絮体破碎再形成行为的计算机模拟

为了深入探讨絮体破碎行为对其分形成长及结构的影响,借助一种简化的絮体破碎模式对絮体破碎/再形成过程进行计算机模拟。通过对比分析破碎前后虚拟絮体的形态特征及其统计特性,得出如下主要结论：（1）絮体发生破碎后,所形成碎片的形态特征直接影响着再形成絮体的形态及恢复程度;（2）絮体外围枝杈结构的破坏,有利于运动粒子进入絮体内部或者均匀地排列在凝聚核周围,改善絮体质心附近颗粒的空间分布,从而有效地提高其致密性和抗剪切破坏能力;（3）在絮体分形成长过程中,存在一个使其由各向同性向各向异性过渡的临界状态,之后发育良好的枝杈对其余枝杈生长的抑制作用增强。此外,在实际操作时还应严格控制絮凝体系的物化条件,不宜使絮体过度破碎,以获得较好的絮凝效果。     

Diffusion of oxygen through activated sludge flocs: experimental measurement, modeling, and implications for simultaneous nitrification and denitrification.

Diffusion of dissolved oxygen through activated sludge flocs was studied, as it represents a potential mechanism for simultaneous nitrification and denitrification in activated sludge systems. Dissolved oxygen profiles through six floc particles collected at different times from a full-scale activated sludge plant demonstrated that that the dissolved oxygen concentration declines through all floc particles. For larger floc particles (2-mm diameter and greater), the dissolved oxygen concentration reached near-zero values at depths depending on process operating conditions. A mathematical model based on diffusion of dissolved oxygen, organic substrate (methanol), ammonia, nitrite, and nitrate through a spherical floc and consumption of dissolved oxygen by heterotrophs and autotrophs accurately predicted the dissolved oxygen profile and required adjustment of only one model parameter--the concentration of heterotrophs. A different dissolved oxygen decline pattern was exhibited for the smaller floc particles characterized, with the dissolved oxygen reaching a non-zero plateau toward the center of the floc. This pattern was not reproduced with the mathematical model developed and suggests that additional mechanisms are responsible for the transport of dissolved oxygen into the center of these flocs. Implications of these results regarding the occurrence of simultaneous nitrification and denitrification include consideration of the factors that affect floc size and distribution (simultaneous nitrification and denitrification is maximized with larger floc particles), coupling of the International Water Association (London) activated models to predict activated sludge composition with diffusion models to consider intrafloc effects, and the effects of substrate diffusion on the apparent half-saturation constant for various substrates in activated sludge systems.     

氢氧化镁混凝性能及絮体特性

以氢氧化镁作为混凝剂,不同浊度高岭土水样为研究对象,运用iPDA在线监测技术对混凝过程絮体形成进行监测,探求了操作条件对絮体特性和混凝过程的影响;同时讨论了FI值和浊度去除的关系。结果表明,当浊度分别为5、10和20 NTU时,最佳投加量分别为21.6、14.4和3.6 mg/L;随着pH的升高,FI指数增大,同时混凝剂的最佳投加量也逐步减小;随着慢速搅拌转速的增大,絮体破碎过程明显,FI指数降低;当转速为60 r/min时,浊度去除率最高。     

Ultraviolet disinfection of fecal coliform in municipal wastewater: effects of particle size.

Suspended solids interfere with the efficiency of disinfection using UV radiation by decreasing the rate of disinfection and inducing tailing. However, conventional measures of solids (total suspended solids, turbidity, and UV transmittance) do not adequately predict the presence or degree of these effects. Bacteria and viruses can become associated with particles in wastewater. A fractionation technique was developed to separate particle-associated bacteria into three fractions, based on particle size. The results show that the degree to which particles interfere with UV disinfection efficiency is dependent on particle size. The small size fraction (< 5 microm) consistently produced a statistically significant faster disinfection rate than the large fraction (> 20 microm), with the unfiltered sample and the medium fraction (particles > 5 microm, but < 20 microm) between the two extremes. Tailing also was observed only in the large fraction. Correlations between the disinfection rate constant and the percentage of large fraction bacteria of a sample were good.     

