Non-apatite Inorganic Phosphorus Research Articles

Calcium oxide-enhanced phosphorus recycling using sewage sludge degradative solvent extraction technology

This study proposes a novel calcium oxide-enhanced phosphorus recycling technique using sewage sludge degradative solvent extraction. We investigated the effects of extraction parameters such as the temperature, holding time, and sludge/extractant ratio on the soluble yield and phosphorus distribution in the residue. The enhancement mechanisms of the apatite phosphorus (AP) content after adding CaO for degradative solvent extraction were also studied. The results showed that the effective separation of organic matter and phosphorus enrichment were simultaneously achieved. An increase in the extraction factors promoted the extraction of organic matter. The peak soluble yield is 13.30 g/100 gSSwhich was obtained at extraction temperature of 300 °C, holding time of 60 min and sludge/extractant ratio of 100/300 g/mL. The soluble matter with high amounts of volatile matter and near-zero ash content has high-value utilization potential. After the degradative solvent extraction, almost all P in the sewage sludge was enriched in the residue. The organic phosphorus (OP) in the residue almost disappeared, and the proportion of non-apatite inorganic phosphorus (NAIP) increased. As the amount of added CaO increased from 0 to 10 g, the proportions of AP in TP increased from 36.55 to 80.15%, while that of NAIP decreased from 61.93 to 14.77%. The transformation of P from OP to the inorganic species during extraction was promoted by the addition of CaO, particularly for the formation of hydroxylapatite.

Effect of Corn Straw Blending on Phosphorus Specification and Bioavailability of Incinerated Sludge Ash

Phosphorus is a depletable resource, and the consumption of phosphorus fertilizer increases with the growing population size. Phosphorus recycled from incinerated sludge ash can be a complement to phosphatic fertilizers in districts suffering from phosphorus resource shortages (e.g., Germany, Japan, and Sweden). The apatite inorganic phosphorus (AP) content in incinerated sludge ash is a key factor influencing the recoverability and bioavailability. Biomass straw is rich in calcium and magnesium minerals and can be used as an additive to be blended with sludge to increase the AP content. However, most of the current studies added excessive amounts of calcium-based or biomass additives, and the bioavailability of various Ca–Mg–P minerals generated after the addition of biomass has not been systematically discussed. In this study, the changes of the phosphorus form in the mixed sludge and biomass with Ca/P in the range of 1.0–2.5 are studied, and the influence of temperature and additives on the phosphorus form and the bioavailability of phosphorus in the ash samples are discussed by combining X-ray diffraction and citric acid (CA) leaching experiments. The AP content is very low in the residue of the sludge or corn straw (CS) that has been burned individually. The sludge and the blended sludge and CS were incinerated at various temperatures. As the incineration temperature increased, the conversion of non-apatite inorganic phosphorus (NAIP) to AP was promoted, but the bioavailability did not change until 1050 °C for samples with a Ca/P of 2.5. In the range from 750 to 950 °C, higher temperature promotes the formation of Ca2P2O7 and CaP2O6. CaP2O6 is insoluble in CA; thus, the bioavailability changes little from 750 to 950 °C, although the AP content increases. With the increase of Ca/P, the conversion of NAIP to AP and the bioavailability of phosphorus were promoted. For the blended sludge and CS ash, Ca7Mg2P6O24 appears at 950 and 1050 °C and the bioavailability also increases.

Co-Pyrolysis of Sewage Sludge and Wetland Biomass Waste for Biochar Production: Behaviors of Phosphorus and Heavy Metals.

Large amounts of sewage sludge (SS) and wetland plant wastes are generated in the wastewater treatment system worldwide. The conversion of these solid wastes into biochar through co-pyrolysis could be a promising resource utilization scheme. In this study, biochar was prepared by co-pyrolysis of SS and reed (Phragmites australis, RD) using a modified muffle furnace device under different temperatures (300, 500, and 700 °C) and with different mixing ratios (25, 50, and 75 wt.% RD). The physicochemical properties of biochar and the transformation behaviors of phosphorus (P) and heavy metals during the co-pyrolysis process were studied. Compared with single SS pyrolysis, the biochar derived from SS-RD co-pyrolysis had lower yield and ash content, higher pH, C content, and aromatic structure. The addition of RD could reduce the total P content of biochar and promote the transformation from non-apatite inorganic phosphorus (NAIP) to apatite phosphorus (AP). In addition, co-pyrolysis also reduced the content and toxicity of heavy metals in biochar. Therefore, co-pyrolysis could be a promising strategy to achieve the simultaneous treatment of SS and RD, as well as the production of value-added biochar.

