Carbon and Nitrogen as Regulators of Algal Growth in Treated Sewage

Continuous flow algal cultures were grown under three different growth conditions using secondary sewage treatment plant effluent as the growth medium. The only variable within each run was the hydraulic residence time. The concentrations of growth regulating nutrients were varied between the runs so comparisons of the algal mass, composition, nutrient uptake, and genera could be made. The importance of CO2 availability for algal growth was also studied. A kinetic theory which based algal growth on cellular nutrient concentration was verified. The second phase of the study was a batch culture study in which the same growth medium was used as in Phase 1. The objective of Phase 2 was to investigate significant similarities and differences between continuous and batch culture growth under otherwise similar growth conditions. Carbon dioxide enriched conditions produced as much as ten times the algal mass as CO2 deficient conditions. Algal blooms dominated by blue-green algae were found to be the result of a successional change from green to blue-green algae under CO2 enriched, nitrogen limited conditions. In the batch culture study algae exhibited a luxuriant nitrogen uptake

Algal Growth and Decomposition: Effects on Water Quality, Phase II

The decomposition and associated nutrient regeneration of three unialgal cultures and one mixed culture containing an indigenous population of bacteria and microscopic animals were studied under dark, constant temperature laboratory conditions. After periods of nutrient-deficient growth ranging from O to 30 days, these cultures were inoculated with decomposer populations and subjected to anaerobic and aerobic environments for the decomposition studies. The extend of decomposition was determined from the percentage volatile suspended solids and percentage particulate COD remaining after 200 days of decomposition. The average extent of decomposition was greater for aerobic than for anaerobic conditions. However, significant portions of the algae remained undecomposed in both cases. A fraction of the initial nitrogen and phosphorus was held within this refractory organic fraction, and the average extent of regeneration of both nitrogen and phosphorus was also greater for aerobic than anaerobic conditions. A correlation between the initial composition of algal matter and the extent to which it decomposed was made. The extent of both anaerobic and aerobic decomposition apparently increased with increasing protein and lipid content and decreased with increasing carbohydrate content. The mathematical model for predicting the extent of nitrogen and phosphorus regeneration proposed by previous researchers was further evaluated. Simplifications and various parameter assumptions were suggested. The critical nitrogen and phosphorus levels in the algae above which excess regeneration occurred were 7% and 0. 7% by weight, respectively

Factors Regulating the Growth of Algae in Continuous Culture in Diluted Secondary Sewage Treatment Plant Effluent and Subsequent Biodegradability

Heterogeneous algal cultures were grown in laboratory continuous culture in continuous flow, completely mixed chemostats in secondary sewage treatment plant effluent diluted to give an ammonia nitrogen concentration of 10 mg/1. Variables were lighting, pH, carbon dioxide availability, and hydraulic residence time. Optimum growth occurred under pH 7.0, excess CO2, and continuous lighting conditions. The availability of artificially supplied excess CO2 greatly increased the mass (standing crop) at steady-state over that produced under otherwise identical conditions for all residence times studied. For the case of excess CO2 availability, the nitrogen concentration in the algal cells regulated growth rather than the concentration of nutrients in solution. A mathematical expression was hypothesized to describe this phenomenon and was confirmed by the experimental results. Under dark-aerobic conditions, the algal cultures exerted a two-stage BOD, the second stage apparently beginning after the death of the algal cells. Longer chemostat residence times during growth produced cultures with lower percentage biodegradability. Carbon dioxide enriched growth conditions produced cultures with lower percentage biodegradability than cultures grown in a carbon dioxide deficient medium

Algal Growth and Decomposition: Effects on Water Quality

The chemical composition of algae grown in batch culture depends mainly on environmental conditions, nutrient availability, presence of predators, cell age, and species. The effects of nutrient availability and cell age on the composition of three unialgal cultures (algae + bacteria) and one hetergeneous culture (algae + bacteria + microscopic animals) were evaluated. The cultures were grown in batch culture under both nutrient-abundant and nutrient deficient conditions and the changes in compositions were observed. Luxurious uptake where nutrients are incorporated into cellular protoplasm at levels greater than those necessary for growth, and super-luxurious uptake, where some nutrients are stored rather than converted into algal protoplasm, were observed. The commonly used model for calculating the weight percentage of protein was inaccurate when super-luxurious uptake occurred. Composition of the cultures was generally characterized by protein synthesis during the nutrient-abundant growth phase, by a fluctuating composition during transition from nutrient-abundant to nutrient-deficient growth, and by lipid and/or carbohydrate synthesis and the establishment of a relatively constant composition during the nutrient-deficient growth phase. Two unialgal cultures accumulated carbohydrates and one accumulated lipids. Soluble extracellular substances were produced in all cultures which caused high concentrations of color