RESUMEN
The objective of this study was to improve the nitrogen removal efficiency and reduce the start-up period of a single-stage partial nitritation-anammox (SPNA) system using iron particle-integrated anammox granules (IP-IAGs). Anammox granules were enriched in sequencing batch and expanded granular sludge bed (EGSB) reactors. The EGSB reactor produced larger and more uniform granules with higher specific anammox activity. IP-IAGs were then inoculated into a two-stage partial nitritation-anammox reactor treating anaerobic digestion (AD) effluent, followed by an internal recirculation strategy to acclimate the granules to oxygen exposure for SPNA. Finally, the SPNA process operated to treat real AD effluent under optimal conditions of 0.05 L/min aeration intensity (0.01 vvm) and 24 h of hydraulic retention time, achieving TNRE of 86.01 ± 2.64 % and nitrogen removal rate of 0.74 ± 0.04 kg-N/m3·d for 101 d.
Asunto(s)
Reactores Biológicos , Nitrificación , Nitrógeno , Aguas del Alcantarillado , Anaerobiosis , Aguas del Alcantarillado/microbiología , Oxidación-Reducción , Eliminación de Residuos Líquidos/métodos , Purificación del Agua/métodosRESUMEN
The internal recirculation plays an important role on the different biological processes of wastewater treatment plants because it has a great influence on the concentration of pollutants, especially nutrients. Usually, the internal recirculation flow rate is kept fixed or manipulated by control techniques to maintain a fixed nitrate set-point in the last anoxic tank. This work proposes a new control strategy to manipulate the internal recirculation flow rate by applying a fuzzy controller. The proposed controller takes into account the effects of the internal recirculation flow rate on the inlet of the biological treatment and on the denitrification and nitrification processes with the aim of reducing violations of legally established limits of nitrogen and ammonia and also reducing operational costs. The proposed fuzzy controller is tested by simulation with the internationally known benchmark simulation model no. 2. The objective is to apply the proposed fuzzy controller in any control strategy, only replacing the manipulation of the internal recirculation flow rate, to improve the plant operation.Therefore, it has been implemented in five operation strategies from the literature, replacing their original internal recirculation flow rate control, and simulation results are compared with those of the original strategies. Results show improvements with the application of the proposed fuzzy controller of between 2.25 and 57.94% in reduction of total nitrogen limit violations, between 55.22 and 79.69% in reduction of ammonia limit violations and between 0.84 and 38.06% in cost reduction of pumping energy.
Asunto(s)
Aguas Residuales , Purificación del Agua , Lógica Difusa , Nitrificación , Nitrógeno/análisisRESUMEN
Wastewater treatment plants (WWTPs) are important routes for releasing microplastics into the environment, with the produced sludge acting as a recipient of microplastics from wastewater. There is little information on the impact of sludge processes on the number of microplastics in sludge. In this study, the presence of microplastics in sludge produced by the Sari WWTP in northern Iran was investigated. Samples were taken in 3 replications and microplastics larger than 37 µm were extracted. The sludge from primary settling tank, clarifier, after sludge thickener and after aerobic digester, and after dewatering contained 214, 206, 200, 238, and 129 microplastics/g dry weight, respectively. According to the amount of sludge produced for each unit, this equals 280, 362, 599, 601, and 276 million microplastics/day, respectively, of which more than 85% were fibers. The numbers of microplastics in the sludge from the output of the sludge thickener and the aerobic digester did not significantly differ. However, their numbers decreased by more than 50% after dewatering, probably due to the destruction of flocs in the digestive process and the release of attached microplastics, which are returned into the wastewater treatment process with the rejected water. Polyester and polyethylene were the predominant types of fibers and particles, respectively. Given the annual amount of sludge produced, more than 100 billion microplastics enter the environment per year. Wastewater sludge, therefore, is an important source for the emission of microplastics, especially fibers, to the environment, warranting further evaluation of the associated environmental hazards.
