In conventional wastewater treatment, biological nutrient removal (BNR) depends on bacterial assimilation for phosphorus removal and nitrification+denitrification for nitrogen removal, with the resulting loss of the fixed nitrogen resource. Alternatively, treatment by microalgae allows for assimilative removal of both phosphorus (P) and nitrogen (N) thereby avoiding the oxygen demand of nitrification and preserving fixed N for fertilizer use. Paddle wheel mixed high-rate ponds have much higher algal productivity than typical oxidation ponds, but even high-rate ponds often cannot grow sufficient algae to completely assimilate the N and P in domestic wastewater. Algae growth in high-rate ponds is usually limited by the inorganic carbon concentration. Addition of carbon dioxide to high-rate ponds, for example from flue gas, eliminates this limitation and accelerates algae growth and nutrient assimilation. This laboratory study explored the extent to which soluble N and P are removed simultaneously by CO2-enriched algae cultures. Algal polycultures were grown on diluted domestic wastewater media that were manipulated to obtain a wide range of N:P ratios (2.5:1 to 103:1). In addition, two levels of trace metal concentrations were studied. Media feeding was semi-continuous. The variables monitored included N and P removals, the range of N:P ratios in the algal biomass, biomass production, and alkalinity. To achieve removal of total N and P, suspended solids also must be removed prior to discharge. Since flocculation and settling is a preferred method of algae removal, the effects of low dissolved nutrient concentrations and media composition on algae sinking potential (settleability) were also investigated. The low trace metal cultures achieved >99% total ammonia nitrogen (TAN) removal for N:P ratios 2.5 through 30 and >98% dissolved reactive phosphorus (DRP) removal for N:P ratios 2.5 through 60 (with one exception at N:P-20). This removal was due to the growth of 180-500 mg/L algal volatile solids. Effluent concentrations were <0.1 mg/L TAN for N:P 2.5 through 30, and <0.5 mg/L TAN for N:P-60. DRP effluent concentrations were ≤0.02 mg/L DRP. After 24 hours of settling in beakers, nearly all cultures had total suspended solids (TSS) concentrations <40 mg/L. Alkalinity consumption increased with increasing N:P ratios. For cultures with the higher trace metal concentrations, nutrient removal was similar: >96% of TAN and >95.9% DRP removal for all N:P conditions. However, settling with these media was poor. TSS concentrations after 24-h of settling were >100 mg/L. No clear relationship for alkalinity was found for these cultures. N:P ratios in the algal biomass correlated with the N:P ratios in the media, except for control cultures that did not receive wastewater. No relationship was found between settling and the N:P ratios of the media or biomass. Nitrogen-fixing algae thrived in media containing N:P ratios of 2.5:1 and 5:1. Algae were found to be plastic in their cellular N:P ratios (4.6 to 63, with wastewater media) which allowed them to simultaneously remove both dissolved N and P to low levels, while growing settleable biomass. These results indicate that CO2-enriched high rate pond systems would be useful in simultaneously removing N and P from wastewaters with a wide range of N:P ratios.

The main goals of this research are to investigate the anaerobic digestibility of algae and to investigate the effects of growth media on the growth rates, nutrient removal kinetics, and extracellular polymeric substances (EPS) characteristics of wild type green algae. Anaerobic co-digestion of algae with sewage sludge is proposed to improve the digestibility of algae. It is hypothesized that the addition of sewage sludge improves the hydrolysis rate of algae, which is often the rate-limiting step for anaerobic digestion. It is also hypothesized that the composition and concentration of nutrients in growth media will affect the kinetics of nutrient removal and the content of EPS, which will influence algae flocculation and subsequent anaerobic digestion. In this research, algae collected from a local wastewater treatment plant were cultivated in synthetic medium, primary wastewater effluent and pure or diluted anaerobic sludge centrate. Light cycles and the level of CO2 addition were varied at different stages of cultivation for nutrient removal and physiochemical properties of algae. Harvested algae were then anaerobically co-digested with varying proportions of sewage sludge under mesophilic condition. Results showed that when algae were digested alone (i.e. no sludge addition) with a small amount of seed sludge, algae were poorly digested. When algae were co-digested with sewage sludge, the gas yield was improved and the gas phase (CH4 generation) was reached faster. The biogas yield of algae increased to a comparable level to that of digestion of waste sludge when 44% (by VS) of seed sludge was inoculated for digestion. The addition of sewage sludge improved the hydrolysis rate and the overall digestibility of algae. Algae grown in primary effluent, which had a balanced N/P ratio showed a higher nutrient removal efficiency. The P-limitation in sludge centrate led to lower nutrient removal efficiency and higher EPS production compared to algae grown in primary effluent, indicating that sludge centrate was a harsher medium for algae growth. In conclusion, microalgae can grow in primary effluent and anaerobic sludge centrate for nutrient removal. Anaerobic co-digestion of algae withwaste sludge was strongly recommended to enhance the biogas generation.

