American Journal of Plant Sciences, 2011, 2, 660-668
doi:10.4236/ajps.2011.25079 Published Online November 2011 (
Copyright © 2011 SciRes. AJPS
Physico-Chemical and Microbial Quality of
Locally Composted and Imported Green Waste
Composts in Oman
Saifeldin A. F. El-Nagerabi1*, Abdulkadir E. Elshafie2, Saif N. Al-Bahry 2, Hasina S. AlRawahi2,
Huda AlBurashdi2
1Department of Biological Sciences and Chemistry, College of Arts and Sciences, University of Nizwa, Birkat Al Mouz, Nizwa,
Sultanate of Oman; 2Department of Biology, College of Science, Sultan Qaboos University, AlKhoudh, Sultanate of Oman.
Received August 7th, 2011; revised September 20th, 2011; accepted October 20th, 2011.
In this work the physical, chemical and microbial properties of four locally composted green waste composts (GWCs)
namely Almukhasib, Grower s, Plantex, and Super along with four imported GWC (Florabella, Mikskaar, Potgrond, and
Shamrock) were studied to evaluate the quality of these composts with the acceptable standards. All composts showed
normal physical properties, except the bad smell from sulfur reducing bacteria in Almukhasib, light brown color
Plantex and one viable weed seed in Shamrock compost. The germination indexes of the composts comparable to the
standard (90%) were 100% for Mikskaar, followed by Shamrock (92%), Florabella (97), Potgrond (95%), Plantex
(98%), Growers (77%), and 5% for both Super and Almukhasib. The physical and chemical properties vary considera-
bly as follows: pH 3 - 10.5, 5.1 - 6.5 (standard 5 - 8), electrical conductivity (EC) 0.4 - 10.2 mS·cm1, 0.8 - 1.8 mS·cm–1
(standard 0.0 - 4.0 mS·cm–1), moisture content (MC%) 29% - 43.7%, 64% - 74% (standard 35% - 60%) and water
holding capacity (WHC%) 92% - 200% and 400% - 800% for the locally produced and imported composts, respectively.
Wide ranges in the chemical properties were expressed as ammonia concentration 512.4 - 1640.1 mg·kg–1, 459.4 -
656.5 mg·kg–1 (standard < 500 mg·kg–1), organic matter 17% - 67.6%, and 53.3% - 66.2% (standard 35%) for the locally
composted and imported composts, respectively. The concentrations of the heavy metals (Zn, Ni, Pb, Hg, As, Cd, and Cr)
were lower than the recommended levels. The average of the bacterial colony forming unit per gram of locally pro-
duced and imported composts rang ed between 260 - 1740 CF U /g and 330 - 2870 CFU/g, whereas the fungal CFU were
10 - 2800 CFU/g and 27 - 1800 CFU/g, respectively. The most probable number (MPN) for coliform ba cteria was 43 -
1100 CFU/g for loca lly produced composts, and 23 - 480 CFU/g for the impo rted comp osts. Therefore, these com posts
can not be used directly without effective treatment as substrate for plant growth, soil amendment and as biofertilizer.
Keywords: Aspergillus Niger, Coliform Bacteria, Physico-Chemical Properties, Green Waste Compost, Heavy Metals,
1. Introduction
Composting is a natural decaying of the organic matter to
stable compost by aerobic and anaerobic actions of bac-
teria, fungi and other organisms [1-3]. This process has
the potential of managing organic materials in the waste
stream such as leaves, farm wastes, animal manure, pa-
per products, sewage sludge and domestic wastes [1,4].
Green waste compost (GWC) is a biodegradable waste
that originates from pure plant materials of garden trim-
mings or garbage collected from vegetable and fruits
markets [5]. It provides benefits for soil biological acti-
vity, and nutritive value to plant growth [6-8]. It im-
proves the physical and chemical properties of the soil
[9], enhances plant growth [10,11], remediates contami-
nated soil [7,12-14], and suppresses some of these soil
borne disease [15,16].
