CHAPTER 4 MATERIALS AND METHODS -...
Transcript of CHAPTER 4 MATERIALS AND METHODS -...
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CHAPTER 4
MATERIALS AND METHODS
4.1 GENERAL
The Bio-Medical Waste (Management and Handling) Rules, 1998
norms state that, at no point of time the bio-medical waste should be mixed
with ordinary garbage. However, it has been the case for years as the entire
bio-medical wastes find place in the compost yards of the Corporation. So the
Coimbatore Corporation has decided not to collect garbage from private
hospitals and nursing homes which are not signing up the common bio-
medical waste treatment facility project. Following the action made by
Coimbatore Corporation, most of the hospitals from 200 beds signed MoU
with the Corporation.
4.2 DESCRIPTION OF THE STUDY AREA
Coimbatore is one of the fast developing cities in South India.
Coimbatore is the second largest city in the state of Tamilnadu. It lies between
latitudes 11°1 N and longitudes 76°58 29 E. The general slope of the
district is towards west. It is located at an elevation of 411.2 m above sea
level and occupying an area of 105.5 km². The temperature during both
summers and winters varies between 37°C to 14°C.Coimbatore has semi-arid
climate with annual rainfall is 61cm and potential evapo-transpiration of 1500
– 2000 mm /year.
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The population becomes very dense due to migration of rural
people. As per the 2001 census, Coimbatore had a population of 1,461,139
within city limits. Males constitute 52% of the population and females 48%.
Water supply for the city is 219Mld-1
. There are more than 35000 small,
medium large and tiny industries and textile mills.
Apart from the Government hospital, the total number of hospitals in
the private sector in Coimbatore Urban area is 76. The district's health
department is amongst the best in terms of implementing government-
initiated health schemes. Also, several rare surgical procedures are being
done. The city also has numerous homeopathic clinics. Fast pace of
industrialization, spiraling population and the increase in the health awareness
have led to the growth of the healthcare industry in Coimbatore. The city
stands second to Chennai in the State of Tamilnadu for highly affordable and
quality healthcare deliveries of international standards. Coimbatore is also the
preferred healthcare destination to the floating population from nearby towns
and districts and also the state of Kerala. The first healthcare centre that was
started in 1909, later became the Coimbatore Medical College Hospital
(CMCH) during 1960s. The Coimbatore medical college hospital has 1200
beds while private hospitals in Coimbatore have 3000beds, corporate
hospitals have 2000 beds and Employee’s state Insurance corporation
hospitals have around 800 beds. With the city corporation hospital beds
added, the total strength is estimated to be a little more than 7500 beds.
Tirupur, Pollachi and Mettupalayam jointly have bed strength may go upto
11,000.
To know the quantity and characteristics of hospital waste
generation, a study was carried in one of the hospitals in Coimbatore. The
hospital founded in 1975 is perhaps the most benevolent of the Trust’s
projects with a great scope of achieving the mission’s prime objective namely
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“Service to Humanity”. The hospital has now grown into an all under one roof
hi-tech medical complex with 400 beds and covering all specialties. Free
medical treatment is provided to the needy poor and with charges for those
who cannot afford the full cost of treatment.
The hospital is well equipped with modern Intensive Coronary Care
Unit (ICCU), Intensive Pulmonary Care Unit (IPCU), Complete diagnostic
and treatment facilities, Modern Kidney Transplant Unit with Heamodialysis
Machine working at very low cost. The hospital also has its own Pharmacy
that serves round the clock and is always well stocked. 24 Hours Cardiac Care
and Accident Care Ambulance unit is also available. A canteen is also
attached for the use of patients and other visitors. The hospital is running with
fully qualified and experienced consultants/ Super specialist Doctors, 46,
Junior Doctors, 49, Staff Nurses, Technicians, Pharmacists and other hospital
menial staffs totaling 580 numbers.
Hospital Statistics
Bed strength : 400
Bed Occupation : 90-110%
Out Patient attendance : over 450/day
Lab Investigation : Around 50000 investigations for OP and
IP Patients / year
Operations : Around 5000 major and 4000 minor / year
4.3 QUANTITY OF BIOMEDICAL WASTE GENERATION
It is important to know the quantity of waste generated in order to
examine the various treatment options. However, estimating the quantity of
the produced waste stream is a difficult task. Waste production depends on
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the hospital’s capacity, the number of medical staff, and the applied practices.
