Assessment of the Effect of Mixing Pig and Cow Dung on Biogas Yield

Household energy is increasingly becoming a scarce resource in developing countries. In these countries, cooking accounts for about 90% of all household energy consumption. Motivated by the need to meet the ever-increasing energy demand and sustainability consciousness, many Governments have promoted renewable energy technologies such as biogas. However, biogas technology in Uganda is constrained by insufficient gas production due to lack of enough feedstock. This paper presents the findings of a research that was carried out to determine the effect of mixing pig and cow dung on biogas yield. Fifteen plastic bottles of capacity one and half litres were used as digesters and each fed with 1kg of pig and cow dung mixture in proportions of 0%, 25%, 50%, 75% and 100% with three replications.  Results from this study show that co-digestion of cow dung with pig manure increased biogas yield as compared to pure samples of either pig or cow dung. Comparing to samples of pure cow dung and pig manure, the maximum increase of almost seven and three fold was respectively achieved when mixed in proportions of 1:1. Ultimately, co-digestion of pig and cow dung is one way of addressing the problem of insufficient gas production in this country. Key words:  Biogas, cow dung, pig manure, co-digestion, compact system, Ugand

Width Prediction of a Side Circular Crescent Failed by a Tillage Tool in a Sandy Clay Loam

Some of the mathematical force models employing limit equilibrium analysis are based on the soil-volume tilled to predict the draft requirements of a tillage tool. At the same time, such models require a preliminary assumption of the soil failure pattern ahead of the tool. It is imperative therefore to accurately determine the dimensions of the idealized soil-failure model to ensure accurate prediction of the soil-volume tilled and thus the tillage-tool draft requirements. Among the commonly idealized models, is the model that divides the soil failure ahead of a simple tillage tool into a center wedge and a side circular crescent on each side of the tool. However, the available model for determining the maximum width of the side circular crescent was found to over predict its size. This was mainly due to being insensitive to soil water content. A study was therefore carried out to develop a model expressing the maximum width of the failed side circular crescent in terms of soil water content. Tests were conducted under field conditions in a sandy clay loam soil using conventional subsoilers in a tandem configuration at an operating depth of 600 mm Unlike the available model, the results showed that the proposed model adequately predicted the maximum width of the failed side circular crescent resulting in satisfactory prediction of the tilled soil volume. This would lead to limit equilibrium analysis based models to sufficiently predict draft requirements of tillage tools. In conclusion it was observed that the size of a failed soil-wedge is more sensitive to soil water content than the geometric dimensions of a tillage tool. Key worlds: Side circular crescent, failed soil-wedge, model, maximum width, tillage too

