Influence of solids residence time and carbon storage on nitrogen and phosphorus recovery by microalgae across diel cycles.

Microalgal treatment systems could advance nutrient recovery from wastewater by achieving effluent nitrogen (N) and phosphorus (P) levels below the current limit of technology, but their successful implementation requires an understanding of how design decisions influence nutrient uptake over daily (i.e., diel) cycles. This work demonstrates the ability to influence microalgal N:P recovery ratio via solids residence time (SRT) while maintaining complete nutrient removal across day/night cycles through carbon storage and mobilization. Experiments were conducted with two microalgal species, Scenedesmus obliquus and Chlamydomonas reinhardtii, in photobioreactors (PBRs) operated as cyclostats (chemostats subjected to simulated natural light cycles) with retention times of 6-22 days (S. obliquus) and 7-13 days (C. reinhardtii). Nutrient loading and all other factors were fixed across all experiments. Elevated SRTs (>8 days) achieved limiting nutrient concentrations (either N or P) below the detection limit throughout the diel cycle. N:P mass ratio in algal biomass was linearly correlated with SRT, varying from 9.9:1 to 5.0:1 (S. obliquus) and 4.7:1 to 4.3:1 (C. reinhardtii). Carbohydrate content of biomass increased in high irradiance and decreased in low irradiance and darkness across all experiments, whereas lipid dynamics were minimal over 24-h cycles. Across all nutrient-limited cultures, specific (i.e., protein-normalized) dynamic carbohydrate generally decreased with increasing SRT. Nighttime consumption of stored carbohydrate fueled uptake of nutrients, enabling complete nutrient limitation throughout the night. Dynamic carbohydrate consumption for nutrient assimilation was consistent with dark protein synthesis but less than that of heterotrophic growth, underscoring the need for algal process models to decouple growth from nutrient uptake in periods of low/no light. The ability to tailor microalgal N:P uptake ratio and target an optimal energy storage metabolism with traditional engineering process controls (such as SRT) may enable advanced nutrient recovery facilities to target continuous and reliable dual limitation of nitrogen and phosphorus.

Energy positive domestic wastewater treatment: the roles of anaerobic and phototrophic technologies.

The negative energy balance of wastewater treatment could be reversed if anaerobic technologies were implemented for organic carbon oxidation and phototrophic technologies were utilized for nutrient recovery. To characterize the potential for energy positive wastewater treatment by anaerobic and phototrophic biotechnologies we performed a comprehensive literature review and analysis, focusing on energy production (as kJ per capita per day and as kJ m(-3) of wastewater treated), energy consumption, and treatment efficacy. Anaerobic technologies included in this review were the anaerobic baffled reactor (ABR), anaerobic membrane bioreactor (AnMBR), anaerobic fluidized bed reactor (AFB), upflow anaerobic sludge blanket (UASB), anaerobic sequencing batch reactor (ASBR), microbial electrolysis cell (MEC), and microbial fuel cell (MFC). Phototrophic technologies included were the high rate algal pond (HRAP), photobioreactor (PBR), stirred tank reactor, waste stabilization pond (WSP), and algal turf scrubber (ATS). Average energy recovery efficiencies for anaerobic technologies ranged from 1.6% (MFC) to 47.5% (ABR). When including typical percent chemical oxygen demand (COD) removals by each technology, this range would equate to roughly 40-1200 kJ per capita per day or 110-3300 kJ m(-3) of treated wastewater. The average bioenergy feedstock production by phototrophic technologies ranged from 1200-4700 kJ per capita per day or 3400-13 000 kJ m(-3) (exceeding anaerobic technologies and, at times, the energetic content of the influent organic carbon), with usable energy production dependent upon downstream conversion to fuels. Energy consumption analysis showed that energy positive anaerobic wastewater treatment by emerging technologies would require significant reductions of parasitic losses from mechanical mixing and gas sparging. Technology targets and critical barriers for energy-producing technologies are identified, and the role of integrated anaerobic and phototrophic bioprocesses in energy positive wastewater management is discussed.

Sites of cerebrovascular injury induced by radiographic contrast media.

The object of this study was to determine the type of cerebral vessel affected by injection of radiopaque contrast agents used in cerebral angiography. Seventeen rabbits were prepared surgically for a left intracarotid injection of methylglucamine iothalamate (Conray 60) or methylglucamine diatrizoate (Reno-M-60). Extravasations of the tracers, Evans blue and horseradish peroxidase, occurred in the left half of the brain and occasionally in the right half. Within those areas of blood-brain barrier breakdown, the frequency of leakage was 60% for arterioles, 25% for venules, and 12% for capillaries. The leakage appeared to be primarily intercellular, rather than intracellular. This study provides evidence that greater blood-brain barrier alterations occur in arterioles and venules than in capillaries following cerebral angiography.

Cerebrovasculature permeability changes following experimental cerebral angiography. A light- and electron-microscopic study.

Morphological alterations of the cerebral vasculature as related to the permeability of plasma proteins and angiographic contrast media following unilateral cerebral angiography were studied. Both Evans blue albumin and horseradish peroxidase were employed as protein tracers for light and electron microscopy investigation respectively. Grey matter regions of the cerebral cortex, cerebellum corpus striatum, hippocampus and midbrain showed the most extensive and consistent leakage of these protein tracers. The most extensive penetration of EBA was noted at 1 hr following cerebral angiography as compared to the 5 or 30 min sample times. Permeability changes were noted in small venules and arterioles as well as capillaries. The extent of permeability, however, was appreciably greater in the capillaires as evidences by rapid extravasation of HRP into the surrounding neuropil extracellular spaces. The glial basement membrane surrounding the perivascular spaces of small venules and arterioles precluded rapid penetration of HRP into the neuropil interstitium. Opening of the tight junctions between the endothelial cells was primarily responsible for the extravasation of HRP in all vessel types. Furthermore, it is out opinion that the hyperosmolar nature of the contrast medium is responsible for opening of these tight junctions.