Progress and perspectives of sludge ozonation as a powerful pretreatment method for minimization of excess sludge production

The treatment and disposal of excess sludge represents a bottleneck in wastewater treatment plants (WWTP) worldwide, due to environmental, economic, social and legal factors. The ideal solution to the problem of sludge disposal is to combine sludge reduction with the removal of pollution at the source. This paper presents an overview of the potential of ozonation in sludge reduction. The full-scale application of ozonation in excess sludge reduction is presented. Improvements in the biodegradability of the ozonated sludge were confirmed. The introduction of ozonation into activated sludge did not significantly influence effluent quality but improved the settling properties of the sludge. An operation with a suitable sludge wasting ratio seems to be necessary to prevent accumulation of inorganic and inert particles for long-term operation. Sludge ozonation to reduce excess sludge production may be economical in WWTP which have high sludge disposal costs and operational problems such as sludge foaming and bulking. The recommended ozone dose ranges from 0.03 to 0.05 g O₃/g TSS, which is appropriate to achieve a balance between sludge reduction efficiency and cost. An effort to design and optimize an economic sludge reduction process is necessary.     

Variation of bulk properties of anaerobic granules with wastewater type

Development of a granular sludge with high strength, high biological activity and a narrow settling distribution is necessary for optimal operation of high-rate upflow anaerobic treatment systems. Several studies have compared granules produced from different wastewaters but these have largely been from laboratory-fed reactors or compared granules from full-scale reactors fed similar wastewater types. Though two authors have commented on the inferiority of granules produced by a protein-based feed, the properties of these granules have not been characterised. In this paper, granules from full-scale reactors treating fruit and vegetable cannery effluent, two brewery effluents and a pig abattoir (slaughterhouse) were compared in terms of basic composition, size distribution, density, settling velocity, shear strength, and EPS content. The results supported previous qualitative observations by other researchers that indicate granule properties depend more on wastewater type rather than reactor design or operating conditions such as pre-acidification level. The cannery-fed granules had excellent shear strength, settling distribution and density. Granules from the two brewery-fed reactors had statistically the same bulk properties, which were still acceptable for upflow applications. The protein-grown granule had poor strength and settling velocity.     

Extracellular polymeric substances (EPS) producing bacterial strains of municipal wastewater sludge: Isolation, molecular identification, EPS characterization and performance for sludge settling and dewatering

Wastewater treatment plants often face the problems of sludge settling mainly due to sludge bulking. Generally, synthetic organic polymer and/or inorganic coagulants (ferric chloride, alum and quick lime) are used for sludge settling. These chemicals are very expensive and further pollute the environment. Whereas, the bioflocculants are environment friendly and may be used to flocculate the sludge. Extracellular polymeric substances (EPS) produced by sludge microorganisms play a definite role in sludge flocculation. In this study, 25 EPS producing strains were isolated from municipal wastewater treatment plant. Microorganisms were selected based on EPS production properties on solid agar medium. Three types of EPS (slime, capsular and bacterial broth mixture of both slime and capsular) were harvested and their characteristics were studied. EPS concentration (dry weight), viscosity and their charge (using a Zetaphoremeter) were also measured. Bioflocculability of obtained EPS was evaluated by measuring the kaolin clay flocculation activity. Six bacterial strains (BS2, BS8, BS9, BS11, BS15 and BS25) were selected based on the kaolin clay flocculation. The slime EPS was better for bioflocculation than capsular EPS and bacterial broth. Therefore, extracted slime EPS (partially purified) from six bacterial strains was studied in terms of sludge settling [sludge volume index (SVI)] and dewatering [capillary suction time (CST)]. Biopolymers produced by individual strains substantially improved dewaterability. The extracted slime EPS from six different strains were partially characterized.     

Rheological characterisation of municipal sludge: A review

Sustainable sludge management is becoming a major issue for wastewater treatment plants due to increasing urban populations and tightening environmental regulations for conventional sludge disposal methods. To address this problem, a good understanding of sludge behaviour is vital to improve and optimize the current state of wastewater treatment operations. This paper provides a review of the recent experimental works in order for researchers to be able to develop a reliable characterization technique for measuring the important properties of sludge such as viscosity, yield stress, thixotropy, and viscoelasticity and to better understand the impact of solids concentrations, temperature, and water content on these properties. In this context, choosing the appropriate rheological model and rheometer is also important.     

Sewage Sludge Production, Treatment and Disposal in the European Union

Sludge production and disposal are entering a period of dramatic change, driven mainly by EC legislation. The urban waste water treatment Directive will result in at least 50% more sludge being produced by the end of 2005 and, during the next decade, sludge disposal to all the established outlets could become increasingly difficult or, in the case of sea disposal, will become illegal. The challenge facing the members of the European Union is how to (a) maintain cost-effective and secure methods of sludge disposal and (b) engender public confidence in all disposal and recycling options. What is required is not so much innovative technology, although this may be essential, but more innovative attitudes and approaches to promotion and defending existing outlets.
This paper describes the likely pattern of sludge production, treatment and disposal which will emerge during the implementation of recent EC directives and other national policies in Europe, and focuses on the areas and issues which require innovative approaches.     