Comparison on anaerobic phosphorus release and recovery from waste activated sludge by different chemical pretreatment methods: Focus on struvite quality and benefit analysis

Phosphorus recovery from waste activated sludge (WAS) is expected to alleviate the shortage of phosphate rock and reduce eutrophication. In this study, acid, alkali and sodium polyacrylate (PAAS) were compared to enhance phosphorus release and recovery from WAS. During anaerobic fermentation (AF) stage, the optimal pretreated conditions for ortho-phosphate release were the pH of 4 (AF 12 h), 13 (AF 12 h) and 22.4 g PAAS/L (AF 24 h) with the phosphorus release efficiencies of 40.9%, 62.6% and 31.7%, respectively. Acid, alkali and PAAS addition were beneficial for apatite phosphorus (AP), non-apatite inorganic phosphorus (NAIP) and organic phosphorus (OP) release from WAS, respectively. Strong acidic (pH = 4) and alkaline (pH = 12 and 13) conditions inhibited the release of soluble ammonia, while PAAS would not have a negative impact on the release of soluble ammonia. By means of precipitation crystallization, the ortho-phosphate could be almost recovered after acid/alkali pretreatment compared with PAAS (88.9%) at optimal Mg/P molar ratio of 1.5:1. The XRD, FT-IR and SEM-EDX analyses confirmed the main component in the product was struvite. The purity of the struvite in the product recovered from acid (named PreAC, 78.9%) and alkali (named PreAL, 89.6%) pretreated sludge were higher than that of the PAAS (named PrePA, 72.3%) by elemental analysis. The mercury and chromium content existed in PreAC were above the Control Standards of Pollutants in Sludge for Agricultural Use, whereas detected heavy metal elements level of the PreAL and PrePA were below the standard. By means of cost analysis, acid/alkali pretreatment could obtain economic benefits compared with PAAS. Thus, those discoveries would broaden the phosphorus recovery way to serve in practice.

Sustainable Utilization of Sewage Sludge through the Synthesis of Liquid Fertilizer

In a world with a growing human population, resources are becoming increasingly scarce. To ensure food supply, fertilizers are often used to accelerate growth when planting agricultural products. Sewage sludge (SS), containing as high as 10–15 wt% Phosphorus (P), can be synthesized into liquid fertilizer. P species in SS can generally be classified into four types: inorganic phosphorus (IP), organic phosphorus (OP), nonapatite inorganic phosphorus (NAIP), and apatite phosphorus (AP). However, OP is not leached out by wet chemical methods and NAIP is not bioavailable. This study investigated the P-form conversion (OP and NAIP to AP) in SS by adding 8 wt% CaO at 300 °C. SS through pretreatment can easily leach out P when combined with organic acid. The content of heavy metals is in accordance with fertilizer regulations in a leaching solution. The solution was mixed with potassium and ammonia compounds to synthesize a liquid fertilizer. To ensure the safe and efficient use of liquid fertilizer and undertake an analysis of heavy metals, an aquatic organisms (D. magna) toxicity test, and the growth of plants test were both used. The liquid fertilizer can be demonstrated to accelerate the growth of plants while not causing the death of D. magna in short time, as the liquid fertilizer has enough nutrients to help the D. magna to survive.

Transformation of phosphorus by MgCl2 and CaCl2 during sewage sludge incineration.

