Pre-coagulation for microfiltration of an upland surface water

The effect of different coagulants on cake formation and hydraulic resistance in membrane filtration of strongly coloured (SUVA> or =4.8) upland surface water has been studied at bench-scale under constant pressure conditions. Coagulants used were aluminium sulphate, polyaluminium chloride, ferric chloride and ferric sulphate. Optimisation of coagulation parameters was carried by conventional jar testing. The R'c (specific cake resistance in m(-2)) values were determined for all coagulants over a range of coagulant doses and slow mixing flocculation periods. Experiments indicated slight differences in cake formation trends between ferric- and aluminium-based coagulants and chloride and sulphate counterions, but that the range of measured R'c values was small (0.9 and 2.6 x 10(18) m(-2)) over the range of doses studied. Greater than 99% UV(254) removal was achieved with every coagulant, whereas dissolved organic carbon (DOC) removal ranged from 78% to 88%. Optimisation of the pre-coagulation-membrane filtration process suggests ferric chloride to be slightly superior for the feedwater matrix studied on the basis of DOC removal, whereas ferric sulphate gave slightly lower filter cake specific resistance values.     

Adsorbent obtained from CEPT sludge in wastewater chemically enhanced treatment

Chemically enhanced primary treatment (CEPT) in municipal wastewater treatment is particularly suitable for rapidly growing cities. The focus on CEPT process now might be the cost of chemicals and disposal of chemical sludge. In this study, the potential application of adsorbent made from CEPT sludge in CEPT wastewater treatment was investigated in various conditions, such as the adsorbent dosage, pH, and dosing modes of ferric chloride and adsorbent. It was found that sludge-derived adsorbent was a good way of sludge disposal while enhanced pollutants removal rate and reduced the fresh ferric chloride dosage. With the use of 10.0 mg L⁻¹ of ferric chloride and 0.6 g L⁻¹ of the adsorbent at the first stage simultaneously, the enhanced removal efficiencies of turbidity, UV₂₅₄, COD, TP were 83.3%, 52.3%, 48.8% and 89.0%, respectively. The experiments showed that ferric chloride dose was reduced about 50%. The pH played a significant role in coagulation and adsorption process.     

Interaction between Cryptosporidium oocysts and water treatment coagulants

The electrokinetic properties of gamma-irradiated Cryptosporidium oocysts in the presence of coagulants (ferric chloride and alum) and coagulant aids (DADMAC based cationic polyelectrolytes) have been studied. The zeta potential of the oocysts was unaffected by the addition of ferric chloride at all pH values (3-10) studied. Addition of alum resulted in reversal of the oocysts charge, which suggests that the initial stage in the coagulation process leading to floc formation proceeds via the adsorption of hydrolysed aluminium species. The cationic polyelectrolyte Magnafloc LT35 was adsorbed onto iron flocs at doses of 0.1 mg/L even against an electrostatic barrier. The cationic polyelectrolyte only adsorbed and caused charge reversal at the oocyst surface at around 0.4 mg/L, suggesting a lower affinity for this surface. These results indicate that the oocysts, unlike inorganic colloidal materials such as metal oxides, appear to possess a lower surface density of active or charged sites. The lower density of sites, combined with the rapid precipitation of iron salts, may be responsible for the lack of specific adsorption of either hydroxylated ferric species or primary iron hydroxide particles on the oocysts. Further, this suggests that a process of sweep flocculation, where oocysts are engulfed in flocs during coagulation and floc formation, is the more likely mechanism involved. By comparison, it is likely that the specific interaction of hydrolysed aluminium species with the oocysts surface would result in a stronger link at the oocyst-floc interface and that the flocculation process may initially proceed via charge neutralisation.     

混凝沉淀法对砷污染物的去除性能研究

采用次氯酸钠和二氧化氯作为氧化剂,三氯化铁和聚合氯化铝作为混凝剂,分别考察了混凝沉淀工艺及预氧化+混凝沉淀工艺对原水中As(Ⅲ)和As(Ⅴ)的去除效果.结果表明:三氯化铁和聚合氯化铝对As(Ⅴ)均有较好的去除效果,投加量大于3 mg/L,即可将As(Ⅴ)由0.1mg/L左右降至0.005 mg/L以下,三氯化铁对As(...     

