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In this study, a black-shading cylindrical water tank made of high-density polyethylene was locally manufactured as a household digestor for treating cow manure in Bangladesh. Effluent slurry instead of water was reused for manure dilution under manure-to-slurry ratios of 1:2 and 1:1, to assess this small prototype's production efficiency and feasibility. The specific biogas production at both ratios matched well, by 0.12 m3/kg VS and 0.14 m3/kg VS, respectively, while the former slurry dilution operation outperformed in daily and accumulative biogas production by 16% and 57%, correspondingly, referring to 0.49 Nm3/d on average and 8.55 Nm3 in total, potentially meeting a 2 h household cooking energy requirement. From a nationwide viewpoint, slurry dilution was proven to be a great initiative to conserve water amounting to 50,286,751 m3 for 114,810 households of 6 person-equivalents annually, while cutting chemical costs by USD 32,720,684/yr and trimming annual greenhouse gas emission by 1.8 million tons of CO2e. This study revealed that a small prototype digestor could be an alternative energy source for cost-effective and eco-friendly household applications. [ABSTRACT FROM AUTHOR]

Background: Anaerobic digestion (AD) has many benefits and is a safe way to generate energy, address the energy shortage problem, and reduce waste and carbon emissions. The study aimed to determine the performance evaluation of prefabricated polyvinyl chloride (PVC) biogas digester and compare different feeding intervals using cow manure. This study was conducted at ambient temperature in three types of feeding practice (daily, 4‐day, and 7‐day feeding interval) to investigate the variation of biogas production and evaluation of digester performances. The composition of biogas, pH, and total volatile fatty acids (TVFA) were measured regularly and weekly basis. The TVC, Escherichia coli, and Salmonella spp. counts were determined by the spread plate technique method using PCA, EMB agar, and SS agar plate, respectively. Results: The comparison results of daily versus 4‐day feeding interval indicated that the total biogas and methane yield was 34% and 28% higher in 4‐day interval feeding. The average digester performance was also 34% higher in 4‐day feeding interval digester than daily feeding digester. However, the comparison results of daily versus 7‐day interval feeding indicated that the total biogas, methane yield, and digester performance were slightly higher in daily feeding. Before and after AD, the bacterial load (TVC, E. coli, and Salmonella spp. count) was reduced by 2–3 logs, and this reduction was also statistically significant (p < 0.05). Conclusion: The performance of PVC digester was highly satisfactory and good enough to fulfil the demand (0.8–1.6 m3) of a five‐member family for cooking both in urban and rural areas of Bangladesh. [ABSTRACT FROM AUTHOR]