Range Of Organic Loadings Research Articles

Constructed Wetlands for Tannery Wastewater Treatment in Portugal: Ten Years of Experience

Wastewaters from tannery industry are complex in composition and providing adequate treatment can be difficult. Constructed wetlands (CW) are regarded as an alternative treatment to the conventional biological systems, as a developing cost-effective and environmentally friendly phytoremediation technology. The present review compiles and integrates information on CWs technology for the needs of the tannery sector. The following issues arise as crucial for the implementation of such systems, namely i) an accurate wastewater characterization and an effective pretreatment before reaching the CW, ii) choosing the plants species better adapted to the imposed conditions, iii) substrate selection and iv) range of organic loadings applied. The examples practiced in Portugal give indication that horizontal subsurface flow systems, with expanded clay media, are a suitable option to be considered when dealing with high organic loading tannery wastewater (up to c.a. 3800 kgCODha−1d−1), being resilient to a wide range of hydraulic variations. Plants such as Phragmites and Typha have shown to be adequate for tannery wastewater depuration, with Arundo donax proving resilient to high salinity wastewaters. The flexibility of implementation allows the CW to be adapted to different sites with different configurations, being suitable as main secondary or tertiary treatment stage.

Lab Scale Study of HRT and OLR Optimization in UASB Reactor for Pretreating Fortified Wastewater in Various Operational Temperatures

This study was carried out for examination of a lab-scale UASB reactor for optimization of organic loading rate and hydraulic retention time in various operational temperatures. The total volume of the reactor was 5 l with an effective height of 160cm and diameter of 5cm. This reactor was used to treat fortified municipal wastewater at volumetric organic loadings of 3.6, 7.2, 10.8, and 14.4kg m-3 d-1 at temperatures 30°C and 20°C and PH 7.6 – 8.4 for the treatment of high-strength enriched municipal wastewater of Ekbatan local treatment plant that located in west of Tehran. The COD of this wastewater have enriched by molasses and milk powder. To prevent PH fluctuation of the influent, NaHCO3 and K2HPO4 were added to wastewater. The result of present work indicated an optimum range for organic loading (7.2 to 10.8kg m-3 d-1) at all temperature condition with COD removal efficiency of about of 85% and 73% in UASB reactor at 30°C and low temperature about 20°C. Moreover, optimum HRT for influent COD concentration of 1200mg/l is shown to be only 4hours. Furthermore nitrate removal efficiency was about 80% at optimized organic loading range, with a sharp decrease beyond this range (e.g. up to 30% decrease for 14.4kg/m3.d and up to 45% decrease for 3.6kg/m3.d)

The effect of organic loading rate on foam initiation during mesophilic anaerobic digestion of municipal wastewater sludge

The impact of increasing organic load on anaerobic digestion foaming was studied at both full and bench scale. Organic loadings of 1.25, 2.5 and 5 kg VS m −3 were applied to bench-scale digesters. Foaming was monitored at a full scale digester operated in a comparable organic loading range over 15 months. The bench scale batch studies identified 2.5 kg VS m −3 as a critical threshold for foam initiation while 5 kg VS m −3 resulted in persistent foaming. Investigation of a full scale foaming event corroborated the laboratory observation that foaming may be initiated at a loading rate of ⩾2.5 kg VS m −3. Experimental findings on foam composition and differences in the quality characteristics between foaming and non-foaming sludges indicated that foam initiation derived from the combined effect of the liquid and gas phases inside a digester and that the solids/biomass ultimately stabilized foaming.

Kinetic Studies for an Aerobic Packed Bed Biofilm Reactor for Treatment of Organic Wastewater with and without Phenol

A laboratory scale aerobic fixed film bioreactor packed with glass beads for biofilm growth was used to evaluate the removal efficiencies of COD and phenol for a carbohydrate—phenol mixture in wastewater. It was done by an indigenous mixed culture inoculums developed after collecting sludge from a return line of an activated sludge plant. The test result on continuous flow in the above biofilm reactor indicated an optimum hydraulic loading range of 4-6.4 m3day-1m-2 for attainment of reasonable amount of COD removal in case of carbohydrate substrate only. The COD removal efficiency, however, gradually depleted from 100% to 54% by gradual increase in organic loading (OLR) from 0.72-4.32 kgday-1m-3, beyond which removal was not significant. For the identical loading conditions, in presence of phenol in the substrate along with carbohydrate, the COD removal was observed varying from 100-40% in the above organic loading range. The COD removal kinetics in presence of phenol also shows a decreasing trend compared to data obtained without the presence of phenol in wastewater that reveals biological inhibition. The experimental data were fitted in a simple plug flow model for evaluating the zero order, first order and Monod form of rate equations to evaluate the kinetics. It was found that Monod type rate equations combining a zero and first order rate expression is the best fit for the above hydraulic and organic loading that gives a best fit half velocity constant value of 35 mgL-1 (R2 = 0.9612).