Effects of chlorination on the adhesion strength and deflocculation of activated sludge flocs.

A side effect of the application of chlorine for controlling filamentous bulking is deflocculation of floc-forming bacteria, which may cause unacceptable effluent deterioration depending on dosing. It was assumed that chlorine may adversely affect the adhesion ability of floc bacteria, promoting their erosion in shear flow. The effect of chlorination on the strength of activated sludge flocs was investigated. The adhesion-erosion (AE) model developed by Mikkelsen and Keiding was used to interpret results from deflocculation tests with varying shear and solids concentration. The AE model yields the adhesion enthalpy (deltaHG/R) of cells in sludge flocs and parameters from the model were used to quantify the sludge in terms of floc strength. Two activated sludges with different initial characteristics were studied. The resulting model parameters showed that the AE model was suitable for quantifying the bond energy of particles to the activated sludge exposed to chlorine. For one activated sludge, adhesion of cells was largely unaffected by the applied chlorine doses. A second sludge showed reduced adhesion strength with chlorine, leading to increasing deflocculation. The simple batch test and AE model proved valuable for assessing the effect of chlorination on the flocs in activated sludge. By use of these procedures, it is possible to determine acceptable chlorine dosing to avoid excessive deflocculation and effluent deterioration.     

共存物质对重金属絮凝齐MCC除镉性能的影响

为进一步拓展天然高分子絮凝剂壳聚糖的应用范围,以壳聚糖、L-半胱氨酸为原料,通过酰胺化反应制备一种具有重金属捕集功能的高分子重金属絮凝剂-2-氨基-3-巯基丙酰壳聚糖（MCC）,研究了水体中常见的阴阳离子、有机配位剂及浊度对MCC除镉性能的影响,探讨了絮体形貌与絮体分形维数及絮凝除镉效果间的关系。结果表明,Na＋、Cl-、N03、F-、SO4 2-的存在对MCC除Cd2＋均有促进作用,Ca2＋表现为明显的抑制作用;低浓度的EDTA对除镉有促进作用,随着EDTA浓度的增大,逐渐转为抑制作用;低浓度的腐殖酸对MCC去除Cd2＋有显著的促进作用;在一定范围内,浊度可促进MCC对Cd2＋的去除;絮体间空隙越多,絮体分形维数越小,除镉效果越好。     

Effects of nitrogen and phosphorus limitation on the activated sludge biomass in a kraft mill biotreatment system.

Unlike wastewater, pulp and paper mill effluents are generally severely deficient in bioavailable nitrogen and phosphorus. The influence of nitrogen and phosphorus limitations on steady-state or typical pulp and paper mill activated sludge floc properties and performance was studied using a bioreactor-fed synthetic raw mill effluent and seeded with mill activated sludge. Limitation of either nitrogen or phosphorus decreased growth, five-day biochemical oxygen demand, and suspended solids removal. Nitrogen limitation greatly enhanced activated sludge floc poly-beta3-hydroxybutyrate (PHB), but not carbohydrate or extracellular polymeric substances (EPS). In contrast, phosphorus limitation increased total floc carbohydrate and EPS, but not PHB. The flocs showed little ability to store either nitrogen or phosphorus. Nitrogen limitation, but not phosphorus limitation, produced much more negative net floc surface charge, increasing fines, while phosphorus limitation, but not nitrogen limitation, increased the floc bound water content and surface hydrophobicity and decreased fines.     

