~ Pergamon

PIT: S0273-1223(98)00418-1

Wal. sa. Tech. Vol. 38, No. I, pp. 327-334, 1998.IAWQ

C 1998Publishedby Elsevier ScienceLtd.Printedin GreatBritain.All rightsreserved

0273-1223198 $19'00+ 0-00

EFFECT OF ADDITION OF ANAEROBICFERMENTED OFMSW (ORGANICFRACTION OF MUNICIPAL SOLIDWASTE) ON BIOLOGICAL NUTRIENTREMOVAL (BNR) PROCESS:PRELIMINARY RESULTS

P. Pavan*, P. Battistoni**, P. Traverso*, A. Musacco* andF. Cecchi***

• Department ofEnvironmental Sciences , Calle Larga S. Marta 2137. 30123 Venice,Italy•• Department ofHydraulic. Via Breece Blanche, 60123 Ancona, Italy••• Department ofChemistry. Chemical Engineering and Materials,Monteluco di Rojo, LAquila,ltaly

ABSTRACT

The paper presents results coming from experiments on pilot scale plants about the possibility to integrate theorganic waste and wastewater treatment cycles, using the light organic fraction produced via anaerobicfermentation of OFMSW as RBCOD source for BNR processes. The effluent from the anaerobicfermentation process, with an average content of 20 gil of VFA+ lactic acid was added to wastewater to betreated in order to increase RBCOD content of about 60-70 mgll. The results obtained in the BNR processthrough the addition of the effluent from the fermentation unit are presented. Significant increase ofdenilrificaton rate was obtained: 0.06 KgN-NOYKgVSS d were denilrified in the best operative conditionsstudied. •Vmax shows values close to those typical of the pure methanol addition (about 0.3 KgN­N03IKgVSS d). A considerable P release (35%) was observed in the anaerobic step of the BNR process,even if not yet a completely developed P removal process. © 1998 Published by Elsevier Science Ltd . Allrights reserved

KEYWORDS

Denitrification rate; Biological nutrient removal; Anaerobic fermentation; Municipal solid waste; RBCOD;VFA.

INTRODUCTION

Biological nutrient removal processes are now extensively studied and full scale applications are presentworld-wide. In particular. in Europe the need to reach the restrictive limits foreseen in the 271/91 ECdirective gives an additional pressure to optimize process management and improving performances. Processlimits are strictly linked to the content of readily biodegradable carbon in the wastewater to be treated.

327

328 P. PAYAN et al.

expecially acetate and volatile fatty acids (VFA) (Wentzel et al., 1987). Several authors give results both inlaboratory and in full scale which show that the light organic fraction in wastewater can be increased byaddition of fermentation products of primary sludge (Rabinowitz et al., 1987; Aesoy & Odegaard, 1994;Isaacs & Henze, 1995).

All these studies consider mainly internal carbon sources, but the addition of external carbon sources aswell, like organic chemicals, is a normally used procedure in the plants. However, this approach can beconsidered only as an additional management cost As recently suggested in many countries (Rec.93) and, inparticular, in Italy (see Decree 22/97 about the new waste policy) the future approach in solid wastemanagement will have to consider the acquisition of organic substrates from separate collections of organicfractions of municipal solid waste (OFMSW). In fact, VFA can be produced, also in higher concentrationcompared with the primary sludge fermentation, using the organic waste as substrate. In this field, theliterature reports some investigations about VFA production from high organic contents substrates, but isdevoted to biofuels utilizations (D'addario et al., 1993). Integration of the Anaerobic fermentation (AF) ofsource sorted (5S) OFMSW and Struvite Crystallization Process (SCP) (Battistoni et al., 1997) with BNRprocesses, was recently proposed by Cecchi et al. (1994) and Pavan et al. (1994). In this approach, the VFArich liquid phase deriving from the AF process is added in the BNR inlet in order to promote thedenitrification and P removal processes. The aim of this paper is to illustrate some results obtained in pilotscale experiments on the integrated AF-BNR process, considering the effect of the addition of AF effluent tothe feed of a BNR process.

