Joël de la Noüe

The potential of microalgal biotechnology: A review of production and uses of microalgae

An overview of the various aspects, promises and limitations of microalgal biotechnology is presented. The factors of importance in microalgal cultivation as well as the culture systems are briefly described. Microalgal biomasses can fulfil the nutritional requirements of aquatic larvae and organisms. The biochemical composition of algae can be improved by the manipulation of culture conditions. The nutritive value of the microalgal biomasses for human and animal consumption is also commented upon as well as some socio-economical aspects. Among the sources of required nutrients (N, P), wastewaters and manures can upgraded as culture media for microalgae the safety of which has to be evaluated. Harvesting of the biomass is one of the bottlenecks. The various techniques, physical, physico-chemical and biological are outlined and their feasibility and economic interest examined. Microalgal biomasses can be submitted to various technological transformations. Various processes are reviewed in the light of their effects on safety and nutritional value. The possible extraction of fine chemicals and the preparation of protein concentrates is also reported on. The various uses of microalgae lead to a possible competition, to be evaluated, between systems for the production of food, energy and chemicals. The review finally covers the application of genetic manipulation to microalgae.

Algae and waste water

Microalgal cultures offer an interesting alternative for waste water treatment (urban, industrial or agricultural effluents) because they provide a tertiary biotreatment coupled with the production of potentially valuable biomass, which can be used for several purposes. We review the main abiotic, biotic and operative factors playing a role in the cultivation of microalgae. Various types of bioreactors are scrutinized keeping in view that the main limitation upon the type of usable bioreactors is the enormous volume of water to be treated. The choice of suitable microalgae and cyanobacteria is examined in terms of productivity and easiness of harvesting. The possible alternatives to harvesting are also reviewed with an emphasis on immobilized systems. Finally, the need for more research and development is discussed.

Wastewater nutrient removal with microalgae immobilized in carrageenan

Abstract Two species of the green freshwater microalga Scenedesmus have been immobilized in beads of κ-carrageenan. Growth curves were similar to those observed with free cells. The uptake of nitrogen and phosphorus from wastewater was similar for free and entrapped microalgae. The reduction of N-NH + 4 was 90% within 4 h at pH 9.0 and 70% within 5 h at an adjusted pH of ∼7.7. From these experiments, we conclude that immobilized Scenedesmus microalgae can grow well within gel beads and that they are as physiologically active for wastewater nutrient removal as free cells .

Biological tertiary treatment of urban wastewaters with chitosan-immobilizedPhormidium

SummaryChitosan:Phormidium aggregates (chitosan: algae=1:2, dry weight basis) were used as a biological tertiary treatment to remove the nitrogen (NH4+, NO2-, NO3-) and phosphorus (PO43-) from a secondary effluent. In a batch system, 71 and 92% of P−PO43-were removed after 6 and 24 h, respectively. The orthophosphate removal rate was identical for all three concentrations of algae-chitosan tested (3.3, 4.6, 5.9 g d. wt.·l-1), and was 90 μg±2 μg P−PO43-·l-1·h-1, for a 90% removal. Under control conditions (chitosan flakes only added to the effluent) 73 and 78% of PO43-were removed after 6 and 24 h respectively. A 95% removal of inorganic nitrogen (NH4+, NO2-, NO3-) was attained after 4–6 h withPhormidium immobilized on chitosan flakes, as compared to 30% with chitosan flakes alone (5 g d. wt.·l-1). The system gave a similar performance when operated semi-continuously over 5 days at a daily retention time of 1.0. In the presence of chitosan-immobilized algae, medium P−PO43-levels were reduced by 87.3%±6.4% after 24 h (61.1 μg±7.0 μg P·l-1·h-1). The reduction of inorganic nitrogen in the medium was 98% after 24 h (370 μg±50 μg N·l-1·h-1). In the presence of chitosan alone, some 60% orthophosphate removal was recorded, whereas no reduction of nitrogen was observed. Disappearance of orthophosphate was attributed to its co-precipitation with calcium released from the chitosan by abrasion. The presence of the algae protected the chitosan from abrasion andPhormidium directly assimilated the orthophosphate and inorganic nitrogen, thus reducing their levels in the effluent.

