InPlant Control and Recycle

Significant in-plant control of both waste quantity and quality is possible, particularly in the soap manufacturing subcategories where maximum flows may be 100 times the minimum. Considerably less in-plant water conservation and recycle are possible in the detergent industry, where flows per unit of product are smaller.

The largest in-plant modification that can be made is the changing or replacement of the barometric condensers (subcategories A, B, D, and E). The wastewater quantity discharged from these processes can be significantly reduced by recycling the barometric cooling water through fat skimmers, from which valuable fats and oils can be recovered, and then through the cooling towers. The only waste with this type of cooling would be the continuous small blowdown from

Table 6 Effluent Limitations for Subpart D, Glycerine Concentration

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

Table 6 Effluent Limitations for Subpart D, Glycerine Concentration

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

4.50

1.50

COD

13.50

4.50

TSS

0.60

0.20

Oil and grease

0.30

0.10

pH

a

a

(b) BAT

BOD5

0.80

0.40

COD

2.40

1.20

TSS

0.20

0.10

Oil and grease

0.08

0.04

pH

a

a

(c) NSPS

BOD5

0.80

0.40

COD

2.40

1.20

TSS

0.20

0.10

Oil and grease

0.08

0.04

pH

a

a

aWithin the range 6.0 Source: Ref. 14.

-9.0.

the skimmer. Replacement with surface condensers has been used in several plants to reduce both the waste flow and quantity of organics wasted.

Significant reduction of water usage is possible in the manufacture of liquid detergents (P) by the installation of water recycle piping and tankage and by the use of air rather than water to blowdown filling lines. In the production of bar soaps (G), the volume of discharge and the level of contamination can be reduced materially by installation of an atmospheric flash evaporator ahead of the vacuum drier. Finally, pollutant carryover from distillation columns such as those used in glycerine concentration (D) or fatty acid separation (B) can be reduced by the use of two additional special trays.

In another document [37] presenting techniques adopted by the French for pollution prevention, a new process of detergent manufacturing effluent recycle is described. As shown in Figure 20, the washout effluents from reaction and/or mixing vessels and washwater leaks from the paste preparation and pulverization pump operations are collected and recycled for use in the paste preparation process. The claim has been that pollution generation at such a plant is significantly reduced and, although the savings on water and raw materials are small, the capital and operating costs are less than those for building a wastewater treatment facility.

Besselievre [2] has reported in a review of water reuse and recycling by the industry that soap and detergent manufacturing facilities have shown an average ratio of reused and recycled water to total wastewater effluent of about 2:1. That is, over two-thirds of the generated wastewater stream in an average plant has been reused and recycled. Of this volume, about 66% has been used as cooling water and the remaining 34% for the process or other purposes.

Table 7 Effluent Limitations for Subpart G, Bar Soaps

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

Table 7 Effluent Limitations for Subpart G, Bar 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

1.02

0.34

COD

2.55

0.85

TSS

1.74

0.58

Oil and grease

0.12

0.04

pH

a

a

(b) BAT

bod5

0.40

0.20

COD

1.20

0.60

TSS

0.68

0.34

Oil and grease

0.06

0.03

pH

a

a

(c) NSPS

bod5

0.40

0.20

COD

1.20

0.60

TSS

0.68

0.34

Oil and grease

0.06

0.03

PH

a

a

aWithin the range 6.0 Source: Ref. 14.

-9.0.

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