microbiota may or may not allow for the retention of species diversity (i.e., a stable
ecosystem may or may not be recovered). For both addition methods, the structural
parameter (microbial population) and the functional parameter (P/R ratio) should be
measured to evaluate the effects of the test effluent.
In the conventional microcosm experiments, chemical addition is usually
performed on the 16th day after the cultivation began, when the system stabilizes.
In the WET test using the microcosm, the medium in the flask must be exchanged for
wastewater, which is then added. At that time, it is necessary to separate the
organisms and the culture medium, and a fresh medium containing wastewater is
added instead of the extracted medium. The addition of the attached microcosm
standard medium increases the number of individuals in the steady state. This is
because organic substances that feed microorganisms are already consumed. In this
case, it is impossible to compare it with the nonadditive system (control), so an
appropriate medium was developed with reference to the amount of organic matter
added at the time of wastewater addition.
Addition of a substrate was conducted by replacing the culture medium in the
flask with wastewater. A fresh medium containing wastewater was added as a
substitute for the extracted medium. However, when the standard microcosm
medium was added as a new medium, the number of individuals in the steady
state increased. Therefore, as a new medium, the amount of peptone in the medium
was adjusted to 0 mg/L, 5 mg/L, 10 mg/L, 20 mg/L, and 40 mg/L and then added
into the medium. The impact of each culture medium was assessed from both the P/R
ratio as the functional parameter and the abundance of microbiota as the structural
parameter in the microcosm (Murakami et al. 2017). The environmental impact and
ecological risk were estimated by comparing the treated microcosms with the
no-addition system (control) in both assessment methods.
With respect to the structural parameters, the abundance of Cyclidium glaucoma, a ciliate primary predator, was greatly increased by increasing the amount of
peptone in the medium; there was no major change in the abundance of other
species in the microcosm. From the P/R ratio, which is the functional parameter, no
change was observed when compared to the no-addition system (control) as shown
in Fig. 9.4. From this, the system was considered stable unless wastewater was
added. Statistical analysis of the DO concentration was performed. The slope (a)
and the coefficient of variation (cv) were obtained assuming that the microcosm
was normally distributed. If they fell within the range of Æ34.13% for each, it was
considered that there was no influence. Since the range of Æ34.13% of the slope of
the DO was 0.0028 ≦ a ≦ 0.0056, it was considered as having no influence on the
medium containing only 5 mg/L. Additionally, since the range of Æ34.13% of the
coefficient of variation of the DO was 0.10 ≦ cv ≦ 0.20, it was considered as
having no effect on the medium containing 0 mg/L to 20 mg/L. Therefore, a
medium containing 5 mg/L of peptone was considered appropriate for adding
wastewater in the microcosm-WET test (Fig. 9.4).
9 Application to the Whole Effluent Toxicity Test
171
ecosystem may or may not be recovered). For both addition methods, the structural
parameter (microbial population) and the functional parameter (P/R ratio) should be
measured to evaluate the effects of the test effluent.
In the conventional microcosm experiments, chemical addition is usually
performed on the 16th day after the cultivation began, when the system stabilizes.
In the WET test using the microcosm, the medium in the flask must be exchanged for
wastewater, which is then added. At that time, it is necessary to separate the
organisms and the culture medium, and a fresh medium containing wastewater is
added instead of the extracted medium. The addition of the attached microcosm
standard medium increases the number of individuals in the steady state. This is
because organic substances that feed microorganisms are already consumed. In this
case, it is impossible to compare it with the nonadditive system (control), so an
appropriate medium was developed with reference to the amount of organic matter
added at the time of wastewater addition.
Addition of a substrate was conducted by replacing the culture medium in the
flask with wastewater. A fresh medium containing wastewater was added as a
substitute for the extracted medium. However, when the standard microcosm
medium was added as a new medium, the number of individuals in the steady
state increased. Therefore, as a new medium, the amount of peptone in the medium
was adjusted to 0 mg/L, 5 mg/L, 10 mg/L, 20 mg/L, and 40 mg/L and then added
into the medium. The impact of each culture medium was assessed from both the P/R
ratio as the functional parameter and the abundance of microbiota as the structural
parameter in the microcosm (Murakami et al. 2017). The environmental impact and
ecological risk were estimated by comparing the treated microcosms with the
no-addition system (control) in both assessment methods.
With respect to the structural parameters, the abundance of Cyclidium glaucoma, a ciliate primary predator, was greatly increased by increasing the amount of
peptone in the medium; there was no major change in the abundance of other
species in the microcosm. From the P/R ratio, which is the functional parameter, no
change was observed when compared to the no-addition system (control) as shown
in Fig. 9.4. From this, the system was considered stable unless wastewater was
added. Statistical analysis of the DO concentration was performed. The slope (a)
and the coefficient of variation (cv) were obtained assuming that the microcosm
was normally distributed. If they fell within the range of Æ34.13% for each, it was
considered that there was no influence. Since the range of Æ34.13% of the slope of
the DO was 0.0028 ≦ a ≦ 0.0056, it was considered as having no influence on the
medium containing only 5 mg/L. Additionally, since the range of Æ34.13% of the
coefficient of variation of the DO was 0.10 ≦ cv ≦ 0.20, it was considered as
having no effect on the medium containing 0 mg/L to 20 mg/L. Therefore, a
medium containing 5 mg/L of peptone was considered appropriate for adding
wastewater in the microcosm-WET test (Fig. 9.4).
9 Application to the Whole Effluent Toxicity Test
171