Phosphorus recycling in sewage treatment plants with biological phosphorus removal.

In this paper, phosphorus balances are calculated for the wastewater purification and sludge treatment stages for wastewater treatment plants (WWTPs) applying Enhanced Biological Phosphorus Removal (EBPR). The possible P-recovery potential is then estimated and evaluated regarding different locations along the process of wastewater purification and sludge treatment, taking the different phosphorus bonding forms into account. Caused by the more favourable bonding forms in the excess sludge as well as possibly also in the sludge ash a recovery of the phosphorus seems especially favoured for WWTPs with EBPR. The processes available for a P recycling are named, and special regard is given to the Phostrip-process, which is a possible recycling process already tested in practice. Further R&D demand consists in basic research regarding disintegration, fermentation or acidic total digestion of excess sludge followed by phosphorus precipitation including separation of the precipitates, MAP-precipitation and separation from digested sludge and on the ability to extract phosphorus and heavy metals from sewage sludge ash. These investigations are a precondition to enable purposeful process developments. At the present state the cost of recycled phosphorus earned from wastewater, sludge and ash, respectively, are a multiple higher than the costs for raw phosphate taking into account the suitable processes. Thus, up to now no phosphorus recycling with a defrayal of costs is possible. The future importance of phosphorus recycling will depend on the market price for raw phosphate, the recycling costs and, furthermore, on the general political framework.     

Vergleich von Verfahren zur Rückgewinnung von Phosphor aus Abwasser und Klärschlamm

Phosphorus (P) is a vital but limited resource. Though Austria has no P deposits, municipal wastewater offers a potential but largely overlooked source of phosphorus. Over the last several years, numerous technologies have been developed for recovering P from various streams at a wastewater treatment plant. This work uses an approach developed by the authors to assess these technologies on the basis of technical, ecological and economic criteria, providing a basis that legislators and political decision-makers can orient a future, optimized P management system on. The study shows that e.g. technologies for recovering P from process water are already available, and that under the right circumstances they can be used to affordably deliver a high-purity, plant-available end product; however, the potential for P recovery is relatively low. In order to arrive at maximal utilization of the phosphorus from wastewater, the future focus should be on recovery from sewage sludge ash. In this regard, mixing with low-phosphorus ash should be avoided. At this time, however, the necessary structures like e.g. monoincineration plants still need to be expanded. Which technology/ technologies will ultimately be used for the treatment of sewage sludge ash depends e.g. on considerations of affordability, heavy metal elimination, and the plant-availability of the P recovered. The advantages of a strategy based on “monocombustion” of sewage sludge are on the one hand the option of using further P-rich material flows (e.g. meat and bone meal) and on the other, the freedom to store the ash for future recovery (creating an Austrian “phosphate mine”).     

Recovery of phosphorus and aluminium from sewage sludge ash by a new wet chemical elution process (SESAL-Phos-recovery process)

The potential of a new wet chemical process for phosphorus and aluminium recovery from sewage sludge ash by sequential elution with acidic and alkaline solutions has been investigated: SESAL-Phos (sequential elution of sewage sludge ash for aluminium and phosphorus recovery). Its most innovative aspect is an acidic pre-treatment step in which calcium is leached from the sewage sludge ash. Thus the percentage of alkaline soluble aluminium phosphates is increased from 20 to 67%. This aluminium phosphate is then dissolved in alkali. Subsequently, the dissolved phosphorus is precipitated as calcium phosphate with low heavy metal content and recovered from the alkaline solution. Dissolved aluminium is recovered and may be reused as a precipitant in wastewater treatment plants.     

城市污水处理厂污泥热值及影响因素分析

以重庆市主城区城市污水处理厂污泥为研究对象,测定了污泥的热值并分析了影响污泥热值的主要因素,探讨了水分对热值利用的影响。结果表明:元素分析法和量热仪法测定的污泥热值较吻合;污水水质、排水体制、污水及污泥处理工艺通过影响污泥挥发分的含量而影响污泥热值,建议消化污泥和合流制区域污水处理厂污泥不宜采用焚烧处理。污水处理厂污泥具有自持燃烧特性时的最高含水率为68%;通过元素分析发现,不同污水处理厂污泥挥发分元素的计量组成基本一致,可用计量化学式CH1.72O0.55N0.12S0.03粗略地表示重庆市主城区污水处理厂污泥挥发分的组成。     

Potentials of using nanofiltration to recover phosphorus from sewage sludge.