城市污水处理厂污泥处理处置规划编制的探讨

针对城市污水厂污泥处理处置带来的一系列问题,近年来不少城市开始对城市污水规划进行补充或编制污泥处理处置相关规划。本文就编制城市污泥规划中的污泥量预测问题、污泥工艺路线问题、污泥处理处置设施布局、厂址等问题进行了探讨,以期对编制城市污泥处理处置规划提供一定的参考。     

SBBGR technology for minimising excess sludge production in biological processes

This paper reports the results of an investigation aimed at evaluating the performance of an innovative technology (SBBGR system - Sequencing Batch Biofilter Granular Reactor), characterised by a low sludge production, for treating municipal wastewater at demonstrative scale. The results have shown that even at the maximum investigated organic load (i.e., 2.5 kg COD/m³ d), the plant removed 80% of COD, total suspended solids and nitrogen content with relative residual concentrations lower than the Italian limits for discharge into soil. The process was characterised by a very low sludge production (i.e., 0.12-0.14 kg TSS/kg COD_removed) ascribable to the high sludge age in the system (θc >120 d). Molecular in situ detection methods and microscopy staining procedures were employed in combination with the traditional measurements (oxygen uptake rate and total protein content) to evaluate both the microbial activity and composition, and the structure of the biomass. A stable presence of active bacterial populations (mainly Proteobacteria) was found within compact and dense aggregates.     

上海市污泥处理处置专项规划简介

城市污泥处理处置技术随着城市化进程的加快越来越受到重视.结合上海制定城市污泥处理处置专项规划的经验,认为在进行技术方案研究的同时,应充分了解整个服务范围内的污泥数量、污泥性质,并对污泥处置的潜在出路进行研究,继而确定处理处置场所的规划,提出实施处理处置的准入条件和法规政策.     

BAF反冲洗污泥的特性及絮凝效能

曝气生物滤池(BAF)反冲洗污泥的处理是影响其工程应用的技术难题之一，为此考察了BAF反冲洗污泥的沉降特性及絮凝性能，系统分析了其在生物一化学强化混凝处理生活污水时的效能及二次污泥的特性。研究结果表明，BAF反冲洗污泥具有较强的生物活性和絮凝活性，将其与金属盐混凝剂组合预处理生活污水时出水水质满足曝气生物滤池的进水水质要求，而且处理过程中产生的二次污泥具有较好的沉降及脱水性能。     

重庆城市污水处理厂污泥处理处置方案选择

三峡库区重庆段污水处理厂产生的污泥由于工艺、管理、机制问题等原因,还没有得到较好的处置。就当前面临的主要问题分析了三峡库区污泥处理处置的必要性,并结合三峡库区自然及社会经济条件等实际情况,提出了污泥处理处置的合理方案。该方案在解决三峡库区污泥出路问题的同时兼顾了环境效益、经济效益、社会效益的统一。     

Minimization of excess sludge production for biological wastewater treatment

Excess sludge treatment and disposal currently represents a rising challenge for wastewater treatment plants (WWTPs) due to economic, environmental and regulation factors. There is therefore considerable impetus to explore and develop strategies and technologies for reducing excess sludge production in biological wastewater treatment processes. This paper reviews current strategies for reducing sludge production based on these mechanisms: lysis-cryptic growth, uncoupling metabolism, maintenance metabolism, and predation on bacteria. The strategies for sludge reduction should be evaluated and chosen for practical application using costs analysis and assessment of environmental impact. High costs still limit technologies of sludge ozonation-cryptic growth and membrane bioreactor from spreading application in full-scale WWTPs. Bioacclimation and harmful to environment are major bottlenecks for chemical uncoupler in practical application. Sludge reduction induced by oligochaetes may present a cost-effective way for WWTPs if unstable worm growth is solved. Employing any strategy for reducing sludge production may have an impact on microbial community in biological wastewater treatment processes. This impact may influence the sludge characteristics and the quality of effluent.     

Digested Sludge Thickening Experiences in Yorkshire Water's Southern Division

S ludge T reatment and disposal costs contribute a large proportion to the overall operating costs of sewage treatment installations. With the increasing drive towards more cost-effective operation it has been recognized that thickening sludge prior to disposal can achieve significant cost savings for limited capital outlay. This paper describes the practical experiences at the Lundwood, Old Whittington, and Aldwarke works of Yorkshire Water (YW) where digested sludge is gravity thickened in shallow tanks of large surface area prior to land disposal. Existing structures have been utilized where possible to minimize capital cost. Digestion plant operational data for the three works are given, and an evaluation is made of cost savings resulting from the post-digestion thickening process.     

Loss of productive soil

Physical properties of activated sludge flocs, especially settling and dewatering properties, are very important for efficient and economical treatment of wastewaters in activated sludge systems.

The physiological and biochemical nature of activated sludge flocs and hence the settling and dewatering properties are greatly affected by the temperature and pH of the aeration basin. Therefore, in this study the effects of temperature and pH on the physical properties (settleability, filterability and compressibility) of activated sludge were investigated.

