ANALIA, Torres; FILIPA;Vaz (DEQI) Valorsul, S.A.

Transcription

1 Case Study: The implementation of a waste collection scheme for the anaerobic digestion plant of Lisbon Area and the characteristics of the biodegradable waste ANALIA, Torres; FILIPA;Vaz (DEQI) Valorsul, S.A. Contact name: Anália Torres Organisation: Department of Studies, Quality and Information of Valorsul SA. Postal address: Plataforma Ribeirinha da CP, Estação de Mercadorias da Bobadela, São João da Talha - Portugal. Telephone: Facsimile: VALORSUL@VALORSUL.PT EXECUTIVE SUMMARY Biodegradable waste is separately collected in restaurants, hotels, supply and retail markets, gardens and parks, among other big producers of this kind of waste in the municipalities of Lisbon Area. The biodegradable waste processing plant of Valorsul was designed to process 40 thousand Mg of biodegradable waste per year in a first stage and 60 thousand Mg per year in a second stage. In terms of electric energy, the plant can produce, respectively, 10 GWh and 14 Mg per year. The waste that arrives at the plant is discharge in two different lines, depending on the level of contaminants. The process consists in a wet two-stage thermophilic anaerobic digestion process. After the digestion step, the organic suspension is dewatered and pre-composted in 5 tunnels, with forced aeration and post-composted in windrows in a covered area. The final compost is refined by passing through a sieve and a densimetric table to remove contaminants. To prevent the entrance of toxic agents in the process, Valorsul supervises the waste received, in terms of physical and chemical characteristics. The results show that the separately collected waste in canteens, markets, restaurants and supermarkets delivered at the plant, have a content of organic materials between 80% and 84%; the paper and contaminants have a variation between 8% and 10 %. In terms of the results of chemical analysis, the waste has a total solids content of 28 g/kg, and a content of 33 g/kg dm of total nitrogen. In order to achieve the quantities of organic waste demanded for the plant a geographical information system (GIS) tool was used to optimize the collection routes. Before the beginning of the waste collection, Valorsul promoted a communication campaign called + Value that involved several communication agents with the objective to instruct the producers about the kind of waste to be disposed and also to get information about their particularities and main concerns. As an instrument of incentive and support, the program includes the deliver of information, as well as a daily collection from Monday to Saturday.

2 There is also a phone number where the producers can get more information or claim when they are not satisfied with the collection proceedings. By the end of 2006, 2229 establishments participated in the selective collection and it was possible to collect Mg of biodegradable waste, that represented to Valorsul a cost of (that corresponds to Mg). The reception control implemented at the plant by Valorsul also aims to evaluate the success of the program, to take conclusions and define solutions for improving the quality of the waste income. We noticed that the incoming waste had relatively high solids content for separate collection, when compared with typical waste from canteens and markets. We verified that the nitrogen content of the biodegradable waste received at the plant is in the range defined by Valorsul, in the tender documents (between 1.9 and 4 % TKN in the incoming waste). From this results it can be noticed a huge difference when comparing to the Northern European countries, where garden waste is included in a significant proportion. INTRODUCTION Valorsul, S.A. is the company responsible for the treatment of the Municipal Solid Waste (MSW) produced in Lisbon, approximately 800 thousand tons per year. It covers a population of inhabitants, which represents 12% of the total inhabitants of Portugal. In 1994, this multimunicipal system for processing and recovery of MSW from Lisbon (North) was created, including the municipalities of Amadora, Lisbon, Loures and Vila Franca de Xira. Valorsul, SA, was contracted to explore and manage a multimunicipal system, which was given the mission of promoting actions that contribute to sanitation and welfare of the population assuring, namely: a) The processing of MSW adjusted to the real necessities of the municipalities, in what concerns quantitative as well as qualitative features, in accordance with applicable national and EU regulations; b) The promotion of the necessary actions in order to implement a proper policy of MSW management, namely in what regards reduction and recovery of recyclables; c) Cost control, efficiently and rationally using the available means in their activities. According to the national waste management policy, a maximization of the recovery of waste must be attained either energetically or through recycling. The guidelines given by the EU through its 6th European Environmental Framework were based in the following principles: waste production prevention, recovery of waste through separate collection, sorting and recycling, energy recovery and, finally, a safe elimination of the waste produced. Keeping this in mind, Valorsul SA has established an Integrated Management System to take care of the MSW produced in its intervention area. This system consists of several operational facilities: a Municipal Solid Waste to Energy Plant (CTRSU); a Processing and Valorization of Bottom-Ash Plant (ITVE); a Biodegradable Waste Processing Plant (ETVO); a Material Recovery Facility (CTE); a Collection Centre (EC); and a Sanitary Landfill (AS), to operate as a system fuse. This paper aims to present the results that are being obtained in the biodegradable waste processing plant in terms of the waste physical and chemical composition and the measures that were implemented close to the producers to control the quality of waste received.

