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Pollution Prevention and Water Conservation Methods

5.1 General

Respondents were given a check list in the survey form that contained various pollution prevention methods and procedures that are known to be commonly used by printed wiring board manufacturers and were asked to indicate which ones are employed at their facilities (see Appendix A, sections 6.1, 6.2, and 6.3). The lists were prepared using methods identified during the NCMS/NAMF study (ref. 1) and through the procedures, including industry review, used to develop the PWB survey form. The pollution prevention methods listed in the survey form are grouped into three categories: (1) good operating procedures; (2) methods to reduce or recover drag-out; and (3) methods to reduce water usage. Space was provided to allow entry of other methods, practices, or procedures which were not listed and a separate section was included to permit respondents to describe any innovative pollution prevention practices. The responses to these questions are summarized and discussed in this section. Where appropriate, the results are compared to those of the NCMS/NAMF survey.

Data presented in this section are aggregated rather than presented on a facility by facility basis. Responses from individual facilities can be found in the electronic database that accompanies this report.

5.2 Good Operating Procedures

Pollution prevention methods listed under good operating procedures include various administrative and equipment related topics that can affect waste generation. The survey results for this category are shown in Exhibit 5-1. Fifty percent of the respondents indicated that they have established a formal pollution prevention program. This result closely matches the NCMS/NAMF survey results of plating shops (ref. 1). Similarly, close results were found with regard to conducting employee education for pollution prevention (68.4% for PWB shops vs 68.2% for plating shops). In general, the PWB facilities make more frequent use than plating shops of pollution prevention methods that relate to chemical inventory, process bath control, and use of chemicals. For example, nearly all of the PWB manufacturing respondents indicated that they perform in-house bath analyses and maintain records of this work. This percentage is noticeably higher than for the plating shops. Other areas where the PWB shops have a higher percentage of application of methods as compared to plating shops includes preventative maintenance of racks and tanks and use of overflow alarms and leak detection. Surprisingly, only 26.3% of the PWB shops indicated that they employ statistical process control (SPC) for bath maintenance. SPC is a potential cost reduction and pollution prevention method that relates to analytical work and record keeping, practices employed by most of these facilities.

Drag-Out Reduction or Recovery Method No. of PWB
Respondents
Using Method
% of PWB
Respondents
Using Method
% of Plating
Shops Using
Method
2
Perform in-house regular process bath analysis 37 97.4 92.1
Maintain records of analysis and additions 37 97.4 85.8
Dump process baths based on analysis rather than schedules 35 92.1 73.6
Have preventive maintenance program for tanks 35 92.1 58.2
Perform regular maintenance and performance checks for racks 32 84.2 65.1
Have overflow alarms in process tanks 31 81.6 15.7
Control inventory levels and access 30 78.9 65.1
Conduct employee education for pollution prevention 26 68.4 68.2
Look for opportunities to reduce energy consumption 24 63.2 --
Have a formal policy statement regarding pollution prevention 20 52.6 49.7
Have a formal pollution prevention program 19 50.0 50.6
Have a leak detection system 16 42.1 14.8
Employ statistical process controls for chemical adds 10 26.3 --
Recycle non-contact cooling water1 1 2.6 --
1 Added by respondent under "Other."
2 Results published in Reference 1.
-- Indicates that method was not listed in that particular survey and not added by any respondents.
Exhibit 5-1. Good Operating Procedures Employed by Survey Respondents

5.3 Drag-out Reduction and Recovery Methods

Drag-out is the clinging film of process solution covering a part when it is removed from a tank. This solution is usually small in volume and high in chemical concentration. The primary purpose of rinsing is to sufficiently remove the drag-out from the part so that the part's surface is relatively free of process chemicals. Rinsing is necessary to clean the surface of the part and to prevent contaminating subsequent process baths. The quantity of rinse water needed to sufficiently clean the part is directly related to the quantity of drag-out and other factors.i When the quantity of drag-out is reduced or the drag-out is recovered and reused, the overall quantity of pollution from a facility is reduced. A summary of respondent data relating to drag-out reduction and recovery methods employed at PWB manufacturing facilities and plating shops is presented in Exhibit 5-2. The use of several key methods by PWB manufacturers and plating shops is compared graphically in Exhibit 5-3.

