Advances in Struvite Precipitation Technologies for Nutrients Removal and Recovery from Aqueous Waste and Wastewater

Abstract

The abatement of nutrient compounds from aqueous waste and wastewater is currently a priority issue. Indeed, the uncontrolled discharge of high levels of nutrients into water bodies causes serious deteriorations of environmental quality. On the other hand, the increasing request of nutrient compounds for agronomic utilizations makes it strictly necessary to identify technologies able to recover the nutrients from wastewater streams so as to avoid the consumption of natural resources. In this regard, the removal and recovery of nitrogen and phosphorus from aqueous waste and wastewater as struvite (MgNH4PO4·6H2O) represents an attractive approach. Indeed, through the struvite precipitation it is possible to effectively remove the ammonium and phosphate content of many types of wastewater and to produce a solid compound, with only a trace of impurities. This precipitate, due to its chemical characteristics, represents a valuable multi-nutrients slow release fertilizer for vegetables and plants growth. For these reasons, the struvite precipitation technology constantly progresses on several aspects of the process. This manuscript provides a comprehensive review on the recent developments in this technology for the removal and recovery of nutrients from aqueous waste and wastewater. The theoretical background, the parameters, and the operating conditions affecting the process evolution are initially presented. After that, the paper focuses on the reagents exploitable to promote the process performance, with particular regard to unconventional low-cost compounds. In addition, the development of reactors configurations, the main technologies implemented on field scale, as well as the recent works on the use of struvite in agronomic practices are presented.

Sequential Treatment of Landfill Leachate By Advanced Oxidation Processes and Struvite Precipitation

“…Although the maximum removal was attained at 60 min, a significant change in removal was observed at 40 min, therefore, struvite can be operated for 40 min. Based on the observations further increase in the reaction may result in redissolution of precipitated struvite and also affect settleability of Struvite [19]. The presence of competitive ions like Ca 2+ , Na + , K + , CO3 2− , and HCO3 − in landfill leachate may interfere in the crystal formation and have a negative effect on the treatment process.…”

The Recovery of Phosphate and Ammonium from Biogas Slurry as Value-Added Fertilizer by Biochar and Struvite Co-Precipitation

“…Comparable explanations were also reported for the decrease in the removal of phosphate in the existence of HCO 3 − ions [131][132][133]. The presence of viable ions in solutions, such as Ca 2+ , K +, Na + , CO 3 2− , and HCO 3 − , will powerfully impact the nucleation and development of struvite [106,[134][135][136].…”

“…This is possibly due to the higher concentration of biogas slurry, which encourages the recovery of nitrogen and phosphorus due to ion activity. According to the supersaturation calculation formula, the supersaturation improved with the increasing rate of ion activity, and supersaturation will affect the nucleation induction time and crystal growth rate of the struvite [33,96,[100][101][102][103][104][105][106]. According to the consequences of the same ion, enhancing the concentration of nutrient ions could promote the forward reaction of struvite precipitation, thereby, improving the recovery efficiency of NH4 + and P [96,104].…”

“…Compared to commercial mineral P fertilizers, struvite is an effective slow-release fertilizer with a comparatively low content of contaminants, which could be the best alternative as the fertilizers are produced from phosphate rock [15,18,19,21]. The worthiness of struvite as a fertilizer has only recently been understood and it is now the focus of increasing research attention [106,123]. A perfect technology would feature maximum P recovery rates, good removal, and an applicable material with low environmental risks, good fertilizing effects, and financial efficiency.…”

Fate of Citric Acid Addition on Mineral Elements Availability in Calcareous Soils of Jordan Valley

“…Acidity has great effects on the nutrient deficiencies, mobilizing some nutrients such as Ca in calcareous soils. Citric acid plays a significant role to decrease bulk density of soil which is indicator of compaction and soil health, it affects infiltration, rooting depth restrictions, available water capacity, soil porosity, plant nutrient availability, and soil microorganism activity, which influence key soil processes and productivity [7].…”