The Effects of Moisture Content on Digestate-Derived Biochar

REPORT ON

INDUSTRIAL TRAINING

AT

The Leibniz Institute for Agricultural Technology,

Potsdam, Berlin, Germany.

Submitted by

Rishabh Ghotge

110909184

In partial fulfillment of the requirements for the award of the degree of

BACHELOR OF ENGINEERING

IN

MECHANICAL ENGINEERING

DEPARTMENT OF MECHANICAL AND MANUFACTURING ENGINEERING

MANIPAL INSTITUTE OF TECHNOLOGY

(A Constituent Institution of Manipal University)

MANIPAL – 576104, KARNATAKA, INDIA

August 2014

Department of Mechanical and Manufacturing Engineering, MIT, Manipal 2

Contents

Acknowledgements……………………………………………………………..3

1) Introduction……………………………………………………………....4

2) Objectives………………………………………………………………...9

3) Work Performed………………………………………………………...10

4) Inferences and Discussion……………………………………………....37

Bibliography……………………………………………………………………39


Acknowledgements

There are a lot of people to whom I am greatly indebted for the successful

completion of this report. I would like to thank my guides, Dr. Jan Mumme and Dr.

Toufiq Reza for their immense contributions and wonderful advice. I would like to

express my profound gratitude to Benjamin Wirth, Ulf Lüder, Maja Werner and

Laureen Herklotz for their valuable guidance in the laboratories and office. I am

immensely grateful to Tobias Hübner, Limbania Aliaga, Buse Atila, Ezgi Erdogan,

Anke Pfeiffer, Anke Kemnitz, Jessica Nover and the entire staff at ATB Potsdam for

their help, kindness and support during my stay there.

I would also like to thank the IAESTE teams in both MIT, Manipal and

Potsdam for making my stay in Germany possible and highly enjoyable as well as my

parents and teachers whose early lessons have always stood me in good stead.

-Rishabh Ghotge


1.0 Introduction

1.1 What is Biochar?

Biochar is a black, friable and highly porous substance obtained after the incomplete

combustion of biomass. It can be made in a process very similar to that of the production of

charcoal. The main method of production of biochar at present is pyrolysis: the heating of a

substance in a closed container in the absence of oxygen, though the process and yield vary

with time, temperature, type of feedstock used, influencing catalysts and other affecting

factors. Biochar has been known for more than a century but interest in it has increased in

recent years because it is thought to offer sustainable solutions to global food requirement,

waste management and recycle, alternative fuel and climate change.

The term biochar was coined by Peter Read and has since come into popular usage, though

biochar is often referred to as agrichar. Biochar was included in the draft agenda for the

Copenhagen Climate negotiations in 2009 and has been a topic of considerable research in

fields like agriculture, mechanical, chemical and process engineering, biotechnology and

climate studies all over the world.

1.2 Origins

Scientists in the 1870s discovered areas of soil in the Amazon Rainforests that differed in

colour from the surrounding soils. Though the regular Amazonian soil was generally reddish,

highly weathered and bleached, possessing very little organic matter, these soils tended to be

darker in colour and were found to contain higher percentages of carbon. Further analysis of

the soil revealed that the presence of this carbon was not a natural process as had been

previously thought, but in fact, the result of the incorporation of incompletely burned

charcoal-like matter by early Amazonian inhabitants who lived in the region between 500

and 2500 years ago. Broken pieces of pottery found at the soil sights were one of the

indicators of the anthropogenic origins of the darker soil. This soil came to be known as

Terra Preta (“black soil” or “dark earth” in Portuguese). Today, the soil is well known in

Brazil for its fertility and is often dug up and sold.

In other parts of the world, biochar or variants of it have traditionally been used to increase

agricultural yields. Leibig (1878) reported the Chinese practice of covering waste biomass

with soil and then burning it for several days until a dark, nutrient- rich soil was produced.


Japanese texts describe the use of ‘fire manure’ and Indian farmers have traditionally added

waste residues from pottery kilns and traditional stoves to their fields.

Biochar has been a focus of academic research since the early twentieth century in Europe

and Japan, but has received greater public attention only in recent years. Much of this

attention is attributed to the recent recognition of the potential of biochar as part of the shift

towards sustainable agricultural systems - a relatively recent movement.

1.3 Properties of Biochar

Biochar possesses a range of properties, many of which vary according to the type of

feedstock and the process used for its production. However, all biochar possess a set of

common properties such as a high percentage of carbon, a chemically stable nature owing to

the presence of aromatic rings of carbon, a low thermal conductivity, high porosity and

correspondingly high surface area and adsorption capacity and an ability to absorb a large

amount of water.

1.4 The Uses and Applications of Biochar

Biochar’s specific properties make it useful for a wide range of applications. Though

traditionally, biochar has been used as an alternative bio-fuel and a soil amender (a material

that improves the soil’s physical properties like a water retaining properties, drainage,

structure, aeration, etc.), it has also found more modern applications in

water treatment and filtration

production of activated carbon

insulation

humidity control

air decontamination

protection from electromagnetic radiation

trapping of heavy metals.

In industry, it can be used in metallurgy, production of cosmetics, plastics and carbon fibre,

medicine, carbon filters, paints, electronics and fuel cells.