化学生物絮凝工艺处理低浓城市污水研究

考察了化学生物絮凝和化学混凝两工艺对低浓度城市污水的处理效果。试验表明，在PAC加入量为70mg／L、PAM加入量为0．5mg／L、絮凝反应时间为35min时，化学生物絮凝工艺对COD的平均去除率为61％，对TP的平均去除率为70％，对SS的平均去除率为90％，效果明显优于化学混凝工艺；在化学生物絮凝工艺中污泥回流不仅可以提高去除效果，而且对进水水质波动有一定的稳定作用。     

聚合氯化铝铁适宜水力条件的研究

通过沉淀后水浊度,研究了影响聚合氯化铝铁混凝效果的水力条件因素,发现:混合强度为100 s-1～170 s-1及1 min左右的混合时间时,混凝效果较好;而絮凝时间和絮凝强度对混凝效果的影响相互制约。     

Cationic lignin polymers as flocculants for municipal wastewater

In this research, two lignin-[2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC) polymers were generated and assessed for their efficiency in treating municipally produced wastewater. The removals of chemical oxygen demand (COD) and turbidity were 47.5% and 71.2%, respectively, for the singular flocculation system at the dosage of 40–70 mg/L. For the dual coagulation/flocculation system, the polymer with a higher charge density (AM2) achieved higher COD and turbidity removals than the polymer with a lower charge density (AM1). To achieve the same organic removal from the wastewater, the alum use could be reduced from 150 mg/L in the single alum use to 35 mg/L in the dual system when used along with 65 mg/L of AM2. In both systems, lignin-METAC polymers exhibited better performance than the flocculant used at a local wastewater treatment plant. Lignin-METAC polymers could be used as bio-based flocculants for the replacement of petroleum-based flocculants and inorganic coagulants.     

Colloid Interaction and Coagulation of Dye Wastewater with Extra Application of Magnetites

The feasibility of treating direct dye wastewater by coagulation is investigated herein. The theoretical development of colloid interactions for coagulation is also reviewed. Ferric chloride and its combination with hydrated lime [Ca(OH) 2 ] is used as a coagulant. Treatment for high strength dye wastewater is preferred and better than medium strength wastewater which showed slow settling velocity and long settling time. The effect of magnetic powder on ferric chloride coagulation system reveals an obvious improvement in settling, particularly for medium strength direct dye wastewater. In addition, increasing magnetite (Fe 3 O 4 ) dosages enhances the treatment efficiency of settling.     

Application of ferrous-hydrogen peroxide for the treatment of H-acid manufacturing process wastewater

1-Amino-8-naphthol-3,6-disulfonic acid (H-acid) is widely used in chemical industries for synthesis of direct, acid, reactive and azoic dye. The wastewater from H-acid manufacturing process is rich in various substituted derivatives of naphthalene and is one of the most hardly-treated wastewaters. A pretreatment method, ferrous ion-peroxide oxidation combined with coagulation, has been studied. The results have shown that the optimum pH value is below 4 and the suitable ferrous ion dosage is 200 mg/l. The COD removal of H-acid wastewater is about 50% and the residue have proved biodegradable when hydrogen peroxide dosage is 30 g/l. Ferrous ion-peroxide oxidation process can also improve efficiency of coagulation treatment. The overall COD removal can reach 90% or more when the concentration of ferrous ion is 200 mg/l, the dosage of hydrogen peroxide is 3 g/l and the ferric chloride dosage of two stage coagulation treatment is 15 g/l and 5 g/l, respectively. The groups on naphthalene ring, such as − + NO₂, SO⁻₃ etc., are substituted by hydroxyl free radical, and then the ring is broken down during oxidation process of H-acid.     

甲基锡废水分隔处理工艺研究及工程实践

硫醇甲基锡生产过程中产生的缩合废水,含有大量有机锡、氨氮、有机硫化物及盐类等污染物,属于高COD、高含盐量、有毒、难降解有机废水。针对此种废水的特点,在实验室研究基础上,确定采用絮凝气浮/加酸蒸发/加碱吹脱/铁炭微电解/絮凝沉淀/生物蠕动床处理工艺。实际工程运行结果表明,对于COD为6 316～12 030 mg/L、氨氮为30 632～39 700 mg/L、氯化铵为102 300～117 600 mg/L、总锡为193.4～201.7 mg/L、总硫为1 276～1 578 mg/L的原水,处理后出水水质可以达到《污水排入城市下水道水质标准》(CJ 3082—1999)。     

