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.     

Phosphorus removal using nanofiltration membranes

A high concentration of phosphorus in wastewater may lead to excessive algae growth and deoxygenation of the water. In this work, nanofiltration (NF) of phosphorus-rich solutions is studied in order to investigate its potential in removing and recycling phosphorus. Wastewater samples from a pulp and paper plant were first analyzed. Commercial membranes (DK5, MPF34, NF90, NF270, NF200) were characterized and tested in permeability and phosphorus removal experiments. NF90 membranes offer the highest rejection of phosphorus; a rejection of more than 70% phosphorus was achieved for a feed containing 2.5 g/L of phosphorus at a pH <2. Additionally, NF90, NF200 and NF270 membranes show higher permeability than DK5 and MPF34 membranes. The separation performance of NF90 is slightly affected by phosphorus concentration and pressure, which may be due to concentration polarization and fouling. By adjusting the pH to 2 or adding sulfuric acid, the separation performance of NF90 was improved in removing phosphorus. However, the presence of acetic acid significantly impairs the rejection of phosphorus.     

Towards a complete recycling of phosphorus in wastewater treatment--options in Germany

Global reserves of mineral phosphorus are finite and the recycling of phosphorus from wastewater, a significant sink for phosphorus, can contribute to a more sustainable use. In Germany, Switzerland, and the Netherlands, an increasing percentage of municipal sewage sludge is incinerated and the contained phosphorus is lost. This paper reviews current technologies and shows that a complete phosphorus recovery from wastewater is technically feasible. Depending on the composition of the sewage sludge ash (SSA), there are various options for phosphorus recovery that are presented. Iron-poor SSAs can be used directly as substitute for phosphate rock in the electrothermal phosphorus process. SSAs with low heavy metal contents can be used as fertilizer without prior metal elimination. Ashes not suitable for direct recycling can be processed by thermal processes. Operators of wastewater treatment plants can additionally influence the ash composition via the selection of precipitants and the control of (indirect) dischargers. This way, they can choose the most suitable phosphorus recovery option. For sewage sludge that is co-incinerated in power plants, municipal waste incinerators or cement kilns phosphorus recovery is not possible. The phosphorus is lost forever.     

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.     

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”).     

Operation of a new sewage treatment process with technologies of excess sludge reduction and phosphorus recovery.

This paper shows the potential application of a new sewage treatment process with technologies of excess sludge reduction and phosphorus recovery. The process incorporated ozonation for excess sludge reduction and crystallisation process for phosphorus recovery to a conventional anaerobic/oxic (A/O) phosphorus removal process. A lab-scale continuous operation experiment was conducted with the ratio of sludge flow rate to ozonation tank of 1.1% of sewage inflow under 30 to 40 mgO3/gSS of ozone consumption and with sludge wasting ratio of 0.34% (one-fifth of a conventional A/O process). Throughout the operational experiment, a 60% reduction of excess sludge production was achieved in the new process. A biomass concentration of 2300 mg/L was maintained, and the accumulation of inactive biomass was not observed. The new process was estimated to give a phosphorus recovery degree of more than 70% as an advantage of excess sludge reduction. The slight increase in effluent COD was observed, but the process performance was maintained at a satisfactory level. These facts demonstrate an effectiveness of the new process for excess sludge reduction as well as for phosphorus recovery.     

Development of a process for the recovery of phosphorus resource from digested sludge by crystallization technology.

Removal and recovery of phosphorus from sewage in form of MAP (magnesium ammonium phosphate) have attracted attention from the viewpoint of eutrophication prevention and phosphorus resource recovery as well as scaling prevention inside digestion tanks. In this work, phosphorus recovery demonstration tests were conducted in a 50 m3/d facility having a complete mixing type reactor and a liquid cyclone. Digested sludge, having 690 mg/L T-P and 268 mg/L PO4-P, was used as test material. The T-P and PO4-P of treated sludge were 464 mg/L and 20 mg/L achieving a T-P recovery efficiency of 33% and a PO4-P crystallization ratio of 93%. The reacted phosphorus did not become fine crystals and the recovered MAP particles were found to be valuable as a fertilizer. A case study in applying this phosphorus recovery process for treatment of sludge from an anaerobic-aerobic process of a 21,000 m3/d sewage system, showed that 30% of phosphorus concentration can be reduced in the final effluent, recovering 315 kg/d as MAP.     

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.     

