Zero Liquid Discharge for Coal-Fired Power Plants

Posted on Updated on

When environmental regulations for coal-fired power plants change, effluent treatment methods currently being used may not be able to meet the new standards. Many power plant operators find that one of the new factors they must face is the EPA’s revised Effluent Limitations Guidelines (ELGs), issued in September 2015.

Recently at a mine-mouth coal-fired plant with a nominal capacity of 1,600 megawatts (MW), designers had done what they thought necessary to comply with regulatory expectations – they designed for zero discharge of process water. For blowdown water from the cooling tower, they made plans to discharge in a way that would meet National Pollutant Discharge Elimination System (NPDES) limits for the permitted outfall.

Process water is recycled internally for other plant processes, including the air quality control system (AQCS), which incorporates the flue gas desulfurization (FGD) system. However, as the wastewater continuously cycles through the two FGD absorber units, a buildup of chlorides and other constituents occurs. The level of total dissolved solids (TDS) in the purge water is controlled by blowdowns triggered by the TDS levels, and makeup water is then added to the system.

The FGD wastewater can contain TDS in excess of 31,000 parts per million (ppm), total hardness of 30,000 ppm, chlorides of 20,000 ppm, and total suspended solids (TSS) of 10,000 ppm. The blowdown wastewater is purged from the system whenever the chloride concentration in the water exceeds 20,000 ppm of chlorides.

The purged high chloride FGD wastewater is then disposed of by mixing it with fly ash and gypsum coal combustion residual (CCR) material in a pug mill. That mixture was originally disposed of at an off-site landfill, located about 20 miles away.

One seemingly small change caused this design to tip off-balance: the decision by the power plant to start its own landfill on site for disposal of the fly ash mixture. This action opened up the plant to the responsibility of managing the landfill leachate – water from precipitation flowing through the landfill, picking up contaminants along the way. The plant’s operators began pumping the leachate from the on-site landfill back to the plant’s recycle basin for re-use as make-up water. However, they found that internal recycling of wastewater is not sustainable at that location, as it results in the cycling up of chlorides and other factors that increase pipeline corrosion.

As a result, from 2014 to 2015, the chloride concentration in the recycle basin increased to three times the previous year’s concentration. The design for chlorides concentration for the recycle basin was set at less than 500 mg/L, but the data show levels approaching 3,000 mg/L within two years. These concentrations seemed likely to go on increasing unless measures were taken to manage the problem.

Problems such as these have been found at many coal-fired power plants. At the root of the problem is the fact that the water-management systems were set up to support the efficient combustion of coal to produce power. However, environmental regulations concerning water use and disposal have become more restrictive. This change has put an increasing operational focus on efficient water management to lessen the discharge of water from the plant and reduce materials of concern in that wastewater.

Thus environmental regulations, such as those intended to support zero liquid discharge (ZLD), now have an increased effect on operations, moving water management up on the priority lists of power plant operators.

One of the most common issues at many coal-fired power plants is the one seen in the story above – that, in many cases, the plant’s operators do not have a comprehensive plan for water use. They lack detailed, accurate data on which parts of the plant use water, how much those parts use, and what constituents the processes add to that water.

Many plants combine their wastewater inputs into a central flow and then treat the water that comes from that single pipe. In such cases, a more focused and cost-effective plan could be developed by segregating flows so that each stream receives only the level of treatment it needs. Segregation of wastewaters can generate substantial opportunities for recycling part of that water flow and limiting the most costly treatment and disposal methods to only the streams that need it.

For example, consider pump seal water. Many plants use clean water around the outside of the seals to reduce the possibility of the pumped fluid escaping. The pump seal water that drips out is gathered and then generally is just placed into the plant’s overall wastewater flow. Since this water is virtually clean, it would make more sense to capture this water separately so it can be treated at low cost, rather than being part of the larger, more complex wastewater flow.

Comprehensive analysis of the many water flows within a plant may be able to point to similar opportunities to segregate wastewater streams so that not all water needs to be treated with expensive methods. Specific data on water use at various points within the plant can help guide the choice of treatment approaches. At the plant described above, an astute review of the wastewater components saved the owner millions of dollars that would have been required for a new treatment plant. Instead, the plant managers were advised to use low-cost techniques for reducing the chlorides in their wastewater flow.

It is important to remember that as the plant’s operations change, the effects on the wastewater stream must be considered. The above-mentioned power plant was impacted by just such a change – the new landfill’s leachate forming a new source of chlorides to be managed.

