TECHNOLOGY IMPROVEMENTS AT A GLANCE
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Since January 2020 various tests and pilots for the removal of different Per-and Polyfluorinated Substances (PFAS) using CERAFILTEC’s Active Cake Layer Filtration (ACLF) process have been successfully executed. The removal of C6-C8 chains including PFOS, PFOA, PFHxA, and HFPO-DA (GenX) as well as C3-C5 short-chain molecules, i.e. PFBA and PFBS are in focus. The tests confirm highly effective removal of PFAS chemicals with substantial cost savings over Granular Activated Carbon (GAC), Ion Exchange (IX) resin, and Reverse Osmosis (RO) processes. The benchmark results are outlined below.
The ACLF process has been established by CERAFILTEC team members over the last decade for the selective removal of dissolved ions. Large plants with over 400,000 m³/d (~100 MGD) total capacity are operating successfully where the ACLF operation has become the go-to solution due to substantial cost savings. The same process also works for the removal of PFAS molecules as well as Dissolved Organic Carbon (DOC), Volatile Organic Compounds (VOC), Trihalomethane (THM), humic acids, drug residues, odor, taste, and color. Just the adsorbent changes to Powdered Activated Carbon (PAC).
Activated carbon is already known to be an effective adsorbent for the removal of PFAS chemicals. CERAFILTEC’s ACLF process now optimizes how the adsorbent is utilized: Maximizing specific surface areas and shortening adsorption pathways. This is done by covering the ceramic flat sheet membrane with a very thin and loose coating of PAC. All water must pass through this coating. This process is only possible with ceramic flat sheet membranes.
The highly effective and efficient adsorption capabilities are based on two facts:
- The smaller the particle size, the larger the specific surface area, the better the adsorption capacity – PAC is about 25 times smaller than GAC particles
- The closer the particles (adsorbent) are to each other, the thinner the boundary layer between the particles, the shorter the pathways of the contaminants (adsorbates) to the adsorbent – up to 45 faster and most effective adsorption
Both conditions are perfectly combined in CERAFILTEC’s ACLF process for the first time.
CURRENT INDUSTRY STANDARDS USING ACTIVATED CARBON
CERAFILTEC's ACLF PROCESS
ADSORBED PFAS MOLECULE(S)
GRANULAR ACTIVATED CARBON (GAC) PARTICLE
REAGGLOMERATED GRANULAR ACTIVATED CARBON (R-GAC) PARTICLE
POWDERED ACTIVATED CARBON (PAC) FILTER BED
PORE
COMMON CARRIER LAYER
CERAMIC ULTRAFILTRATION LAYER
CURRENT INDUSTRY STANDARDS USING ACTIVATED CARBON
ADSORBED PFAS MOLECULE(S)
GRANULAR ACTIVATED CARBON (GAC) PARTICLE
PORE
COMMON CARRIER LAYER
ADSORBED PFAS MOLECULE(S)
REAGGLOMERATED GRANULAR ACTIVATED CARBON (R-GAC) PARTICLE
PORE
COMMON CARRIER LAYER
CERAFILTEC's ACLF PROCESS
ADSORBED PFAS MOLECULE(S)
POWDERED ACTIVATED CARBON (PAC) FILTER BED
PORE
CERAMIC ULTRAFILTRATION LAYER
THE KEY ADVANTAGES OF THE ACLF PROCESS
- Maximized specific adsorption surface area
- Highest adsorption capacity
- Very low consumption of activated carbon – low OPEX
- Very short empty bed contact time (EBCT)
- Able to instantly adjust PAC dosing to changing PFAS feed concentrations
The ideal utilization of the activated carbon adsorbent leads to the lowest total cost of ownership as well as safe and most environmental-friendly operation.
| GranularActivated Carbon | IonExchange | ReverseOsmosis | CERAFILTECACLF | |
|---|---|---|---|---|
| CAPEX savings | o | - | - | + |
| OPEX savings | o | - | - | + |
| Removal of long-chain PFAS | + | + | + | + |
| Removal of short-chain PFAS | - | o | + | + |
| Adaptability to PFAS feed fluctuations | - | - | + | + |
| PFAS disposal* | + | - | - | + |
| Granular Activated Carbon | Ion Exchange | Reverse Osmosis | CERAFILTEC ACLF | |
|---|---|---|---|---|
| CAPEX savings | o | - | - | + |
| OPEX savings | o | - | - | + |
| Removal of long-chain PFAS | + | + | + | + |
| Removal of short-chain PFAS | - | o | + | + |
| Adaptability to PFAS feed fluctuations | - | - | + | + |
| PFAS disposal* | + | - | - | + |
* Ion Exchange resin must be regenerated with chemicals which produced toxic liquid waste volumes contaminated with PFAS;
Reverse Osmosis produces about 10-15% reject stream, concentrated with PFAS
* Ion Exchange resin must be regenerated with chemicals
which produced toxic liquid waste volumes
contaminated with PFAS;
Reverse Osmosis produces about 10-15% reject
stream, concentrated with PFAS
UNIQUE PAC PACKED FILTER BED
Adsorption and ultrafiltration are combined in a single advanced process step – ACLF. The ceramic flat sheet membrane acts as the carrier layer of the packed bed which enables the use of very fine powdered material as the adsorbent. Even the smallest PAC particles are held back by the 0.1 µm membrane. The submerge out-to-in filtration configuration allows for a very loose bed of PAC without compressing the particles onto the membrane – hence no pressure increases and therefore maximum flux operation.