Therefore, an on-site evaluation of the hospital waste generated is considered
most appropriate. In this study, the quantity and characteristics of waste
produced was investigated by personal observations daily for a period of 2
months (May-June 2006). The number of beds in different wards for each
department, as well as the quantity of BMW generated each day as per its
character was recorded and percentages are presented by weight. Precautions
like wearing an apron, face mask and use of thick impermeable gloves were
taken. The principal investigator and the BMW handlers involved in the study
were inoculated against tetanus. Brain storming sessions were held with
health care workers 2 times during the study period. As per the study, inspite
of high sickness rate among the sanitation staff dealing with health care
waste, the awareness regarding the protection of their bodies and manual
handling was found to be missing. The sanitation staff does understand the
relation of waste and diseases but they replied that they have been doing the
same for a very long time so they have become immune to many health
problems. As a protective measure the municipal collection staff wears a head
gear to protect the waste falling on their bodies while loading it in the refuse
van. The sanitation staff working in hospital and health care facilities gets free
medication from their place of work. The interviews revealed that to avoid
absenteeism from work and probably sickness due to handling of waste, the
scavengers get the injections once a week or a prior dose of medicines. And
also they were not fully aware of the BMW management rules. Personnel
responsible for the disposal of BMW were not adequately trained which led to
inappropriate collection, separation of BMW and insufficient implementation
of the regulation. These practices contaminate noninfectious waste as
infectious.
Various departments of study are Anesthesiology, Cardiology ,
Cardiac Surgery, Clinical Lab and Pathology , Dental Surgery, Dermatology,
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Diabetology, ENT Surgery, General Medicines, General Surgery,
Laparoscopic Surgery, Nephrology, Neurology, Neurosurgery, Obstetrics and
Gynecology , Oncology, Ophthalmology, Orthopedics, Pediatrics, Physical
Medicine, Pulmonology, Radiology, Surgical Gastroenterology and Urology.
The various clinics are Cancer Screening, Fertility Clinic, Genetic
Counseling, Gyn. Urology, High Risk Preg, HRT Clinic, Menopause and
Well Baby Clinics, 24 Hours Out – Patient Casualty, Accident and
Emergency Services and the hospital has Heart Foundation and Research
Centre incorporating the division of Intervention Cardiology and the Division
of Cardiovascular surgery equipped with modern facilities. The Cancer
institute has facilities for Multi Modality treatment. Medical Oncology,
Surgical Oncology and Radiation Oncology treatment with Telecobalt
Therapy, Brach therapy and Linear Accelerator with 3D Treatment planning
System, Endoscopies, Colonoscopy, Video bronchoscope, (rigid and fibro
optic) and Laparoscopic cholecystectomy units.
The hospital under study collects the general wastes and Infectious
Bio-medical wastes of the hospital in plastic bins. The general and infectious
biomedical waste are collected from each ward by means of hand cart and
transported by the specially designed four wheeled trolley. During
transportation, the waste is loaded in the trolley without any spillage.
4.4 CHARACTERISTICS OF HOSPITAL WASTES
Healthcare services generate huge quantities of waste with a broad
range of compositions and characteristics which carry a higher potential for
infection and injury than any other type of waste. Hospital wastes which
include general wastes, Infectious wastes, sharps and cytotoxic wastes require
special precautions and handling procedures.
General wastes include paper waste, kitchen wastes, fruit peelings.
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Infectious wastes include the wastes from research and industrial
laboratories, medical and pathological laboratories. The waste contains
discarded live and attenuated vaccines, cultures dishes, human blood and
blood products which include blood as well as serum, plasma and also
pathological waste like tissues, organs, body parts and body fluids.
Sharps includes discarded syringes, needles, cartridges, broken
glass, scalpel blades, saws and any other sharp instruments that could cause a
cut or puncture and could be infected.
Cytotoxic or chemical and pharmaceutical wastes: cytotoxic waste
includes expired cytotoxic drugs and materials such as swabs, tubings, towels,
sharps which are generated during the preparation, transportation and
administration of cytotoxic drug therapy.
4.5 MATERIALS
The materials such as biomedical waste, Organic fraction of
Municipal solid waste, Lime solution, Neem (Azadirachta indica) leaves
extracts, solar disinfector and seed sludge were used in investigations.
