Acid-stimulated phosphate uptake by activated sludge microorganisms under aerobic laboratory conditions

Activated sludge inocula taken from five different wastewater treatment plants were grown aerobically under laboratory conditions on mineral salts medium containing either glucose or skimmed milk powder as carbon source. Cultures showed increases of between 50% and 143% in levels of phosphate uptake from the medium when the growth pH was 5.5 rather than 7.5. Of 100 individual sludge microbial isolates studied, 34 demonstrated such acid-stimulated luxury phosphate uptake; the optimum pH for the process was shown to lie between 5.0 and 6.5. Enhanced phosphate removal by these isolates was accompanied by increases of between 2 and 10.5-fold in their polyphosphate content; this was visualised as intracellular inclusions. Acid-stimulated luxury phosphate uptake by environmental microorganisms is a previously-unrecognised phenomenon that may have application in novel technologies for nutrient removal from wastewaters.     

可沉微藻对室外光照强度的适应性试验研究

在实验室条件下,通过"冲淘"压力可筛选出沉淀率高达97%的可沉微藻。可沉微藻像活性污泥一样在净化功能完成后可通过自然沉降实现藻-水分离,可为污水深度处理提供一种低耗、高效的解决方案。然而,实验室低光照[400μmol/(m²·s)]条件下获得的可沉微藻在真实自然光强度下是否依然可以不断生长繁殖并保持对氮、磷较高的去除率,这是一个工程应用必须面对的现实问题。为此,在实验室条件下增加光照强度至接近自然光水平[800μmol/(m²·s)],观察可沉微藻的生长情况。结果显示,高光照强度对可沉微藻具有抑制作用,使可沉微藻的生长繁殖严重受阻,并降低其光合作用活性(叶绿素a含量)。及时向反应器补充无机碳源CO₂后,可沉微藻经过一定适应期后可恢复生长,并可达到比低光照强度时还高的生物量及较高的氮、磷去除效果(90%以上)。另外,试验还考察了投加营养物硅酸盐、光/暗交替及进水模式对可沉微藻生长与净化性能的影响,结果显示出硅酸盐的双向性作用及光补充基质的优势。     

Foam Formation, Anaerobiosis and Microthrix Parvicella

Microscopic examinations of the sludges associated with two incidents of foam formation in anaerobic digesters are described. In both cases, the dominant filamentous species was Microthrix parvicella. Preliminary growth studies with this species indicated that it could grow in both aerobic and anaerobic environments, but that in an anaerobic regime it did not produce polyphosphate granules. This suggests that M. parvicella may be involved in the luxury uptake of phosphate and, under strict anaerobic conditions, could compete with acetoclastic methanogens for acetate.     

Luxury uptake of phosphorus by sediment bacteria

This note reports the results of experiments aimed at confirming the luxury uptake of phosphorus (P) by sediment bacteria as polyphosphate (Poly-P). Aerobic suspensions of sediments from two different sites were spiked with 1 mg P/L as orthophosphate and augmented with acetate (a fermentation product) or glucose. The orthophosphate was rapidly taken up over a period of a few hours. When these aerobic uptake experiments were made anaerobic and additional organic carbon added, only the acetate-amended sediment released a significant amount of the added phosphorus. It was hypothesised that during the aerobic stage, and with the addition of acetate, some of the phosphorus was accumulated as Poly-P by sediment microorganisms, which was released during the subsequent anaerobic stage (provided acetate was still present). Two lines of evidence--transmission electron microscope analysis of sediment bacteria and 31P-NMR analysis of sediment extracts--are presented to support the hypothesis that a portion of the phosphorus taken up during the aerobic experiments was stored as Poly-P.     

