Biochemical potential evaluation and kinetic modeling of methane production from six agro-industrial wastewaters in mixed culture.

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.

A kinetic study on carboxylic acids production using bovine slaughterhouse wastewater: a promising substrate for resource recovery in biotechnological processes.

Carboxylic acids (CA) are considered high added-value compounds, and their production from wastes has gained economic and environmental notoriety. However, the CA production and kinetic modeling using some agro-industrial wastewaters, such as bovine slaughterhouse wastewater (SHW), are not well reported in the literature. Therefore, the objective of this work was to evaluate the CA production potential using SHW as a substrate under acidogenic conditions and to apply mathematical models to estimate the kinetic parameters of particulate organic matter hydrolysis, soluble organic matter consumption, and CA production. Tests were carried out in quadruplicate batch reactors with a 250-mL reaction volume, with brewery sludge as inoculum and using chloroform (0.05%, v/v) for methanogenesis inhibition. The obtained yield was 0.55 g acids gCODA-1, corresponding to 0.76 gCOD gCODA-1. The production of caproic acid without the addition of electron donors was achieved. Mathematical models that describe exponential growth, such as the first-order exponential model, cone model, and Fitzhugh model, were the most suitable to describe the production kinetics of CA. Finally, SHW seems to be a promising substrate to be investigated in the carboxylic platform.

Fatores que influenciam a produção de ácidos carboxílicos a partir de resíduos agroindustriais / Factors that influence the production of carboxylic acids from agroindustrial wastes

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.

Caracterização físico-química e determinação de coeficientes cinéticos aeróbios de remoção da matéria orgânica de águas residuárias agroindustriais / Physical-chemical characterization and determination of aerobic kinetic coefficients for the removal of organic matter from agro-industrial wastewater

RESUMO Os objetivos do presente trabalho foram realizar uma caracterização físico-química de diferentes águas residuárias agroindustriais (ARA) e aplicar modelos cinéticos de primeira e de segunda ordem para verificar qual deles descreve melhor a progressão da demanda bioquímica de oxigênio (DBO) e para determinar coeficientes cinéticos aeróbios de remoção da matéria orgânica das ARA. Efetuou-se o ensaio de progressão da DBO pela incubação de ARA em um sistema respirométrico (Oxitop®). Os modelos cinéticos de primeira e de segunda ordem foram avaliados por erro quadrático médio (RMSE), erro quadrático médio normalizado (NRMSE) e critério de informação de Akaike (AIC). A cinética de biodegradação aeróbia das ARA avaliadas ajustou-se melhor ao modelo de primeira ordem em termos de DBO total e solúvel. Na progressão de DBO total, o maior coeficiente de desoxigenação de primeira ordem (k') foi o da água residuária de abatedouro - ARB (0,56 d-1) - e o menor foi o da água residuária de suinocultura - ARS (0,16 d-1). Os coeficientes de desoxigenação determinados no presente trabalho mostraram-se representativos, podendo ser utilizados para a simulação de processos de degradação da matéria orgânica em condições aeróbias.

ABSTRACT The aim of the present work was to perform a physicochemical characterization of different agroindustrial wastewaters (AIW), to apply first and second order kinetic models to verify which one best describes the progression of the biochemical oxygen demand (BOD) and to determine the aerobic kinetics coefficients of organic matter removal from AIW. The BOD progression assay was performed from the incubation of AIW in a respirometric system (Oxitop®). The first and second order kinetic models were evaluated by mean square error (RMSE), normalized mean square error (NRMSE), and Akaike Information Criterion (AIC). The aerobic biodegradation kinetics of the AIW evaluated was better fitted to the first order model in terms of total and soluble BOD. In the total BOD progression, the highest coefficient of first-order deoxygenation (k ') was that of slaughterhouse wastewater (SW; 0.56 d-1) and the lowest was that of swine wastewater (SSW; 0.16 d-1). The deoxygenation coefficients determined in the present work were representative, and can be used for the simulation of degradation processes of organic matter under aerobic conditions.

Kinetic modeling of anaerobic carboxylic acid production from swine wastewater.

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.