Anaerobic co-digestion of microalgal biomass, sugarcane vinasse, and residual glycerol from biodiesel using simplex-centroid mixture design: methane potential, synergic effect, and microbial diversity.

Microalgal biomass (MB) is a promising feedstock for bioenergy production. Nonetheless, the cell recalcitrance and the low C/N ratio limit the methane yield during anaerobic digestion. As an alternative to overcome these challenges, MB co-digestion with different feedstocks has been proposed. Thus, this study evaluated the anaerobic co-digestion (AcoD) of MB cultivated in wastewater with sugarcane vinasse (VIN) and residual glycerol from biodiesel production (GLY). Batch tests were conducted using augmented simplex-centroid mixture design to investigate the impact of AcoD on methane production (SMP), synergistic effects, and the influence on microbial community. When compared to MB digestion, 150 NmL CH4.g-1VS, binary and ternary AcoD achieved SMP increases from 120 to 337%. The combination of 16.7:16.7:66.7 (MB:VIN:GLY) showed the highest SMP for a ternary mixture (631 NmL CH4.g-1VS). Optimal synergies ranged from 1.3 to 1.4 and were primarily found for the MB:GLY AcoD. Acetoclastic Methanosaeta genus was predominant, regardless the combination between substrates. Despite the largest SMP obtained from the MB:GLY AcoD, other ternary mixtures were also highly synergetic and therefore had strong potential as a strategic renewable energy source.

Use of nitrate, sulphate, and iron (III) as electron acceptors to improve the anaerobic degradation of linear alkylbenzene sulfonate: effects on removal potential and microbiota diversification.

Linear alkylbenzene sulfonate (LAS) is a synthetic anionic surfactant that is found in certain amounts in wastewaters and even in water bodies, despite its known biodegradability. This study aimed to assess the influence of nitrate, sulphate, and iron (III) on LAS anaerobic degradation and biomass microbial diversity. Batch reactors were inoculated with anaerobic biomass, nutrients, LAS (20 mg L-1), one of the three electron acceptors, and ethanol (40 mg L-1) as a co-substrate. The control treatments, with and without co-substrate, showed limited LAS biodegradation efficiencies of 10 ± 2% and 0%, respectively. However, when nitrate and iron (III) were present without co-substrate, biodegradation efficiencies of 53 ± 4% and 75 ± 3% were achieved, respectively, which were the highest levels observed. Clostridium spp. was prominent in all treatments, while Alkaliphilus spp. and Bacillus spp. thrived in the presence of iron, which had the most significant effect on LAS biodegradation. Those microorganisms were identified as crucial in affecting the LAS anaerobic degradation. The experiments revealed that the presence of electron acceptors fostered the development of a more specialised microbiota, especially those involved in the LAS biodegradation. A mutual interaction between the processes of degradation and adsorption was also shown.

Effect of filtration rates on the performance and head loss development in granular filters during the post-treatment of anaerobic reactor effluent.

This study investigated the performance of a granular filtration system (GFS) composed of a rock filter (RF), a rapid sand filter (RSF), and an activated carbon filter (ACF), applied to the post-treatment of an anaerobic reactor effluent. Four filtration rates (FR) were applied to the GFS (in m3·m-2·d-1): 100-60-60, 100-90-90, 200-120-120, and 200-160-160, for RF-RSF-ACF, respectively. A clarified final effluent with low turbidity (~ 10 NTU), solids (~ 6.5 mg TSS.L-1), and organic matter content (~ 40 mg COD.L-1) was obtained when the GFS worked with FR up to 100-90-90 m3·m-2·d-1. For higher FR, the effluent quality was a little poorer. Principal component analysis showed when the RSF operated at 120 or 160 m3·m-2·d-1, it presented an effluent with higher turbidity which did not affect negatively the ACF performance. The hydraulic load limits in the RSF were reached in periods of 45, 30, and 24.5 h for the FR of 60, 120, and 160 m3·m-2·d-1, respectively, and head loss analysis depicted a more distributed solid retention through the sand depth with the lower FR. Thus, the results revealed that the RF-RSF-ACS system is a promising alternative for effluent polishing of anaerobic reactor, especially when the FR is set at 90 m3·m-2·d-1 or even higher.

Effect of reclaimed water and dehydrated sludge on the morpho-physiology and yield of sorghum.