No description available.

Drainage ditches, or grassed waterways, collect nutrient-laden runoff from agricultural fields and transport it to nearby waterbodies. The high nitrogen and phosphorus content in this water leads to negative effects, such as eutrophication in the receiving waters. In-ditch bioreactors are a simple, inexpensive treatment technology that could potentially remove nitrogen and phosphorus from agricultural runoff. In-ditch bioreactors are intended to reduce flow rate and stimulate denitrification and sedimentation. Using experimental ditch segments and simulated runoff, this study evaluated nutrient removal in 1) vegetated ditches, 2) vegetated ditches with woodchip bioreactors and 3) vegetated ditches with combination woodchip and biochar bioreactors. Biochar was added in an effort to increase phosphorus removal. Inlet and outlet concentrations of nitrate, ammonium and phosphate were measured for each of the three treatments in triplicate. There were no statistically significant differences between treatments on load removed for any of the three nutrients of interest. Issues in measuring outlet flow rate made drawing definitive conclusions on nutrient load reductions difficult. Further experimentation using adjusted outlet flow measuring methods and bioreactor design would help establish whether in-ditch bioreactors are suitable for use as a nutrient removal technology in agricultural grassed waterways. / Master of Science / Drainage ditches, or grassed waterways, are located at the edge of agricultural fields where runoff migrates naturally. These ditches help to direct runoff from the field to receiving waterbodies while reducing erosion. Agricultural runoff often contains high levels of nitrogen and phosphorus from fertilizer added to promote crop growth. When runoff with a high nutrient content reaches a waterbody, it reduces the quality of the water for the plants and animals that live in it and for human recreation or consumption. In-ditch bioreactors are a simple, inexpensive treatment technology that could potentially remove nitrogen and phosphorus from agricultural runoff. In-ditch bioreactors have the potential to remove nitrogen from the water by creating optimal conditions for the microorganisms that transform nitrogen in the water to nitrogen in the air. Phosphorus removal has the potential to be enhanced by in-ditch bioreactors that reduce flow and allow for phosphorus to settle out of the water. In addition, settling of phosphorus may be increased by adding a material, such as biochar, that phosphorus can attach to. Using experimental ditch segments and simulated runoff, this study looked at nutrient removal in 1) vegetated ditches, 2) vegetated ditches with woodchip bioreactors installed and 3) a vegetated ditch with combination woodchip and biochar bioreactors installed. Concentrations of two nitrogen compounds and one phosphorus compound were measured before and after passing through each ditch. There were no significant differences between any of the three ditch types on how much of each compound they could remove. These results are inconclusive due to inaccuracies in measuring flow rate at the outlet of the ditches. Further experimentation using improved flow measuring techniques and bioreactor designs would likely help establish whether in-ditch bioreactors are suitable for use as a nutrient removal technology.

