Dissolved Oxygen Monitoring Research Articles

DOxy: A Dissolved Oxygen Monitoring System.

Dissolved Oxygen (DO) in water enables marine life. Measuring the prevalence of DO in a body of water is an important part of sustainability efforts because low oxygen levels are a primary indicator of contamination and distress in bodies of water. Therefore, aquariums and aquaculture of all types are in need of near real-time dissolved oxygen monitoring and spend a lot of money on purchasing and maintaining DO meters that are either expensive, inefficient, or manually operated-in which case they also need to ensure that manual readings are taken frequently which is time consuming. Hence a cost-effective and sustainable automated Internet of Things (IoT) system for this task is necessary and long overdue. DOxy, is such an IoT system under research and development at Santa Clara University's Ethical, Pragmatic, and Intelligent Computing (EPIC) Laboratory which utilizes cost-effective, accessible, and sustainable Sensing Units (SUs) for measuring the dissolved oxygen levels present in bodies of water which send their readings to a web based cloud infrastructure for storage, analysis, and visualization. DOxy's SUs are equipped with a High-sensitivity Pulse Oximeter meant for measuring dissolved oxygen levels in human blood, not water. Hence a number of parallel readings of water samples were gathered by both the High-sensitivity Pulse Oximeter and a standard dissolved oxygen meter. Then, two approaches for relating the readings were investigated. In the first, various machine learning models were trained and tested to produce a dynamic mapping of sensor readings to actual DO values. In the second, curve-fitting models were used to produce a successful conversion formula usable in the DOxy SUs offline. Both proved successful in producing accurate results.

UV Absorption Spectrum for Dissolved Oxygen Monitoring: A Low-Cost Proposal for Water Quality Monitoring

One of the key indicators of water quality is dissolved oxygen. Even though oxygen is important in environmental monitoring, the sensors for dissolved oxygen are expensive and require periodic maintenance due to the use of membranes. In this paper, we propose using ultraviolet light absorption to estimate dissolved oxygen saturation in water samples. The absorption spectrum of dissolved oxygen in the ultraviolet range is investigated over a water matrix with different levels of complexity. First, the difference between different water matrixes is studied. The results indicate similar variations between river water and tap water matrices for comparative purposes. Both samples present much higher absorbance signals than distilled water. Thus, the rest of the tests were performed with only three water matrixes (ultrapure, distilled, and river water). By aerating, water samples were completely saturated. Then, nitrogen gas was used to remove dissolved oxygen from samples to obtain saturations of 75, 50, 25, and 3%. The absorption was measured from 190 to 380 nm, using LLG-uniSPEC 2. The obtained data were used to generate regression models for selected wavelengths (190, 210, 240, and 250 nm). The differences beyond 260 nm for the studied dissolved oxygen saturations were null. The generated models had correlation coefficients from 0.99 to 0.97 for ultrapure water, 0.98 to 0.95 for distilled water, and 0.90 to 0.83 for river water. The maximum differences were found between samples with 75 and 100% of saturation.

Postextraction monitoring of dissolved oxygen in virgin olive oil

AbstractThe issue of the presence of dissolved oxygen (DO) in virgin olive oil (VOO) is neglected in literature. Available information is limited to the extraction stage of the product life cycle, and studies focused on the subsequent stages from extraction to bottling are virtually absent. The present work aims to fill this gap through a dissolved oxygen monitoring experiment performed at industrial scale. Seven different unit‐operations of the routine working procedure of an Italian industrial company specializing in the marketing of VOO were studied: oil discharge from tanker truck; blend formation; oil transferring to filtration; oil transferring to bottling; precoat‐bodyfeed filtration; polishing filtration; bottling. The overall concentration of DO averages to 2.2 mg L–1, while the oil incoming the company was at 1.5 mg L–1. The unit‐operations can be ordered as “mixing‐for‐blend > precoat‐bodyfeed filtration > transfer‐to‐bottling > bottling,” with a decreasing oxygenation effect. Polishing filtration does not determine a significant DO variation. In the immediate term, the increase in DO does not result in oxidative deterioration of the oil, at least detectable with the peroxides value.Practical Applications: The results provide important information for the management of virgin olive oil on an industrial scale in the postproduction stages up to bottling. First, it was clearly demonstrated that bulk transport operations led to oxygenation of the oil. From this point on, the oil underwent further oxygenation, the extent of which depends on the specific processing operation considered. The oxygenation effect of each operation is different, which means that different interventions with varying intensity in terms of complexity and cost could be applied on a case‐by‐case basis to preserve the oil from oxygenation.

