The overall objective of the ARIDWASTE project is to research, advance and finally develop alternative low cost and environment friendly agricultural practices across Med basin with the use of treated agricultural wastes (AW) by recycling nutrients and water from treated agricultural wastes taking also advantage of the beneficial, unique properties of natural zeolites. ARIDWASTE strategic impacts also focus to the reduction in crop management running costs, strengthening the linkage between agriculture management sector and marketing sector promoting competiveness of Mediterranean agricultural products and profits while contributing to the protection of health, the improvement of the quality of life, environmental sustainability and food safety mainly at the wastes disposal areas. For this, ARIDWASTE includes specific tools and carefully designed actions to guarantee the sustainable use of the treated AW in agriculture and to protect and improve serious degraded cultivated soils in the Mediterranean area such as: comprehensive critical review of AW management strategies; quality tests of treated wastes in terms of their physicochemical properties, soil quality parameters, phytotoxicity and plant response; field tests in selected areas, consisting of a representative farming community in different agro ecological zones; quantitative and qualitative impact analysis of AW application; development of an integrated scenario for the sustainable use of the treated wastes in extensive crop production providing site-specific diagnoses up to recommendations available for end-users, agribusiness sector and policy makers in order to select as appropriate to their local condition. Testing areas allow joint team efforts in assembling information for knowledge gaps, testing and refining methods and technologies, and interaction with ultimate beneficiaries of project activities. The coherent proposal unites top-level interdisciplinary scientific knowledge, expertise and know how while the participants via an active cooperative role with stakeholders lead to consumer demand dissemination of the results and subsequently to the rapid take up of the ARIDWASTE innovative outcomes.
Environmental problems on the application of Agricultural wastes to land
There is an increasing concern in Mediterranean countries about interrelated environmental problems such as erosion, loss of organic matter, salinization leading to desertification and accelerated greenhouse effects. Common agricultural practices such as excessive use of agro-chemicals, deep tillage and luxury irrigation have degraded soils, polluted water resources and contaminated the atmosphere (Wells et al, 2000). Sustainability concerns on the waste management scenarios in Europe for various organic wastes, in combination with the policy driven priorities at the EU, and the subsequent adoption of EU policy at national levels, has given momentum for diversion of organic wastes away from landfills and ultimately on to the land. Over the last decade the use of land as a waste management alternative for a variety of organic wastes (e.g. manure) has received increased attention partly explained by the need to safely recycle these wastes in compliance with EU legislative demands, the increase in the quantity of these wastes requiring management on one hand, and the unacceptability of previously available management options (e.g. ocean disposal, land filling).
Benefits to the environment from the use of agricultural wastes
Application of high quality processed Agricultural Wastes (AW) to land presents a potential way to recover value and eliminate landfilling . Without doubt the controlled use of organic wastes could assist soil protection and improvement of soil fertility. The application of qualitatively high-class and quality assured treated AW (eg. composts) in crops cultivation may significantly contribute to increased yield efficiency, soil improvement and soil remediation due to their reliable hygienisation, their high portion of stable humus, good phosphorous and potassium fertilizing efficiency, slow release of nitrogen fertilizer and their lime effect while, at the same time, it is considered as a sustainable cultivation practice protecting natural resources. In addition, treated solid AW application may contribute to soil quality protection and improvement by improving water holding capacity, decreasing soil bulk density, improving aeration, water status, and aggregate stability, and as a consequence, erosion rates decrease and cation exchange capacity improves. Furthermore, the soil microbial community is activated, its biomass is enhanced, increasing thus beneficial soil organisms and reducing plant pathogens . Repeated application of composted materials enhances soil organic nitrogen content, storing it for mineralization in future cropping seasons, often without inducing nitrate leaching to groundwater.
Potential hazards to environment from the use of agricultural wastes
However, land application could induce potential hazards to soil and consequently to the environment since a range of contaminants can be present in treated organic wastes including heavy metals, recalcitrant organic compounds, and pathogens (Pepper et al., 2006; Singh and Agrawal, 2008; Achiba et al, 2010). Their presence greatly influences public perceptions regarding the safety of land applications although negative impacts of contaminants and pathogens applied to soil can be minimized, when high-quality compost is used for long periods. A precondition for sustainable application of treated wastes is, that the proven rules of the “good codes of practice” are consequently applied. Many countries now have legislation and guidelines that limit the maximum amount of pollutants in treated organic wastes (e.g. composts). According to ECN 2010, potential risks of compost application on soils can be calculated and don’t oppose an environmentally safe utilization.