Quality control of the compost significantly promotes
the recycling of the organic wastes [17]. The compost
must comply with certain national and international stan -
dards and quality grading [5,18]. The qualities of the
compost include physical, chemical and biological pro-
perties such as moisture content, odor, carbon and nitro-
gen contents, phytotoxic substances, harmful elements,
Physico-Chemical and Microbial Quality of Locally Composted and Imported Green Waste Composts in Oman661
weeds, nutrient contents, plant pathogens and effective-
ness to plant growth and soil amendment [19]. These can
be maintained by the maturation of the compost and va-
ried with the degree of transformation achieved by the
organic materials [17]. Nonetheless, there is no single
method that can be adopted universally to all compost
types due to the wide range of feedstock, composting
processes [20-22], and widely different chemical charac-
teristics of organic wastes [23,24]. On the other hand,
pathogens are commonly present in sewage and household
wastes, both of which are commonly composted [25].
Therefore, composting is an efficient method for destruc-
tion of pathogens to safe and acceptable level for human,
animal and plant uses [21,26].
In Oman, land is the major non-renewable resource
facing the challeng ing threat of soil d egrad ation. Sustain-
able agriculture must be environmentally safe and must
produce adequate amounts of quality foods with mini-
mum purchased fertilizers and rely, as much as possible,
on the renewable resources of the farm itself [27,28].
This is especially important in 90% of the farms that
exist in the third world, where agricultural inputs are
often not available or affordable [27]. Thus, compost is
one of the important lo w cost inputs for meeting nutrient
requirements of crops [29]. In Oman, green waste com-
posts are imported from other countries at high cost and
economic burden, therefore, compost industry was lo-
cally developed for production of high quality composts
with affordable prices to the small village farmers. The
present study was conducted to evaluate the physical,
chemical and microbial properties of locally produced
and imported green waste composts in order to determine
their ability to meet the acceptable standards.
2. Materials and Methods
2.1. Compost Samples
Four locally produced green waste composts (Almuk-
hasib, Growers, Plantex, Super), and four imported com-
posts (Florabella, Mikskaar, Potgrond, Shamrock) were
selected. The samples were collected according to the
Gulf standard number GS0901/1997 [5]. Five samples of
1 kg each were collected from the compost bags, mixed
to form composite samples and were then divided into
four working samples. The samples were kept 5˚C for
further analysis.
2.2. Hydrophysical Characterization
Immediately after collection, the samples were visually
inspected for free flowing, hard lumps, objectionable odor,
and color. The particle size of the composts was determined
according to the Gulf standard number GS01167/2002
using three replicates of 100 g oven dried samples [18].
The samples were placed on 12 mm sieves and shaken
for 5 min at 100 shakes per min [30]. The percentage of
the particles greater than 12 mm was calculated as per-
centage by mass of the remaining materials on the top of
the sieve to the mass of the test sample [31].
For testing the phytotoxicity of the compost samples
and the presence of the viable seeds and plant parts, six
plastic pots (10 × 15 cm) were filled with the compost
samples. Three pots were seeded with 100 seeds of
Phaseolus mungo (mungbean) and the remaining three
pots were kept without seeds. As a control, another 100
seeds of P. mungo were inoculated into plastic trays with
moistened cotton and incubated in the green house of the
Biology Department, Sultan Qaboos University and were
moistened daily for 17 days. The pots were examined
regularly for seed germination.
The hydrogen ion concentration (pH), moisture con-
tents (MC%), electrical conductivity (EC), and water
holding capacity (WHC %) of the composts were mea-
sured using basic standard procedures and techniques
[32]. The pH was determined in triplicate with the pH
meter. For calculation of the moisture content, immedi-
ately after the collection of the samples, moisture content
was determined by the oven method [33]. Replicates of
10 g were placed in glass Petri dishes; soft lumps were
crushed with a spatula and dried at 105˚C in an electric
oven for 16 hours. The moisture content was determined
as a percentage to the initial weig ht.
For detection of electrical conductivity (EC) of the
composts samples, replicates of 2 g from each sample
were mixed in 5 ml of distilled water and the mixture
was filtered through filtration unit with regu lar Whatman
filter paper No. 42 (Whatman International Ltd, Maid-
stone, UK). The electrical conductivity of each filtrate
was measured by electrical conductivity meter.
For determination of the water holding capacity (WHC%)
of the composts, 500 g from each sample were added to
pre-weighed dry sieve and pressed evenly. The samples
were saturated with water, kept covered over-night, and
then the dripped water was wiped off the sieve with fine
tissues. The sie ve with the moistened sample was weig hed,
placed in desiccators, allowed to dry and then reweighed
to calculate the amount of water held by the samples.