Tesis por compendio / [EN] Anaerobic membrane bioreactors for urban wastewater treatment present interesting advantages when compared with aerobic treatments, such as less sludge production, lower energy demand and biogas generation. However, the generated effluent cannot generally be discharged without further ammonium and phosphate elimination. This thesis studies the removal of these inorganic nutrients by means of microalgae cultivation. The main objective of this work is therefore to obtain an autochthonous microalgal culture and to investigate its ability to grow on an already existing anaerobic effluent, as well as to research the extent to which ammonium and phosphate can be removed. Moreover, this thesis aims at providing the kinetic expressions which reproduce the main processes involved, in order to provide the basis for process simulation and design. Microalgae were isolated from a local wastewater treatment plant and their ability to grow on the anaerobic effluent -while successfully removing ammonium and phosphate- was demonstrated. An excellent water quality was obtained with a semicontinuous cultivation mode under constant illumination. The Scenedesmus and Chlorococcum genus proliferated more efficiently and thus became predominant in the culture. Results also showed that phosphorus was the limiting nutrient in the anaerobic effluent to be treated. The influence of phosphorus limitation on ammonium and phosphate removal, as well as the influence of temperature in ammonium removal, were then studied under laboratory conditions. Kinetic expressions which reproduce the observed effects were proposed and validated, taking also into account the effect of light intensity. Additionally, a Scenedesmus-dominated culture was grown under varying light and temperature in an outdoor flat-plate photobioreactor, with constant monitoring of light intensity, temperature and ammonium concentration. Acceptable results were obtained in the reproduction of the experimental data, albeit with less accuracy than under laboratory conditions. The work here presented demonstrates the feasibility of coupling a microalgal cultivation system to an anaerobic membrane bioreactor for urban wastewater treatment. The basic factors affecting microalgal nutrient removal are researched, and mathematical models are provided which reproduce these effects. This Ph.D. thesis is enclosed in a national research project funded by the Spanish Ministry of Economy and Competitiveness entitled "Estudio experimental de la recuperación como biogás de la energía de la materia orgánica y nutrientes del agua residual, acoplando un AnBRM y un cultivo de microalgas" (MINECO project CTM2011-28595-C02-01/02). This research was also supported by the Spanish Ministry of Education, Culture and Sport via a pre doctoral FPU fellowship to the author (AP2009-4903) / [ES] En el tratamiento de aguas residuales urbanas, los bioreactores anaerobios de membranas presentan ventajas interesantes frente a los tratamientos aerobios. Algunas de estas ventajas son la menor producción de fangos, un menor consumo energético y la producción de biogás. Sin embargo, y generalmente, el efluente obtenido no puede ser vertido al medio sin una etapa previa de eliminación de amonio y fosfato. La presente tesis estudia la eliminación de dichos nutrientes inorgánicos empleando para ello un cultivo de microalgas. El objetivo principal de este trabajo es, por tanto, la obtención de un cultivo autóctono de microalgas y la evaluación de la capacidad que éstas tienen tanto de crecer en un efluente anaerobio como de eliminar el amonio y el fosfato presentes. Asimismo, se pretenden proporcionar las bases para la simulación y el diseño del sistema de depuración propuesto, mediante la obtención de las expresiones cinéticas que reproducen los principales procesos involucrados. En primer lugar se ha demostrado la capacidad de las microalgas, aisladas en una estación depuradora de aguas residuales, de crecer en el efluente anaerobio y de eliminar con éxito el amonio y fosfato en éste presente. El agua tratada, obtenida a mediante un proceso semicontinuo y con iluminación constante, presenta una excelente calidad. Los géneros Scenedesmus y Chlorococcum han proliferado más eficientemente y han llegado a ser los predominantes en el cultivo. Los resultados obtenidos indican que el nutriente limitante en el efluente a tratar es el fósforo, y por tanto la influencia de la limitación de fósforo en la eliminación de nutrientes ha sido estudiada en condiciones de laboratorio, junto con la influencia de la temperatura en la velocidad de eliminación de amonio. Han sido propuestas y validadas las correspondientes expresiones cinéticas que reproducen los efectos observados, teniendo en cuenta en todo momento la influencia de la intensidad de la luz. Por otro lado, un cultivo de Scenedesmus ha sido cultivado en el exterior, bajo condiciones cambiantes de luz y temperatura, que a su vez han sido monitorizadas constantemente, junto con la concentración de amonio. Los datos obtenidos han sido reproducidos mediante modelación matemática con resultados aceptables, aunque la precisión obtenida es menor que en condiciones de laboratorio. La presente tesis demuestra