A laboratory scale of biogas production using anaerobic digestion of date palm wastes (DPWs) was conducted. The effects of pretreatment of substrate, pH, temperature and type of substrate (dry waste and fresh waste) on the biogas production were investigated in batch mode digesters, also the addition of nitrogen source to reduce the carbon to nitrogen ratio (c/n) was investigated. The results revealed that mesophilic conditions of 35 o C give the highest biogas production, pH below 6 will inhibit the biogas production, and the production of biogas from fresh waste is higher than the dry waste. The percentage of methane gas in the produced biogas reaches 48 % for fresh waste with addition of nitrogen source, the results were encouraging to carry further studies on methane production from DPWs. Keywords: Anaerobic digestion (AD), biogas production, Date palm tree residues.

This study focuses on stability theory for systems of differential equations, concentrating in particular on systems of first-order ordinary differential equations. For this types of system, definitions of the appropriate stability concepts are provided and considering some important methods of establishing stability for equilibrium points ,whereby one can obtain sufficient conditions for these concepts to apply. For doing this, investigations in detail are made to the methods of Lyapunov for ordinary differential equation systems.

A case study was conducted to investigate the reasons behind decline of a CO2 compressor processing capacity in 1,000 tonne/day urea plant. The suspicious sources and the problem route were investigated. Preliminary investigations revealed that the compressor internals suffers from deposits of white powder. Laboratory analysis showed presence of potassium salts. These deposits are believed to be responsible for this decline in the compressor capacity and consequently, reduction of the urea plant productivity. In periodic events during turn/around or when the productivity reduced significantly, the plant has to shutdown for cleaning the compressor. Deionised water (during T/A, every tow years) or online LP steam (during normal operation period) is used for washing and cleaning. Forced shutdown for one day can simply result in direct losses of production worth of thousands US dollars (urea price > $200/m.t.). CO2 feed to urea plant is supplied from acid gas removal section (Benfield section) in ammonia plant that uses hot potassium carbonate solution as absorption solution. The study methodology to identify the main causes of problem is presented along with brief details on process equipment inspection and evaluation, laboratory analysis, and process simulation. Main findings and future plan of work are presented. Key words: Urea Plant, Benfield Process, Carry-over phenomenon, operational analysis 

There has been rapid change in the land use and land-cover types in Tripoli, Libya in the past decade. The major change is the conversion of agriculture and woodlands into urban area Timel\ deWerminaWion of change in feaWXres aW EarWh¶s sXrface is Yer\ imporWanW for XndersWanding Whe relationship between human and natural phenomena in order to encourage better decision making. Detecting regions of change in multi temporal images of the same scene taken at different times is of widespread interest due to a large number of applications in various fields. Remote sensing data are major sources of information widely used for change detection. This research is concerned with land cover / land use change in the south Tripoli city, Libya between 1989 and 2015. This study focuses on observed changes in six classes: urban areas, woodland, irrigated area un irrigated , grazing land and bare areas. This study used Boolean classification by applying supervised classification for three Landsat images . The result shows that, there is a rapid change in land cover and land use due to increase in population, and human activity, this need more urban, more food, the area of urban class are increases from 988.996 hectors in1989 to 4972 hectors in 2015, the people started cut the forest, build new houses and industrial building over the agriculture area without an organize or plane and the area started a complex to study, and the area of woody land decreases from 7310,169 hectors in 1989 to 6321.96 in 2015 , that is why we need to calculate the change detection and give alert to the decision maker to avoid this problem