Removal of humic substances by oxidation/biofiltration processes - A review

The paper is concerned principally with summarising the experience to-date of treating low alkalinity, low turbidity, humic-rich surface waters by the combination of ozone oxidation and biological filtration processes. In the UK, USA and other countries, upland coloured waters have often been treate d by slow sand filtration in which only moderate removals of DOC have been achieved (< 20%). The presence of significant levels of humic matter in fil trate waters has led to difficulties in achieving compliance with the stand ards for colour and THMs, and concern about the stability of residual chlor ine and potential biogrowth in water supply pipework. This has led to sever al investigations leg. in the UK, Sweden and the USA) of the benefits of ap plying ozonation prior to slow sand filtration in view of its known capabil ity to decolorise humic substances and enhance biodegradability of the orga nic fractions. This paper summarises the experience to-date and highlights the benefits and problems that have been identified. Some studies have atte mpted to compare the relative performances of slow sand hirers and granular activated carbon (GAC) filters for the removal of BDOC and the paper revie ws the principal findings of these studies in view of the growing worldwide interest in the application of ozone-GAG. One major limitation with the us e of ozone-GAG is the need periodically to remove and regenerate the carbon , since bed lives for the removal of humic substances are typically short. An alternative approach is to use inorganic adsorbents instead of carbon wh ich have the potential to be chemically regenerated in-situ. The paper refe rs to the results of laboratory tests that have been carried out on the pot ential use of pre-ozonation followed by inorganic adsorbents leg. Activated alumina, bauxite) for the removal of humic substances. (C) 1999 IAWQ Publi shed by Elsevier Science Ltd. All rights reserved.