la viabilidad de combinar un cultivo de microalgas con un bioreactor de membranas para el tratamiento de agua residual urbana. Se exponen asimismo los factores básicos que influyen en la velocidad de eliminación de nutrientes, y se presentan los modelos matemáticos necesarios para reproducir los efectos observados. La presente tesis doctoral se incluye en el marco de un proyecto nacional de investigación financiado por el Ministerio de Economía y Competitividad de título "Estudio experimental de la recuperación como biogás de la energía de la materia orgánica y nutrientes del agua residual, acoplando un AnBRM y un cultivo de microalgas" (CTM2011-28595-C02-01/02). La presente tesis doctoral ha sido también financiada por el Ministerio de Educación, Cultura y Deporte a través de una ayuda para contratos predoctorales de Formación del Profesorado Universitario (AP2009-4903). / [CA] En el tractament d'aigües residuals urbanes, els bioreactors anaerobis de membrana tenen avantatges interessants respecte als tractaments aerobis. Alguns d'aquests avantatges són: menys producció de fangs, menys consum energètic i la producció de biogàs. No obstant això, i en general, l'efluent obtingut no es pot tornar al medi sense una etapa prèvia d'eliminació d'amoni i fosfat. Aquesta tesi estudia l'eliminació d'aquests nutrients inorgànics emprant per a fer-ho un cultiu de microalgues. L'objectiu principal d'aquest treball és, per tant, l'obtenció d'un cultiu autòcton de microalgues i l'avaluació de la capacitat que aquestes tenen tant de créixer en un efluent anaerobi com d'eliminar l'amoni i el fosfat presents. Així mateix, volem proporcionar les bases per a la simulació i el disseny del sistema de depuració proposat, mitjançant l'obtenció de les expressions cinètiques que reprodueixen els principals processos involucrats. En primer lloc, s'ha demostrat la capacitat de les microalgues, aïllades en una estació depuradora d'aigües residuals, de créixer en l'efluent anaerobi i d'eliminar amb èxit l'amoni i el fosfat presents. L'aigua tractada, obtinguda mitjançant un procés semicontinu i amb il·luminació constant, presenta una qualitat excel·lent. Els gèneres Scenedesmus i Chlorococcum han proliferat més eficientment i han arribat a ser els predominants en el cultiu. Els resultats obtinguts indiquen que el nutrient limitant en l'efluent per tractar és el fòsfor, i per tant la influència de la limitació de fòsfor en l'eliminació tant d'amoni com de fosfat ha sigut estudiada en condicions de laboratori, juntament amb la influència de la temperatura en la velocitat d'eliminació d'amoni. S'han proposat i validat les expressions cinètiques corresponents que reprodueixen els efectes observats, tenint en compte en tot moment la influència de la intensitat de la llum. D'altra banda, s'ha cultivat a l'exterior un cultiu predominat per Scenedesmus, sota condicions canviants de llum i temperatura, que al seu torn s'han monitorat constantment, juntament amb la concentració d'amoni. Les dades obtingudes s'han reproduït mitjançant simulació matemàtica amb resultats acceptables, encara que la precisió obtinguda és més baixa que en condicions de laboratori. La nostra tesi demostra la viabilitat de combinar un cultiu de microalgues amb un bioreactor de membrana per al tractament d'aigua residual urbana. La tesi exposa així mateix els factors bàsics que influeixen en la velocitat d'eliminació de nutrients, i presenta els models matemàtics necessaris per a reproduir els efectes observats. Aquesta tesi doctoral s'inclou en el marc d'un projecte nacional de recerca finançat pel Ministeri d'Economia i Competitivitat amb el títol "Estudio experimental de la recuperación como biogás de la energía de la materia orgánica y nutrientes del agua residual, acoplando un AnBRM y un cultivo de microalgas" (CTM2011-28595-C02-01/02). La tesi doctoral ha sigut també finançada pel Ministeri d'Educació, Cultura i Esport a través d'una ajuda per a contractes predoctorals de formació del professorat universitari (AP2009-4903). / Ruiz Martínez, A. (2015). Nutrient removal from an anaerobic membrane bioreactor effluent using microalgae. Study and modeling of the process [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/59409 / Compendio

Master of Science / Department of Agronomy / Scott A. Staggenborg / Volatile energy prices, energy independency, and environmental concerns have increased the demand for renewable fuel production in the United States. The current renewable fuel industry in the United States has developed around the conversion of starch into ethanol fuel, supplied mainly by corn (Zea mays L.) grain. Future energy demands cannot be met by corn grain alone; therefore greater amounts of biomass from traditional and alternative crops must be utilized. Nutrient removal by selected biofuel crops is important in order to determine biomass quality, required fertilizer inputs, and economic viability of biofuel cropping systems. The objectives of this study were to evaluate grain, stover, total biomass, and estimated ethanol yields of annual and perennial C4 crops grown under the same soil and weather conditions; and fermentable carbohydrate (FC) yields from extracted sweet sorghum juice. In addition, nitrogen (N), phosphorus (P) and potassium (K) concentrations of biomass were evaluated to determine total nutrient removal for annual and perennial crops. Field trials, at two locations in northeast Kansas, included corn, sorghum [Sorghum bicolor (L.) Moench] and perennial warm-season grass cultivars. Yields and nutrient removal were greater for annual crops than perennial grasses. Annual crop yields varied among cultivars, but were similar between locations and years. Perennial grass yields improved significantly from the 2007 establishment year to 2008, however nutrient removal was not affected by the yield increase. The highest grain yield and grain nutrient removal amounts were observed for corn across both years and locations. Total biomass yields were greatest for sweet and photoperiod sensitive sorghum cultivars. Average extracted sweet sorghum FC yields were 4.8 Mg ha[superscript]1. Estimated ethanol yields of sweet sorghum were greater than all other crop cultivars. Overall, nutrient removal was most affected by biomass yield variation among crop cultivars; however P concentrations, and subsequent removal, were dependent upon soil P levels at individual locations. These results suggest that annual crops can achieve the greatest biomass yields for multiple renewable fuel conversion processes, but are associated with high nutrient removal levels which must be considered when evaluating biofuel energy cropping systems.

This thesis covers work carried out on algae bioreactors as a tertiary treatment process for wastewater treatment. The process was primarily assessed by the removal of Phosphorus and Nitrogen as an alternative to chemical and bacterial removal. Algal bioreactors would have the added advantage of carbon sequestration and a by-product in the energy rich algal biomass that should be exploited in the existing AD capacity. Laboratory scale bioreactors were run (4.5-30L) using the secondary treated final effluent from the local Loughborough sewage works. In a preliminary series of experiments several different bioreactor designs were tested. These included both batch feed and continuous flow feed configurations. The bioreactors were all agitated to keep the algal cells in suspension. The results demonstrated that the most effective and easy to operate was the batch feed process with the algal biomass by-product harvested by simple gravitational settling. Experiments also compared an artificial light source with natural light in outdoor experiments. Outdoor summer light produced greater growth rates but growth could not be sustained in natural UK winter light. Light intensity is proportional to productivity and algae require a minimum of around 97W/m2 to grow, an overcast winter day (the worst case scenario) was typically around 78W/m2, however this was only available for a few hours per day during Nov-Jan. The process would be better suited to areas of the world that receive year round sunlight. It was shown that phosphorus could be totally removed from wastewater by the algae in less than 24 hours depending on other operating variables. With optimisation and addition of more carbon, a HRT of 10-12 hours was predicted to achieve the EU WFD / UWWTD standard. It was further predicted that the process could be economically and sustainably more attractive than the alternatives for small to medium sized works. Biomass 3 concentrations of between 1-2g/L were found to best achieve these removals and produce the fastest average growth rates of between 125-150mg/L/d. The uptake rates of phosphorus and nitrogen were shown to be dependent on the type of algae present in the bioreactor. Nitrogen removal was shown to be less effective when using filamentous bluegreen algae whilst phosphorus removal was almost completely stopped compared to unicellular green algae that achieved a nitrogen uptake of 5.3mg/L/d and phosphorus uptake of 8mg/L/d. Soluble concentrations of Fe, Ni and Zn were also reduced by 60% in the standard 10 hours HRT. The predominant algae were shown to depend largely on these concentrations of phosphorus and nitrogen, and the strain most suited to that specific nutrient or temperature environment dominated. Nutrient uptake rates were linked to algal growth rates which correlated with the availability of Carbon as CO2. CO2 was shown to be the limiting factor for growth; becoming exhausted within 10 hours and causing the pH to rise to above 10.5. The literature showed this was a common result and the use of CO2 sparging would more than double performance making this process a good candidate for waste CO2 sequestration. Heat generated from combustion or generators with exhaust CO2 would also be ideal to maintain a year round constant temperature of between 20-25°C within the bioreactors. A number of possible uses for the algal biomass generated were examined but currently the most feasible option is wet anaerobic co-digestion. Further economic analysis was recommended on the balance between land area and complementary biomass generation for AD. It was also suggested given the interest as algae as a future fuel source, the process could also be adapted for large scale treatment and algal biomass production in areas of the world where land was available.