Phosphorus (P) recovery from sewage sludge (SS) have been regarded as an effective method of P recycling. The effects of incineration temperature, incineration time, and chlorine additives on the distribution of P speciation during sludge incineration were studied. Moreover, the reactions between model compounds AlPO4 and additives (MgCl2 and CaCl2) were investigated by thermogravimetric differential thermal analysis and X-ray diffraction measurements. The results demonstrated that the increase in temperature and time stimulated the volatilization of non-apatite inorganic phosphorus (NAIP) instead of apatite phosphorus (AP). MgCl2 and CaCl2 can greatly promote the conversion of NAIP to AP. Additionally, AlPO4 reacted with MgCl2 are incinerated at 500-600 °C to form Mg3(PO4)2, which is mainly due to the reaction of the intermediate product MgO and AlPO4. Reactions between AlPO4 and CaCl2 occurred at 700-750 °C and produced Ca2PO4Cl, which can be directly used with high bioavailability. These findings suggested that chlorine additives in the SS incineration process can obtain phosphorus-containing minerals with higher bioavailability to realize the resource utilization of P in sludge.

Characterization and distribution of different phosphorus types in the agricultural areas of Daecheong Lake Watershed, South Korea.

Agricultural areas utilize various types of agrichemicals to enhance crop growth and production. As a consequence, areas treated with excessive amounts of agrichemicals become primary sources of environmental pollutants. This study was conducted to analyze the different types of phosphorus (P) in the agricultural soils in Deacheong Lake Watershed. The effects of cultivation activities in the availability of nutrients that can potentially cause eutrophication of receiving water bodies were also assessed. The total phosphorus (T-P) and phosphate (PO4-P) concentrations in the tributaries draining into the Daecheong Lake were found to be three to seven times higher than the T-P and PO4-P concentrations in Daecheong Lake. The P concentrations in the waterways exhibited significant correlations (p < 0.05) with the soil P, implying that agricultural activities may influence the water quality in Daecheong Lake. Dry field soils had higher T-P concentrations (1246.1 ± 579.9 mg/kg) as compared to paddy fields and in situ soils due to the continuous accumulation of P in the soil strata. Non-apatite inorganic phosphorus (NAI-P) was the most dominant type of P in paddy field soils, whereas organic-P had the highest fraction in dry field soils. Paddy fields can have higher potentials of contributing to eutrophication, since NAI-P is an indicator of algal-available P. T-P concentrations in agricultural soils planted with different crops follows the order: tobacco > corn > perilla > soybean > Chinese cabbage > barley > sweet potato > garlic > potato > red pepper > rice. Generally, shifts in agricultural practices can be used to assess the contribution of agricultural areas in the eutrophication potential of water bodies.

Al-PHOSLOCK thin-layer capping to control phosphorus release from sediment: effect of hydraulic retention time and phosphorus migration/transformation mechanism

This work aimed to (i) investigate the effect of hydraulic retention time (HRT) on controlling the release of phosphorus from sediment and (ii) interpret the phosphorus migration and transformation mechanism in the Al-PHOSLOCK thin-layer capping system. A 35-day laboratory dynamic simulation experiment was conducted by applying the Al-PHOSLOCK thin-layer capping to evaluate the effect of HRT on interrupting the release of phosphorus from contaminated sediments. The total phosphorus (TP), inorganic phosphorus (IP), organic phosphorus (OP), non-apatite inorganic phosphorus (NAIP), and apatite phosphorus (AP) were identified as different phosphorus species and analyzed during the experiment to further elucidate the migration and transformation of phosphorus. The release of phosphorus from contaminated sediment was successfully suppressed by the Al-PHOSLOCK capping layer with an efficiency of higher than 90%. The HRT exerted a dual role on phosphorus controlling: at low HRT, slight water flow facilitated phosphorus migrating out from sediment and diffusing to the overlying water; at high HRT, the migration of phosphorus from overlying water back to sediment was strengthened. It was demonstrated that the phosphorus release was effectively controlled by the Al-PHOSLOCK thin-layer capping under different HRT conditions (static, 0.5 d, 1.0 d, and 3.0 d). The mechanism of phosphorus migration and transformation in the Al-PHOSLOCK thin-layer capping system was elucidated, including three significant stages of physical interception, adsorption, and capture/hold/transform process. This study verified the good capacity of the Al-PHOSLOCK capping system for controlling the release of sediment phosphorus under different HRT. Therefore, it was expected to be a promising approach in the handling of water eutrophication.

