Wastewater Treatment: BPT or BAT? Consider Integrating Both.

Resource Recovery, Technology and Innovation

By Miguel Rodas, Environmental Compliance Inspector (ECI) LA Sanitation & Environment

In the United States, LA Sanitation & Environment (LASAN) operates and maintains one of the world’s largest wastewater collection and treatment systems and administers four environmental programs for the City of Los Angeles (City): Clean Water, Watershed Protection, Solid Resources, and Environmental Quality.  These programs were created to ensure compliance with local, state, and federal regulations. The City proactively maintains over 6,700 miles of sewer lines and 49 pumping plants, in addition to four water reclamation plants across the City, which have a combined treatment capacity of 580 million gallons of wastewater per day.  With the expansion of LASAN’s recycled water program, the City’s Source Control and Pretreatment Program is the key component to achieve maximum reuse of recycled water and biosolids. Through the Federal-mandated Source Control and Pretreatment Program, LASAN has significantly reduced the amount of heavy metals entering the Publicly Owned Treatment Works (POTW).  Going beyond compliance, the next step is to balance environmental protection with the local economy. LASAN’s Industrial Waste Management Division (IWMD), which administers the City’s Source Control and Pretreatment Program, launched an innovative program called LA Industry to demystify regulations and create collaborative business-friendly pathways to help achieve sustainability in the environment and economy.

IWMD recognizes that when local businesses thrive, our City thrives. LA Industry is committed to the continued growth, retention, and success of businesses in the City. One objective for LA Industry is to assist businesses in understanding environmental regulations, especially how they apply to metal finishing. A survey was conducted in October of 2018 that indicated many Metal Finishing Industrial Users (IUs) would benefit from a better understanding of their regulatory requirements and responsibilities regarding water treatment, so IWMD now presents the following information that should assist in providing better understanding of existing environmental regulations.

In the summer 2018 issue of the Clean Water1 CWEA magazine, we introduced the 6Ps model system (Products, Processes, Pollutants, Pretreatment system, Parameters, and Plan of the shop) for facility inspections. Each “P” is an integral piece affecting the other Ps. In other words, a change in one of those Ps triggers a change in another P. The most important P is the pretreatment system (PTS). In this article, we will discuss wastewater treatment considering the Best Practical Technology (BPT) and Best Available Technology (BAT), terms used by the Environmental Protection Agency (EPA) when addressing effluent limitations. We will be examining the components of an industrial wastewater pretreatment system while explaining both control technology, BPT and BAT. Understanding of this wastewater control technology is paramount and would help metal finishers meet their effluent limitations2. Implicit in our discussion is that wastewater being treated is the rinses from the many metal finishing processes; a PTS will not treat concentrated process wastewaters economically.

Regulatory Background

The US census of 2012 reported 416 facilities performing metal finishing operations in California, and all of them using the 332813 NAICS code. While there are direct dischargers3 and indirect dischargers, the big majority of IUs discharge their industrial wastewaters through the local POTW as indirect dischargers. As of March 2019, Industrial Waste Management Division (IWMD) had an inventory of 88 facilities within the City of Los Angeles performing metal finishing operations, and all of them discharging through the local municipal wastewater treatment plants or POTW. Wastewater dischargers from metal finishing operations are regulated under the Effluent Limitations Guidelines (ELGs) for the Metal Finishing Category, 40 CFR 4334 (USEPA, Industrial User Inspection and Sampling Manual for POTWs, January 2017, p. xi). These discharge limitations regulate wastewater discharges from 6 core operations: electroless plating, electroplating, anodizing, coating, chemical etching/milling, and manufacturing of printed circuits boards. In addition, if one of the 6 core operations is performed, wastewater from 40 additional operations is covered under 40 CFR 4334. If a facility does not perform any of the 6 core operations mentioned above, it is not subject to the Metal Finishing ELGs. Through pretreatment programs, POTWs perform on-site inspection and sampling of IUs subject to the pretreatment program regulations. Performance of the pretreatment programs falls under the ultimate goal of the Clean Water Act (CWA)5, and that is “to eliminate the introduction of pollutants into the navigable waters and to achieve fishable and swimmable water quality waters.” Therefore, pollutants contained in metal finishing processes waters, which are potentially hazardous, must be treated to remove the pollutants before being discharged to waterways or POTWs” (Webber, 2013/14, p. 582). Efficiency of the PTS is then paramount in removing the pollutant(s) from the wastestreams generated during metal finishing operations. One of the main goals of EPA’s compliance monitoring efforts is to ensure and document compliance of POTW’s implementation of pretreatment programs (USEPA, NPDS Compliance Inspection Manual, 2017, p. 6).

