compostaje de lodos aerobicos y anaerobicos agregando aserrin

8/13/2019 Compostaje de Lodos Aerobicos y Anaerobicos Agregando Aserrin

1/11

Composting anaerobic and aerobic sewage sludges usingtwo proportions of sawdust

V. Banegas a, J.L. Moreno b, J.I. Moreno a, C. Garca b, G. Leon a, T. Hernandez b,*

a Universidad Politecnica de Cartagena, Paseo Alfonso XIII 52, 30203 Cartagena, Spainb Department of Soil and Water Conservation and Waste Management, Centro de Edafolog a y Biologa Aplicada del Segura

(CEBAS-CSIC), P.O. Box 164, 30100 Espinardo-Murcia, Spain

Accepted 20 September 2006Available online 21 November 2006

Abstract

Sawdust has been proven to be a good bulking agent for sludge composting; however, studies on the most suitable ratio of sludge:saw-dust for sludge composting and on the influence of the sludge nature (aerobic or anaerobic) on the composting reaction rate are scarce. Inthis study two different sewage sludges (aerobic, AS, and anaerobic, ANS) were composted with wood sawdust (WS) as bulking agent attwo different ratios (1:1 and 1:3 sludge:sawdust, v:v). Aerobic sludge piles showed significantly higher microbial activity than those ofanaerobic sludge, organic matter mineralization rates being higher in the AS mixtures. The lowest thermophilic temperatures duringcomposting were registered when the anaerobic sludge was mixed with sawdust at 1:1 ratio, suggesting the presence of substances toxicto microorganisms. This mixture also showed the lowest decreases of ammonium during composting. All this matched with the inhibitoryeffect on the germination ofLepidium sativumseeds of this mixture at the first stages of composting, and with its low values of microbialbasal respiration. However, the ANS + WS 1:3 compost developed in a suitable way; the higher proportion of bulking agent in this mix-ture appeared to have a diluting effect on these toxic compounds. Both the proportions assayed allowed composting to develop ade-

quately in the case of the aerobic sludge mixture, yielding suitable composts for agricultural use. However, the ratio 1:1 seems moresuitable because it is more economical than the 1:3 ratio and has a lower dilution effect on the nutritional components of the composts.In the case of the anaerobic sludge with its high electrical conductivity and ammonium content, and likely presence of other toxic andphytotoxic substances, the 1:3 ratio is to be recommended because of the dilution effect.2006 Elsevier Ltd. All rights reserved.

1. Introduction

Urban organic wastes constitute an alternative source oforganic matter for soils (Catroux et al., 1983; Lue-Hing

et al., 1992). However, their use without prior stabilizationrepresents a risk because of the potentially negative effectsof any phytotoxic or pathogenic substances they may con-tain and because of their very unstable nature (Garcaet al., 1993). Composting is regarded as a suitable way ofrecycling such wastes since it not only helps solve the prob-lem of their disposal but also produces a useful bioamend-ment agent (compost). This end product can be used both

for agricultural purposes and for recovering the degradedsoils of semiarid zones, since its incorporation in soil insuitable conditions increases fertility (Haug, 1993; Tanget al., 2003; Tremier et al., 2005).

Sewage sludges from municipal treatment plants aregood candidates for composting and for agricultural pur-poses (Akhtar and Malik, 2000; Lazzari et al., 2000; GeaLeiva et al., 2003; Barrena et al., 2005) since their organicmatter content can vary from 50% to 70% of the total sol-ids content. Sludge characteristics will depend on the typeand origin of the waters to be purified, as well as on thetype of treatment (aerobic or anaerobic) followed in thewastewater treatment plant. The high moisture content ofsludges means that they cannot be composted alone andthey need to be mixed with dry materials (such as sawdust,

0956-053X/$ - see front matter 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.wasman.2006.09.008

* Corresponding author. Tel.: +34 968396322; fax: +34 968396213.E-mail address:[email protected](T. Hernandez).

www.elsevier.com/locate/wasman

Waste Management 27 (2007) 13171327
mailto:[email protected]:[email protected]


2/11

vegetal remains, straw), which act as bulking agents,absorbing the moisture and providing the composting masswith an appropriate degree of sponginess and aeration(Sanchez Monedero et al., 2001; Iranzo et al., 2004; Tre-mier et al., 2005).

During composting, organic compounds are trans-

formed through successive activities of different microbesto more stable and complex organic matter (Pare et al.,1998; Garca et al., 1993). The rate and extent of thesetransformations will depend on the nature of the startingmaterials and the composting process conditions. Bulkingagents remains in the final compost product since their deg-radation rates are very small, influencing final compostquality; and they also influence the composting perfor-mance (Nakasaki et al., 1986; Alburque et al., 2006).Therefore the nature of sludge and the type and proportionof bulking agent used for composting will influence thecomposting reaction rate and the final compost quality.

Results from the study of bulking agents have not been

consistent. Tang and Katayama (2005), in a study on thecomposting of cattle manure with various bulking agents(rice straw, sawdust, waste paper, and vermiculite), indi-cated that the bulking agent was not degraded within thefirst 14 days of composting and did not affect microbialsuccession. However,Nakasaki et al. (1986)found that lar-ger amounts of rice husks added as bulking agent to sewagesludge yielded a higher CO2 evolution rate and a largernumber of thermophiles per unit dry mass of raw sludge.Vourinen (2000), composting cattle and pig manure,observed that the choice of the bulking agent (chopped bar-ley straw or sphagnum peat) strongly affected the potential

capacity and property for mineralization of organic phos-phorus in manure compost; and Alburque et al. (2006)found that the performance of olive husk compostingwas influenced by the characteristics of the bulking agentsadded (grape stalk or olive leaf).Hay et al. (1988), search-ing for alternative bulking agents for sludge composting,composted sewage sludge with either straw or sawdust ina 1:2 and 1:1 sludge:bulking agent (v:v) ratio, respectively;they observed that both mixtures effectively destroyed indi-cators and pathogenic microorganisms, yielding final com-post products well-stabilized, humus-like in texture, andexempt of objectionable odors.

Sawdust has been proven to bee a good bulking agentfor sludge composting and it has been used in studies oncomposting process performance; however, studies aimedto determine the most suitable ratio of sludge:sawdust foroptimizing the sludge composting performance are veryscarce. The ratios of sludge:sawdust found in the literaturein composting studies are diverse.Molla et al. (2004)used a1:1 (w:w) ratio in a study to evaluate the feasibility of thesolid bioconversion processes in the biodegradation ofwastewater sludge; Bousselhaj et al. (2004), in studyingthe N fertilizer value of sewage sludge co-compost, mixedsewage sludge with different bulking agents (domestic solidwaste, olive cakes and sawdust) using also a 1:1 (w:w) ratio;

andGouxue et al. (2001)composted sewage sludge adding

the amount of sawdust necessary to adjust the C/N ratio to30. Zubillaga and Lavado (2003) in a study of stabilityindices of sewage sludge composts used the ratios of 1:2,2:1 and 1:1 (v:v).Eftoda and Mc Cartney (2004)employedwood chips as bulking agent, assaying the ratios of 1:1, 1:2,1:3 and 1:4.