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Drag-Out Reduction or Recovery Method No. of PWB
Respondents
Using Method
% of PWB
Respondents
Using Method
% of Plating
Shops Using
Method
1
Allow for long drip times over process tanks 29 76.3 60.42
Have drip shields between process and rinse tanks 23 60.5 56.9
Practice slow rack withdrawal from process tanks 20 52.6 38.12
Use drag-in/drag-out rinse tank arrangements 13 34.2 20.82
Use drag-out tanks and return contents to process baths 13 34.2 61.02
Use wetting agents to lower viscosity 12 31.6 32.4
Use air-knives to remove drag-out 10 26.3 2.22
Use drip tanks and return contents to process baths 4 10.5 27.02
Use fog or spray rinses over heated process baths 4 10.5 18.92
Operate at lowest permissible chemical concentrations 3 7.9 34.6
Operate at highest permissible temperatures 2 5.2 17.9
1 Results published in Reference 1.
2 Data are for manually operated methods, which are the predominant type for the plating operations surveyed during the NCMS/NAMF project.
Exhibit 5-2. Drag-Out Reduction and Recovery Methods Data

Exhibit 5-3. Distribution of Drag-Out Reduction and Recovery Methods

In general, the survey results indicate that PWB manufacturers more frequently control the motion of the parts (e.g., slow withdrawal from tank and long drip tanks) as a means of reducing drag-out than either adjusting the bath chemistry, adjusting the solution temperature, or employing drag-out recovery. Plating shops tend to rely more on drag-out recovery than other methods of reducing drag-out losses and also make significant efforts to control process chemistry and bath temperature.

In part, the variance found in the results of the two surveys with regard to drag-out reduction may be due to differences in the shapes of the parts being processed, the permissible latitude in process control, and differences in bath temperatures. The flat surfaces of PWBs improve the performance of control methods for drag-out reduction as compared to the range of part shapes processed by plating shops. For example, parts with flat surfaces, like PWBs, will more completely drain when held for an extended time period as compared to a cup-shaped plated part with internal surfaces (e.g., auto bumper). Although many plating processes require close chemical control, there are some (e.g., chrome plating) that can be operated over a significant range of concentrations of constituents. By reducing the chemical concentration of the bath, platers are able to reduce bath viscosity and in turn, reduce drag-out. PWB manufacturers may have less latitude with regard to varying the bath concentration. Increasing bath temperature is another means of reducing viscosity used to a moderate extent by plating shops. In general, there are a smaller percentage of heated process tanks in PWB shops than in plating shops and therefore less opportunity to take advantage of this method of reducing drag-out. Heated process tanks in PWB facilities where this method may apply include cleaners, permanganate desmear, and micro-etches.

The most common method of drag-out recovery employed in the plating industry is the use of drag-out tanks. Drag-out tanks are initially filled with clean water and are situated immediately after process baths. Parts exiting process tanks are immediately rinsed in the drag-out tank. The contents of the drag-out tank, the initial water and process fluid dragged out by racks and parts, is used to replace evaporate loss in the preceding process tank. Drip tanks (a less sophisticated method of drag-out recovery) are not initially filled with water. They are simply a tank over which racks are hung to drip. The contents of drip tanks are returned to the process tank. Both of these methods require that the process tank is heated in order to evaporate water from the process tank and therefore make "head-room" for the returned solution. As such, drag-out and drip tanks are only applicable to heated process solutions. Only 34.2% of the PWB survey respondents indicated they use drag-out tanks and only 10.5% use drip tanks, compared to 80.5% and 33.6% respectively, from the plating shop survey. The low use of drag-out tanks in PWB shops is possibly due to the permissible latitude in process control and differences in bath temperatures, as discussed above. However, some PWB heated process tanks (cleaners, permanganate, micro-etches) do lend themselves to the use of drag-out tanks for drag-out recovery.

5.4 Rinse Water Use Reduction

The vast majority of wastewater generated at PWB facilities is the result of rinsing. A summary of respondent data relating to rinse water use reduction methods employed at PWB manufacturing facilities and plating shops is presented in Exhibit 5-4. The use of several key rinse water reduction methods used by PWB manufacturers and plating shops is compared graphically in Exhibit 5-5.

