Treatment of slaughterhouse wastewaterin anaerobic sequencing batch reactors

OJ. MASSE and L. MASSE

Agriculture and Agri-Food Canada, P.O. Box 90,2000 Route 108 East, Lennoxville, QC, Canada J1M 123. Agriculture and Agri­Food Canada contribution No. 659. Received 5 July 1999; accepted 6 June 2000.

Masse, D.I. and Masse, L. 2000. Treatment of slaughterhousewastewater in anaerobic sequencing batch reactors. Can. Agric.Eng. 42: 131-137. Slaughterhouse wastewater was treated in four 42-Lanaerobic sequencing batch reactors (ASBRs) operated at 30·C. TwoASBRs were seeded with anaerobic granular sludge from a milkprocessing plant (MPP) reactor and two ASBRs received anaerobicnon-granulated sludge from a municipal wastewater treatment plant.Influent total chemical oxygen demand (TCOD) ranged from 6908 toJJ 500 mgIL, of which approximately 50% were in the form ofsuspended solids (SS). Total COD was reduced by 90% to 96% atorganic loading rates (OLRs) ranging from 2.07 to 4.93 kg m') d· 1 anda hydraulic retention time of 2 days. Soluble COD was reduced byover 95% in most samples. During the start-up period, highconcentrations ofsolids were lost in the effluent, but under steady stateoperation, at OLRs above 3 kg m-3 d- I

, biomass retention was adequateand effluent SS averaged 364 mgIL. Reactors seeded with municipalsludge performed slightly better than those containing the MPP sludge,especially during start-up, but differences between the two sludgesdecreased with time. The biogas contained 75% methane. About90.5% of the COD removed was methanized and volatile suspendedsolid (VSS) accumulation (apparent biomass yield plus undegradedsolids from the influent) was evaluated at 0.068 kg VSS per kg CODremoved. This high degree of methanization indicated that mostsoluble and suspended organics were degraded during treatment inASBRs operated at 30·C.

Quatre bioreacteurs it operations sequentielles (BOS) d'unecapacite de 42 L ont ete utilises pour Ie traitement anaerobie d'eauxusees d'abattoir a30·C. Deux des BOS ont ete ensemences de bouesgranulaires anaerobies provenant d'une usine de transformation du lait(UTL), tandis que les deux autres BOS ont ete ensemences de bouesnon granulaires provenant d'une usine municipale de traitement deseaux usees. La demande chimique en oxygene totale (DCOT) dusubstrat variait de 6 908mgIL it 11 500 mgIL, dont la moitie provenaitde matieres en suspension (MES). La DCOT a ete reduite de 90 % it96% it des taux de charge organique (TCO) variant de 2,07 it 4,93 kgm·3j"1 et it un temps de retention hydraulique de deux jours. La DCOsoluble a ete reduite de plus de 95% dans la plupart des echantillons.On a observe d'importantes pertes de boues pendant la periode dedemarrage, mais en regime stationnaire, ades TCO de plus de 3 kg m·)j"1 , la retention de la biomasse dans les reacteurs etait adequate, et lesconcentrations de MES de l'effluent s'elevaient en moyenne a364mgIL. Le rendement des reacteurs ensemences de boues provenant deI'usine de traitement municipale s'est revele legerement superieur acelui des reacteurs ensemences des boues provenant de I' UTL,notamment pendant la periode de demarrage. Cependant, les ecartsentre les deux types de boues se sont estompes avec Ie temps. Lebiogaz comprenait 75 % de methane. La methanisation de la DCOeliminee s'estelevee a90.5%. L'accumulation de matieres volatiles ensuspension (MVS) (soit Ie rendement apparent en biomasse plusI'accumulation des solides non decomposes du substral) a ete evaluee

it 0,068 kg de MVS par kg de DCO eliminee. Ce niveau eleve demethanisation indique que la plus grande partie de la matiereorganique soluble et en suspension a ete decomposee dans les BOS aucours du traitement anaerobie a30°C.

INTRODUCTION

Slaughterhouses produce a wastewater highly charged in solubleand insoluble organics. In Quebec and Ontario, hogslaughterhouses generally discharge their wastewater inmunicipal sewers after some level of primary and/or chemicalpretreatment at the plant (Masse and Masse 2000). Thesepreliminary treatments, however, are not sufficient to lowerpollutant levels below municipal standards. Slaughterhousesmust therefore pay a surcharge to have their wastewater furthertreated at the municipal treatment plant. Existing in-plantwastewater treatment systems also produce large quantities ofputrefactive and bulky sludge, which requires special handlingand/or further treatment.

