Cut sludge with help from microbial biomass
Scientists have developed a process that can cut the amount of sludge generated from wastewater treatment plants by a factor of 10. This biological treatment is an outcome of the INNOWATECH ('Innovative and integrated technologies for the treatment of industrial wastewater') project, which was supported under the 'Sustainable development, global change and ecosystems' Thematic area of the EU's Sixth Framework Programme (FP6) to the tune of EUR 2.75 million.
Most people recognise that treating industrial wastewater cheaply is possible through biological processes. The problem, however, is that microbes more or less fail to break down industry-generated pollutants, including leather, textiles and pharmaceuticals. Enter a team of scientists from the Water Research Institute (WRI) of the Italian National Research Council that developed a sophisticated technology that allows microbial biomass, which has the capacity to break down wastes, to grow mostly as granules. They developed, tested and scaled up the process.
The researchers call this process 'Sequencing batch biofilter granular reactor' (SBBGR). Pores trap the granules between plastic-support material in a reactor. Less sludge is generated because the microbes are stressed. What happens is that microbes are not in the right environment to proliferate. The result? Less microbes and less waste.
The disadvantage of using a biological system is that removing one kilo of wastewater produces 500 grams of sludge, which in turn must be disposed of. Thanks to this innovative technology, the amount of sludge is much smaller.
'With this technology, you produce only 50 grams of sludge,' explained WRI project coordinator Antonio Lopez. A facility that uses this technology could be 10 times smaller than usual.
Some experts are concerned about the complicating factors that could emerge. For instance, they question what goes into the reactor and biomass concentration. 'If the sludge production is decreased by 10 times, this would not necessarily mean that the bioreactor volume can be decreased by the same ratio,' said Christoph Brepols, an expert in wastewater at the Erft river water association (Erftverband).
Treatment of effluents from leather and textile processing is possible when oxygen and the reactor are integrated. Despite its hefty price, ozone can oxidise and break down most organic compounds. While the innovative technology cannot break down the pollutants 100%, it can transform them into more biodegradable compounds. Less ozone means fewer treatment costs.
'Tannery wastewater is a sort of benchmark in the sector of industrial wastewater,' said Dr Lopez, because not only is its composition complex but its treatment is no easy feat.
The team is optimistic about the use of granular sludge reactors. Sludge output in Europe is growing. More than 5 million tonnes of dry solids were generated by plants 20 years ago, increasing to 10 million by 2007. We currently need between EUR 350 to EUR 750 to dispose of one tonne of dry solids. Therefore, innovative technology is important.