Papers by Author: António Albuquerque

Abstract: The evaluation of the dispersion in vegetated beds may allow indentifying mechanisms that affect the transport and reaction of solutes, namely organic and nitrogen compounds. A set of non-reactive tracer experiments (slag injection) was performed in a vegetated bed (a mesocosm with a LECA-based substratum and colonized with Phragmites australis) used for the removal of organic and nitrogen pollutant loads. Loads of approximately 300 mg COD/L and 30 mg NH₄-N/L and a hydraulic loading rate of 3.5 cm/d were used. The results showed a delay in all the residence time distribution (RTD) curves and a variation in the dimensionless residence time (μ_(m,θ)) of the E(θ) curves, which means that the mass centre of the impulse was late relatively to the expected one. A strong dispersion and tracer retention (due to the presence of stagnated areas and internal recirculation) was observed, especially in the first 33 cm of the bed, which seems to have been related to the presence of complex clusters of roots, solid material, biofilm and LECA particles. An analytical solution of the Multiple-Tanks-in-Series (MTS) model well represents the RTD curves obtained in the tracer experiments. The detected dispersion and dead volume ratios (7% to 12%) did not affect the performance of the bed, which presented mean removal efficiencies of 85% and 60.4% for COD and NH₄-N, respectively.

Abstract: Waste geopolymeric artificial aggregates (WGA) with different atomic ratios of mining waste mud/Na2SiO (4 to 5) and Na2SiO/NaOH (1.25 to 5) were produced using curing temperatures of 20°C and 130°C and its structural stability and pH variation after immersion in water was observed during 3 months. Results showed that WGA with mud/Na2SiO and Na2SiO/NaOH of 5 and 4, respectively, cured at 20°C presented good stability in water and pH decreased from 10 to 7 in 24 days. Compressive strength was determined in additional samples cured at 20°C and 80°C in dry conditions, for 13 curing ages and 15 water immersion periods (up to 14 weeks). Results of this second stage showed that increasing temperature to 80°C accelerated compressive strength gain but only during the first 3 weeks (up to 15.4 MPa). After 24 h in water compressive strength decreased to half of the initial values determined in dry conditions in all samples and, therefore, the increase of temperature did not bring benefits to WGA strength in water. Regardless the curing temperature and the dry curing age comprehensive strength stabilizes between 1 MPa and 2 MPa after 4 weeks immersion in water, which are values that makes WGA suitable to be used as bed material for wastewater treatment processes.