The aggregation of clay minerals and marine microalgal cells : physicochemical theory and implications for controlling harmful algal blooms

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2001In recent years, the use of clay minerals has emerged as one of the most promising strategies for directly controlling harmful algal blooms (HABs). Its principle is based on the mutual aggregation of algal cells and mineral particles, leading to the formation of large flocs that rapidly settle to the ocean floor. This work investigated the effectiveness of various domestic clays against a number of bloom-forming species from the United States. Twenty-five clays were tested against the dinoflagellate, Karenia brevis (formerly Gymnodinium breve), and the chrysophyte, Aureococcus anophagefferens. In general, the highest removal efficiencies (RE > 90% at 0.25 g rl of clay) against K. brevis were found using montmorillonite, bentonite and phosphatic clays (i.e. a product of phosphate mining containing large amounts of montmorillonite). The RE of phosphatic clays remained high (> 80%) even at 0.03 g rl. Kaolinite and zeolite were mostly ineffective against K. brevis. Removal with clay exceeded those for alum, polyaluminum chloride (PAC) and several other polymeric flocculants by a factor of two. However, the combination of phosphatic clay and PAC (at 5 mg rl) decreased the amount of clay needed to maintain 80% RE by one order of magnitude. Cell viability and recovery remained high when clay loading stayed below 0.03 g rl with or without resuspension of the sediment. However, cell mortality approached 100% with 0.50 g rl even with daily resuspension. Between 0.10 and 0.25 g rl, K. brevis survival and recovery depended on the interplay of clay loading, the frequency of resuspension, and duration of contact prior to the first resuspension event. For A. anophagefferens, the RE did not exceed 40% for any clay at 0.25 g rl even in combination with coagulants and flocculants. The highest removal was achieved by thoroughly mixing the clay slurry (e.g. phosphatic clay) into the cell culture. The RE by phosphatic clay varied significantly in a survey consisting of 17 different species from five algal classes. Moreover, the removal trends varied substantially with increasing cell concentration. For example, cell removal increased with increasing clay loading and cell concentration for K. brevis. However, RE dropped below 70% when cell concentration was < 1000 cell ml-1 for clay loadings up to 0.50 g rl. This suggested that a critical number of organisms should be present for clays to remain effective. Similarly, enhanced removal with increasing cell concentration was also found in Akashiwo sanguinea (formerly Gymnodinium sanguineum), Heterosigma akashiwo and Heterocapsa triquetra. In the six remaining species, RE initially increased then decreased, or RE remained constant as more cells were treated. The removal pattern among the species at comparable cell numbers did not correlate with the cross-sectional area (R2 = 0.23), swimming speed (R2 = 0.04), or a type of cell covering (i.e. theca, silica frustule). However, when the total collision frequency coefficients were calculated (including collisions due to cell motility) over the interval when clays were < 50 μm, these values correlated well with the empirical RB's for the flagellated species (R2 = 0.90). These results suggested that collisions due to cell motility may be important during the early stages of aggregation when clay sizes are relatively small (i.e. near the surface where the clay layer is initially added). The electrophoretic mobility (EPM) of marine microalgae displayed a small range of negative values. While the values were smaller that those reported from freshwater species, these results confirmed earlier assumptions that marine species carry a negative charge like their freshwater counterparts. In addition, these results also revealed that the stabilities of cell suspensions in seawater are not controlled by charge neutralization. However, these measurements did not provide direct information on why one species was more readily removed over another by a given clay mineral (e.g. phosphatic clay). The EPM of clays in freshwater also exhibited predictable negative values, with montmorillonites showing the highest stability and phosphatic clays the lowest. Kaolinite and zeolite displayed a range of intermediate values. These differences vanished when the clays were suspended in natural seawater (29.6 salinity), reducing the surface charge to a small range of negative values. This effect occurred even at 1116 of the final salinity (1.85 salinity). Viewed alone, these results did not provide direct information on why one clay mineral worked better than another against a given algal species (e.g. K. brevis). Kinetic and modelling experiments using K. brevis and three minerals revealed some distinct patterns in aggregation and settling among the clays, including how they removed the organisms. After dispersing on the surface, phosphatic clays aggregated quickly by virtue of low stability (low EPM). Cell removal coincided with the onset of settling. Also, kaolinite aggregated quickly and was controlled by size as well as stability. However, cell removal followed clay settling over 40 min, after which cell removal decreased yielding only 46% RE. Bentonite aggregated slowly over 90 min due to its high stability (high EPM), but produced a number of large voluminous flocs that steadily removed the algae. The sinking rate of flocs increased as cells became incorporated, but the onset of settling was delayed when cells were present in phosphatic clay and kaolinite due to a predicted reduction in aggregate density. The process of kinetics and sedimentation were modelled using first order equations for all mineral-algae combinations. Finally, phosphatic clays demonstrated the ability to selectively remove K. brevis in a mixed culture with the dinoflagellate, Prorocentrum micans, or the diatom, Skeletonema costatum. While the RE's were generally comparable to individual cultures, the RE of either species increased in the presence of the other, especially for K. brevis. Similar results were observed in mesocosm studies using a natural assemblage during a Karenia bloom. In fact, the RE of K. brevis were higher than would be predicted from single species laboratory studies given its low initial concentration. Overall, this research demonstrated the effectiveness of clay treatment against a number of HAB species in the U.S. This work also provided new insights into the aggregation phenomenon between minerals and living algal cells by focusing on the physical (cell size), chemical and behavioral (i.e. motility) properties of both particle types, the effect of particle concentration, and the aggregation kinetics of the clay-algae system.This work has been funded by the following: EPA Grant CR827090, Florida Institute of Phosphate Research Grant 99-03-138, Florida Fish and Wildlife Conservation Commission, Contracts MR266, 99157 and Purchase Order No. S7701 615727, Sholley Foundation, and the Cove Point Foundation. Scholarships to the author were provided by the Ford Foundation, and the Education Office of the Woods Hole Oceanographic Institution

