Colloidal silica removal in coagulation processes for wastewater reuse in a high-tech industrial park.

Four experiments of coagulation and flocculation were conducted to investigate the characteristics of colloidal silica removal in a high-tech industrial wastewater treatment plant for reclamation and reuse of the effluent. Experimental results illustrated that poly-aluminium chloride (PACl) showed higher performances on colloidal silica removal than alum. Interestingly, the two coagulants demonstrated the same capacity on silica removal. The specific silica removal capacity was approximately 0.135 mg SiO2/mg Al2O3 when the dosage of coagulants was in the range 30-150 mg/L Al2O3. In addition, the silica was reduced significantly at the condition of pH above 8. Experimental data implied that precipitation of aluminium flocs was the major mechanism for colloid silica removal in PACl and alum coagulation, besides, charge adsorption was also important for improving removal efficiency. Moreover, the addition of polyacrylic acid (PAA) as a flocculant could slightly advance silica removal in the PACl coagulation. The combined PACl/PAA/flocs coagulation was effective for the removal of colloidal silica, soluble COD, and turbidity and also suitable as a pretreatment unit in wastewater reclamation and reuse processes.     

Effects of floc and bubble size on the efficiency of the dissolved air flotation (DAF) process.

Dissolved air flotation (DAF) is a method for removing particles from water using micro bubbles instead of settlement. The process has proved to be successful and, since the 1960s, accepted as an alternative to the conventional sedimentation process for water and wastewater treatment. However, limited research into the process, especially the fundamental characteristics of bubbles and particles, has been carried out. The single collector collision model is not capable of determining the effects of particular characteristics, such as the size and surface charge of bubbles and particles. Han has published a set of modeling results after calculating the collision efficiency between bubbles and particles by trajectory analysis. His major conclusion was that collision efficiency is maximum when the bubbles and particles are nearly the same size but have opposite charge. However, experimental verification of this conclusion has not been carried out yet. This paper describes a new method for measuring the size of particles and bubbles developed using computational image analysis. DAF efficiency is influenced by the effect of the recycle ratio on various average floc sizes. The larger the recycle ratio, the higher the DAF efficiency at the same pressure and particle size. The treatment efficiency is also affected by the saturation pressure, because the bubble size and bubble volume concentration are controlled by the pressure. The highest efficiency is obtained when the floc size is larger than the bubble size. These results, namely that the highest collision efficiency occurs when the particles and bubbles are about the same size, are more in accordance with the trajectory model than with the white water collector model, which implies that the larger the particles, the higher is the collision efficiency.     

聚硅酸氯化铝铁絮凝剂的合成及其特性

利用天津某钢厂的工业废料——盐酸酸洗废液、铁屑和含铝矿等为原料,合成了具有不同摩尔比的无机高分子絮凝剂聚硅酸氯化铝铁(简称PAFSC),采用Zeta电位测定法分析了产品在其水解溶液中的带电情况,并通过絮凝实验对絮凝剂的絮凝机理作了初步分析。通过处理模拟水样,与传统絮凝剂聚合氯化铝(PAC)作了对比实验,结果表明,在投加量相同的情况下,PAFSC具有较高的除浊能力,对开发研制高效、稳定、价廉的无机高分子絮凝剂提供依据。     

Particle count and size alteration for membrane fouling reduction in non-conventional water filtration.

