Combined use of calcium nitrate addition and anion exchange resin capping to control sedimentary phosphorus release and its nitrate‑nitrogen releasing risk

Phosphorus immobilization in sulfide-ferrous oxidation process driven by nitrate reduction during black-odorous sediment remediation

During remediation of black-odorous sediment, the pathways of phosphorus immobilization require clarification alongside the oxidation of sulfide and ferrous. This study separated the oxidation stages of sulfide and ferrous through controlled sodium nitrate dosing ratios and methods, and analyzed the changes in phosphorus species and immobilization effects throughout these processes. Results showed that iron-bound phosphorus was the primary contributor to the phosphorus immobilization in the oxidation process, with increased 19% in ferrous oxidation stage and affected the transformation between phosphorus sources or sinks in the adsorption experiment. Additionally, the increase in abundance of phosphorus uptake and transport genes, and denitrifying phosphorus accumulation genes in sediment after ferrous oxidation (1 %-18 % and 87 %-164 %, respectively) indicated the potential for biological phosphorus immobilization. These results demonstrated that higher degrees of sediment oxidation correlate with stronger phosphorus immobilization capacities, providing theoretical bases for phosphorus immobilization during the restoration of black-odorous water bodies.

Piped-slow-release calcium nitrate dosing: A new approach to in-situ sediment odor control in rural areas

Calcium nitrate addition is economically viable and highly efficient for the in-situ treatment of contaminated sediment and enhancement of surface water quality, particularly in rural areas. However, conventional nitrate addition technologies have disadvantages such as excessive nitrate release, sharp ammonium increase, and weakened sulfide oxidation efficiency owing to rapid nitrate injection into the sediment. To resolve these defects, we propose a piped-slow-release (PSR) calcium nitrate dosing method and investigate its treatment efficiency and underlying mechanisms. The results illustrated that PSR dosing had a longer half-life (t1/2 = 5.08 days) and a lower maximum apparent nitrate escape rate of 1.28 % than conventional nitrate injection and other dosing methods. In addition, the PSR managed the inorganic nitrogen release into the overlying water, and after the treatment, the nitrate, ammonium, and nitrite concentrations of 0 mg/L, 8.60 mg/L, and 0 mg/L on day 28 were close to those of the control group (0 mg/L, 8.76 mg/L, and 0 mg/L, respectively). Moreover, the PSR method maintained a moderate nitrate concentration of approximately 3000 mg/L in sediment interstitial water by its controlled-release design, thus greatly enhancing the sulfide oxidation efficiency by relieving the inhibitory effects of high nitrate concentrations, with 83.0 % sulfide being eradicated within 5 days. Sulfide-ferrous nitrate reduction (denitrification and dissimilatory nitrate reduction to ammonium) genera (e.g., Sulfurimonas, Thiobacillus, and Thioalkalispira) were successively enhanced and dominated the microbial community, and the related functional genes displayed high relative abundances. These results imply that the PSR dosing method for calcium nitrate, characterized by flexible operation, high efficiency, low cost, and controllable processes, is appropriate for remediating black-odorous sediment in rural areas.

Effects of switching redox conditions on sediment phosphorus immobilization by calcium/aluminum composite capping: Performance, ecological safety and mechanisms

There many materials were used in lake restoration to immobilize phosphorus (P) and reduce the effect of eutrophication. Among them, calcium/aluminum composite (CAC) showed a good capacity of P adsorption. However, a comprehensive of its performance, ecological safety, and the mechanism of P passivation in the aluminum-bound P (Al -P) dominated sediments under varying redox conditions remains incomplete. In the current study, both unwashed CAC (UCAC) and washed CAC (WCAC) showed good P adsorption properties, and the greatest maximum capacity for P adsorption (Qmax) reached 206.8 mg/g at pH 8.5 for UCAC. The SRP and TP in the overlying water of the uncapped sediments showed a decrease-increase-decrease trend in a sequence of transition from aerobic to anaerobic to re-aerobic stages. In contrast, the SRP and TP of the two CACs-capped sediments were maintained low. Phosphorus forms in the uncapped sediment also underwent significant changes during continuous variation of dissolved oxygen (DO) levels. In particular, the decrease in iron-bound P (Fe-P) and Al-P was significantly promoted in the anaerobic phase, and the released P was reabsorbed to form mainly Fe-P in the re-aerobic phase. The CACs-capping promoted the transformation of Fe-P to residual P (Res-P), forming a thick static layer in the surface sediment, thus significantly inhibiting sediment P release. Moreover, the CACs-capping did not induce the Al3+ leaching and significant changes of the microbial community in sediments, and their performances of P immobilization could keep stable to resist the redox variation, which promised to be a good choice for P passivation in eutrophic lake sediments dominated by Al/Fe-P. These findings also confirmed that the risk of P release from Al/Fe-P (mainly Al-P)-dominated sediments was strongly influenced by continuously changing redox conditions, and was probably enhanced by the formation of Fe-P from the resorption of the released P.

