Dehydrogenases activity of activated sludge

A study of dehydrogenases activity of activated sludge, return activated sludge, and waste activated sludge from three sewage treatment plants was made. Dehydrogenases activity and protein content of the mixed liquor varied along the aeration basin. Chromium chloride and zinc sulfate were found to be inhibitory to dehydrogenases activity. Return activated sludge and waste activated sludge, in spite of higher content of volatile suspended solids, contained lower dehydrogenases activity. Return activated sludge when kept without aeration and addition of sewage, showed higher dehydrogenases activity; and on aeration, but without addition of sewage, it showed progressively lower dehydrogenases activity.     

Catalase activity of activated sludge

Catalase activity of mixed liquor suspended solids of aeration tank of activated sludge plants in Milwaukee, WI, was measured in sonicated samples. Catalase activity varied in the samples of mixed liquor suspended solids collected from the head and end of the aeration tanks; in return activated sludge; and in waste activated sludge. Catalase activity decreased in mixed liquor suspended solids, on prolonged aeration (8 days), in the absence of added sewage. Volatile suspended solids and catalase activity seemed to bear a relationship.     

Cultivation of aerobic granular sludge in a conventional,continuous flow,completely mixed activated sludge system

Aerobic granules were formed in a conventional, continuous flow, completely mixed activated sludge system (CMAS). The reactor was inoculated with seed sludge containing few filaments and fed with synthetic municipal wastewater. The settling time of the sludge and the average dissolved oxygen (DO) of the reactor were 2 h and 4.2 mg·L^-1, respectively. The reactor was agitated by a stirrer, with a speed of 250 r·min^-1, to ensure good mixing．The granular sludge had good settleability, and the sludge volume index (SVI) was between 50 and 90 mL·g^-1. The laser particle analyzer showed the diameter of the granules to be between 0.18 and 1.25 mm. A scanning electron microscope (SEM) investigation revealed the predominance of sphere-like and rod-like bacteria, and only few filaments grew in the granules. The microbial community structure of the granules was also analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Sequencing analysis indicated the dominant species were α, β, and γ-Proteobacteria, Bacteroidetes, and Firmicutes. The data from the study suggested that aerobic granules could form, if provided with sufficient number of filaments and high shear force. It was also observed that a high height-to-diameter ratio of the reactor and short settling time were not essential for the formation of aerobic granular sludge.     

A modified method for determination of dehydrogenases activity of activated sludge

Examination of the different methods employed to detect dehydrogenases activity of activated sludge by reduction of triphenyl tetrazolium chloride (TTC) indicated the non‐uniformity of the procedures. A modified method is, therefore, developed which consists of incubation of a dilute sonicated sample of mixed liquor suspended solids (MLSS) of activated sludge with TTC in the presence of sodium sulfite, phosphate buffer and cyanide. Triphenyl formazan (TF) formed is first dissolved in acetic acid and later extracted by toluene. Optical density (OD) of the color is measured at 485 nm. Dehydrogenases activity is calculated from the OD and expressed as specific activity per unit weight of protein. Modified method gave less relative dispersion compared to the values obtained on the same but unsonicated samples of MLSS.     

Generalized model of aerobic biological treatment

A unified modelling approach for the aerobic treatment of liquid sewage in aeration tanks, trickling filters and rotating discs is suggested. Processing of numerous experimental data shows that high-level and crude treatments of multicomponent liquid sewage follow differing laws.     

Activated carbon adsorption,activated sludge and ozonation treatments evaluated by impact intensity based on acute toxicity test

A Toxicity Reduction Evaluation (TRE) conducted on various water treatments was successful in optimizing the acute toxicity of the final effluent. In particular, we found that the acute toxicity of the sample water treated by a water treatment process should not be correlated with the concentrations of the parent compounds still remaining in the water. Therefore, it was concluded that an acute toxicity test based on a bioassay must be performed in order to evaluate the efficiency of the water treatment process for various effluents containing environmental pollutants. In addition, the treatability and the resultant toxicity was evaluated as a simple scoring system. The scoring system ranked the treated water in three classes of toxicity with the calculation of several factors for the concerned toxicity. Using an impact evaluation based on the score of the characteristics, different water treatment processes could be directly compared. The new methodology presented here is specifically effective in listing possible unit operations for a water treatment process based on the impact, and thereby enables targeted and cost-effective water treatment.     

