(Received 1 arch 1995; revised version

0s kvmte biomms $km sweet so~%~~~ s’eems to be a good ~~t~~~t~ve for its valstization ii2 ~~~~~~~. The purpose of this work was to establish the best e~~e~~e~t~~ conditions for the aerobic bioconver-

starting with diferent C:IV ratios

&&JO fields with a fetiiliza- tim Eevel of 100 kg and it was cornposted using bovine blood, domestic sludge and yeast extract as nitrogen sources, muting with initial C:N ratios of ~~~~~~irnate~ 20 a

The e~~~~‘rne,~t s can?ed out in a constant tem- perature chamber at 37°C and lasted for two and a half rn~~t~s. es were periodically collected and analyzed. The nit state of the product was also evaluated.

The best quality compost ,jom a fertilizer perspective was obt&ed with dcmestic sludge as a nitrogen source and starhg f;om m initial C:iV ratio equal to about

rting from this C:AT ratio could bring problems contelat of cadmium, so the recommended

startiing c~~~d~t~a~s must be about 3&I.

~~~~-~~~~~~ form of organic waste re conditions may be created which

allow the natural ~~~~r~e~~e of thermophilic tem- er ~a~tic~~a~ conditions o t is possible to compost sol

solid materials of any different origins, but it is important to take into ount the environmental effect of the process and e possibilities of increas- ing the value and reuse of substrates which Et involves.

~o~~~~ti~g is ~a~t~-~~a~age~e~t strategy that must be consider mong the existing possibilities of biomass valori ) but its fertilizer value differs

“Author XI ~Aorn cosrespondence should be addressed.

Peceived 2.5 June 199.5; accepted 3 July 1995)

according to crop an Glimate ~ba~ac~e~~§t~c~ and soil fertility and structure.

AS to the S\~JCXZt S

economics of both utilization taking into account the Bow level of organic matter in th Portuguese soils and the probkzs of structure. The ~o~§ibilitie§ of obtaining hi

atter or other when possible. The scarce ene ifi Portugal make sweet sorgh

interestiug a!terna- due to the go0

sunshine and cocditions of the country.

ust be assessed

have been carried een made on the

nutrient content of the compostkg material was evident in those e~~e~~~e~t~~ Nitrogen acts as a limiting factor for protein synthesis, ~ic~~b~a~ growth and metabolic bioco~~e~~i are other variables, such as the s ~~~d~ti~~, that are also importa Level of composting a&&y and attaining a finai

authors, working on t e same ~~b§t~ate and have presented

of the initial @:i?J

compost (Negro, 1992). The need for a cheap nitro- gen source is of most i~~orta~c~ in this context. For that purpose, it woufd be: if pxsibie, ~~te~~sti~g to use nmesiaf of e~viro~~~~tal concern so that it could also be ‘ncreased in vaPue through the process.

in order to analyze a broad range of po&Mities, three N-sources were considered: bovine blood, a

Sorghum Bovine blood Yeast extract Domestic sludge

Moisture Mineral mat. Organic mat. Carbon (%) 6% dm) (% dm) (% dm)

10.39 7~28 92.72 51,51 IO.67 343 96.57 53.65

9.23 14.38 85.62 47.57 8.22 35.72 64.28 35.71

--__-...__-__..__ Nitrogen C/N (% dm)

--- 0.66 78.05

13.29 4.04 !@92 4.36 2.99 LB.94

Values are averages of three replicate analyses. dm -

Table 2.

TO l-3

Without With rumen rumen

iuoisture (%) 10.39 8.86 8.76 Mineral mat.(% dm) 7.28 11.34 9.64 Organic mat. (% dm) 92.72 8866 90.36 Carbon (% dm) 51.51 49.46 50.20 Nitrogen (% dm) 0.66 1.52 I.11 C:N 78.05 32.54 45.23 Cellulose (% dm) 32.66 33.03 38.28 PhospSorus (% dm) 0.23 0.33 0.34 N:P 2.87 4.61 3.26

To at begining of July. T3 at end of Setember. Values are averages of four replicate compostings.

by-product from cattle slaughtering; yeast ss extract, a possible organic by-product obtain m treated residual wastewaters from biological indus- trial processes; treated domestic sludge, a waste material from domestic wastewater-treatment plants.

s cultivated in experimental niversity campus, in Mont

Lisbon in the southern margin of the Tagus valley.