Enhanced heavy metals removal without phosphorus loss from anaerobically digested sewage sludge

Heavy metals removal without phosphorus loss from anaerobically digested sewage sludge was investigated by conducting batch experiments using hydrogen peroxide and/or iron sulphate under acidified conditions at pH 3. The addition of hydrogen peroxide to the sludge improved the elution efficiencies of As, Cd, Cu and Zn with phosphorus loss from the sludge. The optimum initial concentrations of hydrogen peroxide were. Respectively. 0.1% for As, Cd, Mn and Zn and 0.5% for Cu and Ni. The combined process of 0.1% hydrogen peroxide and 1 g Fe/L ferric sulphate enhanced the initial elution rate of Cu and Cr compared to the addition of either ferric sulphate or hydrogen peroxide, indicating that oxidants stronger than hydrogen peroxide were produced in the sludge. Furthermore, the combined process immobilised phosphorus in the sludge due to co-precipitation with ferric hydroxide or precipitation as ferric phosphate. It was concluded that there is a possibility that the combined process could remove heavy metals effectively without phosphorus loss from anaerobically digested sewage sludge.     

羟基磷酸钙结晶法回收大型水生植物发酵液中磷酸盐研究

为有效回收大型水生植物发酵液中磷,选择挺水植物西伯利亚鸢尾(Iris sibirica L.)和圆币草(Hydrocotyle vulgaris)进行发酵试验,分析不同pH值下发酵液中磷回收的效率和纯度,探索羟基磷酸钙(hydroxyapatite,HAP)结晶法回收水生植物发酵液中磷酸盐的可能性。结果表明:西伯利亚鸢尾和圆币草发酵液中钙磷摩尔数比分别为2.7和10,镁磷比分别为1.4和1.6,适合采用HAP法回收磷酸盐。不同水生植物发酵液调节pH值回收磷曲线相似,在pH为8.5时西伯利亚鸢尾和圆币草发酵液磷酸盐回收率分别达到89%和91%,产生的羟基磷酸钙沉降性能良好。X射线荧光光谱分析分析结果表明pH为8.5时沉淀物中P2O5质量分数超过25%,羟基磷酸钙为主要成分。pH调节超过8.5后沉淀物中碳酸钙含量会随着pH上升而不断增加,影响羟基磷酸钙的纯度,因此,回收磷酸盐适合的pH值为8.5。     

Energy and nutrient recovery from sewage sludge via pyrolysis.

Energy recovery and nutrient reuse from sewage sludge has traditionally been achieved via anaerobic digestion/power generation with land application of the biosolids. By contrast, thermal processes such as pyrolysis have typically been used only for energy recovery. One such technology has demonstrated at commercial scale that all of the energy in sludge can be beneficially recovered and reused. No attempt was however made to recover and reuse sludge nutrients. There are many potential benefits of using pyrolysis for both energy and nutrient recovery. Firstly, unlike digestion, the principal energy product is oil, which can readily be stored and used when required, ensuring that energy recovery is maximised. Secondly is that the sludge nutrients are recovered in the pyrolysis char. Laboratory soil incubation studies using char from the Subiaco demonstration plant were conducted over an eight-week period to confirm nutrient availability. Results from this study showed that the phosphorus in the char is plant available although the nitrogen was insoluble. Based on these results it appears that there is potential to use pyrolysis as an effective means to recover and reuse both the energy and the very valuable phosphorus present in sewage sludges.     

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).     

Evaluation of sludge reduction and phosphorus recovery efficiencies in a new advanced wastewater treatment system using denitrifying polyphosphate accumulating organisms.

A new biological nutrient removal process, anaerobic-oxic-anoxic (A/O/A) system using denitrifying polyphosphate-accumulating organisms (DNPAOs), was proposed. To attain excess sludge reduction and phosphorus recovery, the A/O/A system equipped with ozonation tank and phosphorus adsorption column was operated for 92 days, and water quality of the effluent, sludge reduction efficiency, and phosphorus recovery efficiency were evaluated. As a result, TOC, T-N and T-P removal efficiency were 85%, 70% and 85%, respectively, throughout the operating period. These slightly lower removal efficiencies than conventional anaerobic-anoxic-oxic (A/A/O) processes were due to the unexpected microbial population in this system where DNPAOs were not the dominant group but normal polyphosphate-accumulating organisms (PAOs) that could not utilize nitrate and nitrite as electron acceptor became dominant. However, it was successfully demonstrated that 34-127% of sludge reduction and around 80% of phosphorus recovery were attained. In conclusion, the A/O/A system equipped with ozonation and phosphorus adsorption systems is useful as a new advanced wastewater treatment plant (WWTP) to resolve the problems of increasing excess sludge and depleted phosphorus.     

Biotechnology of intensive aerobic conversion of sewage sludge and food waste into fertilizer.