Achievement of high rate nitritation with aerobic granular sludge reactors enhanced by sludge recirculation events

A ratio control strategy has been used to demonstrate the feasibility of this automatic control procedure for the achievement of stable full and partial nitritation. The control strategy assured constant ratio between the dissolved oxygen (DO) and the total ammonia nitrogen (TAN) concentrations in the bulk liquid of aerobic granular sludge reactors operating in continuous mode. Three different set-ups with different reactor capacities were used (3, 110, and 150 L). High strength synthetic wastewaters and reject water were tested with similar performance. Achieved nitrogen loading rates ranged between 0.4 and 6.1 kgN·m^-3·d^-1, at temperatures between 20°C and 30°C. Granular sludge and nitritation were stable in the long term continuous operation of the reactors. Suitable stable effluent for Anammox has been obtained using the desired TAN setpoint (i.e. 50% of influent ammonium oxidation). An existing biofilm model developed incorporating the implemented control loops and validated in a previous publication was used to investigate the effects of the ammonium concentration of the influent and the biofilm density on the achievement of full nitritation. The model demonstrated how sludge recirculation events led to a stable and significant increase of the biomass concentration in the reactor, which in turn resulted in the achievement of high nitrogen loading rates, due to the action of the control strategy. The model predicted an enhancement of stable full nitritation at higher ammonium concentrations in the influent. Poor influence of the biofilm density in the achievement of full nitritation was predicted with the model.     

The impact of ultrasonic treatment on activity of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria in activated sludge

Conditions for ultrasonic treatment to achieve partial nitritation are optimized. Ultrasound reduces metabolic activity and releases intracellular metabolites. Mechanical shearing is essential to inhibit nitrite oxidation. The ultrasonic treatment of sludge has been considered as an effective method to facilitate the partial nitritation of municipal sewage. This study aims to reveal the effects of ultrasound on ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). The impact factors including ultrasonic irradiation time and intensity, sludge concentration, thermal effect and released free radicals were studied. The maximized difference between the changes in AOB and NOB activities were obtained with 10 g mixed liquor suspended solids (MLSS)/L, using 0.9 kJ/mL ultrasonic energy density and 12 h interval time. The increased ultrasonic intensity destroyed the floc structure of activated sludge, increased the microbial death, and decreased the cellular ATP level. Further, the mechanism exploration indicated that the mechanical shearing could be a critical factor in achieving the nitritation with inhibitory effect on nitrite oxidation.     

Tank-dependence of the functionality and network differentiation of activated sludge community in a full-scale anaerobic/anoxic/aerobic municipal sewage treatment plant

● Environmental parameters affected functional bacteria and network associations. ● The structure and interactions of AS networks changed greatly within tanks. ● Anoxic co-occurrence network was more unstable and easily influenced. ● Composition of functional bacteria had a seasonal succession pattern. ● Tetrasphaera was the major PAO in spring and winter leading a better P removal. Understanding the structures and dynamics of bacterial communities in activated sludge (AS) in full-scale wastewater treatment plants (WWTPs) is of both engineering and ecological significance. Previous investigations have mainly focused on the AS communities of WWTP aeration tanks, and the differences and interactions between the communities in anaerobic and anoxic tanks of the AS system remain poorly understood. Here, we investigated the structures of bacterial communities and their inter-connections in three tanks (anaerobic, anoxic, and aerobic) and influent from a full-scale WWTP with conventional anaerobic/anoxic/aerobic (A/A/O) process over a year to explore their functionality and network differentiation. High-throughput sequencing showed that community compositions did not differ appreciably between the different tanks, likely due to the continuous sludge community interchange between tanks. However, network analysis showed significant differences in inter-species relationships, OTU topological roles, and keystone populations in the different AS communities. Moreover, the anoxic network is expected to be more unstable and easily affected by environmental disturbance. Tank-associated environmental factors, including dissolved oxygen, pH, and nutrients, were found to affect the relative abundance of functional genera (i.e., AOB, NOB, PAOs, and denitrifiers), suggesting that these groups were more susceptible to environmental variables than other bacteria. Therefore, this work could assist in improving our understanding of tank-associated microbial ecology, particularly the response of functional bacteria to seasonal variations in WWTPs employing A/A/O process.     

Enhancement of sludge gravitational thickening with weak ultrasound

Gravitational thickening is the prevailing method to reduce sludge volume but the process is slow and usually requires addition of polyelectrolyte(s). This paper investigated the potential benefits of sonication on enhancing the sludge gravitational thickening with very low energy dose, so called “weak ultrasound”. Results showed that weak sonication significantly changed the sludge settlability and the main mechanism was release of the loosely bounded extracellular polymeric substances. The changes in sludge behaviors by sonication were strongly influenced by power density and sonication duration. Lower sound frequency was slightly better than higher frequency. Weak sonication (<680 kJ·kg^-1 DS) improved the sludge gravitational thickening while high ultrasonic energy deteriorated the process. Considering both the sludge thickening efficiency and energy consumption, the optimum conditions were 0.15 W·mL^-1, 7 s, and 25 kHz. Under such conditions, the energy dose was only 155 kJ·kg^-1 DS, much lower than literature reports, and the sludge settling time was shortened from 24 h to 12?h. Weak sonication could substitute expensive polyelectrolyte coagulant for sludge thickening. Combination of weak sonication and polyelectrolyte could further reduce the settling time to 6 h. The final water content of the thickened sludge was not changed after sonication or polyelectrolyte addition.     