Submitted in complete fulfillment for the degree of Doctor of Philosophy (Biotechnology) in the Department of Biotechnology and Food Technology, Durban University of Technology, Durban, South Africa, 2016. / Many households in developing countries are still without proper sanitation systems. The problems are even more prevalent in rural communities where there are no septic systems in place for the treatment of wastewater. This has resulted in the urgent need for the development and implementation of innovative wastewater treatment systems that are inexpensive, environmental friendly and are able to reduce contaminants to levels that pose no harm to the communities. Constructed rhizofiltration systems have been explored for this purpose. They have been used for many decades in many countries with varying degrees of success at the primary, secondary and tertiary levels of wastewater treatment. Poor optimization of this technology has been due to limited information available about the roles played by the whole system as well as by each component involved in the treatment technology. The current work elucidates the role played by macrophytes and microbial biofilms in the removal of nutrients in the rhizofiltration system. Factors affecting waste removal as well as environmental friendliness of the system were also investigated. The rhizofiltration system was constructed in Durban and was divided into planted (planted with Phragmites australis and Kyllinga nemoralis) and unplanted (reference) section. Dissolved oxygen (DO), pH, water temperature, total dissolved solids (TDS), electrical conductivity (EC) and salinity were monitored. The removal efficiency of nutrients was measured using spectrophotometric methods by measuring the concentration of ammonia, nitrate, nitrite, phosphate and orthophosphate in the wastewater pre- and post-treatment. The total organic carbon, chemical oxygen demand (COD), total Kehldjahl nitrogen, biological oxygen demand (BOD), ammonia, nitrate and the flow rate of wastewater into the system from the settling tank were used for the estimation of carbon dioxide, methane and nitrous oxide emitted from the rhizofilter using the 2009 EPA formulae. Both the planted and reference sections of the system removed nutrients with varying efficiencies. The reduction of nutrients in the rhizofilter was found to be seasonal, with most nutrients removed during the warm seasons. The system also retained more nutrients when wastewater containing low levels of nutrients was used. The unpaired t-test was used to determine the differences between nutrient removals between planted and reference sections. Higher reduction efficiencies of nutrients were obtained in the planted section. Up to 65% nitrite and 99% nitrate were removed while up to 86% total phosphorus was removed in a form of orthophosphate (86%). Removal of total nitrogen was shown to increase under high temperature conditions, while the same conditions decreased the total phosphorus removal. High temperatures also increased the performance of the system. The reduction of nutrients in the system corresponded to reduction of the chemical oxygen demand which also positively correlated to the dissolved oxygen concentration. Considering the discharge limits for all nutrients, the discharges in the effluent of the planted section were within the allowable limits as per South Africa’s Department of Water affairs and Forestry in 2012 but not in 2013. The results obtained in 2013 were due to increased nutrient loading introduced into the system. Diverse microbial communities occurred in the treatment system, with more diversity in the planted section. These organisms were supported by macrophytes in the planted section, and were responsible for nitrogen and phosphorus transformation. This explains why total nitrogen and phosphorus reduction was higher in the planted compared to the reference section. Both the planted and the reference sections of the rhizofiltration system produced the greenhouse gases. When the two sections were compared, the planted section produced more gases. Gases emitted by both sections were lower when compared to emission from sludge treatment reed beds and other conventional systems of wastewater treatments. These findings indicated that constructed rhizofiltration is a cleaner form of waste treatment, producing significantly less greenhouse gases and affecting less of a climate change. Findings of this work have revealed that rhizofiltration technology can be used as a low-cost alternative technology for the treatment of wastewater, using the combination of macrophytes and microbial biofilms. Macrophytes accumulated nitrogen and phosphorus as well as supported diverse microorganisms that metabolized and reduced nutrients in the rhizofiltration unit. / D