The climate is mild and strongly in ocean. Tbe rainfall can reach 71 year, with a maximum in October very low in summertime. The annu ture is about 16°C and July is the hottest month

3G’@, with a maximum of 28~lT). There are 2577 of sunshine/year, with a maximum of 360 h in July. be annual evaporation is about 1508 m

average atmospheric moisture is 72%. The experimental soil was clay type a

of 8.3 in water and 7.2 in KCI, with matter, more than 2 0 mg of extractabl (as P,O,) and 178 mg of extractable l&Q), A fertilizer at 100 kg of N/ha was a the soil.

of the initial rce a inmm

Metal

Co CLl Zn Ni Pb er Cd

Sorghum T,

890 1359 1365 4041 197 8.60 nd 13

105.70 3.60 nd nd nd

Compost T,

Without with rumen rumen

12820 16720 2687 2818 1588 1288

11525 IO194 895 173 28 32.10 nd nd

16.10 14.40 53.40 52~30

nd nd nd nd nd nd nd cd

nd - Not detectable. aSee Table 2 footnotes.

at 103 i_ 2°C _n an eiectric oven 0 constant weight. A.sh: by calcina-

tion at 550 *58”@ for 1 h in a (Cassel). Total organic : difference between total weight (100%) a ash content. Total organic carbon: using the factor to convert the

ic matter to carbon. CelBulos IIuci. Total nitrogen: by the

ast A starter culture of 0.5 g jfres

at 4°C for 2 weeks and ed. This showed it would not have

nal ~~~~~§~t~o~ of the compost mixtures.

Cornposting of sweet so&wn 23

le 4. Compost obtained __-.- -~-- --

Biomass ~a~~~~~g time characterization

TO” T1 TZ T3 ~___---.- C:Nz20 Moisture (%) 20.13 6.64 8S3 14.39

ineral mat. (% dm) 5.76 3.46 7.81 8.97 Brganic mat. (% dm) 94.23 96.55 92.23 91.04 Carbon (“lo dm) 52.35 53.64 51.24 50.58 Ntrogen (% dm) 1.62 1.71 2.05 2.71 @:N 32.32 31.37 25.00 18.66

3X (% dnl) 28.02 36.58 27.72 36.92 horus (% dm) 0.26 0.27 0.30 0.32

6.23 6.33 6.83 8.47

C.N - 30 Mois&e (%) 2044 6.57 8.35 8.81 Mineral mat. (% dm) 6.19 3.80 8.54 9.91 Brganic mat. (% dm) 93.81 96.20 91.47 90~09 Carbon (% dm) 52.12 53.45 50.81 50.05 Nitrogen (% dm) 1.36 1.81 I.61 255 C:N 38.32 28.53 31.56 19.63 Cellulose (% dm) 32.76 37.24 34.92 28~71 ~bos~bur~s (% dm) 0.23 0.26 0.26 0,32

5.91 6.96 6.19 8.23

“See Table 2 and Methods for limes.

le 5. Metal sonteHBt of the cons ____-._

&is content Sampling time (q/kg dm)

C:N z 20 Cm 2 30 -.

TCl Tl TZ T, ;“‘o TI T -2 T3 ___I_ ---

Ca 1949 3116 3093 5978 1849 3241 3612 4744 Mg 1697 1952 2115 2244 2353 2489 2.320 3214 Na 2261 2047 2301 4220 1494 1533 2300 3048 K 8284 10042 10398 12250 8321 9551 11280 12133

435 580 584 672 360 419 436 526 8.60 20.30 19.10 22.4G 11.80 12.20 25.16 30.10

Co nd nd nd nd Ed nd nd nd eu 13 13.80 14 17.50 9.40 9.30 !@I0 13 zn 105.70 110.10 115.20 116.10 83.10 85.40 93”7O 97.50 Ni 3.60 nd nd nd 3.50 3.90 4.96 nd Pb nd nd nd nd Ed nd na nd e nd nd nd Ild fid nd nd nd c nd n d nd nd cd nd nd nd _I__-

wd -- Not detectabie. “See Table 2 and Methods for times.

was based on the variety pulation present, p rIy th ukative organisms shoul

have been able to survive and grow in transient aerobic c~~~~~t~~~s~ such as those existing in com- posting biomass.

1 proceedings were collected in the

fields, cut Into seal feces and ground in the laboratory.

The bovine bksod was obtained at the LiIIicipal Siaughterhouse of Lisbon.

The yeast exiracl use was a commercial product,

in xderr to assure a reproducible eompositioan. mestic treated ge, which vias a biologi-

ined at the ~~aste~~ater

to start from two initia.1 C:N ratios: another near to 30.

The experiment was carried out using glass Basks each one containing 10 g of so

of about 20, 1.81 g of bovine bl ast extract or 15.53 g of d.o

was added. To obtain a C:N near 30, W2 or 5.73 g of the same materiak were ad&d. The actual value of the C:N ratio was not critical, so the material was analyzed after the additio1~ of the nitro-

Humidity (% of wet mat,) SaliniQ (meq/lOO g dm) Organic carbon (% of dm)

umihcation degree (%) umification rate (%)

