Dissolved Oxygen Demand Research Articles

Olive mill wastewater treatment using vertical flow constructed wetlands (VFCWs)

The study explores a synergistic two-phase system to treat olive mill wastewater (OMW), comprising a multilayer adsorbent filter (pretreatment) and a vertical flow constructed wetland (VFCW). The pretreatment phase includes layers of commercial granular activated carbon (CGAC) and volcanic tuff (VT), while the VFCW phase consists of planted tank with Phragmites australis reeds and unplanted tanks. Initially, municipal wastewater is introduced into the VFCW to establish the required microbial community. Then, pre-treated OMW is passed through the VFCW. The removal rates of various pollutants were assessed. The planted VFCW showed superior removal efficiencies, averaging 97.82% for total chemical oxygen demand (CODT), 92.78% for dissolved oxygen demand (CODd), 99.61% for total phenolic compounds (TPC), 98.94% for total nitrogen (TN), 96.96% for ammonium, and 95.83% for nitrate. In contrast, the unplanted VFCW displayed lower removal efficiencies, averaging 91.47% for CODT, 77.82% for CODd, 98.53% for TPC, 97.51% for TN, 92.04% for ammonium, and 90.82% for nitrate. These findings highlight the significant potential of VFCWs, which offer an integrated approach to OMW treatment by incorporating physical, chemical, and biological mechanisms within a single treatment system.Graphical

Improving the dissolved oxygen level in high solids loading cellulosic sugar acids fermentation by restructuring the biorefinery chain

Industrial production of biochemicals and biofuels from lignocellulose feedstock frequently requires aerobic fermentation with high dissolved oxygen demand. Efficient oxygen transfer from the air phase to the liquid phase has been considered as a great challenge due to the high viscosity and solid particles derived from the high solids loading lignocellulosic slurry. Here we presented a solution for aerobic sugar acids (gluconic acid and xylonic acid) fermentation by Gluconobacter oxydans in 30% (w/w) solids loading corn stover hydrolysate without solid/liquid separation. The biorefinery chain was restructured by conducting enzymatic hydrolysis before the submerged biodetoxification instead of solid-state biodetoxification. The viscosity of corn stover slurry decreased to ∼0.03 Pa·s after submerged biodetoxification and the gas-liquid oxygen transfer coefficient (kLa) reached 50.0 at the aeration rate of 0.1 vvm and agitation rate of 500 rpm, which is more efficient for sugar acids conversion than that using solid-state biodetoxified corn stover hydrolysate (only 8.8 kLa at 2.4 vvm, 500 rpm). The cellulosic sugar acids titer reached 156.0 ± 6.9 g/L at 0.1 vvm with 92.9% of the theoretical yield in the restructured biorefinery chain. The techno-economic analysis showed that the minimum selling prices of sugar acids produced by this restructured biorefinery chain was $351.7/ton which was 12.9% lower than that produced by the general biorefinery chain. This efficient process setting including one-pot hydrolysis, submerged biodetoxification, and fermentation provides a practical technical route for lignocellulose-based aerobic fermentation under high solids loading.

Dark fermentation of expired fruit juices for biohydrogen production followed by treatment and biotechnological exploitation of effluents towards bioplastics and microbial lipids

The treatment and biotechnological exploitation of expired fruit juices (EFJ) towards biohydrogen, polyhydroxyalkanoates (PHAs) and lipids production was investigated. The EFJ were initially fermented via an acidogenic consortium, during which the effect of the organic loading rate (OLR, 20–40 g sugars/L.d) on the sugars uptake and the yields of metabolites i.e. hydrogen, volatile fatty acids (VFAs) and lactate, was studied. The increase of the OLR resulted to lower bioconversion of sugars and metabolic shift to lactate production, whereas the highest hydrogen yield, 10.83 ± 0.41 L H2/m3 EFJ, was obtained for the OLR 30 g sugars/L.d. The acidogenic effluents were then utilized for the production of PHAs and microbial lipids, via bacterial heterotrophic and cyanobacterial consortia, respectively. The PHAs produced were in all cases copolymers, and the highest yield, 20.69 ± 1.01 kg PHAs/m3 EFJ was achieved from the effluent with the highest VFAs content. Microbial lipids were also successfully produced from all effluents. The results revealed that low VFAs and high sugars concentration, allowed cyanobacterial growth of up to 373.5 mg /L.d and maximum lipid content of up to 11.7 % d.w. (5.47 ± 0.49 kg biolipids/m3 EFJ), as well as significant substrate degradation (dissolved oxygen demand - d-COD, total nitrogen-ΤΝ, orthophosphates-PO43-, total sugars up to about 93 %, 95 %, 67 % and 96 %, respectively).

