Waste water treatment with anaerobic digestion

Treatment of wastewater:
Solid phase, anaerobic digestion, biogas
digester/settler (small scale)
1

Treatment of wastewater –
Solid phase, anaerobic digestion, biogas digester/settler (small scale)
Troutman Heather
Asiedu-Danquah Kwadwo
January 11, 2015
2
Technologies for Sustainable Water Resource Management

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Anaerobic Digestion Table of Content
REAP
HafenCity University
❖ Technology Overview (schematic)
❖ Detailing technology (Inputs and Outputs)
❖ Variations of the technology
❖ Case study
❖ Methodologies for determining best technologies for projects
❖ Outlook towards our project in Accra

4
Anaerobic Digestion Guides
REAP
Suitable for land and
agricultural
application.
Minimal-to-moderate
training required for
construction and
maintenance.
Efficiency/productivity
of system highly
variable to place-
specific factors.

5
Anaerobic Digestion At a glance
REAP
“Anaerobic digestion (AD) is a microbiological process whereby organic matter
is decomposed in the absence of oxygen. This process is common to many
natural environments such as swamps or stomachs of ruminants. Using an
engineered approach and controlled design, the AD process is applied to process
organic biodegradable matter in airproof reactor tanks, commonly named
digesters, to produce biogas. Various groups of microorganisms are involved in
the anaerobic degradation process which generates two main products: energy-
rich biogas and a nutritious digestate” (Vögeli et al, 2014).

6
Anaerobic Digestion The Benefits of Biogas Technology
REAP
● Social:
○ Improved sanitation: reduction of pathogens, worm eggs and flies
○ Reduction of workload: less firewood collection
○ Improved Indoor air quality: less smoke
● Environmental:
○ Production of non-fossil energy
○ Displacement of greenhouse gas emissions
○ Organic fertilizer and humus production
○ Reduced deforestation
● Economic:
○ Better health = increased work capacity
○ Fertilizer for better crop yields (better health)
○ Fuel substitution
○ Increased productivity hours/day

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Anaerobic Digestion Technology Overview (schematic)
REAP
Source: Tilley, 2008
Sizes: 1,000 - 100,000 L
Hydraulic Retention
Time (HTR)
>15 days - hot climate
>30 days - temperate
>60 days - high
pathogen load
<15°C ambient requires
addition of heat
50°C sustained temp.
in reaction chamber
Above or below ground

8
Anaerobic Digestion Technology Overview (schematic)
REAP
Source: Vögeli et al, 2014
Pretreatment: sort out
inorganics and shred MSW
to max 5cm diameter for
increased efficiency
(surface area for microbe
attachment)
Normally,organic loading
rate/volumes (OLR) equals
slurry outputs.
Recirculation of these
materials with new
organic inputs increases
microbial population,
accelerating digestion.

9
Anaerobic Digestion Inputs: Organics
REAP
Energy Content:
Human excreta < organics
Lignin is non-degradable in
anaerobic conditions.
Source: Vögeli, 2014 adapted from Müller, 2007

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Anaerobic Digestion Inputs: Organics
REAP
TS - total solids as feedstock
5-10% - optimal
VS - volatile solids
biodegradable fraction of TS
70%-95% common
<60% rarely considered
BMP - biological methane
potential used to measure
efficiency
0.36-0.53 m3/kg VS: avg. MSW
Biogas yield factors:
type, composition,
temperature, mixing
Source: Vögeli et al, 2014 adapted from Khalid et al, 2011
TS & VS in biowaste and biogas yield from AD

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Anaerobic Digestion Inputs: Wastewater
REAP
116 studies
26 countries 6 continents
80% in N.A. & Europe
Main factors for variation:
geography, age, ethnicity,
disease, diet (fiber intake), and
treatment/conveyance
technology used.
20-25 kcal/ kg body weight/day
Actual variation wet fecal gen.:
15–1505 (g/cap/day)
126 g/cap/day : Low-income
250 g/cap/day: High-income
Water
L H2
O/flush 6-14
flushes/cap/day 7
L grey water/cap/day 60-90*
* City of Hamburg, Germany (Sievers, et al., 2014)
Source: adapted by author from C. Rose et al., 2015
Daily wet & dry mass of feces produced by
human populations
(14.2%)

12
Anaerobic Digestion Inputs: Wastewater
REAP
Design Guidelines
Rule of Thumb:
20-30 L BG/cap/day
production
300-900 L BG/cap/day
cooking need
(Kossmann et al., 2008)

