Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.enzyme.chem.msu.ru/ekbio/article/hav_met.pdf Äàòà èçìåíåíèÿ: Wed Mar 23 14:21:28 2005 Äàòà èíäåêñèðîâàíèÿ: Mon Oct 1 22:07:13 2012 Êîäèðîâêà:

Heavy metal pollution from Russian landfilileachates its elimination together with other contaminants

and

~

~
C/) 0

s.
Department Russia

Kalyuzhnyi and M. Gladchenko
(1) of Chemical Enzymology, Chemistry Faculty, Moscow State University, 119992 Moscow, Q)

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::3

(E-mail:

svk@enz.chem.msu.ru)

~

(1) 0
Abstract Systematic monitoring of raw leachates (RL) from the operating landfill "Khmet'yevo" during 5"

0

December,

2001-June,

2002

with

regard

to

heavy

metals

(HM)

revealed

that

these

RL

were

moderately

contaminated Fe,In, PbandCd (Cuispresent non-dangerous with in concentrations). contamination This
depends on season the winter leachates are less polluted compared to the summer ones. For removal of HM together with removal of bulk COD, the UASB reactors were applied where, besides elimination of the

~
c8 Q. U1 0 z 0 U1 "C

major

part

of

organic

matter,

concomitant

precipitation

of

HM

in

the

form

of

insoluble

sulphides

inside

the

sludge

bed

occurred

due

to

development

of

the

process

of

biological

sulphate

reduction.

Both

removal

"C

processes

were

quite

efficient

even

during

operation

under

submesophilic

and

psychrophilic

conditions

~

(20-1

O°C).

The

subsequent

submesophilic

aerobic-anoxic

treatment

of

submesophilic

anaerobic

effluents

J,

=

led

to

only

75%

of

total

inorganic

N

removal

due

to

COD

deficiency

for

denitrification

created

by

a

too

@

efficient

anaerobic

step.

On

the

contrary,

psychrophilic

anaerobic

effluents

(richer

in

COD

compared

to

the

~

submesophilic

ones)

were

more

suitable

for

subsequent

aerobic-anoxic

treatment

giving

the

total

N

removal

~

of

95

and

92%

at

20

and

10°C,

respectively.

The

final

effluent

is

approaching

the

current

national

standards

§::

for

direct

discharge

of

treated

wastewater.

~

Keywords

Aerobic-anoxic

biofilter;

biological

sulphate

reduction;

heavy

metals;

landfill

leachate;

UASB

~.

""

reactor

0

0

~

Introduction

According to available statistics,between 130 and 150 mIn. m3 (-27-37.5 mIn. tonnesconsideringa density coefficient of 0.2-0.25) of municipal solid wastes(MSW) areannually generatedin Russiaand more than 96% of theseMSW are currently disposedof via landfilling (Cherp and Vinichenko, 1996; Saveliev, 2003). The exact number of landfills in our country is unknown because its huge territory, not very comprehensivestatistics and existenceof of thousandsof non-sanctionedsites for waste disposal. However, the estimatesshow that, in total, Russian landfills occupy 0.8 mIn. ha, i.e., an area equivalent to 8 cities of the size of Moscow. By the end of the eighties, 88% of landfill sites, according to the inspection of the USSR StateCommittee of Nature (1989), were in unsatisfactorysanitaryconditions producing many dangerousemissionsto the environment (Cherp and Vinichenko, 1996). Besides landfill gas,the main concernis a leachategenerateddue to microbial activity within a landfill, compressionand water flows and containing a wide variety of intermediate organic degradationproducts and inorganic (including metallic) contaminants.The data about flows and compositionsof landfillleachates are limited in Russia.This is related with the fact that the leachatecollection systemsare still not widely implementedthroughout the country. The typical composition of leachatesfrom operating Russian landfills is the following (mg/!, exceptpH): COD-370-20,OOO;BOD- 72-13,300; carbonates (hardness salts)~890-7,600;
Ca 240-2,330; Mg 64-410; Na 85-1,700; K 28-1,700; Fe 0.5-8.7; chlorides-

