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Evaluation of Organic Wastes forCompostingZahir Shah a , Yaakob Mohd Jani b & Farmanullah Khan aa Department of Soil and Environmental Sciences , University ofAgriculture , Peshawar , Khyber Pakhtunkhwa , Pakistanb School of Social, Development and Environmental Studies ,National University of Malaysia , Bangi , MalaysiaAccepted author version posted online: 16 Jan 2014.Publishedonline: 30 Jan 2014.

To cite this article: Zahir Shah , Yaakob Mohd Jani & Farmanullah Khan (2014) Evaluation of OrganicWastes for Composting, Communications in Soil Science and Plant Analysis, 45:3, 309-320, DOI:10.1080/00103624.2013.861909

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Communications in Soil Science and Plant Analysis, 45:309–320, 2014Copyright © Taylor & Francis Group, LLCISSN: 0010-3624 print / 1532-2416 onlineDOI: 10.1080/00103624.2013.861909

Evaluation of Organic Wastes for Composting

ZAHIR SHAH,1 YAAKOB MOHD JANI,2

AND FARMANULLAH KHAN1

1Department of Soil and Environmental Sciences, University of Agriculture,Peshawar, Khyber Pakhtunkhwa, Pakistan2School of Social, Development and Environmental Studies, National Universityof Malaysia, Bangi, Malaysia,

Management of organic wastes is essential to reduce environmental pollution andincrease resources of plane nutrients for crop production. This study was undertakento evaluate major organic wastes produced in northwestern Pakistan for characteris-tics that are useful for composting. Organic wastes such as manures, municipal wastes(MW), crop residues, fruit/vegetable wastes, and yard wastes contained large reservesof nutrients. Manures had high nitrogen (N) and crop residues had low N. Crop residueswere relatively dry (7–12% moisture); MW, poultry manure, sheep manure, leaves,and city garbage were moderately moist (27–47% moisture), whereas cattle manure(CM), fruit and vegetable wastes, and grass clippings were wet (62–89% moisture).The compost developed from mixing MW with CM matured early and had low C/Nratio compared with either source alone. These results suggested that MW could beconverted into compost when mixed with CM. The inoculation of wastes with effectivemicrobes (EM) was ineffective in expediting the process of composting.

Keywords C/N ratio, compost, environment, nutrients, organic wastes

Introduction

Waste management is necessary not only to reduce effects on the environment, health, oraesthetics but also to recover resources such as energy and plant nutrients. Composting ofmunicipal wastes (MW) is one of the management practices for successful utilization ofthese wastes in agriculture (He, Logan, and Traina 1995; Chefetz et al. 1996). Millions oftons of organic wastes, such as municipal solid wastes (MSW), various agro-based indus-trial solid wastes (ISW), and farm wastes are produced annually in the northwestern partof Pakistan (Shah and Anwar 2003; Shah et al. 2005; Shah and Riazullah 2003a). Thesewastes contain considerable reserves of plant nutrients (Shah et al. 2007) with insignificantconcentrations of toxic heavy metals (Shah and Riazullah 2003b). The industrial effluentsin the area are reported to have heavy metals in them beyond the permissible limits (Tariq,Ali, and Shah 2006).

Although some organic wastes in this part of the world are utilized as organic manureson agricultural lands, most of them are burned, landfilled, or dumped aboveground closeto residential areas. This creates numerous environmental problems, such as emission of

Received 28 September 2011; accepted 6 June 2013.Address correspondence to Zahir Shah, Department of Soil and Environmental Sciences,

University of Agriculture, Peshawar, Khyber Pakhtunkhwa, Pakistan. E-mail: zahirshah@aup.edu.pk

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310 Z. Shah, Y. M. Jani, and F. Khan

methane (CH4), carbon dioxide (CO2), nitrogen oxides (NOx), sulfur oxides (SOx) andother greenhouse gases, and other nuisances including generation of odors and attractionof mosquitoes. Water quality also can be impaired by runoff or leaching of contam-inants from untreated waste. These wastes can be converted into a valuable productthrough composting. Composting and the use of compost offer several potential benefitsincluding improved manure handling, enhanced soil tilth and fertility, and reduced envi-ronmental risk. The composting process also produces heat, which drives off moistureand destroys pathogens and weed seeds. With proper management, the composting pro-cess produces a product that has a minimum of odors and closely resembles a humus-likematerial.

