An integrated treatment system for coffee processing wastewater using anaerobic and aerobic process

Ecological Engineering 36 (2010) 1686–1690

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An integrated treatment system for coffee processing wastewater using anaerobic and aerobic process M. Selvamurugan ∗ , P. Doraisamy, M. Maheswari Department of Environmental Sciences, Tamil Nadu Agricultural University, Coimbatore 641 003, Tamil Nadu, India

a r t i c l e

i n f o

Article history: Received 22 December 2009 Received in revised form 16 July 2010 Accepted 19 July 2010

Keywords: Coffee processing wastewater UAHR Aeration Constructed wetland system

a b s t r a c t The experiment was conducted to develop an integrated treatment system for coffee processing wastewater (CPWW) through the combination of biomethanation with aeration and wetland plants treatment. The biomethanation was carried out at different hydraulic retention times (HRTs) using upflow anaerobic hybrid reactor (UAHR) and 18 h of HRT was found to be optimum. The maximum biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total solids (TS) reduction were 66.0%, 61.0% and 58.0%, respectively with organic loading rate of 9.55 kg m−3 day−1 . The reduction of pollution load of the wastewater by microbial action augmented by aeration resulted in the reduction of electrical conductivity (EC), BOD, COD, and total solids (TS). Continuous aeration of wastewater resulted in maximum reduction of BOD (74.6%), COD (68.6%) and TS (49.3%). The wetland plant, Typha latifolia reduced 85.4% and 78.0% of BOD and COD, respectively in biomethanated cum aerated CPWW. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Coffee is a major plantation crop grown worldwide and is one of the most popular beverages consumed throughout the world. India ranks the sixth in the world in coffee production. The average annual production is 0.291 million tonnes from an area of 0.354 million hectares of land. Both Arabica and Robusta varieties of coffee are cultivated mainly in the hilly tracts of South India and Northeastern states. Coffee is processed either by wet or dry method. Wet method of processing results in a coffee of superior quality compared to dry method. Presently in India, around 75–80% of Arabica and 15–20% of Robusta are processed by wet method. Wet processing of coffee uses a lot of water at different stages of its processing. The resultant effluent is rich in total suspended and dissolved solids which are biodegradable. If the wastewater emanating from these operations is discharged in to the natural water bodies without treatment it will pollute the receiving water body (Shanmukhappa et al., 1998). The high rate reactor, most widely used for the treatment of several types of wastewaters is upflow anaerobic sludge blanket (UASB) reactor developed by Lettinga (2001). The upflow anaerobic hybrid reactor (UAHR) configuration has combined the advantages of both UASB and upflow anaerobic filter (UAF) while minimizing their limitations and the reactor was efficient in the treatment of

∗ Corresponding author. Tel.: +91 422 6611252. E-mail address: [email protected] (M. Selvamurugan). 0925-8574/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ecoleng.2010.07.013

dilute to high strength wastewater at high organic loading rates (OLRs) and short hydraulic retention time (HRT). Anaerobic digestion has been applied with different degrees of success, to the treatment of liquid and solid wastes from the coffee processing units (Kostenberg and Marchaim, 1993). Under appropriate operational conditions, anaerobic reactor will remove the organic and suspended solids loads with an efficiency of 70–80%. However, in many cases the produced effluent will require a post-treatment step to produce a final effluent quality that is compatible with the standards set by the environmental control authorities (Sousa et al., 2001). In this study, to ensure that an effluent quality that complies with the Indian Standards for the effluent discharge, different combination of treatments like biomethanation, aeration and constructed wetland technology were adopted as an integrated system for the treatment of coffee processing wastewater. 2. Materials and methods 2.1. Collection and characterization of coffee processing wastewater The study was conducted in the laboratory of Department of Environmental Sciences, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu. Coffee processing wastewater was collected from the coffee processing units located in Thandikudi, Dindigul (District), Tamil Nadu. These samples were preserved for those analyses, which are to be done immediately. The rest of the collected CPWW was stored in the cold room at 4 ◦ C. The wastewater

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Fig. 1. Design details of upflow anaerobic hybrid reactor.

was chemically characterized as per the Standard Methods for the Examination of Water and Wastewater (APHA, 1992).

fresh CPWW at 4 days interval. After four cycles, the replacement of two third of the mixture was done and after the completion of the second cycle regular feeding of the CPWW was done.