The WHC was calculated as percentage mass of the ab-
sorbed water to the mass of the dried sample according
to the gulf standard No. GS01/2002 [18].
2.3. Chemical Analysis
The organic matter (OM) of dried ground samples was
determined by measuring the loss of mass through igni-
tion at 550˚C according to the modified combustion me-
thod suggested by many authors [21,34,35] and adopted
by the Gulf standard NO. GSO1167/2002 [18]. From
each sample, 10 g were used instead of 5 g in order to in-
Copyright © 2011 SciRes. AJPS
Physico-Chemical and Microbial Quality of Locally Composted and Imported Green Waste Composts in Oman
crease the degree of the method accuracy. The samples
were dried to constant mass in an oven at 105˚C and
cooled in desiccators to avoid moisture absorption from
the atmosphere. Ten grams from each sample were put
into an oven-dried porcelain dish, placed in the furnace
and the temperature was increased to 550˚C to convert
the sample into ash. The percentage of the organic matter
was calculated in triplicates as percentage loss of mass to
the mass of the original test sample as a result of ignition.
The ammonia-nitrogen contents of the compost sam-
ples were determined in triplicate using Kjeld ahl method
(Kjeltec Foss, Tecator AB, Hogana, Sweden, N-analy-
zer). For this, 0.5 g from each sample and one keltab
catalyst (SeK2SO4) were added to a digestion tube and
mixed with 10 ml of sulfuric acid. The tubes were di-
gested for 3 hour s, allowed to cool and the concentr ation
of the ammonia was measured.
For the heavy metal concentrations in the compost
samples, 5 g from each sample were mixed with 25 ml of
distilled water and the mixture was filtered with Milli-
pore filter papers. Ten ml from the filtrate were analyzed
with Inductive Couple Plasma (ICP-MS OPTIMA, 3100
RL Spectrometer, Perkin Elmer and Norwalk, USA).
2.4. Enumeration of Microorganisms
The microorganisms including both fungi and bacteria
were isolated from the compost using agar plate method.
One gram from each sample was added to a test tube
containing 9 ml sterile distilled water, vortexed, and se-
rial dilutions were prepared. One ml was aseptically in-
oculated on Potato Dextrose Agar (PDA) for fungal
growth, and similarly Nutrient Agar (NA) was inoculated
for bacterial growth. The inoculated PDA plates were
incubated at 28˚C for 7 days, and the NA plates were
incubated at 37˚C for 48 hours. At the end of th e incuba-
tion period, the number of colony forming units (CFU)
per gram of the compost was calculated. The isolated
fungi were identified using different taxonomic books
and monographs. The presence of coliform bacteria in
the compost samples was screened using the standard
table of the most probable number (MPN) .
2.5. Statistical Analysis
Duncan’s multiple range and one way ANOVA were
used for comparison between the co mpost types with p =
0.05. The analysis was carried out using statistical pack-
age software SPSS (version 11.0).
3. Results and Discussion
3.1. Physical Properties
Four locally produced green waste composts (Almukha-
sib, Growers, Plantex, and Super), and four imported
composts (Florabella, Mikskaar, Potgrond, and Sham-
rock) were examined for their physical, chemical and
microbial properties. The visual inspection showed that
all the samples were physically uniform, free flowing, no
hard lumps, dark brown to black in color, free from ob-
jectionable odor, absent of foreign seeds and particle size
less than 12 mm, except the bad smell of Almukhasib,
light bro wn color of Pl an t ex, and one v i a ble weed seed i n
shamrock (Table 1). These characteristics indicate the
good quality of th e composts, the completion of the d eg-
radation process and compost maturity as suggested by
many authors [23,36]. The bad smell of the composts is
due to production of hydrogen sulfide by sulfur reducing
bacteria or faecal coliforms present in animal dropping
mixed with plant materials without any pretreatment [23].
These odorous fumes contained hydrogen sulfide, me-
thylmercaptan, and methylsulfide, and were present in
large quantities at the initial stage of composting which
decreased rapidly with maturation [19]. The presence of
viable weed seeds and brown color of the composts was
associated with compost immaturity [36].
