End - Of - Pipe Treatment
End-of-pipe treatment is, by definition, not pollution prevention. However, it is an important aspect of pollution control and it sometimes competes financially with pollution prevention options when facilities are developing pollution control strategies. To make informed decisions about implementing pollution prevention alternatives that include consideration of all applicable costs and potential savings requires accurate data. Therefore, the topic of waste treatment was included in the PWB survey project so that the true costs of treatment could be examined. The applicable portion of the survey form requested respondents to describe the type of waste treatment system currently in use at their facilities and to provide operating and cost data. These data are summarized and discussed in this section.
8.2 Wastewater Characterization
Data that characterize the respondent's raw wastewater from their PWB processes are presented in Exhibit 8-1. The data indicate that copper and lead are the most abundant of the regulated metals. Copper was reported to be present by all respondents. Copper concentrations in the raw wastewaters ranged from 0.4 mg/l to greater than 100 mg/l. Factors affecting the copper concentration of raw wastewater may include: the effectiveness of rinse water controls (which will determine the level of dilution); whether or not process solutions that have relatively high copper concentrations (e.g., spent acids and micro-etches) are commingled directly with rinse water; the effectiveness of drag-out reduction and recovery; and the presence of upstream recovery/recycle technologies, such as ion exchange and electrowinning.
(board ft2 per year)
nr = no response
Sixty-two (62%) of the facilities that provided raw wastewater data reported the presence of lead. Concentrations of lead ranged from less than 1 mg/l to 20 mg/l. The primary sources of lead in a PWB manufacturing process are drag-out from the tin-lead electroplating and stripping operations. Lead may also be introduced in small quantities from reflow or solder-leveling operations. Respondents not reporting lead in their raw wastewater may remove lead with a recovery/recycle technology (e.g., ion exchange) upstream, or may not perform lead plating (or, therefore, stripping). Also, possibly due to a higher sensitivity to lead discharges than some other metals, more aggressive drag-out reduction and recovery methods may be practiced for lead sources.
Forty-eight percent (48%) of the facilities that provided raw wastewater data reported the presence of nickel. Nickel concentrations ranged from less than 1 mg/l to 7.5 mg/l. The most common source of nickel in the raw wastewater is nickel electroplating or electroless nickel plating, which serve as an undercoat for gold. Another common process is the electrolytic nickel-gold plating of the connector edge ("tab plating") of certain PWBs (e.g., PC expansion cards). Wastewater flows generated from these operations may be small in comparison to copper or tin-lead plating operations and drag-out from typical nickel-gold tab electroplating process baths is generally low. Not all PWBs require tab nickel-gold plating, and few require full nickel-gold (see Exhibit 3-1, Outer-Layer small portion of the board is actually immersed in the bath, thereby limiting dragout. Respondents not reporting nickel in their wastestream may perform little or no nickel plating or aggressively recover nickel dragout.
Sixteen percent (16%) of the facilities that provided raw wastewater data reported the presence of silver. Only one respondent reported silver in concentrations greater than 1 mg/l. Silver is present in the photographic developer and fix solutions (and associated rinses) required to create film images. Silver is also used at some PWB facilities for electroplating, but less commonly than for photographic purposes.
Total toxic organics (TTO) were reported in raw wastewater by 20% of the respondents. The primary sources of toxic organics are solder mask ink solvents and screen cleaners, certain film strippers, phototool cleaners, and tape residue removing solvents.
8.3 Types of Processes/Systems Employed
Exhibit 8-2 summarizes the respondent's wastewater treatment equipment purchase data. The primary purpose of the wastewater treatment systems employed is the removal of dissolved metals. This is accomplished by the respondents through installation of conventional metals precipitation systems,n ion exchange-based metals removal systems, and combined precipitation/ion exchange systems. The most common type is conventional metals precipitation systems, which includes precipitation units followed by either clarifiers or membrane filters for solids separation. Sixty-one percent (61%) of the respondents reported having conventional metals precipitation systems installed. Polishing filters are also commonly employed following precipitation/solids separation. The use of clarifiers is the predominant method for separation of precipitated solids from the wastewater (only 12.1% of the respondents with conventional precipitation technology reported using membrane filters).
