establish an anaerobic batch system by using guideline vdi 4630 and determine the biogas yield of different substrates in food processing villages

VNU UNIVERSITY OF SCIENCE - TECHNICAL UNIVERSITY OF DRESDEN ® Bui Dieu Linh ESTABLISH AN ANAEROBIC BATCH SYSTEM BY USING GUIDELINE VDI 4630 AND DETERMINE THE BIOGAS YIELD OF DIFF

VNU UNIVERSITY OF SCIENCE - TECHNICAL UNIVERSITY OF DRESDEN

®

Bui Dieu Linh

ESTABLISH AN ANAEROBIC BATCH SYSTEM

BY USING GUIDELINE VDI 4630 AND DETERMINE THE BIOGAS YIELD OF

DIFFERENT SUBSTRATES

IN FOOD PROCESSING VILLAGES

MASTER THESIS

Hanoi - 2011

VNU UNIVERSITY OF SCIENCE - TECHNICAL UNIVERSITY OF DRESDEN

®

Bui Dieu Linh

ESTABLISH AN ANAEROBIC BATCH SYSTEM

BY USING GUIDELINE VDI 4630 AND DETERMINE THE BIOGAS YIELD OF

DIFFERENT SUBSTRATES

IN FOOD PROCESSING VILLAGES

Major: Waste Management and Contaminated Site Treatment

Code:

MASTER THESIS

PROF DR RER NAT DR H.C PETER WERNER

CO2), pH - value, TS (total solids), VS (volatile solids), COD (chemical oxygen demand) The biogas yield (per amount of substrate, per VS of inoculum, per COD

of substrate) and the degradability of different substrates will be evaluated

Objective

The aim of this thesis is from learning the methods of guideline VDI 4630 to establish in practice an anaerobic batch system in the conditions of a Vietnamese laboratory Then it is to control this system to investigate the quality of inocula, the fermentability/ the biogas potential/ the specific biogas activity of different organic wastes from food processing and livestock of a Vietnamese craft village It is also close tied to the one objective of education and technology transfer of INHAND project (project funded by the Federal Ministry for Education and Research of Germany - BMBF; with the project coordinator Institute of Waste Management and Contaminated Site Treatment, Dresden University of Technology) about Integrated management of water, wastewater, waste and energy in craft villages in Vietnam. 

Contents

Contents

Contents ………. II

List of figures ……… V

List of tables ……… VII Acknowledgements.……… IX

1 Introduction……… 1

2 Theoretical Basics……… 4

2.1 Basics of Anaerobic Digestion……… 4

2.1.1 The four stages of decomposition……… 4

2.1.2 Influence Factors of Digestion……… 7

2.1.3 Biogas potential of different substrates……… 13

2.2 End products of fermentation……… 15

3 Materials and methods……… 17

3.1 VDI survey about batchtests for biogas yield determination………… 17

3.1.1 Scope and purpose of Fermentation batchtests……… 17

3.1.2 Methods of VDI 4630 in detecting the biogas yield……… 17

3.1.3 Method of VDI 4630 in approaching the batchtests……… 19

3.2 Analysis method ……… 19

3.2.1 Sampling……… 19

3.2.2 Sample preparation……… 23 3.2.3 Determination of parameters: TS, VS, COD, and CH4 and CO2

Contents

content in biogas……… 25

3.3 Experimental procedure……… 30

3.3.1 Test condition and batch apparatus……… 30

3.3.2 Method to calculate the biogas production, the biogas yield, the biogas composition, the degree of degradation……… 37

4 Evaluation and discussion of the batch experiments……… 41

4.1 Activity potential of different inocula……… 41

4.2 Biogas production and biogas composition of different substrates… 47

4.2.1 Biogas yield (mlN/gVSinoculum, mlN/gCODsubstrate, mlN/ g substrate)… 47 4.2.1.1 Biogas yield of trial 6 with inoculum 5……… 47

4.2.1.2 Biogas yield of trial 7 with inoculum 5……… 50

4.2.1.3 Biogas yield review of different substrates with inoculum 5… 54

4.2.1.4 Biogas yield review of different substrates with inoculum 6… 56

4.2.2 Comparison of biogas yields with theory and literature………… 61

4.2.3 Biogas composition (CH4 and CO2 content)……… 64

4.3 Residue of biogas production……… 66

4.3.1 Degree of degradation of volatile solids……… 66

4.3.2 Degree of degradation of total solids……… 69

4.3.3 Degree of degradation of COD total……… 71

4.4 Error analyis……… 77

5 Conclusion……… 80

References……… 83

Annex- Data records I

Statement under oath XI

Abbreviations

Abbreviations

C/ CR Cassava residues sample

COD Chemical oxygen demand

Inoc Inoculum

lN standard liter, volume under normal condition

mlN standard milliliter, volume under normal condition P/ PM Pig manure sample

List of Figures

List of Figures

Figure 2-1: Four stages of anaerobic degradation (WEILAND, 2003) 4

Figure 3-1: Test apparatus according to DIN EN ISO 11734: Gas volume measurement with a gas pressure measurement instrument (VDI 4630) ……… 18

Figure 3-2: Gas volume measurement with a gas pressure measurement instrument (S Meier, 2009) 18

