A strategy for controlling deposition of struvite in municipal wastewater treatment plants.

This paper presents strategies to reduce the risk of struvite deposition by controlling its location of formation. Two technical routes were investigated: (1) to fix the phosphate into the dewatered sludge cake, and (2) to remove phosphate from centrate or filtrate. Chemicals used include magnesium hydroxide [Mg(OH)2], both of reagent grade and reclaimed from a flue gas desulfurization system, magnesium chloride (MgCl2), calcium hydroxide [Ca(OH)2], ferric chloride (FeCl3) and aluminum sulfate [Al2(SO4)3]. Research results indicate that (1) for anaerobically well-digested sludge, Mg(OH)2 is effective in fixing phosphate into sludge cake and improving sludge dewaterability, and (2) adding Mg(OH)2 into a reactor, located between the sludge dewatering facilities and the centrate or filtrate discharge line, and using air for mixing and carbon dioxide stripping, proves feasible in reducing struvite deposition in centrate or filtrate discharge lines and can generate a potentially valuable plant fertilizer--struvite.     

改性蛭石结合鸟粪石沉淀法回收垃圾渗滤液中氨氮的实验研究

研究了使用氯化镁改性蛭石,利用磷酸铵镁沉淀的原理,在垃圾渗滤液中按比例加入PO43-,处理垃圾渗滤液中氨氮的同时,在蛭石上生成磷酸铵镁沉淀,以便于磷酸铵镁沉淀的回收利用。结果表明,筛取蛭石粒径为60～80目,配制浓度20%的氯化镁溶液浸泡改性蛭石20 min,取25 g改性蛭石,100 mL垃圾渗滤液调节pH为9,按n(NH4+)∶n(PO34-)=1∶1.2的比例加入PO43-离子,垃圾渗滤液中氨氮去除率为85.06%,实验并对磷酸铵镁沉淀进行了结构成分分析,为垃圾渗滤液中氨氮的处理及磷酸铵镁沉淀的回收提供了一种新的方法。     

Removal of nitrogen and phosphate from wastewater by addition of bittern

Removal of nitrogen and phosphate through crystallization of struvite (MgNH(4)PO(4).6H(2)O) has gained increasing interest. Since wastewaters tend to be low in magnesium relative to ammonia and phosphates, addition of this mineral is usually required to effect the struvite crystallization process. The present study evaluated the feasibility of using bittern, a byproduct of salt manufacture, as a low-cost source of magnesium ions. High reaction rates were observed; the extent of nitrogen and phosphorus removals did not change beyond 10 min. Phosphorus removals from pure solutions with bittern added were equivalent to those obtained with MgCl(2) or seawater. Nitrogen removals with bittern were somewhat lower than with the alternate Mg(2+) sources, however. Application of bittern to biologically treated wastewater from a swine farm achieved high phosphate removal, but ammonia removals were limited by imbalance in the nitrogen:phosphorus ratio.     

Effects of anaerobic selector hydraulic retention time on biological foam control and enhanced biological phosphorus removal in a pure-oxygen activated sludge system.

Increased anaerobic selector hydraulic retention times (HRTs) in a high-purity oxygen activated sludge process resulted in an increase in soluble orthophosphate release and biodegradable chemical oxygen demand removal, confirming that enhanced biological phosphorus removal occurs at aeration solids retention times (SRTs) below 1.7 days. Under operating conditions that included biological foam trapping and recycling, an anaerobic selector with HRTs higher than 55 minutes resulted in a decrease in filament counts and effective foam control. Effective norcardioform control is achieved through the combination of metabolic selective pressure and increased soluble organic substrate removal in the anaerobic selector and low aeration SRT.     

酸性条件下剩余污泥中Ca2＋和Mg2＋溶出对磷回收的影响

为了在酸性条件下实现剩余污泥中磷的高效回收，对pH=3时剩余污泥水解酸化过程中氨氮、正磷酸盐和钙镁离子的溶出现象以及磷回收进行了研究分析。结果表明：当pH=3时，所溶出的氨氮、镁离子和钙离子与磷酸盐的摩尔比均大于1，能满足采用鸟粪石沉淀法或者羟磷灰石沉淀法回收磷的要求；但所溶出的钙镁离子的摩尔比大于1，会对鸟粪石沉淀法回收磷的顺利进行有较大影响；有无外加镁剂对磷回收率影响不大。采用改型后的镁型强酸性阳离子交换树脂进行离子交换可以得到较高纯度的鸟粪石沉淀产品，通过XRD检测其纯度为95％以上。     

Phosphorus release in aerobic sludge digestion.