超声波对氢氧化镁混凝性能及絮体特性影响

以氢氧化镁作为混凝剂,不同浊度高岭土水样为研究对象,运用iPDA在线监测技术,探求了超声波对絮体特性和混凝过程的影响。结果表明,在混凝初期的5 s内,增大超声功率能够有利于混凝作用发生。超声功率为80 W,浊度去除率最高。随着超声时间延长到10 s时,超声条件下FI值变小絮凝效果逐渐变差。Zeta电位与絮体粒度存在相关关系。     

Comparison of coagulation performance and floc properties of a novel zirconium-glycine complex coagulant with traditional coagulants

A new inorganic-organic hybrid material zirconium-glycine complex (ZGC) was firstly used as a coagulant in a coagulation process to treat Pearl River raw water. Its coagulation performance was compared with commonly used aluminum (Al) coagulants such as aluminum sulfate (Al₂(SO₄)₃) and polyaluminum chloride (PAC), in terms of water quality parameters and floc properties. ZGC coagulation achieved higher removal of turbidity (93.8 %) than other traditional coagulants. Charge neutralization was proven to act as a dominant mechanism during ZGC coagulation. The aggregated flocs with ZGC showed the fastest growth rate and good recovery ability compared with the other coagulants and achieved the largest floc size within 5 min. The ZGC coagulant can decrease the hydraulic retention time and increase removal efficiency.     

The digestibility of waste activated sludges.

Laboratory digestion studies using waste activated sludges (WAS) were conducted to compare the digestion performance between anaerobic and aerobic processes. Nine samples of WAS from seven wastewater treatment plants were collected and batch-digested under both anaerobic and aerobic conditions for 30 days at 25 degrees C. The cation content of wastewater (both floc and solution phases) and solution biopolymer (protein and polysaccharide) was measured before and after digestion and compared with volatile solids destruction data. The study revealed that each digestion process was associated with a distinct biopolymer fraction, which accounted for differences in volatile solids reduction under anaerobic and aerobic conditions. The anaerobic digestion data showed strong correlations between soluble protein generation, ammonium production, percent volatile solids reduction, and floc iron (Fe). These data suggest that the amount of volatile solids destroyed by anaerobic digestion depends on the Fe content of floc. In aerobic digestion, polysaccharide accumulated in solution along with calcium and magnesium. For aerobic digestion, correlations between divalent cation release and the production of inorganic nitrogen were found. This implies that divalent cation-bound biopolymer, thought to be lectin-like protein, was the primary organic fraction degraded under aerobic conditions. The results of the study show that the cation content in wastewater is an important indicator of the material that will digest under anaerobic or aerobic conditions and that some of the volatile solids will digest only under either anaerobic or aerobic conditions.     

共存物质对重金属絮凝剂 MCC 除镉性能的影响简

为进一步拓展天然高分子絮凝剂壳聚糖的应用范围,以壳聚糖、L-半胱氨酸为原料,通过酰胺化反应制备一种具有重金属捕集功能的高分子重金属絮凝剂-2-氨基-3-巯基丙酰壳聚糖（MCC）,研究了水体中常见的阴阳离子、有机配位剂及浊度对MCC除镉性能的影响,探讨了絮体形貌与絮体分形维数及絮凝除镉效果间的关系。结果表明,Na⁺、Cl^-、NO₃^-、F^-、SO₄^2-的存在对MCC除Cd²⁺均有促进作用,Ca²⁺表现为明显的抑制作用;低浓度的EDTA对除镉有促进作用,随着EDTA浓度的增大,逐渐转为抑制作用;低浓度的腐殖酸对MCC去除Cd²⁺有显著的促进作用;在一定范围内,浊度可促进 MCC对Cd²⁺的去除;絮体间空隙越多,絮体分形维数越小,除镉效果越好。     

Oxidation-reduction potential changes in aeration tanks and microprofiles of activated sludge floc in medium- and low-strength wastewaters.