C/N PQ/NH; B (m&g dm) Germination index (%) Salmonella (MEW) Apparent density @I) Hydraulic retention capacity (% of vol.) Total porosity (% of vol.) Free porosity (% of vol.) Glass (% of dm) Plastics (% of dm) Cd (mg/kg dm) Total Cr (mgikg dm) Hg (mg/kg dm) Ni (mdkg dm) Pb (mgikg dm) @u (mgikg dm) Zn (mgikg dm)

<45 <8Q >20 >50 >30 <25 >? <30 >40

Absent - -

-_ < 0~5 <@3 <3

< 150 <3

<50 < 150 <400 < 800

<45 <25 >25 >SO >3O <35 >I

<50 >9O

Absent 200-500

>55 >85 >I§ <2

<@6 <S

< 30s <S

< 200 <SO0 < 500

< 1000

iomass characterization

~arn~li~g time

C:Nz20 Moisture (%) Mineral mat. (% dm) Organic mat. (% dm) Carbon (% dm) Nitrogen (% dm) C:N Cehuiose (% dm) Phosphorus (% dm) N:P

CN2530 Moisture (%)

ineral mat. (% dm) Organic mat. (% dm) Carbon (% dm) Nitrogen (% dm) C:N Cellulose I% dm) Phosphorus (% dm) N:P

24.72 6.83 854 366 845 7.85 9.95 9.62

91~55 92.15 90.05 90.38 5Q.86 51.20 50.03 50.21

1.98 2.64 I.82 1~81 25.69 19.39 27.49 27.74 29.23 34.28 34.04 39.69

0.64 0.62 I.78 Cl.58 3.09 4.26 I.02 3.12

22.82 6.18 7.42 66%

92.58 93.39 51.44 51.88

1.46 154 35.23 33.69 32~81 37.26

0.50 0.58 2.95 2.66

IO56 1054 89.46 49.70

I.70 29~24 31%6

0.6% 2.50

9.52

12.15 87.85 48.80

1~63 29”94 26+&

050 3.38

“See Table 2 and Methods for times.

gen sources. The mixtures, toget er with the insculum, were

homogenized and the reactors randomly inside a constant temperature char&e They were periodical!y aerated in order to keep aerobic conditions. For each sample there were four replicates.

The study was follswed for two and a during which the four replicates were fully charae- terized: at the beginning (T,); after 2 weeks (Tr); after 6 weeks (TZ); at the end (aa).

he sweet sorghum bio the nitrogen Sources used

o are presented in Table 1.

each of the nitrogen sources to be added. to the sweet sorghtnrn in the ~~~~~§ti~~ reactors in order to obtain aproximately the desired C:N ratio, As the

tical, there was no a

Samp?ing time

--I___- T -~ 0

_l__l_-.___ -.____ Ca 890

1359 2533

17657 197

Mn 8.68 co ad Cu 13~20 zn 141~50 Ni 8”lO a>b nd Cr nd Cd na

T1

1020 1597 2615

19192 203 14.10 nd

14.40 148.80

nd nd nd nd

T2

1125 1582 2446

20584 196 14.70 nd

16.90 157.20

nd nd nd nd

-

a3 To T1 T2 T3

1770 1127 1212 1383 1437 3039 2093 2345 2403 3955 2857 1805 2193 2435 3065

20353 13344 15606 16424 19940 204 271 272 317 17~20 13.20 17.10 22.30 nd nd nd nd nd

15.40 10‘60 IO.40 12.60 16.50 187.90 94.70 103.40 103.20 113.30

nd I.20 nd ad nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd

nd - Not detectabie. “See Table 2 and Methods for times.

estic sl .-l__l---. -_.---_ Biomass Sampling time ~~ara~t~~i~atiQ~

To” l-1 T2 TX ----~ --.--- cm zz 20 Moisture (%) Mineral an&(% dm) Organic mat. f% dm> ,Carbon (% dm)

ineral mat. (% dm) Organic mat. (% &I) Carbon C% dm)

Cehlose (% dm) Phosphorbls (% am) N:R

18.92 5.61 7.11 21.81 13.94 31~61 78.19 83.06 68.39 43.44 47.81 37‘99

2.46 3.73 2.11 17.66 12.82 18.00 29.04 31‘62 42.73

0.72 0.69 1~36 3.39 2.92 3.64

21.72 6.31 6.94 7.38 12.31 IO.15 21.75 24.67 87.69 89.86 78.25 75.33 48.72 49.92 43.48 41.85

1.43 148 1.74 I.75 34~07 33.73 24.99 23.91 32.40 33.69 40~22 37.22

0.52 OGI 058 0.56 2.75 249 3.00 3.12

665 33.80 66.20 36.78

2.54 14~48 35.94

30:;

“See Tab%e 2 and Methods for times.

ed without arty nitro- m the biomass in this

e~~er~rn~~t are ~re~e~t~d in Table 2. Those values were obtained at the beginning (July 1993) and at the end of the e~~~r~rne~t (September 1993).

Two ~~l~~a~~~~~ were considered: wit vine rumen contents addition.

be noticed between the final e compost produced when

inoculum was bad a higher organic matter content and a total nitrogen content, with a

t 4:1. The co~l.~o§~t~o~ of

past obtained when n nal C:N ratio of 3011.

removal of carbonaceous mate content and its microbial pop ~ac~~tat~ve anaerobic microrgan~ as might be ex cellulosic substances especially7 indicating t c~~~~~o~y~~c activity was not as efficient as might

