RESUMO
Methane (CH4) production from anaerobic digestion of solid and liquid agro-industrial wastes is an attractive strategy to meet the growing need for renewable energy sources and promote environmentally appropriate disposal of organic wastes. This work aimed at determining the CH4 production potential of six agro-industrial wastewaters (AWW), evaluating the most promising for methanization purposes. It also aims to provide kinetic parameters and stoichiometric coefficients of CH4 production and define which kinetic models are most suitable for simulating the CH4 production of the evaluated substrates. The AWW studied were swine wastewater (SW), slaughterhouse wastewater (SHW), dairy wastewater (DW), brewery wastewater (BW), fruit processing wastewater (FPW), and residual glycerol (RG) of biodiesel production. RG was the substrate that showed the highest methanization potential. Exponential kinetic models can be efficiently applied for describing CH4 production of more soluble substrates. On the other hand, logistic models were more suitable to predict the CH4 production of more complex substrates.
Assuntos
Reatores Biológicos , Águas Residuárias , Anaerobiose , Animais , Biocombustíveis , Resíduos Industriais , Metano , SuínosRESUMO
RESUMO Os ácidos carboxílicos (ACs) são componentes químicos de base produzidos principalmente a partir da plataforma petroquímica. Entretanto, em razão de impactos ambientais, risco de escassez e elevados preços do petróleo, a produção biológica de AC por meio da digestão anaeróbia de recursos renováveis de baixo custo, como resíduos orgânicos das atividades agroindustriais, vem recebendo atenção crescente. Nesse contexto, o presente artigo objetiva discutir o processo de digestão anaeróbia aliada ao alongamento de cadeia carboxílica, a fim de orientar tomadas de decisão, como, por exemplo, escolha do substrato e definição das condições ambientais e dos parâmetros operacionais. Em geral, as condições que apresentam melhor viabilidade para produção de ácidos carboxílicos de cadeia média (ACCM) são: pH próximo a 6,0; temperatura mesofílica, já que oferece maior estabilidade operacional e os rendimentos obtidos em condições termofílicas não se mostram muito superiores; pressão parcial de hidrogênio (PPH) próxima a 10-5 aliada à limitação de CO2; tempo de residência celular (θc) inferior a 5 dias; e tempo de detenção hidráulica (TDH) baixo para sistemas contínuos. Uma das configurações mais promissoras é o uso de sistemas de dois estágios utilizando baixo pH como inibidor da metanogênese e extração de ACs em linha, para evitar a inibição devido à toxicidade dos produtos.
ABSTRACT Carboxylic acids (CA) are basic chemical components produced mainly through the petrochemical platform. However, due to environmental impacts, risk of scarcity and high petroleum prices, organic production of CA from the anaerobic digestion of low-cost renewable resources, such as organic wastes from agro-industrial activities, has been receiving increasing attention. In this context, the present paper aims to discuss the process of anaerobic digestion allied to the carboxylic chain elongation process, in order to guide decision making such as substrate choice, definition of environmental conditions, and operational parameters. In general, the conditions that present the best viability for MCCA production are: pH close to 6.0; mesophilic temperature since it offers greater operational stability and the yields obtained under thermophilic conditions are not much higher; hydrogen partial pressure (HPP) close to 10-5 combined with CO2 limitation; solids retention time (θc) < 5 days and low hydraulic retention time (HRT) for continuous systems. One of the most promising configurations is the use of two-stage systems using low pH as a methanogenesis inhibitor and inline CA extraction to avoid inhibition due to product toxicity.
RESUMO
This work aimed to evaluate the potential of anaerobic carboxylic acids (CA) production from swine wastewater (SW), perform modeling studies of the acidogenic process and estimate the kinetic parameters. Tests were carried out in four batch reactors with 250 mL reaction volume, with brewery sludge as inoculum and using chloroform (0.05%, v/v) for methanogenesis inhibition. Hydrolysis was the main limiting step of CA production from SW, once that it took more than twenty days for the particulate COD consumption to stabilize and fourteen days to produce 60% of the acids formed. A yield of 0.33 mg mgCODA-1, corresponding to 0.40 mgCOD mgCODA-1, was obtained. Kinetic models describing logistic growth functions were best suited to simulate CA production.