Isolation of five Rubrobacter strains from biodeteriorated monuments

In the last few years, the microbial colonisation of mural paintings in ancient monuments has been attracting the attention of microbiologists and conservators. The genus Rubrobacter is commonly found in biodeteriorated monuments, where it has been reported to cause rosy discolouration. However, to date, only three species of this genus have been isolated, all from thermophilic environments. In this paper, we studied three monuments: the Servilia and Postumio tombs in the Roman Necropolis of Carmona (Spain), and Vilar de Frades church (Portugal), in search of Rubrobacter strains. In all cases, biodeterioration and the formation of efflorescences were observed, and five Rubrobacter strains were isolated. These isolates showed different physiology and migration in denaturing gradient gel electrophoresis, suggesting they might represent new species within this genus. The isolates reproduced some biodeterioration processes in the laboratory and revealed their biomediation in crystal formation.     

Precipitation assessment in wastewater treatment plants operated for biological nutrient removal: a case study in Murcia, Spain

The Murcia Este Wastewater Treatment Plant is the largest wastewater treatment plant in Murcia (Spain). The plant operators have continuously found pipe blockage and accumulation of solids on equipment surfaces during the anaerobic digestion and post-digestion processes. This work studies the precipitation problems in the Murcia Este Wastewater Treatment Plant in order to locate the sources of precipitation and its causes from an exhaustive mass balance analysis. The DAF thickener and anaerobic digester mass balances suggest that most of the polyphosphate is released during excess sludge thickening. Despite the high concentrations achieved in the thickened sludge, precipitation does not occur at this point due to the low pH. The increases in ammonium and pH during anaerobic digestion cause precipitation to take place mainly inside the digesters and in downstream processes. This study shows that 50.7% of the available phosphate is fixed in the digester of which 52.0% precipitates as ammonium struvite, 39.2% precipitates as hydroxyapatite and the remaining 8.8% is adsorbed on the surface of the solids. Thermodynamic calculations confirm the precipitation of struvite and hydroxyapatite and also confirm that potassium struvite does not precipitate in the anaerobic digesters.     

Numerical simulation of flow hydrodynamics of struvite pellets in a liquid–solid fluidized bed

Phosphorus recovery in the form of struvite has been aroused in recent decades for its dual advantages in eutrophication control and resource protection.The usage of the struvite products is normally determined by the size which is largely depended on the hydrodynamics.In this study,flow behavior of struvite pellets was simulated by means of Eulerian–Eulerian two-fluid model combining with kinetic theory of granular flow in a liquid–solid fluidized bed reactor(FBR).A parametric study including the mesh size,time step,discretization strategy,turbulent model and drag model was first developed,followed by the evaluations of crucial operational conditions,particle characteristics and reactor shapes.The results showed that a cold model with the mesh resolution of 16 × 240,default time step of 0.001 sec and first order discretization scheme was accurate enough to describe the fluidization.The struvite holdup profile using Syamlal–O'Brien drag model was best fitted to the experimental data as compared with other drag models and the empirical Richardson–Zaki equation.Regarding the model evaluation,it showed that liquid velocity and particle size played important roles on both solid holdups and velocities.The reactor diameter only influenced the solid velocity while the static bed height almost took no effect.These results are direct and can be applied to guide the operation and process control of the struvite fluidization.Moreover,the model parameters can also be used as the basic settings in further crystallization simulations.     

Selection of cost-effective magnesium sources for fluidized struvite crystallization

Struvite crystallization has been considered a promising approach to recover phosphorus from wastewater. However, its practical application is limited, probably because of the high cost of magnesium(Mg). In this study, a comprehensive economic analysis was conducted using five Mg sources(MgCl_2, MgSO_4, MgO, Mg(OH)_2, and bittern) during the operation of a pilot-scale fluidized bed reactor(FBR), using swine wastewater as the case matrix. First, the economic operating conditions were investigated, and subsequently, the performance and the costs of the five Mg sources were compared. The results indicated that the FBR could be operated most economically at pH of 8.5 and Mg to phosphorus(Mg/P) molar ratio of 1.5. Under these conditions, no significant differences in phosphorus removal and product quality could be found between the five Mg sources. Selecting the most economical Mg source was thus highly dependent on the prices of the reagents and Mg sources. Low-solubility Mg sources were preferable when NaOH was priced higher, while high-solubility Mg sources proved more economical when HNO_3 was expensive. The bittern was the most economical choice only when the distances for total inorganic orthophosphate removal and struvite recovery were shorter than 40 and 270 km, respectively. The current study provides an overview of the economic selection of an Mg source, which can help reduce the cost of struvite crystallization.     

