Eutrophication Problems Research Articles

Achieving win-win outcomes with cerium-loaded porous aluminum sludge hydrogel microspheres for enhanced phosphate removal

Breaking the technical bottleneck of traditional powdered adsorbent in phosphate adsorption application treatment, a macroscopic high adsorption performance aluminum sludge-based composite hydrogel material was constructed to synergistically solve the problems of water eutrophication and aluminum sludge resourcization. In this study, porous Ce-modified aluminum sludge hydrogel microspheres (Ce-AlS-SA) were prepared to improve the surface chemical structure and microscopic morphology of the macroscopic adsorbent material to enhance the adsorption capacity and achieve effective solid-liquid separation. The best adsorption performance of the material (Ce-AlS12-SA1) was obtained when the Ce-AlS: SA: Na2CO3 was 12:1:1, and obtained the optimal adsorption conditions by Response Surface Method (RSM) with 1.5 mg/L of the dosage, 4 of pH and 50 mg/L of Cphosphate. The maximum adsorption of 20.36 mg P/g was obtained by the Langmuir model at 303 K, which was 2.92 times more than raw sludge. According to the Freundlich and pseudo-second-order kinetic model, the adsorption process is chemisorption; the multi-stage adsorption process is reflected in the intraparticle diffusion and film diffusion models. The main mechanisms combined with the characterization analysis are electrostatic gravity, ligand exchange, and inner-sphere complexation. Meanwhile, Ce-AlS12-SA1 shows good resistance to interference in the coexistence of multiple ions. Therefore, this material can be recognized as a new material with in-depth, diversified and practical needs for resourceful utilization, which is expected to achieve extensive engineering applications in the future.

Reducing the water residence time is inadequate to limit the algal proliferation in eutrophic lakes

The eutrophication problem now threatens many lakes and reservoirs. To avoid the occurrence of algal blooms, some cities try to increase the flow rate or directly choose lakes or reservoirs with a short water residence time (WRT) as drinking water sources. However, up to now, whether such a strategy can achieve its goal is still unclear. In this study, a newly restored lake with a WRT of approximately 3 days was chosen to investigate algal growth potential as well as its responses to external nitrogen (N) and phosphorus (P) inputs. The results suggested that although the water quality of the lake could generally meet the environmental quality standards for surface water, dissolved inorganic nitrogen reached a high level with an average value of 1.58 mg/L. Meanwhile, a considerable increase in Chl-a concentration was observed across the flow direction. Especially, in July, Chl-a concentration at the site near the outlet was 8.1 times higher than that at the inlet, and cyanobacteria became the dominant species accounting for 83% of the total cell density. Nutrient enrichment experiments showed that algae could grow rapidly within 3 days with average specific growth rates (μ) of 0.36–0.42 d−1. The addition of N and P furtherly promoted the algal growth, and μ values of the treatments with P addition were the highest at 0.67–0.83 d−1. These results indicated that even if the WRT was reduced to 3 days, the risk of the occurrence of algal blooms still exists, and this undesirable trend would be enhanced by the short-term external nutrient input. Our findings indicated that the hydrodynamic control measures may not be entirely successful in protecting the drinking water source from algal blooms, especially when its influent has already been under eutrophication.

Distribution characteristics and controlling factors of reduced inorganic sulfur forms in Three Gorges Reservoir sediment and its influence on the release of endogenous phosphorus