Each coal-fired plant is different – the type of coal, equipment, and other factors such as local geology – so the following steps may be useful in finding an appropriate solution:

Analyze the current situation: One of the first steps for preparing for the new ELGs is to collect data on the flow and composition of wastewater streams and characterize typical wastewater flows.

Develop plans: Review various limiting strategies, such as reusing wastewater to reduce discharges, and then use mass balance and chemistry modeling tools to evaluate reuse, treatment, and discharge strategies to meet these new limits.

Choose management options: The choice for selecting the appropriate management tool depends on yet another wide range of factors that are better understood after carrying out the first two steps. The toolbox can include:

  • Discharge to a Publicly Owned Treatment Works (POTW)
  • Evaporation Ponds
  • Flue Gas Injection
  • Fixation
  • Deep Well Injection (depending on factors such as geology – experience has found that the tight rock formations of Pennsylvania, for example, are less useable for this purpose than the more appropriate geologic formations of other locations, such as Florida)
  • FGD wastewater treatment system (WWTS) Effluent Reuse/Recycle
  • Settling Ponds
  • Constructed Wetlands, Phytoremediation, and other Natural Based Systems
  • Vapor-Compression Evaporation
  • Physical/Chemical Treatment
  • Physical/Chemical with Added Biological Treatment
  • All the above can be components of a Zero Discharge approach

Other approaches utilities should consider include measures such as using existing evaporation (from cooling towers and FGD absorbers), using blowdown water for conditioning of fly ash, and other water reuse and conservation measures to reduce the amount of wastewater requiring treatment.
Working with a qualified professional with experience in each of these technologies can lead to wiser choices around which systems may be best, given the site-specific factors.

If you have any questions regarding your plant, please contact the post author, Ivan A. Cooper, P.E., BCEE, a principal based in CEC’s Charlotte, N.C., office, at; (704) 226-8074.

Clean Water Act, Section 308 Requests for Information

Posted on Updated on

So…you have received a Request for Information from the US Environmental Protection Agency (USEPA) pursuant to Section 308 of the federal Clean Water Act. A Section 308 request is done when the agency has reason to think that your facilities are not in total compliance with their NPDES permit limits. No need to panic – just start compiling the needed information.

Often the first thing that companies do after receiving a Section 308 letter is to call an experienced environmental attorney to get some assistance in working through this process. Odds are you wouldn’t have received this letter if you did not have some exceedances of NPDES permit limits, so the attorney can help you work through usually inevitable enforcement discussions with the USEPA.

Here are the types of information that the USEPA will typically ask for in Section 308 letters. You will need to pull this information together into one location so it can be copied and shipped to the USEPA:

  1. A list of all of your facilities by name, location, NPDES and mining permit numbers.
  2. Copies of each NPDES permit and permit applications for each identified facility.
  3. NPDES data for the past five years (or more), including your Discharge Monitoring Reports (DMR’s) and, often, the lab sheets upon which the DMR’s were based.
  4. You will need to summarize the information from items #1 through #3 (and any additional requested information) into an Excel spreadsheet(s).

Mining facilities with NPDES permits that have discharge violations of metals, chloride, TDS, TSS, pH, etc. may be faced with hefty fines, as well as corrective measures to address and eliminate non-compliant discharges. These corrective measures typically include additional monitoring and reporting, implementing an electronic environmental database management software, implementing an environmental compliance management system, developing a response plan for eliminating effluent limit violations, and conducting internal and/or third-party environmental audits. Depending on the parameters in question, expensive treatment (or pre-treatment) systems may need to be installed.

Known recent civil penalties have ranged from $4 million to $20 million, which doesn’t include costs for corrective measures. Given the amount of money at stake, it is crucial to go into meetings with USEPA as prepared as possible.

If you have questions about the Section 308 process as it relates to mining companies, please contact Jonathan Pachter in our Pittsburgh office at 1-800-365-2324 or Additional information regarding EPA Section 308 matters can be found at the EPA’s website.

2012 Deadlines and New Requirements Established in Ohio’s New General Permit for Industrial Storm Water Discharges

Posted on Updated on

Ohio EPA recently issued its new Multi-Sector General Permit (MSGP) for Industrial Storm Water Discharges (Ohio EPA General Permit Number OHR000005).  The existing general permit expired at the end of May 2011, and Ohio EPA spent several months soliciting input from industry and regulatory groups to develop a permit that is consistent with US EPA’s MSGP. There are 2012 deadlines for submittals associated with coverage under the new MSGP, along with a series of new requirements. The remainder of this blog describes the deadlines for submittals required to maintain coverage under the new MSGP, and the new permit requirements.