Effects on the migration and speciation of heavy metals by combined capping and biochemical oxidation during sediment remediation

Capping and oxidation by lanthanum-modified bentonite (LMB) and calcium nitrate (CN) has a dual effect of deep phosphorus (P)/arsenic (As) clearance and surface P/As blockade. However, little information is available on the effect of LMB and CN on heavy metals. In this study, we hypothesize that LMB and CN exerted the same synergistic effect on heavy metals as P and As. We verified this through Rhizon samplers, diffusive gradients in thin films technology (DGT) and planar optode (PO) methods. The results showed that individual and combined LMB and CN treatments temporarily decreased but eventually increased the dissolved oxygen of the sediment-water interface (SWI). DGT-labile sulfide in the surface 110 mm sediment, soluble Fe(II) and DGT-labile Fe(II) in the surface 80 mm sediment were eliminated within 30 days by CN and LMB + CN treatments. A temporary sharp increase in soluble Fe, Mn, Co, and DGT-labile Mn, Co, Cu, and Ni was observed in CN and LMB + CN groups probably due to sulfide oxidation and carbonate dissolution. LMB + CN group showed a less-intense increase in DGT-labile metals and less metal release than the CN group (inferred from the total metal content). This indicates that LMB and CN had a synergistic effect on heavy metals. When using the LMB + CN treatment, LMB partly adsorbed and blocked metal release in sulfide and carbonate bound forms and finally transformed them into Fe and Mn oxides and residual forms. We suggest that CN should be combined with capping agents (at an appropriate pH) to compact sediments and block metal exchange at the SWI.

Experimental study on pollution release and sediment scouring of sewage sediment in a drainage pipe considering incubation time

The pollution release and the antiscourability characteristics of pipe sewage sediments can directly determine the blockage status of pipelines and the treatment burden at the outflow (sewage treatment plant). In this study, sewer environments with different burial depths were designed to explore the impact of incubation time on microbial activity, and the impacts of microbial activity on the physicochemical characteristics, pollution release effect and antiscouring ability of the silted sediment in the drainage pipe were further explored. The results showed that the incubation time, sediment matrix, temperature and dissolved oxygen affected microbial activity, but temperature had a greater influence. These factors affected microbial activity and loosened the superstructure in the sediment. In addition, by measuring the indices of nitrogen and phosphorus in the overlying water, it was found that sediment incubated for a certain time released pollutants into the overlying water, and the release amount was obviously affected by high temperature (e.g. 35 ℃). After a certain time (e.g. 30 days), biofilms appeared on the sediment surface, and the antiscourability of sediment was significantly improved, which was reflected in the increase in the median particle size of sediment left in the pipe.

Resuspension and settlement characteristics of lake sediments amended by phosphorus inactivating materials: Implications for environmental remediation

The classical lake internal phosphorus (P) pollution control using P-inactivating materials is typically carried out by reducing the release of soluble P from sediments to overlying water; however, particulate P loading through sediment resuspension could also cause internal P pollution for algae breeding. Therefore, based on lanthanum modified bentonite clay (Phoslock®) and drinking water treatment residues (DWTR), the effect of P inactivating materials on sediment resuspension and settlement were comprehensively investigated to assess the variations in particulate P pollution from sediment. Results showed that both materials could effectively control soluble P pollution from sediment, while both had limited effect on the supplement of particulate P to overlying water. The reason may be that hydrodynamic disturbance was the key factor regulating sediment resuspension and settlement. The disturbance induced the resuspension of different sized sediments, especially <8 μm fractions, while increasing disturbing intensities promoted resuspension of relatively larger sized sediments (e.g., <63 μm). Further analysis suggested that after resuspension and settlement, the efficiencies of reducing bioavailable P by Phoslock® in relatively large sized sediment fraction (e.g., <63 μm) were substantially less than those in relatively small sized sediment (<8 μm). Although the reducing efficacies of DWTR had limited changes in different sized sediments, the remaining bioavailable P were clearly higher in smaller sized sediments with DWTR. The different performances on bioavailable P reduction mainly resulted from the distributions of materials and original P in different sized sediments. These findings indicated the potential supplement of particulate P for algal growth during resuspension and settlement of sediments amended by P inactivating materials. Overall, understanding the sediment P bioavailability and hydraulic properties at different sizes and the lake hydrodynamic conditions is essential to develop appropriate methods to control lake internal P pollution.