Roles of dehydration conditioners on the formation of apatite phosphorus during the pyrolysis of various sludge

Sludge contains a high content of phosphorus (P) which makes the recovery of P from this material attractive. Inorganic apatite phosphorus (AP) could be utilized as a slow-release P fertilizer in a long term, thus transforming P-containing compounds into AP is greatly attractive. Herein, the migration and transformation behaviors of P from two municipal sewage sludge and a food-processing sludge were investigated during pyrolysis, and the effects of two calcium-based conditioners (CaO and CaCl2) on the formation of AP were explored. The results showed that nearly all P remained in sludge below 650 °C but around 22.5–49.0% P released from that at 850 °C, respectively. CaO helped retain phosphorus in sewage sludge at 850 °C, while CaCl2 facilitates its volatilization. Even though, the generation of AP was still improved under the effect of CaCl2. AP amount increased by 7.1–37.5% in food sludge derived char while AP amount increased by 7.3% to 21 times in sewage sludge derived char because of the two calcium-based conditioners. Model experiments showed that CaO could react with non-apatite inorganic phosphorus (NAIP) to generate calcium pyrophosphate and calcium orthophosphate, and CaCl2 could react with NAIP to form calcium pyrophosphate, calcium chlorapatite and phosphide. In general, CaCl2 exhibited a more excellent effect on the formation of AP than CaO while CaO showed more stable performance on the retention of TP.

Behavior of fast and slow phosphorus release from sewage sludge-derived biochar amended with CaO.

The pyrolyzation of sewage sludge (SS) could efficiently transform inherent phosphorus (P) into bioavailable phosphate forms, which endows SS-derived biochar (SSB) the potential as a soil fertilizer. However, the details about the release behavior of P in SSB have not been systematically investigated. This study evaluated the fast and slow P releasing behaviors from SSB and CaO-amended SSB prepared under different pyrolysis temperature. The higher pyrolysis temperature and CaO addition could enhance the conversion of non-apatite inorganic phosphorus (NAIP) into more bioavailable apatite inorganic phosphorous (AP). Acidic and alkaline conditions were favorable for the fast release of P from SSB. Higher ionic strength condition gave greater releasing amounts of TP and the SO42- facilitating a rapid release of TP than those for Cl- and NO3-. SSBs with CaO addition showed a much slower TP release than those without CaO both in fast release (24 h, with CaO: 0.05~0.4 mg TP g-1 SSB, e.g., without CaO 0.5~5 mg TP g-1 SSB) and slow release tests (21 days, with CaO: 1.2~4.1 mg TP g-1 SSB, e.g., without CaO 1.8~5.7 mg TP g-1 SSB). Ortho-P release was more remarkable for the SSB amended with CaO (~54% of TP), which was likely due to the formation of orthophosphate. The results of this study suggested that SSB prepared by high pyrolysis temperature and CaO addition had high potential as a slow P-releasing fertilizer for the soil.

Accelerating phosphorus release from waste activated sludge by nitrilotriacetic acid addition during anaerobic fermentation process and struvite recovery

Phosphorus (P) recovery from waste activated sludge (WAS) could achieve sustainable development and reduce environmental hazards simultaneously. The objective of this study was to enhance P release from WAS by nitrilotriacetic acid (NTA) addition and struvite recovery. The maximal P release efficiency reached 90.3 % from WAS at the dose of 25.0 mM NTA after anaerobic fermentation 12 h. The NTA addition promoted nonapatite inorganic phosphorus (NAIP) and apatite phosphorus (AP) release from WAS while it had a negative effect on organic phosphorus (OP) release. The NTA was beneficial for the protein release from WAS, but it inhibited the release of NH4+-N. By means of struvite precipitation, the PO43−-P and NH4+-N recovery rates at optimal initial pH = 9 of the fermentation supernatant reached 92.9 % and 51.5 %, respectively. Meanwhile, the purity and yield of the produced struvite were 85.8 % and 174.0 mg/g SS (per gram of dry sludge) determined by elemental analysis, respectively. The levels of heavy metals in struvite products were below the permissible limits of Cultivated Land Application Standard. Therefore, the results of this study enriched the P recovery path from WAS to guide the application.

