Branched alkylbenzene sulphonates (ABS) widely used surfactants in the 1950s and early 1960s were subsequently replaced by linear forms in response to evidence that the former are recalcitrant. Though banned in most countries, the use of branched ABS is still widespread in developing countries. In addition to being recalcitrant, they are xenobiotic and, in nature, the biodegradation process of these surfactants requires a lengthy period. This review elaborates the available information on the biodegradation of the branched ABS in relation to their chemical stability, degradation processes, stages of acclimatisation and the microorganisms involved.

The reaction between dicyclohexylamine and iso-alpha acids yields a crystalline product which consists of the dicyclohexylamine salts of trans-iso-cohumulone, trans-lsohumulone and trans-Iso-adhumulone.The presence of only the trans-isomers in the crystalline product was established by proton and carbon NMR. Pure trans-iso-alpha acids can be regenerated from the salt either by treatment with acid or in situ by the use of acidic buffers during HPLC analysis. The dicyclohexylamine salts of the trans-isoalpha acids are stable for extended periods at room temperature, unlike the purified trans-iso-alpha acids, and are thus suitable for use as a standard for iso-alpha acids analysis.Key Words: Iso-alpha acids, standard, HPLC, Nuclear Mag netic Resonance. IntroductionThe analysis of iso-alpha acids in isomeriscd hop extracts and beer is complicated by their instability and the several analogues and isomeric forms which exist. The most widely used method of analysis for the iso-alpha acids measures the ultra-violet (UV) absorption of the iso-alpha acids extracted by iso-octane from acidified beer or acidified hop extract solutions. This method is not specific for iso-alpha acids and contributions from other UV-absorbing components in the solution are included in the total result, expressed as Bitter ness Units (BU)12. The bitterness units are obtained by multiplying the absorption of the iso-octane solution by SO, a factor derived from the dilution factor used and the average extinction coefficients of the iso-alpha acids, assuming that 70% of the absorption of the iso-octane solution is due to iso-alpha acids. However, a multiplication factor of 70 is used for beers bittered with isomeriscd hop extracts or isomerised hop pellets. In order to accurately quantitate the isoalpha acids, it is necessary to separate them from interfering substances, and the most suitable method available is High Performance Liquid Chromatography (HPLC). HPLC sys tems have been devised that separate both isomers and ana logues of the iso-alpha acids3-4, while other systems separate only the analogues*-6-78.

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Branched alkylbenzene sulphonates, recalcitrant xenobiotic compounds, were treated aerobically in a single‐tank activated‐sludge reactor and also by means of three continuous‐stirred‐tank reactors (CSTR) in series. For the single‐tank reactor it was observed that, the longer the hydraulic retention time, the greater were the reductions in biological oxygen demand (BOD), chemical oxygen demand (COD) and methylene blue active substances (MBAS). Reductions of 80%, 60% and 63% were achieved in the levels of BOD, COD and MBAS, respectively. In the case of the three‐CSTR system, acclimatization of the microorganisms was achieved 15 days after start‐up. For this system, the reductions in the levels of BOD, COD and MBAS were 80%, 68% and 69%, respectively.