Dewatering of microalgal cultures : a major bottleneck to algae-based fuels

Microalgae dewatering is a major obstruction to industrial-scale processing of microalgae for biofuel prodn. The dil. nature of harvested microalgal cultures creates a huge operational cost during dewatering, thereby, rendering algae-based fuels less economically attractive. Currently there is no superior method of dewatering microalgae. A technique that may result in a greater algal biomass may have drawbacks such as a high capital cost or high energy consumption. The choice of which harvesting technique to apply will depend on the species of microalgae and the final product desired. Algal properties such as a large cell size and the capability of the microalgae to autoflocculate can simplify the dewatering process. This article reviews and addresses the various technologies currently used for dewatering microalgal cultures along with a comparative study of the performances of the different technologies.

Spirulina (Spirulina platensis) algae supplementation increases microbial protein production and feed intake and decreases retention time of digesta in the rumen of cattle

Cattle consuming pastures low in protein have low liveweight gain due to low rumen degradable protein (RDP) supply and thus low microbial crude protein (MCP) production and efficiency of MCP production [EMCP, g MCP/kg digestible organic matter (DOM)]. Nitrogen supplements can increase MCP production and EMCP of cattle grazing low protein pastures. The objective of this study was to compare the effects of supplementation with a non-protein-N source (NPN), in this case urea and ammonium sulfate (US), with a single-cell algal protein source (Spirulina platensis), on intake, microbial protein supply and digestibility in cattle. Nine cannulated Bos indicus steers [initial liveweight 250.1 ± 10.86 (s.d.) kg] were fed Mitchell grass hay (Astrebla spp; 6.1 g N, 746 g NDF/kg DM) ad libitum and were supplied with increasing amounts of US (0, 6, 13, 19 and 33 g US DM/kg hay DM) or Spirulina 0, 0.5, 1.4, 2.5 and 6.1 g Spirulina DM/kg W.day in an incomplete Latin square design. The response of MCP production and EMCP to increasing amounts of the two supplements was different, with a greater response to Spirulina evident. The MCP production was predicted to peak at 140 and 568 g MCP/day (0.64 and 2.02 g MCP/kg W.day) for the US and Spirulina supplements, respectively. The highest measured EMCP were 92 and 166 g MCP/kg DOM for the US and Spirulina treatments at 170 and 290 g RDP/kg DOM, respectively, or a Spirulina intake of 5.7 g DM/kg W.day. Increasing RDP intake from US and Spirulina resulted in an increase in Mitchell grass hay intake and rumen NH3-N concentration and reduced the retention time of liquid and particulate markers and digesta DM, NDF and lignin in the rumen with greater changes due to Spirulina. Total DM intake peaked at a Spirulina supplement level of 4.6 g Spirulina DM/kg W.day with a 2.3-fold higher DOM intake than Control steers. Rumen NH3-N concentrations reached 128 and 264 mg NH3-N/L for the US and Spirulina treatments with a significant increase in the concentration of branched-chain fatty acids for the Spirulina treatment. The minimum retention time of liquid (Cr-EDTA; 23 and 13 h) and particulate (Yb; 34 and 22 h) markers in the rumen were significantly lower for Spirulina compared with US and lower than unsupplemented animals at 24 and 34 h for Cr-EDTA and Yb, respectively. Spirulina could be provided safely at much higher N intakes than NPN supplements. The results suggest that, at an equivalent RDP supply, Spirulina provided greater increases than US in MCP production, EMCP and feed intake of Bos indicus cattle consuming low protein forage and could also be fed safely at higher levels of N intake.