The arsenic for phosphorus swap is accidental, rather than a facultative one, and the question whether arsenic is nonessential or toxic is quantitative, not a qualitative one

Arsenic shares many physicochemical properties with phosphorus, so that arsenic can be taken up inadvertently by cells through the pathways for phosphorus. As a phosphate analog, arsenate competes with phosphate and enters cells via phosphate transporters. In the cell, arsenate can be recognized as a substrate by enzymes that usually use phosphate as a substrate. The phosphate for arsenate swap results in wasteful ‘futile cycles’ in metabolic pathways, uncoupled oxidative phosphorylation and extreme DNA instability. The disrupting metabolic effects of arsenic have an evolutionary meaning, so that all living organisms—from chemoautotrophic organisms that grow by reducing or oxidizing arsenic to metazoan—carry highly conserved arsenic resistance genes. Arsenic resistance can result from different strategies including selective transport to maximize phosphate uptake and minimize entry of arsenate, active transport to export arsenate, arsenic storage in specialized compartments, enzyme selectivity toward phosphate, and increased efficiency of DNA repair systems. None of these strategies is infallible, though, and susceptibility to arsenic toxicity varies between taxa in many orders of magnitude. Even arsenic-hypertolerant organisms will stop to grow and will eventually die when exposed to arsenic over species-specific resistance limits. The arsenic for phosphorus swap is an accidental one, it does not warrant a conclusion in favor of the essentiality of arsenic to life as we know it.     

Interactions between calcium precipitation and the polyphosphate-accumulating bacteria metabolism

A sequencing batch reactor that is operated for biological phosphorus removal has been operated under different influent calcium concentrations to study the precipitation process and the possible effects of phosphorus precipitation in the biological phosphorus removal process. Four experiments were carried out under different influent calcium concentrations ranging from 10 to 90 g Ca m(-3). The experimental results and the equilibrium study, which are based on the saturation index calculation, confirm that the process controlling the calcium behaviour is the calcium phosphate precipitation. This precipitation takes place at two stages: initially, precipitation of the amorphous calcium phosphate, and later crystallization of hydroxyapatite. Also the accumulation of phosphorus precipitated was observed when the influent calcium concentration was increased. In all the experiments, the influent wastewater ratio P/COD was kept constant. It has been observed that, at high calcium concentration, the ratio between phosphate release and acetate uptake (P(rel)/Ac(uptake)) decreases. Changes in the polyphosphate-accumulating organism (PAO) population and in the glycogen-accumulating organism (GAO) population during the experimental period were ruled out by means of fluorescence in situ hybridization. These results could suggest that PAO are able to change their metabolic pathways based on external conditions, such as influent calcium concentration. The accumulation of phosphorus precipitated as calcium phosphate at high influent calcium concentration throughout the experimental period confirmed that phosphate precipitation is a process that can affect the PAO metabolism.     

Biochemical model for enhanced biological phosphorus removal

Enhanced biological phosphorus (bio-P) removal from wastewater is a promising technology for which the fundamental mechanisms are still unclear. The purpose of this paper is to present a biochemical model that explains bio-P removal mechanisms occurring under anaerobic, aerobic and anoxic conditions of the process. A bio-P bacterium is referred to as one that can store both polyphosphate and carbon (as poly-β-hydroxybutyrate for example). In this communication, observations from the literature are first reviewed and mechanisms of bacterial bioenergetics and membrane transport are summarized. The model for bio-P metabolism under anaerobic, aerobic and anoxic conditions is then presented. The role of polyphosphate under anaerobic conditions is suggested to be as a source of energy both for the reestablishment of the proton motive force, which would be consumed by substrate transport and for substrate storage. The role of the anaerobic zone is to maximize the storage of organic substrates in bio-P bacteria. For this purpose the supply of readily available substrates should be maximized and the presence of electron acceptors (molecular oxygen or oxidized nitrogen) minimized. Under subsequent aerobic or anoxic conditions, bio-P bacteria will accumulate polyphosphates in response to the availability of electron acceptors (oxygen or oxidized nitrogen) for energy production. Carbon reserves in bio-P bacteria should provide energy for growth and for soluble phosphate accumulation as polyphosphate reserves.     