Anaerobic digestion in high-rate reactors represents anattractive alternative for wastewater treatment at theslaughterhouse plant. First, slaughterhouse wastewater isparticularly well suited for anaerobic treatment. It contains highconcentrations of biodegradable organics, mostly from fats andproteins, sufficient alkalinity, and adequate phosphorous,nitrogen, and micronutrient concentrations for bacterial growth.It does not include toxic compounds and has a relatively warmtemperature between 20 and 30·C. Secondly, anaerobicdigestion provides high COD and suspended solid (SS) removalwhile producing a recoverable source of energy in the form ofmethane. It generates very low quantity of sludge and does notrequire aeration or chemical pretreatment. Finally, anaerobicbacteria can survive unfed for long periods of time, an importantfeature for smaller slaughterhouses that operate just a few daysa week or close down during slow or holiday periods.

The anaerobic sequencing batch reactor (ASBR) developedby Agriculture and Agri-Food Canada would be especiallyappropriate for slaughterhouses, because it can operate withlimited capital costs, energy, and manpower. This newtechnology has been successfully applied on laboratory andsemi-commercial scales for the treatment of swine manureslurry (Masse 1995; Masse and Croteau 1998; Masse andDroste 1997; Masse et al. 1996, 1997). The objective of thisproject was to demonstrate the feasibility of using ASBRsoperated at 30·C to treat slaughterhouse wastewater. Data froma five-month experiment are presented and discussed.

CANADIAN AGRICULTURAL ENGINEERING Vol. 42, No.3 July/August/September 2000 131

Fig. I. Opel"ation of the anaerobic sequcncing hatchreactor.

close contact betwecn organics und bacteria. Mixing should be asgentle as possible to uvoid disrupting the fonnation of bacterialnoes. Intennittent mixing is also preferred to continuous mixingbccuuse it improves biollluss settling and rcactor perfonnance(Sung and Dague 1995). The food to micro-org,anism (F/M) ratiois high at thc beginning of the react phasc and organic conversioninto biogas, as predicled by Monod kinetics, is at its maximum(Sung and Dague 1995). The length of the reaCI period will dependon substrntc characteristics and cfnucnt quality requiremcnts. Forwastewaters containing high 55 concentrations, more contact timebetween bactelia and substratc will bc required for the completehydrolysis of particulatcs. \Vhen gas production rat.e has decreasedto a minimum, reactor contcnt is allowed to settle. The low F/Mratio at the end of the react phm;c favours biomass nocculation andsCllling (Sung and Dague 1995). During thc settling phase, thepartial pressure of CO2 above the liquid zone is constant and inequilibrium with dissolved CO2, As a result, no signi ticant quantityof CO., is transferred to thc heudspace. a situation that contributesto the·establishmcnt of quiescent settling conditions. When thebiomass fonns a compact layer at the bottom of the reactor, thesupernatant is drawn to a predetcnnined level. usually at somedistance above the biomass bed. During efflucnt drawdown_microorganisms with poor scttling characteristics are also removedfrom the reactor, leaving behind the heavier bactclial noes (Sungand Dague 1995).

Thc advantages of the ASBR technology include low capitaland operating costs as well as minimum daily maintcnancc.

Removetreatedwastewater

Reactionperiod

Addwastewater

Clarify

Fill

Read

Settle

I I

Influent

----, I

Idle

k:;;:.;;J ~;:-" -. - "-=::.!-': -

Wastewater

LITERATURE REVIEW

Most laboratory studies on the anaerobic lreallncnl ofslaughterhouse wastewater have been conducted with anaerobicfilter reactors (AFRs) or upnow anaerobic sludge blanket(UASB) reactors. The AFR can sustain high organic loadingrates (OLRs) when the wastewater contains mostly solublechemical oxygen demand (SCaD) (Aror:! and ROUlh 1980:Borja et aJ. 1993, 1995a). Borja et aJ. (1994a) reponed a 94.5%COD reduction at an operating temperature of 35·C. an OLR of10.1 kg m-) dol and a hydraulic retention time (HRT) of 12 h.However, raw slaughterhouse wastewater contains highconcentrations of insoluble, slowly biodegradable solids, ortenrepresenting over 50% of the polluting ch:lrge (Masse c[ Masse2000; Sayed et de Zeeuw 1988). Ruiz et aJ. (1997) used an AFRoperated at 3rC to treat slaughterhouse wastewater cOI1lainingbelween 15 and 30% of ils COD as SS. When the OLR wasincreased above 3 kg m-l dol, COD reduction dropped below65% and effluent 55 concentration reached 1000 mgIL. Trill(1992) used an AFR to trcat a slaughterhouse Wilstcw3ter thatcontained 46% of its COD as SS. Reduction in COD rangedfrom 80% at OLRs below 2.5 kg m-l d-I to 30% al 18 kg m-3 dol.Treating the same wastewater after a two-hour scnling periodimproved COD reduction by an additional 10 to 15%. Saxenael al. (1986) treated a slaughterhouse wastewater that containedaboul 1000 mg SS/L in an AFR operaled at 25"C. At OLRsexceeding 2 kg COD 11,-3 d- l , fat and 55 deposition in thebioreaclOr caused a rapid deterioration of the biomass.