还原性无机硫(RIS)包括硫酸盐还原产物和活性铁(Fe_HR)形成的酸可挥发性硫(AVS)、硫的中间产物元素硫(S⁰)及沉积物中硫铁元素的最终积累物质黄铁矿硫(S_py),RIS不仅可以影响沉积物重金属的生物有效性,还控制铁还原及内源磷的释放等生源要素的地球化学行为。为了研究三峡库区沉积物中RIS分布特征及其环境意义,于2017年7-8月和12月采集三峡库区云阳至秭归段17个点的表层沉积物样品并测定其RIS含量。结果表明: 与其他湖泊、河流相比,三峡库区表层沉积物RIS含量较低,其中,AVS的含量为0.06~0.65 μmol/g,S⁰为0.50~1.66 μmol/g,S_py为0.96~17.54 μmol/g. AVS和S⁰含量夏季高于冬季,云阳至秭归段RIS变化趋势大致为先降低后增加再降低,有较明显的季节和地域差异。相关性分析、主成分分析和聚类分析表明,研究区沉积物生物可利用磷(BAP)、Fe_HR及上覆水体SO^2-₄含量为沉积物RIS的主要限制因子。库区冬季RIS与有机磷(Org-P)和可交换态磷(Ex-P)呈显著相关性,当硫化物含量增加时,会促进Org-P的矿化分解和Ex-P向上覆水体迁移,增加释磷风险。同时,本研究从硫驱动富营养化的角度评估了三峡库区存在污染风险的水域。除库区内已发生过典型水华的重点支流外,长滩河和九畹溪也存在富营养化问题。;Reduced inorganic sulfur (RIS) includes acid volatile sulfur (AVS) formed from sulfate reduction products and reactive iron (Fe_HR), elemental sulfur (S⁰), an intermediate product of sulfur, and pyrite sulfur (S_py), the ultimate accumulation material of elemental sulfur and iron in sediments. RIS can affect not only the biological effectiveness of sediment heavy metals, but also control the geochemistry of biogenic elements such as iron reduction and release of endogenous phosphorus behavior. In order to study the distribution characteristics of RIS in the sediments of the Three Gorges Reservoir area and its environmental significance, surface sediment samples were collected from 17 points in the section from Yunyang to Zigui in the Three Gorges Reservoir area in July-August and December 2017, and the RIS content was measured. The results showed that, compared with other lakes and rivers, the RIS content of surface sediments in the Three Gorges Reservoir area was lower, with AVS content ranging from 0.06 to 0.65 μmol/g, S⁰ from 0.50 to 1.66 μmol/g, and S_py from 0.96 to 17.54 μmol/g. The AVS and S⁰ contents are higher in summer than in winter, and the trend of RIS in the section from Yunyang to Zigui is roughly decreasing, then increasing and then decreasing, with obvious seasonal and regional difference. Correlation analysis, principal component analysis and cluster analysis showed that bioavailable phosphorus (BAP), Fe_HR and SO^2-₄ content in the overlying water were the main limiting factors of sediment RIS in the study area. The winter RIS in the reservoir area was significantly correlated with organic phosphorus (Org-P) and exchangeable phosphorus (Ex-P), and when the sulfide content increased, it promoted the mineralized decomposition of Org-P and the migration of Ex-P to the overlying water column, increasing the risk of phosphorus release. Meanwhile, this study assessed the waters at risk of pollution in the Three Gorges Reservoir area from the perspective of sulfur-driven eutrophication. In addition to the key tributaries in the reservoir area where typical water blooms have occurred, the Changtan River and Jiuwan River also have eutrophication problems.

Research Progress on the Treatment of High-Concentration Nitrogen and Phosphorus Wastewater by Struvite Precipitation

Aiming at the problems of eutrophication of water bodies and the shortage of phosphorus resources, the struvite method for treating high-concentration nitrogen and phosphorus-containing wastewater has been widely used because of its high efficiency and low consumption. This paper summarizes the research progress on the treatment efficiency, influencing factors and stability of high concentration nitrogen and phosphorus mixed wastewater in recent years, and on this basis, the feasibility and development prospect of MAP method in the treatment of high concentration nitrogen and phosphorus wastewater are proposed.

Study on water quality simulation and dynamic water environment capacity of Helan County section of the third drainage ditch in Ningxia

The Helan section of the third drainage ditch in Ningxia is selected as the research object, and its water environmental capacity is analyzed; The Daily discharge and water level are calculated according to the measured data; Then the daily concentration values of the main water quality indexes are simulated by one-dimensional hydrodynamic water quality mathematical model; Finally, the dynamic water environment capacity is calculated. The results show that from May to October 2020, the main water quality indicators exceeding the standard in Helan section of the third drainage ditch were total nitrogen and five-day biochemical oxygen demand. Their water environmental capacity was −11.8744 t and −67.1173 t, respectively. Chemical oxygen demand and total phosphorus exceeded the standard severely in some months. There are problems of eutrophication and high organic content in drainage ditches. The primary pollution sources are aquaculture wastewater form fishery, farmland drainage, seasonal flood, and domestic sewage. It is suggested to take preventive measures such as source control, process blocking, and end treatment.

