Effects of thermochemical pretreatment on the anaerobic digestion of waste activated sludge (original) (raw)
Related papers
2011
This study is focused on the effect of thermo alkaline pretreatment on velocity of anaerobic hydrolysis mesophilic and thermophilic of waste activated sludge (WAS), separating the hydrolysis of suspended solids (SS) and dissolved solids (SD). In order to research the hydrolysis of SS, the Sander’s surface model was used, and for the hydrolysis of SD, the Goel’s model of saturation was employed. The pretre tment increased the uperficial rea available for the enzymatic action, due to the reduction of the solids size. The effect of the pretreatment in the anaerobic digestion of the SD in thermophilic conditions, resulted in competitive inhibition over the anaerobic hydrolysis rate, whereas that in mesophilic conditions, resulted in non competitive inhibition. Mathematical simulation of SS to SD and methane consecutive reactions, showed that a 4 % increase in initial thermal-alkaline tr ated sludge di inished the inhibition of SD hydrolysis in the thermophilic anaerobic digestion.
Principles and potential of the anaerobic digestion of waste-activated sludge
Progress in Energy and Combustion Science, 2008
When treating municipal wastewater, the disposal of sludge is a problem of growing importance, representing up to 50% of the current operating costs of a wastewater treatment plant. Although different disposal routes are possible, anaerobic digestion plays an important role for its abilities to further transform organic matter into biogas (60-70 vol% of methane, CH 4 ), as thereby it also reduces the amount of final sludge solids for disposal whilst destroying most of the pathogens present in the sludge and limiting odour problems associated with residual putrescible matter. Anaerobic digestion thus optimises WWTP costs, its environmental footprint and is considered a major and essential part of a modern WWTP. The potential of using the biogas as energy source has long been widely recognised and current techniques are being developed to upgrade quality and to enhance energy use. The present paper extensively reviews the principles of anaerobic digestion, the process parameters and their interaction, the design methods, the biogas utilisation, the possible problems and potential pro-active cures, and the recent developments to reduce the impact of the problems. After having reviewed the basic principles and techniques of the anaerobic digestion process, modelling concepts will be assessed to delineate the dominant parameters. Hydrolysis is recognised as rate-limiting step in the complex digestion process. The microbiology of anaerobic digestion is complex and delicate, involving several bacterial groups, each of them having their own optimum working conditions. As will be shown, these groups are sensitive to and possibly inhibited by several process parameters such as pH, alkalinity, concentration of free ammonia, hydrogen, sodium, potassium, heavy metals, volatile fatty acids and others. To accelerate the digestion and enhance the production of biogas, various pre-treatments can be used to improve the rate-limiting hydrolysis. These treatments include mechanical, thermal, chemical and biological interventions to the feedstock. All pre-treatments result in a lysis or disintegration of sludge cells, thus releasing and solubilising intracellular material into the water phase and transforming refractory organic material into biodegradable species. Possible techniques to upgrade the biogas formed by removing CO 2 , H 2 S and excess moisture will be summarised. Special attention will be paid to the problems associated with siloxanes (SX) possibly present in the sludge and biogas, together with the techniques to either reduce their concentration in sludge by preventive actions such as peroxidation, or eliminate the SX from the biogas by adsorption or other techniques. The reader will finally be guided to extensive publications concerning the operation, control, maintenance and troubleshooting of anaerobic digestion plants.