Impact of Recycled Process Water on Electrochemical Reactivity of Sulphide Ore

The Kevitsa Cu–Ni sequential flotation process is characterised by poor nickel recovery during summer periods (May–September). Evidently, the process water matrix in summer is different from that in other seasons; however, the Cu flotation performance is scarcely affected by the changes in the water matrix across the seasons. Increasingly different process water quality was generated through a grinding-and-dissolution protocol and its impact on the electrochemical reactivity of sulphide ore was studied. The main objective of this approach was to mimic the increasingly different quality of plant process water emanating from a closed-process water loop. Dissolved oxygen demand tests were conducted on the Kevitsa ore using water of varying quality from dissolution loops. The effect of the temperature and fine grind on the oxidation rates was also investigated. The study was coupled with EDTA metal ion extraction and xanthate adsorption tests. These showed that the number of dissolution loops, which has an impact on water quality, has a direct impact on the rate of oxidation of the ore. A fine grind and high temperature both increase the oxidation rates of the ore. The Kevitsa ore is most reactive in the first 10–20 min after milling. Furthermore, oxidation rates are also driven by the amount of pyrrhotite in the ore, with chalcopyrite being the least reactive, as indicated by the EDTA data. Xanthate adsorption is impacted by the water quality and fine grind. The combined effect of water quality, temperature and fine grind is expected to influence the flotation behaviour of sulphide minerals. The poor nickel recovery of the Kevitsa ore during the summer period is attributable to the unfavourable process water quality, which accelerates the oxidation of the ore during the summer period.

Why and How is Burrow Ventilation Initiated? A Case Study of Polychaete Behavior in the Burrow at Different Temperatures

Bioirrigation is a process corresponding to animal-induced transport of porewater solute or exchange between interstitial and overlying waters. How and why the burrowing macrobenthos complete this process remain unclear. Here, we used two infaunal-behavior observation devices to investigate the ventilation behaviors of the benthic polychaete Perinereis aibuhitensis Grube, a species that is widespread along the Asian coast with a wide temperature range, at various temperatures (5°C, 10°C, 15°C, 20°C, and 25°C). The two typical movement behaviors of P. aibuhitensis, axial crawling and radial undulation, as well as associated parameters, were delimited and quantified. We found that the radial undulation frequency of P. aibuhitensis and the associated pumping rate (PR) increased significantly with temperature (T, 5-25°C); this relationship can be described by the regression equation PR = −0.0067T2 + 0.29T - 0.52 (R2 = 0.749, P < 0.05; n = 15). The relationship between axial crawling velocity (ACV) and temperature (T, 5-25°C) can be expressed by the regression equation ACV = -0.0001T3 + 0.0059T2 - 0.063T + 0.28 (R2 = 0.997, P<0.05; n = 15). In general, pumping efficiency increased as temperature decreased, implying that the polychaete increasingly conserved energy at lower temperatures. Peak pumping volume (4.36 L d-1) was observed at 25°C, as a result of radial undulations. Thus, we concluded that radial undulation was the primary movement that led to bioirrigation. The dissolved oxygen demand was the key factor driving the initiation of radial undulation, and the specific aim of radial undulation was to increase oxygen availability by pumping new seawater into the burrow. Thus, radial undulation is critical for polychaete survival. The dissolved oxygen threshold level at which pumping was initiated increased with temperature, suggesting more energy conserved at lower temperatures. This pumping strategy of P. aibuhitensis is consistent with optimality theory, and is here designated the “optimal dissolved oxygen obtainment strategy”.

