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Waf. Sci. Tech. Vol. 36, No. 12. pp. 125-133,1997.© 1997 IAWQ. Published by Elsevier Science Ltd

Printed in Great Britain.0273-1223/97 $17'00 + 0'00

UASB PERFORMANCE IN PRESENCE OFALGAE AND SYNTHETIC MEDIA

Jae Eun Park,* Jong 0 Kim,** Woo Bum Lee,***Sung Taik Leet and Jung Jun Lee*

* Department ofEnvironmental Engineering, Chonnam National University,Kwangju, Korea** Department ofEnvironmental Engineering Education, Mokpo National University,Muan-Kun, Korea*** Department ofEnvironmental Engineering, Yosu National Fisheries University,Yosu, Koreat Department ofBiological Sciences, KAIST, Taejun, Korea

ABSTRACT

An upflow anaerobicsludge blanket (UASB) technology has showed an excellent perfonnance compared toother biological treatment methods when a high organic loading rate of domesticand industrial wastewaterswas applied. The objective of this study was to investigate the effect algae from lake-sediments and syntheticactivated ceramic as media on UASB perfonnance. The algae and synthetic media were introduced to theUASB reactor in order to obtain the enhanced granulation, which resulted in the increase in the UASBperfonnance. 1-3% higher methane content and 3-10% higher COD removal efficiency were obtained in thereactors with the media than in the reactor without the media. The respective gas production rates in reactors1,2, and 3 were 0.15-0.36 m3/kg COD-day, 0.24-0.54 m3/kg COD-day, and 0.24-0.56 m3/kg COD-day. Asorganic loading rate increased, gas production rates increased. © 1997 IAWQ. Published by Elsevier ScienceLtd

KEYWORDS

Algae; synthetic media; granulation; UASB.

INTRODUCTION

Many researchers have studied the anaerobic treatment using the upflow anaerobic sludge blanket (UASB)process in order to treat wastewaters containing high organic matter (Lettinga and Van Velsen, 1980;Brummeler et al., 1985; Lettinga and Hulshoff Pol, 1986). Since Lettinga and his coworkers developed theUASB technology in 1980s, the technology has been widely applied for the treatment of various industrialwastewaters, which range from relatively low to high concentrations (Brummeler et al., 1985).

A typical UASB reactor is composed of an inlet distributor, granular sludge bed, and a gas-solid separator(GSS). Influent flows uniformly upward through the inlet distributor. The GSS is installed inside the reactorin order to separate gases from the water-solid mixture at the top of the reactor. Because media for biologicalgrowth are not added in the reactor, it is important to form the granulation process by agglomeration ofsludge. Granular sludge from an existing UASB reactor is frequently used as inoculated material to initiate anew reactor.

125

126 1. E. PARK et al.

Several factors affect the granulation process of sludge in the vASB reactor such as presence ofMethanothrix and inorganic particles, and selection pressure. In addition, characteristics of influent andinoculated sludge, loading rates, temperature, pH, and nutrients influence the granulation of sludge. The sizeof granular sludge is usually 1-2 mm and is dependent on characteristics of infltfent and inoculated sludge(Hulshoff Pol et al., 1983).

To date, the investgations about physical (Harada, 1988), chemical (Dolfing, 1987; Dubourguier et al.,1988), and biological characteristics (Archer, 1988) of granular sludge have been mostly focused upon.Because a few studies on the enhancement of the vASB performance have been reported, more researchesare still in great need. The objective of this study was to investigate the effect of algae from lake-sedimentsand synthetic activated ceramic as media on vASB performance. The algae and synthetic media wereintroduced to the vASB reactor in order to obtain the enhanced granulation, which resulted in the increase inthe vASB performance.

