Partial ozonation of activated sludge to reduce excess sludge, improve denitrification and control scumming and bulking.

Disposal of sewage sludge is forbidden and agricultural use of stabilized sludge will be banned in 2005 in Switzerland. The sludge has to be dewatered, dried, incinerated and the ashes disposed in landfills. These processes are cost intensive and lead also to the loss of valuable phosphate resources incorporated in the sludge ash. The implementation of processes that could reduce excess sludge production and recycle phosphate is therefore recommended. Partial ozonation of the return sludge of an activated sludge system reduces significantly excess sludge production, improves settling properties of the sludge and reduces bulking and scumming. The solubilized COD will also improve denitrification if the treated sludge is recycled to the anoxic zone. But ozonation will partly inhibit and kill nitrifiers and might therefore lead to a decrease of the effective solid retention time of the nitrifier, which reduces the safety of the nitrification. This paper discusses the effect of ozonation on sludge reduction, the operation stability of nitrification, improvement of denitrification and gives also an energy and cost evaluation.     

Effect of chlorination bulking control on water quality and phosphate release/uptake in an anaerobic-oxic activated sludge system.

This study evaluates the effect of chlorination bulking control on water quality and phosphate release/uptake in an anaerobic-oxic activated sludge system. A series of batch experiments with different specific NaOCl mass dose were conducted to determine the sludge settling properties, supernatant water quality and phosphate metabolism behavior of filamentous bulking sludge. The harvested sludge was from a continuous-flow anaerobic-oxic (A/O) activated sludge pilot-plant, i.e., enhanced biological phosphorus removal (EBPR) system, operated with 15 days of sludge retention time. The filamentous bacteria in the A/O pilot plant were identified to be Thiothrix according to Eikelboom's classification techniques, which was in accordance with the high influent sulfate concentration of this study (50 mg/L sulfate). Increasing NaOCI concentration, as revealed by experimental results, obviously decreased the sludge settling properties (SVI values and zone settling velocities) and meanwhile significantly reduced supernatant water quality (COD, SS, TP) mainly due to higher suspended solids caused by floc disruption. Moreover, the nine-hour batch experiments indicated that high NaOCI dosage (40 mg/gMLSS) completely deteriorated phosphate metabolism of EBPR sludge. Such a high dosage of chlorination further confirmed overdosing through disappearance of intracellular PHB and death of protozoa by microscopic investigation. Still, phosphate release/uptake behavior of EBPR sludge properly functions at low NaOCl dosage (5 mg/g MLSS). Besides, phosphate metabolism worsens rapidly before the SVI value reaches its lowest level. These findings imply that determining NaOCI requirement with merely SVI values can readily result in chlorination overdosing. Proper NaOCI dosage requires a delicately balanced consideration between sludge settling improvement, water quality demand and phosphate metabolism. Batch test of phosphate release/uptake is apparently a prerequisite to conclude an appropriate NaOCl dosage for bulking control.     

Causes of,and control strategies for,Microthrix parvicella bulking and foaming in nutrient removal activated sludge systems

Bench and pilot scale nutrient removal activated sludge units were used to examine the effect of factors such as temperature, substrate type (easily biodegradable in the form of acetate and slowly biodegradable in the form of oleic acid) on Microthrix parvicella growth. The configurations examined include complete mix with and without selectors (anoxic and anaerobic) and plug flow reactors. The results indicate that low temperatures and substrates in the form of long chain fatty acids favour the growth of M. parvicella. With respect to reactor configuration, a plug flow configuration was shown to be quite effective in controlling the growth of M. parvicella and producing a sludge with good settling characteristics, while the presence of a selector, either anoxic or anaerobic, had no significant effect on the growth of M. parvicella.     

大型城市污水处理厂活性污泥法污泥膨胀防控对策

详细解析了倒置A2/O工艺污泥膨胀发生前后的运行状况及活性污泥性状,通过水质数据对比和运行参数比较,探讨在大型城市污水处理厂建立污泥膨胀预警评价体系的可能性。利用工艺参数对典型工艺进行优化调控,提前预防污泥膨胀或在污泥膨胀初期进行防控。     

On-line determination of sludge settling velocity for flux-based real-time control of secondary clarifiers.

