Effects Of Coagulant Dose Research Articles

COAGULANT PREPARATION FROM GLUTARALDEHYDE-CROSSLINKED DURIAN SKIN CELLULOSE FOR TREATMENT OF WASTEWATER GENERATED BY SUGAR PALM STARCH INDUSTRIES

Arenga pinnata starch (APS) production from APS industrial centers in Klaten, Indonesia, produces Arenga pinnata starch mill effluent (APSME). This waste will undoubtedly harm the environment, significantly reducing river water quality. On the other hand, in Gunungpati, Semarang, Indonesia, durian fruit is abundant, it leaves durian skin waste, which may cause environmental pollution. However, durian skin contains cellulose, which has the potential to be valorized for various applications. Therefore, this study evaluated the preparation of natural coagulant from durian skin cellulose crosslinked with glutaraldehyde for treating APSME from APS industrial centers in Klaten, Indonesia. Durian skin flour (DSF), durian skin cellulose (DSC), and glutaraldehyde-crosslinked durian skin cellulose (DSC-G) coagulants were characterized by proximate composition, UV-Vis spectroscopy, Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The effects of coagulant dose, pH, and mixing speed on removal efficiency and sludge volume in DSF, DSC, and DSC-G were compared with polyaluminum chloride (PAC). The study assessed the process efficiency in terms of percentage removals for chemical oxygen demand (COD), biological oxygen demand (BOD5), total dissolved solids (TDS), and total suspended solids (TSS) as 71.38%, 78.23%, 94.79%, and 96.12%, respectively, with a percentage sludge volume of 24%. The results indicated that the optimum DSC-G dosage was 2500 mg/L with an optimum working area of pH at 5.5 and a mixing speed of 90 rpm. DCS-G has a floc stability of -12.33 mV. This study indicated that DSC-G has the potential to be used as a coagulant for the treatment of APSME.

The Use of as Natural Coagulant in Algerian Drinking Water Treatment Plant

The purpose of this work is the study the ability of the plant material Aloe vera to act as natural coagulant using raw water obtained from a drinking water treatment plant (Mila, Algeria). Different solvents such as: NaCl; NaOH and HCl were used as chemical activators to extract the active components from the Aloe vera plant, and different coagulation-flocculation experiments were conducted in a jar test apparatus to evaluate the performance of the extracted coagulant. Also, the effect of coagulant dose on some water parameters such as turbidity, pH, total alkalinity and organic matter were investigated. The results showed that the use of coagulants obtained by using different solvents increases the coagulation efficiency compared to the coagulant obtained from the raw material, for example the maximum turbidity removal efficiency was 28.23, 78.07, 83.46 and 85.15% when using powdered Aloe vera (raw material), AV-NaCl (0.5 M), AV-NaOH (0.05 M) and AV-HCl (0.05 M), respectively. The results defined, that the residual turbidity obtained in this work, where the Aloe vera was used (after treatment by solvents) produced a turbidity lower than the Algerian standard (5 NTU) with initial turbidity (13 NTU). In this study, the infrared spectrum study and analysis has revealed the presence of different functional groups, which are responsible for the coagulation process.

Treatment of Produced Water in the Permian Basin for Hydraulic Fracturing: Comparison of Different Coagulation Processes and Innovative Filter Media

