ADSORBENT FOR ANAEROBIC DIGESTION PROCESSES

Abstract

A particulate carbon adsorbent for use in anaerobic digestion is provided. The particulate carbon adsorbent is substantially planar and comprising between 40-90 wt % carbon. Methods of manufacture of the particulate carbon adsorbent are also provided.

Claims

1. A particulate carbon adsorbent for use in anaerobic digestion, the particulate carbon adsorbent being substantially planar and comprising between 40-90 wt % carbon.

2. The particulate carbon adsorbent for use in anaerobic digestion according to claim 1 formed by pyrolysis of substantially planar organic material.

3. The particulate carbon adsorbent for use in anaerobic digestion according to claim 2, wherein the substantially planar organic material comprises paper or cardboard or similar.

4. The particulate carbon adsorbent for use in anaerobic digestion according to claim 2, wherein the substantially planar organic material comprises a plurality of layers of substantially planar organic material.

5. The particulate carbon adsorbent for use in anaerobic digestion according to claim 2, wherein the substantially planar organic material is a composite material.

6. The particulate carbon adsorbent for use in anaerobic digestion according to claim 5, wherein the composite material is formed from layers of paper and layers of plastic and/or wax and/or aluminium.

7. The particulate carbon adsorbent for use in anaerobic digestion according to claim 1, wherein the anaerobic digestion is carried out in a bioreactor, and as a result, the particulate carbon adsorbent is used in a bioreactor.

8. The particulate carbon adsorbent for use in anaerobic digestion according to claim 1, wherein the particulate carbon adsorbent provides a substrate for the formation of an active biofilm.

9. The particulate carbon adsorbent for use in anaerobic digestion according to claim 1, wherein the particulate carbon adsorbent comprises an active biofilm.

10. The particulate carbon adsorbent for use in anaerobic digestion according to claim 9, wherein the particulate carbon adsorbent comprises an active biofilm prior to use.

11. The particulate carbon adsorbent for use in anaerobic digestion according to claim 10, wherein the particulate carbon adsorbent is pre-inoculated with microorganisms from within fluid obtained from a target system at any stage of the anaerobic digestion process.

12. The particulate carbon adsorbent for use in anaerobic digestion according to claim 1, wherein the particulate carbon adsorbent comprises calcium and/or magnesium ions.

13. The particulate carbon adsorbent for use in anaerobic digestion according to claim 12, wherein the particulate carbon adsorbent comprises from about 0.1 wt % to about 10 wt % calcium ions.

14. The particulate carbon adsorbent for use in anaerobic digestion according to claim 12, wherein the particulate carbon adsorbent comprises from about 1.0 wt % to about 15.0 wt % magnesium ions.

15. A method of manufacture of particulate carbon adsorbents for the use in anaerobic digestion, the method comprising the steps: a) providing a substantially planar organic material; b) pyrolysing the provided substantially planar organic material at a temperature from 300 C. to 800 C.; c) grinding the pyrolysed material resulting from step b); and d) sorting the ground pyrolysed material resulting from step c) to specify the dimensions of the particulate carbon adsorbent required.

16. The method of claim 15, wherein the substantially planar organic feedstock is pyrolysed at a temperature from 400 C. to about 475 C., or wherein the substantially planar organic feedstock is pyrolysed at a temperature from 650 C. to about 800 C.

17. (canceled)

18. The method of claim 15, wherein the substantially planar organic material is shredded before it is pyrolysed.

19. The method of claim 18, wherein the shredded substantially planar organic material is compressed before the step of pyrolysing the substantially planar organic material.

20. An anaerobic digestion process comprising the steps: a) providing a bioreactor; b) adding a feedstock to the bioreactor; c) adding a microorganism composition to the bioreactor; d) adding an adsorbent composition to the bioreactor, the adsorbent composition comprising substantially planar particulate carbon adsorbent that comprise between 40-90 wt % carbon; e) incubating the bioreactor such that microorganisms within the microorganism composition digest the feedstock to produce a digestate and biogas; and f) removing the produced biogas and digestate.

