Performance evaluation of different filter media in turbidity removal from water by application of modified qualitative indices

Water filtration units have been faced problems in water turbidity removal related to their media, which is determined by qualitative indices. Moreover, Current qualitative indices such as turbidity and escaping particle number could not precisely determine the efficiency of the media in water filtration, so defining new indices is essential. In this study, the efficiency of Anthracite-Silica and LECA-Silica media in turbidity removal were compared in different operating condition by using modified qualitative indices. The pilot consisted of a filter column [one meter depth] which consisted of a layer of LECA [450 mm depth] and a layer of Silica sand [350 mm depth. Turbidities of 10, 20, and 30 NTU, coagulant concentrations of 4, 8, and 12 ppm and filtration rates of 10, 15, and 20 m/h were considered as variables. The LECA-Silica media is suitable media for water filtration. Averages of turbidity removal efficiencies in different condition for the LECA-Silica media were 85.8 +/- 5.37 percent in stable phase and 69.75 +/- 3.37 percent in whole operation phase, while the efficiency of total system were 98.31 +/- 0.63 and 94.49 +/- 2.97 percent, respectively. The LECA layer efficiency in turbidity removal was independent from filtration rates and due to its low head loss; LECA can be used as a proper medium for treatment plants. Results also showed that the particle index [PI] was a suitable index as a substitute for turbidity and EPN indices

Study on high-strength anaerobic landfill leachate treatability by membrane bioreactor coupled with reverse osmosis

One of the most important concerns in Tehran municipal landfill is the production of leachate and its potential for water resources pollution, this study was undertaken to examine feasibility of biological and physico/chemical treating of high-strength landfill leachate that was collected from Tehran municipal landfill. Average COD of the leachate in aerobic submerged membrane bioreactor is 68000 mg/L. The reactor with a working volume of 175 L, having membrane module [Hollow fiber] with pore size of 0.1 microm coupled with reverse osmosis with pore size of 0.001 micron was used in this study. The dissolved oxygen [DO] concentration was maintained at 3.2 mg/L and solid retention times [SRTs] and hydraulic retention times [HRT] were controlled at 55 and 15 days respectively, the average Membrane Bioreactor effluent COD was 1733 mg/L with average removal efficiency of 97.46%. The average NH4 -N removal efficiencies was 99%. On the other hand, an almost complete nitrification was achieved during this period. PO[4] -P concentration in the effluent was low and its average removal efficiency was as high as 90%; especially during the operation period. The averages reverse osmosis [RO] effluent COD was 335 mg/L with average removal efficiency of 99.13%. PO[4]-P concentration in the RO effluent was 0.86 mg/L and its average removal efficiency was 99.33%. The use of Membrane technologies, more especially reverse osmosis offers the best solution of achieving full purification with average COD removal efficiency of 99% and solving the problem of water resources pollution

Procedures of starting up and implementing of subsurface wetlands

Background and Purpose: Subsurface flow wetlands are one of the successful treatment methods used for municipal and industrial wastewater treatment, and are economical in terms of energy consumption and workforce. Much research has been conducted on wetland operation output in wastewater treatment, but no enough information is available on their start-up and maintenance. The present study investigates the circumstance of starting up and implementing a wetland

Methods and Materials: In this experimental study, two subsurface flow wetlands with a two-day detention time and two pretreatment units were built. The former was similar to Primary Settling tank with a 4-hour detention time and the latter was similar to anaerobic pond equipped a with digestion pit with a two-day detention time in a pilot scale. The wastewater [BoD5 = 250 mg/l, Tss=320 mg.l and ph=7.2] from municipal network in Sabzevar, Iran was used for irrigation; the pilot implementation and maintenance took one year

Results: Pilot operation indicated that the principal factors in implementing subsurface flow wetland were temperature, nonpenetrateability of the bed, and wastewater ingredients. However, pretreatment and bed obstruction were the limiting parameters of the wetland maintenance

Conclusion: Pretreatment of the subsurface flow of wetlands does not yield a high output; and if anaerobic ponds equipped with digestion pits are used, the treatment output is significantly enhanced, and the wetland operation will face minimum barriers

Excess sludge minimization in conventional activated sludge pilot plant; by three chemical matters