Harmful algae in the planktonic food web of the Baltic Sea

This study deals with algal species occurring commonly in the Baltic Sea: haptophyte Prymnesium parvum, dinoflagellates Dinophysis acuminata, D. norvegica and D. rotundata, and cyanobacterium Nodularia spumigena. The hypotheses are connected to the toxicity of the species, to the factors determining toxicity, to the consequences of toxicity and to the transfer of toxins in the aquatic food web. Since the Baltic Sea is severely eutrophicated, the fast-growing haptophytes have potential in causing toxic blooms. In our studies, the toxicity (as haemolytic activity) of the haptophyte P. parvum was highest under phosphorus-limited conditions, but the cells were toxic also under nitrogen limitation and under nutrient-balanced growth conditions. The cellular nutrient ratios were tightly related to the toxicity. The stoichiometric flexibility for cellular phosphorus quota was higher than for nitrogen, and nitrogen limitation led to decreased biomass. Negative allelopathic effects on another algae (Rhodomonas salina) could be observed already at low P. parvum cell densities, whereas immediate lysis of R. salina cells occurred at P. parvum cell densities corresponding to natural blooms. Release of dissolved organic carbon from the R. salina cells was measured within 30 minutes, and an increase in bacterial number and biomass was measured within 23 h. Because of the allelopathic effect, formation of a P. parvum bloom may accelerate after a critical cell density is reached and the competing species are eliminated. A P. parvum bloom indirectly stimulates bacterial growth, and alters the functioning of the planktonic food web by increasing the carbon transfer through the microbial loop. Our results were the first reports on DSP toxins in Dinophysis cells in the Gulf of Finland and on PTX-2 in the Baltic Sea. Cellular toxin contents in Dinophysis spp. ranged from 0.2 to 149 pg DTX-1 cell-1 and from 1.6 to 19.9 pg PTX-2 cell-1 in the Gulf of Finland. D. norvegica was found mainly around the thermocline (max. 200 cells L-1), whereas D. acuminata was found in the whole mixed layer (max. 7 280 cells L-1). Toxins in the sediment trap corresponded to 1 % of DTX-1 and 0.01 % PTX-2 of the DSP pool in the suspended matter. This indicates that the majority of the DSP toxins does not enter the benthic community, but is either decomposed in the water column, or transferred to higher trophic levels in the planktonic food chain. We found that nodularin, produced by Nodularia spumigena, was transferred to the copepod Eurytemora affinis through three pathways: by grazing on filaments of small Nodularia, directly from the dissolved pool, and through the microbial food web by copepods grazing on ciliates, dinoflagellates and heterotrophic nanoflagellates. The estimated proportion of the microbial food web in nodularin transfer was 22-45 % and 71-76 % in our two experiments, respectively. This highlights the potential role of the microbial food web in the transfer of toxins in the planktonic food web.

A systematic-ecological approach to Baltic Sea ice studies of algae and protists

The seasonal occurrence of sea ice that annually covers almost half the Baltic Sea area provides a unique habitat for halo- and cold temperature-tolerant extremophiles. Baltic Sea ice biology has more than 100 years of tradition that began with the floristic observation of species by the early pioneers using light microscopic techniques that were the only thing available at the time. Since the discovery of life within sea ice, more technologies have become available for taxonomy. Electron microscopy and genetic evidence have been used to identify sea ice biota revealing increased numbers of taxa. Meanwhile ecologists have used light microscopic cell enumeration in addition to the chemical and physical properties of sea ice in attempts to explain the food web structure of sea ice and its functions. Thus, during the Baltic winter, the sea ice hosts more abundant and diverse microbial communities than the water column beneath it. These communities are typically dominated by autotrophic diatoms together with a diverse assortment of dinoflagellates, auto- and heterotrophic flagellates, ciliates, metazoan rotifers and bacteria, which are mostly responsible for the recycling of nutrients. This thesis comprises ecological and systematic studies. In addition to the results of the previous studies carried out on landfast ice, the data presented here provide new insight into the spatial distribution of pelagial sea ice, which has remained largely unexplored. The studies reveal spatial heterogeneity in the pelagial sea ice of the Gulf of Bothnia. There were mismatches in chlorophyll-a concentrations and in photosynthetic efficiencies of the communities studied. The temporal succession was followed and experimental studies performed investigating the community responses towards increased or decreased light in landfast ice in the Gulf of Finland. The systematic studies carried out with established dinoflagellate cultures revealed a new resting cyst belonging to common sea ice dinoflagellate, Scrippsiella hangoei (Schiller) Larsen 1995. The cyst can be used to explain the overwintering of this species during prolonged periods of darkness. The dissimilarities and similarities in the material isolated from the sea ice called for description of a new subspecies Heterocapsa arctica ssp. frigida. The cells obtained in the cultured material were unlike those of the previously described species, necessitating description of ssp. frigida. As a result of its own unique habitus, the subspecies had been noted by Finnish taxonomists during the past three decades and thus its annual occurrence and geographical distribution in the Baltic Sea. This illustrates how combining ecology and systematics increases our understanding of organisms.

