Study of the influence of the reaction parameters on nutrients recovering from digestate by struvite crystallisation

Screening plant growth effects of sheep slaughterhouse waste-derived soil amendments in greenhouse trials

Ameliorative effects of sheep slaughterhouse waste-derived soil amendments (struvite, blood meal, bone meal) were explored and quantified by a series of comparative greenhouse trials. A scoring matrix system was developed for 25 different test plants using 300 agricultural measurements obtained for three basic growth parameters (fresh-dry plant weights and plant heights) and four different fertilizer sources including solid vermicompost. More than 70% of NH₄⁺-N recovery from sheep slaughterhouse wastewater was achieved using a chemical combination of MgCl₂.6H₂O + NaH₂PO₄.2H₂O, a molar ratio of Mg²⁺:NH₄⁺-N:PO₄^3-P = 1.2:1:1, a reaction pH of 9.0, an initial NH₄⁺-N concentration of 240 mg/L, and a reaction time of 15 min. According to SEM micrographs, surface morphology of struvite exhibited a highly porous structure composed of irregularly shaped crystals of various sizes (11.34-79.38 μm). FTIR spectroscopy verified the active functional groups on the proximity of all fertilizer sources within the spectral range of 500-3900 cm^-1. TGA-DTG-DSC thermograms of struvite revealed that the mass loss occurred in two temperature regions and reached a maximum mass loss rate of 1.63%/min at 317 °C. The average percentages of increase (57.55-100.62%) and performance points (69-79) corroborated that the fertility value of struvite ranked first on average in cultivation of the analyzed plant species. Findings of this agro-valorization study confirmed that sheep slaughterhouse waste-derived fertilizers could be a beneficial way to promote bio-waste management and environmentally friendly agriculture.

Effects of Physicochemical Parameters on Struvite Crystallization Based on Kinetics

The precipitation of struvite (MgNH₄PO₄·6H₂O) is considered to be a promising method for the recovery of phosphate from wastewater. In this review, the kinetic models, which are commonly used to explain the process of struvite crystallization, are described. The mixed-suspension mixed-product removal (MSMPR) model is based on the population balance equation (the size-dependent growth model and the size-independent growth model). Thereafter, the first-order kinetic fitting model that aligned with concentration changes in the substrate is summarized. Finally, the several physical and chemical factors that affected the efficiency of struvite crystallization are determined. The supersaturation ratio, which is seen as the driving force of struvite crystallization, is the main factor that influences crystallization; however, it cannot be used in practical applications of engineering because it is indirectly associated with the following factors: pH, the molar ratio of Mg:N:P, and the interference of foreign impurities. In this study, we present conclusions that should be used to guide further research studies, and encourage the engineering practice of wastewater treatment with struvite precipitation.

Crystal seed-enhanced ammonia nitrogen and phosphate recovery from landfill leachate using struvite precipitation technique

Nitrogen and phosphorous are limiting and crucial elements for all living organisms. The recovery of nitrogen and phosphorous as struvite gained attention due to its ecofriendly fertilizer application. In the present study, feasible recovery of NH₄⁺ -N available in the landfill leachate with addition of economically viable waste resources like sewage sludge and Mg²⁺ source as struvite is investigated. However, the fertilizer application of struvite depends upon its purity, which in turn is influenced by pH, molar ratio, and presence of other ions. Laboratory scale studies are conducted to find optimum pH and molar ratio. The results of the studies demonstrated the optimum pH being 9.5 along with PO₄^3- -P: Mg²⁺: NH₄⁺ -N molar ratio of 1:1.3:1 is the best condition for struvite formation. To further augment the struvite precipitation kaolinite seed is added to the solution and optimized seed dose is 20 g/L. Existence of Ca²⁺ and Na⁺ ions in the solution exhibits a negative impact on struvite precipitation. Response surface methodology is employed to understand the interactive influence of parameters on recovery efficiency. The recovered precipitate consists of 82.5% struvite with PO₄^3- -P: Mg²⁺: NH₄⁺ -N ratio 1:1.1:0.9. Also, bioavailability of PO₄^3- -P in the recovered precipitate is 89.3%; this signifies high performance of precipitate as fertilizer. Economic assessment highlights that the struvite production is profitable and the profit gained is 159.5$/m³.

Study of pig manure digestate pre-treatment for subsequent valorisation by struvite

This work evaluates the release of phosphorus contained in the digestate from the anaerobic digestion of pig manure, through an acidification process. The objective of this acidification is to increase the amount of phosphorus available in the digestate liquid fraction and, subsequently, recover this element by chemical precipitation in the form of struvite or calcium phosphate. Two digestate samples (one fresh and one old) were studied and treated by adding various amounts of sulphuric acid to the different digestate fractions (raw digestate, solid fraction and liquid fraction). For the raw digestate, phosphorus releases higher than 95% were obtained for pH 4.0. In the last part of the experiment, the influence of acid pre-treatment on the reaction yield of phosphorus precipitation, in the form of struvite or calcium phosphate, was determined. Improvements in reaction yield were obtained up to 15% for struvite and 80% for calcium phosphate, increasing also in 7.5 times the amount of phosphorus available in the digestate liquid fraction, for both cases.