The effect on the morpho-physiological parameters and yield of sorghum cultivated in a greenhouse with reclaimed water (RW) and (dehydrated sludge (DS) obtained in a sewage treatment plant, was evaluated. Six treatments (T), with five repetitions each, were carried out in entirely randomized blocks. Water (W) was used in T1 (W) (control), T2 (W + NPK), and T3 (W + DS); RW was used in T4 (RW), T5 (RW + P), and T6 (RW + DS). The results showed that irrigation with only RW (T4), or W + DS (T3) was very suitable for the cultivation since an adequate nutritional supply was provided. The positive effects on the morpho-physiological parameters, plant height, stem diameter and stem length (in cm), were: T3 - 148.8, 1.50, and 103, respectively; T4 - 154, 1.70, and 107, respectively; and on the grain production in weight of 1000 seeds (g), and productivity in grains per plant: T3 - 6.97 and 1453, respectively; T4 - 6.81 and 1636, respectively. Both treatments showed for most of the parameters, no significant differences compared with those of T2 or T5 with supplementary fertilizers. A high production of metabolites (mg g-1) like free amino acids was also shown: T3 - 6.45; T4 - 8.43 and proline: T3 - 1.86; T4 - 1.77, known to be a good indication of a plant natural defence against stress conditions, and in soluble protein: T3 - 11.20; T4 - 13.51. Therefore, since the production of such grains with RW or DS can be environmentally and economically beneficial, their use is recommended for small and medium farmers in semiarid regions.

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.

Waste of electrical and electronic equipment management from the perspective of a circular economy: A Review.

In addition to the difficulties involved in the management of conventional solid waste, the management of waste of electrical and electronic equipment (WEEE) is significantly more complex due to its unusual chemical composition and fast generation. Both developed and developing countries have been looking for solutions to deal with the problems caused by the growing flow of WEEE, especially regarding sustainable solutions based on reducing resource exploitation by the recovery of materials from this type of waste. In this context, this work presents a quali-quantitative and comprehensive literature review of the publications on the management of WEEE, from the perspective of a circular economy. The results showed that the first publications on the topic appear in 2006, with a significant increase from 2015, the year when the Circular Economy Action Plan was instituted in the European Community. The most prominent authors have been giving emphasis to researches on recycling, reuse and technologies for the recovery of materials/energy from WEEE. Nevertheless, few studies have been found focusing on the prevention/reduction in WEEE generation, priority actions of the WEEE management hierarchy. The works analysed show that the current management of WEEE, despite considering the circularity of materials, prioritizes the development of technological solutions of the end-of-pipe type, greatly represented by the recovery of materials, instead of preventing the generation, which may be detrimental to long-term sustainability. The work ends with the presentation of a SWOT-TOWS (strengths, weaknesses, opportunities and threats) analysis conducted to define the main strategies for the improvement of WEEE management from a circular economy perspective.

Strategy for the formation of microalgae-bacteria aggregates in high-rate algal ponds.

This work studied the formation of aggregates used for wastewater treatment in high-rate algal ponds (HRAP). For this, the establishment of microalgae-bacteria aggregates in these systems was evaluated, considering strategies for the inoculation and start-up. Two HRAP were operated in parallel, at first in batch mode and then in continuous flow. The wastewater treatment was efficient, with removal rates around 80% for COD and N-ammoniacal. Volatile suspended solids and chlorophyll for the culture grew continuously reached a concentration of 548 ± 11 mg L-1 and 7.8 mg L-1, respectively. Larger photogranules were observed when the system was placed in a continuous regime. The protein fraction of extracellular polymeric substances was identified as a determinant in photogranules formation. During the continuous regime, more than 50% of the biomass was higher than 0.2 mm, flocculation efficiency of 78 ± 6%, and the volumetric sludge index of 32 ± 5 mL g-1. The genetic sequencing showed the growth of cyanobacteria in the aggregate and the presence of microalgae from the chlorophytes and diatoms groups in the final biomass.

Effect of individual or combined physical and chemical factors on the anaerobic biodegradation of linear alkylbenzene sulphonate.

