Advanced nitrogen removal by pulsed sequencing batch reactors (SBR) with real-time control

The feasibility of pH and oxidation reduction potential (ORP) as on-line control parameters to advance nitrogen removal in pulsed sequencing batch reactors (SBR) was evaluated. The pulsed SBR, a novel operational mode of SBR, was utilized to treat real municipal wastewater accompanied with adding ethanol as external carbon source. It was observed that the bending-point (apex and knee) of pH and ORP profiles can be used to control denitrification process at a low influent C/N ratio while dpH/dt can be used to control the nitrification and denitrification process at a high influent C/N ratio. The experimental results demonstrated that the effluent total nitrogen can be reduced to lower than 2 mg/L, and the average total nitrogen (TN) removal efficiency was higher than 98% by using real-time controll strategy.     

Practical consideration for design and optimization of the step feed process

Based on the anoxic/oxic (A/O) step feed process, a modified University of Cape Town (UCT) step feed process was developed by adding an anaerobic zone and adjusting sludge return pipeline. Performance evaluation of these two types of processes was investigated by optimizing operational parameters, such as the anaerobic/anoxic/oxic volumes, internal recycle ratios, and sludge retention times, for removal of chemical oxygen demanding (COD), nitrogen, and phosphorus. Results showed high removal efficiencies of COD of (85.0±1.7)%, ammonium of (99.7±0.2)%, total nitrogen (TN) of (85.5±1.7)%, phosphorus of (95.1±3.3)%, as well as excellent sludge settleability with average sludge volume index of (83.7±9.5) L·mg^-1 in the modified UCT process. Moreover, (61.5±6.0)% of influent COD was efficiently involved in denitrification or phosphorus release process. As much as 35.3% of TN was eliminated through simultaneous nitrification and denitrification process in aerobic zones. In addition, the presence of denitrifying phosphorus accumulating organisms (DNPAOs), accounting for approximately 39.2% of PAOs, was also greatly beneficial to the nitrogen and phosphorus removal. Consequently, the modified UCT step feed process was more attractive for the wastewater treatment plant, because it had extremely competitive advantages such as higher nutrient removal efficiencies, lower energy and dosages consumption, excellent settling sludge and operational assurance.     

Control of sludge settleability and nitrogen removal under low dissolved oxygen condition

Low dissolved oxygen (DO) is an energy-saving condition in activated sludge process. To investigate the possible application of limited filamentous bulking (LFB) in sequencing batch reactor (SBR), two lab-scale SBRs were used to treat synthetic domestic wastewater and real municipal wastewater, respectively. The results showed that prolonging low DO aeration duration and setting pre-anoxic (anaerobic) phase were effective strategies to induce and inhibit filamentous sludge bulking, respectively. According to the sludge settleability, LFB could be maintained steadily by adjusting operation patterns. Filamentous bacteria content and sludge volume index (SVI) were likely correlated. SVI fluctuated dramatically within a few cycles when around 200 mL·g^-1, where altering operation pattern could change sludge settleability in spite of the unstable status of activated sludge system. Energy consumption by aeration reduced under low DO LFB condition, whereas the nitrification performance deteriorated. However, short-cut nitrification and simultaneous nitrification denitrification (SND) were prone to take place under such conditions. When the cycle time kept constant, the anoxic (anaerobic) to aerobic time ratio was determining factor to the SND efficiency. Similarity keeping aerobic time as constant, the variation trends of SND efficiency and specific SND rate were uniform. SBR is a promising reactor to apply the LFB process in practice.     

The combined effects of biomass and temperature on maximum specific ammonia oxidation rate in domestic wastewater treatment

• Actual SAORs was determined using MLVSS and temperature. • Measured SAOR decreased with increasing MLVSS 1.1‒8.7 g/L. • Temperature coefficient (θ) decreased with increasing MLVSS. • Nitrification process was dynamically simulated based on laboratory-scale SBR tests. • A modified model was successfully validated in pilot-scale SBR systems. Measurement and predicted variations of ammonia oxidation rate (AOR) are critical for the optimization of biological nitrogen removal, however, it is difficult to predict accurate AOR based on current models. In this study, a modified model was developed to predict AOR based on laboratory-scale tests and verified through pilot-scale tests. In biological nitrogen removal reactors, the specific ammonia oxidation rate (SAOR) was affected by both mixed liquor volatile suspended solids (MLVSS) concentration and temperature. When MLVSS increased 1.6, 4.2, and 7.1-fold (1.3‒8.9 g/L, at 20°C), the measured SAOR decreased by 21%, 49%, and 56%, respectively. Thereby, the estimated SAOR was suggested to modify when MLVSS changed through a power equation fitting. In addition, temperature coefficient (θ) was modified based on MLVSS concentration. These results suggested that the prediction of variations ammonia oxidation rate in real wastewater treatment system could be more accurate when considering the effect of MLVSS variations on SAOR.     

Effect of short-term atrazine addition on the performance of an anaerobic/anoxic/oxic process

In this study, an anaerobic/anoxic/oxic (A²O) wastewater treatment process was implemented to treat domestic wastewater with short-term atrazine addition. The results provided an evaluation on the effects of an accidental pollution on the operation of a wastewater treatment plant (WWTP) in relation to Chemical Oxygen Demand (COD) and biological nutrient removal. Domestic wastewater with atrazine addition in 3 continuous days was treated when steady biological nutrient removal was achieved in the A²O process. The concentrations of atrazine were 15, 10, and 5 mg·L⁻¹ on days 1, 2 and 3, respectively. The results showed that atrazine addition did not affect the removal of COD. The specific NH₄ ⁺ oxidation rate and NO₃ ⁻ reduction rate decreased slightly due to the short-term atrazine addition. However, it did not affect the nitrogen removal due to the high nitrification and denitrification capacity of the system. Total nitrogen (TN) removal was steady, and more than 70% was removed during the period studied. The phosphorus removal rate was not affected by the short-term addition of atrazine under the applied experimental conditions. However, more poly-hydroxy-alkanoate (PHA) was generated and utilized during atrazine addition. The results of the oxygen uptake rate (OUR) showed that the respiration of nitrifiers decreased significantly, while the activity of carbon utilizers had no obvious change with the atrazine addition. Atrazine was not removed with the A²O process, even via absorption by the activated sludge in the process of the short-term addition of atrazine.     

