Low Influent Concentration Research Articles

Ethylenediamine modified rice hull as a sorbent for the removal of Basic Blue 3 and Reactive Orange 16

The potential of ethylenediamine modified rice hull to remove both basic and reactive dyes from aqueous solutions was studied. Equilibrium sorption data could be fitted into Langmuir and Brunauer-Emmett-Teller isotherm models. Sorption was enhanced by 4.5- and 2.4-fold for Basic Blue 3 and Reactive Orange 16, respectively, in binary dye solutions compared to single dye solutions. Column studies revealed that breakthrough was bed-depth, flow-rate and influent-concentration dependent. Unusual breakthrough curves were obtained for Reactive Orange 16, with very rapid initial breakthrough followed by complete retention at low flow rate, influent concentration and high bed depth. The breakthrough curves of Basic Blue 3 followed the typical S shape of packed-bed systems. Theoretical breakthrough curves at different bed depths and flow rates generated by the two-parameter mathematical model agreed well with the experimental data of single dye solution of Basic Blue 3.

THE EFFECT OF OXYGEN ON PERCHLORATE REDUCTION IN A BIOFILM REACTOR

The purpose of this research was to investigate the effects of low concentration of oxygen on reduction of perchlorate, especially low perchlorate influent concentrations in a biofilm reactor, as well as the effect of flow pattern in a biofilm reactor. Dissolved oxygen averaging 1 mg/L did not inhibit reduction of influent perchlorate from 23 to 426 μg/L in the biofilm reactors when sufficient acetate was added, probably due to limitation of oxygen diffusion into the biofilm. Influent perchlorate ranging from 23 to 426 μg/L was reduced to below detection level (4 μg/L) in the presence of 1 mg/L dissolved oxygen (DO). Chloride was produced in a ratio of 0.37gCl-/gClO₄- and 0.35gCl-/gClO₄- in plug flow and recirculation biofilm reactor which is similar to stoichiometric amount (0.36gCl-/gClO₄-) indicating complete perchlorate reduction at 426 μg/L of ClO₄- feeding. At 23 μg/L influent perchlorate, total biomass solids were 3.18 g and 2.81 g in the plug flow and recirculation biofilm reactors. The most probable number (MPN) analysis for perchlorate-reducing bacteria showed 104 to 105 cells/cm2 in both biofilm reactors throughout the experiments. The effluent perchlorate concentrations were not significantly different in the two different flow regimes, plug flow and recirculation biofilm reactors.

COMPARATIVE EVALUATION OF THE NUTRIENT AND COD REMOVAL PERFORMANCES OF VARIOUS SEQUENTIALLY OPERATED BIOFILM REACTORS

In this paper, the performances of Fixed Bed (FXB), Fluidized Bed (FLB), and Hybrid (HYB, i.e.fluidized bed followed by fixed) operational conditions of biofilm reactors were investigated. The COD (chemical oxygen demand), TN (total nitrogen) and TP (total phosphorus) were taken as performance-indicator parameters. For that purpose, a pilot experimental setup allowing FXB, FLB and HYB operations in a single reactor was run under varying COD (between 500 to 2000 mg COD l-1), TN (between 25 to 100 mg l-1) and TP (between 5 to 20 mg l-1) influent concentrations. The system was operated as sequentially batch (SBR) and a filtering process was added at the end of each operational phase in order to achieve liquid-solid separation. Results indicated that FXB and FLB are two upper and lower cases, and HYB plays a role between them and respond as a best alternative. For example, for the lower influent concentrations (around 500 mg l-1), 84% of COD was removed to final averages of 78±15.4 mg l-1; simultaneously, TN reduced to 18.55±3.48 mg l-1 (corresponding to 31% TN removal) and 60% of TP was treated to final averages of 1.92±0.2 mg l-1 in the HYB operation. When the influent concentrations were increased to 1000 mg l-1, COD removal efficiency of the HYB reactor was reduced to 73% (COD reduced from 1005.3±6.13 mg l-1 to 270.57±13.18 mg l-1) and, due to incomplete organic matter degradation and oxygen deficiency, 40% of TN was removed to final averages of 34.03±5.04 mg l-1 and 56% of TP treated to final averages of 3.98±0.28 mg l-1. Performance of the HYB reactor was decreased when influent concentration increased to 2000 mg COD l-1.