Water quality at Cai river mouth and Tac river mouth, Nha Trang bay (2015–2019)

Deltas of large rivers, especially in arid areas, have been used in ancient times for agriculture and are densely populated. In recent decades, many river deltas have been experiencing an increasing anthropogenic impact, contamination of watersheds, and marine pollution caused by the offshore extraction of hydrocarbons. Combining of these factors determines a considerable research interest in river mouth areas. This paper presents the annual monitoring data on the water environment of the two mouths of the Cai river and Tac river, Nha Trang bay, during the period 2015–2019. Statistical data showed an increase in dissolved oxygen demand (DO), biological oxygen demand BOD5, and the concentrations of ammonia, Zn and Cu. Seasonal variation revealed that most of studied parameters’ concentrations, especially nutrients, were higher in the rainy season. In contrast, the values of total suspended solids (TSS) and hydrocarbon (Cai River), and petroleum (Tac river) demonstrated a decrease. Generally, the average value of BOD5, concentrations of Cu and Pb at the Cai river mouth were lower than those at the Tac river mouth, whereas the concentration of Zn was higher. Overall, the water environment of both mouths was qualified for aquaculture and aquatic organism preservation purposes except for the case of coliform.

Differential flotation of pyrite and Arsenopyrite: Effect of pulp aeration and the critical importance of collector concentration

• Differential oxidation of pyrite and arsenopyrite achieved with pulp aeration. • Recovery of pyrite and arsenopyrite was high when singularly treated. • Xanthate adsorption removed high FeOOH removal from arsenopyrite compared to pyrite. • Adsorption of xanthate on heavily oxidised arsenopyrite surface was slow. • Selectivity was lost at high xanthate concentration. Differences in the oxidation rate and extent of model pyrite and arsenopyrite minerals, augmented by pulp aeration, was investigated using dissolved oxygen demand tests and X-ray photoelectron spectroscopy (XPS) analysis. Flotation studies of single mineral admixture coupled with zeta potential measurements, UV–Vis spectroscopy analysis of collector concentration and ex-situ metal ions in solution after collector addition were ascertained to shed light on reasons for observed window for selective flotation. The highest selectivity was achieved with low collector concentration of 1 × 10 -5 M PAX and selectivity index of 5.2 after 6 min flotation with collector concentration playing a critical role in attaining a good selectivity. Fast adsorption of xanthate and simultaneous oxidation to dixanthogen on slightly oxidised pyrite surface starved heavily oxidised arsenopyrite surface of the collector species, at low collector concentration, leading to its depression. The study was extended to the flotation of an auriferous refractory ore where similar observations were made. 62.7% rejection of pyrite was achieved in the staged flotation process.

Effect of tidal resuspension with oyster biodeposits on nutrient and oxygen dynamics

To test the effect of biodeposit resuspension on nutrient and oxygen dynamics, we performed a 30 d experiment in three 1000 l shear turbulence resuspension mesocosm (STURM) tanks (R) and three 1000 l non-resuspension (NR) tanks. All tanks contained defaunated muddy sediment and brackish estuarine water, received daily additions of oyster biodeposits, and had similar water column root mean square turbulent velocities (~1 cm s-1), energy dissipation rates (~0.08 cm2 s-3), and tidal cycles (4 h mixing-on; 2 h mixing-off). While bottom shear stress was low in NR tanks, high instantaneous bottom shear produced sediment and biodeposit resuspension in R tanks during the mixing-on cycles. Resuspension and biodeposit addition resulted in complex nutrient and oxygen dynamics in the water column as well as altered seabed fluxes. Modeled biodeposit diagenesis demonstrated that added resuspended biodeposit nitrogen in R tanks was nitrified, resulting in high water column nitrate and nitrite concentrations, as well as increasing water column dissolved oxygen demand. Water column dissolved oxygen concentrations were 2.3 times lower in the R tanks than in the NR tanks, whereas deposited organic matter from biodeposits resulted in sediment dissolved oxygen uptake 3 times higher in NR versus R tanks. Sediment dissolved inorganic nitrogen uptake in NR tanks and efflux in R tanks, respectively, were mediated by microphytobenthos abundance and biodeposit deposition. Seabed and water column biogeochemical processes, as mediated by biodeposit resuspension, controlled the nutrient and oxygen balances. Biodeposit resuspension is important when evaluating oysters as support for eutrophication control.

