Carbó inorgànic per millorar la depuració d'aigües residuals

Les estacions depuradores d'aigües residuals són reactors biològics on es cultiva una població complexa de microorganismes que degraden la matèria orgànica present en el medi. En aquest treball s'ha estudiat una possible via per eliminar, a més de la matèria orgànica, el nitrogen i el fòsfor, que afecten la riquesa de nutrients dels ecosistemes.Las estaciones depuradoras de aguas residuales son reactoresbiológicos donde es cultiva una población compleja de microorganismosque degradan la materia orgánica presente en el medio. En este trabajose ha estudiado una posible vía para eliminar, además de la materiaorgánica, el nitrógeno y el fósforo, que afectan a la riqueza de nutrientesde los ecosistemasWastewater Treatment Plant biological reactors where a complexpopulation of microorganisms is grown degrading the organic matter ofthe wastewater. In this work, researchers have studied a possible way toeliminate, as well as organic matter, nitrogen and phosphorus, twoelements that affect nutrients richness of ecosystems

La lluita biològica contra l'eutrofització

La presència de nitrogen i fòsfor a les aigües residuals afavoreix l'eutrofització, que genera un excessiu creixement d'algues, provocant una situació de limitació d'oxigen i la mort de gran part dels éssers vius. Actualment, el fòsfor s'elimina majoritàriament de manera físico-química, en les estacions depuradores d'aigües residuals. Una alternativa més eficient i sostenible és el procés d'eliminació biològica de fòsfor, que consisteix en afavorir el creixement d'uns bacteris capaços d'acumular fòsfor en quantitats superiors a les normals. El present treball arriba a unes sorprenents conclusions sobre la capacitat d'aquests bacteris per eliminar el fòsfor usant els nitritis o els nitrats com a acceptors d'electrons.La presencia de nitrógeno y fósforo en las aguas residuales favorece la eutrofización, que genera un excesivo crecimiento de algas, provocando una situación de limitación de oxígeno y la muerte de gran parte de los seres vivos. Actualmente, el fósforo se elimina mayoritariamente de manera físico-química, en las estaciones depuradoras de aguas residuales. Una alternativa más eficiente y sostenible es el proceso de eliminación biológica del fósforo, que conssite en favorecer el crecimiento de unas bacterias capaces de acumular fósforo en cantidades superiores a las normales. El presente trabajo llega a unas sorprendentes conclusiones sobre la capacidad de estas bacterias para eliminar el fósforo usando los nitritos o los nitratos como aceptores de electrones

Recuperació de sofre elemental a partir d'aigües residuals industrials : una nova aplicació dels sistemes bioelectroquímics

Moltes indústries generen aigües residuals i gasos amb un alt contingut de sulfat. Aquest no és perjudicial pero si és abocat al clavegueram o rius, alguns bacteris el transformen en sulfur d'hidrogen, el qual és tòxic i corrosiu. D'aquí surgeix la importància i necessitat de desenvolupar noves tecnologies, tals com les recents tecnologies bioelectroquímiques, per tractar-les i fins i tot, per reutilitzar i recuperar els compostos de sofre. En aquest estudi, s'utilitzen per primer cop aigües residuals reals industrials procedents del tractament de gasos, on es demostra que gràcies a aquestes tecnologies bioelectroquímiques es propicia el creixement dels bacteris que permeten la recuperació de sofre elemental.Muchas industrias generan aguas residuales y gases con un alto contenido en sulfato. Este no es perjudicial pero si se vierte en colectores o ríos algunas bacterias lo transforman en sulfuro de hidrógeno, el cual es tóxico y corrosivo. De aquí surge la importancia y necesidad de desarrollar nuevas tecnologías, tales como las tecnologías bioelectroquímicas, para tratar e incluso reutilizar y recuperar compuestos de azufre. En este estudio, se utilizan por primera vez aguas residuales reales industriales procedentes del tratamiento con gases, donde se demuestra que gracias a estas tecnologías bioelectroquímicas se propicia el crecimiento de las bacterias que permiten la recuperación de azufre elemental.Industrial activities generate wastewater and gases with high sulfate content. Sulfate is not harmful but if it is disposed into sewers or rivers, some bacteria transform them into hydrogen sulfide, which is toxic and corrosive. Hence the importance and need to develop new technologies, such as microbial bioelectrochemical technologies, to treat and even reuse and recover sulfur compounds. In this study, real industrial wastewater from the treatment of gases is used for the first time demonstrating that bioelectrochemical technologies improve the growth of bacteria that favors the elemental sulfur recovery

