Anaerobic Digestion of Sewage Sludge Using Sequential Reactors: Start- Up and Systems Stabilization /Digestão Anaeróbia De Lodo De Esgoto Utilizando Reatores Sequenciais: Partida e Estabilização Dos Sistemas (original) (raw)
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This study compared the performance of a pilot anaerobic sludge digester under different operating strategies for the purpose of solids removal and stabilization. The influence of increasing organic loading rate -OLR (OP I) and then the effect of hydraulic retention time -HRT reduction (OP II and OP III) in anaerobic process were evaluated. Production of methane, organic matter degradation was used to measure and compare the system´s performance. The experimental time with HRT between 7 and 5 days showed the highest VS efficiency removals (higher than 70%), which positively influenced process stability. The applied OLR of 2.5 and 3.5 kgVS· m -3 ·d -1 resulted in higher yields of methane during OP I. Comparatively, HRT reduction resulted in a better system performance than the increasing OLR approach. The digester provided solids volume reduction over 50% and consequently cost savings which improve the overall sludge management.
Operational Issues and Remedies in the Anaerobic Sludge Digestion Process
2007
Anaerobic sludge digestion is an oft fundamental component of municipal sewage treatment, with operational management often proving both complex and labour-intensive for water authority and council-based entities. Managers of the anaerobic digestion process units, which require significant capital investment to establish within a treatment facility, attempt to maximize the treatment capacity to the limits of design capabilities, often to the detriment of the biological process that drives the organic degradation. Inadequate/deficient heating, operation outside favourable biologically viable conditions, recommissioning following asset maintenance activity, poor sludge drying characteristics and poor and/or inconsistent gas production from process units are all design inadequacies or indicators of poor process unit performance. Operational issues experienced in anaerobic sludge digestion are varied, with specific remedies often a combination of system optimisation and specialist produ...
A continuous digester type was designed at the laboratory scale with an aim to studying and improving anaerobic digestion of organic wastes. The results obtained can be extrapolated at large scale pilot plant. To study the digester start-up we have chosen as a substrate the sludge issued from the wastewater treatment plant located in Adrar city (south west of Algeria). Different parameters have been considered such as pH, VFA, COD, and volume of biogas generated during the digestion process. Résumé -Un type de digesteur en continu a été développé à l'échelle du laboratoire dans le but d'étudier et d'améliorer la digestion anaérobie des déchets organiques. Les résultats obtenus peuvent être extrapolés à l'échelle d'un pilote industriel. Pour étudier ce pilote de digesteur, nous avons choisi comme substrat de la boue provenant de l'usine de traitement des eaux usées, située à Adrar ville (sud-ouest de l'Algérie). Différents paramètres ont été considérés com...
Anaerobe, 2001
Key Words: Activated sludge, anaerobic treatment of sludge, upflow anaerobic sludge blanket reactor (UASB reactor) Design, construction, and starting-up of an upflow anaerobic sludge blanket reactor was carried out. This system was proposed for excess sludge stabilisation, particularly that generated at an activated sludge wastewater treatment facility installed in a sugarcane mill. The upflow anaerobic sludge blanket (UASB) reactor built, had a working volume of 22.3 m 3 and a hydraulic residence time of 22 days. Methane production was at a maximum of 79% volume with an average of 60% for this treatment. For starting up the anaerobic reactor, a suitable inoculum from a neighboring plant was used. As the waste characteristics in both plants were different, an acclimation procedure was followed to achieve granulation. Control and stability of anaerobic reactions were monitored with alkalinity data, using the so-called 'alfa alkalinity' to try to keep its value at around 0.4. Once pseudosteady-state conditions were reached (chemical oxygen demand reduction and methane-rich biogas production within +10 percent), the organic load was steadily increased up to feeding 100% excess sludge. The UASB reactor used to stabilise the excess biomass generated a sludge with a much lower volume than that originally fed. Its design ensured adequate hydraulic flow and biogas production with a high methane content. The bacteria were attached constituting spheres and very minor maintenance operations were required.