1.5 Recent Relevance

In recent times, biochar has gained a lot of publicity, mainly as it has been recognised as a

tool for climate change mitigation. The presence of human-incorporated carbon in the

Amazonian soils has shown that carbon can be sequestered in the earth for long periods of

time. Unlike organic matter, which rapidly degrades into carbon dioxide which then enters

the atmosphere, biochar tends to last in the soil for very long. Thus, the incorporation of

biochar into the soil simultaneously

1. increases the water and nutrient retention capacity of the soil, thereby improving

fertility and reducing leaching of essential macro and micronutrients

2. consumes agricultural, animal husbandry wastes, sewage, bagasse and paper mill

refuse which could otherwise pollute surface water through release into water bodies

or the atmosphere through burning

3. sequesters the carbon safely away from the atmosphere and hydrosphere and

4. provides a carbon neutral fuel

In addition, by-products of the pyrolysis process used to form biochar such as pyroligenous

acids and syn-gas have industrial and fuel applications. Thus, the production of biochar not

only reduces the damage done to the atmosphere by removing emissions from it, as the net

cycle is carbon negative, but also provides an alternative to fossil fuels, which prevents

further emissions.

1.6 Biochar Production Technologies

The manufacture of biochar is done mainly through pyrolysis. Pyrolysis at higher

temperatures tends to favour liquefaction and gasification reactions, as do shorter reaction

times. In such reactions, the quantity of char obtained is low and such reactions are used

when the primary objective of the reaction is to obtain fuel. This is because the liquid and

gaseous products obtained during these reactions are much preferred over solid ones due to

ease of handling, transport and storage. Pyrolysis at a lower range of temperatures and for

longer times tends to increase the char yield.

However, recently, a technique called Hydrothermal Carbonisation has come into use for the

production of biochar. It involves raising the substrate to elevated temperatures and pressures

in the presence of water as a catalyst.


1.7 Biochar and the Leibniz Institut fϋr Agrartechnik (Leibniz Institute for

Agricultural Engineering)

The Leibniz Institute for Agricultural Engineering Potsdam-Bornim (ATB), Germany is a

partly public and partly privately funded institute which was founded in 1992. Today, it is

one of Europe’s leading research institutes, contributing to scientific expertise in a wide

range of fields including material and energetic use of biomass, technology assessment in

agriculture, quality and safety of food and feed and precision farming. Their special focus on

the interaction between biomass production and climate in order to establish a sustainable

bio-based economy in terms of both materials and energy provides a base for decision

makers in policy, agriculture and industry across the world. ATB’s high quality scientific

infrastructure and interdisciplinary approach to research has been instrumental in the

furthering of current understanding of agricultural systems and the role of technology in

them.

The APECS (Anaerobic Pathways to Renewable Energies and Carbon Sinks) team within

ATB focuses on the production of biochar from a variety of feedstock. The current research

includes the following:

Comparison of possible methods for the carbonization of digestate

Characterization and quantification of the properties of the biochar obtained

Optimization of required properties

Quantification of the end effect of biochar as a soil additive

Evaluation of the manufacturing process in terms of performance, economy and

environmental impact.

This project is part of the APECS team’s research to further study the effect of variation of

input in the biochar production process on the quality and quantity of the yield obtained. The

tests have been conducted at a small scale level in order to obtain information that could help

in larger scale pyrolysis models and machines being produced.


1.8 Scope and Parameters of this Project

This project was carried out over a span of two months and the experiments carried out were

chosen so that results could be obtained in this period. The project looks at the three main

uses of biochar – as a fuel, as a soil amender and as a source of activated carbon, but uses

only a few tests to quantify each of them. The laboratory tests were run on very small scales,

whose results may differ significantly from those carried out at larger ones.

1.9 Opportunities for Further Research

Though this project is limited in its scope, it opens up avenues for further research in the

field.

1) Though only digestate has been used as a feedstock for pyrolysis in these

experiments, similar tests might be performed with other feedstock.

2) The Methylene Blue test has been performed as a test of adsorption capacity, though

the BET (Brunauer–Emmett–Teller) test for surface area is more widely accepted.

3) Though the Channiwala formula has been used to calculate the calorific value of the

char, use of a calorimeter or other formulae may give different results with a higher

degree of accuracy.


2.0 Objectives of the Project

Primary Objective:

The aim of this project is to quantify the influence and the extent of influence of moisture

content on the quality of digestate-derived pyrolysis biochar in terms of:

1) Measurement of Calorific value

2) Measurement of Water Holding Capacity

3) Eco-toxicity test

4) Measurement of the Methylene Blue Number

Secondary Objectives:

1) To gain insight into the process of pyrolysis

2) To receive training in research methodology and project management

3) To gain practical experience and exposure to work environments


3.0 Work Performed

3.1.0 Measurement of Moisture Content:

In order to test the effect of moisture content on the pyrolysis char, it was necessary to find

the initial amount of moisture present in the samples of digestate which was to be used as

feedstock. This was essential in order to establish the initial quality of digestate, which upon

identification, might be optimized in order to get the required product.

3.1.1 Digestate:

Organic waste, agricultural waste, and farmyard manure undergoes fermentation reactions in

the absence of oxygen for the production of biogas. Digestate is the residual sludge obtained

from a fermentation reactor after the process of anaerobic digestion and extraction of biogas.

The solid digestate used for pyrolysis in this study was obtained from an on-farm biogas

plant (Hof Karp, Rastow). The biogas plant is fed with cow manure and maize straw –

20,000 tonnes/annum and 15,000 tonnes/annum respectively. The plant has two standing

fermentation reactors, each with a working volume of 1500 m3, and a post-fermenter. The

total retention time is 30 days. The volume load of the fermenter is 5.72 kg oDM/m3d

(organic dry matter per metre cube day). The process is conducted at a mesophilic

temperature of 40°C. The plant produces 500 m3 of gas per day with a methane content of

56% by weight, which is used in a combined heat and power plant with a performance of 1.1

MW. The digestate was mechanically dewatered by a press-screw-separator and then

thermally dried on a belt drier at 70°C for 8 hours on the biogas farm. 20 kg of dried solid

digestate were taken from the farm and stored in a sealed 80 litre barrel to avoid moistening

of the material.

