Decontamination of water by combined solar advanced oxidation processes and biotreatment - Solar Energy Sciences and Engineering Applications - page 385

Figure 12.3.2 Measurement of readily biodegradable COD in a respirometric assay.
could be affected by the amount of biodegradable or hardly biodegradable substances
present in the medium and the presence of any compounds which are toxic or inhibit
cell activity.
The active organisms in activated sludge biomass require molecular oxygen to oxi-
dize the organic load in the wastewater and provide organic carbon to synthesize the
compounds necessary for their continuous growth. The two processes are concurrent
and together determine the treatment's wastewater organic load elimination rate. The
toxicity analysis consists of loading the respirometer with the desired amount of acti-
vated sludge from the WWTP and continuously aerating it until air saturation. Then,
the sample is added and oxygen consumption measured. The percentage of inhibition
can be calculated from the oxygen measurement according to the equipment protocol.
Apart from toxicity assays, activated sludge respirometry analyses are also
employed for assessing the biodegradability of industrial wastewater partially treated
by an AOP. It is used as a short-term biodegradability assay, to evaluate the oxy-
gen uptake rate during the time the sample and the activated sludge are in contact.
Biodegradation parameters such as the maximum oxygen uptake rate and dissolved
oxygen consumption found in the respirometric tests are realistic analyses for evaluat-
ing the efficiency of partial wastewater oxidation (textile wastewater, landfill leachate
wastewater, phenol wastewater, etc.) by an AOP (Goi et al., 2009). In this assay, the
oxygen uptake rate from a mixture of a certain amount of the pretreated wastewater
and activated sludge (in the endogenous phase and with inhibited autotrophic bacterial
activity) is measured during a contact period of around 20 minutes. In the end, the
readily biodegradable fraction of the COD (COD rb ) is found (as a function of the total
oxygen consumption and the biomass growth rate). The COD rb /COD ratio shows the
sample's biodegradability. Over 0.1 means that it is biodegradable and below 0.05
is not. The different wastewater COD fractions (biodegradable, non-biodegradable,
non-soluble, etc.) can also be determined by respirometric assay (Lagarde et al.,
2003). Figure 12.3.2 is a typical oxygen uptake rate graphic. As observed, the area