Nowadays compost producers and municipalities havedeveloped a ratio of sludge:wood wastes that they like.To establish scientifically the use of a particularsludge:sawdust ratio, and to see if this ratio should differdepending on the type of sludge (aerobic or anaerobic),would help to fill the existing gap in this field.

The objective of this study was (i) to compare the perfor-mance during composting of two sewage sludges from dif-ferent treatment plants, which had been processed indifferent ways (aerobically and anaerobically); and (ii) todetermine the influence of using different proportions ofbulking agent (1:1 and 1:3 sludge:sawdust) on the develop-ment of the composting process and on different chemical

and microbiological parameters, in order to establish themost suitable ratio of sludge:sawdust.

2. Materials and methods

2.1. Composting process

An aerobic sewage sludge (AS) and an anaerobic sewagesludge (ANS) from two urban wastewater treatment plantsin Southeast Spain, as well as wood sawdust (WS) as bul-king agent, were used in this study. The aerobic wastewatertreatment plant received domestic wastewater, whereas the

influent of the anaerobic plant had a more industrial com-ponent (mineral treatment for Zn extraction). The maincharacteristics of the sludges and sawdust are shown inTable 1. The sludges were mixed with sawdust at two dif-ferent ratios (1:1 and 1:3 sludge:sawdust, v:v) and submit-ted to a process of aerobic composting with periodicturning. These ratios of sludge:sawdust were chosen onthe basis of our previous studies on sludge composting withother bulking agents (grape debris, municipal wastesorganic fraction, residues from peat humic substanceextraction, wood shavings) (Garca, 1990; Garca et al.,1991; Mena et al., 2003).

Piles of about 3 m3 were prepared (in triplicate) witheach mixture. The composting piles were turned periodi-cally (every 45 days) for 3 mo to maintain adequate O2levels and to homogenize the mixture. Oxygen concentra-tion in interstitial air was monitored with an oxygen sensor(Sensox, Sensotran, Spain), and it was maintained at 1215%. The moisture content of the piles was maintained atabout 6070% of their water holding capacity throughoutthe composting period and the temperatures of the surfaceand the interior of each pile were monitored daily at 810different points for each pile with a digital temperatureprobe. The moisture content of the piles was determinedweekly and when necessary piles were watered by sprin-

klers connected to a water meter. Samples were taken ran-

1318 V. Banegas et al. / Waste Management 27 (2007) 13171327


3/11

domly from within the piles and from the outer layer 1, 15,30, 45, 60, and 90 days after the beginning of the compo-

sting process. Each sample was a mixture of eight subsam-ples taken from different points in the pile. The sampleswere homogenized and sieved through a 2 mm sieve. A partof each sample was stored at 4 C for microbiological anal-ysis, and the rest was air-dried and stored for chemicalanalysis. Data shown in the tables and figures are the meanof the average values of the three composting piles of eachtreatment.

2.2. Physicalchemical and chemical analysis

Electrical conductivity and pH were measured in 1:5(w:v) aqueous extract. The percent organic matter content

in the composting piles was determined by gravimetric loss-on-ignition of oven-dried (at 105C for 24 h) samples,burning to ashes in a muffle furnace at 600 C for 24 h.Water-soluble organic carbon (WSOC) was measured inan aqueous extract 1:10 (solid:liquid) using an automaticTOC analyzer (Shimadzu TOC-500) for liquid samples,which measures total C and inorganic C. WSOC wasobtained by subtracting water-soluble inorganic C fromtotal water-soluble C. Water-soluble carbohydrates(WSCh), in the same extract, were measured with anthroneby the Brink et al. (1960) method. Polyphenolic com-pounds in the water extract were determined by theKuwat-

suka and Shindos method (1973). The nitrogen content

was determined by the Kjeldahl method. The nitrate con-tent was determined by HPLC in the extract obtained by

shaking the sample with hot water (40 C) in a 1:10 ratio,for 2 h, and ammonium was determined by an ammoniumselective electrode, after extraction with 2 M KCl (Keeneyand Nelson, 1982). The total content of P, K, Na, Ca, andheavy metals in sludges were determined after nitric-per-chloric acid digestion. P was determined colorimetricallyas molybdovanadate phosphoric acid. Na and K weredetermined by atomic emission spectrometer, and the restof the elements by atomic absorption spectrometer.

2.3. Respiration experiment

Basal respiration was determined in compost samples

taken 1, 30, 60 and 90 days after the beginning of compo-sting. A portion (2 g) of each sample was placed in hermet-ically sealed flasks (closed flow system) equipped with arubber septum for sampling, and moistened at 5060% oftheir water holding capacity. The samples were then incu-bated at 28 C for 55 days and the CO2 evolved was mea-sured at given time intervals with an infrared gas analyzer(Toray PG-100, Toray Engineering Co. Ltd., Japan)(Hernandez and Garca, 2003). For this purpose, a portionof the air contained in each flask was extracted with syringeand then injected in the infrared gas analyzer for CO2con-tent determination. After each CO2 measurement the sys-

tem was opened for 0.5 h for air renovation. The data

Table 1Characteristics of the sawdust and sewage sludges (dry weight)

Sawdust Aerobic sludge Anaerobic sludge

Humidity (%) 8.03 (0.31) 83.5 (2.2)a 74.1 (2.0)pH (1:5) 5.08 (0.09) 7.6 (0.06) 7.9 (0.05)EC 25 C (dS/m) 1:5 0.20 (0.09) 4.34 (0.35) 9.87 (0.29)Organic matter (g/kg) 994.6 (2.7) 683.4 (10.1) 586.3 (9.3)

Total carbonates (g/kg) 1.20 (0.2) 84.3 (2.1) 26.2 (1.9)Kjeldahl N (g/kg) 1.80 (0.2) 75.8 (2.5) 56.5 (2.1)NitrateN (mg/kg) N.a 22.8 (2.0) 17.3 (1.6)AmmoniumN (g/kg) N.a 4.7 (0.8) 2.2 (0.6)Total P (g/kg) 0.06 (0.01) 18.9 (1.1) 60.4 (2.0)Total K (g/kg) N.a 4.6 (0.2) 4.2 8 (0.2)Chlorides (mg/kg) N.a 877.2 (5.7) 1121 (8.3)Sulphates (mg/kg) N.a 9462 (12.1) 19283 (15.3)Fe (mg/kg) N.a 2958 (80.4) 12353 (100.3)Cu (mg/kg) N.a 364 (50.1) 216 (48.0)Mn (mg/kg) N.a 76 (13.0) 164 (15.0)Zn (mg/kg) N.a 505 (57.0) 2195 (60.2)Pb (mg/kg) N.a 22 (4.7) 111 (6.4)Ni (mg/kg) N.a 22.7 (3.0) 24 (2.0)Cr (mg/kg) N.a 40.4 (3.0) 31 (2.9)

Cd (mg/kg) N.a 1.1 107 > 1.1 106

Salmonella (ufc/25 g) Absence Presence Absence

N.a: Nonanalyzed.a In parenthesis standard deviation based on three samples.