Exploring GHG emissions in the mainstream SCEPPHAR configuration during wastewater resource recovery

Acord transformatiu CRUE-CSICThe wastewater sector paradigm is shifting from wastewater treatment to resource recovery. In addition, concerns regarding sustainability during the operation have increased. In this sense, many water utilities have become aware of the potential GHG emissions during the operation of wastewater treatment. This study assesses the nitrous oxide and methane emissions during the long-term operation of a novel wastewater resource recovery facility (WRRF) configuration: the mainstream SCEPPHAR. The long-term NO and CH emission factors calculated were in the low range of the literature, 1 % and 0.1 %, respectively, even with high nitrite accumulation in the case of NO. The dynamics and possible sources of production of these emissions are discussed. Finally, different aeration strategies were implemented to study the impact on the NO emissions in the nitrifying reactor. Results showed that operating the pilot-plant under different dissolved oxygen concentrations (between 1 and 3 g O m) did not have an effect on the NO emission factor. Intermittent aeration was the aeration strategy that most mitigated the NO emissions in the nitrifying reactor, obtaining a reduction of 40 % compared to the normal operation of the pilot plant

A review on the integration of mainstream P-recovery strategies with enhanced biological phosphorus removal

Acord transformatiu CRUE-CSICPhosphorus (P), an essential nutrient for all organisms, urgently needs to be recovered due to the increasing demand and scarcity of this natural resource. Recovering P from wastewater is a feasible and promising way widely studied nowadays due to the need to remove P in wastewater treatment plants (WWTPs). When enhanced biological P removal (EBPR) is implemented, an innovative option is to recover P from the supernatant streams obtained in the mainstream water line, and then combine it with liquor-crystallisation recovery processes, being the final recovered product struvite, vivianite or hydroxyapatite. The basic idea of these mainstream P-recovery strategies is to take advantage of the ability of polyphosphate accumulating organisms (PAO) to increase P concentration under anaerobic conditions when some carbon source is available. This work shows the mainstream P-recovery technologies reported so far, both in continuous and sequenced batch reactors (SBR) based configurations. The amount of extraction, as a key parameter to balance the recovery efficiency and the maintenance of the EBPR of the system, should be the first design criterion. The maximum value of P-recovery efficiency for long-term operation with an adequate extraction ratio would be around 60%. Other relevant factors (e.g. COD/P ratio of the influent, need for an additional carbon source) and operational parameters (e.g. aeration, SRT, HRT) are also reported and discussed

Exploring key operational factors for improving hydrogen production in a pilot-scale microbial electrolysis cell treating urban wastewater

Altres ajuts: acords transformatius de la UABBioelectrochemical systems (BES) are becoming popular technologies with a plethora of applications in the environmental field. However, research on the scale-up of these systems is scarce. To understand the limiting factors of hydrogen production in microbial electrolysis cell (MEC) at pilot-scale, a 135 L MEC was operated for six months under a wide range of operational conditions: applied potential [0.8-1.1 V], hydraulic residence time [1.1-3.9 d], and temperature [18-30 °C], using three types of wastewater; synthetic (900 mg CODs L−1), raw urban wastewater (200 mg CODs L−1) and urban wastewater amended with acetate (1000 mg CODs L−1). The synthetic wastewater yielded the maximum current density (1.23 A m−2) and hydrogen production (0.1 m3 m−3 d−1) ever reported in a pilot scale MEC, with a cathodic recovery of 70% and a coulombic efficiency of 27%. In contrast, the use of low COD urban wastewater limited the plant performance. Interestingly, it was possible to improve hydrogen production by reducing the hydraulic residence time, finding the optimal applied potential or increasing the temperature. Further, the pilot plant demonstrated a robust capacity to remove the organic matter present in the wastewater under different conditions, with removal efficiencies above 70%. This study shows improved results compared to similar MEC pilot plants treating domestic wastewater in terms of hydrogen production and treatment efficiency and also compares its performance against conventional activated sludge processes

