Bacteria used for bioremediation is not unfamiliar, beingcommonly integrated into WWTPs in activated sludge (AS) or membrane bioreactors(MBR) (Johnson & Sumpter, 2001, Vader et al., 2000). Utilisation of these methodshas been relatively successful, with AS removing over 75% for natural steroidestrogens and around 80% for EE2 from wastewater (.. A majority of EE2 can beremoved from its aqueous medium in influents, although the problem regardingrecalcitrance remains.
Studies have shown that EE2 is predominantly adsorbedonto activated sludge particles, around 60-80% (Johnson & Sumpter, 2001,Layton et al., 2000). NITRIFYING BACTERIAAlthough adsorbed it does not entirely remove thepollutant from the environment but rather changes its medium from aqueous tosolid, thereby not addressing the problem. (Ye & Harper, 2007)As steroidal compounds have low environmentalconcentrations it is unlikely that they act as substrates for growth alone andtherefore concluded that biotrasnformation is a result of cometabolic activity(Shi et al, 2004, Vader et al., 2000). After this deduction, Ye & Harper (2007) investigatedthe compatability of ammonium monooxygenase (AMO) as a mediator for EE2/NH3 cometabolism. Theydemonstrated that AMO could simultaneously remove EE2 and E2 with removalefficiency reaching 70% and 63% respectively. Shi et al.
, 2004Nitrifying bacteria can be categorised into two genus, Nitrosomas andNitrobacter. For example, Neutrosomas europaea has the capacity to produce ammoniummonooxygenase (AMO) that can catalyse the oxidation of ammonia to nitrite. Contarary to alternative research, Gaulke et al (2008) reported thatN.europaea removes EE2 via nitration rather than cometabolic degradation. After introduction of inhibitor, Allythiourea, degradation of EE2 ceasedwhich strongly indicates the importance of nitrifying bacteria in removal ofEE2. Many studies have shown that nitrifying biomass is responsible for EE2degradation Similarly Vader et al found thatNAS could degrade 50 ?g L?1 of EE2 within 6 days. Yoshimotoet al., 2014Identified2 isolates of AS, Rhodococcus zopfii and Rhodococcus equi.
R.zopfii was able toshow particularly strong degrading activities, reducing 100mg of EE2 by 70%within 6 h and completely within 24 . Moreimportantly they extended their research to observe the estrogenic activitiesof the transformation products by using MVLN cells. Of the strainsinvestigated, all decreased estrogenic activities by 100-fold of the originalproduct following 24 h degradation.
Anumber of studies have conducted research with higher concentrations (mg) ofestrogens than those found in the environment (ug). However,the findings can be applied to WWTP by introducing EE2 degrading species intobioreactors to improve removal efficiencies. Nitrifyingbacteria are characterised by their ability to use inorganic carbon to grow althoughlimited by their slow development. Therefore, it has been proposed that longersludge retention times (SRT) are used with suggestions that treatment should beextended past the typical 3-8 h retention time (Yoshimoto et al., 2004., Clouzotet al., 2008, Gaulke et al., 2008)