The new MSGP is a significant shift from the previous general permit.  The new MSGP has grown from 36 pages to more than 140 pages.  The previous permit included broad, non-facility specific, monitoring and recordkeeping requirements. The new MSGP establishes industry-specific requirements for managing and monitoring storm water discharges.  The new MSGP contains new requirements that were contested by industry groups, including the establishment of benchmarks, quarterly visual sampling, and submittal of an annual report.  The new MSGP places additional burdens on both industry and the regulators by requiring virtually every facility in the state to re-apply for a storm water permit, and to revise or update Stormwater Pollution Prevention Plans (SWPPPs).

The effective date of the new MSGP is January 1, 2012.  Individual facilities were to be notified by letter, which Ohio EPA should have mailed prior to December 31, 2011.  Ohio EPA indicates that if you do not receive a letter by January 13, 2012, you should immediately contact the agency.

No action is needed by current permit holders until the letter is received from Ohio EPA.  Important submittal deadlines are:

  •  Existing permit holders are to submit a Notice of Intent (NOI) within 90 days after receiving written notice from Ohio EPA.
  • SWPPPs for existing permit holders are to be updated within 180 days of the effective date of the General Permit.
  • For facilities not covered under a prior NPDES permit, a SWPPP needs to be prepared before submitting a NOI.  The NOI is to be submitted at least 180 days prior to discharge.

It is important to note that facilities renewing their permits must use the NOI form that Ohio EPA developed for this permit.  The form and instructions  can be downloaded from their website.

All facilities are required to design, install, and implement control measures (including Best Management Practices (BMPs)), and describe them in their SWPPP.  As part of the SWPPP, facilities are required to identify a storm water pollution prevention team.  Annual training will also be required, and the facility will need to maintain documentation concerning the training.

The three types of inspections required by the new MSGP include:

  1. Routine facility inspections that are to be conducted at least quarterly, and in some cases more frequently (i.e., monthly).  Documentation of the inspections will need to be maintained on-site as part of the SWPPP.
  2. Quarterly Visual Assessments of storm water quality.  This consists of collecting a sample during the first 30 minutes of discharge from a storm event.  The sample is to be visually inspected for color, odor, floatables, foam, oil, etc.  Documentation will need to be maintained on-site with the SWPPP.
  3. Comprehensive Site Inspections that are to be conducted annually.  Documentation of the inspections will need to be maintained in the SWPPP and recorded in an Annual Report (Ohio EPA will provide the form).

Two types of monitoring are included in the new MSGP: Benchmark Monitoring and Effluent Limitations Monitoring.  The types of monitoring and individual parameters are specified for each of the specific industry sectors within the new MSGP.  Benchmark Monitoring is required for 13 of the Industry Sectors.  The purpose for benchmark monitoring is for evaluating the overall effectiveness of control measures and to know when additional actions are necessary to comply with BMPs. Effluent Limitations Monitoring is required for five (5) industry sectors.  This monitoring is an annual event that is for the most part consistent with the prior permit, but with differences in monitoring parameters.

The new MSGP includes an exemption for monitoring multiple outfalls that are “substantially identical outfalls”.  If a facility has two or more outfalls that discharge substantially identical effluent and drainage areas, there is a provision to monitor only one of the outfalls and report that the results apply to the other substantially similar outfalls.  This exemption does not apply to outfalls covered by numeric effluent limits.

There has also been a minor change in the definition of a “measurable storm event” from the prior permit.  A measurable storm event is defined as a storm event that results in discharge from the facility and follows the preceding measurable storm event by 72 hours (3 days).  There is also a provision for monitoring snowmelt.

The new MSGP contains an exemption to the monitoring requirements for inactive and unstaffed sites.  This exemption applies to benchmark monitoring, quarterly visual inspections, and routine facility inspections.  It will be necessary to make a demonstration, and then certify there are no industrial materials exposed to storm water.  The exemption applies differently to certain industry sectors.

For more information, see the dedicated page on Ohio EPA’s website.

