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The biological treatment techniques used can be classified into attached growth processes and suspended growth processes. Which of the following treatments is classified under attached growth processes?
Activated sludge process
Aerated lagoon
Sludge digestion system
Rotating biological conductor
Rotating biological conductor
Attached growth processes, also known as biofilm processes, utilize a solid medium (media) upon which microorganisms grow to form a biofilm. The Rotating Biological Contactor (RBC) is a classic example where biomass grows on rotating discs partially submerged in wastewater.
CPHEEO Manual on Sewerage and Sewage Treatment Systems
Attached growth processes, also known as biofilm processes, utilize a solid medium (media) upon which microorganisms grow to form a biofilm. The Rotating Biological Contactor (RBC) is a classic example where biomass grows on rotating discs partially submerged in wastewater.
Organic┬аLoading┬аRate=AQтЛЕS0тАЛтАЛ тАФ where Q is flow rate, S0тАЛ is influent BOD, and A is total surface area of discs
Hydraulic┬аLoading┬аRate=AQтАЛ тАФ flow rate per unit surface area of the medium
In an RBC, microorganisms adhere to the surface of rotating plastic discs. As the discs rotate, the biofilm is alternately exposed to wastewater for food uptake and to the atmosphere for oxygen transfer, facilitating aerobic biodegradation of organic matter.
Attached growth systems have higher biomass concentration per unit volume compared to suspended growth systems.
Biofilm development on media provides a stable environment for slow-growing nitrifying bacteria.
Rotating Biological Contactors are highly resistant to shock loads compared to activated sludge systems.
Periodic sloughing of the biofilm is a natural process in these systems.
Lower energy consumption compared to mechanical aeration
High process stability and resistance to organic shocks
Minimal sludge production
Compact footprint
Potential for odor issues if not properly ventilated
High initial capital cost for synthetic media
Mechanical maintenance requirements for rotating shafts
Small to medium municipal wastewater treatment plants
Tertiary treatment for nitrification of secondary effluent
Activated sludge, aerated lagoons, and sludge digestion are all suspended growth systems where microorganisms remain dispersed in the liquid phase.
In suspended growth, oxygen is typically supplied via mechanical aerators or diffused aeration systems.
D is correct тАФ Rotating biological conductor utilizes a fixed-film media for microbial attachment, classifying it as an attached growth process.
In exams, remember that any process utilizing media like rock, plastic, or rotating discs is 'Attached' or 'Fixed-Film', whereas aeration tanks rely on 'Suspended' biomass.
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