96-2,350; sulphates84-730; phosphates 0.3-29; organic nitrogen - 2.4-465; ammoniac nitrogen -0.22-480; pH -4.5-8.6 (Pan, 2001; Kalyuzhnyi eta/., 2003a). Besidesthe above mentionedbulk pollutants, the landfillleachates usually containheavymetals(HM) andother micropollutants (phenols etc). These leachates (if not collected and treated (the typical

51


~

~

! ~ ~
~

~

~ a.

situation for Russia))posedangerousenvironmentalandhealthrisks due to its impact on surface and ground waters.Sincethe dataon HM contaminationof Russianlandfilileachates are very scare, the primary objective of this paper was to perform systematic monitoring of leachates from one of the operatingRussianlandfills with regardto 5 major troublesomeHM (Fe, Zn, Cu, Pb and Cd). The secondobjective was to developan efficient lab scaletechnology for removal of thesemicropollutants together with removal of bulk biodegradableCOD. For this, the UASB reactors were applied where, besideselimination of the major part of organic matter, a concomitant precipitation of HM in the form of insoluble sulphidesinside the sludge bed was expecteddue to the developmentof the processof biological sulphate reduction. In addition to conventional mesophilic regime (30°C), investigations were also carried out at lower temperatures(20 and 10°C) in order to evaluatethe possibility of direct treatmentwithout preliminary heating. This option is especially attractive in Russiadue to a moderate/coldclimate. Finally, as a post-treatmentoption for anaerobiceffluents, the biofil-

g. CD ~ 0

ter operating analternative in aerobic-anoxic regime investigated 10and20°Cfor the was at removal remaining of BOD andnitrogen, whicharealsoa concern discharge surface for into water. Materials and methods
Leachate sampling The raw leachates(RL) were sampledduring December,2001-June 2002 from the leachate collection systemof the operating municipal landfill "Khmet'yevo" (Moscow province).
Laboratory reactors

2 UASB reactors with rectangular cross-section of 37-38 cm2, height of 85 cm, and total working volume of 2.54-2.68 1were used.They were seededwith mesophilic sludge (40 g VSS, specific ac~ticlastic activity - 0.67 g COD/gVSS/dat 30°C) originatingfrom an UASB reactor treating starch industry wastewater (Sklyar et al., 2003) and psychrophilic sludge (12.2 g VSS, specific aceticlastic activity - 0.12 g COD/g VSS/d at 10°C) originating from an UASB reactor treating winery wastewater (Kalyuzhnyi et al., 2001). To mitigate mass transfer limitations usually observed under psychrophilic conditions (Kalyuzhnyi et al., 2001), a recycle of effluent was applied (recycle ratio - 2.5:1). The tubular biofilter (diameter - 5 cm, height - 55 cm, packed by 0.5-2 cm fraction of road metal) had a working volume of 0.7 1and functioned in alternating aerobic/anoxic regime for treatment of the anaerobic effluents. The operation scheme included a sequencing processwith a one-hour cycle consisting of 4 phases.During the first unfed phase,air at a flow rate of 0.8 l/min was pumped through an external loop of the biofilter. Aeration was switched off throughout the second unfed phase while the high recycle rate of effluent (0.125 l/min) was applied to ensure an adequatemixing and a complete consumption of remaining soluble oxygen in the biofilter. During these2 phases, nitrification and oxidation of remaining BOD proceeded.Then the feeding was performed during the 3rd phaseunder the samerecycle rate of effluent. The last phaseincluded only mixing (by effluent recycle) and was variable to close the 1 h working cycle of the programmable multi-channel timer controlling all 3 (air, recycle, feeding) pumps used.During the last 2 phases,denitrification proceeded.In the middle of the external loop of biofilter, an electronic sensorwas inserted for on-line monitoring of soluble oxygen. Secondarysludge from Kur'yanovskaya sewage treatment plant (Moscow) was used as seed sludge for the formation of the attached biofilm. The excess of sludge was periodically withdrawn by intensive backwash of the biofilter. The mesophilic, submesophilic and psychrophilic conditions were imposed by keeping the laboratory reactors inside a thermostat (30 :t 1°C), under ambient temperature in the laboratory (20:t 3°C) or inside refrigerator (10:t 2°C).