Advanced landfill leachate treatment using a two-stage UASB-SBR system at low temperature

A two-stage upflow anaerobic sludge blanket(UASB) and sequencing batch reactor(SBR) system was introduced to treat landfill leachate for advanced removal of COD and nitrogen at low temperature.In order to improve the total nitrogen(TN) removal efficiency and to reduce the COD requirement for denitrification,the raw leachate with recycled SBR nitrification supernatant was pumped into the first-stage UASB(UASB1) to achieve simultaneous denitrification and methanogenesis.The results showed that UASB1 played an important role in COD removal and UASB2 and SBR further enhanced the nutrient removal efficiency.When the organic loading rates of UASB1,UASB2 and SBR were 11.95,1.63 and 1.29 kg COD/(m3·day),respectively,the total COD removal efficiency of the whole system reached 96.7%.The SBR acted as the real undertaker for NH4+-N removal due to aerobic nitrification.The system obtained about 99.7% of NH4+-N removal efficiency at relatively low temperature(14.9-10.9°C).More than 98.3% TN was removed through complete denitrification in UASB1 and SBR.In addition,temperature had a significant effiect on the rates of nitrification and denitrification rather than the removal of TN and NH4+-N once the complete nitrification and denitrification were achieved.     

中试SBR长期运行中粘性膨胀现象及原因分析

通过对SBR中型试验系统长期(200d)处理实际生活污水过程中的污泥膨胀现象进行考察,研究了温度、污泥中胞外聚合物(EPS)含量、污泥负荷及DO浓度与污泥膨胀现象之间的内在联系.试验结果表明,系统污泥膨胀属于粘性膨胀,是一种在低温(16℃以下)条件下容易发生的污泥膨胀现象,且这种膨胀会导致污泥流失并致使系统混合液污泥浓度(MLSS)逐渐降低至1200mg·L-1.粘性膨胀污泥分泌的EPS水平超过正常污泥,即使在正常DO浓度(2.0mg·L-1)和常温(20℃)条件下,粘性膨胀污泥也较难通过人为控制恢复到正常状态.最后,分析得出粘性膨胀的原因主要是温度突变,并提出相应的预防措施.     

关于水文与水资源工程专业教学改革初探

文章从水文与水资源工程专业课程设置、就业氛围和实践教学现状等方面入手,重点通过对专业实验课程占教学比例较小且综合性实验更少、专业实习受课程设置影响及毕业设计师资安排不合理等现状分析了该专业教学环节中存在的不足。提出了升华和优化教学体系,适当增设应用型课程;丰富教学手段,加强实践教学,激发学生自主自觉学习;加大介绍先进测量仪器和测量技术的力度;开放实验室,培养学生科研创新能力;实行产学研结合办学模式,为学生提供研究平台等措施对该专业教学改革的一些建议。     

SBR双颗粒污泥系统脱氮除磷性能研究

以模拟废水为研究对象,对SBR双颗粒污泥系统的脱氮除磷性能进行了考察.试验结果表明,A₂N双颗粒污泥系统能使硝化菌和聚磷菌分别在各自最佳的环境中生长,有利于系统脱氮除磷的稳定和高效运行,可控制性也得到了提高.在COD为300 mg·L^-1条件下,系统对COD的平均去除率达到78.8%,大部分COD被聚磷菌用来合成PHA;当溶解氧控制在3.55~4.90 mg·L^-1和5.60~6.60 mg·L^-1之间时,硝化SBR对氨氮的去除率分别为87.0%和94.5%.除磷SBR仅设置缺氧段时,磷去除率为72%;增设后曝气段后,磷去除率增至85%.NO_x^--N(NO₂^--N+ NO₃^--N)的去除主要发生在缺氧段,在反硝化除磷时作为电子受体被去除,平均去除率为90.6%.     

Anoxic phosphorus removal in a pilot scale anaerobic-anoxic oxidation ditch process

The anaerobic-anoxic oxidation ditch (A²/O OD) process is popularly used to eliminate nutrients from domestic wastewater. In order to identify the existence of denitrifying phosphorus removing bacteria (DPB), evaluate the contribution of DPB to biological nutrient removal, and enhance the denitrifying phosphorus removal in the A²/O OD process, a pilot-scale A²/O OD plant (375 L) was conducted. At the same time batch tests using sequence batch reactors (12 L and 4 L) were operated to reveal the significance of anoxic phosphorus removal. The results indicated that: The average removal efficiency of COD, NH4+, PO43-, and TN were 88.2%, 92.6%, 87.8%, and 73.1%, respectively, when the steady state of the pilot-scale A²/O OD plant was reached during 31-73 d, demonstrating a good denitrifying phosphorus removal performance. Phosphorus uptake took place in the anoxic zone by poly-phosphorus accumulating organisms NO2- could be used as electron receptors in denitrifying phosphorus removal, and the phosphorus uptake rate with NO2- as the electron receptor was higher than that with NO3- when the initial concentration of either NO2- or NO3- was 40 mg/L.