The nature of the carbon source rules the competition between PAO and denitrifiers in systems for simultaneous biological nitrogen and phosphorus removal

The presence of nitrate in the theoretical anaerobic reactor of a municipal WWTP aiming at simultaneous C, N and P removal usually leads to Enhanced Biological Phosphorus Removal (EBPR) failure due to the competition between PAO and denitrifiers for organic substrate. This problem was studied in a continuous anaerobic-anoxic-aerobic (A²/O) pilot plant (146 L) operating with good removal performance and a PAO-enriched sludge (72%). Nitrate presence in the initially anaerobic reactor was studied by switching the operation of the plant to an anoxic-aerobic configuration. When the influent COD composition was a mixture of different carbon sources (acetic acid, propionic acid and sucrose) the system was surprisingly able to maintain EBPR, even with internal recycle ratios up to ten times the influent flow rate and COD limiting conditions. However, the utilisation of sucrose as sole carbon source resulted in a fast EBPR failure. Batch tests with different nitrate concentrations (0-40 mg L⁻¹) were performed in order to gain insight into the competition for the carbon source in terms of P-release or denitrification rates and P-release/C-uptake ratio. Surprisingly, no inhibitory or detrimental effect on EBPR performance due to nitrate was observed. A model based on ASM2d but considering two step nitrification and denitrification was developed and experimentally validated. Simulation studies showed that anaerobic VFA availability is critical to maintain EBPR activity.     

The effect of free nitrous acid on the anabolic and catabolic processes of glycogen accumulating organisms

Nitrite/Free Nitrous Acid (FNA) has previously been shown to inhibit aerobic and anoxic phosphate uptake by polyphosphate accumulating organisms (PAOs). The inhibitory effect of FNA on the aerobic metabolism of Glycogen Accumulating Organisms (GAOs) is investigated. A culture highly enriched (92 ± 3%) in Candidatus Competibacter phosphatis (hereafter called Competibacter) was used. The experimental data strongly suggest that FNA likely directly inhibits the growth of Competibacter, with 50% inhibition occurring at 1.5 × 10⁻³ mgN-HNO₂/L (equivalent to approximately 6.3 mgN-NO₂⁻/L at pH 7.0). The inhibition is well described by an exponential function. The organisms ceased to grow at an FNA concentration of 7.1 × 10⁻³ mgN-HNO₂/L. At this FNA level, glycogen production, another anabolic process performed by GAOs in parallel to growth, decreased by 40%, while the consumption of polyhydroxyalkanoates (PHAs), the intracellular carbon and energy sources for GAOs, decreased by approximately 50%. FNA likely inhibited either or both of the PHA oxidation and glycogen production processes, but to a much less extent in comparison to the inhibition on growth. The comparison of these results with those previously reported on PAOs suggest that FNA has much stronger inhibitory effects on the aerobic metabolism of PAOs than on GAOs, and may thus provide a competitive advantage to GAOs over PAOs in enhanced biological phosphorus removal (EBPR) systems.     

Total dissolved phosphorus: Effects of two molecular weight fractions on phosphorus cycling in natural phytoplankton communities

Although ³²P-uptake kinetics enable the closed mathematical treatment of the phosphorus cycle, several P pools, other than PO₄, do not achieve isotopic equilibrium. This means that the P system could be open to P sources not labelled by the tracer. We tested whether such sources supporting an open system could produce significant changes in phytoplankton biomass in two lakewater communities. Two fractions were concentrated from natural lakewaters ranging from 2 × 10³ to 10⁴ daltons (fraction I) and 10⁴–10⁵ daltons (fraction II). These were then reintroduced to the natural communities at three concentration levels. During the incubation that followed, we assessed the capacity of the added organic matter to deliver phosphorus to the P cycle by monitoring known keypoints: phosphatase activity, ³²PO₄-uptake rate constant, and chlorophyll a. These measurements allowed us to estimate respectively the potential for hydrolysis, the actual product of hydrolysis PO₄ (which disrupts ³²PO₄-uptake rates) and the long-term net uptake of P (growth). Although the fractions did cause decreases in growth, and also increased both phosphatase activity and PO₄ uptake rate constants, none of these could be attributed to an additional delivery of P to the community. Under all conditions tested, the P system remained closed to organic P additions. However, the observed effects could be explained by non P organic matter such as dissolved humic materials acting either directly upon the community, or on phosphorus kinetics. The effects appeared to be pH dependent. We suggest that outside Spring P loading or other sporadic P inputs, the natural community tends to operate within a closed P system, where community dynamics are more strongly affected by non P organic matter than by organic phosphate inputs.     

