Ammonia removal from landfill leachate by struvite formation: an alarming concentration of phosphorus in the treated effluent

Nutrient recovery from municipal solid waste leachate in the scope of circular economy: Recent developments and future perspectives

Holistically considering the current situation of the commercial synthetic fertilizer (CSF) market, recent global developments, and future projection studies, dependency on CSFs in agricultural production born significant risks, especially to the food security of foreign-dependent countries. The foreign dependency of countries in terms of CSFs can be reduced by the concepts such as the circular economy and resource recovery. Recently, waste streams are considered as a source in order to produce recovery-based fertilizers (RBF). RBFs produced from different waste streams can be substituted with CSFs as input for agricultural applications. Municipal solid waste leachate (MSWL) is one of the waste streams that have a high potential for RBF production. Distribution of the published papers over the years shows that this potential was noticed by more researchers in the millennium. MSWL contains a remarkable amount of nitrogen and phosphorus which are the main nutrients required for agricultural production. These nutrients can be recovered with many different methods such as microalgae cultivation, chemical precipitation, ammonia stripping, membrane separation, etc. MSWL can be generated within the different phases of municipal solid waste (MSW) management. Although it is mainly composed of landfill leachate (LL), composting plant leachate (CPL), incineration plant leachate (IPL), and transfer station leachate (TSL) should be considered as potential sources to produce RBF. This study compiles studies conducted on MSWL from the perspective of nitrogen and phosphorus recovery. Moreover, recent developments and limitations of the subject were extensively discussed and future perspectives were introduced by considering the entire MSW management. Investigated studies in this review showed that the potential of MSWL to produce RBF is significant. The outcomes of this paper will serve the countries for ensuring their food security by implementing the resource recovery concept to produce RBF. Thus, the risks born with the recent global developments could be overcome in this way besides the positive environmental outcomes of resource recovery.

Optimization of phosphorus recovery using electrochemical struvite precipitation and comparison with iron electrocoagulation system

A batch monopolar reactor was developed for total phosphorus (TP) recovery using electrochemical struvite precipitation. This study involves the optimization of factors using response surface methodology to maximize the TP recovery. The optimal parameters for this study were found to be a pH of 8.40, a retention time of 35 min, a current density of 300 A/m² , and an interelectrode distance of 0.5 cm, resulting in 97.3% of TP recovery and energy consumption of 2.35 kWh/m³ . A kinetic study for TP removal revealed that at optimum operating conditions, TP removal follows second-order kinetics (removal rate constant(K) = 0.0117 mg/(m² ·min)). The system performance was compared to the performance of an iron electrocoagulation system. The composition of the precipitate obtained during the optimal runs were analyzed using X-ray diffraction and EDS analysis. X-ray diffraction analysis of the magnesium precipitate revealed the presence of struvite as the only crystalline compound. PRACTITIONER POINTS: Electrochemical struvite precipitation has the potential to recover total phosphorus from anaerobic bioreactor effluent. Optimum conditions for phosphorus recovery was found at a pH of 8.4, retention time of 35 min, current density of 300 A/m2, and interelectrode distance of 0.5 cm. The quadratic model predicted complete (100 %) TP recovery under optimized conditions, whereas 97.3 % recovery was observed under experimental conditions. TP removal under optimum conditions followed second-order rate equation (removal rate constant(K) = 0.0117 mg/(m² ·min)). XRD analysis of the precipitate revealed struvite as the only crystalline compound.

Effects of Calcium on the Removal of Ammonium from Aged Landfill Leachate by Struvite Precipitation

Ammonium in landfill leachates is a major contributor to environmental degradation if not effectively treated. However, it could be converted to a valuable fertilizer when it is co-precipitated with phosphate and magnesium as struvite. Low-cost magnesium and phosphate sources are sought to offset the co-precipitation treatment costs, but most of the identified alternative magnesium sources have significant amounts of calcium, which may negatively impact the ammonium removal rates. In this study, the effects of calcium on ammonium removal from high-strength aged field landfill leachate as struvite were investigated. Laboratory-scale batch tests were conducted to assess the effects of the pH, Mg2+:NH4+:PO43−, and Ca2+:Mg2+ molar ratios on ammonium removal. Magnesium chloride salt was used as a model dissolved magnesium source, whereas different compounds derived from dolomite (CaMg(CO3)2) were used as model solid-phase magnesium sources. X-ray powder diffraction and activity ratio diagrams were used to delineate the ammonium removal mechanisms and struvite stability. The ammonium removal rate of the magnesium salt decreased from approximately 97% to 70%, upon increasing the Ca2+:Mg2+ molar ratio from 0 to 1.0, for the Mg2+:NH4+:PO43− molar ratio of 1.25:1:1.25 and pH = 9.5. For similar pH values, as well as the Mg2+:NH4+:PO43− and Ca2+:Mg2+ molar ratios, the ammonium removal rates by the dolomite-derived compounds reached up to 55%, which highlighted the limited availability of magnesium in solid phases, in addition to the negative impacts of calcium. The diffractometric analysis and thermodynamic calculations revealed the stable regions of struvite in the presence of competing solid phases. The new findings in this study could aid in the design of ammonium and phosphate removal and recovery systems by struvite precipitation.