Process Biochemistry, 2005
The performance of mesophilic anaerobic digesters of four large Italian wastewater treatment plants without primary sedimentation were studied. Only the waste activated sludge is stabilised by means of the mesophilic (35-37 8C) anaerobic digestion process. The anaerobic digesters generally worked with a hydraulic retention time in a range of 20-40 days and an organic loading rate of some 1 kg VS/m 3 reactor day. The solids content of the sludge fed to the digesters was in the range 2.6-3.9% and the gas produced per kilogram of volatile solids added was in the range 0.07-0.18 m 3 /kg VS fed . The specific gas production per kilogram of volatile solids destroyed was in the range 0.5-0.9 m 3 / kg VS destroyed and the reduction of the volatile solids concentration was in the range 13-27% (average 18%). These figures are particularly significant when designing anaerobic digesters for the treatment of waste activated sludge as single substrate. Moreover, it was observed that the higher the applied solid retention time in the activated sludge process for wastewater treatment, the lower the gas production. In particular, the specific gas production decreased from 0.18 to 0.07 m 3 /kg VS fed when increasing the solid retention time in the wastewater treatment line from 8 to 35 days. Finally, a mathematical model for the prediction of biogas production on the solid retention time applied in the wastewater treatment process was developed. #
Characterization of sludges for predicting anaerobic digester performance
Water Science & Technology, 2008
Batch anaerobic digestion tests of primary sludge and waste activated sludge were conducted for a duration of 123 days to determine the ultimate degradability of the sludges. For primary sludges the inert fraction of the particulate COD that was predicted by the wastewater models could be employed to predict their biodegradability under anaerobic conditions. The degradation of waste activated sludge was adequately characterized for the first 60 days of digestion using a model that assumed equivalent biodegradability of particulate COD components under aerobic and anaerobic conditions. However after 60 days of anaerobic digestion it appeared that decay of the endogenous products was occurring. This could be described with a first order decay function with a coefficient of 0.0075 d-1. For continuous flow digesters operating at SRTs of 30-60 days, the predicted VSS destruction with the modified model was approximately 10% higher than that predicted on the basis of inert endogenous decay products.
Recovery of the sludge of a wastewater treatment plant by anaerobic digestion and biogas production
2018
The aim of our research work is the realization of anaerobic digestion by using the organic sludge of the urban wastewater treatment plant as a substrate. The biodegradable nature of the wastewater sludge allowed flammable biogas to be recovered after 24 hours of digestion and biogas production reached almost 5 liters for an initial concentration of 70 g / L The rate of reduction in COD (chemical demand in oxygen) of the sludge was estimated at 87.3%. For the good functioning of the digestion one must control the following parameters: type of substrate, pH of the medium, the organic load expressed in COD or BOD, the temperature. Once the operation is conducted we must follow the VFA / CAT (Volatile Fatty Acid/ Complete Alcalimetric Title) parameter which shows if the process will continue or will be stopped. And finally, the C / N ratio gives us an indication if there is more carbon in the medium, this will indicate that the residence time is going to be very long in the reactor and if nitrogen is abundant in the organic matter it is will produce in the digestion medium ammonia which inhibits the degradation process and stops it in the acidogenic phase and the production of biogas. The use of anaerobic digestion can be an interesting solution to dispose of energy from organic waste, while effectively participating in the remediation of these effluents. This renewable energy, inexpensive, non-polluting can replace conventional and nonrenewable fossil fuels.
Waste management (New York, N.Y.), 2011
This paper focused on the factors affecting the respiration rate of the digestate taken from a continuous anaerobic two-stage process treating the organic fraction of municipal solid waste (OFMSW). The process involved a hydrolytic reactor (HR) that produced a leachate fed to a submerged anaerobic membrane bioreactor (SAMBR). It was found that a volatile solids (VS) removal in the range 40-75% and an operating temperature in the HR between 21 and 35 °C resulted in digestates with similar respiration rates, with all digestates requiring 17 days of aeration before satisfying the British Standard Institution stability threshold of 16 mg CO(2) g VS(-1) day(-1). Sanitization of the digestate at 65 °C for 7 days allowed a mature digestate to be obtained. At 4 g VS L(-1) d(-1) and Solid Retention Times (SRT) greater than 70 days, all the digestates emitted CO(2) at a rate lower than 25 mg CO(2) g VS(-1) d(-1) after 3 days of aeration, while at SRT lower than 20 days all the digestates disp...