Rhizosphere acidification of faba bean, soybean and maize

Interspecific facilitation on phosphorus uptake was observed in faba bean/maize intercropping systems in previous studies. The mechanism behind this, however, remained unknown. Under nitrate supply, the difference in rhizosphere acidification potential was studied by directly measuring pH of the solution and by visualizing and quantifying proton efflux of roots between faba bean (Vicia faba L. cv. Lincan No.5), soybean (Glycine max L. cv. Zhonghuang No. 17) and maize (Zea mays L. cv. Zhongdan No.2) in monoculture and intercrop, supplied without or with 0.2 mmol L^− 1 P as KH₂PO₄. The pH of the nutrient solution grown faba bean was lower than initial pH of 6.0 from day 1 to day 22 under P deficiency, whereas the pH of the solution with maize was declined from day 13 after treatment. Growing soybean increased solution pH irrespective of P supply. Under P deficiency, the proton efflux of faba bean both total (315.25 nmol h^− 1 plant^− 1) and specific proton efflux (0.47 nmol h^− 1 cm^− 1) was greater than that those of soybean (21.80 nmol h^− 1 plant^− 1 and 0.05 nmol h^− 1 cm^− 1, respectively). Faba bean had much more ability of rhizosphere acidification than soybean and maize. The result can explain partly why faba bean utilizes sparingly soluble P more effectively than soybean and maize do, and has an important implication in understanding the mechanism behind interspecific facilitation on P uptake by intercropped species.     

Phosphorus limitation in nitrifying groundwater filters

Phosphorus limitation has been demonstrated for heterotrophic growth in groundwater, in drinking water production and distribution systems, and for nitrification of surface water treatment at low temperatures. In this study, phosphorus limitation was tested, in the Netherlands, for nitrification of anaerobic groundwater rich in iron, ammonium and orthophosphate. The bioassay method developed by Lehtola et al. (1999) was adapted to determine the microbially available phosphorus (MAP) for nitrification. In standardized batch experiments with an enriched mixed culture inoculum, the formation of nitrite and nitrate and ATP and the growth of ammonia-oxidizing bacteria (AOB; as indicated by qPCR targeting the amoA-coding gene) were determined for MAP concentrations between 0 and 100 μg PO₄-P L⁻¹. The nitrification and microbial growth rates were limited at under 100 μg PO₄-P L⁻¹ and virtually stopped at under 10 μg PO₄-P L⁻¹. In the range between 10 and 50 μg PO₄-P L⁻¹, a linear relationship was found between MAP and the maximum nitrification rate. AOB cell growth and ATP formation were proportional to the total ammonia oxidized. Contrary to Lehtola et al. (1999), biological growth was very slow for MAP concentrations less than 25 μg PO₄-P L⁻¹. No full conversion nor maximum cell numbers were reached within 19 days. In full-scale groundwater filters, most of the orthophosphate was removed alongside with iron. The remaining orthophosphate appeared to have only limited availability for microbial growth and activity. In some groundwater filters, nitrification was almost totally prevented by limitation of MAP. In batch experiments with filtrate water from these filters, the nitrification process could be effectively stimulated by adding phosphoric acid.     

Phosphate removal in agro-industry: Pilot- and full-scale operational considerations of struvite crystallization

Pilot-scale struvite crystallization tests using anaerobic effluent from potato processing industries were performed at three different plants. Two plants (P1 & P2) showed high phosphate removal efficiencies, 89 ± 3% and 75 ± 8%, resulting in final effluent levels of 12 ± 3 mg PO₄³⁻-P L⁻¹ and 11 ± 3 mg PO₄³⁻-P L⁻¹, respectively. In contrast, poor phosphate removal (19 ± 8%) was obtained at the third location (P3). Further investigations at P3 showed the negative effect of high Ca²⁺/PO₄³⁻-P molar ratio (ca. 1.25 ± 0.11) on struvite formation. A full-scale struvite plant treating anaerobic effluent from a dairy industry showed the same Ca²⁺ interference. A shift in the influent Ca²⁺/PO₄³⁻-P molar ratio from 2.69 to 1.36 resulted in average total phosphorus removal of 78 ± 7%, corresponding with effluent levels of 14 ± 4 mg P_total L⁻¹ (9 ± 3 mg PO₄³⁻-P L⁻¹). Under these conditions high quality spherical struvite crystals of 2-6 mm were produced.     