MATERIALS ANDMETHODS

The fermenter used for AF experiments had a working volume of 0.8 m3 (Pavan et al., 1994). It waselectrically heated and it was fed once a day with a membrane pump. The substrate was source collectedfrom some canteens and supermarkets of the city of Treviso (Italy). It was shredded by a hammer mill andhomogenized in a stirred tank before feeding. The effluent from the fermenter was screened through a screenpress, equipped with a 1 mm sieve. The BNR total volume was 18 m3 (Fig. 1), coming from 18 sections of 1m3each.

Figure I. Scheme of theBNRpilotplantusedin theexperiments.

This reactor configuration allows modifying of the volumes and the numbers of stages. The processconfiguration adopted for this study was derived from the Johannesburg scheme. The relative volumes of thesections were 22.2% anaerobic, 22.2% anoxic, 50.0% aerobic, 5.6% secondary anoxic. The secondaryclarifier working volume was 10 m3. The feed to the plant was taken directly from headworks of the full­scale plant of Treviso city (Italy). Salts addition (NH4CI, (NH.~hHP04) was necessary to increase the verylow nutrient contents in the wastewater used. The chemical and physical-chemical analyses were performedaccording to the Standard Methods (APHA, 1992). The Volatile Fatty Acids (VFA) determination wasperformed using a gas-chromatographic method (Column: Nukol 15m, 0.53 ID; Temperature: 85-125°C,

Additionof OFMWSon BNRprocess 329

30°C/min.; carrier: N2• 5 mllmin). Lactic acid was analysed by ionic chromatography (Column: DionexIonpac ASII , 4mm ID; eluent: NaOH O.2mM, I ml/min).

Kinetic tests (OUR, AUR, NUR) were performed following the procedures reported in Kristensen et at.(1992). RBCOD determinations were carried out following the method reported in Jenkins and Mamais(1993).

RESULTS AND DISCUSSION

Table I shows a resume of the fermentation test results in terms of effluent characteristics, operativeconditions adopted and yields obtained as RBCOD production. The results from the mesophilic conditionsshow that the total acid production was independent of HRT in the range 6-3 d. hence the deduction that theVFA production was almost completely developed in this time. Acetic acid and lactic acid were the maincomponents in all the conditions studied (44 % and 51% in respect of the total acid produced respectively).

Table I. Operative conditions, feed and effluent characteristics and yields obtained in the AF experiments(M =mesophilic conditions. T =thermophilic conditions, standard deviation in parenthesis)

RUN loll loll M3 M4 M' M6 Tt n nOPERATIVE CONDrrONS

HRT.4 6.6(1.3) 4.6(0.4) 4.4(0.2) 4.1(0.4) 2.8(0.2) Ul(0.2) 4.9(0.3) 3.1(0.1) 1.0(0.1)

OUl, KaTVSlm3d 11.0(3.2) 16.1(2.7) 13.2(2.4) 16.4(0.3) 21.8(2.8) 36.2(3.9) 19.1(2.9) 23.7(2.7) 78.3(9 .')

FEED

A.lolicl.aHAcII 1.4(0.1) 1.3(0.2) 6.0(1.0) 3.3(1.0) 1.0(0.1) 2.1(0.1) 1.3(0.4) 1.2(0.3) 1.2(0.2)

VPA.aHAcII 1.7(0.6) 2.0(0.6) 6.7(1.4) 3.9(1.4) 2.0(0.') 2.6(1.0) 2.2(0.9) 1.9(0.3) 2.0(0.')

La<tic,aHAcII 2.4(0.4) 1.7(0.8) 1.9(2.6) ' .3(1.3) (3.2(1.0) 1.1(0.2) 2.8(0.3) 4.1(0.4) '.6(0.1)

EFFWENT

A.lolicl. aHAcII 10.1(1.0) 10.2(1.2) 9.0(0.9) 1.1(0.2) 10.3(1.1) 6.1(0.6) 2.2(0.1) 1.9(0.1) 3.3(0.4)

VPA.aHAI:II 11.7(1.7) 11.3(1.0) 10.2(1.2) 9.9(2.0) 11.1(1.2) 7.9(1.3) 3.0(0 .9) 2.3(0.3) 3.9(0.')