Chemolithotrophic denitrification with elemental sulfur for groundwater treatment

Denitrification for the treatment of nitrates in wastewater typically relies on organic electron donating substrates. However, for groundwater treatment, inorganic compounds such as elemental sulfur (S 0) are being considered as alternative electron donars in order to overcome concerns that residual organics can cause biofouling. In this study, a packed-bed bioreactor supplied with S 0:limestone granules (1:1, v/v) was started up utilizing a chemolithotrophic denitrifying enrichment culture in the form of biofilm granules that was pre-cultivated on thiosulfate. The granular enrichment culture enabled a rapid start-up of the bioreactor. A nearly complete removal of nitrate (7.3 mM) was NO 3 - attained by the bioreactor at nitrate loading rates of up to 21.6 mmol/(L reactor d). With lower influent concentrations (1.3 mM nitrate) comparable to those found in contaminated groundwater, high nitrate loads of 18.1 mmol/(L reactor d) were achieved with an average nitrate removal efficiency of 95.9%. The recovery of nitrogen as benign N 2 gas was nearly stoichiometric. The concentration of undesirable products from S 0-based denitrification such as nitrite and sulfide were low. Comparison of bioreactor results with batch kinetic studies revealed that denitrification rates were dependent on the surface area of the added S 0. The surface area normalized denitrification rate was determined to be 26.4 mmol /(m 2 S 0 d).

Effect of external organic matter on nutrient removal and growth of Phragmites australis in a laboratory-scale subsurface-flow treatment wetland

Coconut dust, which is used intensively in horticultural applications, was tested as an external organic additive in a series of laboratory-scale subsurface-flow constructed wetlands planted with Phragmites australis. The systems were fed with a mixture of NO3(-)-N, NH4+-N, and SRP in tap water to simulate high nutrient loads. In the absence of plants, TN removal efficiency was 66%, and the efficiency increased to > 80% in the microcosm wetlands. TN and NO3- removal efficiencies were marginally increased by coconut-dust treatment in comparison with sand-bed microcosms. Analysis by ANOVA showed that the TN removal from a coconut dust-supplemented sand-bed microcosm was significantly different from a sand-bed microcosm (0.0437 < p < 0.05). All the systems showed an equal capacity to treat NH4+ nitrogen under low influent concentration levels. Phosphorus removal efficiencies were > 98% in all three systems, and a difference between planted and unplanted systems was not observed. Shoot height and shoot densities of P. australis grown in the coconut dust-supplemented medium were significantly higher than those grown in the sand-bed medium. The difference in P. australis growth in response to the coconut dust addition revealed that the added material has the potential to create favourable conditions for plant growth.

Removal of estrogens in municipal wastewater treatment under aerobic and anaerobic conditions: consequences for plant optimization.

The removal of estrogens (estrone E1, estradiol E2, and ethinylestradiol EE2) was studied in various municipal wastewater treatment processes equipped for nutrient removal. A biological degradation model is formulated, and kinetic parameters are evaluated with batch experiments under various redox conditions. The resulting model calculations are then compared with sampling campaigns performed on differenttypes of full-scale plant: conventional activated-sludge treatment, a membrane bioreactor, and a fixed-bed reactor. The results show a > 90% removal of all estrogens in the activated sludge processes. (Due to the analytical quantification limit and low influent concentrations, however, this removal efficiency represents only an observable minimum.) The removal efficiencies of 77% and > or = 90% for E1 and E2, respectively, in the fixed-bed reactor represent a good performance in view of the short hydraulic retention time of 35 min. The first-order removal-rate constant in batch experiments observed for E2 varied from 150 to 950 d(-1) for a 1 gSS L(-1) sludge suspension. The removal efficiency of E1 and EE2 clearly depends on the redox conditions, the maximum removal rate occurring under aerobic conditions when E1 was reduced to E2. Sampling campaigns on full-scale plants indicate that the kinetic values identified in batch experiments (without substrate addition) for the natural estrogens may overestimate the actual removal rates. Although this paper does not give direct experimental evidence, it seems that the substrate present in the raw influent competitively inhibits the degradation of E1 and E2. These compounds are therefore removed mainly in activated sludge compartments with low substrate loading. Theoretical evaluation leads us to expect that diffusive mass transfer inside the floc (but not across the laminar boundary layer) appreciably influences the observed degradation rates of E1 and E2, but not of EE2.