Produced water is the largest volume of waste product generated during oil and natural gas exploration and production. The traditional method to dispose of produced water involves deep well injection, but this option is becoming more challenging due to high operational cost, limited disposal capacity, and more stringent regulations. Meanwhile, large volumes of freshwater are used for hydraulic fracturing. The goal of this study is to develop cost-effective technologies, and optimize system design and operation to treat highly saline produced water (120–140 g/L total dissolved solids) for hydraulic fracturing. Produced water was collected from a salt water disposal facility in the Permian Basin, New Mexico. Chemical coagulation (CC) using ferric chloride and aluminum sulfate as coagulants was compared with electrocoagulation (EC) with aluminum electrodes for removal of suspended contaminants. The effects of coagulant dose, current density, and hydraulic retention time during EC on turbidity removal were investigated. Experimental results showed that aluminum sulfate was more efficient and cost-effective than ferric chloride for removing turbidity from produced water. The optimal aluminum dose was achieved at operating current density of 6.60 mA/cm2 and 12 min contact time during EC treatment, which resulted in 74% removal of suspended solids and 53–78% removal of total organic carbon (TOC). The energy requirement of EC was calculated 0.36 kWh/m3 of water treated. The total operating cost of EC was estimated $0.44/m3 of treated water, which is 1.7 or 1.2 times higher than CC using alum or ferric chloride as the coagulant, respectively. The EC operating cost was primarily associated with the consumption of aluminum electrode materials due to faradaic reactions and electrodes corrosions. EC has the advantage of shorter retention time, in situ production of coagulants, less sludge generation, and high mobility for onsite produced water treatment. The fine particles and other contaminants after coagulation were further treated in continuous-flow columns packed with different filter media, including agricultural waste products (pecan shell, walnut shell, and biochar), and new and spent granular activated carbon (GAC). Turbidity, TOC, metals, and electrical conductivity were monitored to evaluate the performance of the treatment system and the adsorption capacities of different media. Biochar and GAC showed the greatest removal of turbidity and TOC in produced water. These treatment technologies were demonstrated to be effective for the removal of suspended constituents and iron, and to produce a clean brine for onsite reuse, such as hydraulic fracturing.

Enhanced coagulation process by Fe-Mn bimetal nano-oxides in combination with inorganic polymer coagulants for improving As(V) removal from contaminated water

This study investigated the efficient removal of As(V) from contaminated water using enhanced coagulation by Fe-Mn bimetal nano-oxides in combination with poly-ferric chloride (PFC) and poly-aluminum chloride (PAC). The effects of coagulant dose, initial pH, initial As(V) concentration, Fe-Mn nano-oxide dose and flocs properties were investigated. The results showed that the combination of coagulants and nano-oxides significantly increased the As(V) removal efficiency in the optimal coagulants doses (25 mg/L). The As(V) removal efficiencies for PAC and PFC were 82.93% and 88.22% and for PFC + Fe-Mn and PAC + Fe-Mn were increased to 96.83% and 98.26%, respectively. The residual As(V) concentration was decreased to ˂10 μg/L in the presence of Fe-Mn nano-oxides. The best removal efficiencies for PAC + Fe-Mn and PFC + Fe-Mn were in pH 7 and 9, respectively. Based on FESEM - EDX analysis, the combined floc formation by coagulants - nano-oxides and the existence of Fe, Mn and As elements in the precipitated flocs was confirmed, and the PFC + Fe-Mn flocs were more uniform and bigger than PAC + Fe-Mn flocs. Total Fe and Al residual concentrations in optimum dose of PAC + Fe-Mn and PFC + Fe-Mn were 0.15 and 0.25 mg/L and Cl− residue concentrations were 6.87 and 4.72 mg/L, respectively. Therefore, the combination of Fe-Mn bimetal nano-oxides with PFC and PAC coagulants can be a suitable option to improve the removal of As(V) from the contaminated water resources.

Use of thermal water as a natural coagulant for domestic wastewater sustainable treatment

In the last several years, the interest on domestic wastewater treatment has increased due to the rise of water consumption resulted from the world population growth. The excessive use of inorganic coagulants, such as aluminum sulphate, in domestic wastewater treatment processes contributes to generate high negative environmental impacts and risks to living organisms. Besides its low biodegradability, as aluminum sulphate increases metal content in discharged effluents rises, generating toxic sludge. Therefore, searching for clean and sustainable processes for domestic wastewater treatment is important in order to reduce the pollutant discharges into fresh water bodies. In this paper, the potential use of thermal water as a natural coagulant for the domestic wastewater treatment from Manizales city (department of Caldas, Colombia), was studied. The effect of coagulant dose was analyzed and compared with the results of the conventional coagulants. Applying different doses of coagulants in domestic wastewater showed that the best coagulation activity was achieved by adding 35 ml/l of thermal water, and 140 mg/l of aluminum sulphate. In both cases, high turbidity removal efficiency (98.1 %) was achieved. The removal efficiency of Chemical Oxygen Demand (COD) using aluminum sulphate was 81.5 %, and using thermal water was 75.4 %. In conclusion, thermal water has positive coagulation properties; therefore, it is a promising alternative to aluminum sulphate as a natural coagulant on the treatment of domestic wastewater.

