Phosphate recovery from aerobic wastewater Bio-P Sludge through precipitation process: understanding, experimentation and optimization.

Struvite precipitation process is one the most effective approaches for recovery of phosphorus in the form of a valuable product, which could be used as a fertilizer. Despite struvite added value as a product, its application at full scale is not very common worldwide due to its economic concern of requiring the addition of Mg and NaOH to the system. The process of struvite precipitation is generally applied to the dewatered sludge after anaerobic digestion where the concentration of phosphorus is sufficiently high. Although it could be possible to use the aerobic sludge taken from the activated sludge process in which phosphorus release is happening in the anaerobic stage and a luxury uptake occurs in the aerobic zone. Lab-scale experimentation was carried out in this thesis on the process of struvite precipitation using the aerobic sludge taken from Nosedo WRRF, Milan, Italy. The impact of different reaction parameters has been studied on the process of struvite precipitation. Particular attention was paid to the effect of pH, Mg:NH4:P molar ratio and presence of calcium. The results showed that abundant amount of Mg and NH4 are required for significant struvite precipitation. The analysis of precipitates using FTIR, XRD, TGA-MS, ICP-AES and Elemental analysis showed the presence of struvite in notable amounts for the experiments with 5:5:1 molar ratio at pH=8.5 and 9.0. in addition, the use of Ca(OH)2 as an economic pH adjustment reagent showed a decent potential for obtaining an amorphous calcium phosphate (ACP) precipitates alternatively to the pure struvite. Chemical equilibrium modeling and statistical optimization of the process of struvite precipitation were conducted using PHREEQC software and Response Surface Methodology (RSM) respectively with Saturation Index and P removal % as response variables. The results showed that struvite, ACP and calcite are three main solid phases that could precipitate in operating conditions of the experiments. It is also noted that the only parameter affecting significantly on the P removal was the pH while Ca:Mg and NH4:P were also significantly important for the struvite SI. It can be concluded that as the pH increases the P removal also increases but the possibility of struvite precipitation diminishes since the struvite SI is decreasing. Pilot-scale study of the phosphate precipitation process was implemented using synthetic solution with the characteristics of aerobic sludge. The effect of pH and retention time of the reaction were studied. The pH of the reactor was controlled at two points using PID-Time Proportional control system. The result of the pH control was very satisfactory and kept the pH level sufficiently stable during the entire experimentation. The results demonstrated that P removal is not much dependent on the retention time and is decreasing rapidly with the start of the reaction and then reaches at the stable level where it does not improve anymore. It was also observed that RT of 60 minutes is enough for reaction completion but not for substantial crystal growth. The FTIR results showed the possibility of having a ACP-rich product. In addition, using sodium alginate demonstrated a potential for increasing struvite precipitation possibility by reducing calcium concentration by 20% and improving the Mg:Ca ratio

Phosphate recovery from aerobic wastewater Bio-P Sludge through precipitation process: understanding, experimentation and optimization.

Struvite precipitation process is one the most effective approaches for recovery of phosphorus in the form of a valuable product, which could be used as a fertilizer. Despite struvite added value as a product, its application at full scale is not very common worldwide due to its economic concern of requiring the addition of Mg and NaOH to the system. The process of struvite precipitation is generally applied to the dewatered sludge after anaerobic digestion where the concentration of phosphorus is sufficiently high. Although it could be possible to use the aerobic sludge taken from the activated sludge process in which phosphorus release is happening in the anaerobic stage and a luxury uptake occurs in the aerobic zone. Lab-scale experimentation was carried out in this thesis on the process of struvite precipitation using the aerobic sludge taken from Nosedo WRRF, Milan, Italy. The impact of different reaction parameters has been studied on the process of struvite precipitation. Particular attention was paid to the effect of pH, Mg:NH4:P molar ratio and presence of calcium. The results showed that abundant amount of Mg and NH4 are required for significant struvite precipitation. The analysis of precipitates using FTIR, XRD, TGA-MS, ICP-AES and Elemental analysis showed the presence of struvite in notable amounts for the experiments with 5:5:1 molar ratio at pH=8.5 and 9.0. in addition, the use of Ca(OH)2 as an economic pH adjustment reagent showed a decent potential for obtaining an amorphous calcium phosphate (ACP) precipitates alternatively to the pure struvite. Chemical equilibrium modeling and statistical optimization of the process of struvite precipitation were conducted using PHREEQC software and Response Surface Methodology (RSM) respectively with Saturation Index and P removal % as response variables. The results showed that struvite, ACP and calcite are three main solid phases that could precipitate in operating conditions of the experiments. It is also noted that the only parameter affecting significantly on the P removal was the pH while Ca:Mg and NH4:P were also significantly important for the struvite SI. It can be concluded that as the pH increases the P removal also increases but the possibility of struvite precipitation diminishes since the struvite SI is decreasing. Pilot-scale study of the phosphate precipitation process was implemented using synthetic solution with the characteristics of aerobic sludge. The effect of pH and retention time of the reaction were studied. The pH of the reactor was controlled at two points using PID-Time Proportional control system. The result of the pH control was very satisfactory and kept the pH level sufficiently stable during the entire experimentation. The results demonstrated that P removal is not much dependent on the retention time and is decreasing rapidly with the start of the reaction and then reaches at the stable level where it does not improve anymore. It was also observed that RT of 60 minutes is enough for reaction completion but not for substantial crystal growth. The FTIR results showed the possibility of having a ACP-rich product. In addition, using sodium alginate demonstrated a potential for increasing struvite precipitation possibility by reducing calcium concentration by 20% and improving the Mg:Ca ratio

