MEE 528
LIQUID WASTE MANAGEMENT
Learning Objectives
After completing this unit the trainee will be able to:
• Define liquid waste management.
• Describe public health importance of liquid waste.
• Describe the major sources and types of liquid waste.
• Demonstrate common liquid waste disposal methods.
2.1 Introduction
Liquid waste management: A systematic administration of
activities that provide for the proper handling, treatment and
disposal of liquid waste/wastewater or sewage.
2.2 Public health importance of waste
water/sewage
The improper disposal of waste water play a role in the
contamination of surface water, ground water, and the soil
thereby posing health problems. These phenomena persist in
developing countries and affect almost every one.
In Ethiopia, to day, all wastes even in large international cities
like Addis Ababa are drained to the side of roads to ultimately
join small streams or rivers to flow down stream causing water
pollution. All the wastes drained in water ways depends on
the winter rains for cleaning.
Although very high wastewater pollution may not be expected
in the rural Ethiopia, there are some household sewage (liquid
dung, domestic wastewater, etc.) generated from kitchens,
toilets, barns, and other domestic areas.
If household, industrial, or commercial wastes are not properly
disposed, then the disease problems caused by pollution will
still remain to be persistent in the environment.
The disease commonly transmitted through water such, as
Cholera, dysentery and typhoid are waste related. If waste
was safely deposited, or treated and disposed most of the
water born diseases would have not been a problem.
2.3 Classifications of liquid waste/sewage
Waste water or sewage that are generated from a home or
community including toilet, bath, laundry, lavatory, and
kitchen- sink wastes, and surface run off may be classified into
four. These are:
Sanitary sewage
Industrial sewage
Storm sewage or
Mixed sewage (a mixture of all)
Sanitary sewage also called domestic sewage contains
human wastes and wash water from homes, public buildings
or commercial and industrial establishments.
N.B. Domestic sewage/liquid waste here is meant waste from
kitchen, barn, bathroom, laundry, etc., which do not
contain human excreta or sewage
Industrial sewage is the used water from manufacturing
processes, usually carrying a variety of chemical compounds.
Storm sewage, or storm water, is the surface run off caused
by rainfall, it carries organics, suspended and dissolved solids,
and other substances picked up as it travels over the ground.
2.4 Wastewater/sewage composition
Sanitary or domestic wastewater comprises about 99.9%
water and only about 0.1% impurities. In other words, if a 1-
liter sample of wastewater is allowed to evaporate, only about
1gram of solids will remain behind.
Actually, sewage can contain so many different substances,
both suspended and dissolved, that it is impractical to attempt
to identify each specific substances or microorganism. The
total amount of organic materials is related to the strength of
the sewage.
This is measured by the biological oxygen demand, or BOD
and the total amount of suspended solids, or TSS. On the
average, untreated domestic sanitary sewage has a BOD of
about 200 mg/L and a TSS of about 240 mg/L. Industrial
wastewater may have BOD and TSS values much higher than
those for sanitary sewage; its composition is source
dependent.
Another group of impurities that is typically of major
significance in wastewater is the plant nutrients. Specifically,
these are compounds of nitrogen, N, and phosphorus, P. On
the average, raw sanitary sewage contains about 35 mg/L of N
and 10 mg/L of P.
Finally, the amount of pathogens in the wastewater is
expected to be proportional to the concentration of fecal
coliform bacteria. The coliform concentration in raw sanitary
sewage is roughly 1 billion per liter.
2.5 Points to be consider before selecting one
particular sewage disposal technique
There is no single individual sewage disposal technique that
can be universally applied under all conditions. However, the
selection of a particular method will depend upon the following
major factors:
The nature of soil formation and stability of the locality
The availability of adequate land for sewage disposal
The quantity of sewage to be disposed of
The degree of sewage treatment to be achieved
The presence of well water, and whether it is used as
the source of the water supply
The level of the water table of the ground water
The proximity of the disposal site to surface water
sources
The relative cost of the disposal technology
2.6 Liquid waste/sewage disposal methods at
the rural communities or households
level
There are many sewage disposal methods. Some are very
expensive and some need a sophisticated technology. The
following disposal methods are suggested based on the type,
amount and sources of liquid waste found in most rural areas
and small towns in Ethiopia. These methods are the simplest
and cheapest to dispose sewage in rural communities.
A. Disposal by dilution/ “Self-purification of water bodies”
It is a common practice in some communities to discharge raw
sewage into near by water bodies such as rivers, streams,
etc., so that it is diluted or reduced in strength by the water.
⇒ Unsanitary:
• Nuisance (creating offensive condition)
• Water and soil pollutions (a aquatic life start to die
off)
• Spread of infectious organisms greatly increases
B. Cesspool
A cesspool is a pit dug in the ground in order to receive waste
water/sewages from kitchen, toilet or barns. Cesspool can be
classified in to two kinds by its removal mechanisms. These
are:
1. The leaching type of cesspool
2. The watertight cesspool
Leaching type of cesspool or Seepage/soakage or
absorption pit
The leaching type cesspool, otherwise known as a seepage
pit, soakage pit or absorption pit, is a pit dug in the ground to
receive sewage from kitchen, toilet, or barns, and to allow the
liquid to seep, leach or percolate into the ground.
The liquid portion seeps or leaches off into the surrounding
soil, while the solid component (sludge) is retained in the
pit.
The side of the pit is constructed with open joints in order to
facilitate seepage of the liquid portion, while the top most
part (60-90 cm) is plastered to make it watertight as shown
in figure 9.
A concrete slab cover with a man-hole is provide to permit
access to the pit, and an outlet pipe takes the effluent into
another pit or serious of pits
Figure 9: Leaching type of Cesspool
A depth of 2 to 3 meters and a diameter of 90 to 120 cm
will give a reasonable capacity, provided the soil is
adequately porous, and can let the liquids.
The cesspool should be sited at least 30 meters away
from and on a lower level than water wells or other
sources of drinking water.
The height of the ground water table should be at least
1.2o meters below the bottom of the cesspool.
However, it may not be recommend except in very special
circumstances (e.g. it can be used if the soil formation is
sufficiently porous; where water sources are properly
protected).
Improperly used cesspool may create:
• Fly-breeding
• Objectionable odour
• Nuisances
Watertight cesspool
Similar to leaching type except made water proof in order
to receive and store sewage as shown in figure 10.
Inside water tight tank sewage undergoes anaerobic
decomposition but should not considered sewage
treatment
Problem: periodic emptying and disposal of contents
Figure 10: Watertight Cesspool
C. Septic tank
Septic tanks are commonly used for wastewater treatment for
individual households in low-density residential areas, for
institutional such as schools and hospitals, and for small
housing estates. The wastewater may be waste from toilets
only, or may also include Sullage.
The septic tank, in conjunction with its effluent disposal
system, offers many of the advantages of conventional
sewerage.
However, septic tanks systems are more expensive than other
on-site sanitation systems and are unlikely to be affordable by
the poorer people in society. They also require sufficient piped
water to flush all the wastes through the drains to the tanks.
Compartment
dividing wall
Inlet Access cover
Clear space Outlet
Scum
Inlet Sludge
baffle
Outlet
baffle
Figure 11: Schematic of septic tank
2.7 Sewage/wastewater treatment
Why treatment?
Before discharging wastewater back into the environment and
the natural hydrologic cycle, it is necessary to provide some
degree of treatment in order to protect public health and
environmental quality. The basic purposes of sewage
treatment are:
To destroy pathogenic microorganisms
To remove most suspended and
To remove dissolved biodegradable organic
materials.
Sometimes it is also necessary to remove the plant nutrients –
nitrogen and phosphorus. Disinfections, usually with chlorine,
serves to destroy most pathogens and helps to prevent the
transmission of communicable disease.
The removal of organics (BOD) and nutrients helps to protect
the quality of aquatic ecosystems.
Treatment methods
Treatment methods are grouped into three general categories:
Primary treatment: Screening, grit removal, and
sedimentation (settling)
Secondary or biological treatment: biological processes
and additional settling.
Tertiary or advanced treatment: not all sewage
treatment plant requires tertiary (advanced) treatment.
Raw wastewater influent
Screening
Grit removal Screenings/grit disposal
Sedimentation
Secondary treatment Sludge treatment
Tertiary treatment
Disinfections Sludge disposal
Treated wastewater effluent
Figure 12: Schematic overview of a conventional
wastewater treatment system.
Contaminated Waste Management
Learning Objectives
After completing this unit the trainee will be able to:
• Define contaminated waste.
• Demonstrate the purpose of contaminated waste.
• Demonstrate methods of collection and disposal of
contaminated waste
3.1 Introduction
Wastes from hospitals and healthcare facilities may be
contaminated (potentially infectious) or non-contaminated.
Approximately 85% of the general waste produced by health
institutions is non-contaminated waste and poses no
infectious risk to persons who handle it.
Examples of non-contaminated waste include paper, trash,
boxes, bottles, plastic containers and food. They can be
disposed of by the common methods as discussed in chapter
two and three.