Evaluating the eutrophication risk of artificial lagoons–case study El Gouna, Egypt

Eutrophication problem in El Gouna shallow artificial coastal lagoons in Egypt was investigated using 2D TELEMAC-EUTRO-WAQTEL module. Eight reactive components were presented, among them dissolved oxygen (DO), phosphorus, nitrogen, and phytoplankton biomass (PHY). The effect of warmer surface water on the eutrophication problem was investigated. Also, the spatial and temporal variability of the eutrophication was analyzed considering different weather conditions: tide wave, different wind speeds and directions. Moreover, effect of pollution from a nearby desalination plant was discussed considering different pollution degrees of brine discharge, different discharge quantities and different weather conditions. Finally, new precautions for better water quality were discussed. The results show that tide wave created fluctuations in DO concentrations, while other water quality components were not highly influenced by tide’s fluctuations. Also, it was found that high water temperatures and low wind speeds highly decreased water quality producing low DO concentrations and high nutrients rates. High water quality was produced beside inflow boundaries when compared to outflow boundaries in case of mean wind. Moreover, the results show that the average water quality was not highly deteriorated by the nearby desalination operation, while the area just beside the desalination inflow showed relatively strong effects. Different weather conditions controlled the brine’s propagation inside the lagoons. Moreover, increasing the width of the inflow boundaries and injecting tracer during tide and mean wind condition are new precautions which may help to preserve the water quality in a future warmer world. This study is one of the first simulations for eutrophication in manmade lagoons.

Collective management of environmental commons with multiple usages: A guaranteed viability approach

In this paper we address the collective management of environmental commons with multiple usages in the framework of mathematical viability theory. We consider that stakeholders can derive from the study of their specific socioeconomic problem (i) the variables describing the different usage of the commons and its evolution (ii) and a representation of the desirable states for the commons. We then consider the guaranteed viability kernel, subset of the set of desirable states where it is possible to maintain the state of the commons even when its evolution is represented by several conflicting models. This approach is illustrated on a problem of lake eutrophication.

In situ remediation mechanism of internal nitrogen and phosphorus regeneration and release in shallow eutrophic lakes by combining multiple remediation techniques

Large anthropogenic inputs of N and P alter the nutrient cycle and exacerbate global eutrophication problems in aquatic ecosystems. This study in Lake Datong, China, investigates the remediation mechanism of multiple remediation technique combinations (dredging, adsorbent amendment, and planting aquatic vegetation) on sediment N and P loads based on two high-resolution sampling techniques (HR-Peeper and DGT) and P sequential extraction procedures. The results showed that high temperature and low dissolved oxygen considerably enhanced pore water dissolved reactive P (DRP) and NH4+ concentrations attributable to abundant Fe-P and organic matter content in the sediment. Fe reduction is critical for regulating pore water DRP release and promoting N removal. Overall, for Lake Datong, combining multiple remediation techniques is more effective in controlling sediment P loads (pore water DRP, P fluxes, forms of P, and labile P), from a long-term perspective, than a single remediation. Lanthanum-modified bentonite (LMB) inactivation treatment can transfer mobile P in the surface sediment into more refractory forms over time, thereby reducing the risk of sediment labile P release. However, it is difficult to effectively remediate internal P loads owing to inappropriate dredging depths and low biomass of aquatic vegetation. Future lake restoration practices should optimize the selection of different remediation technique combinations based on internal N and P pollution characteristics, while reducing external wastewater input. These results are important for understanding the remediation mechanisms of internal N and P and provide suggestions for sediment management of shallow eutrophic lakes.

