Development of a mechanistic model for biological nutrient removal activated sludge systems and application to a full‐scale WWTP

In wastewater treatment plants (WWTPs) the production of nitrite as an intermediate in the biological nutrient removal (BNR) process has been widely observed, but not been taken into account by most of the conventional activated sludge models yet. This work aims to develop a mechanistic mathematical model to evaluate the BNR process after resolving such a problem. A mathematical model is developed based on the Activated Sludge Model No.3 (ASM3) and the EAWAG Bio‐P model with an incorporation of the two‐step nitrification–denitrification, the anoxic P uptake, and the associated two‐step denitrification by phosphorus accumulating organisms. The database used for simulations originates from a full‐scale BNR municipal wastewater treatment plant. The influent wastewater composition is characterized using batch tests. Model predictions are compared with the measured concentrations of chemical oxygen demand (COD), NH‐N, NO‐N, NO‐N, PO‐P, and mixed liquid volatile suspended solids. Simulation results indicate that the calibrated model is capable of predicting the microbial growth, COD removal, nitrification and denitrification, as well as aerobic and anoxic P removal. Thus, this model can be used to evaluate and simulate full‐scale BNR activated sludge WWTPs. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

冬季活性炭层上微生物的硝化性能研究

为解析工艺运行过程中氨氧化能力和硝化能力变化的原因,研究了冬季活性炭层上微生物的硝化性能。结果表明,在冬季,当有机碳浓度不高、溶解氧充足时,活性炭层对氨氮的去除率达到34%,0.3、0.8、1.3、1.6 m处(自上而下)的炭层对氨氮的平均去除率分别为5.2%、8.3%、11.5%、8.8%。不同活性炭层上的生物量差别不是太大,均值为17.1×108个E.coli/g活性炭。亚硝化菌、硝化菌占细菌总数的比例较大,已成为优势种群。     

BAF-微絮凝工艺处理微污染水试验研究

针对污染严重的地表水,采用BAF-微絮凝工艺处理,研究了气水比、运行周期、加药比、加药量等运行条件对污染物去除的影响。试验结果表明,当BAF气水体积比为3、运行周期为15 d,微絮凝PAC与PAM加药质量比为8、投加量分别为80和10 mg/L时,该工艺对CODCr、氨氮、浊度和悬浮颗粒物的平均去除率分别为88%、94%、99%、99%;处理后水质符合印染及造纸行业的水质要求,且成本仅为0.35元/t;该处理工艺具有较好的市场应用前景。     

Enrichment of Anammox biomass from municipal activated sludge: experimental and modelling results

Anaerobic Ammonia Oxidising (Anammox) biomass was enriched from sludge collected at a municipal wastewater treatment plant, employing a Sequential Batch Reactor (SBR). After 60 days Anammox activity started to be detected, by consumption of stoichiometric amounts of NO₂^? and NH₄⁺ in the system. Fluorescence In Situ Hybridisation analysis confirmed the increase of Anammox bacteria concentration with time. A final concentration of enriched biomass of 3–3.5 gVSS dm^?3 was obtained, showing a Specific Anammox Activity of 0.18 gNH₄⁺‐N gVSS^?1 d^?1 The reactor was able to treat nitrogen loading rates of up to 1.4 kgN m^?3 d^?1, achieving a removal efficiency of 82 %. On the other hand, the start‐up and operation of the Anammox SBR reactor were consequentially modelled with the Activated Sludge Model nr 1, extended for Anammox. The simulations predicted quite well the experimental data in relation to the concentrations of nitrogenous compounds and can be used to estimate the evolution of Anammox and heterotrophic biomass in the reactor. These simulations reveal that heterotrophs still remain in the system after the start‐up of the reactor and can protect the Anammox microorganisms from a negative effect of the oxygen. Copyright © 2004 Society of Chemical Industry     

Turnover of15N ammonium sulfate with dicyandiamide under aerobic and anaerobic soil conditions

The influence of the nitrification inhibitor dicyandiamide (DCD) on the turnover of¹⁵N-labelled ammonium sulfate (AS) was investigated in two soils under aerobic and waterlogged conditions. Nitrification of ammonium sulfate was markedly inhibited by addition of DCD in both soils. Up to 45% of the supplied N was transformed into a non-extractable N form, which only slowly released nitrogen over 147 or 264 days. This immobilization was higher in the presence of DCD than without DCD. In all aerobic experiments, the recovery was 100% ± max. 2.4%, indicating that no gaseous losses of N occurred.If aerobic preincubation of 28 or 42 days was followed by water-logging with H₂O or a solution of glucose, considerable N losses occurred only in presence of the carbohydrate. DCD retarded nitrification and thus reduced losses by denitrification from 61 to 15%.DCD application resulted in an increased immobilization of labelled N into the non-exchangeable soil N fraction. This amounted to more than 50% of the applied N, compared to 39% without DCD.The late Dr. Klaus Vilsmeier, a very dedicated and talented young scientist, died before he was able to finish completely the revised version of this article. We will always keep him in our minds and kindly remember his kind personality as well as his sense of humour and justice. Prof. Dr. Heiner Goldbach on behalf of all members of the department.     