The state diagram for operation of secondary clarifiers is used to design a control algorithm for the return sludge pumping and determination of the actual hydraulic capacity of the biological step of a wastewater treatment plant. On-line input for the control algorithm is derived from a sludge volume sensor and a suspended solids sensor in the form of software sensors giving values for the sludge settling characteristics - settling velocity, sludge volume index, initial settling velocity and the exponent in the Vesilind equation - allowing the control to accommodate the ever changing settling characteristics and thereby keep the suspended solids flux in the clarifiers in balance for both dry weather flows and during rain events. The control algorithm has been implemented, tested and set into normal operation on a full scale wastewater treatment plant.     

The hunt for the G-bacteria in activated sludge biomass

Routine microscopic examination of biomass samples from many activated sludge plants around the world reveals the presence of large numbers of both Gram positive and Gram negative coccoid cells often arranged in distinctive tetrads or sheets of tetrads. Three Gram negative tetrad cocci were successfully isolated into pure culture using micromanipulation from samples of biomass from plants in Tamworth, N.S.W., Australia, Verona, Italy and Macau. After extensive phenotypic characterisation and 165 rDNA sequence analysis, all isolates showed high overall similarity to each other, but were phylogenetically quite different to any previously sequenced bacterium. They have therefore been classified as three species of a new genus, the genus Amaricoccus in the α Proteobacteria in the domain Bacteria. None could accumulate polyphosphate granules, and production of intracellular poly-β-hydroxybutyrate (PHB) granules depended on the carbon source used in the medium. A similar characterisation of the original isolate of the G-bacteria described by Cech and Hartman showed this organism also belonged to the same genus as the other three isolates, but as a distinct species. The practical implications of these observations are discussed.     

Mineralisation of hazardous organic compounds in a sludge reed bed and sludge storage.

Linear alkylbenzene sulphonates (LAS) and nonylphenolethoxylates (NPE) may be detrimental to the environment if spread in inappropriately large concentrations. Mineralisation of LAS and NPE in mesophilic digested sludge was observed during a 9-month monitoring programme where three separate treatment methods were investigated. Sludge was treated in a sludge reed bed under aerobic conditions, by storage in a container under anaerobic conditions, and by storage in a sludge pile turned over mechanically at intervals to improve the oxygen influx. Treatment in a sludge reed bed was shown to be effective. Mineralisation of 98% of LAS and 93% of NPE was observed. Only limited mineralisation occurred on the surface of the sludge stored in a container. A reduction of LAS and NPE of 90% and 43%, respectively, was observed in the sludge which was stored in a pile and frequently turned.     

Evaluation of the adsorption capacity of alkali-treated waste materials for the adsorption of sulphamethoxazole

The present work is to develop potential adsorbents from waste material and employ them for the removal of a hazardous antibacterial, sulphamethoxazole, from the wastewater by the Adsorption technique. The Adsorption technique was used to impound the dangerous antibiotics from wastewater using Deoiled Soya (DOS), an agricultural waste, and Water Hyacinth (WH), a prolific colonizer. The adsorption capacity of these adsorbents was further enhanced by treating them with sodium hydroxide solution and it was seen that the adsorption capacity increases by 10 to 25%. Hence a comparative account of the adsorption studies of all the four adsorbents, i.e. DOS, Alkali-treated DOS, WH and Alkali-treated Water Hyacinth has been discussed in this paper. Different isotherms like Freundlich, Langmuir and Dubinin-Radushkevich were also deduced from the adsorption data. Isotherm studies were in turn used in estimating the thermodynamic parameters. DOS showed sorption capacity of 0.0007 mol g(-1) while Alkali-treated Deoiled Soya exhibited 0.0011 mol g(-1) of sorption capacity, which reveals that the adsorption is higher in case of alkali-treated adsorbent. The mean sorption energy (E) was obtained between 9 and 12 kJ mol, which shows that the reaction proceeds by ion exchange reaction. Kinetic study reveals that the reaction follows pseudo-second-order rate equation. Moreover, mass transfer studies performed for the ongoing processes show that the mass transfer coefficient obtained for alkali-treated moieties was higher than the parent moieties. The breakthrough curves plotted from the column studies show percentage saturation of 90-98%. About 87-97% of sulphamethoxazole was recovered from column by desorption.     

