The mechanism of a new type of modified clay controlling Phaeocystis globosa growth

Phaeocystis globosa is a harmful algal bloom(HAB)species worldwide.Using modified clay(MC)to control HABs and to mitigate their adverse effects is currently a commonly used method in China.In this paper,the effects of oxidized composite modified clay(OXI-MC)on P.globosa were studied from different perspectives.The results show that the OXI-MC could effectively remove P.globosa and inhibit both the growth of residual algal cells and the formation of new colonies.The P.globosa algal biomass removal efficiencies after 3 h reached 90%at a dose of 0.1 g/L,and the number of colonies with different particle sizes was greatly reduced.Compared with those of the control,the superoxide dismutase(SOD)activity,catalase(CAT)activity,and malondialdehyde(MDA)content of the residual algae significantly increased,indicating that OXI-MC caused oxidative stress in the algal cells.In addition,we evaluated the effects of OXI-MC on the photosynthesis of residual microalgae and found that the maximal photochemical efficiency of photosystem II(PSII)under dark adaptation(F v/F m)and actual photochemical efficiency of PSII(ФPSII)decreased,severely damaging the photosynthesis efficiency,implying that OXI-MC effected the photosynthesis system of P.globosa.The results of this study clarify that OXI-MC could remove the most of algal cells and break up the colonies of P.globosa by collision,flocculation,and releasing active substances,as well as inhibit effectively the growth and colony formation of residual P.globosa by causing oxidative stress,reducing photosynthesis activity,accelerating the degradation of polysaccharides,and inhibiting the formation of colonies.

Flocculation of Ulva microscopic propagules using modified clay:a mesocosm experiment

Microscopic propagules of Ulva species(UMPs)spread on Subei Shoal are believed to play a significant role in the formation of the Yellow Sea green tide.Previous laboratory and ship-based studies indicated that modified clay(MC)can effectively remove UMPs from the water column and restrict their germination.To evaluate the effectiveness of this method under natural conditions,a mesocosm experiment was conducted on the Zhugensha sandbank on Subei Shoal.The results show that the suspended particles on the sandbank would partially disturb the flocculation process between the MC and UMPs.However,the MC at a proper dose could effectively remove UMPs from the water column and decrease the adhesion and germination of UMPs on the nylon ropes that comprised the mariculture rafts by>75%.This method was proven a potential strategy to restrict the initial biomass accumulation of green algae on Subei Shoal.However,field trials in larger time-space scales are still needed to assess the efficiency of this method when used in the open sea.

Removal of astrazon golden yellow 7GL from colored wastewater using chemically modified clay

Chemically modified clay(CMC) was used as an adsorbent for the removal of Astrazon Golden Yellow 7GL(AGY-7GL), which is a basic dye from wastewater. For this purpose, the chemically modified clay was first characterized by determining zero point of charge(p Hzpc), and using BET, SEM and FTIR. Then effects of operational parameters on adsorption of AGY-7GL were studied in a batch system. The effect of various parameters such as contact time(0-180 min), pH(2-8), temperature(293-323 K), CMC concentration(0.075-0.5 mg/L) and initial AGY-7GL concentration(75-250 mg/L) were investigated on the adsorption efficiency and capacity adsorption of CMC for the removal of AGY-7GL. Thermodynamic and kinetic parameters were calculated from the results of the adsorption experiment. The evaluation of kinetic models shows that this data best fits the pseudo-second-order model. It is determined that the adsorption equilibrium data works very well with the nonlinear Freundlich isotherm model. Thermodynamic parameters such as ?H^0(19.0 k J/mol), ?G^0(-28.8 k J/mol) and ?S^0(0.148 k J/mol) were also determined. According to the experimental results, it is concluded that CMC could be used as an alternative low cost potential adsorbent for the removal of AGY-7GL from wastewater.

Modelling of the elastoplastic behaviour of the bio-cemented soils using an extended Modified Cam Clay model

An elastoplastic constitutive model based on the Modified Cam Clay(MCC)model is developed to describe the mechanical behaviour of soils cemented via microbially induced calcite precipitation(MICP).It considers the increase of the elastic stiffness,the change of the yield surface due to MICP cementation and the degradation of calcium carbonate bonds during shearing.Specifically,to capture the typical contraction-dilation transition in MICP soils,the original volumetric hardening rule in the MCC model is modified to a combined deviatoric and volumetric hardening rule.The model could reproduce a series of drained triaxial tests on MICP-treated soils with different calcium carbonate contents.Further,we carry out a parametric study and observe numerical instability in some cases.In combination with an analytical analysis,our numerical modelling has identified the benefits and limitations of using MCCbased models in the simulation of MICP-cemented soils,leading to suggestions for further model development.

