Carl J. Soeder

Modeling algal productivity in large outdoor cultures and waste treatment systems

Abstract A deterministic mathematical model was used to describe the production of green microalgae (Scenedesmus obliquus and Coelastrum sphaericum) in outdoor mass cultures. The model was calibrated against 16 months of temperature and irradiance measurements, during which time productivity measurements were made in up to five ponds with surface areas of up to 263 m2. During this period rates of algal dry matter production varied between 1·7 and 16·92 g m−2 day−1. The model predicted productivity to within 4·2% of the observed rates, for the same period. Negative productivity values (loss of biomass) were calculated for the months from November to January. It was concluded that appreciable amounts of biomass could be produced for 7 months per year in temperate areas. Several assumptions were made during the construction of the model, especially with regard to loss factors, such as: respiration, release of exuded organic carbon and photo-inhibition. The latter was included as a separate factor in the model and is merely conceptual. Several applications of the model are discussed, one of which concerns the relation between areal density and productivity, where the optimal areal density for maximal productivity was calculated to be 38–41 g (dry wt) m−2. A distinction was also made between cultures which were mainly autotrophic and waste systems. It was shown that the presence of gilvin and/or tripton would adversely influence productivities and that the contribution of these factors to vertical light attenuation would have to be measured in waste systems.

On the mass culture of microalgae: Areal density as an important factor for achieving maximal productivity

Abstract Scenedesmus obliquus was grown in a bioreactor under constant light and at a temperature of 24°C. From measurements of biomass production, it was possible to determine the influence of areal density on productivity in open as well as closed cultures. Maximal productivity occurred at an areal density of 40 to 45 g(dw) M−2, which was in good agreement with predicted values from a model. The optimal areal density for maximal productivity was influenced by factors such as culture depth, algal species, turbulence, available light, etc., and hence the establishment and maintenance of an optimal areal density is seen as one of the most important operational procedures for the mass culture of algae. Supersaturated concentrations of oxygen resulted in lower productivities due to photorespiration and/or oxidation.

Impact of rotifer grazing on population dynamics of green microalgae in high-rate ponds

Abstract In high-rate algal ponds, the grazing activity of rotifers such as Brachionus rubens or B. calyciflorus often leads to a replacement of Scenedesmus species by Micractinium pusillum. In contrast to many other green microalgae including Scenedesmus, Micractinium pusillum with fully developed spines (setae) cannot be eaten by Brachionus. Ecological conditions for population shifts between Scenedesmus and Micractinium are, therefore, interpreted as a response of the rotifers rather than being due to physiological properties of the algae. Another effect of rotifer grazing on the microbial flora of high-rate ponds is the development of large stable flocs consisting of bacteria and microalgae.

Evidence for the Non-involvement of Nitric Oxide Synthase in Nitric Oxide Production by the Green Alga Scenedesmus obliquus

Summary Studies conducted with N W -nitro-L-arginine (L-NNA) and N G -nitro-L-arginine-methyl ester (L-NAME), the potent inhibitors of nitric oxide synthase (NOS), did not exhibit any inhibitory effect on NO release by Scenedesmus cells grown either under illumination or in the dark supplemented with glucose. Further, these inhibitors did not interfere with the appearance of ‘light-off’ peaks, and the NO peaks also commenced following treatment with Cu, DCMU and glutarate in the presence of L-NNA and L-NAME. Complete suppression of NO production and the elimination of the most common ‘light-off’ peak were observed in algal culture grown in the medium where L-arginine was substituted for NO − 3 . This study therefore demonstrates that L-arginine is neither the substrate for NO production by Scenedesmus , as generally found in the case of animals and some plants, nor is the NOS involved in the nitric oxide production process.

Rates of biogenic oxygen production in mass cultures of microalgae, absorption of atmospheric oxygen and oxygen availability for wastewater treatment

Abstract Oxygen for the aerobic treatment of wastewater in High Rate Algal Pond (HRAP) systems arises from biogenic production by microalgae during photosynthesis and from absorption of atmospheric oxygen through the air/water interphase. The total quantity of available oxygen per m 2 and day determines the permissible BOD loading rate of a HRAP. The quantity of biogenic oxygen production, has for the first time been measured in a closed bioreactor and open chemostatic cultures. Good agreement was obtained between the two methods where more than 1.92 g O 2 g(dry wt) was produced by the microalgae. This was significantly higher than oxygen yields calculated from a generalized compositional formula of algal biomass. In combination with a predictive mathematical model, it was possible to calculate the potential biogenic oxygen production per season for any latitude. This may serve as the basis of feasibility studies on application of HRAP systems.

Evidence supporting nitrite-dependent NO release by the green microalga Scenedesmus obliquus

Summary Studies conducted with respiratory electron transport chain inhibitors and uncouplers such as antimycin A, rotenone, 2,4-dinitrophenol, pentachlorophenol and carbonyl cyanide m-chlorophenylhydrazone resulted in sudden NO bursts in Scenedesmus suspensions incubated under dark-aerobic conditions with supplemented glucose. Anaerobiosis was also found to increase NO production significantly in dark-incubated cells of Scenedesmus . These NO bursts, quite comparable to the usual ‘light-off’ peak (as always appeared after sudden darkening), could be correlated with the increased nitrite concentration under the above-mentioned conditions. Moreover, similar NO bursts concomitant with nitrite accumulation were also observed following supplementation of cycloheximide, MSX, Basta, glutarate and glyphosate. These results therefore support our hypothesis that accumulation of nitrite is the prerequisite for NO production in the case of the chlorophycean microalga Scenedesmus . A hypothetical model for NO formation is proposed.

Biotransformation of 1-naphthalenesulfonic acid by the green alga Scenedesmus obliquus

Abstract Under sulfate limitation, axenic batch cultures of the green alga Scenedesmus obliquus metabolized 1-naphthalenesulfonic acid and partially used the sulfonate as a source of sulfur. The main metabolite, 1-hydroxy-2-naphthalenesulfonic acid, which was not metabolized further in the algal culture, was formed by hydroxylation of the substrate in position 1 and by migration of the sulfonic acid group to position 2 of the naphthalene ring (NIH shift). A smaller amount of 1-naphthalenesulfonic acid was desulfonated. The resulting 1-naphthol was mostly transformed into 1-naphthyl β-d-glucopyranoside.