If you have questions on how the requirements of the new MSGP may apply to your facility(ies), or require assistance updating your facility’s SWPPP, contact Andy McCorkle at 888-598-6808 or by email at

Navigating Muddy Waters – New Effluent Limitation Guidelines Will Impact 21,000 Construction Sites Annually

Posted on Updated on

On November 23, 2009, EPA released the final Construction & Development Effluent Limit Guidelines (C&D ELG).  The final C&D ELG will impact all construction sites disturbing more than one acre by imposing non-numeric effluent limitations.  More importantly, the C&D ELG will impose numeric effluent limits for the first time on all construction disturbing more than 10 acres within approximately 4 years.  Most construction sites will need to use Passive Treatment Systems (PTS) to achieve those limits rather than the typical erosion and sediment control measures currently in use.  EPA estimates as many as 21,000 construction sites annually would need to meet those numeric limit standards.

In the past, sediment control practices have generally been designed based upon a rule of thumb.  Many states rely on 1800 ft3/acre of drainage (or disturbed acre), which doesn’t take into consideration the discharge quality.  In fact, a sediment control measure can have an 80% settling efficiency and still produce a turbid (muddy) discharge.  With this in mind, EPA has been struggling since early 2000 to establish a C&D ELG, with prodding from environmental groups.

In November 2008, EPA published a draft C&D ELG that set the ELG (turbidity) at 13 Nephelometric Turbidity Units (NTUs) for sites that disturbed 30 acres or more, were located in areas of the country with high rainfall intensity, and located on soils that had at least 10% clay.  That incredibly low turbidity limit (13 NTUs) severely limited the stormwater treatment options to Active Treatment Systems (ATS) that, simply put, look and function like small waste water treatment plants.  EPA requested public comment on the draft rule and requested additional data on the cost benefit analysis, treatment feasibility, and other components.  Concerns mounted as those affected began questioning the draft rule, particularly the feasibility of achieving the 13 NTU discharge standard.

EPA published the final C&D ELG in November 2009 with major revisions based on the comments received.  EPA chose to greatly simplify the rule and increase the numeric standard.  Below is a summary of the final rule:

  • All construction projects must install best practicable control technologies.
  • Sediment basins and other impoundments must be dewatered from the surface.
  • The ELG has been set at 280 NTUs.  This limit is a daily maximum average, based upon sampling for storms up to the 2 yr, 24 hr storm.  Discharges from storm events greater than the 2 yr, 24 hr are not required to meet the ELG.
  • Discharges from construction sites must meet an effluent limitation guideline as follows:
    • Within 18 months of the effective date of the rule (August 2011), sites disturbing 20 acres or more must meet the ELG.
    • Within 4 years of the effective date of the rule, sites disturbing 10 acres or more must meet the ELG.
    • For both scenarios above, the size limitations apply to “larger common plans of development” like subdivisions with multiple small lots.

Each state will need to marry the final C&D ELG with their existing monitoring plans, which will be a huge task.  Additionally, EPA has noted that as each state’s construction stormwater permit comes up for renewal, these requirements must be inserted.  EPA is the permitting authority in four states.  Their general permit is due to expire in June 2011 and will be reissued with the ELG requirements in it at that time.  Interestingly, North Carolina’s permit was in the midst of renewal when the ELG rule was finalized, and EPA only allowed their permit to be renewed for 18 months (through August 2011).  After that date, the reissued permit must include the ELG requirements.

As indicated earlier in this blog, PTS will generally be required to meet the numeric standard of 280 NTUs.  A PTS incorporates a flocculant with a standard construction site practice.  An example of a PTS is a jute-lined ditch that has been impregnated with polyacrylamide (PAM).   Design components that must be considered include mixing zones and settling zones.  At this point, we don’t have design tools that dictate the amount flocculant to be used on a site.  Flocculants and soils must be matched (not every flocculant works on every soil), and the applications tweaked in the field for peak performance.  Then the flocculant must be reapplied after rain events.

You can expect to have the ELG requirements inserted into the permit language if your state’s permit expires before August 2011.  If, however, your permit was reissued before the rule was finalized and without the ELG language in it, EPA could administratively open the permit to have the language inserted into it.  I suspect that between June 2011 (when EPA’s Construction General Stormwater permit expires) and August 2011 (the deadline to begin implementing the ELG) some permits may be administratively opened.  That option is certainly possible.

If you have any questions about the C&D ELG, how it may impact an upcoming project, and how you can meet the numeric standard, contact CEC’s Nashville office at (800) 763-2326.