Materials and Methods
3.2 PHASE I: Microbial Population, Stability and Maturity Analysis of Rotary Drum Composting of Water Hyacinth
3.2 PHASE I: Microbial Population, Stability and Maturity Analysis of Rotary Drum Composting of Water Hyacinth
3.2.1 The Compost Material
Different waste mixtures were prepared by mixing of water hyacinth, cow dung and sawdust. Water hyacinth was collected from Amingaon industrial area near Indian Institute of Technology Guwahati (IITG), Assam, India (Figure. 3.2 (a)), Cow dung was obtained from dairy farm near to the IITG campus, Sawdust was purchased from nearby saw mill.
Sawdust and cow dung were mixed thoroughly to form fine powder. Water hyacinth was shredded into small pieces of order 1 cm so as to maintain proper aeration and control the moisture. Sawdust and cow dung powder and water hyacinth were mixed thoroughly in five different proportions as detailed in Table 3.1.
Figure 3.2: (a) Collection site near Amingaon Industrial Area, Guwahati, India (b) Feed- stock materials
3.2.2 Feedstock Preparation
Different waste combinations of the organic waste such as water hyacinth, cow dung and saw dust were mixed together in the ratio of 10:0:0, 5:4:1, 6:3:1, 7:2:1 and 8:1:1 making up the total volume of 150 kg for rotary drum composting as shown in Table 3.1.
The cow-dung brought from the nearby dairy farms was mixed with sawdust by hand to ensure no big clumps were formed. Water hyacinth was shredded into 1-2 cm size using electric shredder and manual chopping. This was done to ensure proper degradation along with aeration. Then all three were mixed together and feed to the drum composter as shown in (Figure. 3.2 (b)). The study of the microbial activity and the physiochemical parameters were done experimentally.
Table 3.1: Waste composition of different mixtures
Trial Composition/
Ratios
Water hyacinth (kg)
Cow dung (kg)
Saw dust (kg)
Trial 1 08:01:01 120 15 15
Trial 2 07:02:01 105 30 15
Trial 3 06:03:01 90 45 15
Trial 4 05:04:01 75 60 15
Trial 5 10:0:0 (Control) 150 0 0
3.2.3 Rotary Drum Composting
Water hyacinth collected from Amingaon industrial area was chopped into 1 cm to 2 cm size and mixed along with cow dung and sawdust. Figure 3.3 depicts the pilot-scale rotary drum composter of 550 L capacity being operated on batch mode. The capacity of the pilot scale rotary drum composter was decided keeping in view of the capability of a single person who can handle around 150 kg of waste by manual rotation. The main unit of the composter is fabricated with 4 mm thick metal sheet with 1.22 m (length) and 0.76 m (diameter). An anti-corrosive coating is present on the inner side of drum. The drum is mounted on a metal stand with rubber rollers. In order to maintain proper mixing, agitation and aeration of the wastes during rotation, 40 mm ×40 mm angles are welded longitudinally inside the drum. Two adjacent holes of 10 cm each are present on top of the drum to remove excess water (Kalamdhad et al., 2008)
Manual turning was done after every 24 h through one complete rotation of the rotary drum to ensure that the material on the top portion moved to the central portion, where it was subjected to higher temperature (Kalamdhad and Kazmi, 2009). After that, aerobic condition was maintained by opening the top half side doors of the two circular faces.
3.2.4 Sampling and Analysis
A total of 1 kg sample was collected for complete analysis. Grab sampling was carried out for sampling. This sample was prepared by taking representative samples from 9 differ- ent points mainly from the middle portion and end terminals of the pilot-scale rotary drum composter after drum rotation so as to ensure homogenized sample. These homogenized samples were collected on 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 days of the composting process. The 1 kg sample was then divided into two parts viz. (A) for physio-chemical analysis (800-900 g) and (B) for biological and microbial analysis (150-200 g). The sub- samples (A) were air dried immediately, ground to pass through 0.2 mm sieve and stored for physio-chemical analysis. The sub-samples (B) were either used or stored at 4◦C for
3.2. PHASE I: Microbial Population, Stability and Maturity Analysis of Rotary Drum Composting of Water Hyacinth
biological analysis of the wet sample within 2 days.
