FACULTY OF ENGINEERING

DEPARTMENT OF CIVIL ENGINEERING

CIV 3203: ENVIRONMENTAL ENGINEERING I

LECTURE 5: ORGANIC WASTE MANAGEMENT
 Generation rates and quantities
For urban, the following values are generally applicable:
•Quantity, Q = 0.09 – 1 Kg/p/day,
•Moisture content, Mw = 60 – 80%
•Organic matter = 65 – 85% on dry matter basis
•Density,  = 460 – 590 Kg/m3

To minimise the hazards to people and the surrounding

environment, the following should be done at/close to the
point of generation:-
 Storage system
 Depending on the ultimate disposal system, storage can either
be:
 Mixed system – all solid waste is placed in one bin or
 Separate system – one bin for putrefiable and another for non-
putrefiable waste.
 The collection bins can be either public or individual (private)
and should have the following basic characteristics:
 A lid to prevent scavengers, rodents and other vermin access to the
waste.
 Sufficient volume to store waste for at least 3 days
 Handles
 Uniform standard size - for better planning of quantities
 Sufficiently heavy (and well placed) so as not to be knocked down
by animals like dogs and cats
 Collection and Transportation
 The factors to be considered for efficient
collection and transportation of solid waste
are mainly economic and the system may
be managed by: -
 Municipal authorities e.g. KCC
 Private firms hired by municipal authorities
 Private firms hired by individuals
 Collection and Transportation
 The collection system should

optimise:
Routing of collection trucks for
maximum collection and minimum
travel distance
Labour organisation
Location of bins for easy access
Labour economics
 Collection and Transportation
 An efficient transportation system

should take into consideration:

Refuse generating characteristics
Carrying capacity of trucks
Location of the ultimate disposal
sites
 Ultimate Disposal/Re-use Ssystems
 There are two types of disposal systems: No energy
recovery and Partial Energy Recovery (PER)

 No energy recovery include:

 Incineration - total burning of refuse to ashes and gaseous
products.
 Open dumps - disposal of solid waste is done without any control
or treatment. This system is discouraged because it facilitates
breeding of vermin and pathogens, generation of noxious gases,
scavengers and is also an eyesore. It pollutes and contaminates
ground water.
 Sanitary land fields - this involves controlled tipping and allows
for land reclamation.
 Burying
A Typical incinerator
 Ultimate Disposal/Re-use Ssystems
 Partial Energy Recovery (PER)
 Composting - manure and biogas can be produced
 Animal feeds - rich in protein
 Recycling - for scrap metal, paper, plastics and animal
feed
 Rendering - extraction of grease for lubrication from
organic wastes.
 The solid waste problem
• EACH YEAR the overall amount of produced wastes is enough to fill the
Mandela National Stadium in Kampala!

garbage

garbage garbage
Mandela National Stadium, Kampala, UG
garbage garbage

• ~ 75% of the produced waste is the biodegradable organic fraction

(vegetables, kitchen wastes,..,) which undergoes a series of problematic
reactions under natural conditions
 Organic waste reactivity
 Aerobic stabilisation/Anaerobic digestion are processes
occurring NATURALLY in organic waste heaps due to the
metabolism of communities of microorganisms and
fungi which use organic wastes as food.
Organic waste simplified formula: CaHbOcNd

CaHbOcNd+(4a+b-2c -3d)/4 O2 aCO2+(b-3d)/2H2O+dNH3

Ca H b O c N d  xH 2O  yCH 4  wCO 2  zNH 3

 The Solid Waste Management System and the
related impacts – Landfilling

infectious deseases
fire hazards
odors
Pictures from the Kampala Landfill, 2009 water contamination
soil pollution
 Organic waste management

• ORGANIC WASTE should be considered as a VALUABLE MATERIAL, i.e. as a

source of materials and energy
• One or more treatment processes could be applied – even in
combination - to recover material and/or energy

Expected outcomes:

Reduction of the amounts (i.e., volume) of wastes to be landfilled

Reduction of the reactivity of the wastes to be landfilled

Products and energy from organic wastes treatment could help the growth
of an economical sector based on APPROPRIATE WASTE MANAGEMENT
 Organic waste management

Direct disposal option:

• Open dumping: NO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

• Direct landfilling

THE DIFFERENT OPTION!

