Rotary Drum Composting and Microbiology of Water Hyacinth Compost
4.1 PHASE I: Microbial Population, Stability and Maturity Analysis of Rotary Drum Composting of Water Hyacinth
4.1.2 Physio-chemical analysis of compost
•Temperature
Periodic measurement of the temperature changes in the compost is an important index to measure the microbial activities. It determines the rate at which many of the biological processes take place and thus, it plays a selective role on evolution and succession of the microbiological communities (Hassen et al., 2001). (Figure 4.1) gives the details of the temperature variations throughout the 20 days of composting period. As compared to all trials, trial 3 showed the maximum temperature of 56.50◦C. As reported by Singh and
Table 4.1: Composition and initial characterisation of waste materials
Trial/Parameter Waste Material (kg)
Water hyacinth Cow dung Sawdust
EC (ds/m) 8.42±0.02 4.63±0.01 0.45±0.02
Volatile Solids (%) 86±0.02 87.2±0.01 96±0.01
pH 5.94±0.01 7.16±0.03 5.85±0.02
Moisture Content (%) 87.3±2.21 74.76±0.78 43.74±0.43
Soluble BOD (g/kg) 795±20 480±30 150±30
Soluble COD (g/kg) 864±20 648±16 432±20
Oxygen Uptake Rate (mg/g vs /day)
1.89±0.9 5.8±0.7 ND
CO2 Evolution Rate (mg/g vs /day)
1.6±2.5 1.44±0.7 0.68±0.4
Spore Forming Bacteria (CFU/g)
1.06×108 9.00×106 8.00×105
Mesophilic bacteria (CFU/g) 1.71×1012 1.40×1014 1.32×109
Actinomycetes (CFU/g) 8.25×109 1.84×109 1.24×108
Streptomycetes (CFU/g) 1.78×107 7.00×108 1.04×108
Fungi (CFU/g) 8.90×109 4.00×106 7.80×105
Total heavy metals (mg/kg dry matter)
Pb 1120±5 800±4 992±5
Cd 39±7 49±1.2 52±4
Zn 168±3.1 174±2.1 120±2.4
Ni 162±8.9 220±1.7 249±2.4
Note:(mean±SD, n=3) SD- standard deviation, ND-Not detected.
Kalamdhad (2012) providing optimum carbon to nitrogen ratio by proper combination of waste materials lead to high temperature rise. The rise in temperature started within 24 h of composting and reached its maximum by 4th day, after this it started to stabilize. It has been reported that during the composting process temperatures of 520◦C to 600◦C was considered to maintain the greatest thermophilic activity (Ryckeboer et al., 2003). The average highest temperature for all the trials was in the range of 50-56.50◦C, but the highest temperature in control reached up to 38.60◦C only. On analyzing the results by ANOVA, the
4.1. PHASE I: Microbial Population, Stability and Maturity Analysis of Rotary Drum Composting of Water Hyacinth
variation in temperature varied significantly between the days (p < 0.05). This indicated that for proper degradation of organic matter cattle cow dung and sawdust are required along with water hyacinth.
Figure 4.1: Variation in temperature profile during composting period
•Volatile solids (VS%)
Volatile solids give an account of the oxidized organic matter when it is heated. Soluble organic material can be easily degraded as being the primary nutrient of microbes (Said- Pullicino et al., 2007). However, the total organic matter in plant material comprises of cellulose, hemicelluloses, reducing sugars and lignin. These are highly biodegradable, but lignocellulose is partially solubilized (almost unchanged) and reorganized to form humus- like substances (López-González et al., 2013). The volatile solids analyzed, reduced from 60 to 48%, 58 to 44%, 67 to 36%, 65 to 40% and 73 to 61% in trials 1, 2, 3, 4 and 5, respectively (Figure 4.2) from 0th to 20th day. On analyzing the results by ANOVA, the decrease in VS% varied significantly between the days (p< 0.05). Highest amount of VS reduction of 46% was observed in trial 3, this much reduction showed incomplete degra- dation. Highest temperature in trial 3 resulted into proper degradation of organic matter as compared to other trials, this resulted into more VS reduction. Due to the presence of complex lignocellulosic material in the available organic matter the reduction of VS requires more time.
0 2 4 6 8 10 12 14 16 18 20 22 30
40 50 60 70 80
VS (%)
Composting period (Days)
Trial 1 Trial 2 Trial 3 Trial 4 Trial 5
Figure 4.2: Variation in Volatile solids (%) during composting period
0 2 4 6 8 10 12 14 16 18 20
5.5 6.0 6.5 7.0 7.5 8.0
pH
Composting period (Days)
Trial 1 Trial 2 Trial 3 Trial 4 Trial 5
Figure 4.3: Variation in pH during composting period
•pH
pH is another factor which greatly influences the composting process by affecting mi- crobial activity. The optimal range for the development of bacteria and fungi is 6.0 to 7.5 and 5.5 to 8.0 respectively (Ryckeboer et al., 2003). The variation in pH changes the avail- ability of hydrogen ions. These hydrogen ions play a vital role in the transport across the microbial membrane and thus, affecting the activities of composting microbes (Plette et al., 1995). A pH range of 6.5 to 8.0 had been reported favourable for microbial growth in wheat straw (Pan and Sen, 2013), pH of 4.0 and 6.5 in food waste and garden clipping composting respectively. However, in present study the initial pH of water hyacinth, cattle (cow) manure and sawdust was observed to be 6.5, 7.2 and 5.9, respectively. The initial
4.1. PHASE I: Microbial Population, Stability and Maturity Analysis of Rotary Drum Composting of Water Hyacinth
and final pH of all the trials was in the range of 5 to 6.6 and 7 to 7.6, respectively. (Figure 4.3) shows the pH range of all the trials. The ANOVA analysis depicted a significant vari- ance of pH between the trials (p< 0.05). The observed pH favored the growth and activity of bacteria, fungi and all other microbes also. All these pH values favored the development of optimum conditions for microbial growth in compost sample.
•Electrical conductivity (EC)
Electrical conductivity (EC) is indirect measurement of soluble salts, and is used as chemical indicator of composting (Pan and Sen, 2013). High EC in the final compost of wa- ter hyacinth slows down plant rooting and reduce the transportation of water and nutrients into the plants (Singh and Kalamdhad, 2013a). The final EC values of all composts were 5.4, 6.2, 2.9, 4.7 and 9 dS/m in trials 1, 2, 3, 4 and 5, respectively (Figure 4.4). It was observed that the EC value decreased with the progress in composting in all trials except trial 5. Similar values of EC in water hyacinth compost were also monitored by Singh and Kalamdhad (2012). However, 6 dS/m of EC has been reported in sludge composting (Pan and Sen, 2013). The volatilization of ammonia and the precipitation of mineral salts is possible reason for the decrease in EC at the later phase of composting (Dhal et al., 2012).
Due to the release of humic substances (which has the capacity to interact with metal ions) reduction of water solubility was observed (Singh and Kalamdhad, 2012), the EC might have decreased. On analyzing the results by ANOVA, EC varied significantly between all the trials (p< 0.05). After 20 days, only compost of trial 3 approached the desired EC value.
Higher number of microbes in final compost would cure and mature the final compost.
0 2 4 6 8 10 12 14 16 18 20 22
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0
Electrical conductivity (dS/m)
Composting period (Days)
Trial 1 Trial 2 Trial 3 Trial 4 Trial 5
Figure 4.4: Variation in Electrical conductivity during period