Effectiveness of an alternating aerobic, anoxic/anaerobic strategy for maintaining biomass activity of BNR sludge during long-term starvation

The effectiveness of an aerobic, anoxic/anaerobic strategy for maintaining the activity of activated sludge performing biological nitrogen and phosphorus removal during long-term starvation is investigated. A lab-scale sequencing batch reactor (SBR) treating abattoir wastewater and achieving high-levels (>95%) of nitrogen, phosphorus and COD removal was used. The reactor was put twice into a so-called "sleeping mode" for a period of 5-6 weeks when the abattoir, where the wastewater was sourced, was closed down for annual maintenance. The "sleeping mode" operation consisted of 15 min aeration in a 6 h SBR cycle. The sludge was allowed to settle in the remaining time of the cycle. The decay rates for ammonia oxidising bacteria (AOB) and nitrite oxidising bacteria (NOB) were determined to be 0.017 and 0.004 d(-1), respectively. These decay rates correlated well with AOB and NOB population quantified using molecular techniques (FISH). There was negligible phosphate accumulation in the reactor during the first 1-2 weeks of starvation, which was followed by a linear net release of phosphate in the remaining 4-5 weeks at a very slow rate of 1-2 mgP gVSS(-1)d(-1). A sudden decrease in the aerobic activities of polyphosphate accumulating organisms (PAOs), observed via anaerobic/aerobic batch tests, occurred after 2 weeks of starvation. This correlated with a dramatic increase of several metal ions in the liquid phase. The underlying reasons are not clear. A resuscitation period with a gradual increase of the wastewater load was applied during the re-startup of the reactor after both "sleeping mode" periods. Each time, the performance of the reactor in terms of nitrogen and phosphorus removal fully recovered in 4 days.     

Phosphorus removal in the activated sludge process

The results from this research suggest that both calcium phosphate precipitation and enhanced biological uptake play a role in phosphorus removal in the activated sludge process when a non-nitrifying, anaerobic-aerobic system is used to treat a low calcium wastewater. The primary removal mechanism was found to be biological uptake, as calcium phosphate precipitation accounted for only 15–27% of the total phosphorus removed. Calcium phosphate precipitation in the aerobic unit was enhanced because of the pH increase in that reactor. This was the result of low CO₂ production (indicated by low specific oxygen uptake values) and intense aeration which caused excessive CO₂ stripping in the aerobic unit     

序批式生物膜法除磷机理研究

利用^31P-核磁共振谱图证实了生物除磷的机理，即除磷菌在厌氧条件下分解胞内的聚磷酸盐并释放出正磷酸盐形式的无机磷酸盐，而在好氧或缺氧条件下吸收胞外的无机磷酸盐后转化为聚磷酸盐而贮存于胞内。同时证明了淹没序批式生物膜反应器中磷的去除是由生物完成的。     

Development of a 2-sludge, 3-stage system for nitrogen and phosphorous removal from nutrient-rich wastewater using granular sludge and biofilms

A novel 2-sludge 3-stage process using a combination of granular sludge and biofilm was developed to achieve biological removal of nitrogen and phosphorus from nutrient-rich wastewater. The system consists of a granular sequencing batch reactor (SBR) working under alternating anaerobic/anoxic conditions supplemented with a short aerobic phase and an aerobic biofilm SBR. The wastewater is first fed to the granular SBR reactor, where easily biodegradable carbon sources are taken up primarily by polyphosphate accumulating organisms (PAOs). The supernatant resulting from quick settling of the granular sludge is then fed to the biofilm SBR for nitrification, which produces oxidized nitrogen that is returned to the granular reactor for simultaneous denitrification and phosphorus removal. While maximizing the utilization of organic substrates and reducing operational costs, as do other 2-sludge processes previously reported in literature, the proposed system solves the bottleneck problem of traditional 2-sludge systems, namely high effluent ammonia concentration, due to its high-volume exchange ratios. An ammonia oxidation rate of 32 mg N/Lh was achieved in the biofilm SBR, which produced nitrite as the final product. This nitrite stream was found to cause major inhibition on the anoxic P uptake and also to result in the accumulation of N(2)O. These problems were solved by feeding the nitrite-containing stream continuously to the granular reactor in the anoxic phase. With a nitrogen and phosphorus removal efficiency of 81% and 94%, respectively, the system produces an effluent that is suitable for land irrigation from a wastewater stream containing 270 mg N/L of total nitrogen and 40 mg P/L of total phosphorus.     

