Abstract
Chemical coagulation is commonly used in raw water and
wastewater treatment plants for the destabilisation of
pollutants so that they can be removed in the subsequent
separation processes. The most commonly used coagulation
chemicals are aluminium and iron metal salts.
Electrocoagulation technology has also been proposed for
the treatment of raw waters and wastewaters. With this
technology, metal cations are produced on the electrodes
via electrolysis and these cations form various
hydroxides in the water depending on the water pH. In
addition to this main reaction, several side reactions,
such as hydrogen bubble formation and the reduction of
metals on cathodes, also take place in the cell. In this
research, the applications of electrocoagulation were
investigated in raw water treatment and wastewater
applications.
The surface water used in this research contained high
concentrations of natural organic matter (NOM). The
effect of the main parameters - current density, initial
pH, electric charge per volume, temperature and
electrolysis cell construction - on NOM removal were
investigated. In the wastewater treatment studies, the
removal of malodorous sulphides and toxic compounds from
the wastewaters and debarking effluents were studied.
Also, the main parameters of the treatment, such as
initial pH and current density, were investigated.
Aluminium electrodes were selected for the raw water
treatment, whereas wastewaters and debarking effluent
were treated with iron electrodes.
According to results of this study, aluminium is more
suitable electrode material for electrocoagulation
applications because it produces Al(III) species. Metal
ions and hydroxides produced by iron electrodes are less
effective in the destabilisation of pollutants because
iron electrodes produce more soluble and less charged
Fe(II) species. However, Fe(II) can be effective in some
special applications, such as sulphide removal. The
resulting metal concentration is the main parameter
affecting destabilisation of pollutants. Current density,
treatment time, temperature and electrolysis cell
construction affect the dissolution of electrodes and
hence also the removal of pollutants. However, it seems
that these parameters have minimal significance in the
destabilization of the pollutants besides this effect (in
the studied range of parameters). Initial pH and final pH
have an effect on the dissolution of electrodes, but they
also define what aluminium or iron species are formed in
the solution and have an effect on the ?-potential of all
charged species in the solution. According to the results
of this study, destabilisation mechanisms of pollutants
by electrocoagulation and chemical coagulation are
similar.
Optimum DOC removal and low residual aluminium can be
obtained simultaneously with electrocoagulation, which
may be a significant benefit of electrocoagulation in
surface water treatment compared to chemical coagulation.
Surface water treatment with electrocoagulation can
produce high quality water, which could be used as
potable water or fresh water for industrial applications.
In wastewater treatment applications, electrocoagulation
can be used to precipitate malodorous sulphides to
prevent their release into air. Technology seems to be
able to remove some toxic pollutants from wastewater and
could be used as pretreatment prior to treatment at a
biological wastewater treatment plant. However, a
thorough economic and ecological comparison of chemical
coagulation and electrocoagulation is recommended,
because these methods seem to be similar in pollutant
destabilisation mechanisms, metal consumption and removal
efficiency in most applications.
Original language | English |
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Qualification | Doctor Degree |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 2 Nov 2012 |
Place of Publication | Espoo |
Publisher | |
Print ISBNs | 978-951-38-7940-2 |
Electronic ISBNs | 978-951-38-7941-9 |
Publication status | Published - 2012 |
MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- electrocoagulation
- water treatment
- wastewater treatment