21. The method of claim 20, wherein the adsorbent composition is pre-inoculated prior to addition to the bioreactor with fluid from the bioreactor that contains the feedstock and microorganism composition of that bioreactor.

22.-32. (canceled)

Description

BRIEF DESCRIPTION OF THE FIGURES

[0135] Embodiments of the present invention will now be described, by way of non-limiting example, with reference to the accompanying drawings.

[0136] FIG. 1: Scanned electron Microscopy (SEM) image of the surface of a particulate carbon adsorbent made from paper cup waste;

[0137] FIG. 2: SEM image of the surface of a particulate carbon adsorbent made from paper cup waste;

[0138] FIG. 3: Optical image of an example particulate carbon adsorbent;

[0139] FIG. 4: Energy-dispersive spectroscopy (EDS) spectra (A and B) of elements present on different points of the surface of a particulate carbon adsorbent;

[0140] FIG. 5: Course of biogas production of syringe fermenters in the first experiment with and without the addition of adsorber (particulate carbon adsorbent). Feeding of propionic acid on day 5. Diagram shows average values of 4 repetitions.

[0141] FIG. 6: Course of biogas production of syringe fermenters in the first experiment with and without the addition of adsorber (particulate carbon adsorbent). Feeding of propionic acid marked by diamonds. Diagram shows average values of at least 2 repetitions.

[0142] FIG. 7: A carbon granule comprising a core of smaller carbon particles (1) and a shell of larger flake-shaped particles (particulate carbon adsorbent) (2).

[0143] FIG. 8: Course of the biogas production in the second anaerobic digestion experiment. The diagram shows average values of three repetitions.

[0144] FIG. 9. Biogas generation from test AD reactors with the addition of 5 g/I Chemical Oxygen Demand (COD) bio-oil from softwood pellets (SWP/BO). The 20 mL of digestate was supplemented with Sodium 2-bromoethanesulfonate (BES) (Be), standard biochar (St), pre-incubated standard biochar (Si), carbon particulate adsorbent according to the invention (CreChar) (Cr) and pre-incubated CreChar (Ci). Control reactors were not supplemented (). All conditions were performed in duplicate with each curve as a mean of the replicates with error bars of standard deviation.

DETAILED DESCRIPTION

[0145] While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

[0146] To facilitate the understanding of this invention, a number of terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as a, an and the are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as outlined in the claims.

Use of Particulate Carbon Adsorbent in Anaerobic Digestion

[0147] The particulate carbon adsorbent was produced from pyrolysed paper-plastic composite material. For two anaerobic digestion experiments, the paper-plastic composite material was pyrolysed into flake-shaped particles (acting as particulate carbon adsorbents according to the invention) with a carbon content of 46%, a pH of 9.7, and an electrical conductivity of 93.7 S/cm (1:20 dilution with purified H.sub.2O). The particles were sieved and only particles that passed through a sieve with an aperture of 0.5 mm but not through a sieve with an aperture of 0.125 mm were selected for further testing. By means of optical microscopy and a binocular magnifying glass the particulate carbon adsorbent was confirmed to have a flake shape with a vertical extent mostly between 0.02-0.30 mm. The surface of the particulate carbon adsorbent formed using the above method are shown in FIGS. 1 and 2. An example particulate carbon adsorbent, or carbon flake, is shown in FIG. 3, as seen via optical microscopy.

[0148] FIG. 4 shows Energy-dispersive spectroscopy results from the surface of the particulate carbon adsorbent (carbon flakes) showing the elemental composition of those surfaces.