It is becoming accepted that organic wastes should be recycled (Clapp, Hayes, andCiaratta 2007). For sustainable development, resources must be recycled, and that actionespecially applies for organic materials of municipal and agro-industrial origins. Soils inmany parts of the world in general and Pakistan in particular are increasingly stressedfrom long-term cultivation practices, and the resulting losses of soil carbon (C) are lead-ing to inevitable degradations of soil structure (Clapp, Hayes, and Ciaratta 2005), lossesof soil fertility and productivity (Shah et al. 2003, 2013; Shafi et al. 2007; Bakht et al.2009), and increased soil erosion. In this context, Senesi et al. (2007) stressed how thescope of organic amendments of various origins may be used to increase or to restorethe organic matter in organically poor or depleted soils to maintain and/or increasecrop production and reduce soil exposure to degradation, erosion, desertification, andpollution.

Before applying organic waste materials to soil, it is essential to ensure that thesematerials do not pose any danger to humans, animals, or the environment. Organic soilamendments are of little value if these are injurious to the crop, its consumers, or thesoil microbial populations or if these amendments are not transformed to humus materialsin the soil environment. Thus, it is essential to ensure the absence of undesired organicand inorganic substances, especially phytotoxic compounds, pathogens, heavy metals, andtoxic chemicals. Many of the phytotoxic substances found in organic wastes can be inacti-vated through composting (Barker 1997). Thus the development of composting as a usefulbiological technology in transforming organic wastes into suitable agricultural productshas been increasing worldwide (Senesi and Bruntti 1996).

This study was undertaken to determine important characteristics of organic wastesproduced in northwestern Pakistan and to study composting of municipal wastes and cattlemanure in the absence or presence of a product called effective microbes (EM).

Materials and Methods

Organic wastes that are common in this region were collected from various parts innorthwestern areas of Pakistan during 2003–2005 and analyzed for important character-istics such as total nitrogen (N), total carbon (C), C/N ratio, and water content. Thesewastes include cattle, poultry (both broiler and layers), and sheep manures; municipalsolid wastes (i.e., city garbage); crop residues and fruit–vegetable processing wastes (i.e.,corn stalk, rice straw, sugarcane bagasse, wheat straw, fruit wastes, vegetable wastes);and grass clippings and leaves. The municipal wastes and cattle manure were tested forcomposting in the absence or presence of a product called EM, which contains selectedspecies of microorganisms including predominant populations of lactic acid bacteria andyeast, and smaller numbers of photosynthetic bacteria, actinomycetes, and other typesof microorganisms (EM Technology, Lahore, Pakistan) using the following treatments:

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Organic Wastes for Composting 311

(1) municipal wastes, (2) cattle manure, (3) municipal wastes + cattle manure, (4) munic-ipal wastes + EM, (5) cattle manure + EM, and (6) municipal wastes + cattle manure+ EM. Each treatment was replicated three times in a randomized complete blockdesign.

Preparation of Compost Feedstock

Waste samples were analyzed initially for water content and then air dried. After drying, allsamples except manures were shredded into smaller pieces (1/2 to 3/4 inches) mechanically.The waste samples were then analyzed for total N, total C, and C/N ratio to develop rawmaterial recipes for composting. Where two waste materials were combined, they wereblended together in such a ratio to have C/N ratio of 30 and water content 50% by weightin the final mix using the following expression:

Desired C/N ratio = (C in 1 kg manure) + S × (C in 1, kg MW) / (N in 1 kg manure)

+ S × (N in 1 kg MW)

where S is the amount of MW to be mixed with 1 kg of manure.The water content was maintained at around 50%. When the two materials were mixed,

the water content (MC) in the mix was determined as follows:

MC = (weight of water in 1 kg manure) + weight of water in MW to be mixed with

manure)/total weight (manure + MW)

Water was added if needed to maintain the desired water level in the mix. For EMtreatments, for every 1 kg organic waste, 3 mL of EM solution was mixed with 9 mL ofsugarcane molasses and 288 mL of clean warm water and then mixed well with the organicwaste.