Osservazione delle zone marine costiere da dati ottici multi-sensore: il caso studio della foce del Volturno

Questo lavoro s’inserisce nell’ambito del progetto bandiera RITMARE (Ricerca ITaliana per il MARE, 2012-2016, MIUR-CNR) che ha lo scopo di studiare, monitorare, gestire e valorizzare la risorsa marina in Italia. A tale fine il telerilevamento è parte integrante al progetto che, in questo studio, viene applicato alla fascia costiera della foce del Volturno. Lo studio si avvale dell’utilizzo di immagini satellitari (RapidEye (2013) e Landsat-8 OLI (2014)) e aviotrasportate (MIVIS (2011)). A supporto dell’analisi delle immagini sono state acquisite misure in-situ di riflettanza e di concentrazione dei seguenti parametri: clorofilla-a (Chl-a), sedimenti totali sospesi (TSM) e sostanza organica colorata disciolta (CDOM) durante una campagna svoltasi in agosto 2014. I dati telerilevati, geocodificati e co-registrati, sono stati pre-elaborati per correggere gli effetti radiometrici ed atmosferici. Le immagini sono state successivamente elaborate per classificare le acque marino-costiere secondo diversi gradi di complessità ottica e per produrre mappe di concentrazione di Chl-a, TSM e CDOM. In particolare, per la generazione delle mappe è stato applicato un approccio semi-empirico basato su analisi di correlazione dei dati in-situ; in particolare tra valori spettrali di riflettanza (es. rapporti di banda) e le corrispondenti misure di concentrazione di Chl-a, TSM e CDOM. I risultati mostrano un gradiente crescente di complessità ottica delle acque spostandosi dalle zone pelagiche verso le aree costiere. In queste aree l’analisi del dato OLI ha mostrato una variabilità spaziale di Chl-a, TSM e CDOM imputabile ai regimi idrologici del fiume Volturno

Simulations and Laboratory Tests for Assessing Phosphorus Recovery Efficiency from Sewage Sludge

Phosphorus is a potential environmental pollutant, which could lead to the eutrophication of water bodies. For this reason, wastewater treatment plants worldwide are often designed and operated to eliminate phosphorous from effluents, at substantial cost. At the same time, phosphorus is an essential nutrient for agriculture and, consequently, human life. Data seem to suggest that the world will run out of phosphorus by around 2300, in the best case scenario, although even shorter estimates exist. This situation evokes the need for more efficient phosphorus recovery technologies, in order to meet current water quality requirements and—at the same time—critical future phosphorous needs. Chemical precipitation is the main process for achieving a phosphorus-containing mineral suitable for reuse as a fertilizer, where Struvite is an example of such a product. In this study chemical equilibrium of struvite precipitation was simulated using US Geological Survey (USGS)’ PHREEQC model, and results were compared to laboratory precipitation tests to evaluate struvite recovery efficiency under various conditions. pH had the most significant effect on the results and P recovery of >90% was achieved at pH = 9.5. Simulations indicated that struvite precipitation is affected by the presence of Amorphous Calcium Phosphate (ACP) and calcite in the final product of the process. The model showed great potential for predicting equilibrium conditions, and could be very helpful for future optimization of the process

Erratum: Daneshgar, S., et al. Simulations and Laboratory Tests for Assessing Phosphorus Recovery Efficiency from Sewage Sludge, <em>Resources</em> 2018, <em>7</em>, 54

The authors wish to make the following corrections to this paper [...

