Development of new materials to concentrate nutrients from digestate Ph.D. Student: Antonis Karachalios Principal Investigators: Dr. Mahmoud Wazne Dr. Xiaoguang Meng

2 Project Summary  The aim of this research is to use natural and modified biosorbents to recover nutrients from the effluent of anaerobic digester (digestate).  Natural and modified including cotton, rice husk, pine bark, and chitosan were systematically modified and tested to recover nutrients from phosphate and nitrate synthetic solutions  Work is ongoing to evaluate more methods that can be used to further improve the biosorbents’ nutrients removal capacity.  The modified biosorbents’ will be tested using field samples to evaluate their ability to remove nutrients from a target waste stream Start date: September 2008 End date: May 2011

3 Objectives  Selection, investigation and characterization of target waste streams  Selection of potential biosorbents for phosphorus and nitrogen (rice husk, oak chips, chitosan, cotton, pine bark, coconut husk, wheat bran, juniper, buckwheat hulls, alfa alfa seeds etc.)  Testing and evaluation of selected biosorbents  Identification and modification of biosorbent functional groups for improved ion removal capacity  Assess the availability of the nutrients from the phosphorus and nitrogen enriched biosorbents

4 Potential benefits  Environmental benefits due to recovery of the nutrients from digestates and other waste streams  Benefits for the technology developers and operators of biogas plants to produce a value added product from digestate  Benefits for the farming community by using the fertilizer product, tailored to specific soil conditions  Utilization of waste products to generate a commercial product

5 Background  Digestate produced by biogas plants is a good source of nutrients for agricultural production.  The high level of soluble nutrients in the liquid fraction is a problem for storage of the digestate during ‘closed periods’ when land spreading is not allowed and for the treatment of the liquid digestate to meet discharge standards if disposal to sewer or surface waters is necessary.

6 Background  Biosorbents have been studied as cost-effective and environmentally-benign means to remove pollutants and nutrients from water  Emphasis has been placed on by-products of agriculture or wood processing that are readily available and have limited utility, thereby making them lower in cost.  Biosorbents’ capacity of removing phosphorus and nitrogen can be significantly improved by impregnating or grafting these sorbents with phosphorus and nitrogen selective functional groups to enhance the biosorbents’ adsorptive and/or ion exchange capacities, thus increasing the amount of phosphorus and nitrogen mass bound per gram of AR or biomass.

7 Background  Anion exchange resins are versatile sorbents that can be used to remove a wide variety of ions from different aqueous media.  The resin can be prepared from high volume, low-cost agricultural by-products as starting materials, that contain variable amounts of cellulose and lignin.  The quaternization of the natural polymers containing cellulose and lignin is accomplished by reacting the natural polymer with a number of quaternary ammonium compounds. These compounds react with the primary alcoholic –OH groups in the glucose moieties of cellulose to yield the anion exchange resin.

8 Raw Biosorbents  Batch tests were conducted to check the adsorption capacity of 10 different biosorbents for phosphorus. The tests were conducted on synthetic phosphate solutions with 0.01 M NaCl. The results indicated that the use of raw materials was not very effective for most of the cases.  All the agricultural residues were milled in a Retsch SK cross-beater mill (Glen Mills Inc., Clifton, NJ) and sieved to retain the minus 20 mesh fraction.  The experimental results of the adsorption isotherms for all the raw biosorbents currently used in this study are shown in Figures 1 and 2.

9 Raw Biosorbents Figure 1:Phosphate adsorption isotherms by raw: Juniper, Alfa Alfa Seeds, Wheat Bran, Buckwheat Hulls, Oak Chips, Coconut Husk, Rice Hulls and Pine Bark.

10 Raw Biosorbents Figure 2:Phosphate adsorption isotherms by raw: cotton and chitosan at three different pH values (pH=5, pH=7 and pH=9)

11 Modified Biosorbents  Three different procedures were used initially to achieve chemical modification of the biosorbent functional groups. All three techniques significantly increased cotton’s adsorption capacity.  In the first technique described by T.L. Eberhardt, S-H Min (2008), cotton underwent a two-stage treatment with solutions of carboxymethyl cellulose (CMC) and ferrous chloride which made the biosorbent more effective to remove phosphate from synthetic solutions.

12 Modified Biosorbents Figure 4: Phosphate adsorption isotherm by modified cotton ** CMC = Carboxymethyl Cellulose

13 Modified Biosorbents Raw Milled CottonRaw Milled Oak ChipsRaw Milled Rice Husk Modified CottonModified Oak ChipsModified Rice Husk Figure 5: Raw and modified biosorbens through the CHMAC procedure  In the second technique described by L.H. Wartelle, W.E. Wartelle (2006), resins are prepared through the quaternization of cotton and other biosorbents, with N-(3-chloro-2- hydroxypropyl) trimethylammonium chloride (CHMAC or Quat 188).

14 Modified Biosorbents Figure 6: Phosphate adsorption Isotherms by modified cotton, oak chips and rice husk through the CHMAC procedure

15 Modified Biosorbents Figure 7: Nitrate adsorption isotherms by modified cotton, oak chips and rice husk through the CHMAC procedure

16 Modified Biosorbents Raw Milled Coconut HuskRaw Milled CottonRaw Milled Oak ChipsRaw Milled Rice Husk Modified Coconut HuskModified CottonModified Oak ChipsModified Rice Husk Figure 8: Raw and modified biosorbens through the Chlorocholine Chloride procedure  In the third procedure described by Abbott et al. (2006), chlorcholine chloride (ClChCl) and urea were pre-mixed to prepare a eutectic solvent. The agricultural residues were then mixed with the eutectic solvent in the presence of NaOH to prepare the resin.

17 Modified Biosorbents Figure 9: Phosphate adsorption Langmuir Isotherms by modified cotton, coconut husk and pine bark through the ClChCl procedure

18 Modified Biosorbents Figure 10: Nitrate adsorption Langmuir Isotherms by modified cotton, coconut husk and pine bark through the ClChCl procedure

19 Conclusions  Raw biosorbents do not seem to facilitate great removal rates  Modified biosorbents have significantly improved the phosphate and nitrate removal capacities. It also appears that the removal uptake is chemisorption based on the shape of the uptake curves; i.e., the shape of the curve appears to be Langmuir-type. This may indicate that physical sorption is not significant.

20 Future Work  Test and evaluate more biosorbents  Use more methods to modify biosorbents’ functional groups  Acquire and characterize a second target waste, preferably from a dairy farm plant, with possibly higher phosphorus and nitrogen concentration  Test biosorbents’ ability to remove nutrients from the target waste stream  Test the effect of other ions (e.g. sulfate) on nutrient removal by the modified agricultural by-products