Mesophilic anaerobic digestion of waste activated sludge in an intermittent mixing reactor: Effect of hydraulic retention time and organic loading rate.

An anaerobic digester was operated at mesophilic temperature and with intermittent mixing conditions to treat waste activated sludge. The organic loading rate (OLR) was increased by decreasing the hydraulic retention time (HRT), and the effect on process performance, digestate characteristics and inactivation of pathogens was investigated. The removal efficiency of total volatile solids (TVS) was also measured by biogas formation. The HRT varied from 50 to 7 days, corresponding to OLR from 0.38 to 2.31 kgTVS.m-3.d-1. The acidity/alkalinity ratio remained within stable limits (lower than 0.6) at 50-, 25- and 17-day HRT; due to an imbalance between the production and consumption of volatile fatty acids, the ratio increased to 0.7 ± 0.2 at HRT of 9 days and 7 days. The highest TVS removal efficiencies were 16, 12 and 9%, which were obtained at 50-, 25- and 17 day-HRT, respectively. Intermittent mixing provided solids sedimentation greater than 30% for almost all HRT tested. The highest methane yields (0.10-0.05 m3.kgTVSfed-1.d-1) were obtained when the reactor was operated at a higher HRT (50-17 days). At lower HRT, methanogenic reactions were likely limited. Zinc and copper were the main heavy metals found in the digestate, while the most probable number (MPN) of coliform bacteria remained below 106 MPN.g TVS-1. Neither Salmonella nor viable Ascaris eggs were found in the digestate. In general, increasing the OLR by decreasing the HRT to 17 days under intermittent mixing conditions provided an attractive alternative to treat sewage sludge despite some limitations due to biogas and methane yields.

A review on hydrothermal carbonization of potential biomass wastes, characterization and environmental applications of hydrochar, and biorefinery perspectives of the process.

It is imperative to search for appropriate processes to convert wastes into energy, chemicals, and materials to establish a circular bio-economy toward sustainable development. Concerning waste biomass valorization, hydrothermal carbonization (HTC) is a promising route given its advantages over other thermochemical processes. From that perspective, this article reviewed the HTC of potential biomass wastes, the characterization and environmental utilization of hydrochar, and the biorefinery potential of this process. Crop and forestry residues and sewage sludge are two categories of biomass wastes (lignocellulosic and non-lignocellulosic, respectively) readily available for HTC or even co-hydrothermal carbonization (Co-HTC). The temperature, reaction time, and solid-to-liquid ratio utilized in HTC/Co-HTC of those biomass wastes were reported to range from 140 to 370 °C, 0.05 to 48 h, and 1/47 to 1/1, respectively, providing hydrochar yields of up to 94 % according to the process conditions. Hydrochar characterization by different techniques to determine its physicochemical properties is crucial to defining the best applications for this material. In the environmental field, hydrochar might be suitable for removing pollutants from aqueous systems, ameliorating soils, adsorbing atmospheric pollutants, working as an energy carrier, and performing carbon sequestration. But this material could also be employed in other areas (e.g., catalysis). Regarding the effluent from HTC/Co-HTC, this byproduct has the potential for serving as feedstock in other processes, such as anaerobic digestion and microalgae cultivation. These opportunities have aroused the industry interest in HTC since 2010, and the number of industrial-scale HTC plants and patent document applications has increased. The hydrochar patents are concentrated in China (77.6 %), the United States (10.6 %), the Republic of Korea (3.5 %), and Germany (3.5 %). Therefore, considering the possibilities of converting their product (hydrochar) and byproduct (effluent) into energy, chemicals, and materials, HTC or Co-HTC could work as the first step of a biorefinery. And this approach would completely agree with circular bioeconomy principles.

Biochar and hydrochar in the context of anaerobic digestion for a circular approach: An overview.

Biochar and hydrochar are carbonaceous materials with valuable applications. They can be synthesized from a wide range of organic wastes, including digestate. Digestate is the byproduct of anaerobic digestion (AD), which is performed for bioenergy (biogas) production from organic residues. Through a thermochemical process, such as pyrolysis, gasification, and hydrothermal carbonization - HTC, digestate can be converted into biochar or hydrochar. The addition of either biochar or hydrochar in AD has been reported to improve biochemical reactions and microbial growth, increasing the buffer capacity, and facilitating direct interspecies electrons transfer (DIET), resulting in higher methane (CH4) yields. Both biochar and hydrochar can adsorb undesired compounds present in biogas, such as carbon dioxide (CO2), hydrogen sulfide (H2S), ammonia (NH3), and even siloxanes. However, an integrated understanding of biochar and hydrochar produced from digestate through their return to the AD process, as additives or as adsorbents for biogas purification, is yet to be attained to close the material flow loop in a circular economy model. Therefore, this overview aimed at addressing the integration of biochar and hydrochar production from digestate, their utilization as additives and effects on AD, and their potential to adsorb biogas contaminants. This integration is supported by life cycle assessment (LCA) studies, showing positive results when combining AD and the aforementioned thermochemical processes, although more LCA is still necessary. Techno-economic assessment (TEA) studies of the processes considered are also presented, and despite an expanding market of biochar and hydrochar, further TEA is required to verify the profitability of the proposed integration, given the specificities of each process design. Overall, the synthesis of biochar and hydrochar from digestate can contribute to improving the AD process, establishing a cyclic process that is in agreement with the circular economy concept.