The effect of secondary capping on the control of phosphorus release from sediment by activated thin-layer capping with Al-PIA.

It is well-known that the activated thin-layer capping covering by secondary capping of contaminated sediment poses a threat to the inactivation of activated material. In this study, the static simulation experiment was conducted to study the effect of secondary capping thickness by sediment on the control of TP release from the sediment by aluminum-based P-inactivation agent (Al-PIA), and to propose the phosphorus adsorption pathway of Al-PIA. The results showed that Al-PIA could effectively reduce the release of phosphorus pollutants from the sediment at the capping intensity of 2kg/m2. When the secondary capping thickness of sediment were 0, 2, 4, 7, 10, and 15mm, the average removal rates of TP were 87.57%, 76.39%, 61.22%, 51.32%, 41.93%, and 32.11%, respectively, indicating that the removal efficiency of phosphorus decreased with the increase of the secondary capping thickness of the sediment. The adsorbed phosphorus by Al-PIA was mainly non-apatite inorganic phosphorus (NAIP) in inorganic phosphorus. With the increase of the secondary capping thickness of sediment, the NAIP proportion of phosphorus adsorbed by Al-PIA increased. Meanwhile, the removal rate of phosphorus in the activated capping system showed a first increase and then decrease trend, and the removal rates of total phosphorus (TP), inorganic phosphorus (IP), and organic phosphorus (OP) were obvious except for that of organic phosphorus (OP).

Influence of microwave-assisted pyrolysis parameters and additives on phosphorus speciation and transformation in phosphorus-enriched biochar derived from municipal sewage sludge

Municipal sewage sludge is rich in phosphorus, the conversion of which into phosphorus-enriched biochar via microwave-assisted pyrolysis (MWAP) can realize the efficient treatment of municipal sewage sludge and the recycling of phosphorus. This follows the concepts of the sustainable development of waste management and “cleaner production”. At present, fundamental knowledge is lacking on the use of MWAP to recover phosphorus from municipal sewage sludge. In this study, the effect of MWAP parameters (temperature, power, and residence time) and additives on the properties of phosphorus-enriched biochar and the migration and transformation of phosphorus were investigated. The pH, surface area, and total phosphorous increased with increasing temperature and power, whereas a greater residence time promoted the conversion of non-apatite inorganic phosphorus (NAIP) into apatite inorganic phosphorous (AP). CaO addition promoted the conversion of NAIP into AP, whereas MgCl2 promoted the conversion of AP into NAIP. The simultaneous addition of CaO and MgCl2 led to antagonism, with CaO being dominant, demonstrating that the original phosphorus components prefer to combine with CaO. Phosphorus recovery was optimal at temperatures 500–600 °C and a residence time of 150 min. The addition of 9% CaO or 6% CaO +6% MgCl2 was sufficient to convert sewage sludge into phosphorus into AP. Under such conditions, AP contents in phosphorus-enriched biochar increased 1.4 times compared to that of additive-free biochar. Our study highlights the potential of MWAP for closing the phosphorus cycle and for producing fertilizers from complex materials, such as municipal sewage sludge.

Evaluation of the Bioavailability of Heavy Metals and Phosphorus in Biochar Derived from Manure and Manure Digestate

The effects of pyrolysis temperature (350, 450, and 550 °C) on the properties of biochar prepared from chicken manure (CM), dairy manure (DM), and their digestates (CMD and DMD) were investigated in this study. The physicochemical properties and the transformation of phosphorous and heavy metal forms in various types of biochar were analyzed, and the bioavailability was assessed to optimize the pyrolysis condition towards biochar land application. The larger specific surface area was found in CM and CMD derived biochars (14.90–22.45 m2/g), as compared to DM and DMD derived biochars (1.17–7.36 m2/g). The highest contents of total phosphorous (TP) and bioavailable non-apatite inorganic phosphorus (NAIP) were obtained in DMD biochar, i.e., 49.31 and 27.03 mg/g TS, respectively. Cu and Zn are identified as the harmful heavy metal elements in manure derived biochars due to its high level of total concentration. When increasing pyrolysis temperature, the fractions of Zn and Cu in exchangeable-, carbonate-, and the organic-bonded state decreased and the fractions of manganese oxidized and residual state increased. Finally, the citric acid leaching treatment was proposed to decrease the Zn and Cu contents in biochar before land application. The overall leaching rates for Cu and Zn were 37–45% and 27–32%, respectively.