인공습지를 이용한 하구담수호 유입하천수 수질개선 현장실험결과 분석

Wetland system is widely accepted as one of natural water purification systems around the world for nonpoint sources pollution control. Constructed wetlands have become a popular technology for treating contaminated surface and waste water. In this study, the field experiment to reduce nonpoint source pollution loadings from polluted stream waters using wetland system was performed from June 2002 to March 2004. Four wetlands were used and the size of each one was 0.8ha. Water of Dangjin stream flowing into Seokmun estuarine reservoir was pumped into wetlands. Inflow and hydraulic residence time of the system was 500 <TEX>$m^3$</TEX>/day∼1,500 <TEX>$m^3$</TEX>/day, 2∼5 days, respectively. After 2 year operation, plant-coverage of the wetlauds was about 70% from bare soil surface at initial stage . Average water quality of the influent was <TEX>$BOD_5$</TEX> 4.17 mg/L, TSS 18.45 mg/L, T-N 4.32 mg/L, and T-P 0.30 mg/L. The average removal rate of <TEX>$BOD_5$</TEX>, TSS, T-N and T-P during the study period was 5.6%, 46.6%, 45.7%, and 54.8%, respectively. Organic (<TEX>$BOD_5$</TEX>) removal rate was low and the reason might be low influent concentration. Wetland removal rate of T-P was about 10% higher than T-N. Performance of the experimental system was compared with existing data base (NADB), and it was within the range of general system performance. Overall, the wetland system was found to be adequate for treating polluted water stream with stable removal efficiency even during the winter period. Most of the nonpoint source pollutions from watershed are transported by streams or ditches, and they could be controled by constructed wetland system before entering the lake or reservoir.

Membrane sequencing batch reactor system for the treatment of dairy industry wastewater

Abstract A membrane separation process was coupled to a sequencing batch reactor (SBR) for biological nutrient removal (BNR) processes and a combined system was named a membrane sequencing batch reactor (MSBR). MSBR was used for the treatment of dairy industry wastewater and optimized to increase the treatment efficiency. Since a diffuser-attached module design, subcritical flux operation, and intermittent suction method were adapted to the system, long-term operation was possible, i.e. the system could be operated for more than 110 days with only one membrane washing. BOD removal was high (97–98%) and stable. SS (suspended solid)-free effluent was obtained by membrane separation. Since nitrogen was mainly consumed as nutrient for synthesis of new cells due to the low influent concentration, the removal rate reached 96%. Phosphorus removal was relatively low because of the limit of the biological process, i.e. removal efficiency ultimately depends on the amount of excess sludge wasting. A removal rate of 80% was reached after system optimization.

Experimental and model assisted investigation of an operational strategy for the BPR under low influent concentrations