Seed germination indexes in compost or compost ex-
tracts are common biological methods to evaluate the
degree of the maturity of the composted materials (the
decomposition of phototoxic substance) and acids pro-
duced during the early active composting stages [24,37].
In the present study, the germination percentages of the
mungbean seeds in the tested composts were reported
(Table 1). The germination percentages (in parenthesis)
of the mungbean seeds in each of the corresponding
compost were as follows: Mikskaar (100%), Shamrock
(92%), Florab ella (97% ), Potgr ond (95 %), Plantex (9 8%),
Growers (77%), and 5% for Super and Almukhasib. The
germination levels in locally produced Super (5%), Al-
mukhasib (5%) and Growers (77%) which were lower
than the acceptable index (>90%) can be attributed to the
phytotoxic effects of the organic acid and ammonia toxi-
city produced during the active composting process [37,
38]. Therefore, these composts were not suitable for many
potential uses. In the present study, the ammonia con-
centration of the imported composts were: Mikskaar
(617.9 mg·kg–1), Shamrock (656.5 mg·kg–1), Florabella
(570.5 mg·kg–1), Potgrond (459.4 mg·kg–1), whereas the
locally produced composts showed relatively higher
ammonia concentration for Super (1640.1 mg·kg–1),
Growers (1156.4 mg·kg–1), Almukhasib (804.2 mg·kg–1),
and Plantex (712.4 mg·kg–1) (Table 2). Similarly, the
electrical conductively (EC) which indicates the salt con-
tents of the compost is injurious to plant roots and pre-
vents their growth [39]. Therefore, the low level of ger-
mination of the bean seeds in locally produced composts
may be associated with the high electric conductivity of
Super (10.2 mS·cm–1), Almukhasib (5.4 mS·cm–1) and
Growers (7.5 mS·cm–1) which were higher than the upper
standard limit (4 mS·cm–1) (Table 3). The imported Mik-
Copyright © 2011 SciRes. AJPS
Physico-Chemical and Microbial Quality of Locally Composted and Imported Green Waste Composts in Oman
Copyright © 2011 SciRes. AJPS
Table 1. Physical properties of the locally produced and imported green waste composts.
Locally produced composts Imported c omposts
Properties Almukhasib Growers Plantex Super FlorabellaMikskaar Potgrond Shamrock
Free flowing + + + + + + + +
Hard lumps _ _ _ _ _ _ _ _
Objectionable odor + _ _ _ _ _ _ _
Normal color + + _ * + + + + +
Particle size < 12 mm) + + + + + + + +
Foreign seeds _ _ _ _ _ _ _ +**
Germination % 5 77 98 5 98 100 95 < 90%
*Light brown color compost; **pre s ence of only one germ i nated weed seed.
Table 3. Hydrophysical properties of the locally produced and imported green waste composts.
Locally produced composts Imported c omposts
Properties Almukhasib GrowersPlantexSuperFlorabellaMikskaarPotgrond ShamrockStandards
pH 10.1 a a 7.8 b 3.0 e 8.1 b 5.2 d 6.4 c 5.6 d 5.1 d 5 - 8
Electrical conductivity (mS·cm–1) 5.4 c 7.9 b 0.4 e 10.2 a1.2 d 0.4 e 0.8 e 1.8 d 0 - 4
Moisture content (%) 29 f 35 e 43.7 d 33 e 65 c 74 a 70.5 b 64 c 35 - 60
Water holding capac it y (%) 92 g 200 e 200 e 144 f 400 d 646 c 80 0 a 57 b
aWithin rows, number with different lower case letters differ significantly (P < 0.05).
