Optimal Control of Algae Biofilm Growth in Wastewater Treatment Using Computational Mathematical Models

Microalgal biofilms are comprised of a syntrophic consortium of microalgae and other microorganisms embedded within an extracellular matrix. Despite significant processes in the application of microalgal biofilms in wastewater treatment, mechanistic understanding and optimization of microalgal biomass yield and productivity under environmental constraints is still lacking. This paper identifies theoretical insights on this challenging biological problem by leveraging novel mathematical and computational tools. In particular, through a computational mathematical model to advance the understanding of microalgal biofilm growth kinetics under environmental constraints through a systematic parameter study. Moreover, design of algae biofilm reactors for optimal biomass yield and productivity in wastewater treatment under different environments is explored. The proposed model could be further calibrated to generate reliable predictions that can improve the design, operation, and management of microalgal biofilms in wastewater treatment

Algae-Based Biofilm Productivity and Treatment of Dairy Wastewater: Effects of Temperature and Organic Carbon Concentration

Production of dairy and associated products is a source of millions of gallons of wastewater every year. Water used in cleaning feeding stalls as well as the liquid component of the animal waste are two of the major volumetric components of this wastewater. This water is nutrient rich, often limiting the viability as a land applied fertilizer. However, these same nutrients could be used as an inexpensive feedstock for the cultivation of algae, which can then be used to produce downstream products including animal feed and aquaculture. As part of this study, algal biomass was cultivated on dairy wastewater from the Utah State University Caine Dairy. A Rotating Algal Biofilm Reactor (RABR) system was used to grow the biomass. The RABR is a biofilm technology designed and developed at Utah State University and has been applied to the treatment of municipal wastewater. In this study, the RABR was adapted for use in a dairy wastewater stream. The RABR was operated at temperatures ranging from 7-27 °C, and organic carbon levels in the wastewater ranged from 300-1200 mg/L of Total Organic Carbon (TOC). Areal algal biofilm growth rates were calculated, and statistical analysis showed that both increasing temperature and levels of organic carbon contributed to an increase in biomass growth and an increase in nutrient removal. Equations were then developed using a linearization method and corresponding constants and equations were generated that can be used to evaluate algal biomass productivity and nutrient removal rates in future experiments and designs for dairy wastewater

Development and optimization of biofilm based algal cultivation

This dissertation describes research done on biofilm based algal cultivation systems. The system that was developed in this work is the revolving algal biofilm cultivation system (RAB). A raceway-retrofit, and a trough-based pilot-scale RAB system were developed and investigated. Each of the systems significantly outperformed a control raceway pond in side-by-side tests. Furthermore the RAB system was found to require significantly less water than the raceway pond based cultivation system. Lastly a TEA/LCA analysis was conducted to evaluate the economic and life cycle of the RAB cultivation system in comparison to raceway pond. It was found that the RAB system was able to grow algae at a lower cost and was shown to be profitable at a smaller scale than the raceway pond style of algal cultivation. Additionally the RAB system was projected to have lower GHG emissions, and better energy and water use efficiencies in comparison to a raceway pond system. Furthermore, fundamental research was conducted to identify the optimal material for algae to attach on. A total of 28 materials with a smooth surface were tested for initial cell colonization and it was found that the tetradecane contact angle of the materials had a good correlation with cell attachment. The effects of surface texture were evaluated using mesh materials (nylon, polypropylene, high density polyethylene, polyester, aluminum, and stainless steel) with openings ranging from 0.05–6.40 mm. It was found that both surface texture and material composition influence algal attachment

Rotating Algal Biofilm Reactors: Mathematical Modeling and Lipid Production

Harvesting of algal biomass presents a large barrier to the success of biofuels made from algae feedstock. Small cell sizes coupled with dilute concentrations of biomass in lagoon systems make separation an expensive and energy intense-process. The rotating algal biofilm reactor (RABR) has been developed at USU to provide a sustainable technology solution to this issue. Algae cells grown as a biofilm are concentrated in one location for ease of harvesting of high density biomass. A mathematical model of this biofilm system was developed based on data generated from three pilot scale reactors at the City of Logan, Utah wastewater reclamation plant. The data were fit using nonlinear regression to a modified logistic growth equation. The logistic growth equation was used to estimate nitrogen and phosphorus removal from the system, and to find the best harvesting time for the reactors. These values were extrapolated to determine yields of methane and biodiesel from algae biomass that could be used to provide energy to the City of Logan if these reactors were implemented at full scale. For transesterification into biodiesel, algae need to have high lipid content. Algae biofilms have been relatively unexplored in terms of cell lipid composition accumulation and changes with regard to environmental stressors. Results indicated that biofilm biomass was largely unaffected by nutrient stresses. Neither nitrogen limitation nor excess inorganic carbon triggered a significant change in lipid content. Biofilm algae grown with indoor lighting produced an average of 4.2% lipid content by dry weight. Biofilm algae gown outdoors yielded an average of 6.2% lipid content by dry weight