V. Banegas et al. / Waste Management 27 (2007) 13171327 1319


4/11

were summed to give a cumulative amount of the CO2evolved after 55 days of incubation. Basal respiration val-ues were obtained by dividing the total amount of CO2released from the sample during the incubation period bythe duration (days) of this incubation, and was expressedas mg CO2C kg

1 soil per day.

2.4. Bacterial indicators determination

For bacteriological determinations, the solid sampleswere suspended in a liquid, allowing the bacteria to distrib-ute themselves evenly throughout the samples. The sampleswere then diluted (1:10) with 100 mM phosphate buffer(pH = 7.2) and homogenized for 10 min in a rotatory stir-rer before the analyses were carried out. To estimate thenumber of viable cells in the different samples, the follow-ing techniques were used: membrane filtration for fecal col-iforms and fecal streptococci, and most probablenumber forSalmonella (APHA, 1989).

2.5. Phytotoxicity test (germination assay)

The germination experiment (in quintuplicate) was car-ried out on filter paper in Petri dishes. Two milliliter ofthe corresponding aqueous extract (1/10, w/v) from thecomposts were introduced into dishes, with distilled waterused as control in other dishes. Ten seeds of watercress(Lepidium sativum) were then placed on the filter paperand the dishes placed in a germination chamber maintainedat 28 C in darkness. The germination percentages withrespect to the control and root lengths were determined

after 5 days. The germination index (GI) was calculatedaccording to the formula proposed by Zucconi et al.(1985): GI = %G Le/Lc, where %G is the percentage ofgerminated seeds in each extract with respect to the con-trol, Le is the mean total root length of the germinatedseeds in each extract, and Lc is the mean root length ofthe control. The control GI value is considered as 100%.

2.6. Statistical analysis

Statistical analysis (ANOVA analysis, and the least sig-nificant difference (LSD) for mean at 95% level) was per-formed with the Statgraph program on data obtained inthe composts at the different composting times.

3. Results and discussion

3.1. Waste organic matter stabilization

The mean values of the average temperatures reached inthe triplicate compost piles of each mixture of sludge:saw-dust are shown in Fig. 1. Differences between replicateswere not statistically significant. Initially the temperatureof the composting piles ranged from 20 to 30 C (meso-philic phase) (Fig. 1). This rose to 4346 C in 810 days

(start of the thermophilic phase) and then reached temper-

atures of between 57 and 61C in 20 days (exceptANS + WS, 1:1) as a consequence of the intense biodegra-dation of the most easily biodegradable fraction of theorganic matter (Hassen et al., 2001). Thereafter, the tem-perature fell gradually for at least 1 mo before reachingambient temperature.

Differences as regards temperature were observed in the1:1 piles. Whereas the maxima thermophilic temperaturesreached in the aerobic sludge piles were similar at thetwo sludge:sawdust ratios assayed, the anaerobic sludgeshowed significantly lower thermophilic temperatures inthe 1:1 piles than in the 1:3. This particular behavior ofthe ANS + WS 1:1, which was observed in the three repli-cates of the pile, could be explained by a toxic effect onmicroorganisms caused by the presence in the sludge ofhigh levels of Zn (see Table 1) and/or other toxic sub-stances derived from the anaerobic treatment. In the 1:3mixture this toxic effect would be diluted by the higher pro-

portion of bulking agent.

0

10

20

30

40

50

60

70

ANS+WS 1:3

AS+WS 1:3

0

10

20

30

40

50

60

70

0 20 40 60 80 100

0 20 40 60 80 100

Composting time, days

Composting time, days

Tempera

tureC

TemperatureC

ANS+WS 1:1

AS+WS 1:1

Fig. 1. Temperature evolution during the composting process of anaerobic (AS) and an anaerobic (ANS) sewage sludge mixed with woodsawdust (WS) at 1:1 and 1:3 sludge:WS proportion. Temperature data arethe mean of the average values from the three compost piles. Vertical barsshow the standard deviation between replicates.



5/11

Temperature profiles were similar for both sludges whenmixed with sawdust at the 1:3 ratio (Fig. 1) and theyreached similar maxima temperatures in the thermophilicphase. However, the AS + WS 1:3 piles reached the ther-mophilic phase earlier than the ANS + WS 1:3 piles,reflecting the more unstable character of the aerobic

sludge, and the greater content of easily biodegradable Cfractions in this sludge.The organic matter (OM) content of the pile gradually

decreased over time during the composting process dueto mineralization processes (Fig. 2). This fall in organicmatter can be attributed in a great proportion to the min-eralization of the sludge OM, since the OM from sawdustwould be formed of a more structured fraction less suscep-tible to microorganism attack (Manios, 2004). Therefore,the microorganisms existing in the composting mass woulduse the labile carbon fractions from the sewage sludge asenergy source, rather than those from the bulking agent(Mena, 2001).

The anaerobic sludge showed a slower OM mineraliza-tion rate than the aerobic sludge, decreases in OM concen-tration with composting being 12.69% and 6.30% forAS + WS 1:1 and 1:3 mixtures, respectively, and 7.87%and 5.57% for the ANS + WS 1:1 and 1:3 mixtures, respec-tively (Fig. 2). This can be explained by the more stablenature of the OM of the anaerobic sludge with a lower con-tent of easily biodegradable compounds.Molla et al. (2004)observed decreases in OM concentration after 75 days ofcomposting of 5.24% and 13.78% for sludge + sawdustand sludge + rice straw, respectively, and Fang et al.(1999) reported decreases of OM concentration of about

9% in sewage sludge composting with coal fly ash.Although the higher proportion of sawdust in the 1:3

pile will favor aeration, the high stability of the bulkingagent, due to its lignocellulosic character, leads to a lowerdecrease in the pile OM concentration.

Organic matter biodegradation influences weightreduction during composting. A mass balance was calcu-lated assuming that fixed solids (ash content) were con-served during the composting process, and that thedegradation of sawdust organic matter during the processwas negligible. The aerobic sludge piles experienced higher

weight losses (36.6%, and 26.21% for 1:1 and 1:3 piles,respectively, on dry weight basis) than the anaerobic sludgepiles (17.66% and 19.29% for 1:1 and 1:3 piles, respec-tively), which is in agreement with the more stable natureof the organic matter of the anaerobic sludge, with a lowercontent of compound easily degradable by microorgan-isms. Hay et al. (1988) reported losses of 42.19% and35.08% for sludge-bedding straw (1:2, v:v ratio) andsludgesawdust (1:1, v:v ratio) piles, respectively. It canbe observed that the higher proportion of sludge in theAS + WS 1:1 mixture led to a higher loss of weight in com-parison with the 1:3 mixture. Conversely, in the case of theanaerobic sludge, weight losses were greater in the 1:3 mix-

ture than in the 1:1 mixture, suggesting a lower microbialactivity in the latter, which is in agreement with the lowertemperatures recorded in the AN + WS 1:1 pile duringthe thermophilic phase of composting.