Drag-Out Reduction or Recovery Method No. of PWB
Respondents
Using Method
% of PWB
Respondents
Using Method
% of Plating
Shops Using
Method
2
Use counterflow rinses 31 81.2 68.2
Use flow controllers 30 78.9 69.8
Use spray rinses 27 71.1 39.0
Track water use with flow meters 25 65.7 11.6
Reactive or cascade rinsing 20 52.6 23.9
Use rinse timers 19 50.0 11.3
Recycle or reuse rinse water 11 28.9 --
Use conductivity or pH controllers 10 26.3 16.0
Use part sensors to activate rinse1 4 10.5 --
Use squeeze rollers to remove water1 1 2.6 --
Use spring-loaded valves to activate rinse1 1 2.6 --
Exhibit 5-4. Rinse Water Use Reduction Methods Data
1 Added by respondent under "Other."
2 Results published in Reference 1.
-- Indicates that method was not listed in that particular survey and not added by any respondents.

Exhibit 5-5. Distribution of Rinse Water Use Reduction Methods

For both types of shops, the primary means of rinse water use reduction is counterflow rinsing. A counterflow rinse is a series of two or more rinse tanks piped together in a manner that clean water enters the final tank of the series and flows into the next tank in a direction opposite that of the work flow. Far less water is required to maintain sufficiently clean water in the system than with a single rinse tank. Eighty-one percent of PWB shops employ this method of water use reduction. This is a higher percentage than for plating shops (68.2%). Flow controllers, which can be used in conjunction with counterflow rinsing, are also very common in PWB shops (78.9% compared to 69.8% in plating shops). Automated water use controllers (i.e., conductivity/pH or timer types) are also more common in PWB shops than in plating shops. Three respondents indicated that they use "part sensors" to reduce water use. Part sensors are used primarily on conveyorized equipment to turn on the water flow when a PWB reaches the rinse module, then automatically turn off the flow until the next part arrives. The fact that rinse water control devices were generally more common in PWB than plating shops is likely a result of stricter rinse criteria (i.e., a more pure rinse water requirement) for PWB manufacturing than for typical plating. Rinse water purity requirements are discussed in Reference 1.

Exhibit 5-6 presents a summary of rinse water reduction achieved by PWB facilities through pollution prevention efforts. Thirty-four percent (34%) of the shops responding to the survey reported that they reduced rinse water consumption since 1990. Eleven percent (11%) reduced their water use by more than half, while 16% reduced water use by one-third or more. However, the majority of shops did not report any rinse water use reduction.

Respondent
ID
Production
(board ft2 per year)
Current
Average
Discharge
(gal/day)
Discharge
Reduction
(gal/day)
Base Year
for Reduction
36930A nr 27,000 0 -
955099 nr 120,000 0 -
55595 nr 20,000 0 -
44486 nr 100,000 0 -
955703 nr 98,000 0 -
6710 15,000 10,560 2,500 1993
947745 40,000 13,000 0 -
44657 42,358 6,000 3,000 1994
29710 57,000 74,000 0 -
502100 60,000 nr 150 -
32482 75,000 31,000 0 -
25503 90,000 5,000 7,000 1993
36930 96,000 nr 60,000 1993
965874 175,000 21,000 0 -
953880 180,000 35,000 10,000 1992
33089 200,000 16,000 3,200 1991
T3 200,000 20,000 0 -
3470 240,000 20,000 3,000 1994
43841 250,000 38,000 50,000 1987
279 250,000 5,200 0 -
237900 273,000 105,000 0 -
273701 280,000 25,000 0 -
41739 300,000 57,125 5,000 1993
959951 320,000 20,000 0 -
42692 360,000 100,000 0 -
358000 500,000 9,000 0 -
43694 500,000 30,000 28,000 1990
37817 540,000 6,000 0 -
42751 540,000 140,000 0 -
T2 600,000 48,000 0 -
133000 600,000 160,000 0 -
T1 936,000 160,000 180,000 1991
740500 1,800,000 400,000 0 -
946587 1,900,000 200,000 0 -
3023 2,300,000 145,000 0 -
31838 3,000,000 280,000 0 -
462800 3,750,000 26,000 0 -
107300 5,000,000 250,000 200,000 1993
nr = no response
Exhibit 5-6. Wastewater Discharge Reduction Achieved Through Pollution Prevention


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