Quantity Measured Unit Value

pH - 8.73

Dry matter content (DM) % by weight 92.6

Organic dry matter content % by weight of DM 89.55

Acetic acid g/l 0.41

Total Kjeldahl-nitrogen (TKN) g/kg 18.55

Ammonia nitrogen (TAN) mg/kg 341.7


Table 1: Results of elemental analysis of the digestate

3.1.2 Methodology used to find the initial quantity of moisture in the digestate:

Initially, the digestate was weighed. It was then crumbled and spread in aluminium trays in

order to expose a maximum surface area so as to achieve homogeneity of drying. The trays

were then dried for 48 hours in an oven at a constant temperature of 105oC. The digestate

was then cooled to room temperature after which it was reweighed. The difference in initial

and final weights gave the weight of water lost. The weight of other volatile substances lost

as a result of the drying process was assumed to be negligible.

Sr. No. Weight of the Tray (g) Weight of the Tray and

Digestate (g)

Weight of Digestate

(g)

1 36.4 387.9 351.5

2 29.1 429.2 400.1

3 36.7 486.4 449.7

4 39.1 971.9 932.8

Table 1: Drying Data

Sr. No. Weight after Drying

(Including Tray) (g)

Loss of Weight

(g)

% Moisture

1 130.4 257.5 73.2

2 138.0 291.2 72.8

3 152.4 334.0 74.3

Average 73.43

Table 2: Drying Data

Where Percentage Moisture = Loss of Weight

Weight of Digestate

Element Unit Value

Carbon %DM 47.6

Hydrogen %DM 7.073

Nitrogen %DM 1.856

Sulphur %DM 0.4023


3.1.3 Notes on Methodology:

1)Though not as accurate as the Karl-Fischer process (a chemical analysis) for

determining the moisture content, drying of the substrate at 105o

C for 144 hours has been

found to be a good indicator of moisture loss. However, as this experiment covers a large

range of moisture percentages which vary greatly, it was not necessary to use such a long

procedure nor was there need for such a high degree of accuracy. Instead, a standard

procedure of drying for 24 to 48 hours has been adopted for this project. This has resulted in

a slight error underestimation of moisture.

2) The digestate was cooled before weighing in order to prevent the heat from the

samples from affecting the springs in the weighing apparatus.

3) The test was performed 3 times in order to reduce experimental error.

3.2 Establishing Moisture Percentages for further analysis:

In order to establish the degree of drying (in order to get the required moisture content)

necessary for the optimisation of the pyrolysis process for required properties of char, the

following methodology was used:

The digestate was first dried completely in an oven for 48 hours in order to eliminate residual

moisture and then water was sprayed onto it to ensure the necessary mass ratios. The sample

size was small and the water was sprayed rather than poured in order to ensure a

homogenous mixture of moist digestate that would simulate the behaviour of naturally dried

digestate. The mixture was then stored at room temperature for at least 24 hours in order to

ensure further homogeneity of the sample.

Samples were made with moisture contents varying from zero to 66% as weight of water to

weight of mixture and then pyrolysed.


3.3 Pyrolysis:

Pyrolysis may be defined as the “thermochemical decomposition of organic materials at high

temperatures in the absence of oxygen, leading to the formation of gaseous and liquid

products as well as carbon-rich residues”.

The temperatures chosen for pyrolysis were 550 and 700o

C, in order to compare them with

Standard Samples of Biochar created by the UK Biochar Research Centre (UKBRC). The

samples were inserted into a tube furnace that had been pre-heated to the required

temperature. Gaseous nitrogen was passed through the furnace tube so as to maintain an inert

and oxygen-starved atmosphere which would not be conducive to combustion of the

feedstock. As the mass of digestate used was very small (of the order of a few grams), a

pyrolysis time of approximately10 minutes was deemed appropriate.

Trial

No.

Percentage of Moisture

0% 33% 66%

1 39.63 41.71 47.95

2 39.17 41.36 53.2

3 37.3 48.6 61.81

Table 3: Char Yields obtained with increasing moisture content at pyrolysis temperature of 550o

Table 4: 550o Pyrolysed Char with Error lines for Standard Deviation

0

10

20

30

40

50

60

70

Trial 1 Trial 2 Trial 3

0%

33%

66%


Table 5: Char Yields obtained with increasing moisture content at pyrolysis temperature of 550o

Table 6: 550o Pyrolysed Char with Error lines for Standard Deviation

While the increasing trend is easy to recognise from the three trials performed at 550o C, the

results obtained from pyrolysis at 700o C are more erratic and show no real pattern. At

500o C, there is a clear correlation between increase in the percentage of moisture in the

digestate and the amount of char yielded by the pyrolysis process but such a relation is not

apparent at 700o C.

0

5

10

15

20

25

30

35

40

45

Trial 1 Trial 2 Trial 3

0%

33%

66%

Trial No. Percentage of Moisture

0% 33% 66%

Trial 1 33.83 32.96 34.42

Trial 2 15.58 30.75 39.54

Trial 3 34.42 27.7 38.7


3.4.0 Water Holding Capacity Testing:

3.4.1 Introduction:

The water holding capacity of a given soil type is the amount of water that it can hold or

retain against the force of gravity: an important agronomic parameter. Soils with higher

water holding capacities tend to retain moisture for longer periods of time, increasing its

availability for root absorption. Also, there is less seepage and wastage of water, reducing the

irrigation required. Since a large percentage of plant nutrients are water soluble, the drainage

of water from the top soil layers results in a loss of nutrients available for use by crops. This

results in a direct loss of soil fertility, as well as contamination of groundwater, thus affecting

the water supply available for future irrigation requirements as well as making it unfit for

human consumption. Higher water holding capacities are hence a desirable property in soil

as they help in nutrient and moisture retention, reduce the need for irrigation and fertilizers

and protect groundwater from contamination.