The effect of six important factors on the anaerobic biodegradation of linear alkylbenzene sulphonate (LAS) was evaluated using a response surface methodology. The factors were: (i) co-substrate concentration (CC), (ii) contact time between LAS and microorganisms, (iii) temperature, (iv) hardness, (v) pH, and (vi) LAS source. The results showed that individually or combined, CC with chemical oxygen demand (COD) ≤50 mg L-1 was the factor that mostly favoured LAS biodegradation; whereas at COD >50 mg L-1, adsorption to sludge and solubilisation in the aqueous medium were favoured. Two-factor interactions promoted the highest percentages of biodegradation (45-52%), adsorption (43-45%), and solubilisation (18-25%). The three-factor interactions resulted in small percentage increases of up to 11%, 5%, and 13% for biodegradation, adsorption, and solubilisation, respectively, compared to those of two-factor interactions. The interactions of four, five, and six factors resulted in a non-significant effect on LAS biodegradation, adsorption, and solubilisation, with percentages close to those quantified for the two- and three-factor interactions. Concentrations of up to 30 mg LAS L-1 did not significantly affect the COD removal efficiency (74-88%) from the medium. These values are commonly obtained in full-scale anaerobic systems used to treat domestic sewage.

Formation and stability of aerobic granular sludge in a sequential batch reactor for the simultaneous removal of organic matter and nutrients from low-strength domestic wastewater.

Simultaneous removal of organic matter, nitrogen, and phosphorus, via simultaneous nitrification and denitrification (SND) and enhanced biological phosphorus removal processes, was evaluated in a pilot-scale sequential batch reactor. The focus was on granule's morphology, stability, microbiological composition, and reactor performance while treating diluted domestic wastewater with total chemical oxygen demand (CODt) of ≈ 200 mg.L-1. The applied organic loading rate was 0.9 ± 0.3 kg CODt.m-3.d-1 in the experiment. Aerobic granular sludge developed gradually. After 87-day operation, granules (diameter ≥ 0.2 mm) were ≥ 50 % of the biomass, and after 168 days, complete granulation was obtained (≥ 80 % of biomass). In the third period (days 168-247, complete granulation), mixed liquor biomass reached a volatile suspended solids (VSS) concentration of 1.2 ± 0.3 g VSS.L-1, with the granules remaining stable until the experimental end. In this period, low effluent concentrations of COD, nitrogen (NH4+-N, NO2--N and NO3--N) and phosphate (PO43-P) were obtained (mg.L-1): 36 ± 11; 4 ± 5; 3 ± 3, 4 ± 5; and 0.9 ± 0.4, respectively. COD, NH4+-N, and PO43--P removal efficiencies (%) were 80 ± 11; 83 ± 20; and 55 ± 24, respectively. Heterotrophic nitrification and SND were observed, resulting in a process efficiency of 31 % even with dissolved oxygen applied to saturation. The phosphate removal was mainly attributed to denitrifying phosphorus accumulating organisms. Pseudomonas, the dominant genus found, acted in nitrogen and phosphorus removal. Pseudoxanthomonas also assisted in phosphorus removal. Bacterial communities in the flocs (≈ 20 % of biomass) during the last period were similar to those in the granules; therefore, they constituted the basis for granule formation, directly contributed to the simultaneous good removal of organic matter and nutrients.

Influence of temperature on aerobic granular sludge formation and stability treating municipal wastewater with high nitrogen loadings.

This study investigated the influence of temperature (20 and 30 °C) on the formation and stability of aerobic granules in sequential batch reactors (SBR). Therefore, two lab-scale SBRs operated at 20 and 30 °C (SBR20 and SBR30) were used. The reactors were fed with municipal wastewater (CODt:TN:TP 100:15:1.7), leading to mean organic loading rates (OLR) of 1.3 ± 0.4 kgCODt m-3 day-1. Both reactors had the same height/diameter ratio of 4.2 and were inoculated with activated sludge from a municipal wastewater treatment plant. The operational conditions were also the same for both temperatures and lasted in stable process parameters for over 100 days. By optimizing the aeration and oxygen concentration, a high removal efficiency of NH4-N (∼99%) and COD (∼90%) was achieved in both reactors, despite the poor C:N:P ratio at the influent. Furthermore, a relatively low oxygen concentration of 2 mg L-1 was defined as the set point for the control strategy. Nevertheless, granulation at 30 °C was significantly faster, resulting in more stable sludge volume index (SVI) values (SVI10/SVI30 < 1.1). The granules formed at 30 °C were also larger, more compact, and considerably more stable against system disturbances. However, at higher temperatures, larger granules might be required for nitrate removal because of the increased oxygen diffusion rates. Finally, microbiological 16S rRNA gene amplicon analysis for both systems indicated major differences relatively to the inoculum sludge only for nitrogen-degrading organisms.