Does duckweed ponds used for wastewater treatment emit or sequester greenhouse gases?

The reduction of greenhouse gases (GHG) emissions is important challenge in the wastewater treatment plants. In this way, the present study aimed to evaluate the GHG emissions and carbon dioxide fixation by duckweed ponds (DWP) applied to treat municipal wastewater in a polishing stage. Two pilot DWP (3000 L) were operated in a series with real wastewater receiving a flow rate of 200 L d-1 and organic load rate of 39 g COD ha-1 d-1. Beyond the standard physicochemical parameters for wastewater monitoring, the gases emissions from pond surface were measures by using a static flux chamber with infrared probes installed inside to detect CO2 and CH4 concentration. Operating the DWP with a load of 18.1 kg TN ha-1 d-1 and 2 kg TP ha-1 d-1, across 425 days of monitoring, higher COD and nutrient removal efficiency was identified (79%, 93% and 84% for COD, TN and TP, respectively). The CO2 emission rate ranged from 3048 to 6017 mg CO2 m-2 d-1 and the fixation rate ranged from 19,592 to 42,052 mg CO2 m-2 d-1. Methane emission was not detected (less than 0.1%). Moreover, low abundance of archaeal community was identified in both DWP. The results showed that in presented conditions, under low COD loading rate DWP could fix at least three times more CO2 than it emits, highlighting the sustainability of this natural technology.

Assessing the inter-annual variability of separation distances around odour sources to protect the residents from odour annoyance.

In recent years, there has been a growing concern about potential impacts on public health and wellbeing due to exposure to environmental odour. Separation distances between odour-emitting sources and residential areas can be calculated using dispersion models, as a means of protecting the neighbourhood from odour annoyance. This study investigates the suitability of using one single year of meteorological input data to calculate reliable direction-dependent separation distances. Accordingly, we assessed and quantified the inter-annual variability of separation distances at two sites with different meteorological conditions, one in Brazil and the other in Austria. A 5-year dataset of hourly meteorological observations was used for each site. Two odour impact criteria set in current regulations were selected to explore their effect on the separation distances. The coefficient of variation was used as a statistical measure to characterise the amount of annual variation. Overall, for all scenarios, the separation distances had a low degree of inter-annual variability (mean coefficient of variation values from 8% to 21%). Reasonable agreements from year to year were therefore observed at the two sites under investigation, showing that one year of meteorological data is a good compromise to achieve reliable accuracy. This finding can provide a more cost-effective solution to calculate separation distances in the vicinity of odour sources.

Feasibility of thermophilic anaerobic processes for treating waste activated sludge under low HRT and intermittent mixing.

Thermophilic anaerobic digestion (AD) arises as an optimized solution for the waste activated sludge (WAS) management. However, there are few feasibility studies using low solids content typically found in the WAS, and that consider uncommon operational conditions such as intermittent mixing and low hydraulic retention time (HRT). In this investigation, a single-stage pilot reactor was used to treat WAS at low HRT (13, 9, 6 and 5 days) and intermittent mixing (withholding mixing 2 h prior feeding). Thermophilic anaerobic digestion (55 °C) was initiated from a mesophilic digester (35 °C) by the one-step startup strategy. Although instabilities on partial alkalinity (1245-3000 mgCaCO3/L), volatile fatty acids (1774-6421 mg/L acetic acid) and biogas production (0.21-0.09 m3/m3reactor.d) were observed, methanogenesis started to recover in 18 days. The thermophilic treatment of WAS at 13 and 9 days HRT efficiently converted VS into biogas (22 and 21%, respectively) and achieved high biogas yield (0.24 and 0.22 m3/kgVSfed, respectively). Intermittent mixing improved the retention of methanogens inside the reactor and reduced the washout effect even at low HRT (<9 days). The negative thermal balance found was influenced by the low solids content in the WAS (2.1% TS) and by the heat losses from the digester walls. The energy balance and economic analyses demonstrated the feasibility of thermophilic AD of WAS in a hypothetical full-scale system, when the heat energy could be recovered from methane in a scenario of higher solids concentration in the substrate (>5% TS).