Effect of COD/SO4ratio and Fe(II) under the variable hydraulic retention time (HRT) on fermentative hydrogen production

The effect of chemical oxygen demand/sulfate (COD/SO₄²⁻) ratio on fermentative hydrogen production using enriched mixed microflora has been studied. The chemostat system maintained with a substrate (glucose) concentration of 15 g COD L⁻¹ exhibited stable H₂ production at inlet sulfate concentrations of 0-20 g L⁻¹ during 282 days. The tested COD/SO₄²⁻ ratios ranged from 150 to 0.75 (with control) at pH 5.5 with hydraulic retention time (HRT) of 24, 12 and 6 h. The hydrogen production at HRT 6 h and pH 5.5 was not influenced by decreasing the COD/SO₄²⁻ ratio from 150 to 15 (with control) followed by noticeable increase at COD/SO₄²⁻ ratios of 5 and 3, but it was slightly decreased when the COD/SO₄²⁻ ratio further decreased to 1.5 and 0.75. These results indicate that high sulfate concentrations (up to 20,000 mg L⁻¹) would not interfere with hydrogen production under the investigated experimental conditions. Maximum hydrogen production was 2.95, 4.60 and 9.40 L day⁻¹ with hydrogen yields of 2.0, 1.8 and 1.6 mol H₂ mol⁻¹ glucose at HRTs of 24, 12 and 6 h, respectively. The volatile fatty acid (VFA) fraction produced during the reaction was in the order of butyrate > acetate > ethanol > propionate in all experiments. Fluorescence In Situ Hybridization (FISH) analysis indicated the presence of Clostridium spp., Clostridium butyricum, Clostridium perfringens and Ruminococcus flavefaciens as hydrogen producing bacteria (HPB) and absence of sulfate reducing bacteria (SRB) in our study.     

A kinetic model of steady state phosphorus fixation in a batch reactor—II. Effect of pH

Measurements of phosphorus fixation at the soil/solution ratio of 250 mg 500^?1 ml at pH = 2, 3, 5, 7 and 8 in a batch reactor with steady input of phosphate were carried out. All results reached a steady state and followed a Michaelis-Menten type equation as predicted for the catalytic process. Maximum rate of reaction showed a decrease with increase of pH due to the competitive effect between OH^? and H₂PO^?₄. The maximum value of 1/K at pH = 5 showed H₂PO^?₄ may be required in phosphorus adsorption for some specific-bonding mechanism with soil.     

亚硝酸盐对聚磷菌厌氧代谢的影响

以2种强化生物除磷(EBPR)系统中的活性污泥为研究对象,考察亚硝酸盐对聚磷菌厌氧代谢的影响,结果表明：不同EBPR系统中的聚磷菌对于亚硝酸盐的耐受能力不同。人工配水富集聚磷菌的活性污泥,当亚硝态氮浓度超过10 mg/L时,聚磷菌吸收VFA受到抑制, PHA的合成减少,磷酸盐的释放增加;处理生活污水的SBR短程脱氮除磷活性污泥,亚硝酸盐的浓度高达30 mg/L时,未对聚磷菌的厌氧代谢造成抑制,但引起异养反硝化菌与聚磷菌竞争VFA,导致PHA合成量和释磷量的减少。富集聚磷菌的活性污泥投加亚硝酸盐后P/VFA     

Photooxidation and subsequent biodegradability of recalcitrant tri-alkyl phosphates TCEP and TBP in water

Biodegradable organic carbon (BDOC) from OH radical oxidation (UV-H₂O₂) of the recalcitrant industrial anti-foaming agents and flame retardants, tri-n-butyl phosphate (TBP) and tris(2-chloroethyl) phosphate (TCEP), was quantified with respect to the fraction of the TBP or TCEP photooxidized. For 50-96% contaminant oxidation via OH, BDOC was similar in solutions of either compound, and ranged from 0.25 to 0.5 mg L⁻¹ (TBP₀ and TCEP₀ = 5 mg L⁻¹). In addition, for this contaminant oxidation range, complete dehalogenation of TCEP was observed, along with a significant change in pH. Oxidation of TCEP results in both H⁺ and Cl⁻ release, while the TBP mineralization pathway results in CO₂, H₂O, H⁺, and PO₄³⁻. For low μg/L levels of TCEP contamination in treated surface waters, UV-H₂O₂ oxidation of TCEP or TBP would not be expected to impact pH or chloride concentrations, however, a portion of the TCEP or TBP oxidation products, likely in non-halogenated aldehyde form, would become an available carbon source for bacterial growth in storage, distribution, or during further physical treatment.     