[0149] A first anaerobic digestion experiment was carried out in 60 mL plastic syringes that were continuously shaken and kept at 37 C. Initially, 8 syringes were each filled with 10 mL of inoculum from a full scale biogas plant that treats sewage sludge. In addition, 4 of the syringes were each amended with 0.2 g of the adsorbent (Carb), as particulate carbon adsorbents according to the invention. The other 4 of the syringes are referred to as the control in the following. On day 5, all syringes were fed with 1 mL of a 1% propionic acid solution to simulate inhibitory conditions. Over the total time of the experiment of 21 days, the gas production was measured frequently. The results shown in FIG. 5 reveal that the biogas production in the syringes that contain the adsorbent (marked with adsorber in FIG. 5) started earlier and was more intense than in the syringes without adsorbent (marked without adsorber in FIG. 5).

[0150] This experiment was extended under the same conditions for 58 days and the results are shown in FIG. 6.

[0151] After the start-up phase of approximately two weeks the gas production of the carbon treatment declined while the control's gas rate was stable at about 2 mL per day. This was mainly attributed to having exhausted the availability of substrate. However, when feeding of propionic acid was continued on day 21, gas production of the adsorbent treatment (Carb) was relatively lower by comparison. A liquor analysis revealed very low concentrations of the phosphorus. Addition of phosphoric acid to both treatments (adsorbent (Carb) and control) on day 42 was followed by a sharp increase in biogas production. Afterwards both treatments performed similarly until digestate was removed for the first time on day 53. After about half of the syringes' content of digestate was removed the control showed an accumulation of organic acids leading to process failure, whereas the adsorbent (Carb) treatment showed stable gas production. This experiment shows that the adsorbent (Carb) material can stimulate and stabilize microbial activity. However, in order to ensure microbial activity nutrients including phosphorus are needed. Because of the adsorbent's (Carb) sorption capacity for phosphorus, the adsorbent (carb) can induce a lack of phosphorus availability in the anaerobic digestion reactor. However, this seems less likely when the adsorbent (Carb) is added in smaller installments rather than in one batch as performed in the experiment. Alternatively, the adsorbent (carb) can be pre-charged with phosphorus before entering the anaerobic digestion reactor.

[0152] In a second anaerobic digestion experiment, the same adsorbent (Carb) was compared with other carbon materials and in addition a phosphorus-enriched variation of the adsorbent (Carb+P) was included. The phosphorus-enrichment increased the adsorbent's phosphorus content from 0.07 mg/g (Carb) to 17.8 mg/g (Carb+P). The experiment was carried out in 100 mL glass syringes that were continuously agitated in a rotating wheel and kept at 37 C. Initially, 15 syringes were each filled with 20 mL of inoculum from a full scale biogas plant that treats sewage sludge (from the same plant as the first experiment). In addition, to a set of 3 syringes 0.4 g of one each of the following carbon materials were added: Carb, Carb+P, activated carbon (AC; identical to the material used for the removal of phosphorous from an aqueous solution and for the carbon adsorbent granules), standard biochar from of the UK Biochar Research Centre made from softwood pellets at 550 C. (SWP; identical to the material used for the removal of phosphorous from an aqueous solution), and the syringes with no addition of carbon material acted as Control. All materials were applied in a particle size of 0.125 to 0.5 mm, except for the AC (0.063-0.25 mm).

[0153] Over the total time of the experiment of 22 days, the gas production was measured frequently. The results shown in FIG. 8 reveal that Carb+P had the strongest effect on biogas production. AC, Carb and SWP were also capable of increasing the biogas production but far less than Carb+P. The performance of Carb and SWP were similar and their impact on the process started later than AC. However, after 22 days, both Carb and SWP had produced more biogas than AC and the Control. This confirms the observation from the first anaerobic digestion experiment that the substantially planar carbon adsorbent (Carb) is an effective anaerobic digestion enhancer, but the microbial availability of phosphorus needs to be ensured in order to benefit from its full performance. As shown here, pre-charging or the substantially planar carbon adsorbent (Carb) with phosphorus is an effective way to overcome a potential phosphorus limitation.

