ABSTRACT
Biomass production by the green algae Scenedesmus obliquus and Chlorella vulgaris in intensive laboratory continuous cultures was considerably affected by the pH at which the cultures were maintained. Carbon photoassimilation experiments revealed that pH values in the range of 8 to 9 were important for determining the free CO(2) concentrations in the medium. With higher pH values, additional pH effects were observed involving a decrease in the relative high affinity of low CO(2)-adapted algae to free CO(2). The carbon uptake rate by high CO(2)-adapted algae after transfer to low free CO(2) medium was characterized by a lag period of about 30 min, after which the affinity of the algae to CO(2) increased considerably. Both continuous growth and carbon uptake experiments indicated that artificially maintained high free CO(2) concentrations are recommended for maximal production in intensive outdoor algal cultures.
ABSTRACT
The effect of free NH(3) inhibition on short-term photosynthesis was investigated in three microalgal species: the freshwater chlorophyte Scenedesmus obliquus, the marine diatom Phaeodactylum tricornutum and the marine chlorophyte Dunaliella tertiolecta. By performing a series of assays at various concentrations of added NH(4)Cl and culture pH, we demonstrated that the inhibitory compound was free NH(3) and that pH played no role in determining the magnitude of inhibition, other than in establishing the degree of dissociation of nontoxic NH(4) to toxic NH(3). When corrections were made for pH, all three species displayed the same sigmoidal response curve to free NH(3) concentration; 1.2 mM NH(3) led to 50% reduction in photoassimilation of C. Based on literature values, some marine phytoplankton appear to be significantly more sensitive to free NH(3) than were the test species, which are noted for their excellent growth characteristics. However, the combination of low algal biomass and strong pH buffering commonly found in most marine and many freshwater environments probably limits the possibilities for NH(3) toxicity to low alkalinity freshwaters and intensive algal cultures in which NH(4) is the main source of N. Such conditions occur commonly in algal wastewater treatment systems.
ABSTRACT
Theoretical considerations confirmed by outdoor experiments indicated carbon limitation of biomass production in high-rate oxidation ponds at certain seasonal and operational conditions. Apparently, free carbon dioxide concentration in the pond is the major determinant of carbonlimiting algal photosynthesis. High concentrations of free CO(2) are provided through bacterial respiration which is the main contributor to algal photosynthesis. At high photosynthetic activities and low organic loadings, free CO(2) concentrations are low; its flux into algal cells determines photosynthesis and biomass production rate in the pond.
ABSTRACT
Regular concentrations of hard detergents in domestic wastewater do not affect algal growth in a high-rate-oxidation pond. The addition of nonionic hard detergent at concentrations above 60 mg/liter decreased the algal concentration in the batch culture, and complete lysis of algal cells was observed within a few days at a detergent concentration of 100 mg/liter.
ABSTRACT
Algae, bacteria, and zooplankton were counted in samples drawn from 120- and 150-m high-rate algae ponds (those used for wastewater treatment). The fraction of nondegraded organic matter was estimated by comparing the ratio of biological and chemical oxygen demands and the bacterial, algal, and zooplankton counts to volatile suspended solids. With pond effluent quality at an acceptable level (around 18 mg of dissolved biological oxygen demand), the algae/bacteria ratio was around 1:100 or even higher, the zooplankton count was negligible, and the bacterial concentration was approximately 10 cells per liter by direct count. The data for bacteria exceeded those of earlier studies by one to three orders of magnitude.
ABSTRACT
Ammonia, at concentrations over 2.0 mM and at pH values over 8.0, inhibits photosynthesis and growth of Scenedesmus obliquus, a dominant species in high-rate sewage oxidation ponds. Photosynthesis of Chlorella pyrenoidosa, Anacystis nidulans, and Plectonema boryanum is also susceptible to ammonia inhibition. Dark respiration and cell morphology were unaffected by any combination of pH and ammonia concentrations tested, thus limiting the apparent effect to inhibition of the normal function of the chloroplasts. Methylamine had the same effect as ammonia, and its penetration into the cells was found to be pH dependent. Therefore, the dependence of toxicity of amines to algae on pH apparently results from the inability to penetrate the cell membrane in the ionized form. When operated at 120-h detention time of raw wastewater, the high-rate oxidation pond maintained a steady state with respect to algal growth and oxygen concentration, and the concentration of ammonia did not exceed 1.0 mM. Shifting the pond to 48-h detention time caused an increase in ammonia concentration in the pond water to 2.5 mM, and the pond gradually turned anaerobic. Photosynthesis, which usually elevates the pH of the pond water to 9.0 to 10.0, could not proceed beyond pH 7.9 because of the high concentration of ammonia, and the algal population was washed out and reduced to a concentration that could maintain a doubling time of 48 h without photosynthesis bringing the pH to inhibitory levels. Under these conditions, the pH of the bond becomes a factor that limits the operational efficiency of the oxidation pond.