Application of struvite precipitation coupled with biological treatment to slaughterhouse wastewaters

In this study, struvite precipitation coupled with an activated sludge process was applied to slaughterhouse wastewaters. Biological treatability characteristics of the wastewater were evaluated in a wide organic loading range of 0.06–0.42 g COD (g MLVSS)−1d−1 to assess COD removal as well as the extent of nitrification. Results of biological treatment of raw wastewater indicated that COD removal varied between 88% and 99% and complete nitrification was achieved at 0.1 g COD (g MLVSS)−1d−1 and lower organic loadings. Biological treatment of the struvite‐precipitated sample, which required no nitrification, yielded 86% COD removal at the organic removal of 0.3 g COD (g MLVSS)−1d−1. Struvite precipitation of both raw and biologically treated wastewater was at effective stoichiometric magnesium and phosphate doses to ammonia and between pH values of 9.0 and 9.5, providing ammonia concentrations of 20–30 mg N L−1 in the effluent and being independent of initial concentrations. The application of struvite precipitation both prior to and after biological treatment resulted in similar effluent qualities and provided the additional benefit of having a high‐rate activated sludge system instead of a low organic loading system with nitrification–denitrification. An additional benefit of struvite precipitation was the production of sludge which had recovery potential as a fertilizer. Among the tested treatment schemes, biological treatment following struvite precipitation seemed to be more advantageous in terms of process stability.

Influence of organic loading on an anaerobic sequencing biofilm batch reactor (ASBBR) as a function of cycle period and wastewater concentration

The effect of organic loading on the performance of a mechanically stirred anaerobic sequencing biofilm batch reactor (ASBBR) has been investigated, by varying influent concentration and cycle period. For microbial immobilization 1-cm polyurethane foam cubes were used. An agitation rate of 500 rpm and temperature of 30±2 °C were employed. Organic loading rates (OLR) of 1.5–6.0 g COD l −1 d −1 were applied to the 6.3-l reactor treating 2.0 l synthetic wastewater in 8 and 12-h batches and at concentrations of 500–2000 mg COD l −1, making it possible to analyze the effect of these two operation variables for the same organic loading range. Microbial immobilization on inert support maintained approximately 60 gTVS in the reactor. Filtered sample organic COD removal efficiencies ranged from 73 to 88% for organic loading up to 5.4 g COD l −1 d −1. For higher organic loading (influent concentration of 2000 mg COD l −1 and 8-h cycle) the system presented total volatile acids accumulation, which reduced organics removal efficiency down to 55%. In this way, ASBBR with immobilized biomass was shown to be efficient for organic removal at organic loading rates of up to 5.4 g COD l −1 d −1 and to be more stable to organic loading variations for 12-h cycles. This reactor might be an alternative to intermittent systems as it possesses greater operational flexibility. It might also be an alternative to batch systems suspended with microorganisms since it eliminates both the uncertainties regarding granulation and the time necessary for biomass sedimentation, hence reducing the total cycle period.

The COD Removal Performance of an Aerobic Fluidized Bed Reactor

Aerobic fluidized bed reactors (FBRs) are used as a new technology in wastewater treatment. In this study, an aerobic fluidized bed reactor with granulated activated carbon (GAC) as carrier material was operated under different conditions, including batch-loading, semicontinuous loading, and continuous loading. The FBR effluent was studied for changes in Chemical Oxygen Demand (COD). In this study, acetic acid was used as a carbon source. During the course of the study while the FBR was operating continuously initial COD influent concentration of the acetic acid was 1,000 ± 100 mg/L. Additional continuous flow investigations were conducted with the influent COD at 2000, 3,000 and 4,350 ± 125 mg/L. The total operation period was 5 months including a 1-month start-up process. Organic loading rate increased from 1.0 kg/day/m3 to 14.4 kg/day/m3. This was achieved by changing the influent water COD concentration and/or the hydraulic loading rate. The average effluent dissolved COD concentration was 141 ± 38 mg/L in this organic loading range. When the organic loading rate increased to 21 kg/day/m3, the effluent COD concentration sharply increased, and at the steady state the effluent COD was 928 mg/L. This can be attributed to an increase in the acetic acid concentration of the influent wastewater, because the hydraulic loading rate in the former mode of operation had remained stable. The biomass concentration in the fluidized bed was measured during continuous operation after the steady-state conditions were obtained. The total biomass concentration increased from 7500 mg/L to 17,300 mg/L during the study period.

