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Tests Using BioSafewater absorbent Biosorb 2000tm for Mercury Removal
To Investigate the Adsorption Capacity of the Adsorbent BioZorb 2000TM for the Removal of Dissolved Mercury
Client: ERCO Worldwide USA
Research Consulting Firm : BioSafe Environmental Solutions Inc.
Mr Don Wilson
Date: November 2014
This research project is a follow-up study concerning the treatment of dissolved mercury levels as they relate to the wastewater streams now being discharged into the environment at the ERCO Worldwide chlorine plant in Port Edwards USA.
In an earlier study, it was demonstrated that the new adsorbent ( Biosorb 2000) was able to reduce the level of dissolved mercury down to extremely low levels. The results indicated that the adsorbent, when incorporated into the current wastewater protocol, could allow ERCO to meet its Permit criteria. Once it was established the adsorbent had the potential to remove significant amounts of dissolved mercury, it was decided to investigate the issue in terms of its adsorption capacity and whether it would be economical to incorporate the adsorbent into the current wastewater treatment process.
It was determined that the best way to approach this problem was set the tests up in “batch adsorption mode”. Zorbtech conducted the experiments in a steady state gravity-fed column. Over the course of 18 days, six batches were tested using 500mg of Biosorb 2000 each time.
Due to the fact that significant multistage crosscurrent adsorption were occurring, it became apparent that other metals in the wastewater stream were occupying adsorbent sites on the adsorbent. A fuller discussion will be considered relating to these issues in later sections of the Report.
In conclusion, it was determined that in terms of removing dissolved mercury, the Adsorbent Capacity of the Biosorb 2000 was approximately 0.663397mg.g-1 . Another interesting observation in terms of the crosscurrent adsorption which is taking place on the adsorbent sites is the fact all the other metals are being adsorbed at an extremely high adsorption rate. The Adsorbent Capacity of the Biosorb 2000 for these other metals = 0.145mg.g-1 . This phenomena is having a huge impact on the capacity of the Biosorb 2000 to lower the level of mercury to previous levels.
To Determine the Adsorption Capacity of the Adsorbent Biosorb 2000
To Set up a Series of Bench Tests to determine an Optimal Mass of Adsorbent to Reduce the Level of Mercury
To Determine the Approximate Surface Area of the Resin
To Determine the Cost Effectiveness of Incorporating Biosorb 2000 into the current wastewater treatment train.
The testing protocol for conducting the bench tests were as follows:
Determine a mass of adsorbent, in this case 500mg of Biosorb 2000 was packed into a column (see image)
Determine a specific volume of water containing the absorbates, in this case 1 sample of 2000ml and 5 samples of 500ml
Determine the batch mechanism to allow a steady state flow rate and resident time, in this case, the following image of the test equipment was set up with a control flow rate of (a) in the first instance of 2.777mg per minute. In the following 5 bench tests a flow rate of .6944mg/min was set up.
Calculate the Adsorption Capacity of the Resin
Determine the amount of Biosorb 2000(mass) required to treat x litres of wastewater
Conceptual Diagram of Testing Process
2000ml control beaker 48’100ml column packed 500mg 1000ml beaker
Summary of Test Results
The primary tests results for Mercury are contained in Table 1.0
Table 1.0 Illustrating The Total Adsorption of Dissolved Mercury on Biosorb 2000
time hrs Hg 1 Hg2 V=ml M=mgQt=Mg Abs
This is total mass (mg) of Mercury adsorbed per gram of Biosorb 2000
In addition to the above results the following table illustrates the mass of the other metals which are occupying sites on the adsorbent.
Table 2.0 Metals Occupying Sites on the sorbent Biosorb 2000
The above two tables illustrate the mass of metals which are being adsorbed onto the surface of the adsorbent Biosorb 2000.
The largest mass which the adsorbent is absorbing from the wastewater is Cr. This metal is utilizing a huge surface area of the adsorbent and the total mass being adsorbed is 145.51mg.g-1 . Therefore, based upon these initial findings, the mass(M) of all metals being adsorbed on the surface of the adsorbent is 146.173mg.gm-1 Although this calculation yields a mass adsorbed per gram, we need to determine the total amount of Biosorb 2000 used per volume of water which contains the absorbates.
