BAKARE, ADEWALEWASIU2025-12-102025-12-102023-12-05https://ir.funaab.edu.ng/handle/123456789/344A Thesis submitted to the Centre of Excellence in Agricultural Development and Sustainable Environment, Federal University of Agriculture, Abeokuta, Nigeria in partial fulfilment of the requirements for the award of degree of Doctor of Philosophy in Environmental System and Climate Change.ABSTRACT A substantial amount of agricultural waste is generated and disposed through dumping and burning in Nigeria. This study assessed effects of co-digestion of animal dungs, water hyacinth and Palm Oil Mill Effluent (POME) on biogas production; and potential of the slurry as soil amendment. The Agricultural waste: Poultry Manure (PM), Pig Dung (PD), Cow Dung (CD) and Water Hyacinth (WH) were co-digested in triplicates each in ratios: 75:25, 50:50 and 25:72 for PM:PD, CD:PM, PD:CD, WH:CD, WH:PD, WH:PM using POME as diluent. The control: PD, CD WH and PM each were 100 %. The digestion was done under a 30-day retention period in 25L plastic digesters (Batch Experiment) The first three substrates with higher biogas production PD:CD (25:75), CD:WH (50:50) and PD:PM (25:75) were used to determine the effect of loading rate of 2.62 L on biogas production in the Continuous Experiment. Effect of scrubbers: iron sponge, silica gel, NaOH, and saw dust to remove H2S, moisture and CO2 respectively on the quality of biogas produced was assessed. The purified biogas was later compressed using car air conditioner compressor into 3 kg LPG cylinder. Flammability test was carried out by using 500 mls of borehole water. The slurry of the highest biogas production and NPK (15:15:15) fertiliser were used to grow Amaranthus hybbridus for four weeks. Plant height, stem girth and number of leaves were collected weekly. Data collected were subjected to descriptive and inferential statistics. Biogas produced was highest (7.166 L) in PD:CD (25:75) followed by 2.000 L in PDPM (25:75) and the lowest in CD:WH (25:75) with 1.666 L. After purification, the methane content ranged from 41 to 50 %, while the CO2 content range from 10 to 15% respectively. During compression, the temperature and pressure increased from 33.4 to 34.6 ℃ and 0 to 6.34 bar for temperature and pressure respectively. As the temperature and pressure increased, the amount of biogas compressed increased from 0 to 102 g. The LPG was 9 seconds faster than biogas at heating the water to boiling point with flame temperatures of 325℃ and 213℃ for LPG and biogas respectively. The soil+slurry had plant height of 61.8 cm, followed by 42.72 cm in soil+NPK while the least height of 41.33 cm was observed in soil only. The stem girth was 11.78, 8.03 and 7.98 mm in soil+slurry, soil+NPK and soil only respectively. The number of leaves was 25 23 and 18 in soil+slurry, soil+NPK and soil only respectively. In conclusion, all the co-digested agriculture waste with palm oil effluent, are rich in biogas. The co-digested of PD:CD (25:75) produced the highest biogas and the slurry improved the growth of Amaranthus hybridusenThesis