Page 402 - Industrial Wastewater Treatment, Recycling and Reuse

374 Industrial Wastewater Treatment, Recycling, and Reuse

9.4 DIFFERENT TYPES OF AEROBIC TREATMENT
TECHNOLOGIES
Selection of treatment technology depends on:
1. Type of wastewater and its characteristics
2. Quality of treated wastewater required
3. Footprint available.

9.4.1 Activated Sludge Process
The ASP, a suspended growth process, is used routinely for biological treat-
ment of both municipal and industrial wastewaters. It is the oldest and most
widely practiced treatment method for treatment of municipal as well as
industrial wastewater; this process is 130 years old and was the result of
the work of Dr. Angus Smith. Dr. Smith discovered that the aeration of
wastewater resulted in the more rapid oxidation of organic matter. The
aeration of wastewater was subsequently studied by a number of investiga-
tors, including Black and Phelps in 1910 and then in 1912 and 1913 by Clark
and Gage respectively. Arden and Lockett, in further investigations, found
that sludge played an important role in the results obtained by aeration. The
process was thus named ASP by Arden and Lockett because it involved the
production of an activated mass of micro-organisms capable of aerobic
stabilization of organic material in the wastewater (Metcalf & Eddy, Inc.
2003). The process finally came into common use in 1920 (Sarin, 2013).
Activated sludge plant involves:
1. Wastewater aeration in the presence of a microbial suspension.
2. Solid-liquid separation following aeration.
3. Discharge of clarified effluent.
4. Wasting of excess biomass.
5. Return of remaining biomass to the aeration tank.
Typically, after primary treatment, suspended impurities are removed from
wastewater using an ASP-based biological treatment system comprised of an
aeration tank followed by a secondary clarifier (Figure 9.4). The aeration
tank is a completely mixed or a plug flow (in some cases) bioreactor where
specific concentration of biomass measured as mixed liquor suspended solids
(MLSS) or mixed liquor volatile suspended solids (MLVSS) is maintained
along with sufficient dissolved oxygen (DO) concentration (typically
2 mg/L) to effect biodegradation of soluble organic impurities measured
as biological oxygen demand (BOD 5 ) or chemical oxygen demand
(COD). The aeration tank is provided with fine bubble diffused aeration
pipework at the bottom to transfer the required oxygen to the biomass