Influence of microbial floatation on membrane fouling due to particles and organic matters in submerged microfiltration

AbstractThis study investigated the effect of microbubble floatation on the fouling of microfiltration membranes. Synthetic feed solutions containing either kaolin or alginic acid were used for the membrane filtration tests. A dissolve air flotation system using a pump-type microbubble generator was adopted as a pretreatment for microfiltration system. A multi-array submerged membrane filtration system was used to monitor the changes in transmembrane pressure with time under various operating conditions. Turbidity removal efficiency, particle counts, and fouling rate for the microfiltration membrane were measured after the microfiltration floatation. The effect of coagulant dose on the treated water quality and membrane performance was also investigated. Results showed that microbubble floatation without coagulant was effective to reduce membrane fouling by kaolin but it was not very effective to control fouling by alginate. With the aid of coagulant, microbubble flotation could control fouling by alginat...

Enhanced Coagulation/Flocculation by Combining Diatomite with Synthetic Polymers for Oily Wastewater Treatment

The objectives are to evaluate the feasibility of treating oily wastewater using synthetic polymers (polyaluminum chloride (PAC), polyferric sulfate (PFS), and polyacrylamide (PAM)) combined with natural diatomite and to refine the operating parameters using diatomite as an adsorbent and a coagulant aid. The enhanced coagulation/flocculation by combining PAC with diatomite was investigated through mechanism analysis compared to the combination of PFS/PAM with diatomite, respectively. The effects of coagulant dose, initial pH, and settling time on chemical oxygen demand (COD) and turbidity were studied using PAC-diatomite in comparison with using PAC only. The enhanced coagulation/flocculation of diatomite with PAC was better than that with PFS/PAM in terms of COD/turbidity removal and floc settling characteristics, considering costs. The PAC-diatomite system reduced more than 70% of COD and 90% of turbidity over a wide pH range (7–10) within 20 min, with the optimum dose of PAC 50 mg/l and diatomite 1250 mg/l. The added diatomite effectively saved over 85% of PAC dose and simultaneously increased over 50% of COD removal efficiency. This study provided a novel and economical approach for diatomite utilization in the treatment of oily wastewater, satisfying the demands of reuse or reinjection into the ground.

Comparison of naturally prepared coagulants for removal of COD and color from textile wastewater

<p>The wastewater generated by the textile industry is rated as the most polluting among all industrial sectors considering both volumes discharged and effluent composition. Present investigation intended for COD and color removal from textile wastewater using naturally prepared coagulants i.e. Surjana Seed Powder (SSP), Maize Seed Powder (MSP) and Chitosan. Effect of coagulant dose, flocculation time and temperature has been studied. The Sludge Volume Index (SVI) and turbidity were examined for various effects. SSP was more effective than Chitosan and MSP for the removal of COD and color and also, Chitosan was more efficient than SSP and MSP considering SVI and turbidity. Maximum percentage reduction corresponds to 75.6 and 62.8 was obtained for removal of COD and color respectively using SSP.</p>

Comparative study of floc characteristics with titanium tetrachloride against conventional coagulants: Effect of coagulant dose, solution pH, shear force and break-up period