The excess sludge treatment and sludge disposal are major factors to the over-all economy of wastewater treatment plants [WWTP]. The ideal solution to the problem of sludge disposal is to combine sludge minimization with contamination removal at the source. In this study, the effect of ozonation, chlorination and 3,3,4,5-tetrachlorosalicylanilide [TCS] to treat part of the return activated sludge flow with the intention of reducing the overall plant yield in a conventional activated sludge pilot, were investigated in a side-stream pilot reactor. It was found that in the case of ozonation 8% g O[3]/g MLSS, and in the case of chlorination 2% g Cl[2]/g MLSS produce the best results. In the utilization of TCS method, the excess sludge production was reduced by 80% per day at a TCS dose of 1% g TCS/g MLSS. In all the above experiments a reduction in the volume of the excess sludge was achieved, while the efficiency of removal chemical oxygen demand [COD] from the reactor without the use of those methods was not significantly different

Treatment of low-strength industrial wastewater using anaerobic baffled reactor

The performance of an anaerobic baffled reactor at the pilot scale, with a 100-L volume and six compartments, that is used to treat low-strength industrial wastewater [671.5 +/- 49.9 mg COD/L, 350.1 +/- 36.8 mg BOD[5]/L and 443.8 +/- 60.7 mg SO[4][-2]/L] was studied. The reactor was started with a hydraulic retention time [HRT] of 25 h at 35 °C, which was gradually reduced to 3.33 h. The best reactor performance was observed with an organic loading rate [OLR] and a sulfate loading rate [SLR] of 4.45 g COD/L.d and 3.32 g SO[4][-2]/L.d, which was obtained at a HRT of 4 h. The COD and SO4-2 removal efficiencies were 78.6% and 89.2%, respectively. Additionally, the majority of the COD and SO[4][-2] removal occurred in the first compartment, up to 51.2% and 69.1%, respectively. Moreover, the pH in the first compartment was also the lowest. Subsequently, when the temperature was reduced to 20 °C at a HRT of 4 h, the maximum removal efficiencies for COD and SO[4][-2] decreased to 59.4% and 66.1%, respectively. In this case, the highest COD and SO[4][-2] removal efficiencies were observed in the third and fourth compartments, respectively, and these compartments had lower pH values. This phenomenon indicates that decrease in temperature causes transference of the acidogenic phase toward subsequent reactor compartments. In addition, these findings further show the potential for sulfate removal of the acidogenic phase

Determination of nanofiltration efficency in arsenic removal from drinking water

Nowadays nanofiltration has been considered for the treatment of organic and inorganic pollutants in surface and groundwater resources. In this study, rejection characteristics of arsenic compounds such as As[III] to form As[2]O[3] and As[V] to form Na[2]HasO[4].7H[2]O by a commercial nanofilter NF90 [DOW-FilmTec] was investigated. Arsenic rejection experiments included variations of feed arsenic concentration, transmembrane pressure and pH. In these experiments, as increasing initial concentration As[V] from 120 micro g/L to 1026 micro g/L in feed water, the percentage of rejection of As[V] decreased from 98.35% to 96.59% [permeate water concentration was 2 micro g/L to 35 micro g/L], while as increasing initial concentration As[III] from 118 micro g/L to 985 micro g/L in feed water, the percentage of rejection of As[III] decreased from 94.07% to 87.51% [permeate water concentration was 7 micro g/L to 123 micro g/L]. Due to increase of pressure from 4 bar to 7 bar, the percentage of rejection of As[V] in finished water increased from 95.68% to 99.02% [permeate water concentration decreased from 21 micro g/L to 5 micro g/L],while the percentage of rejection of As[III] decreased from 80.99% to 95.11% [permeate water concentration decreased from 96 micro g/L to 25 micro g/L]. Also due to increasing pH from 3 to 11, the percentage of rejection of As[V] in finished water increased from 95.45% to 99.00% [permeate water concentration decreased from 22 micro g/L to 5 micro g/L], while the percentage of rejection of As[III] decreased from 86.6% to 94.81% [permeate water concentration decreased from 65 micro g/L to 25 micro g/L]. Finally, nanofiltration application for arsenic removal from drinking water was recognized suitable regarding its proper efficiency and convenience operation and was recommended for point-of-use applications

Evaluation of THMs in Tehran's drinking water and comparison with drinking water outside the city water district