[0154] In practical application, the ideal concentration of the adsorbent depends on the type and amount of inhibitory substances and the desired increase of active microbial biomass in the biogas reactor. Usually, the ideal concentration will be 0.5-3 wt % of the particulate carbon adsorbent to the feedstock. Higher concentrations are not advisable because they will increase the viscosity of the biogas slurry, which makes stirring harder and could interfere with the removal of digestate. However, the ideal concentration of the adsorbent can be found and sustained by monitoring the common biogas process performance parameters e.g. methane concentration and biogas productivity and by measuring the energy consumption of the stirring devices.

Preparation of Particulate Carbon Adsorbent with an Activatable Biofilm

[0155] Pre-incubation with inoculum from the target system may be carried out as follows:

[0156] 1. Mix particulate carbon adsorbent with fermentation liquor from the target anaerobic digestion (AD) plant (the fermentation liquor can be obtained at any stage of the AD process; mixing can be conducted in one of the AD reactors or a separate tank, inoculum should not be stressed; particulate carbon adsorbent concentration should be between 1 and 10%)

[0157] 2. Incubate for at least 24 hrs.

[0158] 3. Transfer the incubated particulate carbon adsorbent to one or more reactors of the AD plant, where performance increased.

[0159] The digestate for the AD tests was obtained from the AD site at Seafield, Edinburgh UK. The plant processes thermally-hydrolysed sludge from the adjacent municipal wastewater treatment plant. AD tests were performed under the guidelines set out by the Fermentation of Organic Materials Standard VDI 4630 with the Hohenheim Biogas Yield Test batch system in 100 ml glass syringes. Reactors were supplemented with 5 g/l COD bio-oil obtained from the pyrolysis of softwood pellets at 350 degrees Celsius.

[0160] Carbon flakes were added dry or pre-incubated to the reactors to assess their impact on biogas production. Pre-incubation was achieved by adding char to the same digestate as used in the reactors to a 1:10 ratio and letting it shake at 37 Celsius for 48 hours anaerobically. Afterwards, the chars were sieved and washed with distilled water and directly added to the reactors. Reactors supplemented with pre-incubated carbon flakes showed a significantly reduced lag time before biogas production and therefore inhibition from bio-oil addition was alleviated (see FIG. 9).

[0161] Without wishing to be bound by theory, it is hypothesised that pre-incubation of the biochar surfaces establishes a core microbiota that is protected from inhibitory stress due to the nature of the char surface topology and biofilm properties and thus capable of continuing AD in the presence of the stress. Conductivity of the char surface may also facilitate Direct Interspecies Electron Transfer (DIET) between microorganisms within the biofilm. The use of inoculum from the target reactor as the source of the biochar-associated microbial biofilm community ensures that no new microorganisms are being introduced to the system and thus there is no additional competition for niches within the reactor environment.

Use of Carbon Adsorbent for Removal of Phosphorous (P) from an Aqueous Solution

[0162] For a phosphorous adsorption experiment following carbon adsorbent materials were tested: [0163] 1. PE paper cup #1 (PC1) pyrolysed at 450 C. with particle size of 0.125-0.5 mm [0164] 2. PE paper cup #1 (PC1) pyrolysed at 750 C. with particle size of 0.125-0.5 mm [0165] 3. PE paper cup #2 (PC2) pyrolysed at 450 C. with particle size of 0.125-0.5 mm [0166] 4. PE paper cup #2 (PC2) pyrolysed at 550 C. with particle size of 0.125-0.5 mm [0167] 5. PE paper cup #2 (PC2) pyrolysed at 750 C. with particle size of 0.125-0.5 mm [0168] 6. PE paper cup #2 (PC2) pyrolysed at 450 C. with particle size of <0.125 mm [0169] 7. PE paper cup #2 (PC2) pyrolysed at 750 C. with particle size of 0.063-0.125 mm [0170] 8. PLA paper cup (PC3) pyrolysed at 450 C. with particle size of 0.125-0.5 mm [0171] 9. PLA paper cup (PC3) pyrolysed at 750 C. with particle size of 0.125-0.5 mm [0172] 10. Activated carbon (AC) with particle size of 0.063-0.25 mm [0173] 11. Standard biochar of the UK Biochar Research Centre made from softwood pellets at 550 C. (SWP) with particle size of 0.125-0.5 mm [0174] 12. Control without adsorbent

[0175] PC1 is an 8 oz white single walled polyethylene (PE)-laminated paper cup made in China for Sainsbury's.