3 2. PROCESS DESCRIPTION Biodegradable waste (BW) is separately collected in restaurants, hotels, supply and retail markets, gardens and parks, among other big producers of this kind of waste in the municipalities of Lisbon Area. A wet two-stage thermophilic anaerobic digestion process followed by a pre-composting stage in tunnel with forced aeration and a post-composting phase in a covered area is used. The plant is dimensioned to treat 40 thousand Mg of BW per year in a first stage and 60 thousand Mg per year in a second stage. In what concerns electric energy and compost produced, the plant is dimensioned, respectively, for 10 GWh and 14 Mg per year. The plant receives waste 6 days per week, processing in 14 hours per day, 302 days per year. Valorsul SA opted for a separate collection of BW as the anaerobic digestion process requires a high quality biodegradable waste as raw material. It also allows the production of better quality compost. The sources of BW and types of collection are shown bellow (Tables 1 and 2). Table 1 - Source of biodegradable waste. Sources Starting Dates (2005) Expected biodegradable waste collection (Mg/year) Valorsul collection 14th March Municipal collection Amadora 1 st April Lisboa 5 th April Loures/Odivelas 19 th July Vila Franca de Xira not started Private entities collection MARL (Lisbon Whole sale Market) and private waste operators February Total Table 2 Types of waste collection. BW Reception Targets Collection Schedule Wet line Canteens, Markets 13h00 21h00 Dry line Figure 1 presents the process flow diagram. Restaurants, Hospitals, Hotels and Supermarkets 23h00-07h00

4 Biodegradable waste Weighing Pre-treatment glass, stones, plastics Anaerobic digestion dewatering biogas electricity heat Wastewater treatment Tunnel composting Exhaust air biofilter Municipal collector pos-composting compost refining glass, stones, plastics compost stockage Figure 1. Process flow diagram. The waste from different sources is discharged in two different lines, in accordance to their source and quality. The wet line was designed to receive waste of better quality, from canteen and markets, and the dry line was conceived to receive the waste from restaurants, hotels and supermarkets, where a higher level of contaminants is expected. The waste from the wet line passes through a sieve and hammer mill before entering the hydrolysis phase. The waste from the dry line has to suffer a pre-treatment that involves a manual sorting, shredding and sieving. Before going to hydrolysis it also passes through a pulper to promote size reduction and the contaminants removal. After two days residence time in the hydrolysis tank, the suspension is sent to the two digesters of 3500 m 3 each, where it stays about 21 days in complete mixture, promoted by the internal recirculation of biogas. In order to induce the inhibition of H 2 S production, small quantities of air are added to the biogas that is recirculated into the digester. After the digestion step, the organic suspension is conducted to dewatering. The dewatered product is pre-composted in 5 tunnels, with forced aeration and post-composted in windrows in a covered area. The final compost is refined by passing through a sieve and a densimetric table to remove contaminants. The exhausted air extracted from the process areas and equipments is used as process air in the composting phase and is treated in two biofilters. In respect to the liquid phase produced in the dewatering, part is used as process water and the excess is sent to a waste water treatment plant, which has a biological treatment with a nitrification-denitrification process, followed by a membrane bioreactor for the solids removal. This pre-treated water can be used in the process and the excess is sent to the municipal collection system.

5 3. THE IMPLEMENTATION OF A SEPARATED COLLECTION SCHEME AND THE PROGRAM + VALUE Valorsul and the Municipalities selected big producers of BW such as restaurants, canteens, hotels, supplying and retail markets, in order to optimize the amount of BW separately collected. A geographic information system (GIS) was implemented to optimise the collection routes. By the end of 2006, the Programme had 2229 participant establishments as presented in Figure 2. Anaerobic digestion plant Door to door organic waste collection Organic waste collection targets Figure 2. Organic waste collection targets. Before the beginning of the waste collection, Valorsul promote a communication campaign called + Value that involved several communication agents with the objective to instruct the producers about the kind of waste to be disposed and also to get information about their particularities and main concerns. In respect to the establishments, and as an instrument of incentive and support, the program includes the offer of containers and periodic washes, the deliver of information, as well as a daily collection from Monday to Saturday. There is also a phone number where the producers can get more information. In terms of the instructions related to the kind of waste to be disposed, the producers are asked to put/avoid, in a specific container, the following: To put! : Solid waste (vegetables, bread, meat, fish, eggs, remaining portions of cakes, tea sack and fruit peel) and paper napkins.

6 To avoid! : Liquid residues; packages and recipients; cups, knifes, forks, spoons, papers of vegetal and aluminum; plastic bags; cigarette ends; textiles and lamps. Figure 3 presents the type of posters that were delivered to the producers with the waste deposition instructions. Figure 3. Poster with waste deposition instructions. Table 3 shows the total organic waste collected in 2006 by the municipalities and Valorsul. Table 3. Quantities of organic waste collected in 2006 Origin Waste Collection (Mg) Municipalities Amadora 810 Lisboa Loures Private companies Valorsul Total In respect to the economic aspects, are presented in Table 4 the costs related to Valorsul, which represents 33% of the total amount of organic waste collected in Lisbon area.

