BSc-MSc (Integrated)

Climate change is one of the serious issues faced currently by humanity.
The uncontrolled emission of Green House Gases play a major role in global
warming, which eventually leads to climate change. The unscientific methods of
waste disposal has serious environmental impacts by continuous emission of
GHGs leading to global warming. Households constitute the basic unit in urban
energy consumption and waste generation. Anaerobic digestion of the organic
fraction of household wastes in a decentralised manner using biogas plants offers
great scope in waste management and generation of cheap renewable energy for
domestic cooking.
The investigations revealed that average amount of organic waste generated
per household was 5.28 kg (5 member family) and that of a hostel mess was 24.9
kg (40 inmates). Kitchen wastes in Kerala had a major fraction as liquids and per
capita food waste generation in households and hostel mess were 42 g and 153 g,
respectively. Average TS of kitchen waste was found as 82 gL-1 and the average
pH was found as 3.86. Average C: N ratio of the kitchen waste was found as
53.88:1. The minimum ratio of kitchen waste and inoculum required for a
successful start-up of anaerobic system was 1:5. Biogas productivity of kitchen
waste was found as 57.57 LL-1and the average specific biogas production from
kitchen waste was estimated as 989.05 L kgTS -1. 80-90 % of the potential of
kitchen waste to generate biogas can be utilized if the HRT was in range of 40-50
days. Thus it is preferable to have a HRT in the range of 40-50 days for domestic
biogas plants working on kitchen wastes. Average methane content in biogas
produced from kitchen waste was enumerated as 62.18%. The preliminary
biomethanation studies revealed the high potential of kitchen waste to generate
biogas.
Portable biogas plants are easily shifted and installed, require less space
and can be placed conveniently in urban conditions. The four types of portable
biogas models used in the study were floating gas holder type (PBP1), floating gas
holder type with water seal (PBP2), fixed gas holder type (PBP3) and KAU
portable split biogas plant (PBP4). The four portable biogas plants (PBPs) were
evaluated by operating them at 50 and 40 day HRT. An increase in mean
volumetric biogas production was observed in 40-day HRT compared to 50 day
HRT in all PBPs. The maximum increase in biogas production was in PBP4 (34.4
%) and the minimum increase (4.0 %) was in PBP3. This indicated that PBP4 was
more suitable for energy production from domestic kitchen waste, which could be
operated at a higher gas volume availability at the shorter HRT of 40-day. The
maximum value of mean biogas productivity was exhibited by PBP2 at 50-day
HRT followed by PBP4 at 40-day HRT. Even though the values were higher at
50-day HRT for all the other three PBPs, the value of PBP4 at 40-day HRT was
11% higher than the mean value for all PBPs at 50-day HRT. Average biogas
productivity in all the PBPs during the 40-day and 50-day HRT periods were 53.9
LL-1d-1and 62.25 LL-1d-1, respectively. It was noteworthy that PBP4 had a biogas
productivity higher than these average values even at the short HRT of 40 days.
The specific biogas production at 40-day HRT in PBP4 was 30 % and 28.5 %
higher than that of the average biogas production of all the PBPs at HRTs of 50
and 40 days respectively. Specific biogas production is a true indicator of the
energy conversion efficiency of the system and hence the results gave a clear
testimony to the superiority of PBP4 over the other PBPs.
When the feeding of kitchen waste was interrupted for 12 days, maximum
reduction was observed in PBP3 (80.80 %) followed by PBP2 (80.62 %) and the
reduction was minimum in PBP1 (72.40%). When the feeding was restarted,
PBP4 regained its biogas production faster (7th day) compared to other plants.
Average N and K content of slurry from kitchen waste fed biogas plant
was found to be 4.025 and 1.315 % respectively, which was notably higher than
that from cow dung fed plant. However the P content (0.54) was lower in kitchen
waste fed plant.
From the study it was inferred that by the use of Portable Biogas Plants
(PBP4) total emission reductions of 1263.53 tonnes of CO2e can be achieved per
annum for 1000 households in the representative urban area of Kerala.