Characterization and Performance of Algal Biofilms for Wastewater Treatment and Industrial Applications

This study was carried out on algal biofilms grown using rotating algal biofilm reactors (RABRs) with the aim of: i) characterizing their growth in terms of photosynthetic activity and morphology ii) evaluating their performance as a wastewater treatment option and a feedstock for biofuels production, and iii) examining the algal-bacteria interactions. A review of algal biofilm technologies currently employed in wastewater treatment processes was made to compare nutrient removal efficiencies, factors that influenced algal biofilm growth, and the different bioproducts generated from algal biomass. Consequently, research efforts were directed towards addressing pertinent issues identified in literature in order to optimize these systems for wastewater treatment and bioproducts production. Successful growth of algal biofilms in municipal wastewater and subsequent removal of nutrients from the wastewater was demonstrated. Photosynthetic and respiration rates observed with depth of the biofilm were influenced by the biofilm composition (single vs. mixed species), culturing conditions (laboratory vs. outdoor), orientation to the light, nitrogen availability (N-replete vs. N-deplete), and dissolved inorganic carbon availability (presence or absence of bicarbonate). Slight enhancement in lipid production was also observed as a result of nitrogen stress and bicarbonate addition. However, the accumulated lipids were not as much as expected or as reported in suspended cultures. Presence of bacteria positively influenced microalgae growth in the mixed cultures but the reverse was not true. In conclusion, photosynthetic activity and biofilm structure were characterized with methods developed for the algal biofilms in this study. For now, productivity of the algal biofilms needs to be maximized in order to fully utilize its potential as a biofuel feedstock and nutrient removal option. Further research on algae-bacteria interactions using species native to the wastewater grown algal biofilms is recommended

Observation of Struvite in the Mixed Microalgae Biofilm Matrix of a Rotating Algal Biofilm Reactor During Nutrient Removal from Municipal Anaerobic Digester Filtrate

Central Valley Water Reclamation Facility (CVWRF) in Salt Lake City is the largest municipal wastewater treatment plant in Utah and must meet new and rigorous nutrient effluent standards–over 95% reduction in phosphorus output by 2025. Filtrate from CVWRF anaerobic digesters contains high levels of nitrogen, phosphorus, and magnesium. Supersaturation of these constituents leads to nuisance struvite precipitation that clogs belts, pumps, and pipes downstream of anaerobic digesters. Struvite is a mineral precipitate composed of equimolar magnesium, ammonium, and phosphate. Controlled precipitation of struvite helps prevent clogging and scaling, removes phosphate from wastewater, and generates a marketable fertilizer product. Struvite was observed within the microalgae biofilm matrix of an outdoor, pilot-scale rotating algal biofilm reactor (RABR) designed to remove nitrogen (N) and phosphorus (P) from anaerobic digester filtrate. East/west biofilm orientation and biomass harvesting interval influence struvite content within the biofilm matrix. Despite RABR influent component ion molar ratios with potential for various magnesium and calcium precipitates, microalgae biofilm provides pH, temperature, and nucleation sites favorable to struvite precipitation. The RABR system removed N and P through biofilm growth and through struvite precipitation. Microalgae biofilm can be harvested and pelletized into fertilizer, and the struvite content will add fertilizer value to the product. More research is needed for optimization and scalability of P removal through combined microalgae biofilm and struvite precipitation

RABRs for Use in Biologically Enhanced Precipitation of Struvite in Anaerobic Digester Effluent (Municipal Wastewater)