4.5.1 BioMedical Waste (BMW)
The BMW used in the study belongs to the category 6 of
Biomedical waste (Management and Handling) Rules, 2000, schedule I. The
category 6 indicates soiled wastes which includes cotton, dressing items,
soiled-plaster casts, lines, bleedings, other materials contaminated with blood
and body fluids. Contaminated cotton and dressing items were taken for
study. The collection was done from the central collecting unit of one of the
hospitals in Coimbatore, where different categories of waste from different
wards of the hospitals are collected as per the schedule II of Biomedical waste
(Management and Handling) Rules, 2000. The collected BMW was stored in
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an air tight container at room temperature and was characterized and used
during the study. Table 4.1 shows the chemical characteristics of BMW.
Table 4.1 Chemical characteristics of IBMW
S.No Parameters Value
1 Moisture content (%) 10-30
2 Total solids(mg l-1
) 17654 -87200
3 Volatile solids (mg l-1
) 7652 -73100
4 COD (mg l-1
) 3396.2 – 16080
5 Alkalinity (mg l-1
) 1400-8150
4.5.2 Organic Fractions of Municipal Solid Waste (OFMSW)
Improper segregation practices in health care institutions have lead
to a mix of MSW with infectious waste, thereby increasing its volume.
Co-treatment of this combined waste is vital. Hence, organic fractions of the
municipal solid waste (OFMSW) were used for co-digestion along with
BMW during the study. These OFMSW were collected from the central
collection unit of the same hospital and it was dried at room temperature and
shredded to a size of 2-4mm. It was stored in a plastic container at room
temperature, characterized and used for study. Table 4.2 shows the chemical
characteristics of MSW.
Table 4.2 Chemical Characteristics of OFMSW
Sl.No. Parameters Value
1 Moisture content (%) 50–70
2 Total solids(mg l-1
) 940–980
3 Volatile solids (mg l-1
) 390–420
4 COD (mg l-1
) 540–1020
5 Alkalinity (mg l-1
) 210–255
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4.5.3 Lime solution
Lime was used to inhibit the adverse effect of infectious BMW.
90.8% purity commercially available lime was used as pretreatment to the
feed stock.
4.5.4 Neem (Azadirachta indica) Leaves Extracts
Mature green neem (Azadirachta indica) leaves were collected and
dried partially. These dried leaves were then crushed and powdered. The
crushed leaves were soaked overnight in water and the next morning the
extract was strained through a piece of cloth; the desired volume of
concentrated extract was used for disinfection.
4.5.5 Box-type Solar Disinfector
Solar energy is freely available and it has the capacity to disinfect
pathogenic organisms in Infectious medical Waste. Hence Solar energy can
be effectively utilized for disinfection purpose using Box-type solar cookers
instead of higher investment like Autoclave, hydroclave and microwave
process in hospitals for sterilization of gloves, mask and IV bottles. After
disinfection in the solar disinfector, the waste needles and sharps can either be
buried in a cemented pit or can be sent for metal smelting operation. Glass
could be sent for recycling. Plastic wastes and other wastes are shredded and
sent for recycling. The metal waste is added to constructed cement pit or sent
for smelting.
A 10 litres capacity of Box- Type Solar disinfector as shown in
Figure 4.1 is made up of galvanized aluminum sheets which consists of two
sections i.e the upper cover and the lower box. The upper cover holds the
reflecting mirror, which is supported by the wooden ribs. The single reflector
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mirror facing the solar radiation reflects the solar energy on the heating area
of the box. The main heating area is painted black. The lower box has a lining
of glass wool in the base to improve the insulation. A transparent glass sheet
covers lower area, which is lined with clips. A rubber lining covers the
periphery of the box on which the glass cover rests. The glass cover sheet
lined with rubber lining and glass wool in the lower box help is used in
raising the temperature. The lower box also has a fitting of electric heating
arrangement which is provided to ensure the job during rainy season or
cloudy days. The electrical attachment consists of indicator lamps, thermostat
and heating elements and it requires power supply of 220 Volts.
The design is easily fabricated in India and currently used for
cooking purpose. The maintenance and repair should not be a problem. For
maintenance, daily cleaning and painting once in three months is adequate.
Electric connections may be checked periodically. A chemical indicator
system (chemical indicator tape) could be developed to monitor the
temperature attained in the system.
Figure 4.1 Solar Disinfector
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4.5.6 Seed Sludge
The distillery spent wash sludge collected from Shakthi Sugars,
Appakudal, used as the seed sludge for the digester.
