Relevance of sludge management practices and substance modeling in LCA for decision-making: A case study in Chile.

Reducing the costs and environmental impacts of sludge management is currently one of the main challenges faced by the wastewater treatment sector. Anaerobic digestion followed by land application has been widely endorsed as a low-impact approach to sludge management, mainly due to the recovery of biogas and the valorization of digestate. However, the influence that the operational conditions of digestion and the management practices of land application can have over the environmental performance of this strategy has been scarcely studied. Furthermore, most of the previous studies dealing with the environmental assessment of this strategy use simplified methods for estimating emissions after land application of sludge, and the lack of systematic accounting of these environmental flows might significantly affect the validity and comparability of the results. Therefore, this work performed an assessment of the influence that 4 relevant practices can have over the environmental impacts of this approach in the context of south-central Chile, providing a mass-balanced inventory for nitrogen, phosphorus and heavy metals in soil based on the ad hoc implementation of models developed for agricultural Life Cycle Assessment (LCA). A total of 16 scenarios were defined and 10 impact categories were evaluated, with the results showing that the environmental impacts were greatly influenced by the variables under study. Overall, solids retention time and the inclusion of pre-treatment mainly influenced climate change, fossil resource depletion and terrestrial ecotoxicity potential, while sludge application rate influenced the eutrophication, water ecotoxicity and human toxicity categories. The type of crop in the receiving soil was a significant driver behind the differences observed in the human toxicity category, which showed the highest variation and relevance in the final weighted result. The results clearly highlight the relevance of using context specific data as well as of quantifying the fate of nutrients, metals and heavy metals during LCA of sludge management. Based on the results, some policy and decision-making recommendations are formulated to optimize the environmental performance of sludge digestion and land application.

Adaptación y validación preliminar de la Escala teoría cultural de cosmovisiones ambientales en población chilena / Preliminary Adaptation and Validation of the Cultural Theory of Environmental Worldviews Scale in Chilean Population

Resumen El presente estudio tuvo como objetivo adaptar y aportar evidencias preliminares de validez de la Escala de teoría cultural de cosmovisiones ambientales en el contexto latinoamericano. Se analizaron evidencias de validez de contenido mediante el juicio de cuatro expertos, validez discriminante y convergente, estructura interna a través de análisis factorial exploratorio y confirmatorio, y consistencia interna a través del coeficiente Omega. Mediante un muestreo no probabilístico por conveniencia, se seleccionaron 500 participantes en edad adulta que residían en la región del Ñuble, Chile. Se obtuvo una versión revisada y adecuada lingüísticamente del instrumento, que presentó coeficientes de concordancia de Kappa que fluctuaron entre considerable y casi perfecto en cuanto a su contenido. Los análisis estadísticos dan cuenta de la idoneidad del instrumento de 15 ítems y un análisis factorial confirmatorio que apoya la estructura interna de cuatro factores (individualismo, igualitarismo, jerarquismo y fatalismo); igual que la versión original. Los coeficientes de consistencia interna fueron aceptables para las cuatro subescalas. Respecto a la validez discriminante se obtuvieron medidas de varianza extraída adecuadas para igualitarismo, jerarquismo y fatalismo (sólo individualismo presentó valores levemente bajo lo esperado), y respecto a la validez convergente se obtuvieron valores adecuados en fiabilidad compuesta para los cuatro factores. Estos hallazgos avalan el uso de la versión en español de la Escala de teoría cultural de cosmovisiones ambientales en población de habla hispana, contribuyendo a la potencial ampliación de estudios socioculturales sobre el medioambiente en Latinoamérica.

Abstract The objective of this study was to adapt and provide preliminary validity evidence of the cultural theory and environmental worldviews scale in the Latin-American context. Content validity evidence was assessed by the judgment of four experts, discriminant and convergent validity, internal structure through exploratory and confirmatory factor analysis, and internal consistency using the omega coefficient. The sample consisted of 500 participants from the Ñuble region, Chile. Regarding the results, a revised and linguistically adapted version of the instrument was obtained, which presented a kappa coefficient ranging from substantial to almost perfect regarding the content. The statistical analysis shown the adequacy of the 15-item instrument and a confirmatory factor analysis which supported the four-factor internal structure (individualism, egalitarianism, hierarchy, and fatalism), as in the original version. The internal consistency assessed using the Omega coefficient was acceptable for the four subscales. Regarding discriminant validity, adequate average variance extracted was obtained for egalitarianism, hierarchy, and fatalism (only individualism presented values slightly lower than expected), while convergent validity showed adequate composite reliability values for the four factors. These findings support the use of the Spanish version of Cultural Theory scale of and Environmental Worldviews in Spanish speaking population, contributing to potential further sociocultural studies about the environment in Latin America.

