Advanced Phosphorus Recovery from Municipal Wastewater using Anoxic/Aerobic Membrane Bioreactors and Magnesium-based Pellets

Abstract:

Phosphorus is an essential and limited nutrient that is supplied by a depleting resource, mineral phosphate rock. The increasing occurrence of harmful algal blooms in lakes and rivers has become an emerging concern threatening human and environmental health. One of the major point sources of nutrients such as nitrogen and phosphorus affecting eutrophication is municipal and industrial wastewater.

Adsorptive removal of phosphorus from wastewater has attracted attention due to its potential for sludge reduction and recovery of P for further applications. Among various adsorbents, magnesium carbonate (MgCO₃)-based materials (particularly beads, tablet, or pellet types) showed great potential for efficient and sustainable recovery of P from wastewater due to its physical and chemical stability in water and eco-friendly properties for agricultural applications.

Physical adsorption of phosphorus in the membrane permeate using solid adsorbents can be a feasible technology to recover phosphorus efficiently from wastewater without further hindrance of particles and microorganisms, which reduce adsorption efficiency of phosphorus from water. This study focuses on validating MgCO₃ pellets in combination with an anoxic/aerobic membrane bioreactor (MBR) for effective phosphorus recovery from municipal wastewater at varying flow rates (i.e., 2.5, 5, and 10 L/d). Phosphate adsorption using the pellets was studied via batch kinetics and sorption isotherms. The pseudo-second-order kinetics model fits best suggesting that the adsorption occurring was chemisorption. Enhanced biological phosphorus removal mechanism through the MBR system provided particle and bacteria-free effluent and improved phosphorus concentration to MgCO₃ pellets.

With primary effluent wastewater, phosphorus removal/recovery efficiency of the system increased from 55.6 % to 94.1 % as the wastewater flow rate decreased from 10 to 2.5 L/d. The effluent phosphorus concentration was below 0.5 mg/L. The adsorption capacity of MgCO₃ pellets was in the range of 0.41 ~ 0.47 mg P/g MgCO₃. The surface of the pellets changed as phosphate was adsorbed as shown by the SEM and XRD analysis. In summary, combining the MBR system with MgCO₃ pellets could be an effective alternative method of phosphorus recovery from wastewater.