If coagulation is not completely successful and produces aggregates which are too small, fouling may increase. In some cases, a deep-bed filter could perhaps provide a solution. The paper examines these effects using experimental results for different waters. Activated sludge effluents, stormy seawater containing microalgae and spent filter backwash water (SFBW) were coagulated by alum or ferric chloride. Sand filtration tests were carried out. Tests were performed in a membrane filtration stirred cell, filtration pilot plant equipped with SDI analyzer (seawater) and pilot UF plant (SFBW). For activated sludge effluent, alum residual ratio curves of turbidity and total particle count (TPC) followed one another. With ferric chloride, low coagulant dosage showed negative turbidity removal. Contact granular filtration reduced membrane fouling intensity. Increasing the dose resulted in higher improvement in membrane flux. For seawater, a filter run period under storm conditions reached 35 hours with satisfactory filtrate quality. An iron chloride dose of 0.3 mg/l during normal conditions and 0.5 mg/l for stormy condition should be injected, mixed well before the filters, while maintaining 10 m/hr filtration rate and pH 6.8 value. For SFBW, alum flocculation pretreatment of SFBW was effective in reducing turbidity, TPC, viruses and protozoa. SFBW settling prior to flocculation did not enhance turbidity and TPC removal. The largest remaining particle fraction after alum flocculation was 3-10 microm in size, both Cryptosporidium and Giardia are found in this size range. Coagulation enhanced the removal of small size particles, a positive impact on reducing membrane fouling potential.     

低温低浊水絮凝工艺的数值模拟与响应面优化试验研究

为探究微涡流絮凝工艺处理低温低浊水时,絮凝区流场流态的变化以及水中浊度、COD_Mn、UV₂₅₄的最优去除效果,采用CFD数值模拟探究不同流量(絮凝时间)下絮凝区流场流态,确定最佳絮凝时间;应用响应面中Box-Behnken的中心组合设计方法,研究了流量、混凝剂投加量与涡流反应器投配比及其交互作用对微涡流絮凝工艺去除浊度、COD_Mn、UV₂₅₄的影响。研究表明:随着絮凝时间的减小,絮凝区内平均湍动能、有效能耗散及其变化率逐渐增大,平均涡旋尺度及其变化率逐渐减小,最佳絮凝时间为18.5~13.6 min;投配比是微涡流絮凝工艺的极显著影响因素,且与加药量、流量具有协同作用;微涡流絮凝工艺处理低温低浊水的最佳工艺参数为:流量6.4 m³/h、混凝剂投加量26.8 mg/L、投配比为2(2/5占比HJTM-1型+3/5占比HJTM-2型涡流反应器)。此时,浊度、COD_Mn、UV₂₅₄去除率分别为85.48%、63.84%和55.37%。     

Effects of surface charge, micro-bubble size and particle size on removal efficiency of electro-flotation.

Flotation is a water treatment alternative to sedimentation, and uses small bubbles to remove low-density particles from potable water and wastewater. The effect of zeta potential, bubble size and particle size on removal efficiency of the electro-flotation process was investigated because previous model-simulations indicated that these attributes are critical for high collision efficiency between micro-bubbles and particles. Solutions containing Al3+ as the metal ion were subjected to various conditions. The zeta potentials of bubbles and particles were similar under identical conditions, and their charges were influenced by metal ion concentration and pH. Maximum removal efficiency was 98 and 12% in the presence and absence of flocculation, respectively. Removal efficiency was higher when particle size was similar to bubble size. These results agree with modelling simulations and indicate that collision efficiency is greater when the zeta potential of one is negative and that of the other is positive and when their sizes are similar.     

Turbidity-based monitoring of particle concentrations and flocculant requirement in wastewater pre-treatment.

The removal of particulate organic material in the first step of wastewater treatment may result in significant savings of reactor volume and energy at wastewater treatment plants, because the organic loading to pursuing unit operations can be reduced. This article describes experiments into the possibility of using turbidity measurements as a tool to quantify the concentration of particles in raw wastewater and, based on the result, assess the organic polymer requirement. A feed forward polymer dosing strategy based on a fixed polymer to influent-turbidity ratio was developed and tested. The experimental work confirms that turbidity measurements can be used to quantify particulate COD. For the investigated wastewater (both untreated and flocculated samples) a linear relationship was found in a wide range of particulate COD (100-900 mg O2 x l(-1)) and turbidity (50-450 NTU). On-line turbidity measurements showed that the particle concentrations in the tested municipal wastewater varied significantly. During dry weather conditions the turbidity fluctuated from 100 to 400 NTU, while in rainy periods fluctuations of 100 to >1,000 NTU were measured. The tested turbidity-related polymer dosing method could be used to create different, constant levels of particle removal, despite large particle concentration variations in the influent. Moreover, it resulted in higher removal efficiencies and a more stable operation compared to the dosing of fixed polymer dose per unit of volume.     