Characteristics of flocs formed by titanium tetrachloride (TiCl4), ferric chloride (FeCl3) and aluminum sulfate (Al2(SO4)3) were comparatively investigated in terms of floc growth rate, size, strength, recoverability and fractal dimension in real water treatment. Impacts of coagulant dose, solution pH and hydraulic conditions, including shear force and break-up period, on floc properties were investigated. Results showed that the floc size followed the order of TiCl4>FeCl3>Al2(SO4)3 within the dose range investigated. The response of floc strength to coagulant dose depended on the coagulant used, while the floc recoverability decreased with the increasing dose regardless of the coagulant used. Within the solution pH range investigated, the floc strength and recoverability showed the following order of Al2(SO4)3>FeCl3>TiCl4 and those of TiCl4 were the least affected by solution pH. Additionally, the floc strength decayed with the increasing shear force and break-up period for the three coagulants. TiCl4 yielded the flocs with the weakest recoverability within both the shear force and break-up period ranges investigated. Moreover, the floc compactness followed the order of FeCl3>TiCl4>Al2(SO4)3 under either shear force condition.

Removal of turbidity from water by dissolved air flotation and conventional sedimentation systems using poly aluminum chloride as coagulant

Flotation is a method in which particles in liquid phase are transported to the surface by air bubbles. In this experimental study, a comparison has been made between conventional sedimentation and dissolved air flotation (DAF) systems to remove turbidity from water. Initially, optimal operational conditions for each system utilized using water artificially turbid with Kaolin. For each system, samples were taken at 20-min interval after the system reached its optimal operational conditions. Parameters, such as turbidity, alkalinity, temperature, pH, and total suspended solids, were measured. For 20, 30–50 and 90–110 NTU, turbidity average removal efficiencies in DAF system were 14.7, 11.1 and 10.9%, respectively, larger than the conventional sedimentation system. The effect of coagulant dose indicated that DAF system with lower dosage of coagulant have higher removal efficiency. On the other hand, the results showed that due to increased efficiency of DAF system, solid concentration of sludge produced in this system was more than the sedimentation system (p < 0.01). However, operation of DAF system needs accurate control devices and experienced technical staff to operate the system.

The cell damage of Microcystis aeruginosa in PACl coagulation and floc storage processes

The damage of cyanobacterial cells and the release of their intracellular microcystins (MCs) present an enormous threat to drinking water. Effective control of cyanobacteria both in coagulation and floc storage processes plays an important significance in avoiding the additional release of MCs during water treatment. In this paper, the cell integrity acted as a key factor to assess the damage of polyaluminum chloride (PACl) coagulation/flocculation process on Microcystis aeruginosa cells. Effects of coagulant dose, coagulation stirring and floc storage time were comprehensively evaluated to regulate M. aeruginosa cell lysis and MCs release. Results showed that all cells were removed intactly by the surface charge neutralization with PACl in the coagulation process. While in floc storage process, PACl caused obvious damage to cells and led to a large amount of MCs release afterthe protective effects of EPSs produced by M. aeruginosa cells were destroyed or decomposed. Coagulation stirring could cause cells lyse earlier than the natural lysis, but this damage was slighter than that of coagulant PACl, which obviously aggravate the cell lysis of M. aeruginosa in flocs after 2days. This study is not only significant for the effective removal of cyanobacterial cells from drinking water sources but instructive for the prevention of secondary pollution of MCs during water recirculation from the sludge treatment to the head of the process.

Use of combined coagulation-adsorption process as pretreatment of landfill leachate