Table 2. Chemical properties and heavy metals concentration (ppm) in the locally produced and imported green waste com-
Locally produced composts Imported c omposts
Properties AlmukhasibGrowers Plantex Super FlorabellaMikskaarPotgrond Shamrock
Ammonia (mg/kg) 804.2 c b 1156.4 b 712.4 d 1640.1 a570.5 g617.9f 459.4h 656.5e <500
Organic matter % 17 g 22 f 67.6 a 25 e 53.3 d 64 c 66.2 b 65 bc 35
Copper (Cu) 0.05 bc 0.11 a 0.03 c 0.04 c 0.05 bc0.08 b 0.12 a 0.06 bc 150 - 250
Nickel (Ni) 0.03 a 0.03 a 0.04 a 0.04 a 0.02 a 0.03 a 0.03 a 0.03 a 50 - 70
Lead (Pb) 0.02 a 0 .02 a 0.03 a 0.03 a 0.01 a 0.03 a 0.03 a 0.02 a 120 - 150
Cadmium (Cd) 0.08 a 0.04 b 0.03 b 0.08 a 0.08 a 0.03 b 0.03 b 0.02 b 3 - 5
Arsenic (As) 0.04 a 0.04 a 0.05 a 0.05 a 0.04 a 0.03 a 0.05 a 0.04 a 15 - 25
Chromium (Cr) 0.34 e 0.54 b 0.29 f 0.39 d 0.45 c 0.50 b 0.19 g 0.57 a 100 - 150
Zinc (Zn) 114.4 b 60 e 100 c 18.8 g 30.0 f 79.4 d 120 a 120.7 a 350 - 500
Mercury (Hg) 0.0059 a 0.0059 a 0.0059 a0.0059 a0.0059 a0.0059 a 0.0059 a 0.0059 a 1.5 - 3
bWithin rows, number with different lower case letters differ significantly (P < 0.05).
skaar (0.4 mS·cm–1), Shamrock (1.8 mS·cm–1), Potgrond
(0.8 mS·cm–1), Florabella (1.2 mS·cm–1), Potgrond (0.8
mS· c m–1), Florabella (1.2 mS·cm–1), and the locally pro-
duced Plantex compost (0.4 mS·cm–1) displayed higher
levels of germination and their electrical conductivity
was within the standard limit (0 - 4 mS·cm–1) which is
not harmful to the plant growth. In a similar study, it was
found that the electrical conductivity varies considerably
and ranged between 0.12 and 17.08 mS·cm–1 [40]. This
wide range of electrical conductivity expressed the di-
versity of the chemical and microbial properties of the
various compost products.
3.2. Hydrophysical Properties of the Compost
The hydrogen ion concentrations (pH) for the compost
varied at the beginning of composting process and ramped
Physico-Chemical and Microbial Quality of Locally Composted and Imported Green Waste Composts in Oman
from 7.3 to 7.7 as the composting proceeded up to 8.8 -
9.6 [2]. All the screened composts, except the locally
processed Almukhasib, showed acceptable pH value (5 -
8.0) (Table 3 ). However, the highly acidic Plantex (pH 3)
may be due to production of phytotoxic organic acids
during immature composting process which causes im-
mediate growth injuries [38]. Therefore, the addition of
this compost to soil may modify the pH of the final mix
and buffer the soil pH [1].
The moisture contents of the composts ranged between
3.1% - 82.7% and varied considerably with the variation
in the composted materials [40]. The moisture content
values for the compost was considerably high in the first
3 weeks of composting after which it increased signifi-
cantly in the later weeks [1]. Therefore, the addition of
compost provides excellent drought resistance and great
efficient water retention. In the present research (Table
3), the moisture contacts of the imported Shamrock is
64%, followed by Florabella (65%), Potgrond (70.5%)
and Mikskaar (74%), which were higher than the ac-
ceptable limits (35% - 60%), comparable to and locally
produced Plantex (43%), Growers (35%), Super (33%),
and Almukhasib (29%). The moisture content ranged
between 50% - 60% and was considered as the optimal
level for further composting [41]. Therefore, the compost
with higher moisture content will inhibit aerobic degra-
dation and enhance the unpleasant odor from the growth
of anaerobic sulfate reducing bacteria. Yet, the ideal
moisture content depends on how one plans to use the
Water retention cap acity of substrate is generally con-
sidered as the quality determining factor [30,42]. The
highest saturation of the compost is 75% and the good
compost must have high water holding capacity and low
filtration rate for supporting the plant growth. In the pre-
sent study (Table 3), the water holding capacity (W HC% )
of the tested composts was found to be more than their
actual weight. The water holding capacity of the imported
composts ranged between 400% and 800% (Florabella
400%, Mikskaar 646%, shamrock 757%, Potgrond 800%)
which is significantly higher than the locally processed
Almukhasib (92%), Super (144%), Growers and Plantex
compost (200%). Therefore, these composts can be used
separately or mixed with sandy soil of low water holding
capacity if they satisfy the other quality control parame-
ters and the essential requirements for the plant growth.