Role of humic substances as refractory organic matter in sustainable water quality assessment and management

AbstractIn northern China, river water originating from or flowing through forests often contains large amounts of oxygen-consuming organic substances, mainly humic substances. These substances are stable and not easily biodegradable, resulting in very high detection values of chemical oxygen demand. However, under natural conditions, the dissolved oxygen demand is not as high. Using experimental values to evaluate river water quality and the impact of human activities on water quality is thus unscientific and does not meet national development goals. In this study, the potential sources of high-concentration chemical oxygen demand in river water in two areas exposed to virtually no anthropogenic activities and strongly affected by humic substances, were analysed. The chemical oxygen demand contributed by humic substances (COD-HSs) was quantified using three methods. The results of water quality monitoring in 2017 and 2018 revealed that the chemical oxygen demand concentrations (5–44 mg/L) predominantly exceeded the standard (15 mg/L). The study results suggest that COD-HSs should be considered separately for objective evaluation and management of water quality, particularly in areas that are seriously affected by COD-HSs, to provide a scientific basis for formulating sustainable water quality management policies.

Comparison of performance, microbial kinetics and microbial community between intelligent and conventional aeration-controlled Anoxic/Oxic systems

This work reports a comparison study between an intelligent aeration-controlled Anoxic/Oxic system and a conventional continuing aeration Anoxic/Oxic system for the removal of major containment, which includes the performance of major containments treatment, microbial kinetics and microbial communities by high-throughput sequencing tool. The results showed that at the end of low dissolved oxygen start-up period, there was few differences on the performance between the intelligent aeration-controlled Anoxic/Oxic system, with a 60% aeration saving, and conventional continuing aeration Anoxic/Oxic system. Moreover, the differences of activated sludge microbial community were significant. The kinetics study shows that the microbial kinetics for the intelligent aeration-controlled Anoxic/Oxic system was faster than for the comparison system, especially the yield coefficient for autotrophic biomass was much higher. The high-throughput sequencing tool also have provided a reasonable comparison of microbial community in aeration tank and indicated that the low dissolved oxygen demand species were more abundant. Meanwhile, the functional relative abundance had little statistical differences. However, the more abundance of low dissolved oxygen demand species gradually represented function of the less abundance species in the end of the start-up process. This study can provide a helpful information in the intelligent aeration-controlled Anoxic/Oxic system optimization to further removal the specific contaminates in the domestic wastewater treatment.

Production of Nile tilapia Oreochromis niloticus grown in BFT using two aeration systems

Aeration systems used in BFT farming need to meet the dissolved oxygen demand from the biota present in the tank, as well as to keep the particulate matter in suspension. In BFT systems, it is common to use blowers, but the choice of an aerator with better efficiency in oxygen transfer and in electric energy consumption is indispensable. The vertical pump model (VPM) aerator is the most used in intensive tilapia production systems in southern Brazil. The objective of this research was to verify if this aerator model can support Nile tilapia farming under BFT system without producing negative impacts on the functionality neither of the biofloc nor in the production indexes. Simultaneous farming on BFT using blowers served as control. Oreochromis niloticus juveniles with an initial density of 7 kg/m3 were used. After 56 days of farming, the VPM aerator obtained significantly better results, both in water quality parameters and in production indexes, when compared to those obtained in the control treatment. The temperature was higher in the treatment of the blowers due to the lower thermal exchange between the atmospheric air and the tank water. Although the VPM caused lower temperatures, it obtained a productivity of 21.2 kg/m3, compared to 20.2 kg/m3 of the blowers. It was concluded that the use of the VPM aerator had no negative influence on both the formation and functionality of the biofloc, obtaining even higher production rates.

