N. De Pauw

Potential of electrolytic flocculation for recovery of micro-algae

Cost-effective harvesting of micro-algae has always been a major bottle-neck not only in the exploitation of pure mass algal cultures but also in waste stabilization ponds, high rate algal ponds, and reservoirs for drinking water production. Most existing algal separation processes have several disadvantages such as intolerable costs, undesirable low dry mass percentages after harvest or algal slurries contaminated with toxic flocculants which can make the algal product unsuitable for further uses as food and feed. The algal separation experiments described in this paper deal with a rather new technique, namely electrolytic flocculation. This technique involves no flocculants and needs only relatively little electricity to flocculate the micro-algae from a suspension and subsequently float the algal flocs. Efficiencies of 95% elimination or more are easily obtained with different taxonomic groups of algae tested while the consumption of current only amounted to about 0.3 kWh/m3.

Mass culture of microalgae in aquaculture systems: Progress and constraints

For several decades considerable efforts have been made to promote the production and use of microalgae as direct food for man. However, the high costs of production and harvesting, and the potential rejection of algal food by consumers for toxicological reasons or concerns, have so far been major obstacles to a real breakthrough (Soeder, 1980). As a result, human consumption of microalgae is limited at present to expensive ‘health’ foods. Hope is rising, however, that in the near future inexpensive Spirulina grown on wastes will be successfully used in human nutrition (Fox, 1980; Olguin & Vigueras, 1981; Becker & Venkataraman, 1982).

Optimisation of T-ISO biomass production rich in essential fatty acids: I. Effect of different light regimes on growth and biomass production

T-ISO is a microalgal strain widely used in aquaculture for its favourable lipid composition. In this study, we report on the results of an optimisation scheme for maximal biomass production under three different photoperiods (24:0, 16:08 and 12:12-h L/D) combined with three photon flux densities (PFD, 120, 220 and 460 μmol photons m−2 s−1) at 25 °C. Sampling for growth took place in both the exponential and post-exponential (light-limited only) phase. Results showed that specific growth rate of T-ISO maximised with an increase of the total PFD supplied per day. Under continuous light, cell size of T-ISO (both cell dry weight (CDW) and cell volume) correlated positively to PFD with a further increase when the cells were transiently light-limited in the post-exponential phase. In contrast, cell dry weight under discontinuous light increased only at subsaturating PFD with a significant decrease in the post-exponential phase. Cell size, as volume, did not correlate to CDW under discontinuous light, revealing an intracellular density change particularly for the 16:08-h L/D regimes. As a result, biomass yield and productivity had different patterns for continuous and discontinuous light whereas cell yield and productivity were simply a function of total PFD per day. Biomass productivity under continuous light was inferior than under discontinuous light, although the final yield was maximal compared to those under discontinuous light.

Performance of two artificial substrate samplers for macroinvertebrates in biological monitoring of large and deep rivers and canals in Belgium and The Netherlands

Harmonization exercises organized by the European Communities in the 1970s on biological water assessment methods for running waters, because the usual methods were difficult or impossible to apply, explicitly stressed the need for development of standardized sampling procedures for monitoring large and deep rivers and canals. To meet this objective, an extensive monitoring campaign was organized in Belgium and The Netherlands to test the efficiency of artificial substrates colonized by macroinvertebrates as an alternative for natural communities sampled with a handnet. Two types of artificial substrates were tested: a Belgian substrate, composed of a plastic netting filled with medium-sized pieces of brick, and a Dutch substrate consisting of a stainless steel box filled with marbles. The collected biocoenoses were compared qualitatively and quantitatively. Water quality was assessed by means of several biotic indexes. The results show that both the Belgian and the Dutch artificial substrate sampler can replace the usual samples obtained by means of a handnet, and provide a correct assessment. A major drawback of the use of artificial substrates in uncontrolled monitoring sites remains the unforeseen losses. For that reason the cost price of the substrates may have to be considered when making a selection.

Implications of taxonomic modifications and alien species on biological water quality assessment as exemplified by the Belgian Biotic Index method

In this paper, some important problems related to taxonomic resolution in water quality assessment by means of macroinvertebrates are discussed. Most quality indices based on macroinvertebrates only require identification up to genus or family level. Although this can be seen as a practical trade-off between taxonomic precision and time constraints and financial resources, it can result in biased assessment scores for certain stream types. An additional difficulty of identification levels other than species is caused by possible changes in taxonomy over time. A given genus may indeed have been split up into two or more genera or a species could be assigned to a different genus. These changes may alter biotic index values calculated over time, due to a change in number of taxa or replacement of one taxon by another one having a different tolerance class. An additional problem is caused by the invasion of exotic species. The genus Corbicula for instance is currently invading Belgian watercourses in increasing numbers. Since no Belgian Biotic Index (BBI) tolerance class is defined for Corbicula, this may cause inconsistencies in index calculations as well. In order to eliminate these, a semi-fixed taxa list, including a tolerance class for each taxon, for BBI calculation is proposed.

