Inhibition of chemical dose in biological phosphorus and nitrogen removal in simultaneous chemical precipitation for phosphorus removal

A study on the influence of chemical dosing on biological phosphorus and nitrogen removal was carried out through batch experimental tests by lab-scale and a full-scale wastewater treatment plant (employing a typical anaerobic-anoxic-oxic treatment). Results indicated that the inhibition of aluminum salt on biological phosphorus release and uptake processes is significant, as well as the inhibition of aluminum salt on Ammonia-Oxidizing Bacteria (AOB) is dominantly observed in the nitrification process and is recoverability. The inhibition of iron salt in biological phosphorus and nitrogen removal is weak, and only the inhibition of iron salt on phosphorus release at anaerobic periods emerge under large dosing. Evidence shows persistent inhibition from the accumulation of chemical doses in sludge mass. Intermittent chemical dosing proves recommendable for simultaneous chemical phosphorus removal.     

Effect of sulfide to nitrate ratios on the simultaneous anaerobic sulfide and nitrate removal

Present investigation deals with the effect of sulfide to nitrate (S/N) molar ratio on the simultaneous anaerobic sulfide and nitrate removal on capacity, stability and selectivity of the process. The volumetric sulfide-sulfur and nitrate-nitrogen removal rates at molar S/N ratio of 5:2 were 4.86 kg (m³ d)⁻¹ and 0.99 kg (m³ d)⁻¹, respectively, which were higher than those at S/N molar ratios of 5:5 and 5:8. Moreover, the fluctuations in the effluent at S/N ratio of 5:2 were less than those at the other two tested ratios. During the operation, the ratio of converted sulfide to converted nitrate tended to approach 5:2. The selectivity for elemental sulfur and dinitrogen was improved when the S/N molar ratio was set at 5:2 rather than 5:5 or 5:8. The process became unstable if the influent sulfide surpassed its critical concentration. The electron balance between reactants was also analyzed for different S/N molar ratios.     

Effect of nitrite from nitritation on biological phosphorus removal in a sequencing batch reactor treating domestic wastewater

Although nitrite effect on enhanced biological phosphorus removal (EBPR) has been previously studied, very limited research has been undertaken about the effect of nitrite accumulation caused by nitritation on EBPR. This paper focused on nitrite effect from nitritation on EBPR in a sequencing batch reactor treating domestic wastewater. Results showed that nitrite of below 10 mg/L did not inhibit P-uptake and release; whereas EBPR deterioration was observed when nitrite accumulation reached 20 mg/L. Due to P-uptake prior to nitritation, nitrite of 20 mg/L has no effect on aerobic P-uptake. The main reason leading to EBPR deterioration was the competition of carbon source. Batch tests were conducted to investigate nitrite effect on anaerobic P-release. Under sufficient carbon source, nitrite of 30 mg/L had no impact on poly-β-hydroxyalkanoate (PHA) storage; contrarily, under insufficient carbon source, denitrifiers competing for carbon source with phosphorus accumulating organisms resulted in decrease of PHA synthesis and P-release.     

Microbial and metabolic characterization of a denitrifying phosphorus-uptake/side stream phosphorus removal system for treating domestic sewage

In this study, an advanced wastewater treatment process, the denitrifying phosphorus/side stream phosphorus removal system (DPR-Phostrip), was developed for the purpose of enhancing denitrifying phosphorus removal. The enrichment of denitrifying phosphorus-accumulating organisms (DPAOs) and the microbial community structure of DPR-Phostrip were evaluated by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), and the metabolic activity of seed sludge and activated sludge collected after 55 days of operation were evaluated by Biolog? analysis. This experimental study of DPR-Phostrip operation showed that nutrients were removed effectively, and denitrifying phosphorus removal was observed during the pre-anoxic period. PCR-DGGE analysis indicated that DPR-Phostrip supported DPAO growth while inhibiting PAOs and GAOs. The major dominant species in DPR-Phostrip were Bacteroidetes bacterium, Saprospiraceae bacterium, and Chloroflexi bacterium. Moreover, the functional diversity indices calculated on the basis of Biolog analysis indicated that DPR-Phostrip had almost no effect on microbial community diversity but was associated with a shift in the dominant species, which confirms the results of the PCR-DGGE analysis. The results for average well color development, calculated via Biolog analysis, showed that DPR-Phostrip had a little impact on the metabolic activity of sludge. Further principal component analysis suggested that the ability to utilize low-molecular-weight organic compounds was reduced in DPR-Phostrip.     

