Methyl tert-butylether (MTBE) used as fuel oxygenate poses problems for water suppliers since it is persistent in the aquatic environment and the removal efficiency by conventional water treatment methods (aeration or activated carbon filtration) is rather low. Substitution by other ether compounds such as ethyl tert-butylether (ETBE), tert-amylmethylether (TAME) or di-isopropylether (DIPE) is discussed, however, their environmental behaviour is similar to that of MTBE. Experiments investigating the elimination efficiency of AOP were carried out in tap water and water from Lake Constance. The elimination efficiency for all treatment processes was found to follow the order: MTBE << TAME approximately equal ETBE < DIPE For all compounds under investigation, neither pure ozonation nor UV irradiation yield a considerable concentration decline. Only the formation of highly reactive OH radicals shows a potential for removing the ethers from water. Therefore the addition of H2O2 in equimolar ratio prior to ozone admixing proved to be quite efficient. The application of combined UV/H2O2 showed good results in all cases; the best concentration decline was achieved with UV/ozone. The rate of elimination of the three substitutes for MTBE (ETBE, TAME and DIPE) is higher in all processes; nevertheless, no complete removal could be achieved. Therefore, from the point of view of water suppliers, the use of other ethers as substitute for MTBE is posing the same problems as MTBE.
MTBE has come into focus of water suppliers since raw water sources had to be closed down in Santa Monica, California, at the beginning of the 1990s. Since then many studies have been undertaken to investigate the removal of MTBE from water. Other ethers which are under discussion as substitutes for MTBE have lately been developed and have to be assessed for their relevance for drinking water production. The present study shows that ethers used as oxygenates in fuel are not easily eliminated by advanced treatment technologies. Neither pure ozonation nor UV irradiation results in a significant concentration decline. The formation of highly reactive OH radicals is necessary to yield a decisive removal of the ethers from water. The application of combined UV/H2O2 or UV/ozone showed in all cases good results. The findings of the lab-scale experiments are verified by measurements in waterworks which have trace concentrations of MTBE in their raw water. Though the elimination process is better with the ethers under discussion as substitutes for MTBE, the removal efficiency is still very low compared to many other substances. A small improvement could be achieved by the substitution but in the end no real progress is made. Therefore, from the point of view of water suppliers the use of other ethers as a substitute for MTBE is posing the same problems as with MTBE.
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