52


Analyses

Sampling of treated wastewaterfor analysis was usually started after 3 hydraulic retention times (HRT) after the changeof working regime for eachreactor in order to ensureits operation in quasi steady-stateconditions. The HM (Fe, Zn, Cu, Pb, Cd) in the RL, the treated effluents andthe reactor sludgewere analysedon a regular basisby atomic absorption spectroscopy. The samples w~re dried «40°C) and pre-treated with concentrated HNO3 and H202 (30%); thereafter the metal content was measuredfrom the eluate. Somesamples(for

.cn

otherHM determinations) were analysed with the ICP-AES.COD, total N and P were analysed spectrophotometrically Hachtubes.All otheranalyse~ using wereperformed by Standard Methods(1995)or asdescribed previously(Kalyuzhnyiet~al., 2003b).All gas

-

~ !::T
~

measurements were recalculatedto standardconditions (1 atm, DOC). Statistical analysis of

~
:s:
G) p;c.

datawasperformed usingMicrosoftExcel. Results and discussion
Monitoring of HM contamination of landflilleachates

g. CD ~ 0

From data presentedin Table 1, it is seenthat HM contamination of the RL was very variable and there was a noticeable difference between the winter and summer RL - the latter onesaremore contaminatedcomparedto the former ones.It is probably related to different water flows through the landfill body during these 2 seasons.However, generally the RL were moderately contaminated with Fe, Zn, Pb and Cd (Cu is present in non-dangerous concentrations).Also the concentrationsof sulphateand COD were more than sufficient to run biological sulphatereduction for the generationof sulphide for HM precipitation.
UASB elimination of HM from the RL

From the data of Table 2, it is se~nthat UASB treatment was quite efficient for removal of HM under all temperature regimes investigated due to their concomitant precipitation/ entrapment on the sludge presumably in the form of sulphides and hydroxides. The HM content (except Fe and sometimesPb) in the anaerobically treatedeffluents approachedthe Russianlimits for drinking water. The accumulation ofHM in the reactor was confirmed by direct measurementof HM sludge content at the start and at the end of each operational regime (Table 3). This accumulation roughly correspondedto the HM removal from the liquid phasefor mesophilic and psychrophilic regimes and apparently did not inhibit specific aceticlastic activity of thesesludges(Table 3). However, after 4.5 months of continuousexperiments,the sludge inside the submesophilic UASB reactor becameheavy - its ash contentincreasedto 70% (Table 3). Under full-scale implementation ofUASB treatment of

Table1
HM/month

HM contamination of RL from landfill "Khmet'yevo" (mg/l, except pH)
Dec-2001 Feb-2002
Mar-2002 Apr-2002 May-2002 Jun-2002

Fe Zn Cu Pb Cd TotalCOO TotalN Ammoniac N TotalP Phosphate-P 8042pH NO - not determined

13.58 1.92 0.24 0.1 0.0008 3,810 162 80 38 7 128 6.7

4.08 1.08 0.08 0.046 0.0054 1,450 128 63 20 7 106 6.53

6.32 1.2 0.04 0.038 0.001 1,430 NO 70 NO 4 61 6.58

170.4 28.8 0.168 0.072 0.001 20,560 781 562 NO 16 355 5.99

17.28 0.86 0.048 0.077 0.024 4,180 NO 164 NO 21 174 8.0

79.2 2.4 0.096 0.058 0.006 9,660 1,080 822 51 8 213 7.52 53


Table 2 Influent and effluent HM concentrations (mg/l) for mesophilic, submesophilic and psychrophilic
UASB reactors treating the RL (steady-state data) HRT, h Fe'n Fe., Zn'n Zn., CU'n CU.. Pb'n Pb.. Cd'n Cd..