Real-time control of aeration tank operation is key to high-efficiency pollutant removal and energy savings. One of the aims of this study was to examine the potential for using redox potential (oxidation-reduction potential [ORP]) to indicate wastewater quality online in aeration tanks treating medium (chemical oxygen demand [COD] of 70 to 150 mg/L) and low (COD of 15 to 30 mg/L) pollutant-concentration wastewaters. The field-scale data provide a good relationship between ORP values and nutrient removal along the length of the aeration tanks. The ORP values increased dramatically as organic matter was removed along the aeration tanks, indicating the improvement of the bulk liquor redox status. Dissolved oxygen higher than 1.0 mg/L was necessary for good biodegradation and improvement of the liquid redox status. Nitrification occurred at higher ORP values (380 to 420 mV) than was the case for organic substrate oxidation (250 to 300 mV). The microprofiles obtained from microelectrode measurements substantiate the heterogeneity of the microbial processes inside activated sludge flocs. Because of microbial oxygen utilization, the aerobic region in the activated sludge floc was limited to the top layer (0.1 to 0.2 mm) of the activated sludge aggregate present in medium-strength wastewater, with an anoxic zone dominating inside the flocs. When dissolved oxygen in the bulk water was higher than 4.0 mg/L, the anoxic zone inside the floc disappeared. At low wastewater pollutant concentrations, the ORP and dissolved oxygen inside the activated sludge aggregates were higher than those from medium-strength wastewater. The prospect of using ORP as an online control approach for aeration tank operation and the potential reasons for activated sludge floc size varying with pollutant strengths are also discussed.     

微污染矿井水中微絮体的形成及分形特征

利用分形理论阐述了微污染矿井水中微絮体形成的分形生长特征,考察了微絮体形成过程中的影响因素,探讨了微絮凝机理,利用絮体的分形维数表征各影响因素对微絮体形态的作用结果,结果表明,微絮体形态与其分形维数之间具有良好的相关性,且分形维数越大,微絮体更加紧实,越易于沉降,滤后水的浊度越小;同时考察了微量铁锰离子对微絮体形态的影响,为微絮凝深床过滤工艺参数的改进提出了建议.     

Effects of wastewater disinfection on waterborne bacteria and viruses.

Wastewater disinfection is practiced with the goal of reducing risks of human exposure to pathogenic microorganisms. In most circumstances, the efficacy of a wastewater disinfection process is regulated and monitored based on measurements of the responses of indicator bacteria. However, inactivation of indicator bacteria does not guarantee an acceptable degree of inactivation among other waterborne microorganisms (e.g., microbial pathogens). Undisinfected effluent samples from several municipal wastewater treatment facilities were collected for analysis. Facilities were selected to provide a broad spectrum of effluent quality, particularly as related to nitrogenous compounds. Samples were subjected to bench-scale chlorination and dechlorination and UV irradiation under conditions that allowed compliance with relevant discharge regulations and such that disinfectant exposures could be accurately quantified. Disinfected samples were subjected to a battery of assays to assess the immediate and long-term effects of wastewater disinfection on waterborne bacteria and viruses. In general, (viable) bacterial populations showed an immediate decline as a result of disinfectant exposure; however, incubation of disinfected samples under conditions that were designed to mimic the conditions in a receiving stream resulted in substantial recovery of the total bacterial community. The bacterial groups that are commonly used as indicators do not provide an accurate representation of the response of the bacterial community to disinfectant exposure and subsequent recovery in the environment. UV irradiation and chlorination/dechlorination both accomplished measurable inactivation of indigenous phage; however, the extent of inactivation was fairly modest under the conditions of disinfection used in this study. UV irradiation was consistently more effective as a virucide than chlorination/dechlorination under the conditions of application, based on measurements of virus (phage) diversity and concentration. Taken together, and when considered in conjunction with previously published research, the results of these experiments illustrate several important limitations of common disinfection processes as applied in the treatment of municipal wastewaters. In general, it is not clear that conventional disinfection processes, as commonly implemented, are effective for control of the risks of disease transmission, particularly those associated with viral pathogens. Microbial quality in receiving streams may not be substantially improved by the application of these disinfection processes; under some circumstances, an argument can be made that disinfection may actually yield a decrease in effluent and receiving water quality. Decisions regarding the need for effluent disinfection must account for site-specific characteristics, but it is not clear that disinfection of municipal wastewater effluents is necessary or beneficial for all facilities. When direct human contact or ingestion of municipal wastewater effluents is likely, disinfection may be necessary. Under these circumstances, UV irradiation appears to be superior to chlorination in terms of microbial quality and chemistry and toxicology. This advantage is particularly evident in effluents that contain appreciable quantities of ammonia-nitrogen or organic nitrogen.     