|Installation||Type of System||Flow
Yes or No2
|3023||Initial System||(not in use)||100||1984||250,000||Chemtronics||3||Y|
|3023||Upgrade 1||ion exchange||40||1992||553,000||Memtek||4||-|
|3023||Upgrade 3||resist strip treatment||-||1995||60,000||JCL Associates||4||-|
|3470||Initial System||ion exchange||0.5||1993||25,000||none||3||Y|
|25503||Initial System||ion exchange||9||1991||45,000||Remco||4||N|
|29710||Initial System||unknown||120||nr||nr||Baker Bros||4||Y|
|29710||Upgrade 1||ion exchange-copper||12||1991||70,000||Bio Recovery||5||-|
|29710||Upgrade 2||ion exchange-nickel||3||1992||46,000||Bio Recovery||5||-|
|29710||Upgrade 3||ion exchange-copper||50||1993||237,000||Kinetco||4||-|
|33089||Upgrade 1||filter press||-||1989||12,000||JWI||4||-|
|33089||Upgrade 2||new tanks, repipe||-||1994||6,000||various||5||-|
|37817||Initial System||ion exchange||10||1989||50,000||Eastern Ind Wtr||3||N|
|41739||Upgrade 1||pre/post-treat upgrade||-||1993||250,000||Gabel Contracting||5||-|
|42692||Initial System||ion exchange||70||1987||250,000||NCA||3||N|
|42751||Upgrade 1||polishing filter||-||1994||16,000||Conrec||3||-|
|42751||Upgrade 2||filter press||-||1994||24,000||JWI||4||-|
|43694||Initial System||ion exchange||20||1990||60,000||Remco||4||N|
|43841||Upgrade 1||filter press||-||1985||13,000||JWI||5||-|
|43841||Upgrade 2||equalization pit||-||1991||400,000||Generic||3||-|
|43841||Upgrade 3||filter bags||-||1993||1,000||Generic||3||-|
|55595||Initial System||precipitation/filter press||15||1976||1,200,000||in-house||4||N|
|107300||Upgrade 1||sludge dryer||-||1992||83,000||Fenton||3||-|
|107300||Upgrade 2||equalization tank||-||1993||43,000||Fedco||5||-|
Thirty-three percent (33%) of the respondents reported using ion exchange as their basic waste treatment technology and another 6.1% used ion exchange in conjunction with conventional metals precipitation units. Thirty-six percent (36%) of the ion exchange systems included electrowinning. The use of ion exchange as a waste treatment technology is more widespread in the PWB industry than in the plating industry where it is found in approximately 6% of plating shops (ref. 1). One reason ion exchange is more common as an end-of-pipe technology for PWB shops is the limited number of regulated ionic species present in PWB wastewater. For most shops, copper, lead, and nickel (see Section 8.2) are the only metal ions present in significant concentrations, all of which are amenable to ion exchange. Furthermore, these metals are also easily electrowinned from ion exchange regeneration solutions, which makes the ion exchange/electrowinning combination an effective metal recovery system for PWB shops. Shops using ion exchange tend to be small- to medium-size with the median sales level being $7.5 million, compared to $14.5 million for all respondents.
Column 8 of Exhibit 8-2 shows the satisfaction ratings given by the respondents for their treatment system or system component. The ratings are based on a scale of 1 to 5, with 1 being a low level of satisfaction and 5 being a high level of satisfaction.
Column 9 of Exhibit 8-2 indicates if the respondent reported that a failure, malfunction, or other event associated with the end-of-pipe system resulted in a permit exceedance. Thirty-two percent (32%) of the respondents indicated that they did experience a permit exceedance due to their system. Some respondents reported the nature of the permit exceedance, these included: pH (7.9% of all respondents), Pb (10.5% of all respondents), Cu (10.5% of all respondents), and Ag (2.6% of all respondents).
8.4 End-of-Pipe Treatment Capital Costs
End-of-pipe wastewater treatment capital costs are included in Exhibit 8-2. Capital costs ranged from $1& 1980 for a flow of 135 gpm) to $4,000 (purchased in 1987 for a 9 gpm flow). For ion exchange systems, costs ranged from $250,000 (purchased in 1987 for a 70 gpm flow) to $40,000 (purchased in 1994 for a gpm flow).
8.5 End-of-Pipe Treatment Operation Costs
Exhibit 8-3 displays the major operating costs associated with end-of-pipe wastewater treatment. For the three largest shops (in terms of sales) that provided data, these costs represent 0.29%, 0.37% and 0.35% of sales. The data indicate that waste treatment operating costs, as a percentage of annual sales, are higher for small shops than for large shops. Fourteen percent (14%) of the shops reporting had costs in excess of 2% of sales with the highest being 3.1%. All of these shops had sales near or below the median sales level for all respondents. The median cost for waste treatment as a percentage of annual sales was 0.83%, and the average was 1.02%. A plot of waste treatment operating costs as a percentage of sales volume for all respondents is presented is Exhibit 8-4.
(board ft2 per year)
($/Kgal of Flow)
| Sludge Costs
($/Kgal of Flow)
nr = no responseExhibit 8-3. Wastewater Treatment Operating Costs
8.6 Sludge Generation and Disposal
Wastewater treatment sludge data were presented previously (Exhibit 7-2) and discussed in Sectio (in terms of production) that provided data generated sludge solids at a rate of 0.048, 0.003 and 0.057 lb/ft2 of production. The variation evidently comes, in part, from product mix. The shop generating only 0.003 lb/ft2 is exclusively a single-sided PWB manufacture, whereas the other two have a product mix of double-sided and multilayer PWBs for which additional process steps increase waste generation, including sludge production.
Eighty-eight percent (88%) of those responding indicated they recycle their wastewater treatment sludge. Costs associated with the disposition of sludge ranged from $2.00/lb to $0.13/lb Annual costs and unit costs are given in Exhibit 7-2.
8.7 Air Pollution Control
Exactly one-half of the respondents to this survey have installed air scrubbers (Exhibit 8-5). The processes listed most frequently as requiring scrubbers were ammoniacal etching, HASL (hot air solder leveling), and wet processes in general.
(board ft2 per year)
|44657||42,358||yes||hot air level|
|29710||57,000||yes||caustic hot baths, formaldehyde,ammonia from etching|
|25503||90,000||yes||cupric chloride etch, copper plating|
|273701||280,000||yes||etching, acid vapors, metal roof rust|
|41739||300,000||yes||acids bases and associated wet process chemistries|
|959951||320,000||yes||etching, stripping, plating, formaldehyde|
|43694||500,000||yes||wet processes areas|
|133000||600,000||yes||plating, etching, electroless, gold plate, solder strip|
|946587||1,900,000||yes||etch, hydrochloric, sulfuric, nitric acids|
|3023||2,300,000||yes||etch, permanganate, microetch, plating|
nr = no response
Exhibit 8-5. Air Pollution Control Devices