Removal of ammonium and phosphorus ions from synthetic wastewater by the microalgae Chlorella vulgaris coimmobilized in alginate beads with the microalgae growth-promoting bacterium Azospirillum brasilense

Coimmobilization of the freshwater microalga Chlorella vulgaris in alginate beads with the microalgae growth-promoting bacterium Azospirillum brasilense under semi-continuous synthetic wastewater culture conditions significantly increased the removal of ammonium and soluble phosphorus ions compared to immobilization of the microalgae alone. In continuous or batch cultures removal of these ions followed a similar trend but was less efficient than in semi-continuous culture. It is proposed that coimmobilization of a microalgae with microalgae growth-promoting bacteria can serve as a tool in devising novel wastewater treatments.     

Stability of enhanced biological phosphorus removal and composition of polyphosphate granules

The influence of varying Ca- and Mg-concentration of the influent wastewater on the enhanced biological phosphorus removal was investigated in an anaerobic-aerobic bench-scale plant. The artificial enhancement of the Mg-concentration in the influent from 15 to 24 mg l(-1) and 31 mg l(-1), respectively, caused a raise of the mean P-removal efficiency from 85 to 97%. The P-elimination was very stable in time. A chemical precipitation of magnesium ammonium phosphate could be excluded. The elemental composition of polyphosphate granules was investigated by electron microscopy and energy dispersive X-ray spectroscopy. The elements Ca, Mg and K were the principal metal components of polyphosphate granules. Concerning the metal composition, different types of granules could be distinguished. The quantitative ratios of Ca, Mg and K varied in dependence on the influent concentration of these metals. A relation between the Mg/Ca-ratio of the granules and the efficiency of enhanced biological phosphorus removal can be supposed.     

Source apportionment of heavy metals and ionic contaminants in rainwater tanks in a subtropical urban area in Australia

Due to prolonged droughts in recent years, the use of rainwater tanks in urban areas has increased in Australia. In order to apportion sources of contribution to heavy metal and ionic contaminants in rainwater tanks in Brisbane, a subtropical urban area in Australia, monthly tank water samples (24 sites, 31 tanks) and concurrent bulk deposition samples (18 sites) were collected during mainly April 2007-March 2008. The samples were analysed for acid-soluble metals, soluble anions, total inorganic carbon and total organic carbon, and characteristics such as total solid and pH. The Positive Matrix Factorisation model, EPA PMF 3.0, was used to apportion sources of contribution to the contaminants. Four source factors were identified for the bulk deposition samples, including ‘crustal matter/sea salt’, ‘car exhausts/road side dust’, ‘industrial dust’ and ‘aged sea salt/secondary aerosols’. For the tank water samples, apart from these atmospheric deposition related factors which contributed in total to 65% of the total contaminant concentration on average, another six rainwater collection system related factors were identified, including ‘plumbing’, ‘building material’, ‘galvanizing’, ‘roofing’, ‘steel’ and ‘lead flashing/paint’ (contributing in total to 35% of the total concentration on average). The Australian Drinking Water Guideline for lead was exceeded in 15% of the tank water samples. The collection system related factors, in particular the ‘lead flashing/paint’ factor, contributed to 79% of the lead in the tank water samples on average. The concentration of lead in tank water was found to vary with various environmental and collection system factors, in particular the presence of lead flashing on the roof. The results also indicated the important role of sludge dynamics inside the tank on the quality of tank water.     