The objectives of this study are to examine the phosphorus release in aerobic sludge digestion and to better understand its governing mechanisms. In this study, phosphorus release was examined using the secondary sludge from both conventional and biological nutrient removal processes. The experiments were carried out at room temperature (22 +/- 2 degrees C), with or without automatic control of pH (4.5 to 7.8), and under three aeration schemes: fully aerobic (dissolved oxygen [DO] at 3 to 4 mg/L), low DO (0.2 to 0.8 mg/L), and cyclic (with alternate on/off aeration). The released phosphorus concentrations were 20 to 80 mg/L for the conventional sludge and 60 to 130 mg/L for the biophosphorus sludge. Higher phosphorus release also occurred at low pH (<6.0). As for the effect of DO, fully aerobic digestion caused higher phosphorus release than the low-DO and cyclic operations. For better understanding, the solid phosphorus in sludge was conceptually categorized into three forms: inorganic phosphorus precipitates, organic cellular phosphorus, and polyphosphate (poly-P) in polyphosphate-accumulating organisms. Dissolution of inorganic phosphorus precipitates is controlled by physical and chemical conditions, with pH being the most important in this study. Lowering the pH to 4 to 6 clearly promoted the release of inorganic phosphorus. Polyphosphate hydrolysis, on the other hand, was found to be regulated biologically (sensitive to occurrence of anaerobic conditions) and was insignificant in the glutaraldehyde-fixed sludge. Phosphorus release from organic phosphorus should correlate with the volatile solid (VS) digestion, which lyses the cells and frees the phosphorus covalently bonded with the organic matters. The amounts of phosphorus released per unit VS digested (deltaP/deltaVS) were therefore calculated for experiments with long periods of constant pH (to minimize interferences from dissolution/precipitation of inorganic phosphorus). The results suggested that some poly-P was hydrolyzed and released accompanying the aerobic VS digestion, but at rates far lower than those under anaerobic conditions.     

Effect of anions and cations on cadmium sorption kinetics from aqueous solutions by chitin: experimental studies and modeling

The effect of ions, including Na(+), Mg(2+), Ca(2+), Cl(-), SO(4)(2-) and CO(3)(2-), at various initial concentrations, on the kinetics of cadmium sorption by chitin was studied at 25 degrees C and free initial pH solution in batch conditions. The presence of these ions in solution was found to inhibit the uptake of cadmium by chitin to different degrees: sodium and chloride ions have no significant effect. For Mg(2+), Ca(2+), SO(4)(2-) and CO(3)(2-) ions, the effects ranged from a large inhibition of cadmium by Ca(2+) and CO(3)(2-) to a weak inhibition by Mg(2+) and SO(4)(2-). These results indicate that the uptake sites of these ions are the same. No ion was found to enhance cadmium uptake. The results also showed that the kinetics of sorption are best described by a pseudo second-order expression than a first or second-order model.     

非稳定状态下除磷过程的特点研究

为了研究非稳定状态下生物除磷的特点,采用序批式间歇反应器(SBR),通过不同的进水方式(连续进水和瞬时进水),系统地考察了进水体积、NOX-N、限制曝气等因素对除磷过程的影响。结果表明,在温度为(23±0.5)℃、pH为7.0～8.0时,厌氧搅拌期连续进水的比释磷量(单位质量污泥(以MLSS计)的释磷量(以PO43-P计))比瞬时进水时高出42.11%。在运行条件相似的情况下,厌氧搅拌期的比释磷量与每周期进水体积无关。相对于连续进水,瞬时进水更有助于促进微生物利用有机底物进行自身的生长。限制曝气对连续进水和瞬时进水的释磷过程都存在明显的影响,在DO小于0.1mg/L的情况下,2者的比释磷量相对非限制曝气时分别降低了57.14%和55.56%。在连续进水时,NOX-N的反硝化结束伴随着释磷速率的突然升高。利用贮存作用并不能每次都成功地抑制丝状菌污泥膨胀。     