2.2. Treatment of coffee processing wastewater 2.2.1. Anaerobic treatment of CPWW using UAHR 2.2.1.1. Design details of UAHR. A laboratory-scale upflow anaerobic hybrid reactor (UAHR) was made of 4 mm thick clear acrylic sheet to study the biomethanation potential of CPWW. The volume of the reactor was 19.25 L. The reactor had a Gas–Liquid–Solid [GLS] separator installed at the top of the reactor. The hybrid reactor is a modified version of the UASB system with PVC frill sheet as the solid support and combines the merits of the UASB and fixed film reactors (Lettinga, 2001). The schematic of UAHR is illustrated in Fig. 1. The wastewater from the container was pumped into the reactor through inlet by a peristaltic pump (Watson Marlow). 2.2.1.2. Reactor seeding. The reactor was seeded with the anaerobic consortia developed from goat rumen fluid and slurry from cow dung based biogas plant and enriched with coffee pulp and CPWW. The seeding was done by mixing equal volume of enriched consortium and CPWW and replacing one third of the mixture with

2.2.1.3. Startup. The reactor startup is very important as it has an impact on continuous and efficient operation of the reactor without any system failure. During the initial startup of the reactor, the CPWW was diluted to have a COD of 2000 mg L−1 . 2.2.1.4. Process optimization of UAHR. The reactor was operated at different HRTs like 24, 18, 12 and 6 h and the biomethanation potential of the reactor was assessed in terms of BOD and COD reduction, methane and total gas production. The reactor was run at least for 5–6 retention time after reaching steady state condition of each HRT. Steady state condition was judged by stable gas production and constant COD and BOD of effluent (Patel and Madamwar, 2002). 2.2.1.5. Biogas production. The biogas was measured by using water displacement method and methane percentage was measured by gas chromatography, with thermal conductivity detector (TCD) having ‘Porapak Q’ column by setting the oven temperature at 80–100 ◦ C, injector temperature at 100–200 ◦ C, detector temper-

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ature at 120 ◦ C and using nitrogen as carrier gas at a flow rate of 30 mL min−1 . 2.2.2. Aeration of biomethanated CPWW Biomethanated coffee processing wastewater (CPWW) was taken in plastic containers of 10 L capacity and aerated with mini aerator with an air dispersion rate of 0.98 L min−1 . The biomethanated coffee processing wastewater was aerated continuously and intermittently based on the treatment details given below for 8 days duration. T1 – biomethanated CPWW without aeration (control); T2 – biomethanated CPWW with continuous aeration; T3 – biomethanated CPWW with intermittent aeration of 12 h interval; T4 – biomethanated CPWW with intermittent aeration of 6 h interval; T5 – biomethanated CPWW with intermittent aeration of 3 h interval. The mixed liquor suspended solids (MLSS) concentration of 2.0 g L−1 was maintained for all the treatments. 2.2.3. Constructed wetland system for the treatment of CPWW For the post-treatment of biomethanated cum aerated CPWW, the sub surface flow constructed wetland system was operated with two local wetland plants viz., Typha latifolia and Colacasia sp. The experiment was conducted with a constructed wetland box fabricated in glass with dimensions of 0.60 m × 0.20 m × 0.30 m. The inflow rate of biomethanated and aerated coffee processing wastewater in to the constructed wetland box was 0.9 L h−1 for all treatments. The residence time was calculated to be 24 h in the constructed wetland system. The experiment was conducted for 21 days and the treated effluent was analysed for various physicochemical properties. The CPWW from the storage container was pumped into the inlet of the fabricated constructed wetland systems and the residence time of the wastewater was calculated following formula given by Crites et al. (1994) Residence time =

reed bed volume × porosity . waste water flow

3. Results and discussion 3.1. Characteristics of coffee processing wastewater Characteristics of CPWW (Table 1) show that the raw CPWW was light to dark brown in color, which is due to the presence of pectin, tannin and its derivatives formed during pulping process. The coloring agents present in the CPWW were organic in nature and contained pulp extractives, pectin, tannin and its degradation products (Mendoza and Rivera, 1998). The pH of the CPWW ranged from 3.88 to 4.11. The pH was rendered acidic by the fermentation of sugars present in the CPWW which are converted to alcohol and CO2 . Then the alcohol is quickly converted in to vinegar or acetic

acid in the fermented pulping water resulting in lower pH (Calvert, 1997). The CPWW contained appreciable amounts of suspended, dissolved and total solids. The higher amount of suspended solids present in CPWW might be due to the presence of pectin, protein and sugars which are biodegradable in nature. The BOD of the CPWW ranged from 3800 to 4780 mg L−1 , which indicates the presence of high amount of organic loads. Still higher BOD concentration of 10,000–12,000 mg L−1 in CPWW was reported by Shanmukhappa et al. (1998). The high level of COD concentration (6420–8480 mg L−1 ) in the CPWW could be attributed to the slowly degrading compounds present in the CPWW. 3.2. Treatment of coffee processing wastewater 3.2.1. Biomethanation of CPWW using UAHR The UAHR was operated at different HRTs of 24, 18, 12 and 6 h and the results are presented in Table 2. During the operation period, the UAHR was fed with raw CPWW having BOD and COD concentration ranging from 3.6 to 4.0 and 6.4 to 7.6 g L−1 respectively. The TS of the feed ranged from 3.6 to 4.1 g L−1 . The pH of the feed remained in the range of 3.88–4.31. At 24 h HRT, in steady state period the COD and BOD removal efficiencies achieved were 70% and 71%, respectively. The maximum TS removal efficiency of 64% was achieved in steady state period. The pH of treated effluent ranged from 6.28 to 6.38. The biogas production of 1.335 L day−1 was achieved with the methane content of 61%. The biogas production per kg of BOD, COD and TS removed were 490, 280 and 535 L, respectively. The COD, BOD and TS removal efficiency decreased to 61%, 66% and 58% at 18 h HRT and further decreased to 52%, 59% and 54%, respectively at 12 h of HRT. This trend is obviously due to the addition of organic load with the lowering of the RT. Fang and Chui (1993) reported that the COD removal efficiency of the UASB reactor was mainly dependent on the COD loading rate and HRT of the reactor operation. Among the different HRTs, 18 h HRT recorded the maximum biogas production of 2.620 L day−1 with the methane content of 60.7%. Similarly, the total quantity of biogas produced per kg of BOD, COD and TS removed was maximum at 18 h HRT in the range of 775.0, 430.0 and 840.0 L, respectively. Fig. 2 shows the efficiency of UAHR in reduction of pollution load as influenced by the HRT. The reactor efficiency in terms of pollution load reduced was maximum at both 24 and 18 h HRTs and 24 h performed with higher efficiency than 18 h HRT. However, its magnitude varied with time. For instance, COD reduction is higher by 9%, BOD reduction by 5% and TS reduction by 5% between 18 and 24 h HRT. The difference of reactor efficiency for the two HRTs was least, but the time taken for pollutant reduction was minimum for 18 h comparing with 24 h HRT. Aerobic treatment is necessary as a post-treatment after anaerobic treatment to meet the Central

Table 1 Characteristics of coffee processing wastewater (CPWW). Parameters

Concentration

Color (CU) Total dissolved solids (mg L−1 ) Total suspended solids (mg L−1 ) Total solids (mg L−1 ) pH Electrical conductivity (dS m−1 ) Dissolved oxygen (mg L−1 ) Biochemical oxygen demand (mg L−1 ) Chemical oxygen demand (mg L−1 ) BOD:COD ratio Total organic carbon (%) Nitrogen (mg L−1 ) Phosphorus (mg L−1 ) Potassium (mg L−1 )

470–640 1130–1380 2390–2820 3520–4200 3.88–4.11 0.96–1.20 2.0–2.6 3800–4780 6420–8480 0.56–0.59 0.36–0.48 125.8–173.2 4.4–6.8 20.4–45.8

Fig. 2. Effect of hydraulic retention time (HRT) on efficiency of UAHR in reduction of BOD and COD.

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Table 2 Performance of UAHR at different HRTs. HRT (h)

24 18 12 6

COD loading rate (kg m−3 day−1 )

COD removal (%)

BOD removal (%)

TS removal (%)

Biogas production (L kg−1 of COD reduction)

Biogas production (L kg−1 of BOD reduction)

Biogas production (L kg−1 of TS reduction)

Methane content (%)

7.01 9.55 14.23 28.41

70 61 52 46

71 66 59 54

64 58 49 42

280 430 390 264

490 775 620 400

535 840 690 440

61.8 60.7 59.4 50.4

Pollution Control Board (CPCB) standards (i.e. COD of <250 mg L−1 for discharge into inland surface water), even though there was major load of pollution reduction. So the reactor is performed better in reduction of pollution load with maximum gas production at 18 h HRT within very short period of time. During biomethanation, a BOD and COD removal of 74.6% and 54.6% with a gas production of 0.46 m3 kg−1 of COD removal was reported by Hajipakkos (1992). In our experiment the gas production obtained with 18 h HRT is about 0.43 m3 kg−1 of COD removed with a BOD and COD removal of 66.0% and 61.0%, respectively. 3.2.2. Effect of aeration on biomethanated CPWW The biomethanated CPWW using UAHR was treated through aeration. The biomethanated CPWW had a pH of 6.30 and EC of 0.50 dS m−1 . The BOD, COD and TS of feed were 1120, 2200 and 1420 mg L−1 , respectively. The characteristics of biomethanated CPWW treated with aeration are given in Table 3. A steady decline in BOD and COD were recorded in all the treatments with maximum BOD and COD removal efficiency of 74.6% and 68.6%, respectively in treatments with continuous aeration for 8 days duration. The treatments that received continuous aeration for 8 days recorded the maximum efficiency when compared to intermittent aeration. This was due to the catalytic activity of microbial enzymes and the enhanced degradation by the enzyme due to additional supply of oxygen. Vishnumurthi (2004) achieved an average BOD removal of 98.98% in the treatment of domestic wastewater through diffused aeration system inoculated with mixed cultures. It was noted that the TS also registered a gradual decline during aeration of CPWW. The treatments that received continuous aeration for 8 days recorded highest TS removal of 49.3%. It was followed by biomethanated CPWW aerated intermittently at 12 h intervals, 6 h intervals and 3 h intervals (35.6%, 27.5% and 22.9% of TS reduction, respectively). This may be due to the continuous degradation of organic substance present in the CPWW by microorganisms and the settling down of degraded material in the bottom of the aeration system. These results are in line with the findings of Choudhury et al. (1998) who observed a TS removal efficiency of 54% in the treatment of Kraft paper mill effluent through sequence batch aeration system.

3.2.3. Constructed wetland treatment of CPWW The raw CPWW, biomethanated CPWW and biomethanated cum aerated CPWW were treated through constructed wetland system with T. latifolia and Colacasia sp. The changes in characteristics of the influent and treated effluent collected from constructed wetland box were analysed and the results are given in Table 4. Among the two wetland species, T. latifolia performed better in all the treatments with maximum BOD reduction of 85.4% in biomethanated cum aerated CPWW. It was followed by Colacasia sp. with 81.2% of BOD removal in biomethanated cum aerated CPWW. Cooper (1993) reported that the BOD5 removal efficiency of 74% in horizontal flow constructed wetland system. Organic matter in the wastewater, represented by BOD is removed in a constructed wetland system mainly through aerobic biological decomposition by the aerobic heterotrophic bacteria (Vymazal, 2005). Similar to BOD, the maximum COD removal efficiency (78.0%) was recorded with T. latifolia in biomethanated cum aerated CPWW. It was followed by 73.7% with Colacasia sp. due to wetland plant treatment of CPWW. Barros et al. (2008) achieved 70–80% of COD and BOD5 removal in two horizontal flow constructed wetland systems operated with UASB treated effluent. The COD reduction was achieved by bacterial degradation, sedimentation of particulate matter and filtration by plant roots. The maximum TS removal efficiency of 57.0% was recorded in biomethanated cum aerated CPWW treated with T. latifolia. It was followed by 54.8% of TS removal in biomethanated cum aerated CPWW treated with Colacasia sp. The average suspended solids removal varied from 30% to 86% in the gravel based sub surface flow unit (Sapkota and Bavor, 1994). TSS removal is almost entirely due to physical processes rather than biological processes associated with the microbial community or with the plants (Ciria et al., 2005). 3.2.4. Overall performance of an integrated treatment system Overall performance of an integrated treatment system was analysed at each stage of treatment and the fully treated wastewater was compared with the safe limit prescribed by the CPCB (Table 5). There was increase in the pH from 4.05 at initial to 7.52 at the final stage. The COD in the untreated CPWW was 7450 mg L−1 , which was reduced to 210 mg L−1 in the final discharge (97% reduc-

Table 3 Changes in physico-chemical characteristics of the biomethanated CPWW during aeration. Treatments

Biomethanated CPWW without aeration Biomethanated CPWW with continuous aeration Biomethanated CPWW with intermittent aeration of 12 h interval Biomethanated CPWW with intermittent aeration of 6 h interval Biomethanated CPWW with intermittent aeration of 3 h interval

pH

EC (dS m−1 )

BOD (mg L−1 )

COD (mg L−1 )

TS (mg L−1 )

Initial

Final

Initial

Final

Initial

Final

Initial

Final

Initial

Final

6.30

6.51

0.50

0.41

1120

780 (30.4)

2200

1660 (24.5)

1420

1190 (16.2)

6.30

7.20

0.50

0.23

1120

285 (74.6)

2200

690 (68.6)

1420

720 (49.3)

6.30

6.80

0.50

0.28

1120

425 (62.1)

2200

900 (59.1)

1420

915 (35.6)

6.30

6.78

0.50

0.33

1120

510 (54.5)

2200

1035 (53.0)

1420

1030 (27.5)

6.30

6.65

0.50

0.35

1120

580 (48.2)

2200

1175 (46.6)

1420

1095 (22.9)

Values in parenthesis indicate percent reduction in BOD, COD and TS over control.

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Table 4 Changes in physico-chemical characteristics of the CPWW during constructed wetland treatment. Treatments

EC (dS m−1 )

pH Initial

Biomethanated CPWW + Typha latifolia Biomethanated CPWW + Colacasia sp. Raw CPWW + Typha latifolia Raw CPWW + Colacasia sp. Biomethanated cum aerated CPWW + Typha latifolia Biomethanated cum aerated CPWW + Colacasia sp.

6.30

Final 7.23

Initial 0.50

7.20 4.01 6.95

5.10 5.24 7.52 7.48

Final 0.45

BOD (mg L−1 )

COD (mg L−1 )

TS (mg L−1 )

Initial

Initial

Initial

1150

0.44 1.05 0.38

0.79 0.81 0.19 0.22

Final 280 (75.6)

2350

290 (74.7) 3600 480

1180 (67.2) 1160 (67.7) 70 (85.4) 90 (81.2)

Final 620 (73.6)

1540

640 (72.7) 7000 950

2960 (57.7) 3180 (54.5) 210 (77.9) 250 (73.7)

Final 740 (51.9) 710 (51.0)

3680 930

1720 (53.2) 1710 (53.5) 400 (57.0) 420 (54.8)

Values in parenthesis indicate percent reduction in BOD, COD and TS over control.

Table 5 Comparison of treated coffee processing wastewater with the safe limits of CPCB. Parameter

pH BOD (mg L−1 ) COD (mg L−1 ) TS (mg L−1 )

Raw coffee processing wastewater

Treated coffee processing wastewater

CPCB safe limits

4.05 4290 7450 3860

7.52 70 (98) 210 (97) 400 (90)

5.5–9.0 100 250 2100

Values in parenthesis indicate pollution reduction efficiency (percent) of overall treatment compared to the raw coffee processing wastewater.

tion). BOD also reduced to 70 mg L−1 from 4290 mg L−1 . The BOD reduction was 98%. The total solids content in the wastewater was 3860 mg L−1 , which was reduced to 400 mg L−1 (90% reduction), due to integrated treatment system. Since the final discharge after the series of treatments was within the safe limit, the treated water was found suitable for reuse in the processing. Considerable reduction in the various pollution parameters was achieved (61% and 66% reduction of COD and BOD respectively) due to the biomethanation through UAHR with 18 h HRT. Aeration and constructed wetland technology, further reduced these parameters to the safe limit. 4. Conclusions Based on the results obtained from the series of laboratory experiments, it could be concluded that the coffee processing wastewater was suitable for biological treatment. For effective disposal of coffee processing wastewater with simultaneous production of energy in the form of methane, the combination of anaerobic–aerobic process, i.e. biomethanation followed by aeration and constructed wetland technology was best suited for the treatment of coffee processing wastewater as an eco-friendly approach. Acknowledgements The authors wish to express their gratitude to the Government of India, Coffee Board, Chickmagalur, Karnataka, India for providing

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