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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

128

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.

129

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

131

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

135

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