Simulations and Laboratory Tests for Assessing Phosphorus Recovery Efficiency from Sewage Sludge

Phosphorus is a potential environmental pollutant, which could lead to the eutrophication of water bodies. For this reason, wastewater treatment plants worldwide are often designed and operated to eliminate phosphorous from effluents, at substantial cost. At the same time, phosphorus is an essential nutrient for agriculture and, consequently, human life. Data seem to suggest that the world will run out of phosphorus by around 2300, in the best case scenario, although even shorter estimates exist. This situation evokes the need for more efficient phosphorus recovery technologies, in order to meet current water quality requirements and&mdash;at the same time&mdash;critical future phosphorous needs. Chemical precipitation is the main process for achieving a phosphorus-containing mineral suitable for reuse as a fertilizer, where Struvite is an example of such a product. In this study chemical equilibrium of struvite precipitation was simulated using US Geological Survey (USGS)&rsquo; PHREEQC model, and results were compared to laboratory precipitation tests to evaluate struvite recovery efficiency under various conditions. pH had the most significant effect on the results and P recovery of &gt;90% was achieved at pH = 9.5. Simulations indicated that struvite precipitation is affected by the presence of Amorphous Calcium Phosphate (ACP) and calcite in the final product of the process. The model showed great potential for predicting equilibrium conditions, and could be very helpful for future optimization of the process

Side-Stream Phosphorus Recovery in Activated Sludge Processes

Precipitation of mineral phosphates from wastewater treatment processes is an excellent method for phosphorus recovery, leading to the formation of compounds with high fertilizing value. Conventionally, P-precipitation processes are mostly applied to supernatant of anaerobic sludge digestates, due to their high P and N residual contents. This study concerns P-recovery in a pilot-scale side-stream reactor from aerobic (activated sludge) wastewater liquor. The effect of process retention time and pH was determined using sodium hydroxide and calcium hydroxide as alternative pH buffer reagents, in both synthetic and real wastewater. Equilibrium mass balance calculations were first applied to estimate the theoretical final composition of P-precipitates under different process conditions; then, actual precipitation experiments were carried out with synthetic wastewater to define optimal process operating parameters in controlled conditions. Results showed that phosphorus precipitation was affected mainly by solution pH and did not significantly depend on the reactor&rsquo;s retention time. These findings were validated by operating the process with real wastewater: on average, 61.2% and 90.4% phosphorus precipitation (recovery) were achieved at pH = 8.5 and 9.0 under a controlled Mg:NH4:P molar ratio of 5:5:1, using sodium hydroxide as acidity buffer. The main fraction of final precipitates consisted of calcium phosphate compounds, while struvite, bobierrite and calcite showed up in smaller proportions. It was also shown that dosage of calcium hydroxide for pH adjustment, without any other chemicals for molar ratios adjustment of the solution, has great potential for P recovery in the form of a calcium phosphate-rich precipitate, usable for fertilizer, with 75.6% phosphorus removal in mineral form at pH = 8.5. The process is much less costly to operate than struvite precipitation, and more energetically sustainable. This scheme could be ideally suited for application in facilities operating under an enhanced phosphorus removal process scheme

Impact of pH and Ionic Molar Ratios on Phosphorous Forms Precipitation and Recovery from Different Wastewater Sludges

Phosphorus is an essential nutrient for plants, which use it as a basic fertilizer component and is expected to increase significantly in the coming years due to higher food crops demand. Unfortunately, the available phosphorus natural reserves are not renewable, and estimates indicate their rapid decline in the future. Urban wastewater, due to its abundance and relatively high phosphorus content, is an excellent candidate for phosphorus recovery, while the element&#8217;s removal from urban effluents was introduced in the 1970&#8242;s to limit the undesired effects of eutrophication. In this study, the process of struvite (and related phosphorous compounds) crystallization was investigated for three different sludge types, and the results were compared. While most studies focus strictly on anaerobically digested sludge for high struvite precipitation efficiency, this study investigated the possibility of inducing precipitation on both aerobic (extended aeration) and anaerobic sludges produced by two wastewater treatment plants in northern Italy. Analysis of precipitates from sludge samples was compared, where the focus was on the aerobic sludge, and its potential for struvite recovery. The effect of different reaction parameters was studied under different operating conditions, and the use and effects of Ca(OH)2 addition as an inexpensive potential pH adjustment reagent was investigated