Assessment of the Physicochemical and Microbiological Parameters of a Teaching Hospital’s Wastewaters in Abidjan in Côte d’Ivoire

This work deals with the physicochemical and microbiological characterization of a hospital wastewater that is directly discharged in water bodies without treatment. Our focus was paid on the teaching hospital of Treichville (Cote d’Ivoire). For the purpose, various physicochemical parameters such as temperature, pH, dissolved oxygen, total dissolved solid, conductivity, nitrate, phosphate, chloride, chemical oxygen demand (COD), biological oxygen demand for five days (BOD5), salinity, and total suspended solids have been assessed. For the microbiological investigations, the parameters consisting in Pseudomonas aeruginosa, Salmonella and total coliforms have been assessed. From the analysis, it has been found that the wastewaters of the teaching hospital of Treichville are highly loaded in organic pollutants and in pathogens bacteria. The values of nitrate, dissolved oxygen demand, COD, BOD5 and biological parameters do not respect the international (WHO) values recommended for the water to be discharged in the environment. The ratio COD/BOD5 has been determined to vary between 1.25 and 2.80. The results showed that the studied wastewater is a domestic type wastewater composed either by mostly biodegradable pollutants or a mixture of biodegradable and non-biodegradable organic pollutants. These wastewaters constitute therefore a risk for the populations since they are discharged in water bodies without any treatment and used by communities.

Assessment of environmental impacts of the semi-intensive tilapia culture system

O principal objetivo do presente estudo é avaliar as características físicas, químicas e bacteriológicas dos efluentes contínuos e da despesca de peixes como a tilápia (Oreochromis niloticus), analisar os possíveis impactos das descargas de águas residuais e propor alternativas para minimizar os seus efeitos. As amostras foram coletadas entre abril e outubro, abrangendo assim todo o ciclo de desenvolvimento de tilápia. A demanda de oxigênio dissolvido é a principal causa de problemas ambientais, mas o índice de eutrofização é baixo, apesar de apresentar consideráveis níveis de fósforo total em comparação com os padrões legais estabelecidos pela Resolução 357/05 do Conselho Nacional do Meio Ambiente do Brasil (CONAMA). O índice de pressão ambiental elevou-se a 2,47, o que reforça a necessidade de medidas que possam minimizar esse impacto. A utilização de águas residuais na irrigação é a melhor alternativa, resultando em uso racional da água, menores taxas de utilização de fertilizantes e redução da poluição hídrica.

Instream Flows: New Tools to Quantify Water Quality Conditions for Returning Adult Chinook Salmon

AbstractThis paper examines the effect of implementing a water transaction program to address potential water quality limitations for returning adult fall-run Chinook salmon in a stream system where the agriculture is the dominant land and water use. Water transactions are becoming an increasingly used approach to provide instream flows during periods when there are competing water uses. Water transactions are often used to achieve ecological objectives, but their water quality or biological effects are rarely quantified. The effects of a water transaction implemented in the Shasta River were evaluated by using a spreadsheet model to quantify changes in dissolved oxygen conditions as they relate to discharge, pool volumes, holding habitat capacity, and potential dissolved oxygen demand by holding fish. The results indicate that water transactions may mitigate potential water quality impairments by decreasing the residence time in holding habitat, and are particularly effective during periods when flows ar...

The effect of regrind mills on the separation of chalcopyrite from pyrite in cleaner flotation

Stirred mills have been widely used for regrinding and are more energy efficient than tumbling mills. These two types of mills present different particle breakage mechanisms and redox environments during grinding. In this study, the effect of regrinding with these two types of mills on the separation of chalcopyrite from pyrite in the cleaner stage was studied. A laboratory rod mill and a laboratory stirred mill were used to regrind rougher flotation concentrates. It was found that chalcopyrite and pyrite exhibited different flotation behavior after regrinding with the rod mill and the stirred mill, resulting in different separability of chalcopyrite from pyrite. The mechanism underpinning this phenomenon was investigated by a range of techniques including dissolved oxygen demand measurements, X-ray photoelectron spectroscopy (XPS) and Time of flight secondary ion mass spectrometry (ToF-SIMS). It was found that the two mills produced different surface oxidation and pyrite activation by copper ions which determined the separation of chalcopyrite from pyrite. This study demonstrates that the selection of a regrind mill should not only depend on its energy efficiency but also the property of surfaces produced for subsequent flotation.

