Aerobes and Effluents - Environmental Biotechnology: Theory and Application - page 140

promise, the uptake of MBR was surprisingly slow. However, over recent years,
the combination of legislative and economic pressures has driven increasing inter-
est and led to the further development of the underlying technology itself to
produce the latest submerged systems. Unlike the plate-and-frame or tubular
membranes encountered in cross-flow systems, these have hollow fibres or flat
sheets located within the bioreactor processing tank itself and have now become
the most commonly encountered form of MBR (Judd, 2006).
Predictably, water companies have been amongst those to adopt the technol-
ogy, but much of the uptake has been by industries which traditionally produce
particularly difficult or recalcitrant wastewaters, as the regulation of effluent qual-
ity has become ever more stringent. With effluent MLSS ranging from 10 000
to 20 000mg/l, COD between 2000 and 4000mg/l, often with high ammoniacal
nitrogen and total Kjeldahl nitrogen (TKN) loads of up to 1000mg/l, pharma-
ceutical companies, in particular have been in the vanguard of this move.
Cellulose Ion-Exchange Media
For effluents requiring a highly selective removal of high molecular weight pro-
teins, cellulose ion-exchange media provides an example of treatment involving
the use of isolated biologically derived materials. The ion exchange medium is
replenished with brine as required, and the proteins collected are removed in the
resulting saline solution, for subsequent coagulation and drying. This enables a
valuable material to be recovered, typically for use as an animal foodstuff, while
reducing the wastewater BOD by 90% or more.
Sludge Disposal
Many of the treatment processes described in this chapter give rise to primary or
secondary sludges. Typically, these by-products require disposal and, like many
forms of solid waste, a proportion have been consigned to either landfill or incin-
eration. For some treated sludges, especially those derived from domestic sewage
or food residuals, agricultural use has been an option, often requiring additional
treatments to ensure its freedom from human pathogens, before land spreading or
injection beneath the surface. The effectiveness of microbes in metal sequestration
means, inevitably, that most treated sludges have a degree of heavy metal con-
tamination, which itself makes possible the accumulation of these contaminants
in soils exposed to these products. In addition, there are increasingly stringent
controls on the release of nitrogen to the environment, particularly within esca-
lating European Union legislation regarding nitrogen vulnerable zones. It would
seem, then, that the future land use of 'spent' sludges is likely to be somewhat
more heavily regulated than previously.