~

46 33 7 80 29 7 126 63 59 15 8

13.58 13.58 4.08 170.4 79.2 6.32 170.4 13.58 79.2 4.08 6.32

1.73 0.26 0.46 1.3 5.9 0.36 1.6 0.54 16.0 0.8 0.94

1.92 1.92 1.08 28.8 2.4 1.2 28.8 1.92 2.4 1.08 1.2

Mesophilic (30°C) 0.94 0.240 0.0970.100 0.20 0.240 0.020 0.100 0.24 0.080 0.020 0.046

0.0600.00080.0001 0.025 0.0008 0.0001 0.014 0.0054 0.0009 0.046 0.010 0.002 0.0010 0.0060 0.0010 0.0005 0.0010 0.0001

~
~ 'S.

~
~

Submesophilic (20°C)
2.40 0.04 0.08 1.60 0.16 2.00 0.30 0.26 0.168 0.096 0.040 0.168 0.240 0.096 0.008 0.040 0.048 0.020 0.020 0.043 0.020 0.060 0.020 0.020 0.072 0.058 0.038 0.072 0.100 0.058 0.046 0.038

~ Co
~ (;,

Psychrophilic(10°C)
0.0150.00100.0005 0.024 0.0008 0.0002 0.010 0.0060 0.0010 0.038 0.0054 0.0034 0.003 0.0010 0.0001

[ g.
CD ~ ~ 0

RLOW.

0.3
limit for drinking water

5

1
:;

0.03

0.0010

. RLOW - Russian
ing the RL
Parameter/regime
Day 01 operation

Table 3 Some sludge characteristics of mesophilic, submesophilic and psychrophilic UASB reactors treat-

Mesophilic 0 25 0

Submesophilic
135 0

Psychrophilic 175

VSS in the reactor, 9 TSSinthereactor,g VSS/TSS, % Aceticlastic activity, .9 COO/g VSS/day. Fe content, I1g/g TSS Zncontent,l1g/gTSS Cu content, 119/gTSS Pb content, I1g/g TSS Cd content, 119/gTSS

40.0 86.9 46 0.67 5,269 1,639 207.3 2.81 0.011
at working

45.1 95.4 47.3 0.75 6,271 2,834 308.2 12.41 0.017

42.2 89.4 47.2 0.31 NO NO NO NO NO

67.1 224.7 29.9 0.28 5,043 1,210 72.8 3.92 0.01

12.2 21.9 55.7 0.13 1,757 509 83.3 5.54 0.02

31.2 55.1 56.6 0.17 45,225 3,915 124.0 8.81 0.04

.

Values were obtained

temperatures

-

30, 20 and 10°C, respectively

NO - not determined

RL, such sludges should be periodically withdrawn from the reactors and disposed of on special landfills or incinerated.
COD removal during UASB treatment

In the preliminary experiments, it was found that all leachate sampleswere non-toxic for anaerobic sludge even in undiluted samples and had a high anaerobic biodegradability (79-91 % on COD basis). The steady-stateresults of COD removal during UASB treatment under various HRT and temperature regimes applied are generalisedin Figures 1-2. It is seenthat in mesophilic conditions when the diluted leachateswere treated (Figure 1a), the total COD removal varied from 75 to 91% dependingon the initial strength of the RL. Only traces of volatile fatty acids (VF A) were detected in the effluents even under the highest organic loading rate (OLR) applied (5.1 g COD/l/d, HRT - 6.8 h). However, such exhaustion of easily biodegradableCOD in the anaerobic effluents might create COD deficiency problems for subsequent biological nitrogen removal becausethe effluent total COD/total N ratio (Figure 1a) was significantly lower than 6 (the practically establishedCOD/N ratio
54

to havea stable denitrification, Henze at., 1999). et


'" ~

~
e
0 U S

.