Figure 3.3: Pilot Scale Rotary Drum Composter (a) Schematic design (b) Pictorial view
3.2.4.1 Physico-chemical Analysis
Different experimental methods were used in the study to accomplish the stipulated ob- jectives. physio-chemical analysis of the solid waste samples including water hyacinth, cow dung and sawdust were carried out in Centre for Environment Laboratory, IIT Guwahati.
Experimental procedures of physio-chemical parameters are explained below.
1. Moisture content (IS:10158-1982)
• Take initial weight of the plate as W1 g.
• Weigh 200±0.1 g of fresh sample in the plate and kept it in an oven operating at a temperature of 105◦C.
• After 24 h the plate was taken out and the final weight of plate with sample was taken as W2g.
• Then the moisture content (MC) of the sample was calculated as:
MC(%) =
200−(W2−W1)×100 200
(3.1) 2. pH (IS:10158-1982)
• About (10 ± 0.1g) of ground sample (screened through 0.22 mm sieve) was taken and dissolved into 100 mL of distilled water.
• Kept it in a horizontal shaker for 2 h.
• Then kept it for about1/2h for settling down the solids.
• Standardize the pH meter (ambient temperature) by immersing the electrode in buffer solution of known pH, normally 4.0 and 7.0.
• Read the pH and adjust correctly with the knob, till the reading indicated the correct value for pH of buffer solution.
• Rinse the electrode with distilled water.
• Then the pH of the suspension was measured with pH meter.
3. Electrical conductivity (EC) (IS:10158-1982)
• About (10 ± 0.1g) of ground sample (screened through 0.22 mm sieve) was taken and dissolved into 100 mL of distilled water.
• Kept it in a horizontal shaker for 2 h.
• Then the diluted sample was filtered through Whatman 42 no. filter paper.
• Rinsed the electrode with distilled water.
• The electrical conductivity, EC of the filtered sample was measured with conduc- tivity meter, and expressed as dS/m.
3.2. PHASE I: Microbial Population, Stability and Maturity Analysis of Rotary Drum Composting of Water Hyacinth
4. Volatile solids (IS: 10158-1982)
• Initial weight of the crucible was taken as W1 g.
• Weigh (10±0.1g) of ground sample (screened through 0.22 mm sieve) in cru- cible and kept it in a muffle furnace operating at a temperature of 550-600◦C for 2 h.
• After 2 h crucible was taken out of the muffle furnace and kept in desiccators for 1/2 h for cooling and then final weight of crucible with sample was taken as W2
g.
• Then the Volatile Solids (V S) content of the sample was calculated as:
V S(%) = (10−(W2−W1))×100
10 (3.2)
3.2.4.2 Biological Analysis
1. Soluble Biochemical Oxygen Demand (APHA, 2005)
• About 10±0.1g of fresh compost was taken in a conical flask and dissolved in 100 mL of distilled water.
• The flask was kept in a horizontal shaker for 2 h
• Then it was filtered using whattman 42 no. filter paper.
• The supernatant of samples were taken and analysed for BOD test using BOD5
test calculation:
BOD5(mg/L) = (D1−D2)
P ×1000 (3.3)
Where D1= Initial DO of sample in mg/L D2= Final DO of Sample after 3 days incubation in mg/L P = Sample volume (mL) diluted to 300 mL with dilution water
2. Chemical Oxygen Demand (APHA, 2005)
• About 10±0.1 g of fresh compost was collected in a conical flask and dissolved in 100 mL of distilled water.
• The flask was kept in a horizontal shaker for 2 h.
• Then it was filtered using Whatman 42 no. filter paper.
• The supernatant of samples were taken and analysed for COD using closed reflux method.
• 1.5 mL of K2Cr2O7 + 2.5 mL of sulphuric acid reagent were added to COD vial.
• It was digested for 2 h in COD digestor at 150◦C and cooled down to room temperature
• Then cooled and titrated against ferrous ammonium sulphate (FAS) using ferroin indicator till colour changes from green to wine red.