The water holding capacity of a soil is also an indicator of other physical properties of the

soil like surface area, particle size, particle size distribution and quantity of organic matter in

it. Generally smaller size clay particles with larger surface areas have better water retention

capacities than loamy and sandy soils in that order. The water holding capacity of soils also

increases with the amount of organic matter in them owing to the affinity that organic matter

has for water.

3.4.2 Terminology in the Water Holding Capacity Experiment

Saturation: The saturation point is reached when all the inter-granular spaces in the

soil are completely filled with water.

Field Capacity: When the excess water is allowed to drain away due to gravity, and

the remaining water is held by the soil against gravity, the soil is at field capacity.

Permanent Wilting Point: The point at which there is no water available for plant

intake is called the permanent wilting point. At this point, plants begin to wilt and do

not recover. However, there is still water in the soil, though it adheres too tightly to

the soil particles for plant to be able to use it.


Gravitational Water: The water that needs to be added to soil at field capacity in

order to saturate it is called the gravitational water.

Water Holding Capacity: The water that needs to be added to the Permanent

Wilting Point in order to bring it to its Field Capacity is called the water holding

capacity of the soil.

Plant Available Water: It is the amount of water in the soil that is of use to plants. It

is often assumed to be roughly half of the water holding capacity.

Notes on Terminology: On an average, soils have as much pore space as solid mass, though

the exact ratios vary according to soil types. These pores may be filled with varying

proportions of air and water. The above terms describe how much of this pore space is

occupied by water. Determination of the water holding capacity of soils is thus an important

factor, yielding information on the kinds of crops that may be cultivated as well as the

amount of irrigation water required in order to avoid both waterlogging and wilting of crops.

3.4.3 Methodology for Finding the Water Holding Capacity of the Soil-Char Mixtures

Though there are many methods used to establish the Water Holding Capacity, the method

used here is one that was formulated by Jäggi W. (1976), and later modified by R. Öhlinger.

Materials and equipment:

1. Soil

2. Biochar

3. Distilled water

4. Ceramic cylinder, inner diameter about 3 cm, closed at one end with a fine frit mesh

and open at the other end

5. Sand bath saturated with water

Procedure:

About 20 g of field-moist, sieved LUFA 2.3 soil (mixed with 1% by weight of char in

most cases) was weighed and added into the cylinders.

These were immersed in a container with water for 1 hour (the water level slightly

higher than the soil column in the cylinders) in order to saturate the soils.


After 1 hour, the cylinders were transferred onto the prepared saturated sand bath for

3 hours. The excess moisture was allowed to drain away to bring the soil to its field

capacity. The mouths of the cylinders were covered with watch glasses to prevent

evaporation losses of water.

The samples were then dried for 24 hours at 105o to remove all residual moisture.

The samples were then cooled to room temperature and weighed again.

Calculation of Results:

%WHC = (Saturated Soil – Dried Soil) x 100

Dried Soil

Notes on Methodology:

The soil used for this experiment was LUFA 2.3 standard soil. LUFA (Landwirtschaftliche

Untersuchungs- und Forschungsanstalt) or the Agricultural Analysis and Research Institute

prepares standard soil samples for laboratory and field experiments conducted in order to

study leaching, degradation, influence on soil micro flora and fauna and pesticide absorption

or desorption of soil.

LUFA soils are naturally and commonly occurring soils collected from select areas in

Germany. The LUFA soils used for this experiment were collected from 0 to 20 cm depth

and had regularly been used for agriculture. They had been kept free of biocidal fertilizers,

organic manure and pesticides for at least 5 years before sampling, though mineral fertilizers

had been used until 3 months before sampling. They were then prepared and sieved with a 2

mm sieve.

LUFA standard soils are in accordance with the Good Laboratory Practice (GLP) guidelines

for permission studies.

The use of standard soils in soil experiments has several advantages:

Long time availability and therefore comparability of tests across larger time frames

No difficulty in searching, procuring, preparing and care of suitable soils

Easy access to all needed data concerning location, history, treatment, sampling

(according to GLP).

Additional information on the LUFA 2.3 soil used may be found on the following pages.


Soil Additive Test No.

Mass of Wet Substrate

Mass of Dry Substrate

Mass Loss Water Holding Capacity

Average WHC

None (Plain Soil)

1 26.64 18.63 8.01 42.99516908 44.73

2 27.26 18.61 8.65 46.48038689

Dry Digestate

1 28.52 18.62 9.9 53.16863588 53.82

2 28.78 18.63 10.15 54.48201825

0% Moist Char made at 550o C

1 28.43 18.66 9.77 52.35798499 51.40

2 28.15 18.71 9.44 50.45430251


1 28.38 18.71 9.67 51.68359166 52.44779155

2 28.62 18.68 9.94 53.21199143


1 28.72 19.66 9.06 46.08341811 47.39862224

2 27.75 18.66 9.09 48.71382637


1 28.05 18.70 9.35 50 52.29946524

2 28.91 18.70 10.21 54.59893048


1 28.26 18.67 9.59 51.36582753 51.04368341

2 28.20 18.71 9.49 50.72153928


1 28.29 18.71 9.58 51.20256547 52.08286309

2 28.65 18.73 9.92 52.9631607

Table 7: Water Holding Capacity Results


Table 8: Water Holding Capacity Graph

The results clearly show that char has a positive effect on the Water Holding Capacity of the

soil used. However, these improvements have not matched the effect of digestate used on its

own. In the various types of char, there is no easily apparent pattern indicating the best type

of char for the purpose of maximizing gains in Water Holding Capacity.

