Non-apatite Inorganic Phosphorus Research Articles

Absorbing oxygen carriers promotes phosphorus recovery from sludge via the microwave thermal conversion process

This study aims to apply the Absorbing oxygen carriers (AOCs) to induce the migration and transformation of phosphorus compounds during the microwave thermal conversion of sludge so the hard-to-extract organic phosphorus (OP) can be converted to easy-to-extract inorganic phosphorus (IP) and be enriched onto the sludge char. The AOCs were recycled by screen separation from the IP-rich sludge char, with the latter being a renewable phosphorus source from sludge. The AOCs in this novel process enhanced the conversion efficiency of OP into non-apatite inorganic phosphorus (NAlP), which was further converted to apatite inorganic phosphorus (AP). Most phosphorus in the sludge char is presented in the form of orthophosphate.

Multiplicative effects of co-incineration of sewage sludge and wasted oyster shells in air, CO2, and steam atmospheres on P speciation and bioavailability and metal ecotoxicity

The study was aimed at the reutilization of oyster shells (OS) as a calcium-based additive to turn sewage sludge ash into phosphate fertilizer, employing the oxygen-enriched combustion technology. This process transformed all non-apatite inorganic phosphorus into apatite phosphorus with the incorporation of a 7.5% Ca-based additive. OS demonstrated comparable effectiveness to CaO in catalyzing this transformation in the oxygen-steam atmosphere. The amount of OS added and the atmosphere type significantly influenced the P bioavailability of sewage sludge ash. The oxygen-steam atmosphere, with its increased water vapor concentration, facilitated the decomposition of CaCO3 and initiated reactions with calcium phosphate to form hydroxyapatite, thus substantially enhancing P bioavailability. The oxygen-steam atmosphere increased not only metal volatilization but also the ecological toxicity of residual metals, particularly Pb, mainly in the form of F2. Excessive OS addition appeared to elevate the toxicity of Cr. Therefore, additional strategies for metal removal or passivation are needed to improve the safety of sewage sludge ash with high metal content.

Phosphorus distribution in the water and sediments of the Ganga and Yamuna Rivers, Uttar Pradesh, India: insights into pollution sources, bioavailability, and eutrophication implications.

River nutrient enrichment is a significant issue, and researchers worldwide are concerned about phosphorus. The physicochemical characteristics and phosphorus (P) fractions of 36 sediment and water samples from the Ganga (Kanpur, Prayagraj, Varanasi) and Yamuna (Mathura, Agra, Prayagraj) rivers were examined. Among the physicochemical parameters, pH exceeded the permissible limit in Ganga and Yamuna River water and sediment samples. Electrical conductivity (EC) and alkalinity were within the permissible limits, whereas total nitrogen (TN) exceeded the limit in Yamuna water. The analysis of phosphorus fractions indicated the dominance of inorganic phosphorus (IP) (76% in Ganga and 96% in Yamuna) over organic phosphorus in both rivers, suggesting the mineralization and microbial degradation as major processes responsible for transforming OP to IP. The positive correlation of pH with IP, AP (apatite phosphorus), and NAIP (non-apatite inorganic phosphorus) explains the release of inorganic phosphorus under alkaline conditions. The correlation between total organic carbon (TOC), TN, and organic phosphorus (OP) indicated the organic load in the rivers from allochthonous and autochthonous sources. Phosphorus released from river sediments and the concentration of phosphate in overlying river water show a positive correlation, suggesting that river sediments may serve as phosphorus reservoirs. The average phosphorus pollution index (PPI) was above one in both rivers, with relatively higher PPI values observed in the Yamuna River, indicating the contamination of sediment with phosphorus, indicating the contamination of sediment with phosphorus. This study revealed variations in the P fractionation of the sediment in both rivers, primarily as a result of contributions from different P sources. This information will be useful for applying different mitigation techniques to lower the phosphorus load in both river systems.