[0176] PC2 is a 12 oz black doubled walled PE-laminated paper cup branded for Marks & Spencer and made by Euro Packaging UK Ltd.

[0177] PC3 is an 8 oz brown single walled polylactic acid (PLA)-laminated paper cup made by Vegware Ltd.

[0178] Materials 2, 5, 7, 9 and 12 were tested in triplicate, the others as single experiments.

[0179] A phosphorous solution was prepared using K.sub.2HPO.sub.4 and deionized water with a measured phosphorous concentration to achieve a phosphorous concentration of 20 mgL.sup.1, which is a relevant concentration in waste waters. The sorption experiment was carried out in centrifuge tubes filled with 10 mg of carbon material and 20 g of the phosphorous solution. The tubes were kept on a shaker. After 24 hrs, the liquid phase was analysed for its phosphorous content and the specific amount of adsorbed (or desorbed) phosphorous by the carbon material was calculated using the control as basis.

[0180] The highest phosphorous sorption was found for the carbon adsorbent that was produced at 750 C. (see Table B). This can be attributed be to a higher concentration of Mg and Ca and in particular to a higher concentration of MgO at higher pyrolysis temperatures as shown in Tab. 1.

TABLE-US-00002 TABLE 2 Measured amount of adsorbed phosphorous by various carbon materials after 24 h Adsorbed phosphorous Pyrolysis Particle size by carbon material Carbon temperature range after 24 h material C. mm mg P/g PE paper cup 750 0.125-0.5 18.05 #1 (PC1) 450 0.125-0.5 0.34 PE paper cup 750 0.125-0.5 4.93 #2 (PC2) 750 0.063-0.125 23.01 550 0.125-0.5 2.24 450 0.125-0.5 0.16 450 <0.125 0.04 PLE paper cup 750 0.125-0.5 22.65 (PC3) 450 0.125-0.5 0.21 AC NA 0.063-0.25 16.40 WP 550 0.125-0.5 0.10 (NA = not available)

[0181] AC showed a negative value of 16.4 mg g.sup.1, which indicates that the AC was activated using phosphoric acid that now leached into the solution.

[0182] All materials that were produced at 450 C. and SWP were in the range of 0.35 to 0.16 mg g.sup.1. The carbon adsorbent produced at 550 C. from PC2 was found to have an adsorption performance in between the 450 C. and 750 C. adsorbents. This corresponds to the formation of MgO starting at 550 C. as shown in Table 1. The adsorption experiment with this material was continued for a retention time of 5 days, which increased the measured adsorption to an average of 5.6 mg g.sup.1. This shows that a longer retention time can increase the level of phosphorous adsorption. Further, it was also shown that the performance of the 750 C. adsorbents are affected by particle size as can be seen when comparing the results from the PC2 materials in both tested particle sizes. The higher sorption capacity of smaller particles can be explained by a higher surface area and more effective Mg and Ca bonding sites.

[0183] Accordingly, these experiments show that the particulate carbon adsorbents of the invention are effective phosphorous adsorbents. In order to be effective the particulate carbon adsorbent should be produced at temperatures of at least 550 C. and from feedstock materials that have a Mg content of at least 1 wt %. The sorption capacity can be increased by grinding the adsorbent into smaller particles sizes. However, smaller particles are more difficult to separate from the treated wastewater and Mg and Ca compounds are more likely to become detached from the carbon adsorbent. Thus, in most applications a particle size in the range of 0.05 mm to 5 mm is ideal.