赣江峡江水库防洪库容研究

根据赣江中下游防洪工程的总体规划,从峡江水库防洪库容与泉港分蓄洪容积的组合出发,拟定了两种洪水调度方案：① 水库和分蓄洪区同时承担防洪任务;② 水库为主、分蓄洪区仅分蓄坝址以下洪水。通过对8个年型整体防洪设计洪水的调洪演算,得到两个方案所需的防洪库容和分蓄洪容积。经综合分析比较,选择方案1作为设计峡江水库防洪库容的采用方案。此方案既充分利用现有的分蓄洪工程,又能在不增加工程投资前提下减少新增的淹没区域,且能满足工程为下游防洪要求。     

Effects of starvation conditions on biomass behaviour for minimization of sludge production in membrane bioreactors.

The behaviour of an activated sludge system in starvation conditions was examined in batch according to substrate impulses defined by different S0/X0 ratio. The answer was characterised by an exogenous phase followed by a starvation one. If at high S0/X0 ratio, bacterial cell multiplication was the main synthesis process during exogenous phase, at low S0/X0 ratio the observed phenomenon was compound storage. In starvation conditions, for the lowest S0/X0 ratio, a rapid decrease in the MLVSS without soluble proteins production was observed. No bacterial lysis occurred and this phenomenon was due to consumption of the storage compounds with a decrease rate equal to 0.74d(-1). For high S0/X0 ratio, as soon as the exogenous phase was completed, a decrease of the MLVSS simultaneously to a soluble protein production was observed. An immediate bacterial lysis occurred with a decay rate equal to 0.53 d(-1). Because MBR systems work generally in low F/M conditions, the activity of the present microbial population is close to the one observed in starvation phase. This work points out that these conditions do not allow net bacterial growth and cells just use lysis products to satisfy their maintenance requirements. These assumptions confirm the feasibility of a decrease of the net biomass production in a MBR when high sludge retention time is operated.     

水布垭枢纽预留防洪库容的防洪作用研究

根据长江中游防洪系统的特点，从流域实测和历史洪水中选取有一定代表性的洪水作为典型，在遵循三峡防洪库容分配方案的前提下，建立典型洪水优化调度数学模型，并用模拟算法求解，以确定清江水布垭枢纽预留防洪库容对长江中游地区的防洪作用。结果表明：清江水布垭枢纽预留５ 亿ｍ３ 的防洪库容对城陵矶地区的防洪作用比较适宜。     

Occurrence and control of filamentous bulking in aerated wastewater treatment plants of the French paper industry.

The occurrence of filamentous bacteria was investigated in 15 French pulp and paper activated sludge wastewater treatment plant (WWTP). Large filamentous populations were present in most of the plants. Identification carried out with conventional methods based on morphological features and staining techniques showed that the four main filamentous bacteria encountered in these industrial WWTP and responsible for bulking belong to the genera Thiothrix sp., Type 021 N, Haliscomenobacter hydrossis and Type 0092. During two years a specific survey was performed for three of these WWTP showing recurrent bulking phenomena. Data from WWTP performance, chemical data and filaments characterization were compared to correlate the presence of specific filaments with process operating conditions.     

Effects of complete sludge retention on biomass build-up in a membrane bioreactor.

The work reports the main results of an experimental activity aimed at evaluating the performance of a membrane bioreactor with complete sludge retention and the characteristics of its biomass. The bench scale system was started-up without any sludge inoculum and fed on real municipal sewage in order to favour biomass selection based on the imposed operating conditions. Process performance was evaluated in terms of COD removal (above 90% on average) and nitrification under two pre-determined volumetric loading rates (0.8 and 1.7 gCOD L(react)(-1), d(-1) on average). The biomass was evaluated in terms of growth, accumulation of inert solids, and bacterial activity. The latter was measured through respirometric tests. The results showed that the suspended solids concentrations (SS) under equilibrium were proportional to the volumetric loading rates in both the experimental periods considered and a relationship between these two parameters was proposed. Also, the organic loading rates reached the same equilibrium value of 0.12 gCOD gTSS(-1) d(-1) in the two periods. Moreover, the system showed very limited sludge production under equilibrium conditions (0.12 gVSS gCOD(rem)(-1) and low biomass activity, although it readily responded to load variations.     

Measurement and modelling of ordinary heterotrophic organism active biomass concentrations in anoxic/aerobic activated sludge mixed liquor.