Pragmatic evaluation of odour emissions from a rendering plant in southern Brazil.

In the food industry and linked activities, environmental impacts relate mainly to the generation of liquid and gaseous effluents. Rendering plants, which process animal by-products, are strongly associated with malodorous emissions. Thus, effective odour-control technologies are required to minimise odour annoyance in nearby communities and thereby public complaints. In this paper, the effectiveness of a biofilter for the treatment of odours from a meat-rendering plant located in southern Brazil was evaluated based on German guideline VDI 3477:2004-11. Samples were collected upstream and downstream of the gas treatment system using a pragmatic approach in order to minimise the cost of such a study. Odour concentration was determined according to European standard EN 13725:2003. The results showed an OER of 8.82 × 108 ouE h-1 and odour removal efficiency lower than the established benchmark set by SEMA Resolution 054/2006, taken as reference for being the only Brazilian regulation to establish quantitative odour emission criteria. Enhancement of the biofiltration system and/or association with other odour abatement technologies are required to increase odour removal, limit impacts and comply with regulatory requirements. The paper also includes a discussion on the current odour regulation in Brazil.

Análise comparativa dos efeitos da carga orgânica e do tempo de detenção hidráulica na digestão anaeróbia mesofílica de lodo adensado de estação de tratamento de esgoto / Comparison of organic loading rate and hydraulic retention time effects on the mesophilic anaerobic digestion of thickened waste activated sludge

RESUMO Esta pesquisa comparou o desempenho de um digestor anaeróbio de lodo sob diferentes estratégias operacionais. Foi avaliada a influência do aumento da carga orgânica volumétrica (COV) (OP I) e o efeito da redução do tempo de detenção hidráulica (TDH) (OP II e OP III) no processo anaeróbio. As cargas aplicadas variaram entre 0,5 e 4,5 kgSV.m-3.d-1 e o TDH foi reduzido de 15 a 5 dias. Produção de gás metano, degradação do material orgânico e a diversidade microbiana foram utilizadas para medição e comparação do desempenho do processo. Foram necessários períodos de aclimatação a cada nova COV aplicada o que levou às instabilidades na remoção de SV e DQO do lodo. A operação com TDH entre 7 e 5 dias apresentou as maiores eficiências de remoção de SV, superiores a 70%, o que influenciou positivamente na estabilidade do processo. As COV aplicadas de 2,5 e 3,5 kgSV.m-3.d-1 resultaram nas maiores produções de metano durante a OP I. Para TDH inferiores a sete dias a produção de CH4 foi prejudicada apesar da existência de microorganismos metanogênicos atuantes no digestor. Comparativamente, a estratégia de redução do TDH resultou em um melhor desempenho do sistema que a fixação da COV. Quanto menor o TDH aplicado, melhor os resultados obtidos na operação do digestor, sugerindo que a eficiência do processo é otimizada em sistemas de alta carga com operação em baixos tempos de detenção hidráulica.

ABSTRACT This study compared the performance of a pilot anaerobic sludge digester under different operating strategies. The influence of increasing organic loading rate - OLR (OP I) and the effect of hydraulic retention time - HRT reduction (OP II and OP III) in anaerobic process were evaluated. The applied loads ranged between 0.5 and 4.5 kgSV.m-3.d-1; HRT was reduced from 15 to 5 days. Production of methane, organic matter degradation and microbial diversity were used to measure and compare the system´s performance. Acclimation periods were taken for each new OLR applied, leading to instabilities in sludge VS and COD removals. The experimental time with HRT between 7 and 5 days showed the highest VS efficiency removals (higher than 70%), which positively influenced process stability. The applied OLR of 2.5 and 3.5 kgVS.m-3.d-1 resulted in higher yields of methane during OP I. CH4 production showed impaired with HRT lower than 7 days, although it was observed active methanogenic microorganisms in the digester. Comparatively, HRT reduction resulted in a better system performance than the increasing OLR approach. The lower HRT applied, the better the results obtained in the operation of the digester, suggesting that the process efficiency is optimized with high load operation at low hydraulic retention times.

High nutrient removal rate from swine wastes and protein biomass production by full-scale duckweed ponds.

