Waste to phosphorus: A transdisciplinary solution to P recovery from wastewater based on the TRIZ approach

Hydrothermal carbonization of combined food waste: A critical evaluation of emergent products

Hydrothermal carbonization (HTC) increasingly appears as an eco-friendly method for managing food waste (FW). In this work, a combination of FW was subjected to HTC, and products were critically evaluated. This involved a lab-scale pressure reactor and optimization of HTC conditions: temperature (220-340 °C) and residence time (90-260 min) via central composite design type of response surface methodology (CCD-RSM). Results showed varying temperatures and residence time to impact the hydrochar (HC) and hydrothermal carbonization aqueous phase (HTC-AP) properties. Although HC produced through HTC exhibited lower ash content (<2%) despite higher fixed carbon (>55 %) with respect to the raw FW, the heating value of HC ranged from 19.2 to 32.5 MJ/kg. Temperature primarily influenced FW conversion, affecting carbonaceous properties. Saturated fatty acids (SFA) were found to be predominant in the HTC-AP under all tested operating conditions (77.3, 48.4, and 37.1 wt% for HTC at 340, 280, and 220 °C in 180 min, respectively). Total phosphorus recovery in HC and HTC-AP respectively peaked at 340 °C and 220 °C in 180 min. The study concludes that HTC holds promise for energy-dense biofuel production, nutrient recovery, and fostering a circular economy.

Effect of struvite (Crystal Green) fertilization on soil element content determined by different methods under soybean cultivation

Struvite is regarded as a promising phosphorus fertilizer alternative to mineral fertilizers; however before fertilizing, soil tests should be undertaken to determine fertilizer recommendations. In May 2022, soil was sampled from a pot experiment with the application of phosphorus set up at the Wroclaw University and Environmental and Life Sciences. Chemical analysis of the soil included total and available phosphorus, potassium, magnesium determined by the Egner-Riehm, Mehlich 3 and Yanai methods. The purpose of the article is to compare soil element extraction by three different methods under struvite fertilization and its use in soybean cultivation. The application of these methods indicated an unambiguous increase in soil Mg content after struvite application. Broadcast soybean fertilization affected the phosphorus content of the soil. The results of the study indicated that different extraction methods presented different contents of P from soil. The content of available phosphorus was circa 122-156 mg kg-1 dm, 35.4-67.5 mg kg-1 dm and 100-159 mg kg-1 dm according to the Mehlich, Yanai and Egner-Riehm methods, respectively. A positive correlation was found between the content of Mg and K in soil determined by the Mehlich 3 and Yanai methods, which may suggest that the Yanai method could be introduced into standard soil chemical analysis in Poland. Such a correlation was not found for phosphorus, which is a difficult element to determine due to the multitude of factors affecting its availability.

Sewage phosphorus recovery through sachets loaded with water treatment plant sludge

Conventional wastewater treatment plants (WWTPs) present low phosphorus (P) removal capacity. Conversely, water treatment plants (WTPs) produce sludge with great P sorption from wastewater; however, directly adding the sludge into the wastewater treatment system could increase the effluent turbidity. As a novel approach, the present study evaluated the performance of WTP sludge within paper sachets for P removal from treated sewage. Different sludge concentrations (2-30 g L-1) and contact times (1-27 d) were applied to treat sewage from a university WWTP outlet. The sludge was characterized by P, Fe, and Al content. Larger sludge masses showed higher P removal efficiencies due to their high Fe content, especially at longer contact times (up to 100% at the final of the experiment). However, there is a more significant P reduction in the first 10 d (more than 90% in the most efficient treatment - 30 mg L-1). Based on the kinetic and isotherm analyses and the sludge chemical composition, precipitation proved to be a mechanism of great importance in P removal. Therefore, WTP sludge sachets can be a promising way to remove P from sewage, and the formed solid waste might be reused as an alternative fertilizer.