Dissolved oxygen monitoring using coating-free, surface-activated, intensity-modulated coreless termination fibre sensors and transducers

The study on the structural change of the coreless termination fibre (CTF) sensing region as a result of surface modification through wet cleaning under three conditions (organic, alkaline, and acidic solutions) resulted in excellent DO sensing and monitoring performance at zero salinity and ambient pressure and temperature. The modulation of light and detection of DO by absorbance-evanescent field sensing mechanism is also disclosed. Coating-free with improved surface-activated, intensity-modulated evanescent field sensor and transducer for DO sensing and monitoring is presented. The experiment showed that the optimised sample, CTF treated with 1 M of sulphuric acid, H2SO4 had produced a good sensitivity of 1.93 × 10−3 a.u./% (with an R-squared value of 0.99 and achieved more than 120% sensitivity improvement as compared to the untreated sensing region of the CTF), stability with variance and standard deviation values of 2.92 × 10−5 and 5.41 × 10−3 respectively and a detection limit of 8.40 %, equivalent to 0.69 mg/L, The optimised sample provided a good selectivity in DO sensing and monitoring in comparison with common colourless and odourless soluble gasses in deionised water, in this study. The sensor also offered a good relative response time compared to a commercial galvanic-based DO transducer used as a reference with the value of 2 µs. Owing to the advantages of structural change of the CTF sensing region with improved optical responses, surface activation, wettability, surface morphology, and surface roughness, the proposed design of the sensor and transducer provides a powerful choice for DO sensing and monitoring.

A new anaerobic, aerobic, nitrification, anoxic reactor (AANAR) with overlaid biological zones: Sulfide removal from wastewater and biogas

Hydrogen sulfide is a by-product from anaerobic digestion of wastewater that can cause a wide range of inconveniences, such as toxicity, corrosion, and foul odor. In this study, a new Anaerobic, Aerobic, Nitrification, Anoxic Reactor – AANAR (364 L), with overlaid biological zones, separated by a modified three phase separator, was evaluated on a pilot-scale to remove both sulfide from anaerobic effluent and biogas simultaneously, to control the foul odor. The AANAR was operated in three different phases: (i) Wastewater flow of 20 Lh−1 using ethanol supplementation to the denitrification process without biogas recirculation on the anoxic zone, (ii) Wastewater flow of 25 Lh−1 using ethanol supplementation to the denitrification process and biogas recirculation on the anoxic zone, and (iii) Wastewater flow of 25 Lh−1 with biogas recirculation on the anoxic zone without ethanol supplementation. The overlaid biological zone was observed by dissolved oxygen monitoring which was verified to be efficiently separated. The dissolved sulfide removal was 99.6 ± 0.5, 99.6 ± 0.1, and 99.8 ± 0.2 % for phase 1, 2, and 3, respectively. The biogas treatment performance to sulfide removal was 89 ± 7.0, 97 ± 2.0, and 96 ± 3.0 % for phases 1, 2, and 3, respectively. Hence, these results show the possibility of biological zones in an AANAR to efficiently remove sulfide from both anaerobic effluent and biogas generated by anaerobic digestion of wastewater.

