Kelly A. Rusch

An assessment of long-term post-restoration water quality trends in a shallow, subtropical, urban hypereutrophic lake

Abstract City Park Lake is a shallow urban hypereutrophic lake located in Baton Rouge, Louisiana, with a surface area of 0.23 km2 and a mean depth of 1.2 m. By the late 1970s, the lake had become highly eutrophic and suffered from frequent and severe algal blooms and fish kills. A major restoration effort was undertaken in 1983 that consisted of dredging and the repair of sewage infrastructure. Immediate improvements in water quality were observed following restoration; algal blooms and fish kills were virtually eliminated for nearly a decade. However, large floating mats of filamentous algae periodically occurred during the early 1990s. Results of a water quality sampling program conducted in 2000 and 2001 indicated that phosphorus has once again reached pre-restoration levels, and nitrogen levels have decreased well below those observed during pre-restoration years. Whereas phosphorus-limited conditions predominated in the years preceding the 1983 restoration, results of the 2000–2001 sampling program indicate that the lake has become nitrogen-limited with respect to photosynthetic activity. This trend in nutrient levels has likely influenced the recent predominance of filamentous over unicellular species of algae observed during the last decade. Nearly 4 years of drought-like conditions beginning in 1998 have resulted in an overall increase in the hydraulic retention time of the lake. This condition has resulted in organic staining of the lake waters, or the development of a tea-like color due to the decomposition of organic compounds. This phenomenon has played a major role in inhibiting the sunlight available for filamentous algal growth since 1998 and the absence of filamentous algae during the 2000–2001 sampling program.

The Effects of Plant Growth Substances and Mixed Cultures on Growth and Metabolite Production of Green Algae Chlorella sp.: A Review

Recent interest in the use of microalgae for the production of biofuels and bioproducts has stimulated an interest in methods to enhance the growth rate of microalgae. This review examines past work involving the stimulation of Chlorella sp. growth and metabolite production by plant growth substances as well as by mixed cultures of Chlorella sp. with bacteria. Plant growth substances known to regulate Chlorella sp. growth and metabolite production include auxins, cytokinins, abscisic acid, polyamines, brassinosteroids, jasmonic acid, salicylic acid, and combinations of two or three of the aforementioned substances. Mixed cultures of bacteria are examined, including both natural bacteria–algae consortia and artificially induced symbioses. For natural consortia, commonly occurring bacterial species, including the genera Brevundimonas and Sphingomonas, are discussed. For artificially induced symbioses, the use of the nitrogen-fixing bacterium Azospirillum is examined in detail. In particular, a variety of studies have involved the coimmobilization of Chlorella sp. with Azospirillum sp. in alginate beads, with the goal of using the mixed culture to treat wastewater. In summary, the use of plant growth substances and mixed cultures provides two methods to increase the growth of Chlorella sp., whether for the production of lipids for biofuels, the production of bioproducts, the treatment of wastewater, or a variety of other reasons.

Development of predictive models for determining enterococci levels at Gulf Coast beaches.

The US EPA BEACH Act requires beach managers to issue swimming advisories when water quality standards are exceeded. While a number of methods/models have been proposed to meet the BEACH Act requirement, no systematic comparisons of different methods against the same data series are available in terms of relative performance of existing methods. This study presents and compares three models for nowcasting and forecasting enterococci levels at Gulf Coast beaches in Louisiana, USA. One was developed using the artificial neural network (ANN) in MATLAB Toolbox and the other two were based on the US EPA Virtual Beach (VB) Program. A total of 944 sets of environmental and bacteriological data were utilized. The data were collected and analyzed weekly during the swimming season (May-October) at six sites of the Holly Beach by Louisiana Beach Monitoring Program in the six year period of May 2005-October 2010. The ANN model includes 15 readily available environmental variables such as salinity, water temperature, wind speed and direction, tide level and type, weather type, and various combinations of antecedent rainfalls. The ANN model was trained, validated, and tested using 308, 103, and 103 data sets (collected in 2007, 2008, and 2009) with an average linear correlation coefficient (LCC) of 0.857 and a Root Mean Square Error (RMSE) of 0.336. The two VB models, including a linear transformation-based model and a nonlinear transformation-based model, were constructed using the same data sets. The linear VB model with 6 input variables achieved an LCC of 0.230 and an RMSE of 1.302 while the nonlinear VB model with 5 input variables produced an LCC of 0.337 and an RMSE of 1.205. In order to assess the predictive performance of the ANN and VB models, hindcasting was conducted using a total of 430 sets of independent environmental and bacteriological data collected at six Holly Beach sites in 2005, 2006, and 2010. The hindcasting results show that the ANN model is capable of predicting enterococci levels at the Holly Beach sites with an adjusted RMSE of 0.803 and LCC of 0.320 while the adjusted RMSE and LCC values are 1.815 and 0.354 for the linear VB model and 1.961 and 0.521 for the nonlinear VB model. The results indicate that the ANN model with 15 parameters performs better than the VB models with 6 or 5 parameters in terms of RMSE while VB models perform better than the ANN model in terms of LCC. The predictive models (especially the ANN and the nonlinear VB models) developed in this study in combination with readily available real-time environmental and weather forecast data can be utilized to nowcast and forecast beach water quality, greatly reducing the potential risk of contaminated beach waters to human health and improving beach management. While the models were developed specifically for the Holly Beach, Louisiana, the methods used in this paper are generally applicable to other coastal beaches.

