Short communication

Composting of cellulosic hospital solid waste: a potentially novelapproach

Suman Ghosha,*, B.P. Kapadnisb, N.B. Singhc

aDepartment of Geosciences, University of Missouri, Kansas City, MO 64110, USAbDepartment of Microbiology, University of Pune, Pune 411 007, India

cDepartment of Environmental Science, University of Pune, Pune 411 007, India

Received 22 July 1999; accepted 14 April 2000

Abstract

A 30-day random sampling of solid waste from King Edward Memorial Hospital, Pune (India), was carried out to generatedata on its characteristics. Biodegradable waste was segregated and composted; the fresh waste was found to be de®cient inreadily available nitrogen and populations of cellulolytic microorganisms did not increase. Supplements were employed and cow

manure-amended composting produced the best quality compost in the shortest time under laboratory conditions.Physicochemical and microbiological parameters were evaluated during composting and it was found that the main cellulose-degrading bacteria belonged to Bacillus sp. Fungi played a minor role during the process. 7 2000 Elsevier Science Ltd. Allrights reserved.

Keywords: Hospital solid waste; Composting; Cellulosic-waste; Cellulose-degrading bacteria; Bacillus sp

1. Introduction

The characteristics of hospital solid waste haveundergone considerable changes over the years. Pre-viously, the waste generated from hospitals was mostlybiodegradable, but introduction of plastic goods likemineral and saline water bottles, carry bags, bloodbags etc. changed the waste character from biodegrad-able to non-biodegradable. The use of new drugs andnew therapeutic techniques, have imparted a highlycomplex and potentially toxic nature to the hospitalwaste stream.

A study (Ghosh, 1998) carried out over 30 randomlyselected sampling days at the King Edward Memorial(KEM) Hospital in Pune, India, showed that the hos-pital solid waste mainly comprises of three major cat-egories:

1. Non-biodegradable glass materials, mainly bottles

2. Non-biodegradable plastic materials that includes

bottles (saline and mineral water), syringes, cath-

eters, blood bags, etc.

3. Biodegradable cellulosic and food materials Ð

includes cotton, bandages, pads, amputated organs,

left over food materials, banana peels, coconut

shells etc.

Besides these, the waste stream also contains small

amounts of metallic appliances, such as needles, for-

ceps, scalpels, scissors etc. The waste characteristic

data collected for the three major groups of waste cat-

egories showed a daily average generation of 270 g of

cellulosic and food materials, 47 g of glass and 32 g of

plastic materials per patient.

In India, most of the hospitals and major health

care centers do not have their own waste handling and

disposal facilities and thus are largely dependent on

government disposal facilities. However, with the gra-

dual increase of health care establishments, the volume

International Biodeterioration & Biodegradation 45 (2000) 89±92

0964-8305/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.

PII: S0964-8305(00 )00042 -1

www.elsevier.com/locate/ibiod

* Corresponding author. Tel.: +1-816-931-3089; fax: +1-816-235-

5535.

E-mail address: sghosh@cctr.umkc.edu (S. Ghosh).

of waste is also on the rise, posing a challenge to civicauthorities for its disposal.

In the past, hospital waste was considered to be apart of Municipal Solid Waste (MSW). However, withrealization that this waste harbours pathogens whichwould lead to the contamination of the MSW, it isnow obligatory to segregate the hospital waste andprovide special treatment.

In developed countries, incineration is still themethod of choice for hospital solid waste disposal.However, high capital cost, complicated operation andmaintenance to comply with environmental regulationshas made incineration a less favored method of medi-cal waste disposal in India.

Land®lling is currently cosidered the best availablesolid-waste disposal method. However, with growingpopulation and increasing urban limits, the availabilityof open land is becoming more di�cult day by day.There is a need to ®nd an easily operable, safe, coste�ective and scienti®cally sound method to dispose ofthe waste, and possibly recover some economic value.Based upon this objective, the e�ectiveness of compost-ing of biodegradable hospital solid waste was evalu-ated.

2. Experimental methodology

Hospital solid waste was collected and composted ina pilot scale study. The waste was collected over aperiod of seven successive days, organic material wasseparated and shredded into a size range of 4±7 cmand thoroughly mixed. A composting stack wasformed using approximately 20 kg in a 16 l containerwith dimensions 60 cm� 45 cm� 30 cm. This pile waskept under ambient environmental conditions for 30days. Following the methods of Miehe (1907), Finsteinand Morris (1975), and Stutzenberger et al. (1970), thecompost was turned every four days to maintain boththe aerobic condition and temperature uniformitythroughout the pile. The moisture content was main-tained at 45% (w/w) by adding water as necessaryduring every turning.

