Use of additives to improve collective biogas plant performances: A comprehensive review

Nowadays, anaerobic digestion (AD) is being increasingly encouraged to increase the production of biogas and thus of biomethane. Due to the high diversity among feedstocks used, the variability of operating parameters and the size of collective biogas plants, different incidents and limitations may occur (e.g., inhibitions, foaming, complex rheology). To improve performance and overcome these limitations, several additives can be used. This literature review aims to summarize the effects of the addition of various additives in co-digestion continuous or semi-continuous reactors to fit as much as possible with collective biogas plant challenges. The addition of (i) microbial strains or consortia, (ii) enzymes and (iii) inorganic additives (trace elements, carbon-based materials) in digester is analyzed and discussed. Several challenges associated with the use of additives for AD process at collective biogas plant scale requiring further research work are highlighted: elucidation of mechanisms, dosage and combination of additives, environmental assessment, economic feasibility, etc.

Agronomic characterization of anaerobic digestates with near-infrared spectroscopy

Anaerobic digestion is an increasingly widespread process for organic waste treatment and renewable energy production due to the methane content of the biogas. This biological process also produces a digestate (i.e., the remaining content of the waste after treatment) with a high fertilizing potential. The digestate composition is highly variable due to the various organic wastes used as feedstock, the different plant configurations, and the post-treatment processes used. In order to optimize digestate spreading on agricultural soils by optimizing the fertilizer dose and, thus, reducing environmental impacts associated to digestate application, the agronomic characterization of digestate is essential. This study investigates the use of near infrared spectroscopy for predicting the most important agronomic parameters from freeze-dried digestates. A data set of 193 digestates was created to calibrate partial least squares regression models predicting organic matter, total organic carbon, organic nitrogen, phosphorus, and potassium contents. The calibration range of the models were between 249.8 and 878.6 gOM.kgDM^-1, 171.9 and 499.5 gC.kgDM^-1, 5.3 and 74.1 gN.kgDM^-1, 2.7 and 44.9 gP.kgDM^-1 and between 0.5 and 171.8 gK.kgDM^-1, respectively. The calibrated models reliably predicted organic matter, total organic carbon, and phosphorus contents for the whole diversity of digestates with root mean square errors of prediction of 70.51 gOM.kgDM^-1, 34.84 gC.kgDM^-1 and 4.08 gP.kgDM^-1, respectively. On the other hand, the model prediction of the organic nitrogen content had a root mean square error of 7.55 gN.kgDM^-1 and was considered as acceptable. Lastly, the results did not demonstrate the feasibility of predicting the potassium content in digestates with near infrared spectroscopy. These results show that near infrared spectroscopy is a very promising analytical method for the characterization of the fertilizing value of digestates, which could provide large benefits in terms of analysis time and cost.

Prediction of organic matter accessibility and complexity in anaerobic digestates

Further characterization to properly assess the fate of organic matter quality during anaerobic digestion and organic carbon mineralization in soils is required. Organic matter quality based on its accessibility and complexity was employed to successfully classify 28 substrate/digestate pairs through principal components and hierarchical clustering analysis. The two first components explained 58.02% of the variability and four main groups were separated according to the feedstock type. A decrease in the accessibility (16-66%) and an increase in the complexity (34-98%) of the most accessible fractions was noticed. Besides, an increase of non-biodegradable compounds (17-66%) was globally observed after anaerobic digestion. The observed trends in the conversion of organic matter during anaerobic digestion have allowed to fill the gap in the modeling of the anaerobic digestion process chain. Indeed, partial least squares regressions have accurately predicted the organic matter quality of digestates from their inputs (R² = 0.831, Q² = 0.593) although the digester operational conditions (temperature and hydraulic retention time) were non-explicative enough. As a novel approach, the predicted digestate quality was used to feed a partial least squares regression model previously developed to predict organic carbon mineralization in soil. The combined models have predicted experimental organic carbon mineralization in soil (R² = 0.697) with a model quality similar to the model for organic carbon mineralization in soil (R² = 0.894). This is the first study that has successfully conceived an additional step in the prediction of organic matter fate from raw substrate before anaerobic digestion to soil carbon mineralization.

Elective tracheostomy during COVID-19 outbreak: to whom, when, how? Early experience from Venice, Italy

PURPOSE

The need for prolonged invasive mechanical ventilation in COVID-19 patients is placing the otorhinolaryngologist in front of an increasing request for tracheostomy. Nowadays, there is uncertainty regarding the timing of tracheostomy, the prognosis of these patients and the safety of healthcare workers. The aim of this study is to evaluate the efficacy and safety of tracheostomy placement in patients with COVID-19.

