An energy autonomous and portable pilot unit for the photocatalytic treatment of wastewater

Abstract

An energy-autonomous and portable pilot unit was designed and manufactured. The unit was placed on a wheeled support consisting of a photovoltaic panel, four (4) metallic photo-reactors, each equipped with 6 W UV-A lamps, two (2) peristaltic pumps of 5 W, and an external recirculation tank. The annular space of reactors was packed with ZnO-coated Duranit spheres. The pilot unit was assessed with regard to the degradation capacity of phenol solution and effluents collected from wastewater treatment plant (WWTP). Measurements of the UV-light intensity were combined with the 2-flux radiation model to determine the radial profile of UV-radiant flux across the annular photoreactor. The experimentally measured transient responses of phenol concentration, total organic, and inorganic carbon were fitted with one-dimensional (1D) numerical models to estimate the apparent 1st order kinetic constant of photo-degradation processes. On average, the energy demand of the unit was counterbalanced by the electric power generated by the photovoltaic panel. The repeated use of the same photocatalysts in all experiments confirmed the long-term energy efficiency of the unit. The apparent kinetic constants of phenol, intermediates species, and total organic carbon (TOC) degradation were found to be governed by the corresponding mass-transfer coefficients of relevant species from the bulk liquid to the active catalyst surface. At early times, the total inorganic carbonates (TIC) concentration increases, and at late times the fast mass-transfer of dissolved CO2 to gas phase compensates for the production of inorganic carbon. Preliminary tests showed that the photocatalytic unit is capable of reducing the COD and TOC of WWTP effluents and occasionally, the concentration of nitrates and ammonia may also decrease.