AnaerobicDigestionOfBiodegradableOrganicsInMunicipalSolidWastes.pdf

(970 KB) Pobierz
ANAEROBIC DIGESTION OF
BIODEGRADABLE ORGANICS IN MUNICIPAL
SOLID WASTES
Advisor: Prof. N.J. Themelis
Submitted in partial fulfillment of the requirements for Master of Science
Degree in Earth Resources Engineering
SHEFALI VERMA
Department of Earth & Environmental Engineering
(Henry Krumb School of Mines)
Fu Foundation School of Engineering & Applied Science
Columbia University
May 2002
964348537.001.png
CONTENTS
i
Executive Summary
Acknowledgement
iii
1. Introduction
1
2. The Anaerobic Digestion (AD)Process
2
2.1 Hydrolysis/Liquefaction
2
2.2 Acetogenesis
3
2.3 Methanogenesis
3
2.4 General Process Description
4
2.5 Various AD Systems
5
3. Important Operating Parameters
6
3.1 Waste Composition/Volatile Solids
6
3.2 pH value
7
3.3 Temperature
7
3.4 Carbon to Nitrogen Ratio (C/N)
8
3.5 Total Solids Content/Organic Loading Rate
8
3.6 Retention Time
9
3.7 Mixing
9
3.8 Compost
9
3.9 Biogas Composition
11
4. Development & Present Status of AD Technology
11
4.1 Historical Background
11
5. Types of AD Systems
15
5.1 Single Stage Process
16
5.1.1 Single Stage Low Solids Process
16
5.1.2 Single Stage High Solids Process
17
5.2 Multi Stage Process
20
5.2.1 Multi Stage Low Solids Process
21
5.2.2 Multi Stage High Solids Process
22
5.3 Batch Process
23
6. Trends in AD Technology
25
7. Case Studies
32
7.1 Valorga Technology
32
7.1.2 Valorga Plant at Tilburg
35
7.2 DRANCO Process
37
7.2.1 Brecht Plant
38
7.3 BTA Process
40
7.3.1 BTA Newmarket Plant
41
8. Potential for use of AD Technology to treat NYC Organic MSW
42
9. Conclusions
46
Bibliography
48
964348537.002.png
 
List of Tables and Figures
Table 1 US Department of Agriculture Compost Heavy Metals Standards
10
Table 2 Concentrations (mg/kg ts) of heavy metals and arsenic in compost
according to regulations in different countries
10
Table 3 Typical Biogas composition
11
Table 4 Current and Planned European Waste Legislation
13
Table 5 Countries with AD Plants
25
26
Table 6 Companies Supplying Anaerobic Plants with capacity > 2,500 tons/year
Table 7. Operating Valorga Plants
34
Table 8. Operating DRANCO Plants
38
Table 9. Brecht Facility Outputs and Costs and Revenues
39
Table 10. Operating BTA Plants
40
Table 11. Composition of NYC MSW
43
Figure 1 The digesters at Tilburg Plant in The Netherlands
2
Figure 2 The flow diagram of low solids AD
5
Figure 3 The DRANCO reactor (A) and Kompagas Reactor (B)
18
Figure 4 The Valorga Digester
19
Figure 5 The Flow diagram of BTA Process
22
Figure 6 The different types of Batch Reactors
23
Figure 7 Worldwide Distribution of AD Plants
27
Figure 8 Annual and Cumulative Capacity of AD Plants treating MSW
28
Figure 9 Comparison between Mesophilic and Thermophilic
29
Figure 10 Comparison between Low Solids and High Solids
30
Figure 11 Comparison between Single Stage and Multi Stage
31
Figure 12 Comparison between AD plants treating Biowaste and Mixed MSW
32
Figure13 The Flow diagram of Valorga Process
33
Figure 14 Comparison of heating value of various waste type
44
ANAEROBIC DIGESTION OF BIODEGRADABLE ORGANICS IN
MUNICIPAL SOLID WASTES
(Shefali Verma )
Executive Summary
This study examined in depth the current status of the anaerobic digestion
technologies for the treatment of the organic fraction of municipal solid wastes
(MSW). Anaerobic digestion (AD) consists of the degradation of organic material in
the absence of oxygen. It produces mainly 55 % methane and 45 % carbon dioxide
gas and a compost product suitable as a soil conditioner.
A review of systems in operation worldwide was made, including types of
process design and their engineering and environmental performance. The study also
provided information on the trend in installed capacity and size of plants, which
indicated that in the late 90's there was a notable rise in size of new plants. The
report compares various AD systems such as mesophilic vs thermophilic operation,
low-solids vs high-solids feed, multi-stage vs single stage reactors, and AD systems
treating mixed wastes vs biowaste. The report also describes in detail the most
important AD processes based on the total solids (TS) content of the slurry in the
digester reactor. Some of these processes are further explained with case studies.
The AD systems for MSW digestion are widely used throughout the world.
Commercially available digesters range from 70m 3 to 5000m 3 reactor capacity. The
smaller digesters make use of the generated biogas (i.e. mixture of CH 4 and CO 2 ) for
heating the digester while larger units generate up to 2 MW of electricity. Much of
the technology is based in Europe, with Germany and Denmark leading the field in
technology.
Evaluation of various AD processes showed that single stage processes are
leading. Multi-stage reactors are too expensive and more complex to operate;
however, these systems provide separate reactors for hydrolysis and methanogenesis
and provide more favorable conditions for the reaction of low-cellulose materials
such as manure, poultry waste. The comparison between single stage, low-solids
(LS) and single stage, high-solids (HS) operation indicates higher gas yields from
i
high solids facilities. For example, the Waasa LS process reports 100-150 m 3 /ton of
waste input and the Valorga HS process 220-250 m 3 /ton of feed to digester. In
addition, the organic loading rate for single stage high-solids (e.g., DRANCO, 15 kg
of Volatile Solids per m 3 per day) is twice that of the single stage low-solids (Waasa,
6 kg VS/(m 3 .d)).
A well-designed AD fosters sustainable development since it recovers energy
thus reducing fossil fuel use and reducing greenhouse gas sources. It also allows
nutrients in the form of compost product to be returned to the land maintaining
nutrient closed loop system.
The advances of AD technology have been supported by legislation. Most
European countries are aiming to limit MSW disposal to landfills to no more than 5% of
the collected material and have increased taxes on landfilling. This will ensure that waste
is properly treated for combustibles and organics rather than being buried in the ground.
The 15% renewable energy by 2010 target as well as schemes such as "green pricing" in
The Netherlands and some other European countries allow AD facilities to sell biogas for
electricity generation at a premium. Similarly, in the United Kingdom, under the Non-
Fossil Fuel Obligation (NFFO) act, electricity is sold at a premium from AD system.
Another factor that has triggered opting for energy recovery from waste is
international agreements with respect to greenhouse gas emissions. Landfills are the
source of large emissions of methane to the atmosphere and methane gas has a global
warming potential (GWP) that is over twenty times that of carbon dioxide. Also, many
utilities are very interested in earning credit for reducing GHG emissions. These utilities
foresee the risk of mandatory GHG control imposed by future regulatory or legislative
actions. Therefore, AD plants will be very attractive for utilities to earn GHG reduction
credits.
In future, the best practicable environmental option will be deriving energy from
waste. Energy recovery technologies include combustion of waste and anaerobic digestion
(AD). However, combustion of the wet stream of MSW does not provide efficient energy
recovery. So the advantages offered by AD are worth exploring for the wet stream of
Municipal Solid Waste (MSW) of New York City and elsewhere.
ii

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika:

Zgłoś jeśli naruszono regulamin