活性污泥动力学模型的建立及在完全混合式污泥系统中的应用

首先建立了微生物衰减系数和污泥浓度、底物浓度的函数关系式,带入Lawrence-McCarty第一方程式得到了Logistic方程形式的微生物生长方程式.在分析污泥泥龄和污泥停留时间关系基础上,引入Monod方程建立了活性污泥动力学模型,推导证明了Lawrence-McCarty方程式是模型静态条件下的表达形式.用建立的活性污泥动力学模型对完全混合式污泥系统进行了模拟,并分析了水力停留时间Hydraulic retention time(HRT)和污泥停留时间Sludge retention time(SRT)对完全混合式污泥系统的影响,表明模型能很好地对活性污泥系统的动态过程进行模拟.根据模型编程画出了污泥系统相关变量关于HRT和SRT变化的三维曲面图,通过编程将复杂模型看作一定输入输出的函数,使得模型更易于应用和推广.     

Modification of the activated sludge model for chemical dosage

Full-scale experiments have been carried out to adapt the activated sludge model ASM2d to include the influence of metal dosage (Fe³⁺ and Al³⁺) for phosphorus removal. Phosphorus removal rates, nitrification rates, as well as pH and sludge settling performance, were evaluated as functions of the metal dosages. Furthermore, models relating certain parameters to the dosage of chemicals have been derived. Corresponding parameters in the ASM2d and the secondary settler models, included in the Benchmark Simulation Model No 1 (BSM1), have been modified to take the metal influence into consideration. Based on the effluent limits and penalty policy of China, an equivalent evaluation method was derived for the total cost assessment. A large number of 300-day steady-state and 14-day open-loop dynamic simulations were performed to demonstrate the difference in behavior between the original and the modified BSM1. The results show that 1) both in low and high mole concentrations, Fe³⁺ addition results in a higher phosphorus removal rate than Al³⁺; 2) the sludge settling velocity will increase due to the metal addition; 3) the respiration rate of the activated sludge is decreased more by the dosage of Al³⁺ than Fe³⁺; 4) the inhibition of Al³⁺ on the nitrification rate is stronger than that of Fe³⁺; 5) the total operating cost will reach the minimum point for smaller dosages of Fe³⁺, but always increase with Al³⁺ addition.     

活性污泥吸附重金属的研究进展

主要从活性污泥对不同重金属(Mn+)的吸附效果、吸附机制、影响吸附的因素,以及Mn+对活性污泥中微生物的影响等四个方面,综述了国内外有关活性污泥吸附Mn+的研究成果.     

改性污泥活性炭对苯乙烯的吸附

以城市污泥为原料制备活性炭,对其进行改性,研究了改性前后的比表面积、表面酸碱基团、对苯乙烯的静态吸附容量、吸附穿透曲线、脱附活化能等吸附性能.结果表明,硫酸铜溶液浸渍改性后可使污泥活性炭比表面积明显提高,其中0.1 mol.L-1硫酸铜溶液浸渍改性的污泥活性炭较改性前的比表面积提高了32%(达704.7 m.2g-1).硫酸铝溶液和硫酸铜溶液浸渍改性可以使污泥活性炭表面酸性基团含量提高、表面碱性基团含量减少;对苯乙烯的静态吸附容量提高到改性前的两倍以上(分别达211.4 mg.g-1和178.8 mg.g-1)、对苯乙烯的动态吸附穿透时间由2 min提高到10 min以上、脱附活化能由2.94 kJ.mol-1提高到6 kJ.mol-1以上.改性后活性污泥炭的吸附性能得到明显提高.     

活性污泥总DNA不同提取方法的比较

为了快速、简便和经济地获得活性污泥的总DNA,以用于分子生物学研究,采用5种不同的DNA提取方法提取活性污泥的总DNA,并通过提取的核酸总量、纯度、是否含有聚合酶链反应抑制剂等指标综合分析不同的提取方法对活性污泥总DNA提取效果的影响.结果表明:蛋白酶K-SDS-酚氯仿法和柱提取DNA试剂盒法提取活性污泥总DNA效果最好,提取DNA总量多,纯度高,可不经纯化直接进行PCR扩增反应。     

Comparison between inhibitor and uncoupler for minimizing excess sludge production of an activated sludge process

In order to study the minimization of excess sludge production, the reduction in the excess sludge production in the presence of an inhibitor and uncoupler was studied in this work. The experimental results show that such an addition could effectively reduce the production of excess sludge. With the energy uncoupling model established in this work, energy uncoupling coefficient (E _u) was used to evaluate the reduction in excess sludge production. The energy uncoupling coefficients in the presence of dinitrophenol (dNP), Zn²⁺, and Cu²⁺ was 0.75, 0.46, and 0.18, respectively. The analysis demonstrated that energy spilling occurred in the presence of dNP, and that dNP was an effective uncoupler for reducing the production of excess activated sludge without affecting the microbial respiration activity.     