Bioavailability transition path of phosphorus species during the sewage sludge incineration process

Sewage sludge incineration ash (SSIA) is rich in phosphorus (P), thus being considered as a reliable source of phosphorus recovery. Different P species behaved significant bioavailability. Based on this, a comprehensive investigation into the bioavailability transition path of P species during sewage sludge (SS) incineration was conducted. P predominantly existed in the form of inorganic phosphorus (IP) in SS with a higher concentration of non-apatite inorganic phosphorus (NAIP) and less concentration of apatite inorganic phosphorus (AP). During the SS incineration process, OP existed in the flocs and cell structures of SS underwent destruction, the released P then combined with metal elements such as Ca, Mg, Fe, and Al to form AP species (Ca/Mg–P) and NAIP species (Fe/Al/Mn–P), and the NAIP decomposition to release into gas phase. This was the initial step for enhancing the bioavailability of P species. As temperature increased and the incineration process progressed, the low-temperature-resistant NAIP dissociated, and the metal-binding sites of Al, Fe and Mn in NAIP species were gradually replaced by the Ca and Mg thus forming thermal stability AP species (Ca/Mg–P, such as CaHPO4, Ca2PO4Cl, and Mg3(PO4)2 et al.). This step was crucial for the bioavailability improvement of P species during the incineration process. Therefore, the IP proportions in TP were extremely high (＞98%), and this value gradually increased as incineration temperature raised. The higher incineration temperature, the lower NAIP concentration and higher AP concentration. Besides, additives such as coal/rice husk/eggshell played a significant affect. Additives wither higher Ca content were inclined to react with P to form Ca/Mg–P (AP), while the presence of SO2 would react with Ca metals to form CaSO4 thus inhibiting the formation of AP species (such as CaHPO4 and CaPO4Cl). This results could provide theoretical support for the efficient and directional migration of P during sewage sludge incineration.

Migration and transformation of phosphorus and toxic metals during sludge incineration with Ca additives

The recycling and utilization of phosphorus resources in sludge is becoming increasingly important. In this study, we compared the conversion of phosphorus and toxic metal passivation effects of different Ca additives under oxygen-rich combustion conditions and elucidated their specific mechanisms of action. The experimental results indicated that four Ca-based additives improved the recovery rate of total phosphorus, and promoted the generation of stable apatite phosphorus (AP). The effect of CaCl2 and CaO was greater than that of Ca(OH)2 and CaSO4. CaCl2 promoted the formation of Ca3(PO4)2 and Ca2P2O7, and CaSO4 improved the conversion of AlPO4 to Ca(H2PO4)2 with increasing temperature. The conversion capacity of CaO on non-apatite inorganic phosphorus to AP was greater than that of Ca(OH)2, and more CaH2P2O7, Ca(PO3)2, and Ca–Al–P minerals were found. Toxic metal percentages decreased after sludge incineration with CaCl2. Compared with CaO and Ca(OH)2, the toxic metal adsorption effect of CaSO4 was more significant. The influence of Ca additives on the conversion of Zn into stable components was as follows: CaCl2 > Ca(OH)2 > CaO > CaSO4. Ca additives reduced the toxic metal contamination level and ecological risk index values, and the order of toxic metal contamination levels was Ni > Zn > Cr > Cu > Mn. The experiment confirmed the conversion of phosphorus and the toxic metal passivation effect of Ca additives during oxy-fuel combustion of sludge, which is beneficial for its resource utilization.

In-situ heterogeneous electro-Fenton based on B, Fe-modified carbon felts for phosphorus nutrients treatment in dredged sediment

A novelty in-situ heterogeneous electro-Fenton based on boron-modified and co-modified carbon felts (CF) such as B-CF, B, Fe-CF and B, Co-CF was employed for phosphorus nutrients treatment in dredged sediment. During which B, Fe-CF (1:1) was the optimal cathode for phosphorus nutrients and organic matter treatment with organic phosphorus (OP) and non-apatite inorganic phosphorus (Fe-P) conversion rates of 26.84% and 63.21%, respectively, since the generated H2O2 on bifunctional cathode could produce ·OH with material surface reduced Fe(II). Characterized by SEM, XRD and XPS, B and Fe were successfully loaded on the electrode with elemental percentages of 0.99% and 4.40%, while B2O3 and Fe2O3 were detected. The operating parameters like initial pH and current density were explored. B, Fe-CF had a high stability and outstanding catalytic capacity for 5 cycles of phosphorus nutrient treatment. The possible mechanism was also proposed based on the electron paramagnetic resonance (EPR) and radical quenching experiment, which demonstrated that ⋅OH and SO4·- mainly contributed to phosphorus nutrients treatment. In this work, a highly efficient and stable carbon material was successfully prepared to treat refractory pollutants in dredging sediment, which provides new ideas and methods for subsequent resource utilization.