upnow anaerobic sludge blanket reactors arc also efficient intreating low 55 slaughterhouse wasteWaicr. At 35°C, COD wasreduced by morc than 90% at OLRs up (0 6.4 kg 111'3 dol (BOIja elal. I994b). AI 25"C, COD was reduced by 78% at an OLR of 6.1kg m'] dol (Zheng and Wu 1985). Lowering the operatingtemperature to 13

Q

C still pennitlcd a 75% COD removal at all

OLR of 3.3 kg m-3 d- l, as long as the HRT was maintained abovc

10 h. Howevcr, at 55 concclllrmions ranging from 15 to 30% ofinfluenl COD, total COD (TCOD) reduction decreased to 70% andSS losses reached 2000 IllgIL, at an OLR above 5 kg Ill" d·1and anoperating temperature of 37"C (Ruiz et al. 1997). Sayed et al.(1984. 1987, 1988) investigated the effect of SS concentration onthe anaerobic digestion of slaughterhouse wastewater in UA5Breaclors operated at 20 and 30"C. Results indicated that a ponionof thc removed COD was not converted into methanc bur waseliminated by other means such as nocculation and adsorption ofcolloidals on sludge panicles and cmrapment of coarse 55 in thesludge blanket. Weekend feed intemtptions pennitlcd a partialdigestion of retained solids (Sayed el al. 1984, 1987). However.when the OLR was increased from 0.5 to 10-20 kg COD m-3 dolover 57 days of continuous loading at 30

Q

C, a suddcn and heavysludge llotation led to the completc loss of biomass from thereaclor (Sayed el de Zeeuw 1988). Process failure lVas allribuledto an excessive accumulation of substratc materinl within thebiomass bed. Sayed el al. (1988) concluded that the controllingfactor in the digestion of unsettled slaughterhouse wastewater wasthe liquefaction "Ite of the adsorbed and elllmpped solids. and Ihusoperating temperature was critical.

Anacrobic sequential batch reactor

The ASBR represents a fairly new design of high-rJte anaerobicsystcm. In ASBRs. four treatment phases (feed. react, scttle. anddraw) are accomplished sequentially in one vessel (Fig. I). Duringthe feed and rcact phases. the rei.1CtQr content is mixed to allow

132 MASSE and tvlA$SE

MATERIALS and METHODS

Fig. 2. Plan of laboratory scale sequencing batch reactor.

Table I. Characteristics of the experimental slaughter-house wastewater.

Parameters Days after ASBR inoculation(mgIL except pH)

0-24 25-58 59-94 95-157

Total COD 6908 9665 11500 9445Soluble COD 3449 4714 5490 4505

Total solids 4892 6098 7121 6119Volatile solids 3647 4864 5724 4779Suspended solids nd· 2135 2658 2900Volatile suspended nd 1936 2458 2546

solids

Total Kjeldahl nitrogen 534 619 735 617Protein 246 89 221 172

1800 3313 3213 2781

pH 7.0 7.4 7.1 6.7Alkalinity (as CaC03) 1056 667 972 889

not determined

Operating conditionsThe four 42-L plexiglas ASBRs used in the experiment areillustrated in Fig. 2. The reactors were located in a temperature­controlled room maintained at 30°C. They were batch-fed everytwo days. The OLR was progressively increased by augmentingthe volume of wastewater fed to the reactors from 2 to 13 L.During the react phase, the digester content was mixed for oneminute every five minutes by recirculating the biogas with dual­head air pumps with a maximum capacity of 22.5 Umin. Nitrogenwas injected in the headspace during drawdown. After effluentdrawdown, the sludge bed was 14 L.

Seed sludgeTwo reactors received 13 L of anaerobic granular sludge from amilk processing plant (MPP) UASB reactor and two reactorsreceived 13 L of anaerobic non-granulated biological sludge froma municipal wastewater treatment plant. The MPP sludge treateda substrate consisting mainly of proteins and fats. Its total andvolatile solid content was 7.4 and 3.2%, respectively. Themunicipal sludge treated the raw sludge from primary andsecondary clarifiers. It had a total and volatile solid contents of4.8and 2.7%, respectively. Although the MPP sludge had 50% moretotal solids than the municipal sludge, volatile content, which givesa better indication of active biomass, was only 19% higher in theMPP than municipal sludge.

