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An Introduction to Biological Treatment and Membrane Filtration 371

conditions. Therefore, biological treatment is an important and integral part
of any wastewater treatment plant that treats wastewater from either a
municipality or industry having soluble organic impurities or a mix of the
two types of wastewater sources. The obvious economic advantage, both
in terms of capital investment and operating costs, of biological treatment
over other treatment processes such as chemical oxidation or thermal
oxidation, has cemented its place in any integrated wastewater treatment plant.
Biological treatment methods can be further divided into different
categories (Sutton, 2006): such as aerobic, anaerobic, anoxic processes
which are used in specific condition of waste to be purified and constituents
to be removed. However we would go in details of aerobic process with
reference to the subject of this article.

Biological treatment
methods

Aerobic Anaerobic

Contact beds
Suspended growth Attached growth UASBs
Hybrid
Anaerobic
Activated sludge Trickling filter Reactors
Extended aeration Moving bed bioreactor
• Sequential batch Rotating bio-disc
reactor Land treatment
• Membrane bioreactor
Aerated lagoons
Waste stabilization pond

9.2.1 Aerobic and Anaerobic (Mittal, 2011)
Before we go in to the discussions of various aerobic biological treatment
processes, it is important to briefly discuss the terms aerobic and anaerobic.
Aerobic, as the title suggests, means in the presence of air (oxygen), while
anaerobic means in the absence of air (oxygen). These two terms are directly
related to the type of bacteria or microorganisms that are involved in the
degradation of organic impurities in given wastewater and the operating
conditions of the bioreactor. Therefore, aerobic treatment processes take
place in the presence of air and utilize those microorganisms (also called