Wastewater Treatment Methods

The soap and detergent manufacturing industry makes routine use of various physicochemical and biological pretreatment methods to control the quality of its discharges. A survey of these treatment processes is presented in Table 11 [13], which also shows the usual removal efficiencies of each unit process on the various pollutants of concern. According to Nemerow [38] and Wang and Krofta [39], the origin of major wastes is in washing and purifying soaps and detergents and the resulting major pollutants are high BOD and certain soaps (oily and greasy, alkali, and high-temperature wastes), which are removed primarily through air flotation and skimming, and precipitation with the use of CaCl2 as a coagulant.

Figure 21 presents a composite flow diagram describing a complete treatment train of the unit processes that may be used in a large soap and detergent manufacturing plant to treat its wastes. As a minimum requirement, flow equalization to smooth out peak discharges should be utilized even at a production facility that has a small-volume batch operation. Larger plants with integrated product lines may require additional treatment of their wastewaters for both suspended solids and organic materials' reduction. Coagulation and sedimentation are used by the industry for removing the greater portion of the large solid particles in its waste. On the other 8hand, sand or mixed-bed filters used after biological treatment can be utilized to eliminate fine particles. One of the biological treatment processes or, alternatively, granular or powdered activated carbon is the usual method employed for the removal of particulate or soluble organics from the waste streams. Finally, as a tertiary step for removing particular ionized pollutants or

Table 8 Effluent Limitations for Subpart H, Liquid Soaps

Effluent limitations [metric units (kg/1000 kg of anhydrous product)]

Table 8 Effluent Limitations for Subpart H, Liquid Soaps

Effluent limitations [metric units (kg/1000 kg of anhydrous product)]

Effluent characteristic

Maximum for any 1 Average of daily values for 30 consecutive days day shall not exceed

(a) BPT

BOD5

0.03

0.01

COD

0.15

0.05

TSS

0.03

0.01

Oil and grease

0.03

0.01

pH

a

a

(b) BAT

BOD5

0.02

0.01

COD

0.10

0.05

TSS

0.02

0.01

Oil and grease

0.02

0.01

pH

a

a

(c) NSPS

BOD5

0.02

0.01

COD

0.10

0.05

TSS

0.02

0.01

Oil and grease

0.02

0.01

pH

a

a

aWithin the range 6.0 Source: Ref. 14.

-9.0.

total dissolved solids (TDS), a few manufacturing facilities have employed either ion exchange or the reverse osmosis process.

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