Desinfecção eletroquímica de águas: avaliação do desempenho de reator composto de membrana cerâmica e eletrodos de esponja de níquel e titânio/platina.

Abstract

Electrochemical disinfection occurs through Electrochemical Anodic Oxidation (EAO) and has been shown to be efficient in the inactivation of various microorganisms. Its main advantages include ability to produce disinfectant species in situ, low energy consumption, compact instrumentation, ease of operation and automation, allowing their application in a decentralized manner. To contribute to the progress of this technology, a tubular electrochemical reactor was developed with foam nickel cathode and platinum coated titanium anode positioned within a nonconductive ceramic membrane. The main aim of this work was to evaluate the performance of this reactor in the generation of disinfecting oxidizing species and the subsequent removal of Escherichia coli and somatic coliphages. The membrane has the function of removing suspended solids, but due to the flow direction it also acts as a turbulence promoter that favors mass transport. The reactor's operation mode was “dead-end” and the electrochemical procedures occurred without recirculation, with theoretical residence times varying between 4.18 and 74.75 s. The development of this work was divided into three phases. The first consisted of making and characterizing ceramic membranes. The second phase of the study evaluated the performance of the reactor in the electrochemical treatment of synthetic waters through experimental planning, with input variables: NaCl, Na2SO4, potential difference and flow. In the third phase, the performance of two reactor prototypes (RET-01 and RET-02) was evaluated in terms of removing turbidity and colour, disinfection, energy consumption and cost of producing treated water according to the physico-chemical and microbiological characteristics of the wastewater. The membranes presented similar pore sizes, and apparent porosities of 42.79% and 53.24% for MR01-10 and MR01-25, respectively, with the average flow of the latter being 12.5 times greater than MR01-10. In the best conditions of the experimental design (Q = 1.6 L min-1, DDP = 12 V, [NaCl] = 1000 mg L-1, [Na2SO4] = 1000 mg L-1) the chlorine electrogeneration in the reactor reached 1.80 mg L-1 and Escherichia coli inactivation was 4.85-log10. The degradation of N,N-dimethyl-p-nitrosoaniline (RNO) obtained in the absence of chlorides showed evidence of the formation of hydroxyl radicals. In phase III, greater efficiency in removing turbidity and color from wastewater was verified in RET-02, due to the use of the MR01-10 membrane, reducing up to 57.2% turbidity and 39.0% color. Escherichia coli inactivation was visibly influenced by the concentration of chlorides, with a reduction of up to 4.67-log10 in the RET-01 reactor, in this same prototype, was obtained 2,33- log10 inactivation of somatic coliphages and the energy consumption for these levels of disinfection was only 0.10 kW h m-3. For the same DDP, disinfection results were better in RET-02 due to the larger anode area and longer residence time, however, energy consumption was also higher.