Effect of particle size and sodium ion concentration on anaerobic thermophilic food waste digestion

Serial basic tests were conducted for the determination of fundamental kinetics and for the actual application of kinetic parameters to food waste digestion with precise measurement of methane production. The effects of food particle size and sodium ion concentration on the anaerobic thermophilic food waste digestion process were investigated. Results of serial tests for the determination of fundamental kinetic coefficients showed the value of k (maximum substrate utilization rate coefficient) and KS (half-saturation coefficient) as 0.24 hr-1 and 700 mg/L, respectively, for non-inhibiting organic loading range. The substrate inhibition coefficient (Ki) was 1000 mg/L for inhibiting organic loading range. No inhibition effect was shown until 5 g/L of sodium ion concentration was applied to the serum bottle reactor. However, the volume of methane gas was decreased gradually to the concentrations of more than 5 g/L of sodium ion applied. All sizes of food waste particle had the same constants (A: 0.45) but the maximum substrate utilization rate constant (kHA) was inversely proportional to particle size. As average particle size increased from 1.02 mm to 2.14 mm, kHA decreased from 0.0033 hr-1 to 0.0015 hr-1. Result reveals that particle size is one of the most important factors in anaerobic food waste digestion.

Process aiders for start‐up of anaerobic fluidised bed systems

Abstract In order to study the start‐up of anaerobic fluidised bed (AFBS) treating ice‐cream factory wastewater, several start‐up protocols were tested applying different aiders while the organic load was increased stepwise. These aiders were: biological preconditioning of the wastewater in a continuous flow‐stirred tank reactor at constant hydraulic retention time; chemical preconditioning of the wastewater with the supplementation of CaCl2 and a mixture of detergents. The protocols enhanced the AFBS start‐up performance. Each start‐up protocol increased the maximum efficiency of COD removal for the range of organic loadings applied by comparison with the control system, although the best substrate removal efficiency was not associated with the best methane yield.

A new concept of upflow clarification in activated sludge separation

An experimental investigation was conducted to evaluate a new concept of upflow clarification. A novel sludge removal mechanism that used the entire floor area for the removal of solids was incorporated in an upflow clarifier. The operating characteristics and design features of the continuous flux upflow clarifier (CFLUC) are described in detail. The laboratory study was conducted to determine the effectiveness of the CFLUC clarifier in separating sludges with different settling characteristics. The different sludge types were produced by an activated sludge system treating a synthetic dairy waste at four different food to microorganism (F: M) ratios. At low organic loadings (0.10–0.24 (g COD)(g MLVSS)−1 (d)−1), the CFLUC clarifier removed 70% of the pinpoint floe that remained during quiescent batch settling conditions. At high organic loadings (0.41–0.83 (g COD)(g MLVSS) −1 (d) −1), the CFLUC clarifier was capable of separating filamentous bulking sludges with poor settling characteristics. Based on the results of the experimental study the upflow clarifier effectively separated all sludge types over the range of organic loadings investigated. Key words: CFLUC clarifier, secondary clarification, upflow clarification, sludge blanket, bioflocculation, bulking sludge, gravity sedimentation.

Relationships between organic loading and zone settling velocity in the activated sludge process

The performance of the activated sludge process is functionally dependent on the settling and compaction properties of the activated sludge. The settling properties of activated sludges vary markedly depending on the presence or absence of filamentous organisms and on the process operating conditions. In this study the process was operated to minimize the presence of filamentous organisms and to investigate the effects of operating process variables, mainly organic loading. It was found that over the range of organic loadings tested, the ZSV increased with organic loading due to the size of the sludge floc which was also directly proportional to the organic loading. The ZSV in aerobically digested sludge was found to decrease with sludge age.

The effects of sludge age and metal concentration on copper equilibrium in the activated sludge process

Abstract This research investigated the general effects and equilibrium behavior of copper in the activated sludge process under a range of organic loadings and influent copper concentrations. This was achieved in a two‐phase experiment using continuous‐flow laboratory scale activated sludge units.

Treatment of high strength acidic wastewater with a completely mixed anaerobic filter

A completely mixed anaerobic filter, in which the influent organic matter concentration is diluted with recirculated effluent, was found to effectively remove organic matter concentrations in high strength acidic wastewater, at a range of organic loadings and shockloads. The methane in the generated gas accounted for 93% of the COD removal in the unit, while a solids balance indicated that only 0.012 g VSS was produced per g COD removed. Due to the low solids production and the initial seeding of the unit with digested sludge no nutrient additions were required during the 518 day period even though the COD:P and COD:N ratios were as high as 4360:1 and 39:1, respectively. Although a possible heavy metal toxicity was observed in the unit, this was eliminated after sulfide addition.

Kinetics of substrate removal in a completely mixed anaerobic filter

AbstractA completely mixed anaerobic filter, in which the influent organic matter concentration is diluted with recirculated effluent, was found to effectively remove organic matter concentrations in high strength acidic wastewater, at a range of organic loadings and shock loads. Increases in organic loading had a substantial effect on the relative organic matter composition of the effluent and the magnitude of the fatty acid fraction showed a pattern inverse to that of the nitrogenous organics. A fixed film model was formulated which indicated that at high substrate concentrations the substrate removal rate is proportional to the square root of the substrate concentration and the specific area of the filter medium. A comparison of the biofilm model and the measured effluent concentrations tended to indicate that the substrate removal rate is primarily affected by substrate concentration, specific surface area, flow rate, and temperature of the unit.