Effects of nitrite on phosphate uptake in anaerobic-oxic process

An anaerobic-oxic (A/O) biological phosphorus removal reactor was operated to study the effect of nitrite on phosphate uptake. The phosphorus uptake profile was determined under different operating conditions. The results indicated that in addition to oxygen and nitrate (DPB_Na, nitrate denitrifying phosphorus removal), to some extent, nitrite could also serve as an electron acceptor to achieve nitrite denitrifying phosphorus removal (DPB_Ni). The quantity and rate of phosphorus uptake of DPB_Ni, however, were evidently lower than that of DPB_Na. The experiment results revealed that nitrite would bring toxic action to phosphate-accumulating organisms (PAOs) when NO₂ ^?-N ? 93.7 mg/L. The nitrite existing in the anoxic reactor made no difference to the quantity and rate of denitrifying phosphorus removal, but it could reduce the consumption of nitrate. Moreover, the data showed that the aerobic phosphate uptake of DPB_Ni was lower than that of anaerobic phosphorus-released sludge in a traditional A/O process. However, there was not much difference between these two kinds of sludge in terms of the total phosphorus uptake quantity and the effluent quality.     

Coupled aerobic and anoxic biodegradation for quinoline and nitrogen removals

Quinoline (C₉H₇N) commonly occurs in wastewaters from the chemical, pharmaceutical, and dyeing industries. As quinoline is biodegraded, nitrogen is released as ammonium. Total-N removal requires that the ammonium-N be nitrified and then denitrified. The objective of this study was to couple quinoline biodegradation with total-N removal. In a proof-of-concept step, activated sludge was sequenced from aerobic to anoxic stages. The ammonium nitrogen released from quinoline biodegradation in the aerobic stage was nitrified to nitrate in parallel. Anoxic biodegradation of the aerobic effluent then brought about nitrogen and COD removals through denitrification. Then, simultaneous quinoline biodegradation and total-N removal were demonstrated in a novel airlift internal loop biofilm reactor (AILBR) having aerobic and anoxic zones. Experimental results showed that the AILBR could achieve complete removal of quinoline, 91% COD removal, and 85% total-N removal when glucose added as a supplemental electron donor once nitrate was formed.     

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.     

Short-term effects of excessive anaerobic reaction time on anaerobic metabolism of denitrifying polyphosphate-accumulating organisms linked to phosphorus removal and N2O production

The short-term effect of anaerobic reaction time (AnRT) (i.e., 90, 120 and 150 min) on the denitrifying phosphorus (P) removal performance and N₂O production was examined using a denitrifying enhanced biologic phosphorus removal (EBPR) sludge acclimatized with mixed acetate (HAc) and propionate (Pro) (in the molar ratio 3:1) as carbon sources. The results showed that when the AnRT was prolonged from 90 to 150 min, the anaerobic polyhydroxyalkanoate (PHA) synthesis was decreased by 15.3%. Moreover, the ineffective PHA consumption occurred in anaerobic phases and contributed to an increased NO ₂ ^? -N accumulation and higher free nitrous acid (FNA) concentrations (?0.001–0.0011 mg HNO₂-N/L) in the subsequent anoxic phases, causing a severe inhibition on anoxic P-uptake and denitrification. Accordingly, the total nitrogen (TN) and total phosphorus (TP) removal efficiencies dropped by approximately 6.3% and 85.5%, respectively; and the ratio of anoxic N₂O-N production to TN removal increased by approximately 3.8%. The fluorescence in situ hybridization (FISH) analysis revealed that the sludge was mainly dominated by Accumulibacter (62.0% (SE_mean = 1.5%)). In conclusion, the short-term excessive anaerobic reaction time negatively impacted denitrifying P removal performance and stimulated more N₂O production, and its effect on P removal was more obvious than that on nitrogen removal.     

Advanced nitrogen and phosphorus removal in A2O-BAF system treating low carbon-to-nitrogen ratio domestic wastewater

A laboratory-scale anaerobic-anoxic-aerobic process (A²O) with a small aerobic zone and a bigger anoxic zone and biologic aerated filter (A²O-BAF) system was operated to treat low carbon-to-nitrogen ratio domestic wastewater. The A²O process was employed mainly for organic matter and phosphorus removal, and for denitrification. The BAF was only used for nitrification which coupled with a settling tank Compared with a conventional A²O process, the suspended activated sludge in this A²O-BAF process contained small quantities of nitrifier, but nitrification overwhelmingly conducted in BAF. So the system successfully avoided the contradiction in sludge retention time (SRT) between nitrifying bacteria and phosphorus accumulating organisms (PAOs). Denitrifying phosphorus accumulating organisms (DPAOs) played an important role in removing up to 91% of phosphorus along with nitrogen, which indicated that the suspended activated sludge process presented a good denitrifying phosphorus removal performance. The average removal efficiency of chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), and NH ₄ ⁺ -N were 85.56%, 92.07%, 81.24% and 98.7% respectively. The effluent quality consistently satisfied the national first level A effluent discharge standard of China. The average sludge volume index (SVI) was 85.4 mL·g^?1 additionally, the volume ratio of anaerobic, anoxic and aerobic zone in A²O process was also investigated, and the results demonstrated that the optimum value was 1:6:2.     

