B2-Environmental problem targeted
Contents
ENVIRONMENTAL PROBLEM TARGETED (max. 10.000 characters)discuss
B2.1
Source-separated collection of municipal solid waste organic fraction works well in Viareggio and Camaiore (Lucca, IT): da novembre ad aprile, ogni giorno, Sea Risorse Spa (SEARIS) ne raccoglie 20 tonnellate. Questo materiale organico che proviene dalla raccolta porta a porta e dalle grandi utenze viene inviato al più vicino centro di compostaggio (composting plant) capace di trattare queste quantità. Ogni giorno da novembre ad aprile un camion con due scarrabili (hook-lift containers) porta 20 tonnellate di frazione organica di rifiuti solidi urbani (OF-MSW) da Viareggio per 100 KM fino a Montespertoli (Florence, IT) e poi torna. Viareggio e Camaiore insieme arrivano quasi a 100,000 abitanti residenti, ma hanno una forte attività turistica che incide fortemente sulla quantità di rifiuti prodotta e raccolta. Da maggio a ottobre i viaggi fino a Montespertoli aumentano raggiungendo picchi anche di nove viaggi al giorno. Ogni anno circa 700 camion fanno quel percorso per portare a destinazine l'esito dell'efficienza della raccolta differenziata. Per ogni viaggio vengono prodotti circa 540 Kg. di CO2, oltre 350 tonnellate ogni anno. Il solo trasporto della OF-MSW da Viareggio a Montespertoli equivale a 27 TOE.
B2.2
Nell'impianto di Montespertoli per compostare 15,000 tonnellate di OF-MSW vengono impiegati 1,050,000 kwh con emissioni equivalenti di 560.7 tonnellate di CO2 e un consumo pari a 241 TOE.
Il problema potrebbe essere considerato "locale" perchè dovuto all'assenza di un centro di compostaggio vicino (anche se questo non toglierebbe il costo energetico e l'impatto ambientale del trattamento).
Dall'impianto di trattamento fanghi di Viareggio (il sito del progetto COWS) vengono oggi (pre-COWS, business-as-usual) inviati al recupero 5200 tonnellate di fanghi ogni anno, con 260 viaggi/anno a 250Km di distanza con emissioni equivalenti a 330 tonnellate di CO2 e più di 50 TOE.
Questa situazione non è locale perché riguarda la maggior parte degli impianti di trattamento dei fanghi da depurazione in Europa.
There are some 36.000 wastewater treatment facilities in Europe today which adopt the anaerobic stabilisation of sewage or waste activated sludge: very often these plants are oversized, due to the low sludge mass loadings originated from wastewater treatment and the low biogas yields of sludge (Bolzonella D., Pavan P., Battistoni P., Cecchi F. (2005). Mesophilic anaerobic digestion of waste activated sludge: influence of the solid retention time in the wastewater treatment process. Process Biochemistry 40(3-4), 1453-1460). At the same time, the total amount of municipal solid waste is continuously rising. Consequently, there are millions of tons of solid waste being produced every year which have to be safely disposed without any negative impact to the environment. As effect of EC waste regulations pushing towards source-separation strategies for MSW management, about 400.000 tons/year of OFMSW coming from source sorted or separately collection approaches are produced.
This scenario suggests that making a solution out of this two problems is desirable. Anaerobic co-digestion of sewage sludge with OF-MSW seems to be an attractive alternative to current disposal strategies (Dereli RK, Ersahin ME, Gomec CY, Ozturk I, Ozdemir O. (2010) Co-digestion of the organic fraction of municipal solid waste with primary sludge at a municipal wastewater treatment plant in Turkey. Waste Management & Research 28(5):404-410).
On the other hand, the availability of energy in sufficient and sustainable amount is a pillar or EU 2020 strategy. Anaerobic digestion as a pre-treatment prior to landfill disposal or composting offers several advantages, such as minimization of masses and volume, inactivation of biological and biochemical processes in order to avoid landfill-gas and odor emissions, reduction of landfill settlements and energy production in the form of methane. Therefore, anaerobic digestion of bio-degradable solid wastes can be considered an alternative option to improve the environment condition caused by organic solid waste and at the same time taking an advantage as an environmentally-friendly resource of energy.
Anaerobic codigestion is hence considered one of the most promising way to give a proper disposal to OF-MSW coming from source or separate collection systems, the yields of anaerobic digestion (AD) process for the treatment of 100 kg of OF-MSW being reported to be 35 kg compostable fraction with 22 and 44 KWh electricity and heat energy, respectively (J. Mata-Alvarez. Biomethanization of the Organic Fraction of Municipal Solid Wastes. IWA Publishing, 2002. ISBN 1900222140).
These figures show that co-digestion of sewage sludge and OF-MSW, would potentially lead to recovery of some 112.000 electrical MW and 180.000 thermal MW in Europe.
Moreover AD has less GHG release potential than aerobic composting. Finally, bringing OF-MSW to existing AD sludge treatement facilities may also reduce further GHG emissions thank to shorter storage before delivery, when highly biodegradable content may be released. Daily deliver to a co-digestion plant avoids anaerobiotic pockets that could release CH4.
STATE OF THE ART AND INNOVATIVE ASPECTS OF THE PROJECT (max. 10.000 characters)discuss
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