Effect of continuous low-concentration ammonia aeration on growth and nitrogen uptake in microalga <i>Botryococcus braunii</i>

The effects of using intermittent aeration during composting on ammonia emissions and dry matter loss were determined during composting of hog manure amended with sawdust. Composting trials lasted three weeks and used pilot-scale 200 liter vessels (four). The experimental design used replication of two treatments, continuous aeration (CA) and intermittent aeration (IA), in two series of experiments (total of eight tests). In the CA sequence, compost temperatures were controlled at 60°C using feedback control on high and low air flow fans while the IA sequence consisted of five minutes of air flow followed by 55 minutes of rest. Mixing ratios of hog manure to sawdust were 1:1.1 and 1:1.7 dry weight basis with resulting C:N ratios of 18.2 ± 1.2 and 23.7 ± 2.2 for the two series of tests. Airflow reduction was 63 percent for IA compared to CA. Percent nitrogen loss between treatments were moderately statistically different (α = 0.14) with average percent nitrogen loss at 29.7 percent for CA and 23.0 percent for IA. Nitrogen loss as ammonia-N was higher for CA than IA (25.9 versus 14.3) but was not statistically different. No significant differences existed in dry solids loss between treatments and the physical and chemical properties of the compost produced from IA were similar to that from CA for each series. Results showed that IA compared to CA may be a practical way to reduce nitrogen loss and ammonia emissions during composting of swine manure with sawdust.

SE—Structures and Environment: Removal of Carbon, Nitrogen, and Phosphorus in Pig Manure by Continuous and Intermittent Aeration at Low Redox Potentials

Reduction in VOC emissions by intermittent aeration in bioreactor landfills with gas-water joint regulation

Low levels of oxygen (O) in the hypolimnion layer of lakes are harmful to benthic animals and fish; they may also adversely affect nutrient cycles. Artificial aeration is often used in lake management to counteract these problems, but the effects of aeration on nitrogen (N) cycling are not known. We studied the effects of hypolimnetic aeration on N dynamics and temperature in a eutrophic lake by comparing continuous and pulsed aeration with a nonaerated station. Aeration decreased the accumulation of NH-N deep in the lake (20-33 m) by supplying O for nitrification, which in turn provided substrate for denitrification and promoted N removal. Aeration also increased the temperature in the hypolimnion. Denitrification rate was highest in the nonaerated deep areas (average, 7.62 mg N m d) due to very high rates during spring turnover of the water column, demonstrating that natural turnover provides O for nitrification. During stratification, denitrification was highest at the continuously aerated station (4.06 mg N m d) and lowest at the nonaerated station (3.02 mg N m d). At the periodically aerated station, aeration pauses did not restrict the increase in temperature but resulted in accumulation of NH-N and decreased the contribution of denitrification as a nitrate reduction process. Our findings demonstrate that hypolimnetic aeration can substantially affect N cycling in lakes and that the effect depends on the aeration strategy. Because N is one of the main nutrients controlling eutrophication, the effects of aeration methods on N removal should be considered as part of strategies to manage water quality in lakes.

To focus on the optimization of immersed ultrafiltration(UF) operation for drinking water treatment, critical flux of the UF membrane and the effect of aeration on it was investigated though the bench-scale experiments. Results show that a critical flux exists in the operation of UF, below which the fouling develops very slowly. The critical flux of UF membrane could be enhanced by both the continuous aeration and intermittent aeration, while the critical flux could not be increased when the aeration intensity exceed a range. It could be seen form the long period of operation that continuous aeration was more effective than intermittent aeration in controlling the membrane fouling.

Effect of artificial aeration on the performance of vertical-flow constructed wetland treating heavily polluted river water