Mechanism on minimization of excess sludge in oxic-settling-anaerobic (OSA) process

The oxic-settling-anaerobic (OSA) process is a promising wastewater treatment technique for efficiently reducing sludge production and improving the stability of process operation. In this paper, the possible factors of sludge reduction such as sludge decay, uncoupled metabolism, and anaerobic oxidation with low sludge production were discussed in the OSA process. It has been confirmed that sludge decay is the decisive cause in the OSA process, accounting for 66.7% of sludge production reduction. Sludge decay includes hydrolysis and acidogenesis of dead microorganisms and particle organic carbon adsorbed in sludge floc and endogenous metabolism. By batch experiments, it has been proven that there is energetic uncoupling in the OSA system since microorganisms were exposed to alternative anaerobic and aerobic environment. It accounts for about 7.5% of sludge production reduction. Soluble chemical oxygen demand (SCOD) released from the anaerobic sludge tank in the OSA process was used as the substrate for cryptic growth. The substrate was used for anoxic denitrifying, anaerobic phosphorus release, sulfate reduction, and methane production. These anaerobic reactions in the sludge anaerobic tank have lower sludge production than in the aerobic oxidation when equivalent SCOD is consumed, which may lead to approximately 23% of sludge reduction in the OSA process. It has been concluded that multiple causes resulted in the minimization of excess sludge in the OSA system. The microbial community structure and diversity of sludge samples from the CAS (conventional activated sludge) and OSA systems were investigated by 16 SrDNA PCR-DG-DGGE (polymerase chain reaction-double gradient-denaturing gradient gel electrophoresis). DGGE profile and cluster analysis showed more abundant species in the OSA system contrasting to microbial communities in the CAS system.     

蛋白质在城市污水活性污泥处理系统中的降解动力学模型研究

研究了蛋白质在厌氧-缺氧-好氧城市污水处理系统中吸附和降解的特性,分别确定了蛋白质在厌氧、缺氧和好氧条件下的吸附等温线模型,建立了蛋白质在厌氧、缺氧和好氧状态下的降解动力学模型,并对模型预测结果进行了验证分析,结果表明,Freundlich模型可以较好地描述蛋白质在厌氧、缺氧和好氧污泥卜的吸附过程,牛血清白蛋白水解成氨基酸是其生物降解过程的控速步骤,序批式动力学降解试验还表明,厌氧降解速率系数K厌、缺氧降解速率系数k缺与好氧降解速率常数的比值分别为0.40和0.98,说明在同一活性污泥系统的厌氧和缺氧条件下,蛋白质也能被较好地降解,模型得到的各池混合液出水中蛋白质的浓度模拟结果与实测结果相一致(相对误差＜10%).无论在厌氧、缺氧还是好氧环境中,酸溶蛋白质没有积累.     

序批式生物膜法同步除磷脱氮特性研究

对淹没序批式生物膜法去除有机物和磷及同步部分脱氮的特性进行了研究。其适合的载体装填密度为30％，水力停留时间为9h，其中厌氧3h，好氧6h，进水COD负荷从0．27kg/(m^3.d)到1．32kg/(m^3.d)均可使除磷率达90％以上，脱氮率达50％－60％。淹没式生物膜法除磷脱氮工艺中的优势菌属为假单胞菌属，其次依顺序为气单胞菌属，芽孢杆菌属，微球菌属，硝化矸菌属，生物膜具有生物量大（MLVSS达5531．7mg/L)，脱落污泥含磷量高（达5．67％），沉降性好（SVI为101．7）的特点，污泥产率为0．1996kg干泥／kgCOD。     

Research on polyhydroxyalkanoates and glycogen transformations: Key aspects to biologic nitrogen and phosphorus removal in low dissolved oxygen systems

