Research trends and strategies for the improvement of anaerobic digestion of food waste in psychrophilic temperatures conditions.

The organic fraction of municipal solid waste is mainly composed of food waste (FW), and traditional disposal practices for this fraction are generally considered to have negative environmental and economic impacts. However, the organic characteristics of this fraction could also be exploited through the anaerobic digestion of FW (FW-AD), which represents unique advantages, including the reduction of the area required for final disposal and environmental pollution and the same time the generation of renewable energy (mainly methane gas), and a by-product for agricultural use (digestate) due to its high nutrient content. Although approximately 88% of the world's population resides in areas with temperatures below 8 °C, psychrophilic conditions (temperatures below 20 °C) have hardly been studied, while mesophilic (66%) and thermophilic (27%) ranges were found to be more common than psychrophilic FW-AD (7%). The latter condition could decrease microbial activity and organic matter removal, which could affect biogas production and even make AD unfeasible. To improve the efficiency of the psychrophilic FW-AD process, there are strategies such as: measurement of physical properties as particle size, rheological characteristics (viscosity, consistency index and substrate behavior index), density and humidity, bioaugmentation and co-digestion with other substrates, use of inocula with psychrophilic methanogenic communities, reactor heating and modification of reactor configurations. However, these variables have hardly been studied in the context of psychrophilic conditions and future research should focus on evaluating the influence of these variables on FW-AD under psychrophilic conditions. Through a bibliometric analysis, this paper has described and analyzed the FW-AD process, with a focus on the psychrophilic conditions (<20 °C) so as to identify advances and future research trends, as well as determine strategies toward improving the anaerobic process under low temperature conditions.

Effect of biosolids on the nitrogen and phosphorus contents of soil used for sugarcane cultivation.

The application of biosolids improves soil nutrient availability and crop productivity; however, their application needs to be carefully evaluated so as to avoid the risk of contamination. In this study, a 12-month field experiment using a randomized block design with factorial arrangement was conducted to evaluate the effects of biosolids on the nitrogen and phosphorus contents of a sugarcane-cultivated inceptisol. Three types of dewatered biosolids were used: anaerobically digested (B), anaerobically digested and thermally dried (BST), and anaerobically digested and lime-stabilized (BA) biosolids. The results showed that biosolid use increases soil nitrogen content by up to 37% of the total Kjeldahl nitrogen, 42% of NO3 -, 13% of NO2 -, and 32% of NH4 +. Biosolid treatments exceeded the phosphorus requirement for sugarcane cultivation by up to 277% for B, 170% for BST, and 368% for BA. The application of biosolids sufficient to meet crop nitrogen requirements significantly increased soil phosphorus content, suggesting an overdose and low crop response to the available phosphorus. The application of biosolids yielded results similar to those of mineral fertilizers, suggesting their potential use in agriculture.

Assessment of maturity of reverse logistics as a strategy to sustainable solid waste management.

Small- and medium-sized enterprises primarily focus on their operations and rarely pay attention to issues related to sustainable solid waste management that originate from their production processes. A suitable strategy to support sustainable solid waste management is reverse logistics. Through the use of maturity models, it is possible to determine the grade to which small- and medium-sized enterprises are prepared to perform this strategy. This study proposes an adapted maturity model to measure maturity levels of reverse logistics aspects at small- and medium-sized enterprises in regions from Colombia in order to contribute to sustainable solid waste management. The maturity model was applied to seven small- and medium-sized enterprises in the plastics sector in the central and southern regions of Colombia by adapting a maturity model that was previously correlated to suggested drivers and barriers in this sector. Results show that maturity levels range from naïve to immature owing to the incipient development of reverse logistics in Colombia. Therefore, it is necessary to establish a holistic vision of the organisation to improve the reverse logistics decision-making process to achieve sustainable solid waste management.

Development and implementation of a water-safety plan for drinking-water supply system of Cali, Colombia.

The water-safety plan (WSP) approach integrates risk assessment and management practices into a drinking-water supply system (DWSS), ensuring water quality from the catchment to the consumer. This research was oriented toward the development and implementation of a WSP in the DWSS for the city of Santiago de Cali, Colombia. We adapted the methodological stages of the WSP established by the World Health Organization: (i.) assemble a WSP team, (ii.) describe the existing DWSS, (iii.) identify hazards and hazardous events, (iv.) evaluate risks, and (v.) plan risk management. In this methodological structure, we propose the use of different risk assessment tools at each step of DWSS, which can be implemented in water systems of different sizes. The results of our study allowed the identification of hazardous events that may compromise the effectiveness of the WSP: Of the 103 events found, 16 were related to the catchment, 40 to treatment processes, 27 to the distribution system, and 9 to consumers, while the remaining 11 were associated with organizational, planning, contingency, and emergency factors. We found that the most critical components of the DWSS are the distribution system and the consumers, with 29.6% and 33.3% of the hazardous events classified as at a very high risk level, respectively. Clearly, improvement and support programs for the WSP were needed to optimize existing control measures and corrective actions and to evaluate new ones to reduce risk levels. The treatment processes and distribution system steps were shown as the main barriers of the DWSS mainly they are under governance of water company, unlike the catchment and consumers which presented higher levels of risk because in these steps the water company has less control and influence. Our research confirms that the WSP is an important tool for decision-making by water-service companies-improving their administrative, financial, organizational, and operational management. It also shows that it is essential that their senior management and other stakeholders be part of the WSP team at each stage of implementation of the DWSS.