Previous studies and projects dedicated to the development of AW treatment technologies focused mainly on the reduction of the wastes organic load and on the reduction or the recovery of valuable substances, such as polyphenols from olive mills wastes (OMW), and succeeded to develop suitable technologies and methods. However, if land distribution is planned the organic load and the toxic substances of treated wastes should not be the only issues of concern. Specific care should be taken also for inorganic constituents and especially for K, Cl-, NO3-, SO42-, P, Mg, Fe, Zn and others, since the very high concentrations disposed on soil change its quality properties drastically, while electrical conductivity and the concentrations of inorganic soil constituents such as K, P, Fe, Cu remain high even after many years from the last disposal.
Variability in agricultural waste reuse standards
There is a clear need for sharing a common rationale for developing waste reuse standards on both sides of the Mediterranean. This is due to the fact that a) there are many E.U. directives and specific Action Plans for different European regions for organic waste management, organic matter decline b) there are still gaps in European and Med policy and legislation on waste in terms of different national and regional legislations, national policies and regulations b) Mediterranean soils require a buildup in organic matter c) absolute necessity for AW management due to the high amounts generated and associated problems d) control of CO2 emissions to the atmosphere and e) agricultural applications do not always have the same determining factors for the different conditions of Mediterranean countries, and thus, guidelines and recommendations of best practices should be clearly developed and promoted. These practices must take into account important specific local conditions, such as waste characteristic, soil type, background levels of nutrients and pollutants for soil, water and plants, the climate, the relevant crops and the local agricultural practices.
Use of natural zeolites in agriculture
Additionally in the context of increasing the efficient use of AW application practices, one of the main measures considered highly effective, biologically justified and environmentally safe especially on degraded soils is the use of natural zeolites. Natural zeolites have physical and chemical properties suitable for a wide range of industrial, agricultural and commercial applications due to their unique physical and chemical properties (crystallinity, thermal stability, well-defined cage structure of molecular size, ion-exchange, etc). Zeolites have been widely used as heavy metals adsorbents, as chemical sieves, as catalysts, as water softeners and as controlled slow release fertilizers and act also as effective carriers of herbicides, fungicides, and pesticides. Zeolites can be successfully used in cultivating different crops such as cereals, forage crops, vegetables, vine and fruit crops due to their exceptionally high ion-exchange capacity . Additionally, studies revealed that zeolites enhance the reduction of VOCs (Volatile Hydrocarbons), and PCPs (polychlorinated polyphenols) concentration in soils due to their high gas adsorption capacity.
Of more than 40 natural zeolite species, clinoptilolite seems to be the most abundant zeolite in soils and sediments. It has a relatively high ion-exchange capacity with a preference for large cations such as NH4+ and K+. The pronounced selectivity of clinoptilolite for large cations, has been exploited in agriculture by using them as amendments to chemical fertilizers to improve the nutrient-retention ability of soils by promoting a slower release of these elements for uptake by plants, reducing thus external inputs of nutrients. Zeolites assist water infiltration and retention in soil due to their porous structure, thus, acting as natural wetting agent assuring a permanent water reservoir in the root zone, and improving the horizontal spread of water after irrigation. Because of this they are excellent soil amendments under dry conditions and non wetting sands. However, despite their very good properties and benefits for agriculture, zeolites have not received wide acceptance and application mainly due to the lack of specific guidelines and application practices and of an integrated scenario for their use.
Although some of the up to now developed technologies for AW treatment have studied the effects of treated wastes on growth and yield parameters of a few crops, it should be noticed that in order AW to be used safely in agriculture, specific cultivation practices should be developed after detailed study of a) the effect of AW on plant growth and yield quality characteristics b) water and nutrients demand of each crops c) the effect of AW on soil and water and air quality d) the environmental conditions and these are exactly what ARIDWASTE proposes: Development of alternative agricultural practices with the use of treated AW by considering all the above factors as significant parameters.
Therefore, since the sustainable exploitation of organic wastes, is becoming a strong issue for Mediterranean countries, through a combination of theoretical and applied knowledge, quality tests and field trials, ARIDWASTE will provide a practical understanding of how different intensive crop production systems can successfully adopt suitable AW application practices and address the challenges and possibilities of AW management.