Large spatiotemporal variability in metabolic regimes for an urban stream draining four wastewater treatment plants with implications for dissolved oxygen monitoring

Urbanization and subsequent expansion of wastewater treatment plant (WWTP) capacity has the potential to alter stream metabolic regimes, but the magnitude of this change remains unknown. Indeed, our understanding of downstream WWTP effects on stream metabolism is spatially and temporally limited, and monitoring designs with upstream-downstream comparison sites are rare. Despite this, and despite observed spatiotemporal variability in stream metabolic regimes, regulators typically use snapshot monitoring to assess ecosystem function in receiving streams, potentially leading to biased conclusions about stream health. To address these important practical issues, we assessed the spatiotemporal variability in stream metabolism at nine sites upstream and downstream of four WWTPs in a suburban stream. We used one year (2017–2018) of high-frequency dissolved oxygen (DO) data to model daily gross primary productivity (GPP) and ecosystem respiration (ER). We found that GPP was 1.7–4.0 times higher and ER was 1.2–7.2 times higher downstream of the WWTPs, especially in spring when light was not limited by canopy shading. Critically, we observed that these effects were spatially limited to the kilometer or so just downstream of the plant. These effects were also temporally limited, and metabolic rates upstream of WWTPs were not different from sites downstream of the plant after leaf-out at some sites. Across sites, regardless of their relation to WWTPs, GPP was positively correlated with potential incident light suggesting that light is the dominant control on GPP in this system. Temporal windowing of DO to proposed regulatory monitoring lengths revealed that the violation frequency of water quality criteria depended on both the monitoring interval and start date. We conclude that spatiotemporal variability in metabolism and DO are crucial considerations when developing monitoring programs to assess ecosystem function, and that evidence of WWTP effects may only arise during high light conditions and at limited scales.

Embedded Wireless Dissolved Oxygen Monitoring Based on Internet of Things Platform

Recently, Internet of Things (IoT) applications are distributing into many areas, such as industry and agriculture. This article presents the embedded wireless Dissolved Oxygen (DO) monitoring system based on IoT platforms. The module contains two types of data sensing, which are water temperature and DO sensors. Both devices are embedded with a wireless IoT module using NodeMCU-ESP8266, an integration WiFi-Microcontroller on a single board. The proposed IoT-DO monitoring system detects information data from the aquaculture pond environment. Namely, the parameters studied are water temperature and DO values. The cloud internet network collects and stores the experimental data and link to the users. The relationship between both parameters is analyzed using Statistical Package for the Social Sciences based Pearson correlation coefficient theory. The findings found that the water temperature and DO values are negatively related, with a statistically significant .05. Water temperature is the principal affection to other parameters of water. In this work, the DO value is studied to relate the water temperature. It was found that when the water temperature increases, the DO decreases accordingly and vice versa.

A soil microbial fuel cell-based biosensor for dissolved oxygen monitoring in water

Water pollution can cause significant depletions of dissolved oxygen (DO) in water systems with serious environmental and economic consequences. Online and continuous monitoring of DO can help prevent or minimise the risks associated with low DO values in water. Current DO sensors are, however, expensive and not suitable for continuous and autonomous in-field operation. In this study, we propose a novel and affordable Ceramic Soil Microbial Fuel Cell (CSMFC) for in situ, continuous and autonomous monitoring of DO in water. The system consists of a submersible ceramic vessel containing a soil-based anodic chamber, while the cathode, wrapped around the vessel, is used as the DO probe. The sensor signal, in terms of output voltage, correlates with the DO in water up to a saturating value of 4.5 ± 1.2 mg L−1, at a maximum voltage output of 321 ± 29 mV (20 ̊C, pH=7, 1.65 mS cm−1) with a sensitivity in the linear range of 53.3 ± 22.6 mV L mg−1. A factorial Design of Experiments (DoE) on pH, conductivity, DO and temperature, shows that the response of the sensor is mainly affected by temperature and DO, as well as by their mutual interaction. The calibration model is normalised by the output voltage baseline, thus accounting for any variability in performance, within the same device during long-term performance and from one device to another, which is a challenge in microbial-based systems. As such, this work not only reports an innovative microbial fuel cell-based DO sensor, but also demonstrates the necessity of a DoE to effectively calibrate the sensor.