Comparison of sludge characteristics and PCR-DGGE based microbial diversity of nanofiltration and microfiltration membrane bioreactors

The objective of this study was to compare the sludge characteristics and microbial community diversity between the submerged nanofiltration membrane bioreactor (NF MBR) and microfiltration membrane bioreactor (MF MBR) treating the same municipal wastewater. The influence of a higher concentration of organic matter and salt was investigated. The results of water qualities showed that the dissolved organic carbon (DOC), total phosphorus (T-P) and salt concentrations of the supernatant in the NF MBR were three, four and two times as high as those in the MF MBR, respectively. The specific oxygen uptake rate of the NF MBR (2.9+/-0.4 mg O(2)g(-1)MLSSh(-1)) was lower than that of the MF MBR (4.3+/-1.1 mg O(2)g(-1)MLSS h(-1)). Result of extractable extracellular polymeric substances showed that the NF MBR sludge had more protein and less polysaccharide compared to the MF MBR sludge, whereas specific amount of total organic carbon were the same in both MBRs. The median floc diameters of the NF MBR and the MF MBR were 72+/-12 microm and 59+/-12 microm, respectively, which could be attributable to the different polysaccharide concentrations between both MBR mixed liquor. A higher concentration of materials (DOC, T-P and salt) in the bioreactor, determined by the high rejection rate of the NF membrane, did not significantly affect the microbial diversity under similar operation conditions.     

聚硅硫酸铁混凝去除石化废水二级出水中有机污染物的研究

采用聚硅硫酸铁(PFSiS)混凝剂对石化废水二级出水进行了强化混凝实验,考察其对有机污染物的去除效果,并对不同时期的絮体微观结构进行了研究。结果表明,PFSiS可有效去除水中COD,当PFSiS投加量为40 mg/L(以Fe计),静置时间为120 min,COD去除率可达50%左右;絮体的微观结构为空间网状结构,随静置时间的延长,絮体密实程度提高,颜色加深。     

Coagulation of highly turbid suspensions using magnesium hydroxide: effects of slow mixing conditions

Laboratory experiments were carried out to study the effects of slow mixing conditions on magnesium hydroxide floc size and strength and to determine the turbidity and total suspended solid (TSS) removal efficiencies during coagulation of highly turbid suspensions. A highly turbid kaolin clay suspension (1,213?±?36 nephelometric turbidity units (NTU)) was alkalized to pH 10.5 using a 5 M NaOH solution; liquid bittern (LB) equivalent to 536 mg/L of Mg²⁺ was added as a coagulant, and the suspension was then subjected to previously optimized fast mixing conditions of 100 rpm and 60 s. Slow mixing speed (20, 30, 40, and 50 rpm) and time (10, 20, and 30 min) were then varied, while the temperature was maintained at 20.7?±?1 °C. The standard practice for coagulation-flocculation jar test ASTM D2035-13 (2013) was followed in all experiments. Relative floc size was monitored using an optical measuring device, photometric dispersion analyzer (PDA 2000). Larger and more shear resistant flocs were obtained at 20 rpm for both 20- and 30-min slow mixing times; however, given the shorter duration for the former, the 20-min slow mixing time was considered to be more energy efficient. For slow mixing camp number (Gt) values in the range of 8,400–90,000, it was found that the mixing speed affected floc size and strength more than the time. Higher-turbidity removal efficiencies were achieved at 20 and 30 rpm, while TSS removal efficiency was higher for the 50-rpm slow mixing speed. Extended slow mixing time of 30 min yielded better turbidity and TSS removal efficiencies at the slower speeds.     