镁盐和炉渣对印染废水的脱色处理

实验研究了不同pH、温度：Mg2＋投量和沉降时间下，镁盐、炉渣、镁盐＋炉渣3种处理对模拟和实际印染废水的脱色效果。结果表明，在pH为11～11．5、沉降30rain、30℃及Mg2＋投加量为500～600mg／L的最优脱色条件下，3种处理对艳红FXC模拟废水的最大脱色率分别为98．41％、98．43％和99．37％，对实际印染废水的最大脱色率分别为90．18％、89．63％和93．33％，其中，镁盐＋炉渣脱色效果最好，这可能与炉渣吸附和起到协同增强Mg（OH）2沉淀效果的作用有关。对水样的液相色谱初步检测分析表明，实际废水脱色处理前后染色基团峰高和种类发生了变化。该研究对盐田富镁卤水和炉渣等废物的资源化开发有重要参考价值。     

MAP法沉淀回收装置的运行条件优化研究

采用一种简易的MAP回收装置,研究了间歇运行条件下反应时间和曝气量对MAP法除磷效果的影响,确定出最佳反应时间为90 min,最佳曝气量为1.2 L/min,相应的除磷率可达98.26%,沉淀回收率为74.54%。当增加一个漏斗形隔板分离反应区和沉淀区并连续运行时,除磷率和沉淀回收率分别为92.11%和63.66%。当不投加镁盐和铵盐而仅调控实际污泥脱水滤液的pH值为9.8时,其连续运行的平均除磷率和MAP回收率分别可达95.16%和70%,运行性能比较稳定。     

Nutrients removal and recovery by crystallization of magnesium ammonium phosphate from synthetic swine wastewater

With synthetic swine wastewater, lab-scale batch experiments were carried out to investigate the effects of pH value, magnesium dosage, calcium and carbonate concentrations on magnesium ammonium phosphate (MAP) crystallization. The morphology of the precipitates obtained was observed by using scanning electron microscopy with energy dispersive X-ray analysis, and the composition of the precipitates was analyzed with X-ray diffraction. The results show that the optimum pH value for MAP crystallization is in the range of 9.5-10.5; the phosphorus removal efficiency increases with the increase of Mg/P molar ratio; the optimum Mg/P molar ratio is 1.4, and excessive Mg dosage does not show significant effect on the efficiency improvement of MAP crystallization; the co-existing of Ca in solution disturbs the morphology and purity of the MAP product, and amorphous calcium phosphate will form when Ca increases to a certain concentration; CO3(2-) can affect the P removal efficiency, but does not obviously affect the morphology and purity of MAP.     

利用白云石回收污泥厌氧消化液中的磷

为经济有效地从污泥厌氧消化液中回收磷,构建了以白云石提供钙镁源的磷回收方法,探讨了磷回收的工艺条件与效果。通过盐酸酸化厌氧消化液以降低其碳酸盐含量,同时利用白云石溶于冷稀盐酸的特性使其钙镁缓慢释放到酸化的厌氧消化液中形成第一步磷回收体系,考察体系酸化pH、白云石与厌氧消化液的固液比以及反应pH对白云石的钙镁释放和磷回收效果的影响;第一步磷回收后的上清液为第二步厌氧消化液磷回收提供钙镁源,研究投加钙磷摩尔比对磷回收效果的影响。实验结果表明,当固液比为5.0时,在酸化pH为4.0～4.5且酸化溶出时间为10 h以及反应pH为9.0的条件下,第一步磷回收产物以磷酸钙盐沉淀为主,厌氧消化液磷回收率及回收产物含磷率（以P2O5计）分别达到99.43%和38.49%;第一步磷回收后的上清液按一定的钙磷摩尔比投加到酸化后的厌氧消化液中进行第二步磷回收,当投加钙磷摩尔比为0.20时,在反应pH为9.0的条件下,回收产物同时含有磷酸钙盐和磷酸铵镁,厌氧消化液中氮、磷回收率分别达到13.19%和90.90%,回收产物氮、磷含量（以P2O5计）分别为0.26%和39.58%;经XRD、XRF、ICP及SEM等分析表征,2步磷回收的产物以磷酸钙盐和磷酸铵镁为主要成分,杂质少。研究表明,利用白云石为钙镁源,通过分别构建不同的磷回收体系可以分步从污泥厌氧消化液中经济有效地回收磷,且磷回收率和回收产物含磷率高。     

Case study II: application of the divalent cation bridging theory to improve biofloc properties and industrial activated sludge system performance-using alternatives to sodium-based chemicals.