Influences of pH, heavy metals and phosphate and their co-influences on the sorption of pentachlorophenol on cyanobacterial biomass

Influences of pH, two types of ions of transition metals (Cu²⁺, Cd²⁺), Na₃PO₄ and their co-influences on the sorption of pentachlorophenol (PCP) on cyanobacterial biomass derived from natural bloom were studied. Sorption of PCP significantly decreases with pH in the range of 3.25-9.00. Although sorption coefficient of ionized PCP is 8.51 times lower than that of neutral species, it is the dominant species at environmentally relevant pH and contributes more to the total sorption of PCP. In the presence of low concentration of Cu²⁺ (≤40 μmol L⁻¹), sorption of PCP was much lower than that of the blank. However, it increased gradually with Cu²⁺, and overpassed the blank when concentration of Cu²⁺ was higher than 50 μmol L⁻¹. Compared with the sole influence of pH, coexisted Cu²⁺ inhibited the sorption of PCP at pH of 3.25 and 4.35, but enhanced it in the pH range of 5.00-9.00. In the presence of Cd²⁺, sorption of PCP first increased then decreased rapidly and finally increased slightly again with Cd²⁺. Except for at pH of 9.00, sorption of PCP at other pH in the presence of Cd²⁺ was much lower than that solely affected by pH. In the presence of Na₃PO₄, sorption of PCP increased rapidly then maintained with Na₃PO₄. Under the influence of both Na₃PO₄ and pH, sorption of PCP at pH from 3.25 to 5.00 was lower than that solely affected by pH, while it increased with pH in the range of 5.00-9.00 and was higher than that solely affected by pH in the range of 6.00-9.00. Ion pairs of pentachlorophenolate-metal facilitated the sorption of PCP, which was largely dependent on pH illustrated by UV-visible and FTIR spectra. Speciations of metals and PCP and the stability constants of ion pairs of pentachlorophenolate-metal greatly affected the sorption. Ionic strength also played an important role for the sorption of PCP.     

Struvite crystallisation and recovery using a stainless steel structure as a seed material

A metallic system acting as a seed substrate has been designed and developed in order to assess its efficiency in recovering phosphorus as struvite. The device, consisting of two concentric stainless steel meshes, was immerged in the upper section of a pilot crystallisation reactor fed with synthetic liquors (MgCl₂·6H₂O, NH₄H₂PO₄,) for 2 h. Apart from soluble PO₄-P removals which remained in the range 79-80% with or without application of the metallic system, it was found that under the specific operating conditions tested the meshes were capable of accumulating struvite at a rate of 7.6 gm⁻² h⁻¹, hence reducing significantly the amount of fine particles remaining in solution from 302.2 to 12 mg L⁻¹ when compared to trials without mesh.     

Phosphorus recovery by struvite crystallization in WWTPs: Influence of the sludge treatment line operation

Phosphorus recovery by struvite (MgNH₄PO₄·6H₂O) crystallization is one of the most widely recommended technologies for treating sludge digester liquors especially in wastewater treatments plants (WWTP) with enhanced biological phosphorus removal (EBPR). In this paper, phosphorus recovery by struvite crystallization is assessed using the rejected liquors resulting from four different operational strategies of the sludge treatment line. Phosphorus precipitation and recovery efficiencies of between 80-90% and 70-85%, respectively, were achieved in the four experiments. The precipitates formed were mainly struvite, followed by amorphous calcium phosphate and, in some experiments, by calcite. The highest global phosphorus recovery taking into account both the sludge line and the crystallizer was achieved when mixed thickening and high elutriation were carried out (8.4 gP/kg treated sludge). However, low struvite content was obtained in the crystallizer with this operation scheme due to the high calcium content in the elutriation stream. Therefore, if the final purpose is to obtain struvite, the reduction of the elutriation flowrate is widely recommended in the case of high water hardness.     

