Answer Key
- The Monod equation describes the relationship between the specific growth rate of microorganisms and the substrate concentration, where the growth rate increases with substrate concentration until it reaches a maximum. The Haldane equation modifies this model to account for inhibitory substrates; it shows that after reaching a maximum, the specific growth rate begins to decrease as the substrate concentration becomes toxic or inhibitory to the microorganisms.
- The three main metabolic phases are oxidation, synthesis, and endogenous respiration. Oxidation (respiration) breaks down organic or inorganic matter to release energy. Synthesis uses this energy, along with organic matter and nutrients, to build new cell material (protoplasm). Endogenous respiration is the auto-digestion or self-destruction of cellular material to provide energy for basic cell functions, especially when external food sources are limited.
- The Food to Microorganisms (M/F) ratio is critical for process control. A low M/F ratio indicates excess food, leading to a maximum rate of metabolism but poor settling characteristics. Conversely, a high M/F ratio signifies a limited food supply (starvation conditions), resulting in a lower metabolism rate but good biomass settling and high BOD removal efficiency.
- Endogenous respiration is the internal process where microorganisms auto-digest their own cellular material to obtain energy for essential functions like motion and enzyme activation. This process becomes dominant when the external food supply (substrate) becomes limited, forcing the cells to break down their own protoplasm for maintenance energy.
- Advantages of recirculation in high-rate trickling filters include: (1) providing continuous seeding of active microorganisms to stimulate biochemical stabilization, (2) distributing the diurnal organic load more uniformly, and (3) increasing flow to improve distribution, reduce clogging, and discourage the growth of filter flies.
- In the Contact Stabilization process, wastewater is mixed with well-activated sludge for a short period (0.5-1.5 hours) where suspended and colloidal BOD is rapidly absorbed. The sludge is then separated and reaerated in a separate activation tank to stabilize the adsorbed material before being returned to contact the incoming wastewater. It is ideally suited for wastewaters where a large portion of the BOD is in suspended or colloidal form.
- The first stage of anaerobic treatment involves acid-forming bacteria converting complex organic materials (proteins, fats, carbohydrates) into simpler organic acids. In the second stage, methane-forming bacteria convert these organic acids into methane and carbon dioxide, which stabilizes the waste and significantly reduces its BOD or COD.
- The three idealized reactor types are the Batch Reactor, where all reactants are added at once; the Plug Flow Reactor, where fluid flows in an orderly fashion without elements overtaking one another; and the Completely Mixed Reactor, where contents are uniformly stirred and homogenous throughout.
- Fixed-film systems are considered more stable due to their higher biomass concentration and greater mass transfer resistance from the bulk solution into the biofilm. This resistance shields the microorganisms from high concentrations of toxins during short-term shock loads, as concentrations in the biofilm change more slowly. Additionally, since the microorganisms are physically retained, washout is prevented even if their growth rate is reduced.
- Acclimation is the process by which microorganisms become more tolerant or adapt to an inhibitory concentration level of a toxic substance. This adaptive response can result from the neutralization of the toxic material by the microorganisms’ biological activity or from the selective growth of a culture that is unaffected by the toxic substance.