Journal of Scientific & Industrial Research 790
J SCI IND RES VOL 69 OCTOBER 2010
Vol. 69, October 2010, pp. 790-793
Effect of recirculation rate on anaerobic treatment of fleshing using UASB reactor with recovery of energy E Ravindranath1*, Chitra Kalyanaraman1, S Shamshath Begum1 and A Navaneetha Gopalakrishnan2 1
Department of Environmental Technology, Central Leather Research Institute (CLRI), Adyar, Chennai, 600 020, India 2
Centre for Environmental Studies, Anna University, Guindy, Chennai 600 025, India Received 16 April 2010; revised 20 July 2010; accepted 26 July 2010
This study presents performance of upflow anaerobic sludge blanket (UASB) reactor in treating liquefied fleshings (LFs) with tannery wastewater (TWW) using liquefaction reactor (LR). With increase in recirculation rate, methane production increased in LR than in UASB reactor due to methanogenic bacteria in LR. UASB reactor with continuous feeding of LFs and TWW resulted with cumulative methane in UASB reactor (128 l) and LR (145 l). Keywords: Biomethanation, Fleshing disposal, Liquefaction, Tannery wastewater treatment, UASB
Introduction Usually processed wastewater from leather processing is collected for further treatment in either common effluent treatment plants (CETP) or effluent treatment plants (ETP) before discharging into water bodies. Unutilized fleshing is dumped in lower-lying regions and riverbanks. Aerobic treatment of organic matter emits volatile compounds (ketones, aldehydes and ammonia)1,2. Hence, anaerobic digestion is the best option with production of biogas, reduced green house gases and pollution control3. Studies are reported on high strength organic wastes (slaughterhouse waste4-6, food waste 7-9 , beverage 10 and pulp and paper 11,12 etc.). Liquefaction of fleshings13 has been carried out under anaerobic conditions in batches. This study presents performance of upflow anaerobic sludge blanket (UASB) reactor in treating liquefied fleshings (LFs) with tannery wastewater (TWW) using liquefaction reactor (LR). Effect of recirculation rates and subsequent methane generation was studied. Experimental Section Solid and Liquid Samples
TWW and solid wastes (wet limed fleshings) (Table 1) were collected from Talco Vaniyambai Tanners Enviro Control Systems Ltd, India. *Author for correspondence E-mail:
[email protected]
Liquefaction Reactor (LR)
Initially LR was filled with UASB reactor effluent. Wet fleshing (150 g) was introduced into LR daily through perforation provided at the top of reactor. Part of effluent from UASB reactor was circulated through LR to facilitate liquefaction of fleshing. LFs were recirculated through UASB reactor. Various recirculation rates studied were 3.0 l/day, 3.2 l/day, 6.5 l/day, 10.6 l/day and 11 l/day. UASB Reactor
Composite TWW (4 l) was fed into UASB reactor daily. Along with TWW, LFs from LR was also introduced into UASB reactor. Inoculum [total solids (TS), 54 g/l and volatile solids (VS), 27 g/l] for UASB reactor was obtained from pilot plant (capacity, 12.5m3) (CLRI, Chennai, India) to treat domestic wastewater. Analytical Methods
Chemical oxygen demand total [COD (T)], TS, VS, alkalinity, sulfate, sulfide and chloride of samples in UASB reactor and LR were measured by standard methods. Volatile fatty acid (VFA) concentration was measured as acetic acid equivalent using a standard distillation method. Samples (50-100 ml) were withdrawn from the top of UASB reactor and LR. pH of influent / effluent of UASB reactor and LR were measured daily by portable pH meter (pH 330, WTW Germany).
RAVINDRANATH et al : ANAEROBIC TREATMENT OF FLESHINGS FROM TANNERY WASTE WATER
791
Table 1—Characteristics of fleshing and tannery wastewater Parameters pH Moisture, % Total solids, mg/l Volatile solids (dry solids), g/g COD (total), mg/l COD of dry solids (total), g/g Sulphate as SO42- (total), mg/l Sulphide as S, mg/l Chloride, mg/l
Composite wastewater 7.5-8.5 10,000-20,000 3000-4000 700-1500 100-200 4000-8000
Fleshing 11-12 80-90 0.4-0.8 1-1.4 -
3000
VFA, mg/l
2400
1800
1200
600
0 0
10
20
30
40
50
60
70
80
90
100
Number of days VFA UAS B - Inf
VFA U AS B - E ff
VFA- LR
Fig. 1—Variation of VFA concentrations in UASB reactor influent, effluent and LR Methane Production
Methane gas produced was passed through soda lime pellets column (length, 0.22 m; diam, 0.03 m) and was measured by wet flow gas meter. Soda lime pellets were changed regularly after entire column turned to blue from pink. Experimental Set up
A bench scale system consisting of glass UASB reactor and LR was fabricated. Entire process was carried out at ambient temperature (30 ± 1°C). LFs (150 g) were added daily in LR and were introduced by peristaltic pumps in UASB reactor. Controlled recirculation was maintained between UASB reactor and LR.
Results and Discussion COD and VFA Concentrations in UASB Reactor Influent, Effluent and LR
Average COD (T) of UASB reactor’s influent and effluent and that of LR were found to be 1767 mg/l, 1296 mg/l and 3005 mg/l respectively. In LR, COD (T) concentration decreased with increase in recirculation rate from 3.2 l/day (3783 mg/l), to 6.5 l/day (2314 mg/l), 10.6 l/day (2146 mg/l) and 11 l/day (1767 mg/l) due to dilution and immediate conversion of digested COD to methane. In anaerobic conditions, acidogenic bacteria convert organic matter to VFA. Influent (TWW), effluent and LR’s average VFA were found to be 749 mg/l, 336 mg/l and 1508 mg/l respectively (Fig. 1).
792
J SCI IND RES VOL 69 OCTOBER 2010
1 60
Cumulative methane production, l
1 40
1 20
1 00
80
60
40
20
0 0
20
40
60
80
10 0
12 0
Noumber of days Cumulative methane one (LR)
C
Cumulative methane one (UASB)
Fig. 2—Cumulative methane production in UASB reactor and LR
Average VFA of UASB reactor’s influent was found to be 42% of average influent COD. Initially VFA in LR was more than 2226 mg/l when recirculation rate was 3 l/day and decreased to 846 mg /l when recirculation rate was 11 l/day. VFA (45%) was converted into methane in LR when recirculation rate increased from 6.5 l/day to 11 l/day. VFA /alkalinity ratio shows stability, well-buffered condition of an anaerobic system. In present study, value of VFA /alkalinity ratio (< 0.4) illustrates stability of UASB reactor. Treated effluent from UASB reactor was continuously recirculated into LR as a source of microbial consortia to liquefy fleshings. LFs were pumped into the bottom of UASB reactor along with TWW. Recirculation of UASB reactor effluent into LR and production of VFA in LR resulted in reduction of pH. Initially, pH value in LR was > 9 and decreased to an average of 7.4 at the end of study. Most of the studies have proved that pH of 6.5 - 7.5 is most suitable for methanogenesis14. pH of UASB influent and effluent were 7.0-7.7 and 7.2-8.0 respectively. Influent and effluent pH values of UASB reactor show favorable condition for methanogenesis. Recirculation Rate on Methane production in UASB Reactor and LR
During start up, recirculation rate was maintained at 3 l/day and later it was maintained in increasing order (3.2 l/day, 6.5 l/day, 10.6 l/day and 11 l/day) to assess
investigation on effect of recirculation rate on methane production. Corresponding average methane production with respect to above mentioned recirculation rate in LR was found to be 0.12 l, 0.59 l, 1.7 l, 2.6 l and 3.3 l. Thus methane production in LR was increasing with increase in recirculation rate due to more microbes (fermentative, acidogenic and acetogenic) were provided in LR. This reflected in consumption of more VFA in LR and was converted into methane in LR itself. On the other hand, incase of UASB reactor, corresponding average methane production was found to be 2.2 l, 1.94 l, 1.46 l, 1.12 l and 0.9 l. It was observed that with increase in recirculation rate, methane production was decreased. VFA, which are responsible for methane production, supplied to UASB reactor in form of LFs was decreased through recirculation in UASB reactor and hence decrease in methane production was observed. Cumulative methane production (Fig. 2) in LR was higher than that in UASB reactor. Methanogens were promulgated in LR through recirculation from UASB reactor. With increase in recirculation rate from 6.5 l/day to 11 l/day, methane production in LR was increased. Totally, 128 l and 145 l of methane were produced in UASB reactor and LR respectively. Conclusions This study shows feasibility of liquefaction of fleshing using UASB reactor and LR. With increase in recirculation rate from 3 l /day to 11 l/day, methane pro-
RAVINDRANATH et al : ANAEROBIC TREATMENT OF FLESHINGS FROM TANNERY WASTE WATER
duction in LR was found to be increased than UASB reactor. Wet limed fleshing generated in tanneries can be treated successfully using this system. Acknowledgements Authors thank Director, CLRI, Chennai for support in research work. Authors also thank Tannery units, Tamilnadu and Mr K Thirumaran for technical support.
7
8
9
References 1
2
3
4
5
6
Bjorkqvist S, Froling M, Harelindingelsten H & Peterson G, Hydrocarbons in biogas from household solid-waste, Environ Technol, 19 (1998) 639-642. De Baere L, Anaerobic digestion of solid waste: state-of-art, in Proc Second Intl Symp on Anaerobic Digestion of Solid Wastes, vol 1, edited by J Mata-Alvarez, A Tilche & F Cecchi (Barcelona, Spain) 15-18 June 1999, 290-299. Baldasano J M & Soriano C, Emission of greenhouse gases from anaerobic digestion processes. Comparison with other MSW treatments, in Proc Second Intl Symp on Anaerobic Digestion of Solid Wastes, vol 2, edited by J Mata-Alvarez, A Tilche & F Cecchi (Barcelona, Spain) 15-18 June 1999, 274-277. Borja R & Bank C J, Performance and kinetics of an upflow anaerobic sludge blanket (UASB) reactor treating slaughterhouse wastewater, J Environ Sci Health, A29 (1994) 2063-2085. Salminen E & Rintala J, Anaerobic digestion of organic solid poultry slaughterhouse waste-a review, Biores Technol, 3 (2002) 13-26. Esa Salminen A & Jukka Rintala A, Semi-continuous anaerobic digestions of solid poultry slaughterhouse waste: effect of hydraulic retention time and loading, Wat Res, 36 (2002) 3175-3182.
10
11
12
13
14
793
Kenichiro T, Tatsuo Y, Tomoko O & Shigeki S, Treatment of liquid fraction separated from liquidized food waste in an upflow anaerobic sludge blanket reactor- Short Communication, J Biosci Bioengg, 87 (1999) 554-556. Gerrero L, Omil F, Mendez R, & Lema, Anaerobic hydrolysis and acidogenesis of wastewaters from food industries with high content of organic solids and protein, Wat Res, 33 (1999) 3281-3290. Shin H S, Han S K, Song Y C & Lee C Y, Performance of UASB reactor treating leachate from acidogenic fermenter in two-phase anaerobic digestion of food waste, Wat.Res, 35 (2001) 3441-3447. Ute A-H & Karl-Heinz R, Two examples of anaerobic pre-treatment of wastewater in beverage industry, Wat Sci Tech, 36 (1997) 311-319. Stefanie J W H, Oude Elferink, Werner J C, Vorstman, A S, Alfons J M & Stams, Characterization of sulfate-reducing and syntrophic population in granular sludge from a full-scale anaerobic reactor treating papermill wastewater, FEMS Microbiol Ecol, 27 (1998) 185-194. Ulas T, Engin G, Tuba E H & Goksel D N, Sequential (anaerobic/aerobic) biological treatment of dalaman seka pulp and paper industry effluent, Waste mgmt, 21 (2001) 717-724. Ravindranath E, Chitra Kalyanaraman, Suthanthararajan R, UmaMaheswari B, Shamshath Begum S, Bhuvaneswari R & Rajamani, S, A scientific remedy for disposal of fleshing generated from tanneries, in Proc Nat Symp on Recent Trends in Industrial Waste Management for Sustainable Development (Annamalai University, Chidambaram, India) 17-18 March 2004, 111-115. Prenico L F, Van Langerak J A & Lettinga G. pH stability in anaerobic bioreactors treating methanolic wastewaters, Wat Sci Tec, 33 (1996) 177-184.