The effluent limitations for industrial wastewater discharge are technology-based numerical limits for specific pollutants; the BPT and BAT are two different levels of control technology, whose main purpose and intent are to prevent the introduction of pollutants into POTWs that may cause interference with their operations or may pass through the POTW (USEPA, Industrial User Inspection and Sampling Manual for POTWs, January 2017, p. 1). The technology-based numerical limitations were developed through historical sampling at selected and best operated facilities (Webber, 2013/14, p. 582). The base level control technology, according to Webber, was called Best Practical Control Technology or simply BPT; on the other hand, the more stringent level was termed Best Available Technology economically achievable, usually referred as BAT. For simplicity’s sake, and for best use of this article, these effluent discharge limitations were based on the performance of certain technology used to remove the pollutants contained in the waste stream generated in the metal finishing operations. According to Webber, the difference between BPT and BAT is that BPT relies on conventional physical-chemical methods to remove the pollutant(s). BAT wastewater treatment technology “includes subsequent polishing filtration and other in-process controls” (Webber, 2013/14, p. 582).


How do IUs assess if the PTS in place is good enough? First, IUs must know the type of process(s) present, the raw materials (chemicals) used, and quantity (load) or concentration of process solutions in their respective process tanks. Using these criteria, IUs can list the possible reasonably expected pollutants in the wastestream (rinses). An IU can determine the easiness or complexity of the PTS and its functionality based on this assessment. This is precisely the job of an ECI6. It should also be the job of the IU. The Industrial Waste Inspector Training Program (IWMD, 1994, p. 43) instructs ECIs that their primary activity is the evaluation of the PTS against BAT criteria7. The ECI must determine whether the IU applies either BPT or BAT control technology (or both), and if an IU will consistently meet its discharge limitations. At this point, you must ask the following questions: what is this technology that was used to come up with the numerical discharge limitations? In other words, what are the components of this pretreatment BPT or BAT model system? Or what factors affect the removal of pollutants from the wastestream(s), or is there any prescribed way(s) of treatment for the discharge of industrial wastewater to a POTW that may meet effluent limitations?

Simplicity or Complexity of PTS

Webber writes that there are at least two factors contributing to the complexity of the PTS. First, the complexity, or easiness, of the PTS needed to “effectively remove pollutants from a wastewater is determined by the type and nature of the pollutants encountered” (Webber, 2013/14, p. 586). EPA based BPT and BAT on the treatment of metal finishing wastewaters using only hydroxide precipitation, clarification, and sludge dewatering (USEPA, Preliminary Review of the Metal Finishing Category, 2018, pp. 2-3). If a cyanide process or hexavalent chromium process exists, treatment of these wastestreams must take place prior to hydroxide precipitation. The wastewater treatment described by this simple procedure is, in effect, using a basic system or BPT control model considering the type and nature of pollutants. To expand further, metal precipitation is accomplished by adding an alkali (caustic, soda ash, etc.) to the solution containing the metal. For example, an IU engaged in zinc plating only will have zinc-bearing rinses and the rinses associated with cleaning of parts. Cleaning generates rinses containing oil & grease, oxides, dirt, and other organic contaminants removed during the surface preparation steps prior to the actual zinc plating. The BPT control relies on the fact that every metal precipitates at a specific pH. Solubility or insolubility of the metal (in this example, zinc) will depend on targeting the correct pH for maximum dropping of this metal out of solution as a hydroxide sludge when allowed to settle down, by gravity (usually overnight), at the bottom of a tank, and subsequently dewatered using a filter press. As you can see in this example, this wastewater treatment can be manually accomplished using simple technology.

