Assessment of microalgae and nitrifiers activity in a consortium in a continuous operation and the effect of oxygen depletion

AbstractBackgroundIndustrial wastewaters with a high content of nitrogen are a relevant environmental problem. Currently, treatments to remove nitrogen are not efficient, so is necessary to develop alternative methods. The objective of this study is to investigate a consortium of microalgae — nitrifying, that due to the symbiosis between them could be an interesting alternative.ResultsIn this study, it was possible to obtain a consortium of nitrifying bacteria (NB) and microalgae (MA) capable of operating with low requirements of dissolved oxygen, using aerobic sludge from wastewater treatment plants. During the operation, this consortium presents removal percentages above 98% of ammonia, even at concentrations of DO of 0.5mgO2L-1. It is estimated that the removal was caused both by the action of nitrifying bacteria and microalgae. It was determined that approximately 60% of the ammonia feed was oxidized to nitrate by nitrifying bacteria, while the algae assimilated 40% of the nitrogen feed at steady state. A methodology for measuring the specific activities of nitrifying bacteria and microalgae by comparing the rates in the variation inorganic nitrogen compounds was established with satisfactory results. An average specific activity of 0.05 and 0.02gNH4+gVSS-1d-1 for nitrifying bacteria and microalgae was determined, respectively.ConclusionsThe consortium it can be obtained in a single continuous operation, and has a high capacity for nitrogen removal with low oxygen content. The consortium could prove to be a more economical method compared to traditional

Treatment of gas-phase methanol in conventional biofilters packed with lava rock

The performance of laboratory scale methanol-degrading biofilters packed with lava rock was checked during almost 1 yr under different conditions. The biomass concentration and biomass adaptation of the inoculum dramatically affected the start-up and the performance of the systems during the first stages of operation. A fast start-up was obtained when using concentrated and adapted inocula, while diluted or non-adapted inocula proved to be much less efficient. The performance of the reactor during long-term operation was significantly affected by the toxic load and moisture content of the gas. Critical loads between 120 and 280 g/m3h were reached during different phases of the study. The reactor had a high stability to EBRT changes when working at values between 48.0 and 91.1 s, showing little or no negative effect when decreasing the EBRT. Hardly any difference was observed regarding performance when using either a downflow or upflow feed, although slightly better results were obtained when working in a downflow mode

Anaerobic Nitrogen Removal: The start-up of an Anammox Reactor with pre-treated Real wastewater from the Anaerobic Digestion of municipal solid waste

In this study, wastewater produced by the Anaerobic Digestion of municipal solid waste and pre-treated by partial-nitrification was fed to a granular Anammox reactor. A conservative exponential Law was used to slowly replace the synthetic wastewater for the pre-treated wastewater, starting at 10%. This strategy was adopted in order to avoid stressful conditions to bacteria, which could thus acclimate to the reactor conditions. The experiment was divided in two phases, the first one with increasing real wastewater ratio and a second phase totally fed with real wastewater. The influent is characterized by a nitrogen loading rate of 1.5gNL-1d-1, with a NO2-N/NH4-N ratio of 1.20. Removal efficiencies were stable during all experiment, around 90%. The Anammox activity also increased during the experimentation. The Volatile suspended solids grown during phase 1 of experiment, with an initial value of 4,2 gVSSL-1. The kinetics assay results also helped checking out the removal rates for ammonium and nitrite, and production rates for nitrate. On the average the specific nitrate and ammonium removal rate, with continues NLR was 0,370,07 g NO2-N gVSS-1d-1 and 0,270,07 gNH4-N/gVSS-1d-1, respectively. For nitrate production was 0,0550,030 gNO3-NgVSS-1d-1, The organic carbon removal was also tested. The effluent values were variable, and real wastewater had no direct effect on the capability of the Anammox process to remove organic carbon. This is due to a perfect partial-nitrification, who allowed the real effluent to have low organic carbon, which not developed inhibition effect to the Anammox bacteria. During phase 2, the reactor was fed with real wastewater without any pre-treatment. This experiment wasn’t very successful, and Anammox system failed. After, was again fed with synthetic wastewater and the bacteria could recover. Results showed that the process can work with this type of wastewater, if a conservative start-up strategy is adopted and a partial-nitrification step is used to remove organic carbon

