Improving the Anaerobic Digestion of Wine-Industry Liquid Wastes: Treatment by Electro-Oxidation and Use of Biochar as an Additive

Treatment of hydrothermal carbonization process water by electrochemical oxidation: Assessment of process performance

Herein electrochemical oxidation (EO) is proposed as a novel path to treat the process water obtained from hydrothermal carbonization of olive tree pruning. The aim of this work is to analyze the organic matter removal achieved by the treatment along with the identification of the chemical species formed after the electro-oxidation process at different experimental conditions. Three different tests were performed in a boron doped diamond cell, using Na₂SO₄ and NaCl as supporting electrolytes to compare the results obtained with the raw process water. The organic matter removal was evaluated by means of total organic carbon and chemical oxygen demand, while Gas Chromatography Mass Spectrometry was used to determine the chemical species present before and after the treatment. The addition of a promoter considerably increased the organic matter removal. In fact, the experiments performed using supporting electrolytes showed the best results in terms of organic matter removal compared to the control experiment (30-40% vs. 17%); This reduction agrees with the volatile fatty acids' measurements. Almost all the chemical species identified in the different feedstocks were partially or totally removed after the EO treatment depending on the experimental conditions. The specific energy consumption and the cost calculated for the treatment is highly dependent on the time of electro-oxidation and the supporting electrolyte used, obtaining values from 1 to 45 €/kg COD_removed. All in all, this work suggests an interesting path towards a further utilization of process water from hydrothermal carbonization processes.

Effect of Electrolysis on Activated Sludge during the Hydrolysis and Acidogenesis Stages in the Anaerobic Digestion of Poultry Manure

This paper focuses on the study of the effect of electrolysis on activated sludge in a microbial electrolysis cell (MEC) under the anaerobic digestion of poultry manure. This study was conducted using a bioreactor design with and without electrodes (conventional condition). Measurements of pH, redox potential (ORP), and total dissolved solids were carried out, as was the microscopy of activated sludge during treatment and gasometry. There was an increase in the yields of CH4 and CO2 compared to conventional conditions. Thus, on the 14th day, there was an increase in the CH4 yield to 35.1% compared with the conventional conditions—31.6%—as well as in the CO2 yield to 53.5% compared with the cell without electrodes—37.7%. Visually, the microscopy of anaerobic activated sludge showed changes in the aggregation process itself, with the formation of cells of clusters of microorganism colonies with branches of a delineated shape. ORP fluctuations were related to the process of the dissociation into ions during the passage of an electric current through the electrodes, and were observed before and after the inclusion of a current into the system. A model of the effect of electrolysis during anaerobic digestion was developed, taking into account the influencing factors on the condition of the activated sludge.

Evaluation of Joint Management of Pine Wood Waste and Residual Microalgae for Agricultural Application

This work addresses the joint management of residual microalgae and pine wood waste through pyrolysis to obtain a solid product for its use as soil amendment and two other by-products (liquid and gaseous) that can be used for energy purposes. Two management routes have been followed. The first route is through the co-pyrolysis of mixtures of both residual materials in several proportions and the later use of their solid fraction for soil amendment. The second route is the pyrolysis of pine wood waste and its direct combination with dried residual microalgae, also using it as soil amendment. The solid fraction assessment shows that from seven solid products (biochar) three stand out for their positive applicability in agriculture as soil amendment. In addition, they also present the benefit of serving as carbon sink, giving a negative balance of CO2 emissions. However, caution is suggested due to biochar applicability being subject to soil characteristics. To ensure the sustainability of the overall process, the energy available in liquid and gaseous fractions has been assessed for covering the drying needs of the residual microalgae in both cases. These results suggest that the pyrolysis process is a sustainable way to manage specific evaluated residues and their products.