Ordinary heterotrophic organism (OHO) active biomass (ZBH) is a key parameter in models for activated sludge systems, which defines quantitatively the kinetic rates of relevant processes. However, ZBH has not been measured directly with consistent success: a simple respirometric batch test has provided varying correspondence between measured and theoretical concentrations. In this paper, the batch test is applied to mixed liquors drawn from well defined anoxic/aerobic parent systems at 10 and 20 d sludge ages, with consistent but poor correspondence between measured and theoretical values. In contrast, aerobic digestion batch tests on the same mixed liquors give good correspondences. It is concluded that the differences between theoretical and batch test measured values are due to the batch test method itself and its interpretation. It is found that the batch test conditions (particularly the substrate/ZBH ratio) influence the kinetic constants derived from the data, and hence the ZBH estimate. Two kinetic models with two competing OHO populations, a fast and a slow grower, are developed and applied to the batch tests and parent systems. The first model is based on kinetic selection only, while the second includes additional metabolic selection. Both models can account for the observations in the batch tests, but the second provides greater consistency between simulations of the parent systems and batch tests.     

Helminth ova control in wastewater and sludge for advanced and conventional sanitation.

Worldwide, the most important reuse of wastewater, in volume, is agricultural irrigation. Therefore, there is a need to properly treat wastewater for such purpose, considering the removal of pathogens while leaving suitable amounts of nutrients and other compounds to increase productivity. Helminth ova are one of the main targeted pathogens in the new guidelines for water reuse in agriculture and aquaculture issued in 2006 by the World Health Organization. However, relatively little research has been done recently on how to remove and inactivate helminth ova from wastewater and sludge and recommendations given several decades ago are still used, but when put into practice, particularly in developing countries, produce unsatisfactory results. One problem is that these criteria were developed using inaccurate analytical techniques and the other is the large number and variety of helminth ova species found in wastewater and sludge from the developing world. In fact, the few technological options to remove and inactivate helminth ova come from research performed using wastewater and sludge with low helminth ova content, and refer almost only to Ascaris (one type of helminth). This paper summarises recent research work and results from practical experience concerning helminth ova control for advanced and conventional sanitation.     

二龙山水电站轴流式水轮机增容改造

本文介绍了二龙山水电站轴流式水轮机改造的必要性和改造的目的要求,分析了两种改造方案的利与弊,介绍了选用JK412转轮的原因和应用效果。改造获得圆满成功,两台轴流式水轮发电机增容45%￣55%。     

蓄水容量曲线设定分布式霍顿模型土壤含水量初值

分布式水文模型对土壤含水量的空间描述能力对土壤墒情模拟、分布式输出等具有重要的意义。但分布式水文模型的土壤含水量空间分布计算,需耗费大量的计算资源。为了提高分布式模型的计算效率,从定性的理论分析和定量的数据比对2个方面,证明蓄水容量曲线和分布式模型中逐单元土壤含水量序列的相关关系,并建立了二者之间的转换公式,据此可以将面平均的土壤含水量转换为空间分布的土壤含水量。用离散蓄水容量曲线法设置分布式模型的土壤含水量初值,并与传统模型预热法进行比较,结果表明两种方法得到的土壤含水量空间分布总体趋势完全一致,次洪模拟效果相同,并且节省了大量的计算资源,极大地提高了分布式模型的计算效率。     

水库实时防洪风险计算及库群防洪库容分配互用性分析

水库防洪调度风险分析是实时防洪决策的重要环节和依据。为评估水库实时防洪风险,本文提出一种基于长系列历史实测径流资料的防洪库容频率曲线推算方法,以此为基础建立了水库实时防洪调度风险分析模型。进一步,从三峡水库实际防洪调度需求出发,分析了三峡水库汛期不同时段实时防洪风险,研究了上游溪洛渡、向家坝水库配合三峡水库进行联合调度时防洪库容频率曲线的变化,以及上下游水库间防洪库容分配及其互用性问题。研究表明,推求的防洪库容频率曲线能帮助判断当前防洪情势,合理利用防洪库容互用性可有效降低三峡水库防洪风险。     

Improving oxygen concentration control in activated sludge process with estimation of respiration and scheduling control.

The paper presents an efficient and simple model-based method of on-line estimation of respiration from the current values of dissolved oxygen concentration and airflow signals. Fast estimation of respiration is important because respiration appears as the most important disturbance signal in the control of dissolved oxygen concentration, and could therefore be used for improving control efficiency. A parameter scheduling PI (proportional and integral) control scheme is proposed, where the estimated respiration signal is used for scheduling of the PI controller parameters, by using local linearization of the process dynamics. The performance of the scheduling controller is compared to a conventional PI controller in simulation using the COST simulation benchmark, and experimentally on an activated sludge process pilot plant.