Laboratory investigation on calcium nitrate induced coupling reactions between nitrogen, phosphorus, sulfur, and metals in contaminated sediments

In recent years, calcium nitrate addition has become a promising and usually used method for in situ sediment remediation. In this study, excess calcium nitrate was applied to column sediments to explore the coupling reactions of elements such as N, Fe, S, and P. Diffusive gradients in thin film (DGT) devices were used to collect labile substances at the sediment-water interface. Rhizon samplers were used to collect soluble substances in interstitial water. Results showed that nitrate addition turned the surface sediment into a more oxidized state, and mobile Fe, S, P, and As were removed in surface ~ 10-cm sediment. Due to different nitrate distributions in corresponding sediment depths, the consumption rates of NH3-N and soluble reactive P were faster in the surface sediment than that in deeper layers. Different from previous researches, the transient increase of soluble Fe was observed in this study, which was probably attributed to the solvation of FeS in the autotrophic denitrification process. According to our results, we suggest that a dosage of far less than 141 g N/m2 and slightly more than 45.3 g N/m2 can be used for the remediation of black and odorous sediment and control of internal P by calcium nitrate.

Removal of inorganic arsenic from aqueous solution by Fe-modified ceramsite: batch studies and remediation trials

During sediment remediation, adsorbent addition is an effective technology for the removal of contaminants but the cost is often high. In this study, a low-cost adsorbent, ceramsite, made from contaminated riverbed sediment was synthesized. The Fe-modified ceramsite (FMC) was used as adsorbent to remove arsenate from aqueous solutions and reduce the inorganic arsenic release from contaminated sediments. Kinetic studies showed that chemisorption mainly governed the adsorption process while batch studies yielded the theoretical adsorption capacity for arsenate of 10.63 mg/g at pH = 7 condition. Co-existing anions and pH have no significant impact on the adsorption process. In the regeneration studies, 91, 86, and 80% of the adsorption capacity were recovered in 3 cycles. In-situ remediation trials revealed that the addition of the adsorbent to sediment surface significantly reduced the release of inorganic arsenic into aqueous system, with a reduction efficiency of 86%. Furthermore, the species of the arsenic in the surface layer was significantly inactivated from an active state to a stable state. These findings highlight the application of the FMC as a facile and cost-effective adsorbent for containment of arsenic in solutions and sediments, demonstrating that they are highly applicable for practical cases.

Mechanism of ammonium sharp increase during sediments odor control by calcium nitrate addition and an alternative control approach by subsurface injection

Nitrate-driven sulfide/ferrous oxidation has been proved a cost-effective approach for river sediments in-situ odor control. However, calcium nitrate addition would sharply increase ammonium concentration in interstitial water and the mechanism was not yet clear. In this work, though sulfide and ferrous iron were efficiently oxidized, about 102% of NH₄⁺ concentration increased in interstitial water on the first day of calcium nitrate injection (30 mg kg dwt^-1), and about 31% more NH₄⁺ increase at the 21st days was observed. To discover the mechanism of ammonium sharp release, desorption kinetics experiment was conducted and the results suggested that the short-time sharp releases of ammonium when calcium nitrate was added could be attributed to the chemical extraction of exchangeable ammonium by calcium ion. Furthermore, at the end of treatment, many genus such as Thiobacillus, Sulfurimonas, Thermomonas, and Clostridium, which were closely related to sulfide and ferrous-driven denitrification and dissimilatory nitrate reduction to ammonium (DNRA), were identified by 16S rRNA Illumina sequencing method. These findings indicated the long-time increase of ammonium might be determined by the biochemical processes (e.g. DNRA) driven by nitrate reduction. Therefore, to avoid the impact of ammonium release, an alternative subsurface injection method was introduced in this work, and the results showed that ammonium releases could be well controlled when the injection position was beneath 10 cm of the sediment surface.

Hazardous wastes treatment technologies

A review of the literature published in 2019 on topics related to hazardous waste management in water, soils, sediments, and air. The review covered treatment technologies applying physical, chemical, and biological principles for the remediation of contaminated water, soils, sediments, and air. PRACTICAL POINTS: This report provides a review of technologies for the management of waters, wastewaters, air, sediments, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) in three scientific areas of physical, chemical, and biological methods. Physical methods for the management of hazardous wastes including general adsorption, sand filtration, coagulation/flocculation, electrodialysis, electrokinetics, electro-sorption ( capacitive deionization, CDI), membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, potassium permanganate processes, and Fenton and Fenton-like process were reviewed. Biological methods such as aerobic, anoxic, anaerobic, bioreactors, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed. Case histories were reviewed in four areas including contaminated sediments, contaminated soils, mixed industrial solid wastes and radioactive wastes.