The objective of this study was to investigate the application of the divalent cation bridging theory (DCBT) as a tool in the chemical selection process at an activated sludge plant to improve settling, dewatering, and effluent quality. According to the DCBT, to achieve improvements, the goal of chemical selection should be to reduce the ratio of monovalent-to-divalent (M/D) cations. A study was conducted to determine the effect of using magnesium hydroxide [Mg(OH)2] as an alternative to sodium hydroxide (NaOH) at a full-scale industrial wastewater treatment plant. Floc properties and treatment plant performance were measured for approximately one year during two periods of NaOH addition and Mg(OH)2 addition. A cost analysis of plant operation during NaOH and Mg(OH)2 use was also performed. During NaOH addition, the M/D ratio was 48, while, during Mg(OH)2 addition, this ratio was reduced to an average of approximately 0.1. During the Mg(OH)2 addition period, the sludge volume index, effluent total suspended solids, and effluent chemical oxygen demand were reduced by approximately 63, 31, and 50%, respectively, compared to the NaOH addition period. The alum and polymer dose used for clarification was reduced by approximately 50 and 60%, respectively, during Mg(OH)2 addition. The dewatering properties of the activated sludge improved dewatering as measured by decreased capillary suction time and specific resistance to filtration (SRF), along with an increase in cake solids from the SRF test. This corresponded to a reduction in the volume of solids thickened by centrifuges at the treatment plant, which reduced the disposal costs of solids. Considering the costs for chemicals and solids disposal, the annual cost of using Mg(OH)2 was approximately 30,000 dollars to 115,000 dollars less than using NaOH, depending on the pricing of NaOH. The results of this study confirm that the DCBT is a useful tool for assessing chemical-addition strategies and their potential effect on activated sludge performance.     

Composition of wet and bulk deposition in Erzurum, Turkey

Seasonal variations in the chemical characteristics of wet and bulk deposition samples collected in Erzurum were investigated for the period March 2002-January 2003. Major cations (Ca2+, K+, Mg2+) and major anions (SO4(2-),NO3-) were determined in bulk and wet deposition samples; pH was also measured in wet deposition. The average pH of the wet deposition at Erzurum was 6.6 due to extensive neutralization of the acidity. A strong relationship between pH and SO4(2-) concentrations was observed in all seasons; however, only a weak relationship was found between pH and NO3-. On a seasonal basis, the correlation between Ca2+ and SO4(2-) concentrations was stronger in winter than in summer. Seasonal variations of ions were examined in both wet and bulk deposition samples. Although maximum concentrations of anions generally occurred during winter and spring, cation concentrations peaked in summer for both wet and bulk deposition. Results indicated that Ca2+ was the dominant cation and SO4(2-) the dominant anion in all deposition samples at Erzurum. Even though correlations among the crustal ions (calcium, magnesium and potassium) were high, the relationship between anthropogenic ions (sulfate and nitrate) was less clear in bulk deposition.     

Effects of reduced return activated sludge flows and volume on anaerobic zone performance for a septic wastewater biological phosphorus removal system.

Enhanced biological phosphorous removal (EBPR) performance was found to be adequate with reduced return-activated sludge (RAS) flows (50% of available RAS) to the anaerobic tank and smaller-than-typical anaerobic zone volume (1.08 hours hydraulic retention time [HRT]). Three identical parallel biological nutrient removal pilot plants were fed with strong, highly fermented (160 mg/L volatile fatty acids [VFAs]), domestic and industrial wastewater from a full-scale wastewater treatment facility. The pilot plants were operated at 100, 50, 40, and 25% RAS (percent of available RAS) flows to the anaerobic tank, with the remaining RAS to the anoxic tank. In addition, varying anaerobic HRT (1.08 and 1.5 hours) and increased hydraulic loading (35% increase) were examined. The study was divided into four phases, and the effect of these process variations on EBPR were studied by having one different variable between two identical systems. The most significant conclusion was that returning part of the RAS to the anaerobic zone did not decrease EBPR performance; instead, it changed the location of phosphorous release and uptake. Bringing less RAS to the anaerobic and more to the anoxic tank decreased anaerobic phosphorus release and increased anoxic phosphorus release (or decreased anoxic phosphorus uptake). Equally important is that, with VFA-rich influent wastewater, excessive anaerobic volume was shown to hurt overall phosphorus removal, even when it resulted in increased anaerobic phosphorus release.     

UniFed SBR工艺除磷脱氮机理研究

采用UniFed SBR工艺试验装置处理实际生活污水,确定了出水不受进水扰动影响的合适排水比.当将进水/排水时间固定为2 h,排水比不高于41.67%时,可以实现进水与出水的分离,保证良好的出水水质.通过试验分析了UniFed SBR工艺的除磷脱氮机理在于:进水/排水阶段在反应池底部先后发生了反硝化作用和厌氧释磷反应,后续曝气阶段发生硝化作用和好氧吸磷,因此通过该工艺,可实现同步除磷脱氮.     