Force modelling and energy optimization for subsoilers in tandem

In the recent past, as more farm power is being demanded on farms, due to increased farm sizes and operating speeds, larger and heavier farm machines are deployed in various farming operations. Their cumulative negative effects have become more apparent with increased incidences of soil compaction problems. This has forced many farmers to practice deep tilling, using subsoilers to break up compacted subsoil layers. In some maize growing regions of South Africa, conventional subsoilers are used in a tandem configuration. The farmers believe that the use of subsoilers in this mode reduces the draft force per unit area tilled. This probably happens because the critical depth for the rear subsoiler is increased beyond its working depth of 600 mm. Operating in this mode necessitated this study, with the ultimate goal of testing an appropriate existing force model for a single tine in predicting the force requirements of the front subsoiler in a tandem configuration. Secondly, to develop an alternative model for the rear subsoiler based on the three-dimensional failed soil-profile and to determine the relative position of the front subsoiler at which energy utilization is optimized. To develop the proposed model, an analytical approach based on limit equilibrium analysis was used and a Matlab-based computer program was coded to solve it. Its verification was conducted through field experiments in sandy clay loam soil. The experiments consisted of a continuous measurement of the horizontal and vertical forces acting on each subsoiler by a two-dimensional force transducer system. At the same time, the three-dimensional and thus the cross-sectional areas of the disturbed soil-profiles at different sections were measured, as well as the soil characteristics. A manual method employing a pin-profile meter was used to measure the vertical cross-sectional areas of the failed soil-profiles at 100 mm intervals. Further more, a technique using an automatic penetrometer and a computer program was developed to identify and map the three-dimensional failed soil-profiles. This technique indicated that the subsoiler failed the soil beyond its maximum operating depth and width. The results also indicated that the soil-failure pattern at close spacing is in phase at both subsoilers, leading to reduced total draft force requirements. At a wider spacing, the soil-failure pattern was out of phase, thus resulting in increased total draft force requirements. At the same time, the cross-sectional area tilled per unit draft force increased with increased spacing. This was because the failed maximum cross-sectional area increased in size faster than the total draft force as the spacing was increased. The proposed model verification results show that the predicted and recorded forces at the rear subsoiler correlated reasonably well at a wider spacing. When the front subsoiler was shallow working and close to the rear subsoiler, the model under- predicted the measured forces on the rear subsoiler, whilst the Swick-Perumpral model over predicted the applied forces to the front subsoiler and this was generally the case at wider spacings. Furthermore the efficiency of the subsoilers was maximized when the longitudinal spacing was such that it allowed the soil failed by the front subsoiler to stabilize before the rear subsoiler reached it. The maximum cross-sectional area failed per unit draft force was recorded when the depth of the front subsoiler was equal to about 80% of the rear subsoiler-operating depth. The knowledge contributed by this research will not only facilitate qualitative field operations and optimize energy use, but also promote better management decisions.Thesis (PhD (Engineering))--University of Pretoria, 2004.Civil Engineeringunrestricte

Characterization of municipal waste in Kampala, Uganda

This study characterized the municipal waste generated in Kampala and delivered to Kiteezi landfill between July 2011 and June 2012 that is, covering the dry and wet months. On each sampling day, waste was randomly selected from five trucks, sorted and weighed into different physical fractions. Samples of the organic waste from each truck were analyzed for total solids, major nutrients, and energy content.In Kampala, Uganda, about 28,000 tons of waste is collected and delivered to a landfill every month. Kampala Capital City Authority (KCCA) records show that this represents approximately 40% of the waste generated in the city. The remaining uncollected waste is normally dumped in unauthorized sites, causing health and environmental problems. However, the organic fraction of domestic waste can provide an opportunity to improve livelihoods and incomes through fertilizer and energy production. This study characterized the municipal waste generated in Kampala and delivered to Kiteezi landfill between July 2011 and June 2012, that is, covering the dry and wet months. On each sampling day, waste was randomly selected from five trucks, sorted and weighed into different physical fractions. Samples of the organic waste from each truck were analyzed for total solids, major nutrients, and energy content. During the wet months, the waste consisted of 88.5% organics, 3.8% soft plastics, 2.8% hard plastics, 2.2% paper, 0.9% glass, 0.7% textiles and leather, 0.2% metals, and 1.0% others. During the dry months, the waste consisted of 94.8% organics, 2.4% soft plastics, 1.0% hard plastics, 0.7% papers, 0.3% glass, 0.3% textile and leather, 0.1% metals, and 0.3% others. The organic waste on average had a moisture content of 71.1% and contained 1.89% nitrogen, 0.27% phosphorus, and 1.95% potassium. The waste had an average gross energy content of 17.3 MJ/kg. It was concluded that the organic waste generated can be a suitable source of some plant nutrients that are useful especially in urban agriculture. Implications: The result of the waste characterization in Kampala was found to be significantly different from that obtained for other Sub-Saharan African (SSA) cities, showing that studies assuming average values for the waste fractions are likely to result in erroneous results. Furthermore, no reduction in organic fraction of the waste was noticed when compared with a study done two decades ago in spite of greatly improved economic status of Kampala city, a finding that is not in agreement with several other similar studies done for other SSA cities