0

10

20

30

40

50

60

Average WHC

Average WHC


3.5.0 Eco- Toxicity Test with Cress Seeds:

Though biochar has been found to improve the water-holding capacity of soils, it may have

other unknown influences on plant growth. It is essential to study and understand these

influences with a view to optimize the manufacturing process to maximise gains and

minimise harm to the soil or crops. Though the terra preta soils in the Amazons have shown

amazing results as soil amenders, the ways that laboratory-produced biochar could affect

seeds, germination, root growth, microbial activity, soil temperatures, soil conductivity and

soil emissions are still being researched. An entire overview of all the ways in which biochar

could affect the soil, the irrigation patterns, the groundwater cycle, crop yields and

agricultural patterns being far beyond the scope of this project, a short experiment has been

performed to test the effect that the biochar has on cress seeds when mixed into the soil. The

test is a preliminary indicator for potential toxicity of substances in the soil as well as soil

amending materials.

Ecotoxicity is a measure of the negative influence that a substance has on eco-systems. The

eco-toxicity test performed with cress gives the effect that the char has on cress germination,

but gives no information about the causes for inhibition, the type of influence (physical,

chemical, biological, etc.). Thus, the test has been designed to give a rough idea of the kind

of effect that biochar will have on plant life when used as a soil amender.

3.5.1 Methodology: The test used is a standard European test for phytotoxicity in

accordance with DIN EN 16086-2.

Materials

Soil or ground coal mixture

Cress seeds (Lepidium sativum)

Distilled water

Beakers, spatulas, tweezers

Petri dishes

Parafilm


Procedure:

The soil or soil-carbon mixture was adjusted to 60% of its pre-determined Water

Holding Capacity.

Approximately 50 g of moist soil mixture was weighed in the Petri dishes (3

replicates)

10 cress seeds were arranged in a row in each Petri dish.

The petri dish was then sealed and made air-tight with parafilm.

The petri dishes were incubated vertically (at about 70-80 ° angle) in an incubator at

25 ° C for 72 hours in complete darkness.

Fig 1: Side and Front Views of Experimental Set-up

Evaluation

The number of germinated seeds was counted and the mean germination rate

determined.

The root length was measured in mm, on which basis the Munoo-Liisa vitality index

was calculated.


Calculations:

1) AGR = GR1 + GR2 + GR3

3

Where GR - germination rate (percentage of germinated seeds per plate)

AGR - average germination rate

2)

Where CVG - coefficient of variation of the rate of germination

3)

Where RLP - root length per plant

RL - root length

NGS - Number of germinated seeds

4) ARLP = RLP1 +RLP2 + RLP3

3

Where ARLP - average root length per plant

5)

Where CVR - coefficient of variance of root length


6)

Where RI - Index of root length

RLc - average root length of the control samples

7) MLV - Munoo-Liisa vitality index (compares the product of seed germination in the

investigated material and the mean root length in the investigation and control

samples)


Results:

Soil Additive

Germination Rate (GR) Average Germination Rate (AGR)

Coefficient of Variation of the rate of Germination

Average Root Length per Plant

Coefficient of Variance of Root Length

1 2 3 1 2 3

None 80% 80% 90% 83.33% 5.66% 40.75 46.75 47 6.44%

Dried Digestate

40% 20% 80% 46.67% 53.45% 40 31.5 42.37 12.30%

0% Moist Digestate (550o C)

70% 90% 90% 83.33% 11.31% 33 31.89 46.89 18.32%


80% 100% 90% 90.00% 9.07% 32.5 68.1 53.44 28.45%


90% 80% 100% 90.00% 9.07% 39.22 47.75 23.5 27.28%


40% 60% 20% 40.00% 40.82% 36.75 26.33 15 34.13%


50% 40% 60% 50.00% 16.33% 44.2 68.75 40.67 24.39%


10% 30% 20% 20.00% 40.82% 28 29.33 55 33.19%

Table 9: Root Length Data


Table 11: Graphical Representation of Plant Vitality Results

Discussion: The results indicate that char can either have a positive or deleterious effect on

plant vitality. Certain chars can have a beneficial influence, especially those formed at lower

temperatures. The results also indicate that the vitality of plants is maximised when the initial

moisture content of the digestate is around 33% before pyrolysis.

00.05

0.10.15

0.20.25

0.30.35

0.40.45

Munoo Liisa Vitality Index

Munoo Liisa Vitality Index

Soil Additive Index of

Root Length

Munoo Liisa

Vitality Index

Dried Digestate 84.67% 16.68%

0% Moist Digestate (550o C) 83.11% 27.90%






Table 10: Plant Vitality Data


3.6.0 Biochar: Use as a source of Activated Carbon:

Activated Carbon is a form of carbon with a very high surface area due to the presence of

low-volume micropores on its surface. It is manufactured by the exposure of materials with

high carbon content (coal, charcoal, coir, etc.) to steam or chemicals at elevated temperature.

Due to its extraordinarily large surface area and correspondingly high adsorption capability,

it is useful over a wide range of applications.

It is used in medicine in order to re-absorb ingested poisons, as a filter for water and gas

purification as well as in distilleries, as a catalyst in fuel cells and for metal extraction.

Increasingly, biochar is being seen as a source of highly porous carbonaceous material for

the production of activated carbon in place of fossil fuel sources.

The Methylene Blue Number is a widely accepted test for the determination of the

adsorption capacity of activated carbon. The test involves the decolourisation of the dye

Methylene Blue due to the immersion of the adsorbing substance in it. The substance adsorbs

the methylene blue particles, leading to a loss of colour of the solution. This colour loss can

be used to determine the concentration of the solution and the decrease in concentration is a

measure of the adsorbing capacity of the substance.

