Our modern society generates large quantities of by-products that, if not adequately recovered, become wastes and residues that pose a very serious threat for the environment as well as for human and animal health.
Waste management is becoming a political priority in many countries. In fact, environment protection is one of the key issues of the sustainable development strategy in the European Union. However, one of the main problems we are facing is the treatment of huge quantities of by-products and primary wastes in an environmentally sound way.
This project aims to contribute to the development and demonstration of innovative approaches, technologies and methods through the recovery of a series of by-products and other organic wastes generated in the communal area of Lorca (Murcia, Spain), mainly for energy production. The management of these wastes represents a cost for the City Council (pruning and garden debris, cull wood, sewage sludge from urban wastewater), livestock farmers (pig manure and carcasses) and agri-food industry (e.g. blood, hair, etc. from slaughterhouses). The management and transportation of these materials involves environmental and health risks, therefore measures to promote in situ treatment and transformation should be encouraged. In addition, the high economic cost of these management processes must be compensated by waste-recovery initiatives.
All this by-products and organic wastes represent a serious problem because of their volume and the scarce or null recovery they undergo. These organic materials (except pig manure) were usually being dumped to a landfill site or the disposal being carried out by an authorized operator.
Estimates of regional, national and European (EU-25) annual production of waste and by-products:
One of the main concerns is how to treat them in an environmentally sound way. Moreover, the flow of these wastes to landfills must be reduced as much as possible and the recycling of organic materials into soil amendments must be encouraged, thus reducing costs and giving value to these residues.
Estimates of regional, national and European (EU-25) waste and by-products management costs:
Composting is so far the most common method for recovering organic by-products and wastes. But we must not forget that composting is a net energy-consuming process; it requires between 50 and 75 kWh per tonne of processed material in the case of municipal solid waste (MSW). On the other hand, most organic wastes and by-products are hard to compost due to their very high water content, often over 80%, which make necessary the use of structuring agents to ensure optimal composting. These agents are not always readily available in all geographic areas and so need to be imported, increasing transport costs and raising the problem of seasonal availability, two issues that can jeopardize the project. But high water content in the composition of the organic materials, that can be unfavourable for composting, is an asset for methanation, a process which require that fermentable materials were as liquid as possible in order to favour the activity of methanogens involved in the process.
The impact of waste management on air, soil and water is prevented and controlled by using different levels of waste treatments and different disposal methods. The choice of the method must ensure the highest safety, the minimum environmental impact and, as much as possible, the waste recovery and the complete recycling of the final products. One of the main trends in waste management policies nowadays is the reduction of the flow of waste sent to landfills and the recycling of organic materials and plant nutrients into soil amendments. Anaerobic digestion (AD) is one of the ways to achieve this objective. Moreover, AD diminishes energy consumption and can even have a positive energy balance. When used to treat MSW, the process of AD for biogas production is a net energy producer, delivering 75-150 kWh per tonne of substrate input.