Small Scale Pilot Plant Thermal Dryer for Sewage Sludge Dewatering System A Preliminary Study

Transcription

1 Small Scale Pilot Plant Thermal Dryer for Sewage Sludge Dewatering System A Preliminary Study Zakaria M.S. 1, a, Suhaimi Hassan 2, b and M. Faizairi 3, c 1 Universiti Teknologi Petronas, Malaysia a safuan_one89@yahoo.com, b suhaimiha@petronas.com.my, c mfaizairi_mnor@petronas.com.my Keywords: Thermal dryer, sewage sludge, moisture content, drying, energy. Abstract. Malaysia expected to face serious problem in sewage sludge disposal in the next few years if this problem is not properly manage and well treated. The common way of sludge disposal in Malaysia is to dispose it on the land, by landfill disposal. However, most of the landfill has been closed since reaching it capacity. This product required innovation and advance solution for treatment and disposal since the production of sewage sludge rapidly increasing and the available solution for their disposal is out dated.one of the ideal solution to dispose the sludge is by converting it into useful energy in the form of solid fuel such as pallet and briquette and burn it as a solid fuel to generate power. However, the main problem faced is it contains high moisture content which is more than 90% of moisture content. In order to convert it into useful energy, the moisture content of the sludge need to be reduced into acceptable level which is below 20%. One of the effective methods to remove the moisture content is by using a thermal dryer. The preliminary results from this study found that the thermal dryer produced 63.32kg/h of dried sewage sludge with moisture content less than 20%. The production rate of this dryer shows positive result and with continuous production, this dryer cable to dry tons of wet sewage sludge. Introduction Sewage sludge is generated from municipal wastewater treatment in the sewage sludge treatment plant. The sewage sludge produced in Malaysia mainly from domestic waste water that collected from housing, urbanization and light industry. The production of sewage sludge in Malaysia rapidly increasing due to economic development, a consequence of rapid urbanization and increased of population causes serious environmental problems for their disposal. The amount of waste water that entering the waste water treatment plant in Malaysia was estimated at 4.9 million cubic meters in 2007 [1]. Recently, Malaysia produced approximately 3 million cubic meters per annum of sewage sludge in waste water treatment plants with annual management and treatment cost about RM 1 billion [2]. The production of sewage sludge expected to increase rapidly which is about 7 million cubic meters in 2020 [3]. Usually sludge from the treatment plant may be used in agricultural land, forest and landfill or in provided disposal sites [4,5]. This method has no more interested since the production of sewage sludge rapidly increasing while most of the landfill has been closed since reaches its capasity.sewage sludge should be given special consideration in handling and treatment as it contains toxic element such as harmful pathogens which is can seriously affect the human health [6]. According the previous work by Abbas et al [7], Malaysian domestic sewage sludge has potential to convert into energy as it has a high heating value which is being predicted to be between 14 MJ/Kg to 16 MJ/Kg using proximate and ultimate analysis. Others study done by Kohila used 14 different samples of sewage from 14 different sewage treatment plants in Malaysia also proved that the Malaysian sewage sludge has high potential of being converted into solid fuel for power generation purpose [8]. The samples were dried by using oven dryer and analyze using proximate and ultimate analysis in order to investigate the properties of sewage sludge for conversion into fuel. The average

2 of higher heating value (HHV) for 14 samples is 17,429.71kJ/kg which is quite high and acceptable for conversion into fuel.the basic behavior of Malaysian sludge has shown its capability and potential to become an alternative source of energy. The characteristic of Malaysian sludge that found have almost similar in other country but the sulfur content quite low compared to the result that obtain in [9]. Based on the characteristic of sewage sludge with high heating value and lower contents of sulfur and ash, Malaysian sewage sludge has high potential of being converted into solid fuel for energy generation purpose.based on the literature survey reviewed, there is no such effort carried out on design and develop the efficient dryer for sewage sludge in Malaysia. The conventional drying method such oven dryer as used in [10] required long time to dry the sludge and only applicable on research purpose only but not in practise for conversion into energy since required high energy, required larger space and takes time to dry the sludge. Methodology The sample of sewage sludge was obtained from the sewage treatment plant in Bunus and the initial moisture content of the sewage sludge was recorded in order to investigate the moisture drop in sewage sludge after the drying process.the schematic of thermal dryer as shown in Fig. 1.This dryer has 6 meter lengths and connected to the light oil burner in order to supply heat to evaporate the water from sewage sludge. The feeder will bring the wet sewage sludge into the inlet of the dryer by using screwfeeder. As the sludge enters the dryer, the screw feeder in the dryer will bring the sludge to the outlet while the burner provides the heat continuously to the screw feeder which is indirectly heated the sludge. The vaporized gases will clean with water scrubber before release to open air. The dryer will operate for one hour and the production rate and energy consumption were recorded. The sample of dried sewage sludge was taken in order to investigate the moisture content and calorific value. The moisture content of sewage sludge measured by taking the sample and fully dried using an oven at 105 for 10 hours and measure the weight. Fig. 1 Schematic of thermal dryer Fig. 2 Full schematic of thermal dryer The different of weight percentage is the moisture content of the sludge. The heating value of sludge was obtained by using Bomb Calorimeter accordance to ASTM D2015. The screwfeeder maintain at constant speed of 10 rpm and 10 pieces of K- type thermocouple were placed along the dryer with same distance and connected to the data logger in order to investigate the temperature profile of the dryer. Full schematic of dryer as presented in Fig 2.