Effect of different biofloc levels on microbial activity, water quality and performance of Litopenaeus vannamei in a tank system operated with no water exchange

In zero-exchange superintensive culture systems, flocculated particles (bioflocs) accumulate in the water column. Consequently, some control over the concentration of these particles must be performed. The objective of this study is to evaluate the effects of three concentrations of bioflocs on microbial activity, selected water quality indicators and performance of Litopenaeus vannamei in a tank system operated with no water exchange. A 44-day study was conducted with juvenile (6.8g) shrimp stocked in twelve 850L tanks at a stocking density of 459shrimpm−3. Biofloc levels were expressed as three presets of total suspended solids (TSS) concentrations, as follows: 200mgL−1 (T200), 400–600mgL−1 (T400–600), and 800–1000mgL−1 (T800–1000). TSS levels were controlled by attaching a 40L settling tank to each culture tank. Reduction of TSS to concentrations close to 200mgL−1 decreased the time of bacterial cell residence and significantly reduced the nitrification rates in the water (P<0.05). The tanks in the T200 treatment had a greater variability of ammonia and nitrite (P<0.05), which led to the need to increase the C:N ratio of the organic substrate to control ammonia through its assimilation into heterotrophic bacterial biomass. But the higher production of heterotrophic bacteria in T200 (P<0.05) increased the dissolved oxygen demand. Nitrification rates were higher (P<0.05) in tanks with TSS concentrations above 400mgL−1, and ammonia and nitrite were significantly lower than in the T200 tanks. We suggest that ammonia and nitrite in the T400–600 and T800–1000 tanks were controlled primarily by nitrifying bacteria, which provided higher stability of these parameters and of dissolved oxygen. Regarding shrimp performance, the reduction of TSS to levels close to 200mgL−1 was associated with better nutritional quality of bioflocs. Nevertheless, differences in biofloc levels and nutritional quality were not sufficient to affect the weight gain by shrimp. The rate of shrimp survival and the final shrimp biomass were lower (P<0.05) when the TSS concentrations were higher than 800mgL−1. Analysis of the shrimps’ gills showed a higher degree of occlusion in the T800–1000 treatment (P<0.05), which suggests that the shrimp have an intolerance to environments with a solids concentration above 800mgL−1. Our results show that intermediate levels of bioflocs (TSS between 400 and 600mgL−1) appear to be more suitable to superintensive culture of L. vannamei since they create factors propitious for maintaining the system’s productivity and stability

Bulking sludge for PHA production: Energy saving and comparative storage capacity with well-settled sludge

Two acetate-fed sequencing batch reactors (SBR) were operated under an aerobic dynamic feeding (ADF) model (SBR #2) and with anaerobic phase before aerobic phase (SBR #1) to select mixed cultures with a high polyhydroxyalkanoates (PHA) storage response. Although kinetic selection based on storage response should bring about a predominance of floc-formers, a bulking sludge with storage response comparable to well-settled sludge was steadily established. An anaerobic phase was introduced before the aerobic phase in the ADF model to improve the sludge settleability (SBR #1), however, due to the consequent increased feast/famine ratio, the performance of SBR #1, in terms of both the maximum PHB (polyhydroxybutyrate) cell content and ΔPHB, was lower than that of SBR #2. SBR #2 gradually reached a steady state while SBR #1 failed suddenly after 50 days of operation. The maximum specific substrate uptake rate and storage rate for the selected bulking sludge were 0.4 Cmol Ac/(Cmol X·hr) and 0.18 Cmol Ac/(Cmol PHB·hr), respectively, resulting a yield of 0.45 Cmol PHB/(Cmol Ac) in SBR #2 in the culture enrichment phase. A maximum PHB content of 53% of total suspended solids and PHB storage rate of 1.36 Cmol Ac/(Cmol PHB·hr) was achieved at 10.2 hr in batch accumulation tests under nitrogen starvation. The results indicated that it was feasible to utilize filamentous bacteria to accumulate PHA with a rate comparable to well-settled sludge. Furthermore, the lower dissolved oxygen demand of filamentous bacteria would save energy required for aeration in the culture enrichment stage.