Phylogenetic studies of cyanobacterial lichens

Phylogenetic studies of cyanobacterial lichens Lichens are symbiotic assemblages between fungi (mycobiont) and green algae (phycobiont) or/and cyanobacteria (cyanobiont). Fossil records show that lichen-like symbioses occurred already 600 million years ago. Lichen symbiosis has since then become an important life strategy for the Fungi, particularly for species in the phylum Ascomycota as approximately 98% of the lichenized fungal species are ascomycetes. The taxonomy of lichen associations is based on the mycobiont. We reconstructed, using DNA sequence data, hypotheses of phylogenetic relationships of lichen-forming fungi that include species associated with cyanobacteria. These hypotheses of phylogeny should form the basis for the taxonomy. They also allowed studies of the origin and the evolution of specific symbioses. Genetic diversity and phylogenetic relationships of symbiotic cyanobionts were also studied in order to examine selectivity of cyanobionts and mycobionts as well as possible co-evolution between partners involved in lichen associations. The suggested circumscription of the family Stereocaulaceae to include Stereocaulon and Lepraria is supported. The recently described crustose Stereocaulon species seem to be correctly placed in the genus, although Stereocaulon traditionally included only fruticose species. The monospecific crustose genus Muhria is also shown to be best placed in Stereocaulon. Family Lobariaceae as currently delimited is monophyletic. Within Lobariaceae genus Sticta including Dendriscocaulon dendroides form a monophyletic group while the genera Lobaria and Pseudocyphellaria are non-monophyletic. A new classification of Lobariaceae is obviously needed. Further studies are however required before a final proposal for a new classification can be made. Our results show that the cyanobacterial symbiotic state has been gained repeatedly in the Ascomycota while losses of symbiotic cyanobacteria appear to be rare. The symbiosis with green algae is confirmed to have been gained repeatedly in Ascomycota but also repeatedly lost. Cyanobacterial symbioses therefore seem to be more stable than green algal associations. Cyanobacteria are perhaps more beneficial for the lichen fungi and therefore maintained. The results indicate a dynamic association of the lichen symbiosis. This evolutionary instability will perhaps be important for the lichen fungi as the utilization of options will perhaps enable lichens to colonize new substrates and survive environmental changes. Some cyanobacterial lichen genera seem to be highly selective towards the cyanobiont while others form symbioses with a broad spectrum of cyanobacteria. No evidence of co-evolution between fungi and cyanobacteria in cyanolichens could be demonstrated.

