الشــركة القــابضــة لـميـاه الـشـرب والـصـرف الـصـح ــي
Holding Company for Water and Wastewater
Sludge management and Biogas
production
By
Dr. Rifaat Abdel Wahaab
Professor of Environmental Science,
Sector Head, Research and Development (R
& D),
Holding Company for Water and Wastewater
(HCWW),
Cairo, Egypt.
11-13 April. 2016,
Flamenco hotel , Cairo , Egypt
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Presentation Outline
Current Status — Where things stand in Egypt?
Governorate-level WWTPs Sludge
Sludge Management and Possible Inter-linkages
Case Study — Gabal El Asfar WWTP
Conclusion
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90 Million Egyptians live in:
222 Cities
4670 Villages
30,000 Settlements 3
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Water & Wastewater Sector 2015: Facts & Figures
Drinking Water Supply
Number of drinking water treatment plants 2700 Plants
Water production (m3/day) 25 Million
Wastewater Treatment
Number of wastewater treatment plants 378 Plants
Treated wastewater (m3/day) 12 Million
Networks
Water distribution networks (km) 150,000 km
Wastewater collection networks (km) 40,000 km
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Wastewater Treatment Technologies
Technology Number of Plants
Activated Sludge 147
Oxidation Ditches 93
Oxidation Ponds 74
Trickling Filters 26
RBCs 18
SBR 7
UASB 5
Anaerobic Baffled Reactor(ABR) 3
Constructed Wetlands 2
Total 375
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WWTPs Categorization according to capacity (m3/d)
Capacities ( m3/d) No. Of WWTP’s
< 1000 13
1000-5000 103
5000-10,000 87
10,000-50,000 109
50,000-100,000 37
100,000-500,000 19
500,000-1,000,000 5
>1,000,000 2
Total 375
الشــركة القــابضــة لـميـاه الـشـرب والـصـرف الـصـح ــي
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General Principles
Sludge management strategies
should be an integral part during
WWTP design process
Sustainable sludge management
options are:
Energy Recovery
Use in agricultural as an
organic fertilizer
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WWTPs-Dry Sludge Produced: Tonne/Day
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Geographical Distribution - Sludge to Energy in
Egyptian Governorates
No. of WWTPs Potential
Governorate
WWTPs (m3 /day) MW/day
Cairo 12 4,000,000 20.0
Giza 7 1,500,000 7.5
Alexandria 13 1,240,000 6.5
Dakahlyia 44 460,000 2.0
Fayoum 25 195,000 1.9
Port Said 6 170,000 1.2
Sharkyia 29 290,000 2.1
Suez 1 190,000 1.3
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Sludge -to -Energy
Biogas Systems
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Biogas definition
• Biogas typically refers to a mixture of different gases produced by the breakdown of
organic matter in the absence of oxygen and nitrate.
• Biogas can be produced from raw materials such as agricultural waste, manure,
municipal waste, plant material, sewage, green wasteorfood waste.
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What Biogas is NOT …
– Biogas is NOT pure methane (natural gas).
– Biogas is NOT biodiesel .
– Biogas is NOT bioethanol .
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How Do Anaerobic Digesters (AD) Work?
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Biochemical process of anaerobic
fermentation/digestion
Step 2: Step 3: Methanogenesis
Step 1: Acetogenesis
Hydrolysis + Acidogenesis
Bacterial
Organic waste Bacterial H2 , CO2,
mass
acetic acid
Carbohydrates mass
Fats
Methan
Protein
Bacterial + CO2
Water
Propionic acid mass
Butyric acid H2 , CO2
Alcohols, acetic acid
Other components
Fermentative Acetogenic Methanogenic
bacteria
bacteria bacteria
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Biogas history
• 3000 BC the Sumerians practiced the anaerobic cleansing of waste
• The Roman scholar Pliny described around 50 BC some glimmering lights
appearing underneath the surface of swamps
• In 1776 Alessandro Volta personally collected gas from the Lake Como to
examine it. His findings showed that the formation of the gas depends on a
fermentation process and that the gas may form an explosive mixture with
air.
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• The English physicist Faraday also performed some experiments with marsh
gas and identified hydrocarbon as part of the it
• Around the year 1800, Dalton, Henry, and Davy first described the chemical
structure of methane
• The final chemical structure of methane (CH4), was first elucidated by
Avogadro in 1821.
