Integrated Environmental Biotechnology - Environmental Biotechnology: Theory and Application - page 264

CaseStudy10.1 MicrobialControlandCellSignalling(Australia)
With so much of environmental biotechnology depending on microbes at the
functional level, the prospect of being able to adjust the metabolic rate of bacteria,
to either speed things up or slow them down, presents a powerful tool. Clearly
such microbial control has potential applications in a wide range of industries and
activities, but arguably its most successful exposition to date has been found in
cleaning up sewer systems.
Sewage itself is inevitably rich with a wide variety of bacteria and their combined
microbial biomass tends to accumulate in the bends and dips of the sewerage pipes
that convey effluent to wastewater treatment plants. Over time, these accretions
eventually form biofilms and subsequently give rise to both foul-smelling gases
and corrosion, accounting for extensive odour control expenditure and costly
infrastructure maintenance.
To combat this problem, the Australian company Biosol researched the cell
signalling chemicals found in nature, ultimately harnessing them to develop com-
mercial products capable of precisely influencing bacterial activity. By effectively
placing the microbes in a state of hibernation, sewage that has been dosed travels
inoffensively along sewer pipes, incapable of forming the biofilms that typically
prove so problematic.
However, once inside the treatment works, a quiescent bacterial population
within the flow would obviously be disastrous. Reversing the process with the
judicious dosing of 'speed-up' signals, microbial breakdown is accelerated and
enhanced, to provide a faster processing, higher treatment throughput, a better
quality final effluent and a lower residual biosolids load. It also offers the potential of
an improved methane yield, which can in turn help power the plant, or alternatively
be made available for export off-site.
The approach is based in 'quorum sensing' - the means by which bacteria become
aware that their population level is at a particular trigger point and then naturally
modify and co-ordinate their behaviour accordingly. Much of the research has
centred on biomedical applications, particularly restoring antibiotic effectiveness,
but Biosol's breakthrough has demonstrated the enormous benefits this technology
could offer a wide range of environmental problems too.
Case Study 10.2 Integrated Sludge Digestion and Biomass Energy
Recovery(Wales/theNetherlands)
Renewable energy has assumed burgeoning importance over recent years and with
the water industry facing calls to simultaneously cut its carbon footprint and improve
treatment levels, any technology that helps achieve both is doubly welcome.
Aiming to generate over 5MW of 'green' power - and cutting D wr Cymru/Welsh
Water's carbon footprint by an estimated 35 000 tonnes of CO 2 equivalent annu-
ally - two new advanced bio-digestion plants are being built in Cardiff and Afan.
Gouda-based Imtech was selected as the operation's process partner, for a solution
that involves thermal hydrolysis of the sludge, heating it to 170 ◦ C for pasteurisation
before it enters the anaerobic digestion phase.
Continuedonpage267