Wastewater Management Technologies
Introduction
The aim of this presentation is to show and share some experiences
related to decentralized sanitation addressing segregation, reuse
and improvement of treated wastewater’s quality.
• 2.5 billion people live without good sanitation;
• 80% of users of improved sanitation live in rural
areas;
• In
Sub-Saharan
Africa,
treating
consumes 12% of the health budget;
diarrhoea
• Conventional system are neither an ecological nor
an economical solution for sanitation problems.
• To supply rural areas with adequate sanitation
facilities,
sustainable
solutions
modeled
on
decentralised systems are required.
SUMMARY

Decentralised Technologies on Wastewater
Management


Septic Tanks, Constructed Wetlands, Composting Toilets,
Biodigestor, Anaerobic Filter, Duckweed Lagoons
Demonstration projects on Wastewater
Management

Tanzania, India, Egypt, Brazil
Decentralised Sanitation Systems
•
Collection, treatment, and final disposition of the wastewater on/or
close to the location;
•
Useful in treating wastes from residences, households, small
villages, isolated communities, etc.
Advantages for decentralized systems:

Economy of structural arrangements such as transportation,
reservation and elevation;

Possibility for reuse of the effluent and potentiality for aquifer
recharging;

A problem in a unit doesn’t collapse the whole system;

Development of the local potentialities: small systems can be
designed, built and managed by local professional, improving the
local economy.
Ecological Sanitation (EcoSan)
•
Ecological Sanitation is a
decentrilised sanitation system
that understands human excreta,
organic wastes and wastewater as
a resource (not as a waste) with
high potential for reuse and
recycling.
•
EcoSan systems enable a
complete recovery of nutrients in
household wastewater and their
reuse in agriculture. They also
help preserve soil fertility and
safeguard long-term food security.
Moreover, they minimise the
consumption and pollution of
water resources.
Ecological Sanitation (EcoSan)
Stages (or Phases)
Waste segregation and possible utilization options. (UNESCO/IHP & GTZ, 2006)
Septic Tank
•
•
This system consists of a closed, often prefabricated tank and
is usually applied for primary sewage treatment. The treatment
consists of sedimentation, flotation and digestion procedures.
Septic tank is designed to receive all kinds of domestic wastes
(kitchen, domiciliar laundries, washrooms, latrines, bathrooms,
showers, etc) and it is economically viable to attend to 100
inhabitants.
•
The aim of primary treatment
is to separate out heavy
constituents (suspended
solids) and particularly light
constituents (floating solids
and scum) from the sewage.
•
Due to its low treatment
efficiency in terms of nutrient
removal, a secondary
treatment is recommended to
polish the final effluent.
Constructed Wetland
•
Constructed Wetlands are man-made systems which aims to simulate
the treatment processes in natural wetlands by cultivating emergent
plants e.g. reeds (Phragmites), bulrushes (Scirpus), and cattails
(Typha) on sand, gravel, or soil media.
Constructed wetlands can serve the
same small communities as natural
wetlands and can be incorporated into
the treatment systems for larger
communities as well;
•
They are subdivided, basically, into
two wide groups:
(i) Surface Flow (the water or sewage
flows through the soil surface); and
(ii) Subsurface Flow. (Vertical and
Horizontal Flow)
•
Subsurface Flow Constructed
Systems
These systems are applied for treatment of wastewater with
low SS content and COD < 500 mg/L. They are therefore an
excellent technology for secondary treatment.
We can subdivide this group in two different types as following:

Subsurface Vertical Flow Constructed Wetland (VSFW)

