Comparative effect of acid and heat inoculum pretreatment on dark fermentative biohydrogen production.

This study delves into the impact of various pretreatment methods on the inoculum in dark fermentation trials, specifically exploring thermal shock at different temperatures (60, 80, and 100 °C) and durations (15, 30, and 60 min), as well as acid shock at pH 5.5. Initial acidification of the substrate/inoculum mixture facilitates H2 generation, making acid shock an effective pretreatment option. However, it is also observed that combining thermal and acid pretreatments boosts H2 production synergistically. The synergy between thermal and acid pretreatments results in a significant improvement, increasing the overall hydrogen production efficiency by more than 9% compared to assays involving acidification alone. This highlights the considerable potential for optimizing pretreatment strategies. Furthermore, the study sheds light on the critical role of inoculum characteristics in the process, with diverse hydrogen-generating bacteria significantly influencing outcomes. The established equivalent performance of HCl and H2SO4 in inoculum pretreatment demonstrates the versatility of these acids in shaping the microbial community and influencing hydrogen production. The analysis of glucose conversion data highlights a prevalence of butyric acid in all trials, irrespective of the pretreatment method, emphasizing the dominance of the butyrate pathway in hydrogen generation. Additionally, an examination of the microbial community offers valuable insights into the intricate relationships between temperature, pH, and microbial diversity. Bacteroidota established its dominance among the bacterial populations, with a relative abundance exceeding 20-25% in the raw inoculum, and this dominance further increased following the treatment. Thermal and acid pretreatments result in significant shifts in dominant microbial communities, with some non-dominant phyla like Cloacimonadota and Spirochaetota becoming more prominent. These shifts in microbial diversity underscore the sensitivity of microbial communities to environmental conditions and pretreatment methods, further highlighting the importance of understanding their dynamics in dark fermentation processes.

Study of the influence of the reaction parameters on nutrients recovering from digestate by struvite crystallisation.

Struvite production by crystallisation is one of the most promising methods of phosphorus recovering from wastewater or livestock waste. Lab-scale batch experiments were carried out to study the effect of supersaturation, magnesium and phosphorous concentration, pH value and temperature on struvite crystallisation reaction using pig manure digestate from an anaerobic digestion plant as raw material. Taguchi methodology has been used as method to define the design of experiments and to analyse the results. In the design of experiments, three levels of each parameter have been studied: Mg/P ratio (1.0-2.0), N/P ratio (4.0-12.0), pH (9.0-12.0) and temperature (20-40 °C). The morphology of the crystals obtained was observed by scanning electron microscopy. The results show that the optimal values of Mg/P ratio, N/P ratio, pH and temperature for struvite crystallisation are 1.5; 4.0; 10.5 and 30 °C, respectively. High supersaturation levels should be avoided to obtain high yields in the process.

Study of pig manure digestate pre-treatment for subsequent valorisation by struvite.

This work evaluates the release of phosphorus contained in the digestate from the anaerobic digestion of pig manure, through an acidification process. The objective of this acidification is to increase the amount of phosphorus available in the digestate liquid fraction and, subsequently, recover this element by chemical precipitation in the form of struvite or calcium phosphate. Two digestate samples (one fresh and one old) were studied and treated by adding various amounts of sulphuric acid to the different digestate fractions (raw digestate, solid fraction and liquid fraction). For the raw digestate, phosphorus releases higher than 95% were obtained for pH 4.0. In the last part of the experiment, the influence of acid pre-treatment on the reaction yield of phosphorus precipitation, in the form of struvite or calcium phosphate, was determined. Improvements in reaction yield were obtained up to 15% for struvite and 80% for calcium phosphate, increasing also in 7.5 times the amount of phosphorus available in the digestate liquid fraction, for both cases.

A novel initiative to counteract illegal dumping in rural areas of Valladolid Province (Spain).