After preparing waste materials in this manner, composting was carried out in woodenbins measuring 4′ × 4′ × 4′ under aerobic conditions. The bins were filled to three quartersof the bin volume with the desired waste samples. The composting materials in the binswere turned over initially once each week for the first 30 days, then twice during the next30 days, and finally once after 30 days. The composting continued for 120 days. Waterwas added when needed to maintain water level of about 50% in the composting materials.Temperature of the composting materials was measured at intervals of 1, 5, 10 20, 30, 40,50, 60, 80, 100, and 120 days of composting.

Composting was determined complete when (i) temperature of the compost had fallento the ambient level, (ii) compost had attained the characteristic dark brown or black color,(iii) it did not emit any more foul odors, and (iv) volume of the finished compost wasreduced by about 50%.

At the end of the experiment, general characteristics (temperature, color, odor, volume)of the compost were recorded. Compost samples were taken from each bin and analyzedfor some chemical characteristics [pH, electrical conductivity (EC), C/N ratio], nutrients[N, phosphorus (P), potassium (K), zinc (Zn), copper (Cu), iron (Fe), manganese (Mn)],and heavy metals [nickel (Ni), chromium (Cr), lead (Pb), cadmium (Cd)].

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312 Z. Shah, Y. M. Jani, and F. Khan

Laboratory Analysis

Estimation of Total Carbon (C). For estimation of total C in compost or in feedstocks,a 10-g sample was taken in a beaker and kept in oven at 80 ◦C for 72 h. After cool-ing in a desiccator, the sample was weighed to determine water content in the sampleand then transferred to furnace to burn to ash at 500 ◦C for 6–12 h. After igni-tion, the samples were cooled in a desiccator, and then the weight of ash remained inthe beaker was recorded. The total C was determined using the following expression(Rynk 1992):

%C = (100 − %ash) /1.8

Determination of Water Content. Water content in waste samples was determinedgravimetrically. For this, known weight of sample was placed in an air-circulated ovenat 80 ◦C and loss in weight was recorded after 72 h. The water content was calculated on awet basis as follows:

Water content (%) = [(Moist weight – Dry weight)/Moist weight] × 100

Determination of N, P, K, and Heavy Metals. Total N in waste samples was deter-mined by the Kjeldhal method (Bremner 1996). For determination of other elements inwaste/compost samples, the nitric acid (HNO3)–perchloric acid (HClO4) wet digestionprocedure as described in Ryan, Estefan, and Rashid (2001) was used. In this method,1 g waste/compost sample was treated overnight with 10 ml 2:1 nitric–perchloric acidmixture followed by digestion on block digester initially at low temperature and thenat 235 ◦C until digestion was completed. Phosphorus in the digest was determined onspectrophotometer (UV-1700 spectrophotometer, Shimadzu Corporation, Kyoto, Japan) at880 nm using the ascorbic acid method (Kuo 1996). Potassium in the digest was deter-mined on flame photometer (Jenway PF-7, Bibby Scientific Limited, Staffordshire, UK)as described in Ryan, Estefan, and Rashid (2001). Micronutrients and heavy metals inthe digest were determined on an atomic absorption spectrometer (Perkin Elmer model2380, Perkin-Elmer, Waltham, Mass., USA) as described in Ryan, Estefan, and Rashid(2001).

Determination of pH and EC. Compost or feedstocks were assessed for pH (Thomas 1996)and EC (Rhoades 1996) in a 1:5 material/water suspension (v/v) using pH meter or ECmeter, respectively.