The influence of a stepwise pH increase on volatile fatty acids production and phosphorus release during Al-waste activated sludge fermentation

In this study, the performance of volatile fatty acids (VFAs) production and phosphorus (P) release during Al-waste activated sludge (Al-WAS) anaerobic fermentation with stepwise pH increases from 8 to 11 was investigated via a long-term acclimation strategy. As results, VFAs concentration increased with increasing pH and the maximum yield of VFAs was 358.03 mg-COD/g VS at pH 11, which was much higher than at pH 8. P was also released during the process, and the P concentration increased gradually from 26 mg/L at pH 8 to 186 mg/L at pH 11, accounting for 35.8% of the total P in the Al-WAS. The P distribution results demonstrated the dissolution of non-apatite inorganic phosphorus (NAIP) and organic P in the sludge contributed to release P into the liquid at pH 8, 9, and 10, while inorganic P release originated from the dissolution of NAIP at pH 11.

Insight into efficient phosphorus removal/recovery from enhanced methane production of waste activated sludge with chitosan-Fe supplementation

Fe(III)-loaded chitosan (CTS-Fe) composite was used for the first time to remove and recover phosphorus (P) from waste activated sludge (WAS) via anaerobic digestion (AD). The P transformation pathway and the effect of CTS-Fe addition on the AD process were investigated using batch experiments. The P fractionation results indicate that non-apatite inorganic phosphorus (NAIP) reduction in the solid phase of sludge at 20 g/L of CTS-Fe addition (6.72 mg/g-SS) was 2.4 times higher than that in the control (2.77 mg/g-SS, no CTS-Fe addition). This is probably brought about by the added CTS-Fe enhanced the reduction of Fe(III)-P compounds in the sludge with phosphate released into the liquid phase. CTS-Fe can efficiently recover 95% of P from the liquid digestate of WAS. Notably, partial Fe(III) on the CTS-Fe was reduced and effectively combined with P to form vivianite crystals on the CTS-Fe surface during the AD process. Characterization analysis demonstrated that ligand exchange and chemical precipitation were the dominant mechanisms for P removal/recovery. Furthermore, the addition of CTS-Fe increased methane production by 11.9 - 32.2% under the tested conditions, likely attributable to the enhanced hydrolysis of WAS under CTS-Fe supplementation. As the P-loaded CTS-Fe particles can be easily separated and recovered from the AD system and further reutilized in agriculture, this study could provide a new approach for simultaneous P removal/recovery and enhanced methane production from AD of WAS.

Migration and transformation mechanism of phosphorus in waste activated sludge during anaerobic fermentation and hydrothermal conversion

This study investigated migration and transformation mechanism of P in waste activated sludge (WAS) during anaerobic fermentation (AF) process and the subsequent hydrothermal conversion (HTC) process. Control of pH during the AF processes was found to be significant, whereby the use of acidic (pH = 5.5) or alkaline conditions (pH = 9.5) facilitated the release of either apatite phosphorus (AP) or non-apatite inorganic phosphorus (NAIP) and organic phosphorus, respectively. At the same pH of 9.5, NaOH promoted the transfer of P into liquid phase, and P in the solid phase was mainly in the form of NAIP. In contrast, Ca(OH)2 enhanced the incorporation of P into the solid products, with the P mainly in the form of AP. The subsequent HTC process promoted the NAIP transferred to AP, and the bioavailability of P in the HTC solid products was decreased. The P K-edge X-ray absorption near edge structure analysis provided detailed information about the phosphates. It demonstrated that the conversion of Ca8H2PO4·6.5H2O to Ca5(PO4)3·OH was facilitated by HTC under the alkaline condition. This study sheds lights on transformation mechanism of P speciations during AF and HTC processes, which would provide fundamental information for effective utilization of P in bio-wastes.