4.6 METHODS
4.6.1 Pretreatment of Infectious BMW
Disinfection of biomedical waste is an essential process to destroy
pathogenic microorganisms. Thereafter medical wastes can be effectively
treated and disposed as municipal solid wastes. Cost effective treatment
options are necessary as an alternative for expensive technologies such as
Incineration, Autoclave, Microwave and Hydroclave processes. Hence, the
investigation was carried out using the following disinfectants, as pre-
treatment techniques for the destruction of pathogenic microorganisms in
similitude infectious biomedical wastes.
1. Lime pre-treatment
2. Neem (Azadirachta indica) leaves extract pre-treatment
3. Solar disinfection
4. Solar disinfection with addition of lime solution
The reaction of lime with wastes is as follows:
Ca(OH)2 + H2CO3 = CaCO3 + 2H2O
Ca(OH)2 + Ca(HCO3)2 = 2CaCO3+2H2O
The lime combines with all the free carbonic acid and with the carbonic acid
of the bicarbonates (half-bound carbonic acid) to produce calcium carbonate,
which acts as coagulant. Substrate which is enclosed within cell membranes
requires release of the cell-bounded substrate before it can be utilized by
viable anaerobes. Though thermal or thermochemical pretreatment results in
an increase the biodegradability it consumes a substantial amount of energy
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compared to chemical consumption. The chemical pretreatment is most
efficient and cost- effective when carried out at ambient temperature. Alkaline
pretreatment is effective in solubilizing munitions grade nitrocellulose into
soluble organic carbon forms. (Jih-Gaw lin et al, 1997). Donald L. Wise
(1981) reported that in alkaline (Lime and Neem leaves extract) refining
process an intramicellar swelling occurs as caustic soda penetrates inside the
cells and dissolves the deeply embedded hemicelluloses which increase the
size of pore spaces and therefore greater digestibility.
4.6.1.1 Lime Pre-treatment
The process is operated either at relatively low temperatures with
the use of strong alkaline solution or at higher temperature using relatively
weak alkaline liquors. Basically alkali pretreatment causes a swelling which
increases the size of pore spaces and separation of lignin from the
carbohydrates through direct solubilization of lignin to hydroxylated
aromatics allowing greater access by enzymes and therefore greater
digestibility. During the study two kg of Infectious BMW was pre-treated
with 100 gm of lime and four litres of water for 53 h.
4.6.1.2 Neem (Azadirachta indica) Leaves Extract Treatment
Neem (Azadirachta indica) leaf extract has a fruit like smell and
contains essential fatty acids, this extract finds large scale personal and
industrial application. Neem extract contains the concentrated form of active
or principle compounds found in neem. Neem extract’s antibacterial
properties can be used in different industries like agricultural industry as
pesticides and insecticides, herbal industry and pharmaceutical industry to
manufacture quality natural products. The antibacterial property of neem can
be utilized for disinfection purpose so Neem (Azadirachta indica) was tried as
disinfectant of pathogens in infectious biomedical waste. During the study
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two kg of Infectious BMW was pre-treated with 100 gm of Neem
(Azadirachta Indica) leaves extract and four litres of water for 53 h.
4.6.1.3 Solar Disinfection
Sunlight possesses appreciable bactericidal activity and plays an
important role in the spontaneous sterilization that occurs under natural
conditions. The action is primarily due to its content of ultraviolet rays, most
of which, however, are screened out by glass and the presence of ozone in the
outer regions of the atmosphere. The pioneering work on the effect of solar
light (UVA plus visible light of 350 - 490 nm) on bacteria was done in the
1940ies by Hollaender. He worked with the effects of “near”- and “far”-UV
light on E. coli and already hypothesized that far- UV (he used 265 nm)
directly damages nucleic acids, whereas near-UV (used was 350 - 490 nm)
produces toxic compounds that destroy other cell components. Twenty years
later, it was found that broad spectrum near-UV light can block the electron
transport chain by photochemical decomposition of aromatic cofactors such
as membrane-associated quinones (reviewed by (Jagger, 1972). Later,
environmental engineers observed that sunlight significantly affects the
survival of coliform bacteria shed into the environment with wastewater
(Evison, 1988; Fujioka et al., 1981; Gameson & Saxon, 1967; Kapuscinski &
Mitchell, 1981; Kapuscinski, 1983). This effect was further investigated by
Acra and coworkers for disinfecting oral rehydration solution and small
quantities of drinking water (Acra, 1980; Acra, 1989) and his idea was further
developed into solar disinfection (SODIS) by Wegelin and colleagues
(Wegelin et al., 1994). Many times not only the effect of UV light but also
that of mild heat (45 - 50°C, assumed to denature essential cellular enzymes)
during exposures of SODIS flasks to the sun is assumed to be responsible for
the inactivation of pathogen. The experiments were carried out daily with new
samples in a box-type solar disinfector for one week. The box solar
disinfector was placed on a high rise building top where plenty of sunlight
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was available. Preheating of the box solar disinfector with metal box was
started at 7 AM in the morning by facing the reflector mirror in the direction
of sun. At 10 AM, 500gms of Infectious biomedical wastes was added to the
metal box and filled with 1.5 litres of water till the waste was immersed. This
was done because water addition improved heat penetration. Exposure period
of the waste was from 10 AM to 4 PM i.e 6 h. The direction of the reflector
mirror was changed every two hours to face the sun. After 4 PM, the waste
was allowed to cool.
4.6.1.4 Solar Disinfection with addition of Lime Solution
Also, solar energy with addition of lime solution was tried as a
disinfectant daily with new samples in a box-type solar disinfector for one
week. Solar energy has the capacity to disinfect pathogenic organisms in
Infectious Biomedical Waste. Lime water also has the capability to destroy
pathogens. The combined effect of solar disinfection with the addition of lime
solution to kill the pathogenic organisms was studied using 500gms Infectious
biomedical wastes in a metal box with 100 gm lime and 1.5 litres water till the
waste was immersed because water addition improved heat penetration.
4.7 ANALYTICAL METHODS
4.7.1 Chemical Analysis
Chemical analyses were performed with a known volume of each
of the sample according to standard methods for the examination of waste and
waste water. The samples were analyzed for pH, Alkalinity and Electrical
Conductivity.
4.7.2 Biological Analysis
Biological analyses (Trivedy and Goel 1986) were performed with
a known volume of each of the samples according to standard methods for the
examination of waste and wastewater. The samples were analyzed for the
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identification of bacteria by Gram staining method, Bio-assay test, MPN of
Coliforms test and the presence of bacterial colonies were determined using
standard plate count technique.
4.7.2.1 Gram staining method
Gram staining method was used to differentiate Gram positive
bacteria from Gram negative bacteria.
Principle: One of the important and most widely used differential
staining techniques in microbiology is Gram’s staining technique. In this
process, the fixed bacterial smear was subjected to the following staining
reagent in the order
1. Crystal violet is the primary strain and it was used to give
colour to the bacterial cell.
2. Iodine solution was used to fix the primary stain.
3. Alcohol was used as decolouriser. Finally a colour stain
Safronin or other suitable counter stain was applied in order to
establish colour contrast of the cells.
4.7.2.2 Bioassay Test
Bioassay (commonly used shorthand for biological assay), or
biological standardization is a type of scientific experiment. Bioassay
(commonly used shorthand for biological assay), or biological standardization
is a type of scientific experiment. Bioassays are typically conducted to
measure the effects of a substance on a living organism and are essential in
the development of new drugs and in monitoring environmental pollutants.
Bioassay is a test in which organisms are used to detect the effect of
any physical or chemical factor in the environment. The bioassays are
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extremely common and are largely used by regulatory agencies to permit the
discharge of safe concentration of various wastes, studying synergistic effect
of chemicals, assessment of efficiency of a waste treatment method and the
concentration of a chemical which can be used without any adverse effect.
The test involves exposing the organisms to the toxicants for a definite period
in the laboratory and observing mortality and/or other effects during study
period. The bioassays can be conducted using several types of organisms like
algae, zooplanktons and macro invertebrates but the fish have been used most
extensively.
Procedure
The known quantity of toxicants [i.e for lime and neem leaves
extract treatment - four litres and for solar disinfection and solar
disinfection with lime solution treatment - 1.5 litres] was poured
with dilution water to make 10 litres in 12 litres capacity
containers.
The dissolved oxygen, pH, alkalinity of the concentration was
measured and the suitability of the conditions assured.
Bioassay test was carried out in each container using ten
numbers of carp family fish with 2 cm length and 5 g weight at
room temperature.
The dissolved oxygen level at frequent intervals was monitored
and corrected immediately by aeration. Also pH, temperature
and alkalinity were monitored every 24 h.
The behavior of fishes was monitored carefully.
4.7.2.3 MPN of Coliforms test
MPN of coliforms test involves inoculating the sample with its
1:100, 1:1000, 1:10000 and 1:100000 dilutions in a nutrient agar medium.
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After the expiry of 48 h incubation period, the tubes were examined for gas
production by the coliform organisms. The test is known as the presumptive
test. Since this reaction may also be produced by the organisms other than
coliforms, the positive tubes from the presumptive test are subjected to
confirmatory test using Brilliant Green Lactose Bile Broth medium with 48 h
incubation period. The density of bacteria was calculated on the basis of
positive and negative combination of the tubes using MPN tables.
4.7.2.4 Standard Plate Count Technique
The Standard plat count (SPC) values provide density of aerobic
and facultative bacteria in sample, which can grow at 37°C. The SPC values
are useful in warning about excessive microbial growth in any water and also
in judging the efficiency of treatments in removing micro-organisms. The
method involves inoculating samples with its 1:100, 1:1000, 1:10000 and
1:100000 dilutions in a nutrient agar medium in Petri dish and counting the
colonies using Colony counter after the expiry of 48h incubation period.
4.7.3 Morphological Studies on Pre-Treated Samples
The morphology studies were conducted for raw waste and
pre-treated samples like lime solution and Neem leaves extract solution
treatment, solar disinfection process and solar disinfection with lime solution
treatment. The samples were dried using vacuum drier and the studies were
carried out using JSM-6390 Scanning Electron Microscopy (SEM) for all
samples to substantiate the effectiveness of all pre-treatment.
4.8 ANAEROBIC DIGESTION
4.8.1 Anaerobic Digestion Experimental Setup
The lab scale experimental digester model of 5litres capacity was
fabricated with transparent fibre glass. Provision was made for checking pH,
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temperature and bio-gas evolved in the course of digestion. A sampling port
of size 1 cm was fitted at the lower end to drain out the effluent for analysis.
Small pebbles are placed at the bottom of the digester in order to avoid the
floc formation. Two digesters were operated at room temperature as the
temperature prevails in mesophilic range in Coimbatore (24 - 35ºC). No
special mixing equipment was employed for mixing the contents in the
digester. The pH in the reactor was maintained in a nearly neutral condition.
The schematic view and pictorial view of the experimental setup is shown in
Figure 4.2 and Figure 4.3.
Figure 4.2 Schematic view of Experimental Setup
7
cm
Gas
collection
bottle
Seeding
sludge and
waste
Gas
measuring
Jar
55 c
m3
cm 1 c
m
10 cm
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Figure 4.3 Pictorial view of Experimental Set-up
4.8.2 Anaerobic Digestion Experimental Procedure
4.8.2.1 BMW Digester
The infectious biomedical waste was pre-treated for pathogenic
reduction. One of the digester was then loaded with the mixture of pre-treated
bio-medical waste and seeding sludge in a proportion of 75% BMW and 25%
Seeding sludge. The pH in the reactor was maintained in a nearly neutral
condition. The supernatant samples from the reactor were drawn through the
sampling probe at 10 days regular time intervals. Table 4.3 denotes the
quantity details of BMW and Mixed waste anaerobic digester.
4.8.2.2 Mixed BMW Digester
The infectious biomedical waste was pre-treated for pathogenic
reduction. The amount of waste generated in the health care institution is in
the ratio of 1:4 (WHO 1999, 2001, 2004, Hosny and El-Zarka 2007). Hence,
for the study, the digester was fed with pre treated BMW, OFMSW and
seeding sludge in the proportion of 75% mixed waste and 25% seeding sludge
with respect to the volume of digester. The pH and temperature was
monitored daily. The pH in the reactor was maintained in a nearly neutral
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condition. The supernatant samples from the reactor were drawn through the
sampling probe at 10 days regular time intervals. Table 4.3 denotes the
quantity details of BMW and Mixed waste anaerobic digester.
Table 4.3 Quantity details for Anaerobic Digesters
S.No. MaterialsQuantity
BMW Mixed
1 Quantity of seeding sludge 1.1 L. 1.1L
2 Quantity of disinfected BMW 500 gms 100 gms
3 Quantity of OFMSW --- 400 gms
4 Amount of water added during
lime stabilization
3.3 L. 3.3 L
4.9 ANALYTICAL METHODS
The characteristics of raw biomedical waste were studied with the
initial COD, Total solids, Volatile Solids and Alkalinity. The Chemical
characteristics of influent of the two digesters were determined (APHA 1998,
2005) and are tabulated in Table 4.4. The supernatant samples from the
reactor were drawn through the sampling probe at 10 days time interval and
the samples were analyzed for COD, total solids, volatile solids and alkalinity.