Microalgae are a diverse group of unicellular microorganisms found in various environments, ranging from small garden ponds to lakes with extreme salinity. Common for all microalgae is their ability to convert solar energy and carbon dioxide into chemical energy via photosynthesis. Additionally, they are capable of assimilating large amounts of nitrogen and phosphorus to produce proteins and lipids. These abilities have made microalgae an interesting candidate for next generation wastewater treatment coupled with production of biogas, a renewable energy source in advancement. At the Nykvarn wastewater treatment plant in Linköping, Sweden, 15,400,000 m3 of wastewater are treated annually to remove nitrogen and phosphorus that otherwise would risk to cause eutrophication in surrounding lakes and rivers. Moreover, the treatment plant manages large amounts of sewage sludge that is anaerobically digested to produce biogas and simultaneously reduce the sludge volumes. At the Nykvarn wastewater treatment plant, dewatering of the digested sludge results in a sludge fraction of about 30 % dry content and reject water, which is very nutrient-rich and therefore requires treatment in a SHARON process before it is reintroduced to the main stream of the wastewater treatment plant. In this thesis, the potential of microalgae for nutrient assimilation was studied by monitoring the nutrient removal efficiency of a mixed culture of microalgae when fed with 1) 100 % incoming wastewater, 2) 80 % incoming wastewater + 20 % reject water and 3) 60 % incoming wastewater + 40 % reject water. Furthermore, the effect of a process additive on the nutrient removal efficiency was evaluated. The results showed that microalgae are capable of removing 100 % of ingoing ammonium nitrogen and phosphate phosphorus when fed with incoming wastewater. At transition to 20 % and 40 % reject water, the culture was light-limited with a resulting ammonium reduction of 60 % and a phosphate reduction of around 30 %. The process additive slightly improved the ammonium reduction, however, mainly by formation of nitrite and nitrate by nitrifying bacteria. Moreover, a bio-methane potential test compared the methane potential of the microalgal biomass and the biomass from the SHARON process. The test resulted in an accumulated methane production around 70 mL g-1 VS-1 for the microalgal biomass and 35 mL g-1 VS-1 for the biomass from the SHARON process. That is, the mixed microalgal culture used in this experiment has a methane potential twice that of the biomass from the SHARON process. Finally, an economic analysis of a microalgae based process for purification of reject water showed that the operating costs exceed those of the SHARON process due to high energy consumption. It is thus necessary to choose a cultivation system that effectively utilize the solar energy, as well as maximize the biogas yield from anaerobic digestion of microalgal biomass.

Native oysters have been promoted as a means to improve water quality in Chesapeake Bay. This project added important insights into the potential of oyster aquaculture to process and remove nutrients from Bay waters. Results clarified that nutrient removal of nitrogen (N), phosphorous (P), and carbon (C) through harvest of cultivated oyster biomass can be quantified and modeled with high levels of statistical confidence. A simple, yet accurate, method is now available for estimating the amount of nutrients removed via harvesting aquacultured oysters. Based on model estimates, 106 harvest sized oysters (76 mm TL) remove 132 kg TN, 19 kg TP, and 3,823 kg TC. Previous work suggested that potentially substantial quantities of N may be removed through enhancement of the coupled nitrification-denitrification pathway in sediments as a result of oyster biodeposition. Using 15N and N2/Ar methods to measure N2 production in sediments, encompassing direct denitrification (DNF), coupled nitrification- denitrification, and anaerobic ammonium oxidation (anammox) pathways, at two oyster aquaculture sites and two reference sites (no aquaculture), we found that oyster biodeposition did not accelerate sediment N removal. We estimate sediment N removal rates via N2 production at an oyster cultivation site producing 5 x 105 oysters (1750 m2) to range from 0.49-12.60 kg N yr-1, compared to 2.27-16.72 kg N yr-1 at a reference site of the same area; making the contribution of oyster cultivation to N removal via sediment N2 production inconsequential as a policy initiative for Chesapeake Bay eutrophication mitigation. Molecular approaches and direct abundance measures have improved our understanding of the sediment microbial community response to oyster biodeposition. Overall, sediments impacted by oyster biodeposition had a significantly different denitrifying community composition than sediments a few meters away or at the non-aquaculture reference sites. Bacterial abundance in sediments was determined by site rather than by oyster biodeposition. No apparent effects of oyster biodeposition were evident in nitrifying bacterial abundance patterns at either site, indicating that oyster biodeposition does not enhance coupled nitrification-denitrification by increasing the abundance of nitrifiers in sediments.