Benefits and drawbacks of integrating a side-stream sludge fermenter into an A2O system under limited COD conditions

Altres ajuts: acords transformatius de la UABThe implementation of a side-stream sludge fermenter (SSSF) has been identified as a possible solution to improve the performance of an anaerobic/anoxic/aerobic (A2O) configuration when treating low COD wastewater. This study systematically evaluated the effects of incorporating a SSSF into an A2O configuration (side-stream enhanced biological phosphorus removal, S2EBPR) for P/N/COD removal under a limited influent COD (CODINF) condition. The performance of the S2EBPR (with the SSSF receiving 6% of the recycled activated sludge and operating with a hydraulic retention time (HRT) of 2.4 d) and A2O were compared under the same limited CODINF (350 mg/L) condition. S2EBPR improved the amount of P removed (26.6%) under a low influent COD/P of only 26.3 compared with A2O of 32.6, and enhanced denitrification (11%) without compromising full ammonium and COD removal. However, the PLOAD to the plant increased due to the P-release in SSSF, resulting in higher effluent P concentration. The methane and energy recovery indexes were around 45% lower than those of A2O. Sequencing analysis revealed a high abundance of PAO in accordance to its higher P removal. This study represents a comprehensive evaluation of the S2EBPR configuration and provides an assessment of its suitability

Revealing the proliferation of hydrogen scavengers in a single-chamber microbial electrolysis cell using electron balances

The bioelectrochemical generation of hydrogen in microbial electrolysis cells (MECs) is a promising technology with many bottlenecks to be solved. Among them, the proliferation of hydrogen scavengers drastically reduces the cell efficiency leading to unrealistic coulombic efficiencies (CE) and cathodic gas recoveries (rCAT). This work provides a novel theoretical approach to understand, through electron equivalent balances, the fate of hydrogen in these systems. It was validated with a long term operated single-chamber membrane-less MEC. In the short term, H2-recycling (i.e. hydrogen being derived to the anode) resulted in rCAT of only 4% and in CE up to 463%. The 80.5% of the current intensity came from H₂-recycling and only the 19.5% from substrate oxidation. In the long term, methane was produced from hydrogen, thus decreasing rCAT to 0 (rCAT ¼ 94.5% when considering methane production). CE was 74.5% suggesting that H₂-recycling only took place when methanogenic activity was marginal

The selective role of nitrite in the PAO/GAO competition

Proliferation of Glycogen Accumulating Organisms (GAOs) accounts as one of the major bottlenecks in biological phosphorus removal systems. GAO outcompeting polyphosphate accumulating organisms (PAOs) results in lower P-removal. Thus, finding optimal conditions that favour PAO in front of GAO is a current focus of research. This work shows how nitrite can provide a novel strategy for PAO enrichment. A propionate-fed GAO- nriched biomass (70% Defluviicoccus I, 18% Defluviicoccus II and 10% PAO) was subjected more than 50 d under anaerobic-anoxic conditions with nitrite as electron acceptor. These operational conditions led to a PAO-enriched sludge (85%) where GAO were washed out of the system (<10%), demonstrating the validity of the new approach for PAO enrichment. In addition, the presented suppression of Defluviicocus GAO with nitrite represents an add-on benefit to the nitrite-based systems since the proliferation of non-desirable GAO can be easily ruled out and added to the other benefits (i.e. lower aeration and COD requirements)