3 Temperature ( C) Temperature ( C) Results and Discussion The initial moisture content of the sewage sludge recorded was 89.45% for both insulated and non insulated dryer. After an hour operating the dryer, all the relevant data and results were collected. The dryer was running with two conditions which is with insulation and without insulation in order to study the effect of insulation on the moisture content and the production rate of the dryer. The heating value of dried sludge obtained through the bomb calorimeter is 14,654 kj/kg. The schematic of temperature profile along the insulated dryer and non insulated dryer as presented in Fig.3 and Fig.4. The total energy consumption by the dryer in term of electricity and diesel within an hour for both dryer were recorded as well for comparing the total energy consumed with total energy produced by both dryer. Details result for both dryers as presented in Table Distance from burner (m) Fig. 3 Temperature profile along the dryer without insulation Distance from burner (m) Fig. 4 Temperature profile along the dryer with insulation Table 1. Result for insulation dryer and without insulation dryer Parameter With Insulation Without Insulation Initial moisture content (wt %) Final moisture content (wt %) Total energy consumed per hour (MJ/h) Total energy produced per hour (MJ/h) Production rate (kg/h) The moisture content of the sewage sludge after drying process for insulated dryer, lower than non insulated dryer since the heat losses to the surrounding for insulated dryer less than non insulated. The insulated dryer has high efficiency compared to the non insulated dryer since consumed same energy for drying process but difference in final moisture content. However, the moisture content after drying process for both dryer are acceptable for conversion into energy since less than 20% of moisture content. The production rate for non insulation dryer higher and insulated dryer are same since the speed of the screw feeder for both dryer are same. The difference in weight for production rate for both dryer are due to the difference in moisture content after drying process.

4 Conclusion The moisture content of sewage sludge after drying process for both dryer was successfully reduced into acceptable level for conversion into energy which is less than 20% of moisture content. This experiment proves that insulated dryer has high efficiency compared to the non insulated dryer. Besides that, this thermal dryer also produced higher amount of dried sludge in a short time compared to the conventional oven dryer. The energy required for the dryer much more less compared to the energy produced makes this dryer is applicable to use for sewage sludge dewatering. The invention to generate energy from the sewage sludge may become reality with the presence of this dryer. References [1] Z. Alam, S. A. Muyibi, and R. Wahid, Statistical optimization of process conditions for cellulase production by liquid state bioconversion of domestic wastewater sludge, Bioresour. Technol., vol. 99, pp , [2] A. H. Molla, A potential resource for bioconversion of domestic wastewater sludge, Bioresour. Technol., vol. 85, pp , [3] F. Salleh, R. Samsuddin, and M. Husin, Bio-Fuel Source from Combination Feed of Sewage Sludge and Rice Waste, Int. Conf. Environ. Sci. Eng., vol. 8, pp , [4] P. Planquart, G. Bonin, A. Prone, and C. Massiani, Distribution, movement and plant availability of trace metals in soils amended with sewage sludge composts : application to low metal loadings, Sci. Total Environ., no. 241, pp , [5] M. Strazar and O. Burica, Total metal concentrations and partitioning of Cd, Cr, Cu, Fe, Ni and Zn in sewage sludge Janez ˇ, Sci. Total Environ., vol. 250, pp. 9 19, [6] J. Jiang, X. Du, and S. Yang, Analysis of the combustion of sewage sludge-derived fuel by a thermogravimetric method in China, Waste Manag., vol. 30, no. 7, pp , [7] A. H. A. M.S.Aris, Characterization of Malaysian Domestic Sewage Sludge for Conversion into Fuels for Energy Recovery Plants, Int. Sysposium Environ. Friendly Energies Electr. Appl., no. November, pp. 1 8, [8] M. F. M. Nor, S. Hassan, and K. Mariapan, Sludge Calorific Value Mapping and Potential Energy Recovery for Malaysia, no. iv [9] S. Werle and R. K. Wilk, A review of methods for the thermal utilization of sewage sludge : The Polish perspective, Renew. Energy, vol. 35, no. 9, pp , [10] N. M. Mokhtar, R. Omar, M. A. M. Salleh, A. Idris, characterization of sludge from the wastewater-treatment plant of a refinery dielectric properties measurements, Int. J. Eng. Technol., vol. 8, no. 2, pp , 2011.

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