Disinfection and formation of disinfection by-products in a photoelectrocatalytic system

In this study, disinfection and formation of disinfection by-products (DBPs) were studied in a photoelectrocatalytic (PEC) treatment system. Disinfection performance of titanium dioxide (TiO₂) in the PEC system was determined through Escherichia coli (E. coli) inactivation. Humic acid (HA) was used as a model organic compound and its removal was monitored by total organic carbon (TOC) measurements using 410 nm (color) and 254 nm (UV₂₅₄) wavelengths. Trihalomethanes (THMs) were measured for the evaluation of DBPs formation during PEC treatment of chloride and HA mixture. It was found that unlike photocatalytic treatment, THMs might form in the PEC system. To investigate the effects of anions on the PEC treatment, chloride (Cl⁻), sulfate (SO₄²⁻), phosphoric acid (H₂PO₄⁻)/hydrogen phosphate (HPO₄²⁻) and bicarbonate (HCO₃⁻) ions were added separately to the HA and bacterial suspensions. Presence of H₂PO₄⁻/HPO₄²⁻ and HCO₃⁻ ions resulted in inhibitory effects on both HA degradation and E. coli inactivation, which were also examined in the photoanode. It was observed that the presence of HA had a strong inhibitory effect on the disinfection of E. coli.     

An investigation of the formation of chlorate and perchlorate during electrolysis using Pt/Ti electrodes: The effects of pH and reactive oxygen species and the results of kinetic studies

The characteristics of chlorate (ClO₃⁻) and perchlorate (ClO₄⁻) formation were studied during the electrolysis of water containing chloride ions (Cl⁻). The experiments were performed using an undivided Pt/Ti plate electrode under different pH conditions (pH 3.6, 5.5, 7.2, 8.0 and 9.0). ClO₃⁻ and ClO₄⁻ were formed during electrolysis in proportion to the Cl⁻ concentration. The generation rates of ClO₃⁻ and ClO₄⁻ under acidic conditions (pH 3.6 and 5.5) were lower than in basic pH conditions (pH 7.2, 8.0 and 9.0). However, the pH of the solution did not influence the conversion of ClO₃⁻ to ClO₄⁻. The effects of intermediately formed oxidants on the production of ClO₃⁻ and ClO₄⁻ were observed using sodium thiosulfate (Na₂S₂O₃) as the active chlorine scavenger and tertiary butyl alcohol (t-BuOH) as the hydroxyl radical (OH) scavenger. The results revealed that electrolysis reactions that involved active chlorine contributed dominantly to ClO₃⁻ production. The direct oxidation reaction rate of Cl⁻ to ClO₃⁻ was 13%. The OH species that were intermediately formed during electrolysis were also found to significantly affect ClO₃⁻ and ClO₄⁻ production. The key formation pathways of ClO₃⁻ and ClO₄⁻ were studied using kinetic model development.     

Lake restoration by hypolimnetic Ca(OH)2 treatment: impact on phosphorus sedimentation and release from sediment

A whole-lake hypolimnetic Ca(OH)₂ addition, that induced calcium carbonate precipitation, combined with deep water aeration has been applied to eutrophic Lake Luzin, Germany during 1996-1998. In this study we investigated the dynamic of phosphorus and its binding forms in seston and sediment before and during the treatment. The sedimentation rates of phosphorus increased within three years of induced calcite precipitation. The phosphorus binding forms shifted to the calcite-bound phosphorus in the settling matter. The increase of calcite-bound P in the settling material did not coincide with the maximum induced CaCO₃-precipitation caused by the hypolimnetic addition of Ca(OH)₂. An impact of chemicals additions and pH on phosphorus binding forms in seston and surface sediments has been studied in laboratory experiments with sediment core incubations and slurry experiments.Laboratory studies showed that the lowest phosphorus flux from sediment was related to the experiment with pH = 7 in overlaying water adjusted with Ca(OH)₂. The adjusting of pH with Ca(OH)₂ leads to a lower P flux of 2.3 mg P m⁻² d⁻¹, while the highest P-flux is attributed to the experiment with the pH which was adjusted with NaOH. Phosphorus fraction which reflects phosphorus binding on carbonates in surface sediments increased within one year of treatment, enhancing the phosphorus retention capacity of sediments.     

