The invention relates to a process for the production of a bioadsorbent material by modifying a surface of the straw used as raw material. As a result of the new process the bioadsorbent produced from common wheat straw or other bread grain straw, such as rye, barley, triticale, or straw waste, is suitable for binding primarily organic substances, organic micropollutants, such as e.g., medicinal substances.

It is well known that the surface of untreated straw, often used as a bioadsorbent material, is capable of binding only small amounts of organic micropollutants. In known processes, activated carbon or biochar is produced from green waste primarily by high-temperature heat treatment, pyrolysis above temperatures of 400 °C. Biocharring, microwave magnetic synthesis, and acrylamide catalysis are known as surface-enhancing technologies specifically developed for bread grain straw, but said technologies do not meet the expectations of modern production technology and the achievable results in terms of both the operations used and their equipment requirements since they are mostly only suitable for binding drug molecules to a limited extent, and can be effectively applied only e.g., to metals or paint residues. Results and efforts related to this can be found, for example, from the studies of Quesada et al. "Surface water pollution by pharmaceuticals and an alternative of removal by low-cost adsorbents: A review", Chemosphere 222 (2019) 766-780., or C.P. Silva et al. "Waste-based alternative adsorbents for the remediation of pharmaceutical contaminated waters: Has a step forward already been taken?", Bioresource Technology 250 (2018) 888-901. It is also clear from these studies that there is no known process that would result in economic and cost-effective binding of drug residues with bread grain straw.

There is a need for a process by which the surface area of straw used as a raw material, which plays an important role in terms of the quality of adsorption, can be increased with simple physico-chemical operations, and with regard to which there is no difference between the individual types of bread grain straw. Basically, the "fibers" in the straw run parallel to each other, but a crumpled structure could provide a larger surface for adsorption and could make desorption more difficult.

The present disclosure provides a process improving the preparation of straw effective usable as bioadsorbent. In this description, bread grain straw types are referred as "straw", and the terms "adsorbent" and "bioadsorbent" are used in the same sense. Similarly, "distilled water" means "deionized water". The set task was solved by process for the production of a bioadsorbent material by modifying a surface of the straw used as raw material, comprising the steps of chopping the straw raw material, removing ingredients different from cellulose by mixing the chopped straw raw material in an alkaline solution, removing the mixed chopped straw from the alkaline solution, flushing the so treated chopped straw by distilled water, drying the flushed straw, preparing a crumpled surface structure from the original surface of the dried straw by stirring the straw in a reactor comprising an aqueous solution containing potassium dihydrogen phosphate (KH2PO4) and citric acid (C ₆ H ₈ O ₇ ) at a temperature in a range of 120-130 °C for 3-4 hours, flushing the stirred straw by distilled water of a temperature in a range of 40-50 °C, and drying the flushed straw having a crumpled surface structure.

In a preferred implementation of the proposed process the straw raw material is chopped to a maximum length of 60 mm.

In a preferred implementation of the proposed process chopping of the straw raw material is carried out in a cutting mill.

In a further preferred implementation of the proposed process removal of ingredients different from cellulose by mixing the chopped straw raw material in an alkaline solution is carried out by stirring the straw raw material in a NaOH solution with a concentration of 0.4-0.6 mol/l for 30- 45 minutes at a temperature in the range of 40-60 °C.

In a further preferred implementation of the proposed process the step of drying the flushed straw having a crumpled surface structure comprises drying the flushed straw having a crumpled surface structure at ambient temperature in the range of 20-23 °C for 8-9 hours, or according to a further preferred implementation the step of drying the flushed straw is carried out in a drying cabinet at a temperature in the range of 35-45 °C for 5-6 hours.

The above and other features and advantages of the present invention will become readily apparent to those skilled in the art by the following detailed description of an exemplary implementation of the process.

