The fraction of the adsorbed NO that is reduced depends on the temperature and the flow rate of N2 gas. Fig.10 shows the fraction of the desorbed NO integrated over the temperatures as the temperatures of the carbon bed was raised. As can be seen, the fraction of the total NO desorbed as NO reaches the maximum at 550°C and that this fraction was less than 100% of the total NO adsorbed, the difference of which being attributed to the reaction of NO with the activated carbon to form N2. The fraction of the adsorbed NO desorbed as NO is 48.2% in the case when NO adsorption was done without the presence of H2O vapor, and 64.5% in the case when NO adsorption was performed with 2% H2O. This result indicates that NO reduction by activated carbon is inhibited by the presence of water vapor. Water vapor can compete with NO for the reaction with activated carbon. From the desorption curve as a function of temperature, the NO desorption mainly took place at temperature below 300°C, while the NO reduction by carbon occurred at temperature above 300°C, the higher the temperature the more effective the reduction is. Since the ramp rate was 40°C per min., it would take 7.5 minutes to raise from 300°C to 600°C, the temperature range when most of the NO reduction takes place. During the 7.5 min. time interval, about 50% of the adsorbed NO was reduced to N2. Consequently, it can be concluded that the complete reduction of NO to N2 at 550°C can be done within 15 minutes in a closed system. Another set of experiments were performed to study the reduction of NO by activated carbon as a function of temperature and W/F, the ratio of the amount of carbon to flow rate of N2. In this study, temperatures were varied between 300 and 550°C and W/F between 10 and 40 g.min/L. Fig. 11 shows that with a feed gas containing 250 ppm NO with the balance N2,indoor growers the fraction of NO reduced by activated carbon increases with the increase of temperature at a given W/F, and the fraction also increases with the increase of W/F at a given temperature.

All of NO was reduced to N2 at 550°C with a W/F above 20 g.min/L, and at 500°C with a W/F 40 g.min/L. It would require a W/F larger than 40 g.min/L to convert all of NO to N2 at temperature below 500C. The NO reduction efficiency also depends on the concentration of NO in the system. Fig 12 shows NO reduction at 500°C for two inlet NO concentrations, 250 ppm and 1000 ppm. As can be seen, higher inlet NO concentrations cause less fraction of NO to be reduced. Only 55% of inlet NO was reduced at 500°C with an inlet NO concentration of 1000ppm and a W/F of 40g.min.L-1. Experiments were conducted at room temperature using rice hull activated carbon to determine at what conditions it would prolong efficient adsorption of NO and that outlet concentrations would be less than SMAC . The principle variables manipulated were inlet oxygen concentration, ranging from 5% to 20%, and weight to flow rate ratio , ranging from 15 to 45 g.min/L . The time that the carbon bed can hold before the NOx concentration exiting the bed exceeds the SMAC, will be called SMAC time. Fig.13 shows SMAC time at different oxygen concentrations. The SMAC time increases along with increases in O2 concentrations. The SMAC time was longer than 6 hours with oxygen concentration of 10% and W/F of 45 g.min/L, while about 10 hours were obtained with an 15% oxygen and W/F of 45 g.min/L. As previously mentioned, oxygen presence enhances NO adsorption, thus allowing the SMAC time to be longer. Increasing W/F, especially above 20g.min/L, also increases the SMAC time. Experiments were conducted to determine the effects of the regeneration on activated carbon in terms of NO removal efficiency, as assessed by the carbon’s SMAC time. Fig.14 shows the SMAC time after different numbers of regeneration cycles. The results indicate that regeneration improves the removal efficiency of NO. This phenomenon is attributed to the increase of surface area and micro-pores of the activated carbon. However, it was observed that additional carbon burns off occurs during regeneration, which causes the overall amount of activated carbon to decrease after each regeneration cycle. The loss of mass was determined to be about 0.16% of activated carbon per cycle of regeneration.

The SMAC time was 163 minutes and 372 minutes for the first and the 8th cycle run, respectively. The larger the activated carbon adsorption efficiency, the longer the SMAC time will be. Currently the world’s human population is concentrated on the coast with estimates ranging from 40-60% of this population living within 100km of the coastline . As of 2006 world population has moved past 6.5 billion with an expected increase of 40% by 2050 . This equates to approximately 2.6 billion additional people by 2050 for a total of approximately 9.1 billion souls living on and consuming resources on Earth. Ninety five percent of current human population growth is concentrated in the developing world and this trend is expected to continue through this century. Further the growth in and migration to coastal regions is expected to increase over the coming decades . Using the above estimates conservatively, by 2050 it is likely over 6.4 billion people will live within 100km of the world’s coastline. This is just shy of the world’s current total population concentrated within 100km of the coast. Given that 95% of this projected increase in human population will be in the developing world, the majority of this mass of people will be concentrated in tropical and subtropical regions with much of the growth adjoined to tropical marine ecosystems . Further, a large portion of this growth arguably will be concentrated in and around marine biodiversity hot spots, as well as linked terrestrial centers of biodiversity . During this same period the world’s coastal population is undergoing significant expansion, the standard of living is also expected to increase significantly in the developing world where the vast majority of this population growth is expected to occur. Over the coming decades the combination of exploding population and substantial increases in standard of living will lead to a significant increase in the demand for energy and protein by the world’s tropical and subtropical coastal population .The production from world marine capture fisheries has remained essentially flat at about 80 million tones since the mid 1980’s. World inland capture fisheries have increased only slightly over the same period . At the same time world fishing effort over the last 20 years has increased significantly and in many cases this effort now targets species that would not have been considered commercially viable in the past as many traditional stocks are overexploited to the point of commercial extinction .

