Abstract
The present study was designed to investigate the bacteria and other factors influencing the augmentation
of biogas production from Cow Manure (CM) and Household Waste (HW) in a lab-based proto-type digester
for its validation. Two types of proto-type digesters were prepared in this study. The Biochemical Methane
Potential (BMP) tests were performed using mono-digestion of CM and co-digestion of CM with 5% HW.
For mono-digestion of CM, the batches were prepared from the manure of hybrid and local breed cows fed
with roughages and mixed ration (roughages and concentrate), adding Inoculum (In.) with a total weightof
200 g. Four experimental groups (HCR, HCM, LCR and LCM) were setup using mixing ratios of CM (25%):
H2O (25%): In. (50%). For co-digestion of CM with 5%HW, the batches were prepared from CM mixed with
5% of Soft Waste (SO), Food Waste (FW), mixed HW (SO and FW) with inoculum and a total weight of 200
g. Three experimental groups (SOCM, FWCM and SOFWCM) were set up using mixing ratios of SO
(5%)/FW (5%)/SOFW (5%):CM (22.5%): H2O (22.5%): In. (50%). For both mono- and co-digestion, the
digesters were set up at ambient temperature for 40 days of Hydraulic Retention Time (HRT) using a water
displacement type of proto-type digesters. The feedstock and digested slurry composition were measured
to determine their effects on biogas production. The bacterial load was analysed before feeding stock and
digested samples after Anaerobic Digestion (AD). The isolation and identification of aerobic/facultative
anaerobic bacteria (especially Escherichia coli and Salmonella spp.) and anaerobic bacteria by using cultural
characteristics and molecular detection by Polymerase Chain Reaction (PCR). For the validation of this
study, Polyvinyl Chloride (PVC) floating dome (7.5 m³) and PVC water tank type (3 m³) domestic biogas
digesters were used and evaluated their performances at different types of feeding intervals (daily, 4-days
and 7-days feeding interval). The composition of biogas (CH4, CO2 and H2S), pH and Total Volatile Fatty
Acids (TVFA) were measured regularly and weekly. The results of mono-digestion of CM indicated that the
biogas and methane yield were highest from the manure of local breed cows fed with mixed ration (LCM).
The average concentration of methane was achieved 52-55% and H₂S was not found in this study. The C:N
ratio was within the range, but not optimal and digested slurry contains a low amount of N, P, K and S. The
results of co-digestion indicated that the biogas yield was found highest in CM co-digested with mixed HW (SOFWCM). Whereas the methane yield was found highest in CM co-digested with fruit waste (FWCМ).
The average concentration of methane was achieved 60–75% and low H₂S content <200 ppm. The C: N ratio
was found within the optimal range. The nutrient contents (N, P, K and S) of digested slurry were
comparatively higher than the mono-digested CM. The co-digestion of CM with 5%HW has achieved 19%
more biogas and 32% more CH4 yields than mono-digestion of CM. The results between two types of digesters, water displacement type digester, was best for biogas and methane production. The bacterial load
before and after AD of the mono-digestion of CM and co-digestion of CM with 5%HW have reduced about.
3 logs and this reduction was statistically significant (p< 0.05). Isolation of aerobic/facultative anaerobic
bacteria (especially E. coli and Salmonella spp.) and anaerobic (methanogenic) bacteria (Methanococcus spp.
and Methanospirillium hungatii) were done and finally confirmed by PCR. For PVC floating dome
digesters, the comparison results of daily versus 4-days feeding intervals indicated that the total biogas and
methane yield was 34% and 28% higher in 4-days feeding interval than daily feeding. The average
performance of the 4-days feeding interval digester and daily feeding digester was measured
type
0.29Nm³BG/m³dcd-1 and 0.19 Nm³BG/m³DGd-1, respectively. In contrast, the comparison results of daily
versus 7-days feeding interval indicated that the total biogas yield and methane yield was slightly higher in
daily feeding. The average performance of the 7-days feeding interval digester and daily feeding digester
were measured 0.22m³BG/m³DGd-1 and 0.23m³BG/m³Dcd-1, respectively. There was a weak positive
correlation between ambient temperature and daily biogas production and digester temperature and daily
biogas production. The pH and TVFA were found within the optimum range. For PVC water tank type digesters, the comparison results of daily versus 4-days feeding interval indicated that the total biogas and
methane yields were 22% and 23% higher in daily feeding compared to 4-days feeding interval. The average
performances of the daily feeding and 4-days feeding interval digesters were 0.43 Nm³BG/m³Dcd-1 and 0.34
Nm³BG/m³DGd-1, respectively. There was a strong positive correlation between digester temperature and
daily biogas production. The pH and TVFA were found within the optimum range. Before and after AD of
three feeding intervals in two digesters, the bacterial load was reduced by 2-3 logs and this reduction was
statistically significant (p< 0.05). The present study concluded that the performance evaluation of PVC water
tank and PVC floating dome type biogas digesters was highly satisfactory and good enough to fulfil the
demand (0.8-1.6 m³) of five-member family cóoking two meals both in semi-urban and rural areas
Bangladesh.
of
Keywords: Anaerobic bacteria, BMP, biogas, cow manure, CH4, digester performance, household waste, prototype digester
The present study was designed to investigate the bacteria and other factors influencing the augmentation
of biogas production from Cow Manure (CM) and Household Waste (HW) in a lab-based proto-type digester
for its validation. Two types of proto-type digesters were prepared in this study. The Biochemical Methane
Potential (BMP) tests were performed using mono-digestion of CM and co-digestion of CM with 5% HW.