Modified local sands for the mitigation of harmful algal blooms

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Harmful Algae (2011): 381-387, doi:10.1016/j.hal.2011.01.003.A new method was developed for marine harmful algal bloom (HAB) mitigation using local beach sand or silica sand modified with chitosan and polyaluminum chloride (PAC). Untreated sand was ineffective in flocculating algal cells, but 80% removal efficiency was achieved for Amphidinium carterae Hulburt and a Chlorella sp. in 3 min (t80 = 3 min) using 120 mg L-1 sand modified with 10 mg L-1 PAC and 10 mg L-1 chitosan. After several hours 92% – 96% removal was achieved. The t80 for removing A. carterae using the modifiers only (PAC and chitosan combined) was 60 min and for Chlorella sp. 120 min, times which are much slower than with the corresponding modified sand. Sands were critical for speeding up the kinetic processes of flocculation and sedimentation of algal flocs. PAC was helpful in forming small flocs and chitosan is essential to bridge the small flocs into large dense flocs. Chitosan was also important in inhibiting the escape of cells from the flocs. Chitosan and PAC used together as modifiers make it possible to use local beach sands for HAB mitigation in seawater. Economical and environmental concerns could be reduced through the use of sands and biodegradable chitosan, but the potential impacts of PAC need further study.The research was funded by the National Key Project for Basic Research (2008CB418105, 2010CB933600). Support for DMA was provided by GOMTOX program through NOAA Grant NA06NOS4780245. Additional support came from NSF grant OCE-0430724, DMS-0417769 and NIEHS grant 1P50-ES01274201 (Woods Hole Center for Oceans and Human Health)

Using clay to control harmful algal blooms : deposition and resuspension of clay/algal flocs