Microalgae growth-promoting bacteria as "helpers" for microalgae: a novel approach for removing ammonium and phosphorus from municipal wastewater

A combination of microalgae (Chlorella vulgaris or C. sorokiniana) and a microalgae growth-promoting bacterium (MGPB, Azospirillum brasilense strain Cd), co-immobilized in small alginate beads, was developed to remove nutrients (P and N) from municipal wastewater. This paper describes the most recent technical details necessary for successful co-immobilization of the two microorganisms, and the usefulness of the approach in cleaning the municipal wastewater of the city of La Paz, Mexico. A. brasilense Cd significantly enhanced the growth of both Chlorella species when the co-immobilized microorganisms were grown in wastewater. A. brasilense is incapable of significant removal of nutrients from the wastewater, whereas both microalgae can. Co-immobilization of the two microorganisms was superior to removal by the microalgae alone, reaching removal of up to 100% ammonium, 15% nitrate, and 36% phosphorus within 6 days (varied with the source of the wastewater), compared to 75% ammonium, 6% nitrate, and 19% phosphorus by the microalgae alone. This study shows the potential of co-immobilization of microorganisms in small beads to serve as a treatment for wastewater in tropical areas.     

Analysing the influence of operating conditions on the performance of algal–bacterial granular sludge processes for wastewater treatment: A review

This article discussed the effect of the main operating parameter involved in the operation of algal–bacterial granular sludge (ABGS) systems as promising biological processes for wastewater treatment. The focus was on the operational ranges reported in the literature capable of achieving better granule properties, good stability and high removal capacities. This review identified that hydraulic retention time (HRT), light intensity (LI) and light/dark periods were the most influential operating factors on the formation, stability, settleability and organic pollutant removal efficiency of ABGS. The discussion argued that ABGS systems enhance industrial and domestic wastewater treatment due to additional advantages that provide the symbiotic interactions to process performance, maintaining lesser operating costs concerning aerobic granular sludges (AGS) and microalgae consortia. This review will improve the understanding of the operation of ABGS systems and thus further expand possible operating combinations that help to enhance microbial interactions, microalgae growth and external aeration self-sufficiency in further research with a focus on its scaling up.     

Algal-bacterial processes for the treatment of hazardous contaminants: a review

Microalgae enhance the removal of nutrients, organic contaminants, heavy metals, and pathogens from domestic wastewater and furnish an interesting raw material for the production of high-value chemicals (algae metabolites) or biogas. Photosynthetic oxygen production also reduces the need for external aeration, which is especially advantageous for the treatment of hazardous pollutants that must be biodegraded aerobically but might volatilize during mechanical aeration. Recent studies have therefore shown that when proper methods for algal selection and cultivation are used, it is possible to use microalgae to produce the O(2) required by acclimatized bacteria to biodegrade hazardous pollutants such as polycyclic aromatic hydrocarbons, phenolics, and organic solvents. Well-mixed photobioreactors with algal biomass recirculation are recommended to protect the microalgae from effluent toxicity and optimize light utilization efficiency. The optimum biomass concentration to maintain in the system depends mainly on the light intensity and the reactor configuration: At low light intensity, the biomass concentration should be optimized to avoid mutual shading and dark respiration whereas at high light intensity, a high biomass concentration can be useful to protect microalgae from light inhibition and optimize the light/dark cycle frequency. Photobioreactors can be designed as open (stabilization ponds or high rate algal ponds) or enclosed (tubular, flat plate) systems. The latter are generally costly to construct and operate but more efficient than open systems. The best configuration to select will depend on factors such as process safety, land cost, and biomass use. Biomass harvest remains a limitation but recent progresses have been made in the selection of flocculating strains, the application of bioflocculants, or the use of immobilized biomass systems.     

