Influent Phosphate Concentration Research Articles

Influence of seasonality, wastewater treatment plant process, geographical location and environmental parameters on bacterial community selection in activated sludge wastewater treatment plants treating municipal sewage in South Africa

This is the first comprehensive study that focusses on the correlation between the bacterial community composition and a range of previously identified selective criteria in activated sludge wastewater treatment plants on the African continent. Multivariate statistical analyses were used to determine the relative significance of the geographical location (factor: site), wastewater treatment plant process (factor: configuration), seasonality (factor: season), and environmental parameters on the bacterial communities in nine wastewater treatments plants from two sites in South Africa using terminal restriction fragment length polymorphism as a screening tool to rationalize the number of samples (to 50 samples) for high throughput (Illumina MiSeq) sequencing.Site was the most significant factor (Global ANOSIM R value = 0.91, p = 0.001), and it was established that the inter-site differences were not climatic in origin but related to differences in the composition of the influent and activated sludge. Previous studies that have reported associations between microbial community structure and environmental parameters have measured influent chemistry, and this is the first time, to our knowledge, that the comprehensive chemical character of activated sludge itself has been included in this type of study. It was found using BEST analysis that the activated sludge ammonia, activated sludge total phosphate and influent chemical oxygen demand were the most significant (p < 0.001) drivers for inter-site bacterial community selection (ANOSIM Global R values of 0.862, 0.782 and 0.428, respectively). This link would not have been established with only influent chemical analyses as there was no significant difference (t-test, p > 0.05) in the average influent phosphate concentrations between the 2 sites, but there was a highly significant difference (p < 0.001, t (15.5)>t-crit (2.01)) in the activated sludge total phosphate concentrations (20.8 ± 17.0 and 127.8 ± 40.2 mg/L). This is notable for all future studies on a global level aimed at identifying factors for selection of microbial communities in activated sludge.

Performance enhancement and population structure of denitrifying phosphorus removal system over redox mediator at low temperature

The development of denitrifying polyphosphate accumulating organisms (DPAOs) presents a strategy to carbon competition between denitrifying bacteria and phosphorus removing bacteria. However, low temperature inhibits the rate of enzyme-catalyzed and substrate diffusion during denitrifying phosphorus removal (DPR). Therefore, the present study assessed the addition of NQS (100 μmol/L) for enhancing the removal of TP and TN in DPR reactors operated at alternating anaerobic and anoxic phases and different influent phosphate concentrations. The results showed that the removal efficiency of TP and TN in NQS-DPR system at 10 °C were 99.9% and 42.0%, respectively, which were 2.1 and 2.0 times higher than that of DPR system. Adding NQS significantly alleviated the increase of pH under anoxic condition and decreased the ORP value of the reactor, which in turn enhanced the PHAs accumulation process. The determination of functional genes (nirK, narG and phoD) showed that Dechloromonas, Lentimicrobium, and Terrimonas were the dominant functional bacteria in NQS-DPR system at 10 °C with the relative abundance of 3.09%, 2.99% and 2.28%, respectively. This study can provide valuable information for the effects of the addition of the redox mediator on denitrifying phosphorus removal technology.

Fixed-Bed Column Technique for the Removal of Phosphate from Water Using Leftover Coal.

The excessive discharge of phosphate from anthropogenic activities is a primary cause for the eutrophication of aquatic habitats. Several methodologies have been tested for the removal of phosphate from aqueous solutions, and adsorption in a flow-through reactor is an effective mechanism to reduce the nutrient loading of water. This research aimed to investigate the adsorption potential of leftover coal material to remove phosphate from a solution by using continuous flow fixed-bed column, and analyzes the obtained breakthrough curves. A series of column tests were performed to determine the phosphorus breakthrough characteristics by varying operational design parameters such as adsorbent bed height (5 to 8 cm), influent phosphate concentration (10–25 mg/L), and influent flow rate (1–2 mL/min). The amorphous and crystalline property of leftover coal material was studied using XRD technology. The FT-IR spectrum confirmed the interaction of adsorption sites with phosphate ions. Breakthrough time decreased with increasing flow rate and influent phosphate concentration, but increased with increasing adsorbent bed height. Breakthrough-curve analysis showed that phosphate adsorption onto the leftover coal material was most effective at a flow rate of 1 mL/min, influent phosphate concentration of 25 mg/L, and at a bed height of 8 cm. The maximal total phosphate adsorbed onto the coal material’s surface was 243 mg/kg adsorbent. The Adams–Bohart model depicted the experimental breakthrough curve well, and overall performed better than the Thomas and Yoon–Nelson models did, with correlation values (R2) ranging from 0.92 to 0.98. Lastly, leftover coal could be used in the purification of phosphorus-laden water, and the Adams–Bohart model can be employed to design filter units at a technical scale.