Author Posting. © Elsevier B.V, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V for personal use, not for redistribution. The definitive version was published in Harmful Algae 4 (2005): 123-138, doi:10.1016/j.hal.2003.12.008.Harmful algal blooms (HABs) may be legitimate targets for direct control or mitigation, due to their impacts on commercial fisheries and public health. One promising control strategy is the rapid sedimentation of HABs through flocculation with clay. The objective of this study was to evaluate flow environments in which such a control strategy might be effective in removing harmful algae from the water column and depositing a layer of clay/algal flocs on the sea floor. We simulated the natural environment in two laboratory flumes: a straight-channel “17-m flume” in which flocs settled in a still water column and a “racetrack flume” in which flocs settled in flow. The 17-m flume experiments were designed to estimate the critical bed shear stress for resuspension of flocs that had settled for different time periods. The racetrack flume experiments were designed to examine the deposition and repeated resuspension of flocs in a system with tidal increases in flow speed. All flume runs were conducted with the non-toxic dinoflagellate Heterocapsa triquetra and phosphatic clay (IMC-P4). We repeated the experiments with a coagulant, polyaluminum hydroxychloride (PAC), expected to enhance the removal efficiency of the clay. Our experiments indicated that at low flow speeds (≤ 10 cm s-1), phosphatic clay was effective at removing algal cells from the water column, even after repeated resuspension. Once a layer of flocs accumulated on the bed, the consolidation, or dewatering, of the layer over time increased the critical shear stress for resuspension (i.e. decreased erodibility). Resuspension of a 2-mm thick layer that settled for 3 hours in relatively low flow speeds (≤ 3 cm s-1) would be expected at bed shear stress of ~0.06-0.07 Pa, as compared to up to 0.09 Pa for a layer that was undisturbed for 9 or 24 hours. For the same experimental conditions, the addition of PAC decreased the removal efficiency of algal cells in flow and increased the erodibility of flocs from the bottom. By increasing the likelihood that flocs remain in suspension, the addition of PAC in field trials of clay dispersal might have greater impact on sensitive, filter-feeding organisms. Overall, our experiments suggest that the flow environment should be considered before using clay as a control strategy for HABs in coastal waters.This project was funded by the Florida Institute of Phosphate Research (Grant # 99-03-138), with facilities provided by the Rinehart Coastal Research Center at WHOI

The importance of human dimensions research in managing harmful algal blooms

Author Posting. © Ecological Society of America, 2010. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Frontiers in Ecology and the Environment 8 (2010): 75–83, doi:10.1890/070181.Harmful algal blooms (HABs) are natural freshwater and marine hazards that impose substantial adverse impacts on the human use of coastal and marine resources. The socioeconomic and health impacts of HABs can be considerable, thereby making a case for “human dimensions” research to support HAB response. Human dimensions research is multidisciplinary, integrating social science, humanities, and other fields with natural science to enhance resource management by addressing human causes, consequences, and responses to coastal environmental problems. Case studies reported here illustrate the importance of human dimensions research. Incorporating such research into the scientific agenda – as well as into management decisions of public agencies concerned with natural resource management, environmental protection, and public health and welfare – requires the development of both strategic guidance and institutional capacity. The recent development of a multi-agency research strategy for HAB response and a strategic plan for human dimensions research represent two important steps in this direction.This paper was developed with partial support from NOAA’s National Centers for Coastal and Ocean Science

Parental Involvement and Its Effect on College Students’ Academic Motivation and Self-Concept

Parental involvement is one of the primary factors that affect children’s development and individuality. However, its effect on the academic motivation and self-concept of college students is not well understood, especially in the Philippines. The present study used the Ecological systems theory by Bronfenbrenner to investigate the effect of varying parental involvement on the academic motivation and self-concept of college students at Dr. Carlos S. Lanting College. Purposive sampling was used among 198 college students from Dr. Carlos S. Lanting College who were identified using a purposive sampling technique. Statistical instruments including descriptive, correlation, and regression analysis were used to examine the data collected and investigate the link between the variables. Based on the regression analysis, it was found that parental involvement only has a significant relationship with academic motivation and not with self-concept. In conclusion, college students have a sense of independence and their self-concept is not affected by parental involvement; nonetheless, parents providing essential support influence their academic motivation