ected. Tine maturation of the compost without any of the additional nitrog sources was not rapid as possible, proving useflr,ljness of su addition, as had been th~or~t~ca~~y ex!Jected (Jack- son et ai,, 1992).

Metals content @%k dm)

ea Mg Na

Fe Mn CO Cu Zn Ni Pb Cr Cd

T0

25974 2769 1365 4041 3906

48

12770 523 10

54.80 35.60

0.10

C:N=20

T1 rz

35663 35088 2997 2813 1474 1447 4689 4638 5574 6693 79.30 94 nd nd

190.60 209.60 639.70 677.10

29.60 30~70 98.20 134.40 64.30 72.40

1.60 5.10

Sampling time

T3 r0

39172 22620 3680 3040 1619 1712 5194 5599 7998 2897 97.40 42.20 nd nd

251.50 76.30 822 404~30 32.40 5.60

150.60 22.20 91.80 37.70

6.90 nd

-_I__ II_-_ C:NZ!SO

-__I T J 1 T2 T3

26728 28042 33231 3272 3053 3520 1433 1767 1808 5843 6416 7164 4244 4420 6392 64~80 66.5 072.7 nd nd

116.10 121.2 y$Fl 43@51! 477.6 632.1

12.10 18.4 22.30 61.10 58.3 86.5 54.30 45~5 61~7 nd 2 3.4

nd - Not detectable. “See Table 2 and Methods for times.

Table 1%.

CN%20 Total Coliforms Faecal Coliforms Total Streptococci Faecal Streptococci Clostridium

C:N=30 Total Coliforms Faecal Cofiforms Total Streptococci Faecal Streptococci Clostridium

Yeast extract

TO” T3

4.0QIz+03 2,20E+06 4.0OE+03 2.20J.s+06 55lE+O8 3.30E+O& 5.25E+05 1.13E-k08 3.60E+07 3.52E+O9

4.65E+O6 8.25E-kO7 4.65E+Q6 8.25E+O7 3.60E+ 08 2.30E+07 1.55E-tO6 5.90E+06 2.52E+08 1.25E+09

Bovine blood

TO T3

2.35B-s04 7.65Ec06 2.35E+04 7.65Ei-06 i.l3E+08 1.40E-k08 9.45E-k07 1~4oE+08 532E+06 9.30E+-07

7.70Et- 04 1.90E+-O7 7.70lz+ 04 1.90E-+07 3.35E+O8 6.25E+-OX 1.67E+08 6.25E-kQ8 2.9QE+06 45OE+O7

N)

Domestic sludge

T “II T3

9.15E-k02 3.IOE-k05 9.15E+O2 3.1OE-k05 1.19E-tO8 4.66E-kO8 l.lOE1-07 7~72E+O7 2~70E-k 08

2.05E+-06 5.15E-k06 2.05E-k06 515Et-06 4.3OE+-OR 2SKSL07 1.40E-kG8 2.17E-kO8 1.8OE-k07

“See Table 2 and

The metal content of the samples is presented in Table 3, showing an apparent concentration of the metals by removal of organic materials. T obtained in both e eriments had a quit content of heavy metals and a useful nutrients.

envy of N addition, according to the nature of the materials were tested,

the N-source to balance carbon camp sented in Tab!es 4 an

extensively degraded was not dangerous. C:N ratio (about 30

were obtained but significant cehlose sadation was attained. A comparison between the quality of

ost obtained and Table 6, e qualifica- es of compost proposed beiro el al.

re presented, sugge oduct obtained n bovine blood was

The second N-source used, yeast extract, was a theoretical situation because this i waste to be used for this purpose. drawn from the analyses in lar to the previous one, but the higher value as a fertikzes, when initial C:N ratio of about 30:1,

The third product us sludge from domestic was sludge produced in Pertagga~

ing ~~virQ~rne~ta~ concern. The treatment of tic ~Ia~tewater is

Cornposting of sweet ~o@zitm 27

ay contain, at the most, eavy-metal contents ftxed irective. According to Sequeira et QI.

s, rticularly zinc and cop- S. igh contents of these

elements are s~~~~t~rnes present for geological rea.sons.

In the present experiment, domestic sewage siudge from kisbo was used. The results of this co- ~~rn~ost~~g experiment are presented in Tables 9 and 10. The results are reasonable, even if cellulose degradation was as extensive as might be expected: during riod considered. Ht could be of interest to exte maturation time.

The compost obtained from an initial G:N ratio of ed as type A, the heavy- table. The major problem

e content in the final product attained 4 ppm for an initial C:N ratio of 2Q:l but only 34 ppm for a C:N ratio of 3O:l. The compost in the case of a C:N ratio of 2Q:l was a B-type for this specific pollutant, T situation was forecast by Sequeira (1994). This thor recommended continu- ous monitoring for this metal because of its ~a~t~c~la.~~y harmful effects2 and the present results have d~~~o~strated the correctness of his sugges- tions.