Statistical Analysis

Data obtained in the experiment were subjected to analysis of variance (ANOVA) appro-priate to the experimental design. Means were compared using the least significancedifference (LSD) test at 5% level of probability. Microsoft Excel (Microsoft Corporation,Redmond, Wash., USA) was used to determine means and standard deviation of surveydata.

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Results and Discussion

Characteristics of Organic Wastes

Manures. The results showed that all manures were rich in N, and the C/N ratios wereless than 20:1 (Table 1). The poultry (layers) manures were highly rich in N and somesamples had N content as high as 8.24%. On average, N levels were as follows: layersmanure 6.32%, cattle manure 2.86%, sheep manure 2.46%, and broiler manure 2.58% N.The average C/N ratios were 8 for layers manure, 13 for broiler manure, 16 for cattlemanure, and 19 sheep manure. Results further revealed that cattle manures were generallymore moist than the other manure whereas manure from broiler had relatively low moisturecontent. On average, cattle manure had 80% water, layers 66%, sheep manure 65%, andbroiler manure 37%. These results suggested that all manures in general and cattle manuresin particular could be ideally mixed with waste materials containing relatively low moisturecontents.

Municipal Wastes. Two types of wastes in this category [i.e., house refuse (food mix,papers, and others) and city garbage] were analyzed for the desired characteristics andthe results obtained are given in Table 1. The results revealed that house wastes generallyhad more N and lower C/N ratios than the city garbage. Nitrogen content in house refuseranged from 0.54 to 2.25% with an average of 1.29% compared with 0.23 to 1.35% (aver-age 0.96%) in city garbage. Similarly, the C/N ratios were 30–75 (average 52) in houserefuse and 49 to 105 (average 67) in city garbage. The house refuse was generally moremoist than the city garbage. The moisture content in house ranged from 59 to 78% (average72%) and in city garbage ranged from 41 to 60% (average 47%). These results suggestedthat either house refuse or city garbage or both materials could be mixed with materialssuch as manure to make a compost.

Crop Residues, Fruit, Vegetable and Yard Wastes. The wastes selected in this category werecorn stalks, rice straw, wheat straw, sugarcane bagasse, fruit wastes, vegetable wastes, andyard wastes. The results obtained on total N, C/N ratio, and water content in these materialsare given in Table 2. The results revealed that grass clippings, fruit wastes, and vegetablewastes had greater N contents than the other waste materials and hence had lower C/N

Table 1Nitrogen concentration, C/N ratio, and water content in selected manures and municipal

wastes

Total N (%) C/N ratio Water content (%)

Waste material Range Mean SDa Range Mean SD Range Mean SD

Cattle manure 2.66–3.58 2.66 0.30 13–18 16 1.63 70–83 80 3.69Broiler manure 1.44–3.73 2.58 0.65 10–17 13 2.25 20–38 31 5.38Layer manure 4.15–8.24 6.32 1.40 4–12 8 2.67 59–78 66 9.07Sheep manure 1.22–3.75 2.46 0.91 11–23 19 3.57 57–60 65 6.81House refuse 0.54–2.25 1.29 0.66 30–75 52 15.45 59–78 72 5.50City garbage 0.23–1.25 0.96 0.29 49–105 67 18.51 41–47 47 5.82

aSD, standard deviation.

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Table 2Nitrogen concentration, C/N ratio, and water content in selected crop residues, fruit,

vegetable, and yard wastes

Total N (%) C/N ratio Water content (%)

Waste material Range Mean SDa Range Mean SD Range Mean SD

Corn stalks 0.54–0.75 0.65 0.18 59–74 65 5.82 10–12 11 0.80Rice straw 0.15–0.42 0.36 0.09 113–1120 121 25.10 7–12 11 1.10Wheat straw 0.35–0.57 0.48 0.10 95–142 122 12.45 9–11 10 0.95Sugarcane bagasse 0.16–0.79 0.51 0.08 95–160 112 16.48 59–81 68 4.62Fruit wastes 0.85–2.47 1.36 0.65 20–49 40 4.28 62–83 80 6.45Vegetable wastes 2.45–3.82 2.86 0.71 10–17 14 2.51 58–89 85 5.71Grass clipping 2.12–6.88 3.13 0.92 10–30 19 2.98 69–87 82 5.68Leaves 0.36–1.37 0.98 0.32 35–70 50 4.40 27–46 38 3.78

aSD, standard deviation.