The behaviour of a pilot scale biological phosphorus removal process (BPR) of the alternating type was investigated during periods of low influent concentrations and increased hydraulic load. A process disturbance of this type result in an increase in the phosphate concentration level in the anoxic/aerobic reactors and in the plant effluent shortly after the influent wastewater returns to normal strength. The accumulation of phosphorus in the system was avoided by the addition of an external carbon source either to the influent or to the effluent from the anaerobic reactor in form of sodium acetate. With the help of such an addition, the internal carbon storage compounds could be maintained at a high level, which is shown by poly-hydroxy-alcanoates (PHA) measurements. Several levels of acetate addition were investigated experimentally in order to determine a minimal amount of internally stored carbon, which could ensure the stabilization of BPR during such dynamic influent conditions. Furthermore reduction of aeration time during periods of low influent concentrations was investigated. It was observed that BPR was stabilized by combining a reduction of aeration time with carbon source addition, which maintained the internal stored carbon at a higher level. This combined control action resulted in a desired high BPR activity when the normal strength of the influent wastewater was re-established. The failure of the BPR process was sometimes observed even when comparatively high concentrations of PHA could be detected and an identification of a minimal PHA level was not possible. During this investigation an extended version of the activated sludge model No. 2 (ASM2), which includes denitrification by phosphate accumulating organisms, is used for the detailed analysis of the experiments. The model predicted the phosphorus build-up after the process disturbance as well as the performance during the stabilized experiments. Assisted by the model, the investigations indicate that a PHA limitation is not the only factor affecting the recovery of the BPR process during periods of low influent concentrations.

Technical Feasibility of the Treatment of Domestic Wastewater by a CEPS-UASB System

Raw domestic wastewater was treated continuously under laboratory conditions for 170 days by a chemically enhanced primary sedimentation (CEPS) followed by an upflow anaerobic sludge blanket (UASB) reactor. The CEPS was carried out with 70 mg FeCl3l−1 from day 1 to 82 and with 24 ml l−1 of the water extract of Moringa oleifera seeds from day 83 to 170. Compared to the natural primary sedimentation (NPS), the CEPS increased the ratio of soluble chemical oxygen demand to volatile suspended solids (CODs/VSS) of the supernatant by a factor 3 and 10 respectively. Although the FeCl3 increased the CODs/VSS ratio, it caused a decrease of the soluble content of the wastewater by a factor 1.4. This resulted in a low influent concentration supplied to the UASB reactor and consequently a low biogas production. However, the reactor achieved 54 % removal of total COD (CODt) at a hydraulic retention time (HRT) of 2 hours and a volumetric loading rate (Bv) of 1.4 g COD l−1 d−1. The Moringa oleifera seeds, besides the increase of CODs/VSS ratio, also allowed to increase the CODs content of the wastewater by a factor 2.2. As a consequence, the reactor produced a higher amount of biogas. The reactor achieved 71 % removal of CODt at a HRT of 2 hours and a Bv of 4 g COD l−1 d−1. The UASB reactor operated without the need to discharge regularly the biological excess of sludge produced. The implementation of the CEPS can decrease the volume needed by a conventional one step UASB reactor by a factor 0.4.

Effect of Sulfur Impregnation Method on Activated Carbon Uptake of Gas-Phase Mercury

The dynamics of granular activated carbon (GAC) adsorbers for the uptake of gas-phase mercury was evaluated as a function of temperature, influent mercury concentration, and empty bed contact time. Sulfur-impregnated carbons exhibited enhanced mercury removal efficiency over virgin carbon due to the formation of mercuric sulfide on the carbon surface. The effect of the sulfur impregnation method on mercury removal efficiency was examined through experi ments conducted on commercially available sulfur-impregnated carbon (HGR) and carbon impregnated with sulfur in our laboratory (BPL-S). Although HGR and BPL-S possess similar sulfur contents, BPL-S is impregnated at a higher temperature, which promotes a more uniform distribution of sulfur in the GAC pore structure. At low influent mercury concentrations and low temperatures, HGR and BPL-S performed similarly in the removal of mercury gas. However, as the temperature was increased above the melting point of sulfur, the performance of HGR deteriorated significantly, while the performance of BPL-S slightly improved. At high influent mercury concentrations, HGR performed better than BPL-S, regardless of temperature. For both HGR and BPL-S, the observed dynamic mercury adsorptive capacities were far below the capacities predicted by the stoichiometry of mercuric sulfide formation. In HGR carbon the sulfur is very accessible, but ag glomeration that occurs at high temperatures causes the sulfur to be relatively unreactive. In BPL-S carbon, on the other hand, the sulfur remains in a highly reactive form, but its location deep in the internal pores makes it relatively inaccessible and prone to blockage by HgS formation.