In this paper, a study was conducted on the effect of polyhydroxyalkanoates (PHA) and glycogen transformations on biologic nitrogen and phosphorus removal in low dissolved oxygen (DO) systems. Two laboratory-scale sequencing batch reactors (SBR1 and SBR2) were operating with anaerobic/aerobic (low DO, 0.15–0.45 mg·L^-1) configurations, which cultured a propionic to acetic acid ratio (molar carbon ratio) of 1.0 and 2.0, respectively. Fewer poly-3-hydroxybutyrate (PHB), total PHA, and glycogen transformations were observed with the increase of propionic/acetic acid, along with more poly-3-hydroxyvalerate (PHV) and poly-3-hydroxy-2-methyvalerate (PH2MV) shifts. The total nitrogen (TN) removal efficiency was 68% and 82% in SBR1 and SBR2, respectively. In the two SBRs, the soluble ortho-phosphate (SOP) removal efficiency was 94% and 99%, and the average sludge polyphosphate (poly-P) content (g·g-MLVSS^-1) was 8.3% and 10.2%, respectively. Thus, the propionic to acetic acid ratio of the influent greatly influenced the PHA form and quantity, glycogen transformation, and poly-P contained in activated sludge and further determined TN and SOP removal efficiency. Moreover, significant correlations between the SOP removal rate and the (PHV+ PH2MV)/PHA ratio were observed (R²>0.99). Accordingly, PHA and glycogen transformations should be taken into account as key components for optimizing anaerobic/aerobic (low DO) biologic nitrogen and phosphorus removal systems.     

糖类在城市污水生物处理系统中的去除机理

研究了厌氧、缺氧和好氧状态下淀粉在城市污水生物处理系统中水相和泥相中吸附和降解的动力学参数,建立了淀粉在厌氧、缺氧、好氧状态下的降解动力学模型,并对模型预测的结果进行了验证.结果表明,Fritz-Schlunder模型可以较好地描述糖类在厌氧、缺氧和好氧污泥上的吸附过程,吸附的大分子糖类迅速水解为低一级的高分子物质和小分子物质;厌氧降解速率系数K厌、缺氧的降解速率系数K缺与好氧的降解速率常数的比值分别为0.40和0.64;所建立的动力学模型能较好的预测出水糖类的浓度(相对误差<10%).     

Effects of Al3+ on pollutant removal and extracellular polymeric substances (EPS) under anaerobic,anoxic and oxic conditions

The highest removal efficiencies of COD and TN were achieved under 10 mg/L of Al³⁺. The highest TP removal efficiency occurred under 30 mg/L of Al³⁺. EPS, PS and PN concentrations increased with the addition of Al³⁺. Sludge properties significantly changed with the addition of Al³⁺. Aluminum ions produced by aluminum mining, electrolytic industry and aluminum-based coagulants can enter wastewater treatment plants and interact with activated sludge. They can subsequently contribute to the removal of suspended solids and affect activated sludge flocculation, as well as nitrogen and phosphorus removal. In this study, the effects of Al³⁺ on pollutant removal, sludge flocculation and the composition and structure of extracellular polymeric substances (EPS) were investigated under anaerobic, anoxic and oxic conditions. Results demonstrated that the highest chemical oxygen demand (COD) and total nitrogen (TN) removal efficiencies were detected for an Al³⁺ concentration of 10 mg/L. In addition, the maximal dehydrogenase activity and sludge flocculation were also observed at this level of Al³⁺. The highest removal efficiency of total phosphorus (TP) was achieved at an Al³⁺ concentration of 30 mg/L. The flocculability of sludge in the anoxic zone was consistently higher than that in the anaerobic and oxic zones. The addition of Al³⁺ promoted the secretion of EPS. Tryptophan-like fluorescence peaks were detected in each EPS layer in the absence of Al³⁺. At the Al³⁺ concentration of 10 mg/L, fulvic acid and tryptophan fluorescence peaks began to appear, while the majority of protein species and the highest microbial activity were also detected. Low Al³⁺ concentrations (<10 mg/L) could promote the removal efficiencies of COD and TN, yet excessive Al³⁺ levels (>10 mg/L) weakened microbial activity. Higher Al³⁺ concentrations (>30 mg/L) also inhibited the release of phosphorus in the anaerobic zone by reacting with PO₄^3-.     

