Project Report: Wastewater Data
This section of the report contains a discussion of wastewater data provided by survey respondents, including discharge type, flow rates, discharge limits, compliance difficulties, and costs for raw water and sewer use charges. Wastewater treatment methods employed by survey respondents are covered in Section 8.0.
4.2 Discharge Types
For the purpose of this survey, the discharge type refers to the destination of wastewater discharges regulated by categorical effluent standards. The three possible selections in the survey questionnaire were direct discharge (i.e., to surface water such as a river or stream), indirect discharge (to a publicly owned treatment works or POTW), or zero discharge (no process wastewater discharge from PWB manufacturing).
The survey data (see Exhibit 4-1) show that the majority of the respondents are indirect dischargers. This is especially true for the small to mid-sized PWB manufacturing facilities. Seventy-seven percent of all respondents indicated that they are indirect dischargers, whereas 94% of the shops with a production rate below 300,000 board ft2 are indirect dischargers.
|Discharge Type||Flow for 12-Mth Period||Cost of Water and Sewer|
(board ft2 per year)
|Direct||In-direct||Zero|| Avg Flow
(gal/ layer ssf)
1Assumes 260-day year.
2 Water and sewer costs are combined.
3 Well water.
4.3 Discharge Flow Rates
Wastewater discharge data are summarized in Exhibit 4-1, columns 6 to 9. Average daily flow rates range from 5,200 gpd (ID# 279) to 400,000 gpd (ID# 740500). The vast majority of water used in PWB facilities is used for rinsing. The quantity of rinse water used is dependent on numerous factors, including types of boards manufactured, production rate, cost of water and sewer use, drag-out rate, use of pollution prevention measures (e.g., extended draining time), the rinsing configuration (e.g., single rinse vs. counterflow rinse), and water use control method (e.g., continuously running rinses vs. those controlled by conductivity controllers). Some of these factors are examined in this section.
The values in columns 7 and 8 express water use in terms of production. In column 7, the values are calculated as the average flow rate in gallons per square feet of production (measured as one side of finished board). The data in column 7 indicate that the production of double-sided boards and multi-layer boards require more rinse water per square feet of production than single-sided boards. For example, the lowest flow rate per square foot of board production is achieved by ID# 462800, whose production is 100% single-sided boards. The highest flow per square foot of board production is used by ID# 29710, whose production is 0% single-sided boards. This relationship is not surprising because the production of double-sided boards and multi-layer boards require the employment of significantly more processing and rinsing steps.
In column 8, the values are calculated as the average flow rate in gallons per square feet of "wetted surface." The wetted surface area was calculated based on the total surface area of all layers of boards manufactured (layer data are given in Exhibit 2-2). Because these adjusted production-based flow rates account for multiple processing and rinsing steps, they are a better means of comparing water use among respondents. Using this method of comparison, the range of water use among respondents is smaller than in column 7, but is still very large (0.90 gal/ssf to 91.2 gal/ssf)d. This leads to the conclusion that some facilities have significantly better water use practices than other facilities.
The high water use variability among PWB manufacturers can be examined by comparing the adjusted production-based flow rates (column 8) to other data. In particular, there appears to be a relationship between the adjusted production-based flow rates and the cost of water and sewer use. For facilities that have very high combined water and sewer costs, the adjusted production-based flow rates are very low. There are three facilities with combined water and sewer costs above $7.00/1,000 gal (ID#'s 279, 3023, and 462800) for which there are adjusted production-based flow rate data. The range of flow rates for these three facilities is 0.90 gal/ssf to 2.70 gal/ssf, well below the median and mean values (8.20 gal/ssf and 12.42 gal/ssf). Alternatively, facilities with very low combined water and sewer costs have high adjusted production-based flow rates. There are three facilities with flow rates above 20 gal/ssf for which there are water and sewer cost data. The range of combined water and sewer costs for these three facilities is $0.03/1,000 gal to $3.00/1,000 gal (themedian and mean values for all facilities providing data are $3.68/1,000 gal and $5.06/1,000 gal).
Variation of water and sewer use costs among survey respondents is likely due in part to geographical location, with higher costs in coastal and arid regions (CAI does not know the location of respondents, will ask IPC to verify this conclusion for final report.).
Low water use rates can be achieved through the implementation of simple water conservation techniques and/or by using technologies such as ion exchange that recycle water. ID# 462800 has achieved the lowest production-based flow rate without the use of any sophisticated recycling technology. Rather, they use flow controllers, rinse timers, and reactive or cascade rinsing.e The data also indicate that facilities that have implemented the ion exchange technology within their processes have a lower average flow rate than those that have not implemented this technology.f
The data also indicate that the use of water conservation methods does not always result in low water use. The four facilities with the highest production-based flow rates do not use ion exchange recycling, but they all indicated that they employ counterflow rinsing, plus some other methods of water conservation. In such cases, it is probable that water is simply being wasted by having unnecessarily high flow rates in the rinse tanks (e.g., flowing water during periods of non-production).
4.4 Discharge Limits and Compliance Difficulties
Discharge limitations of the survey respondents for key pollutants are shown in Exhibit 4-2. Wastewater discharges from printed wiring board manufacturing facilities are regulated by Federal effluent guidelines at 40 CFR Part 413 or Part 433, depending on whether the facility is an independent printed wiring board manufacturer or an integrated facility. The Federal limitations for key pollutants are shown in rows 2 and 3 of Exhibit 4-2. The data indicate that the majority of respondents (63%) must meet discharge limitations that are more stringent than the Federal standards. One respondent reported having limitations higher than the Federal limitations.g The most stringent limitations reported for each of the key pollutants are: 0.25 mg/l Cu (max), 0.05 mg/l Pb (avg), 0.04 mg/l Ni (avg), 0.01 mg/l Ag (avg), 0.01 mg/l CN (avg), and 0.58 mg/l TTO (max).
Very few respondents reported any wastewater compliance difficulties (identified by bold type in Exhibit 4-2).h Of the respondents that reported difficulties, 11% reported difficulties with lead, 8% with copper, and 3% with silver. A large majority of respondents (86%) did not report any compliance difficulties. The majority of those reporting compliance difficulties have discharge limitations lower than Federal standards, but in each case, those limitations are not the lowest limitations imposed on respondents.
|Respondent ID||Cu max
|40 CFR 413||4.5||2.7||0.6||0.4||4.1||2.6||1.2||0.7||1.9||1.0||2.13||-|
|40 CFR 433||3.38||2.07||0.69||0.43||3.98||2.38||0.43||0.24||1.20||0.65||2.13||-|
nr = no response
40 CFR 413 maximum is based on a 4 day average concentration.
40 CFR 433 maximum is based on a monthly average concentration.
Exhibit 4-2. Discharge Limitations and Compliance Difficulties