Effect of Total Solids Concentration of Municipal Solid Waste on the Biogas Produced in an Anaerobic Continuous Digester

Municipal Solid Waste (MSW) contains a relatively large amount of organic matter, which decomposes by the actions of microorganisms under anaerobic conditions to produce biogas. The total solids (TS) concentration of the waste influences the pH, temperature and effectiveness of the microorganisms in the decomposition process. This work investigated various concentrations of the TS of MSW in an anaerobic continuously stirred tank reactor (CSTR) and the corresponding amounts of biogas produced, in order to determine conditions for optimum gas production. Five laboratory-scale anaerobic batch digesters of 5 litres volume each were set up for the digestion of 2kg of shredded MSW diluted to a %TS concentration of 26.7%. The results from the batch experimentation were adapted to the design of a CSTR for the digestion of MSW. The CSTR was simulated over a range of %TS concentration of 4-10, at a maximum fractional conversion of 0.8 to cater for system inefficiencies. Mathematical models were developed for the process and solved using the Microsoft Visual Basic version 6.0 Programme. The results show the amount of biogas produced as a power function of the %TS concentration, indicating that as the process continues, a time comes when any marginal increase in the %TS concentration would no longer contribute to the increasing volume of biogas produced. The results further show that, given the limiting upper boundary of the %TS concentration, optimum biogas production in a CSTR digesting MSW cannot be ascertained with the concentration of the %TS alone

Modelling Soil Compaction Effects on Maize Growth and Yield in a Sandy Loam Soil

A mathematical model has been developed for the prediction of soil compaction effects on the growth and yield of maize crop in a sandy loam soil in tropical climates. The field work was done at the teaching and research farm of Rivers State University, Port Harcourt, Nigeria. A plot of land measuring 18 m x 4 m was divided into five sub-plots of equal dimensions and labelled as: plot 1 – un-compacted and untilled; plot 2 – un-compacted but tilled; and plots 3, 4 and 5 - tilled and compacted to varying degrees of tractor passes, viz 2, 4 and 6 tractor passes respectively. A Massey Ferguson (MF) 90 model disc plough was used for the tillage and an MF 260 model tractor used for the soil compaction treatments. Irrigation, weed and pest control were done equally on all plots when necessary. The maize crops were planted in the month of October and grew to maturity fourteen weeks thereafter. Field measurements gave values of soil bulk densities and moisture contents as 1.20, 1.17, 1.23, 1.28 and 1.35 g/cm3 and 5.17, 6.02, 4.89, 4.43 and 3.39% respectively for plots 1-5. The height and yield of the maize crop at the fourteenth week for the plots 1-5 are respectively 0.941, 1.380, 0.872, 1.146 and 1.402 m and 1192, 2859,1195, 1311 and 2320 kg/ha. The model was development based on the response of the maize crop growth and yield to the different levels of compaction treatment, using dimensional analysis. The field results showed that at p<0.05, there is a statistically significant effect between soil compaction and growth and yield of maize in a tropical sandy loam soil and the model predictions correlated experimental data up to about 99.5%

Seasonal variability of maize yield on a compacted sandy loam soil in a tropical environment

The effect of weather changes on the yield of maize on a compacted sandy loam soil was investigated. The experiment was conducted in the teaching /research farm of the Rivers State University, Port Harcourt, Nigeria. The research started during the wet (rainy) season in October, through the dry season in February. Five experimental field plots were used in the study. The plots were subjected to different levels of compaction by routine tillage operations and wheel traffic, using a Massey Ferguson (MF) 260 tractor and an MF90 disc plough, before the maize seeds were planted. Field data of crop emergence, growth rate and crop yield were taken at regular intervals within the different seasons. Analysis of the results showed an inverse-proportional relationship between maize yield and compaction during the wet season and a direct-proportional relationship during the dry season up to a certain optimal compaction level, when a shift was noticed. It was, therefore, found that different optimum levels of compaction for increased maize yield exist for the wet and dry seasons, respectively. Furthermore, the compacted soil within the optimum limit had better yield during the dry season. On the whole, although the fields with lower bulk densities performed better at the beginning of the study, they were out-performed by those of higher bulk densities by the end of the experiment. Thus, while the plots of bulk densities of 1.17 and 1.23 g/mm 3 had better yield during the wet season, they were out-performed by the plots of bulk densities of 1.28 and 1.35 g/mm 3 during the dry season

Designs of anaerobic digesters for producing biogas from municipal solid-waste

The production of biogas is of growing interest as fossil-fuel reserves decline. However, there exists a dearth of literature on the design considerations that would lead to process optimization in the development of anaerobic digesters aimed at creating useful commodities from the ever-abundant municipal solid-waste. Consequently, this paper provides a synthesis of the key issues and analyses concerning the design of a high-performance anaerobic digester.Anaerobic digesters Biogas Design parameters Economic considerations Municipal solid-waste Technical considerations