Efficacy of nanochitosan impregnated polyurethane foam in removing phosphate from aqueous solutions

A novel potential adsorbent was developed by impregnating chitosan nanoparticles on polyurethane foam (PFC) for the reduction of phosphate in aqueous solutions. The emergence of nanoparticles was first confirmed by the ultraviolet-visible (UV-Vis) spectroscopy. The mean size of chitosan nanoparticles between 56 nm and 112 nm was provided by the field emission scanning electron microscopy (FESEM). The presence of specific elements (C, O, P) in PFC before and after treatment was determined by energy dispersive X-ray (EDX) spectroscopy. The interplay between amino groups in PFC and phosphate ions during adsorption was identified by the Fourier transform infrared (FTIR) spectroscopy. X-ray diffraction (XRD) analysis of PFC showed nearly the same pattern before and after treatment, indicating the stability of sorbent. The point of zero charge experiment described the positive surface charge of PFC below pH 7.4. The experimental studies showed that phosphate removal efficiency by PFC increases from 35.04% to 69.78% with the decrease of influent phosphate concentration from 150 mg/L to 3 mg/L at contact time 6 h and pH 6.5. Hence PFC can be considered as an effective sorbent for removing phosphate at lower concentrations.

Synthesis of mesoporous 2-line ferrihydrite/γ-Al2O3 hybrid adsorbent for the effective adsorption of phosphate for water remediation

A 2-line ferrihydrite/γ-A2O3 hybrid adsorbent (Fh/γ-Al2O3 hybrid adsorbent) precipitated on 10wt% of γ-Al2O3 seed for the effective adsorption of phosphate in water was synthesized from wastewater containing ferric sulfate. The use of γ-Al2O3 seeds for particle initiation made it possible to prepare larger particles that would allow a liquid to flow through. The synthesized Fh/γ-Al2O3 hybrid adsorbent was characterized by X-ray diffraction, 27Al-MAS NMR, N2 adsorption/desorption, SEM analysis, and EpHL measurements. The adsorption performance of phosphate on the synthesized Fh/γ-Al2O3 hybrid adsorbent was evaluated by batch and column tests at phosphate concentration below 10 ppm, which corresponds to the actual phosphate concentration of natural systems. The adsorption mechanism suggested by the batch test was in good agreement with the Langmuir adsorption model, with a maximum adsorption capacity of 33.2 mg/g. On the other hand, the experiment with the column obtained a maximum adsorption capacity of 33.6 mg/g for a volumetric flow rate of 10.25 BV/min and an influent phosphate concentration of 4.75 ppm on 0.5 g of adsorbent. The Fh/γ-Al2O3 hybrid adsorbent was shown to have superior adsorption characteristics to those of other previous research in terms of cost, adsorption efficiency, contact time, maximum adsorption capacity, and desorption efficiency of 95% from the experimental condition based on the surface characterization of the adsorbent.

Removal of phosphorous and nitrogen from wastewater in Brachiaria-based constructed wetland