Organic micropollutants in sewage sludge: influence of thermal and ultrasound hydrolysis processes prior to anaerobic stabilization.

Organic micropollutants (OMP) in the household and industrial wastewater are not efficiently removed by conventional treatment processes and a significant fraction ends in sludge. Proper valorization technologies become fundamental to attain sustainable sewage sludge management, with anaerobic digestion (AD) as one of the preferred strategies. However, it exhibits some limitations that can be overcome with pre-treatment processes. In this study, the influence of different pre-treatment configurations over OMP concentration and removal during AD was assessed. The incorporation of a sequential US - TT-PT resulted in decreased concentrations of 7 of the 9 detected compounds in biosolids compared to conventional AD digestate, with bisphenol-A and ter-octylphenol showing the opposite effect. The results suggest that the assessed PT could improve the removal of sequestered or highly hydrophobic compounds through their solubilization and increased bioavailability.

Evaluation of the ultrasound effect on treated municipal wastewater.

In this research, ultrasound (US; 26 kHz) application was evaluated as tertiary treatment of treated municipal wastewater coming from conventional activated sludge (AS) and constructed wetland (CW) systems. The degree of disinfection was evaluated through the total (TC) and faecal (FC) coliforms and by somatic coliphages (SCs) determinations. The experiments were carried out without temperature control at times of 200, 400 and 600 s and with temperature control (298.1 K) at 600, 1200 and 1800 s. Changes in the concentrations of C, N and P were also studied. The results shown that treatment without temperature control allowed 100% inactivation for TC, FC and SC at 600 s, while maximum with temperature was achieved at 1800 s. Temperature was an important factor influencing pathogens inactivation. In both cases, microorganism concentrations complied with different international guidelines for the reuse of treated wastewater. At 1800 s sonication concentrations of biochemical oxygen demand, chemical oxygen demand and total phosphorus were reduced 39.5, 39.4, 50.0 and 37.3% TN in the AS-treated water and 24.0, 49.8, 20.2 and 7.7% in the CW-treated water, respectively. In both cases, the formation of H⋅ and OH⋅ radicals is most likely related to the observed pollutants removal. While energy consumption of ultrasound was higher than other advanced treatments such as electrocoagulation, its implementation allows the simultaneous removal of pathogens and organic pollutants without the generation of toxic by-products. In conclusion, ultrasound can be implemented as tertiary treatment of municipal wastewater for the removal of biological and organic pollution, according to reuse guidelines in terms of pathogens presence.

Process performance assessment of advanced anaerobic digestion of sewage sludge including sequential ultrasound-thermal (55 °C) pre-treatment.

The aim of this study was to evaluate the performance and digestate quality of advanced anaerobic digestion of sewage sludge including sequential ultrasound-thermal (55 °C) pre-treatment. Both stages of pre-treatment contributed to chemical oxygen demand (COD) solubilization, with an overall factor of 11.4 ±â€¯2.2%. Pre-treatment led to 19.1, 24.0 and 29.9% increased methane yields at 30, 15 and 7.5 days solid retention times (SRT), respectively, without affecting process stability or accumulation of intermediates. Pre-treatment decreased up to 4.2% water recovery from the digestate, but SRT was a more relevant factor controlling dewatering. Advanced digestion showed 2.4-3.1 and 1.5 logarithmic removals of coliforms and coliphages, respectively, and up to a 58% increase in the concentration of inorganics in the digestate solids compared to conventional digestion. The COD balance of the process showed that the observed increase in methane production was proportional to the pre-treatment solubilization efficiency.

Sequential ultrasound and low-temperature thermal pretreatment: Process optimization and influence on sewage sludge solubilization, enzyme activity and anaerobic digestion.

The influence of sequential ultrasound and low-temperature (55°C) thermal pretreatment on sewage sludge solubilization, enzyme activity and anaerobic digestion was assessed. The pretreatment led to significant increases of 427-1030% and 230-674% in the soluble concentrations of carbohydrates and proteins, respectively, and 1.6-4.3 times higher enzymatic activities in the soluble phase of the sludge. Optimal conditions for chemical oxygen demand solubilization were determined at 59.3kg/L total solids (TS) concentration, 30,500kJ/kg TS specific energy and 13h thermal treatment time using response surface methodology. The methane yield after pretreatment increased up to 50% compared with the raw sewage sludge, whereas the maximum methane production rate was 1.3-1.8 times higher. An energy assessment showed that the increased methane yield compensated for energy consumption only under conditions where 500kJ/kg TS specific energy was used for ultrasound, with up to 24% higher electricity recovery.