Effect Of Hydraulic Loading Research Articles

An in-depth analysis of the hydrodynamic behaviour of a high-rate lamellar DAF tank by means of CFD simulations

This research is based on computational fluid dynamics simulations of water and microbubble flow within the tank of a lamellar DAF (L-DAF) clarification system operating under high-rate DAF conditions (12–30 m/h). Firstly, performance of the DAF tank with lamellae was evaluated under two operating conditions in which the flow was either short-circuited or stratified in the absence of lamellae. In addition, the improvement in bubble removal efficiency achieved by the incorporation of lamellae in each scenario was assessed. Secondly, an in-depth analysis was conducted of the flow that develops in the separation zone as a result of placing the lamella pack in that part of the tank. The significant density difference that the lamellae cause to exist between the bubble blanket and clarified water below is responsible for the complex three-dimensional flow observed between the two regions. Analysis of this flow showed a previously undescribed mechanism in which the density gradient plays a crucial role in preventing bubbles from passing through the lamellae and ultimately escaping with the effluent. Finally, the effect of hydraulic loading on the bubble removal efficiency of the L-DAF tank under consideration was researched, and it was found that an L-DAF with a height/length ratio of 0.72 is able to operate at hydraulic loading close to 30 m/h, evidencing good debubbling performance.

Effect of hydraulic loading on bioremediation of municipal wastewater using constructed wetland planted with vetiver grass, Addis Ababa, Ethiopia

Gravel-based pilot horizontal subsurface flow constructed wetland planted with vetiver grass (Vitiveria zinaniodes) and unplanted operated at two hydraulic loading rates: 0.025 m/d and 0.05 m/d was carried out over a 3-year period. The aim of the study was to evaluate the effect of plant and hydraulic loading rate on the organic and nutrient removal performance of the constructed wetland system planted with vetiver grass (Vitiveria zinaniodes) in the removal of chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP) from municipal wastewater. The removal efficiencies of COD, TN, and TP in the planted cell decreased from 95 to 90.8%, 95.2 to 86.8% and 95.2 to 88.5%, respectively, with an increase in HLR from 0.025 to 0.05 m/d. The estimated above-ground biomass of dry weights of vetiver harvested ranged from 10.1 to 10.3 kg DW/m2, the nutrients uptake increased with plant age from 2.4 to 14.6 g N/kg DW and 0.8 to 8.5 g P/kg DW and above-ground biomass nutrient standing stock ranged from 147.5 to 150.4 g N/m2 and 85.5 to 87.5 g P/m2 in 16 months. The higher removal efficiency of COD, TN, and TP was achieved in HSSFCW planted with vetiver grass as compared to unplanted at both hydraulic loading rate operations. The results concluded that both applications of HLR are capable of removing organic matter and nutrients efficiently and vetiver grass can be used for remediation of pollutants in municipal wastewater in Addis Ababa.

Effect of hydraulic loading on the performance of unplanted drying beds treating low-concentrated faecal sludge

To optimize faecal sludge (FS) treatment plants in operation in Dakar (Senegal), this study was conducted to test the effectiveness of the solid/liquid separation on unplanted drying beds under different loading rates and two operation strategies (one or two feedings per campaign). Clogging, purification performances, dryness and hygienic quality were monitored. Results have shown that the load fractionation has reduced the clogging. Only removals of total solids (TS) and slightly those of total Kjeldahl nitrogen and chemical oxygen demand are influenced by the loading rate and the feeding mode. The reduction of faecal coliforms (FC) and helminth eggs (HE) in leachates is, respectively, 1 log unit and 100%. Two to nine days were sufficient to obtain a dryness higher than 80% TS with nominal loads of 13.7–122 kg/m2*year. Concentrations of the dried sludge in FC and HE were, respectively, about 7.104 FCU/100 g and 46 eggs/g with a reduction of 3 log unit after 15 days of drying and 32% in the sludge stored during 30 days. Unplanted beds are not effective for the treatment of low concentrated FS. The use of other technologies such as planted drying beds could be advisable in these types of sludge.