A model-based methodology for managing technological risk

Imperial Users onl

Estimation of greenhouse gas emissions from industrial wastewater treatment plants

The outcome of Kyoto protocol and other National and International agreements influence the design and operation of wastewater treatment facilities by restricting their greenhouse gas (GHG) emissions. Wastewater treatment plants (WWTPs) are recognized as one of the larger minor sources of GHG emissions that produce CO 2 , CH 4 , and N 2 O during the treatment processes. The overall on-site and off-site greenhouse gas (GHG) emissions by WWTPs of food processing industry were estimated by using an elaborate mathematical model. Three different types of treatment systems were examined in this study which included aerobic, anaerobic, and hybrid anaerobic/aerobic processes. The overall on-site emissions were 1952, 1992, and 2435 kg CO 2 e/d while the off-site emissions were 1313, 4631, and 5205 kg CO 2 e/d for the aerobic, anaerobic and hybrid treatment systems respectively. The on-site biological processes made the highest contribution to GHG emissions in the aerobic treatment system while the highest emissions in anaerobic and hybrid treatment systems were obtained by off-site GHG emissions due to on-site material usage. Biogas recovery and reuse as fuel were shown to cover the total energy needs of the treatment plants for aeration, heating and electricity for all three types of operations, and considerably reduced GHG emissions by 512, 673, and 988 kg CO 2 e/d from a total of 3265, 6623, and 7640 kg CO 2 e/d for aerobic, anaerobic, and hybrid treatment systems, respectively. In the end, recommendations were given on feasible approaches to reduce GHG emissions from WWTPs

Modern use of modified Sequencing Batch Reactor in wastewater Treatment

If wastes are not properly managed, it may seep into the earth and aquifers, polluting both the surface and the water table. For public health reasons, leachate is considered a major environmental hazard due of its poisonous and hardy components. Because of this, it must be collected and processed adequately before being released into nature. Currently, there is no single unit procedure for appropriate leachate treatment since traditional wastewater treatment techniques are unable to degrade harmful chemicals contained in the leachate to a suitable level. Consequently, there has been an increase in the study of various leachate treatment procedures in order to maximise operational versatility. Various strategies have been used to degrade the leachate based on its properties, discharge requirements, technological possibilities, regulatory restrictions, and cost concerns. Sequencing batch reactor (SBR) treatment systems for landfill leachate were lauded for their operating flexibility, shock load resilience, and high biomass retention in the interest of long-term sustainability for the environment. Therefore, the current work objective is a deeper study of the features of SBR to identify prospects and unresolved problems in this process. The content analysis method of scientific publications from rating journals indexed in Scopus, PubMed, ScienceDirect, ResearchGate, Google Scholar on the totality of the keywords of this study in various combinations was applied; selection and synthesis of the main characteristics SBR to identify gaps in this area and prospects for future research. An in-depth analysis of the benefits and drawbacks of different leachate degrading processes is provided in this article. The role of integrated leachate treatment technologies with SBR was also highlighted. The effects of various materials, techniques, tactics, and configurations on leachate treatment were also explored in the paper. Critiqued SBR system environmental and operational factors were addressed. Readers of this work are expected to get a better understanding of SBR studies for leachate treatment and to use this information as a guide for their own research in this field. It uses the fill and draw activated sludge system with clarifier and intermittent aeration mode, where all the metabolic reactions and the separation of solid-liquid takes place in a unit tank through a timed control sequence in a non-steady state, variable capacity and suspended growth biological wastewater treatment system. The simultaneous nitrification, denitrification, and phosphorus removal are made possible by combining anaerobic and aerobic processes

A Hierarchical Approach to Equilibrium Cycle Nuclear Fuel Analysis.