Due to the depletion of mineral phosphorus resources there is an increasing demand for efficient phosphorus recovery technologies. In this study the potential of nanofiltration to recover phosphorus from pre-treated sewage sludge is investigated. The efficiency of three commercial nanofiltration membranes (Desal 5DK, NP030; MPF34) was tested using model solutions. Desal 5DK showed the best selectivity for phosphorus. A pH of lower than 1.5 was found to be most suitable. Desal 5DK was used on four different sewage sludge ash eluates and on one sewage sludge. In these experiments it was shown that a separation of phosphorus from undesired components such as heavy metals was possible with significant variations in the efficiency for the different ash and sludge types. Additionally the achievable product recovery was investigated with model solutions. A product recovery of 57.1% was attained for pH 1 and 41.4% for pH 1.5.     

Phosphor: Eine kritische und zugleich unzureichend genutzte Ressource der Abwasser- und Abfallwirtschaft – Stand des Wissens und Ausblick für Österreich und Europa

Currently, the phosphorus (P) used in Austria is essentially of a linear structure. Cyclical ring structures—with the exception of those in manure (slurry, dung) used for local agricultural purposes—are as yet rudimentary. Simultaneously, Austria is entirely dependent on imports of the raw material rock phosphate, partly from geopolitically unstable regions. In contrast, sewage and animal meat and bone meal as significant sources of P are largely ignored. In view of the importance of P, numerous technologies for targeted P recycling from sewage have been developed—some already operational from a purely technical perspective and others already implemented on an industrial scale (particularly, recycling from the liquid phase). In order to make the best possible use of sewage-borne P, recycling from pure sewage sludge or animal meat and bone meal ash combined with sewage sludge ash would be desirable in future. Necessary structures, such as incinerators for sewage sludge alone or in combination with animal meat and bone meal, however, have yet to be developed. In addition to newly developed methods, recyclates (materials that are recyclable) from recycling processes (e.g., struvite), pure sewage sludge ash or animal meat and bone meal ash can be used as secondary raw materials in existing industrial processes, for instance, in the fertilizer or phosphoric acid industries. Neighboring countries Germany and Switzerland already recycle P from sewage sludge and sewage sludge ash to legally binding targets. Implementation in Austria too would initially require (political) commitment and, consequently, changes in the legal framework (e.g., fertilizer legislation) as well as binding standards. Implementation instruments for P recycling could be, for instance: defined recycling quotas for the fertilizer industry (e.g., “Pxx”, according to the E10 bioethanol quota); or levying “phosphorus cents” additional to the sewage treatment and waste management fees, to be used to develop the necessary structures (e.g., incinerators for sewage sludge and animal meal).     

Experience with phosphorus removal and sludge handling and disposal in Flanders.

The way excess sludge must be disposed of is a key factor in the choice of the appropriate phosphorus removal technique at municipal wastewater treatment plants. In Europe the ongoing trend of tightening the sludge spreading rules called for a serious reduction of its agricultural utilisation and the expansion of the (co-)incineration disposal route, which led to a shift towards more sophisticated sludge handling techniques. This paper illustrates the impact of different sludge handling techniques on the performance of chemical and enhanced biological phosphorus removal at municipal WWTPs. The main conclusion is that although enhanced biological phosphorus removal is particularly sensitive to the problem of return liquors from sludge treatment processes indirect dewatering and anaerobic stabilisation cannot be discarded altogether when considering its implementation.     

Evaluating the stabilisation degree of digested sewage sludge: investigations at four municipal wastewater treatment plants.