This study intends to monitor and evaluate the THMs concentration in the 6 different water districts in the city of Tehran as well as one district outside the city water district but inside the city limits. THMs are the main disinfectant by products [DBP] of chlorination, which are suspected to be human carcinogens. Formation of Trihalomethanes [THM] in drinking water depends mostly on raw water qualities such as pH, temperature, treatment process, residence time of water in the distribution system, as well as the bromine, chlorine and naturally occurring organic matter [NOM] concentrations. Because of the low cost of chlorine and convenience of application, chlorination is the most widely used disinfection process for drinking water. This led to a sharp reduction in mortality rate from many water born diseases, but the chlorine from the disinfection process reacts with NOMs in the raw water to form a series of undesired by-products. The most significant group of DBPs is trihalomethanes [THMs], which include chloroform [CHC13], bromodichloromethane [CHCI2Br], dibromochloromethane [CHClBr2], and bromoform [CHBr3]. The concentration of NOM in raw water is the most important parameter in the DBP formation. Increase in the bromine ion concentration shifts the DBPs from the chlorinated compounds to the brominated ones. Chlorination is used as the main disinfection process for the drinking water in Tehran, therefore; it is important to monitor and evaluate the THM's concentration in Tehran's drinking water. Samples were taken from twenty one locations across the city of Tehran in triplicates during the first week-end of April, May, June, July, August and September of 2009 They were collected directly from taps of consumers after letting the water run for several minutes before collecting the water in pre-cleaned glass containers with sodiumthio-sulfate preservative to eliminate any residual chlorine. The samples were analyzed for THMs using EPA method 524.2. A Purge and Trap device [Tekmar] was used to extract all the THMs and trap them in a sorbent tube. Using heat and inert N2 gas the trapped compounds were transferred to a gas chromatograph coupled with a mass spectrometer [6890 GC/5973 MSD, Agilent]. A 30 meter DB-5 capillary column with a 0.25 mm LD and 1 micro film thickness was used to separate the trihalomethanes before sending them to the mass spectrometer detector for identification and quantification. Spiked and duplicated samples were analyzed with every batch to determine the accuracy and precision of the analytical procedures. The data indicates that, the concentration of THMs are much higher in districts which are supplied mostly with surface water sources such as areas in the northern part of Tehran, compared to districts with well water as their main water source which are located mostly in the south and south west part of Tehran. The average concentration of chloroform, bromodichloromethane, dibromochloromethan and bromoform were 2.49 ppb, 2.08 ppb, 0.95 ppb and 0.15 ppb for the city of Tehran. The observed THMs concentrations are below the EPA's recommended MCL value of 80 ppb thus not causing a major adverse health effect on the population of Tehran. The highest average concentrations of chloroform during spring and summer seasons were observed in district 1, and 2 [Figure 1]. The measured concentrations for CHC13during the study period ranged between N.D in district 7 to 9.9 ppb in district 1

Investigation of intermittent chlorination system in biological excess sludge reduction by sequencing batch reactors

The excessive biological sludge production is one of the disadvantages of aerobic wastewater treatment processes such as sequencing batch reactors. To solve the problem of excess sludge production, oxidizing some of the sludge by chlorine, thus reducing the biomass coefficient as well as the sewage sludge disposal may be a suitable idea. In this study, two sequencing batch reactors, each with 20 L volume and controlled by on-line system were used. After providing the steady state conditions in the reactors, sampling and testing of parameters were done during 8 months. The results showed that during the solid retention time of 10 days the kinetic coefficient of Y and Kd were 0.58 mg biomass/mg COD and 0.058/day, respectively. At the next stage, different concentrations of chlorine were used in the reactors intermittently. Results showed that 15 mg chlorine/gMLSS in the reactor was able to reduce the yield coefficient from 0.58 to 0.3 mg biomass/mg COD. In other words, the biological excess sludge was reduced about 48%. But the soluble chemical oxygen demand increased slightly in the effluent and the removal percentage decreased from 95% in the blank reactor to 55% in the test reactor

Preozonation and prechlorination effects on TOC removal by nanofiltration in water treatment

In this study, NF membrane was used for surface water treatment. The rejection of organic material, measured as Total organic carbon [TOC], by Nanofiltration was examined. The effects of application of pre-ozonation and pre-chlorination on TOC removal are discussed and their performances are compared with the performances of Nanofiltraion system without pretreatment process. In NF, natural organic rejection is high and no pre-treatment are required. Coagulation targets large hydrophobic organics which foul NF membranes by precipitation and gel layer formation. The results showed that TOC removal in Preozonation-coagulation was higher than prechlorination-Coagulation. In addition pretreatment increases Nanofiltration efficiency