Towards Energy Efficient Onsite Wastewater Treatment

The objective of this work is to demonstrate that some weaknesses of the onsite packaged WWTP associated with high operational costs and energy inefficiency could be overcome by improved management. The research methodology consists of series of batch studies with sludge from municipal or onsite WWTP, which simulate different working regimes of the onsite WWTPs – daily operation, toilet flushing and dishwasher machine. A simple classical tool, Oxygen Uptake Rate (OUR) is used to prove the hypothesis that regardless the specificity of the onsite WWTPs, namely the irregularity of the flow and load, three parameters follow similar increasing and decreasing trends – inflow rate, inflow pollution load and oxygen demand in the reactor. The literature review has not shown research publication about applicability of (OUR) for management of onsite WWTPs, but has shown experience and knowledge with municipal WWTPs, which were utilized in our study. The results prove that when there is no wastewater generation in the household, the (OUR) in the reactor is very low, 0.0007 to 0.0015 mg/l.s, thus do not require high oxygen supply. However, when wastewater flushes into the onsite WWTP, the oxygen demand increases rapidly and (OUR) reaches the range of 0.0040 to 0.0063 mg/l.s depending on the type and the quantity of the incoming substrate (pollution load). These results, if verified in filed experiments will enable optimization of the energy use during onsite WWTP operation. The suggestion is that the oxygen supply in the reactor should be adjusted according to the demand, respectively proportional to the inflow rate. In addition to the benefit of saving energy, the comprehensive sensors for dissolved oxygen monitoring, which require qualified maintenance could be avoided and replaced by simple sensors for level, which are anyway part of the equipment of most of the onsite packaged WWTP.

U.S. EPA Great Lakes National Program Office monitoring of the Laurentian Great Lakes: Insights from 40 years of data collection

Abstract The U.S. EPA Great Lakes National Program Office (GLNPO) implements long-term monitoring programs to assess Great Lakes ecosystem status and trends for many interrelated ecosystem components, including offshore water quality as well as offshore phytoplankton, zooplankton and benthos; chemical contaminants in air, sediments, and predator fish; hypoxia in Lake Erie's central basin; and coastal wetland health. These programs are conducted in fulfillment of Clean Water Act mandates and Great Lakes Water Quality Agreement commitments. This special issue presents findings from GLNPO's Great Lakes Biology Monitoring Program, Great Lakes Water Quality Monitoring Program, Lake Erie Dissolved Oxygen Monitoring Program, Integrated Atmospheric Deposition Network, Great Lakes Fish Monitoring and Surveillance Program, and Great Lakes Sediment Surveillance Program. These GLNPO programs have generated temporal and spatial datasets for all five Great Lakes that form the basis for assessment of the state of these lakes, including trends in nutrients, key biological indicators, and contaminants in air, sediments and fish. These datasets are used by researchers and managers across the Great Lakes basin for investigating physical, chemical and biological drivers of ongoing ecosystem changes; some of these analyses are presented in this special issue, along with discussion of new methods and approaches for monitoring.

Physical Sensors for Precision Aquaculture: A Review

Aquaculture is presented as a sustainable method to provide fish, although in reality, it is far from being sustainable. Its negative impacts on the environment can be prevented and corrected by the use of sensors, developing precision aquaculture. Sensors are widely used in terrestrial applications, but in underwater environments, their use is constrained by a variety of issues. The aim of this paper is to describe the state-of-the-art of the underwater sensors for water quality monitoring. First, the requirements and challenges of underwater sensors for aquaculture monitoring are discussed in detail. The main challenges are the need of a waterproof isolation or the need to avoid corrosion and biofouling, among others. Second, there are some advantages compared with the terrestrial applications, such as no need of minimized systems or the fact that such systems only require low accuracy. Subsequently, we evaluated the different options available to sense each variable, related to the needs of the aquaculture sensors. For temperature monitoring, thermistors, thermocouples or RTC seem to offer similar advantages. In contrast, for dissolved oxygen monitoring, the optical method seems to be the best option. For turbidity, optical methods are the most employed ones, while for conductivity measurements, the inductive coils are a promising option.

