Filters that burn clean Scientists at the Fraunhofer Institute for Ceramic Technologies and Sintered Metals IKTS, Dresden, Germany, have developed a filter made of foamed ceramics that uses heat to clean itself.

Foamed ceramics have been used as industrial filters for manv I years primarily because they can withstand corrosive chemicals

and rxtremelv high tempera- tures. They are commonlv used to filter molten metals and to absorb particles from exhaust gases, Howcvcr, attempts to use them as soot filters have been unsuccessful because of the low strength of the ceramic material and the complicated process nerdcd to clean them.

Fraunhofvr researchers have no\v created a foamed ceramic that is not only extremely strong, but is also much easier to clean. They have reinforced the ceramic bridges of the foam structure with molten silicone, which gives the ,,“‘OU” ccramir greater rigidity. Electrically conductive graphite contacts arc attached to the open- pored foamed ceramic, to which cables can bc connected to allow an electric current to tlow through the ceramic material.

According to the scientists, if

used as a soot filter in a diesel

engine the heatable foamed

ceramic works in two stages.

Firstly, particles hecomc lodgrd

in the hollow cavities of the foam as the gas passes through, and then the porous ceramic is heated and the soot particles burned off, leaving the filter clean.

Housing for pollutant- eating bugs The University of Tulsa (TU), USA, has received the patent rights from DuPont to commer- cially develop small beads that house bacteria. These bacteria feed on environmentally damag- ing substances and render them harmless.

The beads possess special

Known by its trademarked name Bio-Sep, it consists of porous beads made of a polymer impregnated with activated car-

propertIes that make them an

bon. Despite being approximal.e- Iv the size of a standard ball bcar- ing, they contain more than enough room inside for the bat- tcria saw TU. Once the bacteria

ideal home for bacteria. Firstly,

get inside thev cannot easily get back out, so they multiply until most of the internal volume of

thev contain activated carbon,

the bead is filled.

which not only protects the bac- teria from the toxic compounds

that may be present m wastewa- ter or contaminated groundwa- ter, but also helps to retain low concentration contaminants long enough in the heads for the hac- teria to degrade them. Secondly, the heads are very strong. They can be piled up on top of each other such as in a filter column without collapsing under their own weight.

In industrial applications microorganisms such as bacteria arc routinely housed in biorcac- tars to remo\e pollutants in wastewater and groundwater. TU researchers have shown that using Bio-Sep in bioreactors designed for wastewater trcat-

ment allow ten times more bacteria to bc packed into the biorcactor than normal.

This opens up the possibility of reducing the six of the bioreactor and hence sabing moncv.

Dcpartmcnt of Chemical E ngineering, University of Tulsa, 600 South College, Tulsa, OK 74104, USA. Tel: + I 918631 2000; E-mail: kerrv sublrtt@utulsa.edu

Scientists at the universitv are current]) using Bio-Sep’ to increase the efficiency of hiorrac- tors that remove toxic hvdrgen sulphidc l’rom gases and waste- water produced in the oil and

gas industrv. Thcv are also inves- , tigating other potential applica- tions of Bio-Sep and are seeking

research partners. Contact: Dr K L Sublette,

Filtration+Separation July/August 2000 29