Efficiency evaluation of textile basic dye removal from water by nanofiltration

Nanofiltration, widely developed over the past decade, is a promising technology for the treatment of organic and inorganic pollutants in surface and groundwater resources. The aim of the present research was to study the efficiency of textile dyes removal by a commercial nanofilter NF90 [Dow-Film Tec]. Dye rejection was studied using basic dye [Basic Chrysoidine Cryst Yellow Gold 0.4%] with its relevant additive. Experiments were continued until the fouling time of the membrane. Each experiment was repeated after washing to evaluate the efficiency of the washing process. Results showed that the values of color removal were 97.98% for the simulated textile wastewater containing basic dye. The membrane was sensitive to fouling since most of dyes were used for polyamide textile dyeing. Washing the membrane with a solution including NaOH [pH=12] and HCl [pH=2] showed its efficiency to solve the fouling problem. The filtration process was efficient and promising for reusing wastewater in this industry

study of feasibility for water purification using vertical porous concrete filter

There is a need to find cheaper and simpler techniques for rural water filtration system in developing countries. Using a filter made of blocks for the water treatment enables one to make vertical filters. It is expected that the amount of land utilized would decrease by more than 70% if vertical filters were used. The operation and washing would be simpler than using horizontal sand filters as filters made of blocks would be used instead. The feasibility study focused on finding adequate materials, compositions and methods of making a block with enough resistance to water pressure, sufficient porosity for water transformation, and using inexpensive, readily available materials. A pilot study was used to determine an appropriate thickness. Testing the porous filter in another pilot study using the low overflow rate of river water showed biological growth in that media and an adequate efficiency of about 90-100% was obtained for decreasing the coliform bacteria. Washing in this filter is possible. The amount of water necessary for backwashing is 2.9% of total amount of water, which is passed

Removal of arsenic from an aqueous solution by pretreated waste tea fungal biomass

Arsenic contamination in water poses a serious threat on human health. The tea fungus known as Kombucha is a waste produced during black tea fermentation. The objective of this study was to examine the main aspect of a possible strategy for the removal of arsenates employing tea fungal biomass. The pretreatment of biomass with FeCl3 was found to improve the biosorption efficiency. Arsenics uptake was found to be rapid for all concentrations and reached to 79% of equilibrium capacity of biosorption in 20 min and reached equilibrium in 90 min. The pseudo second-order and first-order models described the biosorption kinetics of As [V] with good correlation coefficient [R2>0.93] and better than the other equations. The data obtained from the experiment of biosorption isotherm were analyzed using the Freundlich and Langmuir isotherm models. The equation described the isotherm of As [V] biosorption with relatively high correlation coefficient [R2>0.93]. According to the Langmuir model, the maximum uptake capacities [qm] of tea fungal biomass for As [V] were obtained 3.98 +/- 10-3 mmol/gr. The effect of Na+, K+, Mg+2 and Ca+2 on equilibrium capacities of As was not significant. The variation of sorption efficiency with pH showed that optimum biosorption takes place in the pH ranges of 6 to 8. Promising results were obtained in laboratory experiments and effective As [V] removals were observed

Evaluation of industrial dyeing wastewater treatment with coagulants and polyelectrolyte as a coagulant aid

Textile industry is the major source of water consumption and wastewater pollution. There are various treatment techniques to remove textile wastewater pollution. Coagulation-flocculation is a widely used process to remove pollution due to suspended particles. In this research, different coagulants like Alum, Lime, FeCl[3], FeSO[4] and MgCl[2] were applied to select the suitable ones with optimum removal efficiency. Settling characteristics of flocs formed in the coagulation process were studied in a laboratory scale settling column unit. Parameters such as color, COD, TSS, turbidity and settled sludge volume have been evaluated. The optimum coagulant dose and pH value were determined by comparing the effectiveness of these coagulants. Results showed other coagulants except lime could eliminate color and COD successfully. In this case, FeSO[4] was chosen as an optimum coagulant for color removal because of the lowest required coagulant dose, minimum settled sludge volume and maximum decolorization