METHODS

A retrospective cohort study on 23 COVID 19 patients, to analyse the timing of tracheostomy, the risk factors associated with in-hospital death and the infection of the involved health care workers. Early tracheostomy was defined as ≤ 10 days and late ones > 10 days.

RESULTS

The mortality rate of COVID-19 patients admitted to ICU that underwent tracheostomy was 18%. The overall mortality of patients admitted to ICU was 53%. The univariate analysis revealed that early tracheostomy, SOFA score > 6, and D-dimer level > 4 were significantly associated with a greater risk of death. At the multivariate analysis SOFA score > 6 and D-dimer level > 4 resulted as significant factors for a higher risk of death. No health care workers associated with tracheostomy are confirmed to be infected by SARS-CoV2.

CONCLUSION

We suggest to wait at least 14 days to perform tracheostomy. In patients with SOFA score > 6 and D dimer > 4, tracheostomy should not be performed or should be postponed. Optimized procedures and enhanced personal protective equipment can make the tracheostomy safe and beneficial in COVID-19 patients.

Comprehensive determination of input state variables dataset required for anaerobic digestion modelling (ADM1) based on characterisation of organic substrates

This article contains the data of 11 organic substrates including physicochemical, biochemical and nutritional characterisations. Additionally, it includes for all substrates the data of organic matter fractionation into easily biodegradable, slowly biodegradable and inert fractions performed with anaerobic respirometry method. Finally, based on physicochemical characterisations and organic matter fractionation, a detailed methodology for the determination of input state variables required for the anaerobic digestion model N°1 (ADM1) was presented and the dataset for all substrates is provided. An example of calculation for one substrate illustrates the methodology for the determination of these variables. Data provided in this article could be useful to any person interested in modelling anaerobic digestion and particularly co-digestion. Data could be also used for implementation of a database for anaerobic digestion modelling.

[Radiotherapy of the tonsillar region. Analysis of prognostic factors]

INTRODUCTION

We report our personal experience with the treatment of tonsillar cancers at the Otorhinolaryngology-Radiotherapy Department of Umberto I Hospital, Mestre, Italy. The results were analyzed by tumor site and stage, lymph node involvement, treatment type and patient age.

MATERIAL AND METHODS

January, 1987, through December, 1995, we treated a hundred and 25 patients with carcinoma of the tonsil and tonsillar region. Most patients were men (M:F = 4:1), with a mean age of 61.9 years (range: 38-87). The lesions were staged at physical examination, chest radiography, bone scintigraphy. US of the liver and neck, CT and/or MRI of the tonsillar region and neck. Eleven patients were in stage I (8.8%), 26 in stage II (20.8%), 31 in stage III (24.8%) and 57 in stage IV (45.6%). Forty-one patients were submitted to tonsillectomy and more/less massive neck dissection: surgery was not radical-in 14 of them. All patients received gamma-photon radiotherapy with a cobalt unit: the minimum dose was 50 Gy after radical surgery and 60 Gy for exclusive irradiation and after nonradical surgery. The hemiblock field technique was always used with the conventional fractionation (2 Gy/day. 1 fraction/day, 5 fractions/week); the treatment was planned with the Theraplan V05-B method on CT scans. When the tolerance dose was reached, the spinal cord was shielded and the dose compensated with 9 MeV electrons. The treatment was discontinued only when needed, and never for more than 7-10 days.

RESULTS

The overall 5-year survival and the 5-year disease-free survival rates were 28% and 45%, respectively; the overall 5-year cause-specific survival rate was 39%. Disease-free survival was 81% in stage I, 52.7% in stage II, 44.2% in stage III and 35.8% in stage IV (p = .005). The 5-year disease-free survival for the patients receiving surgery and irradiation was 62.1%, versus 38.3% for irradiation alone; the rate was 37.6% when neck nodes were involved (N+). One hundred and two patients achieved complete remission (CR), while the other 23 had partial remission (PR). Twenty-eight CR patients recurred; the most common cause of death was failure in primary tumor local control. There were no complications during or after treatment. Secondary lesions were found in 13 patients (10.1%).

CONCLUSIONS

Irradiation alone yields fairly good results in early tonsil carcinoma, while the surgery-irradiation combination should be preferred in large tumors. Better results are expected from kinetic and conformal irradiation techniques with 3D calculations on CT and MR images, which should permit to deliver high doses to strictly targeted areas and to reduce side-effects. Other improvements are expected from new combination therapies.