Comparative Evaluation of Batch and Continuous Anaerobic Digesters in Biogas Production from Municipal Solid Waste using Mathematical Models

An investigation was conducted into the suitability of either of the batch or continuous (CSTR) digesters for anaerobic degradation of municipal solid waste (MSW) in the production of biogas. Mathematical models were developed for the design and evaluation of the two systems. The development of the models was based upon a material balance analysis of the digesters'operation. A Microsoft Visual Basic Version 6.0 Programme was developed for the solution ofthe model equations, and the digesters' operations simulated over a range of percentage total solids (PTS) concentration of 4-10% for the CSTR and 4-30% for the batch digester, and fractional conversion of 0.2-0.8. The results of the simulation show that although the amount of methane (0.0764m3) produced per unit volume of the batch digester is about 4 times less than the amount (0.284m3) per unit volume of the CSTR, the cost per unit volume of the batch digester ($5.98) is 6 times less than that of the CSTR ($33.8), suggesting that the overall cost of producing gas with the batch digester would be more economical. So, it was deduced that the batch digester is better suited for the digestion of MSW for biogas production, compared to the CST

Performance of irrigated maize in a crude-oil polluted soil remediated by three nutrients in Nigeria's Niger Delta

An in-situ simulated crude-oil polluted soil was remediated for 8 weeks by three different nutrients, and then used to plant maize (Farz 26) with a growth period of 14 weeks, with an irrigation depth of 4mm/day. Remediation consisted of the application of 16.667, 22.222, and 27.778 t/ha of NPK (15:15:15) fertilizer, spent mushroom substrate (SMS), and pig slurry (PS) to the polluted soil, laid out in randomized complete block design, with three replications, including a control that was neither polluted nor treated. Physico-chemical and microbial properties of the soil before and during remediation, and growth parameters of the maize were determined. Results indicated that 8 weeks after remediation, 27.778 t/ha of NPK, PS, and SMS reduced total hydrocarbon content (THC) by 87.3, 91.2, and 88.6% respectively. For maize, 14 weeks after planting resulted in a yield of 1.11, 1.20, and 1.17 t/ha from the soil remediated by 27.778 t/ha of NPK, PS, and SMS respectively, while the control yielded 2.58 t/ha. The difference in yields between the control and the remediated soils was significant at 5% level. The result indicated a 53.5% reduction in yield mainly due to the non-restoration of the soil to its original status

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

Emission from Uyo Main Refuse Dumpsite and Potential Impact on Health

This paper presents potential impact on health of emission from landfill site on Uyo village road, Uyo local government area of Akwa Ibom State, Nigeria. Three sampling points were assessed for particulate matter (PM2.5 and PM10), nitrogen dioxide (NO2), sulphur dioxide (SO2), carbon monoxide (CO), hydrogen sulphide H2S, ammonia (NH3), total volatile organic carbon (TVOC) and hydrogen cyanide (HCN) using highly sensitive digital portable meters. The data obtained were expressed in terms of an air quality index. Air quality index indicates that the ambient air can be described as unhealthy for sensitive groups for NO2, unhealthy for SO2 and PM2.5 and moderate for CO, respectively. H2S, NH3, TVOC, HCN, PM10 were not indicated in USEPA air quality standards. It recommended that stringent and proper landfill emissions management together with appropriate burning of wastes should be considered in the study area to ease the risks associated with these pollutants on public health

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