The anaerobic digestion of microalgae is hindered by its complex cell wall structure and composition. Thus, several pretreatment methods have been used for increasing microalgae anaerobic biodegradability. Since the methane yield depends on biomass characteristics, pretreatments should be compared using the same microalgal biomass. In this study, physical pretreatments including thermal (95 degrees C; 10 h), hydrothermal (130 degrees C; 15 min), microwave irradiation (900 W; 3 min; 34.3 MJ/kg TS) and ultrasonication (70 W; 30 min; 26.7 MJ/kg TS) were evaluated in terms of microalgae solubilisation and methane yield increase in batch tests. Organic matter solubilisation was improved in all cases, with the highest increase on soluble proteins, followed by soluble carbohydrates and soluble lipids. This was attributed to the macromolecular and cell wall composition of the main microalgae species composing the biomass, i.e. Monoraphidium sp. and Stigeoclonium sp. Furthermore, the methane yield was increased by 72% for thermal, 28% for hydrothermal and 21% for microwave pretreatments, whereas no significant increase was found for ultrasonication as compared to control. Outstanding results of the thermal pretreatment should be validated in prospective pilot-scale studies in order to quantify the potential increase in biogas production upon continuous operation. (C) 2015 Elsevier B.V. All rights reserved.
Marianna Garfi'; Pedescoll, A.; Carretero, J.; Puigagut, J.; Garcia, J. Desalination and water treatment Vol. 52, num. 31-33, p. 5848-5855 DOI: 10.1080/19443994.2013.811443 Data de publicació: 2014-09-19 Article en revista
This study aimed at determining the reliability and feasibility of constructed wetlands (CWs) performance evaluation by online monitoring. Redox potential (E-H), turbidity and ammonium (NH4) were continuously monitored for one year by means of online sensors in a pilot plant based on horizontal sub-surface flow constructed wetlands (HSSF CWs). Results were compared with conventional laboratory analyses. Online measures and laboratory analyses showed good agreement for NH4 (r = 0.84, p < 0.01). A significant correlation was also found for: online turbidity vs. Total suspended solids (TSS) (r = 0.85, p < 0.01); online turbidity vs. Biochemical oxygen demand (BOD) (r = 0.88; p < 0.01) and E-H vs. BOD (r = -0.62; p < 0.01). Results suggested that in full-scale CWs, continuous monitoring of turbidity, E-H and NH4 would help to both daily monitoring and improvement of CWs performance. A general overview about economic aspects suggested that, continuous monitoring of wastewater quality could be technically feasible and cheaper than traditional chemical-based monitoring.
Pedescoll, A.; Sidrach, A.; Sánchez, J.C.; Carretero, J.; Marianna Garfi'; Bécares, E. Water research (Oxford) Vol. 47, num. 3, p. 1448-1458 DOI: 10.1016/j.watres.2012.12.010 Data de publicació: 2013-03-01 Article en revista
The aim of this study was to evaluate the effect of different horizontal constructed wetland (CW) design parameters on solids distribution, loss of hydraulic conductivity over time and hydraulic behaviour, in order to assess clogging processes in wetlands. For this purpose, an experimental plant with eight CWs was built at mesocosm scale. Each CW presented a different design characteristic, and the most common CW configurations were all represented: free water surface flow (FWS) with different effluent pipe locations, FWS with floating macrophytes and subsurface flow (SSF), and the presence of plants and specific species (Typha angustifolia and Phragmites australis) was also considered. The loss of the hydraulic conductivity of gravel was greatly influenced by the presence of plants and organic load (representing a loss of 20% and c.a. 10% in planted wetlands and an overloaded system, respectively). Cattail seems to have a greater effect on the development of clogging since its below-ground biomass weighed twice as much as that of common reed. Hydraulic behaviour was greatly influenced by the presence of a gravel matrix and the outlet pipe position. In strict SSF CW, the water was forced to cross the gravel and tended to flow diagonally from the top inlet to the bottom outlet (where the inlet and outlet pipes were located). However, when FWS was considered, water preferentially flowed above the gravel, thus losing half the effective volume of the system. Only the presence of plants seemed to help the water flow partially within the gravel matrix.