In the whole territory of Castilla y León (Spain), there are currently more than 2000 waste dumps that will be restored through a novel programme in the period 2017-2019 with an investment of more than 10 M€. Castilla y León regional government is currently implementing this programme in the province of Valladolid for the environmental recovery of areas heavily degraded by the deposit of inert waste, which entails the restoration of illegal dumps in the province bigger than 1000 m2, a total of 133. The programme also includes the implementation of an alternative and legal system for the management of construction and demolition waste, amongst other waste streams. The sealing of landfills and tailings is encompassed within the actions that the regional government is developing in the field of integrated management of waste for their prevention, recovery, recycling and disposal in all the provinces of the community, framed within the line established in the 7th Environmental Action Programme of the European Union. The situation of illegal deposits must be corrected both through direct situations on the affected areas and through measures aimed at ensuring proper management of construction and demolition waste and pruning. This paper shows the first results obtained after the implementation of this regional initiative with the focus set on the description of the implemented waste management programme. The programme provided 2518 services in 2017 managing 6000 t of waste which, without the implementation of this programme, would probably have ended up in illegal dumps. These waste streams included debris (33%), discarded appliances (45%) and pruning (22%). The costs associated with the management of these streams were 25.53 €/t debris, 183.16 €/t appliances and 162.40 €/t pruning.

Anaerobic co-digestion of agro-food waste mixtures in a fed-batch basis.

The agro-food industry (including livestock) generates millions of tonnes of waste products. A solution to this sector's waste disposal challenges was explored by a joint treatment model of organic waste products from several industries. An inventory of agro-food industry organic waste streams with high potential for biogas production was carried out in a logistically viable area (Cider Region, Asturias, Spain). Three industries were selected as those with the higher potential for this study: livestock, dairy and beverage. The kinetics of anaerobic degradation and methane production of four mixtures of selected waste streams were investigated. The specific methane production at five different substrate-to-inoculum ratios (0.50, 0.75, 1.00, 1.50 and 2.00) showed a slightly decreasing trend at the higher ratios. Some hints of a synergistic effect have been observed in mixtures with higher content in milled apple waste, while antagonistic symptoms were noted in mixtures mainly composed of dairy wastes. The estimation of fluxes of waste and methane potentials in the Cider Region suggests centralised anaerobic digestion as a sustainable solution for the valorisation of livestock and agro-food wastes generated in this area. Sector-specific waste streams (livestock and agro-food industry) could cover up to 12% of regional total energy demand.

Effects of inoculum source and co-digestion strategies on anaerobic digestion of residues generated in the treatment of waste vegetable oils.

This work aims at selecting a suitable strategy to improve the performance of the anaerobic digestion of residues generated in the treatment of waste vegetable oils (WVO). Biochemical methane potential (BMP) assays were conducted at 35 °C to evaluate the effects of substrate mix ratio between a mixture of WVO residues (M) and pig manure (PM) co-digesting by using different inocula. Inoculum from an industrial digester fed with organic waste from hotels, restaurants and catering leftovers (HORECA) showed higher methanogenic activity (55.5 mLCH4 gVS(-1) d(-1)) than municipal wastewater treatment plant (mWWTP) inoculum (42.6 mL CH4 gVS(-1) d(-1)). Furthermore, the results showed that the resistance to WVO residues toxicity was higher for the HORECA sludge than for the mWWTP sludge. HORECA inoculum produced more biogas in all the assays. Moreover, the resulting biogas was of better quality, containing an average of 71.1% (SD = 1.6) methane compared to an average of 69.5% (SD = 1.2) methane for test with mWWTP sludge. The maximum degradation rate occurred at the higher PM mix ratio (M/PM:1/3), reaching 26.7 ± 4.3 mLCH4 gVS(-1) d(-1) for mWWTP inoculum, versus 42.0 ± 1,5 mLCH4 gVS(-1) d(-1) achieved for HORECA inoculum. A high reduction of volatile solids (between 70% and 81%) was obtained with both inocula at all M/PM ratios assayed (1/0, 1/3, 1/1 and 3/1 v/v) but, bearing in mind the operation of a full-scale anaerobic plant, the optimal scenario assayed corresponds to the ratio M/PM: 1/3 v/v where shorter lag periods will make it possible to operate at lower hydraulic retention times.

Fentanilo transdérmico en el tratamiento de la fibromialgia / Percutaneous fentanyl in fibromyalgia

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Tiempos de espera y calidad asistencial en urgencias / Waiting time and healthcare quality in emergency department

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