ratios. The C/N ratio ranged from 10 to 30 in grass clippings, 10 to 17 in vegetable wastes,and 20 to 49 in fruit wastes with averages of 19, 14, and 40, respectively. The C/N ratios incrop residues were generally wider and always greater than 59. Among crop residues, cornstalks had relatively more N than other crop residues and hence had relatively narrowerC/N ratio (59–74) than other residues (95–1120). Rice straw had C/N ratio as wide as1120 in some samples. The average C/N ratios were 50 for leaves, 65 for corn stalks,112 for sugarcane bagasse, 121 for rice straw, and 122 for wheat straw. The results showedthat fruit wastes, sugarcane bagasse, grass clippings, and vegetable wastes were more moist(58–89%) than the other waste materials (7–12%). On average, water contents were 82% ingrass clippings, 80% in fruit wastes, 85% in vegetable wastes, 68% in sugarcane bagasse,38% in leaves, 11% each in corn stalks and rice straw, and 10% in wheat straw.

These results suggested that most of the crop residues such as wheat straw, rice straw,sugarcane bagasse, and corn stalks can be mixed with materials having narrow C/N ratiossuch as manures for composting. It was also observed that some wastes such as fruit wastes,vegetable wastes, and sugarcane bagasse had more water content and can be mixed withdrier materials for composting when fresh.

Composting of Selected Organic Wastes Feedstocks

The organic wastes selected for composting feedstocks were cattle manure and municipalwastes. The detail analysis of selected wastes showed that cattle manure was more moistand rich in N contents than municipal waste (Table 3). The C/N ratio was thus narrower incattle manure than municipal waste. Salt contents were generally greater in cattle manurethan in municipal wastes, as indicated by EC and sodium (Na) levels.

Characteristics of Compost Prepared From Cattle Manure and Municipal WastesFeedstocks

Temperature of Composting Pile. Temperatures recorded during the composting processfor 120 days are presented in Table 4. The temperature in all six composting bins atday 1 was 12 or 13 ◦C as it was the month of February. It was, however, noticed that

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Table 3Important characteristics of fresh cattle manure and municipal wastes used

for composing in this study

Characteristic UnitFresh cattle manure

(dry-wt basis)Municipal waste

(dry-wt basis)

Water % 82.9 38.3Solids % 17.1 61.7pH (1:5 H2O) — 8.23 7.2EC dSm−1 1.80 0.20Total C % 50.0 68Total N % 2.00 0.85C/N ratio w/w 25 80Phosphorus (P) % 0.62 0.21Potassium (K) % 1.04 0.44Sodium (Na) % 0.59 0.25Calcium (Ca) % 2.51 2.46Magnesium (Mg) % 0.59 0.41

Table 4Time–temperature patterns for composting municipal waste (MW) and cattle manure

(CM) in the absence or presence of effective microbes (EM) amendments during 120 days(February–May)

Temperature (◦C)

Treatment Day 1 Day 5 Day 10 Day 20 Day 30 Day 40 Day 50 Day 60 Day 80 Day 100 Day 120

MW 12aa 31c 32c 34c 34c 34c 34c 34b 28b 27b 27aCM 13a 37b 40b 43b 43ab 40b 40b 36b 27b 26b 27aMW + CM 13a 41ab 40b 42b 42b 40b 40b 36b 29b 26b 28aMW + EM 16a 48a 50a 49a 50a 50a 49a 46a 43a 42a 28aCM + EM 13a 42ab 42b 42b 43ab 40b 40b 37b 27b 27b 27aMW + CM

+ EM16a 48a 51a 48a 49a 50a 48a 46a 44a 41a 27a

aMeans followed by different letter(s) within columns differ significantly (P < 0.05).