Kinetic analysis of anaerobic phosphorus release during biological phosphorus removal process

Enhanced biological phosphorus removal (EBPR) is a commonly used and sustainable method for phosphorus removal from wastewater. Poly-β-hydroxybutyrate (PHB), polyphosphate, and glycogen are three kinds of intracellular storage polymers in phosphorus accumulation organisms. The variation of these polymers under different conditions has an apparent influence on anaerobic phosphorus release, which is very important for controlling the performance of EBPR. To obtain the mechanism and kinetic character of anaerobic phosphorus release, a series of batch experiments were performed using the excessively aerated sludge from the aerobic unit of the biological phosphorus removal system in this study. The results showed that the volatile suspended solid (VSS) had an increasing trend, while the mixed liquid suspended sludge (MLSS) and ashes were reduced during the anaerobic phosphorus release process. The interruption of anaerobic HAc-uptake and phosphorus-release occurs when the glycogen in the phosphorus-accumulating-organisms is exhausted. Under the condition of lower initial HAc-COD, HAc became the limiting factor after some time for anaerobic HAc uptake. Under the condition of higher initial HAc-COD, HAc uptake was stopped because of the depletion of glycogen in the microorganisms. The mean ratio of Δρ _P/Δρ _PHB, Δρ _GLY/Δρ _PHB, Δρ _P/ΔCOD, was 0.48, 0.50, 0.44, and 0.92, respectively, which was nearly the same as the theoretical value. The calibrated kinetic parameters of the HAc-uptake and phosphorus-release model were evaluated as follows: Q _HAc,max was 164 mg/(g · h), Q _P,max was 69.9 mg/(g · h), K _gly was 0.005, and KCOD was 3 mg/L. An apparently linear correlation was observed between the ratio of Δρ _P/ΔCOD and pH of the solution, and the equation between them was obtained in this study.     

On-line controlling system for nitrogen and phosphorus removal of municipal wastewater in a sequencing batch reactor (SBR)

The objectives of this study were to establish an on-line controlling system for nitrogen and phosphorus removal synchronously of municipal wastewater in a sequencing batch reactor (SBR). The SBR for municipal wastewater treatment was operated in sequences: filling, anaerobic, oxic, anoxic, oxic, settling and discharge. The reactor was equipped with on-line monitoring sensors for dissolved oxygen (DO), oxidation-reduction potential (ORP) and pH. The variation of DO, ORP and pH is relevant to each phase of biological process for nitrogen and phosphorus removal in this SBR. The characteristic points of DO, ORP and pH can be used to judge and control the stages of process that include: phosphate release by the turning points of ORP and pH; nitrification by the ammonia valley of pH and ammonia elbows of DO and ORP; denitrification by the nitrate knee of ORP and nitrate apex of pH; phosphate uptake by the turning point of pH; and residual organic carbon oxidation by the carbon elbows of DO and ORP. The controlling system can operate automatically for nitrogen and phosphorus efficiently removal.     

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.     

Sludge reduction during brewery wastewater treatment by hydrolyzation-food chain reactor system

During brewery wastewater treatment by a hydrolyzation-food chain reactor (FCR) system, sludge was recycled to the anaerobic segment. With the function of hydrolyzation acidification in the anaerobic segment and the processes of aerobic oxidation and antagonism, predation, interaction and symbiosis among microbes in multilevel oxidation segment, residual sludge could be reduced effectively. The 6-month dynamic experiments show that the average chemical oxygen demand (COD) removal ratio was 92.6% and average sludge production of the aerobic segment was 8.14%, with the COD of the influent at 960–1720 mg/L and hydraulic retention time (HRT) of 12 h. Since the produced sludge could be recycled and hydrolyzed in the anaerobic segment, no excess sludge was produced during the steady running for this system.     

Effect of chemical dose on phosphorus removal and membrane fouling control in a UCT-MBR

Phosphorus removal was enhanced effectively by dosing aluminum sulfate and effluent phosphorus concentration was lower than 0.5 mg/L. Sludge activity was not inhibited but improved slightly with addition of aluminum sulfate. EPS concentrations both in mixed liquid and on membrane surface were decreased, contributing to the effective mitigation of membrane fouling. To enhance phosphorus removal and make the effluent meet the strict discharge level of total phosphorus (TP, 0.5 mg/L), flocculant dosing is frequently applied. In this study, the performance of aluminum sulfate dosing in a University of Cape Town Membrane Bioreactor (UCT-MBR) was investigated, in terms of the nutrients removal performance, sludge characteristics and membrane fouling. The results indicated that the addition of aluminum sulfate into the aerobic reactor continuously had significantly enhanced phosphorus removal. Moreover, COD, NH₄⁺-N and TN removal were not affected and effluent all met the first level A criteria of GB18918-2002. In addition, the addition of aluminum sulfate had improved the sludge activity slightly and reduced trans-membrane pressure (TMP) increase rate from 1.13 KPa/d to 0.57 KPa/d effectively. The membrane fouling was alleviated attributed to the increased average particle sizes and the decreased accumulation of the small sludge particles on membrane surface. Furthermore, the decline of extracellular polymeric substance (EPS) concentration in mixed sludge liquid decreased its accumulation on membrane surface, resulting in the mitigation of membrane fouling directly.     

