James J. Bisogni

Relationships between biological solids retention time and settling characteristics of activated sludge

Abstract It was the objective of this study to delineate the relationships between the settling characteristics of a non-filamentous activated sludge grown on a soluble waste, and a rational kinetic based parameter used to characterize the growth or loading rate of the system. The parameters used to characterize settling were Sludge Volume Index (SVI), zone settling velocity, and percentage dispersion. Biological Solids Retention Time ( θ c ), the reciprocal of mean cell growth rate, was used to characterize the metabolic activity level of the activated sludge. The chosen parameter ( θ c ) can be related to food to microorganism ratio and other widely used organic loading expressions. A series of bench scale laboratory aerobic reactors of the Ludzack type were operated as continuous flow systems with internal microbial solids recycle at a constant temperature of 20°C. A 6-h hydraulic retention time was maintained in all units. The values of Solids Retention Times studied varied from 12 days to 0–25 days which corresponds to a range of F/M (lb. BOD 5 lb. −1 MLSS-day) of 0·38–10·2. Operational parameters measured included COD, MLSS, dissolved oxygen, pH, oxygen uptake rates, and nitrogen content of the MLSS. Once steady state operation of the reactors was achieved, settling characteristics, i.e., SVI, zone settling velocity and percentage dispersion, were determined on mixed liquor samples withdrawn from each reactor. In addition, microscopic examination of the activated sludge floc was performed at each value of θ c . Experimental results were analyzed graphically to assess the nature of the relationships between each of the three measured settling parameters and θ c . Based on a criterion of minimal time rate of solids lost to the effluent, it appears that θ c values should be maintained in the range of 4–9 days. The implications of results of this study for design and operation of activated sludge systems are discussed.

Suspended solids characteristics from recirculating aquacultural systems and design implications

Abstract Fish culture water characterization provides basic information for treatment process design. Suspended solids from three recirculating aquacultural systems were investigated to determine specific gravity and particle size distribution. This research revealed that more than 95% of the suspended particles in these systems had a diameter less than 20 microns (μm). The specific gravity of the solid particles was determined as 1.19, resulting in a mean particle weight of 10.6×10 −7 mg. These small particles accounted for 40–70% of the total suspended solids by weight. The results suggest that methods toremove fine solids in recirculating system are necessary.

Ammonium, nitrate, and phosphate sorption to and solute leaching from biochars prepared from corn stover (Zea mays L.) and oak wood (Quercus spp.).

Biochar (BC) was evaluated for nitrogen (N) and phosphorus (P) removal from aqueous solution to quantify its nutrient pollution mitigation potential in agroecosystems. Sorption isotherms were prepared for solutions of ammonium (NH), nitrate (NO), and phosphate (PO-P) using BC of corn ( L.) and oak ( spp.) feedstock, each pyrolyzed at 350 and 550°C highest treatment temperature (HTT). Sorption experiments were performed on original BC as well as on BC that went through a water extraction pretreatment (denoted WX-BC). Ammonium sorption was observed for WX-Oak-BC and WX-Corn-BC, and Freundlich model linearization showed that a 200°C increase in HTT resulted in a 55% decrease in * values for WX-Oak-BC and a 69% decrease in * for WX-Corn-BC. Nitrate sorption was not observed for any BC. Removing metals by water extraction from WX-Oak-350 and WX-Oak-550 resulted in a 25 to 100% decrease in phosphate removal efficiency relative to original Oak-350 and Oak-550, respectively. No PO-P sorption was observed using any Corn-BC. Calcium (Ca) leached from BC produced at 550°C was 63 and 104% higher than from BC produced at 350°C for corn and oak, respectively. Leaching of P was two orders of magnitude lower in WX-Oak-BC than in WX-Corn-BC, concurrent with similar difference in magnesium (Mg). Nitrate and NH leaching from consecutive water extractions of all tested BCs was mostly below detection limits.

Impact of dissolved organic matter on colloid transport in the vadose zone: deterministic approximation of transport deposition coefficients from polymeric coating characteristics

Although numerous studies have been conducted to discern colloid transport and stability processes, the mechanistic understanding of how dissolved organic matter (DOM) affects colloid fate in unsaturated soils (i.e., the vadose zone) remains unclear. This study aims to bridge the gap between the physicochemical responses of colloid complexes and porous media interfaces to solution chemistry, and the effect these changes have on colloid transport and fate. Measurements of adsorbed layer thickness, density, and charge of DOM-colloid complexes and transport experiments with tandem internal process visualization were conducted for key constituents of DOM, humic (HA) and fulvic acids (FA), at acidic, neutral and basic pH and two CaCl(2) concentrations. Polymeric characteristics reveal that, of the two tested DOM constituents, only HA electrosterically stabilizes colloids. This stabilization is highly dependent on solution pH which controls DOM polymer adsorption affinity, and on the presence of Ca(+2) which promotes charge neutralization and inter-particle bridging. Transport experiments indicate that HA improved colloid transport significantly, while FA only marginally affected transport despite having a large effect on particle charge. A transport model with deposition and pore-exclusion parameters fit experimental breakthrough curves well. Trends in deposition coefficients are correlated to the changes in colloid surface potential for bare colloids, but must include adsorbed layer thickness and density for sterically stabilized colloids. Additionally, internal process observations with bright field microscopy reveal that, under optimal conditions for retention, experiments with FA or no DOM promoted colloid retention at solid-water interfaces, while experiments with HA enhanced colloid retention at air-water interfaces, presumably due to partitioning of HA at the air-water interface and/or increased hydrophobic characteristics of HA-colloid complexes.