Efficient phosphate elimination from aqueous media by La/Fe bimetallic modified bentonite: Adsorption behavior and inner mechanism

Nowadays, eutrophication problem in surface waterbodies has attracted specific attention. Herein, we reported facile synthesis and application of La/Fe engineered bentonite (LFB) for efficient phosphate elimination. Results indicated that bimetallic modified LFB composite could achieve efficient phosphate removal at pH 2–6, and satisfactory selectivity was implied by stable phosphate capturing within the interference of competing species (Cl−, NO3−, HCO3−, SO42−, F− and HA). Pseudo-second-order model could satisfactorily depict the kinetic behavior at different initial concentrations, indicating chemisorption of phosphate on LFB surface. Isotherm study suggested that phosphate adsorption behavior could be fitted well with Sips isotherm equation, indicating that both homogeneous monolayer adsorption and heterogeneous multilayer coverage of phosphate on LFB surface occurred within the investigated conditions. Adsorption thermodynamics implied the spontaneous and endothermic feature of phosphate loading on LFB composite. Characterization analysis confirmed successful La and Fe loading on bentonite, and electrostatic attraction and ligand exchange were the main adsorption mechanism. The high adsorption capacity, cost-effective feature and strong affinity towards phosphate demonstrated certain potential of as-prepared LFB composite for phosphate separation from eutrophic water.

Environmental impact bonds as a transformative policy innovation: Frames and frictions in the construction process of the Nutrient-EIB

Impact bonds have emerged as a policy innovation with the potential to change public policies towards being more outcome-based and pre-emptive – and more effective in answering sustainability challenges. This financial instrument has been used for social problems and only recently for environmental issues. One example is the Nutrient-EIB (environmental impact bond) which is in preparation to be implemented in Southwest Finland. We study involved stakeholders’ framings of the Nutrient-EIB's potential for solving problems of eutrophication of the Baltic Sea and the lock-in situation of recycled fertiliser development. Based on stakeholder interviews, we identify three interpretative frames: applying the impact investing logic, challenging agri-environmental policy, and extending experimental policy-making. We recognise frictions between the frames regarding the required knowledge base and scale. We discuss how visions of transformative outcomes may challenge each other and what kinds of barriers transformative policy innovations may face.

Removal mechanisms of phosphate from water by calcium silicate hydrate supported on hydrochar derived from microwave-assisted hydrothermal treatment

The discharge of phosphorus in water has led to the problems of eutrophication and waste of phosphorus resources. Here, calcium silicate hydrate supported on hydrochar derived from microwave-assisted hydrothermal treatment (w-CH/CSH) was developed for phosphate removal. The characterizations of w-CH/CSH were examined through scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometer, and specific surface area analyzer. Batch adsorption experiments were conducted to identify the adsorption characteristics of phosphate onto w-HC/CSH. Results showed that the best w-HC/CSH adsorbent was successfully prepared. The CSH was uniformly distributed on the hydrochar surface and the specific surface area (SSA BET ) of w-HC/CSH increased to 98.76 m 2 /g. The phosphate adsorption was governed by chemisorption on heterogeneous surfaces and could be better fitted by the pseudo-second-order and Freundlich model. The film diffusion and intraparticle diffusion were the rate-limiting process of phosphate adsorption. The underlying mechanisms were mainly attributable to the surface microprecipitation including Ca 3 (PO 4 ) 2 , Ca 8 H 2 (PO 4 ) 6 , Ca( H 2 PO 4 ) 2 , CaHPO 4 and Ca 5 (PO 4 ) 3 Cl, and the ligand exchange with the CaCO 3 and oxygen-containing functional groups. • Porous w-HC/CSH was prepared by microwave-assisted hydrothermal treatment. • Adsorption was better fitted by pseudo second order and Freundlich model. • Film diffusion and intraparticle diffusion governed the phosphate adsorption process. • Surface microprecipitation and ligand exchange were the main mechanisms of phosphate removal.