La<tic,aHAcII 16.3(1.3) 10.1(2.1) 9.6(2.6) 6.3(3.3) 12.4(3.0) 12.6(2.0) 4.7(0.') 3.3(0.1) 13.2(2.1)

YIELDS

A<lolic,m aCOOIITVS 141.1 149.1 166.2 146.4 133.4 "'.7 36.2 33.4 49.7

OIhorVPA+1actic:, 201.1 131.1 163.6 IOU 149.1 194.0 63.' ,2.3 175.'maC00I8TVS

A test performed at HRT=I d (meso 6 condition) show more or less the same global production ofVFA+lactic acid mainly due to high lactic acid concentration and to an acetate concentration that is 30% lessthan in the other conditions (see Table 1). The results obtained from thermophilic experiments show that theyields in terms of VFA are much lower than in mesophilic conditions and are less dependent on HRT; theVFA production ranged between 33.4 and 49.7 gCODlKgTVS fed (TVSf). The lactic acid production isshown in Table I, where a marked increase of lactic acid production at the lower HRT (I day) can beobserved (175.5 gCODlKgTVSf). Considering these results. the effluent used for the BNR tests wasproduced in mesophilic conditions, using an HRT and OLR values in the range previously studied.

330 P. PAVANet al.

Table2. BNRtestsresults (standard deviation in parenthesis)

Run I 2 3(wastewateralone) (wastewater+sa1ts) (wastewater+sa1ts

+AFeffiuent)

INLET

TSS,mg/l 273(142) 291(126) 311(125)

COD,mgOtI 129(20) 181(62) 271(96)

SCOD,mgOtl 21(8.8) 47(16) 121(60)

RBCOD, mgOtl(·) 15(3.8)[11.6%) 28(14)[15.4%) 103(68)[38%]

TKN,mgll 11.7(2.8) 26.0(4.7) 24.5(5.6)

N-NH"mg/1 9.0(3) 25.0(5.9) 21.5(3.3)

p-PO., mgll 0.6(0.25) 11.1(3.0) 8.9(2.8)

Ptot,mgll 1.6(0.7) 12.0(2.7) 10.3(1.3)

CODrrKN 11 7 II

OUTI..ET

TSS,mgll 5.8(1.6) 8.0(1.1) 8.5(1.l)

COD,mgOtI 20(17) 29(14.7) 24(21.7)

SCOD,mgOtI 12(7.8) 18(12.4) 19(15.9)

TKN.mgll 1.7(1.4) 2.0(1.2) 1.2(1.1)

N-NH"mgll 1.3(1.0) 2.0(1.2) 0.0(-)

N-NO"mgll 4.3(1.3) 20.0(6.5) 7.0(3.2)

P·PO••mgll 0.4(0.2) 8.3(4.2) 6.4(3.6)

Ptot,mgll 0.9(0.5) 10,.0(2.5) 7.0(4.4)

N in WAS.o/,TS 4.0 4.3 4.5

P in WAS,'loTS 1.0 1.25 3.0

OPERATIVECONDnlONS

FIM,KgCODl1cgMLSS d 0.10 0.12 0.15

NIM, KgNlKgMLSS d 0.009 O.DtS 0.014

HRT.h 9 9 9

SRT,d 35 28 18

MLSS,mgll 3270(133) 4420(341) 5110(121)