Citizen Science for Dissolved Oxygen Monitoring: Case Studies from Georgia and Rhode Island

Abstract Citizen science is emerging as an increasingly viable way to support existing water monitoring efforts. This article assesses whether water quality data collected by large numbers of volunteers are as reliable as data collected under strict oversight of a government agency, and considers the potential of citizen science to expand spatial and temporal coverage of water monitoring networks. The analysis hinges on comparison of data on water temperature and dissolved oxygen (DO) in freshwater streams and rivers collected by four entities: the United States Geological Survey (USGS) network of field scientists, the USGS network of automated sensors, the Georgia Adopt-A-Stream volunteer water monitoring program, and the University of Rhode Island Watershed Watch (URIWW) volunteer water monitoring program. We find that volunteer-collected data exhibit the expected relationship between temperature and DO. Furthermore, we find that volunteer- and USGS-collected data lie in roughly the same range, although...

The Influence of Optic and Polarographic Dissolved Oxygen Sensors Estimating the Volumetric Oxygen Mass Transfer Coefficient (KLa)

Aeration is usually the most energy intensive part of the wastewater treatment process. Optimizing the aeration system is essential for reducing energy costs. Field tests oriented to estimate parameters related to oxygen transfer are a common approach to compare aeration systems. The aim of this research is to assess the effect of dissolved oxygen probe lag on oxygen transfer parameter estimation. Experimental procedures regarding to process automation and control were applied to quantify dissolved oxygen probe lag. We have measured oxygen transfer in clean water, under a wide range of conditions (airflow rate, diffuser characteristics and diffuser density), with optic and polarographic sensors for dissolved oxygen measurement. The oxygen transfer was measured as per ASCE Standard procedures. Nonparametric statistical tests were used to compare the estimated volumetric mass transfer coefficient KLa with different sensors. According to the results, there is not significant influence of the probe lag (also known as time constant) or probe characteristics on the parameters used to assess oxygen transfer efficiency. This fact has great relevance in common practice of aerobic process for wastewater treatment because dissolved oxygen monitoring is used as an input for decision making related to the energy optimization in the aeration system. Findings from these tests contradict previous studies which claim that lag time in polarographic sensors for the dissolved oxygen measurement can bias estimate KLa.

Low-Intensity, Stocker-Based Channel Catfish Culture

AbstractLow-intensity production of Channel Catfish Ictalurus punctatus is characterized by low stocking rates, low installed aeration capacity, and no automated dissolved oxygen monitoring. Two studies conducted in nine 0.25-acre ponds quantified production characteristics of stocker Channel Catfish stocked for low-intensity food-fish production in single- or multiple-batch culture. In the multiple-batch study, 0.5-lb stockers (carryover fish) were stocked at 4,500 fish/acre and 0.044-lb fingerlings at 6,000 fish/acre. Stockers were grown to mean individual weights of 1.25, 1.75, or 2.25 lb. In the single-batch study, 0.5-lb stockers were stocked at 3,500, 4,500, and 5,500 fish/acre. All fish were fed a feed containing 32% protein daily to apparent satiation. Ponds were harvested in October and fish were weighed. Growth of carryover fish and understock (fingerlings) in multiple-batch culture was linear and growth-curve slopes did not differ significantly. Carryover fish size-class distributions differed ...

Upscale of recombinant α-L-rhamnosidase production by Pichia pastoris Mut(S) strain.

