© 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Waste Management and the Environment, D Almorza, CA Brebbia, D Sales & V Popov (Editors). ISBN 1-85312-907-0

Effects of operational conditions on dry distillation characteristics of organic solid wastes

A. Sane, Y. Bando & M. Nakamura Department of Civil Engineering, Nagoya Universi@, Japan.

Abstract

Wood chip, cotton and dogfood were used as the sample of organic solid wastes. The change in weight of sample with the temperature in nitrogen atmosphere was investigated by using a thermogravimetry. The elements in solid residue and the components in effluent gas were analyzed by using a CHN analyzer and a gas chromatography, respectively. In all samples, the weight decreases drastically in the range of 500 to 700 K and CH4 is mainly produced at the temperature of 600 -1100 K. Two experiments on dye adsorption and wastewater treatment by activated sludge method were carried out as applications of the solid residue. The solid residue obtained under a certain condition showed higher performance of adsorption. The addition of solid residue enhanced the performance of waste water treatment.

1 Introduction

Organic solid wastes in Japan are mainly treated by incineration. However, the environmental load in incineration is so high that recently dry distillation has been employed as the treatment of organic solid waste. By the dry distillation, organic solid wastes are transformed to gas, tar and solid residue. The gas and solid residue are used as fuel and activated coke, respectively. Although the tar is a little troublesome, the environmental load is rather low [1-5]. The dry distillation at high temperature becomes popular for the municipal solid wastes. However, for the industrial organic solid wastes such as wood, clothes and food which are qualitatively homogeneous, the dry distillation at low temperature is considered to be proper. The dry distillation at low temperature has advantages of easy operation and low cost. In this study, three different samples were used and the effects of operational conditions on the dry © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Waste Management and the Environment, D Almorza, CA Brebbia, D Sales & V Popov (Editors). ISBN 1-85312-907-0

24 Waste Management and the En~’irownent

1 , T7.–- 1 n-.....1- 1 t“I 0.8 ■( ~ 0.6 t 1 ,0 t

o~ 300 500 700 900 1100 1300

T~[K]

Figure 1: Change in weight of sample with temperature.

distillation characteristics at low temperature were experimentally studied. The applications of solid residue as dye adsorbent and particle immobilizing microbe for wastewater treatment were also examined.

2 Dry distillation characteristics

The effects of operational conditions on the dry distillation characteristics at low temperature were examined.

2,1 Experimental method

Wood chip, cotton and dogfood were used as the samples of waste wood, clothes and food, respectively. Before the dry distillation, the samples were put in the dryer at 330 K during 24 h. The dry distillation was performed in the thermogravimetry using nitrogen as the carrier gas, and the change in weight of sample with the temperature was measured. The elements in solid residue and the components in effluent gas were analyzed by using a CHN analyzer and a gas chromatography, respectively.

2.2 Results and discussion

The change in weight of sample with temperature is shown in Figure 1. The rate of rising temperatureis 0.17 K/s. In all samples, the weight drastically decreases in the range of 500 to 700 K and slightly does beyond 700 K. Therefore, the main dry distillation is completed below 700 K. The phenomenon in this temperature range is referred as the dry distillation at low temperature. In this range, the decrement in weight of cotton is the largest while that of dogfood is gradual. The fractions of residuary weight at 700 K are different among three samples. This might be caused by the different composition in samples. The decreasing rates of weight at temperatures beyond 700 K are almost the same for three samples, The decrement in weight in the temperatures range from 700 to 1300 K is about 10 wt%. © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Waste Management and the Environment, D Almorza, CA Brebbia, D Sales & V Popov (Editors). ISBN 1-85312-907-0

Waste Management and the En~’irownent 25

\N

Dogfood

1 I

300 700 900 1300 T~[K]

Figure 2: Change in element fraction in residue with temperature

The change in element fraction in solid residue with the temperature is shown in Figure 2. Assuming that the residue consists of C, H, N and O, the fi-action of O can be calculated from the values measured by CHN analyzer, In all samples, the &action of C increases but that of H decreases with increasing temperature, because much hydrocarbons are released flom the sample at higher temperatures. The flaction of O decreases in wood and cotton, but is almost unchanged in dogfood, The fraction of N in wood and cotton is very few, but there is a significant fraction of N in dogfood due to the protein included, © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Waste Management and the Environment, D Almorza, CA Brebbia, D Sales & V Popov (Editors). ISBN 1-85312-907-0

26 Waste Management and the En~’irownent

0.6 Ke Sample ■ ●y 0.5 Wood . ■ g 0.4 A Cotton Dogfood E 0,3 co g s ● v 0.2 AA , u 0,1 * ● o I -, I ,,, 300 500 700 900 1100 1300

T~[K] Figure 3: Change in CH4 concentration in effluent gas with temperature.

1.4

1,2 - , 1 M

0.2

v(-) Wood Cotton Dogfood Wood Cotton Dogfood Sample Sample

Figure 4: Concentration of each component in effluent gas.

