Jan 08, 2018

Electrifying Effluent

J.L. Kinder writes on treating landfill leachate to meet discharge limits

Landfill leachate is a notoriously complex and highly contaminated effluent stream with a reputation for being one of the most challenging wastewaters to treat. Leachate is a murky black effluent that results from rain or groundwater mixing with toxic municipal and industrial wastes in landfills, where it picks up volatile organic and inorganic chemicals, heavy metals and pathogens. If not managed properly, landfill leachate poses drastic health and environmental risks to flora and fauna in surrounding communities. If this cocktail of contaminants leaches into nearby soil, groundwater and surface water, it can lead to the spread of deadly waterborne diseases.

With industrialization progressing at a rapid rate in developing nations, waste and leachate management is an important global issue. Widespread diseases caused by landfill pollution have reduced the average human life expectancy in some areas to 35 years old. To prevent public health crises and foster sustainable global economic development, it is essential that the wastewater industry quickly and effectively treat landfill leachate with reliable technology.

China’s environmental protection agency recently tightened the country’s discharge standards. As a result of these new rules, landfill managers are finding that conventional treatment technologies are unable to meet the new discharge requirements.

The most popular wastewater technologies rely on biological processes. While these solutions are efficient at treating low to medium organic contamination loads, when applied to a highly contaminated effluent like landfill leachate, they lack the long-term operational and economic efficiencies needed to serve modern landfills. Other conventional treatment methods use disk tubular reverse osmosis (RO) membranes to sift out contaminants based on size. While straightforward in theory, these filter-based treatment methods clog easily and require frequent maintenance, which drives up on-site operating costs. As such, Chinese authorities and landfill management stakeholders are searching for alternative wastewater solutions to meet the new discharge standards and address leachate responsibly, efficiently and cost effectively.

OriginClear’s Electro Water Separation with Advanced Oxidation (EWS:AOx) treatment process can be part of the solution. The process combines electrically induced gas flotation and advanced oxidation to remove particulate and fully-dissolved or miscible contaminants from leachate without the use of bioremediation tanks or the addition of of harsh chemicals.

It also scales to fit application sizes in a continuous process that uses small doses of electricity to gather oils and suspended solids for easy removal. Advanced oxidation relies on oxidants generated when the wastewater stream contacts a series of electrodes. The combined process of electro-water separation and advanced oxidation is fast, versatile and low-maintenance. The only chemicals needed are small amounts of sodium hydroxide (NaOH). The technology also has a small footprint, uses a low amount of consumables and treats leachate in a matter of hours, as opposed to the days it can take for biological remediation.

New Technology for Updated Standards

In October 2015, OriginClear introduced the system to a project at a city landfill site in Shenyang, China. Located in northern China where winter temperatures can plunge greatly, the site faces an average leachate discharge of 2,000 tons per day with minimal treatment. As such, the site operator required a solution beyond traditional treatment processes to address the landfill’s leachate effluent. The goal for this initial demonstration was to use the system to reduce chemical oxygen demand (COD) from 10,000 mg/L to 100 mg/L and Ammonia (NH4) from mid-300 mg/L to 8 mg/L. This pilot project also was an opportunity to proove the concept of the technology in a real-time scenario in rough conditions.

Design & Installation

OriginClear created an end-to-end seven-step treatment process designed to maximize contaminant removal. To optimize efficiency, the flow rate was set to match the full tank capacity of the advanced oxidation module.

A chemical coagulation method was chosen as the initial stage. Operators pretreated influent water with chemical additives. These included Iron(II) Sulfate Heptahydrate to allow contaminants to accumulate more easily, and sodium hydroxide (NaOH) to raise the pH to 10 and further assist flocculation. After adding NaOH to the holding tank, the treatment operators visually identified extreme flocculation and a black product coming out of the influent wastewater solution.

Once pretreated and flocculated, the influent water entered the electro-flotation (EF) unit. In this step, the reactor tubes generated a dense cloud of micron-sized gas bubbles to make the suspended solids float to the water surface. The resulting sludge—a large gray mat of suspended solids—was then mechanically recovered for off-site waste disposal or incineration.