Figure 3-3: Map showing position of Dai Lam village……… 21

Figure 3-4: Water hyacinth at main sewer… 21

Figure 3-5: Rice residues and cassava residues sampling at households… 22

Figure 3-6: Pig manure at a small swine farm of a household ……… 22

Figure 3-7: Homogenizing cassava residues by blender……… 23

Figure 3-8: Homogenizing water hyacinth by blender……… 24

Figure 3-9: Filling the bottles by weighing method……… 30

Figure 3-10: Closing bottles with silicone stoppers 31

Figure 3-11: Creating the vacuum inside the bottles 31

Figure 3-12: Lovibond conditioning cabinet 32

Figure 3-13: K2000 Pressure table - EXTECH manometer 407910 32

Figure 3-14: MultiLabP4 33

Figure 3-15: MEMMERT drying cabinet 33

Figure 3-16: TDW muffle furnace 33

List of Figures

Figure 3-17: Lovibond ET 108 and MERK spectroquant TR320 block

digesters 31Figure 3-18: PI 722N instrument in measuring COD 34Figure 3-19: Gas chromatograph Shimadzu GC-2010 34Figure 4-1: Biogas yield without blank on different inocula [mlN Biogas/ g

COD sodium acetate] 44Figure 4-2: Biogas yield with blank on different inocula [mlN Biogas/ g

COD sodium acetate] 45Figure 4-3: Biogas yield with blank on inoculum 5 of trial 6 [mlN Biogas/ g

VS Inoculum] 48Figure 4-4: Biogas yield without blank on inoculum 5 of trial 6 [mlN

Biogas/ g COD substrate] 49Figure 4-5: Biogas yield with blank on inoculum 5 of trial 7 [mlN Biogas/ g

VS Inoculum] 52Figure 4-6: Biogas yield without blank on inoculum 5 of trial 7 [mlN

Biogas/ g COD substrate] 52Figure 4-7: Biogas yield with blank on inoculum 5 of trial 6-7 [mlN

Biogas/ g VS Inoculum] 54Figure 4-8: Biogas yield without blank on inoculum 5 of trial 6-7 [mlN

Biogas/ g COD substrate] 55Figure 4-9: Biogas yield with blank on inoculum 6 of trial 9 [mlN Biogas/ g

VS Inoculum] 58Figure 4-10: Biogas yield with blank on inoculum 6 of trial 9 [mlN Biogas/ g

COD substrate] 59Figure 4-11: The corrected biogas composition of different samples 65

(WESSELAK, 2009) 12Table 2-6: Biogas composition and yield of different groups of

substances (Biogas Guide 2006) 13Table 2-7: Properties of renewable resources (FNR, 2005) 14Table 3-1: Description about sources of six inocula 20Table 3-2: Description of the batchtests for investigating the quality of six

inoculums 36Table 3-3: Description of the batchtests for investigating the biogas

potential of different substrates 37Table 4-1: Description of the experimental approach and parameters in

trials investigating quality of six inocula 42Table 4-2: Summary of biogas yield without blank and SLR on different

inocula 46Table 4-3: Description of the experimental approach and parameters in trial 6 47Table 4-4: Summary of biogas yield and SLR of trial 6 49Table 4-5: Description of the experimental approach and parameters in trial 7 51

List of Tables

Table 4-6: Summary of biogas yield and SLR of trial 7 53

Table 4-7: Description of the experimental approach and parameters in trial 9 56 Table 4-8 Summary of biogas yield and SLR of trial 9 60

Table 4-9: Comparison of biogas yields with theory 62

Table 4-10: Comparison biogas yields of water hyacinth samples with literature 63 Table 4-11: Biogas composition of different samples in trials 6, 7, 9 64

Table 4-12: Volatile solids of different samples 66

Table 4-13: Degree of degradation of volatile solids 68

Table 4-14: Total solids content of different samples 69

Table 4-15: Degree of degradation of total solids 70

Table 4-16: Chemical oxygen demand of different samples 72

Table 4-17: Degree of degradation of COD 73

Table 4-18: Degree of degradation of COD 75

Table 4-19: Degree of degradation of COD 76

Acknowledgements

Acknowledgements

Special thanks I would like to say to my supervisor Prof Dr Nguyen Thi Diem Trang for giving me the opportunity to make this thesis at Faculty of Chemistry, Hanoi University of Science in the Double-Degree-Program between the Hanoi National University and the Dresden University of Technology Many thanks also to my German supervisor Prof Dr Peter Werner

Special thanks also to Msc Tran Thi Nguyet (from Institute of Waste Management and Contaminated Site Treatment, Dresden University of Technology) and Dipl.-Ing Sebastian Meier (from Institute for Water Quality and Waste Management, Leibniz University Hannover) – team members of INHAND project who enthusiastically supervised me during the course of this thesis

Thanks to the help in inocula collecting of Prof Dr Nguyen Viet Anh, from the Centre for Environmental Engineering of Towns and Industrial areas (CEETIA), Hanoi University of Civil Engineering and the help in gas composition analysis of

Mr Thai Ha Vinh, from Monitoring and Environmental Analysis Department, Monitoring and Analysis of Working Environment Station, National Institute of Labor Protection Thanks also to the help in sample preparation of the staff (Mrs Nguyen Thi Diem Huong, etc) in the laboratory of Monitoring Centre for Natural Resources and Environment of Bac Ninh province

Thanks to the students of the Environmental Chemistry laboratory (Thang, Cham, Thao, Lan, etc) for their friendship with me during the experimental period time

Special thanks also to my family members for their great support in all the time of this master course!