Analytical Model of Dual-Media Biofilter for Removal of Organic Air Pollutants

A steady-state mathematical model is presented to describe the kinetics of volatile organic compound (VOC) removal in biofilters that consist of a mixed compost and granular activated carbon (GAC) medium. The model describes the basic transport of VOCs from the gas phase into the liquid phase of the compost biofilm and into the carbon particles, using the assumptions of diffusion as characterized by Fick's law. The kinetics of biological degradation of substrate (pollutant) in the compost biofilm are assumed to follow a Monod-like relationship. Experimental data were compared with model predictions under steady-state conditions for treatment of a mixture of benzene, toluene, ethylbenzene, and o-xylene (BTEX) vapors. Best results were obtained when model applications were divided according to first-order biodegradation kinetics for relatively low influent concentrations (<50 ppm) of pollutants and zero-order reaction for higher (235–440 ppm) influent concentrations. In both instances, the model produced suitable approximation of experimental bed depth versus concentration profiles at steady state for individual compounds in biofilters containing small but varying amounts of GAC. The presence of GAC improved BTEX removal efficiencies over a biofilter containing only compost.

Sludge granulation in a UASB reactor for the treatment of soda-anthraquinone chemical wheat-straw pulp black liquor

Two lab-scale UASB reactors were used to treat black liquor. In both the reactors, granulation was achieved. Granular sludge could be formed with or without supplementation of biodegradable carbohydrates in the treatment of black liquor, although the supplementation could accelerate the rate of granulation and lead to a quick enhancement of COD removal. The UASB reactor without a gas-solid separator (GSS) was more suitable for sludge granulation, due to accelerated wash-out of the dispersed sludge. Low influent concentration was also essential for granulation. At a loading of 10 kg COD/m 3 d, 40–46% of influent COD and 56–65% of BOD were removed. The specific yield of biogas was 510 l/kg COD removed.

Biosorption process for removing lead (II) ions from aqueous effluents usingPseudomonassp.

Biosorption of lead from aqueous solutions was studied using microorganisms isolated from soil samples. The parameters of solution pH, initial metal concentration and residence time were studied. It was found that cell free extract of Pseudomonas sp. biosorbs metal ions more effectively than whole cells. The removal efficiency was usually higher at low influent lead concentration and long residence time. Presence of other cations and anions inhibited lead uptake in the following order : for the cations, Mn2+ > Zn2+ > Cd2+; for the anions SC>42‐> Cl‐.

Removal of micro-organisms by filtration through unwoven cloth coated with a pyridinium-type polymer.

Unwoven cloth coated with 32 mg/g of a copolymer of N-benzyl-4-vinyl-pyridinium chloride and styrene was found to be effective in removing micro-organisms from water. In experiments demonstrating removal of Escherichia coli by filtration through ten sheets of the unwoven cloth, the rate of removal was 99.99% at a filtration rate of 2.6 cm/h, and remained at 99% even at a high filtration rate of 300 cm/h and a low influent concentration of the bacterial cells such as 10(3) cells/ml. The rate of removal tended to increase with a decrease in the influent bacterial concentration. Seven other bacteria and two yeasts were effectively removed by filtration through the unwoven cloth. Filtration through the unwoven cloth was also effective in removing spores of fungi from water but was not very effective in removing bacteriophage T4 from aqueous solution.

Treatment of BTXE Compounds at Low Flow Rates

This chapter focuses on a treatment analysis query submitted by Joseph P. Nestor, a hydrogeologist with the Southern Pump and Tank Co. in Charlotte, North Carolina. The basic contaminants in ground water are benzene, toluene, xylenes, and ethylbenzene (BTXE). The BTXE compounds will each float on the ground water. The bioreactor can treat BTXE compounds to the 30 to 40 ppb range. The carbon adsorption and biological treatment system would be affected by much lower influent concentrations. Carbon adsorption is a separation process whereby the contaminants to be removed from the water are attracted to and held at the surface of activated carbon granules. Air stripping is a separation technology that takes advantage of the fact that certain chemicals are more soluble in air than in water. An air stripper only separates the organics from the water. The air stripper will be affected by regulations that cover air emissions.