When treating municipal wastewater, the disposal of sludge is a problem of growing importance, representing up to 50% of the current operating costs of a wastewater treatment plant. Although different disposal routes are possible, anaerobic digestion plays an important role for its abilities to further transform organic matter into biogas (60-70 vol% of methane, CH 4 ), as thereby it also reduces the amount of final sludge solids for disposal whilst destroying most of the pathogens present in the sludge and limiting odour problems associated with residual putrescible matter. Anaerobic digestion thus optimises WWTP costs, its environmental footprint and is considered a major and essential part of a modern WWTP. The potential of using the biogas as energy source has long been widely recognised and current techniques are being developed to upgrade quality and to enhance energy use. The present paper extensively reviews the principles of anaerobic digestion, the process parameters and their interaction, the design methods, the biogas utilisation, the possible problems and potential pro-active cures, and the recent developments to reduce the impact of the problems. After having reviewed the basic principles and techniques of the anaerobic digestion process, modelling concepts will be assessed to delineate the dominant parameters. Hydrolysis is recognised as rate-limiting step in the complex digestion process. The microbiology of anaerobic digestion is complex and delicate, involving several bacterial groups, each of them having their own optimum working conditions. As will be shown, these groups are sensitive to and possibly inhibited by several process parameters such as pH, alkalinity, concentration of free ammonia, hydrogen, sodium, potassium, heavy metals, volatile fatty acids and others. To accelerate the digestion and enhance the production of biogas, various pre-treatments can be used to improve the rate-limiting hydrolysis. These treatments include mechanical, thermal, chemical and biological interventions to the feedstock. All pre-treatments result in a lysis or disintegration of sludge cells, thus releasing and solubilising intracellular material into the water phase and transforming refractory organic material into biodegradable species. Possible techniques to upgrade the biogas formed by removing CO 2 , H 2 S and excess moisture will be summarised. Special attention will be paid to the problems associated with siloxanes (SX) possibly present in the sludge and biogas, together with the techniques to either reduce their concentration in sludge by preventive actions such as peroxidation, or eliminate the SX from the biogas by adsorption or other techniques. The reader will finally be guided to extensive publications concerning the operation, control, maintenance and troubleshooting of anaerobic digestion plants.
article_wjpr_1506675639 (2).pdf
Solid waste is a waste that includes predominantly household waste with some times the addition of commercial wastes collected by a municipality with in a given area. Batch Anaerobic reactor was set up to decompose the waste to produce methane, co2, hydrogen and other gases in traces. Anaerobic digestion of wastes was carried out in the laboratory at room temperature, to assess the biogas production. The total biogas production from the wastes was found to be 6lit/kg. The results from the biomethanation process showed that an increase in gas production was observed with increase in digestion period, when bioconversion parameters were found to be favorable for the production of gas.
An anaerobic digestion process for the treatment of food waste was investigated in laboratory scale batch reactors. The effect of temperature (30°C-60°C) on the biogas production was investigated in the reactors with hydraulic retention time of 30 d. The volumetric yield of biogas was noted at regular intervals using water displacement method. The food wastes used in this experiment were subjected to characterization studies before and after digestion. The experimental results show that the temperature of 50°C produced higher biogas yield compared with other temperatures.
Thermal pre-treatment of primary and secondary sludge at 70 degrees C prior to anaerobic digestion
Water science and technology : a journal of the International Association on Water Pollution Research, 2005
In general, mesophilic anaerobic digestion of sewage sludge is more widely used compared to thermophilic digestion, mainly because of the lower energy requirements and higher stability of the process. However, the thermophilic anaerobic digestion process is usually characterised by accelerated biochemical reactions and higher growth rate of microorganisms resulting in an increased methanogenic potential at lower hydraulic retention times. Furthermore, thermal pre-treatment is suitable for the improvement of stabilization and could be realized at relatively low cost especially at low temperatures. The present study investigates the effect of the pre-treatment at 70 degrees C on thermophilic (55 degrees C) anaerobic digestion of primary and secondary sludge in continuously operated digesters. Thermal pre-treatment of primary and secondary sludge at 70 degrees C enhanced the removal of organic matter and the methane production during the subsequent anaerobic digestion step at 55 degree...
Prediction of thermal hydrolysis pretreatment on anaerobic digestion of waste activated sludge
Water Science & Technology, 2008
Sludge disintegration technology refers to an additional pre-treatment step of sludge treatment process which has been developed to improve performance of the subsequent unit processes digestion, dewatering and the final sludge output quality. Disintegration and hydrolysis usually are the rate-limiting process steps. Therefore, efficient pre-treatment of sludge enhances accessibility for anaerobic bacteria, leading to improvement of the anaerobic biodegradability. Moreover, the main purpose of pretreatment is an enhancement of biogas generation. Among other disintegration technologies i.e. physical, chemical, and biological pre-treatment, the use of high temperature for sludge pre-treatment is particularly attractive because of its sanitation potential and its impact on sludge dewatering.