The dynamic effects of potassium limitation on biological phosphorus removal

A full-scale sewage treatment plant designed for biological phosphorus removal may experience short- or long-term shortage in potassium of the influent. In this study, using an anaerobic-aerobic sequenced batch reactor system, inoculation sludge from laboratory-, pilot- and full-scale phosphorus removal plants was exposed to different potassium-phosphorus ratios in the influent. By simulating the conditions which may occur in practice, it was shown that potassium is an essential factor in biological phosphorus removal processes. When the system was exposed to severe shortage of potassium in the influent: (a) phosphorus removal was absent, (b) polyphosphate concentration in the biomass decreased exponentially due to sludge wasting and (c) the anaerobic phosphorus release and the related acetate uptake was only affected after several days of potassium absence, likely due to insufficient content of polyphosphate in the biomass to allow full acetate uptake under anaerobic conditions. In contrast, the system achieved complete phosphorus removal when potassium was present in excess amounts.     

污泥焚烧灰分磷回收潜力分析及其市场前景

磷资源不可替代又不能再生。现代工业攫取磷矿大多用于磷肥生产,通过作物收获的粮食、蔬菜以及饲养畜禽肉类进入人体,而随食物进入人体的大多数磷(90%)会随排泄物进入污水(无粪尿返田情况)。尽管最终进入污水中的磷占开采磷矿的比例很小(<5%),但这是人类除动物粪便与作物秸秆外唯一可能实现磷人工循环的位点,相对于转移进作物中的磷来说该比例超过1/4。因此,在废弃粪尿返田之原生态习惯的情况下,从污水处理过程中回收磷则显得非常重要。目前从污水处理过程中回收磷存在许多方式与产品,而与污泥焚烧灰分相关的磷回收程度最高,可达90%。为此,首先基于全球磷资源危机与我国磷流向及其估算,揭示磷回收的必要性和急迫性。然后,对与污泥焚烧相关的灰分磷回收技术以及潜在应用进行总结和分析。最后,根据肥效实验与成本估算,认定灰分再生磷肥比传统矿石磷肥具有潜在市场前景,特别是它的可持续意义。     

Long-term impact of anaerobic reaction time on the performance and granular characteristics of granular denitrifying biological phosphorus removal systems

Removal of nitrogen and phosphorus (P) from wastewater is successfully and widely practiced in systems employing both granular sludge technology and enhanced biological P removal (EBPR) processes; however, the key parameter, anaerobic reaction time (AnRT), has not been thoroughly investigated. Successful EBPR is highly dependent on an appropriate AnRT, which induces carbon and polyphosphate metabolism by phosphorus accumulating organisms (PAOs). Therefore, the long-term impact of AnRT on denitrifying P removal performance and granular characteristics was investigated in three identical granular sludge sequencing batch reactors with AnRTs of 90 (R1), 120 (R2) and 150 min (R3). The microbial community structures and anaerobic stoichiometric parameters related to various AnRTs were monitored over time. Free nitrite acid (FNA) accumulation (e.g., 0.0008–0.0016 mg HNO₂–N/L) occurred frequently owing to incomplete denitrification in the adaptation period, especially in R3, which influenced the anaerobic/anoxic intracellular intermediate metabolites and activities of intracellular enzymes negatively, resulting in lower levels of poly-P and reduced activity of polyphosphate kinase. As a result, the Accumulibacter-PAOs population decreased from 51 ± 2.5% to 43 ± 2.1% when AnRT was extended from 90 to 150 min, leading to decreased denitrifying P removal performance. Additionally, frequent exposure of microorganisms to the FNA accumulation and anaerobic endogenous conditions in excess AnRT cases (e.g., 150 min) stimulated increased extracellular polymeric substances (EPS) production by microorganisms, resulting in enhanced granular formation and larger granules (size of 0.6–1.2 mm), but decreasing anaerobic PHA synthesis and glycogen hydrolysis. Phosphorus removal capacity was mediated to some extent by EPS adsorption in granular sludge systems that possessed more EPS, longer AnRT and relatively higher GAOs.