Duckweed ponds have been successfully used in swine waste polishing, generating a biomass with high protein content. Therefore, the present study evaluated the efficiency of two full-scale duckweed ponds considering nutrient recovery from a piggery farm effluent (produced by 300 animals), as well as the biomass yield and crude protein (CP) content. A significant improvement in the effluent quality was observed, with the removal of 98.0% of the TKN (Total Kjeldahl Nitrogen) and 98.8% of the TP (Total Phosphorous), on average. The observed nitrogen removal rate is one of the highest reported (4.4 g/m(2)day of TKN). Additionally, the dissolved oxygen level rose from 0.0 to 3.0mg/L, on average. The two ponds together produced over 13 tons of biomass (68 t/ha year of dry biomass), with 35% crude protein content. Because of the excellent nutrient removal and protein biomass production, the duckweed ponds revealed a great potential for the polishing and valorisation of swine waste, under the presented conditions.

The aesthetics of smells: the sense of smell and nursing.

This study aims to present reflections on the meaning of olfactory sensations and perceptions, as well as their relevance as a phenomenon present in Nursing practice. It stresses the importance of the smells' chemical language in the hospital environment, emphasizing some deductions about the aesthetics of smells from the Nursing perspective. The authors conclude that a deeper aesthetic/philosophical and technical/scientific comprehension of smell emanations will contribute to human care, especially in Nursing diagnoses and prescriptions, environmental quality regulation and therapeutics.

The aesthetics of smells: the sense of smell and nursing / Estética de los olores: el sentido del olfato y la enfermería / Estética dos odores: o sentido do olfato e a enfermagem

This study aims to present reflections on the meaning of olfactory sensations and perceptions, as well as their relevance as a phenomenon present in Nursing practice. It stresses the importance of the smells' chemical language in the hospital environment, emphasizing some deductions about the aesthetics of smells from the Nursing perspective. The authors conclude that a deeper aesthetic/philosophical and technical/scientific comprehension of smell emanations will contribute to human care, especially in Nursing diagnoses and prescriptions, environmental quality regulation and therapeutics.

Este estudio presenta reflexiones acerca del significado de las percepciones y sensaciones olfativas y suya pertinencia como fenómeno presente en la práctica de la Enfermería. Destaca la importancia de la linguage química de los olores en el ambiente hospitalario, puntuando algunas deducciones sobre la estética de los olores por la enfermería. Concluye que la mayor comprensión estético/filosófica y técnico/científica de las emanaciones odorantes podrá contribuir para el cuidado humano, especialmente en el diagnóstico y prescripción de Enfermería, vigilancia de la calidad ambiental y terapéutica.

Este estudo apresenta reflexões acerca do significado das percepções e sensações olfativas e sua pertinência como fenômeno presente na prática da Enfermagem. Destaca a importância da linguagem química dos odores no ambiente hospitalar, pontuando algumas deduções sobre a estética dos odores pela enfermagem. Conclui que a maior compreensão estético/filosófica e técnico/científica das emanações odorantes poderá contribuir para o cuidado humano, especialmente no diagnóstico e prescrição de Enfermagem, vigilância da qualidade ambiental e terapêutica.

Avaliação de impactos de odores em bacias hidrográficas com produções de suínos / Evaluation of odor impacts in hydrographic basins with swine production

A bacia hidrográfica de Rio Fragosos, no oeste catarinense e a bacia hidrográfica do Rio Cachoeirinhas, no sul de Santa Catarina foram unidades pilotos para a aplicação de duas metodologias para avaliações de odores provenientes da suinocultura. Na bacia do Rio Fragosos ficou destacado para a grande maioria das pessoas situações de ambiente desagradável, muito desagradável e extremamente desagradável. As concentrações dos odores obtidos na bacia do Rio Cachoeirinhas, determinadas a montante e a jusante de uma propriedade piloto, no interior de uma granja de criação de animais, sobre uma unidade de armazenamento de seus dejetos e na residência de um produtor variaram de 257 UO/m³à 963 UO/m³. Estas concentrações indicaram intensidades de odores com níveis forte a muito forte.

The River Fragosos hydrographic basin in the west of Santa Catarina and the River Cachoeirinhas hydrographic basin in the south of Santa Catarina were the pilot units for the application of two methodologies for the evaluation of odors originating from swine rearing. In From the results obtained for the River Fragosos basin, for the great majority of responses, unpleasant, very unpleasant and extremely unpleasant environmental situations were highlighted. The odor concentrations obtained for the River Cachoeirinhas basin, determined upstream and downstream of a pilot property, inside animal rearing smallholdings, above a waste storage unit and a producer's home, varied from 257 OU/m³to 963 OU/m³. These concentrations indicate odor intensities with strong and very strong levels.