Considering the prevalence of eutrophication of water bodies, sustainable treatment technologies like constructed wetlands (CWs) have come up as a promising alternate for nutrient removal and wastewater treatment. The present study was undertaken to investigate the potential of Brachiaria-based constructed wetland for removal of phosphorus and nitrogen in different seasons of a sub-tropical region. The CW cell could efficiently remove phosphate and nitrogen under varying influent concentrations across different seasons. Average removal of total phosphate increased from 55.2% (winter) to 78.5% (spring), 80.7% (autumn), and 85.6% (summer), and maximum removal rate was 384.4 mg/m2-day during the summer season. The soluble/available phosphate was removed on priority owing to its easy bio-availability. The removal efficiency of Brachiaria increased with increasing influent phosphate concentration (5–20 mg/l), if supplemented with nitrogen maintaining the N:P ratio of 5:1. This highlighted the characteristic of Brachiaria to absorb chemical shocks w.r.t. phosphate. The neutral pH (6.2–8.3) and oxidising conditions in rhizosphere ruled out possibility of binding of phosphate with cations (Ca, Fe, and Al) in sediments. Ambient temperature and sunshine hours regulated evapotranspiration and hence nutrient removal. Simultaneous removal of nitrogen (75.6–84.6%) by Brachiaria indicated that it can serve dual purpose of nutrient removal and fodder-production for livestock, thus serving as a sustainable prototype for rural communities in sub-tropical regions.

The adsorption of phosphate using a magnesia-pullulan composite: kinetics, equilibrium, and column tests.

A magnesia-pullulan (MgOP) composite has been developed to remove phosphate from a synthetic solution. In the present study, the removal of phosphate by MgOP was evaluated in both a batch and dynamic system. The batch experiments investigated the initial pH effect on the phosphate removal efficiency from pH3 to 12 and the effect of co-existing anions. In addition, the adsorption isotherms, thermodynamics, and kinetics were also investigated. The results from the batch experiments indicate that MgOP has encouraging performance for the adsorption of phosphate, while the initial pH value (3-12) had a negligible influence on the phosphate removal efficiency. Analysis of the adsorption thermodynamics demonstrated that the phosphate removal process was endothermic and spontaneous. Investigations into the dynamics of the phosphate removal process were carried out using a fixed bed of MgOP, and the resulting breakthrough curves were used to describe the column phosphate adsorption process at various bed masses, volumetric flow rates, influent phosphate concentrations, reaction temperatures, and inlet pH values. The results suggest that the adsorption of phosphate on MgOP was improved using an increased bed mass, while the reaction temperature did not significantly affect the performance of the MgOP bed during the phosphate removal process. Furthermore, higher influent phosphate concentrations were beneficial towards increasing the column adsorption capacity for phosphate. Several mathematic models, including the Adams-Bohart, Wolboska, Yoon-Nelson, and Thomas models, were employed to fit the fixed-bed data. In addition, the effluent concentration of magnesium ions was measured and the regeneration of MgOP investigated.

Microbial Population Dynamics During Domestication and Cultivation of Biofilm to Remove and Enrich Phosphate

The purpose of this study was to develop a method to remove and recover high concentration phosphate solutions from wastewater. An experiment was carried out to cultivate and enrich phosphorus accumulating organisms (PAOs) in the biofilm with nylon as the biological carrier using artificial water distribution. Microflora morphology, species diversity, and the genetic relationship of biofilm during the process of biofilm domestication were studied by scanning electron microscopy (SEM) and MiSeq high-throughput sequencing. In addition, the feasibility of recycling a high concentration of phosphate in the conventional biofilm within a short time was validated. The membrane was hung in the biological carrier when the reactor was operated for 10 d. After the hanging of the film succeeded, the effluent COD was below 50 mg·L-1, the effluent phosphorus was close to zero, and the removal efficiency of phosphorus reached to above 95%. The operation was stable at this level for 40 d. The results from the SEM indicated that the microbial morphology in the biofilm was uniform with full oval-shaped spheres with a clear profile. MiSeq high-throughput sequencing indicated that the dominant phylum in the reactor included Proteobacteria, Chloroflexi, Bacteroidetes, Actinobacteria, Ignavibacteriae, and Nitrospirae. Proteobacteria, as the dominant genera, increased from 47% to 58%. Rhodocyclaceae, as the dominant phosphorus accumulating bacteria, increased from 17.9% to 28.9%. During the recovery period, the concentration of the phosphorus solution increased from 40mg·L-1 to 82 mg·L-1 by increasing the influent phosphate concentration and the COD concentration in the anaerobic phase, meeting the requirement of phosphorus recovery with the struvite method.