Landfill leachate is an important pollution factor resulting from municipal landfill sites. Physical and chemical processes are the better option for pretreatment or full treatment of landfill leachate. This article presents a combination of pre-treatment method (coagulation and adsorption) for leachate collected from municipal solid waste open dumping site. Physico chemical characteristics of stabilized and fresh leachate were examined. Coagulation process was examined by using alum and ferric chloride. A low cost adsorbent, fly ash was used for adsorption studies. Coagulation studies were carried out for fresh and stabilized leachate. Adsorption studies have been conducted for alum pre-treated stabilized leachate. Effect of coagulant dose, adsorbent dose, pH and contact time were carried out. The effective optimum coagulant dosages were 0.6 g/L and 0.7 g/L for alum and ferric chloride respectively for stabilized leachate and incase of fresh leachate 0.8 g/L and 0.6 g/L for alum and ferric chloride respectively. For the alum pretreated stabilized leachate, the maximum COD removal is 28% using fly ash adsorbent with equilibrium time of 210 min and optimum dose of 6 g/L. Overall COD removal efficiency of 82% was obtained by coagulation using alum and adsorption using fly ash for stabilized leachate. The results obtained showed that combined coagulation and adsorption process can be used effectively for stabilized leachate treatment.

Removal of Perfluorooctanoate from Water by Polyaluminium Chloride Coagulation

The removal of perfluorooctanoate （PFOA） and turbidity from model solution by coagulation was investigated. A polyaluminum chloride (PACl) was used as a coagulant in the coagulation process. The effects of coagulant dose, slow mixing time, solution pH value and initial turbidity on the removal of both PFOA and turbidity from water were studied. It was found that the removal rate of PFOA in water increase along with the increase in slow mixing time, initial turbidity and PAC dose. The removal rate of PFOA is more effective at the near neutral solution pH values and the high initial turbidity. The removal percents of PFOA exceed 80% at the optimal condition. The removal mechanism was speculated to be the electrostatic interaction and hydrophobic interaction in coagulation process.

Removal of perfluorooctanoate from surface water by polyaluminium chloride coagulation

Perfluorooctanoate (PFOA) has been detected in surface water all over the world, and little is known of its removal by coagulation in water treatment plants. In this study, polyaluminium chloride (PACl) was used to remove PFOA from surface water, and the effects of coagulant dose, solution pH, temperature, and initial turbidity on the removal of both PFOA and suspended solids (SS) from water were investigated. Since the SS had high sorption affinity for PFOA, most PFOA was adsorbed on the particles and removed via the SS removal in the coagulation process. PFOA concentrations in aqueous phase decreased with increasing initial turbidity and PACl dose, while they increased with increasing solution pH and temperature. Other perfluorinated compounds (PFCs) with different C–F chain lengths and functional groups were also compared with PFOA. It was proved that hydrophobic interaction played an important role in the adsorption of PFOA on the SS. The addition of powdered activated carbon (PAC) before the coagulation process significantly enhanced the removal efficiency of PFOA in water, and the residual PFOA concentrations in water were less than 1 μg/L after the addition of 1–16 mg/L PAC and subsequent coagulation when the initial PFOA concentrations were in the range of 0.5–3 mg/L.

Removal of antimony(V) and antimony(III) from drinking water by coagulation–flocculation–sedimentation (CFS)

Antimony occurs widely in the environment as a result of natural processes and human activity. Although antimony is similar to arsenic in chemical properties and toxicity, and a pollutant of priority interest to the USEPA and the EU, its environmental behaviors, control techniques, and even solution chemistry, are yet barely touched. In this study, antimony removal from drinking water with coagulation–flocculation–sedimentation (CFS) is comprehensively investigated with respect to the dependence of both Sb(III) and Sb(V) removal on the initial contaminant-loading level, coagulant type and dosage, pH and interfering ions. The optimum pH for Sb(V) removal with ferric chloride (FC) was observed at pH 4.5–5.5, and continuously reduced with further pH increase. Over a broad pH range from 4.0 to 10.0, effective Sb(III) removal with FC was obtained. Contrary to the effective Sb removal with FC, the degree of both Sb(III) and Sb(V) removal with aluminum sulfate (AS) was very low, indicating the impracticability of AS application for antimony removal. The presence of phosphate and humic acid (HA) markedly impeded Sb(V) removal, while exhibited insignificant effect on Sb(III) removal. The effects of coagulant type, Sb species and pH are more pronounced than the effects of coagulant dose and initial pollutant concentration. After preliminarily excluding the possibility of precipitation and the predominance of coprecipitation, the adsorption mechanism is used to rationalize and simulate Sb/FC coagulation with good result by incorporating diffuse-layer model (DLM).