Subsurface Horizontal Flow Constructed Wetland (HSFW)
Subsurface Vertical Flow
Constructed Wetland (SVFW)
•
In SVFW the wastewater is loaded onto the planted filter bed’s
surface. The pollutants are removed or transformed by
microorganisms that are attached to the filtersand and the plants’
root system.
•
Due to the biofilm presents in the
filter material, and high Oxygen
concentration in the system, vertical
flow systems have been applied for
both BOD5 and SS removal and
nitrification promotion;
•
However, it is important ensure that
the filter is not saturated or covered
with water in order to secure a high
oxygen level in the filter.
Subsurface Horizontal Flow
Constructed Wetland (SHFW)
•
In SHFW the sewage is uniformly fed in the inlet work and due to a
longitudinal slight slope (~1%) the liquid flows through the pores
of the filter bed until it reaches the outlet work.
•
SHFW usually provide high treatment
effect in terms of removal of organics
(BOD5, COD) and suspended solids
(SS). The removal of nitrogen and
phosphorus is lower but comparable
with conventional treatment
technologies which do not include
special nutrient removal step.
Composting Toilets
•
•
A composting toilet system contains and processes excrement, toilet
paper, carbon additive, and sometimes, food waste.
As a nonwater-carriage system, a composting toilet relies on
unsaturated conditions where aerobic bacteria break down waste.
•
•
•
When exposed to an unfavorable
environment for an extended period of
time, most pathogenic microorganisms will
not survive. However, caution is essential
when using the compost end-product and
liquid residual in case some pathogens
survive.
The composting unit must be constructed
to separate the solid fraction from the
liquid fraction and produce a stable,
humus material with less than 200 MPN
per gram of fecal coliform.
If sized and maintained properly, a
composting toilet breaks down waste 10 to
30% of its original volume.
Biogas Digestor
•
•
•
•
Biogas latrines and communal biogas plants are, in principle, a
more advanced form of the septic tank system.
When human excreta is combined with animal and agricultural
wastes and water, it will give off gas as it decomposes.
The mix of gases produced is called ‘biogas’ which can be used for
cooking and lighting.
Biogas plants typically store
the wastes for about 30 days
which can remove some of
the pathogenic organisms but
by no means all.
Anaerobic Filter
•
Anaerobic filters are used for wastewater with a low content of
suspended solids (e.g. after primary treatment in septic tanks) and
narrow COD/BOD ratio. Biogas utilisation may be considered in case of
BOD > 1.000 mg/l.
•
The anaerobic filter, also known
as fixed bed or fixed film reactor,
includes the treatment of nonsettleable and dissolved solids by
bringing them in close contact
with a surplus of active bacterial
mass.
•
The larger the surface for
bacterial growth, the quicker is
the digestion.
Duckweed-Based Wastewater
Stabilizations Ponds
•
•
In general, duckweed ponds are used to treat domestic or
agricultural wastewaters.
Lemnaceae have the greatest capacity in absorbing macro-elements
(e.g. nitrogen, phosphorus, potassium, calcium, sodium and
magnesium among others);
•
•
Effluents with both a high BOD and
nutrient load may require adequate
primary treatment to reduce the organic
load.
Plants must be harvested regularly in
order to prevent dead plants forming
bottom sludge.
Kind of treatment
Type
Septic Tank
Subsurface Flow
Constructed
Wetlands
Kind of wastewater
treated
sedimentation, flotation Domestic wastewater
and digestion
(communities until 100
inhabitants)
biological and physical
processes
Composting Toilets unsaturated and aerobic
conditions provide
biological and physical
decomposition
Advantages
Disadvantages
Simple, durable, easy Low treatment efficiency,
maintenance, small necessity of a secondary
area required
treatment, effluent not
odorless
Domestic and agricultural Low or no energy
system clogging;
wastewaters; small
requirements;
recommended as a
communities; tertiary
Provide aesthetic,
secondary treatment, large
treatment for industries.
commercial and
areas required;
habitat value.
human excreta, toilet paper, Resulting "humus"
If not well sized and
carbon additive, food waste used as a resource;
maintained can be a
conservation of
environmental problem and
water resources;
a threat for human being,
recycling of
due to its contaminant
nutrients.
potential
human excreta, animal and Recycling of
Biogas plants can be
agricultural wastes
resource; gas
expensive to build and
produced is used for difficult to operate. Poor
cooking and lighting maintenance leads to loss
of gas production and
blockage of the digester
tank with solids.
pre-settled
simple and fairly
costly in construction
domestic and
durable if well
because of special filter
industrial
constructed and
material, blockage of filter
wastewater of
wastewater has been possible, effluent smells
narrow
properly pre-treated, slightly despite high
COD/BOD ratio
high
treatment efficiency
treatment efficiency,
little permanent
space required
Biogas Digestor
Sedimentation, flotation
and digestion
Anaerobic Filter
anaerobic
degradation of
suspended and
dissolved
solids
Duckweed Based
Wastewater
Stabilizations
Ponds
sedimentation,
Domestic and agricultural
anaerobic degradation wastewater;
and sludge stabilization
No clogging risk;
High nutrient
removal rates
Necessity of large areas;
necessity of constant