Biological treatment of real textile wastewater containing sulphate, salinity, and surfactant through an anaerobic-aerobic system.

Real textile wastewater containing high salinity (up to 12.6 g·kg-1) and surfactant (up to 5.9 mg·L-1 of linear alkylbenzene sulfonate - LAS) was submitted to biological treatment for colour (up to 652 mg Pt-Co·L-1) and sulphate (up to 1,568.6 mg SO4-2·L-1) removal. The influence of ethanol and molasses supplementation was firstly evaluated in anaerobic batch reactors for the removal of dyes and sulphate. Subsequently, aiming to remove aromatic amines (dye degradation by-products), an anaerobic-aerobic continuous system supplemented with molasses was applied. Supplementation had no influence on colour removal (maximum efficiencies around 70%), while it improved sulphate reduction (23% without supplementation against 87% with supplementation), and conferred robustness to the reactors, which recovered quickly after higher salinity impact. The aerobic reactor removed aromatic amines when the level of surfactants was lower than 1.0 mg LAS·L-1, but the performance of the system was hindered when the concentration was increased to 5.9 mg LAS·L-1. Findings suggest that the supplementation of an easily biodegradable organic matter might be a strategy to overcome wastewater fluctuation in composition.

Start-up strategies to develop aerobic granular sludge and photogranules in sequential batch reactors.

In this study, start-up strategies to develop conventional aerobic granular sludge (AGS) and algal aerobic granular sludge (AAGS) (photogranules), were investigated. The granulation experiment was conducted in four sequencing batch reactors (SBR), of which two were conventional SBRs (RC1, RC2) used as control, and two were photo-SBRs (R1, R2). R1 and RC1 were operated with a 40-min feeding during the reactors´ anaerobic cycle period, whereas R2 and RC2 with a 60-min feeding. All the reactors were operated in two phases with a C:N = 4:1 in Phase I and 8:1 in Phase II. In Phase I, AGS in RC1 and RC2 was formed 15 days before the AAGS development in R1 and R2. However, the AAGS generally presented better stability and higher diameter. On the other hand, AGS presented greater abundance of extracellular polymeric substances producing organisms, such as Xanthomonadacea and Rhodocyclaceae. Chemical oxygen demand (COD) and NH4+-N removal efficiencies were similar in all the four reactors of approximately 70% and 60%, respectively. In this phase, despite the good biomass structure, the reactors were not able to completely oxidize the high influent concentration of NH4+-N (100 mg.L-1) and COD (400 mg.L-1). This can be associated to the short time of the aerobic phase and low biomass content. In Phase II in all the reactors, a good increase in COD and NH4+-N removal efficiencies to values above 95% and 93%, respectively, was achieved under a higher C:N ratio of 8 with lower influent concentration of NH4+-N (50 mg.L-1). The 60-min anaerobic feeding period in R2 and RC2 resulted in greater removal efficiency of nitrogen, confirming that small variation on cycle periods can affect the biomass composition; the biomass presented more compact granules and larger diameters under 60 min-feeding when compared with those obtained with 40 min-feeding in Phase I.

Strategies for the improvement of home medical waste management during the COVID-19 pandemic.