Continuous Quantitative Automatic Collector for Fish Feces

Abstract A method for the automatic collection of fish feces is described. Drainage water from fish tanks is filtered through revolving hemispheric metallic screens which quickly remove feces from the water and propel them into a refrigerated pan, where they are immediately frozen. Operation of the system-requires minimal attention and is not time-consuming. As indicated by the total collection of an inert tracer, chromic oxide, this method enables quantitative recovery of feces and makes digestibility determinations possible, even by the direct method.

Polar cyanobacteria versus green algae for tertiary waste-water treatment in cool climates

Forty-nine strains of filamentous, mat-forming cyanobacteria isolated from the Arctic, subarctic and Antarctic environments were screened for their potential use in outdoor waste-water treatment systems designed for cold north-temperate climates. The most promising isolate (strain E18, Phormidium sp. from a high Arctic lake) grew well at low temperatures and formed aggregates (flocs) that could be readily harvested by sedimentation. We evaluated the growth and nutrient uptake abilities of E18 relative to a community of green algae (a Chlorococcalean assemblage, denoted Vc) sampled from a tertiary treatment system in Valcartier, Canada. E18 had superior growth rates below 15°C Canada. (µ = 0.20 d-1 at 10°C under continuous irradiance of 225 µmol photon m-2 s-1) and higher phosphate uptake rates below 10°C (k = 0.050 d-1 at 5°C) relative to Vc (µ=0.087 d-1 at 10°C and k = 0.020 d-1 at 5°C, respectively). The green algal assemblage generally performed better than E18 at high temperatures (at 25°C, µ = 0.39 d-1 and k = 0.34 d-1 for Vc; µ = 0.28 d-1 and k = 0.33 d-1 for E18). However, E18 removed nitrate more efficiently than Vc at most temperatures including 25°C. Polar cyanobacteria such as strain E18 are appropriate species for waste-water treatment in cold climates during spring and autumn. Under warmer summer conditions, fast-growing green algae such as the Vc assemblage are likely to colonize and dominate, but warm-water Phormidium isolates could be used at that time.

A comparative study of four systems for tertiary wastewater treatment by Scenedesmus bicellularis: New technology for immobilization

Immobilization appears to be one of the best techniques to separate physically micro-algal cells from their culture medium for the purpose of algal tertiary wastewater treatment. High operation costs and other drawbacks of large-scale physico-chemical methods of harvest led to a comparative study of biotreatment systems. Before treatment began, Scenedesmus bicellularis cells were conditioned (starved) under four different sets of conditions: 1) non-immobilized cells with air bubbling (NCA); 2) cells immobilized in alginate beads (CBW) and 3) cells immobilized on alginate screens (CSW), all conditioned in synthetic culture medium depleted in N and P; 4) cells immobilized on alginate screens but conditioned in air at 100% relative humidity (CSA). Starvation was started under a light:dark photoperiod of 16:8 h. Starved cells were then used to treat wastewater for a 2-h period. The performance of each system was evaluated by determination of residual NH4-N and phosphate ions and by growth (dry weight, total chlorophyll, cell count, protein content). We then tested the capacity of microalgae immobilized on screens to eliminate N and P from a secondary municipal wastewater effluent and examined the influence of temperature and starvation. The quality of treated effluents was improved considerably with the system using CSA or CSW model. For CSA model, the protein content was 22.4 pg cell-1 compared to 12.9, 9.5, 9.1 pg cell-1 for NCA, CBW and CSW models, respectively. The CBW and CSW models were efficient for chlorophyll synthesis. The residual ammonium content in natural wastewater after 2 h of treatment with CSA model was 39% at 6±2 °C and reached 100% removal at 18±2 °C. With the first 2 h, the removal of orthophosphate was inferior (53%) at 6±2 °C, but 88 to 100% at 18±2 °C depending on starvation times. Long starvation times (72 or 96 h) caused damage to cells and uptake of nutrients was lower than with 54 h starvation. This work demonstrates that by using immobilization on screens, removal of nutrients from wastewater was higher than with conventional biological tertiary wastewater treatments (free cells or bead-shaped alginate particles).