Sustainable production of nanoporous carbons: Kinetics and equilibrium studies in the removal of atrazine.

Nanoporous carbons have been prepared from mangosteen peels-derived chars by physical activation under CO2 flow as a function of temperature. As an example of circular bioeconomy, these sustainable adsorbents were used to remove atrazine, a common pesticide from the agroindustry. Several adsorption models such as Langmuir (two parameter), Sips and Redlich-Peterson (three parameters) were applied to verify the influence of carbon's properties on the uptake of atrazine. Additional kinetic models (pseudo-first order, pseudo-second order and Avrami's) allowed to establish that a mixture of physisorption and chemisorption describes the interaction between the nanoporous carbons and atrazine. As a general fact, an important diffusion of atrazine from the bulk of solution to the surface of carbons was observed. All samples were able to remove atrazine, but the highest uptake was found in the carbon with the highest contribution of micropores to the total pore of volume and with the lowest content of basic surface groups. Several correlations between the kinetic and equilibrium parameters for the atrazine adsorption were found as a function of the textural properties and surface chemistry. Based on the kinetics and equilibrium parameters, the present work proposes a mechanism for the atrazine adsorption on nanoporous carbons contributing to the understanding of the interactions between pollutant molecules and the surface functional groups on nanoporous carbons in the liquid-solid interface.

Evaluation of mixing ratio and frequency of turning in the co-composting of biowaste with sugarcane filter cake and star grass.

This work studied the effect of mixing ratio (MR) and turning frequency (TF) in biowaste composting (BW) with sugarcane filter cake (SFC) and star grass (SG), both on process performance (temperature, static respiration index, total organic carbon, total nitrogen and total phosphorus) and on product quality (pH, cation exchange capacity, electrical conductivity, organic matter, nutrients, stability, maturity, total coliforms and faecal coliforms), through the Principal Components Analysis (PCA). The Pearson correlation coefficients were calculated for all the quality parameters. A joint effect of mixing ratio and turning frequency was demonstrated, highlighting the importance of studying the operational parameters simultaneously. The results of the PCA showed that the best operating conditions and therefore higher product quality is achieved with a TF of twice a week and MR between 20 and 30% of SFC or SG. Additionally, it was found that a frequency of one turn per week generates the lowest product quality, regardless the co-substrate and the MR. The best treatment corresponded to BW composting with MR of 20% SFC and TF of two turnings per week. The obtained results allow to optimize the operation in composting facilities.

Efecto del pretratamiento térmico de residuos de alimentos sobre la producción de metano / Effect of the thermal pretreatment of from food waste on methane production

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.

Field assessment of bacterial communities and total trihalomethanes: Implications for drinking water networks.

Operation and maintenance (O&M) of drinking water distribution networks (DWDNs) in tropical countries simultaneously face the control of acute and chronic risks due to the presence of microorganisms and disinfection by-products, respectively. In this study, results from a detailed field characterization of microbiological, chemical and infrastructural parameters of a tropical-climate DWDN are presented. Water physicochemical parameters and the characteristics of the network were assessed to evaluate the relationship between abiotic and microbiological factors and their association with the presence of total trihalomethanes (TTHMs). Illumina sequencing of the bacterial 16s rRNA gene revealed significant differences in the composition of biofilm and planktonic communities. The highly diverse biofilm communities showed the presence of methylotrophic bacteria, which suggest the presence of methyl radicals such as THMs within this habitat. Microbiological parameters correlated with water age, pH, temperature and free residual chlorine. The results from this study are necessary to increase the awareness of O&M practices in DWDNs required to reduce biofilm formation and maintain appropriate microbiological and chemical water quality, in relation to biofilm detachment and DBP formation.

Effect of inoculum on the anaerobic digestion of food waste accounting for the concentration of trace elements.