Home care services (HCS) are important to assist patients with difficulties in accessing conventional health services. Nevertheless, in times of COVID-19 pandemic, the traditionally offered service needs to be restructured to protect health professionals, patients and their families. In this context, this article aims to identify the impacts resulting from the COVID-19 pandemic on home medical waste management (MWM), converting threats into opportunities, and weaknesses into management strengths. Three months before the pandemic (from October to December), a comprehensive survey was conducted on the practices of home care services and MWM with health professionals, caregivers and patients in Caruaru (Brazil). Quali-quantitative information was collected by structured and semi-structured interviews. For evaluation, the SWOT-TOWS analysis was applied to identify the threats and weaknesses of the practices of HCS and MWM, and to propose strategies to ensure the protection of public health and the environment. The results showed that the main weaknesses found were the lack of training of health professionals and the lack of guidance given by them to caregivers of patients, both related to MWM. Except for sharp waste, all other MWM practices have proved to be inadequate, posing threats, especially in a pandemic period. Four action strategies to improve HCS and MWM were identified: (i) providing MWM training to HCS personnel based on ISO standards; (ii) providing MWM information to caregivers and patients; (iii) planning actions to optimize the service during the pandemic; and (iv) sharing HCS management with municipal decision makers. Between December 2020 and January 2021, semi-structured interviews were performed only with health professionals, to verify the impacts and changes that have occurred in HCS in the COVID-19 pandemic. Comparing the results of the two surveys, improvements were achieved, including the incorporation during the pandemic of some strategies identified in the first phase of the research.Implications: Home care service plays a fundamental role in the quality of life of patients and in the sustainability of the public health system in Brazil. In the pandemic period, HCS was impacted with routine changes and the adoption of new personal protective equipment. Our results showed the need to promote strategies to improve HCS to preserve the health of professionals and patients attended, in the pandemic and post-pandemic period. The strategies identified in the study contributed to improvements in the provision of the service and in the management of medical waste that is still inadequate. Such issues are of interest to municipal health management, which has adopted some of the suggested strategies. The thousands of HCS distributed in Brazilian municipalities can also adopt the strategic actions resulting from this research.

Modelagem matemática para sistema de tratamento de esgoto doméstico com remoção simultânea de matéria orgânica e nitrogênio / Mathematical modeling for domestic sewage treatment system with simultaneous removal of organic matter and nitrogen

RESUMO Neste trabalho, avaliou-se o uso do modelo matemático ASM3 para um sistema piloto de reator compartimentado anaeróbio/anóxico e aeróbio tipo MBBR, utilizado para a remoção simultânea de matéria orgânica e nitrogênio em esgoto doméstico. A simulação computacional foi implementada pelo software ASIM. Selecionou-se um conjunto padrão de parâmetros para o modelo, com uma combinação dos valores calibrados e dados da literatura. Com a modelagem computacional foi possível incluir as características operacionais próprias do sistema de tratamento e, embora o modelo não tenha tido sua capacidade de previsão dos parâmetros validada, foi possível verificar a aplicabilidade do ASM3 para as fases operacionais definidas neste estudo.

ABSTRACT In this work, the use of the ASM3 mathematical model for a pilot system of anaerobic/anoxic and aerobic MBBR compartmentalized reactor, for the simultaneous removal of organic matter and nitrogen in domestic sewage, was evaluated. The simulation was implemented by the ASIM software. A standard set of parameters was selected for the model, with a combination of calibrated values and literature data. With the computational modeling, it was possible to include the operational characteristics of the treatment system and, although the model capacity to predict the parameters could not be validated. Nevertheless, it was possible to verify the applicability of the ASM3 model for the operational phases defined in this study.

Selecting the best electron donor and operational temperature for the rapid biotransformation of the insensitive munitions compound 2,4-dinitroanisole (DNAN) by anaerobic sludge.

2,4-Dinitroanisole (DNAN) is a toxic compound increasingly used by the military that can be released into the environment on the soil of training fields and in the wastewater of manufacturing plants. DNAN's nitro groups are anaerobically reduced to amino groups by microorganisms when electron donors are available. Using anaerobic sludge as the inoculum, we tested different electron donors for DNAN bioreduction at 20 and 30 °C: acetate, ethanol, pyruvate, hydrogen, and hydrogen + pyruvate. Biotic controls without external electron donors and abiotic controls with heat-killed sludge were also assayed. No DNAN conversion was observed in the abiotic controls. In all biotic treatments, DNAN was reduced to 2-methoxy-5-nitroaniline (MENA), which was further reduced to 2,4-diaminoanisole (DAAN). Ethanol or acetate did not increase DNAN reduction rate compared to the endogenous control. The electron donors that caused the fastest DNAN reductions were (rates at 30 °C): H2 and pyruvate combined (311.28 ± 10.02 µM·d-1·gSSV-1), followed by H2 only (207.19 ± 5.95 µM·d-1·gSSV-1), and pyruvate only (36.35 ± 2.95 µM·d-1·gSSV-1). Raising the temperature to 30 °C improved DNAN reduction rates when pyruvate, H2, or H2 + pyruvate were used as electrons donors. Our results can be applied to optimize the anaerobic treatment of DNAN-containing wastewater.

The key role of oxygen in the bioremoval of 2,4-diaminoanisole (DAAN), the biotransformation product of the insensitive munitions compound 2,4-dinitroanisole (DNAN), over other electron acceptors.

