waste water treatment with anaerobic digestion

Treatment of wastewater:Solid phase, anaerobic digestion, biogas

digester/settler (small scale)

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

Troutman HeatherAsiedu-Danquah Kwadwo

January 11, 2015

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Technologies for Sustainable Water Resource Management

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Anaerobic Digestion Table of Content REAPHafenCity 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

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Anaerobic Digestion Guides REAPHafenCity University

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.

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Anaerobic Digestion At a glance REAPHafenCity University

“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).

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Anaerobic Digestion The Benefits of Biogas Technology REAPHafenCity University

● 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) REAPHafenCity University

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

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Anaerobic Digestion Technology Overview (schematic) REAPHafenCity University

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.

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Anaerobic Digestion Inputs: Organics REAPHafenCity University

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 REAPHafenCity University

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 REAPHafenCity University

116 studies26 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-income250 g/cap/day: High-income

Water L H2O/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%)

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Anaerobic Digestion Inputs: Wastewater REAPHafenCity University

Design GuidelinesRule of Thumb:

20-30 L BG/cap/dayproduction

300-900 L BG/cap/daycooking need

(Kossmann et al., 2008)

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Anaerobic Digestion Biochemical Process REAPHafenCity University

(1) HydrolysisBacteria transform complex organic materials into liquified polymers and monomers(2) Acidogenesis

Acidogenic bacteria convert monomers of sugars and amino acids into acids + C2H6O + CH3CO2

- + H2 + CO2 + NH3 (indirect)(3) Acetogenesis

BOD & COD reduced, pH decreased - long-chain and volatile fatty acids and alcohols transformed to H+ + CO2 + CH3COO-

(4) MethanogenesisCH3COO- + H+ -> CH4 + CO2

Anaerobic Digestion / biomethanation / biomethanisation

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Anaerobic Digestion Parameters and Process Optimization REAPHafenCity University

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 REAPHafenCity University

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 REAPHafenCity University

Biogas Appliances:

● Gas cookers● biogas lamps● radiant heaters● incubators● refrigerators● engines

150-300 L biogas/person/meal60-80% efficiency in biogas cooker

30-40 L BG/1 L H2O boil120-140 L BG/0..5 kg rice160-190 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 REAPHafenCity University

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, baccaraFertilizing 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)

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Anaerobic Digestion Outputs: Digestate Applications REAPHafenCity University

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

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Anaerobic Digestion Health Risks REAPHafenCity University

Key to safe production of slurry (pathogen destruction) is retention time, which is governed by temperature.

Thermophilic50-60°C : few days

Mesophilic20-30°C : > 20 days

Psycrophilic10-20°C : > 100 days

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Anaerobic Digestion Maintenance: Minimal REAPHafenCity University

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 REAPHafenCity University

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 PlantsEarth pit

Ferrocement

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Anaerobic Digestion Fixed-Dome Digester: Overview REAPHafenCity University

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

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Anaerobic Digestion Fixed-Dome Digester: Example REAPHafenCity University

Constructed underground with bricks in Lesotho

Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014).

Chinese fixed-dome plant

Janata model

Deenbandhu

CAMARTEC model

AKUT fixed dome plant

AKUT Maendaleo

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Anaerobic Digestion Floating drum digester: Overview REAPHafenCity University

1

21 - Digester

2- Gas collector, fixed dome

3- Inlet for waste

4- Outlet

5 -Overflow tank

3

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Anaerobic Digestion Floating drum digester: Example REAPHafenCity University

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

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Anaerobic Digestion Tubular digester: Overview REAPHafenCity University

1 - Digester & gas holder

2- Inlet for waste

3- Outlet

1

2 3


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Anaerobic Digestion Tubular digester: Example REAPHafenCity University

Applied in Most south American countries

Examples of Tubular digestersVögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014).

Gas storage Reservoir

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Anaerobic Digestion Horizontal Plants: Overview REAPHafenCity University

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

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Anaerobic Digestion Earth Pit: Overview REAPHafenCity University

1 - Digester

2- Plastic sheet gasholder

3- Inlet for waste

4- Outlet

5 -Overflow

1

2 3

4

5

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Anaerobic Digestion Ferrocement: Overview REAPHafenCity University

1 - Digester

2- Plastic sheet gasholder

3- Inlet for waste

4- Outlet

1

2 3 4

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Anaerobic Digestion Variations of the Technology: Comparison REAPHafenCity University

❖ Design principle

Fixed-Dome Digester Floating Drum Digester Tubular Digester

Continuousfeed (Daily input)

Mixed digester

Continuousfeed

Mixed digester

Continuousfeed

Mixed digester

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❖ Input materials

animal excrements, Human excreta, Household waste

animal excrements Household waste(in some cases Human excreta)

Domestic wasteanimal excrements


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❖ Gas storage

Internal Gas storage up to 20 m³ (large)

Internal Gas storage drum size (small)

External plastic bags


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❖ Gas pressure

Between 60 and 120 mbar

Up to 20 mbar Low, around 2 mbar


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❖ Technical aspect

(High); masonry, plumbing

(High); masonry, plumbing, welding

(Medium); plumbing


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❖ 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)


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❖ Agitation

Biogas pressure Manual steering Not possible


Destroy swimming layers

Activate the activities of bacteria

Even distribution of temperature

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❖ 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)

-


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Anaerobic Digestion Variations of the Technology REAPHafenCity University

Decentralised Co-Digestion

of Faeces and OrganicSolid Waste in Lesotho

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Anaerobic Digestion Case Study (Rationale of the project) REAPHafenCity University

Problem: lackof water and yearly emptying of septictanks Bodies involved: TED (Technologies for Econ. Dev’t) & BORDA (Bremen Overseas Research and Development Association)

Design: Waste water treatment & other organic matter


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Anaerobic Digestion Case Study (Description of the Design) REAPHafenCity University

Mainly black- and grey water from the toilet, bathroom, kitchen and laundry

kitchen waste and livestockwaste (pig and chicken manure)

Digester volumes: 8m3 to 100 m3 and sometimes more

1. Digester2. Anaerobic Baffled Reactor3. Planted Gravel Filter


Scheme of DEWATS Biogas System of TED-BORDA

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Anaerobic Digestion Case Study (Gas Production) REAPHafenCity University

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


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Anaerobic Digestion Case Study (Quality and use of Effluent) REAPHafenCity University

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

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Anaerobic Digestion Case Study (Results of the project) REAPHafenCity University


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

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Anaerobic Digestion Methodologies for technology selection REAPHafenCity University

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)

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Anaerobic Digestion Outlook: Biogas for Better Life REAPHafenCity University

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

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Anaerobic Digestion Outlook towards further project (Accra, Ghana)REAPHafenCity University

3 MillionPopulation

15%% connected to wastewater treatment

80 million Amount wastewater generation/day in Liters

90% directly discharged into water bodies without treatment

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Anaerobic Digestion Outlook towards further project (Accra, Ghana)REAPHafenCity University

Thank you for your attention...

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Anaerobic Digestion References REAPHafenCity University

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 Scienceand Technology (Eawag). Dubendorf, Switzerland.

Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014). “Anaerobic Digestion of Biowaste in Developing Countries: Practical Information and Case Studies” Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dubendorf, 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>