Joint research project

An integrated system for sustainable water management in agriculture

Project leaders
Eliana Lanfranca Tassi, Amira Hamdan
Agreement
EGITTO - ASRT - Academy of Scientific Research and Technology
Call
CNR/ASRT biennio 2018-2019 2018-2019
Department
Earth system science and environmental technologies
Thematic area
Earth system science and environmental technologies
Status of the project
New

Research proposal

A key issue of water resource management in the Mediterranean area is the imbalance between the increasing water demand and the limited supply. In Italy, for example, agriculture uses 51% of total available water; and this is particularly true in Egypt, where agriculture accounts for about 80% of the total water use in the country. Indeed, many Egyptian soils do not retain water efficiently and require intensive irrigation to maintain a suitable water supply during the growing season. Thus, the effective use of water resources in agriculture represents today a major challenge, especially in arid and semiarid regions.

This proposal deals with the feasibility study at laboratory scale and implementation in experimental sites of a "green" integrated system for small-scale farming intended to reduce the water demand on one side and to increase the water holding capacity of soils on the other. The integrated system will consist of a wastewater bioremediation system for the reuse of clean water in agriculture, coupled with the use of specifically prepared absorbent materials (hydrogels), which, when dispersed in the top soil, release the stored water according to the crop needs.
The research will therefore involve two major elements:
1) Bioremediation. The use of microorganisms to degrade or reduce the concentration of hazardous wastes on a contaminated site is a well-known eco-friendly and low-cost solution of wastewater treatment. Some common microorganism used in the process of remediation are Acromobacter, Alcaligenes, Arthrobacter, Bacillus, Corneybacterium, Flavobacterium, Micrococcus, Pseudomonas, Vibrio and Sphingomonas species. The main species involved in effective wastewater treatment include lactic acid bacteria-Lactobacillus plantarum, L. casei, Streptococcus lacti, and Photosynthetic bacteria- Rhodopseudomonas palustrus, Rhodobacter spaeroide, etc.

2) Hydrogels. Over the past 40 years, hydrogels have been suggested in a broad range of application fields, and among them also in agriculture as soil amendments to increase water retention. In hydrogels, water is absorbed during watering, and then released to the soil together with nutrients in a needed amount keeping the soil humid over long periods of time, thus saving high amounts of water. However, most of the hydrogels on the market are prepared from synthetic polymers that remain undegraded in soils and groundwater representing a serious health and environmental problem. Recently much interest has been given to the preparation of hydrogels from natural polymers, such as starch, chitosan, lignin, alginate and cellulose, which are bio-renewable resources and environmental friendly materials. These however have the drawback of forming weak gels, which are degraded easily and hence cannot provide for a mid- or long-term functionality over more than one growing season. Biodegradable biocompatible superabsorbent hydrogels with reasonable strength have been obtained by chemically modifying different polysaccharide matrices [1]. Chemical modification of polysaccharides normally includes grafting with water-soluble acrylic monomers, such as for instance acrylamide or the ionizable acrylic acid and acyloylglycine. Crosslinking with divinyl monomers, such as for instance methylenebisacrylamide, improves mechanical strength. Modification strategies normally rely on radical reactions triggered by peroxide- or aza-initiators. However, radically polymerized grafts are not biodegradable and, following the long-term degradation of the polysaccharide portion of superabsorbent hydrogels, residual polyvinyl polymers inevitably accumulate in soil. Our approach is to chemically graft onto polysaccharide water-soluble biodegradable and biocompatible lateral segments of polyamidoamine structure [2], obtaining novel hydrogels. Insertion of carboxyl groups in their repeat units will increase the natural water-absorption ability. Grafting will be carried out by the direct Michael-type addition of polyamidoamine oligomeric precursors end-capped with bisacrylamide terminals, spontaneously triggered at basic pH values in the presence of polysaccharides, therefore not requiring environmentally hazardous catalyzers. The chain length of the polyamidoamine oligomers can be tuned so they can act as crosslinkers. Hemicellulose, which represents over 30% of dry matter of rice straw, produced in high quantities in Egypt, will be used as polysaccharide. Indeed, hemicellulose can be extracted from agricultural residues; considering that the fractionation and purification of hemicelluloses from lignocellulosic feedstock is typically a tedious and costly process, less-refined hemicellulose biomass can be used for a more sustainable and low cost product.

The project will be divided into six phases:
1. wastewater collection and characterization for the regulated parameters for water quality discharges, and clarification of any suspended solid;
2. laboratory growth test in batch tanks for the selection of suitable bacteria for bioremediation. The suitability of bacterial species will be verified against their tolerance to the specific wastewater contaminants, rapid growth and reduction of contaminants concentration in the outflow water;
3. set up of a horizontal subsurface wastewater flow system, consisting of 2 or 3 tanks containing inert material of different grain sizes and the growth of bacteria selected in the previous action;
4. preparation and characterization of the most suitable PAA/polysaccharide hydrogel on the basis of water retention capacity and degradation behavior;
5. laboratory trials to test the efficiency of the produced hydrogel in water retention when added to soil;
6. field experimentation of the whole system.

References:
[1] Guilherme et al., European Polymer Journal 72 (2015) 365-385
[2] Ferruti, Journal of Polymer Science: Part A, Polymer Chem, 2013, 51, 2319-2353

Research goals

The overall goal of this project is to design a sustainable management system for wastewater reuse and reduced water consumption. This will be realized (i) by using a bioremediation technology for obtaining water suitable for irrigation from wastewaters, and (ii) by applying biodegradable and biocompatible hydrogels to soils in order to increase water retention thus reducing the amount of water required by agriculture. Thanks to the use of natural polymers from agricultural residues, the system will represent an example of circular economy. Furthermore, polyamidoamines (PAAs) are obtained by means of sustainable, low-energy consuming processes, and comply with nearly all desirable requirements for this application, such as bio- and eco-compatibility, effectiveness in aqueous systems, low cost and easy scaling up of preparation, biodegradability with long-term degradation to non-toxic products. Specific goals concern the systems investigated. In fact, the thorough characterization of the hydrogels synthesized and optimized for their use as soil amendments, will allow novel materials with great applicative interest to be obtained. Other goals are: (i) the exchange of ideas and techniques between two research groups with complementary expertise in environmental science; (ii) the training of students and young researchers; (iii) the establishment of a strong collaboration for further common projects.

Last update: 15/06/2025