Some waste from healthcare facilities, however, is
contaminated. If not disposed of properly, contaminated
wastes may carry microorganisms that can infect the people
who come in contact with the waste as well as the community
at large.
Contaminated wastes include blood, pus, urine, stool and
other body fluids, as well as items that come in contact with
them, such as used dressings. Wastes from operating rooms
(human tissue, blood or blood soaked sponges, gauze or
cotton) and laboratories (blood, feces, sputum, urine
specimens and microbiological cultures) should be considered
contaminated. Soiled medical devices or items that can inflict
injury (e.g., used needles and scalpel blades) are capable of
spreading blood borne diseases such as hepatitis B, hepatitis
C and AIDS, and are also considered contaminated waste.
Definitions:
• Contaminated. State of having been actually or
potentially in contact with microorganism. As used in
healthcare, the term generally refers to the presence of
microorganisms that could be capable of producing
disease or infection.
• Container. Vessel in which waste is placed for handling,
transportation, storage and/or eventual disposal.
• Disposal. Intentional burial, deposit, discharge, dumping,
placing or release of any waste material into or on air,
land or water. Disposal is undertaken without the
intention of retrieval.
• Encapsulation. Filling a sharps container that is three-
quarters full with cement or clay, which, after hardening,
can be disposed of safely in a landfill,
• Hazard. Intrinsic potential property or ability of any agent,
equipment, material or process that can cause harm.
• Infectious waste. The part of medical waste that is
capable of causing infectious diseases.
• Scavenging. Manual sorting of solid waste at landfills
and removal of usable materials.
• Segregation. Systematic separation of solid waste into
designated categories.
• Sharps. Hypodermic needles, suture needles, scalpel
blades, scissors, wire sutures, broken glass or any object
that can cause a puncture or cut.
3.2 Purpose of contaminated waste
management
The purpose of contaminated waste management is to:
• Protect people who handle waste items from accidental
injury,
• Prevent the spread of infection to healthcare workers who
handle the waste,
• Prevent the spread of infection to the local community, &
• Safely dispose of hazardous materials (toxic chemicals
and radioactive compounds).
Open piles of contaminated waste should be avoided
because they:
• Are a risk to those who scavenge and unknowingly reuse
contaminated items,
• Allow persons to accidentally step on sharp items and
injure themselves,
• Produce foul odors, and
• Attract insects and animals.
3.3 Collection and disposal of contaminated
waste
Proper disposal of contaminated waste may include:
• Pouring liquids or wet waste directly into a safe
sewerage system.
• Incinerating (burning) items to destroy the item as well
as any microorganisms. (This is the best method for
disposal of contaminated waste. Burning also reduces
the bulk volume of waste and ensures that the items are
not scavenged and reused.)
• Burying all contaminated wastes to prevent further
handling.
Proper handling of contaminated waste minimizes the spread
of infection to healthcare personnel and to the local
community. Whenever possible, contaminated waste should
be collected and transported to disposal sites in leakproof,
covered waste containers.
• Use plastic or galvanized metal containers with tight-fitting
covers for contaminated wastes. Many facilities now use
colored plastic bags to alert handlers to the contents and
to keep the general (non contaminated) waste separate
from contaminated waste.
• Use puncture-resistant sharps containers for all
disposable sharps (sharps that will not be reused).
• Place waste containers close to where the waste is
generated and where convenient for users (carrying waste
from place to place increases the risk of infection for
handlers). This is especially important for sharps, which
carry the highest risk of injury for health workers and staff.
• Equipment that is used to hold and transport wastes must
not be used for any other purpose in the clinic or hospital.
(Contaminated waste containers should be marked as
such.)
• Wash all waste containers with a disinfectant cleaning
solution (0.5% chlorine solution plus soap) and rinse with
water regularly.
• When possible, use separate containers for combustible
and noncombustible wastes prior to disposal. This step
prevents workers from having to handle and separate
wastes by hand later.
- Combustible (burnable) wastes include paper, cardboard
and contaminated wastes such as used dressings and
gauze.
- Noncombustible (non burnable) wastes include glass and
metals.
Use personal protective equipment (PPE) when handling
wastes (e.g., heavy-duty utility gloves and closed protective
shoes).
Wash hands or use a waterless, alcohol-based antiseptic
hand rub after removing gloves when handling wastes.
It is important to train all community health workers and
healthcare workers, including physicians, to keep
contaminated and non-contaminated waste separate. For
example, throwing a hypodermic needle into a wastebasket in
a patient’s room automatically makes that container hazardous
for housekeeping staff to handle. And, if discovered, that
wastebasket now needs to be handled and disposed of as
contaminated waste.
