I. de Vicente

Sediment phosphate fractionation and interstitial water phosphate concentration in two coastal lagoons (Albuferas de Adra, SE Spain)

The concentrations of o-phosphate and dissolved inorganic carbon were monitored in the interstitial water of the sediment in two highly eutrophic coastal lagoons, Laguna Honda and Laguna Nueva (SE, Spain) from July 2000 to August 2001. Additionally, the organic matter concentration and the P-fractions in the sediment were analysed. Despite their proximity, these two lagoons showed many significant differences (P<0.05). The P-concentration in the interstitial water of the top sediment was higher in the Laguna Honda (up to 1 mg l−1), especially during summer, when both sites registered their highest values. By contrast, the concentration of organic matter and organic P-fractions were higher in the sediment of the Laguna Nueva. The concentration of the organic matter in the vertical profile of the sediment decreased with depth in the Laguna Nueva (from 17% at 0 cm to 7% at 15 cm, annual mean value) while it increased in the sediment of Laguna Honda (from 9% at 0 cm to 12% at 15 cm, annual mean value). The P-concentration in the interstitial water and the organic matter in the top sediment of Laguna Honda followed a seasonal pattern and, were both correlated with the temperature of the bottom water (r=0.706, P<0.05 and r= -0.929, P<0.01, respectively). The inorg-P fractions comprised 63% of the Tot-phosphate in the sediment of Laguna Honda, whereas org-P fractions (68%) dominated in the sediment of Laguna Nueva. The concentrations of Tot-P in the sestonic material collected at three different depths of the water column averaged 2.2 mg g−1d.w. in Laguna Honda and 2.5 mg g−1d.w. in Laguna Nueva. The average atomic C:P ratio of the sestonic material was significantly higher in Laguna Honda than in Laguna Nueva, but the top sediment in Laguna Nueva had a C:P ratio significantly higher than that of the sestonic material (average: 416 and 162, respectively).The different biodegradability of the organic matter in the top sediment probably explained the differences found in sediment composition between these two lagoons. We suggest that the P-reclying from the sediment to the interstitial water was faster in Laguna Honda due to the higher biodegradability of the organic matter. By contrast, the lower biodegradability of the organic matter in the top sediment of Laguna Nueva was probably due to a higher contribution of vascular plants which could explain the organic matter accumulation detected in this lagoon.

Setting up High Gradient Magnetic Separation for combating eutrophication of inland waters.

To find new approaches to devise technologies for handling with eutrophication of inland waters is a global challenge. Separation of the P from water under conditions of continuous flow is proposed as an alternative and effective method. This work is based on using highly magnetic particles as the seeding adsorbent material and their later removal from solution by High Gradient Magnetic Separation (HGMS). Contrast to other methods based on batch conditions, large volumes of water can be easily handled by HGMS because of decreasing retention times. This study identifies the best working conditions for removing P from solution by investigating the effects of a set of four different experimental variables: sonication time, flow rate (as it determines the retention time of particles in the magnetic field), magnetic field strength and the iron (Fe) particles/P concentration ratio. Additionally, the change of P removal efficiency with time (build up effect) and the possibility of reusing magnetic particles were also studied. Our results evidenced that while flow rate does not significantly affect P removal efficiency in the range 0.08-0.36 mL s(-1), sonication time, magnetic field strength and the Fe particles/P concentration ratio are the main factors controlling magnetic separation process.

The influence of pH on manganese removal by magnetic microparticles in solution

An extensive experimental work is reported that aims to assess the efficiency in manganese (Mn) removal from aqueous solution by carbonyl iron microparticles using magnetic separation techniques. A set of batch experiments are performed to explore the effect of pH, adsorbent concentration, surface coating and contact time for achieving the highest Mn removal efficiency. Mn removal efficiency is extremely high (>98%) for pH values larger than 9 as a result of the chemisorption of Mn oxides onto magnetic microparticles. In contrast, Mn removal efficiency for pH < 9 was significantly reduced as Mn remains as a soluble cation. In this manuscript we demonstrate that the efficiency clearly increases when increasing the adsorbent concentration and when using MnOx(s) coated magnetic particles instead of bare particles. Desorption rates from Mn-loaded magnetic particles at different pHs were always lower than 15%. Furthermore, Mn removal efficiency remained at a very high value (>95%) when reused particles were employed in the adsorption process.

Chemical interferences when using high gradient magnetic separation for phosphate removal: consequences for lake restoration.