Pichia pastoris is currently one of the most preferred microorganisms for recombinant enzyme production due to its efficient expression system. The advantages include the production of high amounts of recombinant proteins containing the appropriate posttranslational modifications and easy cultivation conditions. α-L-Rhamnosidase is a biotechnologically important enzyme in food and pharmaceutical industry, used for example in debittering of citrus fruit juices, rhamnose pruning from naringin, or enhancement of wine aromas, creating a demand for the production of an active and stable enzyme. The production of recombinant α-L-rhamnosidase cloned in the MutS strain of P. pastoris KM71H was optimized. The encoding gene is located under the control of the AOX promoter, which is induced by methanol whose concentration is instrumental for these strain types. Fermentation was upscaled in bioreactors employing various media and several methanol-feeding strategies. It was found that fed batch with BSM media was more effective compared to BMMH (Buffered Methanol-complex Medium) media due to lower cost and improved biomass formation. In BSM (Basal Salt Medium) medium, the dry cell weight reached approximately 60 g/L, while in BMMH it was only 8.3 g/L, without additional glycerol, which positively influenced the amount of enzyme produced. New methanol feeding strategy, based on the level of dissolved oxygen was developed in this study. This protocol that is entirely independent on methanol monitoring was up scaled to a 19.5-L fermenter with 10-L working volume with the productivity of 13.34 mgprot/L/h and specific activity of α-L-rhamnosidase of 82 U/mg. The simplified fermentation protocol was developed for easy and effective fermentation of P. pastoris MutS based on dissolved oxygen monitoring in the induction phase of an enzyme production.

Intelligent Dissolved Oxygen Control System for Intensive Carp System

Success in designing affordable automated control systems for aquaculture will be widely applicable because it will enhance water management. Intensive recirculation systems have the potential for a significant increase in production per volume of water requiring dissolved oxygen monitoring and control. An intelligent Lab View dissolved oxygen sensing unit was designed using only one oxygen sensor and its transmitter for monitoring several tanks. Peristaltic pumps extracted water from each tank without adding oxygen to the sample. Measurements were auto-calibrated and statistically diagnosed using the air dissolved oxygen measurements. Dissolved oxygen sensor membrane fouling from algal blooms, sediments or suspended water droplets that still attaching to the membrane at the moment of oxygen measurements in the air were analyzed; the system controlled membrane fouling problems. Dissolved oxygen changes with temperature and fish feeding were analyzed from three tanks having each carps in a different growth stage. Dissolved oxygen mass balance was studied to gain a better understanding of events which can contribute to low dissolved oxygen concentration, such as heavy plankton blooms and high temperature.

Enhanced Lipid Production by Co-cultivation and Co-encapsulation of Oleaginous Yeast Trichosporonoides spathulata with Microalgae in Alginate Gel Beads

This study attempted to enhance biomass and lipid productivity of an oleaginous yeast Trichosporonoides spathulata by co-culturing with microalgae Chlorella spp., optimizing culture conditions, and encapsulating them in alginate gel beads. The co-culture of the yeast with microalgae Chlorella vulgaris var. vulgaris TISTR 8261 most enhanced overall biomass and lipid productivity by 1.6-fold of the yeast pure culture at 48 h and by 1.1-fold at 72 h. After optimization and scale-up in a bioreactor, this co-culture produced the highest biomass of 12.2 g/L with a high lipid content of 47 %. The dissolved oxygen monitoring system in the bioreactor showed that the microalgae worked well as an oxygen supplier to the yeast. This study also showed that the co-encapsulated yeast and microalgae could grow and produce lipid as same as their free cells did. Therefore, it is possible to apply this encapsulation technique for lipid production and simplification of downstream harvesting process. This co-culture system also produced the lipid with high content of saturated fatty acids, indicating its potential use as biodiesel feedstock with high oxidative stability.