100
80

;::
-+40

COD/N -0I
I

~
I
I

Removal

-+-

COD/N -0I "

Removal
, 12
0

4

0

~
'"

1

3e
a 20
1:S

.~

260 0 40
0 Eo- 20

: :
3,810: 50

~ 0

~
0

8

~

:
I

I

E

0

e 2
2 80 64 48 32 16' HRT, hours 0

10 .~ 8 7 6
4

8 0
U
d "

0 U

1,840 0 0

IE ~

S ~

2 O.

IE~

cn

0 HRT, hours

'<

~
~
:T
~ 0-

Figure 1 Total COD removal and effluent total COD/total
operation of mesophilic (a) and submesophilic (b) UASB

N ratio versus HRT under quasi.steady
reactors treating the RL (figures on the

state
graphs -

~.

influent total COD concentrations

in mg/l)

~
G) 6i" 00 :T
0

'ii. ~

100
80

~ ~<:::::t:~~'
-+COD/N -0-

'
I

Removal

,12
I'~ I

~
7'" 0

>
2 "

~
60

,9
40 20
0 ': I

" U
~

S

: :: ,,, :
: 3,810

I

~ ~
0 0

,6

, :
: 1,840

3
0

U ..
§ -

8

180

144

108

72

36

0

HRT, hours

Figure 2 Total COD removal and effluent total COD/total N ratio versus HRT under quasi-steady state operation of psychrophilic UASB reactor treating the RL (figures on the graphs - influent total COD concen.
trations in mg/l)

.

Under submesophilic conditions (Figure 1b), the total COD removal varied from 81 to 87% and from 51 to 70% for diluted and concentratedRL, respectively, The effluent total COD/total N ratio exceededthe targeted value of 6 only during treatment of high strength leachate(HRT of 80 h), Thus, submesophilic anaerobic effluents in the majority of cases will also needan external COD for subsequent nitrogen removal. A decrease working temperatureof the U ASB reactor to 10°C required an increaseof of HRT and, hence, a decreaseof OLR becausethe bacterial activity dropped substantially at theseconditions (Kalyuzhnyi et al., 2001). From Figure 2, it is seenthat in spite of higher HRT applied, the total COD removal (Figure 2) slightly dropped compared to mesophilic and submesophilic regimes (Figure 1). However, taking into account a need in easily biodegradableorganic matter for subsequentnitrogen removal, the effluent COD characteristics were superior comparedto those from mesophilic and submesophilic regimes due to the presenceof remaining VF A (data not shown) - the effluent total COD/tota. N ratio exceeded6 during all HRT applied independently on the strength of the RL (Figure 2). A general performance ofpsychrophilic and submesophilic UASB reactors may imply that the Khmet'yevo leachatescan be efficiently treated without any heating in warm periods. However, some energy expenses(at least to maintain a working temperature around 10°C) will be necessaryfor cold periods during a full-scale implementation of anaerobic treatmentof theseleachates.
Aerobic-anoxic post-treatment of anaerobic effluents

.

c:"

A successful start-up of the biofilter in the nitrifying mode (at 20°C) was achieved in three weeks using mesophilic and submesophilic anaerobic effluents containing low concentrations of biodegradable COD as a substrate. When the effluent ammonia

55


~ ~ -< ~

concentrationsreachedvalues around 2 mg N/l, the biofilter was switched on in alternating (aerobic-anoxic) operation. During run 8MI (Table 4), when anaerobically treated(in psychrophilic regime) diluted RL were f~d, the averagetotal COD removal accountedfor 73% with the total COD effluent concentrations slightly oscillating around 0.19 g COD/l. It is close to the aerobic biodegradability limit of theseRL (0.15 g COD/l). The efficiencies of ammonia removal and denitrification were 93 and 80% (on the average) resulting in the average inorganic nitrogen removal of 75% (Table 4, run 8Ml). The effluent ammonia, nitrate and nitrite concentrations oscillated around 4, 12 and 1.5 mg N/l, respectively (Table 4, run 8Ml).

~.

".

