Drying of Activated Sludge Under Partial Vacuum Conditions?An Experimental Study

Hippinen, Ilkka; Ahtila, Pekka

doi:10.1081/ldrt-200034247

Cited by 4 publications

(9 citation statements)

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“…However, this conclusion was made based on laboratory-scale experimentation. [4] Leonard et al [17] investigated the influence of three operating variables, i.e., inlet air temperature, superficial velocity, and humidity, on wastewater sludge drying kinetics, and concluded that the temperature of the inlet air was the main operating parameter affecting the kinetics of drying. It was also reported that the drying of activated sludge was mainly controlled by external limitations.…”

Section: Conventional Drying Technologiesmentioning

confidence: 99%

“…However, there is no information available at full scale. Hippinen and Ahtila [4] reported an experimental approach for the drying of activated sludge under partial vacuum by means of waste energy streams. Waste heat sources are widely available in pulp and paper mills, particularly since recent environmental legislation and restrictions have prompted mills to minimize water consumption, which leads to an increase in the temperature of water in the system.…”

Section: Conventional Drying Technologiesmentioning

confidence: 99%

“…[2] The combined sludge from primary and secondary treatment consists of a muddy mass of microorganisms, fibrous materials, lignin, mineral components (limestone and phosphorous), clay, inert solids rejected during the recovery process, ash, and water. [3,4] The possibility of recycling this sludge to the process is limited, and landfilling is increasingly restricted due to mounting environmental pressures and high costs. Therefore, combustion can provide a competitive disposal method, as long as the dry solids content of the sludge is maintained above the critical level for good combustion.…”

Section: Pulp and Paper Mill Mixed Sludgementioning

confidence: 99%

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Emerging Biodrying Technology for the Drying of Pulp and Paper Mixed Sludges

2006

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Effective sludge management is increasingly critical for pulp and paper mills due to high landfill costs and complex regulatory frameworks for options such as sludge landspreading and composting. Sludge dewatering challenges are exacerbated at many mills due to improved in-plant fiber recovery coupled with increased production of secondary sludge, leading to a mixed sludge with a high proportion of biological matter that is difficult to dewater. Various drying technologies have emerged to address this challenge of sludge management, whose objective is to increase the dryness of mixed sludge to above critical levels (%42% dryness) for efficient and economic combustion in the boiler for steam generation. The advantages and disadvantages of these technologies are reviewed in this article, and it is found that many have significant technical uncertainties and/or questionable economics. A biodrying process, enhanced by biological heat generation under forced aeration, is introduced that has significant promise. A techno-economic analysis of the batch biodrying process at a case study mill showed an annual operating cost savings of about $2 million, including the elimination of landfilling practices and supplemental fuel requirements in the boiler. It was shown that if a biodrying residence time of less than 4 days can be achieved, payback periods of 2 years or less can result in many mills. The potential for the development of a continuous biodrying reactor and the fundamentals of its mathematical modeling are thus presented. Compared to the batch reactor configuration, it is expected that the continuous process would result in improved process flexibility and controllability, lower investment and operating costs due to shorter residence times, and an improved potential to fit into the crowed pulp and paper mill site.

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Section: Conventional Drying Technologiesmentioning

confidence: 99%

Section: Conventional Drying Technologiesmentioning

confidence: 99%

Section: Pulp and Paper Mill Mixed Sludgementioning

confidence: 99%

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Emerging Biodrying Technology for the Drying of Pulp and Paper Mixed Sludges

2006

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“…The second area includes heat drying technology by hot wind, rotating disc and rotary kiln system. Some studies have been able to produce a dried powder with <40 wt% water content by allowing direct contact of the dewatered cake to a heat source at 200-600 o C [5][6][7]. Unfortunately, the cost of the heat drying method is almost double that of ocean dumping.…”

Section: Introductionmentioning

confidence: 99%

A study on air jet drying for water content reduction of sludge

Lee

Cho²

2010

Korean J. Chem. Eng.

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An air jet drying system composed of a turbo blower, an air ejector and three stage cyclones is constructed to produce a dried powder through water content reduction of dewatered cake obtained from sludge treatment process. The air flow to be ventilated by the turbo blower forms a high speed flow field by passing through the air ejector and a circulative flow field by passing through the cyclones. Dewatered cake, 100 mm in size, is disintegrated by jet and collision through passing the air ejector and becomes fragmented with size no more than 2 mm. These fragmented particles follow air flow and are dried as moisture is evaporated from particle surface. A powder composed of 1.6 mm spherical particles is produced from pilot scale equipment of 1 ton/hr under the conditions of air velocity, maximum flow rate and air temperature profile of 84 m/sec, 180 m 3 /min and 73-28 o C, respectively. The air dried powder with average water content of 49.8 wt% is recovered after drying the dewatered cake with water content of 83.3 wt% in a real operation, indicating 33.5 wt% decrease in water content. It is estimated that the power consumption of the air jet drying system requires 92 kWh/Ton to reduce the water content by 33.5 wt%, which is no more than a half against heat drying system to consume 164 kWh/ton.

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“…In an activated sludge process, part of the biomass that undergoes sedimentation in secondary clarification ponds is recirculated to the aeration ponds to sustain the growth of microflora, as the remaining biomass is dewatered generating a semi-solid organic residue commonly referred to as biosludge. Sludge is generally dewatered by centrifuges, filter or various pressing machines, which are, however, unable to remove intracellular and chemically bound water present in the sludge suspensions [4,5]. Although mechanical dewatering has been regarded as the most energy efficient way of removing large quantities of water from sludge suspensions, mechanically dewatered sludge can only reach a maximum dry solids content (DSC) of 18-50% depending on the sludge type and dewatering unit [6].…”

Section: Introductionmentioning

confidence: 99%

Response surface optimization of a novel pilot dryer for processing mixed forest industry biosludge

Mäkelä

Geladi

2015

Int. J. Energy Res.

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Summary As a promising sludge handling alternative capable of utilizing the secondary energies in industrial environments, we investigated the use of a novel pilot‐scale cyclone dryer for processing industrial mixed sludge from the forest industry. Attainable sludge dry solids contents (%) and respective specific energy consumption of drying (kWh kg−1 H2O) were successfully modelled by response surface methodology based on a constructed design of experiments. Predicted sludge dry solids and the specific energy consumption of drying varied between <30–65% and <0.4–1.8 kWh kg−1 H2O depending on controlled inlet air temperature, sludge feeding rate and humid air recirculation levels. The response models were further optimized for efficient combustion of processed sludge with inlet air temperatures corresponding to potentially available secondary heat. According to the results, energy efficient drying of mixed sludge with a specific energy consumption <0.7 kWh kg−1 H2O can be performed with inlet air temperatures ≥60 °C corresponding with pilot‐scale feeding capacities between 300–350 and 550 kg h−1 depending on inlet air temperature. These findings suggest that the introduction of novel drying systems capable of utilizing the available secondary energies of industrial environments could significantly improve the energy efficiency of sludge drying and potentially allow considerable cost savings for industrial operators. Copyright © 2015 John Wiley & Sons, Ltd.

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Drying of Activated Sludge Under Partial Vacuum Conditions?An Experimental Study

Cited by 4 publications

References 0 publications

Emerging Biodrying Technology for the Drying of Pulp and Paper Mixed Sludges

Emerging Biodrying Technology for the Drying of Pulp and Paper Mixed Sludges

A study on air jet drying for water content reduction of sludge

Response surface optimization of a novel pilot dryer for processing mixed forest industry biosludge

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