By Patrick Stanford
The growing need to prevent impacts to groundwater and surface water caused by landfills is driving developments in water treatment that may see application elsewhere. There has been a growing list of products including asbestos and PCBs that were once heralded as “wonder materials,” that have turned out to have negative impacts on the environment and people.
Some of those impacts come from water that falls as precipitation on the landfill and then percolates through it, picking up potentially harmful materials like heavy metals, salts and more recently constituents of concern.
Landfill operators have long become accustomed to building into their landfills, complex systems of impervious liners, piping, sumps and pumps to gather up this leachate and prevent it from leaking into surface and groundwater. Typical landfill procedure is to discharge leachate to the sewer for dilution and discharge to the environment. Other, more progressive landfills treat leachate to isolate and concentrate impurities in the water, so that most of the liquid meets relevant standards for release into surface water. Remaining concentrate is held back for further treatment.
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The big challenge for landfills is to capture and isolate enough impurities so that the bulk of the leachate can be permitted for discharge. That is particularly hard in the case of per- and polyfluoroalkyl substances (PFAS), which are considered environmentally problematic at nanograms per litre (parts per trillion) detection levels. What works for the demanding task of removing constituents of concern from leachate may well meet requirements for other types of industrial wastewater management too.
Getting informed about the available tools
A wide range of tools is currently being used for treating landfill leachate, and it is important to understand the potential role of each. As full disclosure, note that Rochem Americas provides solutions around one particular type of technology. The following is a summary of the tools at the industry’s disposal to address problems posed by emerging contaminants of concern:
Biological treatment – Biological treatment usually works well in the situations for which it is designed, specifically involving degradable organic compounds. It can be useful for publicly owned treatment works (POTWs), or pretreatment of landfill leachate to reduce treatment costs before it enters the sewer. The problem is that biological treatment is not particularly effective in treating most emerging constituents of concern. There is increasing concern among municipalities that their systems are not sufficient to protect against hazards present in industrial wastewater. This includes landfill leachate and may limit discharges to POTWs.
Oxidation processes – Oxidation processes use chemistry, electricity, light and other methods to break down organics into simpler compounds. Most landfill leachate contains ultraviolet (UV) inhibitors or quench agents, so that they just absorb the UV energy. Many POTWs have switched from chlorine disinfection to UV disinfection. This means they may have no choice but to reject landfill leachate because it can reduce the effectiveness of UV disinfection for the municipality’s own wastewater.
Activated carbon – Activated carbon works well for treating many kinds of effluent. It works by adsorbing contaminants, so the compounds stick to the surface of the carbon. The problem is that other organics tend to have more success than PFAS in adhering to the carbon molecules. Because those other organics also adsorb onto the carbon, it takes a lot of activated carbon to remove them before the PFAS get to the front of the line for removal.
Ion exchange – Ion exchange also suffers from interference of other organics before the process can get working on removing PFAS. There are some PFAS specific ion exchange systems available, but they still face the problem of fouling by organic compounds.
Evaporation – Evaporation is an effective technology, particularly as some operations have been able to fire evaporators with their own landfill generated gas supply. One potential risk is the transfer of the constituents of concern into the atmosphere. Many of these compounds have relatively low vapour pressures, so they tend to stay within the liquid. While further research needs to be done on this issue, initial results appear promising.
Incineration – Incineration will deal with the problem, if it is done at a high enough temperature. One problem with this treatment technology is the cost, which can be about $0.25 per litre, plus hauling costs. Another problem is the limited availability of suitable incinerators.
Membrane technologies – Membrane technologies offer the ability to separate out a wide range of constituents of concern (again, as full disclosure, this is the technology Rochem Americas designs and manufactures). Reverse osmosis (RO) is one type of membrane technology.
A closer look at reverse osmosis for wastewater treatment
RO uses a semi-permeable membrane to remove ions, molecules and larger particles from the water being treated, such as landfill leachate. A pump is used to push the leachate against the membrane. Smaller molecules, such as water, pass through the membrane, while larger particles stay behind.
The result is that the concentrate (residual leachate) is retained on the pressurized side of the membrane and the permeate (RO-treated effluent) can pass to the other side.
Recent improvements in membrane technology, plus improved systems for keeping the membranes clear, mean that fouling does not impede the efficiency of the process. RO is a well-established and proven technology in use worldwide for desalination of seawater to produce freshwater. Cargo and passenger ships, as well as naval vessels use RO to provide drinkable water.
It is also used in high purity industrial process applications such as manufacturing of electronic components, pharmaceuticals, chemicals and medical applications.
Since the late 1980s, RO has become a proven technology for landfill leachate treatment and is widely used at landfills across Europe, with over 300 leachate treatment systems installed worldwide, and tens of systems running in the U.S. and at least one in Canada.
So, what can we learn from all this?
One lesson is that the push for tighter standards for landfill effluent is largely a technology-driven phenomenon. Just a few years ago, it was barely possible to measure concentration in the parts-per-million range. Now we are able to measure down to parts per trillion. So, it can be said that the landfill sector is being asked to reach extreme levels of contaminant management for leachate, largely because it is now possible to measure it.
Will requirements for leachate continue to tighten? Probably, as there are thousands more compounds that are not yet on the regulatory radar. We can expect that as the ability to test for more materials grows, there will come more requirements to test for those materials.
From this we can note that the issue of PFAS and other constituents of concern is more of a politically driven process, rather than scientific. We can argue about the toxicology of materials like PCBs and asbestos, but public sensitivity about these substances is moving faster than our understanding about the science-based toxicology and risk.
Be careful about solutions that depend on outside entities. If you’re using third-party incineration, for example, note that the company providing that service may go out of business or increase prices to a level beyond what you can pay. Landfills that depend on POTW services through a sewer connection are particularly vulnerable to a decision that will stop the leachate processing solution cold.
It is important for landfill operators and anyone else who manages industrial wastewater to stay informed and take action when appropriate.
Patrick Stanford is with Rochem Americas, Inc. Email: firstname.lastname@example.org
Read the full article in ES&E Magazine’s April/May 2020 issue below.