Further reduction of volatile suspended solids (VSS) during a post-stabilisation step was applied to evaluate the stabilisation degree of digested sewage sludge. For this purpose digested sludge was collected at four municipal wastewater treatment plants (WWTPs) and further stabilised in lab-scale chemostat reactors either under anaerobic or aerobic conditions. Experimental results showed that even in adequately digested sludge a consistent amount of VSS was degraded during aerobic post-stabilisation. It seems that aerobic conditions play a significant role during degradation of residual VSS. Additionally, specific VSS production (gVSS/peCOD110.d) as well as specific oxygen uptake rate were shown to be suitable parameters to assess the degree of sludge stabilisation at WWTPs. Fourier transform infrared spectroscopy was used to reveal changes in the sludge composition. Spectra of treated and untreated sludge samples indicated that the major component of residual VSS in stabilised sludge for instance consisted of biomass, while cellulose was absent.     

Can a wastewater treatment plant be a powerplant? A case study

Today wastewater treatment plants are evaluated not only in terms of their treatment efficiency but also concerning their energy efficiency. Increasing energy efficiency can be realized either through operational optimisation or by realising an already existing potential for energy generation on-site. The main source of energy at a municipal wastewater treatment plant is the biogas produced in the anaerobic sludge digester. Studies indicate excess digester capacities of about 20% in Germany available for co-fermentation of organic substrates other than sewage sludge. This paper presents an example of a municipal wastewater treatment plant going towards an energy self-sufficient operation and even a surplus energy production as the result of an increasing co-fermentation of sludge from grease skimming tanks. In 2005 on average 113% of the electricity consumed for plant operation was generated on-site in gas engines. Co-fermentation of about 30% (related to the total dry residue input) of grease interceptor sludge in the presented case does not only effect a 4-times increased gas yield, but also an intensified 20% higher anaerobic degradation of the organic matter of the sewage sludge and thus having a positive influence not only on the energy and financial balance but also on the anaerobic sludge stabilisation with respect to the degradation degree of the organic fraction.     

An investigation of agricultural use potential of wastewater sludges in Turkey--case of heavy metals.

Landfilling is one of the most common methods that are used in the final disposal of sludge world wide, as well as in Turkey. However, increasing sludge quantities and limited landfilling areas make this method difficult to apply. The use of sludge in agriculture presents a possible alternative for disposal. However, it also poses some risks to be evaluated. In this respect, it is important to identify the heavy metal content of sewage sludges because of its adverse health effects. This study aims to determine the heavy metal contents of sludges and wastewaters from three different wastewater treatment plants in Turkey. The selection of plants was carried out according to the different treatment technologies applied to wastewater and sludge in those plants. Heavy metal analysis of sludges and wastewaters was conducted using a microwave assisted digestion procedure. After sampling and analysis, the results show that all the related metal concentrations are below the values that are set in the Soil Pollution Control Regulation of Turkey. However, in two of the three plants, Zn and Ni concentration should be tracked carefully.     

污泥堆肥土地利用对土壤环境及高羊茅特性的影响

结合北京市污泥堆肥土地利用现状．研究了污泥堆肥对土壤环境及高羊茅（Festuca arundinace。）的影响。旨在为北京市污泥堆肥用于高羊茅园林生产提供理论依据,促进资源再利用。研究结果表明．施用污泥堆肥增加了高羊茅栽植小区土壤养分含量,特别是土壤中有机质含量增加明显,与空白对照相比增加了43．9％～73．2％,对土壤养分状况具有一定的改良效果;施用污泥堆肥后,高羊茅栽植小区土壤中重金属含量虽有不同程度的增加。但均远低于相关标准限值．且土壤重金属污染综合指数小于土壤安全限值0．7．表明种植小区土壤未受到重金属污染：施用污泥堆肥对高羊茅生长具有一定的促进作用．与空白对照相比．高羊茅总生物量增长率为16．7％～50．0％。综合分析试验结果,确定污泥堆肥用于高羊茅的适宜施用量为2kg／m^2。     

城市污泥资源化利用现状及发展探讨

随着城市污泥产量连年增长,污泥处理问题迫在眉睫。由于用地日益紧张和潜在的环境污染问题,传统的处置方法如填埋已经不符合发展要求。作为污水处理厂的伴生产物,污泥含有大量有机物、氮、磷等营养物质,经过适当处理,可以变废为宝。因此,资源化利用是解决污泥问题的主要发展趋势。通过分析国内外城市污泥的处置现状,对污泥资源化技术进行了分类,并就污泥在土地利用、建材利用、能源利用和其他方面的应用进行了详细综述,同时还分析了资源化利用存在的问题,指出污泥资源化利用和发展需要因地制宜、合理开发,需要继续提高工艺水平,推进技术创新,完善政策法规。     

Extraction efficiency of phosphate from pre-coagulated sludge with NaHS.

