The effect of the minerals on the activated carbon on NO adsorption efficiency was studied

Parametric studies on the production of activated carbon and the adsorption of NO by the carbon have been conducted. The optimal conditions and effectiveness of this procedure to regulate NO emissions have been determined.The activated carbons were characterized by the measurement of their average pore size and surface area. There are three types of pores which can develop in the carbon particles: micro-pores , mesopores and macropores . BET surface area of wheat straw char carbonized at temperatures between 300°C and 700o C is shown in Fig.3. The surface area passes through a maximum of 105.2 m2 /g at a pyrolysis and activation temperature of 600o C and 650o C respectively. The BET surface area of sweet potato stalk exhibits similar behaviors as that of wheat straw, being 88.1 m2 /g, 84.7 m2 /g, and 132 m2 /g at a pyrolysis temperature of 300°C, 400°C, and 600°C, respectively. The decrease in surface area beyond 600°C is caused by sample burning off. Using temperatures much lower than 600o C would compromise the maximum amount of effective adsorption surface area attainable . It is not only important to run reactions at temperatures low enough to prevent burn off and ash formation but also high enough to generate effective surface areas, which would be at 600o C for wheat straw. Fig.4 shows the BJH adsorption cumulative pore area of wheat straw activated carbon generated at different pyrolysis and activation times. It is evident from the plot that samples derived from longer pyrolysis and carbonization times exhibited a higher micro-pore count compared to shorter times. As with temperature generation optimum, however,greenhouse pot too long pyrolysis and activation reaction times cause an adverse increase in burn off percentage. Though wheat straw carbonized with a pyrolysis time of six hours and activation time of 2 hours still demonstrated a higher cumulative pore area than the shorter times, it also produces larger amounts of burn off. Since reaction temperatures were kept below 600o C, ash formation that would have diluted effective surface area was prevented.

Even though ash does not form, pyrolysis and activation times must still be chosen to create a balance between pore formation and burn off, one that would generate a high micro-pore count but at the same time, minimize material loss. The optimal pyrolysis and activation times for wheat straw are 2 hours and 1 hour respectively.Optimal pyrolysis and activation temperatures and times for carbon preparation were determined based on the amount of NOx that can be adsorbed by the activated carbon. The adsorption capacities of wheat straw activated carbons generated by different pyrolysis and activation temperatures are shown in Fig.5. A gas mixture containing 250ppm of NO, 5% O2, 10% CO2, with N2 as the balance was passed, at a flow rate of 250ml/min, through a turbular reactor containing 2g of activation carbon at 25o C. It is evident from the plots that the WS-2-600-1-650 activated carbon had the best adsorption efficiency. Samples carbonized above 600o C have higher ash concentrations than those carbonized below, while those carbonized below have lower percent micro-pore counts and surface area—both explaining why wheat straw generated at 600o C had the best adsorption efficiency. The NO adsorption efficiencies of wheat straw samples carbonized by differing pyrolysis and activation times are shown in Figure 6. It is evident from the plots that activated carbons carbonized by prolonged pyrolysis and activation times have better adsorption efficiencies than those carbonized by shorter times due to higher pore count and BET surface area. The micro-pore count and the surface area of activated carbon increases with an increase of the preparation time, which explains why the samples with the longest pyrolysis and activation times have the best adsorption efficiencies. However, prolong activation results in more burnoff and the production of ash. A balance must be reached when setting reaction parameters, one that will generate the largest surface area without a significant burnoff. We have found that the optimal pyrolysis and activation times for wheat straw are two and one hour, respectively. The hydroponic biomass possesses high mineral content. The activated carbon was first soaked in water to dissolve the soluble minerals and then dried to remove the moisture from the carbon particles. The adsorption experiments using the mineral-free activated carbon were performed and the results indicate that the NO adsorption efficiency was substantially improved .