Insensitive munitions compounds, such as 2,4-dinitroanisole (DNAN), are replacing conventional explosives. DNAN is anaerobically reduced to 2,4-diaminoanisole (DAAN), a toxic aromatic amine. However, the removal of DAAN under different redox conditions is yet to be elucidated. Herein, we analyzed DAAN consumption in biotic and abiotic microcosms when exposed to different redox conditions (without added electron acceptor, without added electron acceptor but with pyruvate as a co-substrate, with sulfate, with nitrate, and with oxygen), using an anaerobic sludge as inoculum. We observed that DAAN autoxidation, an abiotic reaction, was significant in microaerobic environments. DAAN also reacted abiotically with heat-killed sludge up to a saturation limit of 67.4 µmol DAAN (g VSS heat-killed sludge)-1. Oxygen caused the fastest removal of DAAN in live sludge among the conditions tested. Treatments without added electron acceptors (with or without pyruvate) presented similar DAAN removal performances, although slower than the treatment with oxygen. Sulfate did not exhibit any effect on DAAN removal compared to the treatment without added electron acceptors. Nitrate, however, inhibited the process. An enrichment culture from the microcosms exposed to oxygen could be developed using DAAN as the sole substrate in microaerobic conditions. The enrichment profoundly changed the microbial community. Unclassified microorganisms accounted for 85% of the relative abundance in the enrichment culture, suggesting that DAAN microaerobic removal might have involved organisms that were not yet described. Our results suggest that DAAN microaerobic treatment can be coupled to DNAN anaerobic reduction in sludge, improving the treatment of DNAN-containing wastewaters.

1,3-Propanediol production from glycerol in polyurethane foam containing anaerobic reactors: performance and biomass cultivation and retention.

The use of batch and upflow anaerobic reactors filled with polyurethane foam for pure glycerol fermentation was evaluated. The best reactor operational conditions to obtain high yield and productivity of 1,3-propanediol (1,3-PDO) as the main product and the role of the polyurethane foam in the growth and retention of suspended and attached biomass in the reactors were investigated. In the experiment at 30 °C with a batch reactor (700 mL), biomass growth was mostly as immobilized attached cells, and the achieved 1,3-PDO yield was up to 0.58 mol mol-gly-1. In the experiment (30 °C) with an upflow anaerobic reactor (717 mL), glycerol loading rates (gly-LR) ranging from 6.94 to 15.47 g gly L-1 day-1 were applied during a 102-day period. During the operation, average 1,3-PDO yield was 0.47 mol mol-gly-1, reaching a maximum of 0.51 mol mol-gly-1 at gly-LR of 13.57 g gly L-1 day-1. High 1,3-PDO productivity (5.35 to 5.44 g L-1 day-1) was obtained when gly-LR was 13.57 to 15.47 g gly L-1 day-1. Comparing the close yield values in both batch and continuous reactors and based on microbial evaluation, it is concluded that most of the 1,3-PDO generated in the continuous reactor was due to the suspended biomass retained by the foam cubes. The Clostridium genus was the predominant 1,3-PDO producer. Good yields and productivities with packed reactors were attributed to polyurethane foam used for mixed culture growth and retention. Consequently, they are worth considering for 1,3-PDO production from pure glycerol.

Cultivo de melancia no semiárido irrigado com diferentes lâminas de esgoto doméstico tratado / Watermelon cultivation in the semi-arid irrigated with different heights of treated domestic sewage

RESUMO O objetivo deste trabalho foi avaliar a viabilidade agronômica do uso de esgoto doméstico tratado em reator anaeróbio para o cultivo de melancia tipo Crimson Sweet. Em estudo de campo no Sertão Pernambucano, avaliou-se a aplicação de quatro lâminas de irrigação por meio do sistema de gotejamento. Foram avaliadas as lâminas de 50, 75, 100 e 125% baseadas nos resultados da evapotranspiração e nas exigências do sistema de irrigação adotado. A caracterização do efluente tratado indicou conformidade com as recomendações para a aplicação agrícola, entretanto a concentração de sólidos suspensos (114 mg.L-1) demandou maior frequência de limpeza dos gotejadores. Foram observados um aumento da capacidade de troca catiônica e uma redução do pH do solo em todos os tratamentos. O tratamento com lâmina a 125% resultou em frutos de maiores tamanho (20,78 cm) e peso (7,12 kg.un-1), bem como de produtividade média (61,1 t.ha-1). Estes valores são superiores às médias nacional e do Estado de Pernambuco, demonstrando a viabilidade agronômica do reúso nas condições testadas.

