Modelling biological and chemically induced precipitation of calcium phosphate in enhanced biological phosphorus removal systems

The biologically induced precipitation processes can be important in wastewater treatment, in particular treating raw wastewater with high calcium concentration combined with Enhanced Biological Phosphorus Removal. Currently, there is little information and experience in modelling jointly biological and chemical processes. This paper presents a calcium phosphate precipitation model and its inclusion in the Activated Sludge Model No 2d (ASM2d). The proposed precipitation model considers that aqueous phase reactions quickly achieve the chemical equilibrium and that aqueous-solid change is kinetically governed. The model was calibrated using data from four experiments in a Sequencing Batch Reactor (SBR) operated for EBPR and finally validated with two experiments. The precipitation model proposed was able to reproduce the dynamics of amorphous calcium phosphate (ACP) formation and later crystallization to hydroxyapatite (HAP) under different scenarios. The model successfully characterised the EBPR performance of the SBR, including the biological, physical and chemical processes.     

The precipitation of phosphorus from wastewater through pH variation in the presence and absence of coagulants

Phosphorus and calcium present in the aeration tanks of two activated sludge systems were found to form an inorganic precipitate with a stoichiometric molar ratio Ca: P = 2. Variations in the solution pH resulted in the release of P and Ca into the solution (lower pH) or the precipitation of them from solution (higher pH). Lowering of the pH due to the addition of the aluminum coagulants resulted in the release of phosphorus and calcium into the solution and therefore in an apparent lower efficiency of the coagulants. It was also found that after the addition of the coagulants, the nature of the supernatant suspended solids changed from biological to chemical.     

亚铁盐化学除磷在昆山港东污水处理厂的应用

江苏昆山港东污水处理厂的Carrousel2000型氧化沟工艺按A^2／O方式运行,当原水TP为6．2mg／L、BOD5／TP为11左右时,很难使出水TP≤0．5mg／L。在对上游排污企业采取限排措施后,原水TP降为2．65mg／L,但出水TP仍无法达标,为此开展了向曝气池投加亚铁盐进行化学除磷的生产性试验。结果表明,当FeSO4投药量控制在凡（Fe^2＋）：n（TP）≥1．5时,可使出水TP达标。     

磷酸铵镁法处理含氮磷废水研究进展

叙述了磷酸铵镁在废水中的形成机理及其在废水处理中的应用现状。在废水处理中利用镁盐作沉淀剂可以同时去除废水中的氮和磷，该方法去除率高、反应速度快、污泥体积小，同时还可回收磷酸铵镁，具有一定的应用前景。     

Uptake and release of phosphate by a pure culture of Acinetobacter calcoaceticus

Uptake and release of phosphate by a pure culture of Acinetobacter calcoaceticus were investigated under aerobic and anaerobic conditions. The total phosphorus content of this bacterium varied from 0.3 to 1.7 mmol g⁻¹ dry cells or from 0.93 to 5.3% of dry cell weight under various culture conditions. The log-phase cells accumulated polyphosphates of 0.33−0.64 mmol P g⁻¹ dry cells. ³¹P NMR spectra suggested that a portion of polyphosphates was likely bonded to some sort of structural components of the cell. A. calcoaceticus release phosphate linearly with time when transferred from aerobic to anaerobic conditions. The release rate was in the range of 5.9–14.7 × 10⁻³ mmol P g⁻¹ dry cells h⁻¹ and about 4–8% of cellular phosphorus was released during the initial 6 h. During the process of phosphate release acetate was not taken up by this bacterium.     

Modification, calibration and verification of the IWA River Water Quality Model to simulate a pilot-scale high rate algal pond

We implemented the IWA River Water Quality Model No. 1 (Reichert et al., 2001. River Water Quality Model No. 1, IWA Scientific & Technical Report No. 12) to simulate water-quality characteristics in two pilot-scale High Rate Algal Ponds. Simulation results were compared with two years' of data from the ponds. The first year's data from one pond were used for model calibration; the remaining data were used for validation. As originally formulated and parameterized, the model consistently yielded summer-time algal biomass concentrations which were too low - with consequent failures in its reproduction of dissolved oxygen, pH and nutrient dynamics. We experimented with various structural/parametric changes to improve the model's performance. The most effective strategy was to greatly increase the respiratory losses suffered by the heterotrophic osmotrophs (thereby giving the algae access to a larger fraction of the incoming dissolved organic carbon and nitrogen). This suggests that CO₂-bubbling alone cannot entirely preclude resource-limitation of algal production. We doubt that our parameterization of heterotrophic osmotrophs is correct and infer that the algae derive a large fraction of their nutrition by direct osmotrophic uptake of dissolved organic matter. This inference is supported by the literature concerning the physiology of the dominant algal species in our ponds.     

污水厂出水SS偏高问题研究及措施

研究了上海某A/B/C活性污泥工艺污水处理厂出水SS偏高的问题,对影响出水SS的主要影响因素进行了综合分析,并提出了工艺调整措施,在实际运行中取得了较好的效果。     

某污水处理厂两种工艺脱氮除磷效果对比分析

本文通过测定两种工艺出水的水质参数TN、TP,对A—O和A—A-O两个工艺进行了对比分析,探讨了聚磷菌,硝化菌,反硝化菌的微生物学特征,分析了池中污水脱氮除磷的机理及其影响因素。     

鹤山市某城镇污水处理厂脱氮除磷工艺改造实践

鹤山市某城镇污水处理厂由于早期设计存在缺陷,出水的氨氮和总磷一直未能稳定达标.为满足达标排放的要求,在不新增主体构筑物的情况下,通过增加混合液回流系统、完善污泥回流系统、改进污泥处理流程等,将原污水处理工艺改造成为A2/O工艺,使该城镇污水处理厂处理工艺具备了脱氮除磷的功能.改造后出水水质能达到排放标准的要求.     

Control of sulfide in sewer systems by dosage of iron salts: comparison between theoretical and experimental results, and practical implications

Removal of sulfide species from municipal sewage conveyance systems by dosage of iron salts is a relatively common practice. However, the reactions that occur between dissolved iron and sulfide species in municipal sewage media have not yet been fully quantified, and practical application relies heavily on empirical experience, which is often site specific. The aim of this work was to combine theoretical considerations and empirical observations to enable a more reliable prediction of the sulfide removal efficiency for a given dosing strategy. Two main questions were addressed, regarding the dominant sulfur species that results from the oxidation of sulfide by Fe(III) and the dominant precipitation reaction between Fe(II) and sulfide species. Comparison of thermodynamic prediction obtained by an equilibrium chemistry-based computer program (MINEQL+) with experimental results obtained by dosing ferrous salts showed that the product of precipitation is FeS under all operational conditions tested. Regarding the reaction between ferric salts and sulfide species, analysis of thermodynamic data suggested that the dominant product of sulfide oxidation under typical pe/pH conditions prevailing in municipal raw wastewater is SO(4)(2-). However, comparison between sulfide removal in laboratory experiments conducted with multiple samples of raw municipal sewage with a varying composition, and the prediction of MINEQL+ showed the main sulfide oxidation product to be S(0). In order to reduce sulfide in sewage to <0.1 mgS/l a minimal molar ratio of around 1.3 Fe to 1 S should be applied when ferrous salts are used, as compared with a minimal ratio of 0.9 Fe to 1 S required when ferric salts or a mixture of ferrous and ferric salts (at a 2 Fe(III) to 1 Fe(II) ratio) are used. It appears that the high Fe to S(-II) ratios often recommended in practice can be reduced considerably by applying tight in-line control.