The change in colour, known as the degree of extinction, is measured using a

spectrophotometer, which can identify the intensity of a specific wavelength of light. The

wavelength chosen for the test is 600nm, the wavelength of light at which the stock solution

of methylene blue was found to have maximum intensity.

3.6.1 Terminology:

The methylene blue number is defined as the maximum amount of methylene blue

adsorbed by one gram of activated carbon (AC).


3.6.2 Methodology:

Preparation of the standard solutions:

1000 ml flask

250 ml Erlenmeyer flasks with stopper (5x)

100 mg methylene blue, powdery

For preparing the stock solution, 100 mg methylene blue was dissolved in deionized water

and filled up to the 1000 ml line. It was then sieved in a 0.2 mm fine nylon mesh

For preparing several concentrations of methylene blue solutions (15, 30, 50, 75, 90

mg/L) from the stock solution (S1) was diluted and filled up with deionized water to 50

ml.

15 mg/L → 7.5 ml of S1

30 mg/L → 15 ml of S1

45 mg/L → 22.5 ml of S1

75 mg/L → 37.5 ml of S1

90 mg/L → 45 ml of S1

Preparation of the samples:

0.025 g of each type pf Activated Carbon was added to 50 ml of each standard solution

and allowed to shake in a water bath for 24 hours at room temperature.

After shaking, only the liquid of each sample was carefully filled in centrifuge tubes and

centrifuged for 10 minutes in order to separate potentially remaining particles from the

liquid.


UV/Visible Spectrophotometer:

The sample liquids and also the standard solutions were filled into cuvettes. Initially, a blank

which in this case was deionized water, was measured. Then the wavelengths λ of the

standard solution with the highest concentration were identified and the wavelength with the

highest value of extinction was identified. The extinctions of all the samples and standard

solutions were then gauged relative to the blank in terms of intensity of this chosen

wavelength.

Analysis:

A calibration curve was created from the data of the standard solutions, with concentration

on the x-axis and the extinction on the y-axis. A trend line was plotted and its equation

was used to calculate the remaining concentration of methylene blue. The methylene blue

number (MBN) is defined as

MBN = (Co – Ce) V in mg/g

M

where Co [mg/L] is the initial concentration of methylene blue,

Ce [mg/L] the remaining concentration of methylene blue, V [L] is the volume of methylene

blue and M [g] the mass of activated carbon.

The equation for the percentage adsorbed [%] is as follows:

100 x (Co - Ce)

Co


Results:

Concentration (mg/L) Extinction

0 0

15 0.534

30 1.025

45 1.5

75 2.43

90 2.849

Table 12: Concentration vs. Extinction Results

Figure 2: Linear trend between Concentration and Extinction

y = 31.651x - 1.4848 R² = 0.999

-20

0

20

40

60

80

100

0 1 2 3

Concentration (mg/L) vs. Extinction

Concentration (mg/L)

Linear (Concentration(mg/L))


Sample Extinction Concentration (mg/L)

Mean Concentration

Methylene Blue Number

Percentage Absorbed

Dry char at 550o

2.333 72.356983

2.286 70.869386 70.66892967 58.66214067 29.33107033

2.22 68.78042

33% Moist Char at 550oC

2.279 70.647829

2.372 73.591372 73.20100967 53.59798067 26.79899033

2.428 75.363828


1.879 57.987429

1.558 47.827458 55.49755033 89.00489933 44.50244967

1.964 60.677764


2.687 83.561437

2.774 86.315074 85.428846 29.142308 14.571154

2.777 86.410027


2.686 83.529786

2.68 83.33988 83.04447067 33.91105867 16.95552933

2.646 82.263746


2.525 78.433975

2.423 75.205573 77.94865967 44.10268067 22.05134033

2.581 80.206431

Table 13: Methylene Blue Numbers of Various Chars


Table 14: Graphical Representation of Methylene Blue Number Results

The data reveals that higher moisture contents favour higher surface areas, as do lower

pyrolysis holding temperatures. However, these values are far removed from the Methylene

Blue values obtained from the testing of commercial grade activated carbons, which range

from 200 to 500. However, these chars may be further activated thermally or chemically to

obtain higher quality activated carbons with pore size suited to the requirement.

0

10

20

30

40

50

60

70

80

90

100

Methylene Blue Number

Methylene BlueNumber


3.7.0 Measure of Calorific Value:

Biochar, with its high carbon content and similarity in composition to fossil-fuel coal and

charcoal, has a lot of potential as a source of solid fuel. Because of its organic origins, it is a

renewable fuel. In addition, the carbon emissions released through the combustion of biochar

were absorbed from the atmosphere using photosynthesis, making the process carbon neutral

over a span of many years. It can also be used with existing infrastructure in thermal

powerplants, simplifying the possibility of a switch from fossil fuels.

The calculation of the calorific value is important in terms of understanding the use of

biochar as a fossil fuel alternative as well as in the energy balance of the charring process.

The feasibility of biochar usage as fuel depends on the ratio of the amount of energy that it

yields to the amount of energy required for its synthesis.

3.7.1 Terminology:

Calorific Value: It is the heat generated upon the combustion of a unit weight of the

specified fuel.

Lower Calorific Value (Net Heating Value): It is the quantity of heat released when a unit

weight of fuel, initially at 25o C undergoes complete combustion and all the reaction products

are returned to 150o C. It assumes that the latent heat of vaporisation of the water in the

reaction products is not recovered.

Gross Calorific Value (Higher Heating Value): It is the quantity of heat released when a

unit weight of fuel, initially at 25o C undergoes complete combustion and all the reaction

products are returned to 25o C. It takes into account the latent heat of vaporisation of the

water in the reaction products.