ABSTRACT The aim of this paper was to assess the agronomic viability of using anaerobically treated domestic sewage in cultivation of Crimson Sweet watermelon. In a field experiment conducted in the semi-arid region of Pernambuco state, Brazil, four treatments (T) were used to assess the effects of irrigation using dripping system on fruits and soil. Four heights of 50% (T1), 75% (T2), 100% (T3) and 125% (T4), based on the calculated evapotranspiration and irrigation needs, were applied. The treated effluent characteristics indicated compliance with the recommendations for agricultural application, but the concentration of suspended solids (114 mg.L-1) demanded frequent cleansing of the dripper blockages. We observed an increase in the cation exchange capacity and a decrease of the soil pH in all the treatments. The best results were obtained with the treatment T4 (height of 125%), which showed watermelons of bigger size (20.78 cm), as well as the highest productivity (61.1 t.ha-1) and fruit weight (7.12 kg.un-1). These values are higher than those of the country and Pernambuco state, demonstrating the agronomic feasibility of reuse under the studied conditions.

The effect of methanogenesis inhibition, inoculum and substrate concentration on hydrogen and carboxylic acids production from cassava wastewater.

Manipueira is a carbohydrate-rich agro-industrial waste from cassava processing. It is considered well suitable for biotechnological processes, such as hydrogen and carboxylic acids production, due to the high content of easily degradable organic matter. However, the proper methanogenesis inhibition method, inoculum type, and organic loads are factors still limiting the processes. The objective in this work was to evaluate the effects of such factors on byproducts production in anaerobic reactors. Batch experiments were conducted with 2.3-L flasks during two operational phases. In the first phase (P1), inhibition of methanogens in the sludge was evaluated using acetylene (1% v/v of headspace) and heat treatment (120 °C, 1 atm for 30 min). In the second phase (P2), three inoculum types obtained from common anaerobic sludges (bovine rumen and sludges from municipal and textile industrial wastewater treatment plants) were individually assayed. P2 aimed to identify the best inoculum, based on hydrogen production ability, which was tested for three initial concentrations of manipueira in terms of chemical oxygen demand (COD) (10, 20 and 40 g O2/L). Results of P1 indicated that either acetylene or heat treatment efficiently inhibited methanogenesis, with no methane production. However, the maximum H2 production potential by applying heat treatment (~ 563 mL) was more than twice compared with that by acetylene treatment (~ 257 mL); and butyrate was the main carboxylic acid by-product (~ 3 g/L). In P2 experiments after sludge heat treatment, the highest hydrogen yield (1.66 ± 0.07 mol H2/mol glucose) and caproic acid production (~ 2 g/L) were observed at 20 g O2/L of manipueira COD, when bovine rumen was the inoculum. The primary metabolic degradation products in all P2 experiments were ethanol, acetic, butyric, propionic and caproic acids. The finding of caproic acid detection indicated that the applied conditions in manipueira anaerobic degradation favored carbon chain elongation over methanogenesis.

Multi-criteria analysis for municipal solid waste management in a Brazilian metropolitan area.

The decision-making process involved in municipal solid waste management (MSWM) must consider more than just financial aspects, which makes it a difficult task in developing countries. The Recife Metropolitan Region (RMR) in the Northeast of Brazil faces a MSWM problem that has been ongoing since the 1970s, with no common solution. In order to direct short-term solutions, three MSWM alternatives were outlined for the RMR, considering the current and future situations, the time and cost involved and social/environmental criteria. A multi-criteria approach, based on the Preference Ranking Organization Method for Enrichment Evaluations (PROMETHEE), was proposed to rank these alternatives. The alternative that included two private landfill sites and seven transfer, sorting and composting stations was confirmed as the most suitable and stable option for short-term MSWM, considering the two scenarios for the criteria weights. Sensitivity analysis was also performed to support the robustness of the results. The implementation of separate collections would minimize the amount of waste buried, while maximizing the useful life of landfill sites and increasing the timeframe of the alternative. Overall, the multi-criteria analysis was helpful and accurate during the alternative selection process, considering the similarities and restrictions of each option, which can lead to difficulties during the decision-making process.