Measuring in-stream retention of copper by means of constant-rate additions

Human practices entail inputs of nutrients and toxicants such as heavy metals to the fluvial ecosystems. While nutrient dynamics in fluvial ecosystems have been widely studied for over three decades, dynamics of toxicants still remain unclear. In this investigation, the nutrient spiraling concept and associated methodologies to quantify nutrient retention in streams were applied to study copper (Cu) dynamics in streams. The present study aimed to quantify total dissolved Cu retention using a simplified system of indoor channels colonized with fluvial biofilms. Cu retention was studied at sub-toxic concentrations to avoid negative/lethal effects on biota. In addition, Cu retention was compared with retention estimates of a macronutrient, phosphate (PO₄³⁻), which has been widely studied within the context of the nutrient spiraling concept. The methodology used allowed a successful quantification of Cu and PO₄³⁻ retention. The results showed higher retention efficiency for PO₄³⁻ than for Cu. The biofilm played a key role in retaining both solutes. Although retention efficiency for both solutes was higher in the experiments with colonized substrata compared to uncolonized substrata, we found a positive relationship between uptake rate and chlorophyll-a only for PO₄³⁻. Finally, retention efficiency for both solutes was influenced by water discharge, showing lower retention efficiencies under higher flow conditions. These results suggest that the fate and toxic effects of copper on stream biota may be strongly influenced by the prevailing environmental conditions. Our results indicate that the experimental approach considered can provide new insights into the investigation of retention of toxic compounds in fluvial systems and their controlling mechanisms.     

Production of polyhydroxyalkanoates in open, mixed cultures from a waste sludge stream containing high levels of soluble organics, nitrogen and phosphorus

In this study, the production of polyhydroxyalkanoates (PHAs) from waste activated sludge (WAS) was evaluated. PHAs were produced from fermented WAS pretreated via high-pressure thermal hydrolysis, a stream characterised by high levels of nutrients (approximately 3.5 g N L⁻¹ and 0.5 g P L⁻¹) and soluble organics. PHA-storing organisms were successfully enriched at high organic loading rates (6 g COD_sol L⁻¹ d⁻¹) under aerobic dynamic feeding in sequencing batch reactors at a sludge retention time of 6 d with a short feast length less than 20% of the cycle, and a maximum substrate concentration during feast of 1 g COD_VFA L⁻¹. The biomass enrichment, characterised by a decrease in species evenness based on Lorenz curves, provided a biomass that accumulated 25% PHA on a dry-biomass basis with yields on VFA of 0.4 Cmol Cmol⁻¹ in batch tests. The PHA consisted of ∼70 mol% 3-hydroxybutyrate and ∼30 mol% 3-hydroxyvalerate, and presented high thermal stability (T_d = 283-287 °C) and a molecular mass ranging from 0.7 to 1.0 × 10⁶ g mol⁻¹. Overall PHA storage was comparable to that achieved with other complex substrates; however, lower PHA storage rates (0.04-0.05 Cmol PHA⁻¹ Cmol X⁻¹ h⁻¹) and productivities (3-4 Cmol PHA L⁻¹ h⁻¹) were probably associated with a biomass-growth and high-respiration response induced by high levels of non-VFA organics (40-50% of COD_sol in feed) and nutrients. PHA production is feasible from pretreated WAS, but the enrichment and accumulation process require further optimisation. A milder WAS pretreatment yielding lower levels of non-VFA organics and readily available nutrients may be more amenable for improved performance.     

A novel post denitrification configuration for phosphorus recovery using polyphosphate accumulating organisms

Enhanced biological phosphorus removal (EBPR) has been widely used to remove phosphorus (P) from wastewater. In this study we report a novel modification to the EBPR approach, namely enhanced biological phosphorus removal and recovery (EBPR-r) that facilitates biological recovery of P from wastewater using a post denitrification configuration. The novel approach consists of two major steps. In the first step, a biofilm of phosphorus accumulating organisms (PAOs) is exposed to a wastewater stream in the absence of active aeration, during which P is taken up by the biofilm using nitrate and residual dissolved oxygen as electron acceptors. Thus, P and nitrogen (N) removal from wastewater is achieved. During the second step, the P enriched biofilm is exposed to a smaller recovery stream supplemented with an external carbon source to facilitate P release under anaerobic conditions. This allows P to be recovered as a concentrated liquid. The EBPR-r process was able to generate a P recovery stream four time more concentrated (28 mg-P/L) than the wastewater stream (7 mg-P/L), while removing nitrate (denitrification) from the wastewater stream. Repeated exposure of the biofilm (10 P-uptake and release cycles) to a recovery stream yielded up to 100 mg-P/L. Overall, EBPR-r is the first post denitrification strategy that can also facilitate P recovery during secondary wastewater treatment.