“Why Has the Water Turned Green?” A Problem of Eutrophication in Primary School

This paper analyses how 224 students from the fifth and sixth grade recognise the key aspects, i.e., the causes, consequences, and solutions of the eutrophication problem affecting the relevant ecosystem in their region. Two instruments were used: a report sheet in which students work through the causes and consequences associated with the problem; and a personal letter addressed to the competent authority, which proposes solutions. The results show that students from the sixth grade recognised more complete interconnections between the agricultural development of the area and the changes that occurred in the ecosystem. In the identification of the key phases of the eutrophication process, students from both courses presented similar difficulties. Regarding the solutions, some reluctance was observed to limit agricultural activity. This reveals that students’ social perceptions about the importance of agriculture for their region may be a possible influence on their solutions. Finally, five models were established regarding the understanding that students reach of the problem as a whole. More than half of students were included in the same model, comprising those who were able to adequately identify the causes and whole process of eutrophication, as well as those who defended the advantages of the proposed solution. Educational implications are discussed in this paper.

Analysis of the eutrophication in a wetland using a data-driven model.

Eutrophication is a major problem in the international Anzali wetland (northern Iran). The present research initially aimed to determine the trophic state index (TSI) in ten sampling sites in the main parts of the Anzali wetland (western, eastern, central, and Siahkeshim parts). After determining the TSI in the wetland, a data-driven method (classification tree model with a J48 algorithm) was implemented to predict the trophic condition in the wetland based on a set of water quality and physical-structural variables. One hundred twenty samples related to chlorophyll-a (the model's output) and environmental variables (the model's inputs) were measured monthly during 1-year study period (2017-2018). Based on the TSI calculation, the western, Siahkeshim, eastern, and central parts of the wetland are classified as eutrophic, super-eutrophic, hyper-eutrophic, and hyper-eutrophic, respectively. When all environmental variables were introduced to the model (with five-time randomization effort, pruning confidence factor = 0.01, and seven-fold cross-validation), eight variables (bicarbonate, pH, water temperature, electric conductivity, dissolved oxygen, total phosphorus, water depth, and water turbidity) were predicted by the model. The model predicted that an increase in total phosphate, water turbidity, and electric conductivity concentration may contribute to the hyper-eutrophic state of the wetland. In contrast, the hyper-eutrophic of the wetland is associated with a decrease in water depth, dissolved oxygen, and pH concentration. According to ANOVA test, the trophic condition in the wetland can be affected by spatial and temporal patterns. Anthropogenic pressures such as the influx of chemicals particularly the nutrients (phosphorus and nitrogen) are the main cause of water enrichment (eutrophication problem) in main parts of the Anzali wetland ecosystem.

Magnesium chloride-modified potassium humate-based carbon material for efficient removal of phosphate from water

BackgroundTo solve the problem of eutrophication caused by phosphate, a metal-loaded biocarbon composite material is considered to be an effective adsorbent for removing phosphate. MethodsIn this study, potassium humate was used to prepare modified potassium humate-based carbon material (MPHCM) through magnesium chloride modification and rapid pyrolysis. Significant findingsStudies have shown that MPHCM can effectively remove phosphate from water. At 318 K and with pH=3, the maximum adsorption capacity reached 181.96 mg P g−1, and the adsorption process conformed to the pseudo-first and pseudo-secondary adsorption kinetic models and the Langmuir adsorption model. This adsorption process involved physical and chemical adsorption, which indicated monolayer adsorption. The main adsorption mechanisms for MPHCM were protonation, electrostatic interactions, ligand exchange and inner sphere complex precipitation. Six desorption cycles verified the excellent reproducibility of MPHCM for phosphate removal. Therefore, this study provides a new adsorbent for phosphate removal and expands the application range of potassium humate-based carbon materials.