Introduction

1 Introduction

In view of the challenges in the global and regional energy markets and facing the needs for global climate protection as well as the increasing efforts in developing rural areas, the utilization of renewable energies has to be advanced In this context, the usage of biogas plays an exceptional role as it is a highly flexible fuel with respect to a wide range of input substrates Biogas also offers various options in

providing and using energy on a local, regional and global scale

Vietnam is no exception to the trend biogas applications to replace fossil energy Biogas production has been studied and applied long in Vietnam, but until 2003, it became the real attention when the Ministry of Agriculture and Rural Development collaborated with the Netherlands Development Organization to build renewable energy project, the “Support Project to the Biogas Program for the Animal Husbandry Sector in Some Provinces of Vietnam.” By the end of 2008, the project has supported construction of over 56,000 household biogas plants, provided training for 500 provincial and district technicians, 700 biogas mason teams, and organized thousands of promotion workshops and trainings for biogas users Up to now, the project has become a national program “Biogas program for the Animal Husbandry Sector of Vietnam” that supports the implementation of household biogas digesters throughout Vietnam By the end of 2012, the team aims to complete 164,000 biogas plants (including large plants) in 58 provinces throughout

Vietnam and gain 1.5-3 tradable emission rights per year per digester(1) This program raises the effective movement of production technology and application of biological energy, reduces environmental pollution in rural areas, creates jobs and improves living standard for Vietnamese farmers and minimizes the greenhouse effects Along with that, the World Bank is also currently funding an array of manure management demonstration projects in Vietnam, ranging from small household -scale systems to village-scale systems(2)

Introduction

The studies(3) of biological energy have been simultaneous developing, as well as Prof Dr Bui Van Ga – director of Da Nang University and his colleagues at the Research Center for Environmental Protection (Da Nang University) with research focused on biogas refining and motor applications, or the teams from Hanoi Polytechnic University and Ho Chi Minh Polytechnic University with research on completed conversion of gasoline and diesel to biogas fuel running engines Therefore, Vietnamese farmers now are utilizing the produced biogas not only in cooking, lighting, heating but also generating electricity for their own farms by their own capital The only pity is that the farmers can not sell surplus generated power into general grid Besides, the Bio-Gas Project in the framework of the "Go Green - Green Journey" by Toyota Vietnam (TMV) in collaboration with the General Department of Environment and Ministry of Education and Training has been installing 500 generator powered by bio-gas in households, farms, small and medium enterprises from 2008 up to 2012

Based on those, biological energy has developed at a larger scale, focusing on the factories, farms, producing biogas from waste water of tapioca starch plants, seafood processing plants, rubber production plants, etc Up to now, Vietnam has

achieved 11 CDM (4) Projects (5) in validation, with the credit period from 2009/2010

to the end of 2020/2030, in the field of waste/ waste water treatment and biogas capture (mainly in tapioca starch sector) with the parties involved as limited

companies, corporations from Japan(4), France(1), Netherlands (5), Germany(1)

(5)

http://noccop.org.vn

Introduction

The development of biogas production and application with all the domestic potential and overseas support has been bringing great benefits for Vietnam’s economic development and environmental improvements For that, contributing to the studies of biogas in Vietnam, this thesis focused on the method of German guideline (VDI 4630) to assess the potential of recovery of organic waste in a Vietnamese food processing village by biogas production Firstly, it is to establish

an anaerobic batch system for biogas production in the laboratory in the North of Vietnam Then, experiments with this system were set up to investigate the quality

of inocula from different sources around Hanoi And with chosen inocula, substrates

as organic waste of Dai Lam village - a wine production and pig breeding village in Bac Ninh province were assessed Parameters of process were pH, temperature, TS,

VS, and COD Biogas potential and the fermentability of these substrates were evaluated and interpreted by using VDI- 4630 guideline

Theoretical Basics

2 Theoretical Basics

2.1 Basics of Anaerobic Digestion

2.1.1 The four stages of decomposition

The methane fermentation process comprises four stages that organic materials being degraded by anaerobic microorganisms in the absence of oxygen The degradation of high molecular weight starting substrates such as carbohydrates, fats and protein via low molecular weight compounds (fatty acids and alcohols) to methane, which is the main component of biogas Figure 1 shows a degradation process which is described below:

Figure 2-1: Four stages of anaerobic degradation (WEILAND, 2003)

In the first stage (hydrolysis), facultative anaerobic microorganisms hydrolyze the biomass with the aid of extracellular enzymes (exoenzymes(1)) to low molecular weight components Here, the organic substance is transferred by addition or temporary storage of water molecules in a dissolved form The facultative anaerobic

Acetogenic Bacteria

Methanogenic Bacteria

Carboxylic acids Alcohols

Acetate

H 2 / CO 2

Biogas

CH 4 / CO 2

Theoretical Basics

bacteria which were created to consume the remaining dissolved oxygen present with low required redox potential (less than - 330 mV) are the obligatory anaerobic bacteria (methanogens) The rate of hydrolysis is determined by the substrate composition, temperature, pH value (optimum pH = 6, (BISCHOFSBERGER, et al., 2005)), and the concentration of microorganisms For example, sugar and hemicelluloses are hydrolyzed very well, whereas pectin and lignin are difficult to hydrolyze Therefore, the higher the proportion of shares in the easily cleavable substrate is, the faster the digestion process of the bacterial cells run The hydrolysis

is therefore generally regarded as rate-limiting step of anaerobic (and aerobic) degradation (ROEDIGER et al., 1990)