Carbon Granules

[0184] In an embodiment, the carbon flakes for the carbon granule's shell are produced from pyrolysed paper-plastic composite material and a seaweed extract is used as binder for both the core and shell. For an agglomeration experiment, the paper-plastic composite material was pyrolysed into flake-shaped particles with a carbon content of 46%, a pH of 9.7, and an electrical conductivity of 93.7 S/cm (1:20 dilution with purified H.sub.2O). The particles were sieved and only particles that passed through a sieve with an aperture of 0.5 mm but not through a sieve with an aperture of 0.125 mm were selected for further testing. By means of optical microscopy and a binocular magnifying glass the carbon particles were confirmed to have a flake-shape with a vertical extent mostly between 0.02 mm to 0.30 mm. A commercial seaweed-extract (Original Organic Seaweed Extract by MaxiCrop) with a total solids content of 8% and a pH of 8.5 was used as binder. As core material for the agglomerates, activated carbon with a mesh size of 100 to 400 was purchased from Sigma Aldrich. The agglomeration was performed in a wet drum granulator using a round tin box with a diameter of 24 cm and length of 13 cm. The initial amounts of activated carbon used for granulation were 17.4 g (for a control without a shell), 20.6 g for a granule with an intended mass-based core-to-shell ratio of 20:1 (thin shell) and 10.7 g for a granule with a mass-based core-to-shell ratio of 1:1 (thick shell). The right amount of activated carbon was fed into the drum and granulated at 60 rpm. Each three minutes the granulation process was checked. The binder, that was diluted 1:1 with H.sub.2O, was added in 4-6 installments by means of a spray bottle. The total amount of binder corresponded to a binder-to-activated carbon ratio of 1.8 to 1.

[0185] When granulation of the activated carbon was visible after 21 minutes (thin shell granule) or 15 minutes (thick shell granule), the right amount of carbon flakes was added into the drum. For the thin-shelled granule, granulation was continued for 10 min and no further binder was added. For the thick-shelled granule, granulation was continued for 21 minutes with 4 installments of binder addition. In total, 1.2 mass parts of binder were added to 1 mass part of carbon flakes. The control batch without a shell was granulated for a total of 20 min. After granulation, the granular agglomerates were dried at 105 C. until a stable weight was observed. The granule diameter varied mostly between 1-10 mm.

[0186] For testing the mechanical stability only granules with a diameter of 5-8 mm were selected. To simulate harsh mechanical stress, the granules were subjected to 5 and 10 min inside the same drum as used for granulation run at 60 rpm. After 5 and 10 min, 21% and 58% of the granules without shells were crushed, whereas the thin-shelled granules crushed by only 8 and 22% and the thick-shelled granules by only 3% and 3%. This shows that carbon agglomerates with a shell of flake-shaped carbon particles have a significant higher durability than unshelled agglomerates. Further, the produced carbon granules were tested for their disintegration behaviour in water and all granule types were observed to disintegrate instantly as desired

[0187] In another embodiment, no binder but only water is used to agglomerate the carbon particles for the core granule. Binder was only used to form the shell of carbon flakes. Again, the carbon flakes for the granule's shell are produced from pyrolysed paper-plastic composite material and a seaweed extract is used as binder.

[0188] For an agglomeration experiment, the same activated carbon, carbon flakes, binder and wet drum granulator were used as in the previous experiment. The amount of activated carbon was 16.2 g. Before granulation, 16.2 g of water was added to the activated carbon. The material was granulated for 5 minutes then further 5.3 g of H.sub.2O was added. After additional 10 minutes, formation of granules with diameters of 5-15 mm were observed and 1.62 of carbon flakes for shell formation were added. After further 8 minutes of granulation, most of the carbon flakes were picked up by the wet granules to form the shell as desired. Then 1.62 g of the seaweed extract (no dilution) was sprayed on the granules and granulation was continued for further 3 minutes. Subsequently, a second layer of carbon flakes was added to the granules by adding further 1.62 g of carbon flakes and 1.62 g of seaweed extract. Finally, after further granulation for 7 minutes, a third batch of 1.62 g of seaweed extract was sprayed on the granules and granulation was continued for further 7 minutes. After this, granulation was stopped and the granules were dried at 60 C. until their weight was stable. The granules were observed to have a 1 mm larger diameter due to the shell. In contrast to agglomerated activated carbon that was produced with neither shell nor binder and that were observed to already disintegrate during drying, the shelled carbon granules sustained the drying process fully intact. When some granules were cut open their content of activated carbon was found in loose state. Thus no significant amounts of binder had entered the granules' core zone.