Study on adsorption and recovery utilization of phosphorus using alkali melting-hydrothermal treated oil-based drilling cutting ash

Oil-based drill cutting ash (OBDCA) was treated by alkali melting-hydrothermal method and used as novel adsorbent (AM-HT-OBDCA) for the recovery of phosphorus (P) in water body. The experiment parameter for preparation of AM-HT-OBDCA was optimized, including alkali melting ratio (M_OBDCA: M_NaOH), alkali melting temperature and hydrothermal temperature. The adsorption process of phosphorus on AM-HT-OBDCA was fit well with the pseudo-second-order model and the Langmuir model. The calculated theoretic adsorption capacity of phosphorus on AM-HT-OBDCA was 62.9 mg/g. The adsorption behavior was spontaneous and endothermic. The effect of pH value and interfering ions on the adsorption of phosphorus in AM-HT-OBDCA was investigated. The main existing form of adsorbed phosphorus on AM-HT-OBDCA was sodium hydroxide extraction form phosphorus (NaOH-P), including iron form phosphorus (Fe-P) and aluminum form phosphorus (Al-P). Precipitation and ligand exchange were the main mechanisms of phosphorus adsorption on AM-HT-OBDCA. The AM-HT-OBDCA used for phosphorus adsorption (AM-HT-OBDCA-P) could be further utilized as fertilizer to promote plant growth. The results of this study provide fundamental data and evaluation support for resource utilization of OBDCA. These results will also provide a reference for the adsorption and recovery utilization of phosphorus using solid waste-based adsorbent.

Transcriptome analysis of the phosphate starvation response sheds light on strigolactone biosynthesis in rice

Phosphorus (P) is a major element required for plant growth and development. To cope with P shortage, plants activate local and long-distance signaling pathways, such as an increase in the production and exudation of strigolactones (SLs). The role of the latter in mitigating P deficiency is, however, still largely unknown. To shed light on this, we studied the transcriptional response to P starvation and replenishment in wild-type rice and a SL mutant, dwarf10 (d10), and upon exogenous application of the synthetic SL GR24. P starvation resulted in major transcriptional alterations, such as the upregulation of P TRANSPORTER, SYG1/PHO81/XPR1 (SPX) and VACUOLAR PHOSPHATE EFFLUX TRANSPORTER. Gene Ontology (GO) analysis of the genes induced by P starvation showed enrichment in phospholipid catabolic process and phosphatase activity. In d10, P deficiency induced upregulation of genes enriched for sesquiterpenoid production, secondary shoot formation and metabolic processes, including lactone biosynthesis. Furthermore, several genes induced by GR24 treatment shared the same GO terms with P starvation-induced genes, such as oxidation reduction, heme binding and oxidoreductase activity, hinting at the role that SLs play in the transcriptional reprogramming upon P starvation. Gene co-expression network analysis uncovered a METHYL TRANSFERASE that displayed co-regulation with known rice SL biosynthetic genes. Functional characterization showed that this gene encodes an enzyme catalyzing the conversion of carlactonoic acid to methyl carlactonoate. Our work provides a valuable resource to further studies on the response of crops to P deficiency and reveals a tool for the discovery of SL biosynthetic genes.

Techno-Economic Analysis of Scenarios on Energy and Phosphorus Recovery from Mono- and Co-Combustion of Municipal Sewage Sludge

This study evaluates the techno-economic feasibility of energy and phosphorus (P) fertilizer (PF) recovery from municipal sewage sludge (MSS) through incineration in new combustion plants. We evaluated the economic impact of five critical process design choices: (1) boiler type, (2) fuel (MSS mono-combustion/co-combustion with wheat straw), (3) production scale (10/100 MW), (4) products (heat, electricity, PF), and (5) ash destination. Aspen Plus modeling provided mass and energy balances of each technology scenario. The economic feasibility was evaluated by calculating the minimum selling price of the products, as well as the MSS gate fees required to reach profitability. The dependency on key boundary conditions (operating time, market prices, policy support) was also evaluated. The results showed a significant dependency on both energy and fertilizer market prices and on financial support in the form of an MSS gate fee. Heat was preferred over combined heat and power (CHP), which was feasible only on the largest scale (100 MW) at maximum annual operating time (8000 h/y). Co-combustion showed lower heat recovery cost (19–30 €/MWh) than mono-combustion (29–66 €/MWh) due to 25–35% lower energy demand and 17–25% higher fuel heating value. Co-combustion also showed promising performance for P recovery, as PF could be recovered without ash post-treatment and sold at a competitive price, and co-combustion could be applicable also in smaller cities. When implementing ash post-treatment, the final cost of ash-based PF was more than four times the price of commercial PF. In conclusion, investment in a new combustion plant for MSS treatment appears conditional to gate fees unless the boundary conditions would change significantly.