Performance of vertical flow constructed wetlands for faecal sludge drying bed leachate: Effect of hydraulic loading

The discharge of raw faecal sludge directly into the environment is a common practice that threatens environmental and public health in low-income countries. Planted drying beds are a promising and low-cost option for treatment of faecal sludge and the production of fodder plants, but current research shows the leachate quality does not meet guidelines for discharge. This paper investigates the use of Vertical Flow Constructed Wetlands (VFCWs) planted with Echinochloa pyramidalis for polishing of leachate from faecal sludge drying beds. At a pilot-scale, three hydraulic loads (50, 100 and 150mm/d) were applied with single loadings once a week on VFCWs (corresponding to 31±9, 63±19, 94±28g/m2/month of BOD5; 21±6, 42±12, 63±19 TKN; and 2±1; 4±4; 6±6 PO4–P, respectively, for hydraulic loading rates of 50, 100 and 150mm/d). Infiltration flow rate, plant growth, rhizospheric bacteria, and leachate characteristics were monitored. VFCWs were effective in reducing on average more than 80% of the pollutants monitored (COD, BOD5, NH4–N, TKN, PO4–P, and faecal bioindicators), which met all National Cameroon and WHO guidelines for safe reuse in agriculture, except for total nitrogen and faecal indicators. Results confirmed a correlation between plant density and rhizospheric bacteria growth with increasing hydraulic load. These are important results, demonstrating that VFCWs can operate efficiently at multiple hydraulic loadings, and are hence adaptable to different sized treatment schemes. It also illustrates that if plant production for fodder is a goal, increased loading rates are preferable as they achieve overall treatment goals and result in greater plant production.

The effects of hydraulic loading and NaCl concentrations on the regeneration of exhausted homoionic natural zeolite

A study of the suitable operational conditions for the regeneration of exhausted homoionic natural zeolite with ammonium was carried out. Laboratory-scale columns using NaCl solutions with concentrations of 2 and 4 mol/L and hydraulic loadings of 4, 6 and 8 bed volumes per hour (BV/h) were assessed. For both NaCl concentrations studied, the hydraulic load of 6 BV/h showed the highest ammonia nitrogen output from the exhausted zeolite bed. Results showed that the hydraulic load (BV/h) had a greater influence on the regeneration efficiency than the concentration of the regenerating solution.

Effects of hydraulic loading and room temperature on performance of anaerobic/anoxic/aerobic system for ammonia-ridden and phenol-rich coking effluents

A lab-scale anaerobic/anoxic/aerobic (A 1/A 2/O) system with three cycles was developed to purify high-strength coking effluent, 8, 000–15, 000 mg chemical oxygen demand (COD)/L, characterized by high levels of toxic organics and ammonia, 1200–1700 mg phenol/L and 700–1800 mg ammoniacal-nitroge/L. Besides the partial return of settled sludge to the anaerobic column, partial final effluent was also circulated to anaerobic unit to dilute and detoxify the feed as well as to the anoxic unit. During the pseudo-steady-state operation, more than 90% COD and 100% phenol removals were stably achieved while approximately 60% ammoniacal-nitrogen was removed. The performance of different stages in the A 1/A 2/O system in terms of Hydraulic Retention Time ( θ H), from 18 to 30 d, and room temperature, from 21°C to 30°C, was investigated. The modification of θ H did not have a substantial effect on the overall COD and phenol removal for the A 1/A 2/O system, but considerably influenced the distribution of COD removal between A 1 stage and A 2/O stages, and ammonium removal for A 2/O stages and A 1/A 2/O system. Elevated room temperature increased overall ammonium removal and ammonium removal at A 2/O stages, whereas the effect of temperature on ammonium removal at A 1 stage was relatively weak.

Rational design of packed saturators

The paper describes the development of a mathematical model for predicting the mass transfer efficiency of packed saturators used for dissolved air flotation. The first part of the paper deals with the equilibrium condition, i.e. the maximum attainable air concentration with a packed saturator at 100% transfer efficiency. The second part derives a kinetic model based on concentration-driven diffusion and the Lewis-Whitman two-film theory. The transfer rate constant across the laminar liquid film and the wetted packing area are estimated with the Onda correlations. The model is finally used to demonstrate the effects of hydraulic loading, packing depth, packing size and temperature on saturator efficiency.