From the results it was observed that, as the operating temperatures of the reactors were increased, zone settling velocities decreased, whereas sludge volume indices and specific resistance to filtration values increased. Up to 25°C sludges showed low compressibilities. However, they became highly compressible by the increase in temperature after 25°C.

On the other hand, with the increase of the pH of the reactor zone settling velocities, specific resistance to filtration values and compressibility coefficients increased, whereas sludge volume indices decreased.     

Treatment and Disposal of Municipal Sludge in The Netherlands

This paper reviews the sludge treatment and disposal operation in The Netherlands where the total volume of sludge is increasing and the sales potential is falling due to stringent quality requirements. The sludge can no longer be recycled to agriculture and has to be dumped on land. The techniques available for this purpose make sludge disposal much more expensive.
A meticulous analysis of the entire sludge chain seems to be necessary to control the costs and minimize the environmental impact, and a start has recently been made on the formulation of ideas in this context.     

影响污泥深度机械压力脱水因素的探讨

根据污泥处理处置技术在实际应用中存在的缺陷,指出污泥的深度脱水是污泥处理处置的关键环节。因此,污泥深度脱水技术面临着巨大的技术需求和市场需求。介绍了污泥深度脱水性能的表征方法,指出模拟恒压压滤脱水后泥饼的含水率能够较好地表征污泥深度脱水性能。同时,从污泥性质、调理剂预处理、过滤压力及操作、过滤介质等方面分析了污泥深度机械压力脱水的影响因素。     

重庆市城市污水厂污泥处理处置规划及有关问题

对重庆市城市污水厂污泥处理处置规划进行了简要介绍,对规划目标的确定、污泥产率指数的确定方法、污泥处理处置技术路线的选定、污泥处理处置管理体制等进行了探讨.     

Clear model fluids to emulate the rheological properties of thickened digested sludge

Optimising flow processes in wastewater treatment plants requires that designers and operators take into account the flow properties of the sludge. Moreover, due to increasingly more stringent conditions on final disposal avenues such as landfill, composting, incineration etc., practitioners need to produce safer sludge in smaller quantities. Anaerobic digestion is a key treatment process for solids treatment and pathogen reduction. Due to the inherent opacity of sludge, it is impossible to visualise the mixing and flow patterns inside an anaerobic digester. Therefore, choosing an appropriate transparent model fluid which can mimic the rheological behaviour of sludge is imperative for visualisation of the hydrodynamic functioning of an anaerobic digester.Digested sludge is a complex material with time dependent non-Newtonian thixotropic characteristics. In steady state, it can be modelled by a basic power-law. However, for short-time processes the Herschel-Bulkley model can be used to model liquid-like properties.The objective of this study was to identify transparent model fluids which will mimic the behaviour of real sludge. A comparison of three model fluids, Carboxymethyl Cellulose (CMC), Carbopol gel and Laponite clay revealed that these fluids could each model certain aspects of sludge behaviour. It is concluded that the rheological behaviour of sludge can be modelled using CMC in steady state flow at high shear rates, Carbopol gel for short-time flow processes and Laponite clay suspension where time dependence is dominant.     

城市有机质废弃物的生物质能源回收技术与工程案例

我国未经有效处理的城市污水厂剩余污泥和有机质废弃物产生量巨大,对环境造成了巨大威胁,因此提出污泥和城市有机质废物厌氧共发酵工艺。该工艺尽可能回收生物质能源并对生物质进行资源化利用,不仅能解决城市污泥和有机质废弃物的出路问题,而且对于缓解当前我国能源短缺和土壤矿化问题起到重要作用。简要介绍了厌氧消化的典型工艺流程、优势、工程应用的影响因素及国内外的进展与案例分析。综合以上分析可知,该工艺是获得生物质能源的有效方式,技术上具有可行性,是实现环境效益、社会效益和经济效益统一的有效途径。     

The effect of temperature control on biological wastewater treatment processes

A model has been developed to simulate the effect of temperature control on the performance of a completely mixed activated sludge wastewater treatment system. From calculations based on the model it is demonstrated that effluent quality is significantly improved for any increase in temperature from 10° to 30°C, irrespective of solids retention time (SRT) and sludge settling characteristics. A trade-off exists concerning the effects of temperature on the sludge disposal and oxygen requirements of the system. Although any increase in temperature above 20°C will significantly reduce the sludge production rate, it will also contribute to increased air flow power requirements. The results suggest that a suitable compromise may be reached with a temperature between 23 and 27°C and an SRT between 8 and 14 days.     

Thermal Treatment and Ultimate Disposal of Sewage Sludge in Japan

The shortage of land together with heavy industrialization in Japan makes incineration, and its associated process of sludge melting, favoured methods for the disposal of sewage sludge. The technology used in Japan for thermal drying of sludge and sludge incineration is similar to that used in other industrialized countries. The sludge melting processes which are used in a few installations are unusual. Most of the ash or slag which is produced from the burning of sewage sludge is disposed of by landfill, although an increasing amount of ash and slag is being disposed of by incorporation into construction materials.