Study of Phosphorus Removal by Using Sponge Iron Adsorption

Phosphorus is one of the key elements causing lake eutrophication. This paper deals with phosphate removal by Sponge iron in batch and fixed-bed operation. Isotherm and kinetic studies are conducted. The isotherm data is described by the Freundlich and Langmuir model, while the kinetic data of adsorption is fitted by the pseudo-second-order kinetic model. The saturated adsorption capacity of Langmuir isothermal equation is about 3.25 mg/g. The concomitant anions have adverse effect on phosphate adsorption and the effects follow the order: NO3− > Cl− > SO42−. The phosphate adsorption capacities of SI were improved significantly under the acidic condition. The results of the fixed-bed operation show that, with the increase of the influent phosphate concentrations, the breakthrough curve becomes steeper while the break point time decrease. According to the Adams–Bohart model, the critical height of the column decrease from 0.135 to 0.105 m when the contact time increased from 10 to 30 min with the influent concentration of 1.0 mg/L. According to BDST model, the critical bed depth is 0.15 m when the influent concentration of phosphate is 1.0 mg/L and the contact time (h) is 20 min.

Inhibitory Effects of Phosphate and Recovery on a Nitrification System

The effect of phosphate concentration on nitrification was studied by using a stabilization nitrosation system, which was started up in a continuous flow reactor by inoculating sludge from a municipal wastewater treatment plant. The results showed that the nitrification system was started successfully after operating for 14 days. The conversion rate of ammonia nitrogen reached 92.2%, the nitrite accumulation rate was 73.66%, and the nitrite generation rate was 14.42 g·(m3·d)-1. There was no effect of phosphate concentration on the nitrosation system between 10 and 30 mg·L-1; and the conversion rate of ammonia nitrogen was decreased with the continuous increase in phosphate concentration. When the concentration of phosphate was 80 mg·L-1, with an ammonia conversion rate 13.6%, accumulation rate of nitrite of 18.19%, and nitrite generation rate of 0.54 g·(m3·d)-1, the reaction was severely inhibited. After reducing the influent phosphate concentration to 0, with the ammonia nitrogen conversion rate at more than 80%, nitrite accumulation rate improved to 86.96%, and the nitrite generation rate being 15.63 g·(m3·d)-1, the system recovered after operating for 14 days.

Influence of Phosphate on Nitrogen Removal Efficiency of ANAMMOX Sludge

In this study, the effect of phosphate concentration on the nitrogen removal efficiency of ANAMMOX sludge was researched. The inhibition kinetic parameters were fitted and the abundance of ANAMMOX bacteria in the reactor before and after phosphate inhibition was analyzed by Real-time PCR. The short-term experiments showed that there was no significant effect on the nitrogen removal efficiency of ANAMMOX sludge when phosphate concentration was less than 30mg·L-1. With the increase of influent phosphate concentration, the removal rate of nitrogen decreased rapidly. When the phosphate concentration was raised to 200mg·L-1, the activity of ANAMMOX sludge reached a complete inhibition state. The parameters of phosphate inhibition were fitted by Haldane inhibition model. The half-inhibition constant was 70.1 mg·L-1. The long-term results showed that when the phosphate concentration was less than 50 mg·L-1, the effect on the nitrogen removal efficiency of ANAMMOX sludge was not significant. When the phosphate concentration reached 70-90 mg·L-1, The activity of ANAMMOX sludge was obviously affected, and the stability could be restored after a certain period. Increasing the phosphate concentration had a more significant effect and resulted in a longer recovery time. Finally, when the concentration of phosphate reached 100 mg·L-1, the nitrogen removal efficiency of ANAMMOX was seriously inhibited. The rate of nitrogen removal decreased from 158.33 g·(m3·d)-1 to 60.17 g·(m3·d)-1, resulting in 62% inhibition. The results of real-time PCR showed that the concentration of ANAMMOX was decreased from (9.97±0.86)×107 cells·mL-1 to (8.26±0.54)×107 cells·mL-1 in the restraining sludge system, and there was a relatively reduced trend.

