Download - Basics of Anaerobic Digestion

Introduction to anaerobic digestionBiogas STU

ERASMUS EXCHANGE STUDENTSFebruary 2014___________________________Ing. Juan Jos Chvez [email protected]

Ing. Juan Jos Chvez [email protected]

Part 1: Waste


Anthropogenic activities

Anthropogenic activity (Anthropos means human, geny means origin): An effect or object originated by human activity


Waste

Definition of waste, according to the EU Waste Framework Directive:

Any substance or object which the holder discards or intends or is required to discard

Waste management: All the processes involved in dealing with the waste of human activities, including its prevention, reduction, collection, transport, handling, storage, recycling, processing, incinerating, landfill among others.


Waste Recovery and Disposal Codes

Waste related activities are classed as recovery (R) or disposal (D) as defined in the Waste Framework Directive (2006/12/EC).

...

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European Waste Catalogue

The European Waste Catalogue is a hierarchical list of waste descriptions, each given a code number.


Philosophy of Waste Management

Avoidance or preventionMinimization or reduction

Reuse or recyclingMaterial recoveryEnergy recovery

IncinerationLandfill disposal

T H E OR Y

R E A L I T Y


Examples of Waste Management

PET bottles



Blackwaters or sewage



08 01 13 - Sludge from paint or varnishcontaining organic solvents or otherdangerous substances



Automobile assembly plant

Industry08 01 13

15 01 01

15 01 02

16 01 22

19 08 12

Etc...

External waste management, contracts with competent and authorized waste companies

Internal waste management: Prevention, reduction and reuse policies; development of a waste separation strategy, improvement of the collection process. Analysis of material and energy recovery possibilities

Internal waste management:Sales from selected materials for its material or energy recovery


Waste recovery

Waste recovery is the selective extraction of disposedmaterials for a specific next use, obtaining the maximumpractical benefits from products. It aims to reduce:

The consumption of fresh raw materials

Energy consumption

Air pollution

Water pollution

Material recovery

Energy recovery


Material recovery of waste

Recycling: Process of turning selected waste products into new (recycled) products

Regeneration of organic and inorganic components (solvents, chemical substances, etc.)

Compost: Aerobic processes that transform organic waste into a fertilizer or soil amendment


Energy recovery of wasteWaste-to-energy

Thermal technologies: Gasification (a set of chemical reactions that uses limited

oxygen to convert a carbon-containing feedstock into a synthetic gas, or syngas CO2 + CO + H2)

Pyrolysis (a thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen. For example, the bio-oils)

Thermal depolymerization Plasma arc gasification or plasma gasification process (PGP)

Biological technologies: Anaerobic digestion (Biogas CH4 + CO2) Fermentation (examples are ethanol, lactic acid, hydrogen) Other biological treatments


Part 2: Anaerobic digestion


Biological treatment processes

Aerobic treatment process: Biological processes that occur in the presence of oxygen.

Anaerobic treatment processes: Biological process that occur in the absence of oxygen.

Substrate: It is the term used to denote the organic matter or nutrients that are converted during biological treatment


1. Energy contained in WW

2. Organic carbon contained in WW

Comparison of aerobic and anaerobic processes(Wastewater treatment processes)

ANAEROBIC AEROBIC

90 % biogas5 7 % synthesis of new biomass3 5 % losses

60 % synthesis of new biomass40 % losses

ANAEROBIC AEROBIC

95 % biogas (CH4 + CO2)5 % synthesis of new biomass

50 % CO250 % synthesis of new biomass


Anaerobic digestion

Anaerobic digestion (AD) is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen.

AD is often used for industrial or domestic purposes at managing waste.

This process yields a final product of mainly methane and carbon dioxide, a rich biogas suitable for energy production, widely used as a renewable energy.


This degradation process can be divided up into four phases,named hydrolysis, acidogenesis, acetogenesis and methanation

Anaerobic digestion

Hydrolysis Acidogenesis Acetogenesis Methanogenesis

Carbohydrates

Fats

Proteins

Sugars

Fatty acids

Aminoacids

Alcohols

Acetic acid

CO2 , H2

CO2 , H2

Ammonia

BIOGASCH4 + CO2

H2S


Applications of anaerobic digestion

Stabilization of sludge in WWTP

Treatment of industrial wastewaters

Landfill gas-to-energy

Biogas stations



Stabilization of sludge in WWTP



Treatment of industrial wastewaters



Landfill gas-to-energy


Biogas stations

The main goal of biogas stations is to produce a certain quantity of biogas from determined organic substrates, in order to generate a stable and continuous amount of energy.


Pre-treatmentAnaerobic digestion

SubstrateBiogas

Digestate


Biogas stations

Substrates for biogas stations

The substrate and the efficiency of its conversion intobiogas are the factors that will determine the viabilityof the process.


According to the solid content of the substrate:

Dry fermentation technology (when TS is greater than ~25%)

Types of biogas stations


Anaerobic fermenters (PFR)


Collectors of leachate or percolate for its recirculation into the sprinkling system


Biogas holders


Process control


Cogeneration unit (CHP)


Types of biogas stations

Liquid or wet fermentation technology (TS less than ~15%)


Part 3: Operation of a biogas station


Process parameters

Temperature

pH-value (Hydrogen partial pressure)

Concentration of microorganisms (Retention time)

Inoculation and cultivation

Mixing (agitation)

Volume and organic load

Type of substrate (organic content and C/N/P ratio)

Presence or formation of inhibitors Flow recirculation and bypass

Biogas recirculation and removal

Specific surface of material (Mass transfer)

Redox potential

Etc...


Process parameters

Temperature operational ranges Cryophilic (0 20 C)

Psychrophilic (20 30 C)

Mesophilic (30 40 C)

Thermophilic (40 60 C)


Process parameters

pH-value (Hydrogen partial pressure)

The measure of the acidity or basicity of the tank aqueous environment. The pH optimum of the methane - forming microorganism is at pH = 6.7 7.5.

Biogas digestion failure(Acid fermentation)


Process parameters

Concentration of microorganisms (Retention time)

Methanogenic microorganisms have a long generation time in general. To avoid washing out of the reactor, hydraulic retention time must be at least 10-15 days with reactor systems which do not have facilities for retaining and returning biomass. Nevertheless, retention times are recommended to be of 50 days and more. In comparison with this, the regeneration times of hydrolytic and acid-forming bacteria are significantly shorter, so that with them there is hardly any risk of washout.

[days]


Process parameters

Inoculation and cultivationThe start-up phase of an anaerobic plant often last 2-4 months. The cultivation of desired cultures of bacteria can fail completely, i.e., the anaerobic digestion doesnt take place and the biogas is not produced. To avoid these problems, the reactors are often inoculated with an anaerobic sludge from other fermentation process.

Hydrolytic b.

Methanogenic b.


Process parameters

Volume and organic loading rateThe volume (organic) loading rate depends on several factors such temperature range of the process, organic dry-matter content in the substrate, retention time, dosing system, among others. Mostly, biogas digesters are designed to decompose 75% of the total degradable matter, due to economical and/or operational reasons.

OLR [kg VS.m-3.d-1], [kg COD.m

-3.d-1]


Process parameters

Type of substrate

Dry matter and organic dry matter content

Terminology:Abb. SK* Meaning Units

DM - Dry matter content kg TS. ton SUBSTRATE-1

oDM - Organic dry matter content kg VS. ton SUBSTRATE-1

TS Xc Total solids (settable solids) g TS.kg SAMPLE-1

VS Xorg Volatile solids g VS. kg SAMPLE-1

TSS Xc,WW* Total suspended solids (retained by a membrane filter)

g TSS. kg SAMPLE-1

VSS Xorg,WW* Volatile suspended solids g VSS. kg SAMPLE-1


Process parameters

Organic matter content and its measurementAbb. SK* Meaning Units

TOD TCHSK Theoretical oxygen demand Total oxidation Stoichiometric amount of O2 needed for a hypothetical total oxidation

mol O2 , g O2

COD CHSK Chemical oxygen demand - OxidabilityIt is an oxygen equivalent of the organic matter that can be oxidized by using a strong chemical oxygen agent in acid solutions

mg COD . l SAMPLE-1

BODx BSKx Biochemical oxygen demand - BiodegradabilityMeasurement of dissolved oxygen used by microorganisms for the biochemical oxidation of organic matter

mg BOD . l SAMPLE-1

Correlation among measurements of organic content

TOD > COD > BODx


Process parameters

Type of substrate

Organic matter content and its measurementAbb. Meaning Units

TOC Total organic carbonIt is a parameter that measures the composition of substrates (Firstly C and then C/H/O/N/P/S ratio). Organic carbon is oxidised to CO2 at high temperatures in the presence of catalysts.

mol C, g Cmol N, g Nmol O, g Oetc.

DOC Dissolved organic carbonIt is a parameter that measures the composition of dissolved organic compounds in aqueous solutions.

-


Process parameters

Type of substrate Nitrogen content and its measurement

Abb. Meaning Units

NH4-N Ammonium nitrogen or total ammoniacal nitrogen (NH4+ + NH3) mg.l

-1

NH4+ Ammonium ion mg.l-1

NH3 Free ammonia or ammonia mg.l-1

NH3-N Ammonia nitrogen mg.l-1

Norg Kjeldahl nitrogen or organic nitrogen (Protein N and non-protein N e.g. urea, nucleic acids, polymers, etc.)

mg.l-1

TKN Total Kjeldahl nitrogen (= NH4-N + Norg) mg.l-1

NOx-N Total oxidised nitrogen (NO3-N + NO2-N) mg.l-1

NO3-N Nitrate nitrogen mg.l-1

NO2-N Nitrite nitrogen mg.l-1

TN Total nitrogen (sum of all nitrogen compounds) mg.l-1


Process parameters

Type of substrate

Phosphorus content and its measurementAbb. Meaning Units

PO4-P Phosphate phosphorus, orthophosphate mg.l-1

Porg Phosphorus content of organic P compounds mg.l-1

TP Total phosphorus mg.l-1

complex P Complex bonded P, that cannot be precipitated with chemicals mg.l-1


Part 4: Modelling at laboratory


Laboratory bioreactors

Characteristics of our reactors: CSTR model

Semi-continuous feeding

Single-stage anaerobic digestion

Mesophilic conditions (37oC)

Inoculum: Stabilized excess sludge from WWTP

TS of reactors sludge is less than 15%

OLR of reactor is less than 3 gVS.L-1.d-1



Dry matter (DM)

Organic dry matter (oDM)

Loss on ignition (LOI)

Laboratory oven(105oC, 6 h)

Laboratory furnace(105oC, 3 h)

Analytical balance



Gravimetric method:

Calculation Units

DM = (md-me)/(ma-me) . 1000 g TS/kg sample or %

iDM = (mb-me)/(ma-me) . 1000 g IS/kg sample or %

oDM = DM - iDM g VS/kg sample or %

LOI = oDM/DM . 100 %

e = empty a = added d = driedb = burnt

DM = Dry matteroDM = organic dry matteriDM = inorganic dry matterLOI Loss on ignition

TS Total solidsVS Volatile suspended solidsIS inorganic suspended solids


Calculate TS, VS, LOI1. Maize silage

me = 100,252 g

ma = 101,586 g

md = 100,819 g

mb = 100,325 g

2. Poultry manureme = 50,125 g

ma = 55,155 g

md = 51,131 g

mb = 50,438 g

Dry matter and organic dry matter contentExercises

Literature says: Maize silage has a DM = 20-40 % and a oDM = 95%.DM (LOI) Poultry manure has a DM = 10-29 % and a oDM = 70%.DM (LOI)


Organic loading rate of reactor

Organic loading rate (OLR) means how much organic matter is being introduced into the reactor in an interval of time.

For this purpose, we can use either the COD or the VS parameter.

OLRCOD = Vsubstrate.CODsubstrate/Vsludge

OLRVS = substrate.VSsubstrate/Vsludge


Organic loading rate of reactorExercises

Calculate the amount of substrate that have to be loaded into the biogas plant.1. Maize silage

OLR = 3 kg VS.m-3.d-1

Vdigester = 3 000 m3 (The digester is filled with sludge at its 85%

capacity)

2. Poultry manure with grass silage at a ratio of 5:2

OLR = 1,5 kg VS.m-3.d-1

Vdigester = 1 500 m3 (The digester is filled with sludge at its 78%

capacity)

Grass silage (DM = 30%, oDM = 85%.DM)


Biogas yield

Specific biogas production (Biogas yield)

m3. kg-1 TS

m3. kg-1 VS

l . g-1 TS

l . g-1 VS


Laboratory analysis

Determination of:

COD concentration

NH4-N concentration

PO4-P concentration

VFA concentration

Heater Spectral colorimeter (spectrophotometer)


Language key


Laboratory equipment for chemistry


CHONPS compounds

Download - Basics of Anaerobic Digestion

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