A second stack was inoculated with one-year-oldcomposted waste (2:1) and again run for 30 daysunder ambient conditions. Further stacks were pre-pared to assess supplements. Fresh waste, one year oldinoculum and supplements (separate addition of cowmanure, autoclaved cow manure, horse manure andfood waste) were mixed in a 4:1:1 ratio by weight.Horse manure and food waste supplemented stackswere run at ambient as above and were also assessedunder laboratory conditions where temperature wasmaintained at 408C. Cow manure supplemented com-post was only run at 408C under laboratory con-ditions. T

able

1

Summary

ofPhysiochem

icalandmicrobialparametersa

Tim

e

(days)

Tem

perature

(8C)b

pH

bC/N

bCellulolyticbacterialcountb

(CFU/gm)

Cellulolyticfungalcountb

(CFU/gm)

Initial

Max.

Initial

Final

Initial

Final

Initial

Final

Initial

Final

Noinoculum

orsupplements

under

amb.conditions(C

ontrol)

30

24.0

25.7

5.5

5.7

55.0

54.4

00

00

Inoculum

aided

composting(butwithoutanysupplement)under

amb.condition

30

24.0

26.3

5.6

5.9

52.7

52.3

1.1�103

0.5�102

1.1�102

0

Cow

manure-aided

compostingunder

lab.condition

16

40.0

59.5

6.9

8.6

27.0

10.2

2.3�106

3.7�106

1.9�105

0

Autoclaved

cow

manure-aided

compostingunder

lab.condition

32

40.0

58.2

6.9

8.5

27.0

12.2

2.3�106

2.9�106

1.9�105

0

Horsemanure-aided

compostingunder

lab.condition

16

40.0

58.2

6.2

8.6

28.5

12.7

2.2�106

3.0�106

0.7�104

0

Horsemanure-aided

compostingunder

amb.condition

24

22.0

53.1

6.2

8.7

28.5

13.2

2.2�106

2.3�106

0.7�104

0

Foodwaste-aided

compostingunder

lab.condition

32

40.0

67.8

4.0

8.2

28.5

12.4

1.2�106

5.1�106

1.2�104

0

Foodwaste-aided

compostingunder

amb.condition

48

24.0

62.3

4.0

10.6

28.5

13.5

1.2�106

1.8�106

1.2�104

0

aamb.:Ambient;lab.:Laboratory.

bFiverandom

samplesweretaken

both

from

centerandedgeofthestacksandparameterswereanalyzed.Thetabulateddata

isthearithmetic

meanofthe®ve-sample

analysis.

S. Ghosh et al. / International Biodeterioration & Biodegradation 45 (2000) 89±9290

Temperature, pH, C/N (carbon/nitrogen) ratio,moisture content, TVC (total viable count) of bacteria,cellulose-degrading bacteria, fungi and cellulose-degrading fungi were monitored in the composts, tak-ing random samples both from the center and edge ofthe stacks. Carbon content was determined by usingthe formula C = [(100 ÿ % ash)61.8]. Nitrogen con-tent was calculated by the micro-Kjeldahl method(Hawk et al., 1949). The initial C/N ratio was adjusted(by adding required amount of supplements) tobetween 26 and 30 (Tchobanoglous et al., 1993).

3. Results and discussion

The compost without inoculum and supplement(control), showed little activity over the 30-day period.The waste contained large amounts of cellulosic ma-terials, so cellulose-degrading microorganisms werethought to be essential for biodegradation of thewaste. However, addition of previously compostedhospital solid waste to supply a cellulolytic population,did not improve degradation (as found from the moni-tored parameters) over a 30-day period. The C/N ratiowas found to be very high, indicating nitrogen de-®ciency in the waste.

Composts amended with horse manure Ð and cowmanure Ð achieved maturation under laboratory con-ditions within 16 days (assessed as time taken for C/Nratio to reach 10±14 [Table 1]). On the basis of extentof degradation of waste, ®nal C/N ratio and structureand texture, the cow manure-amended compost was ofmuch better quality than the food waste and horsemanure-amended compost.

