Submitted in Partial Fulfillment of the Requirements for the Award of the Degree of

Fig.4.5 Effect of total solids on biogas production from pretreated and untreated (a) sugarcane bagasse and (b) rice straw mixed with cow dung. Fig.5.23 Validation of reformed modified Gompertz model for lignocellulosic biomass mixed with cow dung with present study.

Background

Motivation

The main occupation of the people in most of the developing countries is crop cultivation. The outbreak of the plague in September 1994 was also a result of the large piles of rubbish left uncollected in the city of Surat, Gujrat, which provided an ideal habitat for rats [World Resources, 1996-97].

Composition and properties of biogas

Furthermore, the removal of carbon dioxide from the biogas produced by anaerobic digestion is important in terms of reducing atmospheric pollution. Also, to increase the calorific value of biogas, it is necessary to remove the carbon dioxide present in it.

Applications of biogas

Anaerobic digestion process

Types of biomethanation process

Commonly used feed materials for biogas production

Pretreatment of biomass

Pretreatment is a process that changes the cellulose structure of biomass, resulting in rapid hydrolysis of both cellulose and hemicellulose, producing biogas in a short time. In this process, the lignin content of the biomass is firstly degraded by various means such as mechanical/physical, chemical, biological, etc.

Purification of biogas

This chapter presents the kinetic study of biogas production from lignocellulosic biomass mixed with cattle manure. P is the cumulative value of the specific biogas production (ml/g VS). A is the biogas production potential (ml/g VS).

Fig. 2.1 Growth rate of methanogens under psychrophilic, mesophilic and thermophilic conditions [Liar e tal., 1997]

Objective of the present work

Organization of thesis

The results of the kinetic investigation and modeling are presented and discussed in the same chapter. The design and development of a carbon dioxide scrubber and the results of biogas purification using soda lime are discussed in Chapter 6.

Introduction

Factors affecting bio-methanation processes

Effect of temperature on biogas production
Effect of feed material on biogas production
Effect of co-digestion of biomass on biogas production
Effect of Carbon and Nitrogen ratio on biogas yield
Effect of loading rate (LR) on biogas production
Role of pH on biogas production
Effect of hydraulic retention time (HRT) on biogas production
Effect of mechanical stirring and agitation on biogas yield
Effect of additives on biogas production
Effect of toxicity on biogas production
Influence of total solid (TS) on biogas production

Sambo et al., 1995 studied the effect of temperature on biogas production and found that gas production was highest at 50°C followed by 60°C and 40°C, respectively. Mahanta et al., 2004 reported that for cattle dung the maximum gas production was achieved with 8% TS.

Influence of biofilm carrier on biogas production

Heavy metals (e.g. copper, nickel, chromium, zinc, lead, etc.) in small concentrations help in the normal growth of bacteria but in high concentration the same heavy metals have toxic effects [Youngsukkasem et al., 2013]. Pinho et al., 2004 reported that support media made of polyurethane matrices in batch reactor along with mechanical agitation improves biogas production.

Pretreatment of biomass

A comparative study by Mshandete et al., 2008 examined the effectiveness of waste sisal fibers, pumice and glass beads as biofilm carriers and found that sisal fibers were the most effective among these materials. These characteristics make biochar a potential candidate as a cheap and available source for the immobilization of microbial cells in anaerobic digesters [Lehmann et al., 2011].

Design and performance of anaerobic digesters

Methods involving thermal management of digester

Insulation of digester

Heating of digester substrate

Solar heating of digester

The sludge temperature of the conventional biogas plant with water heater, solar cover and removable insulation was the highest followed by the conventional biogas plant with water heater and solar canopy, then the conventional biogas plant with water heater compared to a conventional plant of biogas without any assistance.

Kinetic modeling study

Kinetic models based on biogas production
Kinetic models based on bacterial growth
Kinetic models to calculate hydraulic retention time (HRT)
Models based on influence of temperature
Kinetic models to simulate biogas accumulation

According to this model, the specific growth rate of microorganisms is given by Eq. From the figure it is observed that the specific growth rate of microorganisms increases monotonically with substrate concentration.

Figure 2.8 shows dependency of specific growth rate on substrate concentration according to Monod model

Carbon dioxide removal from biogas

Physical absorption
Chemical absorption by caustic scrubbing
Scrubbing by aqueous solution of MEA
Adsorption on a solid surface
Membrane separation
Cryogenic separation

Savery et al., 1972 reported that three agents NaOH, KOH and Ca(OH)2 can be used in the chemical treatment of biogas to remove CO2. Alonso-Vicario, 2010 studied CO2 removal from biogas by pressure swing adsorption (PSA) with thermal desorption using two synthetic molecular sieves and natural zeolite (clinoptilolite) as adsorbent material.