A 100% NO removal efficiency was obtained for the entire 2 hr experiment, using a gas mixture containing 250 ppm NO and 10% O2 and at a W/F of 30g.min.L-1. The improved NO removal efficiency by the activated carbon with mineral removed is attributed to the increase of the carbon surface area, which was otherwise covered by the minerals. Because of this finding, the parametric study on the NO removal efficiency was performed mostly with the activated carbon having mineral content removed by water dissolution. The adsorbed NO can be desorbed from the activated carbon if temperature of the carbon bed is raised. Further increases of temperature results in the reduction of NO by activated carbon to produce N2. Simultaneously, the activated carbon is regenerated as a result of the reduction of NO to N2. Experiments on the reduction of the adsorbed NO by the activated carbon were performed by heating the NO saturated carbon under anaerobic conditions. In order to evaluate the behavior of the process over time, a purge gas flow of 1.0 L/min N2 was passed through the carbon bed and subsequently directed to the NOx analyzer. Desorption was conducted with a temperature ramp rate of 40°C/min from room temperature to 600o C. As the temperature of the carbon bed was increased, NO was desorbed from the surface of the activated carbon. Further increase of the temperature results in the reduction of NO by the activated carbon to N2. The fraction of the adsorbed NO that is reduced to N2 can be calculated by subtracting the NO coming out of the carbon bed from the total amount of NO adsorbed. The fraction of the adsorbed NO that is reduced depends on the temperature and the flow rate of N2 gas. Fig.13 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 was less than 100% of the total NO adsorbed, 38.5% and 9.1% for sweet potato and wheat straw activated carbons, respectively. The difference of which is attributed to the reaction of NO with the activated carbon to form N2. From the desorption curve as a function of temperature, the NO desorption mainly took place at temperature below 450°C, while the NO reduction by carbon occurred at temperature above 450°C,30 plant pot the higher the temperature the more effective the reduction is. 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 500°C and W/F between 10 and 40 g.min/L. Fig.14 shows that, in the case of the sweet potato activated carbon, 100% of NO was reduced to N2 at 500°C with a W/F above 10 g.min./L, while at 450°C it would require a W/F above 30 g.min./L. For wheat straw activated carbon, NO can be reduced to N2 at lower temperatures and smaller W/F ratios than those of sweet potato . All inlet NO was reduced to N2 at 450°C with a W/F above 15g.min.L-1. Higher temperatures or larger W/F ratios are favorable for NO reduction. The NO reduction efficiency also depends on the concentration of NO in the system. Fig. 16 shows NO reduction by sweet potato and wheat straw activated carbons at 450C with two inlet NO concentrations, 250 ppm and 1000 ppm. The results indicate that the higher the inlet NO concentrations, the smaller the fraction of the inlet NO is reduced at a given W/F. All of inlet NO was not reduced to N2 by the sweet potato activated carbon until the W/F reached 30 g.min/L and 40 g.min/L for 250 ppm and 1000ppm of inlet NO respectively. The activated carbon made from wheat straw can reduce NO more effectively than that from sweet potato. The entire inlet NO was reduced by the wheat straw activated carbon with a W/F of only 15 g.min/L and 30 g.min/L for 250ppm and 1000ppm of NO, respectively. The space maximum allowable concentration of NO in a human occupied cabin is 4.8ppm. Experiments were conducted to determine conditions for NO adsorption on SP-2-600-1-650 at room temperature such that the NO concentration exiting the carbon bed is less than 4.8ppm. The activated carbons before and after the removal of minerals with water dissolution were both examined. The parameters studied included inlet oxygen concentration , and carbon weight to flue gas flow rate ratio . The time that the carbon bed can hold before the NOx concentration exiting the bed exceeds the SMAC will be called SMAC time. Fig.17 and 18 show that the SMAC time for both activated carbons increase with the increase of W/F and oxygen concentrations. The removal of minerals from the activated carbon increases the surface areas and results in a much longer SMAC time. The SMAC time was 22 min., 30 min., 36 min., and 62 min. with a W/F of 45 g.min/L when flue gas contains 5%, 8%, 10%, and 15% O2, respectively using the activated carbon containing mineral. However, the SMAC time was substantially increased to 145 min, 215 min, 330 min, and 500 min at a W/F of 45 g.min/L with flue gas containing 5%, 8%, 10%, and 15% O2 using the activated carbon with mineral removed. 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. 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 were determined to be about 0.99% for wheat straw and 0.49% for sweet potato stalk activated carbon per cycle of regeneration at 600°C. Lastly, due to the extent of the mission, the sufficiency of the amount of inedible biomass in providing the activated carbon for the life support systems should be assessed. With a six person crew, such as the mission planned for Mars, the average food consumption is about 0.25kg/d per capita . Six people would need 1.5kg of wheat per day. Wheat straw yield depends on the specific varieties harvested and is widely affected by agronomic and climatic factors. An average ratio of 1.3 kg of straw per kg of grain is found for most common varieties . Burnoff accounts for about 66.7% at 600o C in pyrolysis and 650o C in activation, while the loss of carbon mass from soaking and drying was determined to be about 14.4%. So as a result, 203kg of wheat straw activated carbon can be produced per year. By incinerating feces, inedible biomass and trash, between 3g and 30 g of NOx can be produced per day, depending mostly on the amount of nitrogen in the inedible biomass. The range in the amount of NOx produced covers 90% pre-treatment removal of nitrogen to no pretreatment . . About 10% of nitrogen in the waste forms NOx . Regeneration of the adsorbing activated carbon shall occur once a week via the reduction reaction. The loss of carbon mass was determined to be about 0.99% at 600o C per cycle of regeneration, After one year, all the activated carbon should be incinerated and replaced. Calculations based on the above assumptions yield 210g NO emissions per week, and the adsorption capacity of NO by the activated carbon is 5.46mg/g carbon, which will need at least 38.5kg of wheat straw activated carbon all year long. These can be distributed among one adsorption tank, just with a load of 64.6kg of wheat carbon in the beginning of the year. Every week, the tank should been regenerated.