Assessing the use of activated sludge process design guidelines in wastewater treatment plant projects: A methodology based on global sensitivity analysis

Design inputs (wastewater characteristics, operational settings, effluent requirements or safety factors,…) need to be supplied when using activated sludge process design guidelines (ASPDG) to determine the design outputs (biological reactor volume, the dissolved oxygen demand or the different internal/external recycle flow-rates). The values of the design inputs might have strong effects on the future characteristics of the plant under study. For this reason, there is a need to determine how both design inputs and outputs are linked and how they affect wastewater treatment plant (WWTP) designs. In this paper we assess ASPDG with a methodology based on Monte Carlo (MC) simulations and Global Sensitivity Analysis (GSA). The novelty of this approach relies on working with design input and output ranges instead of single values, identifying the most influential design inputs on the different design outputs and improving the interpretation of the generated results with a set of visualization tools. The variation in these design inputs is attributed to epistemic uncertainty, natural variability as well as operator, owner and regulator decision ranges. Design outputs are calculated by sampling the previously defined input ranges and propagating this variation through the design guideline. Standard regression coefficients (SRC), cluster analysis (CA) and response surfaces (RS) are used to identify/interpret the design inputs that influence the variation on the design outputs the most. The illustrative case study uses the widely recognized Metcalf & Eddy guidelines and presents a didactic design example for an organic carbon (C) and nitrogen (N) removal pre-denitrifying activated sludge plant. Results show that the proposed GSA can satisfactorily decompose the variance of the design outputs (R2 > 0.7): aerobic (VAER) and anoxic (VANOX) volume, air demand (QAIR) and internal recycle flow rate (QINTR). Response surfaces are proposed to facilitate the visualization of how, when and why the design outputs may change when the most influential design inputs are modified. Finally, it is demonstrated that the proposed method is useful for process engineers providing a regional instead of a local picture of a design problem.

Fish Growth Model for Nile Tilapia (Oreochromis niloticus) in Wastewater Oxidation Pond, Thailand

The bioenergetics fish growth model of Nile Tilapia (Oreochromis niloticus) cultured in the cages in wastewater oxidation pond is presented. The oxidation pond is located in the very successful project area “The Leam Phak Bia Environmental Study Research and Development Project under Royal Initiatives Petchaburi Province” in Thailand. There are five oxidation ponds connected in series in the research area. The measurement of Nile tilapia growth is taken in the third pond in which the water quality is in the effluent standard. The water quality and fish weight are measured in each month for one year period. The fish growth model in the form of ordinary differential equation is introduced to understand the behavior of fish growth due to various environmental factors which are dissolved oxygen demand (DO), water temperature, concentration of plankton, ammonia and biochemical oxygen demand (BOD). In this presented model, we have introduced a new form of food assimilation efficiency as a function of fish weight. It is found that the predicted fish weight obtained from the model is in good agreement with the measurements. Also, this presented model can be applied to predict the fish weight in a wastewater stabilization pond when environmental factors have been changed.

Dissolved Oxygen Demand at the Sediment-Water Interface of a Stream: Near-Bed Turbulence and Pore Water Flow Effects

A microbial dissolved oxygen (DO) uptake model was developed for a stream bed, including the effect of turbulence in the flow over the bed and pore water flow in the porous bed. The fine-grained sediment bed has hydraulic conductivities 0.01≤k≤1 cm/s, i.e., sediment particle diameter 0.006≤ds≤0.06 cm. The pore water flow is driven by pressure fluctuations at the sediment-water interface, mostly attributable to near-bed coherent motions in the turbulent boundary layer above the sediment bed. An effective mass transfer coefficient (De) coupled to a pore water flow model was used in the DO transport and DO uptake model. DO flux across the sediment-water interface and into the sediment, i.e., sedimentary oxygen demand (SOD), was related to hydraulic conductivity and microbial oxygen uptake rate in the sediment and shear velocity at the sediment-water interface. Simulated SOD values were validated against experimental data. For hydraulic conductivities of the sediment bed up to k≈0.01 cm/s, the pore water f...