Coupling electrokinetic technique with hydrothermal carbonization for phosphorus-enriched hydrochar production and heavy metal separation from sewage sludge

Hydrothermal carbonization is a promising treatment technology for wet organic solid wastes, due to its energy-efficient production of functionalized carbonaceous materials. However, the usage of sewage sludge (SS) derived hydrochar as phosphorus (P) fertilizer for agricultural soil is inhibited by the presence of heavy metals (HMs). Appropriate HM removal technology is required prior to its land application. In this study, an innovative FeCl3-assisted electrokinetic technique coupling with hydrothermal carbonization (FEK–HTC) is proposed to produce SS hydrochars with reduced HM content and increased P-retention. FEK–HTC treatment showed synergistic effects in terms of P retention and HM content reduction (56–64 % for Ni, Cu, and Zn). Furthermore, the toxicity of the remaining HMs was dramatically reduced, e.g., by 39.35 % in the case of Zn. Additionally, FEK–HTC transformed P species in hydrochars into highly bio-available form. Electrokinetic treatment resulted in decreased pH values of SS feedstock and promoted the solubilization and erosion of Ca-associated P, resulting in higher non-apatite inorganic phosphorus contents (12.47 to 23.19 mg·g−1) compared to hydrochars from untreated sludge. The P migration patterns during the FEK-HTC treatment were assessed based on the combined result of chemical extraction, 31P NMR, X-ray absorption near edge structure (XANES), and diffusive gradients in thin film (DGT). DGT analysis showed that the addition of treated hydrochars greatly increased the available P content in the soil. The results provide new insights into applying FEK-HTC technique for SS management.

Utilizing CaCl2 to promote the enrichment and bioavailability of phosphorus in incinerated sludge ash.

Recovering phosphorus from incineration sludge sewage ash (ISSA) is a well-established technology, with a greater recovery potential than that of supernatant or sludge. ISSA can be utilized as a secondary raw material in the fertilizer industry, or as a fertilizer if heavy metal concentrations do not exceed permissible limits, thus reducing the cost of phosphorus recovery. Increasing the temperature to produce ISSA with higher solubility and plant availability of phosphorus is advantageous for both pathways. But a decrease in the extraction of phosphorus is also observed at high temperatures, thereby diminishing the overall economic benefits. In this study, CaCl2 was utilized to mitigate the decrease in the extraction rate and also to promote the bioavailability of phosphorus. The addition of CaCl2 (80 g/kg of dry sludge) effectively promoted the conversion of non-apatite inorganic phosphorus to apatite inorganic phosphorus at a rate of 87.73% at 750 °C. Furthermore, the decrease in the extraction rate of phosphorus at 1,050 °C was comparatively smaller in the presence of CaCl2. If iron flocculants are used to capture P in wastewater management, it may be necessary to pay special attention to the amount of addition and incineration temperature to maximize the economic potential of recycling.

Migration and Conversion of Phosphorus in Hydrothermal Carbonization of Municipal Sludge with Hydrochloric Acid

Phosphate ore is a non-renewable resource, so finding a replacement is necessary. Municipal sludge has significant recycling potential because of its high phosphorus content and large discharge characteristics. The migration and transformation of phosphorus in municipal sludge treated with different concentrations of HCl were studied using the standards, measurements, and testing phosphorus extraction protocol from two aspects: phosphorus complexation and mineral form. After the hydrothermal carbonization treatment without HCl, the hydrochar retained 99.7% of phosphorus in the sludge, and the organophosphorus percentage was about 30%. In the hydrothermal carbonization treatment with the addition of 0.5–2.5% HCl, the phosphorus content in the hydrochar decreased gradually from 99.5% (46.18 mg/g) to 91.8% (64.17 mg/g) that of the original sludge, and the proportion of non-apatite inorganic phosphorus increased from 34% to 94%. Hydrochloric acid provides a low-pH environment and promotes the dissolution of calcium-related phosphorus precipitates and enhances the dehydration reaction. This study provides technical support for the recovery of phosphorus resources from municipal sludge.

