Evaluation of disinfection treatment systems for municipal wastewater reclamation and reuse

The efficiency of a number of tertiary treatment systems--filtration, ozonation, chlorination with low levels (TRC < 0.2 ppm) and high levels (TRC < 1 ppm) of residual chlorine--in the disinfection of secondary effluent was assessed in a purification plant treating mixed sewage of municipal (83%) and industrial mainly textile origin (17%). Maximum purification effect was observed when, following secondary treatment with biological oxidation, the sewage was submitted to combined filtration--ozonation treatment (reduction in bacterial indicators of from 4.9 to 7.2 log10 units) or with chlorination with high levels of residual chlorine (reduction in the bacterial indicators of between 2.8 and 4.6 log10 units). However, only ozonation reduced viral indicators with respect to inflow sewage by more than 3 log10 units, the limit considered acceptable for a biological treatment system with supplementary tertiary disinfection treatment. Ozonation however did not complete control all the biological forms present in the sewage, in particular the viruses, present in 36% of ozonized samples at concentrations of from 1 to 480 PFU/100 mL. Ozonation and high-concentration chlorination do not seem to be unfavorably influenced by wastes from laundry and deyng processing; achieving a complete decolorization of the treated effluent, they prove to the suitable treatments for mixed sewage of municipal and industrial mainly textile origin.