Stabilization of phosphogypsum using class C fly ash and lime: assessment of the potential for marine applications.

Phosphogypsum (PG, CaSO(4).H(2)O), a solid byproduct of phosphoric acid manufacturing, contains low levels of radium ((266)Ra), resulting in stackpiling as the only currently allowable disposal/storage method. PG can be stabilized with class C fly ash and lime for potential use in marine environments. An augmented simplex centroid design with pseudo-components was used to select 10 PG:class C fly ash:lime compositions. The 43cm(3) blocks were fabricated and subjected to a field submergence test and 28 days saltwater dynamic leaching study. The dynamic leaching study yielded effective calcium diffusion coefficients (D(e)) ranging from 1.15 x 10(-13) to 3.14 x 10(-13)m(2)s(-1) and effective diffusion depths (X(c)) ranging from 14.7 to 4.3mm for 30 years life. The control composites exhibited diametrical expansions ranging from 2.3 to 17.1%, providing evidence of the extent of the rupture development due to ettringite formation. Scanning electron microscopy (SEM), microprobe analysis showed that the formation of a CaCO(3) on the composite surface could not protect the composites from saltwater intrusion because the ruptures developed throughout the composites were too great. When the PG:class C fly ash:lime composites were submerged, saltwater was able to intrude throughout the entire composite and dissolve the PG. The dissolution of the PG increased the concentration of sulfate ions that could react with calcium aluminum oxides in class C fly ash forming additional ettringite that accelerated rupture development. Effective diffusion coefficients and effective diffusion depths alone are not necessarily good indicators of the long-term survivability of PG:class C fly ash:lime composites. Development of the ruptures in the composites must be considered when the composites are used for aquatic applications.

Modeling the major limitations on nitrification in floating-bead filters

A model was developed and calibrated to experimental data, to formulate a theoretical description of nitrification in bead filters. The model results were consistent with the literature, indicating that the inverse relationship between solids accumulation and nitrification is mediated by an oxygen limitation. This result was central to an explanation of why differing optimal backwash intervals in gently- and aggressively-washed filters are related to: (1) differences in harvest fraction, which fixes the relationship between backwash interval and interstitial solids concentration and (2) differences in biofilm retention, which controls the average biomass age thereby determining total biomass concentration.

Effect of organic carbon, C:N ratio and light on the growth and lipid productivity of microalgae/cyanobacteria coculture

Current culture methods based on monocultures under phototrophic regimes are prone to contamination, predation, and collapse. Native cultures of multiple species are adapted to the local conditions and are more robust against contamination and predation. Growth, lipid and biomass productivity of a Louisiana native coculture of microalgae (Chlorella vulgaris) and cyanobacteria (Leptolyngbya sp.) in heterotrophic and mixotrophic regimes were investigated. Dextrose and sodium acetate at C:N ratios of 15:1 and 30:1 under heterotrophic (dark) and mixotrophic (400 μmol m−2 s−1) regimes were compared with autotrophic controls. The carbon source and C:N ratio impacted growth and biomass productivity. Mixotrophic cultures with sodium acetate (C:N 15:1) resulted in the highest mean biomass productivity (156 g m−3 d−1) and neutral lipid productivity (24.07 g m−3 d−1). The maximum net specific growth rate (U) was higher (0.97 d−1) in mixotrophic cultures with dextrose (C:N 15:1) but could not be sustained resulting in lower total biomass than in mixotrophic cultures with acetate (C:N 15:1), with a U of 0.67 d−1. The ability of the Louisiana coculture to use organic carbon for biomass and lipid production makes it a viable feedstock for biofuels and bioproducts.