Limitations of carrageenan microbound diets for feeding white sturgeon, Acipenser transmontanus, larvae

Utilization of carrageenan microbound (CMB) diets by white sturgeon larvae was evaluated using biochemical, histological and histochemical methods. Compared with a control group fed Biodiet, a commercial salmonid diet, larvae fed the CMB diets for 16 days had a significantly (P < 0.05) higher moisture content but lower growth, survival, and whole body amino acid and lipid contents. Although growth and survival of CMB-fed larvae were significantly higher than those of starved larvae, histological signs such as degenerated cells in liver and intestine are indicative of starvation-like conditions. Feeding CMB diets also induced a decrease in activity of alkaline phosphatase, aminopeptidase M, and nonspecific esterase in the brush border of intestinal cells. Even though the CMB diets present three desirable characteristics for sturgeon larvae such as appropriate size, soft texture and availability on the bottom of tanks, they are not recommended because they have three major drawbacks. First, CMB diets have to be kept fresh, and distributed in solution for a bottom feeder like sturgeon. Second, sturgeon larvae have trouble locating and ingesting the CMB diets. Finally, assimilation of nutrients from CMB diets is possibly restricted by limited ability of sturgeon larvae to break down and digest the carrageenan matrix.

First feeding of winter flounder (Pseudopleuronectes americanus) larvae: use of Brachionus plicatilis acclimated at low temperature as live prey

Abstract Brachionus plicatilis are used as live prey for rearing winter flounder larvae at first feeding. This rotifer is grown between 20 and 25 °C (its optimal growth temperature) and then introduced into the 10 °C water in which larvae are reared. The rapid thermal difference between the two media is thought to reduce B. plicatilis quality and consequently affect larval rearing efficiency. In order to optimize larval rearing, a study was conducted to compare the effects of two different diets on larval growth performance and nutritional condition: (1) larvae fed B. plicatilis reared at 24 °C and (2) larvae fed B. plicatilis reared at 24 °C but acclimated overnight at 10 °C. Comparisons were undertaken using morphometric measurements, nucleic acid (RNA/DNA) ratios, total protein content, trypsin activity, and triacylglycerol/sterol ratios. Fatty acid composition of larvae was also studied with a focus on the levels and ratios of three essential fatty acids (docosahexaenoic acid or DHA, eicosapentaenoic acid or EPA, and arachidonic acid or AA). Unique information regarding trypsin activity and lipid components (phospholipid, triacylglycerol, and sterol) of winter flounder larvae is provided in this study. Trypsin activity was detected very early in larvae and was not affected by acclimation of prey. Phospholipid, triacylglycerol, and sterol composition showed no significant difference between the two diets tested and was characterized by high phospholipid content as well as low triacylglycerol and sterol contents. EPA, DHA, AA, DHA/EPA, and DHA/AA decreased from days 12 to 26. Interestingly, DHA content was significantly higher in larvae fed acclimated rotifers and AA content decreased significantly in 26-day-old larvae fed acclimated B. plicatilis . Overall results indicate that overnight acclimation of B. plicatilis at 10 °C is not important for optimizing the rearing of winter flounder larvae although it does influence the fatty acid composition.

Traitement tertiaere d'un effluent domestique secondaire par culture intensive de la cyanobactérie Phormidium bohneri

Abstract Phormidium bohneri, a self‐flocculating cyanobacterium, was grown outdoors in a 75 1 intensive culture basin (semi‐continuous system) and used for the tertiary treatment of domestic wastewater. The behavior, growth and purification potential of P. bohneri were studied. The nutrient removal efficiency (max.: Ni = 83%, 12.5 mgN 1‐1 d‐1; Pi =81%, 1.3 mg P l‐1 d‐1) of this process allows a quite rapid treatment of the secondary effluent (hydraulic retention time=1d). Stripping account for about 62% of nitrogen (NH3) removal while 38% is assimilated by P. bohneri. Inorganic phosphorus is removed mainly by precipitation (57%) and to a lesser extent is taken‐up by Phormidium (43%). The cyanobacterial biomass (P: 1.1%, N: 8.6%, protein: 53.5%, dry weight basis) can be easily harvested after the treatment by settling.