The removal of nitrilotriacetic acid during biological sewage treatment and its effect on metal removal: Part 2–Under shock loading

Using an activated sludge pilot plant, the effect of a variation in the load of the potential detergent builder nitrilotriacetic acid on its biodegradation and heavy metal removal has been studied. Variations in the influent nitrilotriacetic acid load have been undertaken at two different base concentrations, 7·5 and 15 mg litre −1. The effectsof sludge age and influent heavy metal concentrations on the biodegradation of nitrilotriacetic acid have also been studied. When the influent nitrilotriacetic acid concentrations was increased to simulate the ‘wash day’ the additional concentrations were not always fully degraded. This effect was most marked at low sludge age and high influent metal concentration. When the biodegradation of nitrilotriacetic acid was incomplete, the removals of lead, nickel and zinc were reduced. Moreover, nickel and zinc previously absorbed were mobilised from the mixed liquor.

Determination of biological removal of organic constituents in quench waters from high-BTU coal-gasification pilot plants

Studies were initiated to assess the efficiency of bench scale, activated-sludge treatment for removal of organic constituents from coal-gasification process effluents. Samples of pilot plant, raw-gas quench waters were obtained from the HYGAS process of the Institute of Gas Technology and from the slagging, fixed-bed (SFB) process of the Grand Forks Energy Technology Center. The types of coal employed were Bituminous Illinois No. 6 for HYGAS and Indian Head lignite for SFB process. These pilot plant quench waters, while not strictly representative of commercial condensates, were considered useful to evaluate the efficiency of biological oxidation for the removal of organics. Biological reactors influent and effluent samples were extracted using a methylene chloride pH-fractionation method into acid, base, and neutral fractions, which were analyzed by capillary-column gas chromatography/mass spectrometry. Influent acid fractions of both HYGAS and SFB condensates showed that nearly 99% of extractable and chromatographable organic material comprised phenol and alkylated phenols. Activated sludge treatment removed these compounds almost completely. Removal efficiency of base-reaction organics was generally good, except for certain alkylated pyridines. Removal of neutral-fraction organics was also good, except for certain alkylated benzenes, certain polycyclic aromatic hydrocarbons, and certain cycloalkanes and cycloalkenes, especially, at low influent concentrations.

Treatment of combined and raw sewages with the dissolved air flotation process

Daily, sewage treatment works (STWs) receive large volumes of fats, oils and greases (FOG), by-products of food preparation. To increase FOG removal at STW, conventional primary sedimentation tanks (PSTs) can be enhanced using chemical coagulant or through dissolved air flotation (DAF) techniques. This work aimed to assess the potential benefits of enhanced primary treatment for FOG removal through an energy and costs analysis. To achieve this, a five-year sampling programme was conducted monthly at 15 STWs measuring FOG concentrations in crude and settled sewage (i.e. after primary treatment). In addition, two DAF pilot systems were trialled for four months and their performance, in terms of FOG removal, was assessed and compared to that of a control primary clarifier. Across the 15 STWs, influent FOG concentrations were found at 57 ± 11 mg.L−1. Chemical coagulants dosed prior to PSTs increased FOG removal rates on average to 71% whilst traditional sedimentation only achieved 50% removal. Effluent FOG concentrations were found between 12–22 mg.L−1 and 19–36 mg.L−1 respectively. By contrast, DAF achieved FOG effluent concentrations on average at 10 ± 4 mg.L−1 corresponding to 74% removal from a relatively low influent concentration of 40 ± 30 mg.L−1. Thus, enhanced primary treatments have the potential to reduce organic load to secondary treatment and increase energy generation through anaerobic digestion. The overall net energy balance was estimated at 2269 MWh.year−1 for the DAF compared to 3445 MWh.year−1 for the chemically-enhanced PST making it a less financially attractive alternative. Yet, in the case where the works require upgrading to accommodate flow or load increases, DAF appeared as a sensible option over sedimentation offering significantly lower capital costs and footprint. In relation to FOG management, upgrading all STWs is not realistic and will require understanding where the benefits would be the highest.