RESUMEN
Sewage sludge is regarded by wastewater treatment plants as problematic, from a financial and managerial point of view. Thus, a variety of disposal routes are used, but the most popular is methane fermentation. The proportion of macromolecular compounds in sewage sludges varies, and substrates treated in methane fermentation provide different amounts of biogas with various quality and quantity. Depending on the equipment and financial capabilities for methane fermentation, different methods of sewage sludge pretreatment are available. This review presents the challenges associated with the recalcitrant structure of sewage sludge and the presence of process inhibitors. We also examined the diverse methods of sewage sludge pretreatment that increase methane yield. Moreover, in the field of biological sewage sludge treatment, three future study propositions are proposed: improved pretreatment of sewage sludge using biological methods, assess the changes in microbial consortia caused with pretreatment methods, and verification of microbial impact on biomass degradation.
Asunto(s)
Reactores Biológicos , Aguas del Alcantarillado , Aguas del Alcantarillado/química , Anaerobiosis , Fermentación , Metano , Biocombustibles , Eliminación de Residuos Líquidos/métodosRESUMEN
Under the Industrial Emissions Directive (IED), coke production wastewater must be treated to produce an effluent characterised by a total nitrogen (TN) <50â¯mg/L. An anoxic-aerobic activated sludge pilot-plant (1â¯m3) fed with coke production wastewater was used to investigate the optimal operational requirements to achieve such an effluent. The loading rates applied to the pilot-plant varied between 0.198-0.418â¯kg COD/m3.day and 0.029-0.081â¯kg TN/m3.day, respectively. The ammonia (NH4+-N) removals were maintained at 96%, after alkalinity addition. Under all conditions, phenol and SCN- remained stable at 96% and 100%, respectively with both being utilised as carbon sources during denitrification. The obtained results showed that influent soluble chemical oxygen demand (sCOD) to TN ratio of should be maintained at >5.7 to produce an effluent TN <50â¯mg/L. Furthermore, nitrite accumulation was observed under all conditions indicating a disturbance to the denitrification pathway. Overall, the anoxic-aerobic activated sludge process was shown to be a robust and reliable technology to treat coke making wastewater and achieve the IED requirements. Nevertheless, the influent to the anoxic tank should be monitored to ensure a sCOD:TN ratio >5.7 or, alternately, the addition of an external carbon source should be considered.
Asunto(s)
Desnitrificación , Residuos Industriales/análisis , Nitrógeno/metabolismo , Aguas del Alcantarillado/análisis , Eliminación de Residuos Líquidos/métodos , Aguas Residuales/análisis , Coque , Proyectos PilotoRESUMEN
Using waste sludge internal carbon source for nitrogen removal in wastewater has drawn much attention, due to its economic advantages and sludge reduction. In this study, the performance of enhanced denitrification with waste sludge thermal hydrolysate and fermentation liquid as carbon sources at different SCOD/N (soluble chemical oxygen demand/NO3--N) was investigated. The optimum SCOD/N was 8 for sludge thermal hydrolysate and 7 for fermentation liquid, with NO3--N removal efficiency of 92.3 and 98.9%, respectively, and no NO2--N accumulation. To further understand the fate of sludge carbon source during denitrification, the changes of SCOD, proteins, carbohydrates, and volatile fatty acids (VFAs) were analyzed, and three-dimensional fluorescence excitation-emission matrix (EEM) spectroscopy with fluorescence regional integration (FRI) analysis was introduced. The utilization of SCOD was consistent with NO3--N reduction, and the utilization efficiency of different organic matter was as follows: VFAs > proteins > carbohydrates. The soluble organic-like materials (region IV) were the most readily utilized organic matter according to three-dimensional fluorescence EEM spectroscopy. Regarding denitrification mechanisms, the denitrification rate (VDN), denitrification potential (PDN), heterotroph anoxic yield (YH), and the most readily biodegradable COD (SS) were also investigated.