[
~

~ Co

g. CD ~ 0

During runs8M2-8M4, the biofilter wasfed with strongnitrogenous anaerobic effluentsthatrequired longeraeration a phase HRT (Table4). Duringrun 8M2,theaverage and totalCODremovalaccounted 85%with thetotal CODeffluentconcentrations for oscillating around1.5g COD/l (Table4). Theefficiencies ammonia of removalanddenitrification were73 and99%(on the average) resultingin the average inorganicnitrogenremovalof 72% (Table4, run 8M2). Insufficientnitrification probablywasdueto the high COD/N
ratio (15.2) of anaerobiceffluent used for feeding during this run. An excessof COD leads to intensive development of heterotrophs making the reactor biofilm thick (mass transfer limitations and clogging) as well as to inhibition of autotrophic nitrifiers (Henze et al., 1999). In order to avoid such undesiredphenomena,the submesophilic anaerobiceffluents with lower COD/N ratio were used during run 8M3. The averageefficiency of ammonia removal increased(to 90%) but the averageefficiency of denitrification decreased 83%) (to compared to the corresponding values obtained during run 8M2 (Table 4). The total inorganic nitrogen removal increased to 75% (on the average) giving the total effluent inorganic nitrogen concentrations around 196 mg N/l (run 8M3, Table 4). The elevated total nitrogen concentrationsin the effluents were related with both incomplete nitrification and

Table

4 Operational

parameters

and efficiency

of the biofilter treating

the anaerobic

effluents

(mean:l: stan-

dard deviation) Parameter!run Temperature,.C Aerationphase,min 1stmixing,min Feedingphase,min 2nd mixing,min HRT,days InfluentCOD/N OLR,gCOD/l/d InfluentCODtot,g/l EffluentCODtot,g/l CODtotremoval,% InfluentpH EffluentpH Inf.N.NH3,mg/l Eff.N-NH3,mg/l N-NH3removal,% Eff.N-NO3,mg/l Eff.N-NO2,mg/l
*Denitrif.effic., %

SMI 19-21

SM2

SM3

SM4

PI

P2 8-12 35 8 2 15 7.10:1:0.17 7.9 0.85:1:0.08 5.96:1:0.52 0.89:1:0.13 86.5:1:1.7 7.41 :1:0.10 7.72:1:0.14 752:1:2 30:1:1 96.0:1:0.1 33.1:1:1.5 0.3:1:0.1
95.4:1:0.2

18-22

18-22
40 10 3 7 4.29:1:0.07 4.9 0.89:1:0.16 3.81 :1:0.70 1.47:1:0.44 63.6:1:5.2 7.71 :1:0.09 7.07:1:0.10 784:1:21 78:1:9 90.1:1:1.0 117:1:14 1.5:1:1.1

~
t;:;-~~ -I~~=c';"

25 25 9 20 2 8 24 0.98:1:0.1 3.81 :1:0.47 10.3 15.2 0.71 :1:0.07 2.61 :1:0.35 0.70:1:0.03 10 0.18:1:0.01 1.53:1:0.49 73.0:1:1.1 84.7:1:4.9 7.30:1:0.05 7.74:1:0.23 8.37:1:0.05 7.05:1:0.11 67:1:4 660 4.1:1:2.0 178:1:25 93:1:3 73.1:1:3.8 12:1:5 1:1:1 1.5:1:0.3 Traces
80:1:7

7-10

9-11 41 6 4 19 2 15 13 20 5.09:1:0.06 1.12:1:0.1 7.4 9.3 1.12:1:0.08 0.64:1:0.1 5.72:1:0.38 0.68:1:0.08 1.08:1:0.06 0.18:1:0.02 80.5:1:1.5 75:1:3 6.9:1:0.1 7.35:1:0.1 8.04:1:0.14 8.23:1:0.09 771:1:2 73:1:8 18.8:1:0.9 5.0:1:2.5 97.7:1:0.1 93:1:2 18.0:1:4.5 9:1:5 0.4:1:0.1 1.7:1:0.9
75:1:10

16-19

~'~?'
~;-;~~;::~~~ ~~~~@

99.2:1:0.383.3:1:2.297.6:1:0.6

Eff.Ntot.inorg,mg/l
*Ntt removal, % Inf.op~nP'&4,mg/l Eff.P-PO4,mg/l

18:1:5
75.0:1:8.3 9.4:1:0.1 5.2:1:0.1

182:1:26
72.4:1:3.9 17 4.6:1:0.8

196:1:22
75.1:1:2.6 14.9:1:5.8 8.1:1:5.4

37:1:5

16.7:1:8.9

63:1:2

95.2:1:0.773.2:1:11.291.6:1:0.3 18.9:1:0.1 11.0:1:0.7 18.7:1:0.1 9.8:1:0.5 10.2:1:0.2 14.9:1:0.3