In the exemplary implementation wheat straw is used as a starting raw material comprising on average 30-45% cellulose, 20-25% hemicellulose, 15-20% lignin and many smaller organic components. Latter can vary depending on the current soil, and their common feature is that they are water-soluble substances. Raw material straw of 100 g is chopped by cutting it into 20- 60 mm long pieces using a cutting mill, however, other means for chopping known for a person skilled in the art can be used. The weight indicated naturally only applies to the present example, the procedure can be applied to raw materials of different weights with modified quantitative parameters. For example, a cutting knife mill of the type "Pulverisette 19" of Fritsch GmbH, DE, can be used as a cutting mill, but any other suitable device can be used. After shredding or chopping the straw to size, materials other than cellulose, i.e., lignin and other organic components of the straw, shall be removed. For this purpose, the straw is mixed in 5 I of distilled water at a temperature of 40-50 °C for 1 hour. In this example, the stirring is performed with a magnetic stirrer of the type "DLab MS-H280-Pro" manufactured by AA Labor Kft., HU, but any other suitable device can be used. This duration is approximate, a tolerance of ±10 minutes does not cause any change in the result. It can be observed that during stirring the solution becomes discolored, it acquires a yellowish-brown color. After that, the solid phase and the liquid phase are separated, the easiest way is to pour off the liquid phase. Then, residual lignin content of the straw is removed by an alkaline treatment, by stirring the straw in a NaOH solution with a concentration of 0.4-0.6 mol/l at a temperature of 40-60 °C for 30-45 minutes, taking 5 I of solution for 100 g of straw material. After that, the solid phase and the liquid phase are separated by pouring off the liquid phase, then the straw is rinsed with distilled water. The straw is then dried, in this example at ambient temperature for 8-9 hours, but the drying can also be carried out in a drying cabinet at a temperature of 35-45 °C for 5-6 hours. The straw is then conditioned at ambient temperature for 60-80 minutes, while it is mixed and aerated several times so that all surfaces can dry properly.

In the next phase the surface of the straw will be modified, comprising creating a crumpled structure from the original surface of the straw. For this purpose, a solution of 5 I comprising citric acid with a concentration of 0.03 mol/l from a range of 0.02-0.05 mol/l and potassium dihydrogen phosphate (KH2PO4) with a concentration of 0.025 mol/l from a range of 0.015- 0.035 mol/l is used. The straw already treated as described above is placed in a medium-volume pressure-resistant reactor, then mixed with the prepared 5 I solution, and the resulting suspension is stirred in the reactor at a temperature of 120-130 °C for 5-6 hours. In this example, the medium-volume pressure-resistant reactor is a reactor of Buchi AG, CH, but any other suitable device can be used. At the end of the process, the liquid phase is poured off, and the prepared adsorbent is rinsed several times with distilled water. In accordance with one embodiment of the process of this invention, the rinsed adsorbent is mixed in distilled water at a temperature of 40-50 °C for 1-2 hours. The liquid phase is then poured off, and the adsorbent is left to dry by mechanically mixing it several times, checking the state of drying by hand. Similar to the previous drying, in this example the drying is carried out at ambient temperature in the range of 20-23 °C for 8-9 hours, but the drying can also be carried out in a drying cabinet at a temperature of 35-45 °C and for 5-6 hours.

The individual operations can be effectively performed on all values of the ranges given in connection with the example, in accordance with current technology, location and equipment park. With the disclosed process, a significantly larger potential adsorption surface by transforming the surface can be prepared. Modification of the surface of the biosorbent material can be checked, for example, by scanning electron microscopic measurements.

The bioadsorbent material produced by the process according to the invention can be used independently or, for example, based on experiments, it can be mixed in an amount of approximately 20% with adsorbents used during the post-treatment of polluted water, such as granulated activated carbon. It is primarily suitable for binding organic pollutants with electric charge, such as acidic and basic active pharmaceutical ingredients, such as diclofenac, lidocaine, or antibiotics, such as ofloxacin, ciprofloxacin. Significance of the process is the obtaining useful raw materials during recycling of green waste. While in the foregoing specification this invention has been described in relation to a preferred embodiment thereof, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.