Determining the rate of desorption and the equal rate of adsorption involves using the standard Langmuir Isotherms
At equilibrium rate of adsorption = rate of desorption
k1 C(qm – q) = K2q
In this Research Study, we have taken the position that the equilibrium had been reached. In other words, the metals in the concentration of metals in solution and the “concentration” of the same metals are in the absorbed state. It should be noted that further data analysis will be required to prove this relationship.
Surface Area Analysis
In order to determine the amount of adsorbent to treat X liters, the surface area of the adsorbent needs to be calculated. This calculation will yield the approximate area and the possible number of sites located on the surface of the adsorbent. This is an extremely complex area of research as it pertains to the properties of amorphous silica surfaces.
The research involves the physical removal of the absorbates from the surface of the Biosorb 2000. This research could be the basis for further study relating to the amount of adsorbent required to treat a given volume of wastewater. In this Research Study, Zorbtech has attempted to determine the surface of the adsorbent by applying the following formula. This formula may not apply directly to the Biosorb 2000 resin, however, it may give us a model for the next phase of this research project. The calculation is based on the following assumptions. The goal at this stage is to determine the surface area of the adsorbent Biosorb 2000.
The internal surface of the silca is porous and contains cylinder pores. This is assuming the monolayers on the surface of the adsorbent contain pores of this nature.
The diameter of the particles 5nm
The porosity of 50%
Particle Density of 1gm/Cm3
Porosity = pore volume/volume
The volume of the cylinder pores can be computed based on the following arguments
number of pores n (amount/g)
the pore radius R(m)
the pore length L (m):
Vad = nπR2 L
Surface Area EquationAad /Vad = 2/R
Surface Area Calculation Vad 2/R =(5x10-7 m3 /g) 2/2.5x10-9 m =400m2g
Estimated Volume(litres) of Wastewater Treated with 1 gram of Biosorb 2000
Estimated volume of water 1 gram of Biosorb 2000 can adsorb containing 0.66gm/l of HGII = 8,773 litres
The calculation is an approximation due the fact that the following parameters were not taken into consideration:
The particle size of the silica was not determined
The mass of the metals adsorbed on to the silica was never physically removed or analyzed
The surface of the silica was never analyzed for the number of sites which would adsorb mercury molecules
The number of absorbing sites on the surface of the silica was never calculated
The number of molecules of each metal which was absorbed on the surface was never calculated
Further studies will be required in order to give an accurate estimation as to the volume of molecules/water which would occupy 100% of the surface
Summary and Recommendations
It may be worthwhile to briefly describe the range of issues which presented a challenge to meeting the goals of the ‘Research Study” as it relates to fully understanding the complexities associated with “Adsorption” and in particular in terms of wastewater containing multiple absorbates .
During the initial testing phase, it became apparent that the sites on the adsorbent were being occupied by many other metals including mercury. Although the study did not reveal the exact number of sites which were located on the surface, the study did indicate that approximately 99% of the sites were occupied by other metals. Less then1% of the sites were occupied by HGII.
Conduct another series of adsorption capacity tests whereby the other metals would be stripped from the wastewater.
Conduct another series of adsorption tests whereby the mass of adsorbates could be stripped off the surface.
Conduct another series of adsorption tests with the average HGII level less then 7.7523ppb.
Determine the actual capacity based on the number of sites which will actually be occupied by the HG molecules
The Research Study identified several important issues surrounding the treatment of the wastewater being discharged from the Port Edwards facility. The most important piece of information was the fact that due to the existence of many other absorbates( metals), the level of mercury could not be reduced to the required levels as noted in the existing Permit.
Zorbtech is confident that the adsorbent Biosorb 2000 can reduce the level to acceptable levels once a pre-treatment train has been incorporated into the wastewater treatment strategy now in place at the Port Edwards plant.
Zorbtech Environmental Solutions Inc.
1lex area of research as it pertains to the properties of amorphous silica surfaces.