Summary

Effect of temperature, being one of the important parameters on gas yield, was also considered in the studies. In the next chapter (Chapter 3) the characterization of the selected lignocellulosic biomass collected from the Northeast Region of India is presented.

Introduction

Characterization of Biomass Feedstock

Proximate analysis

Moisture content
Volatile matter content
Ash content
Total solid content
Fixed carbon content

Ultimate analysis
Chemical oxygen demand (COD)
Calorific value of feed materials
Fibre analyses of biomass

After cooling the samples to room temperature in the desiccator, the final weight of the dried samples is recorded with pre-weighed jars. The percentage TS content of the sampled biomass is then calculated using Eq.

Sample preparation

The fiber content of lignocellulosic biomass such as cellulose, hemicellulose and lignin can be determined by analyzing the neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) using the reflux apparatus (Goering, et al. 1970). NDF is usually used to estimate the total lignocellulosic materials (including cellulose, hemicellulose and lignin), while ADF is used to estimate the content of lignin and cellulose.

Results and discussion

Proximate analysis
Ultimate analysis
Calorific value of biomass
Chemical oxygen demand of biomass
Fibre analysis

It is noted that the data obtained from the proximate analysis of the food material in this paper are quite comparable with most of the available literature. It is noted that the cellulose content in the aforementioned lignocellulosic biomasses is quite good.

Selection of lignocellulosic biomass

Summary

As a result, the fermentation of lignocellulosic biomass takes long periods compared to other non-lignocellulosic biomass. Pre-treatment of biomass breaks down the lignin part of the biomass in advance and thus exposes the cellulose part of the biomass which makes it easier for the bacteria to decompose the biomass effectively and thus avoid delay in the hydrolysis process.

Introduction

Preparation of substrates

Mixing biomass with cow manure at a ratio of 1:3 was found to result in C:N mixtures ranging from 25:1 to 30:1. To repeat, cow manure was mixed with each biomass at a ratio of 1:3 for the entire experiment, so that the C:N ratio in the mixed substrate was controlled in the range of 25:1-30:1.

Table 4.1 C:N ratio of biomass before and after mixing with cattle dung Sl.

Experimental set-up

A mercury glass thermometer (range -10 °C to 110 °C) attached to the biodigester through the stopper is used to measure the daily temperature of the substrate, and a digital pH meter is used to determine the pH of the substrate. fermented substrate. The temperature of the substrate is measured twice a day with the help of a thermometer placed through the stopper.

Materials and methods

Parameters of biomethanation study

Ambient and digestate temperature
pH
Volume of biogas production
Measurement of methane and carbon di-oxide
Measurement of cumulative production of biogas

The solution bottle containing saline solution is mounted on the batch reactors through connecting tubes. When the production of biogas takes place in the biogas tanks, it is transferred to the solution bottle with acidified brine solution through the connection pipe and presses the solution inside.

Results and discussion

Effect of agitation on biogas production
Effect of particle size and total solid on biogas production
Effect of temperature on biogas production

Effect of temperature on daily biogas production
Effect of temperature on cumulative biogas production

Effect of co-digestion of biomass with cattle dung
Effect of addition of biochar on biogas production

It is observed that biogas production is highest at 55°C, followed by that at 50°C. But the cumulative biogas production by rice straw and rice husk powder mixed with cattle manure does not appear promising, as shown in Figure 1.

Fig. 4.2 Effect of agitation on biogas production from cattle dung

Summary

It also presents the effect of temperature on the kinetics of biogas production from the substrate. It presents the kinetic parameters of mathematical model regarding biogas production rate in batch anaerobic digestion processes assuming that the biogas production rate in batch mode corresponds to the specific growth rate of methanogenic bacteria in the biodigesters.

Application of first order kinetic model to biogas generation

Effect of temperature on kinetic rate constants

Under the same condition, Abdullahi et al., 2011 found that the kinetic rate constant, k is -0.31 for cattle manure. Like cow dung, the kinetic rate constant, k, increases with increasing temperature from 35 to 55°C.

Modified Gompertz model applied to experimental data

Effect of temperature on kinetic constants

Cumulative biogas production from lignocellulosic biomass mixed with cow dung is simulated using a modified Gompertz model, and the experimental biogas accumulation data are shown together with the model data in a graph of cumulative biogas production versus HRT. Under mesophilic conditions, the maximum biogas production potential and the maximum biogas production rate are achieved at 35 °C.

