Advanced treatment for municipal wastewater reuse in agriculture. UV disinfection: parasite removal and by-product formation

This paper reports the experimental results of a pilot-scale (100 m3/h) investigation, carried out at the West Bari (S. Italy) municipal wastewater treatment plant, focused on parasite removal and disinfection by-product (DBP) formation during the UV disinfection of clarified (CL) and clarified-filtered (F) secondary municipal effluents at doses necessary for achieving the Italian microbial limit for unrestricted reuse of wastewater in agriculture (2 CFU/ 100ml of total coliforms). The investigation demonstrated that parasites like Giardia lamblia cysts and Cryptosporidium parvum oocysts were both significantly affected by UV radiation and that potential UV-promoted formation of DBPs (nitro-phenols and N-nitroso-amines) did not occur according to GC/MS and LC/MS analytical evidences. O&M costs ranged from € 17.5 up to € 35/1000 m3 for effluent F and CL respectively.

The experimental results of a 9-month pilotscale (100 m3/h) investigation, carried out at the West Bari (S. Italy) municipal wastewater treat- ment plant, focused on parasite removal and disinfection by-product (DBP) formation during the UV disinfection of clarified (CL) and clarifiedfiltered (F) secondary effluents at doses (160 and 100 mWs/cm2 respectively) necessary for achieving the total coliforms standard of 2 CFU/100 ml for unrestricted reuse of wastewater in agriculture, provided the following indications: 1. At the above doses, UV radiation was rather effective in both feeds towards protozoan parasites like Giardia lamblia cysts and Cryptosporidium parvum oocysts (approx. 60 and 65% removal respectively); Nematodes eggs were never found in the feeds admitted to disinfection because already removed by clarification and sedimentation; 2. The multiple barrier concept involving clarification and filtration prior to UV disinfection was confirmed to be the most effective approach for complete parasite removal in wastewater treatment; 3. None of the N-derivatives (i.e. nitro-phenols and N-nitroso-amines) searched for after UV disinfection of both feeds was detected by GC/MS analytical technique whilst LC/MS analyses excluded also the formation of non-volatile DBPs, suggesting the absence of detectable photochemical reactions at UV doses usually used in wastewater disinfection; 4. O&M costs of UV disinfection averaged € 17.5 and € 35/1000 m3 for F and CL feed respectively. Further investigation is planned to assess UV effectiveness towards viruses, to exclude UV promotion of other DBPs, to prevent effluent recontamination (bacteria photoreactivation by cell repair and regrowth) and to evaluate possible Table 2 Cost estimates for UV disinfection of CL and F feeds at West Bari pilot plant Feed F CL UV dose, mWs/cm2 Total coliforms target achieved, CFU/100 ml O&M costs, €/1000 m3 Electric power Lamp replacement Total 6.7 13.5 10.6 21.3 17.3 34.8 synergy and/or catalytic effects of UV radiation with long-acting chemical disinfectants such as H2O2.