The change in CH4 concentration in effluent gas with the temperature is shown in Figure 3. The concentration is very low due to the dilution by carrier gas. It is found that CH4 is produced at temperatures of 600-1100 K. The concentration of each component in effluent gas is shown in Figure 4. The ordinate, C/CcHq,Woo,jexpresses the relative value to CH1 concentration in effluent gas of wood. When the sample temperature is 700 K, CH4 concentration is the highest in every sample. Among three samples, CH4 concentration for wood is the highest. This result indicates that wood is easily decomposed by the dry distillation at low temperature, When the sample temperature is 900 K, the difference in CH4 concentration between wood and cotton becomes smaller, and CH4 concentration for dogfood exceeds that for wood. Dogfood is found to decompose at a higher temperature. © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Waste Management and the Environment, D Almorza, CA Brebbia, D Sales & V Popov (Editors). ISBN 1-85312-907-0

Waste Management and the En~’irownent 27

Table 1. Dry distillation condition and dye removal

sample Solld residue ot wood Activated carbon 1 l~J Ouu bUU O(JU R: [KJs] 0.008 0.17 0.17

OH [h] O 0 4 ~D [-1 0.05 0!10 0,29 0.59

3 Applications of solid residue to environmental remediation

3.1 Dye adsorption

The effect of dry distillation conditions on the dye adsorption performance of solid residue was examined.

3.1.1 Experimental The solid residues of wood obtained under the different conditions of dry distillation were used as an adsorbent, Activated carbon was also used as a standard adsorbent for comparison. The residues were washed, dried at 330 K during 24 h and cmshed into small pieces with about 100 pm in diameter. Reactive Black dye was used as an adsorbate with an initial concentration of 0.1 kg/m3. The residues and activated carbon of 2 mg were added to the solution of 10 mL in test tubes. The test tubes were shaken at 300 K during 24 h. The dye concentration was measured by using a UV spectrometer and the dye removal was calculated,

3.1.2 Results and discussion The dry distillation condition and the dye removal are shown in Table 1. The removal by the residue obtained by heating rate of 0.008 Kls with no holding time is only 0.05. The removal increases up to 0.10 as the heating rate increases to 0,17 Ws. For the removal by the residue obtained at the same heating rate with the holding time for 4 h at 600 K, it becomes 0.29, which corresponds to a half of the removal of activated carbon. It is considered from the above results that the holding time enhances the production of micro and me so pores in the residue.

3.2 Wastewater treatment

The effect of solid residue addition on the performance of wastewater treatment was examined. Here, it is expected that the residue has a role of immobilizing microbe.

3.2.1 Experimental Model wastewater was treated by means of limited aeration method of activated sludge. Two columns with 0,100 m in diameter and 1,00 m in height were used. A draft tube with 0.050 m in diameter and 0.50 m in length was inserted to the © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Waste Management and the Environment, D Almorza, CA Brebbia, D Sales & V Popov (Editors). ISBN 1-85312-907-0

28 Waste Management and the En~’irownent

columns, The model wastewater consisted of glucose, polypepton and KH2P04, and respective concentrations were 0.33, 0.60 and 0.02 kg/m3 (BOD : TN : TP = 100: 10: 1). The concentration of the activated sludge which was acclimated with the model wastewater was 3.0 kglm3. The solid residue particle of dogfood was added into one column (20 vol%), but no particle was added into another column. The liquid volume was 5 L, The aeration was done during 8 h a day and the air flow rate was set to be 7 vvh [air volume / (liquid volume oh)]. The concentration of total nitrogen in effluent was measured.

3.2.2 Results and discussion The residue particles were smoothly circulated by liquid circulation flow due to the airlift. When the removals become stable (after three days from the start of experiment), the removal of total nitrogen in the column with the residue addition was 0,78, while that without the residue addition was 0,47. Biotilm was observed on the surface of residue particles. From these, it is considered that nitrobacter was immobilized to the residue particle and the vitrification is enhanced. That is, the solid residue obtained from the dry distillation is expected to be applied as the immobilizing carrier. Since the residue particles gradually become smaller by the fluidization, it is desired to increase the mechanical strength.

4 Conclusions

In this study, the dry distillation characteristics were studied and the applications of residue were examined. The following facts are obtained.

(1) The dry distillation characteristics at low temperature are different by the composition of organic solid waste. (2) The decrement in weight is larger in dry distillation at low temperature than in that at high temperature. (3) CH4 concentration is the highest in effluent gas. (4) It is expected that the solid residue is applied to the adsorbent and immobilizing carrier.

Nomenclature

c = concentration [ Vol% ] M = mole [ mol ] Ms = total mole of solid residue [ mol ] R~ = heating rate [lUs] Ts = temperature of sample [K] w = weight [kg] Wo = initial weight [kg]

~D = removal of dye $ = time :;; © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Waste Management and the Environment, D Almorza, CA Brebbia, D Sales & V Popov (Editors). ISBN 1-85312-907-0

Waste Management and the Ern’ironment 29

4 = holding time [s] BOD = biochemical oxygen demand [ mgiL ] TN = total nitrogen [ mgiL ] TP = total phosphorus [ mgiL ]

References

[1] S., Iida, Development of batch-type dry distillation/gasification technology for ASR (automobile shredder residue). JSAE, 20, pp. 259-279, 1999.

[2] D., Li, W,, Li & B., Li., Study on co-carbonization of coal with waste plastics. J Fuel Chem. Tee, 27(2), pp. 165-169, 1999

[3] K., Yamamoto, S., Misawa, K., Hizuka & R., Mimura, Experimental study on developing uses of RDF by carbonization. Hailibutugakkaironnbunnsi, 11(4), PP. 195-203,2000.

[4] T, Yoshida., The treatment by carbonization and e~ectiveuse of waste, NTS, 2001.