Biogas produced from reactor was measured daily using gas displacement
method.
Table 4.4 Chemical characteristics of Influent of Anaerobic Digesters
ParameterValue
BMW Digester Mixed Digester
Moisture content (%) 10-30 50-60
Total solids (mg l-1
) 22620 24370
Volatile solids (mg l) -1
16370 23760
COD (mg l-1
) 3773 3971
Alkalinity(mg l-1
) 12000 4650
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4.10 METHODOLOGY FOR DETERMINATION OF
BIOKINETIC COEFFICIENTS
Process kinetics plays an important role in the development and
operation of anaerobic treatment systems. Based on the biochemistry and
microbiology of the anaerobic process, kinetics provides a rational basis for
process analysis, control and design. In addition to the quantitative description
of the rates of waste utilization, process kinetics also deals with the
operational and environmental factors affecting these rates. A sound
knowledge of kinetics allows for the optimization of performance, a more
stable operation as well as better control of the process.
4.10.1 Reaction Rates and Reaction Rate Coefficients
In a batch reactor, flow is neither entering nor leaving the reactor
i.e. flow enters, is treated, and then is discharged, and the cycle repeats). The
liquid contents of the reactor are mixed completely.
For homogeneous reaction, the rate of reaction ‘r’ is
0 c
dCV QC QC r V
dt (4.1)
Q = O for batch reactor, then the rate reaction equation becomes
c
dCr KC
dt (4.2)
KT
0
Ce
C (4.3)
where rc = Rate of conversion
K = First order reaction rate coefficient, T-1
C = Concentration of organic matter remaining, ML-3
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C0 = Initial concentration of organic matter, ML-3
T = Detention time, T
Figure 4.4 Determination of Reaction rate Co-efficient [K]
Experimental data provided microbes count reduction for various
detention times during all disinfection process i.e. Lime, Neem leaves extract,
Solar disinfection, Solar disinfection with lime solution. Concentration of
microbes count remaining after all pretreatment was taken as, ‘C’ and for
anaerobic digestion process of disinfected BMW and Mixed BMW, COD was
considered as ‘C’. A graph C /C0 versus ‘T’ [Figure 4.4] is used to determine
the reaction rate coefficient (K).
4.10.2 Rate of Utilization of Soluble Substrates and its Effect on
Microbial Growth Rate
Using BMW and mixed waste anaerobic digester experimental data
biokinetic co-efficients were determined using (Metcalf and Eddy 2003)
su
s
kXSr
(K S) (4.4)
Slope =K–In
(C
/C0)
T
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where rsu = rate of substrate concentration change due to utilization
(mgL-1
.d)
k = Maximum specific substrate utilization rate (‘d-1
’)
X = Biomass concentration, (mgL-1
)
S = growth-limiting substrate concentration in solution (mgL-1
)
Ks = half – velocity constant (mgL-1
),
m= kY (4.5)
where Y = Maximum yield co-efficient (Dimensionless parameter)
m = Maximum specific growth rate (‘d-1
’) and also using
sud
r1Y k
X (4.6)
where kd = Endogenous decay co-efficient (‘d-1
’)
= Detention time (d)
A graph 1/S versus X /(S0–S) was drawn and the straight line
intercept gives 1/ k and slope equal to Ks / k. Thus Ks and k were determined
as shown in Figure 4.5.
Figure 4.5 Determination of Ks and k
1/S
Slope = Ks/k
/ (
S0–S
)
Intercept 1/k
136
And a graph (S0–S)/ X versus 1/ c was drawn, the straight line intercept
gives the value of Kd and slope equal to Y, and m was determined as shown
in Figure 4.6 using COD as S, Detention time as and VS as X .
Figure 4.6 Determination of Kd and Y
The physical, chemical and biological processes that control the
fate of the constituents dispersed to the environment are numerous and varied.
Important constituent transformations and removal processes operative in the
environment, along with the constituents affected are rate-dependent,
representative rate expressions used to model these processes such as
adsorption/desorption, algal synthesis, bacterial conversion, chemical
reactions, filtration, natural decay, photosynthesis/respirations.
Slope = Y
(S0–S)/ X
1/
c
Intercept kd