Asunto(s)
Reactores Biológicos/microbiología , Carbono/análisis , Ácidos Grasos Volátiles/análisis , Aguas del Alcantarillado/química , Aguas Residuales/química , Purificación del Agua/métodos , Anaerobiosis , Análisis de la Demanda Biológica de Oxígeno , China , Desnitrificación , Fermentación , Nitrógeno/análisisRESUMEN
BACKGROUND: Cluster analysis is the most common unsupervised method for finding hidden groups in data. Clustering presents two main challenges: (1) finding the optimal number of clusters, and (2) removing "outliers" among the objects being clustered. Few clustering algorithms currently deal directly with the outlier problem. Furthermore, existing methods for identifying the number of clusters still have some drawbacks. Thus, there is a need for a better algorithm to tackle both challenges. RESULTS: We present a new approach, implemented in an R package called Thresher, to cluster objects in general datasets. Thresher combines ideas from principal component analysis, outlier filtering, and von Mises-Fisher mixture models in order to select the optimal number of clusters. We performed a large Monte Carlo simulation study to compare Thresher with other methods for detecting outliers and determining the number of clusters. We found that Thresher had good sensitivity and specificity for detecting and removing outliers. We also found that Thresher is the best method for estimating the optimal number of clusters when the number of objects being clustered is smaller than the number of variables used for clustering. Finally, we applied Thresher and eleven other methods to 25 sets of breast cancer data downloaded from the Gene Expression Omnibus; only Thresher consistently estimated the number of clusters to lie in the range of 4-7 that is consistent with the literature. CONCLUSIONS: Thresher is effective at automatically detecting and removing outliers. By thus cleaning the data, it produces better estimates of the optimal number of clusters when there are more variables than objects. When we applied Thresher to a variety of breast cancer datasets, it produced estimates that were both self-consistent and consistent with the literature. We expect Thresher to be useful for studying a wide variety of biological datasets.
Asunto(s)
Análisis por Conglomerados , Algoritmos , Neoplasias de la Mama/metabolismo , Neoplasias de la Mama/patología , Femenino , Humanos , Método de Montecarlo , Análisis de Componente PrincipalRESUMEN
Releases of organic compounds and phosphorus from phosphorus-accumulating granular sludge (PGS) and phosphorus-accumulating flocculent sludge (PFS) during low-temperature thermal pretreatment and anaerobic fermentation were investigated. Meanwhile, biogas production potential and microbial community structures were explored. The results indicate that much more soluble chemical oxygen demand (SCOD) and phosphorus were released from PGS than from PFS via low-temperature thermal pretreatment because of the higher extracellular polymeric substances (EPS) content in PGS and higher ratio of phosphorus reserved in EPS. Furthermore, PGS contains more anaerobes and dead cells, resulting in much higher SCOD and volatile fatty acids release from PGS than those from PFS during fermentation. PGS fermentation facilitated the n-butyric acid production, and PGS exhibited the hydrogen production potential during fermentation due to the presence of hydrogen-producing bacteria. Therefore, anaerobic fermentation combined with low-temperature thermal pretreatment can facilitate the recovery of carbon and phosphorus as well as producing hydrogen from PGS.
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Bacterias Anaerobias/metabolismo , Carbono/metabolismo , Frío , Fermentación , Hidrógeno/metabolismo , Fósforo/metabolismo , Aguas del Alcantarillado , Anaerobiosis , Biocombustibles , Carbono/química , Precipitación Química , Ácidos Grasos Volátiles , Hidrógeno/química , Fósforo/química , Aguas del Alcantarillado/química , Aguas del Alcantarillado/microbiologíaRESUMEN
Chemical treatment processes have mostly been considered as an efficient way for biosolid minimization. The improvement of sludge dewatering was more a welcome side-effect of these sequential processes. In this study, heat-activated sodium peroxydisulphate (PDS) and potassium peroxymonosulphate (MPS) were applied in order to disintegrate waste activated sludge (WAS). PDS and MPS treatment of WAS results in the polymer transfer of organic matter from the solid phase to the liquid phase. Our research work was done for chemical disintegration of WAS by PDS and MPS in doses of 0.2%, 0.4%, 0.6%, 0.8% and 1% (169.5, 339.0, 508.5, 678.0 and 847.5â mgâ [Formula: see text]) activated at temperatures of 60°C and 90°C for 30â min. The application of these methods causes the soluble chemical oxygen demand value to increase in the supernatant. In addition, there was a positive influence on the sludge volume index which decreased for the highest doses of PDS of over 63% and 77% and MPS of over 78% and 82% through heat activation at temperatures of 60°C and 90°C, respectively. Furthermore, MPS was more successful in the floc particle destruction, therefore it caused a higher sludge settlement acceleration (sedimentation/compaction speed) than PDS. The experimental results demonstrated that the application of heat-activated PDS and MPS may become a novel effective way of processing sewage sludge.