EXPERIMENTAL METHODS AND MATERIALS

vASB reactor

This study was carried out using the apparatus schematically shown in Fig. 1. The UASB reactor setupconsisted of three identical laboratory-scale reactors of 9.0 cm ID and 55cm long (5.5 L capacity). Eachreactor included an effective part, which contained the sludge bed, and a settler compartment, which wasequipped with a gas outlet. Temperature of the reactor was maintained at 35±I·C in the temperaturecontrolled room. Influent wastewater was fed to the reactor through a feed distributor using a Masterflexpump (Cole-Parmer, Niles, USA) from an influent tank. The outlet gases were collected by a gas collector,whereas effluent was collected in an effluent tank.

eIIIuent tank

Figure I. Schematic diagram of the reactor.

Three reactors were operated under the different mixing ratio of inoculated sludge. Reactor 1 (R1) was filledwith gr~ular ~lud?e (2L) and digested sludge (lL), whereas reactor 2 (R2) was operated in the presence ofsynthetic medIa WIth granular sludge (2L) and digested sludge (lL). Lake-sediments (lL) were additionallytransf~rred to a r~actor 3 (R.3) wi~hout media. The performance of each reactor was studied and comparedone WIth another 10 order to mvestIgate the improved UASB operations.

In order to activate the inoculated granular and digested sludge in the reactors the reactors were run at an.1 d' f 3 'organIC oa 109 rate 0 0.67 kgCOD/m .day in the beginning of operation. The hydraulic retention time

(J:IR!) was gradually decreased from 12 to 8 hr. The vASB operation at 12 hr HRT was run for 40 days.Slffillarly, the UA~B reactor at 10 hr HRT was operated for 40 days. The organic loading rates ranged from8 to 12 kgCOD/m .day during this study.

VASB perfonnance in presence of algae 127

As shown in Table 1, influent COD concentration ranged between 3930 - 4330 mgIL. The ratio of influentCOD, N, and P was 350-450:7: 1. The pH, VA, and gas production rate were measured daily, whereas theother parameters were analyzed frequently depending on sampling time.

Table 1. The composition of a synthetic wastewater

Parameter

TCOD

SCOD

SS

VSS

T-N

T-P

Total alkalinity

Bicarbo. alkalinity

Volatile acid

A synthetic wastewater and a nutrition solution

Concentration

(mg/L)

3930-4330

3820-4200

350

114

128-150

11.5-18.4

1000-1200

510-560

760-560

A synthetic wastewater as a substrate was prepared weekly at a desired COD concentration in a 20 L plasticholding tank. Glucose was diluted with tap water. The composition and concentration of the wastewater arepresented in Table 1. Value of SCaD in the wastewater ranged from 3930 to 4330 mglL. A nutrient solutionwas also prepared and introduced to the reactors. (NH4hHP04 and NH4CI were supplied as nutrients andmany minerals (MgS04, FeCI3.H20, CaCI2.2H20, ZnCI2, etc) and trace metals as essential elements weresupplied for bacteria growth. Average influent COD, T-N, and T-P ranged 4150, 139, and 15 mgIL,respectively.

Characteristics of sludge and lake-sediments added

The UASB reactors were inoculated with digested anaerobic sludge from a municipal sewage treatmentplant in Kwangju City andinactive granular sludge. The inactive granular sludge had been kept at a roomtemperature after the operation of an UASB reactor had been finished. Before the granular sludge wastransferred into the reactors, the sludge was graded with USA ASTM No. 10 (0.0787 inch) sieve to removelarger size sludge. Volumes of digested and inactive sludge are 1 and 2 litres, respectively. The lake­sediments were obtained from a sample of a lake soil.

The compositions of the digested sludge, granular sludge, and lake-sediment are shown in Table 2.Alkalinity, volatile acids (VA), total COD (TCOD), total solids (TS), and volatile soilds (VS) of the inactivegranular sludge were higher than those of the digested sludge. The TS of the lake-sediment showed thehighest value.