The initial temperature for the cow manure-aidedcomposting process was 408C, which rose to 59.58Cand then fell to 58.48C over the course of the exper-iment (measured at the center of the stack). Amongthe other sets, the maximum temperature was noted toreach 67.88C for food waste-aided composting carriedout under laboratory conditions.

Temperatures in the pasteurization range of 50±708C leads to the destruction of enteric pathogenicorganisms (Tchobanoglous and Burton, 1996). Mosthuman pathogens are mesophilic, so when the composttemperature rises to the thermophilic condition, thepathogens are killed. A properly composted waste maybe used as a soil conditioner in agricultural or horti-cultural applications (Tchobanoglous and Burton,1996) without the fear of pathogenic outbreaks.Further pilot-scale studies are needed to examinee�ects of the compost on plants and common soilmicro¯ora.

A trend of change in pH (Table 1) from acidic to al-kaline range was noted for all the sets of experiments.The highest pH 10.6 was observed during the ®nal

stage of food waste-aided composting where excessivesmell of ammonia was also noted. The change of pHfrom slightly acidic (depending on the nature of wasteand supplements used) to alkaline range can be attrib-uted to the accumulation of alkaline metabolic pro-ducts of microorganisms generated during the processof composting. The smell of ammonia, noted duringfood waste-aided composting, is most probably due tothe accumulation of protenacious materials in pockets.

Microbiological parameters also showed consider-able variation. The results showed that the bacterialpopulation dominates over the fungal population. Atthe ®nal stage, the bacterial and cellulose-degradingbacterial populations showed marked increase whilethe fungal population showed a drastic decrease andthe cellulose-degrading fungal population was entirelywiped out. The probable reason for bacterial domi-nance during the composting process is the increase intemperature, making conditions unfavorable for mostof the fungal growth but allowing bacteria to dominateover fungi (Dye and Rothbaum, 1964).

Based on di�erent morphological and biochemicalparameters, a major pure culture of cellulose-degradingbacteria was isolated, and identi®ed as Bacillus sp.Another group of cellulose-degrading, gram-negativerods was observed, which needs further study foridenti®cation.

Composting with autoclaved cow manure tooknearly double the time required for non-autoclavedcow manure-aided composting when all other con-ditions were the same. It was also noted that in thisexperiment, the initial microbial count was much lessand so also the ®nal count (Table 1).

Comparing the time required to ®nish the compost-ing process (under laboratory conditions), the qualityof end-product obtained (based on extent of degra-dation of waste, ®nal C/N ratio and texture and struc-ture of the ®nal compost), and the cellulose-degradingmicrobial count, cow manure was found to be the bestsupplement for composting of such highly cellulosicwaste. Due to time constraint and drop of ambienttemperature below 108C (which was thought to be det-rimental of microbial activity), cow manure-amendedcomposting was not carried out under ambient con-ditions. So the data to compare the cow manure-amended composting with the horse manure and foodwaste-amended composting are not available. If anenriched cellulose-degrading microbial population isused as the inoculum at the initial stage, it maydecrease the time required for decomposition of waste.

4. Conclusions

The experimental results show the possibility ofdevelopment of an alternate technology for disposal of

S. Ghosh et al. / International Biodeterioration & Biodegradation 45 (2000) 89±92 91

biodegradable portion of hospital waste, but furtherstudies are needed for safe implementation of suchpractices. Laboratory studies need to be transferred topilot the large scale and more in depth studies ofmicrobial ecology will be needed, speci®cally the studyof survival of pathogens.

The main conclusions that can be drawn from theabove work are:

1. The biodegradable portion of medical waste is de-®cient in easily available nitrogen. External nitro-gen sources in the form of supplements aretherefore essential to achieve biodegradation of thiswaste.

2. This waste was also de®cient in cellulolytic microor-ganisms, so an external supplement in the form ofan inoculum may be essential.

3. External periodic adjustment of moisture is essentialto achieve degradation.

4. Maintenance of the temperature in the mesophilicrange (above 378C) speeds the process.

5. Cow manure is the most e�ective naturally availablesupplement, acting both as a source of nitrogen andmicrobial population essential for biodegradation.

6. Bacteria dominate over fungi during the compostingprocess and most of the bacteria are Bacillus sp.Although this could be attributed to the survival of

bacterial spores alone.7. Segregation of waste at the source is essential for

the process.

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