Subsequently, the hydrolysis products in the second stage of fermentation (acidification) fermented intracellularly by the bacteria, the bacteria excrete mainly carboxylic acids, ethanol, ammonia, hydrogen sulphide and carbon dioxide The acidogenic bacteria here have a large tolerance, so that the pH value for the acidification of carbohydrates may fall below 4.0 (BISCHOFSBERGER et al., 2005) The degradation of the hydrolysis and acidification can be inhibited by its own metabolic products One hand, the bacteria produce only insufficiently dissolved substrate exoenzymes, on the other hand, these exoenzymes are sensitive

to pH values less than 6.5 (ROEDIGER et al., 1990)

Because methanogenic bacteria produce methane only from acetic acid, hydrogen and carbon dioxide in the third stage (acetogenesis), the carboxylic acid and alcohol

of the second stage can be converted to acetic acid, carbon dioxide, water and hydrogen Ammonia is mineralized to ammonium

In the fourth stage (methanogenesis) methanogenic bacteria convert acetic acid, hydrogen and carbon dioxide to methane The methane formation is carried out for 70% of the acetic acid degradation (also called acetate-degrading, see equation 2-1) and about 30% of the conversion of carbon dioxide and hydrogen (ROEDIGER et al., 1990) See equation 2-2

CH3-COO- + H2O Æ CH4 + HCO3- (Equation 2-1)

Theoretical Basics

4 H2 + CO2 Æ CH4 + 2 H2O (Equation 2-2)

The methane formation can also occur with a few methanogenic bacteria from

formic acid, methanol and methyl amine (CH3NH3) (BISCHOFSBERGER et al.,

2005) For methanogenesis, the optimum pH is 7 and the optimum temperature is at

35 ° C and 55 ° C (ROEDIGER et al., 1990)

There are 13 species of methane-forming bacteria, of which 11 species have their

optimum working environment in the mesophilic range and one type in the

thermophilic environment Another type is thermo-tolerant and can operate in

mesophilic and thermophilic range

Throughout the fermentation process, hydrogen inhibits the acetogenic bacteria The

close symbiosis between the acetogenic bacteria and the methanogenic bacteria is

an important prerequisite, since methanogenic bacteria prevent the inhibitory effects

of excess hydrogen, by converting the hydrogen with carbon dioxide to methane

(see equation 2-2) The symbiosis should be adjusted by the mixing process in the

reactor with registered shear forces, in order not to destroy it

After a trouble-free decomposition of organic substrates, there is an energy-rich gas

mixture which consists mainly of methane and carbon dioxide An average biogas

composition is given in Table 2-1

Table 2-1: Average composition of biogas (FNR, 2005)

Theoretical Basics

2.1.2 Influence Factors of Digestion

Anaerobic degradation processes involve a number of factors that determine the growth and activity of microorganisms significantly We distinguish effects due to operational factors (temperature, mixing, residence time, organic loading rate) and the influence of substrate components (C: N: P ratio, pH - value, concentration of inhibitory substances and nutrients, etc) Some of these factors influence each other and are mutually dependent Selected factors are briefly explained in the following sections

Mixing

Optimum mixing of the reactor is set to achieve sufficient contact between bacteria and fermentation substrate Temperature and concentration differences are compensated in the fermenter by mixing Without or with insufficient mixing, the mass of bacteria would decrease and easily demolished at the bottom to rise up the fermentation and form a floating layer through which the gas outlet would escape more difficult On the contrary, with vigorous mixing, there is the danger to those living in small communities, symbiosis acetogenic and methanogenic bacteria communities are affected by too high shear forces (GRONAU et al., 2007)

Temperature

The maximum metabolic rate and the maximum growth rate of organism is a function of the temperature For example, different optimal temperature possesses involved anaerobic microorganisms Therefore, a classification of organisms is based on temperature ranges, micro-organisms can be distinguished with psychrophilic (< 25°C), mesophilic (25 - 40°C) and thermophilic (45 - 60°C) (BISCHOFSBERGER et al., 2005) In industrial processes there are mainly mesophilic or thermophilic microorganisms The choice of the temperature range depends on factors such as the substrate properties, the hygiene degree, or the residence Since mesophilic fermentation processes have a greater diversity of methanogens (12 species), they are shown against thermophilic fermentation processes (only two species of methane bacteria) as a stable It should be noted that

Theoretical Basics

the species Methanosarcina barkeri(2) are both the mesophilic and thermophilic methane bacteria (DORNACK, 2001) Since methane bacteria are very temperature-sensitive, and are adversely affected even at low temperature, a constant temperature control of anaerobic reactors is necessary (ROEDIGER et al., 1990) With extreme temperature fluctuations, the bacteria respond with lower metabolic rates and reproductive performance (DORNACK, 2001)

pH value

The pH - value arises from the metabolic products of naturally present microorganisms and the different self-regulating buffer system The predominant organisms in the degradation phase species have different optimal pH During hydrolysis and acid-forming, bacteria find their pH optimum at 4.5 to 6.3, methane bacteria thrive best in a very narrow pH - 6.8 to 7.5 (FNR, 2005) A shift in the pH - value out of the narrow range from 6.6 to 8.0 can be rough interference to substrate degradation, result in the bacterial growth rate and metabolism (FAULSTICH, 1995) For example, the stable of hydrolyzing substrates can be inhibited by an excess of lime, because the required optimum pH is not created by the buffering action of the lime The consequence is lower gas yields

Factors influencing the anaerobic degradation are summarized in table 2-2 below

Table 2-2: Factors influencing the anaerobic degradation (WEILAND, 2001) modified