Collected specimens that were damaged were identified to the closest identifiable morphospecies

Existing literature on the effects of urbanization on species occurrence, abundance, and diversity often relies on urban-rural gradient studies . These studies generally find that increased urbanization decreases the diversity of organisms . Confirming these findings are an abundance of patch-matrix literature suggesting that the quality of the habitat patch itself, its size, and the composition of the matrix surrounding it are determining factors for species occurrence in fragmented landscapes . Specific to UA, higher imperviousness surrounding urban farms has been related to decreased parasitoid abundance and richness , decreased predator abundance and richness , and even decreased predation on sentinel prey . To better understand PH richness and abundance in urban farms and associated biological control services, we conducted an in-situ survey at urban community farms in the East Bay of the San Francisco Bay Area, USA. Eleven farms participated in 2018 and ten farms in 2019. Farms were asked to participate in research based on two factors: 1. farm size, to ensure a comparative sample of small, medium, and large farms, and 2. high or low levels of surrounding impervious surface per the National Landscape Cover Database . Landscape factors and APM practices of farms were measured. APM practices included area of non-crop usage , area of production, crop plant abundance , crop richness, floral richness,plastic plant pot sizes and percent of farm surface with complex ground covers including mulch and leaf litter. Landscape factors included percent of impervious surface at 200-, 500-, and 1000-meter radii. Sampling iterations occurred from May to mid-October each year. On-farm non-crop area was defined as a not actively managed area of the farm occupied by non-crop flora. Farm size in m2 was calculated through Google Earth Pro and ground-proofed during on-farm spatial measurements. Brassica abundance was determined by counting all brassicas on the farm when sampling occurred.