INTEGRATION BETWEEN
or reuse/recovery option:

• Animal feeding

• Biological Aerobic Treatment (Composting)

• Biological Anaerobic Treatment (Anaerobic Treatment)

 (Organic) waste management

• The evaluation of the different processes and technologies should be

evaluated taking into account some relevant issues, such as:

• the quality and quantity of the wastes

• the technological complexity both of the construction and
the operation phase
• the technical, economical as well as environmental
sustainability

• According to this, strategies to recover material and energy from wastes

should be investigated, taking advantages also - and not only - by
processes and technologies already developed around the world
 (Organic) waste management
• Processes for recovering material and energy from wastes MUST be
applied under CONTROLLED CONDITIONS in order to :
• avoid adverse impacts on environment and human health
caused by the processes themselves
• improve the quality of the products for proper utilization
without causing hazards to people and the environment
• improve the quality/management of process by-products

• develop technologies which are sustainable from a technical,

economical as well as environmental point of view

• encourage the industrial scale-up of the process

 Bio-stabilization under controlled conditions:

Composting generates a material:

 soil-like and odor-free;

 with high humic acid content (C451H410O228N32SP);

 with high buffering capacity;

 with no potential for flies, plants, breeding …
 Anaerobic digest. under controlled conditions:

Anaerobic digestion generates:

i) a solid or a slurry which is still reactive from a

biological point of view
ii) an effluent which is very reach in nutrients  it
should be carefully managed (direct use as fertilizer
or composting)

iii) biogas
 Organic waste composition and management
• Kitchen waste + market waste + animal manure + human faeces

Suitability of biological treatment of waste

Different behaviour at the disposal site (for biogas and leachate

production)

Waste components can be represented as descriptive

biodegradability categories:
‘readily’
‘moderately’
‘slowly degradable’
‘biologically inert’
 Organic waste characterization
Volatile Solids (VS) content (determined by ignition at 550°C)
Chemical Oxygen Demand (COD)
Biochemical Oxygen Demand (BOD5, BOD7, BOD20, BODU)

Lignin content (LC) of a waste: estimation of the

biodegradable fraction (BF):

BF = 0.83-0.028 LC
Half-degradation time (t1/2):

Content(%)
Highly biodegradale: t1/2 = 1 y Complex
sugars

Moderately biodegrable: t1/2 = 5 y simple sugars

Slowly biodegradable: t1/2 = 15 y time

 Organic waste characterization
Color
Physical
Odor
Stability measurement

•Temperature and heat development

•pH
•VS content evolution over time
Chemical/physical •C/N
•Humic acid
•Soluble Nitrogen compounds NH4+
NO3-
•Black Index

•Self-heating test
Biological •Respirometric Test
•Biogas evolution
 Bio-stabilization of Organic Waste
Presence of oxygen (composting):
CaHbOcNd+(4a+b-2c -3d)/4 O2 aCO2 +(b-3d)/2H2O+d NH3

DH°biox = 5550 cal/g SV

Biodegradable waste
DH°biox = 104,2 kcal/mol O2
(or Organic Matter, O.M.)

Absence of oxygen (Anaerobic Digestion):

Ca H b O c N d  xH 2O  yCH 4  wCO 2  zNH 3

Biodegradable waste
(or Organic Matter, O.M.)
 Aerobic bio-stabilisation/composting

T=55°C GAS (N2 O2 C02 NH3 vapour VOC)

Blending agents
seeding
heat
water
WASTE COMPOST
T=25°C T>30°C
water water
VS VS
• biodegradable AIR • biodegradable
• inert • inert
T=25°C (N2, O2, CO2, H2O vapour)
 Windrow periodic turning (FN)
Residence time = 180 d

Surface and
volume

v/s = 2 - 2,5 m3/m2

v/s = 0,6 - 1 m3/m2
a = 55° h = 2,5 m
a = 45° h = 2 m
l=3m l=5m
 Evolution of the Composting process

T and pH C/N

Yard waste Yard waste + sludge

1 2 3
Industrial sludge Time (d)
Time (d)

Note: Oxygen demand evolution is similar to T

 Aerated windrows Residence time = 120 d

AIR

AIR
AIR

Cured compost andDP wood

< 100 mm c.a.
chips acting as biofilters
 The Anaerobic digestion process

Ca H b O c N d  xH 2O  yCH 4  wCO 2  zNH 3

Biodegradable waste
(or Organic Matter, O.M.)
 The Anaerobic digestion process


x  a    
×
Ca H b O c N d  xH 2O  yCH4  wCO2  zNH 3
b c 3d 
 4 2 4 
 4a  b  2c  3d 
y 
 8 
 4a  b  2c  3d 
w 
 8 
zd
 The Anaerobic digestion process

Ca H b O c N d  xH 2O  yCH 4  wCO 2  zNH 3

Biodegradable waste
(or Organic Matter, O.M.)

 Thermodynamic equilibrium can be attained at very

long time
 Anaerobic process is a staged process
 Hydrolysis and Acidogenesis acetogenesis
Complex organic matter
The Anaerobic digestion process
ITALIAN COOPERATION
Carbohydrates Protein Fats

Stage 1
Hydrolytic & Fermentative Microorganism
propionate
butirrate
Volatile Fatty acids Alcohols Chetons