7 Table 4. Costs of Valorsul collection Description Waste collection + communication Units /Mg Waste Collection 57,5 Containers /month Containers washing /month Total costs in Figure 4 shows the picture of a vehicle of Valorsul collection program + Value. Figure 4. Picture of a vehicle of Valorsul collection program + Value. 4. THE CHARACTERISTICS OF BIODEGRADABLE WASTE In order verify the quality of the material and to detect and avoid the entrance of toxic agents in the biological process, Valorsul has implemented a reception control that involves a daily waste sampling. The results obtained are related to the physical waste characterized in 2006 as presented in Table 5: Table 5. Waste characterization in 2006 Physical Characterization of the waste Wet line Dry line Mg % Mg % Organics , ,5 Paper 813 7, ,0 Contaminants Plastic 567 5, ,1 glass 51 0, ,9 metals 28,1 0,3 79,3 0,4 Others (wood, textiles, composite packages) 143,9 1,4 431,8 2,2 total 791 7, ,5

8 The results show that the waste separately collected have a similar composition in the two lines, despite the slightly tendency to a higher content of organic fraction in the waste discharged in the wet line. The content of organic materials is between 84,4% and 80%; the paper and contaminants have a variation between 8% and 10 %, in the wet line and in the dry line, respectively. In terms of variation of the chemical parameters, Table 6 presents the characteristics of the waste, analysed during the period of November 2006 to April Table 6. Chemical characteristics between November 2006 and April 2007 Parameter Unit Dry Line Wet Line dry matter [% original sample] 28,08 26,84 TOC [g/kg dm] 423,74 433,98 Total nitrogen (TKN) [g/kg dm] 33,75 32,30 Organic nitrogen (N) [g/kg dm] 33,35 31,87 P [g/kg dm] 5,38 4,35 S [g/kg dm] 4,11 2,70 K [g/kg dm] 10,59 9,53 Ca [g/kg dm] 17,50 15,87 Mg [g/kg dm] 2,00 1,29 Na [g/kg dm] 11,27 8,39 Cl [g/kg dm] 9,35 8,08 lipophilic content [g/kg dm] 82,93 70,47 Fe [g/kg dm] 0,61 0,59 Cu [g/kg dm] 0,01 0,01 Zn [g/kg dm] 0,05 0,04 Mn [g/kg dm] 0,07 0,11 B [g/kg dm] 0,01 0,01 Ni [g/kg dm] n.d. 0,001 Cr (total) [g/kg dm] n.d. 0,001 Cr VI (soluble) [g/kg dm] n.d. n.d. Mo [g/kg dm] n.d. n.d. Cd [g/kg dm] 1,81E-04 n.d. Pb [g/kg dm] n.d. 0,004 Hg [g/kg dm] 6,17E-05 5,19E-05 In terms of chemical characteristics, the waste produced in the markets and canteens (wet line) have a similar composition to the waste collected in the restaurants (dry line). Concerning the variation of TS and VS, Figure 5 presents the evolution of these parameters per line between November 2006 and May 2007.

9 ST (%) WET LINE 100,0 90,0 80,0 70,0 60,0 50,0 40,0 30,0 20,0 10,0 0, week SV (%) WET LINE 100,0 90,0 80,0 70,0 60,0 50,0 40,0 30,0 20,0 10,0 0, week ST (%) DRY LINE 100,0 90,0 80,0 70,0 60,0 50,0 40,0 30,0 20,0 10,0 0, week SV (%) DRY LINE 100,0 90,0 80,0 70,0 60,0 50,0 40,0 30,0 20,0 10,0 0, week Figure 5. Evolution of TS and VS per line between November 2006 and May The results obtained lead to the conclusion that in the wet line the TS content is around 25,7% while the content of SV is of 76,6%. In respect to the dry line, the average values obtained for the TS and VS are of 29,5% and 74,0%, respectively. At the plant we could observe that the incoming waste had relatively high solids content for SC- OFMSW (Selectively Collected Organic Fraction of Municipal Solid Waste), even when coming from canteens and markets (Cecchi, F. et al., 2003). We could also confirm the expected high nitrogen content of the biodegradable waste received at the plant. At the time of the tender, Valorsul defined the range % TKN in the incoming waste. We see that we are not much above the middle of the given range. This is a consequence of the kind of waste collected: food waste separately collected in restaurants, canteens, markets and supermarkets. Deleted: 5. DISCUSSION

10 The implementation of a separately collection requires a great investment in developing adequate tools like a GIS and the strategy of communication that includes data collection, communication planning, target training and a customer relationship management system to respond efficiently to customer needs throughout the time. It is also extremely important to monitor customer s satisfaction, as it is the customer that separates the waste, particulary when there is no mandatory regulation on this subject. Valorsul also controls the waste received in terms of physical and chemical characteristics, in order to prevent the entrance in the process of any toxic agent and to evaluate the success of the program, to take conclusions and define solutions for improving the quality of the waste income. 6. REFERENCES Cecchi, F., Traverso, P., Pavan, P., Bolzonella, D., Innocenti, L.(2003) Characteristics of the OFMSW and behaviour of the anaerobic digestion process. In Biomethanization of the Organic Fraction of Municipal Solid Wastes, Mata-Alvarez (Ed.) IWA Publishing, London, pp