Luis Enrique Rodríguez Gómez

Dynamic membrane technology has recently been investigated for wastewater treatment due to its reduced installation and operating costs compared to conventional membrane systems. However, it has been little studied in combination with photobioreactors, which provide efficient nutrient removal. This study investigates the feasibility of dynamic membrane photobioreactors for the secondary treatment of domestic wastewater. A laboratory unit equipped with a nylon module was tested using a mixed culture of microalgae-bacteria, which removed 93% and 76% of phosphorus and nitrogen, respectively. However, the dynamic membrane build-up on the support layer shows non-uniform growth, a compact structure with low permeability and is not able to effectively separate the suspension from the effluent.

Direct membrane filtration of municipal wastewater has attracted a considerable interest in recent years. Preventing severe membrane fouling is a crucial issue in the process development. This paper aims to assess the effectiveness of a rotating hollow fiber module in enhancing fouling control. The effect of rotation speed, intermittence and permeate flux was studied in short-term tests at lab-scale. A combined filtration model considering residual fouling, intermediate pore blocking and cake filtration was used to analyze the effect of the shear induced by rotation. Results showed a significant flux improvement by increasing rotation shear stress and showed a nearly linear correlation between the threshold flux (ranged between 12 and 32 L·h⁻¹·m⁻²) and the rotation speed. A proper rotation intermittence (10/15 on/off) was found, which may maintain a fouling control comparable to that achieved for continuous rotation. For a given energy demand, the optimal operating conditions involve high speeds (≥180 rev·min⁻¹) with low to moderate intermittences. Analyzing the relative contribution of the different feedwater fractions on membrane fouling, colloidal particles and macromolecules were found to be the main contributors.

This work provides information on nitrification with nitrite accumulation in low strength ammonia (below 50 mg L⁻¹ NH₄–N) and low organic matter (below 150 mg L⁻¹ COD) reclaimed wastewater. In the South Tenerife reclaimed wastewater pipeline (62 km long), injection of O₂ has been applied to promote a nitrification process in order to improve water quality and to avoid anaerobic conditions. Nitrification occurs, in most cases, with nitrite accumulation. The amount of oxidized nitrogen compounds produced increases with the oxygen dose applied. The nitrification process is usually favoured instead of the organic matter transformation, due to the low organic matter/ammonia nitrogen ratio of water. The influence of organic matter content on nitrification has been analysed, and a good suitability for COD has been found as an indicator for nitrification limitation (for the range of COD and NH₄-N concentrations of the system). Nitrification limitation has been observed above 85 mg L⁻¹ COD, and nitrification inhibition above a concentration of 105 mg L⁻¹. In addition, the limitation of nitrite oxidation bacteria activity (nitrite accumulation) by free ammonia and temperature has been assessed, finding that, for the range of free ammonia (0.6–2.1 mg L⁻¹ NH₃) and temperature (20.4–27.0°C) in the study, temperature plays a much more relevant role than free ammonia on nitrite accumulation. The lower limiting temperature for nitrite build-up in the system has been 21.0°C. Below this temperature, nitrite accumulation did not exist or was very low. GRAPHICAL ABSTRACT