This research involved developing an expert system that allows a nuclear fuel engineer to quickly provide answers to strategic nuclear fuel management questions, which are typically broad based. Current nuclear fuel analysis research concentrates on getting more accurate and precise answers at the expense of using large computer programs to get answers that are too specific to answer the broad based questions. The expert system brings together several artificial intelligence techniques to allow a nuclear fuel engineer to consider several scenarios in a general way in order to quickly answer the fuel management questions asked. The expert system is based upon a hierarchy of several abstraction levels using a constraint propagation system at the lowest level. The constraint propagation system prevents a novice nuclear fuel engineer from studying a scenario with input conditions that contradict standard nuclear fuel management relationships. The other abstraction levels include generic number representations, generic mathematical operators, and generic relationships for economic analysis. The highest level of the hierarchy is the knowledge base for nuclear fuel analysis of the equilibrium nuclear fuel cycle. The simplicity of adding other number representations to the expert system is demonstrated by implementing an interval number representation. Since the mathematical operators used at the knowledge domain level are generic, any new number representations, such as fuzzy numbers, could be added without having to change the basic domain knowledge. An example session shows how the system can be used to provide guidance to a nuclear fuel analyst in search of a good nuclear fuel management strategy. By using the interval number representation, the example session includes a simple sensitivity study on how some of the input variables\u27 uncertainty affects the objective variable\u27s value

Seleção de bactérias produtoras de PHB utilizando efluentes

Mestrado em Biotecnologia - Biotecnologia Industrial e AmbientalPolyhydroxybutyrate is a type of biodegradable plastic, fully synthesized by bacteria, with similar properties to the ones of conventional plastics. This biopolymer can be produced by mixed cultures (activated sludge form waste water treatment plants) using the volatile fatty acids present in waste streams. Although the huge potential of this process, its application for the industrial production of PHB still lacks development. Throughout this work, three different strategies to obtain PHB-producing bacteria by using waste streams were tested. In the first one PHB-producing bacteria were first selected by aerobic dynamic feeding conditions, while simultaneously providing hydrogen gas, followed by an accumulation stage. In the second strategy the conventional aerobic dynamic feeding conditions were imposed, followed by an accumulation stage. And a third one, where a mixed culture was straightly submitted to the accumulation stage, without previous selection. Aerobic dynamic feeding was operated in cycles og 8 hours (3 cycles per day). In the first two strategies, feast phase was intended to last 2h30 and the famine 5h30 for a feast/famine ratio of 0.45. While the accumulation stage lasted 22 hours. High biomass concentration were achieved using strategy 1, in a stable reactor, and it was possible to accumulate PHB up to 59 % of the VSS with a PHB production yield of 0.30 g SLB/g COD fed. The second strategy resulted in less stable rectors, and a PHB content of 40 % of the VSS was achieved, but with PHB production yields as low as 0.09 g PHB/ g COD. Furthermore, it was no always possible to produce PHB as carbon source seemed to be directed to other metabolic pathways. A PHB production yields of 0.31 g PHB/g COD consumed was achieved with the third strategy, although only with a PHB content of 21 % of VSS. The production of PHB was verified firstly by a thermogravimetric method developed at Avecom previously to this work. This method was replaced by other that comprises the extraction of PHB using 1,2 propylene carbonate as solvent. The development of this method is also addressed in this project.Polihidroxibutirato é um tipo de plástico biodegradável, completamente sintetizado por bactérias, com propriedades semelhantes aos plásticos convencionais. Este biopolímero pode ser produzito por culturas mistas (lamas ativadas de estações de tratamento de águas) usando os ácidos orgânicos voláteis presentes no efluente. Embora este processo apresente um enorme potencial, ainda é necessário o seu desenvolvimento para a sua aplicação na produção de PHB a escala industrial. Durante este trabalho, foram testadas três estratégias diferentes para a seleção de bactérias produtoras de PHB forma testadas. A primeira, em que as bactérias produtoras de PHB foram primeiro selecionadas por condições de alimentação dinâmica aeróbia, com a alimentação simultânea de hidrogénio, seguida de uma fase de acumulação. Uma segunda estratégia, onde a alimentação dinâmica aeróbia foi utilizada, seguida de uma etapa de acumulação. E uma terceira, em que uma cultura mista foi imediatamente submetida a uma fase de acumulação, sem seleção prévia. Nas duas primeiras estratégias a alimentação dinâmica aeróbia consistiu em ciclos de 8 horas (3 ciclos por dia), em que se pretendeu-se que a fase de fartura durasse 2h30 A fase de fome por seu lado durou 5h30 para um rácio fome/fartura de 0.45. A fase de acumulação durou 22 horas. Foram atingidas altas concentrações de biomassa usando a estratégia 1, num reactor estável, em que foi possível atingir um conteúdo em PHB de 59 % dos SSV, com um rendimento de produção de PHB de 0.30 g SLB/g CQO alimentado. A segunda estratégia resultou num reactor menos estável. Um conteúdo em PHB de 40 % dos SSV foi obtido, embora o rendimento de produção de PHB tenho sido só 0.09 g PHB/g CQO. Para além isso, nem sempre foi possível produzir PHB, visto que a fonte de carbono parecia ser direcionada para outras vias metabólicas. Foi atingido um rendimento de produção de PHB de 0.31 PHB/g CQO na terceira estratégia, no entanto o conteúdo em PHB foi só 21 % dos SSV. A produção de PHB foi inicialmente verificada por um método termogavimétrico desenvolvido na Avecom previamente a este trabalho. Este método foi posteriormente substituído por outro que envolve a extração de PHB usando carbonato de propileno como solvente. O desenvolvimento deste método é abordado no presente trabalho