[0189] For practical application, all types of wet drum granulates can be used to produce the shelled-carbon granules. However, preferably the system allows continuous spray feeding of the binder as well as continuous feeding of carbon particles. Drying could be performed in the same granulator or separately by various batch or continuous types of dryers e.g. belt dryers. After the drying step, additional treatments can be conducted in order to remove dust and granules that are outside the desired size range. This can be achieved by common mechanical or pneumatic separation systems. In cases where the binder and flake-shaped carbon particles are tolerated inside the granules' core, removed dust and outsized granules can be recycled to the agglomeration process. Therefore, the outsized granules should be crushed first. In a preferred setup, the heat for drying the granules is obtained from an onsite pyrolysis kiln that produces the carbon particles for either the granules' core, the shell or both. The pyrolysis gas that is produced during pyrolysis can be burned onsite to fuel the drying process.

[0190] FIG. 7 shows an embodiment of the granular aggregate comprising a core of smaller carbon particles (1) and a shell of larger flake-shaped particles (2).

[0191] The carbon adsorbent granules so produced can then be used in a number of applications, such as in anaerobic digestion, treatment of wastewater, phosphorous capture and soil amendment.

[0192] The following methods and apparatus were used in order to determine the parameters given with regard to the invention:

Atomic Adsorption (for Total Mg and Ca Analysis of the Particulate Carbon Adsorbent)

[0193] The solid samples were digested as described in the following: 0.5 g of sample material was weighed into crucibles, heated to 500 C. and held at this temperature for 8 h. After cooling, the samples were placed in a steam bath and 5 mL of concentrated (70%) HNO.sub.3 (analytical grade, Fisher Scientific) was added and evaporated to dryness. After cooling, 1 mL HNO.sub.3 and 4 mL H.sub.2O.sub.2 (30%, analytical grade, Fisher Scientific) were added and evaporated to dryness. Next, 2 mL HNO.sub.3 was added to dissolve the solids. The resulting solution was filtered through Whatman No. 41 filter paper and the volume increased to 50 mL with DI water. The solutions were than analysed by a ThermoFisher Scientific ICE 3000 atomic absorption spectrometer.

Phosphorous Analysis (for the Particulate Carbon Adsorbent and Phosphorus Solution)

[0194] For solid samples, the some digestion as for atomic adsorption was used. The solutions were analysed by automated colorimetry (Auto Analyser III, Bran & Luebbe, Norderstedt, Germany).

XRD (for Identification of Mg Bonding Types in the Carbon Adsorbent)

[0195] A Bruker AXS D8 Advance Diffractometer with copper anode x-ray tube and Sol-X Energy Dispersive detector was used. The running conditions for the X-Ray tube were 40 kV and 40 mA. Experiments were carried out in the range of 2265 with a step size of 0.05 and 1 sec per step. Data analysis was performed by Bruker's DI FFRAC EVA software and Bruker's TOPAS software was used for semiquantitative analysis. The samples were analysed in powdery form with a particle size below 0.125 mm.

EDS (for Determination of the Mineral Composition on the Particulate Carbon Adsorbent's Surface)

[0196] A Carl Zeiss SIGMA HD VP Field Emission SEM and Oxford AZtec ED X-ray analysis were used.

Elemental Analysis (for the Carbon Content of the Particulate Carbon Adsorbent)

[0197] The elemental (CHN) analysis was performed in quadruplicates using a Flash 2000 Elemental Analyser.

REFERENCES

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