Hydrolysis / acidification Methane fermentation

Theoretical Basics

Ratio of nutrient elements

The C/N ratio and the C/N/P/S ratio can be used as an indicator of the optimal supply of carbon and nutrients If the C/N ratio is too high then the used carbon is not completely eliminated and therefore the methane potential not fully exploited This ratio is shifted to nitrogen, there is the danger of the formation of ammonia which is toxic in too high on the bacteria The C/N/P/S ratio is used to draw conclusions about the nutrient supply of the bacteria

Trace elements

For the growth and survival of the bacteria, trace elements that do not exceed certain levels should also be required (see Table 2-3) The trace elements must present in dissolved form The natural sources of entry for the trace elements in agricultural biogas plants are agricultural soils, etc, which can be distinguished between natural and anthropogenic influences such as pedogenesis fertilizer, emissions from industry and traffic

The incorporation of trace elements in plant and animal feces is based on feeding and additives and other input sources Lacking of trace elements, so as at too high concentrations, a delay occurs that can lead to the stoppage of the anaerobic degradation

Theoretical Basics

Table 2-3: Micro-nutrients for the anaerobic degradation

Concentration (mg/l organic matter)

Element

according to SAHM3 according to KLOSS (4) According to SEYFRIED (5)

Inhibiting and toxic substances

During anaerobic degradation, a variety of substances in high enough concentrations have inhibitory effects The inhibitors can be distinguished

according to their origin such as inhibitors in the degradation by addition of

substrate or inhibitors as intermediates Inhibitors which are introduced by adding

substrate, include substances which were used for cleaning and disinfection

purposes or for the treatment of animal diseases Also, herbicides, salts or heavy

metals, including essential heavy metals can be toxic in high enough concentrations

Theoretical Basics

Table 2-4: Inhibitory concentrations of various elements (WESSELAK, 2009)

Inhibitor Limiting concentration (mg/l)

up to 600 mg/l Na2S (in adapted cultures)

up to 1000 mg/l H2S (in adapted cultures)

Iso butyric from 50

Because bacteria can adapt well to different populations of individual inhibitors, very different maximum allowable concentrations of toxic substances are published

in the literature The different threshold concentrations also result from the interaction between the ingredients, the type of fermenter and the operation of the plant (KALTSCHMITT et al., 2009)

The addition of substrates with high proportions of carbohydrates and fats may lead

to the inhibition process, when the hydrolytic and acid-forming bacteria break down organic matter faster than the acetogenic and methanogenic bacteria convert the resulting acids into biogas This process can be determined by the ratio of the organic acids to alkalinity (VOA(6) / TAC(7)) Values below 0.4 indicate a stable       

Theoretical Basics

process and interpret values greater than 0.8 indicate a process of inhibition (MAEHNERT, 2007) The degradation of proteins forms end products of acetic acid and ammonia, and there may be an increase of hydrogen sulfide If there are acetic acid, ammonia and hydrogen sulphide in dissolved, undissociated form and in high concentrations, these substances act as cytotoxins and the methane formation is inhibited Methane-forming bacteria take on only the acid in undissociated form (see Eq 2-3) The acidity constant of acetic acid is given as pKa = 4.75, ie in the pH range of methanogenic bacteria between 6.8 to 7.5 acetic acid is largely dissociated acetate as before (BRANDENBURG, 2008) Concentrations of 50 mg / l H2S are considered directly inhibiting process, while the failure of essential trace elements

as insoluble sulfides is possible the indirect inhibition

CH3COOH ' CH3COO - + H+ (Equation 2-3)

The inhibitory effect of ammonia increases with higher pH values and higher temperatures, because the equilibrium between ammonium and ammonia is strongly

pH and temperature dependent For the anaerobic fermentation, a total concentration of NH3/NH3 + H + greater than 3 g / l is critical (MAEHNERT, 2007)

Table 2-5: Inhibitory concentrations of various heavy metals

(WESSELAK, 2009) Heavy metals

(ions)

Limiting concentration (mg/l)

Heavy metals (carbonates)

Theoretical Basics

2.1.3 Biogas potential of different substrates

The anaerobic degradation of glucose to carbon dioxide and methane can be

described approximately by (Eq 2-4)

C6H12O6 Æ 3CH4 + 3CO2 (Equation 2-4)

Biomass is not only from carbohydrates and biogas consist not only carbon dioxide

and methane If the exact composition of the fermentation substrate was determined

in terms of the number of carbon, oxygen and hydrogen atoms, then BUSWELLS

and MUELLER (BUSWELL, et al., 1952) simplified the equation

CnHaOb + (n– a/4 – b/2)H2O Æ (n/2 + a/8 – b/4) CO2 + (n/2 – a/8 + b/4) CH4

(Equation 2-5)

CnHaObNcSd + (n– a/4 –b/2 + 3c/4 + d/2)H2O Æ (n/2 – a/8 + b/4 + 3c/8 + d/4) CO2 + (n/2 + a/8 – b/4 – 3c/8 – d/4) CH4 + c NH3 + d H2S

(Equation 2-6) (Equation after BOYLE (BOYLE, 1976))

Table 2-6: Biogas composition and yield of different groups of substances

(Biogas Guide 2006) Groups of

substances

Molecular Weight (g/mol)

Mole fractions in Biogas (mol)

Molar volume in Biogas (g/mol)

Possible biogas yield (l/g)