猪场废水厌氧消化过程中的除磷效果

采用序批式半连续厌氧消化试验方法,研究猪场废水厌氧消化过程中磷的去除情况。结果表明,水力停留时间（HRT）为1、3、6和9 d的厌氧反应器平均除磷率分别为65.0%、81.1%、82.7%和83.0%,而COD平均去除率分别为54.5%、82.3%、87.0%和85.9%。厌氧反应器除磷能力随沼气产量的增加而增加,说明厌氧反应器中磷的去除与产甲烷过程密切相关。对厌氧消化前后的污泥进行浸提后发现,厌氧消化过程中,化学反应生成磷酸盐沉淀的除磷作用十分显著,污泥中正磷酸盐,与铁结合的磷化合物（Fe-RP）,还原可溶性磷,与钙、镁离子结合的磷化合物（Ca-RP、Mg-RP）以及无机或有机聚合磷增加量分别为0.027 8～0.101 5、0.013 5～0.081 0、0.2165～0.430 5、23.4～54.8和7.2～21.5 mg.g-1;且总体而言,HRT越长,污泥中与不同金属结合的磷增加量就越大。从HRT、磷和有机物的去除效果以及沼气产气速率3个方面综合考虑,猪场废水厌氧消化反应器的HRT控制在3 d为宜。     

Optimization of denitrifying phosphorus removal in a pre-denitrification anaerobic/anoxic/post-aeration + nitrification sequence batch reactor (pre-A<Subscript>2</Subscript>NSBR) system: Nitrate recycling,carbon/nitrogen ratio and carbon source type

Because the efficiency of biological nutrient removal is always limited by the deficient carbon source for the low carbon/nitrogen (C/N) ratio in real domestic sewage, the denitrifying phosphorus removal (DNPR) was developed as a simple and efficient method to remove nitrogen and phosphorous. In addition, this method has the advantage of saving aeration energy while reducing the sludge production. In this context, a pre-denitrification anaerobic/anoxic/post-aeration + nitrification sequence batch reactor (pre-A₂NSBR) system, which could also reduce high ammonia effluent concentration in the traditional two-sludge DNPR process, is proposed in this work. The pre-A₂NSBR process was mainly composed of a DNPR SBR and a nitrifying SBR, operating as alternating anaerobic/anoxic/post-aeration + nitrification sequence. Herein, the long-term performance of different nitrate recycling ratios (0–300%) and C/N ratios (2.5–8.8), carbon source type, and functional microbial community were studied. The results showed that the removal efficiency of total inorganic nitrogen (TIN, including NH₄⁺-N, NO₂^– -N, and NO₃^– -N) gradually increased with the nitrate recycling ratios, and the system reached the highest DNPR efficiency of 94.45% at the nitrate recycling ratio of 300%. The optimum C/N ratio was around 3.9–7.3 with a nitrogen and phosphorus removal efficiency of 80.15% and 93.57%, respectively. The acetate was proved to be a high-quality carbon source for DNPR process. The results of fluorescence in situ hybridization (FISH) analysis indicated that nitrifiers and phosphorus accumulating organisms (PAOs) were accumulated with a proportion of 19.41% and 26.48%, respectively.

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厌氧除磷同步脱氮及影响因素研究

采用鸡粪污泥为种泥,在厌氧混合连续流反应装置内进行厌氧还原磷产生磷化氧功能菌的富集,进行硝酸盐、硫酸盐、不同碳源和氮源条件下厌氧除磷效率的研究,并考察磷化氧的生成与硝酸、总磷、氨氮去除的关系.结果表明,(1)SO_4~(2-)-S适宜的投加量为26 mg·L~(-1),不投加NO_3~--N.水中含有氧化态的无机物在厌氧条件下与磷争夺[H]导致厌氧除磷的效率下降.(2)合适的碳源为葡萄糖1 000 mg·L~(-1),纤维素不适合作为碳源,合适的氮源为蛋白胨500 mg·L~(-1),水中含有的还原糖和有机氮源促进磷化氧的生成.(3)pH值控制在6.5～7.0的范围,最适宜的生长温度在35℃左右.(4)氨氮的去除率随着总磷的去除率而增加,在厌氧条件下可达到同时脱氮除磷的效果.磷的去除由厌氧除磷菌还原磷生成磷化氧完成,氨氮由生成氮气或生成蛋白质来去除.