Ammonia removal from low-strength municipal wastewater by powdered resin combined with simultaneous recovery as struvite

• Powdered resin was employed for ammonia recovery from municipal wastewater. • Powdered resin achievedefficient ammonia removal under various working conditions. • Co-existing cations indicated competitive adsorption of ammonia. • Ammonia was recoveredby two-stage crystallization coupled with ion exchange. Low-strength municipal wastewater is considered to be a recoverable nutrient resource with economic and environmental benefits. Thus, various technologies for nutrient removal and recovery have been developed. In this paper, powdered ion exchange resin was employed for ammonia removal and recovery from imitated low-strength municipal wastewater. The effects of various working conditions (powdered resin dosage, initial concentration, and pH value) were studied in batch experiments to investigate the feasibility of the approach and to achieve performance optimization. The maximum adsorption capacity determined by the Langmuir model was 44.39 mg/g, which is comparable to traditional ion exchange resin. Further, the effects of co-existing cations (Ca²⁺, Mg²⁺, K⁺) were studied. Based on the above experiments, recovery of ammonia as struvite was successfully achieved by a proposed two-stage crystallization process coupled with a powdered resin ion exchange process. Scanning electron microscopy (SEM) and X-ray diffractometry (XRD) results revealed that struvite crystals were successfully gained in alkaline conditions (pH= 10). This research demonstrates that a powdered resin and two-stage crystallization process provide an innovative and promising means for highly efficient and easy recovery from low-strength municipal wastewater.     

Effect of culture conditions on the formation of struvite by Myxococcus xanthus

The amount of struvite (MgNH₄PO₄·6H₂O) produced by Myxococcus xanthus as well as the culture parameter values (pH, total phosphorus, total Kjeldahl nitrogen) were dependent on the culture medium used. Struvite formation started during the exponential phase and the maximum concentration was observed at the beginning of stationary growth phase. The addition of each medium component to the liquid culture influenced the amount of crystal produced. This amount did not depend on the pH increase during the culture period. The moment of the bacterial growth phase, at which each medium component was added, influenced the struvite formation.     

Morphological diversity of Struvite crystals produced by Myxococcus Coralloides and Myxococcus Xanthus

We studied the morphological diversity of struvite crystals produced by Myxococcus coralloides and Myxococcus xanthus in different culture conditions. We discussed the similarities of these crystals with the struvite morphology studied previously following the theory of the periodic bond chains.     

Simultaneous removal of phosphorus and potassium from synthetic urine through the precipitation of magnesium potassium phosphate hexahydrate

This study investigated the simultaneous removal of P and K from synthetic urine through the precipitation of magnesium potassium phosphate hexahydrate (MPP, MgKPO₄·6H₂O) in bench-scale experiments. Results show that the removal efficiencies of P and K are mainly determined by the solution pH and the molar ratio of Mg:K:P. Co-precipitation of struvite-type compounds, i.e., magnesium ammonium phosphate hexahydrate (MAP, MgNH₄PO₄·6H₂O), magnesium sodium phosphate heptahydrate (MSP, MgNaPO₄·7H₂O), and MPP, was confirmed by analysis of the solid precipitates using a Scanning Electron Microscope/Energy Dispersive X-ray Apparatus and an X-ray Diffractometer. The co-precipitation significantly influenced the removal of K. As much ammonium as possible should be removed prior to MPP precipitation because MAP had higher tendency to form than MPP. The inevitable co-precipitation of MPP and MSP resulted in the addition of more MgCl₂·6H₂O and Na₂HPO₄·12H₂O to obtain the high removal of K. In total, the removal efficiencies of P and K were 77% and 98%, respectively, in the absence of ammonium when pH was 10 and the molar ratio of Mg:K:P was 2:1:2. The results indicate that the MPP precipitation is an efficient method for the simultaneous removal of P and K to yield multi-nutrient products.     

污水处理中鸟粪石法磷回收技术研究进展

针对水体富营养化和磷资源短缺的困境,从污水中利用鸟粪石法回收磷成为一个重要的选项。围绕高效低耗的鸟粪石回收目标,本文梳理了鸟粪石法磷回收思路、技术特征、不同类型反应器的发展,为新型鸟粪石磷回收技术的开发提供了支撑。     

Effect of saline water ionic strength on phosphorus recovery from synthetic swine wastewater

Declining worldwide phosphate rock reserves has driven a growing interest in exploration of alternative phosphate supplies. This study involved phosphorus recovery from swine wastewater through precipitation of struvite, a valuable slow-release fertiliser. The economic feasibility of this process is highly dependent on the cost of magnesium source. Two different magnesium sources were used for phosphorus recovery: pure magnesium chloride and nanofiltration(NF) saline water retentate. The paper f...