Before passing through the advanced oxidation unit, the wastewater flowed through an ultrafiltration (UF) membrane to improve clarity. In this step, specifically designed electrodes oxidized hard-to-remove dissolved and miscible contaminants in the wastewater using reactive oxygen species and halogens generated in situ, with no reagent addition. Hydrogen chloride also was added to the wastewater stream to bring the pH of the solution down to 6.5.

Once processed by the system, the wastewater went through traditional downstream treatment processes: a UF membrane to remove any trace contaminants, followed by an RO system for final polishing, which consisted principally of TDS removal. By treating the wastewater before introducing it to the downstream technologies, the bulk of the contaminants, including bacteria, were removed. This reduced the risk of clogging and fouling due to biofilm formation.

With this pre-treatment, the effluent stream’s COD fell by 75%, Ammonia levels fell by 70% and Sulfur levels fell by 65%. Treatment operators observed the black and murky wastewater was reduced to a light brown color, and the final discharge appeared crystal clear after passing through the final RO membrane. On-site testing showed final Ammonia levels at 8 ppm and COD below 100.

Progressing from the Pilot

The composition and contamination levels of landfill leachate vary greatly from site to site, making replicability of treatment systems highly case dependent. Variables like landfill contents, landfill age, surrounding geography and local recycling habits change the leachate effluent, which in turn changes the wastewater treatment solution needed for the site. For example, a treatment system at a landfill in rural China would have very different requirements than one located in New York City. As such, design specialization for leachate treatment leads to more effective results.

The system used in the initial China pilot demonstration was based on the standard OriginClear offering and was not specialized for the particular landfill site. Because of this, the results achieved reflect a baseline for leachate removal, with further customization potentially leading to more efficient results. This project used converted micro-algae harvesting equipment, designed for a very specific organic load. Also, due to construction constraints, the residence time in the advanced oxidation module was limited to 15 minutes, which, while being sufficient for moderately contaminated effluents, is in most cases below the usually required time for higher levels of contamination. Despite these limitations, the module chain demonstrated an ability to abate the major contamination factors found in landfill leachate.

Assessing the Cost

Due to the high variability in wastewater composition—treatment methods and local discharge requirements vary from site to site—little information is available on landfill treatment costs. Interviews with end users in China suggest that existing leachate treatment costs are $10 to $15 per sq meter of wastewater, while a cost analysis of EWS:AOx suggests the total cost of OriginClear’s treatment ranges from $1.27 to $7.83 per sq meter of wastewater.

The system’s major operating cost factors are electricity appropriately optimized pH adjustment and coagulation enhancement additives to prepare the wastewater for treatment. For tougher wastewater applications like landfill leachate, the system’s operating costs proportionally will increase with a longer running time and the need for more upfront additives.

Continued Research & Refinement

More recently, OriginClear progressed with further validation of this solution for landfill leachate applications. The technology is being rolled out commercially to licensees and joint venture partners around the world, including further sites in China, Malaysia and Hong Kong. Additionally, it entered into a research agreement with Florida Atlantic University (FAU) to further test and validate the EWS:AOx technology. As part of this relationship, OriginClear and FAU will jointly test the treatment process on leachate originating from the U.S. and compare the results with those obtained from the China test. This further analyzes the system specialization needed to treat different types of leachate.

Beyond this application, the system shows promise in remediating not just leachate, but any industrial wastewater with a high contaminant load. The results taken from the pilot and the treatment scheme as a whole demonstrated an ability to reduce leachate’s high contamination levels and return clarified water.

OriginClear and partners also are exploring options for retrofitting existing flotation units, as well as responsive residence time and energy input combinations. This would enable the advanced oxidation system to adapt to contamination load variations over long periods of time. Additional studies also will address optimization paths for enabling synergistic interactions with complementary modules to address total dissolved solids.

About the author

J.L. Kindler is president and CEO for OriginClear. Kinder can be reached at [email protected].