56

*Calculated as: [1 - ([N-NO~ef + [N-NO2]et1/([N-NH3]in- [N-NH3]et1I*100 *Calculated as: [1 - ([N-NO3]ef+ [N-NH~ef+ [N-NO2]et1/([N-NH3]iJ)*100


COD deficiency to have a stable denitrification (COD/N ratio during run SM2 was around 5). On the contrary, during run SM4 when the COD/N ratio was 7.4 (i.e. between the correspondingvalues for runs SM2 and SM3), the biofilterwas able to remove 95% of total inorganic nitrogen giving the effluent with total inorganic nitrogen concentrations around 37 mg Nfl. It seemsthat it is hardly possible to reach a lower level of ammonia in the effluent due to an imminent drawback of this relatively simple biofilter construction where wastewater filling and effluent withdrawal were performed simultaneously in a CSTR regime. The better performancecan be expectedunder disruption of filling and withdrawal

.cn

~
"<

phases the biofilter as in sequencing in batch biofilm reactor (SBBR) constructions (Wildereretat.,2001).
~ A decreaseof working temperatureof the biofilter to 10°C required an increaseof HRT

~ ::r ~. ~

~
~ Co
g. CD

because nitrifying-denitrifyingactivity of the biofilm droppedsubstantially these the at conditions (Henzeet at., 1999).The optimalconditionsfor anaerobically treated diluted RL werefoundwhenHRTwas1.12days(runPI, Table4). In thisregime, effluentcharthe
acteristics were quite similar to those from run SM1 with regard to total COD and nitrogen content as well as concentrations of nitrogen species- ammonia, nitrate and nitrite (Table 4). Switching of the psychrophilic biofilter on feeding with strong nitrogenous anaerobic effluents required a further decreaseof HRT and an increase of duration of the aeration phase(run P2, Table 4). The corresponding process optimisation led to the averagetotal inorganic nitrogen removal accounting for 92% with the total inorganic nitrogen concentrations in the effluents around 63 mg Nfl from which only 30 mg Nfl was representedby ammonia (run P2, Table 4). Thus, during all runs, the remaining nitrogen concentrations were above the current national standards(10 mg Nfl) for direct discharge of treated wastewater. A simple and inexpensive post-treatment steps like a collection/stabilisation pond (they are usually available at landfills) or constructed wetland will probably be required to ensure a safe discharge of the treated leachates (by proposed sequencedtechnology) to surface waters.

~

Conclusions 1. Systematicmonitoring of Khmet'yevo 1andfil11eachates during December,2001-June, 2002 with regard to HM content showedthat they were moderately contaminated with Fe, Zn, Pb and Cd (Cu is presentin non-dangerousconcentrations).This contamination
depends on season

-

the winter leachates are less polluted compared to the summer

ones. 2. The U ASB reactors were quite efficient for removal of HM (due to their precipitation/ entrapmenton the sludge) and bulk COD from Khmet 'yevo landfilileachates even during operation under submesophilic and psychrophilic conditions (20-10°C). 3. The application of aerobic/anoxic biofilters at 10-20°C; allowed an elimination of biodegradableCOD and more than 92% of inorganic nitrogen from the anaerobiceffluents. However, the remaining nitrogen concentrations were above the current national standardsfor direct dischargeof treated wastewater.A simple and cheappost-treatment step like a stabilisation pond or constructedwetland will probably be required to ensure a safedischargeof the treatedleachatesto surfacewaters.

Acknowledgements The financial support of INCa Copernicus (contract No ICA2-CT-2001-10001) is gratefully acknowledged.We thank company "Ecotechprom" (Moscow) for delivering the landfilileachates. 57


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