The Elimination of Channeling and Foam Overturning in Continuous Mode Adsorbing Colloid Flotation with a Sodium Dodecylsulfate/Dodecanoic Acid Mixture

Abstract The effect of hydraulic loading, surfactant concentration, and air flow rate on the removal of Cr(III), Ni(II), and Zn(II) from chromium stream electroplating wastewater by adsorbing colloid flotation using a sodium dodecylsulfate/dodecanoic acid mixture was investigated. Typically, heavy metal concentrations of 81 ppm Cr(III), 55 ppm Ni(II), and 3.3 ppm Zn(II) were reduced to 1.2 ppm Cr(III), 3.2 ppm Ni(II), and 0.05 ppm Zn(II) at a hydraulic loading of 22.9 m3/m2·h (3 L·min−1), an air flow rate of 45.8 m3/m2·h (6 L·min−1), 40 ppm dodecanoic acid, and 80 ppm sodium dodecylsulfate, and using a 10-cm inner diameter column. A novel mode of operation (high liquid carryover) was used whereby a large proportion of the liquid entering the column leaves the column with the foam.

Short and Long-Term Responses to Changes in Hydraulic Loading in a Fixed Denitrifying Biofilm

The long- and short-term effects of hydraulic loading were investigated in a pilot packed tower bioreactor used for denitrifying a groundwater used for drinking water. Field experiments were conducted at hydraulic loading rates of 3.63 and 7.24 m3/hr/m2. The long-term (21 day average) performance of the denitrification reactor and the short-term response (48 hour) to regular air scour are reported here. In summary, an increase in hydraulic loading resulted in a long-term increase in the half-order denitrification rate constant, so that, on average, nitrate removal was maintained in the 5.2 m tower. At the lower hydraulic loading rate (3.63 m3/hr/m2) denitrification performance in the first 48 hours after air scour was maintained; however at twice the hydraulic loading, several days were required to restore the biofilm performance to long-term average levels.

Effect of Soil and Effluent Characteristics on Phosphorus Sorption in Dosed Columns

AbstractThe effects of soil and effluent loading characteristics on long‐term P retention and movement in soil columns were investigated. Six soil columns, 0.120 to 0.160 m deep and 0.20 m diam, were obtained from < 2‐mm fraction of Rosewall gravelly sandy loam (Inceptisols) and Qualicum gravelly loamy sand (Inceptisols). The columns were subjected to an instantaneous daily dose, except on weedends and holidays, of three effluent treatments over a period of 609 d. The three effluent treatments varied in P concentration and hydraulic loading levels; low (7.8 mg P/L, 0.0158 m/d), moderate (15.7 mg P/L, 0.0158 m/d) and high (15.7 mg P/L, 0.0315 m/d). The soils in the columns were kept unsaturated during the experiment. Continued effluent loading resulted in P breakthrough and a decrease in P sorption by soils. In five of six columns, P sorption by soils reached equilibrium. Both pore volume at P breakthrugh (PVBT) and P sorption at equilibrium (PSEQ) appeared to be affected by preferential movement of effluent through macropores. Irrespective of the mode of effluent flow, an increase in effluent P concentration and hydraulic loading decreased PSEQ; the effect of hydraulic loading on PSEQ was, however, more pronounced. Doubling the P loading through an increase in effluent P concentration decreased PSEQ by 2 to 11%; however, a similar increase in P loading obtained by a twofold increase in hydraulic loading, decreased PSEQ by 12 and 34% in Rosewall and Qualicum soils, respectively. Strong influence of effluent flow rate on PVBT, masked the effect, if any, of soil type and effluent loading on PVBT. The implications of these results with respect to wastewater renovation capability of a septic tank drainfieid were discussed.

Theory of Clarifier Operation. IV. Orthokinetic Flocculation in Concentrated Slurries

Abstract The operation of a continuous-flow sludge blanket clarifier is simulated by use of the continuity equations. The result of including an orthokinetic flocculation term due to the small-scale turbulence generated by the falling particles is examined and compared with the results obtained when only a “catch-up” flocculation mechanism is included. Turbulence flocculation permits the agglomeration of fines and results in an increase in clarifier efficiency. The effects of hydraulic loading and influent solids volume fraction are studied.