DISSOLVED AIR FLOTATION (DAF) FOR PRIMARY AND TERTIARY TREATMENT OF MUNICIPAL WASTEWATERS

ABSTRACT Tertiary treatment of municipal wastewater by dissolved air flotation was studied on a pilot‐scale. The effects of coagulant dose, flocculation pattern, dispersion water recycle ratio and hydraulic surface load on process performance were evaluated. The treatment of primary effluents by dissolved air flotation was investigated to assess the suitability of this process for the treatment of heavily polluted effluents and wastewater treatment plant by‐passes. The tertiary dissolved air flotation process typically achieved 90–99 % reductions in the numbers of enteric microbes (total coliforms, enterococci and F‐RNA coliphages). The average reductions of total phosphorus and chemical oxygen demand were 55–81 % and 28–39 %, respectively. Increasing the polyaluminium chloride coagulant dose from 2 to 10 mgAl3+ l−1 and the dispersion water recycle ratio from 11 to 22 % improved the efficiency of the process. Changes in the flocculation conditions (range of G‐values 10–55 s−1; retention time 4–8 min) and hydraulic surface load (5 or 10 m h−1) did not clearly affect the process efficiency. The dissolved air flotation process decreased the numbers of enteric microbes and reduced total phosphorus, chemical oxygen demand and suspended solids from the primary treated wastewaters on average by 98–99.8%, 90 %, 47% and 77 %, respectively. The dissolved air flotation process was demonstrated to be a suitable method for efficient tertiary treatment of wastewaters, as well as for the elimination of peak pollution loads or by‐pass wastewaters during the treatment plant overloading situations.

Orthophosphate and metaphosphate ion removal from aqueous solution using alum and aluminum hydroxide

The removal of orthophosphates (10 −2 kg P m −3), condensed phosphates (10 −2 kg P m −3), and mixtures of both (5 × 10 −3 kg P m −3 as orthophosphate and 5 × 10 −3 kg P m −3 as metaphosphate) in aqueous solution is studied using alum and aluminum hydroxide. The effects of coagulant dose, pH, temperature, aging of aluminum hydroxide, and presence of different ions are investigated. On the basis of the experimental results, alum is much more efficient in phosphorus removal than aluminum hydroxide even if, in both cases, at the conditions studied, the active coagulant form is Al(OH) 3. The differences then could be due to the higher activity of the in situ formed hydroxide. Orthophosphates and metaphosphates seem to have similar behavior vs pH variation: maximum removal is achieved at pH values 5–6 in all cases. On the other hand, in the simultaneous presence of both P forms, orthophosphate and metaphosphate ions have different affinities for the surface sites of aluminum hydroxide, since for both alum and aluminum hydroxide, orthophosphates are preferentially removed compared to metaphosphates, due probably to orientation effects and the charge per P atom. The presence of sodium, potassium, magnesium, sulfate, chloride, and magnesium, at the concentrations studied and for a pH value of 6, does not influence P removal. Temperature variation, between 25 and 60 °C, does not affect alum efficiency but both P forms are increasingly removed with increasing temperature, probably due to polymer Al(OH) 3 breaking, producing new surfaces for adsorption. Aging decreases sorption capacity of Al(OH) 3, while crystallites of increasing size are formed. Finally adsorption of both P forms is best described by the Freundlich isotherm [ K F = ( 49.1 – 69.1 ) × 10 −3 ( m 3 kg −1 ) 1 / N , 1 / N : 0.14–0.19 for T = 25 – 60 ° C ] and [ K F = ( 1.58 – 2.79 ) × 10 −3 ( m 3 kg −1 ) 1 / N , 1 / N : 2.17–2.47 for T = 25 –6 0 ° C ] for orthophosphate and metaphosphate, respectively.

