evaluation of a rotary drum drier processing pre-dried chicken manure

Biological Wastes 19 (1987) 3-23

Evaluation of a Rotary Drum Drier Processing Pre-dried Chicken Manure

J. Poels, H. Van Langenhove, W. Van der Biest & G. Neukermans

Faculty of Agricultural Sciences, State University of Gent, Coupure L 653, 9000 Gent, Belgium

(Received I0 March 1986; accepted 7 May 1986)

A B S T R A C T

Pre-dried manure from laying hens was processed discontinuously in a rotary drum drier. During 6 drying experiments the technical performance and the operation were investigated. Special attention was given to the environmental aspects of the drying process.

The dried end-product with a 90% dr)' matter content qualified as a completely sanitized organic fertilizer of high value. About 10 tonnes o f fresh material with 35% dr)," matter could be processed in one drying cycle of about 20 h, including 2 h for filling and emptying. The installation was safe and operated fully automatically. A high thermal efficiency of ca. 85% was noted.

Chemical and sensory analyses were performed on the rotary drier emissions. The characteristics of the emissions met the regulations concerning the maximum allowable concentrations as stated in the West German legislation.

Preliminary economic evaluations indicated that the feasibility of drying chicken manure was determined by the dry matter content of the fresh manure, the price of this manure, the utilized capacity of the drier and the price of the end-product.

I N T R O D U C T I O N

Agricul ture scarcely p roduces wastes in the strict sense and as a matter of fact c a nno t even afford to do so. On the cont ra ry , agriculture has the

3 Biological Wastes 0269-7483/87/$03.50 © Elsevier Applied Science Publishers Ltd, England, 1987. Printed in Great Britain

4 J. Poels, H. Van Langenhove. W. Van der Biest, G. Neukermans

capacity to utilize a great number of wastes from domestic or industrial origin with profits to agriculture as well as to the public and industrial sector (Poels & Verstraete, 1985). For instance, left-overs from kitchens and restaurants, molasses, vinasses, beetpulp, citrus pulp, potatoes wastes, etc., have been used for years as livestock feeds. On the other hand, residues from wood and steel industries, such as bark and metal slags, are utilized as fertilizers in horticulture and agriculture. Recently, a solid-state methaniz- ation process was developed for the stabilization of the organic fraction of solid waste (De Baere et al., 1985). In this way energy is recovered as biogas (50-60% CH,,) and the digested residue is a highly stabilized and hygienically acceptable compost. Furthermore, the application of a drying process can upgrade many wet materials such as wastes from slaughter- houses, breweries, fish and potato processing industries. The dried end products are valorized as feed for live-stock. Materials such as pre- dried chicken manure and digested residues from solid-state fermentations can be further dried to produce a dry commercial fertilizer.

The discontinuously working rotary drum drier described in this paper possesses important advantages for treating agriculture and food industry wastes. The conditioning of basic materials, e.g. toasting soja, and the preparation of feed by mixing fodders, are processes that can also be carried out by the rotary drum drier.

In this study, the drying of pre-dried chicken manure from laying hens was investigated. The rotary drum drier is evaluated with special attention to the technical performance and operation, the quality of the end products and the environmental aspects of the drying process.

METHODS

Working mechanism and description of the rotary drum drier

The rotary drum drier is installed horizontally. A schematic drawing is given in Fig. 1. The drum is rotated by means of a chain drive and a 4 kW motor with a reduction of 1/140. The rotation speed is adjustable and usually an operation speed of 1.5 rpm is maintained. The cylinder, with a length of 4m and an inner diameter of 2.4m, is insulated with 5cm rockwool. The drier is operated discontinuously. It is equipped with a horizontal conveyor-belt (3) and is filled through a funnel (2). About 8 t of wet material can be brought into the drum in ca. 30 min.

The cylindrical combustion-chamber (2 m long, 1.6m diameter) in the front is equipped with a two-step burner (4) which is fed with gasoil. With a consumption of 15 litres of gasoil per hour and per spray nozzle (2 items) a

Processing of pre-dried chicken manure 5

6 1

L L,0 Fig. 1.. Scheme of the drier installation. (1), Drum; (2) funnel; (3) conveyor belt; (4) two-step burner; (5) combustion-chamber; (6) ventilator; (7) electronic control unit; (8) crusher; (9)

motor; (10) balance.

maximum thermal capacity of 300 kW can be reached. The combustion- chamber (5) is installed in such a way that a ventilator (6) (1"5 kW) is able to suck supplementary air through a 10cm gap. This supplementary air, together with the combustion air, is used to dry the material in the drum drier. The air, saturated with water, leaves the drier, past a dust-removing cyclone, through the funnel and is emitted to atmosphere. The temperature in the combustion-chamber always remains lower than 130°C, in contrast to most conventional driers which operate at 400-700°C. The weight of the drum drier content can be registered at any moment by means of a balance which is installed under the entire drying system. In this way, a simple and accurate determination of the end point of the drying process is possible. To improve the mixing effect caused by the rotation of the drum, blades are installed on the inner side of the wall. In addition, the continuously- operating conveyor-belt causes a supplementary mixing effect during the whole drying cycle.

The drying system operates automatically by means of an electronic control unit (7). At any moment a switch-over from automatic to manual operation and vice-versa is possible. Each operation, such as the rotation of the drum and the ventilation, and important parts of the system, e.g. the motors, are double protected by safety measures. First, an electronic safe guarding is applied and then a second supplementary safety measure is foreseen. For example, the thermostat in the funnel automatically switches off the whole system if the temperature of the ventilation air exceeds a previously adjusted critical value. Further, a revolution counter continuously controls the number of revolutions per time unit. If a motor failure causes a standstill of the drum, the operation of the whole system

6 J. Poels. H. Van Langenhore, W. Van der Biest, G..Veukermans

stops immediately. Besides a thermic safeguarding, the ventilator also has an extra safety measure by means of pressure recorders.

As a consequence of these safety measures, the drying system demands a minimum of labour and can operate overnight without any problem. When the materials in the drum have had a sufficient residence time, e.g. when the desired weight is attained, the burners are switched off and the ventilation continues during 1-2 hours, to cool the end product to room temperature. Finally, a crusher (8) produces a homogeneous end product.

Poultry manure

In this study, 6 drying cycles were monitored. The basic material was pre- dried manure from laying hens. The laying hens were lodged in Californian cages. The chicken manure was pre-dried from a dry matter content of about 20-22% to 35-40% by means of a newly-introduced drying system. This drying system was installed in the Californian cages and used ventilation air, pre-heated via a heat exchanger, which flowed over the manure via perforated pipes.

Chemical analyses

Determination of the dry matter (DM) and the volatile solids (VS) were as Merck (1973). NH4- -N was determined according to Bremner and Keeney (1965). The determinations of the Kjeldahl-N analyses were as Bremner (1960). Potassium and calcium were determined by the flame photometry method of Cottenie et al. (1982), and the spectrophotometric determinations of phosphates were according to Scheel (1936).

Microbiological analyses

To characterize the hygienic quality of the end product, the total colony forming units were determined as well as the presence of faecal coli, faecal streptococci and salmonella. A sample of 10 g manure was homogenized in 90 ml of physiological saline. The determination of the different bacterial groups used standard procedures:

(i) Total colony forming units: nutrient agar plates incubated at 37°C for 72 h.

(ii) Faecal coli: MacConkey agar (Difco) plates incubated at 44°C for 24 48 h.

(iii) Faecal streptococci: Bacto KF Streptococcus agar (Difco) plates incubated at 37°C for 48-72 h.


(iv) Salmonella: presumptively isolated by direct inoculation on Triple Sugar agar slants (Difco) at 37°C for 48 h after enrichment for 3 days at 37°C in selenite broth.

Gas chromatography-mass spectrometry

Chemical analysis of odour problems was done in different steps. First gas chromatography-mass spectrometry (GC-MS) was applied to identify volatile organics in the emissions. The next step was the selection of compounds contributing to the odour problem, which is usually based on the comparison of odour threshold data of identified compounds. Finally, odorous compounds were quantitatively determined. GC-MS analyses were performed according to an analytical scheme consisting of: sampling by adsorption on Tenax GC, followed by thermal desorption, glass capillary-gas chromatography and electron-impact mass spectrometry. The system has been described in detail by Van Langenhove etal. (1982). Since volatile organic acids can scarcely be detected with the procedure described above, a specific method was used to measure the presence of these compounds. Air was sampled by absorption in a 0'05 N KOH solution in a Pavelka Trap. Samples were acidified with HC1 and extracted with ether. Aliquots of the ether extracts were analysed by GC. The apparatus was a Varian 3700 GC provided with an FID detector: glass capillary- column length 25m, i.d. 0"5ram, stationary phase FFAP (6mgml-1), carrier gas helium (4 ml min- 1).

Organic sulphur and nitrogen compounds were quantitatively determined. Amines were sampled by sorption on a cation-exchange resin in the H + form, packed in a small glass tube (length 10 m, i.d. 3 mm). The ion- exchange resin was transferred to a small vial (3 ml) and 1 ml ofa 5 y NaOH solution was added. One/A of the basic solution was analyzed by GC. The apparatus was a Varian 3700 GC with TSD (thermionic selective detection), column length 3 m, i.d. 2 mm packed with Carbowax 20 M 2%, KOH 2%, on Chromosorb.

For the quantitative determination of organic sulphur compounds sampling was performed by adsorption on Porapak Q. After thermal desorption, compounds were analysed by a Tracor 560 GC with FPD detection, glass capillary column length 50 m, i.d. 0-5 mm, stationary phase SE-30 (6 mg litre- 1).

Olfactometry

Olfactometry is a sensory technique, in which a panel of human observers is used to determine the number of times an odorous sample has to be diluted

8 J. Poels, H. Van Langenhot'e, W. Van der Biest, G. Neukermans

before half of the panel cannot discriminate the diluted odour sample from odour-free air. The result is called the odour-dilution ratio (ODR) or the number of odour units per m 3. The first term is preferred, since it gives a better expression of what is really measured than the ratio between two air streams does. Odour-dilution ratios can be used to compare the relative importance of different odour sources and to predict the environmental impact of an odour source by means of dispersion calculations.

The olfactometer used in these analyses was constructed according to the principles of dynamic forced-choice triangle olfactometry.

Air from a compressor was purified by active carbon adsorption and delivered at 0"3MPa (pressure regulator). This air stream was used as odour-free air and delivered through 3 ports at a flow rate of 1.5 m 3 h-1 each.

Odorous air was diluted first in a predilution system, with dilution factors gradually variable between 1-5 and 300 dilutions. For samples with low ODR, this system was not used. The prediluted air was then delivered to a stepwise dilution system, with a ratio of two between two consecutive dilutions. The range of dilutions for the entire system varied from 25 to 70 000. For each measurement, panelists had to evaluate three air streams, one of them being the diluted odour sample the other two being odour-free air (triangle test). Panelists were asked to indicate the odorous sample. Ten panelists varying in age from 25 to 40 years were used in these analyses.

Samples were taken in polyethylene bags, reinforced with aluminium foil. Condensation in the sample bags was prevented by mixing odorous air with odour-free air (1/10) during sampling. Samples were analyzed within 48 h.

RESULTS AND DISCUSSION

Technical evaluation

Table 1 and Table 2 summarize some technical results obtained during 6 drying experiments. During the experiments 1 to 4, chemical and microbiological analyses were performed. Table 3 shows the chemical characteristics of fresh and dried chicken manure. In experiment 4, the lowest gasoil consumption should be noted. This was probably caused by the highest dry matter content (48.0%) of the fresh chicken manure.

The dry matter content varied from 36-4 to 48"0%. Normally, dry matter contents between 35 and 40% may be expected as an average value over a whole year. The 48.0% noted in experiment 4 was obtained during a warm, summer period in July 1985. The dried chicken manure had a dry matter content between 88"3% and 91.1%. The amount of water evaporated per

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10 J. Poe&. H. Van Langenhore, W. Van der Biest, G. Neukermans

TABLE 2 Summary of the Principal Measurements of the Drying Process

Total duration of 6 drying experiments (h) 45.75 Total quantity of fresh chicken manure to treat (kg) 26 670 Average dry matter value (%) 40-50 Average quantity of fresh manure dried per hour (kg h-1) 583 Total quantity of dried chicken manure (kg) 12 165 Average dry matter value (%) 89.7 Average quantity of dried manure produced per hour (kg h - t ) 265 Total amount of water evaporated (kg) 14 505 Average quantity of hot water evaporated per hour (kg h-1) 317 Electricity consumption (kWh) 345 Average electricity consumption per hour (kWh h - 1) 7.5 Electricity consumption per 100 kg dried manure (kWh 100 kg-1) 2"8 Total fuel consumption (litre) 1 198 Average gasoil consumption per 100kg dried manure (litre 100kg-1) 9'8 Average gasoil consumption per 100kg evaporated water (litre 100 kg-1) 8"3 Average thermal efficiency (%) 86.2 Average energy consumption per 100kg dried manure (MJ 100 k g - l j 367 Average temperatures

incoming air 15 outcoming air through the funnel 70 in the drum 75

Average flow rate of air through the funnel (m 3 h - 1) 1 500

hour in experiments 3 and 4 was significantly lower than in the other experiments. The explanation is that in these two experiments the drum was more filled, namely about 5.5-6t of fresh manure versus 3.5-4t, and consequently the evaporation of water in experiments 3 and 4 was more difficult. In all these experiments, the thermal efficiency of the drying

TABLE 3 Chemical Analysis of Chicken Manure Before and After the

Drying Process

Parameter Before drying After drying

D M ( % ) 40"5_+ 5"16 n = 4 89.7_ 1-53 n = 4 VS (%) 27"6__+4-14 n = 4 63.7+0-80 n = 4 Ash (%) 12.9 ___ 2-25 n = 4 26'0 + 1-89 n = 4 Total N(%) 19.8_+2.73 n = 4 26-0_+ 1"66 n = 4 N H ~ - - N (%) 4.5_+ 0.47 n = 4 5.4+ 1-15 n = 4 Org. N (%) 15.4 + 2.67 n = 4 20-6 + 1'27 n = 4 P205 (%) 16.3 -+ 0-96 n = 4 30-0 _+ 4'30 n = 4 K20 (%) 12.1 _+2-51 n = 4 23-0_+3-69 n = 4 CaO (%) 27.4 _+ 4"19 n = 4 85-6 + 7"13 n = 4

Processing of pre-dried chicken manure It

process varied between 75.6% and 96.5% with an average of 86"3%. During the six drying cycles 26 670 kg of fresh chicken manure with a mean dry matter content of 40-5% were treated, resulting in 12 165 kg of end product with 89-7% DM on the average. Thus 14 505 kg of water was evaporated with 1198 litres of gasoil. Theoretically, about 36 800 MJ are necessary to evaporate this amount of water. In these calculations an evaporation heat of 2" 18 MJ per kg water was used. Further, the heat necessary for heating up the water in the fresh manure from room temperature (15°C) to 100°C was taken into account and amounted to ca. 5200 MJ. Gasoil (specific density 0"835kglitre-~) has a net calorific value of 35"6MJlitre-1 (Berkowitz, 1979). A mean thermal efficiency of 86.3% was reached in these 6 drying experiments. This efficiency is fairly high as compared to rotary drum driers which operate at temperatures of 350-400°C and reach an efficiency of ca. 60% (Priem, 1974). The temperatures measured at the end of the drum during a whole drying cycle did not exceed 75°C, while the temperature in the combustion-chamber and perhaps at the other end of the drum was maintained at 130°C. These relatively low drying temperatures influence the thermal efficiency to a great extent. The average temperature of the water-saturated air in the funnel reached 70°C and the air had a flow rate of ca. 1500m 3 per hour.

Sensory analysis

Odour emissions can be analyzed either by chemical or by olfactometric means. Chemical analyses yield information about the identity and concentrations of compounds .present in emissions. From these data, emission factors can be calculated and, if necessary, these data form a sound basis for the selection of abatement techniques. In order to evaluate the impact of the rotary drum drier emissions, samples were taken for identification and for the qualitative determination of organic compounds.

Results of the GC-MS identification are summarized in Table 4. The hydrocarbons and benzaldehyde are incomplete combustion products of the fuel. Since hydrocarbons (Van Gemert & Nettenbreyer, 1982) show high olfactory thresholds it is unlikely that these compounds contribute significantly to the odour of the emissions.

Organic sulphur compounds have a typically pungent odour character, trimethylamine causes a fishy odour, while pyridine has a characteristic burnt odour. These compounds have odour detection thresholds in the sub- ppb to 10 ppb level and contribute to the odour of the drier emissions.

Linear and iso-organic acids from acetic to caproic were detected in different samples. However, not every acid was present in every sample. Concentrations of the acids were below the limit of quantification, which in the conditions used in these analyses were; for acetic acid, 0 '2ppm,

12 J. Poels, H. Van Langenhove, W. Van der Biest, G. Neukermans

TABLE 4 Organic Compounds Identified by GC-MS in the Rotary Drum Drier Emissions (Kovats Indices are Given in Brackets)

Organic sulphur compounds Dimethyl sulphide (505), dimethyl disulphide (724), dimethyl trisulphide (948)

Organic nitrogen compounds Trimethylamine (< 500), pyridine (721)

Linear aliphatic hydrocarbons From octane (800) to tridecane (1300)

Aromatic hydrocarbons Benzene (645), toluene (753), ethylbenzene (350), m,p-xylene (854), styrene (876), o-xylene (880), propylbenzene (941), 1,3,5- trimethylbenzene (959), p-cymene (1014), indane (1021), p- diethylbenzene (1043), naphthalene (1170), 2-methylnaph- thalene (1283)

Aromatic aldehydes Benzaldehydes (933)

for propionic acid, 0-15 ppm and for all other acids, 0"i ppm. From these results it can be concluded that organic acids were present in the emissions but that their concentrations were so low that contribution to the odour was negligible. A possible explanation for the low acid concentration is the high amount of ammonia present in the manure. Acids, which were undoubtedly formed by microbiological activity in the chicken manure, were neutralized by ammonia and remained as ammonia-salts in the dry matter.

Drfiger-tube tests for hydrogen sulphide indicated that concentrations were below the limits of detection.

Based on the results of the identification of the odours in the dryer emissions it was decided to perform quantitative measurement of organic sulphur and nitrogen compounds.

Results of the quantitative measurements are given in Table 5. From these results it can be seen that dimethyl disulphide is the most important organic sulphur compound, with a maximum concentration of 3"3 ppm. Dimethyl sulphide was quantifiable in 6 out of the eleven samples, with a maximum concentration of 0.48 ppm. Dimethyl trisulphide was more often detected (in 10 of the eleven samples) than dimethyl sulphide. However, concentrations of dimethyl sulphide were generally lower, reaching a maximum of 0"33 ppm. Maximum concentrations measured for the organic nitrogen compounds were 0.17ppm for trimethylamine and 4"5ppm for pyridine.

Based on these maximum concentrations and on a volumetric emission


TABLE 5 Concen t ra t ions in ppm (v/v) of Volatile Organic Sulphur C o m p o u n d s and Amines in

the Drier Emissions (Symbols are as follows: DMS, dimethyl sulphide; D M D S , dimethyl disulphide; DMTS, dimethyl trisulphide; TMA, t r imethylamine; n.d., not determined; and - - ,

below level of detection.)

Experiment Time (h) after DMS DMDS D M T S TMA Pyridine starting the drying cycle

2 1 0"48 0.024 0-017 0.066 0-2 2 - - 0.115 0-073 0.17 - - 4 - - 1"45 - - 0"004 - - 5 - - 1"93 - - 0"016 - -

3 2 0-021 0-022 - - 0"06 O" 16 3 0"007 0'017 0"018 0"16 0"13 4 - - 0"44 0-027 0"035 - - 6 - - 0-95 0"028 0003 - -

4 3 0"26 0"36 0"009 0-004 3"4 4 0'07 0"71 0'022 0"003 3"3 5 0"13 3-26 0"33 - - 1"9 6 n.d. n.d. n.d. - - 4.5

rate of 1500m3h -1 (343K), emission factors were calculated. Also the ratios of the maximum concentrations in the emission and the odour- threshold concentrations of the different odours were calculated. Odour- threshold concentrations were based on data given by Van Gemert & Nettenbreyer (1977) and Fazzalari (1978). Results are summarized in Table 6. The figures mentioned in Table 6 are useful for comparison with emission

TABLE 6 Maximum Emission Rates and Ratios of the Max imum Concen t ra t ions and O d o u r

Threshold Concen t ra t ions of the Odours

Compound Maximum Maximum Odour threshold Ratio emission rate concentration concentration A:B

(gh -1) (mgm -3) × 103(mgm -3) A B

Dimethyl sulphide 1-6 1" 1 2'8 400 Dimethyl disulphide 16 10.7 3'8 2 800 Dimethyl tr isulphide 1.2 0.8 5.4 160 Tr imethylamine 0"5 0.3 0.5 600 Pyridine 20 13.7 95 140

14 J. Poels, H. Van Langenhove, W. Van der Biest, G. Neukermans

rates and maximum allowable concentrations as stated in West German legislation (Technische Anleitung zur Reinhaltung der Luft). In this legislation organic chemicals are classified in three classes .The odours identified in this study belong to Class 1, for which a maximum emission concentration of 20 mg m-3 is stated, at least if the emission rate exceeds 0"1 kg h-1. As can be seen from Table 6, the characteristics of the rotary drum drier emissions satisfy these regulations.

The odour-dilution ratio of certain organic compounds was determined for a number of samples. Preliminary samples were taken from experiment 5, a second set of samples was taken from experiment 6. Results of the olfactometric analyses are represented graphically in Fig. 2.

The lowest and highest ODR were 2450 and 15 600. Seven out of the eight samples ranged between 2450 and 6830. The maximum ODR occurred after 4 h in the drying cycle.

Ammonia concentrations in the emissions were measured by Dr~iger-tube

O.D.R.

x 10 3

15

10

l i 1, o 5 lo t i m e (h)

Fig. 2. Results of the olfactometric analyses. II, experiment 5 and; "A', experiment 6. Time is from the beginning of the drying cycle.


300 pp, ~H

250

200

150

I00

50

hour@ 0 ,' . . . . . , ,' " ~ i ~ ; , t ~ ~ .

0 I 2 3 4 5 6 7 8 9 10

Fig. 3. NH3-emissions during 5 drying experiments. Time is from the beginning of the drying cycle.

methods. The important point as far as the odour problem is concerned, is that the maximum NH 3 concentrations were 350 ppm. Since ammonia has a high odour detection threshold (ppm level), it means that this compound is not important for the odour problem.

Fig. 3 shows N H 3 concentrations during 5 drying cycles. The NH 3 emissions are mostly below 150ppm, only 3 out of the 36 measurements

10 g NH~-N/kg

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8

7

6

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3

2

I d , : : y ~

0 i i I t I i i , I , I t

0 5 10 15 20 25 30 35 ;O .~5 50

Fig. 4. N H 4 + - - N concentrations of pre-dried chicken manure incubated at 14~C and 35°C.

16 J. Poels, H. Fan Langenhove, W. Van der Biest, G. .Veukermans

exceeded this value. These minor emissions are due to the fact that the pre- dried chicken manure was never older than 5 days. Thus, the degradation of proteins, resulting in increasing N H ~ - - N levels, was limited. Laboratory experiments in buckets (Fig. 4) clearly proved that the r + N H.~--N content of

+ pre-dried chicken manure increased; to 8-10 = o NH,, - - N after 2-3 weeks of storage at 35°C and 14°C, respectively.

Drying experiments with chicken manure from a deep-pit house, which had a content of ca. 7g N H 2 - - N k g - I and an age of 1-2 months, demonstrated NH3-emissions of 500-800 ppm during several hours (Fig. 5). In contrast with the values o f N H 3 found in the experiments with pre-dried chicken manure, only 1 out of the 18 measurements was lower than 150 ppm. All others varied between 300 and 500 ppm.

' 1 0 0 0 ppm NH 3

goo ~: r

80O / \ / \ / \ i \

1i \ • 600 " • \

/ \ • '~ .

400 ! 1 \.,//--- / i

zoo ~-.% 1 O0 " ~ ' "

hour'8 0 I } I I t I t ! t i

0 1 2 3 4 5 6 7 8 9 lO

Fig. 5. NH3-emissions during 2 drying experiments with chicken manure from a deep-pit house. Time is from the beginning of the drying cycle.

Chemical analyses (Table 7) indicated that during a drying cycle of 10 h, 5 .1gNH4+--Nkg -I DM had disappeared or ca. 12.2kg N H ~ - - N per drying cycle. NHa-emissions calculated with a mean volumetric emission rate of 1500m 3 per hour containing 150ppm NH 3 during a cycle of 10 hours result in a total NH3- -N emission of 1"1 kg per cycle. The difference between these two calculation methods suggests the possibility that N H ~ - - N also leaves the drier in other forms than NH 3.

These total N H 3 - - N emissions are relatively low. A house of 20000 laying hens is considered and an average weight of 2 kg per laying hen is supposed. The maximum ventilation standard for laying hens is 4 m 3 per kg live weight per hour. Calculations with 25% of the maximum ventilation


TABLE 7 Chemical Composition of Fresh and Dried Chicken Manure on Base of the Dry Matter

O.M. Ash Total N NHf,--N Organic N P:O_~ K,.O CaO

Fresh chicken manure n = 4 680=4-46 32,0=4"48 49.1_+5"39 ll-2_+2.02 37-9--4.60 40.5_-357 29.6_+2-45 67.6=3.85 Dried chicken manuren=4 71-I_+1"67 29"9_-1"67 29"0_+2"24 6"l_.1,37 22"9=1-53 33"6=5-34 25'6_--4"34 96.4+908

capacity give an indication of the total N H 3 - - N emission during a normal day. Air of laying hen houses contains 10-15 ppm NH 3 or 12"5 ppm on the average. With a ventilation capacity of 1 m 3 per kg live weight per hour, the total N H 3 - - N emission amounts to 7"5 kg per day. Further, the maximum ventilation standard for fattening pigs is 1 m 3 per kg live weight per hour. The air of pig houses contains 5 - 1 0 p p m NH 3 or on the average 7.5 ppm. A pig house with 1000 fattening pigs causes a total NH3- -N emission per day of 6-7 kg. In these calculations, 60 kg is chosen as the mean weight of one pig and only 25% of the maximum ventilation is taken into account. Compared to the ammonia emission of animal houses during one day, the rotary drum drier causes emissions during one drying cycle without serious odour problems. Nevertheless, it is advised that only fresh manure is processed in the drying system.

Utilization of dried manure

The chemical compositions of fresh, pre-dried chicken manure and the dried chicken manure are summarized in Table 3. About 70% of the dry matter is organic. The presence of faecal coli, faecal streptococci and salmonella was examined to measure the degree to which the dried chicken manure had been made hygienic. The results (Table 8) indicate that a complete destruction of faecal coli, faecal streptococci and salmonella is obtained in a 10h drying cycle. In practice, when the rotary drum is completely loaded, one cycle must always have a duration of at least 10 h.

Since 1980, the prices per unit of chemical fertilizers have increased by 27%, 48% and 55% for N, P205 and K20 respectively (Fig. 6). As a consequence, the application of chemical fertilizers becomes more and more expensive. In February 1985 the following prices per unit of fertilizers were noted: 29 BFkg -1 N, 34BFkg -1 P205, 15BFkg -1 K20 and 4-5 BFkg -1 lime (BF = Belgian Francs). A value of 0.75 BFkg-1 organic material is awarded to organic matter. The theoretical value of dried chicken manure amounts to ca. 2650 BF t-1. In this calculation the organic nitrogen is not taken into account. This dried chicken manure qualifies as an organic

18 J. Poels, H. l'an Langenhot'e, W. Van der Biest, G. Neukerrnans

TABLE 8 Levels of Indicator Bacteria and Qualitative Presence of Salmonella sp.

in Fresh and Dried Chicken Manure

Number o f experiment 1 2 3 4

Duration of the drying cycle (h) 6-75 6.50 I0'0 11"0

Fresh chicken manure C F U g - l manure 10.109 91.10 s 26.10 s 34.108 Faecal coliforms g -1 31"103 10.104 ND ND Faecal streptococci g - 1 25'105 12.105 12-10"* 11-I0"* Salmonellae (+ or - ) + + + +

Dried chicken manure C F U g - l manure 32"10'* 68.105 41'106 11"105 Faecal coliforms g - 1 ND ND ND ND Faecal streptococci g - ' 29"103 7.104 ND ND Salmonellae (+ or - ) . . . .

CFU, Colony Farming Units. + , Present. - , Not present. ND, None detected.

40 BF/UNIT

35 / ~P20 s 30 ~ N

25

15 / ~ o

5 ~ ~__~---.-~-~ CoO yeGr

0 i i ~ I i i, I 1970 Ig72 1974 Ig76 1978 Ig80 1982 ig84

Fig. 6. Changes in the prices ofchemical fertilizers during the period 1970-1984 (IEA, 1970 -1984).


fertilizer of full value and is completely sanitized. Organic matter material contributes to the maintenance of the humic fraction in soils (Greenland, 1977). Over the last two decades, the increased application of chemical fertilizers and the decreased application of traditional manures has diminished the humic fraction of soils in strictly agricultural regions. In the long run, this situation will have a negative impact on soil structure and soil fertility and is therefore not acceptable. On the other hand, intensive animal production with large concentrations of animals in some regions produces large quantities of liquid manures. The highest priority should be given to making use of these wastes. Processes or systems which are able to concentrate organic wastes open possibilities for their profitable transport to agricultural regions and must be favoured.

In this context, the present drying system contributes in a positive way to the protection of the environment.

E C O N O M I C EVALUATION

Capacity of the drier

The maximum capacity of the drier is 10 t flesh chicken manure (35% DM) per cycle. On the average 320 kg of water per hour are evaporated (Table 2). This means that 6110kg of water must be evaporated and that 3980kg dried manure (90% DM) is produced. The duration of one drying cycle is estimated to be 21h (19 hours for drying and 2 hours for filling and emptying). In practice ca. 300 cycles per year may be possible. In this way, 3000t of fresh manure (35% DM) are upgraded to 1167t of end product (90% DM).

Size of the farm

On the average one laying hen produces 0"16kg manure (22% DM) per day. By means of pre-drying it must be possible to obtain a manure with a mean DM-content of 35%. In warm summer periods, higher values can be obtained, in winter periods lower values are possible. During one year 1000 laying hens produce 12"8 t of DM or 14.2t of dried manure (90% DM). Figure 7 shows the relation between the utilized capacity of the rotary drum drier and the number of laying hens which must be present.

Input and output

To work one year on full capacity 3000 t or 4050 m 3 flesh pre-dried chicken manure (35% DM) are necessary. The maximum price which will be paid

20 J. Poe&, H. Van Langenhove, W. Van der Biest, G. Neukermans

I00 -

90

80

70

60

50

n u ~ oF loyln 9 hQne(xlO00)

4 0 I I t I I t 4 0 5 0 6 0 7 0 8 0 9 0 1 O0

Fig. 7. Relation between the utilized capacity of the drier and the number of laying hens.

for pre-dried chicken manure is estimated at 250 BFm-3. This way the value of the input amounts to 1 012000BF. The price of the bulk end- product varies between 4000 and 6000 BF t - t . In this study, the economic evaluation has been performed with prices of the dried chicken manure of 4000 BF, 5000 BF and 6000 BF per tonne.

Total costs for the drying process

The total investment costs for the installation of a drier with a capacity of 10t of fresh pre-dried chicken manure per cycle are estimated at 3 680000 BF, crusher included. This installation has a lifetime of 8 years. The price of the building (25 m x 10 m) is 4000 BF m- 2 or 1 000 000 BF. The maintenance costs of the drier are ca. 160 BF per drying cycle or 48 000 BF per year. For the maintenance costs of the building 1% of the investment cost per year, or 10 000 BF, are taken into account.

The operating costs are mainly due to the energy consumption. In this evaluation a gasoil consumption of 9"8 litres per 100 kg of end product and 2.8 kWh per 100 kg of end product (Table 2) are used. The price of one k w h is 4.5 BF and of one litre gasoil 15.0 BF. The labour costs of 2 h per drying cycle are 1000 BF. Table 9 gives a schematic survey of the operation costs of the drying process during one year.

Internal rate of return of the drying process

The internal rate of return (IRR) is the interest or discount rate for which the actualized values of the expenses due to the total investment are equal

Processing o f pre-dried chicken manure 21

TABLE 9 Operation Costs of the Drying Process Over One Year

Costs BF %

Purchase money fresh chicken manure l 012000 31.3 Operation costs

Energy consumption gasoil 1 715000 53"0 electricity 147 200 4.5

Maintenance costs drier 48 000 1"8 building 10000 0"0

Labour costs 300000 9-3

Total costs 3 232000 99"9

to the actualized value of the proceeds as a consequence of the investment. The IRR can be calculated with the following formula:

tl

Ot L I° = (1 + r ) ' + (1 + r)"

t = 0

where I o is the amount of the total investment at the start of the operation of the project; r is the IRR (internal rate of return which is sought); L is the value of the installation after n years (for the sake of simplicity, this liquidation value is fixed at zero); n is the lifetime of the installation, which is estimated at 8 years; and O~,2...,, is the gross revenues minus the direct expenses during year 1,2,. . . , t . In this study O, is considered to be a constant so that the formula can be transformed into:

1 1

(1 + r) s Io = O,

r

By iteration the best fit can be obtained. If the capitalization interest is lower than the internal rate of return, the project can be evaluated as being profitable. Figure 8 gives a survey of the IRR as a function of the utilized capacity of the drier. It is very obvious that the yield of the drying process is to a great extent influenced by the effectively utilized capacity as well as by the price of the end product. In practice, it is advisable to investigate the quantities of pre-dried chicken manure which are available before a drying

22 J. Poels. H. Van Langenhot'e. W Van der Biest, G. Neukerrnans

100 IRR(Z)

90

80 .~

70

60 ~

40 i - ~ " " ' - ~ - ~ " " - " ' - ' ~

30 ~ ' " ~

u t l 1 lzed c a p a c i t y

50 60 70 80 gO lO0 Fig. 8. Internal rate of return as a function of the utilized capacity of the drier at different

prices of the endproduct (FI, 4000 BF t - i; + , 5000 BF t - 1; and A, 6000 BF t - 1).

process is planned. One could process chicken manure from different farms in order to give more profitable results.

CONCLUSIONS

Pre-dried chicken manure (35% DM) can be upgraded to an end product (90% DM) that qualifies as a completely sanitized organic fertilizer of good value. About 10t of fresh manure can be processed in one drying cycle of about 21 h, including 2 h for filling and emptying. The operation is safe and fully automatic and a thermal efficiency of ca. 85% is obtained.

The characteristics of the emissions meet the regulations concerning the maximum allowable concentrations stated in the West German legislation. Preliminary olfactometric analyses resulted in odour dilution ratios between 2450 and 15 600. Ammonia concentrations in the emissions were mostly below 150ppm. The highest detected value was 350ppm. This compound is not important for odour problems if only fresh, pre-dried chicken manure is processed.

Preliminary economical evaluations indicate that the feasibility of drying chicken manure is determined by the dry matter content of the fresh manure, the utilization capacity of the dryer and the price of the end- product. It is not advisable to dry chicken manure if the dry matter content is below 35 %, if the purchase price of the fresh manure exceeds 250 BF m-3, if the utilized capacity of the drier does not reach 75-80% and, finally, if the price of the end-product does not amount to 4000 BF t-1


A C K N O W E E D G E M ENTS

Thanks are expressed to the Board of Administrators and the Direction of the Belgian Institute for the Encouragement of Scientific Research in Industry and Agriculture ( IWONL, Brussels) and Laborelec who sub- sidized this research. The friendly and skilful cooperat ion with Mr W. Broucke, farmer and constructor of the system, is also acknowledged.

R E F E R E N C E S

Bercowitz, N. (1979). An introduction to coal technology. Academic Press, New York. 345 pp.

Bremner, J. M. (1960). Determination of nitrogen in soil by the Kjeldah[ method. J. Agric. Sci., GG, 17-33.

Bremner, J. M. & Keeney, R. D. (1965). Steam distillation methods for determination of ammonium nitrate and nitrite. Anal. Chem. Acta., 32, 485-95.

Cottenie, A., Verloo, M., Kiekens, L., Velghe. G. & Camertynck, R. (1982). Chemical analyses of plants and soils. Laboratory of Analytical and Agrochemistry, State University Gent, Belgium.

De Baere, L., Verdonck, O. & Verstraete, W. (1985). High rate dry anaerobic composting process for the organic fraction of solid wastes. Seventh Symposium on Biotechnology for Fuels and Chemicals, May, 14-17, 1985, Gatlinburg, TN.

Erste Allgemeine Verwaltungsvorschrift zum Bundes-Immisions schutzgesetz. (1974). Technische anleitung zur reinhaltung der luft. Gemeinsames minister- blatt. Bundesministerium des Innern Bonn, 4 September 1974.

Fazzalari, F. A. (1978). Compilation of odour and taste threshold z'alues data. American Society for Testing and Materials. Baltimore, MD.

Greenland, D. J. (1977). Soil damage by intensive arable cultivation: temporary or permanent? Phil. Trans. R. Soc. Lond., 281, 193-208.

IEA Institute Economique Agricole (1970-1984). Statistiques de I'LE.A. Minist6re de l'agriculture, Manhattan Centre, Office Tower, Bolwerklaan 21, 1210 Bruxelles.

Merck, E. (1973). Die untersuchung yon wasser. E. Merck, Darmstadt. Poels, J. & Verstraete, W. (1985). La coordination dans le traitement des d6chets en

agriculture. Revue de l'Agriculture, 38, 413-31. Priem, R. (1974). Het drogen van kippenmest. Mededelingen van bet Rijksstation

voor Landbouwtechniek, Publ. hr. 55/S.D.B.I_.-20, Merelbeke, Belgium. 84 pp. Scheel, K. C. (1936). Die colorimetrische bestimmung der phosphors~.ure in

di.ingemitteln mit dem pulfrich-photometer. Z. Anal. Chem., 105, 256-69. Thiele, V. (1982). Olfaktometrie yon H2S. Ergebnisse des VDI ringvergleichs.

Staub-Reinhalt-Luft, 42, 11-15. Van Gemert, L. J. & Nettenbreyer, A. H. (1977). Compilation of odour threshold

values in air and water. National Institute, Zeist, Central Institute for Nutrition and Food Research, TNO, Zeist. The Netherlands. Supplement 1982.

Van Langenhove, H. R., Van Wassenhove, F. A., Coppin, J. K., Van Acker, M. R. & Schamp, N. M. (1982). Gas chromatography, mass spectrometry identification of organic volatiles contributing to rendering odours. Environ. Sci. Technol., 16, 883-6.

evaluation of a rotary drum drier processing pre-dried chicken manure

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