Sampling and analysisAt each feeding, all four digesters received the same volume ofwastewater. Biogas production was monitored daily with wet cupgas meters. Biogas composition (methane, carbon dioxide,hydrogen sulphide, and nitrogen) was determined weekly by gaschromatography. Methane content was corrected for nitrogen,since N2 gas was used as a filler during drawdown. Effluentsamples were collected at a port situated 80 mm (5 L) above thesurface of the 14.L sludge bed. Approximately 250 to 500 mL wasallowed to flow out of the reactor before the sample was collected.The effluent was analysed for soluble COD (SCOD) and TCOD,

9 SkIdge sampang part. cillo usedfor WdgBwastage

10 t.tmoIQucr orQ)OInOtant~port

11 GaaClUb12 Gaameter

13 FeedortuOO

1 300 11m dam81Br pIaldgIas cIgaster

2 SlJdge bocIzcne

3 \QtaI:)l8 Wlkm8 zcne4 Head spcx:e zane6 Gall8Cb:UaIIDnme6 BIDgaa I8CKUa!Icn puT1)

7 tdUJntlnG8 B'IUJnt InG

Another important feature is that ASBRs allow batch as well assemi-continuous or intermittent feeding. At the slaughterhouse, thewastewater could be fed to the reactor as it is produced during the8-h working shift, thus eliminating the need for an equalising tankor recycling line. The main disadvantage is that biogas productionis not uniform, making it difficult to plan a biogas-use strategy(Masse et at. 1997). Another drawback is that limited controlstrategies and experimental data are available, especiallyconcerning the use of ASBRs for slaughterhouse wastewatertreatment. Morris et aI. (1998) treated slaughterhouse wastewaterin two 11.5 L ASBRs. The ASBRs were operated at 30"C andreactor content was mixed 30 severy 10 min. The HRT rangedfrom 18 to 36 h. The SCOD was reduced by over 90%, but TCODremoval declined from about 60% at an HRT of 36 h to 30% at 18h. Lower TCOD reduction probably reflected high SS losses dueto poor biomass settling, especially at low HRT. No other reportsfrom the use of ASBRs to treat slaughterhouse wastewater areavailable at this time.

SubstrateThe wastewater was collected at a hog slaughterhouse in St­Valerien, Quebec, approximately once a month, in 200-L barrels.At the slaughterhouse, the wastewater was screened to remove hairand solids larger than 1 mm. In the laboratory, the wastewater wasmixed, transferred to IQ-L jugs, and stored at -15"C. It was heatedto approximately 20°C before feeding the reactor. Wastewaterquality over the study period is given in Table I.

CANADIAN AGRICULTURAL ENGINEERING Vol. 42, No.3 July/August/September 2000 133

85

135 137 139days

83 days 84

d) OLA =1.46 kg m4 0'HRT=6days

b) OLA '" 4.93 kg m4 0'HRT= 2 days

-- municipal sludge

50

2 40

~ 30

j2010

021 82

.-60do

i 45.ep30

:::E16

0109 133107 108

days

19 20days

c) OLR ... 4.39 kg m4 d"HRT=2days

a) OLA =0.74 kg m4 0 1

HRT=2days

-- milk processlng plant sludge

Fig. 4. Methane production during four cycles atdifferent times over the experimental period.

was generally higher in reactors seeded with MPP than municipalsludge. Over the whole start-up period, SS concentration averaged1400 mg/L in the former and 900 mg/L in the latter. The MPPsludge consisted of large but light granules, which were of thefilamentous type described by Lettinga et al. (1987). Thesespherical granules can have a diameter up to 5 mm in size. Theyare mainly composed of intertwined filamentous organisms andthey fall apart easily. Under mixing in the ASBRs, the granulesslowly disintegrated into small bacterial flocs and free floatingfilamentous microorganisms left the reactors during drawdown.Biomass loss thus contributed to high effluent SS concentrationsin the reactors seeded with MPP sludge. Total COD, which is thesum ofsoluble and particulate COD, also tended to be higher in theeffluent from reactors inoculated with MPP than municipal sludge(Fig. 3). It ranged from 3692 to 576 mgIL in the former and from2437 to 341 mgIL in the latter.