For mono-digestion of CM, the batches were prepared from the manure of hybrid and local breed cows fed
with roughages and mixed ration (roughages and concentrate), adding Inoculum (In.) with a total weightof
200 g. Four experimental groups (HCR, HCM, LCR and LCM) were setup using mixing ratios of CM (25%):
H2O (25%): In. (50%). For co-digestion of CM with 5%HW, the batches were prepared from CM mixed with
5% of Soft Waste (SO), Food Waste (FW), mixed HW (SO and FW) with inoculum and a total weight of 200
g. Three experimental groups (SOCM, FWCM and SOFWCM) were set up using mixing ratios of SO
(5%)/FW (5%)/SOFW (5%):CM (22.5%): H2O (22.5%): In. (50%). For both mono- and co-digestion, the
digesters were set up at ambient temperature for 40 days of Hydraulic Retention Time (HRT) using a water
displacement type of proto-type digesters. The feedstock and digested slurry composition were measured
to determine their effects on biogas production. The bacterial load was analysed before feeding stock and
digested samples after Anaerobic Digestion (AD). The isolation and identification of aerobic/facultative
anaerobic bacteria (especially Escherichia coli and Salmonella spp.) and anaerobic bacteria by using cultural
characteristics and molecular detection by Polymerase Chain Reaction (PCR). For the validation of this
study, Polyvinyl Chloride (PVC) floating dome (7.5 m³) and PVC water tank type (3 m³) domestic biogas
digesters were used and evaluated their performances at different types of feeding intervals (daily, 4-days
and 7-days feeding interval). The composition of biogas (CH4, CO2 and H2S), pH and Total Volatile Fatty
Acids (TVFA) were measured regularly and weekly. The results of mono-digestion of CM indicated that the
biogas and methane yield were highest from the manure of local breed cows fed with mixed ration (LCM).
The average concentration of methane was achieved 52-55% and H₂S was not found in this study. The C:N
ratio was within the range, but not optimal and digested slurry contains a low amount of N, P, K and S. The
results of co-digestion indicated that the biogas yield was found highest in CM co-digested with mixed HW (SOFWCM). Whereas the methane yield was found highest in CM co-digested with fruit waste (FWCМ).
The average concentration of methane was achieved 60–75% and low H₂S content <200 ppm. The C: N ratio
was found within the optimal range. The nutrient contents (N, P, K and S) of digested slurry were
comparatively higher than the mono-digested CM. The co-digestion of CM with 5%HW has achieved 19%
more biogas and 32% more CH4 yields than mono-digestion of CM. The results between two types of digesters, water displacement type digester, was best for biogas and methane production. The bacterial load
before and after AD of the mono-digestion of CM and co-digestion of CM with 5%HW have reduced about.
3 logs and this reduction was statistically significant (p< 0.05). Isolation of aerobic/facultative anaerobic
bacteria (especially E. coli and Salmonella spp.) and anaerobic (methanogenic) bacteria (Methanococcus spp.
and Methanospirillium hungatii) were done and finally confirmed by PCR. For PVC floating dome
digesters, the comparison results of daily versus 4-days feeding intervals indicated that the total biogas and
methane yield was 34% and 28% higher in 4-days feeding interval than daily feeding. The average
performance of the 4-days feeding interval digester and daily feeding digester was measured
type
0.29Nm³BG/m³dcd-1 and 0.19 Nm³BG/m³DGd-1, respectively. In contrast, the comparison results of daily
versus 7-days feeding interval indicated that the total biogas yield and methane yield was slightly higher in
daily feeding. The average performance of the 7-days feeding interval digester and daily feeding digester
were measured 0.22m³BG/m³DGd-1 and 0.23m³BG/m³Dcd-1, respectively. There was a weak positive
correlation between ambient temperature and daily biogas production and digester temperature and daily
biogas production. The pH and TVFA were found within the optimum range. For PVC water tank type digesters, the comparison results of daily versus 4-days feeding interval indicated that the total biogas and
methane yields were 22% and 23% higher in daily feeding compared to 4-days feeding interval. The average
performances of the daily feeding and 4-days feeding interval digesters were 0.43 Nm³BG/m³Dcd-1 and 0.34
Nm³BG/m³DGd-1, respectively. There was a strong positive correlation between digester temperature and
daily biogas production. The pH and TVFA were found within the optimum range. Before and after AD of
three feeding intervals in two digesters, the bacterial load was reduced by 2-3 logs and this reduction was
statistically significant (p< 0.05). The present study concluded that the performance evaluation of PVC water
tank and PVC floating dome type biogas digesters was highly satisfactory and good enough to fulfil the
demand (0.8-1.6 m³) of five-member family cóoking two meals both in semi-urban and rural areas
Bangladesh.
of
Keywords: Anaerobic bacteria, BMP, biogas, cow manure, CH4, digester performance, household waste, prototype digester