ABSTRACT Historical rainfall records are relevant in hydrometeorological studies because they provide information on the spatial features, frequency, and amount of precipitated water in a specific place, therefore, it is essential to make an adequate estimation of missing data. This study evaluated four methods for estimating missing monthly rainfall data at 46-gauge stations in southwestern Colombia covering 1983-2019. The performance of the Normal Ratio (NR), Principal Components Regression (PCR), Principal Least Square Regression (PLSR), and Artificial Neural Networks (ANN) methods were compared using three standardized error metrics: Root Mean Square Error (RMSE), Percent BIAS (PBIAS), and Mean Absolute Error (MAE). The results generally showed a better performance of the nonlinear ANN method. Regarding the linear methods, the best performance was registered by the PLSR, followed by the PCR. The results suggest the applicability of the ANN method in regions with a low density of stations and a high percentage of missing data, such as southwestern Colombia.

RESUMO Os registros históricos de precipitação são relevantes para os estudos hidrometeorológicos porque fornecem informações sobre as características espaciais, frequência e volume de precipitação de água em um local específico, portanto, é essencial realizar uma estimativa adequada dos dados faltantes. Esta pesquisa avaliou quatro métodos para estimativa de dados de precipitação faltantes mensalmente em 46 estações de medição no sudoeste da Colômbia, abrangendo os anos de 1983 à 2019. O desempenho dos métodos de Razão Normal (NR), Regressão de Componentes Principais (PCR), Regressão por Mínimos Quadrados Principais (RMQP) e Redes Neurais Artificiais (RNA) foram comparados usando três métricas padronizadas para os erros: Raiz do Erro Médio Quadrático (REMQ), Percentagem BIAS (PBIAS) e Erro Absoluto Médio (EMA). Os resultados com frequência mostraram um melhor desempenho do método ANN não-linear. Com relação aos métodos lineares, o melhor desempenho foi registrado pelo PLSR, seguido pelo PCR. Os resultados sugerem a aplicabilidade do método ANN em regiões com baixa densidade de estações de medição e alta porcentagem de dados faltantes, como o sudoeste da Colômbia.

RESUMEN Los residuos de alimentos son el componente principal de los residuos sólidos municipales y dado su elevado contenido de materia orgánica tienen alto potencial de producción de metano, mediante la digestión anaerobia; sin embargo, la predominancia de material lignocelulósico dificulta su hidrólisis. En este estudio, mediante ensayos de potencial bioquímico de metano, se evaluó el efecto de diferentes condiciones de pretratamiento térmico del sustrato, aplicando temperaturas entre 72 - 128°C y tiempos de exposición de 15 - 33 minutos sobre el rendimiento de producción de CH4. Para evaluar el efecto de las condiciones de pretratamiento, se empleó la metodología de superficie de respuesta y la aplicación de los modelos cinéticos de primer orden y de ajuste de Gompertz modificado. Los parámetros cinéticos identificados fueron validados, mediante niveles de confianza, usando la matriz de información de fisher. Se encontró que la región óptima, para alcanzar un mayor rendimiento en la digestión anaerobia, en cuanto a la producción de CH4, superior a 150mLCH4 gSV-1 y tiempos de la fase de latencia menores a 1 día, fue alrededor de 100°C, con tiempos de exposición cercanos a 15 minutos, condición en que se alcanzó una mayor solubilidad y mejorando positivamente la etapa hidrolítica del proceso anaerobio.

ABSTRACT Food waste are the main component of the municipal solid waste and given their high content of organic matter, have high potential for methane production through the anaerobic digestion. However, the predominance of lignocellulosic material hinders its hydrolysis. In this study, by means of assays of biochemical methane potential, the effect of different thermal pre-treatment conditions of the substrate was evaluated by applying temperatures between 72 - 128°C and exposure times of 15 - 33 minutes on the conditions on the performance of CH4. To evaluate the effect of pretreatment, we used the Response Surface Methodology accompanied by the application of first order kinetic and modified Gompertz models. The identified kinetic parameters were validated using confidence levels using the fisher information matrix. It was found that the optimal region, to reach a higher yield in the anaerobic digestion with regard to the production of CH4 higher than 150mLCH4 gVS-1 and lag-phase times less than 1 day, was around 100°C with exposure times close to 15 minutes, condition in which a greater solubility was reached and positively improving the hydrolytic stage of the anaerobic process.

