Page 281 - Materials Chemistry, Second Edition

4.5 Impact Categories, Impact Indicators and Characterisation Factors 265

2. Conversion of ‘1 kg N’ in (kg of phosphate equivalents):
A molar ratio in the algae biomass of n(P)/n(N) = 1/16 and a molar ratio of
n(P)/(PO 3– ) = 1/1 results to
4
m(N)× M(PO 4 3− )
3−
m(PO 4 )=
M(N)× 16
−1
(M(N) = 14 g mol −1 and M(PO 4 3– ) = 95gmol )
For 1 kg N thus 0.42 kg phosphate equivalents are calculated.
3. Conversion of 1 kg NO in (kg of phosphate equivalents):
A molar ratio in the alga biomass of n(P)/n(N) = 1/16, a molar ratio of
n(N)/n(NO) = 1/1 and a molar ratio of n(P)/n(PO 3− ) = 1/1 results to
4
3− )
m(NO)× M(PO
3− )= 4
m(PO
4
M(NO)× 16
−1
(M(NO) = 30 g mol −1 and M (PO 4 3− ) = 95 g mol )For 1 kg NO thus 0.2 kg
phosphate equivalents are calculated.
Similarly aquatic EPs (as phosphate equivalents) of arbitrary nutrients containing
P and N can be calculated. Specification of the EP as phosphate equivalent have
been largely accepted (for an over fertilisation of soil, see below). For the most
important emissions the EP values are shown in Table 4.14.

Besides compounds containing P and N only the over-fertilisation effect according
to the COD of organic compounds is integrated into the characterisation. The COD
is a concentration related sum parameter often applied in waste water analysis
and therefore often available in the inventory (LCI). A prerequisite for the use
of these data for LCA is that the determination of COD loads is possible. All
substances contained in water that can be oxidised with potassium dichromate
under defined conditions are considered. The result is given as the mass of
−1
oxygen (mg l ) necessary for the oxidisation of the substances in the water if
oxygen were the oxidising agent. Both biologically degradable and biologically
non-degradable organic materials as well as some inorganic materials are included.
As the stoichiometry of the oxidation reaction is well-known, the COD can be
calculated according to the known formula of the substance to be oxidised. Because
biologically non-degradable organic substances as well as inorganic substances
included within the COD do not contribute to eutrophication, the BOD would be
−1
better suited for this impact category. Here the mass of oxygen (in mg l ), which
is utilised by bacteria in the course of the use of organic compounds as nutrition
within a defined time period is indicated. The BOD is therefore a measure for
biologically degradable substances in the water and simulates processes that induce
the decrease of oxygen concentration in the water. However, many more data for
the COD are provided from waste water analysis. The BOD has to be determined