Bacteria than cometabolic degradation. After introduction of inhibitor,

Bacteria used for bioremediation is not unfamiliar, being
commonly integrated into WWTPs in activated sludge (AS) or membrane bioreactors
(MBR) (Johnson & Sumpter, 2001, Vader et al., 2000). Utilisation of these methods
has been relatively successful, with AS removing over 75% for natural steroid
estrogens and around 80% for EE2 from wastewater (.. A majority of EE2 can be
removed from its aqueous medium in influents, although the problem regarding
recalcitrance remains. Studies have shown that EE2 is predominantly adsorbed
onto activated sludge particles, around 60-80% (Johnson & Sumpter, 2001,
Layton et al., 2000).

 

NITRIFYING BACTERIA

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Although adsorbed it does not entirely remove the
pollutant from the environment but rather changes its medium from aqueous to
solid, thereby not addressing the problem.

 

(Ye & Harper, 2007)

As steroidal compounds have low environmental
concentrations it is unlikely that they act as substrates for growth alone and
therefore concluded that biotrasnformation is a result of cometabolic activity
(Shi et al, 2004, Vader et al., 2000).

 

After this deduction, Ye & Harper (2007) investigated
the compatability of ammonium monooxygenase (AMO) as a mediator for EE2/NH3 cometabolism. They
demonstrated that AMO could simultaneously remove EE2 and E2 with removal
efficiency reaching 70% and 63% respectively.

 

Shi et al., 2004

Nitrifying bacteria can be categorised into two genus, Nitrosomas and
Nitrobacter. For example, Neutrosomas europaea has the capacity to produce ammonium
monooxygenase (AMO) that can catalyse the oxidation of ammonia to nitrite.

 

Contarary to alternative research, Gaulke et al (2008) reported that
N.europaea removes EE2 via nitration rather than cometabolic degradation.

 

After introduction of inhibitor, Allythiourea, degradation of EE2 ceased
which strongly indicates the importance of nitrifying bacteria in removal of
EE2.

 

 

Many studies have shown that nitrifying biomass is responsible for EE2
degradation

 

Similarly Vader et al found that
NAS could degrade 50 ?g L?1 of EE2 within 6 days.

 

Yoshimoto
et al., 2014

Identified
2 isolates of AS, Rhodococcus zopfii and Rhodococcus equi. R.zopfii was able to
show particularly strong degrading activities, reducing 100mg of EE2 by 70%
within 6 h and completely within 24 .

 

 

More
importantly they extended their research to observe the estrogenic activities
of the transformation products by using MVLN cells. Of the strains
investigated, all decreased estrogenic activities by 100-fold of the original
product following 24 h degradation.

 

A
number of studies have conducted research with higher concentrations (mg) of
estrogens than those found in the environment (ug).

 

However,
the findings can be applied to WWTP by introducing EE2 degrading species into
bioreactors to improve removal efficiencies.

 

Nitrifying
bacteria are characterised by their ability to use inorganic carbon to grow although
limited by their slow development. Therefore, it has been proposed that longer
sludge retention times (SRT) are used with suggestions that treatment should be
extended past the typical 3-8 h retention time (Yoshimoto et al., 2004., Clouzot
et al., 2008, Gaulke et al., 2008) 

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