混凝法强化城市污水厂一级处理的试验研究

混凝法可以强化城市污水厂的一级处理 ,对于武汉市水质净化厂而言 ,混凝剂聚合氯化铝的投加量指标为 0 .2 72mg/mg胶体状COD。该方法与常规城市污水二级处理法相比 ,运行费用低 ,并可达到较好的去除有机污染物的效果     

Chemical coupling of photocatalysis with flocculation and adsorption in the removal of organic matter

An experimental investigation was made to study the effects of chemical coupling of flocculation and adsorption with photocatalysis in treating persistent organic pollutants in wastewater. The photocatalysis alone showed initial reverse reaction when titanium oxide (TiO(2)) was used in catalysis. The effect of the pretreatment of adsorption with powdered activated carbon (PAC) on photocatalysis was studied. The results showed that PAC adsorption followed by photocatalysis was not effective in alleviating reverse reaction. On the other hand, when PAC and TiO(2) were added simultaneously, the reverse reaction was eliminated. Further, the organic removal was also improved by simultaneous PAC and TiO(2) additions. When flocculation with ferric chloride (FeCl(3)) was used as pretreatment, the organic removal efficiency was superior. The initial reverse reaction was also eliminated/minimized. However, inadequate doses of FeCl(3) (less than 30 mgl(-1)) resulted in initial reverse reaction and inferior DOC removal.     

Simulation and optimization of chemically enhanced primary/activated sludge treatment for small communities

Over the last two decades, the use of coagulation and flocculation has been emphasized for the enhancement of primary sedimentation in municipal wastewater treatment plants. This work is concerned with the development of an approach for the simulation and optimization of a chemically enhanced primary treatment (CEPT)/activated sludge scheme for municipal wastewater treatment using ferric chloride as a coagulant. A mathematical model has been developed which comprises empirical relations for the CEPT stage based on reported experimental data. The activated sludge model has been based on reported rules of thumb.

Optimization has been undertaken using the BOX Complex Routine to minimize a cost objective function with controlling parameters. The effect of varying operating cost components on the cost function has been also assessed via sensitivity analysis.

Results indicate that, for small communities, the addition of a CEPT stage is recommended based on technical and economic consideration for current and prospective costs and prices.     

气浮工艺用于海水淡化预处理试验研究

以三氯化铁和聚合氯化铝作为混凝剂,氯水作为氧化剂,考察了气浮工艺用于海水淡化预处理的运行效果.结果表明:预氧化可以强化混凝+气浮预处理工艺对浊度、CODMn、UV254和TOC的去除效果,三氯化铁的最佳投加量为15～20 mg/L,聚合氯化铝最佳授加量为6～10mg/L,最佳气浮回流比为15％;在最佳运行条件下,预处理...     

Treatment of cotton textile wastewater using lime and ferrous sulfate

This technical note summarizes the results of a textile wastewater treatment process aiming at the destruction of the wastewater's color by means of coagulation/flocculation techniques using ferrous sulfate and/or lime. All the experiments were run in a pilot plant that simulated an actual industrial wastewater treatment plant. Treatment with lime alone proved to be very effective in removing the color (70-90%) and part of the COD (50-60%) from the textile wastewater. Moreover, the treatment with ferrous sulfate regulating the pH in the range 9.0+/-0.5 using lime was equally effective. Finally, the treatment with lime in the presence of increasing doses of ferrous sulfate was tested successfully, however; it proved to be very costly mainly due to the massive production of solids that precipitated.     

化学沉淀法去除水中汞的试验研究

在实验室条件下,利用混凝搅拌设备模拟水厂净水工艺,研究了化学沉淀法对汞的去除效果.结果表明,调整原水pH>10.5(反应后pH>10.1),采用三氯化铁或聚合硫酸铁作为混凝剂,投加量为5 mg/L,能将水中汞从0.005 mg/L降低至<生活饮用水卫生标准>限值(0.001mg/L)以下,是一种有效去除汞污染物的应急处...     

预氯化对混凝/超滤工艺处理滦河高藻原水的影响

利用混凝/超滤中试系统处理高藻期滦河水,为了克服藻类对超滤膜系统的影响,采用预氯化措施,考察了其对中试系统处理效果的影响.结果表明,在有效氯投量为2 mg/L、混凝剂氯化铁投量为4 mg/L的条件下,预氯化/混凝/超滤工艺对COD_(Mn)和UV_(254)的去除率分别为51.6%和19.6%;预氯化在提高中试系统对有机物去除效果的同时,能够有效减缓膜污染,且膜出水中的消毒副产物和微囊藻毒素浓度均低于<生活饮用水卫生标准>(GB 5749——2006)的限值.     

