What is Cell Generation Time in STP?

Even though bacteria are made up of only one cell, they are incredibly complicated.

Bacteria account for roughly 95% of all microorganisms in activated sludge. They may rapidly grow (cell generation time) by dividing into two identical cells as long as enough nutrients are available. The pace at which a bacterial cell reproduces, or the cell generation time, is continually changing due to cell division (fission). The reproduction rates of aerobic, facultative, and nitrifying bacteria vary greatly between (and within) groups. Furthermore, bacterial populations are always changing, competing with one another, increasing and diminishing as the bioreactor's circumstances change.

Factors affecting the time it takes for cells to form

One important consideration is whether we're talking about cell production in a municipal or industrial wastewater system, or a hybrid of the two. For the purpose of simplicity, assume that a municipal wastewater treatment facility has less stresses than an industrial treatment system. For example, industrial wastewater treatment facilities are more likely to see larger changes in organic load, ammonia load, wastewater pH, wastewater temperature, and so on. "Abiotic factors" are what they're termed.

Nonliving components or operating variables in a biological treatment unit that impact the activity and development of the biomass are referred to as abiotic factors. Alkalinity, ionized ammonia, dissolved oxygen, hydraulic retention time (HRT), nutrients, and other abiotic variables all play a role in the activated sludge process.

Cell generation in graphical form

A: In a municipal activated sludge system with adequate abiotic variables, cell growth time can be as quick as every 11 minutes. Starting with a single bacterial cell at time 0, when this first cell multiplies (doubles) 11 minutes later, with each subsequent set of cells doubling every 11 minutes, the bacterial population grows to 17,592,186,044,416 cells!!

This is an incredible pace of growth, necessitating a significantly greater sludge squandering rate than typical industrial wastewater systems, which have a longer cell formation period.

B: Cell division can stretch out to every 30 minutes or more in the highly stressful environment of an industrial bioreactor, where less-than-ideal circumstances predominate. Starting with a single bacterial cell at time 0, when this first cell multiplies (doubles) 30 minutes later, with each subsequent set of cells doubling every 30 minutes, the bacterial population rises to just 65,536 cells after 480 minutes or eight hours.

C: The cell growth period for nitrifying bacteria is extremely sluggish, taking anywhere from 48 to 72 hours under ideal circumstances. The generation period for nitrifiers in a pressured environment might be as lengthy as 15 days. Pay attention to the X-axis' scale. The time was measured in HOURS in the two preceding figures. The scale for the nitrifier growth rate in the graph below has been changed to DAYS. The nitrifying population has only expanded to 32,768 bacterial cells after 30 days of cell division, with cell division occurring every 48 hours!

When striving to recover from disturbed conditions in general, and inhibitory or toxicity difficulties in particular, the rate at which bacteria multiply becomes critical. Recovery may take longer, probably much longer, at slower cell production rates, necessitating bioaugmentation to accelerate biological therapy. Given the sluggish cell growth rate of nitrifiers, this is especially important in the case of plants that nitrify.

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