The second factor, contributing to the complexity of the PTS is the load of pollutant(s). The complexity of the PTS will increase depending not only on the type and number, but also on the load of pollutants, and the strength or concentration of pollutants in the wastestream(s). The system necessary for discharge of industrial wastewater by indirect dischargers using BPT or BAT control technology uses two ways of wastewater treatment: a) end-of-line physical/chemical wastewater control and b) the use of in-process controls (NEIC, 1977, p. 38). The first one is the treatment of wastestream simply relying on physical/chemical treatments, as described above. The second way is the case when the basic control technology or BPT is not enough and may need to be enhanced by applying BAT control technology, which include in-process controls such as the segregation of wastewater by chemistry and strength. This scenario assumes an IU needs to treat cyanide-bearing wastewater, hexavalent chrome-bearing wastestreams, and other pollutants types such as nickel, copper, cadmium, etc. The cyanide-bearing wastestream would need to be treated by chlorination (oxidation set by pH/ORP parameters accordingly to cyanide load); the chrome-bearing wastestream would need to be treated by reduction from chromium VI to chromium III (set pH/ORP parameters accordingly by load of hex-chrome present).

The use of additional chemical additives or chelating agents in process tanks increases the complexity of the PTS. This must lead to the segregation of wastestreams (by chemistry). In this case, an IU needs to consider the addition of coagulants or other specialty metals precipitants in the wastestream to reduce metal solubility. Each metal requires a specific pH to precipitate8 the maximum concentration of metal hydroxide or sulfide present in the wastestream. Once the target pollutants are segregated and treated, the precipitated metal(s) is allowed to settle (as sludge) and removed using a lamella clarifier or settling by gravity overnight. After the solids are removed, a final discharge to the POTW can be performed either continuously or by a batch mode. A neutralization/pH adjustment step may be included prior to final discharge through the designated sampling point. In summary, BPT prescribes removal of pollutants by physical/chemical treatment that includes chemical metal hydroxide precipitation, physical gravity settling/clarification, and final physical removal of solids, all of which can be accomplished by using simple practical methods. On the other hand, BAT effluent quality is achieved, in addition to the conventional physical/chemical treatment, using in-process controls (NEIC, 1977, p. 38), such as wastewater polishing technology (i.e., ion exchange, different types of membrane filtration devices with different micron sizes). In-process controls are also specially incorporated to conserve rinse waters, i.e., drag outs, use of reclaim tanks, still rinses, overall rinse water conservation, and other feasible recovery techniques and various pollution prevention practices (next topic on this series of articles) (NEIC, 1977, p. 38). Other waste minimization and best management practices (BMPs) include rigorous housekeeping programs, use of spray rinses or air knives to minimize solution drag outs, recycling of wastewaters to plating baths to compensate for surface evaporation losses.

To minimize pollutant types and loads, writes Webber, “Increasingly today’s metal finishers are modifying processes and getting rid of certain finishes to eliminate problem pollutants and the resultant system complexity or simply to reduce discharge violations” (Webber, 2013/14, p. 586). It is worth noting that the US EPA’s policy does not require IUs to install the technology that was used to establish the effluent limitation at time of the promulgation of the ELGs. In fact, a facility may use any technology that allows it to meet the performance levels established by the effluent limitation guidelines (ELG). However, the EPA9 does require IUs to meet the effluent limitations by implementing equivalent BPT or BAT practices. Nonetheless, when an IU violates its effluent limitation, or becomes a chronic violator, a deficient PTS is most likely the cause. The Control Authority (CA) has the power to intervene and address the non-compliance problems. In the case of City of Los Angeles, IWMD becomes involved by issuing administrative orders that require IUs to initiate improvements to the PTS (ERP & ERG, 2017, pp. 2-7). In addition, when an IU becomes a chronic violator, the CA may require the IU to not only demonstrate performing extra self-monitoring sampling that their system is optimally run, but also integrate pollution prevention practices into the core of their operations to reduce the loading in the wastestream. It is worth noting that EPA not only sets numerical effluent standards, but also non-numerical requirements, such as BMPs10. EPA promotes programs that recycle waste byproducts (wastewater) and reduce sources of pollution.

