Mechanism and application of hydrothermal carbon-based electrosorption for selective phosphorus removal

Selective removal and recovery of phosphorus from wastewater is a huge challenge for water purification. In particular, phosphite is an often-neglected contaminant that is more soluble and resistant to biotransformation than phosphate. Herein, we develop an electrochemical system for phosphorus removal using nitrogen-doped graphene aerogel loaded with ferrocene-polyaniline (Fc-PANI@NGA) electrodes. The results demonstrate that this electrochemical system can selectively adsorb phosphate and phosphite in comparison to other anions and promote the oxidation of phosphite to phosphate. The high affinity of Fc-PANI@NGA to both phosphate and phosphite due to the faradic reactions and specific hydrogen-bonding interactions ensures high selectivity of P over Cl–, SO42–, and NO3–. The redox reversibility of Fc to Fc+ due to its interaction with O2/H2O2 led to the formation of •O2– and •OH, which are predominantly responsible for the oxidation of phosphite to phosphate. This system enables the phosphate and phosphite adsorption capacities of 29 mg PO43– g–1 and 24 mg HPO32– g–1, respectively, and high phosphite conversion efficiency (99.3% at a cell voltage of ±1.6 V), exhibiting high selection efficiency and stable regeneration performance. Density functional theory calculation verifies the selective adsorption mechanism of phosphate and adsorption/oxidation of phosphite on the Fc-PANI@NGA electrode.

Identification of trigger factors selecting for polyphosphate- and glycogen-accumulating organisms in aerobic granular sludge sequencing batch reactors

Functionalized biobased carbon electrodes for selective phosphorus removal by capacitive deionization: Application and theory study

Emulsion synthesis of cellulose/lanthanum alginate /La (Ⅲ) composite microspheres for efficient and selective adsorption of phosphate

The role of silica in biomass for calcium-modified biochar: Phosphorus removal mechanism and potential as a phosphate fertilizer application.

Adsorbents featuring high-affinity phosphate-binding proteins (PBPs) have demonstrated highly selective and rapid phosphorus removal and recovery.

Phosphorus to an optimum extent is an essential nutrient for all living organisms and its scarcity may cause food security, and environmental preservation issues vis-à-vis agroeconomic hurdles. Undesirably excess phosphorus intensifies the eutrophication problem in non-marine water bodies and disrupts the natural nutrient balance of the ecosystem. To overcome such dichotomy, biodegradable polymer-based adsorbents have emerged as a cost-effective and implementable approach in striking a "desired optimum-undesired excess" balance pertaining to phosphate in a sustainable manner. So far, the reports on adopting such adsorbent-approach for wastewater remediation remained largely scattered, unstructured, and poorly correlated. In this background, the contextual review comprehensively discusses the current state-of-the-art in utilizing biodegradable polymeric frameworks as an adsorbent system for phosphate removal and its efficient recovery from the aquatic ecosystem, while highlighting their characteristics-specific functional efficiency vis-à-vis easiness of synthetic and commercial viability. The overview further delves into the sources and environmental ramifications of excessive phosphorus in water bodies and associated mechanistic pathways of phosphorus removal via adsorption, precipitation, and membrane filtration enabled by biodegradable (natural and synthetic) polymeric substrates. Finally, functionality optimization, degradability tuning, and adsorption selectivity of biodegradable polymers are highlighted, while aiming to strike a balance in "removal-recovery-reuse" dynamics of phosphate. Thus, the current review not only paves the way for future exploration of biodegradable polymers in sustainable cost-effective adsorbents for phosphorus removal but also can serve as a guide for researchers dealing with this critical issue.

Selective removal of phosphorus from wastewater combined with its recovery as a solid-phase fertilizer

Influx of Phosphorus (P) into freshwater ecosystems is the primary cause of eutrophication which has many undesirable effects. Therefore, P discharge limits for effluents from WWTPs is becoming increasingly common, and may be as low as 10 μg/L as P. While precipitation, filtration, membrane processes, Enhanced Biological Phosphorus Removal (EBPR) and Physico-chemical (adsorption based) methods have been successfully used to effect P removal, only adsorption has the potential to recover the P as a usable fertilizer. This benefit will gain importance with time since P is a non-renewable resource and is mined from P-rich rocks. This article provides details of a process where a polymeric anion exchanger is impregnated with iron oxide nanoparticles to effectuate selective P removal from wastewater and its recovery as a solid-phase fertilizer. Three such hybrid materials were studied: HAIX, DOW-HFO, & DOW-HFO-Cu. Each of these materials combines the durability, robustness, and ease-of-use of a polymeric ion-exchanger resin with the high sorption affinity of Hydrated Ferric Oxide (HFO) toward phosphate. Laboratory experiments demonstrate that each of the three materials studies can selectively remove phosphate from the background of competing anions and phosphorus can be recovered as a solid-phase fertilizer upon efficient regeneration of the exchanger and addition of a calcium or magnesium salt in equimolar (Ca/P or Mg/P) ratio. Also, there is no leaching of Fe or Cu from any of these hybrid exchangers.