The recovery of phosphorus from sewage and sludge treatment systems is particularly important because it is a limited resource and a large proportion of the phosphorus currently used in Japan must be imported. We have been experimentally evaluating recovery methods with sulphide. In this study, we focussed on the extraction of phosphate from the sludge, and sought to achieve a greater extraction efficiency and to validate the extraction mechanism. We conducted three experiments, i.e. a sludge-type experiment, a coagulant ratio of pre-coagulated sludge experiment, and a concentration of pre-coagulated sludge experiment. Phosphate was extracted not with normal sewage sludge but with pre-coagulated sludge and FePO4 reagent at S/Fe = 1.0-2.0. A coagulant ratio of 23mg Fe L(-1) was required in the precoagulation process to effectively extract phosphate. A high concentration of pre-coagulated sludge was required for the phosphate extraction. The mass balance was calculated, and 44.0% of phosphorus was extracted to supernatant, and 98.5% of iron and 98.3% of sulphur (44.1% of sulphur was sulphide). Thus, phosphate can be selectively separated from iron by the phosphate extraction method with NaHS, and phosphorus and iron can be recovered and reused at sewage treatment plants using ferric chloride as a coagulant.     

Potentials and limits of anaerobic digestion of sewage sludge: energy self-sufficient municipal wastewater treatment plant?

Anaerobic digestion is the only energy-positive technology widely used in wastewater treatment. Full-scale data prove that the anaerobic digestion of sewage sludge can produce biogas that covers a substantial amount of the energy consumption of a wastewater treatment plant (WWTP). In this paper, we discuss possibilities for improving the digestion efficiency and biogas production from sewage sludge. Typical specific energy consumptions of municipal WWTPs per population equivalent are compared with the potential specific production of biogas to find the required/optimal digestion efficiency. Examples of technological measures to achieve such efficiency are presented. Our findings show that even a municipal WWTP with secondary biological treatment located in a moderate climate can come close to energy self-sufficiency. However, they also show that such self-sufficiency is dependent on: (i) the strict optimization of the total energy consumption of the plant, and (ii) an increase in the specific biogas production from sewage sludge to values around 600 L per kg of supplied volatile solids.     

Resource recovery from excess sludge by subcritical water combined with magnesium ammonium phosphate process.

The amount of excess sludge produced in municipal wastewater treatment plants in Japan is increasing every year as the urban population increases. Phosphorus in excess sludge could be a potential phosphorus resource since at present, phosphate rock is being exhausted all over the world. Every year, Japan imports large quantities of phosphorus from abroad but much is discharged as excess sludge. Therefore, the solubilization process, one method of recovering phosphorus from sludge, could be a promising solution. In this study, a subcritical water process, a new technology that solubilizes sludge under subcritical conditions, was applied before the phosphorus in sludge was recovered with the magnesium ammonium phosphate (MAP) process. As a result, the solubilization rate of excess sludge achieved approximately 80% and about 94-97% of the phosphorus could be recovered.     

Dutch analysis for P-recovery from municipal wastewater.

There is a considerable practical interest in phosphorus recovery from water authorities, elementary P-industry, fertilizer industry and regulators in a number of countries. Due to a handful of full-scale plants worldwide, P-recovery can be seen as technically feasible. However, the economic feasibility of P-recovery from sewage can still be judged as dubious. The most important reason for this is that the prices of the techniques (in euro/tonne P) are much higher compared to the prices of phosphate rock. In this paper an analysis is given to recover phosphate from municipal wastewater for the elementary P-industry Thermphos International B.V. and the fertiliser industry Amsterdam Fertilizers B.V. in The Netherlands. Several scenarios are evaluated and the end products of these scenarios are compared to the quality required by both industries. From a Dutch study it became clear that all end products from the final sludge treatment do not provide a good source of secondary phosphate. As a consequence of this, the most preferred possibility for P-recovery is to extract phosphate before sludge goes to the final sludge treatment. Different scenarios can be selected based on the position of P-recovery in the WWTP configuration, the type of P-recovery product, and the precipitation technique. Local conditions will determine which scenario is the most expedient. Because it is more realistic to judge a practical situation instead of theoretical estimations based on literature, some local situations have to be assessed in sufficient detail to gain more feeling for the expenses and possible savings of P-recovery. One important actor that should be involved in the process management around P-recovery, is the national government. Especially, the Government have the responsibility for sustainable development and should have attention for some stimulation of P-recovery in The Netherlands. Water authorities and the P- and fertilizer industry made already some good steps.     