Influence of wastewater treatment on sludge production and processing

The challenge of stricter wastewater standards is resulting in configuration changes to wastewater treatment. As facilities upgrade, the type of sludge produced is changing, with growing quantities of secondary and chemical sludge at the expense of primary sludge. It is already understood that secondary sludge is harder to treat than its primary equivalent; therefore, increasing the quantity of this type of sludge will have detrimental impacts downstream. As legislation tightens further, extended aeration times may be required during processing to remove more nutrients. Work has shown that extended aeration further exacerbates the treatability of secondary sludge. This paper explains how tightening wastewater legislation fundamentally alters the nature of the sludge produced, and how these alterations impact further processing, especially with respect to sludge production and type; sludge energy content; performance of anaerobic digestion and dewatering, and potential for thermal energy recovery.     

Selective inhibition of nitrite oxidation by chlorate dosing in aerobic granules

Partial nitrification was successfully achieved with addition of 5mM KClO(3) in the aerobic granules system. Batch tests demonstrated that KClO(3) selectively inhibited nitrite-oxidizing bacteria (NOB) but not ammonia-oxidizing bacteria (AOB). During stable partial nitrification, the influent pH was kept at 7.8-8.2, while the DO and temperature were not controlled in the SBR. When the NH(4)-N and COD levels were kept at 100mg/l and 400mg/l in the influent, the NH(4)-N and COD removal efficiencies reached 98.93% and 78.65%, respectively. The NO(2)-N accounted for 92.95% of the NO(χ)-N (NO(2)-N+NO(3)-N) in the effluent. Furthermore, about 90% of the chlorate was reduced to nontoxic chloride, thus it would not cause environmental problem. SEM showed that the main composition of the aerobic granules was bacilli and coccus bacteria. FISH analysis revealed that AOB became the dominant nitrifying bacteria, whereas NOB were detected only in low abundance. Chlorate could be used to control the development and maintenance of aerobic granules sludge for partial nitrification.     

Modeling the decay of ammonium oxidizing bacteria

A bench-scale sequencing batch reactor was used to study factors affecting the endogenous decay of the ammonium oxidizing biomass (AOB) in different operating conditions. AOB decay was very sensitive to oxygen concentration, and increased up to 0.4 d⁻¹ for oxygen concentration of 7 mg O₂ L⁻¹. The decay in anaerobic conditions was shown to be very low (0.03 d⁻¹) when compared to literature data.The effect of nitrite and nitrate on AOB decay was also studied. The correlation was quite weak suggesting that both nitrate and nitrite absence had little impact on decay which is contrary to what is typically assumed in some of the existing process models. A simple expression for the decay of AOB was proposed, calibrated and validated using the results of batch kinetic tests and of the continuous sequencing batch reactor monitoring.     

曝气生物滤池对印花废水的脱氮效果研究

采用曝气生物滤池(BAF)处理印花废水,重点考察了水力停留时间(HRT)、C/N值、气水比对其脱氮效果的影响.结果表明:在HRT为4 h、C/N值为2、气水比为5:1的条件下,BAF可达到最佳脱氮效果,对TN、NH<,4><'+>-N的去除率分别达到50%、90%以上.     

Effects of carbon dioxide deficiency and metal toxicity on biological oxygen demand

In this study, the effects of carbon dioxide (CO₂) deficiency on the biological growth under respirometric conditions, first‐ and second‐order biological oxygen demand (BOD) progressions using two different BOD measurement techniques and metal toxicity effects on the respirometric BOD are investigated. The effects of CO₂ deficiency in the growth of bacteria and related effects on the first‐ and second‐stage BOD progressions are investigated using various media with respirometers in comparison with the BOD dilution method. CO₂ deficiency causes significant retardations on the growth of bacteria and the second‐stage respirometric BOD values are suppressed. CO₂ seems to be an essential nutrient for the growth of microorganisms and for the oxygen uptake progressing rates. HgCl₂, HgSO₄, CuSO₄, K₂Cr₂O₇, ZnSO4 and Al₂(SO₄)₃ inorganic metal compounds cause significant retardations in the respirometric BOD values obtained from a synthetic autotrophic medium. Effects are found to be dependent on the applied concentrations of these chemicals in the medium.