Theoretical Basics

The equation for BUSWELLS and BOYLE (Eq 2-6) is used to determine the respective proportions of carbon dioxide and methane in the biogas The calculation of the biogas potential of the three main groups of carbohydrates, fats and proteins after BUSWELLS equation provides the results in Table 2-6 Under the full anaerobic reduction a higher methane content in biogas in fats and proteins is expected than the carbohydrates The average methane content in biogas is 50 - 75 vol.%

Table 2-7: Properties of renewable resources (FNR, 2005)

Substrate TS

(8) [%]

VS (9) [%]

N [% TS]

Biogas yield [m³/t VS]

CH4-content [Vol.-%]

Cattle

manure 8 - 11 75 - 82 2,6 – 6,7 200 – 500 60

Pig manure approx 7 75 - 86 6 - 18 300 – 700 60 – 70 Corn silage 20 - 35 85 - 95 1,1 - 2 450 – 700 50 – 55 Rye - whole

crop silage 30 - 35 92 - 98 4,0 550 – 680 approx 55 Grass silage 25 - 50 70 - 95 3,5 - 6,9 550 – 620 54 – 55

Beet leaf 16 75 - 80 0,2 - 0,4 550 – 600 54 – 55

Renewable resources offer in terms of the fermentation substrate, a number of favorable properties Such are, for example, a high organic content, the amount of nutrients and trace elements, and a low impurity content Some selected substrates and their properties are listed in Table 2-7 The very high specific gas yield of renewable resources as compared to cattle or pig manure makes sense with fermentation biogas plants Furthermore, the substrates brought nutrient and trace element content into the fermenter for optimal performance of important microorganisms

Theoretical Basics

2.2 End products of fermentation

End products of anaerobic digestion are biogas and digestate and process water is mentioned as a possible intermediate The topic of biogas production has already been discussed above in detail

An agricultural biogas plant can be generally considered as a closed system and no technical treatment of residues, no process water is provided in this system A treatment of the digestate can be, for example separation in solid and liquid phase or dewatering and composting Water in the waste treatment process can be subject to various process-relevant parameters such as pH, salt concentration and others, returned to the fermenter

The digestate without subsequent treatment are primarily used as fertilizer The agricultural use and the application of the fermented substrates at the recovery fermentation depend on the bio-waste regulation The organic dry matter content is reduced by the fermentation, in which the degree of degradation of manure of species and accounting system-specific parameters and fermentation parameters are dependent The viscosity of the slurry is reduced by the anaerobic digestion and thus has a positive effect on the pumping, homogenization and spreading of degestate Odor-active substances are further reduced by the fermentation, the degradation of the organic acids also helps to reduce the corrosion of the plant The total nitrogen content is not reduced by the fermentation process The increase in

pH compared to unfermented manure takes the ammonia content into the digestate Ammonia losses can be increased by the storage and spreading of residues The masses of the ingredients of the digestate as phosphorus, calcium, potassium and magnesium are not reduced by the fermentation The sulfur content is reduced by discharge of hydrogen sulfide and the remaining sulfur is present mainly as elemental sulfur in the digestate Heavy metals are not subject to biological degradation and accumulate in the digestate Epidemic of health hazards bacteria are decimated within days under mesophilic conditions by 90% By short-circuit

Theoretical Basics

currents in fully mixed reactors, these bacteria and germs are on agricultural use again Sufficiently long residence times should be observed in order to avoid gas emissions from the digestate (F SCHOLWIN, 2006)

Materials and Methods

3 Materials and methods

3.1 VDI survey about batchtests for biogas yield determination

3.1.1 Scope and purpose of Fermentation batchtests

According to guideline VDI 4630, batch procedure can be applied to all kind of organic materials which can be representative So that, organic wastes chosen in this thesis such as cassava residues, rice residues, pig manure and water hyacinth would

be sampled and prepared as instructed in this guideline to achieve homogenous state

Fermentation batchtests with VDI methods help to evaluate the possible biogas yield, the degradability, the degradation speed, the inhibitory effect of these wastes

in Dai Lam village – a representative craft village of wine production and pig breeding in Bac Ninh province which is located in the North of Vietnam

3.1.2 Methods of VDI 4630 in detecting the biogas yield

In VDI 4630, there are six possible methods of detecting the gas such as gas volume measurement with the head water systems (the eudiometer, the gas sampling tube), with gas pressure measurement instrument, with plastic bags, with syringe sampler and with the gas meter Each of the test apparatus has its own strengths and weaknesses

In case of this thesis (with the instruction of the Institute for Water Quality and Waste Management, Leibniz University Hannover, Germany) gas volume measurement with a gas pressure measurement instrument was properly applied The gas volume is measured indirectly by a pressure measurement instrument and calculated from the gas pressure registered and the gas temperature measured The test apparatus of this method is shown in figure 3-1

Materials and Methods

Figure 3-1: Test apparatus according to DIN EN ISO 11734: Gas volume

measurement with a gas pressure measurement instrument (VDI 4630)

This system is also known as “Constant- Volume- Reactor”, in which water and gas phase are temperature controlled at 370C and gas quantity determination via pressure slope The automatic model – modified of the base model - applied in the Institute for Water Quality and Waste Management, Leibniz University Hannover, Germany is shown in figure 3-2

Figure 3-2: Gas volume measurement with a gas pressure measurement

instrument (S Meier et al., 2009)