3.7.2 Methodology:

Many investigations into the nature of coals, biomass and organically derived fuels such as

biochar have revealed as many as 31 empirical formulae for the calculation of the HHV

(Higher Heating Value) of the fuel based on its elemental composition. The first one was

suggested by Dulong (1880) and is still in use, though it has been modified many times.

Channiwala and Parikh put forward a formula in 2002 based on the study of 22 such

correlations. It is supposed to be applicable to almost any fuel and it has been confirmed that

it is applicable to biochar (Kieseler et.al, 2013). It is given below:

HHV = 0.3491 C + 1.1783 H + 0.1005 S - 0.1034 O - 0.0151 N - 0.0211 ash.

However, the ash percentage was not calculated and the residual percentage was assumed to

be the oxygen percentage.

3.7.3 Results:

Char Nitrogen

%

Carbon

%

Sulphur

%

Hydrogen

%

Oxygen

%

Calorific Value

0% Moist Char at 550o C 2.605 63.45 0.4943 3.169 30.2817 22.76364157

33% Moist Char at 550o C 2.488 57.22 0.5503 3.197 36.5447 19.98154147

66% Moist Char at 550o C 2.538 54.48 0.5728 3.838 38.5712 19.57226392

0% Moist Char at 700o C 1.955 57.51 0.4766 2.338 37.7204 18.94969484

33% Moist Char at 700o C 2.254 61.91 0.4854 2.444 32.9066 21.10475106

66% Moist Char at 700o C 2.278 58.18 0.5047 2.627 36.4103 19.65753163

Table 15: Elementary Analysis and Calorific Values of Obtained Chars


Table 16: Trend line displaying decreasing calorific value with temperature and moisture rise

3.7.4 Inference: Though the pattern obtained is not obviously apparent, the insertion of the

trendline displays the tendency of the calorific value of the chars to decrease. This may be

attributed to either the decrease in carbon and hydrogen percentages or to the increase in

oxygen content.

0

5

10

15

20

25

0% MoistChar at

550 deg. C

33% MoistChar at

550 deg. C

66% MoistChar at

550 deg. C

0% MoistChar at

700 deg. C

33% MoistChar at

700 deg. C

66% MoistChar at

700 deg. C

Calorific Value

Calorific Value

Linear (Calorific Value)


4.0 Inferences and Discussion:

The data explores the possibilities for biochar use for its three main identified purposes,

namely as fuel, as a soil amender and as a source of activated carbon.

4.1 Fuel:

The calorific value of the chars obtained is comparable to that of average quality coals (in the

lignite and bituminous range) and has a higher value than wood, but is still less than charcoal.

However, it must be kept in mind that the feedstock used was the digestate obtained from the

slurry of a biogas plant, during which process, energy had already been extracted from the

agricultural waste. The use of this digestate for biochar production is an added bonus.

The char obtained is a viable alternate solid fuel, provided that it can be manufactured on the

scales required. It will provide better quality fuels to those who rely on firewood, preventing

deforestation while simultaneously making use of agricultural and domestic residues. Also,

since no food crops are being utilized and no extra land is being brought under cultivation for

specific biochar production, the food vs. fuel controversies are avoided. However, care must

be taken that excessive diversion of carbonaceous matter from fields do not affect the natural

carbon cycles and enough organic material is saved for composting, mulching and other

methods of returning carbon to the soil.

The results reveal a higher calorific value for chars that have lower moisture contents and

lower temperatures, suggesting that digestate should be initially dried before undergoing low

temperature pyrolysis.

4.2 Soil Amendment:

Biochar has clearly been shown to improve the Water Holding Capacity of the soil, thus

improving its ability to retain moisture ensuring survival of crops in spite of lower rainfall or

irrigation. The fact that dried digestate was found to improve the Water Holding Capacity of

the soil better than any of the chars is countermanded by the loss in plant vitality that was

found to be the result of addition of dried digestate to the soil. However, though one variety

of char improved plant vitality, a majority of them did not, suggesting that further research

needs to be done in order to identify the characteristics of the chars that cause them to


influence plant growth.

Considerable research is going on currently on methods of mixing chars with compost,

manure, fertilizers or even effective micro-organisms to give them fertilizing properties in

addition to their soil amendment properties.

4.3 Surface Area:

Though the surface area is of great importance in terms of soil amendment also, it is also an

indicator of the possibility of using the char as a source of activated carbon, an important

adsorbing material, which is extensively used in medicine, pharmaceuticals and the chemical

industry.

The surface area of the chars obtained by the pyrolysis of digestate was not to be as good as

commercial grade activated carbon, requiring further thermal of chemical treatment for the

expansion of pore size. However, digestate derived coal is potentially a source of high grade

activated carbon.


Bibliography:

1. Owens, Fred and Soderlund, Steve - Methods for Measuring Moisture Content

of Grains and Implications for Research and Industry.

2. CarbonZero Project Switzerland - Origin of Biochar - Terra Preta

(http://www.biochar.info/biochar.terra-preta.cfml)

3. Biochar India - Discovering Biochar use and practices (Sept, 2013)

(http://www.biocharindia.com/)

4. Schmidt, Hans-Peter, Ithaka Journal for Ecology, Winegrowing and Climate

Farming (Dec 2012) (http://www.ithaka-journal.net/55-anwendungen-von-

pflanzenkohle?lang=en)

5. Final Report : Review of the plant growth and weed propagule tests used in the

PAS100 specification for quality compost , WRAP, UK (2009)

(http://www2.wrap.org.uk/downloads/Review_of_the_plant_growth_and_weed_p

ropagule_tests_used_in_the_PAS100_specification_for_quality_compost.43f0907

9.6964.pdf)

6. Norum, Rodney A. and Miller, Melanie - Measuring Fuel Moisture Content in

Alaska: Standard Methods and Procedures, General Technical Report, Forest

Service, United States Department of Agriculture.