Microwave treatment and struvite recovery potential of dairy manure

Microwave digestion of liquid dairy manure was tested for the release of nutrients, such as orthophosphates, ammonia-nitrogen, magnesium, calcium and potassium, both with and without the aid of an oxidizing agent (hydrogen peroxide). The orthophosphate to total phosphorus ratio of the manure increased from 21% to greater than 80% with 5 minutes of microwave treatment. More than 36% of total chemical oxygen demand (t-COD) of the manure was reduced when microwave digestion was assisted with peroxide addition. In addition, the volatile fatty acids (VFAs) distribution shifted to simpler chain acids (acetic acid in particular) with an increase in operating temperature. In the second part of the study, digested manure with increased soluble phosphate was tested for the recovery of struvite (magnesium ammonium phosphate) at different pH. It was found that up to 90% of orthophosphate can be removed from the solution. Overall, it was concluded that the oxidizing agent-assisted microwave digestion process can be used upstream of anaerobic digestion, following which the anaerobically digested manure can be used for struvite recovery. Thus, this microwave digestion process presents the potential for enhanced efficiencies in both manure digestion and struvite recovery.     

催化铁与生物法耦合除磷工艺特性

为了研究催化铁与生物耦合后对生物除磷特性的影响，实验采用人工配水用厌氧／好氧间歇流式富集培养聚磷微生物。对比发现，催化铁与生物耦合组中厌氧末段ORP降低了约60mV，pH值小幅度的上升（≤0．3），整个培养过程中铁离子的浓度开始快速增加，之后趋于稳定（约40mgFe／gMLSS）。对好氧末段污泥SVI值比较发现，耦合工艺污泥沉降性能得到改善。除磷曲线比较发现，耦合组中厌氧末段磷的释放量下降，而好氧阶段磷的吸收速率增加；胞内聚合物提取表明，耦合组厌氧末段聚磷菌细胞内PHA含量有提高，好氧末段糖原含量有下降。磷形态提取分析表明，耦合组好氧末段污泥中无机态PO3 4-- P含量更高。低浓度铁离子可以起到与生物耦合同步除磷的目的，本工艺长期运行未发现耦合体系中催化铁对除磷的抑制作用。     

磷酸铵镁沉淀法预处理垃圾渗滤液

探讨了用磷酸铵镁沉淀法预处理垃圾渗滤液时,沉淀剂种类、pH值、物质摩尔配比和反应时间等因素对氨氮去除效果的影响。得出了处理氨氮浓度为2 677.34 mg/L的垃圾渗滤液时,在兼顾所用镁盐量尽量低和处理出水氨氮或磷酸盐的残留量都比较低的较佳实验条件为:沉淀剂种类为:MgSO4.7H2O和Na2HPO4.12H2O,反应时间为20 min,pH=9.5,n(Mg)∶n(P)∶n(N)=1.3∶1.15∶1.0。在较佳实验条件下,垃圾渗滤液的NH3-N去除率为97.05%,处理出水PO34--P含量为8.35 mg/L,NH3-N含量为75.86 mg/L。对所得沉淀物进行了成分分析和X-衍射光谱、扫描电镜表征,表明大部分沉淀物为磷酸铵镁物质。     

Microwave treatment and struvite recovery potential of dairy manure

Microwave digestion of liquid dairy manure was tested for the release of nutrients, such as orthophosphates, ammonia-nitrogen, magnesium, calcium and potassium, both with and without the aid of an oxidizing agent (hydrogen peroxide). The orthophosphate to total phosphorus ratio of the manure increased from 21% to greater than 80% with 5 minutes of microwave treatment. More than 36% of total chemical oxygen demand (t-COD) of the manure was reduced when microwave digestion was assisted with peroxide addition. In addition, the volatile fatty acids (VFAs) distribution shifted to simpler chain acids (acetic acid in particular) with an increase in operating temperature. In the second part of the study, digested manure with increased soluble phosphate was tested for the recovery of struvite (magnesium ammonium phosphate) at different pH. It was found that up to 90% of orthophosphate can be removed from the solution. Overall, it was concluded that the oxidizing agent-assisted microwave digestion process can be used upstream of anaerobic digestion, following which the anaerobically digested manure can be used for struvite recovery. Thus, this microwave digestion process presents the potential for enhanced efficiencies in both manure digestion and struvite recovery.