加药量和水力搅拌速度对雨水混凝效果的影响

为降低分流制雨水中悬浮颗粒物及其他污染物浓度,减轻城市景观河道的水体富营养化程度,对取自泵站的雨水进行混凝沉淀工艺优化实验。以PAC为混凝剂,采用Zeta电位仪、激光粒度仪和iPDA在线监测技术对混凝过程进行监测,考察了混凝剂投加量和水力搅拌速度对絮体形成和分流制雨水处理效果的影响,结果表明,混凝剂投加量和混合水力搅拌速度直接影响絮体Zeta电位和聚沉特性;混合搅拌速度控制混凝反应速率,絮凝速度梯度影响絮体形成粒径。FI曲线特征参数对控制混凝工艺具有指导意义。PAC投加量为35 mg/L,混合阶段搅拌速度800 r/min,搅拌30 s,絮凝阶段采用150、108和60 r/min的转速各自搅拌5 min,沉后水中剩余颗粒总数最少,浊度、COD和总磷去除效果最佳。     

Phosphorus removal from piggery effluents of varying quality using lime and physico-chemical treatment methods

The choice of management practices for the treatment of piggery effluent prior to its disposal to waterways or land is governed by the desire to simultaneously minimise the cost of treatment whilst minimising pollution of the environment. Laboratory experiments were conducted to compare the removal of total and total filterable phosphorus (P) (<0.45 microm) from ortho-phosphate solutions or piggery effluent by hydrated lime or lime kiln dust alone, or from recycled piggery effluent by lime and physico-chemical treatment methods. In addition, the ability of lime to remove P from recycled piggery effluent at an intensive piggery was assessed. Most P in lime treated effluent was present in the >0.45 microm fraction because of the presence of unsettled flocs of P impregnated lime. The efficiency of total P removal by hydrated lime and lime kiln dust decreased as effluent quality declined. The efficiency of removal of total filterable P by hydrated lime or lime kiln dust was not affected by effluent quality. Hydrated lime was more efficient in removing P from effluent or ortho-phosphate solutions, but lime kiln dust was more cost effective. More than 95% of total P was removed from recycled piggery effluent when physico-chemical treatment followed settling with or without lime. The physico-chemical treatment decreased total P mainly by decreasing the number of suspended particles in the effluent and by precipitating some total filterable P as iron, aluminium or calcium compounds.     

Implication of hydraulic properties of bioremediated diesel-contaminated soil

The hydraulic properties, such as hydraulic conductivity and water retention, of aged diesel-contaminated and bioremediated soils were examined and implications of the hydraulic properties for assessing bioremediation performance of soils were proposed. Bioremediation of diesel-contaminated soil was performed over 80 d using three treatments; (I) no nutrient added, column-packed soil, (II) nutrient added, column-packed soil, and (III) nutrient added, loosen soil. Diesel reduction in treatment I soil (control soil) was negligible while treatment III showed the greatest extent of diesel biodegradation. All treatments showed greatest rates of diesel biodegradation during the first 20 d, followed by a much retarded biodegradation rate in the remaining incubation period. Reduction of the degradation rate due to entrained diesel within inaccessible soil pores was hypothesized and tested by measuring the hydraulic properties of two column-packed soils (treatments I and II). The hydraulic conductivity of treatment II soil (nutrient added) was consistently above that of treatment I soil (no nutrient added) at pressure heads between 0 and 15 cm. In addition, the water retention of treatment II soil was greater at pressure heads <100 cm (equivalent to pore size of >30 microm), suggesting that biodegradative removal of hydrocarbons results in enhanced wettability of larger soil pores. However, water retention was not significantly different for control and biodegraded soils at pressure heads >100 cm, where smaller size soil pores were responsible for the water retention, indicating that diesel remained in smaller soil pores (e.g., <30 microm). Both incubation kinetics and hydraulic measurements suggest that hydrocarbons located in small pores with limited microbe accessibility may be recalcitrant to bioremediation.