Feasibility of Ultraviolet Light Emitting Diodes as an Alternative Light Source for Photocatalysis

The objective of this study was to determine whether ultraviolet light emitting diodes (UV-LEDs) could serve as an alternative photon source efficiently for heterogeneous photocatalytic oxidation (PCO). An LED module consisting of 12 high-power UV-A LEDs was designed to be interchangeable with a UV-A fluorescent black light blue (BLB) lamp in a Silica-Titania Composite (STC) packed bed annular reactor. Lighting and thermal properties were characterized to assess the uniformity and total irradiant output. A forward current of (I(sub F)) 100 mA delivered an average irradiance of 4.0 m W cm(exp -2), which is equivalent to the maximum output of the BLB, but the irradiance of the LED module was less uniform than that of the BLB. The LED- and BLB-reactors were tested for the oxidization of 50 ppmv ethanol in a continuous flow-through mode with 0.94 sec space time. At the same irradiance, the UV-A LED reactor resulted in a lower PCO rate constant than the UV-A BLB reactor (19.8 vs. 28.6 nM CO2 sec-I), and consequently lower ethanol removal (80% vs. 91%) and mineralization efficiency (28% vs. 44%). Ethanol mineralization increased in direct proportion to the irradiance at the catalyst surface. This result suggests that reduced ethanol mineralization in the LED- reactor could be traced to uneven irradiance over the photocatalyst, leaving a portion of the catalyst was under-irradiated. The potential of UV-A LEDs may be fully realized by optimizing the light distribution over the catalyst and utilizing their instantaneous "on" and "off' feature for periodic irradiation. Nevertheless, the current UV-A LED module had the same wall plug efficiency (WPE) of 13% as that of the UV-A BLB. These results demonstrated that UV-A LEDs are a viable photon source both in terms of WPE and PCO efficiency