~~~cr~~~a~ numbers are presented in Table 11. The non-exislence of accepted microbiological standards does not allow an objective assessment of the results [Jackson ee al, I Nevertheless, such a standard could be useful we present these values as a possible level at which compost could be considered as acceptable and without environmental concern.

Sweet sorghum biomass ca:n be used for vomposting if co other reasonable alternative exists, or if there is

he addition of a nitrogen source is essential for this type of bioconversion.

ossible products or wastes to be from domestic wastewater treat- ood alternative to be considered. It

is a material of e~v~r~~rne~ta~ concern that can be

re-.used through this treatment ark ehe final pro is a g~~d-q~a~~~ compost with value as a

nutrient source. The problem faced w n sludge is used as a N-

that the cant

and the recommended starting ratio must be about 3G:l.

.?ackson, 9. V., Merillot, .I.- 6% C Eermire, P. (1992). Cooriposting aizd Compost ualily Assumnce Cn&n‘a. Eommission of the European Communities, Luxem-

J. (1992). Laboratory cornposting assays of sweet sorghum bagasse with different additives. 7th 3tropean Conj: on Biomass for EnerQ and Environment, Agriculture and InduTy, Florence, Italy.

Wlbeiro, H. et ol (1994). An Eval~uxtion of Thee ~~~~cip~l Solid ‘FKastes. dnstituto Superior de Agronomia, Eisboa, Dortugal.

%&igues, A. M. & Ferreira, L. _T. (1992) Compostagem do Sorgo Sacarino. elat6rio no Bmbits da discipEina de Jrocesscs Biolecno ices de Valorizar,ao de Residues. <Gomposting of sweet sorghum,. Academic assay for the subject “Biotechnological processes of waste valoriza- Cm’.) Universidade Nova de k&boa, &boa, ortugal. odrigues, A. M. et al. (1994). Co-composting of sweet sorghum waste material after sugar extraction utilizing domestic sludge as N and P source. 8th I%ropea~z COHJ: OIZ Biomass ,for Energy and Environme?af Agkdture and

et al. (1993). E3ehaviou.r of copper and zHnc in a sludge-treated soil. ~nte~~~t~o~~~ Cm@ on Envirmmental Poilution, European Centre for Pollution Research.

Seqpeira, E. M. (1994). Impact0 da apli@o de lamas resi- duais no solo. Seminario sobre ‘Tratamento e destino final de Pamas de aguas residuais’. (Applance of sewage sludge on soils. Seminar on ‘Treatmen: and final dis- posal of waste water sludge’.) Laboratorio Nacionai de ?%rgenharia Civil, Lisboa, Portugal.