• B é champ identified in 1868 that a mixed population of microorganisms is
required to convert ethanol into methane
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• In 1876, Herter reported that acetate, found in wastewater, stoichiometrically forms
methane and carbon dioxide in equal amount
• Louis Pasteur tried in 1884 to produce biogas from horse dung collected from Paris
roads. Together with his student Gavon he managed to produce 100 L methane from
1 m 3 dung fermented at 35 °C
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First attempts at using biogas
• in 1897 the street lamps of Exeter started running on gas from waste water
• In 1904 Travis tried to implement a two -step process which combined the purification
of waste water with the production of methane
• In 1906 Sohngen accumulated acetate in a two -step process. He found that methane
was formed from three basic materials: formate plus hydrogen plus carbon dioxide.
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In 1906 the technician Imhoff started
constructing anaerobic waste water
treatment units in the Ruhr, Germany.
He installed so - called “ Imhoff tank ”
with separate spaces for sedimentation
and digestion. The residence time of
the bio waste was 60 days
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• Around 1930 it was first tried to
remove water, carbon dioxide, and
sulfide from the biogas, to compress it
in gas bottles, and to use it as fuel for
automobiles.
( first Biogas bottles and cars )
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• in Stuttgart in 1949 (Stuttgart) the addition of fat after fat separation enabled the yield
of biogas to be increased
• In Halle, experiments on digestion were performed by adding waste liquorice, rumen,
lignin and/or cereals
• Around 1950 Poebel conducted some extensive research on co - fermentation in the
Netherlands by including organic waste of households in his experiment
• Around the same time (1930 – 1940) the idea came up to use agricultural waste to
produce biogas. Buswell ’ s target was to provide the whole amount of gas consumed
by Urbana, a small city in Illinois. He examined many different natural materials.
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• In parallel, Ducellier and Isman started building simple biogas machines in Algeria to supply
small farmhouses with energy. This idea was brought to France, and many people installed their
own small and technically very simple biogas plants.
• Around 1945, only Germany started using agricultural products to produce biogas. Imhoff again
was leading. In 1947 he claimed that the excrement of one cow delivered 100 times more
biogas than the sewage sludge of one single urban inhabitant.
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• The first small biogas plant with a horizontal cylindrical vessel for fermentation was developed in Darmstadt,
and in 1950 the first larger biogas plant was inaugurated in Celle. In total, about 50 plants were installed
during the following years in Germany.
• in 1950, Barker detected the methane - forming bacteria Methanosarcina and Formicicum methanobacterium (
fundamental research )
• in 1967 , Bryant indicated that methane - forming microbial cultures consisted of a minimum of 2kinds of
bacteria. One type responsible for converting ethanol to acetate and hydrogen, and the other for forming
methane via chemical reaction of carbon dioxide and the free hydrogen ( today they are 4 kinds )
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Bio gas world wide
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Biogas In Germany
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• 1955 the importance of biogas was significantly reduced, as biogas was not profitable any
longer due to an excess of oil and in 1959 all Biogas plats were shutdown except 2
• In 1970 and later and because of the oil crisis in the world the Biogas industry started again The
number of facilities went up to 15 in Bavaria and up to 10 in Baden – Wuerttemberg
• By 1990s, biogas technology was stimulated for two reasons:
1. The profitability of using power derived of biogas
2. The recycling management and Waste Avoidance
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Holding Company for Water and Wastewater
Biogas Production
Carbohydrates 790 liters / kg 50% CH4 50% CO2
Lipids 1,250 liters / kg 68% CH4 32% CO2
Proteins 700 liters / kg 71% CH4 29% CO2
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Biogas production
COD balance method
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Answer
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الشــركة القــابضــة لـميـاه الـشـرب والـصـرف الـصـح ــي
Holding Company for Water and Wastewater
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Holding Company for Water and Wastewater
Typical proprieties of Biogas
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parameters affect anaerobic digestion?
– Temperature
– Retention Time
– pH-level
– Carbon/Nitrogen ratio (C/N ratio)
– Proportion of dry matter in substrate = suitable viscosity
– Agitation (mixing) of the substrate
If any one of these determinants is outside acceptable range, the digestion may be
inhibited
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Substrate temperature in the digester
Anaerobic fermentation can work in an ambient
temperature between 3oC and 70oC and, if colder, the
reactor has to be insulated and/or heated.
