A comparative study of sand and natural zeolite as filtering media in tertiary treatment of wastewaters from tourist areas

Abstract

Anaerobic effluents from a fixed bed reactor treating sewage water from tourist areas were treated by two high rate filters at laboratory scale one packed with sand and the other with natural zeolite with the aim of obtaining final effluents with quality for irrigation of land or disposal in tourist zones. The ranges of particle sizes for the two filtering media used were: 1–3 mm and 0.6–2.5 mm for both media and particle sizes of 0.35–1 mm also for the zeolite. The evaluation of different particle sizes demonstrated that the particle range of 1–3 mm for both media was more effective than the rest of size ranges studied in the removal of pollutant particles. It was found that turbidity removal was similar for sand and zeolite although the filter packed with zeolite had lower pressure losses and better hydraulic behaviour. A maximum ammonia nitrogen removal of 95% was obtained in the first hour of filtration for zeolite medium, although the removal decreased progressively achieving a minimum value of 50% at 8 h of operation. The ammonia nitrogen removal values were always higher than those observed in the sand bed. For the smallest particle size (0.35–1 mm) of the zeolite bed, the total coliforms, removal was near to 100%, while for the other particle sizes the removal percentages were in the range of 90–96% without significant differences between sand and zeolite. Therefore, the final concentration of total coliforms obtained after the filtration with zeolite (0.35–1 mm) can be considered adequate for water reuse in land irrigation.