Industrial steel waste-based adsorbent: An effective phosphate removal from aqueous media

This work offers the alternative to mitigate the problem of eutrophication of water bodies that can result in a serious threat to environment and aquatic life by using steel wastes for phosphate removal. Produced on the scale of thousands of tons per year, these wastes can contribute to air, soil, and water pollution when discharged without a proper management. In this context, this work evaluates the potential of phosphate remediation by adsorption applying steel industry wastes, addressing two important environmental problems at once. For the first time, blast furnace sludge (BFS) and the powder from Kanbara reactor (KR) without pre-treatment were used for the elucidation of the removal mechanism of phosphate, employing the method of sequential extractions, kinetic studies, and thermodynamics. The chemical and structural analyses demonstrated the materials present an irregular morphology with most of the pores in the mesopore range being mainly composed by alkali metals and metal oxides. Although approximately 99% of phosphate removal efficiency was reached for both wastes in 24 h, the speciation studies showed phosphate and KR interacts too strongly making its reuse hardly feasible and therefore not suitable from a practical point of view. For BFS, on the contrary, the thermodynamic data indicated a physisorption process offering the advantage of reutilization. In addition, about 97% of phosphate removal is achieved during the first 10 min of adsorption, regardless the solution pH, thus offering good prospects in aggregating value to steel industry wastes as adsorbents being in line with a sustainable economy.

Remote sensing of chlorophyll-a concentrations in coastal oceans of the Greater Bay Area in China: Algorithm development and long-term changes

Extensive human activities and climate change in recent decades have triggered severe eutrophication problems in the coastal oceans in the Greater Bay Area (GBA) of China. However, a comprehensive characterization of the spatial and temporal patterns of chlorophyll-a (Chl-a, a major indicator of phytoplankton biomass) in this region is not available. Our study attempts to fill this gap by using long-term satellite observations. With massive in situ datasets from underway sampling systems, we developed a novel hybrid Chl-a retrieval algorithm combining the recalibrated OC3 and line-height-based (BL443) algorithms for waters with different turbidity levels. Satellite-retrieved Chl-a values with the hybrid algorithm agreed well with in situ measurements, with an uncertainty level of 33.8 %. Long-term analysis revealed significant decreasing trends over the inner Pearl River Estuary (averaged at 0.054 μg/L yr−1), while significant increasing trends were found in eastern Daya Bay (averaged at 0.035 μg/L yr−1). The developed algorithm is expected to aid routine Chl-a monitoring in the adjacent oceans of the GBA, and the long-term datasets here can serve as critical information for further coastal conservation and management efforts.

Estimation of nutrient loads with the use of mass-balance and modelling approaches on the Wełna River catchment example (central Poland)

Nitrogen and phosphorus budgeting is considered to be a key tool for policy makers and stakeholders when dealing with nutrient contamination issues, however no unified method has been employed in countries affected by this eutrophication problem. The current study offers a detailed insight into the estimations of nutrient loads and their distribution between different sources for a middle-sized agricultural catchment, with the use of two approaches: mass balance (static) and modelling (dynamic). Both methods revealed similar contributions of analysed nutrient sources, although the final estimates in the chosen calculation profile were divergent due to the various reasons related to the methods’ specificity. The advantages and disadvantages of both approaches have been specified in our study, and a hybrid solution on a local and country wide scale has been proposed.

Removal of Phosphate from Wastewater with a Recyclable La-Based Particulate Adsorbent in a Small-Scale Reactor

It is crucial to develop an effective and easily recoverable phosphate absorbent for the control of eutrophication problems in polluted rivers. In this study, a stable particulate adsorbent with a diameter of 5 mm synthesized from lanthanum, activated carbon, and zeolite (La-CZ) was developed, characterized, and tested for the removal of phosphate from wastewater in a small-scale reactor, which was designed to easily recycle La-CZ with a basket. Batch studies showed that La-CZ could reach adsorption equilibrium within 2 h and the maximum phosphate sorption capacity was 18.2 mg g−1. The experimental data showed good compliance with the Langmuir isotherm model and pseudo-second-order kinetic model, implying that chemisorption dominates the phosphate uptake process. La-CZ exhibited a stable adsorption capacity over a wide pH range (3–7), while the adsorption capacity decreased slightly under alkaline conditions. Although Nitrates (NO3−) and Carbonate (CO32−) had some effects, normal coexisting ions such as Chloride (Cl−), Sulfate (SO42−), and Fluorine (F−) had no significant effects on the phosphate adsorption capacity of La-CZ. The main form of phosphate removed from the reaction system was HCl-P (77.68%), as determined through phosphorus fractionation. In particular, this study designed a replaceable filler-type reactor integrating a reflux and aeration system, 98.8% of phosphorus could be removed from actual wastewater, and La-CZ could be reclaimed easily. This work provides an excellent reference for particulate adsorbents that can efficiently remove phosphate in practical applications in the future.