Clearly the production of world capture based fisheries has peaked and continued over exploitation arguably will lead to even lower production in the future. Aquaculture will be key to meeting future world demand for fisheries products and reducing fishing pressure on the world’s aquatic ecosystems. And, arguably is the only long-term viable option for increasing fisheries production. The data clearly demonstrates this trend, as aquaculture production has provided the only significant increase in world fisheries production over the past 20 years : the same period capture based fisheries have remained flat.While in the long-term aquaculture offers a positive alternative to capture based fisheries, current practice are not sustainable. Of the negative externalities produced by nearly all current aquaculture operations nutrient-rich waste streams, discharged into the surround aquatic environment,danish trolley are generally the most significant problem. This issue likely has the largest negative impact in naturally oligotrophic environments such as most tropical and subtropical marine systems. This in combination with warm sunny conditions equates to a heightened risk to these environments from aquaculture derived nutrients. Tropical marine systems are at risk of significant ecological destabilization even from relatively minor inputs of nutrients such as nitrogen, phosphorous and sugars from aquaculture activities . On the other hand, these same factors –consistent high levels of sunlight, warm water, and an aquaculture supplied nutrient stream– can be harnessed to create an algal culture system to remove nutrients from aquaculture waste water, and at the same time produce animal feeds, fertilizers and bio-fuels.With the right system in place, nutrients in aquaculture waste water are not “waste” but a valuable commodity. The mechanism proposed by this paper to achieve this outcome is essentially a poly culture system with an output of food, and an additional output of bio-fuels. The system would utilize algal culture for bio-fuel production as a mechanism to remediate nutrient rich aquaculture waste streams. A food and fuel poly culture operation would capture the negative externality of nutrient discharge into the environment and convert it to a net benefit for the poly culture enterprise, as well as a positive externality to the surrounding community and ecosystem . The primary external inputs to a FFP system would be solar energy, water and nutrients in the form of animal feeds and fertilizers. The system would provide food and work in the form of energy for electricity, transportation, etc. to the associated human population while having no significant output into the surrounding ecosystem other than clean water . Nutrient loads in the waste water from the agriculture and aquaculture activities would be removed and utilized by the algal culture system to produce bio-fuels. The system’s carbon footprint would be essentially net neutral, as the same amount CO2 produced through the combustion of bio-fuels to produce energy by the system would be taken up by subsequent crops of algae for bio-fuels . Admittedly this is a simplistic analysis of what in application will undoubtedly have other possible unintended impacts on the surrounding ecosystem, such as escape of domesticated stock and/or pathogens from the poly culture operation.

With good poly culture facility design and management, and careful plant and animal stock selection the majority of such issue can be virtually eliminated.Algal culture can produce bio-diesel, ethanol and methane, and may in the future be capable of producing hydrogen . The product of bio-diesel, ethanol and methane through algal culture is similar to current terrestrial production of bio-fuels, but algal culture offers a number of advantages over the current agricultural feed stocks used for bio-fuels such as corn and soybeans. The main advantage being most algae species are significantly more energetically efficient than any terrestrial plant species. Microalgae are particular efficient, with many species conservatively 10-20 times more energetically efficient than terrestrial plants . Figure 4 provides a simplified overview of the bio-fuel production process for algae as a feed stock to produce bio-diesel, ethanol and methane. Bio-diesel production is the simplest and least energy intensive of the three. Oil derived from algal culture is combined with 10-14% alcohol by volume and a catalyst in a simple reactor. The catalyst initiates a chemical process known as transesterification in which the glycerin in the oil drops out and is replaced by the alcohol.The reaction occurs efficiently at relatively low temperatures: 110-120 °F . Ethanol is produced through yeast based fermentation of algae derived starches and sugars. The fermentation process is simple and non energy intensive, but distillation requires large amounts of energy to heat the fermented product in the distillation process. Methane is produced through digestion of algae derived organic matter by methanogenic microbes. The digestion process is moderately simple and can produce heat energy as a byproduct, but for methane to be usable as a fuel it must either be compressed or liquefied which is energy intensive and mechanically technical. All three of the above bio-fuel production processes have some waste and/or coproduct issues, all of which can be resolved if taken into consideration upfront as part of system design process.While the production of bio-diesel, ethanol and methane can all be incorporated into the bio-fuel part of a FFP system, from this point forward the focus will be on bio-diesel. In most cases the production of bio-diesel will be the more appropriate option in developing world locations. Bio-diesel offers the advantage of a simple low-tech refining process, relatively low energy input and easy and safe storage, handling and transport when compared to ethanol and methane.