Rotating Algae Biofilm Reactor (RABR) technology has been researched in studies over the past decade directed at nutrient management for water resource recovery facilities (WRRFs). This study investigated the growth of slow-release fertilizer crystals, referred to as struvite, in the algae biofilms of Rotating Algae Biofilm Reactors (RABRs) at the Central Valley Water Reclamation Facility, the largest water resource recovery facility in the State of Utah. RABRs used anaerobic digester (AD) filtrate as their nutrient source. AD effluent is high in nutrients like nitrogen and phosphorus. The levels of both phosphorus and nitrogen (in the form of ammonia) are regulated by the State of Utah, and WRRFs must limit the amounts deposited into receiving waters including rivers, streams, and lakes. Struvite, being partially composed of both ammonia nitrogen and phosphorus, can help remove both elements from the water when it is formed by natural chemical precipitation. Because struvite is also an effective slow-release fertilizer, struvite formation helps treat wastewater, recycle phosphorus and ammonia nitrogen, and provide economic value from wastewater. RABRs were built as laboratory scale, bench scale, and pilot scale. AD effluent filtrate was analyzed to determine ion concentration data and this data was then used to calculate and predict struvite solubility over a range of pH values and used in computer modeling to predict likely precipitates. Chemical instrumentation including Scanning Electron Microscope (SEM) and Electromagnetic X-Ray Dispersion Spectroscopy (EDS) technologies were used to identify crystals in RABR biofilms and to determine their composition. Results of this research showed that struvite could precipitate at the pH values of the AD effluent filtrate. Further, high light intensity representative of sunlight increased the pH inside of the biofilms which enhanced struvite formation. Chemical instrumentation analysis by SEM/EDS showed that struvite had formed in the pilot RABR biofilm. It was also observed that the pilot scale RABR produced struvite within the biofilm when the biofilm was exposed to the atmosphere for a sufficient time to allow evaporation of water (at least 2 minutes). This research has demonstrated that struvite precipitation using RABRs can provide an innovative technology for nutrient management by WRRFs

Dynamic interactions in an artificial phototrophic biofilm for biotechnological applications

In the present study, a comprehensive investigation of the dynamic processes in an artificial algal biofilm immobilized on a porous substrate has been conducted. Experimental investigations including microsensor measurements were carried out. For this purpose, the microsensor setup used for profiling submerged biofilms was modified to enable measurement on the investigated biofilms. To achieve an accurate evaluation of the data acquired through microsensor measurements, a new mathematical method was developed, and a 20 μm depth resolution has been suggested for future photosynthetic activity measurements. After the establishment of the microsensor methods, a systematic microsenser investigation was carried out: the distribution of dissolved oxygen, pH value and photosynthetic productivity profiles of algal biofilms in a porous substrate biofilm photobioreactor (Twin-Layer photobioreactor) exposed to different surface irradiance and/or exposed to different gas phase CO2 concentrations were measured. The results acquired from these experiments offered important insights into the processes in such biofilms: E.g. light penetration depth, maximal dissolved oxygen concentration and pH distribution. The results show, as expected, photosynthesis in the biofilms occurs only near the biofilms surface (i.e. in the illuminated zones), and dark respiration in the inner part of the biofilm could be the reason of the observed biomass productivity decrease with prolonged cultivation. Also, increases in surface irradiance and/or gas phase CO2 concentrations led to an increase in photosynthetic productivity of the investigated biofilm. No photoinhibition was observed in the studied biofilms, although exceptionally high dissolved oxygen concentrations (12 times of that in normal atmosphere) have been recorded. The model (as described in the 3rd manuscript, Li et al. 2015d) developed in the study has proven to be very effective in predicting experimental observations. The results show clearly the importance of taking into account not only adsorption and scattering, but also the adaptation of the pigment content of the biomass for investigating radiative transfer in PSBR biofilms. Also, through the development of the model, important insights into the dynamic processes in the investigated biofilm were acquired: E.g., it is very likely that the facilitated CO2 transfer plays an important role in inorganic carbon transport in the studied biofilms when the CO2 concentration supplied in the gas phase is low; macronutrients (N and P) do not limit growth even at high surface irradiance and high gas phase CO2 concentrations as long as they are sufficiently supplied in the medium; and the buffering of the medium with a strong buffer will have significant effects on the inorganic carbon availability in the studied biofilm. Through this study, a solid basis has been established for future investigation on PSBR biofilms. The methods and model developed in this study are established specifically for investigating biofilms grown in the Twin-Layer porous substrate biofilm photobioreactor. However, with minor modifications and/or additional experimental measurements, they can be easily applied to other phototrophic biofilm systems or for investigation and/or optimization of commercial scale systems

Benthic diatom monitoring and assessment of freshwater environments: standard methods and future challenges

Fil: Soizic, Morin. National Research Institute of Science and Technology for Environment and Agriculture; FranceFil: Gómez, Nora. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología Dr. Raúl A. Ringuelet; ArgentinaFil: Tornés, Elisabet. University of Girona. Institute of Aquatic Ecology; SpainFil: Licursi, Magdalena. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología Dr. Raúl A. Ringuelet; ArgentinaFil: Rosebery, Juliette. Aquatic Ecosystems and Global Changes Research Unit; Franc