Risk assessment for a wastewater treatment plant including ozonation and GAC filtration as reclamation steps in view of a reuse

Properly treated wastewater may be an alternative water source for reuse. In this context, in order to assess and manage the risks for the environment and the human health, EU Regulation 2020/741 requires the implementation of a water reuse risk management plan. To this end, the current study presents the risk assessment carried out for a wastewater treatment plant (preliminary treatment, sedimentation, conventional activated sludge system) where the reclamation facility consists of an ozonation followed by a granular activated carbon filtration with a UV disinfection as a safety/emergency step. Attention is towards the suitability of the final effluent for reuse and the health of the plant workers. At first, failure modes and the related effects are identified by means of the Failure Mode and Effects Analysis (FMEA); then scores (1-5) are assigned to the expected probability of occurrence of each failure and to the magnitude of the related effects (1,2, 4, 8, 16). Finally the two scores are multiplied providing a final score measuring the risk associated to each failure mode. The higher the final score, the higher the risk. Critical failures are those with a final score greater than 32, according to WHO recommendations. Among the eighty failure modes identified for the 55 treatment components, the critical ones were only three (final score = 64) and referred to the aerator and the sludge recirculation pump. According to this analysis, the existing preventive safety measures were reviewed and new ones were suggested to improve the reliability of the system.