Fate and distribution of phosphorus in coking wastewater treatment: From sludge to its derived biochar

Due to the phosphorus (P) deficiency in coking wastewater, sufficient P needs to be provided in the treatment process to maintain biotic activity. However, most of the dosed P sources are transferred to the sludge phase out of the chemical equilibrium. After an in-depth investigation of P morphology changes in coking wastewater treatment, it is found that above 71.6 % P applied to the full-scale O/H/H/O (oxic-hydrolytic & denitrification-hydrolytic & denitrification-oxic) process for coking wastewater treatment is ended up in the sludge phase of the aerobic reactors in the forms of non-apatite inorganic phosphorus (NAIP). Theoretical simulations suggest that the P forms precipitates such as FePO4·2H2O, AlPO4·2H2O, MnHPO4 at pH < 7, and Ca5(PO4)3OH at pH > 7. Microbial utilization of P in coking wastewater treatment is swayed by precipitation, pH and sludge retention time (SRT). By pyrolysis treatment of the waste sludge at 700 °C, phosphoric substances in coking sludge are enriched and converted into Ca5(PO4)3OH, Ca5(PO4)3Cl, Ca3(PO4)2, etc. with apatite phosphorus (AP) accounting for 65.7 % of total phosphorus. Moreover, the heavy metals in biochar were below the national standard limits for discharge. This study shows that hazardous waste (coking sludge) can be transformed into bioavailable products (P-rich biochar) through comprehensive management of the fate of P. Combined with the O/H/H/O process, the mechanisms of phosphorus consumption in coking wastewater treatment are revealed for the first time, which will facilitate a reduced consumption of phosphorus and provide a demonstration for other phosphorus-deficient industrial wastewater treatment.

Effects of carbon sources on phosphorus speciation transformation process, characteristics of extracellular polymeric substances, and microecology in anaerobic systems

The effects of different carbon sources on the transformation process of the form of phosphorus and microecology were examined in an anaerobic system using glucose and L-malic acid as carbon sources. Results showed that for these two carbon sources (glucose and L-malic acid), the average removal efficiencies of chemical oxygen demand by up-flow anaerobic sludge bed reactors were 97.16 % and 88.63 %, and the average removal efficiencies of total phosphorus were 11.38 % and 5.68 %, respectively. The average concentrations of phosphine in anaerobic reactors using glucose and L-malic acid as carbon sources were 160.73 mg/m3 and 90.80 mg/m3 over days 24–40, respectively. When glucose was used as carbon source, the proportions of biologically available phosphorus (i.e., the sum of non-apatite inorganic phosphorus and organic phosphorus content) within total phosphorus in sludge on days 0, 20, and 40 were 76.22 %, 77.90 %, and 85.04 %, respectively. Glucose could better promote the enhancement of dehydrogenase activity than L-malic acid. The carbon source affected the activity of alkaline phosphatase, and the enzyme activity was stronger when glucose was used as carbon source. Kyoto Encyclopedia of Genes and Genomes functional analysis showed that amino acid metabolism and carbohydrate metabolism dominated. On days 0, 30 and 60, the relative abundances of carbohydrate metabolism in microorganisms using glucose as carbon source were 0.26 %, 0.36 %, and 0.34 % higher than those with L-malic acid as carbon source, respectively.

Enhanced recovery of phosphorus in sewage sludge-derived biochar with CaCO3: Phosphorus speciation and slow-release phosphorus behavior