哈尔滨磨盘山水厂生产废水回用性能研究

净水厂生产废水直接回用到水厂前端,将使原水浊度升高,在一定范围内可增加絮凝核心,提高颗粒的碰撞概率强化低温低浊水的混凝效果。以哈尔滨磨盘山水厂生产废水为对象,研究了生产废水的沉降性能和活性性能。研究表明,生产废水含有氢氧化物的活性成分,回用后能够强化混凝效果,而且含固率、回用混合水浊度及生产废水浊度具有较好的线性相关。     

电浮选法净化含高浓度Cu2+和Zn2+的废水研究

以自制的间歇式电浮选柱为反应容器,采用电浮选方法对含高浓度Zn^2+和Cu^2+混合离子废水进行了净化试验研究,浮选过程中考察了pH值、电流密度、初步浮选时间、离子强度4个主要因素对浮选效率的影响。试验选用混合离子的整体去除效率为评价指标,优化了电浮选方法净化含混合重金属Zn^2+和Cu^2+的实验条件,得到了较好的浮选条件。该方法操作简单,处理效果较理想,对实际利用电浮选法处理重金属离子废水工程具有一定的参考价值。     

水库疏浚底泥絮凝沉降室内试验研究

泥浆絮凝沉降效率是影响湖库疏浚工程进度的重要因素。为探索不同絮凝剂(有机、无机)对疏浚泥浆絮凝沉降效率的影响,以通济桥水库疏浚底泥为研究对象,通过室内试验先分析1种有机絮凝剂(PAM)和5种无机絮凝剂(PAC,FeCl₃,Na₂CO₃,Na₂SiO₃·9H₂O,KAl(SO₄)₂·12H₂O)单独作用下疏浚泥浆的絮凝沉降效果及上清液水质的优劣情况,然后对有机、无机絮凝剂进行优化组合试验,确定絮凝沉降效果和上清液水质最优的设计配比方案。试验结果表明:①PAM可以有效促进疏浚泥浆土颗粒的絮凝沉降,但对上清液的去浊率较低;CO₃^2-可以促进细颗粒絮凝结合成大颗粒,提高颗粒的沉降速率;Fe³⁺,Al³⁺具有改善上清液浊度的作用,但对促进泥浆絮凝沉降效果有限。②每1 000 mL疏浚泥浆中采用10 mL PAM+2 g PAC+2 g Na₂CO₃的有机-无机絮凝剂组合为最佳方案,既能快速促进疏浚泥浆的絮凝沉降,又能有效降低上清液的浊度。试验成果可为类似疏浚工程中选择絮凝剂最佳配比方案提供参考。     

Simultaneous optimization of multiple performance characteristics in coagulation-flocculation process for Indian paper industry wastewater

The goal of this study was to optimize the coagulation-flocculation process in wastewater generated from the paper and pulp industry using a grey relational analysis (GRA)-based Taguchi method. Process parameters included types and doses of natural coagulants and coagulant aid, and pH. To track the efficiency of the treatment process, the following responses were chosen for optimization: chemical oxygen demand (COD), total dissolved solids (TDS) and turbidity of wastewater, alone or in combination or all together. Analysis of variance showed that the type and dose of the coagulant aid were the most significant parameters, followed by pH and the dose of the coagulant; the type of coagulant used was found to be insignificant in the coagulation-flocculation process. Optimization of process parameters to achieve lower turbidity and greater removal of COD and TDS was verified in a separate confirmatory experiment, which showed improvements in COD and TDS removal and a decrease in turbidity of 8.2, 6.35 and 26.17%, respectively, with the application of the Taguchi method and GRA.     

Equalization characteristics of an upflow sludge blanket-aerated biofilter (USB-AF) system.