The formed PAC packed bed layer leads to an ideal pathway through which each water molecule and PFAS contaminant must travel. This packed bed layer is almost perfectly even distributed and creates a maximum number different and very narrow pathways. As a result, there is a very short path for the adsorbate/contaminant to immediately diffuse to the adsorbent surface and to migrate into the adsorbent pores.
FREE PFAS MOLECULE
ADSORBED PFAS MOLECULE(S)
MEMBRANE BODY (SUBSTRATE)
THICKNESS ~2.5 mm
POWDERED ACTIVATED CARBON PACKED BED;
THICKNESS < 2 mm
FILTERED WATER CHANNEL ~2×2 mm
ULTRAFILTRATION MEMBRANE LAYER;
PORE SIZE 0.1 µm
THICKNESS < 80 µm
AMBIENT PRESSURE SIDE
NEGATIVE (SUCTION) FILTRATION PRESSURE SIDE
CLEAN FILTERED WATER
CONTAMINATED RAW WATER
BENCHMARK STUDY 1
Comparison between CERAFILTEC’s ACLF, coconut-based GAC, and bituminous reagglomerated GAC single-stage vessel design: The feed water characteristics and the mixture of different PFAS chemicals with 800 ng/L of PFOS and 920 ng/L of PFOA have been simulated to benchmark against available reference data*.
In the graphs illustrated below: The further to the right the PFAS concentration curves exceed the USEPA threshold of 70 ng/L (horizontal red line), the better the technology performance i.e. higher adsorption effectiveness, lower operating costs.
CERAFILTEC’s ACLF process outperformed both GAC types. 3.9x and 4.2x higher number of bed volumes respectively for PFOS and PFOA removal were achieved by CERAFILTEC compared to the best results from CMR reagglomerated GAC solution to meet the 70 ng/L USEPA threshold.
BENCHMARK STUDY 2
Comparison between CERAFILTEC’s ACLF, bituminous reagglomerated GAC, and IX resin – GAC and IX both as single and dual (lead-lag) vessel design; CERAFILTEC as single-stage design only: The feed water characteristics and the mixture of different PFAS with extremely high contaminations of 27,400 ng/L of PFOS and 11,500 ng/L of PFOA chemicals have been simulated to benchmark against available reference data**.
CERAFILTEC’s single-stage ACLF process outperformed the double vessel reagglomerated GAC design with 5.3x higher number of bed volumes for PFOS and 2.9x higher number of bed volumes for PFOA at the 70 ng/L USEPA limit. Compared to the lead IX resin results, ACLF achieved ~15% higher number of bed volumes for PFOS and ~55% higher number of bed volumes for PFOA.
The reference value for the lag IX resin stops at 21,000 bed volumes for PFOS. At this number, the ACLF achieved an equal removal performance. For PFOA, the lag IX resin achieved a 27% higher bed volumes compared to ACLF. It is important to highlight that a lead-lag double-stage design significantly increases the required capital investment and operating costs compared to a single vessel process.
BENCHMARK STUDY 3
Comparison between CERAFILTEC’s ACLF (single-stage), bituminous reagglomerated GAC (single-stage), and IX resin (lag vessel in a double-stage design): The feed water characteristics and the mixture of different PFAS chemicals with C6 PFAS chains – PFHxA and GenX – have been simulated to benchmark against available reference data**.
CERAFILTEC’s ACLF process outperformed the reagglomerated GAC design with 4.2x higher number of bed volumes for short chain PFHxA, and 1.8x higher number of bed volumes compared to IX resin at the 70 ng/L USEPA limit.
It is to highlight that based on existing literature, GenX is extremely hard to remove from water sources with hardly any available GAC and IX long term studies. Despite the very high GenX feed water concentrations of 7,100 ng/L, the ACLF process achieved highly effective removal results with very economical operations.