Biotechnology for intensive aerobic bioconversion of sewage sludge and food waste into fertilizer was developed. The wastes were treated in a closed reactor under controlled aeration, stirring, pH, and temperature at 60 degrees C, after addition of starter bacterial culture Bacillus thermoamylovorans. The biodegradation of sewage sludge was studied by decrease of volatile solids (VS), content of organic carbon and autofluorescence of coenzyme F420. The degradation of anaerobic biomass was faster than biodegradation of total organic matter. The best fertilizer was obtained when sewage sludge was thermally pre-treated, mixed with food waste, chalk, and artificial bulking agent. The content of volatile solid and the content of organic carbon decreased at 24.8% and 13.5% of total solids, respectively, during ten days of bioconversion. The fertilizer was a powder with moisture content of 5%. It was stable, and not toxic for the germination of plant seeds. Addition of 1.0 to 1.5% of this fertilizer to the subsoil increased the growth of different plants tested by 113 to 164%. The biotechnology can be applied in larger scale for the recycling of sewage sludge and food wastes in Singapore.     

Ultrafiltration and nanofiltration in the pulp and paper industry using cross-rotational (CR) filters.

Ultra- and nanofiltration with high shear CR-filters have been utilized for cleaning of clear filtrates and effluents from the pulp and paper industry. The aim was to find out how different nanofiltration membranes operate at high shear conditions. The filtration efficiency of the membranes was evaluated by measuring flux, retention and fouling at various recovery and pH conditions. High fluxes (approximately 100 L/(m2h)) for nanofiltration membranes were measured when circulation waters from the paper machine were filtered at neutral conditions. In the filtration of discharge of external activated sludge treatment plants we measured fluxes around 150 L/(m2h) even at a concentration factor of 12. The best NF membranes removed over 80% of the organic carbon and of the conductivity and almost completely eliminated the color. With acidic waters fluxes and retentions were significantly lower. The NF270 membrane from Dow and the Desal-5 membranes from Osmonics had the highest flux and retention properties. However, the Desal-5 membrane lost its retention properties slowly, which restricts its use in the high shear CR-filter. CR-nanofiltration can be used in the pulp and paper industry without feed pre-treatment by ultrafiltration. This increases the attractiveness of high shear CR-nanofiltration.     

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。     

The effects of nano-materials on the behaviors of sludge mortar specimens.

In this research, nano-composites are added to sewage sludge ash to create a mixture, which then replaces part of cement. Nano-composites are manufactured from pure quartzose sand. The influences of different amounts of nano-composites and sludge ash on mortar are evaluated. Cement, sludge ash (0%, 10%, and 20%), and nano-composites (0%, 0.5%, 1%, 2%, and 3%), which defined as the percent weight of cement and sludge ash, are mixed together in batches to make mortar specimens. Results show that the flowability of sludge ash mortar reduces with increasing amount of cement replaced and of nano-composites added. The compressive strength of mortar lowers when more amounts of cement are replaced by sludge ash, but increases with more quantity of nano-composites added. Moreover, the study shows that nano-composites can fortify the compressive strength of mortar. With the help of efficiency of compressive strength, nano-composites benefit most to the mortar with replacement of 10% sludge ash, followed by the substitution of 20% and 0%.     

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。     

Rethinking sewage treatment by enhancing primary settling with low-dosage lime.

This work presents a thorough fractionation of COD in raw sewage, followed by pilot plant coagulation tests with low-dosage lime (pH 9). Through a physical separation (sieving and crossflow filtration) total COD in the raw sewage was partitioned among eight size fractions in the range of 150-0.02 microm. In addition, respirometric tests were performed to measure the biodegradability of the different size fractions. More than 60% of COD was associated with settleable and supracolloidal particles (size > 1 microm), which are characterised by slow biodegradability. Coagulation with lime increased COD removal efficiencies in the primary treatment from typical 30-35%, up to 65-70%, suggesting that lime may induce the almost complete removal of the slowly settling, slowly biodegradable supracolloidal particles in the primary treatment. On the basis of these results a non-conventional sewage treatment scheme is proposed, considering that there is plenty of space for improving primary treatment efficiency through sewage coagulation. Higher primary treatment efficiency may present several advantages, including lower aeration energy in the subsequent biological unit and higher energy recovery from sludge digestion.     

Performance of membrane-coupled organic acid fermentor for the resources recovery form municipal sewage sludge.

This study focused on the treatment performance of membrane-coupled organic acid fermentor (MOF) with intermittent reciprocal air/ozone backwashing for the keeping of high permeation flux as well as for the effective recovery of dissolved organics from municipal sewage sludge. Intermittent reciprocal air/ozone backwashing was effective for membrane fouling reduction. When MOF was operated under the conditions of pH 5.5, hydraulic retention time (HRT) of 2 days and 20 days of solids retention time (SRT), most favourable fermentation efficiency was attained. Great inhibition for acid producing by intermittent reciprocal air/ozone backwashing was not observed during long-term operation. MOF with intermittent reciprocal air/ozone backwashing is believed to be an effective system for the recovery of organic matter from municipal sewage sludge and membrane fouling reduction.