Analytical methods

COD, SS, VSS, and alkalinity were analyzed on the basis of Standard Methods (1992). The T-N and T-Pwere analyzed by UV Spectrophotometer (HewlettPackardModel). The gases generated from the reactorswere collected using a wet gas meter (Shinakawa W-NK-0.5A) and analyzed by Drager (Multiwarn, CP).The analysis of elements, C (Carbon), H (Hydrogen), a (Oxygen), and N (Nitrogen), was determined by EP(Series CHNS/O Analyzer). Scanning electronic microscopy (SEM) was used to investigate granulation ofsludge. In addition, denitrifying bacteria and sulfatereduction bacteria were checked by cultivation of cells.

128 J. E. PARK t!l al.

Table 2. Characteristics of the seeded sludge and lake-sediment

Parameter

pH

Alkalinity(mgIL)

VA(mg/L)

TCOD(mglL)

TS(mglL}

VS(mg/L)

Granular sludge

7.1

3572

40

32500

38600

25700

Digested sludge

7.22980

3529600

3580018400

Lake-sediment

6.9

31360

55400

21245

4000

RESULTS AND DISCUSSION

Performance of the UASB reactors

The reactor 1 (Rl) was filled with granular sludge and digested sludge, whereas the reactor 2 (R2) or 3 (R3)contained synthetic ceramics or algae in lake-sediment additionally. Figure 2 shows the performances ofthree reactors as a function of influent and effluent COD variation for 120 days. The UASB operation at 12hr HRT was run for 40 days. Similarly, the UASB reactor at 10 hr HRT was operated for 40 days. Theorganic loading rates ranged from 8 to 12 kgCOD/m3.day during this study. Effluent concentration in theboth reactors quickly increased when HRTs were changed. COD removal efficiencies increased to 95% in40 days after changing of HRT from 12 to 10 hr. In case of HRT of 8 hr, COD removal efficiencies slowlyincreased.

Table 3 summarizes the comparison of the average performance of three reactors at hydraulic retention timesof 8-12 hr. The overall performance of the reactors was satisfactory with respect to COD removalefficiencies. 3-10% higher removal efficiency was observed in the reactor containing algae or ceramics. Theremoval efficiency of the Rl was reduced to 80% at an organic loading rate of 12 kg COD/m3.day.However, in case of the R2 and R3, removal efficiency was obtained more than 90% at the same organicloading rate. It has been reported that the addition of media in a reactor increased microbial population.Therefore, anaerobic bacteria were present on the surface of the ceramic and more organic carbon wasremoved. Effluent concentration in the both reactors quickly increased whenever HRTs changed.

5000 r----: ------""':"":'-:--------"""":"-:--------,HRT= 12hr lOhr 8hr-- ---------+--------- 1-----------1

--~-------

~ 3000Cis'8 2000 -~ Eflluent(Rl) -- Eflluent(R2) -- Effluent(RJ} - Influent

1000 _:.- .......~.:

20 40 60 80 100 120Day

Figure 2. Variation of influent and effluent COD as a function of HRT.

UASB perfonnance in presence of algae 129

Table 3. Average influent and effluent COD concentration, COD removal, and methane composition foreach reactor

Inf. Reactor 1 Reactor 2 Reactor 3

HRT(hr) 8 10 12 8 10 12 8 10 12

Average COD(mglL) 4150 830 470 350 545 329 480 550 200 180

Removal eff.{%) 80 90 9290 95 94 89 9595

Methane comp.{%) 70 69 58 7070 61 70 70 61

Alkalinity and VA

Figure 3 illustrates the variation of alkalinity as a function of HRT. Influent alkalinity ranged between 1000and 1200 mgIL as CaC03, whereas respective effluent alkalinity of R1, R2 and R3 were between 1170 and1400 mgIL. Alkalinity of effluent was approximately 200 -250 mg/L higher than that of influent due tosolubilization of carbon dioxide generated by anaerobic treatment.

20 r------------------------.....8hr10 hrHRT= 12 hr

t-------------!-------------+----------

, .,

,:':,j'.'\ L.:~ 5.JJ.'~>"': 1..- ~a .... "''' \ ... I ~ ~ -~,,\ \ - .. ~ (,..---/__ .~ .. :.. :..- ~ ,... .. :......-t, ~ _.. .. ~ ~......., ..-. ~ ~ ..'. .- .w:: - J • "..-------• • ... ~ ~ ..... .-i . '\ •• _ '.• --.. 'l ... • -.

