As características da fracção orgânica dos RSU recolhidos selectivamente na área metropolitana de Lisboa e a sua influência no comportamento do processo de digestão anaeróbia

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Engenharia do Ambiente, perfil Engenharia Sanitária

A Study of Single Stage Semi‐Dry Anaerobic Digestion of Organic Fraction of Municipal Solid Waste

Solid waste generation is a natural consequence of human activity and is increasing along with population growth, urbanization and industrialization. Improper disposal of the huge amount of solid waste seriously affects the environment and contributes to climate change by the release of greenhouse gases. Practicing anaerobic digestion (AD) for the organic fraction of municipal solid waste (OFMSW) can reduce emissions to environment and thereby alleviate the environmental problems together with production of biogas, an energy source, and digestate, a soil amendment. The amenability of substrate for biogasification varies from substrate to substrate and different environmental and operating conditions such as pH, temperature, type and quality of substrate, mixing, retention time etc. Therefore, the purpose of this research work is to develop feasible semi-dry anaerobic digestion process for the treatment of OFMSW from Kerala, India for potential energy recovery and sustainable waste management. This study was carried out in three phases in order to reach the research purpose. In the first phase, batch study of anaerobic digestion of OFMSW was carried out for 100 days at 32°C (mesophilic digestion) for varying substrate concentrations. The aim of this study was to obtain the optimal conditions for biogas production using response surface methodology (RSM). The parameters studied were initial pH, substrate concentration and total organic carbon (TOC). The experimental results showed that the linear model terms of initial pH and substrate concentration and the quadratic model terms of the substrate concentration and TOC had significant individual effect (p < 0.05) on biogas yield. However, there was no interactive effect between these variables (p > 0.05). The optimum conditions for maximizing the biogas yield were a substrate concentration of 99 g/l, an initial pH of 6.5 and TOC of 20.32 g/l. AD of OFMSW with optimized substrate concentration of 99 g/l [Total Solid (TS)-10.5%] is a semi-dry digestion system .Under the optimized condition, the maximum biogas yield was 53.4 L/kg VS (volatile solid).. In the second phase, semi-dry anaerobic digestion of organic solid wastes was conducted for 45 days in a lab-scale batch experiment for substrate concentration of 100 g/l (TS-11.2%) for investigating the start-up performances under thermophilic condition (50°C). The performance of the reactor was evaluated by measuring the daily biogas production and calculating the degradation of total solids and the total volatile solids. The biogas yield at the end of the digestion was 52.9 L/kg VS for the substrate concentration of 100 g/l. About 66.7% of volatile solid degradation was obtained during the digestion. A first order model based on the availability of substrate as the limiting factor was used to perform the kinetic studies of batch anaerobic digestion system. The value of reaction rate constant, k, obtained was 0.0249 day-1. A laboratory bench scale reactor with a capacity of 36.8 litres was designed and fabricated to carry out the continuous anaerobic digestion of OFMSW in the third phase. The purpose of this study was to evaluate the performance of the digester at total solid concentration of 12% (semi-dry) under mesophlic condition (32°C). The digester was operated with different organic loading rates (OLRs) and constant retention time. The performance of the reactor was evaluated using parameters such as pH, volatile fatty acid (VFA), alkalinity, chemical oxygen demand (COD), TOC and ammonia-N as well as biogas yield. During the reactor’s start-up period, the process is stable and there is no inhibition occurred and the average biogas production was 14.7 L/day. The reactor was fed in continuous mode with different OLRs (3.1,4.2 and 5.65 kg VS/m3/d) at constant retention time of 30 days. The highest volatile solid degradation of 65.9%, with specific biogas production of 368 L/kg VS fed was achieved with OLR of 3.1 kg VS/m3/d. Modelling and simulation of anaerobic digestion of OFMSW in continuous operation is done using adapted Anaerobic Digestion Model No 1 (ADM1).The proposed model, which has 34 dynamic state variables, considers both biochemical and physicochemical processes and contains several inhibition factors including three gas components. The number of processes considered is 28. The model is implemented in Matlab® version 7.11.0.584(R2010b). The model based on adapted ADM1 was tested to simulate the behaviour of a bioreactor for the mesophilic anaerobic digestion of OFMSW at OLR of 3.1 kg VS/m3/d. ADM1 showed acceptable simulating results.

Biometanazione della frazione organica di rifiuti solidi urbani da raccolta indifferenziata mediante codigestione con refluo zootecnico o addizione di solfuro di sodio