MLVSSlMLSS 0.72 0.72 0.78

Qin.m'fd 47 47 47

Qr/Qin 0.6 0.6 0.6

QMIJQin 3.0 2.9 2.9

Yobs,KgSVlKgCOD d 0.23 0.21 0.30(.) Squarebraclcets: percentage of COD

Addition of OFMWS on BNRprocess 331

The BNR tests (see Table 2) were carried out in order to evaluate the consequences of fermented OFMSWaddition to the plant feed . Table 2 shows the inlet and outlet characteristics and the operative conditionsadopted. In run I wastewater alone was used, while in run 2 and 3 nutrient salts were added to the feed tomagnify the effects of the nutrient removal process. In fact, as can be seen, the nutrient content in thewastewater coming from the Treviso plant (run l) is very low (TKN=I1.7 mgll, Ptot=1.7 mgll). TheRBCOD fraction is only 15 mg02n. In these conditions, important fractions of the Nand P are removed bythe normal biomass synthesis during period 1. This is clear from the data reported in Table 3: the nitrogenamount removed as waste activated sludge (WAS) (0.07 KgN/d) represents approximately 25% of the totalN removed (0.278 KgN/d). The absence of a significant denitrification step was confirmed by the kinetic teston heterotrophic biomass (NUR), which shows very low values of k « 0.01 KgN-N03IKgVSS d; see Table4). Considering this data, about 0.200 KgN/d of the total N is denitrified, clos ing the balance and reachingan overall N removal of 51% (see Table 3). No P release was observed in the anaerobic step in this periodand little variation between in and out can be observed (1.6 and 0.9 mgP-P0.fl respectively, see Table 2). Inorder to underline the effects on nutrient removal, some salts were added to the feed, to reach a TKN contentof about 25-26 mgll and a P content of 12 mgll (see Table 2). In this way, due to salts addition, the biomasssynthesis cannot involve a N fraction as high as in the previous period. In fact, as can be seen from the datareported in Table 2, 20 mgN-N03n are released in the effluent. Only a little effect can be observed in Pcontent before and after the process (from 12 to 10mgll, see Table 2).

600 600 r.:::-~:---------;:===::::;-]500 Fig.2 .. I-In -out I 500 Fig.2 .b I--In -outlI~ I~ri~ ri~

~ 200 §200

100 100o 0 -l--+-~=+==f=:;:'::;::::p._=;::z,__~

316 336 356 376 396 0416 0436 0436 04041 04046 0451 0456 0461 0466 0471 0476 0481t,days t,days

Fig.2.d I-TKNIn _TKNoul _N.N03olA1

~.

040 W;;2.d-;::============~3530

~ 25

e 2015105o+--+-~~~""'=¢~""""'_-+-ll"""""=­0436 04041 04046 0451 0456 0461 0466 0471 0476 0481

t, days

,(0 r;;::;-:-----;:::::::;::::==:::;::::==~~~35 Fig.2.e 1__TKNItI - TKNOIA - N-1/03o<.t I

~~ ~-i'y:\;105o •

316 351 358 373 399 0409 0422 0426 0428 04304t, days

1-Plotin ....... Ptotoutl1-PIoUn - Plot out!30 r---------------,2724 Fig.2.r

21~18E 15

12963O+-_.........--+-_+-+-+-~_~+-'

356 376 396 416 436 436 441 446 451 456 461 466 471 476 481t, days t, days

Figure 2. (a-f)Trends of COD, Nand P in andoutduring BNRtest- run2 (a, C, e) and3 (b, d. f).

30 T:"::-::-=-----;:::==~;::::;:::::;l27 Fig.2.e20421

a18

E1512963O+----+--+--+--+--+-----+-+--I-'316 336

332 P. PAVANet al.

The results from run 2 can be confirmed considering the mass balances, that show that the biomass synthesiscontinues to play an important role in the removal eficiency: 38% of the total N is removed as sludge wasted(WAS), while the N denitrified, resulting from the low denitrification rate value (only 0.01 KgN­N03IKgVSS d see Table 4), alIows the closure of the balance with a total N removal of 20%. This can berelated to the characteristics of the organic matter in the feed, that has a low RBCOD fraction (11.6%).Furthermore, from the comparison of the TSS and COD in the feed (300 mgll and 180 mgOtI respectively),it is possible to hypothesize that a high fraction of Slowly degradable COD (SBCOD) is present in thisinfluent, which is absorbed by the biomass, whose effectively active fraction is then lowered. P removalprocess seems to be absent, as the PIal concentrations in the influent and in the effluent are almost the same(12 and 10 mgll respectively, see Table 2). In run 3, the fermenter effluent is added to the wastewater, inorder to increase of 60-70 mg0211 the RBCOD content in the influent (compare influent characteristics inTable 2). This amount was determined according to the mass balance presented in Cecchi et al. (1994),where the mass streams of OFMSW and wastewater obtainable per equivalent inhabitant were evaluated.The increase of COD (see Table 2: average COD in the inlet, run 2 and 3) in the influent did not induceappreciable variations of COD in the effluent, even considering the first two days after the fermentateaddition (see Fig. 2b).

476456436

\STARTADOmON

376 396 416t, days

356336

5,----------------~4.5

43.5

~ 3?F. 2.5a: 2

1.51

0.5O+-+--+-+--....-."'"""'""--+--+-+--+-+--t---+--+--+--+-'316

Figure3. P contentin WAS(1Vsrrs = 0.72-0.78).