The recovery of phosphorus (P) from sewage sludge through pyrolysis is one of the most promising alternatives to alleviate the shortage of P supply in the future. Adding calcium additives is beneficial to the conversion of available P and helps to improve the recovery and utilization efficiency of P in biochar. This study thoroughly examined the influence of CaCO3 on the speciation and slow-release behavior of P in sludge during pyrolysis at 500 and 700 °C. The addition of CaCO3 could enhance the conversion of non-apatite inorganic phosphorus (NAIP) into more accessible apatite phosphorus (AP). We observed that adding CaCO3 (2.5–20 %) to raw sludge at 500 °C increased the proportion of AP in inorganic phosphorus (IP) from 65.2 to 97.3 % but did not increase the concentration of AP, which remained between 31.03 and 31.64 mg/g. At 700 °C, introducing CaCO3 (2.5–20 %) boosted the AP content from 35.08 to 41.38 mg/g and increased the proportion of AP in IP from 67.7 to 98.6 %. Moreover, irrespective of the pyrolysis temperature being 500 °C or 700 °C, the final main form of P in biochar with CaCO3 was Ca5(PO4)3OH, according to experimental characterization results (X-ray photoelectron spectroscopy and X-ray diffraction) and thermochemical calculations. Additionally, the efficacy of citric acid (CA) in releasing biochar-bearing P was tested in a laboratory extraction experiment for 21 days. CaCO3-amended biochar showed a significantly slower total phosphorus (TP) release than the biochar without CaCO3 daily, and the amount of TP decreased with increasing amounts of added CaCO3. The finding of this study indicates that biochar generated by adding 10 % CaCO3 has the highest AP concentration (41.38 mg/g) at 700 °C, and its TP-release efficiency in CA is 0.29–1.98 mg/g in 21 days, which shows remarkable potential as a soil fertilizer with slow P release.

Sequential wet extraction of phosphorus from sewage sludge using alum sludge: Reassessing the aluminium-phosphorus speciation using experimental and simulation approach

Sewage sludge (SS) is a reclaimable phosphorus (P) source for fertilizer production, but it has a high toxic trace element (TE) concentration. Using alkaline leaching of SS, P can be extracted without simultaneous extraction of TEs. However, low P recovery efficiency during alkaline leaching is a major challenge. This study explored alkaline leaching of P from alum sludge (AS)-amended dry SS, with or without acidic pretreatment. The amendment with AS was intended to promote apatite to non-apatite inorganic phosphorus conversion for a higher alkaline P recovery. The highest orthophosphate (ortho-P) alkaline recovery was 74 % for the acid-pretreated SS + AS mix. Amending SS with AS averted the loss of ortho-P during acidic pretreatment by 59 % compared to the reference case (unamended SS). Standards Measurements and Testing (SMT) analysis revealed apatite to non-apatite inorganic phosphorus conversion during acidic pretreatment, especially in the amended SS. This conversion was due to the dissolution of Ca-P and adsorption of dissolved ortho-P on Al(OH)3 during acidic pretreatment. Visual MINTEQ modelling, solid-state NMR (31P, 27Al and 31P-1H CP-HETCOR) and Al 2p XPS data indicated a high abundance of Al(OH)3(s), which enhanced the ortho-P adsorption. There was no formation of AlPO4, possibly because the acid-sludge mixture reached the metastable equilibrium and not the true equilibrium during acidic pretreatment. 31P liquid NMR, SEM, FTIR and XRD provided additional insight into the effects of acidic pretreatment on sludges. Overall, Ca-P to Al-P conversion enhanced alkaline ortho-P recovery by about 12 % compared to the reference case (unamended + non-pretreated). This study demonstrated that P leaching efficiency from SS can be improved (with appropriate process modifications) irrespective of the intrinsic property of SS, thus making alkaline P recovery applicable in many regions globally. Additionally, the chemical co-treatment of SS + AS proposed is a prospective dual waste management strategy.

Phosphorus concentrations in sediments from the equatorial Amazon estuary, Furo of Muriá, Pará State, Brazil

We characterized the spatial and seasonal distributions of different phosphorus fractions in surface sediments from the Furo of Muriá estuary by chemical fractionation. Five phosphorus species were successfully separated: phosphorus bound to Fe/Al oxyhydroxides (non-apatite inorganic phosphorus (NAIP) ranging from 164.54 to 280.32 μg g-1), phosphorus bound to calcium (apatite phosphorus (AP) ranging from 63.02 to 102.80 μg g-1), inorganic phosphorus (IP, ranging from 227.21 to 378.61 μg g-1), organic phosphorus (OP, ranging from 30.33 to 135.88 μg g-1) and total phosphorus (TP, ranging from 257.54 to 507.73 μg g-1), in which 88% of TP is constituted by IP. Statistical results showed that seasonality was not a major factor influencing phosphorus concentrations. Considering the classification of estuarine sediment conditions, we can conclude that the TP concentrations found in Furo of Muriá do not yet indicate the risk of environmental deterioration.