Nitrification performance of a bubble-washed bead filter for combined solids removal and biological filtration in a recirculating aquaculture system

Laboratory studies were conducted to evaluate the nitrification performance of a bubble-washed bead filter as affected by backwashing frequency and feed loading rate. The bubble-washed bead filter was used for combined solids capture and biological filtration in a recirculating tilapia (Oreochromis niloticus) culture system. The filter was tested at feed loading rates of 16, 24, and 32 kg day−1 m−3 beads. Backwashing frequencies varied and had to be adjusted at each feed loading rate for satisfactory nitrification, to maintain total ammonia nitrogen (TAN) and nitrite–nitrogen (NO2–N) at concentrations below 1.0 mg l−1. In general, more frequent backwashing improved filter performance, and was necessary at higher feed loading rates. It was essential to provide adequate flow through the bead filter (at least 50 l min−1 kg-feed−1 day−1) to keep the effluent DO greater than 2 mg l−1 just prior to backwashing. At the highest feed loading rate tested of 32 kg day−1 m−3 beads, favorable performance was observed at five backwashes in a 24 h period, achieving average areal TAN and NO2–N conversions of 331 and 451 mg m−2 day−1, equivalent to volumetric conversions of 380 g TAN day−1 m−3 beads and 518 g NO2–N day−1 m−3 beads.

The hydraulically integrated serial turbidostat algal reactor (HISTAR) for microalgal production

Abstract A hydraulically integrated serial turbidostat algal reactor (HISTAR) for the mass production of microalgae was designed, constructed and preliminarily evaluated. The 9266-l experimental system consists of two enclosed turbidostats hydraulically linked to a series of six open continuous-flow, stirred-tank reactors (CFSTRs). The system was monitored and controlled using GENESIS process control software. A production study was preformed using Isochrysis sp. (C-iso) to assess system stability and production potential under commercial-like conditions. The study was performed at the following target system parameters: system dilution rate of 0.49 per day, pH 7.6, nitrogen=10 mg l −1 , phosphorus=2 mg l −1 , and artificial illumination (photosynthetic photon flux density) from 1000 W metal halide lamps=800 μmol s −1 m −2 . At steady state conditions, daily harvested algal paste was 1454 g (wet), mean areal system productivity=47.8±3.04 g m −2 per day (17.1±1.09 g C m −2 per day) and mean CFSTR6 density=105.5±6.71 mg l −1 .

Salinity and Soluble Organic Matter on Virus Sorption in Sand and Soil Columns

The objective of this research was to study the sorption and transport of bacteriophage MS-2 (a bacterial virus) in saturated sediments under the effect of salinity and soluble organic matter (SOM). One-dimensional column experiments were conducted on washed high-purity silica sand and sandy soil. In sand column tests, increasing salinity showed distinct effect on enhancing MS-2 sorption. However, SOM decreased MS-2 sorption. Using a two-site reversible-irreversible sorption model and the double layer theory, we explained that pore-water salinity potentially compressed the theoretical thickness of double layers of MS-2 and sand, and thus increased sorption on reversible sorption sites. On irreversible sorption sites, increasing salinity reversed charges of some sand particles from negative to positive, and thus converted reversible sorption sites into irreversible sites and enhanced sorption of MS-2. SOM was able to expand the double layer thickness on reversible sites and competed with MS-2 for the same binding place on irreversible sites. In sandy soil column tests, the bonded and dissolved (natural) soil organic matters suppressed the effects of pore-water salinity and added SOM and significantly reduced MS-2 adsorption. This was explained that the bonded soil organic matter occupied a great portion of sorption sites and significantly reduced sorption sites for MS-2. In addition, the dissolved soil organic matter potentially expanded the double layer thickness of MS-2 and sandy soil on reversible sorption sites and competed with MS-2 for the same binding place.

Microalgal production using a hydraulically integrated serial turbidostat algal reactor (HISTAR) : a conceptual model

Abstract A hydraulically integrated, serial turbidostat algal reactor (HISTAR) was mathematically modeled and developed for the mass production of microalgae. HISTAR, which hydraulically links precisely controlled turbidostats with continuous-flow stirred-tank reactors (CFSTRs) into a single production technology, was conceptualized emphasizing contaminant mitigation at the design stage to maintain system stability. This paper discusses the conceptual basis for the development of HISTAR and presents a theoretical overview of the CFSTRs. Mathematical modeling, using first-order algal growth kinetics combined with CFSTR reactor kinetics, was used to investigate the effects of system dilution rate, D s ; net algal specific growth rate, U a ; number of reactors, N ; input algal biomass, X i ; and contaminant concentration, C n , on algal productivity, as well as local dilution rate, D n , on suspended contaminant washout. The simulation results allowed the determination of preliminary design ranges for prototype development.