Asunto(s)
Contaminantes Químicos del Agua , Purificación del Agua , Monitoreo del Ambiente , Irán , Microplásticos , Plásticos , Aguas del Alcantarillado , Eliminación de Residuos Líquidos , Aguas Residuales , Contaminantes Químicos del Agua/análisisRESUMEN
A design-based dynamic simulation tool was developed to evaluate the effects of altered operation conditions on the performance of a landfill leachate treating pre-anoxic oxidation ditch folowed by external ultra filtration and nano filtration membranesby using the actual influent data and operational constants collected for 18 months. In the summer of 2017, the MBR suffered from reduced membrane fluxes due to deterioration of activated sludge flocs after the failure of flow booster providing the internal circulation and decreasing influent C/N ratio. Although two external pumps were activated in place of the broken flow booster, the required internal recirculation ratio (IR) predicted by the simulation could not be provided. It was concluded that due to low IR, the activated sludge retaining longer in the anoxic tank lost its floc integrity and caused decreased membrane fluxes. Simulation findings also showed that if the COD/N ratio drops below 4.8, no matter how high the IR is, it is unlikely to achieve a NOx-N concentration below 30 mg/l in the effluent. On the other hand, contrary to expectations, both the actual and estimated nitrification efficiencies were very high due to the moderately high temperature (>20 °C) and DO (2-3 mg/l) values in the aerobic basin.
Asunto(s)
Nitrógeno , Contaminantes Químicos del Agua , Reactores Biológicos , Desnitrificación , Nitrificación , Aguas del AlcantarilladoRESUMEN
The pollutant removal performance of traditional horizontal subsurface flow (HSSF) constructed wetlands (CWs) is limited because of the dissolved oxygen (DO) supply is insufficient. The aeration of HSSF CWs usually improves their pollutant removal performance, but a high DO induces the accumulation of nitrate-nitrogen (NO3--N) and suppresses the improvement of total nitrogen (TN) removal. In this study, an integrated solution that involved in-tank front aeration and internal recirculation (FAIR) was used to improve the pollutant removal performance of HSSF CWs. Based on the experimental results, the FAIR system significantly increased the removal efficiencies of biochemical oxygen demand (BOD) from 53.8-76.0% to 82.0-91.7% and reduced the BOD concentration in the effluent to below 10 mg L-1. The removal efficiency of ammonia-nitrogen (NH3-N) increased from 15.1-78.3% to 98.5-98.6% while the removal efficiencies of the total Kjeldahl nitrogen (TKN) of the control and FAIR HSSF CWs were 18.2-77.1% and 93.5-94.3%, respectively. HSSF CWs with FAIR outperformed aerated HSSF CWs in the removal of NH3-N and TKN. The effects of two recirculation flow ratios (Rr = recirculation flow rate/influent flow rate), 14.3 and 3.0, on the improvement of pollutant removal performance were investigated. The lower Rr did not significantly affect the improvement of BOD, NH3-N, and TKN, but a higher Rr resulted in more severe accumulation of NO3--N. The removal efficiency of TN in control HSSF CWs ranged from 20.4% to 75.5%, and in the FAIR HSSF CW was 71.6% for Rr = 14.3 and 81.3% for Rr = 3.0. However, the FAIR system did not enhance the removal performance of total phosphorus, suggesting that the DO level and internal recirculation were not dominant mechanisms for the removal of phosphorous. The easy maintenance of the FAIR system made it a superior modification for improving the pollutant removal performance of HSSF CWs.
Asunto(s)
Contaminantes Ambientales , Humedales , Amoníaco , Nitrógeno , Fósforo , Eliminación de Residuos LíquidosRESUMEN
A sulfur cycle-driven bioprocess was developed for co-treatment wet flue gas desulfurization wastes with municipal sewage, as a result of sludge minimization. In this process, organics removal (one of the main objectives in sewage treatment) is closely associated with biological sulfate/sulfite reduction (BSR). In the previous studies, both the pros and corns of sulfite (SO32-) in microbial activities were demonstrated. In this study, we are motivated to unveil the detailed role of SO32- in organic compound removal in the sulfur conversion-associated process. In addition, the effect of internal recirculation (IR) of UASB reactor was also explored. The results demonstrated that sulfite does inhibit the organic removal rate via depressing the acetate oxidation to inorganic carbon. And the inhibition is reversible when influent sulfite concentration decreased from 400 to 132â¯mgâ¯S/L, corresponding to the relative sulfate/sulfite-reducing genera increased from 18.66 to 38.62%. And the fermenting-related bacteria significantly decreased when an internal recirculation was employed for the UASB reactor. The results of this study could shed light on the understanding of the roles of sulfite and IR in organic compound removal performance and microbial community structures in BSR, which could be in turn beneficial to optimize the organic removal capacity of the sulfur bionconversion-concerning sewage treatment technology.