Crop plant richness was determined by eight meter transects measured perpendicular to garden beds three times during the growing season. Different cultivars of the same species were counted separately when measuring crop richness. Floral richness was surveyed three times per growing season by completing a comprehensive count of each flowering plant at each survey site. Randomized 4m2 quadrats were used to estimate percent of and type of cover . Ground cover quadrats were measured across crop and non-crop areas. Percent of surrounding impervious surface for each farm was measured using the NLCD at 8m resolution .Collection of PH was accomplished by using an insect vacuum on Brassica oleracea cultivars, including broccoli, kale, collards, and tree collards. Each sampled plant was randomly selected and was only sampled if it was standing free of other herbaceous cover and flowering plants. A total of nine plants of each cultivar present were sampled per visit. Vacuum sampling occurred monthly from May to October. Vacuuming of each plant lasted for five seconds. For this work, we assume that sampled wasps were performing foraging or host-seeking behaviors on selected plants . Each sample was frozen until processed by extracting all PH and identifying them to the lowest taxonomic level possible per previous literature . PH identification was accomplished using Hymenoptera of the World . Chalcidoidea were identified with the Annotated keys to the Genera of Nearctic Chalcidoidea , and Braconidae using the Manual of the New World Genera of the Family Braconidae .Cabbage aphids, Brevicoryne brassicae were visually identified and abundance was assessed by doing a total count on three random leaves on nine brassicas per cultivar, including counts of apterous, alate, and parasitized aphids. Aphid abundance counts were performed monthly from May to October on non-vacuum sampling days to reduce PH disturbance. Parasitism rates were calculated as number of parasitized aphids divided by number of total aphids on each leaf.

Generalized linear mixed models were constructed using the MASS R package to explore whether APM practices or landscape factors affected PH abundance on common brassicas. Each response variable: All PH, PH super family, family, and subfamily abundance, overall site PH diversity, and rates of aphid parasitism were modeled with both local and landscape factors. Local factors include the percent of mulch ground cover, floral and crop richness, production, and non-crop area. Landscape factors include percent impervious surface at 200, 500, and 1000m radii, and farm size. Seasonal factors included both year and season and were assessed as categorical variables: early-season , mid-season , and late-season . The fitdistrplus package in R was used to find appropriate distributions for modeling . A negative binomial or Poisson distribution with a log link function was selected as appropriate given the zeroinflation of the count data. Models were fitted with the glmer.nb or glmer function in R package MASS . Preliminary models with all measured local and landscape factors were constructed for each response variable. Explanatory variables of low importance for all response variables were excluded from subsequent models. Final models were assessed for fit using the Akaike Information Criterion and diagnosed for over or under-dispersion by comparing observed residuals with expected residuals using the DHARMa package in R. Poorly fitted models were excluded from the results . Partial regression plots for final models were developed using the “effects” package in R and are reported in Results . The slope of the line in these plots represents the association between a single explanatory variable and a response variable accounting for the effects of each other variable within the fitted model.To test the local and landscape effects on the enemies hypothesis vis-a-vis APM on populations of PH in urban agroecosystems, we collected data from twelve urban farms in the San Francisco Bay Area over a period of two growing seasons. Participating farms were selected to represent a continuum of size, spatial composition, and surrounding imperviousness.

