Sistema de ultrafiltração por gravidade como alternativa ao tratamento de água no ponto de uso

Abstract

The lack of clean water remains a major concern for most developing countries. Domestic water treatment technologies are growing in popularity to meet the drinking water needs of the population. So-called Point-of-Use Technologies (TPU) use physical and/or chemical treatment (for reuse of surface water and wastewater) to remove contaminants. Among the existing POUs, gravity ultrafiltration has been drawing attention due to its efficiency in the removal of several contaminants. Therefore, the present work evaluated the efficiency of the gravity ultrafiltration system as a technological alternative applied to the treatment of water intended for human consumption at the point of use. The experimental system used consists of 3 treatment stages: Stage 1: Naylo screen (water pre-treatment). Stage 2: Gravity ultrafiltration membrane operated with low transmembrane pressure (40 mbar). Stage 3: Disinfection. The research was divided into two stages: in the first stage, biofilm formation occurred on the ultrafiltration membrane. Permeate flux stabilization occurred after the 7th day of operation in the experimental system. The ultrafiltration membrane produced a flow rate of 1.3 L.h-1 of treated water over a period of 10 months with stable flow. After biofilm formation, the study water was conducted to the experimental system to perform the physical-chemical and microbiological analyses. After ultrafiltration with biofilm, 100% color removal and 96% turbidity removal occurred. 100% removal of helminth eggs was also observed. Regarding cyanobacteria, total coliforms, E. coli and heterotrophic bacteria, the removal was 78, 97, 72.6 and 66%, respectively. It was necessary to add the disinfection step after treating the UF water with biofilm, since drinking water cannot contain microorganisms. Thus, sodium hypochlorite was used at dosages of 15, 30 and 45 mL for 40 liters of water treated after UF. The best dosage found to remove 100% of the remaining microorganisms was 30 mL of sodium hypochlorite. After the toxicity tests with Lactuca sativa, the sample showed a germination index (GI) of 90%. In the second stage, the flow rate in the ultrafiltration membrane without biofilm was 2.1 L.h-1, performing a backwash. The study water showed removal of 100% of color, 94% of turbidity and 100% of helminth eggs. Regarding cyanobacteria, total coliforms, E. coli and heterotrophic bacteria, the removals were, respectively: 72, 99, 70 and 80%. Although ultrafiltration without biofilm showed better retention of microorganisms, it was also necessary to add the disinfection step to inactivate the remaining microorganisms. The dosage of 30 mL of sodium hypochlorite was also used, the same germination index of the first stage was observed in the sample of the second stage. Therefore, the system proposed in this research can be considered as an alternative, effective, low-cost treatment, providing quality treated water for human consumption.