Materials and Methods

3.1.3 Method of VDI 4630 in approaching the batchtests

According to VDI 4630, the batch fermentation tests should be conducted at least as double determinations (or better as triple determinations) with investigated samples

as well as reference and blank (zero) samples

Based on VDI 4630 and instruction of the Institute for Water Quality and Waste Management, Leibniz University Hannover (S Meier et al., 2009), steps of a batchtest with rising pressure system can be described as following:

- Pretreatment of biomass (reducing COD of inoculum) by etiolation

- Analysis 1: TS, VS, pH of inoculum, COD of substrates

- Precalculation of substrate amount, gas space, expected pressure increase

- Preparation of inoculum and substrates

- Bottle weighing and filling with inoculum, substrate, free oxygen water, buffer

- Flushing with nitrogen Closing bottles and creating vacuum (0.2 barabs)

- Incubating at constant temperature (37oC) and measuring pressure increase until it remains constant

- Analysis 2: Gas composition analysis (The methane content should be determined more than once during the fermentation test, it is best at regular intervals)

- COD, TS, VS, pH of digestate

During the course of test, the fermentation material should be sufficiently mixed such

as shaking the bottles each day to resuspend the sediments and the scum layers

Materials and Methods

methanogens can remove inhibitory byproducts of the faster growing hydrolyzing and acid producing processes Since investigated substrates as food process byproduct, fresh plant might not be high on methanogen’s favorite places to live, or substrates as fresh manures which have large population of methane producing organisms need long time process

For that, six inocula around Hanoi were collected and tested the quality

Table 3-1: Description about source of six inocula

septic tank (dewatered)

Lab of Prof Nguyen Viet Anh in the Centre for Environmental Engineering of Towns and Industrial areas (CEETIA), Hanoi University of Civil Engineering

Materials and Methods

b Substrates

Substrates were water hyacinth, rice residues, cassava residues, pig manure which were collected in Dai Lam village-a wine production and pig breeding village in Bac Ninh province

Figure 3-3: Map showing position of Dai Lam village

Materials and Methods

- Rice residues and cassava residues were collected twice at wine processing households Samples were homogenized by stirring in the bucket and taken on

different areas of the bucket (on the top, at the bottom, and from the middle)

Figure 3-5: Rice residues and cassava residues sampling at households

(INHAND photo documentary)

- Pig manure was collected twice at small swine farm of a household Samples

were homogenized by taken on different areas of one pile

Figure 3-6: Pig manure at a small swine farm of a household

(INHAND photo documentary)

Materials and Methods

3.2.2 Sample preparation

Water hyacinth, rice residues, cassava residues, pig manure were preliminarily prepared in laboratory of Monitoring Centre for Natural Resources and Environment of Bac Ninh province Then samples were transported in tight cap- plastic box to Environmental Chemistry Laboratory, Faculty of Chemistry, Hanoi University of Natural Sciences, Hanoi National University for next steps

Rice residues and cassava residues

The fresh sample was mixed as much as possible to crush and homogenize by blender

Figure 3-7: Homogenizing cassava residues by blender

(INHAND photo documentary)

Preparing a dilution: (often rate 1: 200 for COD total and 1:10 for COD of filtered sample)

- Dilution for COD total measurement: The homogenized sample was weighed and filled into a volumetric flask Fill up with distilled water until calibration mark Shake the volumetric flask to homogenize the sample Transfer the liquid into a

Materials and Methods

beaker glass Put the beaker glass on a stirring plate and add magnetic stirrer (do not stir too fast.) During stirring take the sample for analysis by pipette

- Dilution for measuring COD of filtered sample: The fresh sample was filtered two times by coarse filter paper and by 0.45µm pore size membrane filter with plastic syringe Take the filtered liquid into volumetric flask by pipette Fill up with distilled water until calibration mark Shake the volumetric flask to homogenize the sample Transfer the liquid into a beaker glass Put the beaker glass on a stirring plate and add magnetic stirrer (do not stir too fast.) During stirring take the sample for analysis by pipette

Water Hyacinth

Remove the leaves and the stems from the plant and cut it in small pieces separately Mix thoroughly then weigh 200 gram of sample Put into the mill Add 500ml distilled water Operate the blender as the sample is homogenized thoroughly Pour the liquid into 1l volumetric flask Wash the mill clear by 200ml distilled water Pour the wash water into the volumetric flask Fill up with distilled water until calibration mark Shake the volumetric flask to homogenize the sample The dilution rate is 1:4

Figure 3-8: Homogenizing water hyacinth by blender

(INHAND photo documentary)

Materials and Methods

Transfer the liquid into a beaker glass Put the beaker glass on a stirring plate and add magnetic stirrer (do not stir too fast) During stirring take the sample for analysis by pipette Dilution with appropriate rate for COD analysis (often rate 1:20 for COD total and 1:5 for COD of filtered sample)

Pig Manure

Fresh sample was mixed thoroughly and weighed for 200gram Put into the mill Add 500ml distilled water Operate the blender as the sample is homogenized thoroughly Pour the liquid into 1l volumetric flask Wash the mill clear by 200ml distilled water Pour the wash water into the volumetric flask Fill up with distilled water until calibration mark Shake the volumetric flask to homogenize the sample Transfer the liquid into a beaker glass Put the beaker glass on a stirring plate and add magnetic stirrer (do not stir too fast) During stirring take the sample for analysis by pipette Dilution with appropriate rate for COD analysis (often rate 1:100 for COD

total and 1:10 for COD of filtered sample).The dilution rate was 1:4

3.2.3 Determination of parameters: TS, VS, COD, and CH 4 and CO 2 content

in biogas

TS (Total Solids or dry matter) measurement

TS was measured as specification APHA-SMWW (1)_ 2540G (103-1050C) Ceramic crucibles (50ml or 30ml) were put in put in muffle furnace at 5500C for 1 hour (in this case, they were put in drying cabinet at 1050C for 1 hour), then weighed the first time Fresh samples were poured into ceramic crucibles, weighed the second time, then put into drying cabinet at 1050C for 24 hours (or to constant weight), after cooled down in glass desiccator, weighed the third time TS was specified based on fresh mass