Renewable molybdate complexes encapsulated in anion exchange resin for selective and durable removal of phosphate

The potential phosphorus shortage along with phosphorus pollution has drawn global attention, calling for effective technologies for phosphorus removal and recovery from wastewater. Capacitive deionization (CDI) is a promising technology for salt removal and nutrient recovery. However, their performances suffer from limited ion storage capacity and low selectivity, e.g., phosphate removal was lower than the other salts. Herein, guanidinium-functionalized polyelectrolyte-coated carbon nanotube (Gu-PAH/CNT) electrodes were prepared through the self-assembly technique. The Gu-PAH/CNT electrodes selectively adsorbed phosphate ions and prevented the repulsion of coions due to the combined effect of the ion-selective polyelectrolyte layer and the NH protons of Gu groups, resulting in strong electrostatic and hydrogen-bond interactions with phosphate ions. The Gu-PAH/CNT anode was coupled with a COOH-CNT cathode for selective capture of phosphate in a CDI device. The phosphate ion adsorption capacity of Gu-PAH/CNT electrodes is up to 23–30 mg PO43– g–1 in a phosphate solution with a wide pH range and mixtures (NaH2PO4/NaCl, NaH2PO4/Na2SO4, and NaH2PO4/NaNO3) at 1.2 V, presenting superior electroadsorption capacity, phosphate selectivity, and stable regeneration property. These encouraging results demonstrate that functionalized polyelectrolyte-modified electrode materials act as powerful platforms for effective and selective removal and recovery of specific contaminants from wastewater.

This study aimed to investigate how the production process of metal impregnated biochars (MIBs) affects their selectivity in the simultaneous adsorption of organic matter and dissolved phosphorus from the aqueous phase. MIBs were produced via a two-step pyrolysis procedure including impregnation of metal oxides in the structure of the softwood-derived biochars, resulting in copper-impregnated biochar (Cu-MIB) and iron-impregnated biochar (Fe-MIB). The tailoring process was conducted by optimization of pyrolysis temperature during the biochars production stage. The MIBs were characterized via advanced characterization analyses to acquire structural, elemental, and morphological properties of the adsorbent. The surface area of MIB (99 m2/g and 92 m2/g for Cu-MIB and Fe-MIB respectively) decreased compared to pristine biochar (571 m2/g), indicating a successful impregnation of metal oxide particles within the porous carbon structure. The effect of operational parameters on adsorption as well as selectivity tests were examined in the batch mode. The optimum doses for NOM removal were 2 g/l for Fe-MIB (96%) and 0.5 g/l for Cu-MIB (87%). For phosphorus removal, optimum doses were 1 g/l for Fe-MIB (95%) and 2 g/l for Cu-MIB (93%). The lower pH values favored adsorption for both MIBs. In the binary solution of NOM and phosphorus, the NOM was selectively adsorbed by the Cu-MIB, whereas phosphorus was selectively removed by the Fe-MIB. The results provide a deeper understanding of the tailoring process of biochars for producing new biochars as selective adsorbents for specific target pollutants.

Breaking hydrogen bond in metal free carbon nitride to induce peroxymonosulfate nonradical activation: Surface-mediated electron transfer

Two lab-scale aerobic granular sludge sequencing batch reactors were operated at 20 and 30°C and compared for phosphorus (P) removal efficiency and microbial community composition. P-removal efficiency was higher at 20°C (>90%) than at 30°C (60%) when the sludge retention time (SRT) was controlled at 30 days by removing excess sludge equally throughout the sludge bed. Samples analyzed by fluorescent in situ hybridization (FISH) indicated a segregation of biomass over the sludge bed: in the upper part, Candidatus Competibacter phosphatis (glycogen-accumulating organisms--GAOs) were dominant while in the bottom, Candidatus Accumulibacter phosphatis (polyphosphate-accumulating organisms--PAOs) dominated. In order to favour PAOs over GAOs and hence improve P-removal at 30°C, the SRT was controlled by discharging biomass mainly from the top of the sludge bed (80% of the excess sludge), while bottom granules were removed in minor proportions (20% of the excess sludge). With the selective sludge removal proposed, 100% P-removal efficiency was obtained in the reactor operated at 30°C. In the meantime, the biomass in the 30°C reactor changed in color from brownish-black to white. Big white granules appeared in this system and were completely dominated by PAOs (more than 90% of the microbial population), showing relatively high ash content compared to other granules. In the reactor operated at 20°C, P-removal efficiency remained stable above 90% regardless of the sludge removal procedure for SRT control. The results obtained in this study stress the importance of sludge discharge mainly from the top as well as in minor proportions from the bottom of the sludge bed to control the SRT in order to prevent significant growth of GAOs and remove enough accumulated P from the system, particularly at high temperatures (e.g., 30°C).

The development of biochar-based granule-like adsorbents suitable for scaled-up application has been attracting increasing attention in the field of water treatment. Herein, a new formable porous granulated biochar loaded with La-Fe(hydr)oxides/montmorillonite (LaFe/MB) was fabricated via a granulation and pyrolysis process for enhanced phosphorus (P) removal from wastewater. Montmorillonite acted as a binder that increased the size of the granulated biochar, while the use of Fe promoted the surface charge and facilitated the dispersion of La, which was responsible for selective phosphate removal. LaFe/MB exhibited rapid phosphate adsorption kinetics and a high maximum adsorption capacity (Langmuir model, 52.12 mg P g−1), which were better than those of many existing granulated materials. The desorption and recyclability experiments showed that LaFe/MB could be regenerated, and maintained 76.7% of its initial phosphate adsorption capacity after four adsorption cycles. The high hydraulic endurance strength retention rate of the developed material (91.6%) suggested high practical applicability in actual wastewater. Electrostatic attraction, surface precipitation, and inner-sphere complexation via ligand exchange were found to be involved in selective P removal over a wide pH range of 3–9. The thermodynamic parameters were determined, which revealed the feasibility and spontaneity of adsorption. Based on approximate site energy distribution analyses, high distribution frequency contributed to efficient P removal. The research results provide a new insight that LaFe/MB shows great application prospects for advanced phosphate removal from wastewater.Graphical