pagesThe main aim of this study was to determine the effects of physical and chemical pretreatments on biogas production from two agricultural wastes (maize straw and cattle manure). The total solids (TS) were 86.1% and 41.2% for the cattle manure and maize straw respectively while the volatile solids (VS) were 82.0% for cattle manure and 51.6% for maize straw (both interms of total biomass). 5% TS was used for both biomasses in the measurement of reducing sugars and the Biochemical methane potential (BMP) test.Solubility was determined by measuring the reducing sugar concentration using the Miller method (Miller 1959). Biomass samples were seeded with sludge seed on a 50:50 biomass to sludge ratio. The pH of the mixture was regulated to between 7.0 and 7.5 and placed in an incubator at 37 o C (mesophilic temperature range). Biogas measurements were done daily and carbon dioxide was measured once in a week.Two chemical pretreatment methods were applied on both biomasses; acid and alkaline pretreatments assisted with heat. The most effective pretreatment method for maize straw was alkaline pretreatment producing the highest concentrations of daily and cumulative biogas with an average increase of 163%. Acid pretreatment of maize straw lasted between 24 to 27 (the fewest number of days) compared to all other pretreatments applied.i Physical pertreatment methods applied on maize straw include; comminution, microwave and liquid hot water pretreatment. The Microwave pretreated samples produced the highest increase in biogas production of about 3 folds.Cattle manure was pretreated with H2SO4, NaOH, microwave and liquid hot water (LHW). Acid pretreatment was more effective for cattle manure than maize straw with both acid concentrations increasing biogas production. Cattle manure samples treated at LHW 135 o C produced the highest cumulative amount of biogas resulting in a 103% increase. Microwave pretreatment was also very effective resulting in 97% increase in methane production which lasted for 32 days.

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Bio-fixation of carbon dioxide (CO2) by microalgae has been recognised as an attractive approach to offset anthropogenic emissions. Biological carbon mitigation is the process whereby autotrophic organisms, such as microalgae, convert CO2 into organic carbon and O2 through photosynthesis; this process through respiration produces biomass. In this study Dunaliella tertiolecta was cultivated in a semicontinuous culture to investigate the carbon mitigation rate of the system. The algae were produced in 1.2-L Roux bottles with a working volume of 1 L while semicontinuous production commenced on day 4 of cultivation when the carbon mitigation rate was found to be at a maximum for D. tertiolecta. The reduction in CO2 between input and output gases was monitored to predict carbon fixation rates while biomass production and microalgal carbon content are used to calculate the actual carbon mitigation potential of D. tertiolecta. A renewal rate of 45 % of flask volume was utilised to maintain the culture in exponential growth with an average daily productivity of 0.07 g L(-1) day(-1). The results showed that 0.74 g L(-1) of biomass could be achieved after 7 days of semicontinuous production while a total carbon mitigation of 0.37 g L(-1) was achieved. This represented an increase of 0.18 g L(-1) in carbon mitigation rate compared to batch production of D. tertiolecta over the same cultivation period.