Although the total amount of OM degraded duringcomposting was higher in the AS + WS 1:1 pile than inthe AS + WS 1:3 pile, as reflected by pile weight loses,the percentage of the starting sludge OM degraded duringcomposting was higher in the latter pile (about 68.1% and74% for piles 1:1 and 1:3, respectively, dry wt.), indicatingthat organic matter degradation was more intense in the1:3 pile. This can be explained by higher porosity of this

pile as a consequence of the higher proportion of bulkingagent.

The water-soluble carbon fraction (WSOC), composedof sugars, aminoacids, polyphenols, peptides and fulvicacids (Mena et al., 2003; Charest et al., 2004), representsthe most labile organic matter fraction and constitutesthe carbon source used first by the microorganisms asenergy source. This explains the decrease of the contentof WSOC, WSCh and phenolic compounds in all the com-posting piles during composting (Fig. 3).

The aerobic sludge mixtures showed a significantlyhigher WSOC content than the anaerobic sludge mixture,which can be explained by the increased stability of theorganic matter in the latter following its anaerobic treat-ment. This higher stability of the anaerobic sludge is alsoresponsible for the slower WSOC mineralization observedin the ANS piles with respect to the AS piles (Fig. 3).The 1:1 AS:WS mixture had the greatest content of thesefractions, both at the onset and end of the compostingprocess.

The addition of bulking agent reduced significantly theproportion of WSOC, WSCh and phenolic compounds,with the 1:3 mixtures showing the lowest values for bothtypes of sludge, meaning that the bulking agent used hada smaller content of these compounds than the biosolids

being composted. However, the higher or lower proportion

60

70

80

90

100

Days

Organicmatter(%)

AS+WS 1:1, LSD: 1.42

AS+WS 1:3, LSD 1.84

ANS+WS 1:1, LSD: 2.31

ANS+WS 1:3, LSD:1.83

0 20 40 60 80 100

Fig. 2. Evolution of the organic matter content (%) in the compost pilesduring the composting process of an aerobic (AS) and an anaerobic (ANS)sewage sludge mixed with wood sawdust (WS) at 1:1 and 1:3 sludge:WSproportion. Data shown are the mean of the average values from threecompost piles. LSD is the least significant difference in the means at the95% confidence level. Vertical bars show the standard deviation between

replicates.



6/11

of bulking agent in the mixtures did not seem to influencehow this carbon fraction evolved during composting.

In all of the mixtures, the WSOC and particularly thewater-soluble carbohydrate contents fluctuated duringcomposting, especially in the aerobic sludge mixtures.These fluctuations can be due to the fact that these frac-tions are dynamic and there is a constant formation anddestruction of these types of C substances during compo-sting. The hemicellulose and cellulose fractions are knownto diminish during composting, sometimes giving rise tonew, more biodegradable substrates as they decompose(Charest et al., 2004). It is therefore possible that new

water-soluble carbon compounds of microbial origin will

be formed during the process since composting is, afterall, a process of synthesis (Charest and Beauchamp, 2002;Charest et al., 2004).Chantigny et al. (2000)indicated thatnew microbial carbohydrates were released in a soilamended with de-inking paper sludge. It cannot be dis-carded that the variability due to sampling, as well as

between the three replicates of the pile, can contribute tothe observed fluctuations.The evolution of the nitrogen content during compo-

sting would be conditioned not only by the quantity oftotal nitrogen and its mineralization rate, but also by theloss of this element through volatilization, denitrification,leaching and several immobilization processes that mayoccur in the compost (Hutchings, 1985). Due to their highprotein content, sewage sludges are characterized by theirhigh nitrogen content compared with other organic wastes,the nitrogen occurring principally in the organic form(Moreno, 1985).

The Nkjeldahl (organic N plus NH

4 N) concentration

in the composting mass (Table 2) remained constant duringcomposting or even increased in some composts by the endof the process. The increase measured in some of the pileswas due to the loss of weight in the mass being compostedas a result of organic matter degradation (Kapetanioset al., 1993; Huang et al., 2004) and was mainly observedin the piles in which the reduction in OM had been partic-ularly pronounced. The increase observed in some compostby the end of composting may even have been due to pro-cesses of non-symbiotic nitrogen fixation.Beauchamp et al.(2006) observed N2-fixation in non-sterile compostamended with sucrose, after its thermophilic stage. The

addition of bulking agent had a diluting effect on this nutri-ent, since the values for the same type of sludge were lowerin the 1:3 mixture than in the 1:1 mixture.

The mixtures destined for composting did not initiallycontain nitrates but, as composting progressed, the differ-ent piles became enriched in nitrates because the ammo-nium formed during the first phases of organic matterdegradation was oxidized to nitrate by the action of nitrify-ing bacteria (Table 2). Composting, as indicated byGarca(1990), reduces the quantity of ammonium but increasesthe nitrates due to the stimulation of nitrification processes,an effect also observed by other authors (Mena, 2001; Par-kinson et al., 2004; Huang et al., 2004).

Nitrification processes were favored in the AS piles withrespect to the ANS piles, nitrate contents in the final AScomposts being significantly higher than in the respectiveANS composts (Table 2). The 1:1 piles yielded highernitrate content in the resulting composts than the 1:3 piles,which probably was simply due to the higher amount oforganic N in the 1:1 piles with larger amount of sludge.

Basal respiration provides information on the state ofmicrobial populations and their capacity to decomposeorganic compounds, together with information concerningwhich populations are metabolically active. For this rea-son, basal respiration is widely used to monitor microbial

activity and organic matter decomposition (Anderson,

0

2

4

6

8

10

12

14

16

0 15 30 45 60 75 90 105

Waterso

lubleorganicCg/kg

AS+WS (1:1), LSD 0.57

AS+WS 1:3, LSD 0.88

ANS+WS 1:1, LSD 0.49


0

1

2

3

4

0 15 30 45 60 75 90 105

Watersolublecarbohydrates,g/kg

AS+WS 1:1, LSD 0.32

AS+WS 1:3, LSD 0.17



0

1

2

0 15 30 45 60 75 90 105

Days

Days

Days

Watersolu

blepolyphenolsg/kg

AS+WS 1.1, LSD 0.04

AS+WS 1:3, LSD 0.05



Fig. 3. Changes in water-soluble C fractions during the compostingprocess of an aerobic (AS) and an anaerobic (ANS) sewage sludge mixedwith wood sawdust (WS) at 1:1 and 1:3 sludge:WS proportion. Datashown are the mean of the average values from three compost piles. LSDis the least significant difference in the means at the 95% confidence level.Vertical bars show the standard deviation between replicates.



7/11

1982). Its value is obtained by dividing the CO2 releasedduring an incubation experiment by the duration of theexperiment.