Application of ferrous hydrogen peroxide for treatment of DSD-acid manufacturing process wastewater

A pretreatment method for the biological treatment of wastewater from 4,4'-diaminostilbene-2,2'-disulfonic acid (DSD-acid) manufacturing processes, a refractory dye intermediate wastewater, based on combined ferrous hydrogen peroxide oxidation and coagulation-flocculation, was developed. When the wastewater was treated with ferrous hydrogen peroxide oxidation ([Fe2+] = 2.7 mmol/L, [H2O2] = 0.21 mol/L) after a flocculation using an organic flocculant TS-1 at a dosage of 3 g/L, the overall COD and color removals were 64 and 62%, respectively. BOD5/COD value of the effluent was 0.3. Ferrous hydrogen peroxide oxidation treatment can reduce the solubility of organic molecules with sulfonic group and increase the efficiency of coagulation treatment. The COD and color removals were both more than 90% when FeCl3 was used as the coagulation (dosages of two-step coagulation were 0.031 and 0.012 mol/L respectively) after a ferrous hydrogen peroxide oxidation pretreatment at a H2O2 dosage of 0.06 mol/L.     

Biotransformation of arsenic species by activated sludge and removal of bio-oxidised arsenate from wastewater by coagulation with ferric chloride

The potential of activated sludge to catalyse bio-oxidation of arsenite [As(III)] to arsenate [As(V)] and bio-reduction of As(V) to As(III) was investigated. In batch experiments (pH 7, 25 degrees C) using activated sludge taken from a treatment plant receiving municipal wastewater non-contaminated with As, As(III) and As(V) were rapidly biotransformed to As(V) under aerobic condition and As(III) under anaerobic one without acclimatisation, respectively. Sub-culture of the activated sludge using a minimal liquid medium containing 100mg As(III)/L and no organic carbon source showed that aerobic arsenic-resistant bacteria were present in the activated sludge and one of the isolated bacteria was able to chemoautotrophically oxidise As(III) to As(V). Analysis of arsenic species in a full-scale oxidation ditch plant receiving As-contaminated wastewater revealed that both As(III) and As(V) were present in the influent, As(III) was almost completely oxidised to As(V) after supply of oxygen by the aerator in the oxidation ditch, As(V) oxidised was reduced to As(III) in the anaerobic zone in the ditch and in the return sludge pipe, and As(V) was the dominant species in the effluent. Furthermore, co-precipitation of As(V) bio-oxidised by activated sludge in the plant with ferric hydroxide was assessed by jar tests. It was shown that the addition of ferric chloride to mixed liquor as well as effluent achieved high removal efficiencies (>95%) of As and could decrease the residual total As concentrations in the supernatant from about 200 microg/L to less than 5 microg/L. It was concluded that a treatment process combining bio-oxidation with activated sludge and coagulation with ferric chloride could be applied as an alternative technology to treat As-contaminated wastewater.     

Characterisation of the impact of coagulation and anaerobic bio-treatment on the removal of chromophores from molasses wastewater

The performance of a coagulation sequence using aluminium chlorohydrate (ACH) and a low MW polydiallyldimethylammonium chloride (polyDADMAC), and ferric chloride, for decolourising a high-strength industrial molasses wastewater was compared at bench scale. At their optimum dosages, ACH/polyDADMAC gave higher colour removal than FeCl₃ (45% cf. 28%), whereas COD reduction was similar (∼30%), indicating preferential removal of melanoidins (a major contributor to the colour) by ACH/polyDADMAC. Size exclusion chromatography and fluorescence excitation-emission matrix spectrometry suggested that chromophoric Fe-organic complexes were formed during FeCl₃ treatment of the molasses wastewater, which appeared to compromise decolourisation efficiency. Anaerobic bio-treatment of the wastewater enhanced the coagulation efficiency markedly, with FeCl₃ achieving 94% colour and 96% COD removal, while ACH/polyDADMAC gave 70% and 56% removal, respectively. The improved decolourisation was attributed to the decrease in low MW organics (<500 Da) and biopolymers by the biological treatment, leading to reduced competition with melanoidins for interaction with coagulant/flocculant. For both the wastewater and the biologically treated wastewater, ACH/polyDADMAC treatment gave flocs with markedly better settling properties compared with FeCl₃.