Influence of zeta potential on the flocculation of cyanobacteria cells using chitosan modified soil

Using chitosan modified soil to flocculate and sediment algal cells has been considered as a promising strategy to combat cyanobacteria blooms in natural waters. However, the flocculation efficiency often varies with algal cells with different zeta potential (ZP) attributed to different growth phase or water conditions. This paper investigated the relationship between ZP of microcystis aeruginosa and its influence to the flocculation efficiency using chitosan modified soil. Results suggested that the optimal removal efficiency was obtained when the ZP was between -20.7 mV and -6.7 mV with a removal efficiency of more than 80% in 30 min and large floc size of > 350 μm. When the algal cells were more negatively charged than -20.7 mV, the effect of chitosan modified soil was depressed (< 60%) due to the insufficient charge density of chitosan to neutralize and destabilize the algae suspension. When the algal cells were less negative than -6.7 mV or even positively charged, small floc size (< 120 μm) were formed, which may be difficult to sink under natural water conditions. Therefore, manipulation of ZP provided a viable tool to improve the flocculation efficiency of chitosan modified soil and an important guidance for practical engineering of cyanobacteria blooms control

Cyanobacterial bloom mitigation using proteins with high isoelectric point and chitosan-modified soil

A new environmental friendly method was developed for cyanobacterial blooms mitigation using local lake shore soil modified by protein with high isoelectric point (pI) and chitosan jointly. Results suggested that 5 mg/L lysozyme (pI ≈ 11) and 100 mg/L bromelain (pI ≈ 9.5) modified 10 mg/L soil can both reduce the surface charge of microcystis aeruginosa, the dominant species forming cyanobacterial blooms, from -26 mv to -10 mv and remove 73% and 60% of algal cells in 30 min, respectively. The limited improvement of removal efficiency was due to the small flocs (< 60 μm) formed by charge neutralization, which need more than 90 min to settle in static condition. However, when the small flocs were linked and bridged by the other modifier, chitosan with long polymer chain, large flocs of about 800 μm and 300 μm were fomed and more than 80% of algal cells were removed in 5 min and 30 min by lysozyme-chitosan modified soil and bromelain-chitosan modified soil, respectively. The lower removal ability of bromelain-modified soil was due to the lower charge density leading to less powerful in destabilization of algal cells. Depending on the bi-component modification mechanism including charge neutralization of proteins with high pI and netting and bridging function of chitosan with long polymer chain, it is possible to flocculate cyanobacterial blooms in natural waters effectively using locally available materials

Amphoteric starch-based bicomponent modified soil for mitigation of harmful algal blooms (HABs) with broad salinity tolerance: flocculation, algal regrowth, and ecological safety

The treatment of harmful algal blooms (HABs) by in-situ flocculation is an emerging technology capable of efficiently removing HABs from natural waters. However, differences in salinity, pH and algal species in freshwaters and seawaters can influence the flocculation treatment. In this study, we developed a bicomponent modified soil using amphoteric starch (AS) and poly-aluminium chloride (PAC) in order to effectively flocculate microalgae under broad salinity conditions. Specifically, the impacts of water salinity (0–3.3%), pH (3–11), and algal species (Microcystis aeruginosa and marine Chlorella sp.) were investigated in order to evaluate efficiency, dosage and mechanisms of algae flocculation. The results showed that AS-PAC modified soils possessed excellent resistance to salinity change due to the anti-polyelectrolyte effect of AS, which contributed to 99.9% removal efficiency of M. aeruginosa in fresh and saline waters, and Chlorella sp. in marine water, respectively. The dosage of the flocculant modifier was only 10–20% of that of another proven modifier (i.e. Moringa oleifera), which substantially reduced the material cost. The high salinity tolerance of algal flocculation by the AS-PAC modified soil was attributed to the synergistic processes of charge neutralization and netting-bridging. Thus, this study has developed a universal flocculant and revealed fundamental mechanisms for the mitigation of HABs under broad salinity conditions