Non-crop area was a significant predictor for all PH, cynipoid, and braconid wasps. Effects of APM practices were varied, but increased crop richness and mulch coverage were associated with increased abundance of all Chalcidoidea, including the Aphelinidae. Increases in crop richness also showed an increase in parasitism rates of aphids on brassica crop plants. Unexpectedly, Floral richness showed a negative relationship to the abundance of all PH, as well as chalcids, and all Braconidae. All PH showed a significant decline in abundance during the late season of 2019. All measures of impervious surface surrounding urban farms had no effect on PH abundance or aphid parasitism on the urban farms. Landscape effects to arthropod mediated ES continue to have mixed results and this research supports previous findings in urban agriculture which show both negative and positive effects to natural enemy abundance and diversity . Non-crop areas identified in this research are difficult to identify explicitly as either managed or unmanaged and existed on a spectrum that was often difficult to quantify in interviews or through survey work. However, these areas most frequently had been improved with flowering perennials or annuals, medicinal or “native” flora, and farmers typically stated the purpose as providing a resource for wildlife or beneficial insects. Previous research supports farmer efforts. Structural diversity has been found to elicit positive responses with regard to diversity and abundance of predators and PH in previous UA studies . These areas may provide critical over-wintering habitat in annual cropping systems,blueberry plant container additional hosts or prey, shelter, floral nectar resources for nectarivorous insects . Our findings suggest that these non-crop areas have the potential to influence agroecosystem function in UA, and may be an important part of APM practices, even in highly fragmented landscapes. Moreover, floral richness had little effect on PH abundance, or parasitism of aphids, signaling that increase in PH abundance were not due to floral nectar within these non-crop areas. Another mechanism that may be of importance are the spatial composition of the agroecosystem. Our research did not take into account the overall distribution of non-crop area within the farm, which may have failed to account for spatial heterogeneity that has been found to illicit positive and negative biological control responses in agroecosystems . Future research on urban farms should account not only for the proportion of non-crop areas, but also spatial heterogeneity to further explore these effects. Overall, APM practices, such as increased mulch coverage and crop plant richness were important predictors of PH abundance, and increased aphid parasitism rates. The connection between mulch, complex ground covers, and increased abundance and diversity of parasitic wasps has been previously observed in urban agroecosystems , a variety of natural habitats, and rural agroecosystems . It is unlikely that mulch would provide a direct resource for PH, but PH may benefit from mulch as a potential overwintering habitat or it may provide habitat for potential hosts. Many of the collected PH were parasitoids of dipteran larvae; these larvae are herbivorous but complete part of their life cycle in soils. I suggest that the overall biodiversity of urban farms with increased mulch coverage may create a bottom-up trophic cascade that increases overall soil arthropod diversity benefiting PH populations. Floral richness had a negative effect on PH abundance in all models. Floral richness was chosen as an explanatory variable as it has previously been found to increase PH abundance in UA . The vast majority of PH are nectarivorous, and this additional nectar resource has been suggested frequently as a strategy for increasing populations, potentially leading to increased parasitism . However, conflicting data raises questions about this on farm manipulation and whether PH seek hosts in the same area they feed, or they disperse to increase fecundity . A large proportion of our overall sample of PH were cynipoids, potentially from the genus Alloxysta, known hyperparasitoids of both dominant primary aphid parasitoids in our sample, Aphidiinae, and Aphelinidae . These reductions in primary aphid parasitoid populations may be due to direct or indirect negative effects from this hyperparasitoid that also feeds on floral nectar . In urban agroecosystems, floral provisioning as a habitat manipulation may be complicated by the inherent fragmentation and quality of the urban matrix.

For floral resources to be an effective APM practice, this resource must be limited. Potential concentrations of alternate off-farm floral resources may complicate this affect. While this research expanded upon previous findings and can be of utility for urban agroecosystem management, many questions remain. Firstly, the effects of hyperparasitism on biological control in UA. Our third most collected taxon was Cynipoidea, many of which are often hyperparasitoids of aphid parasitizing wasps . Given that these cynipoids were collected from plant foliage in close proximity to many primary aphid parasitoids, there is some anecdotal evidence that these cynipoids were engaging in host-seeking behavior. If some of the measured on-farm management practices, such as increased non-crop areas also increase abundance of Cynipoidea, this could result in decreased biological control services. In this case, floral provisioning may potentially be acting as an ecosystem disservice . Unfortunately, we were unable to collect parasitized aphids and rear any hyperparasitoids during this research, but these findings suggest that hyperparasitism in fragmented UA landscapes may be a mechanism affecting APM strategies in UA. Crop plant richness positively affected the abundance of all Chalcidoidea and the subfamily Aphelinidae. Crop richness was also a predictor of greater parasitism rates of cabbage aphids on sampled brassica. Similar findings in rural and urban agroecosystems, including increased PH abundance and biological control services in relation to increased crop diversity have been previously documented . Given that intercropping is commonly practiced in UA, these results validate the efficacy of the practice, and offer an opportunity to investigate the extent of the effect in future research efforts. 4.3 Seasonal factors Seasonal effects on PH abundance were mixed, but many affects were measured in the second year of our sampling. Of note, in 2019, we had fewer sampling events as one farm was unable to participate in our study, but more PH were collected in that year despite the smaller sampling pool. Rates of aphid parasitism were significantly decreased between mid- and late season in 2019. It is unknown what drove these effects, but notable that such a significant difference could occur between sampling seasons. Future research efforts should consider seasonal differences and weather when drawing conclusions about on-farm or landscape factors to PH abundance or diversity or associated biological control services.