Fig. 5.8 Comparison of experimental and model data for saw dust

Kinetic model development for biogas production

For rice husk powder, the biogas production potential, A, and the maximum biogas production rate, U, are quite low compared to the other lignocellulosic biomass considered for the experiment. The effect of temperature on the average value of biogas production potential, A of the above biomass, is shown in Fig.

Fig. 5.14 Effect of temperature on Biogas production potential, A

Validation of the reformed modified Gompertz model

Validation for cattle dung with present work

5.19, 5.20 and 5.21 to the modified Gompertz equation, a reformed form of an equation for cattle dung is obtained as shown in Eq. 5.22) represents the modified modified Gompertz model for clean cattle excrement.

Validation for cattle dung with literature

Validation for lignocellulosic biomass with present study

Summary

It is also observed that agitating the digestate improved biogas production from cattle manure by 69% compared to without agitation. Budiyono, Widiasa IN, Johari, S., and Sunarso., The influence of total solid content on biogas yield from cattle manure using rumen fluid inoculum.

Table 6.1 Design parameters of the scrubber

Various biogas purification methods

Design and development of experimental set-up

Details of the design procedure of the experimental structure are described in Appendix VI. It is based on the design of the carbon dioxide scavenger box used in gas masks.

Materials and methods

The temperature rise during the exothermic reaction throughout the washer is analogous to a moving temperature front. However, in the second step of the reaction, water is produced as a by-product of the chemical reaction that takes place inside the washer (Eq. 6.2).

Table 6.2 Typical composition of sodalime [Schon, 2012]

Experimental set-up and procedure

Therefore, in this study, the effects of various parameters on biogas production are analyzed to find out the optimal performance of the lignocellulosic biomass. In the current research, the production of biogas from lignocellulosic biomass mixed with cattle manure is studied in small-scale laboratory setups.

Fig. 6.8 Compression of biogas Fig. 6.9 Biogas passed through the scrubber

Results and discussion

Temperature distribution in scrubber

The relationship between reaction and temperature is used to give an indication of the absorption of carbon dioxide in the scrubber. Twelve K-type thermocouples were mounted radially and centrally on the carbon dioxide scrubber to study the temperature distribution of the scrubber during biogas flow through the unit.

Figure 6.14 presents the central temperature distribution in the carbon dioxide scrubber from the inlet port to the outlet port

Methane enrichment

While at an inlet pressure of 4 and 5 bar the percentage of carbon dioxide in the exhaust appears to be less than 5% at all the above flow rates. However, the absorption of carbon dioxide upon further increasing the inlet pressure from 4 to 5 bar does not appear to be very significant.

Fig. 6.17 Percentage of CO 2 in purified biogas using vertical scrubber Table 6.3 Percentages of CO 2 in Biogas after purification with vertical scrubber

Comparison of results of horizontal and vertical scrubbers

The reason may be due to the effect of gravity which helps to keep the biogas in the scrubber longer in the case of vertical scrubber compared to that of horizontal scrubber. Similarly at inlet pressure of 1 to 3 bar, carbon dioxide percentage in outlet is found to be 0.7 to 5.5% higher in case of horizontal scrubber compared to vertical scrubber at all gas flow rates considered.

Fig. 6.19 Comparison of results obtained from horizontal and vertical scrubber at (a) 1 lpm, (b) 2 lpm, (c) 3 lpm, (d) 4 lpm and (e) 5 lpm

Comparison of results of biogas enrichment with literature

For inlet pressures of 4 and 5 bar, the percentage of carbon dioxide in the outlet of a vertical scrubber is found to be less than 5% at gas flow rates of 1 to 5 lpm, whereas the percentage of carbon dioxide in the outlet of a horizontal scrubber is more than 5% below same condition. The reason can be attributed to the fact that in case of vertical scrubber the gas flow has to be moved against gravity which helps the gas to stay inside the scrubber for a longer time as compared to horizontal scrubber.

Summary

Introduction

Contribution of the present work

Characterization of biomass
Parametric study on lignocellulosic biomass
Kinetic study of biomethanation processes
Biogas purification using chemical absorption method

Therefore, the biomass is mixed with cattle manure in a ratio of 1:3 to adjust the C:N of the substrate for better biogas production. Biogas production appears to be highest at 55°C for all biomass considered for the parametric study, as well as for pure cattle manure.

Scope for future work

Budiyono, IqbalSyaichurrozi and SiswoSumardiono., Biogas production kinetically from vinasse waste in batch mode anaerobic digestion.