Experimental and Numerical Modelling of Struvite Precipitation and Nutrient Recovery from Municipal Wastewater Using Anaerobic Baffled Reactors

Phosphorus and Nitrogen are valuable elements since they are the base of the fertilizers used for crop production and their restricted availability. Thus, these nutrients may be considered increasingly as an asset that should be recovered from wastewater and reused as fertilizer rather than a nutrient that must be removed and disposed. Therefore, the recovery of these nutrients is of economic interest.

Struvite (magnesium ammonium phosphate) is a slow-release fertilizer containing these elements which can be recovered through sludge processing. Various full-scale systems are currently used for struvite recovery. However, there is a need for development of new technologies to recover struvite directly from wastewater instead of sludge.

In this case, the capital and operation costs could be fundamentally decreased. Anaerobic baffled reactor (ABR) seems to be an appropriate system for this purpose.

ABR is a system capable of treating low and high strength wastewaters with main applications as a pre-treatment unit, and on-site and decentralized sanitation system. ABR reactor consists of a series of up-flow anaerobic reactors in which the wastewater flows through different compartments separated by baffles. The series of compartments in ABR enable increased contact time between the wastewater and the active biomass accumulated in the system.

Meanwhile because of this configuration, ABRs can naturally segregate the phases of hydrolysis, acidogenesis, and methanogenesis among the sequential compartments of the reactor. This is one of the most interesting advantages of ABR over other anaerobic systems which is considered in this research as a key point in the function of ABR for nutrient separation and recovery.

Application of ABR as a nutrient recovery system can reduce the capital and operational cost of both treatment and recovery facilities. In addition, higher effluent and sludge quality and well-shaped struvite crystals are expected using a simpler system.