temperatures increased variably but substantially in all composting bins after 5 days. Thetemperature in municipal waste alone bin rose to a maximum of 34 ◦C at day 20 andremained the same for up to 60 days, and then dropped to 28 ◦C and eventually to 27 ◦Cby the end of 120 days. These results revealed that considerable increase in temperatureof composting bins began before day 5 and the gradual decline in temperature began after50 or 60 days. The temperatures during 5–100 days were significantly (P < 0.05) great-est in bins where municipal wastes were mixed with cattle manure. The inoculation withEM did not bring any significant change in temperature of composting bins. Since therelease of heat is related directly to the microbial activity, temperature is a good processindicator. Based on this criterion, the composting process was faster in manure or manureplus municipal wastes treatments than in the municipal wastes alone treatment. It was,however, observed that temperature of composting bins did not reach to thermophilicrange, probably due to the relatively small size of the piles.

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Table 5Some characteristics of compost prepared from municipal waste (MW) and cattle manure

(CM) with or without EM

CompostpH

(1:5)EC

(dS/m)Total C

(%)Total N

(%)C/Nratio P (%)

K(%)

MW 7.1ca 0.2a 54bc 1.20c 45a 0.25b 0.68aCM 7.8a 1.6a 48c 1.85ab 26b 0.67a 1.22aMW + CM 7.3bc 0.8a 50c 1.73b 29b 0.58a 0.93aMW + EM 7.6a 0.2a 62a 1.25c 50a 0.38b 0.62aCM + EM 7.4b 1.4a 49c 1.90a 26b 0.50ab 0.96aMW + CM + EM 7.5b 1.8a 59ab 2.06a 29b 0.92a 1.13a

aMeans followed by different letter(s) within columns differ significantly (P < 0.05).

General Characteristics of Finished Compost. The general characteristics of compostsrecorded by the end of 120 days were temperature, color, odor, and volume. The tempera-ture recorded by the end of 120 days of composting was almost uniform in all compostingbins (26–28 ◦C). Color of the finished compost was black or dark brown to black. Therewas very little odor in all but not in the manure plus municipal wastes bins. The volumewas reduced in all composting bins, but the reduction varied with the composting materi-als. The volume reduction was measured from reduction in height of composting piles. Thevolume in municipal waste–only treatment reduced by about 20 or 25%. Volume reductionin manure-only treatments was about 35 or 40%. However, where manure and munici-pal wastes were mixed, the volume was reduced by 45 to 47%. The decrease in volumecould be attributed to loss of organic substances upon degradation of organic materials bymicroorganisms (Grigatti, Ciavatta, and Gessa 2004). These results indicated that manurealone or manure plus municipal wastes was converted to compost but municipal wasteswithout mixing with other materials did not convert into compost. The temperature recordgives similar indications.

Chemical Characteristics of Finished Compost. The composts from different compost-ing bins were analyzed for important chemical characteristics and the results obtained arepresented in Table 5. The pH of all compost was on the alkaline side, but the electrical con-ductivity in none of the compost was greater than 2.0 dS m−1. The pH was significantlygreatest (7.8) for compost formed alone from cattle manure. The significantly lowest pH(7.1) was recorded in the municipal waste compost. However, the EC of composts did notdiffer significantly. The alkaline value is attributed to proton consumption during decom-position of volatile fatty acids and to mineralization of organic N to ammonium (NH4)-N(Beck-Friis et al. 2003). Values of pH and EC achieved at 120 days of compost formedfrom municipal wastes or cattle manure were within the range acceptable for plant growthrecommended by Rynk (1992) and similar to other values reported for municipal organicwastes (Cooperband and Middleton 1996; Tognetti et al. 2005).