Equalization characteristics of the upflow sludge blanket-aerated bio-filter (USB-AF) were investigated with the fluctuated raw domestic sewage. Recycle of nitrified effluent from AF to USB triggered the equalization characteristics of the sludge blanket on both soluble and particulate organic matter. Increment of EPS in sludge blanket by nitrate recycle was detected and removal of turbidity and particulates increased at higher recycle ratios by bio-flocculation. Increased TCOD removal in the USB was due to both denitrification of recycled nitrate and entrapment of the particulate organic matter in sludge blanket. Capture of both soluble and particulate organic matter increased sludge blanket layer in the USB, which improved the reactor performances and reduced the organic load on the subsequent AF. Overall TCOD and SS removal efficiencies were about 98% and 96%, respectively in the USB-AF system. Turbidity in the USB effluent was about 44, 20 and 5.5 NTU, at recycle ratios of 0, 100 and 200%, respectively. Particle counts in the range 2-4 microm in the USB effluent were higher than those in influent without nitrate recycle, while particle counts in the range of 0.5-15 microm in the USB effluent decreased 70% at recycle ratio of 200%. The major constituent of EPS extracted from anaerobic sludge was protein and total EPS increased from 109.1 to 165.7 mg/g-VSS with nitrate recycle of 100%. Removal efficiency and concentration of T-N in the UBS-AF effluent was over 70% and below 16 mg/L, respectively.     

Effect of internal recycle rate on the high-strength nitrogen wastewater treatment in the combined UBF/MBR system.

An anaerobic/aerobic system combining an anaerobic upflow-sludge bed filter (UBF) and an aerobic membrane bioreactor (MBR) was operated to enhance organic and nitrogen removal efficiency. The internal recycle rate, which is one of the most important operation factors that affects overall removal efficiency, was varied from 100% to 300% of the influent flow. Under these conditions, the overall removal efficiencies of organic and nitrogen and characteristics of membrane fouling in the combined system treating the synthetic wastewater including high concentration of organics and nutrients were studied. As a result, nitrogen removal efficiency was increased to 67% when the internal recycle rate was 300% of influent flow rate. As the internal recycle ratio increased from 100% to 200%, protein content decreased by 17% and carbohydrate content increased by 12%. However, there was no remarkable difference in total extracellular polymeric substances (EPS) content. At the high recycle rate of 300%, the surface charge of sludge was decreased while hydrophobicity (specific ultraviolet absorbance, SUVA) was increased. The differences in SUVA and surface charge were 11% and 1%, respectively. It is concluded that SUVA and EPS composition were important parameters affecting membrane fouling in the combined system.     

小秦岭某金矿氰化废水处理试验

采用碱氯法对小秦岭某金矿提金后的含氰废水进行了处理试验,实验室试验主要考察了药剂使用量、pH值、反应时间等对除氰效果的影响。对ρ(CN-)为33.5 mg/L和22.5 mg/L的含氰废水,经一次处理的试验结果表明,处理后水中ρ(CN-)为0.10~0.28 mg/L,CN-去除率大于99%,低于国家ρ(CN-)≤0.50 mg/L的排放标准;扩大试验在实验室试验最优条件下进行,达到了实验室试验同样的处理效果,对处理合格后的废水进行了返回系统使用试验,实现了处理后废水部分或一定时间内全部返回系统使用,局部实现了微氰废水零排放。     

石英砂加载混凝工艺的DOM去除特征与混凝机理

为处理未纳入管网的市政污水,采用石英砂加载混凝工艺,考察石英砂的粒径及其投加量对处理效能的影响,分析了溶解性有机物(dissolved organic matters,DOM)的去除特征,并探讨了石英砂加载混凝机理。结果表明,与常规混凝相比,当石英砂的粒径和投加量分别为200目和 1.0 mg/L 时,石英砂加载混凝工艺对污水中浊度、COD的去除率分别为97.55%、59.2%,优于常规混凝;石英砂加载混凝工艺可明显去除芳香类、共轭双键、疏水性有机物,主要促进了腐殖质类物质的削减;石英砂通过架桥作用增加了絮体的密度,进而显著改善了絮体的沉降性能、强度;絮体的沉降性能、强度及再稳性能随着石英砂粒径的降低而升高。     

Phosphorus recovery from wastewater through struvite formation in fluidized bed reactors: a sustainable approach.