Basal respiration in our experiment decreased duringcomposting to reach more or less stable values by 60 days(Fig. 4). Such a fall is indicative of strong microbial activity

at the beginning of the process, when a large quantity ofeasily biodegradable organic compounds still exists. At thistime, microbial activity is at its maximum since the micro-organisms existing in the composting mass have access tothe substrates which may act as an energy source for them(Ayuso et al., 1996). As these compounds are degraded, themedium becomes richer in more stable compounds whichare less accessible to the microorganisms and so their activ-ity and corresponding respiration diminish. A statisticallysignificant relationship (r= 0.65; p 6 0.01) was foundbetween the WSOC content and the respiration values(accumulative values of CO2).

The 1:1 mixture containing aerobic sludge showed the

highest basal respiration rates, underlining its richness inbiodegradable C fractions from the organic matter usedcompared with the anaerobic sludge. The mixture of thesame sludge with bulking agent in a proportion of 1:3increased the mass of more stable organic matter becauseof the lignocellulosic character of the sawdust used, result-ing in lower microbial activity and basal respiration rate.This suggests that the aerobic sludge used did not containsubstances toxic to the microorganisms, so that the 1:1mixture, with its higher sludge content and thereforegreater quantity of poorly stabilized organic mater, stimu-lated the activity of the microorganisms present in the mass

and their respiration.The anaerobic sludge in the two mixtures studied, on

the other hand, showed lower basal respiration valuesthan the aerobic 1:1 mixture (Fig. 4), which can beexplained by the more stable nature of the organic mattercontained in this sludge as a consequence of the stabiliza-tion it had undergone in the treatment plant.

Unlike in the aerobic sludge, the basal respiration valuesobserved in the anaerobic sludge at the beginning of com-

Table2

EvolutionofNfractionsduringcomposting

D

ays

Kjeldahlnitrogen(g/kg)

NH4

Nmg=kg

NO3N(mg/kg)

AS+WS

(1:1)

AS+WS

(1:3)

ANS

+WS

(1:1)

ANS+WS

(1:3)

AS+WS

(1:1)

AS+WS

(1:3)

ANS+WS

(1:1)

ANS+WS

(1:3)

AS+WS

(1:1)

AS+WS

(1:3)

ANS+

WS

(1:1)

ANS+WS

(1:3)

1

14.5

0

11.2

5

27.5

0

14.9

0

712

638

1256

610

0

0

0

0

(0.5

7)

(1.0

4)

(2.68)

(2.4

0)

(22.02)

(37.32)

(125)

(14.12)

15

14.5

0

11.4

8

27.3

0

12.2

0

743

652

1237

572

0

0

0

0

(1.6

9)

(1.8

3)

(2.18)

(1.7

6)

(70.01)

(37.21)

(294)

(29.10)

30

15.9

8

10.1

0

26.9

8

13.0

0

400

311

1040

510

0

118

0

83

(0.0

4)

(0.2

8)

(0.99)

(1.3

9)

(24.83)

(21.10)

(77.12)

(103)

(4.1

3)

(4.1

9)

45

16.9

7

10.0

7

23.1

7

15.6

1

344

54

1054

455

120

123

110

89

(0.2

8)

(0.3

9)

(1.74)

(0.1

6)

(14.51)

(8.4

3)

(29.13)

(152)

(3.1

0)

(5.1

3)

(4.16)

(5.6

7)

60

14.1

7

9.70

19.6

7

16.6

0

283

49

989

361

134

134

183

95

(0.3

3)

(1.1

2)

(3.44)

(1.7

7)

(16.43)

(2.3

1)

(70.17)

(42.00)

(5.3

0)

(6.0

8)

(5.32)

(6.1

0)

90

18.8

0

11.0

0

27.5

0

20.1

5

180

26

970

334

246

135

193

123

(0.5

0)

(1.4

1)

(3.11)

(0.7

1)

(8.0

3)

(8.0

4)

(58.22)

(0.0

8)

(8.3

2)

(4.8

9)

(13.2)

(6.1

0)

In

parenthesisstandarddeviationfromthree

samplescompositedfromthethreecompostpiles.

Fig. 4. Changes in basal respiration during the composting process of anaerobic (AS) and an anaerobic (ANS) sewage sludge mixed with woodsawdust (WS) at 1:1 and 1:3 sludge:WS proportion. Data shown are themean of the average values from three compost piles. Vertical bars show

the standard deviation between replicates.



8/11

posting and after 30 days were lower in the 1:1 mixturethan in the corresponding 1:3 mixture probably becausethe sludge, after its anaerobic treatment, contained reduc-ing substances that were toxic to the microorganisms pres-ent. In the 1:1 mixture, with its higher proportion of sludge,microbial activity would have slowed down due to the

inhibitory action of these reducing compounds. The highEC value of this mixture (Table 2) might also have inhib-ited the microbial activity since, as observed by Garcaand Hernandez (1996), high salinity in soils reduces micro-bial populations and their activity. When a larger amountof bulking agent was added (1:3 mixture), the greater aer-ation of the composting mass, together with the dilutionof possible reducing substances and of the salinity that itproduces, would have encouraged microbial activity andrespiration (Fig. 4). Once the most labile compounds hadbeen decomposed, basal respiration fell, the values at theend of composting (60 and 90 days) being similar in thetwo ANS + WS mixtures (Fig. 4).

3.2. Compost sanitization

One of the problems posed by the direct use of sewagesludges in agriculture is the risk of plant and human con-tamination by pathogens. Fresh sludges showed a highdensity of fecal coliforms (Escherichia coli) and fecal strep-tococci, and the aerobic sludge also showed presence ofSalmonella(Table 1).

According to Stentiford (1996), temperatures higherthan 55 C favor sanitation, values between 45 and 55 Cfavor biodegradation, and those between 35 and 40C

favor microbial diversity. In our experiment the maximumtemperatures reached during composting ranged between57 and 61 C (except for ANS + WS 1:1).These tempera-tures, which were maintained for several days during theprocess, ensured that the composting process followedwas suitable for stabilizing organic matter and suppressingpathogenic microorganisms. In the ANS + WS 1:1 pile, thetemperature peaked at 45 C; however, the time that thistemperature was maintained during composting appearsto have been enough to sanitize the compost as indicatedby the decrease of the measured bacterial indicators withcomposting.

During the composting process, Salmonella, fecal coli-forms (E. coli), and fecal streptococci, were determined insamples taken after 1, 30, 60 and 90 days of composting.

At the high temperatures reached during composting mostpathogens were destroyed, making resulting composts saferfor agricultural use (Table 3).

Salmonella is considered as the most specific and prob-lematic microorganism from a hygienic point of view, sinceit is a universal bacteria with a high growth capacity (Hay,

1996). Although the presence ofSalmonellawas detected inthe fresh aerobic sludge, it was not detected in thesludge:sawdust mixtures from the starting of the compo-sting process, probably due to the dilution effect of the bul-king agent.

E. coli are the most representative microorganismswithin fecal coliforms (Le Minor, 1984). Most coliformsdied when they are exposed to a temperature of 55 C for1 h or 60 C for 1520 min. The concentration of this path-ogen was considerably reduced during the composting pro-cess. Although the ANS + WS 1:1 mixture only reached45 C during the thermophilic phase, the period of time thistemperature is maintained seems enough to reduce this

pathogen in the resulting compost (Table 3). Fecal strep-toccoci are considered one of the best indicators of fecalcontamination, and are more resistant to environmentalfactors than fecal coliforms. The density of this pathogenwas also reduced during composting.