Influence of Post- and Pre-Acid Treatment during Hydrothermal Carbonization of Sewage Sludge on P-Transformation and the Characteristics of Hydrochar

Phosphorus (P) recovery from alternative P-rich residues is essential to meet the growing demands of food production globally. Despite sewage sludge being a potential source for P, its direct application on agricultural land is controversial because of the obvious concerns related to heavy metals and organic pollutants. Further, most of the available P recovery and sludge management technologies are cost-intensive as they require mandatory dewatering of sewage sludge. In this regard, hydrothermal carbonization (HTC) has gained great attention as a promising process to effectively treat the wet sewage sludge without it having to be dewatered, and it simultaneously enables the recovery of P. This study was conducted to analyse and compare the influence of acid (H2SO4) addition during and after HTC of sewage sludge on P leaching and the characteristics of hydrochar. The obtained results suggested that despite using the same amount of H2SO4, P leaching from solid to liquid phase was significantly higher when acid was used after the HTC of sewage sludge in comparison with acid utilization during the HTC process. After HTC, the reduction in acid-buffering capacity of sewage sludge and increase in solubility of phosphate precipitating metal ions had a greater influence on the mobilization of P from solid to liquid phase. In contrast, utilization of H2SO4 in different process conditions did not have a great influence on proximate analysis results and calorific value of consequently produced hydrochar.

Recovery of phosphorus from eutrophic water using nano zero-valent iron-modified biochar and its utilization

Effective removal and recovery of phosphorus (P) from the aquatic environment was of great significance for eutrophication control and P recovery. This study investigated the effects of different environmental conditions on P adsorption by biochar (BC) and the feasibility of applying the P-laden BC as a fertilizer for plant growth. The nano zero-valent iron (nZVI) modified reeds BC prepared at 700 °C (Fe-700-BC) had the maximum P adsorption capacity of 95.2 mg g^-1, which was higher than those prepared at 300, 500, and 900 °C. The addition of Fe-700-BC reduced the concentration of total phosphorus (TP) in the overlying water, in which the soluble reactive phosphorus (SRP) almost completely removed, as well as had a certain inhibitory effect on the growth of algae. Simultaneously, Fe-700-BC reduced the contents of different fractions of P (weakly adsorbed inorganic phosphorus (WA-Pi), potential active inorganic phosphorus (PA-Pi), and Fe/Al-bound inorganic phosphorus (Fe/Al-Pi)) by adsorbing the soluble P released from the sediments, especially in the case of disturbance. Fe-700-BC had no significant effect on the diversity and richness of the microbial community in the sediment. Moreover, P-laden BC was safe and environmentally friendly for application in the soil and tended to increase stem and root length, fresh and dry weight at low doses (0.5 wt%) in wheat planting experiments. The present work could provide a reference for solving the problems related to eutrophication and P deficiency.

From wastewater to fertilizer products: Alternative paths to mitigate phosphorus demand in European countries

Phosphorus (P) is a non-renewable resource, irreplaceable for life and food production, and currently considered a Critical Raw Material to the European Union (EU). Due to concerns about the rate of consumption and limited reserves in countries with sensitive geopolitical contexts, it is urgent to recover P from urban and industrial flows. Indeed, the municipal wastewater treatment plants (WWTP) are considered relevant sources with several hot spots, especially sewage sludge with estimated recovery efficiencies of >80%. The most promising recovery strategies are based on thermal treatments (e.g., incineration of sludge) following by wet-chemical or thermo-chemical leaching, precipitation, and adsorption. The direct application of sludge on soil is no longer a primary route for P reintegration in the value-chain for countries as Switzerland, Germany, and The Netherlands. In fact, Switzerland and Austria paved the way for implementing P recovery legislation, focusing on recovery from raw sewage sludge or ashes. Indeed, industrial technologies with sludge ash as input show high recovery efficiencies (Ashdec® and Leachphos® with 98 and 79%) and lower environmental impacts, whereas Pearl® technology has about 12% recovery efficiency with wastewater as input. After all, struvite emerges as the most recovered product with recent access to the internal market of EU fertilisers and similar growth performance compared to triple-super-phosphate. However, several studies leave open the possibility of introducing loaded adsorbents with P as soil amendments as a new alternative to conventional desorption. Briefly, P recovery should be a compromise between efficiency, environmental impacts, and economic revenues from the final products.