Recovery of phosphate as struvite (MgNH4PO4.6H2O), before it forms and accumulates on wastewater treatment equipment, solves wastewater treatment problems and also provides environmentally sustainable, renewable nutrient source for the agriculture sector. A pilot-scale fluidized bed reactor was used to recover phosphate through crystallization of struvite, from anaerobic digester centrate at the Lulu Island Wastewater Treatment Plant, Richmond, British Columbia, Canada. The desired degree of phosphate removal was achieved by maintaining operating pH (8.0-8.2), and recycle ratio 5-9, to control the supersaturation conditions inside the reactor. The performance of the system was found to be optimal when in-reactor supersaturation ratio was 2-6. Among several other operating parameters, apparent upflow velocity and magnesium to phosphate molar ratio were also found important to maintain system performance, both in terms of efficiency of phosphate removal and recovery as struvite pellets. A narrow window of upflow velocity (400-410 cm/min) was found to be effective in removing 75-85% phosphate. TOC level inside the rector was found to affect the performance to some extent. The precipitation potential of struvite could be successfully predicted using a thermodynamic solubility product value of 10(-13.36) and its temperature dependence in PHREEQC.     

高浊水处理投药方式的选择

在常规处理条件下,对西南岷江地区突发性非多砂高浊水进行了原水特性的分析及絮凝优化试验。结果表明,采用单级絮凝、分级沉淀工艺,先投加PAC,60~120s后投加PAM,对高浊度原水有良好的去除效果。原水浊度为15000NTU时,投加200mg/LPAC、0.4~0.5mg/LPAM,静沉30min后,出水浊度为1.73~2.48NTU。     

柱状气浮分离器处理含油污水实验研究

乳化后的含油污水中,油滴细小分散、稳定不易团聚上浮。常规采用药剂破乳和加热处理方法,会增大企业生产成本。柱状气浮除油技术因其设备结构简单、节能高效,无二次污染等优点受到相关企业重视。气浮除油效率受到多种参数制约,而压力、分流比、污水的矿化度和单位时间内的气浮强度是几个关键因素。该文以实验研究为主,提出了综合除油率和气浮强度两个评价指标。尝试在实际生产环境内的可控制因素中,找到影响气浮除油效率的关键因素,用以改进柱状气浮分离工艺。     

高压脉冲放电处理含氰废水的影响因素探讨

焦化废水中含有大量的氰化物,必须采取有效措施进行去除,传统去除方法运行成本高、操作复杂。提出了用高压毫微秒脉冲产生的非平衡等离子体处理含氰废水的方法,对其影响因素pH值、放电时间、气流量、放电条件等进行了大量的实验研究,结果表明:溶液初始pH值为9.09,放电2 h,放电电压46 kV时氰化物的去除率最高可达93.2%,氰化物质量浓度可降至0.26 mg/L。实验对比了放电与不放电氰化物的去除效果:相同条件下放电后氰化物的去除率大大提高,为焦化废水中氰化物的去除提出了一种新的方法。     

新型中置式高密度沉淀池优化投药试验研究

通过小试和生产性试验对新型中置式高密度沉淀池的投药系统(包括回流污泥、混凝剂及助凝剂PAM的投加)进行了详细研究.小试研究表明回流污泥和混凝剂投加量的增大降低了上清液浊度,PAM的投加略微降低了上清液出水浊度,但影响不大.生产性试验研究结果表明,实际生产运行中可灵活利用回流污泥来提高絮凝效果,在合理的范围内回流污泥投加量越大,絮凝效果越好;沉淀池随着混凝剂投加量的增大,出水浊度逐渐降低,同时,不同的回流污泥投加量条件下混凝剂投加对沉淀池出水浊度的影响表现出不同特性;增大PAM投加量对直接提高沉淀池的絮凝效果以及降低出水浊度的贡献不明显,PAM投加量的增大间接引起回流污泥投加量变大是导致出水浊度变小的原因.