Interactions between harmful algae and calanoid copepods in the Baltic Sea

The aim of the studies reported in this thesis was to examine the feeding interactions between calanoid copepods and toxic algae in the Baltic Sea. The central questions in this research concerned the feeding, survival and egg production of copepods exposed to toxic algae. Furthermore, the importance of copepods as vectors in toxin transfer was examined. The haptophyte Prymnesium parvum, which produces extracellular toxins, was the only studied species that directly harmed copepods. Beside this, it had allelopathic effects (cell lysis) on non-toxic Rhodomonas salina. Copepods that were exposed to P. parvum filtrates died or became severely impaired, although filtrates were not haemolytic (indicative of toxicity in this study). Monospecific Prymnesium cell suspensions, in turn, were haemolytic and copepods in these treatments became inactive, although no clear effect on mortality was detected. These results suggest that haemolytic activity may not be a good proxy of the harmful effects of P. parvum. In addition, P. parvum deterred feeding, and low egestion and suppressed egg production were consequently observed in monospecific suspensions of Prymnesium. Similarly, ingestion and faecal pellet production rates were suppressed in high concentration P. parvum filtrates and in mixtures of P. parvum and R. salina. These results indicate that the allelopathic effects of P. parvum on other algal species together with lowered viability as well as suppressed production of copepods may contribute to bloom formation and persistence. Furthermore, the availability of food for planktivorous animals may be affected due to reduced copepod productivity. Nodularin produced by Nodularia spumigena was transferred to Eurytemora affinis via grazing on filaments of small N. spumigena and by direct uptake from the dissolved pool. Copepods also acquired nodularin in fractions where N. spumigena filaments were absent. Thus, the importance of microbial food webs in nodularin transfer should be considered. Copepods were able to remove particulate nodularin from the system, but at the same time a large proportion of the nodularin disappeared. This indicates that copepods may possess effective mechanisms to remove toxins from their tissues. The importance of microorganisms, such as bacteria, in the degradation of cyanobacterial toxins could also be substantial. Our results were the first reports of the accumulation of diarrhetic shellfish toxins (DSTs) produced by Dinophysis spp. in copepods. The PTX2 content in copepods after feeding experiments corresponded to the ingestion of <100 Dinophysis spp. cells. However, no DSTs were recorded from field-collected copepods. Dinophysis spp. was not selected by the copepods and consumption remained low. It seems thus likely that copepods are an unimportant link in the transfer of DSTs in the northern Baltic Sea.

Applications of coralline hydroxyapatite with bioabsorbable containment and reinforcement as bone graft substitute : An experimental study

The aim of the present experimental study was to find out if the applications of coralline hydroxyapatite (HA) can be improved by using bioabsorbable containment or binding substance with particulate HA in mandibular contour augmentation and by using bioabsorbable fibre-reinforced HA blocks in filling bone defects and in anterior lumbar interbody fusion. The use of a separate curved polyglycolide (PGA) containment alone or together with a fast resorbing polyglycolide/polylactide (PGA/PLA) binding substance were compared to the conventional non-contained method in ridge augmentation in sheep. The contained methods decreased HA migration, but the augmentations did not differ significantly. The use of the containment caused a risk for wound dehiscence and infection. Histologically there was a rapid connective tissue ingrowth into the HA graft and it was more abundant with the PGA containment compared to the non-contained augmentation and even additionally rich when the HA particles were bound with PGA/PLA copolymer. However, the bone ingrowth was best in the non-contained augmentation exceeding 10-12 % of the total graft area at 24 weeks. Negligible or no bone ingrowth was seen in the cases where the polymer composite was added to the HA particles and, related to that, foreign-body type cells were seen at the interface between the HA and host bone. The PGA and poly-dl/l-lactide (PDLLA) fibre-reinforced coralline HA blocks were studied in the metaphyseal and in the diaphyseal defects in rabbits. A rapid bone ingrowth was seen inside the both types of implants. Both PGA and PDLLA fibres induced an inflammatory fibrous reaction around themselves but it did not hinder the bone ingrowth. The bone ingrowth pattern was directed according to the loading conditions so that the load-carrying cortical ends of the implants as well as the implants sited in the diaphyseal defects were the most ossified. The fibre-reinforced coralline HA implants were further studied as stand-alone grafts in the lumbar anterior interbody implantation in pigs. The strength of the HA implants proved not to be adequate, the implants fractured in six weeks and the disc space was gradually lost similarly to that of the discectomized spaces. Histologically, small quantities of bone ingrowth was seen in some of the PGA and PDLLA reinforced coralline implants while no bone formation was identified in any of the PDLLA reinforced synthetic porous HA implants. While fragmented, the inner structure of the implants was lost, the bone ingrowth was minimal, and the disc was replaced by the fibrous connective tissue. When evaluated radiologically the grade of ossification was assessed as better than histologically, and, when related to the histologic findings, CT was more dependable than the plain films to show ossification of the implanted disc space. Local kyphosis was a frequent finding along with anterior bone bridging and ligament ossification as a consequence of instability of the implanted segment.