Farrel (1992)recommended a safe density of fecal coli-forms for compost of 1000/g solid, because Salmonella isconsidered to be absent from all samples containingamounts of fecal coliforms lower than that. Strauch(1987)considered fecal streptococci to be more useful indi-cators of the desinfection processes in sewage sludge com-posts. For compost sanitation, this author recommended a

limit of 5 102

CFU g1

(fresh weight) for fecal coliformsand 5 103 CFU g1 (fresh weight) for fecal streptococci.The density of pathogens observed in all the final compostsobtained (Table 3) was below these limits in our case.

It should be noted that the uncomposted sewage sludgescontain a great amount of pathogenic microorganisms(Table 1). Therefore, when they are used as soil organicamendment without composting there is a high risk ofpathogen contamination both for the users and for the soiland crops growing in it.

3.3. Compost quality for agricultural use

Electrical conductivity and pH are two importantparameters to be considered when a material is to be used

Table 3Changes in density of fecal coliforms (FC) (Escherichia coli)and fecal streptococci (FS) during the composting process (ufc/g)

Days AS + WS (1:1) AS + WS (1:3) ANS + WS (1:1) ANS + WS (1:3)

FC FS FC FS FC FS FC FS

1 4.6 105 2.1 105 1.5 105 2.1 105 2.4 105 >1.1 105 >1.1 106 >1.1 105

15 1.2 102 2.4 103 2.1 102 1.1 104 4.6 104 1.1 105 2.4 104 7.5 103

30 2.1 103 1.5 104 1.2 103 1.1 105 7.5 102 2.1 104 2.8 103 9.3 104

45 4 101 2.3 103 5.1 102 2.8 103 2.4 102 7.5 103 1.1 103 4.8 103

60


9/11

as organic amendment since the physicalchemical andmicrobiological reactions taking part in the soil are influ-enced by them.

Compost pH values decreased significantly throughoutcomposting (Table 4). The evolution of this parameter dur-ing composting was similar in all the composting piles

regardless of the proportion of bulking agent or the sludgenature (aerobic or anaerobic).Several authors have pointed to the existence of changes

in pH during the first days of composting (Iglesias Jimenezand Perez Garca, 1989; Garca, 1990; Daz, 1990). We,too, observed a slight but significant decrease in pH (Table4), presumably due to the loss of ammonium through vol-atilization and nitrification accompanied by the fact that inthe bio-oxidation phase of degradation simple organicacids are formed and polysaccharides are decomposed(El-Housseini et al., 2002). The composts obtained showedpH values that were suitable from an agricultural point ofview, and are within the range of values currently found for

this type of waste (Garca, 1990; Mena, 2001; El-Housseiniet al., 2002).

Compost EC is of great importance from an agriculturalpoint of view since it can be a limiting factor of plantgrowth and seed germination. Santamara-Romero andFerrera (2001) and Garca and Hernandez (1996)indicatedthat EC higher than 8 dS m1 had a negative effect on soilmicrobial populations and on organic matterbiotransformation.

EC increased significantly throughout the compostingprocess (Table 4). The ANS + WS (1:1) mixture showedthe highest values of this parameter, which is indicative

of a high salt content. The higher proportion of bulkingagent (1:3 mixtures) resulted in a decrease of the EC values,although the evolution of this parameter during compo-sting was unaffected. ANS yielded at the two bulking ratiosfinal composts with higher EC than AS.

The seed germination test helps us to establish the effi-cacy of the composting process for eliminating phytotoxicsubstances. This test revealed that the fresh aerobic sludgecontained lower amount of phytotoxic substances than theanaerobic fresh sludge, the inhibitory effect on seed germi-nation of the immature AS + WS 1:1 compost being lesspronounced than that of the immature ANS + WS 1:1compost.

The 1:1 AS + WS mixture showed a certain phytotoxiccharacter at the beginning of the composting process (days145), when the germination index (GI) values for L. sati-vumseeds were significantly below those obtained with thecontrol (GI for control = 100%) (Fig. 5). However, by days6090 this effect had disappeared, to be replaced by a posi-

tive effect. The 1:3 AS + WS mixture already showed a GIof 93% at the beginning of composting, which illustrateshow the diluting effect of the bulking agent lowers the con-centration of phytotoxic substances, no inhibitory effect onseed germination being observed in this mixture at the dif-ferent sampling times.

The GI values for the 1:1 ANS + WS mixture were verylow by days 160 (Fig. 5), pointing to the presence of phy-totoxic substances for germination and growth. This inhib-itory effect disappeared during composting and the GIvalue at day 90 was similar to the control value, meaningthat the phytotoxic substances had disappeared or losttheir negative effect.

The 1:3 ANS + WS mixture showed high GI valuesfrom the onset, presumably due to the diluting effect ofthe bulking agent used on the salts and any other phyto-toxic substance that might have existed. As in the case ofthe aerobic sludge compost, the positive effect of this bio-solid on germination was evident once the phytotoxic sub-stance had diminished or been eliminated.

Table 4Changes in pH and electrical conductivity (dS m1) during the composting processa

Days pH Electrical conductivity

AS:WS (1:1) AS:WS (1:3) ANS:WS (1:1) ANS:WS (1:3) AS:WS (1:1) AS:WS (1:3) ANS:WS (1:1) ANS:WS (1:3)

1 7.44 (0.04) 7.63 (0.36) 7.09 (0.01) 7.11 (0.11) 2.02 (0.04) 1.23 (0.17) 5.68 (0.08) 2.71 (0.05)15 7.32 (0.04) 6.80 (0.02) 6.81(0.03) 7.07 (0.01) 2.28 (0.02) 1.56 (0.10) 5.71 (0.05) 2.78 (0.01)30 7.04 (0.01) 6.85 (0.05) 6.72 (0.02) 6.09 (0.11) 2.58 (0.02) 2.21 (0.04) 5.97 (0.07) 3.82 (0.35)45 6.88 (0.01) 6.58 (0.14) 6.42 (0.02) 6.55 (0.05) 2.86 (0.05) 2.10 (0.31) 6.19 (0.10) 4.32 (0.28)60 6.75 (0.01) 6.68 (0.10) 6.24 (0.02) 6.88 (0.10) 2.96 (0.05) 2.08 (0.33) 6.53 (0.29) 4.38 (0.05)90 6.54 (0.03) 6.66 (0.03) 6.38 (0.02) 6.20 (0.03) 3.20 (0.03) 2.22 (0.11) 5.96 (0.12) 4.27 (0.02)

a

In parenthesis standard deviation from three samples composited from the three compost piles.

Fig. 5. Change in the germination index values ofLepidium sativumseedsduring the composting process of an aerobic (AS) and an anaerobic (ANS)sewage sludge mixed with wood sawdust (WS) at 1:1 and 1:3 sludge:WSproportion. The control value of GI was 100%. Vertical bars show thestandard deviation between replicates.