Municipal sludge management and disposal in South Korea: status and a new sustainable approach.

Based on figures from 2002, 5216 ton/d of the municipal sludge is produced from 184 large municipal wastewater treatment plants in 111 cities with total treatment capacity of 19,229,745 m3/d. Even though the large amount of sludge disposal has depended greatly on ocean disposal and landfills until recently, the fraction of sludge reuse has gradually increased from 2.7% to 7%, since 1991. Due to a need of resources recovery from the sludge, high cost requirement of incineration and legislative regulation, recent new research is mainly focused on resources recovery and its reuse from the municipal sludge, such as high performance acid fermenter with pathogen reduction, crystallization (struvite and hydroxyapatite) using waste lime, cofermentation of municipal sludge with food waste, aerobic composting with P crystallization, vermistabilization, lime treatment, etc. Current research and practical activities with some efforts for the new technical development as well as environmental law and regulation are reviewed.     

生物接触氧化流化床处理氨氮污水的实验研究

为了提高生物接触氧化流化床处理氨氮污水的脱氮效果,采用生物接触氧化流化床在自然温度下处理人工配制模拟生活污水实验的方法,研究了氨氮污水脱氮处理的可行性、方法与效果。实验结果表明:氨氮被氧化成硝酸可由两类独立的细菌分别催化完成;反应的适宜温度为20~35℃;亚硝酸菌的最适pH值为7~8.5之间,硝酸菌为6~7.5;亚硝酸菌和硝酸菌溶解氧质量浓度在0.5 mg/L以上才能取得较好的硝化效果。反应器内填料粒径在10 mm左右有利于提高氨氮的去除效率;间歇式进水方式使活性污泥具有良好的沉降性,可为氨氮的去除提供良好的环境条件。     

Anaerobic co-digestion of sludge with other organic wastes and phosphorus reclamation in wastewater treatment plants for biological nutrients removal.

This paper deals with the performances obtained in full scale anaerobic digesters co-digesting waste activated sludge from biological nutrients removal wastewater treatment plants, together with different types of organic wastes (solid and liquid). Results showed that the biogas production can be increased from 4000 to some 18,000 m3 per month when treating some 3-5 tons per day of organic municipal solid waste together with waste activated sludge. On the other hand, the specific biogas production was improved, passing from 0.3 to 0.5 m3 per kgVS fed the reactor, when treating liquid effluents from cheese factories. The addition of the co-substrates gave minimal increases in the organic loading rate while the hydraulic retention time remained constant. Further, the potentiality of the struvite crystallisation process for treating anaerobic supernatant rich in nitrogen and phosphorus was studied: 80% removal of phosphorus was observed in all the tested conditions. In conclusion, a possible layout is proposed for designing or upgrading wastewater treatment plants for biological nutrients removal process.     

EGSB反应器的启动运行研究

采用两个小试规模的EGSB(ExpandedGranularSludgeBed)反应器 ,分别接种厌氧絮状污泥和颗粒污泥来研究其启动规律。试验结果表明 ,接种厌氧絮状污泥的R1反应器 ,由于出水循环的采用导致严重的污泥流失 ,首先应按UASB反应器的运行方式培养出颗粒污泥后 ,再按EGSB反应器方式运行 ,共需 78d才能完成启动 ;接种厌氧颗粒污泥的R2反应器 ,采用适宜的回流比有利于细菌的生长和反应器运行效果的改善 ,在经过短暂的无回流驯化后 ,即可按EGSB运行方式启动运行 ,仅需 32d即完成启动。