No abstract

The objective of this research was to investigate the performance of a hollow fibre membrane bioreactor (HFMB) for hydrogenotrophic denitrification of contaminated drinking water. In the HFMB, H 2 flows through the lumen of the hydrophobic hollow fibres and diffuses to an attached H 2 oxidizing biofilm. Nitrate in the contaminated water serves as an electron acceptor. A hydrogenotrophic denitrifying culture was enriched from a wastewater seed. Batch culture experiments were conducted to compare heterotrophic (methanol as electron donor) and hydrogenotrophic denitrification rates and to investigate the conditions required for the HFMB studies. The batch cultures demonstrated mixotrophy, with denitrification rates of 30 g NO − 3-N m −3 d −1 for heterotrophic and 18 g NO − 3-N m −3 d −1 for hydrogenotrophic conditions. A laboratory-scale HFMB was constructed that utilized 2,400 polypropylene hollow fibres with an inner diameter of 200 m, an outer diameter of 250 m and a 0.05 m pore size. After a 70-day start-up period, the NO − 3 loading rate was gradually increased over a three-month period. The NO − 3 utilization rate reached a maximum of 770 g NO − 3-N m −3 d −1 at an influent NO − 3 concentration of 145 mg NO − 3-N l −1 and a hydraulic residence time of 4.1 hours. Influent NO − 3 concentrations of up to 200 mg NO − 3-N l −1 were almost completely denitrified. Tests with contaminated water from the Cape Cod aquifer resulted in an increase in product water turbidity and dissolved organic carbon (DOC) concentrations.

Removal of nitrogen from anaerobically digested swine manure centrate was investigated in a photo-sequencing batch reactor (PSBR) with alternating light and dark periods. Microalgal photosynthesis was shown to provide enough oxygen for complete nitritation during the light period. With addition of an organic carbon source during the dark period, the reactor removed over 90% total nitrogen (TN) without aeration other than by mixing. Overall, 80% of the TN removal was through nitritation/denitritation and the rest was due to biomass uptake. The high concentrations of ammonia and nitrite and low dissolved oxygen concentration in the PSBR effectively inhibited nitrite oxidizing bacteria, resulting in stable nitritation. The hybrid microalgal photosynthesis and shortcut nitrogen removal process has the potential to substantially reduce aeration requirements for treatment of anaerobic digestion side streams. The PSBR also produced well settling biomass with sludge volume index of 62 ± 16 mL mg(-1).

Microalgae feedstock production can be integrated with wastewater and industrial sources of carbon dioxide. This study reviews the literature on algae grown on wastewater and includes a preliminary analysis of algal production based on anaerobic digestion sludge centrate from the Howard F. Curren Advanced Wastewater Treatment Plant (HFC AWTP) in Tampa, Florida and secondary effluent from the City of Lakeland wastewater treatment facilities in Lakeland, Florida. It was demonstrated that a mixed culture of wild algae species could successfully be grown on wastewater nutrients and potentially scaled to commercial production. Algae have demonstrated the ability to naturally colonize low-nutrient effluent water in a wetland treatment system utilized by the City of Lakeland. The results from these experiments show that the algae grown in high strength wastewater from the HFC AWTP are light-limited when cultivated indoor since more than 50% of the outdoor illumination is attenuated in the greenhouse.An analysis was performed to determine the mass of algae that can be supported by the wastewater nutrients (mainly nitrogen and phosphorous) available from the two Florida cities. The study was guided by the growth and productivity data obtained for algal growth in the photobioreactors in operation at the University of South Florida. In the analysis, nutrients and light are assumed to be limited, while CO2 is abundantly available. There is some limitation on land, especially since the HFC AWTP is located at the Port of Tampa. The temperature range in Tampa is assumed to be suitable for algal growth year round. Assuming that the numerous technical challenges to achieving commercial-scale algal production can be met, the results presented suggest that an excess of 71 metric tons per hectare per year of algal biomass can be produced. Two energy production options were considered; liquid biofuels from feedstock with high lipid content, and biogas generation from anaerobic digestion of algae biomass. The total potential oil volume was determined to be approximately 337,500 gallons per year, which may result in the annual production of 270,000 gallons of biodiesel when 80% conversion efficiency is assumed. This production level would be able to sustain approximately 450 cars per year on average. Potential biogas production was estimated to be above 415,000 kg/yr, the equivalent of powering close to 500 homes for a year.