Start-up is the period during which the anaerobic bacteria arebeing acclimatized to new environmental conditions and substrate.A new equilibrium is slowly established between the variouspopulations of microorganisms, until the biomass can stably andefficiently degrade the substrate at maximum or target OLR. A 40­day start-up was reported for a mesophilic (30 to 35°C) anaerobiccontact reactor treating slaughterhouse wastewater (Kostyshyn etala 1988). Borja et ala (1994a) also reported a 40-day start-up for anAFR treating slaughterhouse wastewatercontaining mainly solubleorganics. Methanol was mixed with the substrate during the firstmonth of start-up to encourage the proliferation of methanogens.With the ASBRs, the start-up period may possibly have beenshortened. Figure 4a shows methane production during a two-daycycle, 18 days after the beginning of start-up. Average methaneproduction rate declined from 8.5 Ud in the first 16 hours of thecycle to 2.4 Ud during the second day. The sharp decrease inbiogas production after 24 hours indicated that most organics weredegraded within one day and the OLR could have been increasedmore rapidly. After 25 days of operation, the OLR was graduallyincreased from 1.04 to 3.29 kg m-3 d-I over a 20-day period withoutdetrimental effect on effluent SCOD (Fig. 3). However, higher gasproduction at the end of the react phase created turbulentconditions during settling, which resulted in a temporary increase

50

2 40

1=10

160 0106

160

••••••munlclpaJ sludge

operation ~I

50

402CD 30

Organic loadlng rate 12010

080 100 120 140 160 18

days

60 80 100 120 140 160days

4020o

--milk proc. plant sludge

20 40 60 80. 100 120 140I days

2260j\)'!~~!Total COD". : ~ !'& 1600 ..... : ". iE • ~ I ••~,•••

760 ~~~••••••• : ~

~~ ----o , ~-,--..,....-.....,....-.....,

o 20 40 160 80 100 120 140I days

1000

760

~600E

250

6

\, 4'?E 3

8 2

~

1\J:. I Suspended solids1600 :~ I'& 1000 : \ I

E 600 •••••• .... 1

, -.o , , ,

RESULTS and DISCUSSION

Start-upVolumetric OLR (kg TCOD/m3 of sludge per day of cycle) andeffluent SCOD, TCOD, and SS concentrations during theexperimental period are presented in Fig. 3. During start-up, theOLR was progressively increased from 0.49 to 3.29 kg m-3 d-I overa 55-day period. Effluent SCOD decreased from over 1000 mgILin the first few days of start-up to 281 and 155 mgIL on day 28, inreactors seeded with MPP and municipal sludge, respectively.Soluble COD remained well below 250 mgIL in all reactor effluentduring the rest of the start-up period. Effluent SS concentration

Fig. 3. Volumetric organic loading rate and quality ofemuent from four anaerobic sequencing batchreactors treating slaughterhouse wastewater at30°C.

solid content, ammonia-nitrogen (NH4-N), total Kjeldahl nitrogen(TKN), volatile fatty acid (VFA) concentration, pH, and alkalinity.Protein concentration was calculated by multiplying the differencebetween TKN and NH4-N by 6.25 (AOAC 1984). Analyses weredone according to methods outlined in APHA (1992). Volatilefatty acid concentration was determined by gas chromatography.

134 MASSE and MASSE

On day 92, the OLR was reduced from 4.93 to 4.39 kg m·3 d".However, the wastewater contained a higher fraction ofundissolved solids (Table n, and the amount of SS fed to thedigesters was increased from 16.0 to 18.8 gld. Over the next twoweeks, effluent SCOD fluctuated between 331 and 645 mgIL (Fig.3). Figure 4c presents methane production during one cycle at thehigher SS loading rate. During the last six hours of the cycle,methane was still produced at a rate of lOUd. High biogasproduction maintained turbulent conditions in the reactors duringthe settling phase, and unsettled biomass was removed with theeffluent. Average effluent SS concentration increased from 215 to460 mgIL. After three weeks of feeding with the high SSwastewater, effluent SCOD concentration had decreased below300 mg/L in every reactor, but SS concentration was stillfluctuating between 150 and 500 mgIL.

After 133 days of continuous operation, the HRT wasincreased to six days for one cycle. Methane was still produced ata rate of 5.5 Ud on day 4 and 2.2 Ud on day 6 (Fig. 4d). Thereactors produced approximately 60 L of methane over the six-daycycle, for an average of0.49 L of methanelg ofCOD fed, while thetheoretical maximum methane yield at 30°C is 0.39 Ug of CODremoved. Continued methane production above the theoreticalmaximum yield was probably caused by the degradation of the SSthat had settled with the microorganisms at the end of each cycleand accumulated within the biomass bed. This slow accumulationof SS in the reactors suggests that the operational strategy shouldinclude occasional feed interruptions to allow the completedegradation of the undissolved solids, even though the ASBRprocess can lower COD concentrations to acceptable values atOLR of 4.93 kg m·3 dol.