10/11

Several authors (Garca, 1990; Pascual et al., 1997;Mena, 2001) have indicated that the decomposition ofthe organic matter during composting involves the disap-pearance of phytotoxic substances, such as low molecularweight organic acids. Furthermore, the initial excess ofammonium in the samples may also contribute to the inhi-

bition of germination.

4. Conclusions

It can be concluded that sawdust can be considered agood bulking agent for use with sewage sludges. Both theproportions assayed allowed composting to develop ade-quately in the case of the aerobic sludge mixture. However,the 1:1 proportion seems more suitable for aerobic sludges,with its low concentration of phytotoxic substances, since ithas a lower dilution effect on the nutritional components ofthe compost and is more economical (less expenses intransport and bulking agent). In the case of more problem-

atic sludges, such as the anaerobic sludge mixture studied,with its higher conductivity and the presence of other toxicand phytotoxic substances, a 1:3 proportion is to be recom-mended because of the dilution effect on these parameterswhich are so harmful to microbial activity and plants.

Acknowledgement

This work has been undertaken thanks to a Project sup-ported by the Council of Education and Science (Fun-dacion Seneca) of the Murcia Regional Government,Spain.

References

Akhtar, M., Malik, A., 2000. Roles of organic soils amendments and soilorganisms in the biological control of plant-parasitic nematodes: areview. Bioresour. Technol. 74, 3547.

Alburque, J.A., Gonzalbez, J., Garca, D., Cegarra, J., 2006. Effect ofbulking agent on the composting of alperujo, the solid by-product ofthe two-phase centrifugation method for olive oil extraction. ProcessBiochem. 41, 127132.

Anderson, J.P.E., 1982. Soil respiration. In: Page, A.L., Miniller, R.,Kenny, D.R. (Eds.), Methods of Soil Analysis, Chemical andMicrobiological Properties, Part 2, second ed., Agronomy, vol. 9American Society of Agronomy, Madison, Wisconsin, USA.

APHA, 1989. Methods for the Examination of Water and Wastewater(17th ed.), APHA/AWWA/WPCF, Washington, USA.Ayuso, M., Hernandez, T., Garca, C., Pascual, J.A., 1996. Evolution of

urban wastes for agricultural use. Soil Sci. Plant Nutr. 42, 105111.Barrena, R., Vazquez, F., Gordillo, Ma.A., Gea, T., Sanchez, A., 2005.

Respirometric assays at fixed and process temperatures to monitorcomposting process. Bioresour. Technol. 96, 11531159.

Beauchamp, C.J., Levesque, G., Prevost, D., Chalifour, F.P., 2006.Isolation of free-living dinitrogen-fixing bacteria and their activity incompost containing de-inking paper sludge. Bioresour. Technol. 97,10021011.

Bousselhaj, K., Fars, S., Laghmari, A., Nejmeddine, A., Ouazzani, N.,Ciavatta, C., 2004. Nitrogen fertilizer value of sewage sludge co-composts. Agronomie 24, 487492.

Brink, R.H., Dubar, P., Linch, D.L., 1960. Measurement of carbohydrates

in soil hydrolysates with anthrone. Soil Sci. 89, 157166.

Catroux, G., Hermite, P., Suess, E., 1983. The influence of sewage sludgeapplication on physical and biological properties of soil. In: Proceed-ing of a Seminar held in Munich 1981. D. Reidel Publishing Company,Amsterdam, The Netherlands, p. 253.

Chantigny, M.H., Angers, D.A., Beauchamp, C.J., 2000. Decompositionof de-inking paper sludge in agricultural soils as characterized bycarbohydrate analysis. Soil Biol. Biochem. 32, 15611570.

Charest, M.H., Beauchamp, C.J., 2002. Composting of de-inking papersludge with poultry manure at three nitrogen levels using mechanicalturning: behaviour of physico-chemical parameters. Bioresour. Tech-nol. 81, 717.

Charest, M.H., Antoun, H., Beauchamp, C.J., 2004. Dynamics of water-soluble carbon substances and microbial populations during thecomposting of de-inking paper sludge. Bioresour. Technol. 91, 5367.

Daz, M.A., 1990. Compostaje de lodos residuales: aplicacion agronomicay criterios de madurez. (Composting of residual sludges: agronomicapplication and maturity criteria.) Ph.D. Thesis, Faculty of Sciences,Autonomic University of Madrid.

Eftoda, G., Mc Cartney, D., 2004. Determining the critical bulking agentrequirement for municipal biosolids composting. Compost Sci. Util.12, 208218.

El-Housseini, M., Fahmy, S.S., Allam, E.H., 2002. Co-compost produc-tion from agricultural wastes and sewage sludge. Soils, Water andEnvironment Research Institute, ARC, Egypt, Paper No. 1755.

Fang, M., Ma, K.K., Wong, J.W.C., Wong, M.H., 1999. Composting ofsewage sludge and coal fly ash: nutrient transformations. Bioresour.Technol. 67, 19.

Farrel, J.B., 1992. Fecal pathogen control during composting. In: Hointik,H.A.J., Keener, H.M. (Eds.), Proceeding of the International Com-posting Research Symposium. Ohio State Univ. Press, Columbus, OH,pp. 282300.

Garca, C., 1990. Estudio del compostaje de residuos organicos. Valor-acion agrcola. (Study of organic waste composting. Agronomicevaluation.) Ph. D Thesis, University of Murcia.

Garca, C., Hernandez, T., 1996. Influence of salinity on the biological andbiochemical activity of a calciorthid soil. Plant and Soil 178, 255263.

Garca, C., Hernandez, T., Costa, F., 1991. Changes in carbon fractionsduring composting and maturation of organic wastes. Environ.Manage. 15, 433439.

Garca, C., Hernandez, T., Costa, F., 1993. Evaluation of the organicmatter composition of raw and composted municipal wastes. Soil Sci.Plant Nutr. 39, 99108.

Gea Leiva, T., Artola Casacuberta, A., Sanchez-Ferrer, A., 2003.Application of experimental design techniques to the optimization ofbench-scale composting conditions of municipal raw sludge. CompostSci. Util. 11, 321329.

Gouxue, L., Zhang, F., Sun, Y., Wong, J.W.C., Fang, M., 2001. Chemicalevaluation of sewage sludge composting as a mature indicator forcomposting process. Water, Air, Soil Pollut. 132, 333345.

Hassen, A., Belguith, K., Jedidi, N., Cherif, A., Cherif, M., Boudabous,A., 2001. Microbial characterization during composting of municipalsolid waste. Bioresour. Technol. 80, 217225.