The maximum N content of 1.9% was recorded in compost prepared from cattlemanure + EM, whereas the lowest N content of 1.20% was in municipal wastes compost.These differences were statistically significant (P < 0.05). Similarly, the significantly low-est C/N ratio (26:1) was recorded for compost prepared from cattle manure. However, theC/N ratios of composts prepared from cattle manure alone or cattle manure + municipal

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Organic Wastes for Composting 317

waste were at par with each other. The C/N ratio for the compost prepared from munici-pal waste alone was significantly greatest than that from cattle manure. The significantlygreatest P content of 0.92% was obtained in compost prepared from cattle manure (CM)+ MW + EM. The municipal waste alone had the significantly lowest P content (0.25%).Although statistically nonsignificant, the maximum K content of 1.22% was obtained incompost prepared from CM alone followed by 1.13% in CM + MW + EM compost. Thecompost from MW alone had the lowest K content (0.68%). Sager (2007) reported thatthe amount of K decreased in the order pig manure > cattle manure > pig dung > poultrydung > compost. Similarly the greatest concentrations of P were found in pig dung and pigmanure. The K/P ratio was greatest in cattle manure and lowest in pig and poultry dung.These results showed that compost prepared from manure was rich in major nutrients.

Micronutrient and Heavy Metal Concentrations in Finished Compost. The concentrationsof micronutrients (Zn, Cu, Fe, Mn) obtained in the finished compost are presented inTable 6. The significantly lowest Zn concentration of 63.6 mg kg−1 was recorded in thecompost prepared alone from municipal waste. The significantly greatest Zn concentra-tion of 82.4 mg kg−1 was observed in the compost formed alone from cattle manure. Thetotal Cu content was also lowest (11.2 mg kg−1) in the compost prepared from municipalwaste and greatest (64.5 mg kg−1) in the compost prepared alone from cattle manure. Allcomposts were quite rich in Fe, containing over 6200 mg kg−1. The greatest Fe content of7620 mg kg−1 was present in compost formed from cattle manure followed by 6800 mgin compost formed from cattle manure plus municipal wastes. However, differences in Feconcentration between different composts were nonsignificant (P < 0.05). The Mn con-centration ranged from 185 mg kg−1 in compost formed from cattle manure to 254 mg incompost from municipal waste and these differences were statistically nonsignificant. Thecomposition of compost prepared from municipal solid waste, however, varies from placeto place. Saha et al. (2010) reported that heavy-metal contents in composts from biggercities (>1 million population) were greater by about 86% for Zn, 155% for Cu 194% forCd, 105% for Pb, 43% for Ni, and 132% for Cr than those from smaller cities (<1 mil-lion population). The same study showed that composts prepared from source-separatedbiogenous wastes contained, on average, lower concentrations of heavy metals—Zn (by63%), Cu (by 78%), Cd (by 64%), Pb (by 84%), Ni (by 50%), and Cr (by 63%)—comparedto those prepared from mixed waste. Sager (2007) reported that Zn ranged from 49 to405 mg kg−1 in cattle manure and from 92 to 739 mg in poultry manure, Cu ranged from

Table 6Micronutrient and heavy-metal concentrations (mg kg−1) in compost prepared frommunicipal waste (MW) and cattle manure (CM) in the absence or presence of EM

Compost Zn Cu Fe Mn Ni Cr Pb Cd

MW 63.6ba 16.6b 6662a 254a 52.4a 18.8c 95.0a 7.2aCM 82.4a 64.5a 7620a 185b 12.5c 58.3a 26.4d 11.1aMW + CM 70.4ab 44.5ab 6800a 259a 36.4b 37.0b 45.8c 12.8aMW + EM 74.5a 43.1ab 6204a 218ab 47.2a 38.4b 78.9ab 9.1aCM + EM 60.5b 42.8ab 6440a 280a 29.7bc 35.9b 42.7cd 7.8aMW + CM + EM 71.8ab 36.6ab 6742a 227ab 43.7ab 41.1ab 72.2b 6.9a

aMeans followed by different letter(s) within columns differ significantly (P < 0.05).