Reduction in soluble, particulate, and total COD Figure 5presents average reduction in SCOD, TCOD, and SSconcentration at OLRs ranging from 1.73 to 4.93 kg m-3 d".Soluble COD reduction decreased slightly with increased OLR,but it remained between 94 and 98% over the whole period.Reduction in S5 increased with OLR. As more 55 was loaded intothe reactors, a greater proportion of the 55 was probably removedby biological degradation as well as physical separation duringsettling. However, low OLRs also coincided with earlier periods,during which biomass losses were the largest. Total COD wasreduced by 90 to 96% with no obvious trend with respect to OLRrate. A TCOD reduction of 82% at an OLR of 1.73 kg m-3 dol wascaused by high 55 losses during start-up (day 26 to 32).

Methane and biomass yield The biogas averaged 75.0%methane, 24.6% carbon dioxide and 0.4% hydrogen sulphide.Figure 6 presents the COD removed via methane production (2.57kg COD per m3 of methane at 30°C) and total COD removed(TCODinllucnt- 5CODeffiucn,) during the experiment. The differencebetween the two curves is a measure of volatile suspended solid(V5S) accumulation, i.e. apparent bacterial yield (true biomassyield minus decay) as well as undegraded V55 from the substrate.Over the experimental period, 90.5% of the COD removed wastransformed into methane. This high degree of methanizationindicated that most soluble and particulate COD fed to the A5BRswas effectively degraded within the HRT. Solid accumulationrepresented 0.095 g of COD/g of COD removed, or 0.068 g ofVSS/g of COD removed (based on 1.41 g COD per g V55). BOIjaet al. (1995b) calculated a true biomass yield of 0.07 g V55/gCOD removed in AFRs treating slaughterhouse wastewater at35°C. Under similar conditions, Metzner and Temper (1990)

Soluble COD

c 98 •~ •;:,

i 95~0

•92

1 2 3 4 5OlA (kg COD m-3 d'1)

100 Total COD

c 95 • • • •0 •15 •;:, 90 •'C!(/. 85

801 2 3 4 5

OlA (kg COD m-3 cf1)

100 Suspended solids

c •0 8013::I'Ce 60(/.

•401 2 3 4 5

alA (kg COD m-3 cf1)

Fig. S. Reduction in soluble COD, total COD, and sus-pended solids with respect to organic loading rates.

in effluent SS concentration to 3498 and 1792 mgIL in reactorsseeded with MPP and municipal sludge, respectively. However, atthe end of the start-up period, SS concentration had decreased to370 and 191 mgIL in effluent from both types of reactors,respectively.

OperationEmuent SCOD, TCOD, and SS concentration Between day 55and 90, the OLR was increased from 3.29 to 4.93 kg m-3 dol(Fig. 3). Effluent SCOD remained below 300 mgIL in mosteffluent samples. Average SS concentration was 236 and 162mgIL and TCOD concentration averaged 703 and 481 mg/L inreactors seeded with MPP and municipal sludge, respectively. TheASBRs inoculated with municipal sludge were still performingslightly better than the ones seeded with MPP sludge, butdifferences between reactor progressively decreased.

Figure 4b shows methane production during a two-day cycleat an OLR of4.93 kg m-3 dol. Methane production rate averaged 32Ud in the first 18 h of the cycle and 8.5 Ud in the last 5 h.Although effluent SCOD was 167 mg/L at the end of the cycle,biogas production remained important, indicating that particulateswere still being hydrolysed and methanized. Low VFAsconcentration in reactor effluent throughout the experimentalperiod, ranging from trace amounts to 100 mg/L, also suggestedthat methanization of the SCOD was rapid compared to particulatehydrolysis.

CANADIAN AGRICULTURAL ENGINEERING Vol. 42. No.3 July/August/September 2000 135

CONCLUSION

buffer (Fanin 1987). Effluent pH also increasedslightly during treatment, and ranged from 7.4 to7.9.

REFERENCES

AOAC. 1984. Official Methods ofAnalysis ofthe Association ofOfficial Analytical Chemists. Arlington, VA: Association ofOfficial Analytical Chemists.

APHA.1992.StandardMethodsfortheExaminationofWaterandWastewater. Washington, DC: American Public HealthAssociation.

Arora, H.C. and T. Routh. 1980. Treatment of slaughterhouseeffluents by anaerobic contact filter.1AWPC Technical AnnualVI & VII: 67-78.

BOlja, R., C.J. Banks and Z. Wang. 1994a. Performance andkinetics ofan upflow anaerobic sludge blanket (UASB) reactortreating slaughterhouse wastewater. Journal ofEnvironmentalScience and Health A29:2063-2085.

BOlja, R., C.J. Banks and Z. Wang. 1994b. Stability andperformance of an anaerobic downflow filter treatingslaughterhouse wastewater under transient changes in processparameters. Biotechnology and Applied Biochemistry 20:371­383.

BOlja, R., C.J. Banks and Z. Wang. 1995a. Effect of organicloading rate on anaerobic treatment of slaughterhousewastewater in a fluidised-bed reactor. Bioresource Technology52: 157-162.

BOlja, R., C.J. Banks and Z. Wang. 1995b. Performance of ahybrid anaerobic reactor, combining a sludge blanket and afilter, treating slaughterhouse wastewater. AppliedMicrobiology and Biotechnology 43:351-357.

Borja, R., M.M. Duran and A. Martin. 1993. Influence of thesupport on the kinetics of anaerobic purification ofslaughterhouse wastewater. Bioresource Technology 44:57-60.

Dague, R.R., C.E. Habben and S.R. Pipaparti. 1992. Initial studieson the anaerobic sequencing batch reactor. Water Science andTechnology 26:2429-2432.

days

_·_-CH4-COO

-coo removed

6000

5000

S4000

83000

2000 Slaughterhouse wastewater containing between1000 6908 and 11 500 mgIL of TCOD was treated in

o+-"'-::;:~...---__----r---.........----r--~-----, four 42-L ASBRs operated at 30°C. Total COD20 40 60 80 100 120 140 160 was reduced by 90 to 96% at OLRs ranging from

2.07 to 4.93 kg mo3 d-I and an HRT of two days.Soluble COD was reduced by over 95%. Resultsindicated that at a steady state operation of 4.93kg m-3 d- I, the reactors will be stable in terms ofeffluent quality and biomass retention. The two

reactors seeded with anaerobic sludge from a municipal treatmentplant originally performed better than the two reactors inoculatedwith a sludge from a milk processing plant, but difference betweensludges decreased with time. The reactors produced a biogascontaining 75% methane. About 90.5% of the COD removed weremethanized. Solid accumulation, including apparent biomass yieldand undegraded SS, was evaluated at 0.068 g VSS per g CODremoved. The high degree of methanization suggested that mostsoluble and suspended organics in slaughterhouse wastewaterweredegraded during treatment in the ASBRs.

Fig. 6. Cumulative gas production (CH4-COD) and COD removed duringthe experimental period.

obtained a net accumulation ranging between 0.05 and 0.07 gVSS/g COD removed.

Over the experimental period, however, there was a net loss ofbiomass from the reactors. At the beginning of the experiment,total solid content in the sludge bed averaged 75 400 and 48 900mgIL in the reactors seeded with MPP and municipal sludge,respectively. After 139 days of operation, total solid content in thesludge bed averaged 18 700 mgIL in all reactors. Biomass loss wasmostly observed during start-up when large amounts of sludge leftthe reactors with the effluent. However, sludge quality in terms ofVSS content improved. Volatile solids represented 69% of totalsolids at the end of the experiment, while it originally accountedfor 43 and 55% of total solids in the MPP and municipal sludge,respectively.Nitrogen and protein In the raw slaughterhouse wastewater,TKN ranged from 534 to 735 mg/L (Table I). In effluent, it variedbetween 473 and 808 mgIL. During the first month of start-up,total nitrogen was higher in effluent than influent, probablybecause of the large losses of bacteria, which contain 10 to 15% oftheir weight as nitrogen (Grady and Lim 1980). Afterwards,nitrogen reduction during treatment averaged 13% in all reactors.Bacterial synthesis is the main sink for influent nitrogen. The lowgrowth rate and low yield ofanaerobic bacteria translates into lowoverall nitrogen removal.

Ammonia-N represented from 14 to 46% of total nitrogen ininfluent, and from 75 to 98% of total nitrogen in effluent. Theproportion ofammonia-N in effluent was lower at the beginning ofthe experimental period, due to low degradation rate of influentCOD and large biomass losses in effluent. During that period,effluent protein content reached 1100 and 620 mgIL in reactorsseeded with MPP and municipal sludge, respectively. Thereafter,protein concentration in effluent averaged 241 and 139 mgIL forboth types of sludge, respectively, corresponding to a proteinreduction of 92 and 95%, respectively, due to mineralization oforganic nitrogen.Alkalinity and pH Influent alkalinity ranged from 667 to 1056mgIL as CaC03, and pH from 6.7 to 7.4 (Table I). During the firsttwo weeks ofthe experiment, effluentalkalinity was approximately2100 and 3200 mgIL in reactors seeded with MPP and municipalsludge, respectively. During the remainder of the experimentalperiod, alkalinity averaged 2550 mgIL in all reactors,corresponding to an increase of over 200% in alkalinity duringtreatment. The increase in alkalinity was mainly caused by themineralization of protein into ammonia. The latter combines withthe carbonic acid in solution to form an ammonium bicarbonate

136 MASSE and MASSE

Fannin, K.F. 1987. Start-up, operation, stability, and control. InAnaerobic Digestion ofBiomass, eds. D.P. Chynoweth and RIsaacson, 171-196. London, England: Elsevier AppliedSciences.

Grady C.P. and H.C. Lim. 1980. Biological WastewaterTreatment. New York, NY: Marcel Dekker Inc.

Kostyshyn, C.R, W.A. Bonkoski and J.E. Sointio. 1988.Anaerobic treatment of a beef processing plant wastewater: Acase history. In Proceedings of the 42'u' Industrial WasteConference, 673-692. Ann Arbor, MI: Ann Arbor Science.

Lettinga, G., W. de Zeeuw, W. Wiegant and L. Holshoff Pol.1987. High-rate anaerobic granular sludge UASB-reactors forwastewater treatment. In Bioenvironmental Systems, I, ed. D.L.Wise, 132-159.

Masse, DJ. 1995. Psychrophilic anaerobic digestion of swinemanure slurry in intermittently fed sequencing batch reactors.Ph.D. thesis. Ottawa, ON: University of Ottawa.

Masse, DJ. and F. Croteau. 1998. La digestion anaerobiepsychrophile du lisier de porc a I' interieur de bioreacteurs aoperations sequentielles. Final report presented to theFederation des producteurs de porcs du Quebec. Agricultureand Agri-Food Canada, Lennoxville, QC.

Masse, 0.1. and R.L. Droste. 1997. Microbial interaction duringanaerobic treatment of swine manure slurry in a sequencingbatch reactor. Canadian Agricultural Engineering 39:35-41.

Masse, 0.1., RL. Droste, KJ. Kennedy, N.K. Patni and J.A.Munroe. 1997. Potential for the psychrophilic anaerobictreatment of swine manure using a sequencing batch reactor.Canadian Agricultural Engineering 39:25-33.

Masse, 0.1. and L. Masse. 2000. Characterization of wastewaterfrom hog slaughterhouses in Eastern Canada and evaluation oftheir in-plant wastewater treatment system. CanadianAgricultural Engineering 42: 139-146.

Masse, 0.1., N.K. Patni, R.L. Droste and KJ. Kennedy. 1996.Operation strategies for psychrophilic anaerobic digestion ofswine manure slurry in sequencing batch reactors. CanadianJournal ofCivil Engineering 23: 1285-1294.

Metzner, G. and U. Temper. 1990. Operation and optimization ofa full-scale fixed-bed reactor for anaerobic digestion of animalrendering wastewater. Water Science and Technology 22:373­384.

Morris D., S. Sung and R.R Dague. 1998. ASBR treatment ofbeef slaughterhouse wastewater. Downloaded from theinternet (http://ce.ecn.purdue. edu.l-alleman/w3­piwc/paperslsung.html).

Ruiz, 1, M.C. Veiga, P. de Santiago and R. Blazquez. 1997.Treatment of slaughterhouse wastewater in a UASB 'reactorand an anaerobic filter. Bioresource Technology 60:251-258.

Saxena, K.L., S.N. Kaul, M.Z. Hasan, S.K. Gadkari and S.D.Badrinath. 1986. Packed bed anaerobic reactor for treatment ofmeat wastes. Asian Environment 8:20-24.

Sayed, S.K.l, L. van Campen and G. Lettinga. 1987. Anaerobictreatment of slaughterhouse waste using a granular sludgeUASB reactor. Biological Wastes 21:11-28.

Sayed, S.K.l, 1. van der Zanden, R Wijffels and G. Lettinga.1988. Anaerobic degradation of the various fractions ofslaughterhouse wastewater. Biological Wastes 23: 117-142.

Sayed, S.KJ. and W. de Zeeuw. 1988. The performance of acontinuously operated flocculent sludge UASB reactor withslaughterhouse wastewater. Biological Wastes 24:199-212.

Sayed, S.K.l, W. de Zeeuw and G. Lettinga. 1984. Anaerobictreatment of slaughterhouse waste using a flocculent sludgeUASB reactor. Agricultural Wastes 11:197-226.

Sung, S. and RR. Dague. 1995. Laboratory studies on theanaerobic sequencing batch reactor. Water EnvironmentResearch 67:294-301.

Tritt, W.P. 1992. The anaerobic treatment of slaughterhousewastewater in fixed-bed reactors. Bioresource Technology41:201-207.

Zheng, Y. and W. Wu. 1985. A study of meat packing plantwastewater treatment with upflow anaerobic sludge blanketprocess. In Anaerobic Digestion 1985, 327-337. Proceedingsof the 4th International Symposium on Anaerobic Digestion.Guangshou, China.

CANADIAN AGRICULTURAL ENGINEERING Vol. 42, No.3 July/August/September 2000 137