7. Austin, Anna - A New Climate Change Mitigation Tool, Biomass Magazine.

8. Ernsting, Almuth and Smolker, Rachel - Biochar for Climate Change

Mitigation: Fact or Fiction, Feb 2009.

9. Lehmann, Johannes and Joseph, Stephen - Biochar for Environmental

Management: Science and Technology, Earthscan Publishers, 2009.

10. Bridgwater, A.V. and Grassi, G. – Biomass Pyrolysis Liquids Upgrading and

Utilisation, Elsevier Science Publishers, England (1991).

11. Morris, Emma – Black is the New Green, Nature, Vol. 442 (10th

August 2006).

12. Haefele, Stephan M. – Black Soil, Green Rice, Rice Today, (June 2007)

13. Özçimen, Didem – An Approach to the Characterization of Biochar and Bio-oil,

Bioengineering Department, Yildiz Technical University, Turkey.

14. Funke, A., Mumme, J. , Koon, M. , Diakite´, M. - Cascaded production of

biogas and hydrochar from wheat straw: Energetic potential and recovery of

carbon and plant nutrients, Elsevier (2013)

15. Funke, Axel, Reebs, Felix and Kruse, Andrea - Experimental comparison of

hydrothermal and vapothermal carbonization, Elsevier (2013).

http://www.biochar.info/biochar.terra-preta.cfml

http://www.biocharindia.com/


16. Zhang, Yuanhui - Hydrothermal Liquefaction to Convert Biomass into Crude

Oil, Blackwell Publishing (2010)

17. Inyang, Mandu, Gao, Bin, Pullammanappallil, Pratap , Ding, Wenchuan,

Zimmerman, Andrew R. - Biochar from anaerobically digested sugarcane

bagasse, Elsevier (2010)

18. Mumme, Jan, Eckervogt, Lion, Pielert, Judith, Diakité, Mamadou, Rupp,

Fabian, Kern, Jürgen -Hydrothermal carbonization of anaerobically digested

maize silage, Elsevier (2011)

19. Libra, Judy A., Ro, Kyoung S, Kammann, Claudia, Funke, Axel , Berge,

Nicole D, Neubauer, York, Titirici, Maria-Magdalena, Fühner, Christoph,

Bens, Oliver, Kern, Jürgen and Emmerich, Karl-Heinz - Hydrothermal

carbonization of biomass residuals: a comparative review of the chemistry,

processes and applications of wet and dry pyrolysis, Biofuels (2011)

20. Sukiran , Mohamad Azri, Kheang, Loh Soh, Bakar, Nasrin Abu and May, Choo

Yuen - Production and Characterization of Bio-Char from the Pyrolysis of

Empty Fruit Bunches, American Journal of Applied Sciences (2011)

21. Reza, M. Toufiq, Becker, Wolfgang, Sachsenheimer, Kerstin and Mumme, Jan -

Hydrothermal carbonization (HTC): Near infrared spectroscopy and partial

least-squares regression for determination of selective components in HTC solid

and liquid products derived from maize silage, Elsevier, 2014.

22. Schouten, Socrates, van Groenigen, Jan W., Oenema, Oene and Cayuela, Maria

L. - Bioenergy from cattle manure? Implications of anaerobic digestion and

subsequent pyrolysis for carbon and nitrogen dynamics in soil, Bioenergy

(2012).

23. Reza, M. Toufiq, Andert, Janet, Wirth, Benjamin, Busch, Daniela, Pielert,

Judith, Lynam, Joan G. and Mumme, Jan - Hydrothermal Carbonization of

Biomass for Energy and Crop Production, Appl. Bioenergy (2014).

24. Agronomy Department, University of Florida – Dry and Organic Matter

(http://agronomy.ifas.ufl.edu/research/forage-evaluation-support-laboratory/dry-

and-organic-matter/)

25. Agvise Laboratories, USA – Water Holding Capacity

(http://www.agvise.com/educational-articles/water-holding-capacity/)

26. Acharya, Madhu Sudan, Rauchecker, Markus and Wu, Wie - Determination of

water absorption and water holding capacities of different soil mixtures with

MINIDRAIN system to enhance the plant growth, Geophysical Research Vol.

16, Institute of Geotechnical Engineering, University of Natural Resources and

Life Sciences (BOKU), Vienna, Austria (2014)


27. Sheppard, Jessica (Avon Catchment Council) and Hoyle, Fran (Department of

Agriculture and Food, Western Australia) – Water Availability

(https://s3.amazonaws.com/soilquality-production/fact_sheets/12/original/Phys_-

_Water_Availability_web.pdf)

28. Zhang X, Xia X, Ivanov I, Huang X, Logan BE - Enhanced activated carbon

cathode performance for microbial fuel cell by blending carbon black ,

Department of Civil & Environmental Engineering, Penn State University

(Feb 2014)

(http://www.ncbi.nlm.nih.gov/pubmed/24422458)

29. Norit Activated Carbon– What is Activated Carbon?

(http://www.norit.com/carbon-academy/introduction/)

https://s3.amazonaws.com/soilquality-production/fact_sheets/12/original/Phys_-_Water_Availability_web.pdf

https://s3.amazonaws.com/soilquality-production/fact_sheets/12/original/Phys_-_Water_Availability_web.pdf

http://www.ncbi.nlm.nih.gov/pubmed/24422458

http://www.norit.com/carbon-academy/introduction/

The Effects of Moisture Content on Digestate-Derived Biochar

Documents

Transcript of The Effects of Moisture Content on Digestate-Derived Biochar