Landfill leachate, or “black water”, which is created when rain or ground water percolates through the mass of mixed municipal and industrial waste in landfills, has come under new China EPA water discharge standards. The country has implemented new rules for discharge and is funding the effort to modernize the methods and systems for handling this effluent.
Landfill leachate, or “black water”, is now under new China EPA water discharge standards
Mainstream treatment solutions for landfill leachate in most cases include the use of biological processes. These processes are indeed efficient and economical when treating low to medium organic contamination loads in relatively stable quality wastewater streams such as municipal wastewater, but also show their limitations in terms of long term efficiency and cost when applied to leachate treatment.
Authorities, agencies and industry stakeholders in China and other countries are actively looking for alternative solutions to the treatment of this effluent, which is one of the most highly contaminated and highly complex byproducts of industrial operations.
Electro Water Separation with Advanced Oxidation (EWS:AOx™), which OriginClear developed in the United States, is a sequential combination of electrically induced gas flotation (EWS) and advanced oxidation (AOx). AOx relies on in-situ generated powerful oxidants, resulting from known chemical reactions occurring when the wastewater stream contacts a series of specifically designed electrodes.
Biological treatment has limitations; EWS:AOxTM is a fast & versatile option
It is a fast, versatile and low maintenance process using minimal electricity and a relatively small, optimized quantity of simple chemical additives like NaOH whose component atoms are part of, and vanish with, process reactions. In China, OriginClear cooperates with local engineering firms to propose integrating EWS:AOx™ in sequence with downstream treatment solutions, resulting in a complete solution.
The firm and its partners have conducted a series of demonstrations and tests in East Asia to further confirm that the process can and does address landfill leachate treatment issues, while also defining process parameters for full size commercial systems. This in turns allows us to estimate the operation’s financials, both as to Capital Expenditure (CapEx) and Operating Expenses (OpEx). CapEx being subject to system size and manufacturing conditions, we chose not to discuss this point here, but we estimated an average OpEx based on the process parameters defined during these various tests.
On-site demonstration in Northern China
The goal for this initial demonstration was to reduce COD from 10,000 to 100 and Ammonia (NH4) from the mid 3000 ppm to below 8. The user considered current technology (DTRO membrane) as not effective and costly due to the high rate of replacement cartridges.
Our mission was to show proof of concept of technology in a flow-through scenario, live and in real time. At this point, neither CapEx nor OpEx was considered, but obviously would come into play should the demonstration show EWS to be a viable technology.
The demonstration took place at a rural northern China city landfill. Leachate discharge is 2000 tonnes/day, with very few amenities. The site is remote, with sub-zero temperatures in winter.
There are 4 key stages of treatment
The pilot system here has been designed as a combination of EWS:AOx™ modules and polishing units (ultra-filtration and reverse osmosis), arranged in a specific sequence to obtain maximum treatment efficiency from each module. This is shown in the schematic diagram below.
Below is an overview of the process:
1. The process sequence starts with an electro-flotation phase in the A25 EWS Flotation unit, where suspended solids are removed out of the water stream. A “mat” of micron-sized gas bubbles lifts the suspended solids up to the water surface where it can be raked off (see image 1)
2. Then the product water is sent through an ultra-filtration (UF) system to remove the final traces of suspended solids (image 2), for a better efficiency of the following step, Advanced Oxidation
3. Once fully clarified, the water undergoes Advanced Oxidation (AOx) process in the A12 AOx module (image 3), where dissolved contaminants are oxidized and mineralized. AOx is an electrochemical process where strong oxidants such as hydrogen peroxide, ozone, hydroxyl radicals or chlorine compounds are generated in situ, without any chemical addition
4. The final step, Reverse Osmosis, will handle the remaining contaminants with increased efficiency as the bulk of contamination, including bacteria that causes fouling in RO membranes, will have been removed.
Lab results EWS:AOx™ output prior to Reverse Osmosis
Despite some limitations with the machines used in this pilot, the EWS:AOx™ modules chain has clearly demonstrated its ability to abate the major contamination factors that can be found in landfill leachate, as shown in the table below.
75% drop in COD levels & 70% drop in ammonia levels after treatment
Further tests and demonstrations
The composition and contamination levels of landfill leachate, like the Municipal Solid Waste where it originates, significantly change with each site’s geographical location (local food culture, recycling habits, etc…), as well as landfill age. Due to the inherent variability of this application, further pilots needed to be conducted to determine a standardized solution for most landfills.
In addition to the initial on-site demonstration, several pilots have been arranged using leachate from various sources and ages to best assess the versatility and ability of EWS:AOx™ to handle influent variability.
For ease of handling, subsequent tests were done in EWS:AOx™ lab cells (each module cell having a batch treatment capability of 4 liters). The most significant results are summarized in the table below:
Pilots in China & Malaysia also show significant pollutant reductions …
…average COD reduction of 77%
Due to the high variability in composition, treatment methods as well as local discharge requirements, little information is available on landfill treatment costs. However, the table below1 suggests a marginal cost bracket between USD 8.91/m3 (MBR or CAS to POTW) and USD94.5/m3 (CAS+RO to local discharge). Interviews with end-users in China suggest that existing leachate treatment OpEx range between USD10 and USD15 per tonne.
Interviews with end-users in China suggest that existing leachate treatment OpEx range between USD10 & USD15 per tonne
The major operating cost factors of EWS:AOx™ are electricity, the appropriately optimized pH adjustment and, if needed, coagulation enhancement additives. While the present document does not claim to be exhaustive and reflect an exact comparison with the cost figures given above, field and lab tests added to other experiments realized with different wastewater feedstocks suggest the following total operation costs:
3 main operating cost factors: electricity, pH adjustment & coagulation enhancement additives
Promising remediation seen and more research to follow
EWS:AOx™ shows promise in remediating not just leachate, but any industrial wastewater with a high contaminant load. The combination of reactor tubes with high shear and contact zones, electro-induced flotation and Advanced Oxidation demonstrated its efficiency not only as a stand-alone system, but also for reducing the load on polishing systems such as membranes or Reverse Osmosis units. Separate tests have pointed to a significant reduction in membrane fouling.
Further options e.g. retrofitting existing flotation units being explored
Construction engineering is currently exploring options for retrofitting existing flotation units, as well as responsive residence time and energy input combinations to enable AOx to adapt to contamination load variations over long periods of time.
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