harvesting; unsuitable in
very windy regions.
Nutrients removal
COD, BOD, TSS;
grease.
TSS; COD; TN; TP.
Volume reduced
from 10 to 30%;
pathogens.
Similar to septic
tanks systems; The
long period of
storage can also
remove some
pathogens.
BOD, TDS, TSS
BOD, SS, TN, TP,
metals
Wastewater Demo Projects
Some best-practices in wastewater management are
shown in the following picture. Different techniques on
wastewater treatment and management of GEF and nonGEF projects are presented below.
Wastewater Demo Projects
Kleruu Teacher’s College - Tanzania
Before the introduction of a Constructed Wetland system, the
College was treating its wastewater through a combination of a
mechanical aeration system and a pond. However, operation of
the mechanical system failed because of high costs of electricity
and lack of regular maintenance.
The pond was
malfunctioning, ignored,
lacked de-slugging and
released untreated effluent
to the downstream
communities.
Wastewater Demo Projects
Kleruu Teacher’s College - Tanzania
A Subsurface Horizontal Flow Constructed Wetland was installed
to replace the pond. The need to operate the mechanical system
accordingly ceased.
The performance of the
installed constructed
wetland is very promising,
with a BOD removal rate of
90%, 76% in nitrate and
69% in heavy metals
(cupper and chromium).
Wastewater Demo Projects
Lake Manzala Engineered Wetland
Project (LMEWP)
Problem Analysis:
•
A large number of towns and villages have no proper sanitary waste
system. The most common solution adopted is septic tanks dug into the
ground, some without proper flooring
•
Agricultural drainage discharges flow untreated from farmers’ fields into
the Nile river and then into the Mediterranean Sea. Most agricultural
fields in Egypt are treated with chemical fertilizers, pesticides and face
increasing salinity.
•
Pollution of Lake Manzala has seriously threatened the health of local
people and the viability of economic activities such as fisheries, raising
livestock, and farming.
Wastewater Demo Projects
Lake Manzala Engineered Wetland
Project (LMEWP)
At Lake Manzala the wastewater is pumped into ponds where sediments
are allowed to settle. The water then flows through 60 acres of
constructed wetlands where more than 75 percent of toxins are
removed. Even in its experimental stage, the wetland treated 25,000m3
of wastewater per day from the Bahr el-Baqar drain.
At just ¼ of the cost of conventional
methods, the pilot wetland has
removed 61 percent of the BOD, 80
percent of SS, 15 percent of TP, 51
percent TP, and 99 percent of total
coliform bacteria.
Wastewater Demo Projects
Decentralized Wastewater Management at
Adarsh College - India
This School Project is a Pilot Project demonstrating alternative decentralized
sanitation solutions to the Badlapur Municipality Council. The Council plans to
replicate the concept in other areas after evaluating the findings of decentralized
reuse-oriented school sanitation project.
The number of students attending Senior and Junior College is about 1,400 and
1,200 per day, respectively.
Applied sanitation components
Decentralized Wastewater Management at
Adarsh College - India
Anaerobic Baffled
Reator
Anaerobic Filter
Wastewater Demo Projects
Vertical flow constructed wetlands New Danish Guidelines
In order to achieve the requirements of Danish Ministry of Environment
for single houses and dwellings in rural areas, a full-scale system was
constructed to treat the sewage from a single household with four
persons.
The sewage was pre-treated in a three-chamber sedimentation tank
(septic tank) prior to discharge into the vertical flow wetland to
minimise the risk of clogging of pipes and the vertical filter.
Wastewater Demo Projects
Vertical flow constructed wetlands New Danish guidelines
It can be seen from the Table above that recirculation of water results in
lower effluent concentrations, and hence better performance. The inlet
concentration also decreases, but this is artificial because of the dilution from
the recirculated effluent water to the sedimentation tank.
Due to its low performance in phosphorus removal, the system might be
extended with a simple chemical dosing system in the sedimentation tank to
remove this nutrient.
Wastewater Demo Projects
Duckweed Lagoons - Zimbabwe
This Study was carried out to investigate the
potential use of Duckweed -Based Waste
Stabilization Ponds for wastewater treatment in
small urban areas in Zimbabwe.
The final effluent from Gutu Growth Point is
discharged into nearby gum plantation before
flowing into nearby river.
•
•
•
BOD
COD
Nitrates
Phosphates
TSS
Removal
50%
50%
70%
80%
90%
The system have performed well in
relation to nitrogen uptake;
Despite the high phosphate levels in the
effluent, the reduction rate is a sign that
Duckweed Lagoon is an alternative for
phosphorus removal in wastewater
treatment.
The total duckweed cover in the
maturations ponds suppressed the growth
of algae that normally results in a build up
of Total Suspended Solids when the algae
die.
Biogas Demo Projects
Swineculture and Water - Brazil
Santa Catarina has 7.2 millions
swine
•
Each swine produce 10L swine
waste/d
= 26 millions m3/year
= 650.000t COD/year
= 35.000t N/year
= 15.000t P/year
•
Many researchers believe that swineculture is an activity with the biggest
responsibility for water resources environmental impact.
Electricity generator by Biogas
CH4
Methane Combustion= CO2
Swine waste
Food
CO2
Duckweeds Lagoon