Stage 2
Formate
Acetogenic Bacteria
Acetate H2+CO2
Omoacetogenic Bacteria

methanogenesis
Acetoclastic Hydrogenofilic

Stage 3
bacteria bacteria

CH4+CO2 CH4+H2O
 The Anaerobic digestion process

Ca H b O c N d  xH 2O  yCH 4  wCO 2  zNH 3

Biodegradable waste
(or Organic Matter, O.M.)
 Thermodynamic equilibrium can be attained after a
very long time
 Anaerobic process is a staged process:
 Sensitive (operating conditions should be checked)
 Equilibrium (O.M. stabilisation)cannot be reached
for technical constraints
 Anaerobic digestion and composting should be
interrelated
CH4+CO2
evaluation of biogas flow
+other study of the options for biogas utilization
gases (electricity + heat + fuel for electrolitic cell
for drinking water tretament)
Human
excreta
Anaerobic liquid effluent
digester Green Compost

solid residue

Food
Composting unit
waste
 Parameters affecting/controlling process yield
 Feedstock composition (C/N), pH, T, moisture
Feedstock C/N ratio Biogas yield Frequent
(m3/kgVS) problems
Pig slurry 3-10 0.25-0.50 High dilution
(low-yield)
Cow slurry 6-20 0.20-0.30 Low yield

Chicken 3-10 0.35-0.60 Inhibition

slurry (due to NH4+)
Solid Waste > 30 0.08-0.80
Anaerobic digestion and composting should be
interrelated
 Design option
Single-stage reactor: all the phases in one reactor Anaerobic
digester
Double-stage reactors:
1st reactor : hydr.+ acedogen.
2nd reactor: fermentation
Flow type: Batch /continuous/ sequencing batch reactor -
mixed or not
Biomass (microorganism): suspended growth; attached
growth Dry process (TS > 20%)
Solid content:
Semi-dry process (8<TS<20%)
Wet process (5<TS<8%)
SIZING CRITERIA: Organic Volumetric Load, kgTVS/(m3*d)
(it varies as a function of the process)
 PROCESS COMPLEXITY:

from simple and low-cost…

Human
excreta
Anaerobic
digester

Effluent+
Food solid
waste residue
PROCESS COMPLEXITY:
to high…

T = 50-58°C
 PROCESS COMPLEXITY:
to high…

PROCESS ECOTEC
PROCESS COMPLEXITY:
to high…

TBW BIOCOMP PROCESS

 Parameters affecting/controlling process yield

 Feedstock composition (C/N)

 Particle size
 Moisture content
 pH and alkalinity
 Temperature
 Presence of inhybiting/toxic compounds
All the parameters should be monitored
 Composting and Anaerobic digestion
Anaerobic Digestion: Main product
Composting: Main product COMPOST
METHANE
Benefits: Benefits:

Improve the properties of soils for It recovers the energy content of the
agricolture (texture, pH, permeability, wastes
resistance to acidification…)
Biogas can be used as fuel to produce
It can be utilized for landscaping energy and heat for different purposes

It can be used for gardening Wood and charcoal can be partially or

totally substituted
Economical advantages (projects and
small enterprises funded by micro-
credits)
 Composting and Anaerobic digestion
Anaerobic Digestion: Main product
Composting: Main product COMPOST
METHANE
Benefits: Benefits:

Improve the properties of soils for It recovers the energy content of the
agricolture (texture, pH, permeability, wastes
resistance to acidification…)
Biogas can be used as fuel to produce
It can be utilized for landscaping energy and heat for different purposes

It can be used for gardening Wood and charcoal can be partially or

Indoor air pollution from wood and charcoal fires
totally substitued
results
Economical advanteges (projects an in some 1.6 million deaths each year (World
small enterprises funded by micro- Health Organization, WHO, 2009)
credits)
 How can the research activities contribute to
improve the situation?
 Composting and anaerobic digestion are processes
occurring NATURALLY in organic wastes heaps due to
the metabolism of communities of microrganisms and
fungi which use organic wastes as food.

 So why is it important to study carefully the process

before building composting plants/anaerobic digesters
at a full scale and before marketing compost and using
compost for agriculture or using biogas?
 Critical issues
Unaerobic Digestion: Main product
Composting: Main product COMPOST
METHANE
CRITICAL ISSUES CRITICAL ISSUES
Produced compost: Produced biogas: Biogas composition
Biological unstability/presence of (%CH4, %CO2), biogas quantities, trace
viruses and pathogens, high nitrogen contaminants contents (H2S)
contents, high heavy metals contents
Solid residues:
Gaseous emissions: Unstability, presence of viruses and
trace organic compounds (critical pathogens, high nitrogen contents, high
issues: bad smell) heavy metals contents

Liquid emissions: Liquid emissions:

A highly polluted liquid effluent A liquid effluent heavily polluted for
(leachate) to be collected the high nitrogen and organic carbon
content
 Organic N
Copper
Zinc
Lead
Some of the parameters to be
Cadmium
investigated according to EU
Nichel
to evaluate compost
Mercury
suitability for reuse!
Exavalent chromium
Plastics
Glass
Communities of
Pathogens
pH
…
A problem with the Anaerobic digester design
 A problem with the Anaerobic digester design

AS A GENERAL RULE: first study the process than move to the proper
design (taking safety in mind!)
THE END