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A Novel Membrane Bioreactor for By-Product Recovery

Many inorganic waste streams are contaminated with organic chemicals and, as such, are classified ashazardous waste. The cost implications of disposing of such wastes are high and likely to rise in thefuture. Some companies, however, are addressing this problem by treating the waste before finaldisposal. Commonly used techniques, such as steam stripping and carbon adsorption, still leave a

residue of concentrated contaminated residue, which requires disposal. t the same time, to!ic organicchemicals such as benzene can be degraded using micro"organisms, but the high acidity, alkalinity orsalt concentration associated with inorganic waste streams will often preclude such treatment.

#igure $% &rinciples of 'peration

Membrane (!traction Technology )M(T* +td has developed an alternative technology to e!tract andtreat such to!ic organic molecules from inorganic waste streams. ith the support of the(nvironmental Technology -est &ractice &rogramme )(T-&&*, M(T has built a pilot plant at (lftochem / +td, at idnes in Cheshire, which uses an (!tractive Membrane -ioreactor )(M-* to

remove and completely break down the benzene and other organic contaminants from a solution of012 w3v aluminium trichloride. The (T-&&, a 4overnment &rogramme managed by ( Technologyplc, has published two documents to inform companies interested in using this technology, entitled%#5611Recovery of Aluminium Trichloride Solutions Using Membranesand #&611A Novel MembraneBioreactor for the Recovery of Valuable By-Products.

The (M- technology presents a cost"effectivealternative to traditional recovery methods. The cost ofwaste disposal is cut7 the cost of operating thebioreactor is much less than the energy costs of steam

stripping, or of carbon adsorption units7 and theresultant decontaminated waste stream may have othersaleable uses. This is indeed the case at tochem. Thecompany uses #riedel"Crafts reactions to produce ring"substituted aromatic molecules such as benzophenonesand isobutylacetophenone. These reactions proceed inaluminium trichloride )lCl0* and yield an aqueoussolution contaminated with traces of benzene and thereaction products. 8isposal costs for the waste lCl0Pilot Plant at lf Atochem

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solution are 9:1 );o secondary to!ic waste streamis produced.

Pilot Plant

The overall aim of the pro?ect was to construct a pilot plant capable of treating 6"0 tonnes of lCl0solution per day over a si!"month period to generate long"term operating data and provide sufficientmaterial to e!plore commercial opportunities.

The membrane modules consist of silicone rubber tubes housed in a shell, like a shell and tube heate!changer. The viscous nature of the lCl0solution results in large pressure drops for a given flowrateand consequently the design calculations indicated that the waste solution should be pumped throughthe module shells so that the membrane module pressure limits are not e!ceeded. t a flow rate of $11litres3hour of lCl0solution and with $61m

6of membrane area, greater than @@.@2 removal of organiccompounds can be achieved.

(lf tochem provided a feed system for the pilot study, which was designed to separate any carried"over organic phase from lCl0solution prior to the pilot unit and allow easy return of the separatedorganic phase to the production process. fter treatment the pollutant"free solution is collected in astorage tank.

#ollowing initial commissioning, the plant tests were suspended. The original silicone rubbermembranes were e!amined and some were found to have been damaged. +aboratory tests indicatedthat an unidentified compound in fresh lCl0had weakened the membrane. n alternative material "ethylene"propylene"diene"monomer )(&8M* A was used as a replacement and its effectivenesscompared. fter a further si! months of tests, from May to 'ctober $@@B, the new membranes showedno sign of damage and the improved design modules allowed organic free lCl0solution to begenerated by a single pass through the membranes.

5egular monitoring during the pilot study period showed that the (M- system was effective evenduring periods of large variations in effluent quality and concentrations of organic molecules. t wasalso found that very low levels of contamination were treated effectively.

8uring the study period, the (lf tochem plant produced several different products and theeffectiveness of the bioreactor remained constant. The results suggested that these production changeshad little or no effect on the micro"organisms. The main advantage of the technology over itscompetitors is the bioreactorDs ability to eliminate the organic compounds at source. hen comparingthe environmental burden of the alternatives, (M- technology has a lower energy demand than steamstripping devices and produces no to!ic waste. The energy demand is less than half of that needed forcarbon adsorption, when using a regenerative package, and has a reduced demand compared to using acarbon adsorption container system. The technology also benefits from stability in the face of solids

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contamination. hereas a carbon adsorption unit would cease to operate if contaminated, the (M-system continued to function when fine inorganic or organic solids were pumped through themembrane modules.

-oth the capital and operating costs of the (M- technology are lower than its competitors, andaccording to 8r. Sim, technical manager at (lf tochem,

EThe (M- has proved to be a simple, cost effective and reliable technologyE.

&ossible uses could include point source treatment for diverse and difficult wastes such asdibromoethane in >a-r7 dichloroethane in hypochlorite7 dichloroaniline in >a'=7 chloronitrobenzenein =Cl7 chlorobenzene in >a'=7 aniline in /7 and phenol in saline wastewater. The technology is bestapplied at the source of emission, typically in scrubber overflow liquors or aqueous phases fromaqueous"organic phase separations. &ilot trials have been undertaken C =illhouse in -lackpool,=ickson and elch in Castleford, -ush -oake llen in idnes, and Solvay 8eutschland in =annover,4ermany.

#or further information and free copies of #5611Recovery of Aluminium Trichloride Solutions UsingMembranesand #&611A Novel Membrane Bioreactor for the Recovery of Valuable By-Products!contact the (nvironment and (nergy =elplineTel% 1B11 :B: