Methodology

In general, the processes that have been done in the present study were first, drying each material in an oven, following with hydrothermal carbonization of each mixture, and then milling (figure 12) and preparing hydro-char products for elemental analysis, calorific value determination, and germination test. The following table (table 10) summarizes different measurements and devices used to analyse hydro-chars. Samples were taken from solids after each experiment.

Table 10. Summary of Analytical Methods

Hydro-char quality

assessment test Unit Description Measuring instrument

Solids

Calculating dry matter FM %

Measurement of hydro- chars’ solid fraction and

raw substrates

Memmert Universal drying Oven UNE400

Calorific value MJ/Kg

Measuring the higher heating value of the dried hydro-char and of

raw substrates

IKA C200 Oxygen Bomb calorimeter

Elementary analysis

(C, H, N, S) DM %

Measuring C, H, N and S of the dried Hydro-

char and raw substrates

Eurovector EA 3000 CHNS-O Elemental

Analyzer

3.2.1 Hydrothermal Carbonization Experimental Procedure

An experimental design of the substrates mixtures presented in table 11 shows how many percentage of a substrate was applied in which test. So, totally eight tests were done started with applying 100% of each substrate. Then, fermented sludge considered as the main waste stream that needs to be managed; therefore four tests were done with different mixture of sludge and agricultural residues. Hence, in test 4, 20% of sludge and 80% of Barley silage, and in test 5, 50% of each was prepared to use for HTC. The same portions were applied for the mixture of sludge and maize silage in tests 6 and 7. In the last experiment, T8, a combination of one third of each substrate was used.

Table 11. Experimental Design of the conditions and Substrates’ Mixture

HTC Tests

Temperature (°C)

Time (Hours)

Substrates (%)

SD BS MS

T 1 200 6 100 n n

T 2 200 6 n 100 n

T 3 200 6 n n 100

T 4 200 6 20 80 n

T 5 200 6 50 50 n

T 6 200 6 20 n 80

T 7 200 6 50 n 50

T 8 200 6 33 34 33

n = not used

Abbreviations that are used trough out the following sections summarized with a brief explanations in table 12.

Table 12. Methodology Abbreviations

Abbreviations

HTC Tests Substrates Hydro-chars

T1 = 100% Sludge T1f = Sludge (SD) T1h = Hydro-char of T1 T2 = 100% Barley T2f = Barley (BS) T2h = Hydro-char of T2 T3 = 100% Maize T3f = Maize (MS) T3h = Hydro-char of T3 T4 = 80% Barley+20% Sludge T4f = calculated fresh feed for T4 T4h = Hydro-char of T4 T5 = 50% Barley+50% Sludge T5_f = calculated fresh feed for T5 T5_h = Hydro-char of T5 T6 = 80% Maize+20% Sludge T6f = calculated fresh feed for T6 T6h = Hydro-char of T6 T7 = 50% Maize+50% Sludge T7f = calculated fresh feed for T7 T7h = Hydro-char of T7 T8 = 34% Barley+ 33%Maize+

33%Sludge

T8f = calculated fresh feed for T8 T8h = Hydro-char of T8

Note: Every item that is not mentioned as calculated, are really measured

To manage the time, everything got prepared the day before, in which the test was going to be run. First step was to calculate the amount of extra water that was needed to add to each material for each test. Therefore, table 13, was prepared to present the moisture content of each material; the drying procedure has been done under the same methodology for each substrate, in which substrates were dried in a drying chamber at 102°C for 24 hours. Moisture content was computed by weighing samples before and after drying and then by subtracting these two

values. Values for moisture content and dry matter are presented in percentage in table 13.

Table 13. Substrates’ moisture content calculation and drying condition

Substrates Temperature Duration

(h) Calculation of moisture content Weight (g) Weight

difference

Dry matter

%

Moisture content

% Before

drying

After drying

T1f 102 24 100 11 89 11 89

T2f 102 24 41 20 21 49 51

T3f 102 24 70 38 32 54 46

The value of moisture content is one of the parameters that improve reactions in HTC process. Accordingly, before starting each HTC test, the value of moisture content was ready for the feedstock, which was necessary to calculate the extra water needed. Biomass ratio that was considered for each experiment was 80% moisture and 20% solid. Thus, it represents that there was no need to add water to fermented sludge in the first test (T1), since 89% of it was liquid and enough to run the reactor for a HTC test.

Second HTC test (T2) has been done using 100% of barley. Since the moisture content was 51%, to have 80% moisture for the test, 435ml water added to 300 grams of barley. Every detail of calculation for material preparation was the same in each test, which are gathered in index 3. Barley and maize silage were used in the shape and size as their real size that is why grams of their solid phase were chosen differently according to the capacity that they occupied in the reactor.

3.2.1.1 HTC reactor set-up

The hydrothermal carbonization experiments were carried out with an experimental HTC reactor used for research purposes, which located at BOKU, Department of Material Sciences and Process Engineering Institute of Chemical and Energy Engineering.

Figure 11. 1.5 Liters self-built reactor used for HTC experiments at Chemical and Energy Engineering Institute, BOKU University

The reactor (figure 11) had about 1.5 L capacities. In order to use the reactor under a safe condition and to run the test as proper as it should be done, some safety points, had to be followed. Two third of the reactor has to be filled to have also a free space so as to avoid too much of pressure during HTC process. Therefore, totally one liter of materials, includes solid and liquid phase, were needed for each test, while this method changed in some tests considering the volume of silage. After fixing the reactor with its 12 screws manually with no more extra forces like using drill, a bit of nitrogen gas was blew over a tube to the reactor connected from temperature sensor in order to eliminate oxygen. In this case, every time the temperature sensor had to be removed and nitrogen tube was attached for a while.

During each HTC test, the reactor has been placed in a metal box isolated with glass wool all around the reactor, plugged into the power and attached temperature and pressure sensors to the sensors coming from a power machine, which is manufactured by B&R company (www.br-automation.com). The power system programed to read temperature and pressure from reactor, and the desired temperature was also set on the system to control the heat of the reactor up to the 200°C. Heating power safety was set to 80%, and also to prevent over shooting, there was another temperature option to be set to 180°C; therefore, at this point the heating power is reduced 10% automatically for threshold safety.

Inner pressure and temperature are recorded during each experiment. Temperature data is collected from the centre of the reactor by a temperature sensor. Data could be saved on a memory stick directly right from the power system or saved on a computer with the help of Automation Studio software, which was connected to the main power system and could read data from the power machine. Automation Studio software is linked to a program named OPC-

HTC.vi, which is encoded with Lab View software. OPC-HTC is encoded to show data (temperature, pressure and time) and at the same time can be used to save data on the computer as an excel file.

Then the metal box was covered and fixed by four screws. The over pressure valve was also covered and fixed to the box for more safety in case of any trouble shooting and breaks.

For power safety also there was a wire, which has to be connected to somewhere to the box or reactor so as to have a connection to the ground.

By pressing a button on the power machine, system starts to heat the reactor. It takes about 10 minutes that the temperature reaches 100°C; at this point, the pressure valve was opened in every test, to get rid of gases and be sure of oxygen elimination. The starting point was when the temperature exceeded to the 180°C, and then after 6 hours, the system was shut down and was prepared for the next step. Condition and parameters of HTC process was constantly the same in all 8 HTC tests (table 11; Figure 18).

The next step was cooling down the reactor. There are two ways of cooling down the reactor; one is easily leave the system to be cooled over night, or using cooling system.

Cooling system is kind of a water-pumping machine, which can be simply connected by tubes to a pipe, attached to the body of the reactor. Pressurized cold water flows over the pipe, thus the reactor starts to be cooled down. After about 45 minutes, reactor reaches to a proper pressure and temperature, so as to be able to handle and carry on for the next steps. In this study the cooling system was used in most experiments for avoiding time consumption.

Products of the HTC test had to be separated as solid and liquid phase, and be weighed right after emptying the reactor. Solid part was dried for 24 hours in an oven heated up to 102°C. Then again the dried matter was weighed to calculate water and solid fraction of the output product.

Figure 12. Milling device used to prepare samples for Elemental Analysis, Calorimetric Test and Germination test, at Waste Management Institute,

BOKU University

A simple test also has been done on the liquid phase in two steps of drying, in order to determine volatiles and remaining ash. Knowing volatile fraction of a liquid or HTC recycled water helps to know its heat potential and its overall usefulness. First step was simply drying 100 ml of samples at 102°C for 24 hours and then 550°C for one hour for the next step. Before and after each step, samples were weighed (index 2).

3.2.2 Analytical methods 3.2.2.1 Elemental Analysis

One gram of each milled-sample of Hydro-chars, plus the raw materials themselves were sent to the Microanalytic Laboratory, Faculty of Chemistry at Vienna University for a double elemental analysis. Labeled samples have to be packed in 3 mL Eppendorf vials. According to the standard method description (J. Theiner, 2014), C/H/N/S analysis is performed by using a Eurovector EA 3000 CHNS-O Elemental Analyzer. For each individual analysis run, between 0.75 and 3.0 mg of a sample are taken. Mineralization of the sample material is done by “flash combustion ®“ applying 25 kPa oxygen at 1,000 °C. Results of the analysis (table 15) and discussion are presented in chapter 4.

3.2.2.2 Calorific value

Calorific value and germination tests were also applied on the same samples. The value of heat of combustion for each sample was tested and calculated by a bomb calorimeter device (figure 13) at the Institute of Agricultural Engineering, Department of Sustainable Agriculture, University of Natural Resources and Applied Life Sciences located in Tulln, Austria. This test has been done twice on each sample, including raw materials and hydro-chars. Approximately one gram of each sample had to be prepared in shape of a pellet to be easily placed in a small glass sample cup, which then was located in to a cylindrical container so-called vessel bomb (figure 14). A 50J cotton string also was placed into the glass cup in contact to the sample pellet. After adding 1ml of water to the vessel, its door was sealed and the pressure of the vessel bomb was fixed to 30bar and was placed into the water container. The device was filled with water up to the marked zone, and then the rest of the process was automatically run after giving the actual weight of the pellet to the device. It takes about 15 minutes that the final result appears on the screen in the form of J/g (table 17, index 5). However, unit of MJ/kg was used in calculations.

Figure 13. IKA C200 Oxygen Bomb Calorimeters, Pelleting Press and Pressure Device

a. b.

https://opentextbc.ca/chemistry/chapter/5-2-calorimetry/ Photo taken by Samar Seyedsadr, October 2016

Figure 14. a. Schematic view of inside a Bomb Calorimeter b. Bomb Cell, 50J cotton strings, and other accessories

For ‘percentage change’ calculation (details in chapter 4) between the measured C and HHV contents of the mixtures and their calculated contents from mono substrates, two steps were followed:

First: compute the difference between measured and calculated values.

‘Difference’ = measured value – calculated value

Second: divide the ‘Difference’ by the calculated value and multiply the result by 100.

‘Percentage Change’ = ‘Difference’ ÷ calculated value × 100.

3.2.2.3 Germination Potential test

In order to examine the germination potential of hydro-chars and the effects that hydro- chars may have on the soil structure, leachate and the volatile effect on the seed germination, a method from Buss and Masek (2014) paper gave an inspiration to be followed in the present study. By this means, all 8 hydro-chars and 3 raw materials were tested. Materials needed for germination test were some cress seeds, sand in the size of 0.3-1.0 mm, small pots and boxes, and filter papers. This germination test was run in triple, at the green house of AIT institute in Tulln. In each boxes one sample was examined in three phases. First phase was a small pot with some holes filled with a mixture of 40 grams of sand and 1 mg of the sample; second phase included seeds on a pot to examine volatile effect placed above the first pot; and the last phase was for examining leachate effect, in which seeds where placed on a filter paper on the lowest level of the box, as it shown in the Figure 15. 30 seeds were applied for each phase in a box, in a total of 90 seeds. Each 33 boxes covered and isolated with a plastic cover (figure 16).

After 72 hours the germinations were counted. In order to make comparison a bit more simple, the germinations categorized in four groups, well-germinated; early stage; short root and no germination (figure17).

a. b.

Figure 15. Shows the order of three phases in a box, an example of before (a) and after (b) germination test

Results and analysis of germination test are presented at the section 4.3 and more details summarized in index 6. Statistical analysis was carried out for data obtained from germination tests using STATISTICA Software Version 7.1. Data were analysed by one-way ANOVA, followed by Duncan Test for post hoc comparison. The level of significance was set at p<0.05.