Il presente elaborato è stato finalizzato allo sviluppo di un processo di digestione anaerobica della frazione organica dei rifiuti solidi urbani (FORSU oppure, in lingua inglese OFMSW, Organic Fraction of Municipal Solid Waste) provenienti da raccolta indifferenziata e conseguente produzione di biogas da impiegarsi per il recupero energetico. Questo lavoro rientra nell’ambito di un progetto, cofinanziato dalla Regione Emilia Romagna attraverso il Programma Regionale per la Ricerca Industriale, l’Innovazione e il Trasferimento Tecnologico (PRRIITT), sviluppato dal Dipartimento di Chimica Applicata e Scienza dei Materiali (DICASM) dell’Università di Bologna in collaborazione con la Facoltà di Ingegneria dell’Università di Ferrara e con la società Recupera s.r.l. che applicherà il processo nell’impianto pilota realizzato presso il proprio sito di biostabilizzazione e compostaggio ad Ostellato (FE). L’obiettivo è stato la verifica della possibilità di impiegare la frazione organica dei rifiuti indifferenziati per la produzione di biogas, e in particolare di metano, attraverso un processo di digestione anaerobica previo trattamento chimico oppure in codigestione con altri substrati organici facilmente fermentabili. E’ stata inoltre studiata la possibilità di impiego di reattori con biomassa adesa per migliorare la produzione specifica di metano e diminuire la lag phase. Dalla sperimentazione si può concludere che è possibile giungere allo sviluppo di metano dalla purea codigerendola assieme a refluo zootecnico. Per ottenere però produzioni significative la quantità di solidi volatili apportati dal rifiuto non deve superare il 50% dei solidi volatili complessivi. Viceversa, l’addizione di solfuri alla sola purea si è dimostrata ininfluente nel tentativo di sottrarre gli agenti inibitori della metanogenesi. Inoltre, l’impiego di supporti di riempimento lavorando attraverso processi batch sequenziali permette di eliminare, nei cicli successivi al primo, la lag phase dei batteri metanogeni ed incrementare la produzione specifica di metano.

Life Cycle Assessment comparativo tra il processo di co-digestione della frazione organica dei rifiuti solidi urbani e dei fanghi di depurazione disidratati e il sistema di gestione attuale. Il caso di Bagnacavallo (RA)

Waste management is becoming, year after year, always more important both for the costs associated with it and for the ever increasing volumes of waste generated. The discussion on the fate of organic fraction of municipal solid waste (OFMSW) leads everyday to new solutions. Many alternatives are proposed, ranging from incineration to composting passing through anaerobic digestion. “For Biogas” is a collaborative effort, between C.I.R.S.A. and R.E.S. cooperative, whose main goal is to generate “green” energy from both biowaste and sludge anaerobic co-digestion. Specifically, the project include a pilot plant receiving dewatered sludge from both urban and agro-industrial sewage (DS) and the organic fraction of MSW (in 2/1 ratio) which is digested in absence of oxygen to produce biogas and digestate. Biogas is piped to a co-generation system producing power and heat reused in the digestion process itself, making it independent from the national grid. Digestate undergoes a process of mechanical separation giving a liquid fraction, introduced in the treatment plant, and a solid fraction disposed in landfill (in future it will be further processed to obtain compost). This work analyzed and estimated the impacts generated by the pilot plant in its operative phase. Once the model was been characterized, on the basis of the CML2001 methodology, a comparison is made with the present scenario assumed for OFMSW and DS. Actual scenario treats separately the two fractions: the organic one is sent to a composting plant, while sludge is sent to landfill. Results show that the most significant difference between the two scenarios is in the GWP category as the project "For Biogas" is able to generate “zero emission” power and heat. It also generates a smaller volume of waste for disposal. In conclusion, the analysis evaluated the performance of two alternative methods of management of OFMSW and DS, highlighting that "For Biogas" project is to be preferred to the actual scenario.

Biometanazione della frazione organica dei rifiuti solidi urbani attraverso codigestione con letame bovino

An anaerobic consortium, capable of efficiently converting into methane the organic fraction of mechanically sorted municipal solid waste (MS-OFMSW), was obtained through a dedicated enrichment procedure in a 0.36 L up-flow anaerobic recirculated reactor. This result was obtained after several micro-reactor fed-batch procedures that allowed to obtain only a few methanization of the MS-OFMSW.

Produção de biopolímeros por culturas microbianas mistas selecionadas

Com a realização deste trabalho, pretendeu-se efetuar uma seleção de culturas mistas em reatores semi-descontínuos (SBR) com capacidade de acumulação de polihidroxialcanoatos (PHA). Para a seleção de culturas foram utilizados inóculos provenientes de diferentes Estações de Tratamento de Águas Residuais (ETAR) e ácidos orgânicos voláteis (AOV) como fonte de carbono. Foram testadas diferentes condições como a proveniência do inóculo, as cargas orgânicas aplicadas e a seleção de culturas utilizando soro de queijo. Verificaram-se elevadas remoções da CQO (acima de 90%) em grande parte dos ensaios realizados, apresentando uma acumulação de PHA por parte de algumas espécies de bactérias presentes. Ocorreu o aparecimento de microrganismos filamentosos com capacidade de acumulação de PHA em alguns ensaios, levando a serem testadas como culturas acumuladoras de PHA. A estabilidade das culturas mistas não foi atingida, mesmo havendo ensaios com 80 dias de operação. Efetuaram-se ensaios de acumulação de PHA em reatores descontínuos, utilizando as culturas selecionadas anteriormente em reatores SBR, com AOV provenientes da acidificação anaeróbia de diferentes resíduos (Fração Orgânica dos Resíduos Sólidos Urbanos - FORSU e Soro de Queijo). Verificou-se uma melhor acumulação por parte das culturas selecionadas com soro de queijo, na qual a quantidade de polímero acumulado triplicou.