Vízügyi Közlemények, 1971 (53. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(66) TERTIARY TREATMENT By Dr. Öllös, Géza (For the Hungárián text see pp. 361) In the present paper the experiences and information gained by the author during a UN (WHO) sponsored study tour are reviewed from both theoretical and practieal aspets. In Section 1 the second and third stages of treatment are compared and the objcctives of tertiary treatment are outlined. It is demonstrated that in future water management the tertiary treatment will assume an icreasingly important role, for reducing the pollution on the recipients, for permitting the rcuse of water and for diminishing sanitary hazards. In Section 2 the mechanical (micro straining, rapid filtration, immediate filter, gravel layer) and biologicat (slow filtration, trickling over grass surfaces, oxidation ponds) methods pertaining to tertiary treatment are reviewed. The potential practical applications of each, the considerations to be remembered during the design and the experiences gained during operation are discussed. An important conclusion is for instance, that micro strainers and rapid filters are suited primariliy for application at major treatment plants, although rapid filters arc used at small plants as well. Slow filters are preferably applied at small plants. In Section 3 the basic processes of nitrification and denitrification are detailed, deseribing the conditions under which nitrogén compounds can be removed by the second biological stage of treatment. The potential extent of removal, the operaiing conditions and expericnce gained therewitli are considered. In Section 4 the conventional biological methods of treatment (infiltration intő the soil, oxidation ponds, trickling filters, activated sludge process) are discussed, concluding that these arc less suited for removing nitrogén compounds. A method ol' treatment ensuring more effective removal is e.g. the biological method suggested by Wuhrmann, in which altér nitrification taking place in the activated-sludge basin, denitrification is accomplished in a separate basin under anaerobic conditions. For ensuring the successive processes of nitrification and denitrification tbc efforts at effective oparation control assume special importance. The conditions thereof are discussed in detail in this section. In Section 5 the possibilities of phosphate removal are summarized. The role of chemical methods is shown to predominate in the processes developed so far. Beyond the action of the conventional salts Al(III), Fe(III) and Ca(II) the role of the La(IIl) salt is alsó indicated. It is pointed out lurther that one of the difficulties encountered in the removal of phosphates is due to the circumstance thatbesides the salts mentionod above, the chemical reactions are influenced alsó by the sulphatemontmorillonite-, kaolinite- and lluoride content of the wastewater. In Section 0 attention is callcd to the more advanced methods of teriiarij treatment, which are retated to the reuse of wastewaters and tlius capable of meeting stricter demands on water quality. These treatment processes are in most cases closely rclated to the technology used in the treatment of drinking water. The importance of t he application of ozone and ion exchangcrs is emphasized in the present section. In Section 7 the Z —M method is presenled of the chcmical-physical methods of treatment more recenlly introduced. The essenlial feature of these methods is that by the chemical treatment (consisting usually of chemical coagulation) tliey attempt to remove the non-dissolved organic whereas by tbc physical treatment (involving usually the application of active carbon) tbc dissolved organic substances. In view of the increasing importance of quality aspeets in water management furtber considerable improvement is belicved to become necessary in the methods ol' tertiary treatment (and wastes treatment in generál). The protection of recipients and llie necessity for making increasing rcuse ot water will result logically in more severe quality requirements and, in turn, in more sophisticated methods of treatment.