La cantidad y calidad del inóculo empleado en los procesos de Digestión Anaerobia (DA), incide significativamente sobre la biodegradabilidad y la cantidad de metano que se produce. Esta investigación evaluó el efecto de la procedencia de inóculos de plantas de tratamiento de aguas residuales municipales (PTAR) sobre la producción de metano como una fuente de energía renovable, a partir de la DA de Biorresiduos de Origen Municipal (BOM), analizando como aspectos claves la relación Sustrato-Inóculo (S/I) y la capacidad buffer del inóculo. Los experimentos se realizaron a escala de laboratorio mediante ensayos de Potencial Bioquímico de Metano (PBM) en el rango mesofílico con un Tiempo de Retención de Sólidos (TRS) de 21 días; dos de los inóculos procedieron de reactores UASB y el otro de un digestor anaerobio de lodos. Las relaciones S/I oscilaron entre 0,5 y 12gSVsustrato gSV-1inóculo. Aunque se encontró que no existen diferencias estadísticas significativas entre los inóculos (p>0,05), el inóculo procedente del digestor anaerobio presentó un mejor desempeño debido a su mayor capacidad buffer. La relación S/I presentó diferencias estadísticas significativas (p<0,05), siendo las relaciones inferiores a 1 las que presentaron las mejores producciones de metano (>70mLCH4gSV-1sustrato), tasas de hidrólisis (0,15-0,21d-1) y fases de latencia (2,7-9,3d).

The quantity and quality of inoculum used in the Anaerobic Digestion (AD), impact seriously on the biodegradability and the amount of methane produced. This research evaluated the effect of the source of inoculum municipal wastewater treatment plant (WWTP) on the production of methane as a source of renewable energy AD from Municipal Biowaste (MB), analyzing the Substrate-Inoculum (S/I) ratio and the buffering capacity of the inoculum as key aspects. The experiments were performed on a laboratory scale by testing Biochemical Methane Potential (BMP) in the mesophilic range with a retention time of solids (RTS) 21 days; two inoculums from UASB reactors and the other of an anaerobic sludge digester. The S/I ratios ranged between 0.5 and 12gVSsubstrate gVS-1inoculum. Although it was found that there were no statistically significant differences between the inoculum (p>0.05), the inoculum from the anaerobic digester presented a better performance because of its greater capacity buffer. The S/I ratio showed statistically significant differences (p<0,05), being below 1 ratio that presented the best productions of methane (> 70mLCH4gVS-1substrate) hydrolysis rates (from 0,15 to 0,21d-1) and phases of lethargy (2,7-9,3d).

A quantidade e qualidade do inoculo utilizada na Digestão Anaerobia (DA), um impacto significativo sobre a biodegradabilidade e a quantidade de metano produzido. Esta pesquisa avaliou o efeito da fonte de inóculo de estações de tratamento, águas residuais municipais (ETARM) na produção de metano como fonte de energia renovável, a partir de DA resíduos biológicos de origem municipal (RBOM), analisando como aspectos importantes a relação substrato-inóculo (S/I), a capacidade buffer do inoculo. Os experimentos foram realizados em escala laboratorial por testes bioquímicos metano (BMP) na gama mesofílica com um tempo de retenção dos sólidos (TRS) de 21 dias; Dois inóculos foram de reatores UASB e outra de um digestor de lodo anaeróbio. O S/I a relação variou entre 0,5 e 12gSVsubstrato gSV-1inoculo. Embora verificou-se que não houve diferenças estatisticamente significativas entre o inóculo (p>0,05), o inóculo do digestor anaeróbico apresentou um desempenho melhor por causa de seu buffer de maior capacidade. A relação S/I mostrou diferenças estatisticamente significativa (p<0,05), sendo as relações menores a 1 que apresentaram as melhores produções de metano (> 70mLCH4gSV-1substrato) taxas de hidrólise (de 0,15 a 0,21d-1) e fases de letargia (2,7-9,3d).

Biowastes (BW), the main raw materials for the composting installations in developing countries, are characterized for containing uncooked food wastes (FW), high moisture content, low porosity, acidic pH, and low C/N ratios which affects the overall composting process (CP). In this study, we evaluated the effect of adding sugarcane bagasse (SCB) and star grass (SG) (Cynodon plectostachyus (K. Schum.) Pilg.) as bulking materials (BM) over the quality of the substrate, progress of the process, and quality of the obtained product. In this sense, two pilot-scale experiments were performed. The first one contained a substrate formed by 78% BW and 22% SCB (pile A). The second experiment contained a substrate formed by 66% BW and 34% SG (pile B). For each experiment, control treatments (piles A’ and B’ respectively) were performed by using 100% BW without BM. The results showed that in both cases the adding of BM improved substrate quality (pH, moisture, and total organic C content [TOC]), speeding up the starting step (2-3 d) and reducing the duration of the thermophilic phase of CP (3 d). However, the physico-chemical properties of both BM increased cooling and maturation phases duration (between 15 and 20 d). Obtained products quality was improved in terms of higher TOC, cation-exchange capacity, bulk density, and higher water holding capacity. Application of obtained products A and B could improve some soil properties like major nutrient, water retention, and increasing the organic matter.

