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Zahedi S.,Catalan Institute for Water Research | Icaran P.,FCC Aqualia | Yuan Z.,University of Queensland | Pijuan M.,Catalan Institute for Water Research
Bioresource Technology | Year: 2016

Free nitrous acid (FNA) has been shown to enhance the biodegradability of waste activated sludge (WAS) but its effectiveness on the pre-treatment of mixed sludge is not known. This study explores the effectiveness of four different FNA concentrations (0, 2.49, 3.55, 4.62 mg N-HNO2/L) and three exposure times (2, 5, 9 h) lower than the ones reported in literature (24 h) on WAS characteristics and specific methane production (SMP). FNA pre-treatment reduced sludge cell viability below 10% in all cases after an exposure time of 5 h, increasing the solubility of the organic matter. The treated mixed sludge was used as substrate for the biochemical methane production tests to assess its SMP. Results showed a significant increase (up to 25%) on SMP when the sludge was pretreated with the lowest FNA concentration (2.49 mg N-HNO2/L) during 2 and 5 h but did not show any improvement at longer exposure times or higher FNA concentrations. © 2016 Elsevier Ltd. Source

Malek P.,University of Edinburgh | Ortiz J.M.,FCC Aqualia | Schulte-Herbruggen H.M.A.,University of Edinburgh
Desalination | Year: 2016

A novel directly coupled wind-electrodialysis system (wind-ED) with no energy storage was developed. The aim was to perform laboratory experiments, investigating the impact of wind speed (2-10 m/s), turbulence intensities (0-0.6 TI), and periods of oscillation (0-180 s) on desalination performance and energy consumption. The system produced good quality drinking water (< 600 mg/L NaCl) over the range of parameters tested. Water production and energy consumption increased with wind speed, until both parameters levelled off at wind speeds above the rated value of the wind turbine (vrated: 7.9-8.4 m/s). The impact of wind speed fluctuations on system performance was insignificant up to a TI of 0.4 (i.e., moderate fluctuations). The water production declined under high turbulence intensity fluctuations (TIs ≥ 0.5) and long periods of oscillation (> 40 s). The main challenge in direct coupling of ED to wind energy was not the magnitude of fluctuations but the impact of power cycling off during long periods of oscillation and lengthy periods of no wind. Interestingly, the specific energy consumption of the process remained relatively unaffected by the fluctuations, suggesting the system to be an electrically robust and reliable off-grid desalination technique for remote water stressed locations. © 2015 Elsevier B.V. Source

Morales N.,University of Santiago de Compostela | Val del Rio A.,University of Santiago de Compostela | Vazquez-Padin J.R.,FCC Aqualia | Mendez R.,University of Santiago de Compostela | And 3 more authors.
Chemosphere | Year: 2015

Nowadays the application of Anammox based processes in the wastewater treatment plants has given a step forward. The new goal consists of removing the nitrogen present in the main stream of the WWTPs to improve their energetic efficiencies. This new approach aims to remove not only the nitrogen but also to provide a better use of the energy contained in the organic matter. The organic matter will be removed either by an anaerobic psychrophilic membrane reactor or an aerobic stage operated at low solids retention time followed by an anaerobic digestion of the generated sludge. Then ammonia coming from these units will be removed in an Anammox based process in a single unit system. The second strategy provides the best results in terms of operational costs and would allow reductions of about 28%.Recent research works performed on Anammox based processes and operated at relatively low temperatures and/or low ammonia concentrations were carried out in single-stage systems using biofilms, granules or a mixture of flocculent nitrifying and granular Anammox biomasses. These systems allowed the appropriated retention of Anammox and ammonia oxidizing bacteria but also the proliferation of nitrite oxidizing bacteria which seems to be the main drawback to achieve the required effluent quality for disposal. Therefore, prior to the implementation of the Anammox based processes at full scale to the water line, a reliable strategy to avoid nitrite oxidation should be defined in order to maintain the process stability and to obtain the desired effluent quality. If not, the application of a post-denitrification step should be necessary. © 2015 Elsevier Ltd. Source

Morales N.,FCC Aqualia | Val Del Rio A.,University of Santiago de Compostela | Vazquez-Padin J.R.,FCC Aqualia | Gutierrez R.,FCC Aqualia | And 7 more authors.
Water Science and Technology | Year: 2015

The anammox-based process ELAN® was started-up in two different sequencing batch reactor (SBR) pilot plant reactors treating municipal anaerobic digester supernatant. The main difference in the operation of both reactors was the dissolved oxygen (DO) concentration in the bulk liquid. SBR-1 was started at a DO value of 0.4 mg O2/L whereas SBR-2 was started at DO values of 3.0 mg O2/L. Despite both reactors working at a nitrogen removal rate of around 0.6 g N/(L d), in SBR-1, granules represented only a small fraction of the total biomass and reached a diameter of 1.1 mm after 7 months of operation, while in SBR-2 the biomass was mainly composed of granules with an average diameter of 3.2 mm after the same operational period. Oxygen microelectrode profiling revealed that granules from SBR-2 where only fully penetrated by oxygen with DO concentrations of 8 mg O2/L while granules from SBR-1 were already oxygen penetrated at DO concentrations of 1 mg O2/L. In this way granules from SBR-2 performed better due to the thick layer of ammonia oxidizing bacteria, which accounted for up to 20% of all the microbial populations, which protected the anammox bacteria from non-suitable liquid media conditions. © 2015 IWA Publishing. Source

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