Nanoscale Zero-Valent Iron Has Minimum Toxicological Risk on the Germination and Early Growth of Two Grass Species with Potential for Phytostabilization

Two Poaceae species, Agrostis capillaris and Festuca rubra, were selected for their potential as phytostabilizing plants in multicontaminated soils. These species are resistant to contamination and maintain high concentrations of contaminants at the root level. Nanoscale zero-valent iron (nZVI) is an engineered nanomaterial with the ability to stabilize metal(loid)s in soils; its potential toxicological effects in the selected species were studied in a germination test using: (i) control variant without soil; (ii) soil contaminated with Pb and Zn; and (iii) contaminated soil amended with 1% nZVI, as well as in an hydroponic experiment with the addition of nZVI 0, 25, 50 and 100 mg L⁻¹. nZVI had no negative effects on seed germination or seedling growth, but was associated with an increase in shoot growth and reduction of the elongation inhibition rate (root-dependent) of F. rubra seedlings. However, applications of nZVI in the hydroponic solution had no effects on F. rubra but A. capillaris developed longer roots and more biomass. Increasing nZVI concentrations in the growing solution increased Mg and Fe uptake and reduced the Fe translocation factor. Our results indicate that nZVI has few toxic effects on the studied species.

Combined use of calcium nitrate, zeolite, and anion exchange resin for controlling phosphorus and nitrogen release from sediment and for overcoming disadvantage of calcium nitrate addition technology

Ca(NO₃)₂ addition has proved to have a high potential to immobilize internal phosphorus (P) in sediments; however, it cannot effectively stop the release of ammonium-nitrogen (NH₄⁺-N) from sediments into overlying waters (OL-waters). Additionally, the addition of Ca(NO₃)₂ alone has high risk of nitrate-nitrogen (NO₃^--N) releasing into OL-waters. To overcome the shortcoming of the Ca(NO₃)₂ addition method, we reported an integrated method, i.e., a combined method based on Ca(NO₃)₂ injection, zeolite capping, and anion exchange resin (AERN)-contained floating system suspending (Ca(NO₃)₂/zeolite/AERN). The effectiveness and mechanism of the Ca(NO₃)₂/zeolite/AERN method for simultaneously controlling the release of soluble reactive P (SRP) and NH₄⁺-N were investigated, and the NO₃^--N releasing risk of this method was evaluated. It was found that the joint use of Ca(NO₃)₂ injection, zeolite capping, and AERN-contained floating system suspending not only could effectively suppress the release of SRP and NH₄⁺-N from sediments into OL-waters simultaneously, but also had much less risk of NO₃^--N releasing into OL-waters as compared to the single Ca(NO₃)₂ injection method and the combined Ca(NO₃)₂/zeolite method. The inhibition of the reductive dissolution of the P-bound Fe(III) oxides/hydroxides by the presence of nitrate and the adsorption of ammonium on the zeolite played very important roles in the interception of SRP and NH₄⁺-N releasing into OL-waters by the Ca(NO₃)₂/zeolite/AERN method. After the sediment remediation using the Ca(NO₃)₂/zeolite/AERN approach, the increase in the content of residual P in the sediment layer of 0-50 mm, the decrease of mobile P in the sediment layer of 0-10 mm, and the increased NH₄⁺-N adsorption capacity for the sediment layer of 0-10 mm would be conductive to the interception of SRP and NH₄⁺-N liberation in the long run. Results of this research suggest a promising application potential of the Ca(NO₃)₂/zeolite/AERN method in the simultaneous control of the release of SRP and NH₄⁺-N from sediments.

Effect of ferric chloride on phosphorus immobilization and speciation in Dianchi Lake sediments

Immobilization of phosphorus in lake sediments and control of internal-loading phosphorus release have become crucial aspects of eutrophication lake management. In this study, the immobilization efficiency of phosphorus by ferric chloride in Dianchi Lake sediments was investigated. In addition, effects of the dosage of ferric chloride and contact time on the release of phosphorus from sediments were investigated. Laboratory experiments revealed that ferric chloride can effectively inhibit the release of phosphorus from sediments. At a ferric chloride dosage of 10 mg/g, the total phosphorus concentration of the overlying water was reduced by ~87%. With the increase in the contact time, the amount of phosphorus immobilized by ferric chloride increased. To further evaluate the feasibility of ferric chloride for immobilising phosphorus in sediments, an amplification experiment with a water volume of 50 L was carried out. By the addition of 6 mg/g of ferric chloride, the total phosphorus concentration of the overlying water was still less than 0.01 mg/L after 100 days. At the same time, the phosphorus species in the sediment after treatment with ferric chloride were analyzed. Results revealed that ferric chloride mainly converts unstable exchangeable phosphorus (Ex-P), ferric phosphate (Fe-P) and organic phosphorus (Or-P) into more stable occluded phosphate (O-P), reducing the possible release of phosphorus from sediments. Practical applications of ferric chloride to control the release of phosphorus from Dianchi Lake sediments were discussed.