Biowastes are the predominant fraction of municipal solid waste (MSW) of developing countries. Biowastes are characterized by a high content of organic matter; characteristics which facilitates its transformation through biological processes such as anaerobic digestion (AD). Using biochemical methane potential (PBM) assays, in this study we evaluated the influence of substrate-inoculum (S/I) ratio on the AD of biowaste from MSW. The S/I ranged between 0.25 to 9 gSVsustrate*gSVinocolum-1. Sludge from an anaerobic digester of the domestic wastewater treatment plant located in Cali-Colombia, was used as inoculum. It were found that the S/I ratio has an effect on the AD (p < 0.1). Best results was obtained with the ratio 0.25 gSVsustrate*gSVinocolum-1 (176.19 mLCH4*gSV-1 and a rate of 73.12% biodegradability), while 9 gSVsustrate*gSVinocolum-1 produced the lowest results (17.56 and 7.29% respectively). Furthermore, it was found that S/I ratios lower than 2 gSVsustrate*gSVinocolum-1 provided a suitable process. In the other hand, with S/I ratios greater than 2, the process becomes unstable due to acidification processes, caused by accumulation of VFA's; those VFA's cannot be he stabilized due to the low buffering capacity of the system.

En los países en desarrollo, los biorresiduos son la fracción predominante de los residuos sólidos municipales (RSM); los biorresiduos tienen un alto contenido de materia orgánica, característica que favorece su transformación a través de procesos biológicos como la digestión anaerobia (DA). En este estudio, mediante ensayos de potencial bioquímico de metano (PBM), se evaluó la influencia de la relación sustrato-inóculo (S/I) sobre la DA de biorresiduos de origen municipal (BOM), utilizando relaciones de 0.25 a 9 gSVsustrato*gSVinóculo-1. Como inóculo se empleó lodo de un biodigestor anaerobio de una planta de tratamiento de aguas residuales domésticas. Se encontró que la relación S/I tiene efecto sobre la DA de los BOM (p < 0.1), en donde la relación 0.25 produjo los mejores resultados (producción de 176.19 mLCH4*gSV-1 y un índice de biodegradabilidad de 73.12%, mientras que la relación de 9 generó los más bajos resultados (17.56 mLCH4*gSV-1 y 7.29%, respectivamente). También se encontró que las relaciones S/I menores de 2 gSVsustrato*gSVinóculo-1 permiten un proceso adecuado; con valores mayores, el proceso se desestabiliza debido a la ocurrencia de procesos de acidificación por la acumulación de los AGV's que no logran estabilizarse por la baja capacidad buffer del sistema.

Los biorresiduos de origen municipal-BOM, se caracterizan por su alto contenido de materia orgánica, humedad y nutrientes, además de ser residuos fácilmente acidificables, lo que los convierte en una fuente contaminante cuando se disponen inadecuadamente. La digestión anaerobia-DA es una alternativa tecnológica para el control de la contaminación de los BOM y la obtención de una fuente de energía renovable, como el metano; sin embargo, variables, como el pH, pueden afectar el proceso. Este estudio evaluó, a escala de laboratorio, mediante ensayos de Potencial Bioquímico de Metano-PBM, a una temperatura de 30oC, durante 40 días, la influencia del pH sobre la DA de BOM. Los valores de pH del sustrato variaron entre 5,5 a 8,0 unidades, utilizando como inóculo lodo, proveniente de la biodigestión anaerobia de lodos, de una planta de tratamiento de aguas residuales domésticas. Se evidenció que los pH ácidos correspondientes a 5,5 y 6,0 unidades, presentaron la menor producción de metano, del orden de 70,0 y 71,0 mLCH4*gSV-1, respectivamente, mientras que los pH cercanos a la neutralidad, lograron los mejores resultados, siendo la producción a un pH de 7,0 unidades la mayor, la cual, fue 126,0mLCH4*gSV-1. Los resultados están acordes con el comportamiento de la capacidad buffer, que fue más adecuada, entre 7,0 y 8,0 unidades, garantizando estabilidad del proceso anaerobio y evitando así la ocurrencia de fenómenos de inhibición. Para lograr estos niveles de pH, se hace necesario adicionar un alcalinizante, debido a las características ácidas de los BOM.

Municipal bio-wastes-MBW are characterized by their high content of organic matter, humidity, nutrients, and additionally are wastes easily acids, which makes them a source of pollution when are improperly disposed. Anaerobic digestion-AD is a technological alternative for MBW pollution control as well as for methane production as a renewable energy source; however, parameters such as pH can affect the process. This study evaluated at laboratory scale thought Biochemical Potential Methane-BPM assays at a temperature of 30oC during 40 days, the influence of pH on the MBW-AD. The pH values tested ranged from 5.5 to 8.0 units, using as inoculum sludge coming from the sludge anaerobic digestion of a domestic wastewater treatment plant. It was noticed that the acid pH between 5.5 and 6.0 units had the lowest methane production, 70.0 and 71.0mLCH4*gVS-1 respectively; while pH values near to the neutrality achieved the best results, being the highest production of methane corresponding to a pH of 7.0 units, reaching a value of 126.0mLCH4*gVS-1. Similarly, it was found that pH values from 7.0 to 8.0 units had the best buffer capacity, ensuring stability of the anaerobic process and avoiding inhibition phenomena. To achieve this condition, it is necessary to apply pH adjust due to the acid characteristics of the MBW.