Characterization of University Residential and Canteen …
199
2.3 Compost Harvesting and Product Characterization
Each composting system required monitoring to promote a successful compost pile
by ensuring sufficient water and an appropriate temperature. For the windrow (openair) compost, the pile was turned every 5 days to aerate it while avoiding overturning
that may cause reduced microbial activity. Water was then added at 100–200 mL
after turning the pile to achieve an optimum moisture content as measured with a
soil moisture sensor (PMS710). The optimum moisture content is within the range
of 40–60% mc (Rynk 1992). At less than 40% moisture, bacteria slow their activity
and may become dormant. But with more than 60% moisture, water will force air
out of the pile pore spaces, suffocating the aerobic bacteria. Anaerobic bacteria
will then take over, resulting in unpleasant odors. An optimum level of moisture in
vermicompost also aids worm movement inside the pile. If the compost pile is too
dry, worms will be unable to move to the upper layer of the pile in order to consume
the foods deposited there.
For C-1, V-1, and V-2, the final compost product was collected after 7–10 days
of composting on 2.5 kg food waste. For the windrow bin system (C-1), waste was
considered mature or at the end stage of decomposition when the pile temperature
was at 40–60 °C. For the V-4 and V-5 compost bins, the vermicompost was collected
after 20 days of processing on 4 kg of vegetable and fruit waste. This harvesting
period was calculated based on the assumption that worms eat nearly their body
weight per day (Edwards 2004), and that they produce 50% of their body weight as
a cast (Nagavallemma et al. 2004).
To harvest the product of vermicomposting, black-colored topsoil from each worm
bin was extracted. It was then stored inside a plastic bag and brought to the laboratory
for chemical and physical testing. Nitrogen was measured using the Total Kjeldahl
Nitrogen by Digestion and Titration Method ASTM D3590-A (2006). Phosphorus
testing was carried out at the UMS Environmental Laboratory using a spectrophotometric method (Hach DR6000). Potassium testing was conducted by digesting
compost products according to the ISO16729:2013 Standard and measured using
an Atomic Absorption Spectrometer (AAS) (Perkin Elmer 4100). Other chemical
properties of the compost products were also measured such as pH, temperature, and
conductivity (Hanna digital meter).
The comparison of compost products was also quantified in terms of moisture
content, water absorption, and bulk density. Moisture content (wet basis) was measured by drying the compost soil at 105 °C in an oven for approximately 24 h and then
calculating the percentage difference between wet and dry soils. Bulk density was
measured using an approximately 500 g container, compacted to ensure the absence
of large void spaces, and was calculated by dividing the weight of the material by
the volume of material in the container.
The growth substrate evaluation for 6 weeks was measured for the compost products of C-1, V-1, and V-2 using the Growing Index (GI) adapted from Edwards (2004),
which is based on plant growth rate in terms of height, width, and leaf growth. Plant
height measures the vertical height of the plant from the lowest part to the top, includ-
199
2.3 Compost Harvesting and Product Characterization
Each composting system required monitoring to promote a successful compost pile
by ensuring sufficient water and an appropriate temperature. For the windrow (openair) compost, the pile was turned every 5 days to aerate it while avoiding overturning
that may cause reduced microbial activity. Water was then added at 100–200 mL
after turning the pile to achieve an optimum moisture content as measured with a
soil moisture sensor (PMS710). The optimum moisture content is within the range
of 40–60% mc (Rynk 1992). At less than 40% moisture, bacteria slow their activity
and may become dormant. But with more than 60% moisture, water will force air
out of the pile pore spaces, suffocating the aerobic bacteria. Anaerobic bacteria
will then take over, resulting in unpleasant odors. An optimum level of moisture in
vermicompost also aids worm movement inside the pile. If the compost pile is too
dry, worms will be unable to move to the upper layer of the pile in order to consume
the foods deposited there.
For C-1, V-1, and V-2, the final compost product was collected after 7–10 days
of composting on 2.5 kg food waste. For the windrow bin system (C-1), waste was
considered mature or at the end stage of decomposition when the pile temperature
was at 40–60 °C. For the V-4 and V-5 compost bins, the vermicompost was collected
after 20 days of processing on 4 kg of vegetable and fruit waste. This harvesting
period was calculated based on the assumption that worms eat nearly their body
weight per day (Edwards 2004), and that they produce 50% of their body weight as
a cast (Nagavallemma et al. 2004).
To harvest the product of vermicomposting, black-colored topsoil from each worm
bin was extracted. It was then stored inside a plastic bag and brought to the laboratory
for chemical and physical testing. Nitrogen was measured using the Total Kjeldahl
Nitrogen by Digestion and Titration Method ASTM D3590-A (2006). Phosphorus
testing was carried out at the UMS Environmental Laboratory using a spectrophotometric method (Hach DR6000). Potassium testing was conducted by digesting
compost products according to the ISO16729:2013 Standard and measured using
an Atomic Absorption Spectrometer (AAS) (Perkin Elmer 4100). Other chemical
properties of the compost products were also measured such as pH, temperature, and
conductivity (Hanna digital meter).
The comparison of compost products was also quantified in terms of moisture
content, water absorption, and bulk density. Moisture content (wet basis) was measured by drying the compost soil at 105 °C in an oven for approximately 24 h and then
calculating the percentage difference between wet and dry soils. Bulk density was
measured using an approximately 500 g container, compacted to ensure the absence
of large void spaces, and was calculated by dividing the weight of the material by
the volume of material in the container.
The growth substrate evaluation for 6 weeks was measured for the compost products of C-1, V-1, and V-2 using the Growing Index (GI) adapted from Edwards (2004),
which is based on plant growth rate in terms of height, width, and leaf growth. Plant
height measures the vertical height of the plant from the lowest part to the top, includ-