The impact of increased loading rate on granular media, rapid depth filtration of wastewater

The impact of loading rate on tertiary filtration of wastewater was studied using a pilot-scale, dual-media, rapid depth filtration system. Loading rates of 12.2, 15.3, 18.3, 21.4, and 24.4 m/h were tested on parallel filter columns treating the same coagulated secondary wastewater to determine the impact on removal of turbidity, particles (2–15 μm), total coliform bacteria, Escherichia coli, and MS2 bacteriophage, as well as on the particle deposition profile in the filter bed. Increasing the loading rate from 12.2 to 24.4 m/h decreased the removal efficiencies for all metrics. The observed impact of loading rate on particle removal was similar to that predicted by a clean-bed filtration model, although the model significantly underestimated the removal efficiencies of the smaller particles. For two loading rates, 12.2 and 18.3 m/h, the effect of coagulant dose was also studied; the negative impact of loading rate on removal efficiency was eliminated by increasing the coagulant dose for the higher loading rate, which also resulted in removal of particles deeper in the filter bed. For all conditions studied, loading rate had no observable impact on the ability to disinfect filter effluents with chloramines. The results of this research indicate that loading rates higher than those typically used in tertiary filtration can produce acceptable effluent quality, and support a regulatory approach based on filter effluent turbidity.

Destabilisation of oil–water emulsions and separation by dissolved air flotation

The roles of aluminium and ferric sulphates as destabilising agents for oil–water emulsions that have been stabilised by a non-ionic surfactant (Span 20) are investigated in terms of oil removal. The effects of coagulant dose, pH, and the duration and intensity of both slow and fast mixing are considered. Electrokinetic measurements indicate that oil droplets have a negative zeta potential that is weakly dependent on pH. The chosen coagulants are shown to be effective in reducing the zeta potential of the oil droplets, and charge reversal was observed for aluminium sulphate. Oil removals up to 99.3% at pH 8 and 99.94% at pH 7 are seen for aluminium sulphate and ferric sulphate respectively. Rapid mixing times of around 120s and flocculation times ranging from 15 to 20min appear to be optimal for the DAF separation. It is concluded that relatively low average mixing speeds for coagulation and flocculation are essential for efficient operation.

Optimisation of combined coagulation and microfiltration for water treatment

The effect of upstream coagulant dosing for full-flow microfiltration of an upland-reservoir water has been investigated. The process, run under conditions of constant flux and pH and based on a ferric salt, is compared with a published study of another full-flow process based on alum dosing and operated at constant pressure and coagulant concentration. The current study includes data for the residual deposit remaining following backflushing by reverse flow. Results are presented in terms of the specific-cake resistance (R′ c , m −2) as a function of pH or coagulant dose. Reasonable correlation with classical cake filtration theory was obtained, such that R′ c was assumed to be independent of run time and cake thickness. The following trends have been noted: • The optimum pH for the alum-based system appears to be between 7.5 and 8 on the basis of cake resistance. • The effect of coagulant dose between 18 and 71 μM Fe 3+ is much more significant than a change in pH between 5 and 9 for the alum system: a 53-fold increase in specific flux compared with a 7-fold increase with reference to the limiting R′ c values at pH 4.8 and 7.7. • A low coagulant dose (0.018 mM, 1.0 mg l −1 Fe 3+) appears to have a slightly detrimental effect on downstream microfiltration operation. The low coagulant doses apparently cause incomplete aggregation of colloidal particles such that internal fouling of the membrane takes place. • The residual (cleaning cycle) deposit resistance followed roughly the same trend as the backflush cycle-cake resistance with coagulant concentration, but with a much reduced value (about 16 times lower, on average). • An optimum coagulant dose of 0.055 mM (3.1 mg/l) Fe 3+ can be identified on the basis of operational cost based on coagulant cost and cake resistance, all other aspects of the system being substantially unchanged. It is concluded that coagulation with downstream microfiltration offers a cost-effective means of removing natural organic matter, achieving a THMFP removal of around 80% at the optimum dose.