Enhanced transformation of phosphorus (P) in sewage sludge to hydroxyapatite via hydrothermal carbonization and calcium-based additive

Phosphorus (P) recovery from sewage sludge is one of the promising substitutes to the phosphate ores to alleviate the shortage of P supply in the future. In this study, how hydrothermal carbonization (HTC) temperature functioned in the migration and transformation of P from sewage sludge during HTC process was clarified. The enhancement effect of Ca-based additive on the transformation of P to hydroxyapatite via HTC was systematically studied. Additionally, leaching characteristics of P in the hydrochars with Ca-based additive were analyzed to assess their P-bioavailability. Results indicated that favoring by increased pH in the process water, HTC temperature played a significant role in the migration and transformation of P during HTC. Therefore, higher HTC temperature was beneficial for P enrichment and transformation to apatite phosphorus in the hydrochars. Both alkaline environment and existence of sufficient calcium ions were essential for enhanced formation of apatite phosphorus during HTC. Adding CaO could stimulate almost complete transformation of non-apatite inorganic phosphorus to apatite phosphorus such as hydroxyapatite, causing a maximum increase of apatite phosphorus by 252%. Concurrently, P-bioavailability by 2% (w/w) formic acid extraction of the hydrochars increased by 233% at CaO = 4%. These findings were confirmed by XRD analyses. Ca-associated apatite phosphorus such as Ca5(PO4)3OH and Ca2P2O7 ∙ 2H2O, was detected in the hydrochars. With the assistance of thermochemical calculation, transformation pathways of P after CaO addition have been proposed, which coincided with our experimental results well. The stable P-containing minerals of hydroxyapatite (Ca5(PO4)3OH) was calculated at equilibrium state.

Migration and transformation of phosphorus in waste activated sludge during ozonation.

For phosphorus (P) recovery from waste activated sludge (WAS), the most important step is to release P into the solution. This study aimed to explore the migration and transformation of P in WAS during ozonation based on the Standards Measurements and Testing Program analysis. The results showed that WAS contained 7.10% P element and could be selected as potential substitution of phosphate rock. Inorganic phosphorus (IP) was the major P fraction in raw WAS (68.10%), and non-apatite inorganic phosphorus (NAIP) occupied 62.40% of IP. Ozonation facilitated the P application in agriculture as the bio-available P in the solid phase increased by 23.63% at ozone dosage 0.20 gO3/gSS. The highest concentration of total phosphorus in liquid (TP(L)) (40.68mg/L) was achieved at ozone dosage 0.20 gO3/gSS, and 89.62% of TP(L) was PO43--P, which was easy to be recovered by struvite precipitation. The contributions of different P fractions in solid phase to TP(L) were related to ozone dosage. The analysis of P mass balance suggested that the optimum ozone dosage for P recovery was 0.15 O3/gSS.

Source identification of phosphorus in the river-lake interconnected system using microbial community fingerprints

Phosphorus, one of the primary limiting factors for eutrophication, plays a crucial role in the ecology health of aquatic ecosystems. However, understanding phosphorus bioavailability and source contributions in contaminated lake sediments which could help develop effective eutrophication management plans is limited largely due to the lack of appropriate methods in large catchments with a complex arrangement of sources. Based on the significant relationships between sediment, phosphorus and microbial community, source-specific microbial community fingerprints formed by machine-learning classification SourceTracker might shed light on determining dominant phosphorus sources in the river-lake systems in the era of high-throughput sequencing. This study was conducted in Dongting Lake that suffered accelerated eutrophication due to considerable phosphorus input from the inflow-rivers. The results of phosphorus fractionation according to the Standards, Measurements and Testing harmonized procedure indicated that sediments in the central lake had a higher concentration of non-apatite inorganic phosphorus (Mann-Whitney U test), which deserves greater attention on the risk of phosphorus release. The significant relationships between phosphorus fractionations, sediment and bacterial community were established with the spearman correlation and network analysis. SourceTracker analysis indicated that the major inflow-rivers of phosphorus sources to Dongting Lake were the Songzi, Miluo, and Xinqiang Rivers. The effects of sediment diffusion distance on phosphorus source apportionment were further confirmed. Taken together, our results contribute to an improved understanding of phosphorus fractionations and source contributions in the river-lake systems and its potential impact to eutrophication management plans.