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Questions and Answers
Who is considered a pioneer in the use of algae to treat wastewater?
Oswald
What is the primary mechanism by which microalgae remove nutrients from wastewater?
Assimilation of nutrients as the algae grow
What percentage of phosphorus removal is attributed to phosphorus precipitation caused by high pH induced by algae?
Up to 90%
What is the benefit of microalgae to heterotrophs in secondary treatment?
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What is the effect of pH increase during photosynthesis on wastewater?
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What is the potential use of microalgal biomass?
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What is the characteristic of algae that enables them to synthesize organic molecules?
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What is the stoichiometric formula for the most common elements in an average algal cell?
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What is the primary limiting factor for algal growth in wastewater, despite high nutrient concentrations?
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List two biotic factors that affect algal growth.
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What is the overall stoichiometric formula for photosynthesis?
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What is the enzyme required for microalgae to convert HCO3– to CO2?
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What percentage of algal carbon in high rate algal ponds is derived from heterotrophic utilization of organic carbon?
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What is the mode of carbon nutrition that can be shifted from autotrophy to heterotrophy in some algal species?
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Why may extra carbon dioxide be necessary for algal growth?
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How can atmospheric CO2 be provided to algal cultures?
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Why is CO2 enrichment essential in microalgae cultures?
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What form of inorganic carbon is present at higher pH values, and why is it a problem for algal growth?
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What is the preferred nitrogen compound for microalgae, and why?
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Why are high concentrations of ammonium (>20 mg NH4+-N per liter) not recommended for microalgae cultures?
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What is the most energy-demanding nitrogen source for microalgae, and why is it used?
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What is the term used to describe the uptake of nitrogen in excess of immediate metabolic needs by microalgae?
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In what form do microalgae take up phosphorus, and what is the process of uptake?
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What is the role of phosphatases in the uptake of phosphorus by microalgae?
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What is the form in which microalgae store excess phosphorus in their cells?
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What are the micronutrients required by microalgae in smaller amounts?
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What is the role of a chelating agent like EDTA in commercial algal cultures?
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How do microalgae obtain energy?
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What percentage of total incident solar energy is converted into chemical energy in outdoor ponds?
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What strategies do microalgae use to remain near the water surface to catch enough light?
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Why are algae in deeper parts of a culture vessel often light limited?
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What is the purpose of gas vacuoles in some cyanobacteria?
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What is the negative effect of high algal density on light availability in cultures?
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Why is turbulence essential in algal cultures cultivated in raw wastewater?
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What is the recommended depth range for algal culture ponds to prevent light limitation?
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What is the negative effect of excessive light on algal growth?
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What is the optimal temperature range for microalgal growth?
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Why is overheating a problem in algal cultures, especially in humid climates?
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How does pH affect algal growth and species composition?
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What is the effect of pH on inorganic carbon availability?
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Study Notes
Oswald and Algae-Based Wastewater Treatment
- Oswald, a pioneer in using algae to treat wastewater, died in 2005 at the age of 86.
- His work laid the foundation for using microalgae in wastewater treatment and nutrient removal, which has shown great promise since the 1960s.
Microalgae Characteristics
- Microalgae are mostly autotrophs, synthesizing organic molecules from inorganic nutrients.
- The stoichiometric formula for the most common elements in an average algal cell is C106H181O45N16P.
Factors Affecting Algal Growth
- Abiotic factors: temperature, nutrient concentration, light (quality and quantity), O2 and CO2, pH, salinity, toxic chemicals
- Biotic factors: pathogens (bacteria, fungi, viruses), predation by zooplankton, competition between species
- Operational factors: mixing, dilution rate, harvesting frequency, addition of bicarbonate, depth
Carbon Assimilation
- Microalgae assimilate inorganic carbon (mostly CO2) during photosynthesis.
- The overall stoichiometric formula for photosynthesis is: 6 H2O + 6 CO2 + light ⇒ C6H12O6 + 6 O2
- Algae can use organic carbon sources, such as organic acids, sugars, acetate, or glycerol, through heterotrophic metabolism.
Nitrogen Assimilation
- Nitrogen is the second most important nutrient for microalgae, comprising up to 10% of the biomass.
- Nitrogen sources: ammonium (NH4+), nitrate (NO3-), urea (NH2CONH2), nitrite (NO2-), amino acids (arginine, glutamine, asparagine), and nitrogen gas (N2) through nitrogen fixation.
Phosphorus Assimilation
- Phosphorus is an essential macronutrient for microalgae, taken up as inorganic orthophosphate (PO43-).
- Algae can assimilate excess phosphorus, storing it in polyphosphate (volutin) granules.
Other Nutrients
- Other macronutrients: sulphur, potassium, calcium, magnesium
- Micronutrients: manganese, molybdenum, copper, iron, zinc, boron, chloride, nickel
- Some algal species require additional nutrients, such as sodium, silicon, cobalt, iodine, vanadium, and selenium.
Light and Microalgae
- Microalgae are phototrophs, using light energy to produce chemical energy through photosynthesis.
- Light intensity affects algal growth, with excessive light leading to photoinhibition.
- Turbulence is essential to expose all cells to light and prevent light limitation.
Temperature and Microalgae
- Temperature affects algal growth, with an optimum temperature range for growth.
- Increased temperature enhances growth until an optimum is reached, after which growth rate declines.
- Overheating is a problem in humid climates, while low temperatures limit growth in cold climates.
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Description
This quiz covers the abiotic and biotic factors that influence algal growth, including temperature, nutrient concentration, light, and biotic factors like pathogens and predation.