; i·e;"J--~-_. -_ •• - ... -fL.w- -----

\.l

~ Emuent(Rl) - Emuent(R2)~ Emuent(R3) - Influent

12010080604020

oL-__---' ~ _"_ ....... .....____J

o

8hr10 hrHRT=12 hr I

Day

Figure 3. Variation of influent and effluent alkalinity as a function of HRT.

12

9;J"---'+£---v.a£ ~ I"""""'<:. -~ I - -~~ .~O 5868 E)

--4-+ ...... ;.44-..... ~•

• -- EfT(Rl) -.- EfflR2) --+-- EfT(R3) -€r- Inf

oL_-....I----~----''----~--.....l...----Jo 20 40 60 80 100120

Day

Figure 4. Variation of effluent VA as a function of HRT.

J. E. PARK et al.

iation of volatile acid as acetic acid was presented in Fig. 4. About 25% higher volatile acid at 8 hr of~ was produced. During the operation of reactors, the ranges of effluent pH in both reactors wereveen 6.9 and 7.6, which means appropriate environment for methane bacteria growth.

production

shown in Fig. 5, the respective gas production rates in reactors 1,2, and 3 were 0.15-0.36 m3/kg COD­, 0.24-0.54 m3/kg COD-day, and 0.24-0.56 m3/kg COD-day. As organic loading rate increased, gasiuction rates increased. It was foundthat optimal operating condition of organic loading rate can be 10:OD/m3.day.

:ent of methane gas in total composition is shown in Table 3. 1-3% higher methane gas was produced inR2 and R3 than in the R1. It was likely that the algae or media stimulated the growth of bacteria, gasiuction, and methane composition.

1110HRT (bour)

8o

0.5 I--·----------------·-------~

~ f DRl~R2I1R36 0.4ole 0.3-

Table 4. Physical and chemical characteristics of the granular sludge

R1 R2 R3Diameter(mm) 0.5-4.7 0.8-4.0 0.8-4.0

Settling velocity(em/sec) 0.5-1.4 0.8-1.7 0.8-1.7C(%) 38.8 35.4 20.0H(%) 6.0 5.7 3.5N(%) 5.7 8.0 4.6S(%) 4.0 4.7 3.2Ash(%) 11.8 13.5 32.7

dge characterization

~ular sludge having size of 0.7 to 5.5 mm was developed by the effect of inoculation using lake­Iment, even when granular size was distributed 0.5 to 4.7 mm in the reference condition (reactor I).>le 4 presents the physical and chemical characteristics of granular sludge taken from both reactors. Themeter of granular sludge in the R3 was consistently higher than that in the R1 and the reported values byIshoff Pol et ai. (1983).

VASB performance in presence of algae 131

The settling velocity of granular sludge in R3 was higher than those in RI. It clearly showed that the seedsof lake-sediments were useful to develop a granular sludge hardened. Chemical analysis showed thatgranules contained large amounts of carbon. The differences of chemical characteristics of granular sludgein the RI and R3 were obtained probably due to the addition of lake-sediment.

Table 5 shows nitrate and sulfate reduction rates by each anaerobic bacterium in the reactors. More than twotimes higher nitrate reduction rate in the R3 was observed compared to the R1 and R2, whereas sulfatereduction rates were close. It seemed likely that the algae from lake-sediments induced the increase ofbacteria populations under anaerobic conditions.

Table 5. Denitrification and sulfate-reduction rates of each granular sludge

Reactor

R1

R2

R3

Nitrate reduction

rate (J.l mollhr)

120.7

145.5

349.4

Denitrification

rate (J.l mol/hr)

50.1

38.7

66.5

Sulfate reduction

rate (J.l mollhr)

4.7

5.6

5.7

Structure of granular sludge was observed using SEM as shown in Fig. 6. The overall structures of granularsludgein the Rl were similar to those of previously reported studies. But the structures of granular in the R3were very complex, unique and constituted of various bacterial morphotypes entrapped in a heterogeneousmatrix. Methanobacterium was observed in all the sections as dispersed and non-oriented. Anothermorphotype identified like algae was also arranged as microcolonies. Methanosarcina sp. were alwayspresent but in low numbers, and Methanosaeta were observed mainly in this section. It was reported thatMethanosarcina were present when a reactor contained a high concentration of acetic acid (Wiegant andLettinga, 1985; Wiegant et ai., 1986).

CONCLUSIONS

The following conclusions can be drawn on the findings of this study:

1. It was found that inoculation of algae from lake-sediment and synthetic media as a seed sludge to anVASB reactor enhanced the granulation process.

2. Inoculation of algae and media increased COD removal efficiency and methane content in biogas notonly in thethe beginning of operation periods, but also in the stable periods. At an organic loadingrate over lOkg/m3.day, the UASH reactor was capable of achieving the COD removal efficiency asmuch as 90%.

3. More than two times higher nitrate reduction rate in reactor containing the lake-sediments was found,whereas the sulfate reduction rates in two reactors showed similar results.

4. Methanobacterium and Methanosaeta as methanogenic bacteria were observed mainly In thegranular sludge.

132 J. E. PARK et al.

•

~, utk U X!S0----- 500 .... 1fl 150806

Figure 6. Photographs of granular by SEM.

REFERENCES

Archer, D. B. (1988). Report on the microbiological aspects of granulation. In Granular Anaerobic Sludge; Microbiology andTechnology. Proc. the GASMAT-Workshop, Pudoc Wageningen, The Netherlands, pp. 107-111.

Brummeler, E. T., Hulshoff Pol, L. W., Dolfing J., Letting, G. and Sehnder, A. J. B. (1985). Methanogenesis in an upflowanaerobic sludge blanket reactor at pH 6 on an acetate-propionate mixture. Appl. Environ. Microbiol., 49, 1472-1477.

Dubourguier, H. C, Busson, M. N., Tisser, J. P., Prensier, G., and Albagnac, G. (1988). Structural characteristics and metabolicactivity of granular methanogenic sludge on a mixed defined substrate. In Granular Anaerobic Sludge; Microbiology andTechnology, Proc. the GASMAT Workshop, Produc Wageningen, The Netherlands, pp. 78-86.

Dubourguier. H. C, Prensier, G., Samain, E. and Albagnac (1985). Granular Methanogenic Sludge. Energy from Biomass.Elsevier Applied Science, pp. 542-546.

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UASB perfonnance in presence of algae 133

Lettinga, G. and Viaben, J. N. (1980). Feasibility of the upflow anaerobic sludge blanket (UASB) process for the treatment oflow-strength wastes. In Proc. 35th Ind. Waste Conf. Purdue Univ., pp. 625-634.

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Lettinga, G. and Hulshoff Pol, L. W. (1986). Advanced reactor design, operation and economy. Wat. Sci. Tech., 18,99-108.Lettinga, G. and Zeeuw, W. D. (\985). Anaerobic wastewater treatment based on biomass retention with emphasis on the UASB­

process. In Anaerobic Digestion 1985 9th, China State Biogas Association, Guangzhou, China, pp. 279-301.Mosey, F. E. (1983). Kinetic descriptions of anaerobic digestion. In 3rd Int. Sym. on Anaerobic Digestion, Boston.Standard Methods for the Examination of Water and Wastewater (\992), 18th edn, American Public Health Association,

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Wiegant, W. M. and de Man, A W. A. (\986). Granulation of biomass in thennophilic upflow anaerobic sludge blanket reactorstreating acidified wastewater. Biotech. Bioeng., 28, 718-727.

Wiegant, W. M. and Lettinga, G. (\985). Thennophilic anaerobic digestion of sugar in upflow anaerobic sludge blanket reactors.Biotech. Bioeng., 27,1603-1607.