13
Anaerobic Digestion Biochemical Process
REAP
(1) Hydrolysis
Bacteria transform complex
organic materials into
liquified polymers and
monomers
(2) Acidogenesis
Acidogenic bacteria convert
monomers of sugars and
amino acids into acids +
C2
H6
O + CH3
CO2
-
+ H2
+ CO2
+
NH3
(indirect)
(3) Acetogenesis
BOD & COD reduced, pH
decreased - long-chain and
volatile fatty acids and
alcohols transformed to H+
+
CO2
+ CH3
COO-
(4) Methanogenesis
CH3
COO-
+ H+
-> CH4
+ CO2
Anaerobic Digestion / biomethanation / biomethanisation

14
Anaerobic Digestion Parameters and Process Optimization
REAP
1. Substrate Temperature
2. Available nutrients
3. Retention time
(flow-through time)
4. pH level : 7-8.5 =i deal,
< 6.2 = toxic
5. Nitrogen inhibition and
C/N ratio : 8-20 = optimal
6. Substrate solid content
and agitation
7. Inhibitory factors :
heavy metals, antibiotics,
detergents
1. ± 0.5-1°C/h perturbations can disrupt cycle
2.
3. Too fast = incomplete pathogen destruction vs. too slow = washout of bacteria
4. 6. Removal of metabolites, inoculation, preclusion of
scum formation, avoidance of temperature gradient,
uniform bacteria population density.
5. 7.
Source: GTZ, 2015

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Anaerobic Digestion Outputs: Biogas
REAP
CH4 + CO2 + trace
gases
Inefficient (compared
to aerobic digestion)
which is why biogas
remains as byproduct.
Source: Vögeli et al., 2014 adapted from Cecchi et al., 2003
Typical biogas composition from biowaste

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Anaerobic Digestion Outputs: Biogas
REAP
Biogas Appliances:
● Gas cookers
● biogas lamps
● radiant heaters
● incubators
● refrigerators
● engines
150-300 L biogas/person/meal
60-80% efficiency in biogas cooker
30-40 L BG/1 L H2
O boil
120-140 L BG/0..5 kg rice
160-190 L BG/0.5 kg legume
120-150 L BG/day - biogas lamp
2,000-3,000 L BG/day - 100 L volume
refrigerator
1 m3
BG = 2 L BG = 6 kWh = 21.6 MJ
= 10 kg (wet weight) biowaste

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Anaerobic Digestion Outputs: Digestate
REAP
Rich in nutrients and soil organisms
Reduction of soil erosion
Reduction of nitrogen wash-out
(production of plant-available
ammonia rather than unavailable
nitrate and nitrite)
Favorable crop reaction: potatoes,
radishes, carrots, cabbage, onions,
garlic, oranges, apples, guavas,
mangoes, sugarcane, rice and jute
Unfavorable crop reactions: wheat,
oilseed, cotton, baccara
Fertilizing effect dependent on: plant
type, soil type, climate
Almost odorless
Source: EPA, 1995 adopted from Sommers, 1977
Amount of stable
humus formed from
digested sludge is
twice the amount
that will form from
with decayed dung.
10 tons/ha - irrigated
5 tons/ha - dry farms
(FAO, 1996)

18
Anaerobic Digestion Outputs: Digestate Applications
REAP
A. Post-treatment
1. Compost / landfill
2. Constructed wetland
3. Fish / animal feed
substitute at rate
< 20% (FAO, 1996)
B. Direct Use
4. Drip irrigation
5. Spread application
to agricultural lands
1
2
5
4
3

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Anaerobic Digestion Health Risks
REAP
Key to safe production
of slurry (pathogen
destruction) is
retention time, which
is governed by
temperature.
Thermophilic
50-60°C : few days
Mesophilic
20-30°C : > 20 days
Psycrophilic
10-20°C : > 100 days

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Anaerobic Digestion Maintenance: Minimal
REAP
Weekly/monthly (prophylactic) maintenance work
● clean gas appliances;
● lubricate movable parts (slides, guiding frame of floating drum plants,
taps etc.);
● servicing of biogas-driven engines within the prescribed time intervals;
● maintenance of pressure relief valves and under pressure valves;
● maintenance of slurry agitator / mixer;
● control gas appliances and fittings on tightness and function
Annual maintenance work
● Check the plant in respect of corrosion and, if necessary, renew
protective coating material;
● Check the gas pipes for gas tightness (pressure check). If necessary,
search the leakage and repair the parts concerned.
Repair: Problem Identification
Source: GTZ, 2015

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Anaerobic Digestion Types of Small Scale Biogas Digesters
REAP
Numerous types exist
Simple in design and for
small scale and domestic
use
3 most common types
Fixed-Dome digesters Floating Drum digesters Tubular digesters
Horizontal Plants
Earth pit
Ferrocement

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Anaerobic Digestion Fixed-Dome Digester: Overview
REAP
1 - Digester
2- Gas collector, fixed
dome
3- Inlet for waste
4- Outlet
5 -Overflow tank
6-Scheme of Gas
collector
2
1
3
4
5
6

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Anaerobic Digestion Fixed-Dome Digester: Example
REAP
Constructed underground with bricks in Lesotho
Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrügg C. (2014).
Chinese fixed-dome
plant
Janata model
Deenbandhu
CAMARTEC model
AKUT fixed dome plant
AKUT Maendaleo

24
Anaerobic Digestion Floating drum digester: Overview
REAP
1
2
1 - Digester
2- Gas collector, fixed
dome
3- Inlet for waste
4- Outlet
5 -Overflow tank
3
4
5

25
Anaerobic Digestion Floating drum digester: Example
REAP
Floating drum digester for market and household waste in India
Constructed underground with
bricks and metals
Constructed above the ground with
fibre glass reinforced plastics
KVIC model
Pragati model
Ganesh model
Pre-fabricated
reinforced concrete
Fibre-glass reinforced
polyester
Plastic water
containers or
fiberglass drums
BORDA model

26
Anaerobic Digestion Tubular digester: Overview
REAP
1 - Digester & gas
holder
2- Inlet for waste
3- Outlet
1
2 3

27
Anaerobic Digestion Tubular digester: Example
REAP
Applied in Most south
American countries
Examples of Tubular digesters
Gas storage Reservoir

28
Anaerobic Digestion Horizontal Plants: Overview
REAP
Horizontal biogas plants are usually chosen when shallow installation is called for
(groundwater, rock). They are made of masonry or concrete
Problem: Leakage
1 - Digester
2- Gas collector
3- Inlet for waste
4- Outlet
1
2
3
4

29
Anaerobic Digestion Earth Pit: Overview
REAP
1 - Digester
2- Plastic sheet
gasholder
3- Inlet for waste
4- Outlet
5 -Overflow
1
2
3
4
5

30
Anaerobic Digestion Ferrocement: Overview
REAP
1 - Digester
2- Plastic sheet
gasholder
3- Inlet for waste
4- Outlet
1
23
4

31
Anaerobic Digestion Variations of the Technology: Comparison
REAP
❖ Design principle
Fixed-Dome Digester Floating Drum Digester Tubular Digester
Continuous
feed (Daily input)
Mixed digester
Continuous
feed
Mixed digester
Continuous
feed
Mixed digester

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REAP
❖ Input materials
animal excrements,
Human excreta,
Household waste
animal excrements
Household waste
(in some cases
Human excreta)
Domestic waste
animal excrements

33
REAP
❖ Gas storage
Internal Gas
storage up to 20
m³ (large)
Internal Gas
storage drum
size (small)
External plastic bags

34
REAP
❖ Gas pressure
Between 60 and
120 mbar
Up to 20 mbar Low, around 2 mbar

35
REAP
❖ Technical
aspect
(High); masonry,
plumbing
(High); masonry,
plumbing,
welding
(Medium); plumbing

36
REAP
❖ Lifespan
> 15 years
Low maintenance
(3–5 years in humid
areas, or 8 –12 years in
a dry climate)
High maintenance - Steel
drum
5 years
Depending on chosen
liner)

37
REAP
❖ Agitation
Biogas pressure Manual steering Not possible
Destroy swimming layers
Activate the activities of bacteria
Even distribution of temperature

38
REAP
❖ Size
5 to 200 m³
Up to 100 m³(small
to middle-sized farms
(digester size: 5-15m3)
or in institutions and
larger agro-industrial
estates (digester size:
20-100m3)
-

39
Anaerobic Digestion Variations of the Technology
REAP
Decentralised Co-
Digestion
of Faeces and Organic
Solid Waste in Lesotho

40
Anaerobic Digestion Case Study (Rationale of the project)
REAP
Problem: lack
of water and yearly
emptying of septic
tanks
Bodies involved: TED
(Technologies for Econ. Dev’t)
& BORDA (Bremen Overseas
Research and Development
Association)
Design: Waste water
treatment & other
organic matter
Vögeli Y., Lohri C. R., Gallardo A., Diener S.,
Zurbrügg C. (2014).

41
Anaerobic Digestion Case Study (Description of the Design)
REAP
Mainly black- and grey
water from the toilet,
bathroom, kitchen and
laundry
kitchen waste and
livestock
waste (pig and chicken
manure)
Digester volumes: 8m3
to 100 m3 and
sometimes more
1. Digester
2. Anaerobic Baffled
Reactor
3. Planted Gravel Filter
Scheme of DEWATS Biogas System of TED-BORDA

42
Anaerobic Digestion Case Study (Gas Production)
REAP
Higher Biogas from
animal excreta
Avg. cooking time for
households with 5
people - 2.5 hours
Long gas storage can
lead to a decrease in
the average daily gas
production
-Leakages
-Automatic Pressure
release

43
Anaerobic Digestion Case Study (Quality and use of Effluent)
REAP
Differences of COD’s
Target Effluent COD
concentration -0.12 g/L
Use: Irrigation
COD of Inflow compared to effluent from Digester, ABR and PGF

44
Anaerobic Digestion Case Study (Results of the project)
REAP
Cost of digester per m3 - 83 -667 USD
No regular emptying of storage tanks and problems
associated with it
Biogas system replaces other energy systems
Effluent could be used for irrigation

45
Anaerobic Digestion Methodologies for technology selection
REAP
Main factors influencing selection of particular design:
● Costs: construction and conveyance
● Local materials
● Durability (higher construction cost vs. long-term assurance)
● Inputs (continuous vs. batch design), C/N ratio (20-30 optimal)

46
Anaerobic Digestion Outlook: Biogas for Better Life
REAP
The vision of the Initiative is to succeed in the implementation of biogas technology in African countries as a market-oriented partnership
between governments, private sector players, civil society agents and international development partners. The specific targets of the initiative
to be achieved by 2020 include:
● two million biogas plants installed (90% operation rate)
● 10 million Africans benefiting in daily life from the plants
● 800 private biogas companies and 200 biogas appliance manufacturing workshops involved or established
● 100,000 new jobs created
● comprehensive quality standards and quality control systems developed and in use
● one million toilets constructed and attached to the biogas plant
● 80% of the bio-slurry used as organic fertilizer
● agricultural production raised by up to 25%
● health and living conditions of women and children improved, and the deaths of women and children reduced by 5000 each year
● drudgery reduced by saving 2-3 hours per household each day in fetching wood, cooking and cleaning the pots
● health costs saved of up to US$80-125 per family, per year
● 3-4 million tonnes of wood saved per year
● greenhouse gas emissions annually reduced by 10 Mtonnes of CO2
equivalent.
The total financing required is $2 billion, out of which $800 million is to be expected from public funding (national and donors) and the sale of
carbon credits. For the latter, the Initiative developed a proposal for a new methodology specifically aiming at the trading of emission
reductions from household digesters.
Signed 2007 Nirobi

47
Anaerobic Digestion Outlook towards further project (Accra, Ghana)
REAP
3 Million
Population
15%
% connected to wastewater
treatment
80 million
Amount wastewater
generation/day in Liters
90% directly discharged
into water bodies without
treatment

48
Anaerobic Digestion Outlook towards further project (Accra, Ghana)
REAP
Thank you for your
attention...

49
Anaerobic Digestion References
REAP
C. Rose, A. Parker, B. Jefferson, E. Cartmell (2015) “The Characterization of Feces and Urine: A Review of the Literature to Inform Advanced
Treatment Technology” Critical Reviews in Environmental Science. Vol. 47, Is. 17, p.1827-1879
EPA - United States Environmental Protection Agency (1995) “Process Design Manual: Land Application of Sewage Sludge and Domestic
Septage” National Risk Management Research Laboratory (EPA/625/R-95/001)
FAO - Food and Agriculture Organization of the United Nations (1996) “Biogas Technology: A training manual for extension”Support for
Development of National Biogas Programme (FAO/TCP/NEP/4451-T)
GTZ - Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ), GmbH. (2015) “AT Information: Biogas” Information and Advisory Service
on Appropriate Technology (ISAT).
Kossmann, Werner; Pönitz, Uta; et al. (n.d.) “Biogas Digest: Biogas Basics” Information and Advisory Service on Appropriate Technology
(ISAT). Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ), GmbH. vol. 1.
Lüthi, Christoph et al, 2011. Community-Led Urban Environmental Sanitation Planning (CLUES). Swiss Federal Institute of Aquatic Science
and Technology (Eawag), Dübendorf, Switzerland.
Sievers, Jan Christian; Oldenburg, Martin; Albold, Andrea; Londong, Jörg (2014) “Characterisation of Greywater - Estimation of Design
Values” KREIS Project. German Federal Ministry of Education and Research (BMBF)
Tilley, Elizabeth et al, (2008) “Compendium of Sanitation Systems and Technologies” Swiss Federal Institute of Aquatic Science
and Technology (Eawag). Dübendorf, Switzerland.
Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrügg C. (2014). “Anaerobic Digestion of Biowaste in Developing Countries: Practical
Information and Case Studies” Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dübendorf, Switzerland
Wim J. van Nes & Tinashe D. Nhete (2007) “Biogas for a better life: An African initiative” Renewable Energy World Magazine 10(4) <http:
//www.renewableenergyworld.com/articles/print/volume-10/issue-4/bioenergy/biogas-for-a-better-life-an-african-initiative-51480.html>

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