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High rate anaerobic fixed bed reactor with floating supports for the treatment of effluents from small agro-food industries

M. TORRIJOSLBE, INRA, France

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This work is an Indo -French collaboration between:

- The Indian Institute of Technology (IIT) of Roorkee, India

- The Kumaraguru College of Technology of Coimbatore, India

- The laboratory of environnemental Biotechnology (LBE) - INRA Narbonne, France

PARTNERS of the PROJECT

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AIM of this WORK

- To determine the basic principles for the design of upflow anaerobic fixed bed reactor (UAFBR) packed with small floating supports for the treatment of agro-food effluents of different nature and concentration

- To evaluate the quantity of biomass inside the reactors and the specific biomass activities,

- To study the hydrodynamics inside the reactor to determine the behaviour of the reactor with respect to the clogging.

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Anaerobic Fixed Bed Reactors

- Anaerobic fixed bed reactors: - are composed of a vertical bed which contains an inert media which acts as a stationary support for microbial attachment.

- Two kinds of supports can be used: - the well ordered supports and

- the loose supports.

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Characteristics of the Support used in this study

Small floating supports of polyethylene materialSize : 29 mm high, 30/35 mm diameterDensity : 0.93 Void space : 90 %Specific Area : 320 m2/m3

excellent thermoplastic materials for biological carrier mediaNon-toxic and non-reactive in most biological applications

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Outlet

Feed

Biogas

Fluidisationpump

support :

Outlet

Biogas

Fluidisationpump

Working Conditions Unclogging Conditions

Upflow fixed bed reactor with floating support

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Characteristics of the different substrates used

NA4.40-5.10NANATOC, g/L

1.36- 2.230.10-0.130.72-0.750.12-0.17VSS, g/L

1.56-3.400.15-0.201.17- 1.200.15-0.25TSS, g/L

4.0- 4.55.2- 5.53.5 – 4.06.3-6.5pH

22.0-38.017.2-20.08.4- 11.21.4-2.4CODs, g/L

~ 30~ 20~ 10~ 1.9CODt, g/L

Taken from a middle-size cheese factory near Narbonne (France) and was diluted in the ratio of 1:2 to simulate the effluents of cheese dairies without whey recovery

Lactose, proteins, lipids, milks minerals

Prepared by diluting red wine at 11° (alcohol fraction) in the ratio of 1:10+ AddedMicronutrients(COD:N:P = 400:7:1)

Ethanol

Raw pineapple juice was diluted in the ratio of 1:15 + AddedMicronutrients(COD:N:P = 400:7:1)

Simple sugars; and citric and malic acids.

Synthetic wastewater –prepared using Peptone, Meat extract, Starch, Cellulose + Micronutrients

--

Preparation

Primary Constituents

Cheese dairy wastewaterWinery effluentsFruit-canning wastewater

Diluted wastewater

Parameter

-NA = ‘Not analysed’

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Reactor at laboratory scale

Volume of the reactor 10 L

Recirculation Rate(except for diluted WW)

10 L / h

Support Media 8 L

Temperature of the reactor

33 °C

Inoculum usedanaerobic sludge(10% of reactorvolume)

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Typical operating strategy of the reactor withDiluted wastewater (HRT - OLR profile)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 10 20 30 40 50 60 70 80 90 100Time, day

HR

T, d

ay

0.0

1.0

2.0

3.0

4.0

5.0

6.0

OLR

, kg

CO

D/m

3.d HRT, day

OLR g COD/L.d

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Fig 1: Temporal profile of OLR and CODs removal efficiency for the reactor treating winery effluents.

0

20

40

60

80

100

0 20 40 60 80 100 120 140 160 180Time in days

CO

Ds

rem

oval

(%)

0

10

20

30

40

50

60

70

OLR

(Kg

CO

D/m

3.d)

COD removal %OLR Kg COD/m3.d

Typical operating strategy of the reactor withHigh Strength Wastewater:(HRT - OLR profile)

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0.630.930.610.58* Specific activity (g COD/g of VS. d)

65718364* % VS/TS (Biomass inside the supports)

269226342206* Total biomass in g VS

916710887• Biomass entrapped between the supports or in

suspension in the liquid phase, in g VS

178159234119* Entrapped biomass inside the supports, in g VS

Biomass inside the reactor at the end of the experiment

3.8 + 1.50.86 + 0.031.2 + 0.60.16 + 0.03* Average SS concentration @ outlet (g/L)

0.310.30.190.12* Minimum SCOD @ outlet (g/L)

Effluent data

1727195• Max OLR (Kg COD/m3.d) with 80% removal

efficiency

4019124* Minimum HRT (h) with 80% removal efficiency

Reactor operating data

2.61.41.20.25* Initial SS concentration (g/L) at feed

2818.59.51.75* Initial soluble COD (g/L) at feed

3020101.9* Total COD (g/L) at feed

Influent data

CHEESE-DAIRY ww

WINERYWW

FRUIT-CANNING WW

Diluted wastewatersPARAMETERS

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Residence time distribution (RTD) study

The objective of this part was only to known the global efficiency of the liquid mixing.

A pulse of tracer sodium chloride (25-mL of a solution of 300 g NaCl/L) was introduced into the bottom of the reactor along with the feed inlet.

A tracer mass balance of 92 % shows that NaCl did not accumulate in the reactor during the RTD study.

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Liquid mixing and reactor clogging- Diluted wastewater

0

0.25

0.5

0.75

1

0 2 4 6 8

θ

Ε(θ)

CSTRExperimental RTD for domestic ww

Fixed bed with a recirculation flow of 10 l/h

Presence of large dead zone volumes and; t = 3.4 h and tE = 9.7h Thus Liquid mixing : showed a poor efficiency. Recirculation improves liquid mixingA sequential recirculation flow could be used to improve the macro mixing within the fixed bed.

Experimental RTD for diluted ww

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RTD curves for the High strength effluents with recirculation

Fig 2. Residence Time Distribution curves

0

0.5

1

1.5

2

0 1 2 3 4 5T

E(T

)

Fruit canning

Winery wastewater

Cheese-whey

CSTR

The degree of liquid mixing is still acceptable because:

(i) the experimental mean residence time was very close to the theoretical one (tE = 0.9t),(ii) of the relatively high value of the dispersion coefficient (D/uL = 2.9)calculated from a relationship derived from analogous form of Fick’s law (Levenspiel, 1962)

where σ 2 is the variance of the RTD curve.

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Conclusions

This study reveals that a UAFB reactor with small floating polyethylene supports was very efficient in the treatment of low to high strength agro-food industrial effluents.

High OLRs could be reached even for the very diluted effluents.

The study of the attached biomass showed that it was possible to fix a high quantity of solids on the support.

Low-density polyethylene supports used in this study appears to be an excellent colonisation matrix and was able to retain between 0.7 g and 1.6 g dried solids per support.

Biomass retention in the reactor was contributed to both entrapment within the support and a filtration effect of the support on the biomass in suspension. This result was confirmed by the specific activity values which were very close to that of suspended biomass.

Since the treatment efficiency is good, the media clogging is not a real problem at the end this experiments. However, long term investigation need to be realized to know if the hydrodynamic strengths generated both by liquid velocity and biogas flow are sufficient to maintain good macro-mixing within the fixed bed.

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ACKNOWLEDGEMENTS

French Embassy in India in providing financial support.

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