3.3. Chemical Properties of the Compost
Wide range in the values of the chemical properties of
the compost expressed the diversity of various compost
products and the raw materials used [40]. The total car-
bon contents (TC) for various composts were in the range
of between 16.9% - 51.0%. A approximately 11% - 27%
of the total carton was lost during the 7 days of active
composting, and 62% - 66% during the whole compost-
ing time [43]. In the present results (Table 2), the total
organic matter for the imported Potgrond (66.2%),
Shamrock (65%), Mikskaar (64%), Florabella (53.5%),
and locally produced Plantex (67.6%), were relatively
higher than the standard set by the Gulf countries (35%
and optimum 40% - 60%) [5]. On the other hand, the
organic contents of the locally produced Super (25%),
Growers (22%), and Almukhasib (17%) were below the
standard limit. The high organic matter contents of the
compost indicate the presence of uncomposted organic
materials that can be degraded slowly by microorganisms
and eventually used by higher pl ant s [44].
Heavy metals, as harmful elements, are one of the de-
terminant factors for compost quality [19]. They may
come from sewage water, addition of manure from chic-
ken and other animal dung, and from soil added to the
composted materials. They are released from compost
and negatively affect the plant during the slow degrada-
tion process. On the contrary, compost reduces the mo-
bility of some toxic metals to the plants through forma-
tion of some complexes. In this study, although ther e are
significant variations in the heavy metals concentrations
(Zn, Ni, Pb, Hg, As, Cd, Cr) between the screened com-
posts, the concentration levels of heavy metals in the
compost samples were lower than the acceptable limits
recommended by the Gulf countries [5]. Similar standard
limits were adopted in Germany [45], and Canada [46].
Nonetheless, the high contents of heavy metals may be
due to addition of these metals to animal feeds [19] or
contamination during the composting process [47].
3.4. Microbial Estimates of the Compost
It is natural to have large numbers of bacteria and fungi
in the compost during composting process and they are
essential for slow degradation of partially decomposed
organic materials [1]. The pathogenic fungi and bacteria
were normally detected in composted household wastes,
and sewage sludge [25]. Nonetheless, composting is an
efficient method for destruction of pathogenic microor-
ganisms in the compost to a safer level for humans, ani-
mals and plants [21,26]. Reasonable amounts of micro-
organisms are still present in the compost at maturity [1].
In the present study, the average of the bacterial colony
forming unit per gram of the compost were as follows:
Plantex (260 cfu/g), Almukhasib (280 cfu/g), Shamrock
(330 cfu/g), Growers (1490 cfu/g), Potgrond (1720 cfu/g),
Super (1740 cfu/g), Mikskaar (2580 cfu/g), and Flora-
bella compost (2870 cfu/g), whereas the colony forming
unit of fungi in the compost were Almukhasib (10 cfu/g),
Shamrock (30 cfu/g), Super (190 cfu/g), Florabella (200
cfu/g), Mikskaar (270 cfu/g), Plantex (360 cfu/g), Pot-
Copyright © 2011 SciRes. AJPS
Physico-Chemical and Microbial Quality of Locally Composted and Imported Green Waste Composts in Oman
Copyright © 2011 SciRes. AJPS
grond (1800 cfu/g), and Growers (2800 cfu/g) (Table 4).
It is evident that the imported Florabella, Mikskaar, and
the locally produced Super composts have the highest
bacterial colonies, whereas the imported Potgrond, and
the locally produced Growers and Plantex contain rela-
tively high numbers of fungal colonies. These large num-
bers of bacterial and fungal colonies were responsible for
the slow degradation of the organic matter as suggested
by several authors [21,23,48]. Most of the fungi involved
in the slow degr adation of the screened composts be long
to the thermophilic genus and moisture tolerant Asper-
gillus. In the present study (Table 4), A. niger was the
predominant species recovered from all compost types
(100%) at the later stage as reported by many authors [1,
48,49]. This fungus was followed by A. fumigatus (75%),
A. sparsus (50%), yeasts (50%), A. flavus (37.5%),
where the remaining fungi such as A. restrictus, A. ver-
sicolor, Cladosporium spp., and Penicillium spp. were
recovered from 50% of the compost types, and to a lesser
extent Acremonium sp. and A. ochraceous (12.5%). In
similar studies, different species of Aspergillus and Peni-
cllium were isolated from the compost [1,8,48].