A promising method for lake restoration is the treatment of lake inlets through the specific adsorption of phosphate (P) on strongly magnetizable particles (Fe) and their subsequent removal using in-flow high gradient magnetic separation (HGMS) techniques. In this work, we report an extensive investigation on the chemical interferences affecting P removal efficiencies in natural waters from 20 Mediterranean ponds and reservoirs. A set of three treatments were considered based on different Fe particles/P concentration ratios. High P removal efficiencies (>80%) were found in freshwater lakes (conductivities<600 μ S cm(-1)). However, a significant reduction in P removal was observed for extremely high mineralized waters. Correlation analysis showed that major cations (Mg(2+), Na(+) and K(+)) and anions (SO(4)(2-) and Cl(-)) played an essential role in P removal efficiency. Comparison between different treatments have shown that when increasing P and Fe concentrations at the same rate or when increasing Fe concentrations for a fixed P concentration, there exist systematic reductions in the slope of the regression lines relating P removal efficiency and the concentration of different chemical variables. These results evidence a general reduction in the chemical competition between P and other ions for adsorption sites on Fe particles. Additional analyses also revealed a reduction in water color, dissolved organic carbon (DOC) and reactive silicate (Si) concentrations with the addition of Fe microparticles.

A microcosm experiment to determine the consequences of magnetic microparticles application on water quality and sediment phosphorus pools

This study used microcosms to evaluate the effects of adding iron (Fe) magnetic microparticles (MPs) on water quality, focusing on P concentrations in the water column and sediment. Two treatments were considered for a constant 85:1 MP:PMobile molar ratio: T-W, applying MPs on the surface water layer; and T-S, applying MPs on the sediment. MP addition reduced P concentrations in lake water and sediment, with both treatments producing a mean reduction of 68±6% in dissolved inorganic P concentration (DIP) over a 70-day oxic period and reductions of 80±8% (T-W) and 80±4% (T-S) over a 5-day anoxic period. MPs also decreased reactive silicate (Si) concentrations by around 50% in both periods, but dissolved organic carbon (DOC) was reduced by only 15% at 24h after MP addition. Despite the marked decrease in DIP concentration due to MP addition, there was no reduction in chlorophyll a (Chla), because post-treatment total P concentrations (>200μgL-1vs. >700μgL-1 before treatments) remained higher than required for changes in the biological community (0.05-0.1mgL-1). With T-S treatment, there was a reduction of 15% in P bound to Al oxides, clay minerals, and humic substances (P→NaOH) and of 12% in labile organic P (Org-PLabile) versus controls. P bound to humic substances (P→NaOH, Humic) was reduced by 11-22% in both treatments. Finally, T-W rather than T-S treatments are recommended for future whole-lake applications to achieve more effective P removal from water and sediment and a higher percentage MP recovery.

Acute and chronic effects of magnetic microparticles potentially used in lake restoration on Daphnia magna and Chironomus sp.

Magnetic microparticles (MPs) have been recently proposed as a new and promising tool for restoring eutrophicated waters. In this study, we analyzed the acute (immobilization) and chronic effects of iron (Fe) MPs on Daphnia magna and on the benthic macroinvertebrate Chironomus sp. In the chronic toxicity tests the offspring production (male and female) in D. magna and the mortality of larvae and pupae, and adult emergence in Chironomus sp. experiments were used as the endpoints. The concentration of MPs that caused 50% of immobilized individuals (EC50) in the acute toxicity test was much higher in D. magna (0.913g MPs l-1) than in Chironomus sp. (0.445g MPs l-1). The results of chronic toxicity tests in D. magna showed that in presence of dissolved Fe (dFe), parthenogenetic reproduction was significantly affected, while no significant effect on mortality of larvae and pupae and on adult emergence was detected in Chironomus sp. test. Taking into account both that long-term exposure is not likely to occur and the regular dose of MPs potentially used in a restoration plan, we conclude that MPs is a riskless (no toxic effect on planktonic and benthic organisms) and efficient (high P adsorption capacity) tool for lake restoration.

Determining major factors controlling phosphorus removal by promising adsorbents used for lake restoration: A linear mixed model approach

Phosphorus (P) removal from lake/drainage waters by novel adsorbents may be affected by competitive substances naturally present in the aqueous media. Up to date, the effect of interfering substances has been studied basically on simple matrices (single-factor effects) or by applying basic statistical approaches when using natural lake water. In this study, we determined major factors controlling P removal efficiency in 20 aquatic ecosystems in the southeast Spain by using linear mixed models (LMMs). Two non-magnetic -CFH-12® and Phoslock®- and two magnetic materials -hydrous lanthanum oxide loaded silica-coated magnetite (Fe-Si-La) and commercial zero-valent iron particles (FeHQ)- were tested to remove P at two adsorbent dosages. Results showed that the type of adsorbent, the adsorbent dosage and color of water (indicative of humic substances) are major factors controlling P removal efficiency. Differences in physico-chemical properties (i.e. surface charge or specific surface), composition and structure explain differences in maximum P adsorption capacity and performance of the adsorbents when competitive ions are present. The highest P removal efficiency, independently on whether the adsorbent dosage was low or high, were 85-100% for Phoslock and CFH-12®, 70-100% for Fe-Si-La and 0-15% for FeHQ. The low dosage of FeHQ, compared to previous studies, explained its low P removal efficiency. Although non-magnetic materials were the most efficient, magnetic adsorbents (especially Fe-Si-La) could be proposed for P removal as they can be recovered along with P and be reused, potentially making them more profitable in a long-term period.