For many developing nations, biogas has traditionally been used for household cooking and lighting. Methane (CH 4) content in biogas has to be increased by removing incombustible carbon dioxide (CO 2) and potentially corrosive constituents such as hydrogen sulphide (H 2 S) and moisture. This study set out to increase biogas from 55.8% CH 4 , 43% CO 2 , 0.85% oxygen (O 2), 75.1 ppm H 2 S to >80% methane and non-traceable H 2 S without enhancing raw biogas pressure. By using a single scrubber column and varying water scrubbing system operating parameters of packing material type, packing depth, water and gas flow rates, appropriate parameters for achieving the above objective were determined. The experiments were carried out at an average digester pressure of 1.0589bar. Results show that packing a column with steel-wire mesh to a depth of 0.4m increases the volumetric percentage of CH 4 in biogas to >80% for water to gas flow rate ratios 1.9 and above. Increasing the packed depth to 0.8m increases volumetric percentage of CH 4 in biogas to 80% at a lower ratio of 0.7. This increase in packed depth resulted in an improvement from 1800 litres to 700 litres of water for every m 3 of raw biogas upgraded. However, to achieve >80% CH 4 in marble packed columns of similar depths, the water to gas flow rate ratio has to be raised above 2.5.

The threat posed by plastics to the environment has prompted the development of bioplastics. Starch plasticized by glycerol is a key renewable resource in the production of high-quality bioplastics. Previous studies have availed information on the mechanical quality of starch-based bioplastics however there is limited information about their degradation pattern in the natural environment which this research presents. Bioplastics were buried in holes in loam sandy soil and weekly photographic data and weight were collected to reveal the effect of degradation. Weather parameters of rainfall, temperature, relative humidity, sunshine intensity and sunshine hours were recorded to establish influence of weather on degradation. A control set up in the laboratory was used to compare the results. Over time the tests revealed that as the hydrophilic enzymes break down the bioplastic, its weight initially increases (up to 87%) due to absorption of moisture and after saturation, the bioplastic is disintegrated which initiates decomposition and the bioplastic weight is steadily reduced. Degradation was further enhanced by invasion of soil organisms like worms, termites among other soil microbes. Rainfall (r = 0.857) increased the moisture in the soil which initially increased the weight of the bioplastic up to a point when the hydrophilic enzymes set into breakdown the bioplastic then the weight started to drop. This was the same case for relative humidity (r = −0.04) however; the sunlight intensity (r = 515) and hours of illumination indirectly affect the process by influencing microbial activity. An increase in the sunshine intensity increased the activity of soil organisms up to a point beyond which increased exposure caused the organisms to burrow deeper in the soil. Increase in microbial activity increased the rate of degrada-How to cite this paper: AhimbisibweJournal of Agricultural Chemistry and Environment tion of the buried bioplastics which took five to ten weeks to fully decompose (98.3%). The reduced time of degradation means that starch-based bioplastics have a high potential as sustainable substitute for petroleum-based plastics.

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