Evaluation of kinetic and statistical models for predicting breakthrough curves of phosphate removal using dolochar-packed columns

The sustainability in utilizing dolochar packed columns under dynamic conditions for phosphate removal from aqueous solutions, has been carried out in this study. The assessment of efficacy of the bed under varying experimental conditions of bed depth, flow rate and influent phosphate concentration revealed that, an increase in bed depth and initial phosphate concentration or a decrease in flow rate resulted in increased breakthrough and exhaustion time. Thomas, modified dose response (MDR) and Clark models were applied to simulate the experimental breakthrough curves following nonlinear regression analysis. Also bed depth service time (BDST) model was engaged to scale up the adsorption process by means of linear regression approach. All the models with a very high coefficient of correlation (R2>0.93) predicted the breakthrough curves equally well. Good consistency was observed among experimental bed adsorption capacity (8.56mgg−1) and those predicted by Thomas (9.21mgg−1) and MDR models (8.81mgg−1). Statistical modeling proposed quadratic models for breakthrough and exhaustion time, with R2 values of 0.99 in both the cases. Soil column analytical test confirms slow release of phosphate from spent dolochar. The results confirm the sustainable application of dolochar packed columns for phosphate abatement in large scale accompanied by the utilization of spent dolochar as a source of phosphate.

Metabolic Response of "Candidatus Accumulibacter Phosphatis" Clade II C to Changes in Influent P/C Ratio.

The objective of this study was to investigate the ability of a culture highly enriched with the polyphosphate-accumulating organism, “Candidatus Accumulibacter phosphatis” clade IIC, to adjust their metabolism to different phosphate availabilities. For this purpose the biomass was cultivated in a sequencing batch reactor with acetate and exposed to different phosphate/carbon influent ratios during six experimental phases. Activity tests were conducted to determine the anaerobic kinetic and stoichiometric parameters as well as the composition of the microbial community. Increasing influent phosphate concentrations led to increased poly-phosphate content and decreased glycogen content of the biomass. In response to higher biomass poly-phosphate content, the biomass showed higher specific phosphate release rates. Together with the phosphate release rates, acetate uptake rates also increased up to an optimal poly-phosphate/glycogen ratio of 0.3 P-mol/C-mol. At higher poly-phosphate/glycogen ratios (obtained at influent P/C ratios above 0.051 P-mol/C-mol), the acetate uptake rates started to decrease. The stoichiometry of the anaerobic conversions clearly demonstrated a metabolic shift from a glycogen dominated to a poly-phosphate dominated metabolism as the biomass poly-phosphate content increased. FISH and DGGE analyses confirmed that no significant changes occurred in the microbial community, suggesting that the changes in the biomass activity were due to different metabolic behavior, allowing the organisms to proliferate under conditions with fluctuating phosphate levels.

The Effect of Solids Residence Time on Chemical Phosphorus Removal in Low Concentration Applications.

The effect of solids residence time (SRT) on steady state phosphorus (P) removal when striving for ultralow concentrations through metal salt addition was studied. Lab-scale continuous flow sequencing batch reactors (SBRs) were operated under high (6.4 mg P/L; 1.4 mol Fe/mol P) and low (3.4 mg P/L; 2.6 mol Fe/mol P) influent phosphate concentrations to characterize P removal. Residual P concentrations, particle size distribution, and microscopy analyses were determined over a range of SRTs. A majority of P removal (94% with 3.4 mg P/L; 83% with 6.4 mg P/L) occurred immediately after iron (Fe) addition with additional removal in the SBRs (3.3-4.8% with 3.4 mg P/L; 5.5-8.8% with 6.4 mg P/L). Soluble P uptake was higher for SRTs ≤ 7.4 days with 3.4 mg P/L and ≤ 14.3 days with 6.4 mg P/L. Normalized P uptake (μg P/mg total suspended solids [TSS]) decreased with SRT providing evidence that aging changed floc properties relevant to P removal. Floc size was found to have no distinguishable influence on P removal. However, changes in floc morphology were consistent with P removal trends.

Prevalence of 'Candidatus Accumulibacter phosphatis' type II under phosphate limiting conditions.