Modeling of ammonia speciation in anaerobic digesters

Anaerobic digestion of high-nitrogen wastes such as animal manure can be inhibited by high concentrations of un-ionized ammonia, NH(3) (aq). Understanding the toxicity of NH(3) (aq) to anaerobic digestion requires a method for determining its concentration. Previous work on ammonia toxicity in anaerobic digesters has utilized a simple equilibrium calculation for estimating NH(3) (aq) concentration from total ammonia, temperature, and pH. This approach is not appropriate for concentrated solutions. In this work, a speciation model for major solutes in anaerobic digesters, based on Pitzers ion-interaction approach, is presented. Model simulations show that the simple equilibrium calculation (without corrections for non-ideal behavior) substantially overestimates NH(3) (aq) concentration for all but dilute digesters. This error in concentration determination increases with total solids content and is estimated to be greater than 40% for a digester fed dairy manure with 5% total solids or swine manure with 3% total solids. However, including an estimate of the activity coefficient for NH(4)(+) in the simple equilibrium calculation results in much more accurate estimates of NH(3) (aq) concentration. In this case, the estimated error is less than 10% in the absence of struvite precipitation at the highest total solids contents considered.

Suspended-Solids Removal by Foam Fractionation

Abstract Solids characteristics of foam condensate collected from recirculation aquacultural systems by a foam fractionator were investigated. Particle sizes were analyzed with a particle counter. Foam fractionation removed suspended particles as well as dissolved solids. The majority of the solids removed by foam fractionation were organic. Most of the suspended particles removed were smaller than 30 um in diameter.

Modeling surfactant removal in foam fractionation: I — Theoretical development

Abstract Surfactant removal by foam fractionation was theoretically analyzed by treating surfactant mass transfer from a bulk solution onto a moving bubble as a convective diffusion process. A mathematical model expressing the removal rate as a function of pertinent parameters was developed. The parameters included superficial air velocity, bubble size, bubble rising velocity, surfactant diffusion coefficient, and concentration. The model indicated that surfactant removal can be described as a first-order process whose rate increases with the diffusion coefficient, the superficial air velocity and the surfactant concentration in the bulk solution, but decreases with bubble size and bubble rising velocity. Based on the assumption of a completely mixed reactor within a section of a foam fractionator, a simplified model for foam fractionation under batch operation conditions was also presented. This simplified model provides a theoretical basis according to which the diffusion coefficient of surfactants can be determined and the model itself can be verified with experimental data.

Modeling surfactant removal in foam fractionation: II — Experimental investigations

Abstract Experiments were conducted to evaluate a mathematical model developed for surfactant removal by foam fractionation. Concentration changes of proteins which were believed to be the major surfactants in fish culture water were analyzed for different fractionator operating conditions. Experimental results indicate that a foam fractionator operated under batch conditions can be treated as a completely mixed reactor. The diffusion coefficient of proteins as surfactants was in the order of 10−12 m2/s. Protein removal rate by a foam fractionation process was proportional to the protein concentration in bulk solution and air flow rate. Other pertinent parameters that were also evaluated included bubble size and bubble rising velocity. Predictions of protein removal rates were given for fractionators operating at batch mode conditions.

The use of alkalinity as a conservative tracer in a study of near-surface hydrologic change in tropical karst

Abstract Water shortages commonly increase in frequency following forest clearance on lands overlying karst in the tropics. The mechanism underlying this hydrologic change is likely to depend on the land use which follows forest cover. To determine the flow paths which prevail for a progression of land uses common to the uplands of Leyte, Philippines, samples of interflow were collected during the rainy season and titrated to determine their alkalinities. The ratio of the measured alkalinity to the value predicted by equilibrium calculations for each sample was used as an indication of the contact time of the water with the limestone. The responses of the alkalinity saturation ratio and the runoff depth to increasing rainfall depth were used to substantiate the hypothesis that epikarst infilling and changing soil structure create throttles to percolation and infiltration. The forest site was found to generate interflow primarily as pipe flow, with the infiltration and percolation throttles rarely exceeded. Similarly, infiltration was not limiting for the slash/mulch site; however, the level of soil disturbance was adequate to initiate a throttle at the epikarst which increased the volume of interflow generated. The total percolation was similar for the plowed and slash/mulch sites; however, the interflow was decreased at the plowed site by reduced infiltration at the soil surface. The throttles to surface infiltration and epikarst percolation were even greater at the pasture sites, resulting in high runoff generation. However, comparatively greater infiltration was observed in the pasture having contour-hedgerows.

Bubble size distribution in a bubble column applied to aquaculture systems

Abstract Bubble size distribution affects the gas-liquid mass transfer rates during aeration and foam fractionation processes employed in recirculating aquacultural systems. The effects of air flow rate, protein concentration and air stone pore size on bubble characterization were investigated. Bubble size was measured photographically in conjunction with image-processing techniques. The study indicated that bubble size increased with air flow rate and air stone pore size, but decreased with protein concentration. Within the tested range of these variables, the geometric diameters of the majority of the bubbles (90%) were within the range of 0·5–3·0 mm, and the bubble sizes followed a normal distribution.