Final Words

Again, it is worth mentioning the purpose and goal of the Clean Water Act (CWA): to eliminate pollution from occurring. POTWs and IUs (in our case, metal finishers) have both requirements and responsibilities, which are delineated in federal regulations, 40 CFR 403. On the one hand, POTWs are required to develop and implement pretreatment programs to control the toxics, hazardous pollutants that are introduced by industries into public sewers. On the other hand, IUs are required to treat their industrial wastewater in accordance with effluent limitations. Not only are IUs responsible for making sure their PTS meet the required complexity (or simplicity), but also to meet the functionality of the PTS. Two fundamental concepts can be mentioned at this final point: simple complexity and minimal function. The first one refers to all the necessary components (which could be simple traditional technology) that work together to effectively achieve its goal: remove the pollutant(s) to a level below the requirements. The second concept is that of minimal function, which provides a way to recognize that a device (or in our case, a PTS) in the real world, has to work at a certain minimal level of efficiency to be of any practical use. In the case of the pretreatment system (PTS), in order to remove the toxic, harmful concentration of pollutant(s) from the wastestream, each component of the system play an important role. Thus, in order to remove the toxic, harmful concentration of pollutant(s) from the wastestream, each component (monitoring devices such pH/ORP, pumps, chemicals, etc.) of the system play an important role. Should any of these components or chemicals are absent; the minimal functionality of the entire system would render the treatment of wastewater inefficient.

One last word regarding wastewater treatment technology: First, that “the processes that generate wastewater in metal finishing operations have not changed substantially” since promulgation of ELGs. Secondly, that “most metal finishing facilities continue to use conventional chemical precipitation and clarification wastewater treatment technologies (the technology basis for the existing ELGs)”. Only a few facilities “have installed advanced treatment technologies such as membrane filtration polishing steps” (USEPA, Preliminary Review of the Metal Finishing Category, 2018, pp. 5-1).


Enforcement Response Plan and Enforcement Response Guide. (2017, August). ERP & ERG. City of Los Angeles, CA, USA: IWMD.

IWMD. (1994). Lesson 3, Conduct Compliance Inspections. Industrial Waste Inspector Training Program. City of Los Angeles, CA, US: IWMD.

NEIC. (1977). Summary Pretreatment Criteria. Retrieved March 3, 2019, from https://www.epa.gov/libraries/region-9-environmental-information-centerlibrary-services

USEPA. (2017). NPDS Compliance Inspection Manual. Washington D.C: US EPA.

USEPA. (2018, November 19). Effluent Guidelines. Retrieved from EPA: https://www.epa.gov/eg/learn-about-effluent-guidelines

USEPA. (2018). Preliminary Review of the Metal Finishing Category. US EPA.

USEPA. (January 2017). Industrial User Inspection and Sampling Manual for POTWs. Washington DC: Office of Compliance.

Webber, T. J. (2013/14, Fall). Wastewater Treatment. (R. E. Tucker, Ed.) 81st Universal Metal Finishing Guidebook, 111(7), pp. 582-594.

1 Clean Water is issued five times a year by the California Water Environment Association (CWEA). http://cweawaternews.org/magazines.

2 Effluent guidelines are national regulatory standards for wastewater discharged to surface waters and municipal sewage treatment plants. EPA issues these
regulations for industrial categories, based on the performance of treatment and control technologies. https://www.epa.gov/eg/learn-about/effluent-guidelines.

3 A direct discharger is a point source that discharges pollutants to waters of the US such as streams, lakes or oceans. https://www.epa.gov/eg/learn-abouteffluent-guidelines#self.

4 Certain electroplating and metal finishing facilities that began operation before July 15, 1983, and discharge wastes to POTWs are covered under the
Electroplating Category (40 CFR Part 413).

5 Clean Water Act (CWA) is US legislation enacted in 1972 to restore and maintain US clean and healthy waters; the act was originally known as the Federal Water
Pollution Control Act that was amended in 1972 and became known as the Clean Water Act. https://www.bing.com/search?q=clean+water+act+of+1972.

6 ECI-Environmental compliance inspector; other agencies or POTWs may use a different title.

7 I contend that the evaluation of the PTS against the BPT criteria should be the first evaluation since BPT represents the simplest complexity or most basic
technology used in wastewater treatment.

8 Metal hydroxide precipitation is a formation of a separable solid from a solution by adding an alkaline chemical such sodium hydroxide (caustic).

9 https://www.epa.gov/eg/learn-about-effluent-guidelines.

10 BMP is a term used to describe best management practices intended to be implemented by a facility in order to reduce generation of waste.