Surface World February 2020 Surface World February 2020 | Page 126
WATER & EFFLUENT TREATMENT
WE ARE AT SURFACE WORLD LIVE 2020
Dam good river management
By Xavier Mear, Product Manager, Lhoist UK
“Water is not a commercial
product but a heritage
to be protected.”
Increasing levels of European legislation, led
by the Water Framework Directive, is putting
great pressure on companies involved with
wastewater treatment.
Nutrient removal and reduction technologies
will continue to be at the centre of efforts on
water protection. The presence of nutrients,
especially nitrogen and phosphorous in
wastewater effluents and their impacts on
natural water bodies, continue to be a major
concern for companies involved with
wastewater treatment.
Phosphates, like nitrates, are responsible for
eutrophication, causing a deterioration of an
aquatic ecosystem by the proliferation of
certain plants, including algae. Industrial
emissions, but also urban waste streams,
contain these pollutants.
Eutrophication – keeping
the industry awake at night
The presence of phosphorous in rivers and
lakes is responsible for eutrophication,
resulting in the uncontrolled proliferation of
algae and excessive
consumption of dissolved
oxygen in the body of the
water. It is thereby less
available for other living
species, and in particular
fish, making it necessary
to restrict phosphorous
discharges into natural
water courses.
Strategies
The removal of Phosphorous can take place
successfully through a process called
enhanced biological phosphorous removal.
Specific bacteria are selectively enriched and
accumulate large quantities of phosphorous
within their cells (up to 20% of the mass).
When the biomass enriched in these bacteria
is separated from the treated water, these
biosolids have a high fertiliser value.
A well-buffered system maintains the pH
where biological activity is optimised and
allows for a more efficient use of oxygen,
leading to reduced energy costs. Treating
wastewaters using lime-based reagents
increases the wastewaters’ buffering capacity
and helps the phosphorous removal step.
Phosphate precipitation
Chemical precipitation is used to remove
inorganic forms of phosphate by the addition
of a coagulant and a mixing of wastewater
and coagulant. The multivalent ions most
commonly used are calcium, aluminium and
iron.
The formation of calcium phosphate salts in
aqueous solutions takes place following the
development of supersaturation, with excess
calcium ions reacting with the phosphate to
precipitate hydroxyapatite.
Aluminium and Iron
Calcium Alum is widely used precipitating phosphates,
as are ferric chloride and sulfate. For both
reagents however, the resulting AlPO4
precipitates need to be removed by
flocculation via the excess addition of a
metal hydroxide, and typically lime is added
to enhance this treatment step
Calcium is usually added to the process as
hydrated lime Ca(OH)2. It is reported that
addition of lime makes it possible to remove
85-90% of the inorganic orthophosphates
present in wastewater. For more information on Neutralac
please contact Xavier Mear, Product
manager at Lhoist UK on 07968
755590 or [email protected]
Separating phosphate
from aqueous solutions
exist and the physico-
chemical processes
utilised are based on
precipitation phenomena
by use of salts of calcium,
iron or aluminium, or
adsorption phenomena.
Phosphate removal may
also be achieved by
biological processes.
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