Common temperature ranges for bacteria:
• Psychrophillic bacteria below 20oC
• Mesophillic bacteria 20 – 40oC
• Thermophillic bacteria above 40oC
Methane production is very sensitive to changes in temperature
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Anaerobic sludge digestion
• Mesophilic (30 °C – 38 °C) anaerobic
digestion (4)
– Two-stage digestion
• 1 high-rate digester + 1 storage
tank
• Problems; uncompleted
stabilization → gas production →
Turovskiy, 2006
bad sludge settleability→ high
solid content in the effluent →
recirculation of the effluent
• Not used any more, due to higher
capital costs
38
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Anaerobic sludge digestion
• Mesophilic (30 °C – 38 °C) anaerobic digestion (5)
– Separate sludge digestion
• Activated sludge and primary sludge are treated
separately
• They offer better process control
39
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Anaerobic sludge digestion
• Thermophile anaerobic digestion (50
°C – 57 °C)
– Biochemical reaction rate increase with
temperature, doubling every 10 °C
– Process is faster than mesophilic
Bischoffsberger, 2005
– Process more sensitive to temperature
variations
– Better solids, bacteria destruction and
sludge settleability than mesophilic
– Higher energy requirements, less stable,
poorer supernatant quality due to dissolved
solids
40
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pH –value is crucial for a good result
pH is a central parameter for controlling the anaerobic process
• Optimal production when pH 7.0 – 7.2
• Inhibition (due to acids) if pH < 6.2
• Inhibition (due to ammonia) if pH > 7.6
Deviation from the optimum range results in:
• Lower gas yield
• Inferior gas quality
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C/N ratio is important
Microorganisms need N (nitrogen) and
C (carbon) for their metabolism
Methanognic organisms prefer a C/N ratio of between 10:1 and 20:1
N must not be too low, or else shortage of
nutrient
Recommendation:
Mix different substrates
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Nitrogen inhibition
If N concentration is too high (>1,700 mg/l of NH4-N)
and pH is high, then growth of bacteria is
inhibited due to toxicity caused by high levels of
(uncharged) ammonia
Methanogens, however, are able of adapt to
5,000 - 7,000 mg/l of NH4-N given the pre-requisite that
the uncharged ammonia (NH3 controlled by pH) level does
not exceed 200-300 mg/l
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Changes in dry matter (DM) concentration inside the digester
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Stirring the substrate
Stirring improves the efficiency of digestion by:
• Removing metabolites (gas removal)
• Bringing fresh material in contact with bacteria
• Reducing scum formation and sedimentation
• Preventing temperature gradients in the digester
• Avoiding the formation of blind spots (short cuts)
However, excessive stirring disturbs the symbiotic relationship between the different bacteria
species
Simple biogas units normally do not have mechanical stirring devises
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Mechanical mixing
External pumping
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Gas injection
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Egypt Success Story- Gabal El Asfar WWTP
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GAWTP―Background
Conventional Biological treatment process for activated
sludge, both primary and secondary treatment
Serve a population of ~ 10 million residents (approx
1.7 M m3 / day)
Significant removal efficiency in pollution paramètres
(BOD, COD and TSS removal reached to more than
95%)
Treated WW’s are currently used for agriculture
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GAWTP Background-Continue...
20 primary anaerobic digesters with a capacity of
11,000 m3 each;
10 secondary anaerobic digesters with a capacity of
9,000 m3 each,
2 biogas holding tanks with a capacity of 11,000 m3
each,
10 internal combustion engines with a capacity of
2.3 MW each.
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Gabal El Asfar WWTP
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Gabal el Asfar WWTP
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GAWWTP
Greenhouse Gas ―Generation and Management
Biogas production average = 90,000 m3/day
About 60,300 m3 CH4/day
Methane captured provides ~12 MW
More than 60 % of the plant’s energy requirements is
covered (45 million EGP /year, operation cost recovery)
More than 400,000 tonne CO2e/year , contribution to GHGs
depletion
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Conclusion
Sludge management in Egypt is not an option but a necessity
Efficient use of biogas from sludge anaerobic digestion is
considered a potential of operational cost recovery.
Sludge biogas is very attractive source of green energy
through:
Reducing GHG and, consequently climate change impacts;
A vital solution for the current energy shortage in Egypt, that
minimizing the use of fossil fuel.
Sludge is an effective low-cost replacement for chemical
fertilizers , new land reclamation & desert soils conditioners.
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Sludge Management & GHGs
Each cubic meter (m3 ) of biogas contains the equivalent of
8.5 KWh of calorific energy.
The biogas value in Cairo WWTPs ONLY could generate
about 20.0 MW/day
2 KWh is enough energy to power a 100W light bulb for 20
hrs
Based on the ration of 3 m3 CH4 = 1 tonne CO2e, this
gives a reduction of GHG emission of ~ 250,000 tonne/
day of CO2e
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