Municipal wastewater treatment plants in the USA produce over 6.2 · 10 6 t of dried sewage sludge every year. This microorganism-rich sludge is often landfilled or used as fertilizer. Recent restrictions on the use of sewage sludge, however, have resulted in increased disposal problems. Extraction of lipids from sludge yields an untapped source of cheap feedstock for biodiesel production. Solvents used for extraction in this study include n-hexane, methanol, acetone, and supercritical CO 2 . The gravimetric yield of oil was low for nonpolar solvents, but use of polar solvents gave a considerably increased yield; however, the percentage of saponifiable material was less. Extraction of lipids with a mixture of n-hexane, methanol, and acetone gave the largest conversion to biodiesel compared with other solvent systems, 4.41% based on total dry weight of sludge. In situ transesterification of dried sludge resulted in a yield of 6.23%. If a 10% dry weight yield of fatty acid methyl esters is assumed, the amount of biodiesel available for production in the USA is 1.4 · 10 6 m 3 /year. Outfitting 50% of municipal wastewater plants for lipid extraction and transesterification could result in enough biodiesel production to replace 0.5% of the national petroleum diesel demand (0.7 · 10 6 m 3 ).

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Pecan [Carya illinoinensis (Wangenh.) C. Koch] is indigenous to the Mississippi River drainage system of the United States. Climate in the native pecan region ranges from humid to semiarid and from mild to harsh winters. Rainfall is bimodal with peaks in March to April and in August to September. Pecan is site specific and is the climax tree species on loamy, well drained, first bottom river land with a relatively high water table. Detrimental effects from pecan's shade intolerance from its more vigorous, sympatric species are minimized as these species are specific to differ sites. Pecan's deep and phreatophytic rooting habit ensures soil moisture during drought periods and facilitates pecan's survival in semiarid regions. Root development in the humus-surface layer ensures nutrient uptake from the most nutrient rich layer of the soil and, when the lower soil profile is saturated, aeration for the roots and water and nutrient uptake. The bimodal rain pattern replenishes soil profile moisture and its timing ensures seed germination, stand establishment, well-developed seed, and minimal drought stress. Natural selection for freeze tolerance and for minimum fruit development time allows survival in areas with harsh winters and short growing seasons. Regulation of seed germination and budbreak by heating and chilling results in pecan being native in cold and warm climates, greatly increasing the native range. The northern limit for pecan is dictated by heat units; the southern limit is restricted by lack of bimodal rains and vivipary. Reproductive stress is caused by the high lipid content of seed, but is counteracted by a long juvenile growth period of the seedling, by a small nut size and low percentage kernel, and by “off” production years of the tree. Nut and percentage kernel decrease as the growing season decreases which contributes to species survival in geographical regions with a short growing season. Selection for small nuts with low percentage kernel is enhanced by predators. Tree reserves are depleted by heavy production during “on” years and are replenished during “off”years. Perpetuation of pecan forests is apparently from sib/half sib seedlings following predator satiation while dissemination into new areas may be mainly by predators. Pecan and its pests successfully co-exist. Major defense against fruit feeders is escape in time, leaf feeders by biological associations and accommodation, and leaf diseases by confrontation. Heterozygous progenies from cross-pollination provide ample genetic diversity for continuous pecan selection to endure pressures imposed throughout a wide climatic range. Ecological adaptions within native pecan forests should be used in developing and maintaining commercial pecan orchards.

Extraction of rice bran lipids was performed using supercritical carbon dioxide (SC-CO 2 ) and liquid propane. To provide a basis for extraction efficiency, accelerated solvent extraction with hexane was performed at 100°C and 10.34 MPa. Extraction pressure was varied for propane and SC-CO 2 extractions. Also, the role of temperature in SC-CO 2 extraction efficiency was investigated at 45, 65, and 85°C. For the SC-CO 2 experiments, extraction efficiencies were proportional to pressure and inversely proportional to temperature, and the maximal yield of oil achieved using SC-CO 2 was 0.222 ± 0.013 kg of oil extracted per kg of rice bran for conditions of 45°C and 35 MPa. The maximal yield achieved with propane was 0.224 ± 0.016 kg of oil per kg of rice bran at 0.76 MPa and ambient temperature. The maximum extraction efficiencies of both SC-CO 2 and propane were found to be significantly different from the hexane extraction baseline yield, which was 0.261 ± 0.005 kg oil extracted per kg of rice bran. A simulated economic analysis was performed on the possibility of using SC-CO 2 and propane extraction technologies to remove oil from rice bran generated in Mississippi. Although the economic analysis was based on the maximal extraction efficiency for each technology, neither process resulted in a positive rate of return on investment.

Leaves of `Stuart' pecan [Carya illinoensis (Wangenh.) C. Koch] with various levels of Zn deficiency were analyzed for physiological indicators of leaf vigor. Leaf chlorophyll content, stomatal conductance, and net photosynthesis were adversely affected by Zn deficiency. In leaves with severe Zn deficiency, each of these indicators increased 3- to 5-fold with a doubling of leaf Zn concentration, but stabilized as leaf Zn approached the sufficiency range (14 μg·g-1). High intercellular CO2 associated with low net photosynthesis indicates that stomatal aperture was not the cause of the reduction of net photosynthesis under Zn deficiency.