Haug, R., 1993. The Practical Handbook of Compost Engineering. LewisPublishers, Florida, p. 717.Hay, J.C., 1996. Pathogen destruction and bio-solids composting. Biocycle

33, 7677.Hay, J., Chang, S., Ahn, H., Kellogg, H., Caballero, R., 1988. Alternative

bulking agent for sludge composting. Biocycle 22, 4651.Hernandez, T., Garca, C., 2003. Estimacion de la respiracion microbiana

del suelo. (Estimation of microbial soil respiration.) In: Garca, C.,Hernandez, T., Gil-Sotres, F., Trasar-Cepeda, C. (Eds.), Tecnicas deanalisis de parametros bioqumicos en suelo. Medidas de actividadesenzimaticas y biomasa microbiana. (Techniques for the analysis ofbiochemical parameters in soil. Measurements of enzymatic activitiesand microbial biomass.) Mundi Prensa, Madrid, pp. 313346.

Huang, G.F., Wu, Q.T., Wong, J.W.C., Nagar, B.B., 2004. Effect of C/Non composting of pig manure with sawdust. Waste Manage. 24, 805

813.



11/11

Hutchings, N.S., 1985. The use of three different types of sewage sludgeand ammonium nitrate for the nitrogenous fertilization of a grass-white clover sward. Resour. Conserv. Recycling 11, 263272.

Iglesias Jimenez, E., Perez Garca, V., 1989. Evaluation of city refusecompost maturity. A review. Biol. Wastes 27, 115143.

Iranzo, M., Canizares, J.V., Roca-Perez, L., Sainz-Pardo, I., Mormeneo,S., Boluda, R., 2004. Characteristics of rice straw and sewage sludge ascomposting materials in Valencia (Spain). Bioresour. Technol. 95, 107112.

Kapetanios, E.G., Loizidou, M., Valkanas, G., 1993. Compost productionfrom Greek domestic refuse. Bioresour. Technol. 43, 1316.

Keeney, D.R., Nelson, D.W., 1982. Nitrogen inorganic forms. In: Weaber,R.W., Angle, S. Bottomley, P.S. (Eds.), Methods of Soil Analysis, Part2, Chemical and microbiological properties, second ed., Agronomy,vol. 9, pp. 643698.

Kuwatsuka, S., Shindo, H., 1973. Behavior of phenolic substances in thedecaying process of plant. Identification and quantitative determina-tion of phenolic acids in rice straw and its decayed products by gaschromatography. Soil Sci. Plant Nutr. 19, 219227.

Lazzari, L., Sperni, L., Bertin, P., Pavoni, P., 2000. correlation betweeninorganic (heavy metals) and organic (PCBs and PAHs) micropollu-tant concentrations during sewage sludge composting processes.Chemosphere 41, 427435.

Le Minor, L., 1984. Escherichia Coli. In: Le Minor, L., Veron, M. (Eds.),Bacteriologie Medicale. Flammarion Medicine Sciences, Paris, pp.240353.

Lue-Hing, C., Zenz, D.R., Kuchenrither, R., 1992. Municipal sewagesludge management. In: Proceedings of Utilization and Disposal.Tecnomic Publ. Co. Inc., Lancaster.

Manios, T., 2004. The composting potential of different organic solidwastes: experience from the island of Crete. Environ. Int. 29, 10791089.

Mena, E., 2001. Compostaje de lodos de depuracion urbana: Unaadecuada estrategia para su reciclado en el suelo. (Composting ofurban sewage sludges: A suitable strategy for their recycling in soil).

Mena, E., Garrido, A., Hernandez, T., Garcia, C., 2003. Biorremediationof sewage sludge by composting. Commun. Soil Sci. Plant Anal. 34,957971.

Molla, A.H., Fakhrul-Razi, A., Alam, Md.Z., 2004. Evaluation of solid-state bioconversion of domestic wastewater sludge asa promisingenvironmental-friendly disposal technique. Water Res. 38, 41434152.

Moreno, J.I., 1985. Lodos de depuradoras urbanas: caracterizacion yaplicacion agrcola. (Urban sewage sludges: characterization andagricultural use.) Ph. Thesis University of Murcia.

Nakasaki, K., Kubota, H., Shoda, M., 1986. Effects of a bulking agent onthe reaction rate of thermophilic sewage sludge composting. J.Ferment. Technol. 64, 539544.

Pare, T., Dinel, H., Schnitzer, M., Dumontet, S., 1998. Transformation ofcarbon and nitrogen during composting of animal manure andshredded paper. Biol. Fert. Soils 26, 173178.

Parkinson, R., Gibbs, P., Burchett, S., Misselbrook, T., 2004. Effect ofturning regime and seasonal weather conditions on nitrogen andphosphorous losses during aerobic composting of cattle manure.Bioresour. Technol. 91, 171178.

Pascual, J.A., Ayuso, M., Garcia, C., Hernandez, T., 1997. Characteriza-tion of urban wastes according to fertility and phytotoxicity param-eters. Waste Manage. Res. 15, 103115.

Sanchez Monedero, M.A., Roig, A., Paredes, C., Bernal, M.P., 2001.Nitrogen transformation during organic waste composting by theRutgers system and its effects on pH, EC and maturity of thecomposting mixtures. Bioresour. Technol. 78, 301308.

Santamara-Romero, S., Ferrera, R., 2001. Dynamics and relationshipsamong microorganisms, organic-C and total-N during composting andvermicomposting. Agrociencia 35, 377383.

Stentiford, E.I., 1996. Composting control: principles and practice. In: DeBertoldi, M., Sequi, P., Lemmes, B., Papai, T. (Eds.), The Sciences ofComposting. Blakie Academic and Professional, Glasgow, UK, pp.4959.

Strauch, D., 1987. Microbiological specifications of disinfected compost.In: De Bertoldi, M., Ferranti, M.P., LHermite, P., Zucconi, F. (Eds.),Compost: Production, Quality and Use. Elsevier, London, pp. 210229.

Tang, J., Katayama, A., 2005. Relating quinine profile to the aerobicbiodegradation in thermophilic composting processes of cattle manurewith various bulking agents. World J. Microbiol. Biotechnol. 21, 12491254.

Tang, J.C., Inoue, Y., Yasuta, T., Yoshida, S., Katayama, A., 2003.Chemical and microbial properties of various compost products. SoilSci. Plant Nutr. 49, 273280.

Tremier, A., de Guardia, A., Massiani, C., Paul, E., Martel, J.L., 2005. Arespirometric method for characterising the organic composition andbiodegradation kinetics and the temperature influence on the biodeg-radation kinetics, for a mixture of sludge and bulking agent to be co-composted. Bioresour. Technol. 96, 169180.

Vourinen, A.H., 2000. Effect of the bulking agent on acid and alkalinephosphomonoesterase and b-D-glucosidase activities during manurecomposting. Bioresour. Technol. 75, 133138.

Zubillaga, M.S., Lavado, R.S., 2003. Stability indexes of sewage sludgecompost obtained with different proportions of bulking agent. Com-mun. Soil Sci. Plant Anal. 34, 581591.

Zucconi, F., Monaco, A., Forte, M., de Bertoldi, M., 1985. Phytotoximsduring the stabilization of organic matter. In: Gasser, J.K.R. (Ed.),Composting of Agricultural and Other Wastes. Elsevier Appil. Sci.Publi, England.


compostaje de lodos aerobicos y anaerobicos agregando aserrin

Documents