Current techniques and practice of MBT and composting, advantages and constraints

Transcription

1 ISWA Main Sponsors: Current techniques and practice of MBT and composting, advantages and constraints PhD. Ramón Plana - Organic Wastes Management Consulter BT Working Group, ISWA plana.compost@gmail.com - Sao Paulo November 12 th, 2015

2 Who said this? We must recognize that soil has a value higher than gold. Unfortunately, the world does not yet appreciate this vital fact. For those of us sitting here, soil is the source of our food, the very future of humanity. But for the urbanized world, soil is just dirt, mud and no-one has a proper understanding of it. Mahatma Gandhi Barack Obama Bono, from U2 Noah Seattle, Duwamish chief Manfred Kern, Bayer CropScience UN meeting in Bonn (Germany),

3 The loss of fertile soil Fertility of the soils depends directly of its organic matter content Economic losses in Europe by soil degradation. Factors Economic cost (Billions y -1 ) Loss of organic matter 3,4 5,6 Erosion 0,7 14 Desertification > 3,3 Soil is not a renewable resource 3 Source: Soil Thematic Strategy (EC, 2006b)

4 Urban waste composition Organic waste is the main component in the urban waste worldwide. So we can transform a waste into a needed resource if we return it to the soil in the adequate forms. 4 Source: World Bank, 2012

5 Urban wastes what do we want to do with them? Just get rid of them Non-separated collection (impurities). Transportation (long distances). Centralised Big-size facilities (MBT plants). High management costs + low recycling rates. Efficiency (material and energy) is highly questionable. To transform waste into a resource Source Separated Collection of the main components (biowaste, paper, metal, plastics, glass, ). Transportation (shorter distances). Decentralised Small-size facilities. Lower management and environmental costs. Final products of high quality (return to soil and complete the cycle). 5

6 Collection versus Quality of Biowaste Mixed collection (single container) MBT Separated collection (single container) Separated collection (door to door) Composting 6

7 MBT facilities and composting facilities Mechanical Biological Treatment facilities (MBT) are designed and operated to manage high quantities of mixed collected urban wastes. Organic matter is the main fraction in those wastes and the objective is to achieve its stabilization. Part of the non-organic materials are separated and recovered for recycling. An important percentage of this recycling usually happens in other countries like China. It is usual that biological treatment includes anaerobic digestion followed by the stabilization of the digestate by aerobic process. MBT facilities Composting facilities 7 Average capacity of MBT and composting facilities in Spain Capacity (t year -1 )

8 MBT facilities and composting facilities Una auditoría encargada hace más de dos años por el Consejo de Dirección del Consorcio de Residuos de Navarra plantea la necesidad de acometer diversas mejoras en la planta de tratamiento de El Culebrete ya que considera que la recuperación de materiales es baja, no se produce la energía suficiente y el compost obtenido no se puede emplear para los cultivos por su alto contenido en plomo y cadmio. An audit commissioned over two years ago by the Board of the Consortium of Waste of Navarre raises the need to undertake improvements to the treatment plant The Culebrete as it believes that the recovery of materials is low, no energy is produced sufficient and compost obtained can not be used for crops because it has high levels of lead and cadmium. 8

9 MBT facilities and composting facilities Reception 60% (mass) Clasification & pretreatment Biostabilization Biostabilized Recovered materials Materials for recycling Landfilling 9

10 Biowaste management the source material The main differences in the concept between MBT and composting facilities are: The collection method of the organic waste: Mixed Source separated Objective of the biological process Biodrying stabilization Produce compost Collection of organic waste Objective of the biological process MBT facility Mixed with other fractions Biodrying stabilization Composting facility Source separated Produce compost 10

11 Source material MBT facility Composting facility Organic matter is mixed with other materials (plastic, metal, paper, glass, e-wastes, ). This means a transference of certain substances, mainly heavy metals, to the organic matter and its contamination for further use. 11 If the source separate collection is well designed and citizens participate the content of non-organic materials is very low (< 2% Gipuzkoa, Spain; < 5% Milan, Italy). This purity of the organic matter means that the material can be treated easily by biological processes and transform it in a valuable product.