P-limitation in enhanced biological phosphorus removal (EBPR) systems fed with acetate, has generally been considered as a condition leading to enrichment of organisms of the genotype’ Candidatus Competibacter phosphatis’ expressing the glycogen-accumulating organisms (GAO) phenotype. Recent studies have demonstrated in short-term experiments that organisms of the genotype ‘Candidatus Accumulibacter phosphatis’ clade I and II, known to express the polyphosphate-accumulating organisms (PAO) phenotype can switch to the GAO phenotype when poly-P is absent, but are performing the HAc-uptake at lower kinetic rates, where clade I showed the lowest rates. The objective of this study was to verify whether organisms of the genotype ‘Candidatus Accumulibacter phosphatis’ can also be enriched under P-limiting conditions while expressing a GAO phenotype and more specifically to see which specific clade prevails. A sequencing batch reactor was inoculated with activated sludge to enrich an EBPR culture for a cultivation period of 128 days (16 times the solids retention time) under P-limiting conditions. A mixed culture was obtained comprising of 49 % ‘Candidatus Accumulibacter phosphatis’ clade II and 46 % ‘Candidatus Competibacter phosphatis’. The culture performed a full GAO metabolism for anaerobic HAc-uptake, but was still able to switch to a PAO metabolism, taking up excessive amounts of phosphate during the aerobic phase when it became available in the influent. These findings show that P-limitation, often used as strategy for enrichment of ‘Candidatus Competibacter phosphatis’, does not always lead to enrichment of only ‘Candidatus Competibacter phosphatis’. Furthermore, it demonstrates that ‘Candidatus Accumulibacter phosphatis’ are able to proliferate in activated sludge systems for periods of up to 128 days or longer when the influent phosphate concentrations are just enough for assimilation purposes and no poly-P is formed. The ‘Candidatus Accumulibacter phosphatis’ retain the ability to switch to the PAO phenotype, taking up phosphate from the influent as soon as it becomes available.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-016-0214-z) contains supplementary material, which is available to authorized users.

Use of phosphorus-sorbing materials to remove phosphate from greenhouse wastewater

High phosphate content in wastewater is currently a major issue faced by the North American greenhouse industry. Phosphate-sorbing material filters could provide a means of removing phosphate from wastewater prior to discharge to the environment, but the characterization of economically viable materials and specific recommendations for greenhouse wastewater are not available. Batch and column experiments were used to examine the capacity of two calcium-based waste materials, basic oxygen furnace slag and a concrete waste material, to remove phosphate from greenhouse nutrient solution at varied operating conditions. Material columns operating at a hydraulic retention time (HRT) of 3 h consistently removed >99% of influent phosphate at a concentration of 60 mg/L over repeated applications and demonstrated high phosphate retention capacity (PRC) of 8.8 and 5.1 g P/kg for slag and concrete waste, respectively. Both materials also provided some removal of the micronutrients Fe, Mn and Zn. Increasing HRT to 24 h increased P retention capacity of slag to >10.5 g P/kg but did not improve retention by concrete waste. Decreasing influent phosphate concentration to 20 mg/L decreased PRC to 1.64 g P/kg in concrete waste columns, suggesting fluctuations in greenhouse wastewater composition will affect filter performance. The pH of filter effluent was closely correlated to final P concentration and can likely be used to monitor treatment effectiveness. This study demonstrated that calcium-based materials are promising for the removal of phosphate from greenhouse wastewater, and worthy of further research on scaling up the application to a full-sized system.

Continuous flow aerobic granular sludge reactor for dairy wastewater treatment.

The focus of this study was to assess the treatment performance and granule progression over time within a continuous flow reactor. A continuous flow airlift reactor was seeded with aerobic granules from a laboratory scale sequencing batch reactor (SBR) and fed with dairy wastewater. Stereomicroscopic investigations showed that the granules maintained their integrity during the experimental period. Laser diffraction investigation showed proof of new granules formation with 100-500 μm diameter after only 2 weeks of operation. The treatment performances were satisfactory and more or less similar to the ones obtained from the SBR. Thus, removal efficiencies of 81-93% and 85-94% were observed for chemical oxygen demand and biological oxygen demand, respectively. The N-NH(+)(4) was nitrified with removal efficiencies of 83-99% while the nitrate produced was simultaneously denitrified - highest nitrate concentration determined in the effluent was 4.2 mg/L. The removal efficiency of total nitrogen was between 52 and 80% depending on influent nitrogen load (39.3-76.2 mg/L). Phosphate removal efficiencies ranged between 65 and above 99% depending on the influent phosphate concentration, which varied between 11.2 and 28.3 mg/L.