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Oxidantes/química , Peróxidos/química , Aguas del Alcantarillado/análisis , Aguas del Alcantarillado/microbiología , Eliminación de Residuos Líquidos/métodos , Análisis de la Demanda Biológica de Oxígeno , Floculación , CalorRESUMEN
This paper describes a series of studies on the effects of food waste disintegration using an ultrasonic generator and the production of volatile fatty acids (VFAs) by anaerobic hydrolysis. The results suggest that ultrasound treatment can significantly increase COD [chemical oxygen demand], proteins and reducing sugars, but decrease that of lipids in food waste supernatant. Ultrasound pre-treatment boosted the production of VFAs dramatically during the fermentation of food waste. At an ultrasonic energy density of 480W/L, we treated two kinds of food waste (total solids (TS): 40 and 100g/L, respectively) with ultrasound for 15min. The amount of COD dissolved from the waste increased by 1.6-1.7-fold, proteins increased by 3.8-4.3-fold, and reducing sugars increased by 4.4-3.6-fold, whereas the lipid content decreased from 2 to 0.1g/L. Additionally, a higher VFA yield was observed following ultrasonic pre-treatment.
Asunto(s)
Ácidos Grasos Volátiles/biosíntesis , Alimentos , Eliminación de Residuos/métodos , Sonido , Residuos/análisis , Anaerobiosis , Análisis de la Demanda Biológica de Oxígeno , Fermentación , HidrólisisRESUMEN
An integrated corn ethanol-methane fermentation system was proposed to solve the problem of stillage handling, where thin stillage was treated by anaerobic digestion and then reused to make mash for the following ethanol fermentation. This system was evaluated at laboratory and pilot scale. Anaerobic digestion of thin stillage ran steadily with total chemical oxygen demand removal efficiency of 98% at laboratory scale and 97% at pilot scale. Ethanol production was not influenced by recycling anaerobic digestion effluent at laboratory and pilot scale. Compared with dried distillers' grains with solubles produced in conventional process, dried distillers' grains in the proposed system exhibited higher quality because of increased protein concentration and decreased salts concentration. Energetic assessment indicated that application of this novel process enhanced the net energy balance ratio from 1.26 (conventional process) to 1.76. In conclusion, the proposed system possessed technical advantage over the conventional process for corn fuel ethanol production.
Asunto(s)
Biocombustibles/análisis , Biotecnología/métodos , Etanol/síntesis química , Semillas/química , Zea mays/química , Aminoácidos/análisis , Anaerobiosis , Alimentación Animal , Biomasa , Carbohidratos/análisis , Fermentación , Laboratorios , Proyectos Piloto , TermodinámicaRESUMEN
Anaerobic digestion of manure and other agricultural waste streams with subsequent energy production can result in more sustainable dairy operations; however, importation of digester feedstocks onto dairy farms alters previously established carbon, nutrient, and salinity mass balances. Salt and nutrient mass balance must be maintained to avoid groundwater contamination and salination. To better understand salt and nutrient contributions of imported methane-producing substrates, a mass balance for a full-scale dairy biomass energy project was developed for solids, carbon, nitrogen, sulfur, phosphorus, chloride, and potassium. Digester feedstocks, consisting of thickened manure flush-water slurry, screened manure solids, sudan grass silage, and feed-waste, were tracked separately in the mass balance. The error in mass balance closure for most elements was less than 5%. Manure contributed 69.2% of influent dry matter while contributing 77.7% of nitrogen, 90.9% of sulfur, and 73.4% of phosphorus. Sudan grass silage contributed high quantities of chloride and potassium, 33.3% and 43.4%, respectively, relative to the dry matter contribution of 22.3%. Five potential off-site co-digestates (egg waste, grape pomace, milk waste, pasta waste, whey wastewater) were evaluated for anaerobic digestion based on salt and nutrient content in addition to bio-methane potential. Egg waste and wine grape pomace appeared the most promising co-digestates due to their high methane potentials relative to bulk volume. Increasing power production from the current rate of 369 kW to the design value of 710 kW would require co-digestion with either 26800 L d(-1) egg waste or 60900 kg d(-1) grape pomace. However, importation of egg waste would more than double nitrogen loading, resulting in an increase of 172% above the baseline while co-digestion with grape pomace would increase potassium by 279%. Careful selection of imported co-digestates and management of digester effluent is required to manage salt and nutrient mass loadings and reduce groundwater impacts.