Enhancement of activated sludge performance on ammonium removal by clinoptilolite

This study evaluated the influence of clinoptilolite on the performance of activated sludge system shocked by high concentration of ammonium. The ammonium and chemical oxygen demand (COD) removal from the experimental reactor containing clinoptilolite and from the clinoptilolite-free control reactor was determined. The ammonium and COD removal was approximately 8 and 20% higher in the experimental reactor than in the control reactor, respectively. The removal increased with an increase in clinoptilolite concentration over the tested range up to 50?mg?L^?1. The presence of clinoptilolite resulted in the sludge flocs being more compacted with smoother surfaces and edges. Molecular biological analysis revealed that clinoptilolite increased the DNA diversity, richness, and evenness of sludge microbes. The enhanced-performance activated sludge previously treated with clinoptilolite was less influenced by the shock of ammonium than non-treated sludge in terms of the ammonium and COD removal. These results suggest that clinoptilolite enhanced the performance of activated sludge system in the removal of ammonium and COD. Amendment of activated sludge with natural zeolites may thus improve the efficiency of wastewater treatment.     

驯化的活性污泥强化降解土壤中氯酚的研究

以接种驯化的活性污泥为生物强化手段,在小型生物泥浆反应器中,研究了受氯酚污染土壤的修复情况.考查了添加驯化活性污泥对土壤中氯酚降解的强化效果,并对土壤中邻氯苯酚(2-CP)、对氯苯酚(4-CP)和2,4-二氯酚(2,4-DCP)在单一污染体系中的降解情况进行了研究.结果表明,在生物泥浆反应器中添加用邻氯苯酚(2-CP)驯化的活性污泥可以明显地促进土壤泥浆中2-CP的降解,是一种有效的强化手段.该方法对土壤中的4-CP和2,4-DCP也有较好的降解效果,对三种氯酚的降解速率由大到小的顺序为2-CP,4-CP,2,4-DCP.反应结束时,泥浆体系中剩余的氯酚基本都残留在土壤中,固液分离后的水相可以直接排放或者在土壤修复过程中循环利用.     

Fate of proteins of waste activated sludge during thermal alkali pretreatment in terms of sludge protein recovery

Maillard reaction between reducing sugars and amides happened during pretreatment. Over 90 min of TAH at the optimal condition, 67.59% sludge proteins was solubilized. 15.84% soluble proteins broke down to materials with small molecular weight. Proteins are the major organic component s of waste activated sludge (WAS); the recovery of sludge proteins is economically valuable. To efficiently recover sludge proteins, WAS should undergo hydrolysis pretreatment to fully release proteins from sludge flocs and microbial cells into aqueous phase. One of the most widely used chemical methods for that is thermal alkali hydrolysis (TAH). Here, the soluble protein concentration achieved the highest level over 90 min of TAH pretreatment at 80°C; the sludge floc disintegration and microbial cell destruction were maximized according to the content profiles of bound extracellular polymeric substance (EPS) and ribonucleic acid (RNA) of sludge. Both less proteins broken down to materials with small molecular weight and less melanoidin generated were responsible. TAH pretreatment at 80°C for 90 min resulted in the solubilization of 67.59% of sludge proteins. 34.64% of solubilized proteins was present in soluble high molecular; 1.55% and 4.85% broke down to polypeptides and amino acids. The lost proteins via being converted to ammonium and nitrate nitrogen accounted for 9.44% of solubilized proteins. It was important to understand the fate of sludge proteins during TAH pretreatment in terms of protein recovery, which would be helpful for designing the downstream protein separation method and its potential application.     

Isolation of Thiobacillus sp from aerobic sludge of distillery and dairy effluent treatment plants and its sulfide oxidation activity at different concentrations

In the present study two strains of Thiobacillus sp were isolated from aerobic sludge of distillery and dairy effluent treatment plant using standard methods of isolation and enrichment. Experiments were conducted using isolated cultures in batch bioreactor with initial sulfide concentration of 75 and 150 mg/l. The effect of initial sulfide concentration on the activity of isolated Thiobacillus sp was studied. Sulfide oxidizing capacity was also determined at different initial sulfide concentrations. The results from the study indicate the possible isolation of Thiobacillus cultures from native source and application in the full-scale reactor