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318 Z. Shah, Y. M. Jani, and F. Khan

8 to 117 mg in cattle manure and from 28 to 182 mg in poultry manure, and Mn rangedfrom 40 to 312 mg in cattle manure and from 91 to 807 mg in poultry manure. Theseresults showed that compost prepared either from manure alone, municipal wastes alone,or municipal wastes combined with manure contained all the four essential micronutrients(Zn, Cu, Fe, Mn), of which Fe was present in the greatest concentration followed by Mn,Zn, and Cu.

The concentration of heavy metals in the finished compost showed significant vari-ation. The concentrations of Ni, Pb, and Cd were generally greater in compost preparedfrom municipal wastes, whereas Cr and Cd were greater in compost prepared from cat-tle manure. The Ni concentration ranged from 12.5 mg kg−1 in compost prepared fromcattle manure to 52.4 mg in compost prepared from municipal waste. The Cr concentra-tion ranged from 18.8 mg kg−1 in compost prepared from municipal waste to 58.3 mg incompost prepared from cattle manure. The lowest concentration of 26.4 mg kg−1 of Pbwas recorded in compost prepared from cattle manure, whereas the greatest concentrationof 95.0 mg was found in compost prepared from municipal waste. The Cd concentrationranged from 7.2 mg kg−1 in the compost of municipal waste to 12.8 mg in the compost ofcattle manure and municipal wastes.

These results suggested that municipal waste compost was generally high in Ni andPb, whereas cattle manure compost was high in Cr and Cd. Greater concentrations of Niand Pb in the municipal wastes compost could be attributed to the presence of batter-ies (mainly disposable), traces of kitchen utensils, and paints/dyes used in some localindustries. Greater Pb concentrations in compost may result from atmospheric deposi-tion as soils usually get a much greater Pb load from atmospheric precipitation thanfrom fertilizers (Sager 1997; Sager and Scholger 2002). Shah and Riazullah (2003b) alsofound higher concentrations of heavy metals in different manures. However, the qual-ity of compost prepared from municipal solid wastes varies considerably from place toplace. Silva et al. (2007) found that the municipal wastes compost obtained from themain composting plant in Galicia (Spain) had a lower C/N ratio (15) than peat (84) orpine bark (211), and the nutrient concentrations of composted urban waste or manurewere much greater than those of peat or composted pine bark. Saha, Panwar, and Singh(2010) investigated physicochemical properties, fertilizing potential, and heavy-metal pol-luting potentials of municipal solid waste produced in different cities in India and foundthat, except for a very few samples, samples had normal pH and EC. However, com-posts prepared from source-separated biogenous wastes contained, on average, greaterorganic matter (by 57%), total N (by 77%), and total P (by 78%) but lower concen-trations of heavy metals Zn (by 63%), Cu (by 78%), Cd (by 64%), Pb (by 84%),Ni (by 50%), and Cr (by 63%) than those prepared from mixed waste. However,organic matter and major nutrients N and P contents in MSW composts were gener-ally low as compared with other composts. Saha, Panwar, and Singh (2010) furtherstated that as per regulatory limits of different countries, very few compost sampleswere in marketable classes and some samples were found suitable for some restricteduse.

Conclusions

Among wastes, manures had high N contents and low C/N ratios. Crop residues, on theother hand, had high C and C/N ratios. Corn stalks, wheat straw, and rice straw wererelatively dry; poultry manures, leaves, and city garbage were moderately moist; cattlemanure, sugarcane bagas, fruit wastes, vegetable wastes, and grass clippings were mostly

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Organic Wastes for Composting 319

wet; municipal wastes, sheep manure, and poultry manure (layers) were moderate to highin moisture. Municipal wastes mixed with cattle manure can be converted to compost whenthe two wastes are mixed together at C/N ratio 30 and moisture content around 50%. Theinoculation of wastes with EM was ineffective in expediting the process of composting.

Funding

The project was executed at the Department of Soil and Environmental Sciences,University of Agriculture, Peshawar, in collaboration with the National University ofMalaysia (UKM) and funded by Pakistan Agriculture Research Council, Islamabadthrough the Agricultural Linkages Program (ALP) scheme.

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