of air). |
| Disinfection |
The removal of
pathogens. This can be done in a number of ways (e.g. boiling water,
ultra-violet radiation, chlorination). |
| Dissolved air flotation (DAF) |
The process of
removing suspended solids (such as oils and grease particles) by floating them
using very small air bubbles and skimming them. Pressurised air is dissolved in
the water, and when the pressure is reduced to atmospheric very small bubbles
are produced. |
| Dissolved oxygen (DO) |
Dissolved oxygen is
the oxygen that is dissolved in water. At an ambient temperature of 20 oC
the amount is about 9 mg/L (parts per million). The small amount of oxygen that
can be dissolved in water limits its availability to aquatic organisms, and can
be readily depleted by wastewater. See Biochemical Oxygen Demand. |
| Drying bed (sludge) |
A bed of sand on
which wet sludge is placed for drying. Moisture is removed by evaporation and
percolation through the sand bed. Excess water is removed from the base of the
bed for further treatment. |
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|
| Environmentally sensitive zones |
Environmentally
sensitive zones refer to water bodies, such as rivers, lakes and seas, that are
sensitive to addition of nutrients (nitrogen and phosphorus). See
Eutrophication. |
| Eutrophication |
Eutrophication refers
to the process or conditions of a water body that receives and contains
excessive amounts of nutrients. These conditions result in algal bloom. Toxins
may be produced by some algae. The decay of the algae can result in depletion
of oxygen from the water body. |
| Evapotranspiration |
In wastewater
treatment it refers to the removal of the water by use of plants. The plants
act a biological pump by absorbing moisture through their roots and transpiring
it to the atmosphere. Water can be distributed in a trench filled with gravel
and topped with sand or soil (Evapotranspiration trench) or when the water
table is high, into a bed of sand above ground (Evapotranspiration bed). |
| |
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| Facultative lagoon |
Wastewater treatment
lagoon which contains a high level of oxygen during the day but a low level at
night. Algae in the lagoon produce the oxygen during sunlight hours by
photosynthesis, and taking carbon dioxide produced by the respiration of
bacteria consuming the organic waste. See Lagoon. |
| Filter drains |
Permeable materials
located below ground to store stormwater run-off. Run-off flows to the storage
area via a permeable surface. |
| Filter press (sludge) |
Pressure filter
consisting of plates and frame. Sludge slurry is pumped under pressure onto a
filter medium placed on the plates. Solids are retained on the filter and water
passes through, thus dewatering the sludge. |
| Filter strips (stormwater) |
Vegetated surface
that allows stormwater run-off to flow evenly to collection areas while at the
same time filters solids out of the water. |
| |
|
| Garburator |
Garburator is usually
installed beneath a kitchen sink to shred kitchen waste and dispose it with
wastewater. Treatment of the wastewater involves removing the kitchen waste
from the wastewater, so it may not be considered as a desirable method for
disposing of kitchen waste. |
| Grass filtration |
See Overland Flow |
| Grease trap |
Grease trap is a
device to remove grease from wastewater, so that the grease does not interfere
with downstream treatment of the wastewater (e.g. blockage). |
| Greywater |
Wastewater from
bathroom, laundry and kitchen. See Blackwater. |
| Grit removal |
The removal of solids
that settle relatively quickly from wastewater (e.g. sand particles). This is
usually carried out in a settling time with a short residence time. |