Effect of different light regimes on the docosahexaenoic acid (DHA) content of Isochrysis aff. galbana (clone T-ISO)

The culture of Isochrysis aff. galbana Green (T-ISO) in hatcheries is promoted for its high docosahexaenoic acid (DHA) content which favours the successful rearing of aquatic larvae. In this paper we identified the need for well-defined culture conditions of microalgae if sufficient DHA content is the final goal. Using photoperiods of 24:0 h, 12:12 h, and 16:8 h L/D combined with photon flux densities (PFDs) of 110, 220, and 460μE m-2 s-1, batch cultures of T-ISO were sampled for DHA content in the exponential as well as the post-exponential (light limited) growth phase. The various light regimes resulted in differences of DHA content of T-ISO revealing influences and strong interactions among the three variables studied. For fast and economic production of T-ISO cells rich in DHA it is recommended to harvest batch cultures at the end of the exponential phase using high photon flux densities (PFDs) under 12:12 h L/D cycles. The same regime or lower PFD under 24:0 h L/D seem to be sufficient for a continuous culture optimization scheme. In any case a strict following of culture protocols is very important since there is evidence for coexistence of different clones within the parental cultures leading to different results depending on which one prevails.

Comparison of brackish water plankton assemblages of identical salinity ranges in an estuarine tidal (Westerschelde) and stagnant (Lake Veere) environment (S.W.- Netherlands). I. Phytoplankton)

SummarySpecies composition, abundance and seasonal distribution of the phytoplankton of brackish water ecosystems depend not only on salinity but on several other environmental factors too.In stagnant brackish waters (Lake Veere) the easily established stability of the water masses proved to be an ecological masterfactor in relation to phytoplankton development, equaling salinity in importance.In tidalbrackish waters (Westerschelde estuary) turbulence acts as an ecological masterfactor in relation to phytoplankton development, dominating salinity in importance within the chosen salinity ranges.

First isolation of “Brachyspira hampsonii” from pigs in Europe

Infections with Brachyspira species in swine occur in most swine-rearing countries and can result in substantial economic losses. Of all swine-related Brachyspira species Infections, classical swine dysentery, caused by Brachyspira hyodysenteriae , results in the most severe clinical symptoms (eg, mucohaemorrhagic diarrhoea, weight loss, poor feed conversion). B hyodysenteriae was first recognised as the cause of swine dysentery in 1971 (Taylor and Alexander 1971). At that time, the strong haemolysis of B hyodysenteriae appeared indicative for pathogenicity since other, weakly haemolytic Brachyspira (formerly Serpulina , Serpula and Treponema ) appeared to be commensal, and were therefore named Brachyspira innocens (Kinyon and Harris 1979). Several reports of clinical disease caused by weakly haemolytic Brachyspira indicated that not all weakly haemolytic Brachyspira species were non-pathogenic for pigs (Taylor and others 1980, Neef and others 1994). Further research of these weakly haemolytic isolates including DNA-DNA hybridisation, resulted in the designation of three more weakly haemolytic species, namely Brachyspira intermedia , Brachyspira murdochii and Brachyspira pilosicoli (Trott and others 1996, Stanton and others 1997). These weakly haemolytic species of Brachyspira diverge in the severity of clinical symptoms they cause. B pilosicoli is pathogenic and causes spirochetal colitis in pigs, which is marked by non-haemorrhagic diarrhoea and a poor feed conversion. For B intermedia and B murdochii , the pathogenic potential is less clear-cut. Although both species have been isolated from clinical cases of diarrhoea, the clinical symptoms are mild or absent in experimental infections, and yet, high numbers of spirochetes are necessary to cause an effect (Jensen and others 2004, Jensen and others 2010). Recently, a new type of Brachyspira infection has been described. Outbreaks of mucohaemorrhagic diarrhoea, caused by strongly haemolytic Brachyspira strains inconsistent with B hyodysenteriae , were reported in the USA and Canada. Phylogenetic analysis of these strains …

Development and application of predictive river ecosystem models based on classification trees and artificial neural networks

Prediction of freshwater organisms based on machine learning techniques is becoming more and more reliable due to the availability of appropriate datasets and modelling techniques. Artificial neural networks (Lek and Guegan 1999), fuzzy logic (Barros et al. 2000), evolutionary algorithms (Caldarelli et al. 1998), cellular automata (Gronewold and Sonnenschein 1998), etc. proved to be powerful tools to perform ecological modelling, especially when large datasets are involved. Models have several interesting applications in river management. They allow for a better interpretation of the results, easing the cause-allocation of the actual river status and increasing the insight needed to improve assessment systems (Fig. 6.1.). Models also allow for simulating the effect of potential management options and thus supporting decision-making. The development of effective and efficient monitoring networks based on models is probably another important advantage.

Copepod biomass in an estuarine and a stagnant brackish environment of the S.W. Netherlands

In the mesohaline zone of the Westerschelde estuaryEurytemora affinis is the dominant copepod, demonstrating large biomass values nearly throughout the year. In the meso-polyhaline Lake VeereAcartia tonsa is abundant, mainly during summer. In spring a small population ofEurytemora americana is found.The tidal estuary harboured far denser copepod populations throughout the year than the stagnant brackish lake water. The average yearly copepodid+adult biomass in the Westerschelde estuary was approx. 850 mg/m3 (wet weight), in Lake Veere approx. 130 mg/m3.Temporarily low oxygen values did not influence negatively the copepod populations in the Westerschelde estuary.The seasonal distribution of the dominant copepods in both areas is explained in the light of recent litterature data.PerennialEurytemora affinis abundance in the Westerschelde estuary must be mainly caused by large concentrations of nannodetritus particles, bacteria included, throughout the year.Acartia tonsa in Lake Veere has to thrive mainly on nannophytoplankton.