Various pathogenic bacteria were isolated from diffe-
rent composts and composted materials [1,21]. The ma-
jor faecal coliforms found in the raw materials composed
of Escherichia coli, where in the finished compost the
majority of the faecal coliforms were probably of non-
faecal origin [21]. Therefore, the species composition of
the faecal coliforms can vary considerably depending on
the composted materials and composting system. In the
present results, the most probable number (MPN) was
used to determine the faecal contamination of the com-
posts. Our findings (Table 4) showed that locally pro-
duced Almukhasib was highly contaminated with coli-
forms (1100 cfu/g), followed by the imported Florabella
(480 cfu/g), Potgrond (240 cfu/g), and to a lesser extent
by locally produced Plantex (150 cfu/g), Growers (93
cfu/g), Super (43 cfu/g), and the imported Mikskaar (43
cfu/g) and Shamrock (23 cfu/g). The presence of higher
number of coliforms in the locally processed Almukhasib,
followed by imported Florabella and Potgrond indicates
the possible contamination of these composts with sew-
age water or other animal products during composting
process, which was confirmed by isolation of coliform
bacteria as suggested by many researchers [1,21]. There-
fore, there is a high possibility of transmission of serious
diseases during handling and usage of these composts in
addition of expected infestation of the cultivated plants
with serious pathogenic bacteria.
4. Conclusions
It is apparent that all the investigated composts were free
from most of the physical constraints, except the light
brown color of Plantex, bad smell of Almukhasib and
viable seed in Shamrock which indicates immaturity of
the composts. The locally processed composts contain
phytotoxic acids, ammonia, and with high electrical con-
ductivity which affect the seed germination. The mois-
ture contents of the imported Florabella, Mikskaar, Pot-
grond, and Shamrock were higher than the locally pro-
Table 4. Microbial properties of the locally produced and imported green waste composts.
Locally produced composts Imported c omposts
Properties Almukhasib GrowersPlantexSuper FlorabellaMikskaar Potgrond Shamrock
Bacteria (CFU/g) 280h *c 1490 e 260 g 1740 c2870 a 2580 b 1720 d 330 f
Fungi (CFU/g) 10 h 2800 a 360 c 190 f 200 e 270 d 1800 b 30 g
MPN (CFU/g) 1100 a 93 e 15 0 d 43 f 480 b 43 f 240 c 23 g
Acremonium sp. - - - - - - + -
Aspergillus flavus - - + + - - - +
A. fumigatus - + + + - + + +
A. niger + + + + + + + +
A. ochraceous - - + - - - - -
A. sparsus + - - + - + - +
A. restrictus - - - + - + - -
A. versicolor - - - - + - - +
Cladosporium sp. - + - - - - + -
Penicillium sp. - - - + + - - -
Yeasts + + - - - - + +
cWithin rows, number with different lower case letters differ significantly (P <0.05).
Physico-Chemical and Microbial Quality of Locally Composted and Imported Green Waste Composts in Oman
duced Almukhasib, Growers, Plantex, and Super com-
posts. The water holding capacity was significantly higher
in all composts and meets the standard limit. The total
organic matters were higher in the imported composts in
comparison with the locally composted materials. The
heavy metals contents of all composts were below the
acceptable limits. The composts were contaminated with
variable levels of saprophytic fungi and colifor m bacteria.
It is evident the imported composts were relatively better
than the locally produced composts, however, none of
them meet most of the recommended characteristics [50].
Therefore, they can not be used directly and without any
treatment as media for plant growth, soil biofertilizer and
for soil amendment. Therefore, there is a high necessity
for setting detailed legislation, regu lation policies, proper
testing methods, quality control measurements, and strong
quarantine regulations for exportimport and local produ-
ction of green waste composts. Attention should be given
to the local production of high quality composts which
serve the environment, waste management, recycling in-
dustry and satisfaction of the local markets.
5. Acknowledgements
We thank the Department of Biology, College of Science,
Sultan Qaboos University for providing space and facul-
ties to carry out this research. Dr. Tom Hughes of Uni-
versity of Nizwa Writing Center proof read the English
of this manuscript. Dr. Peter Cowan of the Department of
Biological Sciences and Chemistry, University of Nizwa,
improved the scientific content of the article.
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