Table 3. Mass balance of BNR tests

Run 1 2 3

N removed, (Nin·Nout), Kgld 0.278 0.235 0.804

N in WAS.Kgld 0.070 0.090 0.185

N denitrified, Kgld(.) 0.200 0.160 0.720

P removed, (Pin·Pou!), Kgld 0.031 0.094 0.160

P in WAS.Kgld 0.035 0.025 0.123

Cremoved,% 82 84 91

Nmnovcd,% 51 20 68

P removed, % 44 33 46(-)consIdering the rates given In table4

This fact is evident when considering the period after day 468-470, when the inlet COD coming fromwastewater plant about doubled the normal levels (up to 400 mgOtI). In general. improvements of processbehaviour can be found in the remarkable variations of N removal (compare Figs 2c and 2d). The reductionof N03 in the effluent was observed also since the beginning of the fermentate addition (average: 7 mgN·NO II vs. 20 mgN·NO II in run 2). This improvement can be also observed comparing the denitrification

Addition ofOFMWS on BNR process 333

rates values reported in Table 4, which shows an increase of about 600%. Considering the mass balance data(see Table 3), one can observe that 0.804 KgN/d were removed, 0.720 KgN/d (80%) of which weredenitrified, notwithstanding the fact that N in WAS in run 3 was twice that in run 2: O.I80 KgN/d vs. 0.090KgN/d respectively. This result is related to the increased Yobs (from 0.2 to 0.3 KgSSY/KgCOD d), due bothto better COD fed and to the lower SRT applied (from 28 to 18 d respectively).

The effectiveness of the fermented effluent in the denitrification step was also tested considering the Ymax'whose mean value was 0.28 KgN-N03/KgVSS d. This value compares well with the one that can beobtained using pure methanol as RBCOD source or with other easily biodegradable substrates (Beccari etal., 1993). The P removal process was also studied, notwithstanding it was not completely developed. Thiscan be evaluated comparing Figs 2e and 2f, where inlet and outlet P contents in run 2 and 3 are drawn. Ascan be seen, in run 2 P removal process was substantially absent, while in run 3 an average removal of about46% was observed (see Table 3). Sometimes, but not in the whole period, a P release of about 35% in theanaerobic step was observed. The P content in WAS, shown in Fig. 3, increased from about 12.5 gPlKgTS inrun 2 to about 30 gP/KgTS in run 3. These data are in agreement with the values of Popel et al. (1993),'typical of average biological phosporous removal conditions'. These results are possibly due to the shorttime considered as start-up of the process: even if the plant has been working for several months, the periodin which the RBCOD was added is about 60 days long, undoubtedly lower in respect to the periods normalIyconsidered for EPBR processes (Jardin and Popel, 1994).

Table 4. AUR and NUR during the experiments (*)

Run I 2 3

AUR, KgN·NH,lKg VSS d 0.05(0.002) 0.055(0.00I) 0.055(0.001)

NUR, KgN·NO,IKg VSS d -o.ot 0.01 (0.005) 0.06(0.002)(*) Allvaluesreported to20·C.using: K...O'C&K,., *1I1.12J(TlO) (Ekama e Marais, 1984)

CONCLUSIONS

The research carried out clearly demonstrates how it is possible to reach a deep connection between theMSW and wastewater cycles, in order to have better management of the resources. In particular:

the AF effluent addition, in the ratio given by the normal stream of waste/watewater production,shows a remarkable increase of the den itrification rate: from 0.01 do 0.06 KgN-N03/KgVSS d;the NURmax test shows that the AF effluenl gives Vrnax values near to the ones obtained withexpensive organic substrates, such as methanol and similar: 0.28 KgN-NOJ/KgVSS d;P removal process was partialIy present, but the not very high concentration of P in WAS (3%) andthe low release in anaerobic stage (35%) suggest that the process needs longer to completelydevelop.

The topics need some other investigations, in order to confirm and improve the results obtained and toindicate the effects of changes of the characteristics of the AF effluent (the variation of lactic/acetate ratio,for example) on BNR process.

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Beccari, M., Passino. R.,Ramadori, R. andVismara, R.(1993). Rimozione di azotee fosforo daiIiquami, Hoepli, pp.241.

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