Disinfection of secondary effluents by infiltration percolation

Among the most attractive applications of reclaimed wastewater are: irrigat ion of public parks, sports fields, golf courses and market gardening. Thes e uses require advanced wastewater treatment including disinfection. Accord ing to WHO guidelines (1989) and current rules and regulations in Tunisia, faecal conform levels have to be reduced to < 10(3) or 10(2) CFU/100 mL. In Tunisia, most wastewater plants are only secondary treatment and, in order to meet health related regulations, the effluents need to be disinfected. However, it is usual for secondary effluents to need filtration prior to di sinfection. Effectiveness of conventional disinfection processes, such as c hlorination and UV radiation, are dependent upon the oxidation level and th e levels of suspended solids of the treated water. Ozonation is relatively expensive and energy consuming. The consideration of the advantages and dis advantages of conventional techniques, their reliability, investment needs and operational costs will lead to the use of less sophisticated alternativ e techniques for certain facilities. Among alternative techniques, soil aqu ifer treatment and infiltration percolation through sand beds have been stu died in Arizona, Israel, France, Spain and Morocco. Infiltration percolatio n plants have been intermittently fed with secondary or high quality primar y effluents which percolated through 1.5-2 m unsaturated coarse sand and we re recovered by under-drains. In such infiltration percolation facilities, microorganisms were eliminated through numerous physical, physicochemical a nd biological inter-related processes (mechanical filtration, adsorption an d microbial degradation respectively). Efficiency of faecal coliform remova l was dependent upon the water detention times in the filtering medium and on the oxidation of the filtered water. Effluents of Sfax town aerated pond s were infiltrated through 1.5 m deep sand columns in order to determine th e performance of infiltration percolation in the polishing of secondary eff luents. Elimination of bacteria (total and coliforms, faecal streptococci) and their relationship with the hydraulic load and the temperature were inv estigated.