12 Reception MBT facility Composting facility Reception pit where the trucks unload the collected waste. These areas can be closed and under low pressure to avoid negative impacts (odours, leachates). There is a reduction of the traceability of the waste source and is difficult to separate inadequate materials. Reception areas have to be designed for adequate management of fresh biowaste. The adequate design and operation of these areas are key to avoid any environmental impacts. 12

13 Pretreatment MBT facility Composting facility It is necessary to open bags and separate the materials from the organics. Separation of non-organic materials is done by their physical characteristics (magnets, Foucalts, infrared, X-rays, ). Open bags and mixing with bulking material are the main tasks. Mixing can be done with specific equipment or adapting others (p.e. cattle feeders). Homogeneity and porosity of the mixture is the key for a successful and efficient process in the following steps. 13

14 Pretreatment MBT facility Composting facility Equipment like DANO drums are used to change the physical characteristics of the organic matter and make separation easier. When the non-organic materials content is around 10% it can be used a trommel or sieve to separate materials by size (> 80mm). Obviously there are not perfect systems and many materials of small size (plastics, glass, ) are not separated from the organic matter. 14

15 Biological treatment MBT facility Composting facility The main objective is to use the biological activity to heat the organic mass, dry it and degrade it (biodrying) Composting process has water deficit and no water is added in this stage, so the material will get dry and the biological degradation will stop at certain point. To complete the composting process and obtain a good product it is necessary to control certain parameters (temperature, moisture, porosity, ). As the composting facility can be relatively small and/or manageable, is easiest to control the biological process. 15

16 Biological treatment MBT facility Composting facility Usually there is not addition of bulking or complementary agent. The packaging and other non-organic elements still present in the material are considered enough to give porosity. To add bulking material is essential to produce quality compost from source separated collection of household biowaste. Otherwise it will means leachates, anaerobic conditions and high ammonia emissions. 16

17 Mechanical treatment MBT facility Composting facility There is some kind of dynamic effect over the material to increase the efficiency of the process and to force the loss of water. Drums, turners of different kind, etc are the most usual equipment for this task. Due to the environmental conditions and the material compounds (specially glass) the maintenance of the machines is essential. 17 In composting facilities the dynamic systems means an advantage for the efficiency of the process, but the control of emissions is deficient. Other strategies use forced aeration to maintain aerobic conditions, but the material should not be kept too much time without a turning.

18 Emissions control MBT facility Composting facility The high treatment capacity of these facilities makes absolutely necessary to have specific treatments for gaseous emissions. Scrubbers, biofilters, acid/basic precipitations, are the most usual. The need of treatment for gaseous emissions should be decided depending on the size of the facility, its location and process conditions. Biofilters are the most common systems. They must be properly maganaged. 18

19 Sieving and refining MBT facility Composting facility Depending of the content of non-organic materials there is necessary to incorporate more complex sieving and refining systems at the end of the process in both models. In MBT plants it is necessary to include a densimetric table to take out all the stones, small pieces of glass, plastics, etc, that are mixed with the organic material. If the household biowaste has a low content of non-organic materials, very simple sieving systems can be used. 19

20 Final product: Biostabilized and compost MBT facility Composting facility Each country has its own legal requirements to consider it compost and there are also EU directives for its use in organic farming. Legal quality will depends of heavy metals content. Stabilization of organic matter and hygenization of pathogens are a must. It should fulfil certain requirements to be considered stabilized. Final destination: - Landfill (or for cover landfills) - Incineration - Usually banned and/or rejected for agriculture use 20

21 Conclusions Main differences between MBT and composting facilities are related to the source material and the kind of product that wants to be obtained. When the separation and classification of waste materials is not done in the origin (households) it has to be done by mechanical systems. It means a lower efficiency in the quantity and the quality of classified waste materials for recycling. MBT systems and technologies allow to fulfil the stabilization of the organic waste but it can not be use to return it to the crop soils. Landfill and incineration are their only options, but it is lost all the material value of the organic matter and its nutrients content. Composting facilities can be very simple and efficient, but only if the source separate collection of biowaste is done properly and the biological process is known and controlled. Design and operation are key factors for the success of these facilities. They can even be small and local creating a net of facilities sharing resources and staff. A high quality and valuable product (compost) can be obtained, but it does not means that it will be automatically sold at high prices if there is not a marketing plan for identify customers and their needs. 21

22 Muito obrigado pela sua 22