In order to clarify the role of oxygen in the growth and development of rice and its mechanism of nitrogen,three rice genotypes,i.e.,"Guodao 1"(indica),"Xiushui 09"(japonica),and "Brazilian upland rice"(upland rice),were cultured in nutrient solution with continuous aeration to measure the growth-related parameters and the activity of enzymes related to nitrogen me-tabolism at tillering stage.The results showed that,compared with the control,lower chlorophyll content in leaves was found in all the genotypes.The dry weights of shoots and roots were decreased by 44% and 40% for "Guodao 1" under continuous aeration,respectively,whereas no significant effects were observed for the "Brazilian upland rice" and "Xiushui 09".The root length,spe-cific surface area,and the intensity of α-naphthylamine oxidation of roots were increased significantly by continuous aeration,irrespective of the genotypes.The nitrogen accumulation in the "Guodao 1" and "Brazilian upland rice" under aeration was re-duced by 35.8% and 36%,respectively.Therefore,the nitrate reductase activity(NRA) in leaves was significantly increased,while the glutamine synthetase activity(GSA) was decreased under aeration.The NRA in leaves of "Xiushui 09" under continu-ous aeration tended to increase(P 0.05) in comparison to the control.Thus,continuous aeration could increase the surface area and oxidation intensity in rice roots,and reduce the chlorophyll content and GSA in rice leaves,which may reduce nitrogen ab-sorption and dry matter accumulation.In addition,these were significant differences in responses of rice genotypes to continuous aeration.

Investigation of nitrogen metabolism of phytoplankton, especially their nitrogen uptake, started in the eighties concerning to the eutrophication of Lake Balaton. The experiments were carried out in two basins of the Lake and its two pollution control reservoirs (Marcali and Upper Kis-Balaton). Detailed description of these waters is given by Herodek and Voros in this volume. Due to the low ambient concentrations of ammonium, nitrate and urea the 15 N technique was the only useful method to determine the nitrogen uptake of algae. N2-fixation was measured by acetylene-reduction and the primary production by 14 C method. The light dependence of nitrogen and carbon uptake was described with an exponential saturation equation and used for the calculation of surface related daily uptake. The results showed a high preference of algae for ammonium in all of the investigated waters. Its contribution to the daily nitrogen supply of phytoplankton varied between 50 - 90%. Despite its higher ambient concentrations nitrate uptake was generally less important with maximum of 40%. The interaction of ammonium and nitrate uptake demonstrated suppression of nitrate uptake at ammonium addition. After ammonium, urea was the other important nitrogen source of algae reaching up to 75% of daily nitrogen assimilation. N2- fixation was significant only at the time of high primary production and great nitrogen fixing cyanobacterial contribution. Nitrogen uptake experiments and loading data of the Lake suggest that annual external nitrogen load is one tenth of that utilised by algae. The predominant process supplying nitrogen to the phytoplankton is the regeneration of nitrogen in the water column and in the sediment.

High production and efficient harvesting of microalgae containing high omega-3 levels are critical concerns for industrial use. Aeration can elevate production of some microalgae by providing CO2 and O2. However, it may lower the production of others by generating shear stress, causing severe cell damage. The mixotrophic dinoflagellate Gymnodinium smaydae is a new, promising microalga for omega-3 fatty acid production owing to its high docosahexaenoic acid content, and determining optimal conditions and methods for high omega-3 fatty acid production and efficient harvest using G. smaydae is crucial for its commercial utilization. Therefore, to determine whether continuous aeration is required, we measured densities of G. smaydae and the dinoflagellate prey Heterocapsa rotundata in a 100-L semi-continuous cultivation system under no aeration and continuous aeration conditions daily for 9 days. Furthermore, to determine the optimal conditions for harvesting through centrifugation, different rotational speeds of the continuous centrifuge and different flow rates of the pump injecting G. smaydae + H. rotundata cells into the centrifuge were tested. Under continuous aeration, G. smaydaeproduction gradually decreased; however, without aeration, the production remained stable. Harvesting efficiency and the dry weights of omega-3 fatty acids of G. smaydae + H. rotundata cells at a rotational speed of 16,000 rpm were significantly higher than those at 2,000–8,000 rpm. However, these parameters did not significantly differ at injection pump flow rates of 1.0–4.0 L min-1. The results of the present study provide a basis for optimized production and harvest conditions for G. smaydae and other microalgae.

The effect of aeration on treatment efficiency and bioenergy generation of septic-tank effluent in constructed wetland-microbial fuel cell

Effect of aeration modes and influent COD/N ratios on the nitrogen removal performance of vertical flow constructed wetland

Intermittent aeration of landfill simulation bioreactors: Effects on emissions and microbial community

Oxygen dynamics, organic matter degradation and main gas emissions during pig manure composting: Effect of intermittent aeration

Removal of pharmaceuticals by a pilot aerated sub-surface flow constructed wetland treating municipal and hospital wastewater

Effects of intermittent and continuous aeration on accelerative stabilization and microbial population dynamics in landfill bioreactors