Control of disinfection by products formation potential by enhanced coagulation

Jar-test experiments were conducted to study enhanced coagulation effectiveness in removal of disinfection by products [DBPs] from Zayandehrud River at Isfahan Province-the center part of Iran- in 2004. In this study, the removal of suspended and colloidal particles and natural organic matter [NOM] at various coagulant doses and coagulation pHs was assessed through raw and treated water measurements of turbidity, UV254 absorbance, TOC, and dissolved organic carbon [DOC]. The trihalomethane formation potential [THMFP] was also determined by a mathematical relationship with TOC. Results indicated that NOM removal was a function of coagulant type, coagulant dose, and pH of coagulation. In general, TOC, DOC, and UV254 absorbance removal enhanced with increasing coagulant dose. However, further increases in coagulant dosage had little effect on disinfection by-products precursors removal. Ferric chloride was consistently more effective than alum in removing NOM. Coagulation pH was appeared to be a determining factor for maximum NOM removal and the removal of DBPs precursors by enhanced coagulation was significantly enhanced at pH 5.5 in comparison with initial pH of water. Furthermore, it is specified that preadjustment of pH with sulfuric acid reduced the coagulant dosage and thus, production of sludge. The reduction in THMFP was consistent with the trends observed for DBPs precursors removal data [i.e. UV254 and TOC data]

Physicochemical and biological treatability studies of urban solid waste leachate

In this research, physical, chemical and biological treatability of Tehran solid waste leachate was studied. Results indicate that the amount of COD for the fresh raw leachate of Tehran is equal to 66,608 mg/l. The leachate is transferred to an equalization tank for storage and pH control process. After neutralization, leachate is introduced to an up flow and down flow anaerobic reactor. The effluent of anaerobic reactor is conducted to a sequencing batch reactor. Sequence batch reactor [SBR] effluent was pumped in to sand and activated carbon filters, after chemical coagulation and clarification. Results showed that anaerobic reactor with detention time of 3 days had a 35% COD removal and increasing the detention time to 4.5 days would improve the COD removal to 45%. Nutrient adjustment with phosphorus and nitrogen increased the initial 23% efficiency of sequence batch reactor to 44%. The effluent COD of SBR reactor was 21,309 mg/l. Recycling of aerobic reactor effluent with incoming feed to anaerobic reactor reduced the anaerobic reactor influent COD to 20,000 mg/l and this caused 53% and 57% COD removal in the anaerobic and aerobic effluent, respectively. The total systems COD performance increased to 80% and SBR effluent COD eventually reduced to 4,000 mg/l. Coagulation, flocculation and sedimentation processes were practiced to make the 4,000 mg/l effluent COD comply with environmental standards of Iran. The optimum coagulant found to be ferric chloride with the dosage of 50 mg/l at pH of 12, which reduced 10% of COD to an amount of 3,676 mg/l. The effluent was stored in a tank and then pumped in to pressure sand filter and afterwards to activated carbon filter. The COD removal was three and 90% for sand and activated carbon filters, respectively. The total process reduced the remaining COD to 36 mg/l, which is in compliance with environmental standards of Iran

evaluation of THMs in drinking water of Iran and a method of removal

Chlorination of natural water containing humic compounds, produce significant amount of disinfectant by - products. The most important of such compounds are THlvIs and halo acetic acids, suspected to cause cancer in animals and human. Studies showed that under usual processes of water treatment plants, THMs can not be removed effectively. Since chlorination is the final process of treatment, it is necessary to suggest a method for removing such compounds. The primary goal of this research was to study the possibility of the presence of THMs in the drinking water and the procedures for its removal. In the first phase of this study which was done in 1996, the quality of raw and fmished water in the case of total THMs were studied for Ahwaz, Isfahan, Bandar- Abbas, Shiraz, Mashhad and Tehran. The THMs determination was done for three months in all cities, but for Tehran, fulfilled ten months for raw and seven months for the tap waters. Total THM concentrations were determined by liquid-liquid extraction and gas chromatography. Results varied from less than 5 micro gr/lit [the lowest concentration detectable by the method] to 732 micro gr/lit [THM.F.P. In for BandarAbbass tap water]. Four samples out of 185, showed that total THM concentrations were above the 100 micro gr/lit [MCL]. In the second phase of the study, Granular Activated Carbon was used to determine its ability to remove the THM, from the water. Tap water was spiked to 500 micro gr/lit using bromoform and chloroform, and then passed through the activated carbon filter. The effluent and influent of the filter were analyzed periodically to determine the concentration of THMs. After 1360 liter of spiked water was passed through, breakthrough was measured. GAC absorption follows Frendlich isotherm. K and n parameters were determined