The transformation and regulation of phosphorus in model compound and waste biomass from hydrothermal conversion

In this study, the degradation behaviour of phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) during hydrothermal conversion (HC) and the effect of alkali additives on phosphorus forms during HC of phospholipids and different phosphorus-containing wastes were investigated. The mechanism of phosphate-alkali-directed regulation and transformation was discussed and analysed with batch hydrothermal treatment experiments and characterizations such as XRD and SEM. The obtained results showed that DOPC degradation was divided into two periods, i.e., the initial accumulation of phosphorus-containing precursors with increasing temperature, followed by complete degradation to H3PO4 as treatment continued. In addition, compared with the activation of P by NaOH, Ca(OH)2 is more favourable for the stabilization of P and the migration of non-apatite inorganic phosphorus (NAIP) to apatite inorganic phosphorus (AP). The pH and appropriate feed Ca/P molar ratio during HC determine the degree to which total phosphorus is converted to Ca-bound P. The findings reveal the mechanism of phosphate-alkali-directed regulation and transformation and provide a theoretical reference for the efficient treatment of phosphorus-containing waste and the alkali-directed production of high-phosphorus bioavailability products.

CaO-assisted hydrothermal treatment combined with incineration of sewage sludge: Focusing on phosphorus (P) fractions, P-bioavailability, and heavy metals behaviors

Dewatering of sewage sludge (SS) was the prerequisite for saving its drying energy and sustaining its stable combustion. Hydrothermal treatment (HT) has been a promising technology for improving SS dewaterability with high energy efficiency. However, the knowledge of phosphorus (P) transformation and heavy metals (HMs) behaviors in the combined HT and incineration process was still lack. P fractions, P-bioavailability, HMs speciation, and their environmental risk in the ash samples from this combination process were evaluated and compared with those from the co-incineration of SS and CaO. The combination process was superior to the latter one in the light of P and HMs. CaO preferred to enhance the transformation of non-apatite inorganic phosphorus (NAIP) to apatite phosphorus (AP) initially with enriched P and increased P-bioavailability in the resultant ash samples. The combination process further reduced the values of risk assessment code and individual contamination factor with the increment of the stable F4 fraction in HMs. Significant reduction of potential ecological risk was observed with the lowest global risk index of 43.76 in the combination process. Optimum CaO addition of 6% was proposed in terms of P and HMs. The work here can provide theoretical references for the potential utilization of P from SS to mitigate the foreseeable shortage of P rocks.

Performance comparison of phosphorus recovery from different sludges in sewage treatment plants through pyrolysis

Recycling of phosphorus (P) from pyrolysis sewage sludge is a good methodology to deal with the deficit of P resources and safely dispose the sewage sludge. However, it is essential to determine the type of sludge in sewage treatment plants (STPs) along with the most appropriate pyrolysis temperature. These factors affect the form and bioavailability of recoverable P. Thus, four kinds of sludge in a typical STP were selected, and three pyrolysis temperatures including 300, 500, and 700 °C were set to find a suitable strategy for P recovery. The results indicated that with increasing pyrolysis temperature, more organic phosphorus (OP) was transformed into inorganic phosphorus (IP) and more non-apatite inorganic phosphorus (NAIP) was converted to apatite phosphorus (AP, mainly Ca3(PO4)2, Ca(H2PO4)2, Mg3(PO4)2, Ca3Mg3(PO4)4, and Ca5(PO4)3OH). Compared to other sludges, dewatered cake sludge (CS) pyrolyzed at 700 °C had the highest AP content, about 1.1–3.6 times that in other pyrolysis products, and the highest Ca5(PO4)3OH content containing 35.8% of total phosphorus (TP). The contents of P-2% citric acid (CA) and neutral ammonium citrate (NAC) in CS obtained by pyrolysis at 500 °C reached 45.6 and 49.6 mg/g, respectively, which were 1.1–3.0 and 1.1–2.8 times that of P-CA and P-NAC in other sludges and their biochars, respectively. Moreover, the diethylenetriaminepentaacetic acid extraction analysis indicated that the good stability of heavy metals in CS-derived biochar was better than that in the feedstock. Hence, to ensure the efficiency and safety of P, CS is used as raw material in STPs to recover P resources. CS-500 can be used as the direct P source of land owing to the highest concentration of bioavailable P (P-CA and P-NAC), while CS-700 can be used to represent a slow-release P fertilizer because it contains the highest concentration of AP.

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.