The production of renewable energy in the form of methane from the anaerobic digestion (AD) of food waste (FW) varies depending on factors such as the quantity and quality of the inoculum. This research evaluated the influence of trace elements (Ca, K, Fe, Zn, Al, Mg, Co, Ni, and Mo) present in inoculum from different sources (wastewater treatment plants (WWTPs): 2 agro-industrial WWTPs and 1 municipal WWTP) on the AD of FW. This study found that the source of the inoculum determines the content of macronutrients and trace elements, which can alter the requirements of the AD process and therefore affect methane production. The inoculum obtained from municipal WWTPs contain potentially inhibitory concentrations of Zn and Al that negatively affect methane production (<70 mL CH4·gVS-1), the hydrolysis constant (<0.19 d-1), and the lag-phase (>7 days). It was also found that high concentrations of trace elements such as Ni (35.2 mg kg-1) and Mo (15.4 mg kg-1) in the inoculum increase methane production (140.7 mL CH4·gVS-1) and hydrolysis constant (>0.18d-1) in addition to presenting short lag-phase (<1 day) in the AD of food waste.

GESTIÓN DE RESIDUOS SÓLIDOS EN CADENAS DE SUMINISTRO DE CICLO CERRADO DESDE LA PERSPECTIVA DE LA INVESTIGACIÓN DE OPERACIONES / SOLID WASTE MANAGEMENT IN CLOSED-LOOP SUPPLY CHAINS FROM THE PERSPECTIVE OF OPERATIONS RESEARCH

La integración de los flujos reversos y directos en la cadena de suministro, trae beneficios al reducir costos y evitar el daño ambiental porque se recupera valor de los residuos sólidos; esta integración se conoce como la cadena de suministro de ciclo cerrado. La mayoría de experiencias que relacionan cadena de suministro de ciclo cerrado y decisiones de gestión de residuos sólidos, provienen de países desarrollados con estrictas regulaciones ambientales y usan técnicas de invetigación de operaciones. El objetivo se este artículo es identificar la factibilidad de aplicar técnicas de investigación de operaciones a las decisiones de gestión de residuos sólidos en las cadena de suministro de ciclo cerrado en países en desarrollo como Colombia. Se identificaron variables importantes de los articulos revisados tales como los diferentes tipos de residuos, las regiones y el uso de técnicas de optmización, simulación y multicriterio. La metodología de vigilancia tecnológica se uso para correlacionar estas variables. Los resultados mostraron que la técnica de multicriterio es usada con más frecuencia porque permite la consideración de varios aspectos en una misma decisión; por lo tanto, el uso de esta técnica sería conveniente para enfrentar efectivamente las principales decisiones en las incipientes cadenas de suministro de ciclo cerrado en países en desarrollo.

The integration of reverse and direct flows within the supply chain is highly benefitial to reduce costs and avoid the enviromental damage because value from the solid waste is recovered; this integration is known as closed-loop supply chain. Most of the reported experiences regarding closed-loop supply chains and solid waste management decisions come from developed countries with strict environmental regulations and use of operations research techniques.This paper aims to identify the feasibility of applying operations research techniques to solid waste magement decisions within closed-loop supply chains in developing countries such as Colombia. Important variables such as the different kinds of solid waste, the regions and the use of optimization, simulation and multi-criteria techniques were identified by reviewing research articles. Technologic watch methodology was used to correlate these variables. The results showed that the multi-criteria technique is most frequently used because it allows including different aspects related to a single decision; therefore, the use of this technique would be appropiate to effectively approach the main decisions at the emerging closed-loop supply chains in developing countries.

Effects of the incorporation of drinking water sludge on the anaerobic digestion of domestic wastewater sludge for methane production.

Water purification and wastewater treatment generate sludge, which must be adequately handled to prevent detrimental effects to the environment and public health. In this study, we examined the influence of the application of settled sludge from a drinking water treatment plant (S(DWTP)) on the anaerobic digestion (AD) of the thickened primary sludge from a municipal wastewater treatment plant (S(WWTP)) which uses chemically assisted primary treatment (CAPT). On both plants the primary coagulant is ferric chloride. The study was performed at laboratory scale using specific methanogenic activity (SMA) tests, in which mixtures of S(WWTP)-S(DWTP) with the ratios 100:00, 80:20, 75:25, 70:30 and 00:100 were evaluated. Methane detection was also performed by gas chromatography for a period of 30 days. Our results show that all evaluated ratios that incorporate S(DWTP), produce an inhibitory effect on the production of methane. The reduction in methane production ranged from 26% for the smallest concentration of S(DWTP) (20%) to more than 70% for concentrations higher than 25%. The results indicated that the hydrolytic stage was significantly affected, with the hydrolysis constant Kh also reduced by approximately 70% (0.24-0.26 day(-1) for the different ratios compared with 0.34 day(-1) for the S(WWTP) alone). This finding demonstrates that the best mixtures to be considered for anaerobic co-digestion must contain a fraction of S(DWTP) below 20%.