Multivariate optimization of phosphate removal and recovery from aqueous solution by struvite crystallization in a fluidized-bed reactor

Struvite crystallization has been widely studied for phosphate removal and recovery from aqueous systems. In this study, struvite crystallization was carried out in a fluidized-bed reactor. Multivariate optimization was conducted using Box–Behnken design (BBD) with influent pH, influent phosphate concentration, and Mg/P molar ratio as independent variables. The output variables comprised total and dissolved phosphate concentrations, ammonium and magnesium concentrations, and fines concentrations. Experimental values of the total phosphate and dissolved phosphate concentrations ranged from 25.6 to 109.4 mg/L and from 7.6 to 39.3 mg/L, respectively, while the fines concentration varied from 5.2 to 101.6 mg/L. Quadratic mathematical models describing the response behavior of experimental BBD data were generated for total phosphate, dissolved phosphate, and fines concentration. The model p-values ( <0.0001) were significant and their lack-of-fit p-values ( >0.05) were insignificant. Numerical optimization of process parameters was conducted to minimize total and dissolved phosphate, ammonium and magnesium concentrations, and fines concentration in the effluent. At influent phosphate concentration of 300 mg/L, the results converged to a set of operating conditions: pH 9.5 and Mg/P = 1.3. The close agreement between the data from the validation experiment and the model-predicted values (relative error < 10%) indicates the robustness of the models.

Gastropod shell column reactor as on-site system for phosphate capture and recovery from aqua system

Gastropod shell (GS), whose distribution is worldwide and mineralogical assemblage is aragonite, was packed in a glass column and evaluated for phosphate capture and recovery from aqua system. The column reactor was operated in a batch-continuous mode, considered as a close approximation to a practical water treatment system, for 30 days. The time–concentration profile parameters were derived at different influent phosphate concentrations and hydraulic residence time (HRT) to determine the performance efficiency of the reactor column. The mechanism of phosphate removal was investigated and phosphate fractionation protocol was employed to elucidate the form and pattern of phosphate distribution in the spent reactor. Variations in influent phosphate concentration and HRT had minimal influence on the time–concentration profile parameters and the performance efficiency of the column reactor within the process variables studied. The first order rate constant (k1) showed that increase in the HRT of the influent in the SS column reactor does not enhance the phosphate removal. The value of the saturation index (SI) obtained over the 30 days period were all positive and the thermodynamic parameter (ΔG) was <0 which is an indication of supersaturation, the significant role of precipitation as a mechanism of phosphate removal in the reactor and spontaneity of the precipitation reaction. The order of distribution of each fraction of P, relative to the total phosphorus (T-P) in the phosphate laden SS, is as follows: dicalcium phosphate (Ca2-P) (42.5%)>ten-calcium phosphate (Ca10-P) (40.50%)>octacalcium phosphate (Ca8-P) (16.65%)>occluded phosphate (O-P) (0.35%). The simple appraisal of the fertilizer value of the spent reactor showed that it would preferentially serve as a soil conditioner cum fertilizer in acidic soil.

A membrane-free, continuously feeding, single chamber up-flow biocatalyzed electrolysis reactor for nitrobenzene reduction

A new bioelectrochemical system (BES), a membrane-free, continuous feeding up-flow biocatalyzed electrolysis reactor (UBER) was developed to reduce oxidative toxic chemicals to less- or non-toxic reduced form in cathode zone with oxidation of electron donor in anode zone. Influent was fed from the bottom of UBER and passed through cathode zone and then anode zone. External power source (0.5 V) was provided between anode and cathode to enhance electrochemical reactions. Granular graphite and carbon brush were used as cathode and anode, respectively. This system was tested for the reduction of nitrobenzene (NB) using acetate as electron donor and carbon source. The influent contained NB (50–200 mg L −1) and acetate (1000 mg L −1). NB was removed by up to 98% mainly in cathode zone. The anode potential maintained under −480 mV. The maximum NB removal rate was up to 3.5 mol m −3 TV d −1 (TV = total empty volume) and the maximum aniline (AN) formation rate was 3.06 mol m −3 TV d −1. Additional energy required was less than 0.075 kWh mol −1 NB. The molar ratio of NB removed vs acetate consumed varied from 4.3 ± 0.4 to 2.3 ± 0.1 mol mol −1. Higher influent phosphate or acetate concentration helped NB removal rate. NB could be efficiently reduced to AN as the power supplied of 0.3 V.