Laboratory-determined Phosphorus Flux from Lake Sediments as a Measure of Internal Phosphorus Loading

Eutrophication is a water quality issue in lakes worldwide, and there is a critical need to identify and control nutrient sources. Internal phosphorus (P) loading from lake sediments can account for a substantial portion of the total P load in eutrophic, and some mesotrophic, lakes. Laboratory determination of P release rates from sediment cores is one approach for determining the role of internal P loading and guiding management decisions. Two principal alternatives to experimental determination of sediment P release exist for estimating internal load: in situ measurements of changes in hypolimnetic P over time and P mass balance. The experimental approach using laboratory-based sediment incubations to quantify internal P load is a direct method, making it a valuable tool for lake management and restoration. Laboratory incubations of sediment cores can help determine the relative importance of internal vs. external P loads, as well as be used to answer a variety of lake management and research questions. We illustrate the use of sediment core incubations to assess the effectiveness of an aluminum sulfate (alum) treatment for reducing sediment P release. Other research questions that can be investigated using this approach include the effects of sediment resuspension and bioturbation on P release. The approach also has limitations. Assumptions must be made with respect to: extrapolating results from sediment cores to the entire lake; deciding over what time periods to measure nutrient release; and addressing possible core tube artifacts. A comprehensive dissolved oxygen monitoring strategy to assess temporal and spatial redox status in the lake provides greater confidence in annual P loads estimated from sediment core incubations.

Laboratory-determined phosphorus flux from lake sediments as a measure of internal phosphorus loading.

Eutrophication is a water quality issue in lakes worldwide, and there is a critical need to identify and control nutrient sources. Internal phosphorus (P) loading from lake sediments can account for a substantial portion of the total P load in eutrophic, and some mesotrophic, lakes. Laboratory determination of P release rates from sediment cores is one approach for determining the role of internal P loading and guiding management decisions. Two principal alternatives to experimental determination of sediment P release exist for estimating internal load: in situ measurements of changes in hypolimnetic P over time and P mass balance. The experimental approach using laboratory-based sediment incubations to quantify internal P load is a direct method, making it a valuable tool for lake management and restoration.Laboratory incubations of sediment cores can help determine the relative importance of internal vs. external P loads, as well as be used to answer a variety of lake management and research questions. We illustrate the use of sediment core incubations to assess the effectiveness of an aluminum sulfate (alum) treatment for reducing sediment P release. Other research questions that can be investigated using this approach include the effects of sediment resuspension and bioturbation on P release.The approach also has limitations. Assumptions must be made with respect to: extrapolating results from sediment cores to the entire lake; deciding over what time periods to measure nutrient release; and addressing possible core tube artifacts. A comprehensive dissolved oxygen monitoring strategy to assess temporal and spatial redox status in the lake provides greater confidence in annual P loads estimated from sediment core incubations.

Intensive nursery production of the Pacific white shrimp Litopenaeus vannamei using two commercial feeds with high and low protein content in a biofloc-dominated system

The efficiency of shrimp production in limited exchange systems can be improved by optimizing the protein content of the feed. Therefore, a 62-d nursery study was conducted with 10-day-old Litopenaeus vannamei postlarvae stocked (5000PL10m−3) in four 40m3 raceways to evaluate the effect of high (40%) and low (30%) crude-protein (HP40 and LP30, respectively) diets and molasses supplementation on selected water quality indicators and shrimp performance under limited water exchange. Each raceway was equipped with a real-time dissolved oxygen monitoring system and a foam fractionator to control particulate matter. The level of molasses used in this study was effective in preventing significant ammonia accumulation in the culture medium. However, these supplementation levels were not effective in preventing nitrite accumulation. The HP40 treatment had significantly higher nitrite, nitrate and phosphate concentrations than the LP30 treatment. Shrimp mean final weight (0.94 vs. 1.03g) and specific growth rate (SGR) (11.03 vs. 11.19% day−1) were significantly different between treatments (P<0.05) LP30 and HP40, respectively, while mean survival (∼82% vs. 84%) and protein efficiency ratio (PER) (3.89 vs. 3.28) were not (P>0.05). The data suggest that substituting high-protein (40%) with low-protein (30%) feed in the nursery phase in a biofloc dominated system operated with minimal discharge may provide an alternative to improve shrimp biofloc technology, through improved water quality, cheaper (lower protein) feed and reduced environmental impact.