Seasonal fluctuations in blue-green algae, especially in heterocystous species in polluted coastal waters off Helsinki city, in the northern part of the Gulf of Finland

Tiivistelmä

Bioconvection in an anisotropic scattering suspension of phototactic algae

Phototaxis is a directed swimming response dependent upon the light intensity sensed by microorganisms. Positive phototaxis denotes motion directed towards the source of light and negative phototaxis is motion directed away from it. In this paper, we investigate the onset of bioconvection in a suspension of anisotropic scattering phototactic algae illuminated by collimated radiation at the top. The basic state of the system is defined by the zero fluid flow and the up and down swimming, caused by the positive and negative phototaxis, is balanced by the diffusion. A comprehensive numerical study of the linear stability is presented with particular emphasis on the forward scattering effect. The onset of bioconvection occurs either via a stationary mode or an oscillatory mode. The transition from a stationary mode to an oscillatory mode or vice versa has been observed as the anisotropic coefficient is varied for certain parameter values. (C) 2012 Elsevier Masson SAS. All rights reserved.

Treatment efficacy of algae-based sewage treatment plants

Lagoons have been traditionally used in India for decentralized treatment of domestic sewage. These are cost effective as they depend mainly on natural processes without any external energy inputs. This study focuses on the treatment efficiency of algae-based sewage treatment plant (STP) of 67.65 million liters per day (MLD) capacity considering the characteristics of domestic wastewater (sewage) and functioning of the treatment plant, while attempting to understand the role of algae in the treatment. STP performance was assessed by diurnal as well as periodic investigations of key water quality parameters and algal biota. STP with a residence time of 14.3 days perform moderately, which is evident from the removal of total chemical oxygen demand (COD) (60 %), filterable COD (50 %), total biochemical oxygen demand (BOD) (82 %), and filterable BOD (70 %) as sewage travels from the inlet to the outlet. Furthermore, nitrogen content showed sharp variations with total Kjeldahl nitrogen (TKN) removal of 36 %; ammonium N (NH4-N) removal efficiency of 18 %, nitrate (NO3-N) removal efficiency of 22 %, and nitrite (NO2-N) removal efficiency of 57.8 %. The predominant algae are euglenoides (in facultative lagoons) and chlorophycean members (maturation ponds). The drastic decrease of particulates and suspended matter highlights heterotrophy of euglenoides in removing particulates.

A Preliminary Check-List of the Marine Algae of the Moss Landing Jetty: An Annotated Floristic Compilation. Annual Report, Part 7, 1973

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Relative tolerance of mat-forming algae to copper

This study documents the relative tolerance of the common, weedy mat-forming green algae Hydrodictyon , Oedogonium , Pithophora , Rhizoclonium , and Spirogyra to copper. In addition, the copper tolerance of the cyanobacterial (blue-green algal) mat-forming Oscillatoria was assessed.

Water quality and harmful algae in Southeastern coastal stormwater ponds

Several long-term monitoring studies describing the water quality and biological condition of Southeastern estuaries (National Estuarine Eutrophication Assessment Project, South Carolina Estuarine and Coastal Assessment Program (SCECAP), Environmental Monitoring and Assessment Program (EMAP), South Carolina Harmful Algal Bloom Program (SCHAB), South Carolina Tidal Creek Project, and others) have been developed. Many of the same water quality issues determined for open estuaries are also found in coastal stormwater ponds, and there are important interactions between the man-made ponds and the natural systems. Researchers have highlighted problems such as nutrient eutrophication, bacterial and chemical contamination, hypoxia, and harmful algal blooms (HABs). This technical memorandum summarizes the state-of-the-knowledge of water quality indicators (dissolved oxygen, nutrients, and chlorophyll a), and harmful algae in Southeastern coastal stormwater ponds. (PDF contains 31 pages)