Al2O3/Fe3O4/ZrO2 ternary oxide sorbent: Synthesis, characterization and sorption behavior to fluoride and phosphate ions from aqueous solution

ABSTRACT. Excess quantities of fluoride and phosphate in water bodies can lead to fluorosis and eutrophication problems, respectively. In search of a promising adsorbent targeting these ions, Fe3O4/Al2O3/ZrO2 ternary oxide was synthesized via co-precipitation method and characterized by X-ray diffraction (XRD), Fourier transform-infrared (FTIR) and Brunauer-Emmer-Teller (BET). Its specific surface area was found to be 205 m2/g. The effects of solution pH, adsorbent dose, contact time, agitation speed and initial fluoride and phosphate concentrations were also investigated and the optimum values were 4, 0.5 g, 12 h, 100 rpm and 20 mg/L, respectively, for fluoride and 5, 0.1 g, 8 h, 100 rpm and 10 mg/L, respectively, for phosphate. Fluoride and phosphate adsorptions fitted well with Freundlich and Langmuir isotherm models, respectively and their kinetic data correlated well with the pseudo-second order model. Desorbability study revealed that maximum desorption was achieved at pH 12. Thermodynamics study on the other hand showed that adsorption of fluoride was nonspontaneous and endothermic whereas that of phosphate was spontaneous and exothermic. Application on real water sample decreased the concentration of fluoride from 4.92 to 1.97 mg/L in ground water and phosphate from 1.7 to 0.35 mg/L lake water showing its potential as a promising adsorbent.
 
 KEY WORDS: Adsorption, Fluoride, Phosphate, Ternary oxide sorbent, Isotherm models
 
 Bull. Chem. Soc. Ethiop. 2022, 36(3), 555-569. 
 DOI: https://dx.doi.org/10.4314/bcse.v36i3.6 

Phosphorous remediation using alginate/glomalin biobeads: Examining structural cohesivity, nutrient retention, and reapplication viability

Excess nutrient loading from agriculture and urban runoff into limnetic and marine ecosystems is associated with harmful algal blooms that result in eutrophication. Sequestration of nutrients such as phosphorus (P) and nitrogen (N) from agricultural outflows and recycling them as soil amendments would be an environmentally and economically sustainable strategy to alleviate this problem. This study explored the use of biobeads constructed with phytoplankton, Chlorella vulgaris, alginate and glomalin as a possible medium for a cyclic culture-harvest-reapply (CHR) system to address the problem of eutrophication. These “biobeads” were constructed from different concentrations of sodium alginate, C. vulgaris, and glomalin. Bead vitality was evaluated by introducing C. vulgaris to both eutrophic (phosphate ∼1.5 ppm) and hypereutrophic (phosphate ∼4.0 ppm) solutions and measuring phosphate removal. After 9 days in the eutrophic solution, biologically active groups reduced orthophosphate concentrations by an average of 1.35 ppm (80%). In the hypereutrophic solution, an average of 1.52 ppm total phosphate removal (38%) was observed over 5 weeks. The addition of glomalin in high concentrations increased the structural cohesivity of the hydrogel matrix, while low concentrations had an inverse effect. Reapplication of these biobeads to topsoil did not reduce plant growth or plant health parameters. These data suggest that glomalin, in appropriate proportions, is a suitable secondary scaffolding for a sodium alginate hydrogel immobilization medium. The alginate beads of immobilized C. vulgaris could be a promising treatment technique for phosphorus-containing urban wastewater. Further research is warranted to assess long-term impacts on nutrient dispersal and soil quality upon reapplication.