Programmed cell death induced by modified clay in controlling Prorocentrum donghaiense bloom

Modified clay(MC),an effective material used for the emergency elimination of algal blooms,can rapidly reduce the biomass of harmful algal blooms(HABs)via flocculation.After that,MC can still control bloom population through indirect effects such as oxidative stress,whichwas initially proposed to be related to programmedcell death(PCD)at molecular level.To further study theMC induced cell death in residual bloom organisms,especially identifying PCD process,we studied the physiological state of the residual Prorocentrum donghaiense.The experimental results showed that flocculation changed the physiological state of the residual cells,as evidenced by growth inhibition and increased reactive oxygen species production.Moreover,this research provides biochemical and ultrastructural evidence showing that MC induces PCD in P.donghaiense.Nuclear changes were observed,and increased caspase-like activity,externalization of phosphatidylserine and DNA fragmentation were detected in MC-treated groups and quantified.And the mitochondrial apoptosis pathway was activated in both MC-treated groups.Besides,the features of MC-induced PCD in a unicellular organism were summarized and its concentration dependent manner was proved.All our preliminary results elucidate the mechanism through which MC can further control HABs by inducing PCD and suggest a promising application of PCD in bloom control.

Numerical Modeling of the Behaviour of a Road Structure on Compressible Soil: Case of the Road Section at the Beau-Rivage-Djassin Intersection

This document presents a study of the behaviour of a pavement structure on compressible soil and the evaluation of its durability. The objective of this study is to highlight the impact of taking into account the non-linear elastic behaviour of soils and granular materials in the design process. To this end, a numerical modelling of the pavement of the beau-rivage-Djassin crossroads section in Porto-Novo was carried out, based on a compressible soil whose behaviour will be considered elastoplastic. The subgrade soil on the section is made up of several sub-layers. The layer of soft, highly plastic clay was modelled according to a modified Cam Clay behaviour, a model of swelling clay soils. The fine sand layer and the granular layers of the structure are modelled according to Mohr-Coulomb behaviour. The loading is considered to be uniformly distributed according to the assumptions of the Burmister model in the French standard. A first verification with ALIZE allowed to validate the structure on the basis of the rutting deformation at the head of the platform εz = 359.6*10-6 which remains lower than the admissible deformation εz,adm = 360*10-6. The numerical calculation was carried out using the finite element method, the code of which is implemented under the PLAXIS v21 software. A comparative study with the results of the ALIZE design revealed that the numerically calculated strains εz = 585*10-6 are higher than those of ALIZE. These numerical strains, which are higher than the elastic strains, do not meet the validation criteria that the strains under loading must remain below the allowable strains. An evaluation of the pavement durability was carried out and it was found that the pavement would only last under traffic for 3 years before the first fatigue deformations appeared.

In situ stabilization of arsenic in soil with organoclay,organozeolite,birnessite,goethite and lanthanum-doped magnetic biochar

Arsenic(As)is a known carcinogen and naturally occurring semi-metal in soils and in the Earth's crust.Contamination of soils and water with As poses a serious threat to millions of people worldwide due to its health hazards and toxicological properties.Hence,devising novel and efficient methods for remediation of contaminated areas has attracted a great deal of interest across the globe.In this study,we investigated the usefulness of synthetic birnessite,goethite,hexadecylpyridinium chloride-modified montmorillonite(HDPC-M),hexadecylpyridinium bromide-modified zeolite(HDPB-Z),and lanthanum(La)-doped magnetic biochar produced from eucalyptus bark(La-Euchar)as adsorbents at 10%dosage for As stabilization in a soil spiked with 1000 mg kg^(-1)As.The effectiveness of the above adsorbents in As immobilization in soil was assessed using single-step extractions with 2 mol L^(-1)HNO_(3)and deionized water,the simplified bioaccessibility extraction test(SBET)method,and sequential extraction with the modified Community Bureau of Reference(BCR)method.Application of the adsorbents shifted the exchangeable fraction of As to more recalcitrant fractions and dramatically reduced the exchangeable fraction by 6%-99%and the extractable amounts with HNO_(3),deionized water,and SBET method by 30%-92%,17%-95%,and 12%-90%,respectively,compared to the unamended control.The immobilizing effects of adsorbents on As decreased in the sequence of birnessite>La-Euchar>goethite>HDPB-Z>HDPC-M.Birnessite exhibited great affinity for As and drastically reduced As extractability by more than 90%in all single extractions.The results revealed that HDPC-M,HDPB-Z,La-Euchar,birnessite,and goethite are promising immobilizing agents for in situ stabilization of As in terrestrial environments.

Profiles of and variations in aluminum species in PAC-MC used for the removal of blooming microalgae

Polyaluminum chloride modified clay(PAC-MC)is a safe and efficient red tide control agent that has been studied and applied worldwide.Although it is well known that the distribution of hydrolytic aluminum species in PAC affects its flocculation,little is known about the influence of particulars aluminum species on the microalgae removal efficiency of PAC-MC;this lack of knowledge creates a bottleneck in the development of more efficient MCs based on aluminum salts.The ferron method was used in this study to quantitatively analyze the distributions of and variations in different hydrolytic aluminum species during the process of microalgae removal by PAC-MC.The results showed that Ala,which made up 5%–20%of the total aluminum,and Alp,which made up 15%–55%of the total aluminum,significantly affected microalgae removal,with Pearson’s correlation coefficients of 0.83 and 0.89,respectively.Most of the aluminum in the PAC-MC sank rapidly into the sediments,but the rate and velocity of settlement were affected by the dose of modified clay.The optimal dose of PAC-MC for precipitating microalgae was determined based on its aluminum profile.These results provide guidance for the precise application of PAC-MC in the control of harmful algal blooms.