(1)

APHA-SMWW: American Public Heath Association- Standard Methods for the examination of

Water and Wastewater

Materials and Methods

VS (Volatile Solids or organic dry matter) measurement

VS was measured as specification APHA-SMWW_ 2540G (5500C) Ceramic crucibles with dry matter were put into muffle furnace, kept at 5500C for 1 hour After cooled down in glass desiccators, weighed the last time VS was specified based on fresh mass

COD (Chemical Oxygen Demand) total of homogenized fresh sample and COD soluble of the filtered sample

COD was measured as method of Environmental Chemistry laboratory, Chemistry department, Hanoi University of Sciences which is modified from specification APHA-SMWW_ 5520D-Closed Reflux, Colorimetric Method

Reagents preparation

a Digestion solution, high range: Add to about 500 ml distilled water 10.216 g

K2Cr2O7, primary standard grade, previously dried at 150°C for 2 hours, 167 ml concentrated H2SO4, and 33.3 g HgSO4 Dissolve, cool to room temperature, and dilute to 1000 ml

b Sulfuric acid reagent: Add Ag2SO4, reagent or technical grade, crystals or powder, to concentrated H2SO4 at the rate of 5.5 g Ag2SO4/kg H2SO4 Let stand 1 to

2 days to dissolve Mix

c Potassium hydrogen phthalate standard (KHP): HOOCC6H4COOK: Lightly crush and then dry KHP to constant weight at 110°C Dissolve 850 mg in distilled water and dilute to 1000 ml KHP has a theoretical COD of 1.176 mg O2/mg and this solution has a theoretical COD of 1000 μg O2/ ml

Procedure

a Treatment of samples:

Materials and Methods

Place 2.5ml of sample in culture tube, then add 1.5ml of digestion solution, carefully run sulfuric acid reagent down inside of vessel so an acid layer is formed under the sample-digestion solution layer Tightly cap tubes, and invert each several times to mix complete

Wear face shield and protect hands from heat produced when contents of vessels are mixed Mix thoroughly before applying heat to prevent local heating of vessel bottom and possible explosive reaction

Place tubes in block digester preheated to 150°C and reflux for 2 hours behind a protective shield

b Measurement of dichromate reduction:

Cool sample to room temperature slowly to avoid precipitate formation, place vessels in test tube rack Once samples are cooled, vent, to relieve any pressure generated during digestion Mix contents of reaction vessels to combine condensed water and dislodge insoluble matter Let suspended matter settle so that optical path

is clear Measure absorption of each sample at selected wavelength 605nm

c Setting up calibration curve:

Ten standards from potassium hydrogen phthalate solution were prepared with COD equivalents to cover concentration range: 0 to 1000 μg O2/ ml Make up to volume with reagent water; use same reagent volumes, tube, or ampule size, and digestion procedure as for samples Curve was linear

CH 4 and CO 2 content measurement

CH4 content was measured by GC (gas chromatography) method with FID (flame inonization detector) CO2 content was measured by GC method with TCD (thermal conductivity detector)

Materials and Methods

Principle of Gas Chromatography

In gas chromatography a mobile phase (a carrier gas) and a stationary phase (column packing or capillary column coating) are used to separate individual compounds The carrier gas is nitrogen, argon-methane, helium, or hydrogen For packed columns, the stationary phase is a liquid that has been coated on an inert granular solid, called the column packing, that is held in borosilicate glass tubing The column is installed in an oven with the inlet attached to a heated injector block and the outlet attached to a detector Precise and constant temperature control of the injector block, oven, and detector is maintained Stationary-phase material and concentration, column length and diameter, oven temperature, carrier-gas flow, and detector type are the controlled variables

When the sample solution is introduced into the column, the organic compounds are vaporized and moved through the column by the carrier gas They travel through the column at different rates, depending on differences in partition coefficients between the mobile and stationary phases

Flame Inonization Detector

Flame ionization detector—The flame ionization detector (FID) is widely used because of its high sensitivity to organic carbon-containing compounds The detector consists of a small hydrogen/air diffusion flame burning at the end of a jet When organic compounds enter the flame from the column, electrically charged intermediates are formed These are collected by applying a voltage across the flame The resulting current is amplified by an electrometer and measured The response of the detector is directly proportional to the total mass entering the detector per unit time and is independent of the concentration in the carrier gas Apparatus as specification APHA-SMWW_2720C

Use instrument system equipped with a thermal conductivity detector (TCD), carrier-gas flow controllers, injector and column temperature setting dials, TCD current controller, attenuator, carrier-gas pressure gauge, injection port, signal

Materials and Methods

output, and power switch Some columns require temperature programming while others are isothermal Preferably use a unit with a gas sampling loop and valve that allow automatic injection of a constant sample volume

Injection: 10ul, split 10, 2000C

b Analysis of CO 2by running GC/ TCD equipment program: