Biogas production from plant biomass used for phytoremediation of industrial wastes

Bioresource Technology 98 (2007) 1664–1669

Biogas production from plant biomass used for phytoremediation of industrial wastes V.K. Verma, Y.P. Singh, J.P.N. Rai

¤

Ecotechnology Laboratory, Department of Environmental Science, G.B. Pant University of Agriculture and Technology, Pantnagar 263 145, India Received 10 February 2006; received in revised form 25 May 2006; accepted 25 May 2006 Available online 10 July 2006

Abstract In present study, potentials of water hyacinth (Eichhornia crassipes) and water chestnut (Trapa bispinnosa) employed for phytoremediation of toxic metal rich brass and electroplating industry eZuent, were examined in terms of biogas generation. Inability of the plants to grow in undiluted eZuent directed to select 20%, 40% and 60% eZuent concentrations (with deionized water) for phytoremediation experiments. Slurry of both the plants used for phytoremediation produced signiWcantly more biogas than that by the control plants grown in unpolluted water; the eVect being more pronounced with plants used for phytoremediation of 20% eZuent. Maximum cumulative production of biogas (2430 c.c./100 g d m of water hyacinth and 1940 c.c./100 g d m of water chest nut) and per cent methane content (63.82% for water hyacinth and 57.04% for water chestnut) was observed at 5 mm particle size and 1:1 substrate/inoculum ratio, after twenty days incubation. Biogas production was quicker (maximum from 8–12 days) in water hyacinth than in water chestnut (maximum from 12–16 days). The qualitative and quantitative variations in biogas production were correlated with COD, C, N, C/N ratio and toxic metal contents of the slurry used. © 2006 Elsevier Ltd. All rights reserved. Keywords: Phytoremediation; Methanogenesis; Anaerobic digestion; Brass industry eZuent; Heavy metals; Slurry; Inoculum potential

1. Introduction With the change from an agriculture based society to an industrial one, waste water treatment which is essential for aesthetic, health, ecological and other view points has become a serious problem (Demirci and Demirer, 2004; Clarke and Baldwin, 2002). Until now, several options such as land application (Sommer and Hutchings, 2001), ground injection (Morken and Sakshaug, 1998), reverse osmosis (Thorneby et al., 1999) and constructed wetlands (Clarke and Baldwin, 2002) have been proposed for waste water treatment/disposal. However, aquatic plant based treatment systems are low cost technologies which can be adopted by developing counties like India for recycling/treatment of waste water, especially contaminated by heavy/toxic metals

*

Corresponding author. Tel.: +91 5944 233 904; fax: +91 5944 33473. E-mail address: [email protected] (J.P.N. Rai).

0960-8524/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2006.05.038

(Vandecasteele et al., 2005; Jang et al., 2005; Figueira and Ribeiro, 2005). Potential productivity of water hyacinth and water chestnut in nutrient enriched waste waters has lead to its selection for phytoremediation of various industrial eZuents (Singhal et al., 2003; Verma et al., 2005) and the produced biomass as a feed stock for biogas production to achieve economic success in energy harvest. Anaerobic digestion is proven as a relatively eYcient conversion process for producing a collectable biogas mixture with average 60% methane content (Chankya et al., 1993; Chawla, 1986; Ghosh et al., 1981) which can be used as a substitute of fuel in boilers and the resultant left over slurry as end product, having high N, P and K content, for agricultural application (Tafdrup, 1994). Quality and quantity of biogas production depend up on the feed stock characteristics (Tada et al., 2005; Demirci and Demirer, 2004) as well as on the digester operating conditions (StaVord et al., 1980). Informations regarding eVect of toxic metals sequestered during phytoremediation on quality and quantity of biogas are limited

V.K. Verma et al. / Bioresource Technology 98 (2007) 1664–1669

(Patel et al., 1993; Singhal and Rai, 2003). The present study was undertaken to evaluate the eVect of substrate particle size, substrate/inoculum ratio and toxic metal load on qualitative and quantitative production of biogas from phytoremediated biomass of water hyacinth and water chestnut. 2. Methods 2.1. Substrate/feed stock Plants of water hyacinth and water chestnut were collected from ponds located in Baheri and Chhatarpur, Pantnagar, India. Due to inability of the plants to grow in undiluted brass and electroplating industry eZuent, 20%, 40% and 60% eZuent concentrations were prepared with appropriate amount of deionized water. Both the plants grown in diVerent eZuent concentrations for 30 days were chopped separately to maintain 20 mm pieces, sun dried, Wnally oven dried at 60 °C for 48 h and ground. Slurries of four particle size (2, 5, 10 and 20 mm) were prepared by using appropriate sieve and grinding for laboratory scale digesters.

1665

kept in incubator at 35 § 1 °C. Biogas production was measured at four days interval up to 20 days of incubation by employing water displacement technique. On each observation date, 20 ml of biogas was sampled from each treatment for per cent methane and carbon dioxide content analysis. While calculating the cumulative biogas production the sampled amount was added in each treatment. To assess the impact of substrate: inoculum ratio on biogas production, other sets of digesters were run after feeding with the mixtures of substrate and Wltered inoculum in varying combinations so as to yield 1:0.5, 1:1, 1:2 and 1:3 substrate: inoculum ratio with optimum particle size i.e. 5 mm of substrate at 35 § 1 °C incubation temperature. Biogas produced was measured qualitatively and quantitatively. 2.4. Biogas composition Nucon Make-5700 gas chromatograph with TCD, Porapak Q stainless steel column (180 cm long, 3 mm outer diameter, Xow rate 60 ml/min) employing nitrogen as mobile phase, was used for determining per cent methane and carbon dioxide content in the biogas.

2.2. Inoculum 2.5. Physico-chemical analysis Actively digested dairy cattle manure slurry was collected from a 6 m3 size biogas plant at Pantnagar, Wltered and used as inoculum to prepare four substrate/ inoculum ratios i.e. 1:0.5, 1:1, 1:2 and 1:3.

The composition of slurry at initial and Wnal stage was analyzed for carbon by procedure of Walkley and Blacks (1934), for nitrogen by microkjeldahl technique, COD, Cu and Cd by the methods outlined in APHA (1995).

2.3. Feeding and biogas production 3. Results To investigate the optimum particle size of slurry for biogas production, twelve digesters were started gradually by feeding separately with slurry of four particle sizes (i.e. 2, 5, 10, 20 mm) in triplicate; each inoculated with equal amount of Wltered inoculum to result in 1:1 substrate: inoculum ratio at a given eZuent concentration. All sets were

3.1. Relative changes in feed stock characteristics Various physico-chemical characteristics (Table 1) of the plant slurry used as feed stock for anaerobic digestion depicted maximum decrease in organic carbon (34.07% for

Table 1 Physico-chemical characteristics (initial and Wnal) of slurry used for biogas production (§SE) Slurry type

Day(s) Parameters Organic carbon (%)

Total nitrogen (%)

C/N ratio COD (mg/g dry wt) Cu (g/g dry wt)

Cr (g/g dry wt)

Water hyacinth grown in 0 unpolluted water (control) 20 20% Brass industry eZuent 0 20 40% Brass industry eZuent 0 20 60% Brass industry eZuent 0 20

36.4 § 0.50 25.3 § 0.50 40.2 § 0.20 26.5 § 0.20 38.1 § 0.40 29.7 § 0.50 34.2 § 0.60 25.2 § 0.60

1.32 § 0.10 1.36 § 0.20 1.10 § 0.05 1.21 § 0.20 1.21 § 0.10 1.28 § 0.15 1.28 § 0.02 1.32 § 0.10

22.4 17.0 26.1 19.7 29.3 20.1 23.9 17.5

1250.0 § 5.50 139.5 § 1.10 1348.0 § 7.50 111.5 § 3.00 1325.0 § 5.40 146.6 § 4.50 1280.0 § 8.50 165.0 § 2.50

0.00 0.00 1.82 § 0.01 2.22 § 0.06 3.10 § 0.02 3.51 § 0.08 5.30 § 0.10 5.60 § 0.20

0.00 0.00 0.89 § 0.04 1.21 § 0.04 1.50 § 0.05 1.82 § 0.03 1.92 § 0.01 2.28 § 0.10

0 Water chestnut grown in unpolluted water (control) 20 20% Brass industry eZuent 0 20 40% Brass industry eZuent 0 20 60% Brass industry eZuent 0 20

29.6 § 0.50 23.7 § 0.25 32.2 § 0.25 24.3 § 0.35 31.6 § 0.20 25.2 § 0.40 30.1 § 0.10 23.4 § 0.50

1.51 § 0.03 1.58 § 0.05 1.39 § 0.05 1.44 § 0.06 1.37 § 0.20 1.42 § 0.04 1.53 § 0.15 1.58 § 0.05

24.1 16.0 28.0 20.9 30.5 18.8 22.4 15.9

1148.0 § 7.50 129.5 § 2.50 1228.0 § 7.50 88.8 § 2.20 1205.0 § 5.50 136.0 § 1.50 1180.0 § 6.50 169.8 § 2.10

0.00 0.00 1.30 § 0.05 1.58 § 0.01 2.61 § 0.04 2.88 § 0.05 3.82 § 0.05 4.12 § 0.05

0.00 0.00 0.42 § 0.02 0.63 § 0.05 0.71 § 0.02 1.01 § 0.03 1.31 § 0.10 1.58 § 0.08

1666

V.K. Verma et al. / Bioresource Technology 98 (2007) 1664–1669

water hyacinth and 24.53% for water chestnut) after fermentation of 20% eZuent grown plant biomass. In contrast, per cent increase in total nitrogen (9.0% for water hyacinth and 6.3% for water chestnut) was observed to be maximum. This resulted into more reduction in C/N ratio of the water hyacinth slurry (39.3%) than that of water chestnut (31.4%), after fermentation of 20% eZuent grown plant biomass. Content of heavy metals (Cu and Cr) was magniWed (5.6 g/g dry wt Cu and 2.28 g/g dry wt Cr in water hyacinth; 4.12 g/g dry wt Cu and 1.58 g/g dry wt Cr in water chestnut) in left over slurry of 60% eZuent grown plants after twenty days incubation. This was primarily due to the reduction of organic content after 20 days incubation leading to increased metal concentrations. However, the relative magniWcation of metals was maximum in the slurry of both the plants grown in 20% eZuent concentration. 3.2. EVect of particle size and inoculum potential on cumulative biogas production Cumulative biogas production was maximum at 5 mm particle size of both the plants grown in 20% eZuent, after 20 days incubation of 1:1 substrate/inoculum ratio (Table 2). Water hyacinth slurry was relatively more eYcient for biogas production (20.16%) than water chestnut. In general, both the plants produced larger volume of biogas from the eZuent grown biomass (29.94% for water hyacinth and 25.97% for water chestnut) than that of control i.e. unpolluted water grown plant biomass. However, minimum bio-

gas production was observed from 60% eZuent grown biomass of both the plants. A little diVerence in optimum substrate/inoculum ratio was observed (1:1 for water hyacinth and 1:2 for water chestnut) for maximum biogas production by the slurry of plants grown in 20% eZuent concentration. Slurry of water hyacinth was relatively more eYcient than that of water chestnut at a given concentration treatment, yielding larger volume of biogas than that of control (Table 3). However, minimum biogas production was recorded from 60% eZuent grown biomass of the two plants at 1:0.5 substrate/inoculum ratio. At all substrate/inoculum ratios, water hyacinth slurry was more eYcient than water chestnut for biogas production. 3.3. Rate of biogas production Maximum rate of biogas production was recorded from 8–12 days incubation for water hyacinth (189.2 c.c./ 100 g d m per day) and 12–16 days incubation for water chest nut biomass (175.0 c.c./100 g d m per day) (Table 4). Biogas production rate increased initially up to 12 days in water hyacinth and 16 days in water chestnut, afterward decreased substantially. 3.4. Qualitative variation in biogas with respect to diVerent particle size, inoculum potential and heavy metal content Maximum methane content (63.82% for water hyacinth and 57.04% for water chestnut) was recorded in biogas

Table 2 Cumulative biogas production at diVerent particle sizes of the slurry inoculated with 1:1 substrate/inoculum ratio after 20 days of incubation at 35 § 1 °C Slurry type

Cumulative biogas production (c.c. § SE/100 g dry matter) Particle size (mm)

Water hyacinth grown in unpolluted water (control) 20% Brass industry eZuent 40% Brass industry eZuent 60% Brass industry eZuent

2 1475 § 2.50 2110 § 5.00 1970 § 4.20 1310 § 2.50

5 1910 § 1.55 2780 § 3.25 2070 § 1.20 1625 § 2.25

10 1315 § 1.00 1960 § 2.20 1995 § 1.50 1345 § 2.50

20 1250 § 1.20 1720 § 1.10 1680 § 1.05 1110 § 1.75

Water chestnut grown in unpolluted water (control) 20% Brass industry eZuent 40% Brass industry eZuent 60% Brass industry eZuent

1335 § 1.50 1570 § 2.50 1695 § 3.00 1470 § 2.00

1715 § 2.80 1970 § 3.50 1965 § 1.80 1710 § 1.80

1245 § 2.00 1420 § 1.50 1330 § 2.50 1300 § 2.00

1148 § 1.20 1295 § 1.10 1210 § 1.20 1045 § 1.50

Table 3 Cumulative biogas production at 5 mm particle size of the slurry inoculated with various substrate/inoculum ratio after 20 days of incubation at 35 § 1 °C Slurry type

Cumulative biogas production (c.c. § SE/100 g dry matter) Substrate/inoculum ratio

Water hyacinth grown in unpolluted water (control) 20% Brass industry eZuent 40% Brass industry eZuent 60% Brass industry eZuent

1:0.5 1430 § 2.10 2665 § 3.75 1695 § 3.20 1320 § 2.50

1:1 1910 § 1.55 2780 § 3.25 2070 § 1.20 1625 § 2.25

1:2 1870 § 1.50 2430 § 3.50 2010 § 1.50 1550 § 2.25

1:3 1660 § 1.20 1790 § 1.10 1800 § 1.05 1440 § 1.75

Water chestnut grown in unpolluted water (control) 20% Brass industry eZuent 40% Brass industry eZuent 60% Brass industry eZuent

1335 § 1.40 1690 § 2.50 1430 § 3.20 1090 § 21.50

1715 § 2.80 1970 § 3.50 1965 § 1.80 1710 § 1.80

1540 § 1.80 2090 § 4.50 1804 § 1.80 1540 § 2.00

1160 § 1.20 1620 § 1.10 1680 § 1.20 1335 § 1.50

V.K. Verma et al. / Bioresource Technology 98 (2007) 1664–1669

1667

Table 4 Rate of biogas production within diVerent time intervals from slurry of water hyacinth and water chestnut (particle size 5 mm and 1:1 substrate/inoculum ratio) at 35 § 1 °C Time interval (days)

Rate of biogas production (c.c. § SE/100 g dry matter per day) Water hyacinth Unpolluted water (control)

0–4 4–8 8–12 12–16 16–20

52.5 § 1.20 98.3 § 1.30 158.6 § 2.50 136.5 § 2.10 28.5 § 1.10

Water chestnut 20% eZuent

40% eZuent

60% eZuent

73.4 § 1.10 139.5 § 2.10 189.2 § 1.85 164.2 § 1.75 36.5 § 1.20

63.5 § 1.00 128.5 § 1.20 170.5 § 2.50 152.5 § 2.20 30.1 § 1.10

48.5 § 1.20 112.4 § 2.10 140.1 § 1.80 125.6 § 1.75 24.2 § 1.10

Unpolluted water (control) 42.1 § 1.50 81.2 § 1.25 111.5 § 2.20 138.2 § 2.20 17.0 § 1.40

20% eZuent

40% eZuent

60% eZuent

78.1 § 1.10 122.1 § 2.00 139.5 § 2.25 175.0 § 2.20 23.5 § 1.20

66.5 § 1.10 102.6 § 2.20 129.5 § 2.10 150.0 § 1.50 19.4 § 1.75

41.5 § 0.80 95.2 § 1.50 116.2 § 2.20 131.5 § 1.75 18.0 § 1.50

Table 5 Qualitative comparison of the biogas generation at 1:1 substrate/inoculum ratio and diVerent particle size after 20 days of incubation at 35 § 1 °C (§SE) Slurry type

Particle size of the slurry (mm) 2 CO2 (%)

Water hyacinth grown in unpolluted water (control) 20% Brass industry eZuent 40% Brass industry eZuent 60% Brass industry eZuent Water chestnut grown in unpolluted water (control) 20% Brass industry eZuent 40% Brass industry eZuent 60% Brass industry eZuent

5 CH4 (%)

CO2 (%)

10 CH4 (%)

CO2 (%)

20 CH4 (%)

CO2 (%)

CH4 (%)

44.80 § 1.20

32.20 § 1.25

42.10 § 0.75

47.50 § 1.50

54.20 § 1.40

35.20 § 1.10

52.50 § 1.00

33.15 § 1.20

52.38 § 1.05 44.60 § 1.25 42.12 § 1.20

43.20 § 1.30 47.20 § 1.30 52.66 § 1.20

32.13 § 1.20 43.01 § 1.75 38.20 § 1.20

63.82 § 1.75 54.20 § 1.25 57.80 § 1.00

47.21 § 1.20 53.68 § 1.25 41.3 § 1.20

42.30 § 1.25 37.11 § 1.30 43.25 § 1.25

51.50 § 1.10 52.45 § 2.20 54.80 § 1.00

38.20 § 1.30 36.10 § 1.60 39.50 § 2.30

43.50 § 1.10

32.50 § 1.30

40.00 § 1.10

44.20 § 3.00

44.50 § 1.10

34.20 § 1.20

48.50 § 2.00

32.15 § 1.50

41.20 § 1.20 42.20 § 1.60 40.1 § 1.50

44.20 § 1.20 49.25 § 1.20 47.40 § 2.15

32.52 § 1.00 46.50 § 1.30 45.20 § 1.50

57.04 § 1.50 51.40 § 1.10 51.00 § 2.10

35.20 § 1.10 39.00 § 1.30 47.10 § 1.25

54.30 § 1.10 31.42 § 1.00 46.40 § 1.20

41.40 § 2.30 56.50 § 3.50 44.50 § 1.50

49.50 § 1.50 33.60 § 2.50 42.50 § 1.75

Table 6 Qualitative comparison of the biogas generation at 5 mm particle size of the slurry inoculated with diVerent substrate/inoculum ratios after 20 days of incubation at 35 § 1 °C (§SE) Slurry type

Substrate/inoculum ratio 1:0.5 CO2 (%)

Water hyacinth grown in unpolluted water (control) 20% Brass industry eZuent 40% Brass industry eZuent 60% Brass industry eZuent Water chestnut grown in unpolluted water (control) 20% Brass industry eZuent 40% Brass industry eZuent 60% Brass industry eZuent

1:1 CH4 (%)

CO2 (%)

1:2 CH4 (%)

CO2 (%)

1:3 CH4 (%)

CO2 (%)

CH4 (%)

54.50 § 1.50

36.50 § 2.50

56.30 § 1.10

38.10 § 1.30

47.51 § 1.00

39.20 § 1.00

54.50 § 0.80

34.26 § 1.20

37.50 § 1.85 45.2 § 1.20 53.4 § 1.50

58.50 § 2.20 46.30 § 1.20 31.02 § 1.30

36.18 § 1.20 48.53 § 1.05 52.5 § 1.30

61.60 § 1.20 48.36 § 1.10 32.2 § 1.20

40.12 § 0.80 49.25 § 1.20 56.20 § 0.75

52.28 § 1.20 39.20 § 1.15 38.21 § 0.80

42.56 § 0.75 48.26 § 0.90 58.80 § 1.30

48.25 § 1.00 42.61 § 1.20 29.80 § 0.80

48.20 § 1.50

32.6 § 2.20

44.30 § 1.00

35.00 § 0.75

48.03 § 1.20

41.26 § 0.75

56.10 § 1.20

34.20 § 0.75

37.50 § 2.00 53.50 § 2.50 56.30 § 2.10

55.30 § 2.50 34.20 § 1.50 40.30 § 1.50

35.50 § 1.25 48.62 § 1.05 44.30 § 1.20

57.04 § 1.10 36.60 § 2.01 42.36 § 1.50

40.80 § 0.95 45.08 § 0.80 40.30 § 1.50

51.26 § 1.05 39.50 § 1.10 52.00 § 0.50

52.30 § 0.75 54.00 § 0.50 52.00 § 0.80

34.20 § 1.10 37.15 § 1.20 27.00 § 1.25

produced after 20 days incubation of 5 mm particle size and 1:1 substrate/inoculum ratio of 20% eZuent grown plant biomass. Further, increase in particle size and substrate/ inoculum ratio enhanced carbon dioxide content of the biogas (Tables 5 and 6). However, minimum methane content of the biogas was found at 1:3 substrate/inoculum ratio of the 60% eZuent grown plant biomass. Unlike cumulative biogas production, 1:1 substrate/inoculum ratio of water chestnut slurry was observed to be optimum, yielding maximum methane content (57.04%) at 5 mm particle size slurry of the 20% eZuent grown plants, after twenty days incuba-

tion. EVect of heavy metals (Cu and Cr) sequestered by the plants during phytoremediation on biogas production, as given in Tables 3–6, exhibited maximum production and highest methane content in biogas produced from the slurry of the plants grown at lowest eZuent concentration (20%). Increased heavy metal content in plants growing in higher concentrations of eZuent showed conspicuous reduction in biogas production and methane content. However, carbon dioxide content in biogas exhibited erratic behavior with increasing heavy metal content at higher eZuent concentrations.

1668

V.K. Verma et al. / Bioresource Technology 98 (2007) 1664–1669

4. Discussion The experimental results (Table 2–6) evidenced the positive role of brass and electroplating industry eZuent, at low concentration, on biogas generation from phytoremediated biomass, which might be due to the better utilization and accumulation of micronutrients (Demirci and Demirer, 2004; Magbauna et al., 2001; Salminen and Rintala, 2002) and organic pollutants by both the aquatic plants, and thereby enhanced the growth of methanogens (Demirci and Demirer, 2004; Singhal and Rai, 2003).The increase in C and N content in the slurry of plants used in phytoremediation was also due to high accumulation/utilization of the organic pollutants from industrial wastewater. Maximum enhancement in biogas production over the control by 20% eZuent grown plant biomass could be well correlated with maximum reduction in COD and C/N ratio of slurry after 20 days incubation. A similar observation has been reported by Demirci and Demirer (2004) using broiler and cattle manure as a substrate for biogas production. However, this eVect was more pronounced with water hyacinth than water chestnut, which might be accounted for relatively high water content and soft organic matter with Wne texture of the former providing favorable conditions for anaerobic digestion to produce more biogas (Chankya et al., 1993). Often the C/N ratio is used as an index of the suitability of organic feeds (TERI, 1985) for methanogenesis, but there is no agreement in the literature on the ‘ideal’ C/N ratio. The ‘ideal’ C/N ratio proposed for methanogenesis varies from12 to 72 (DeRenzo, 1997; Huang and Shih, 1981; Ghosh et al., 1981), to which all the present experimental sets followed, but showed disparate biogas generating abilities. This supports the contention that, besides C/N ratio, several other factors including temperature, pH and nutrient addition (Hanisak et al., 1980; Mackie and Bryant, 1995; Demirci and Demirer, 2004), per cent volatile content of organic matter and C/P ratio (Ghosh et al., 1981), iron (Speece and Perkin, 1985), vitamins (Huang and Shih, 1981) and natural inhabitants (Ghosh et al., 1981, 1985), known to inXuence biogas production, might have also contributed in present study. In higher concentration of eZuent grown biomass, methane content in the biogas was severely reduced owing to methanogenesis inhibition caused due to toxic eVects of higher concentrations of metals (Lin, 1992; Singhal and Rai, 2003). However, the lower concentrations of these metals have been reported (Salminen and Rintala, 2002) to serve micronutrients for methanogenic bacteria, which might have enhanced the process of methanogenesis and thus methane content in biogas , especially produced from the slurry of 20% eZuent grown plants. Relatively greater and quicker biogas production from water hyacinth than water chestnut biomass might be due to high water content (91.50%), as has been argued by Jain et al. (1990) and Gupta (1979) with a variety of aquatic and terrestrial plants. In present study methane content of the biogas ranged from 38 to 63% for water hyacinth and 32–57% for

water chestnut, yielding maximum at 5 mm particle size and 1:1 substrate/inoculum ratio and thus, conferring optimum feed stock characteristics for biogas production. The feed stock characteristics generating maximum biogas in present study are quite comparable with that of others (Demirci and Demirer, 2004; Tada et al., 2005; Jain et al., 1990; Ghosh et al., 1985). In this study the diVerential eVect of substrate particle size on biogas production, as has also been observed by Hobson (1991) and Angelidaki and Ahring (1993) elsewhere, depicted the importance of easily available safe and active sites for methanogens to grow. Finer substrate particle size resulted in greater amount of easily degradable/ soluble organic matter, which favored the methanogenesis (Moorhead and Nordstedt, 1993; Maeng et al., 1999; Demirci and Demirer, 2004). On this basis, the best quality and quantity of biogas generation at 5 mm particle size could be visualized as optimum substrate particle size having maximum safe and active sites and highest soluble/degradable organic load for methanogens. Role of inoculum potential, providing microbial culture and soluble substrate to initiate the process of methanogenesis assumes equal importance (Tafdrup, 1994; Dagnall, 1995; Ghosh et al., 1985). Maximum cumulative production of biogas and per cent methane content at 1:1 substrate/inoculum ratio, observed in this study, could probably be due to creation of favorable conditions for anaerobic digestion. For example, the conversion of propionate, an important intermediate in complete decomposition of complex organic matter to acetate could proceed only when the products of former reactions (i.e. hydrogen and formate) were removed eYciently by methanogens of obligate nature (Schink, 1997; Stamns, 1994). However, further increase in inoculum volume coupled with increasing heavy metal concentration reduced the quality and quantity of biogas, demonstrating their vital role in biogas generation by way of altering acidogens population in methanogenesis, as has been observed by Hashimoto (1989). The signiWcance of particle size and inoculum potential on biogas production was also emphasized by Moorhead and Nordstedt (1993), who opined that Wner particles promoted biogas production. Further, unlike the Xoating nature of water hyacinth, the submerged water chestnut having higher content of N in slurry made it a diYcult substrate for anaerobic digestion and thus produced less biogas. This also conforms with the observations of Salminen and Rintala (2002), Angelidaki and Ahring (1993) and Ghosh et al. (1985). Although, studies demonstrating biogas generation from the plant biomass employed for phytoremediation of industrial wastes are scarce, the quantitative and qualitative increase in biogas generation from water hyacinth and water chestnut grown in brass and electroplating industry eZuent again underlines the positive role of eZuent enhancing biogas production due to the presence of various pollutants serving as micronutrients for aquatic macrophytes/methanogens, especially at lower concentrations. In fact, the two fold beneWts (i.e. treatment of brass and electroplating

V.K. Verma et al. / Bioresource Technology 98 (2007) 1664–1669

industry eZuent employing aquatic weeds and recovery of biogas energy from the generated biomass), though derived at laboratory scale in this study, could strengthen the economic success of energy generation from waste. Acknowledgements The research facilities provided by G.B. Pant University of Agriculture and Technology, Pantnagar and Wnancial assistance from Indian Council of Agricultural Research, Government of India, in the form of research project are gratefully acknowledged. References Angelidaki, I., Ahring, B.K., 1993. Thermophilic anaerobic digestion of livestock waste: eVect of ammonia. Appl. Microbiol. Biotechnol. 38, 560–564. APHA, 1995. Standard Methods for Examination of Water and Wastewater, 19th ed. American Public Health Association Inc., Washington DC, USA. Chankya, H.N., Borgaonkar, S., Meena, G., Jagadish, K.S., 1993. Solid phase biogas production with garbage or water hyacinth. Bioresource Technol. 46, 227–231. Chawla, O.P., 1986.Advances in Biogas Technology Publication and Information Division Indian Council of Agricultural Research, New Delhi, India (pp. 75–95). Clarke, E., Baldwin, A.H., 2002. Responses of wetland plants to ammonia and water level. Ecol. Eng. 18, 257–264. Dagnall, S., 1995. UK strategy for centralized anaerobic digestion. Bioresource Technol. 52, 275–280. Demirci, G.G., Demirer, G.N., 2004. EVect of initial COD concentration, nutrient addition, temperature and microbial acclimation on anaerobic treatibility of broiler and cattle manure. Bioresource Technol. 93, 109–117. DeRenzo, D.J., 1997. Bioconversion of Solid Waste and Sewage Sludge in Energy from Bioconversion of Waste Material. Noyes Data, Dark Ride, NJ. Figueira, R., Ribeiro, T., 2005. Transplants of aquatic mosses as biosorbent of metals released by a mine eZuent. Environ. Pollut. 136, 293–301. Ghosh, S., Henry, M.P., Christopher, R.W., 1985. Hemicellulose conversion by anaerobic digestion. Biomass 6, 257. Ghosh, S., Klass, D.L., Chynoweth, D.P., 1981. Bioconversion of Macrosystis pyrifera to methane. J. Chem. Tech. Biotechnol. 31, 791–807. Gupta, O.P., 1979. Aquatic Weeds: Their Menace and Control. A Textbook and Manual. Today and Tomorrow Printers and Publishers, New Delhi (pp. 1–272). Hanisak, M.D., William, L.D., Ryther, J.H., 1980. Recycling of nutrients in residues from methane digester of aquatic macrophytes for new biomass production. Resou. Recov. Conserv. 4, 313–323. Hashimoto, A.G., 1989. EVect of inoculum/substrate ratio on methane yield and production rate from straw. Biol. Waste. 28, 247–255. Hobson, P.N., 1991. The treatment of agricultural wastes. In: Wheatley, A. (Ed.), Anaerobic Digestion: A waste treatment technology. Elsevier Applied Science, London, pp. 93–138. Huang, J.J.H., Shih, J.C.H., 1981. The potential of biological methane generation from chicken manure. Biotechnol. Bioeng. 23, 2307–2314. Jain, S.K., Gujral, G.S., Vasudevan, P., 1990. Production of biogas from aquatic biomass a comparison with terrestrial biomass. Res. Ind. 35, 104–107.

1669

Jang, A., Seo, Y., Bishop, P.L., 2005. Removal of heavy metals in urban runoV by sorption on mulch. Environ. Pollut. 133, 117–127. Lin, C.Y., 1992. EVect of heavy metals on volatile fatty acid degradation in anaerobic digestion. Water Res. 26, 177–183. Mackie, R.I., Bryant, M.P., 1995. Anaerobic digestion of cattle waste at mesophilic and thermophilic temperatures. Appl. Microbiol. Biotechnol. 43 (2), 346–350. Maeng, H., Lund, H., Hvelplund, F., 1999. Biogas plants in Denmark: techonogical and economic developments. Appl. Energ. 64, 195–206. Magbauna, J.B.S., Adams, T.T., Johnson, P., 2001. Anaerobic co-digestion of hog and poultry waste. Bioresource Technol. 79, 165–168. Moorhead, K.K., Nordstedt, R.A., 1993. Batch anaerobic digestion of water hyacinth: EVect of particle size, plant nitrogen content and inoculum volume. Bioresource Technol. 44, 71–76. Morken, J., Sakshaug, S., 1998. Direct ground injection of livestock waste slurry to avoid ammonia emission. Nutr. Cycl. Agroecosys. 51, 59–63. Patel, V.B., Patel, A.R., Patel, M.C., Madamwar, D.B., 1993. EVect of metals on anaerobic digestion of water hyacinth-cattle dung. Appl. Biochem. Biotechnol. 43 (1), 45–50. Salminen, E.A., Rintala, J.A., 2002. Semi-continuous anaerobic digestion of solid poultry slaughterhouse waste: eVect of hydraulic retention time and loading. Water Res. 36, 3175–3182. Schink, B., 1997. Energetics of syntrophic cooperation in methaneogenic degradation. Microbiol. Mol. Biol. Rev. 61, 262–280. Singhal, V., Rai, J.P.N., 2003. Biogas production from water hyacinth and channel grass used for phytoremediation of industrial eZuents. Bioresource Technol. 86, 221–225. Singhal, V., Kumar, A., Rai, J.P.N., 2003. Phytoremediation of pulp and paper mill and distillery eZuents by water hyacinth. J. Sci. Indust. Res. 62, 319–328. Sommer, S.G., Hutchings, N.J., 2001. Ammonia emission from Weld applied manure and its reduction. Eur. J. Agron. 15, 1–15. Speece, R.E., Perkin, G.F., 1985. Nutrient requirement for anaerobic digestion. In: Antonopoulos, A.A. (Ed.), Biotechnological Advances in Processing Municipal Wastes for Fuels and Chemicals. Argonne National Laboratory, Argonne, Illinois, pp. 195–207. StaVord, D.A., Hawkes, D.L., Horton, T., 1980. Methane production from waste organic matter. In: Environmental Conditions for Control of Digester Performances. CRC Press Inc., Bocca Ratton, FL, p. 149. Stamns, A.J.M., 1994. Metabolic interactions between bacteria in methanogenic environments. Antonie Van Leeuwenhoek. 66, 271–294. Tada, C., Yang, Y., Hanaoka, T., Sonoda, A., Ooi, K., Sawayama, S., 2005. EVect of natural zeolite on methane production for anaerobic digestion of ammonia rich organic sludge. Bioresource Technol. 96, 459–464. Tafdrup, S., 1994. Centralized biogas plants, combined agriculture and environmental beneWts with energy production. Water Sci. Technol. 30 (12), 133–141. Tata Energy Research Institute (TERI), 1985 Biogas Technology: An information package. Tata Energy Documentation and Information Centre, Bombay, India, p. 189. Thorneby, L., Persson, K., Tragardh, G., 1999. Treatment of liquid eZuents from dairy cattle and pigs using reverse osmosis. J. Agr. Eng. Res. 73 (2), 159–170. Vandecasteele, B., Quataert, P., Tack, F.M.G., 2005. EVect of hydrological regime on the metal bioavailability for the wetland plant species Salix cinerea. Environ. Pollut. 135, 303–312. Verma, V.K., Gupta, R.K., Rai, J.P.N., 2005. Biosorption of Pb and Zn from pulp and paper industry eZuent by water hyacinth (Eichhornia crassipes). J. Sci. Ind. Res. 64, 778–781. Walkley, A., Blacks, C.A., 1934. An examination of DegtjareV methods for determining soil organic matter and a proposed modiWcation of the chromic acid titration method. Soil Sci. 37, 29–38.