Specific oxygen, ammonia, and nitrate uptake rates of a biological nutrient removal process treating elevated salinity wastewater

Anaerobic/anoxic/aerobic systems inoculated without and with NaCl acclimated cultures, i.e., Models A and B, respectively, were fed with a synthetic wastewater at various salinity levels. After achieving a steady state, the systems were shocked with 70 g/l NaCl for four consecutive days before returning to pre-shock conditions. At the steady-state, the specific oxygen uptake rates (SOURs) increased with an increase of sodium chloride concentration (from 5.40 to 9.72 mg O₂/g mixed liquor suspended solids (MLSS)-h at 0–30 g/l NaCl for Model A and from 6.84 to 17.64 mg O₂/g MLSS-h at 5–30 g/l NaCl for Model B). In contrast, the specific ammonia uptake rate (SAUR) and specific nitrate uptake rate (SNUR) decreased with increasing chloride concentration (from 4.76 to 2.14 mg NH₃–N/g MLSS-h and 2.50 to 1.22 NO3–N/g MLSS-h, for Model A, and from 3.84 to 2.71 mg NH₃–N/g MLSS-hr and 2.54 to 1.82 mg NO₃–N/g MLSS-hr, for Model B). During the shocked period, the SOUR in most scenarios increased whereas the SAUR and SNUR tended to decrease. The impact of the chloride shock on nitrifiers was more obvious than on denitrifiers; however, after a certain recovery period, the activities of both nitrifiers and denitrifiers in terms of SAUR and SNUR were approximately the same as those prior to shock.     

Microbial community of granules in expanded granular sludge bed reactor for simultaneous biological removal of sulfate, nitrate and lactate

This study studied the cultivation of granules from an expanded granular sludge bed reactor that simultaneously transforms sulfates, nitrates, and oxygen to elementary sulfur, nitrogen gas, and carbon dioxides, respectively. The living cells accumulate at the granule outer layers, as revealed by the multicolor staining and confocal laser scanning microscope technique. The microbial community comprises sulfate-reducing bacteria (SRB, Desulfomicrobium sp.), heterotrophic (Pseudomonas aeruginosa and Sulfurospirillum sp.), and autotrophic denitrifiers (Sulfurovum sp. and Paracoccus denitrificans) whose population dynamics at different sulfate and nitrate loading rates are monitored with the single-strand conformation polymorphism and denaturing gradient gel electrophoresis technique. The Desulfomicrobium sp. presents one of the dominating strains following reactor startup. At high sulfate and nitrate loading rates, the heterotrophic denitrifiers overcompete autotrophic denitrifiers to reduce SRB activities. Conversely, suddenly reducing nitrate loading rates completely removes the heterotrophic denitrifier Sulfurospirillum sp. from the granules and activates the autotrophic denitrifiers. The physical fixation of different groups of functional strains in granules fine-tunes the strains' activities, and hence the reactor performance.     

Effect of ferrous sulphate on nitrification during simultaneous phosphorus removal from domestic wastewater using a laboratory scale anoxic/oxic reactor

In the present study a laboratory scale anoxic/oxic reactor was used to remove the important eutrophication nutrients such as phosphorus and nitrogen from synthetic domestic wastewater. Phosphorus was removed through simultaneous precipitation and was carried out using the coagulant ferrous sulphate FeSO₄ · 7H₂O. Total phosphorus in the effluent was controlled to below 1 mg/l using a ferrous to phosphorus molar ratio of 2.1. pH after the addition of coagulant plays a major role in determining the molar ratio of the precipitant. Nitrogen was removed biologically in the anoxic/oxic system and the effect of simultaneous precipitation on nitrification and denitrification was investigated. The nitrification rate of the system remained unaffected during simultaneous precipitation and varied from 0.046 to 0.059 g N–NH₄ ⁺/g VSS/day. Denitrification was complete and was not affected by the coagulation process. The nitrogen removal efficiency varied from 78% to 85%. COD removal efficiency was not affected during simultaneous precipitation and was varied from 94% to 98%. The highly efficient nitrogen removal in the presence of simultaneous precipitant ferrous sulphate makes the process an ideal option for nutrient removal.     

Effect of operating modes on simultaneous anaerobic sulfide and nitrate removal in microbial fuel cell

The effect of operating modes on the simultaneous sulfide and nitrate removal were studied in two-chamber microbial fuel cells (MFCs). The batch and continuous operating modes were compared and evaluated in terms of substrate removal and electricity generation. Upon gradual increase in the influent sulfide concentration from 60 to 1,020 S mg L^?1, and the hydraulic retention time decrease from 17.2 to 6 h, the MFC accomplished a good substrate removal efficiency whereby nitrogen and sulfate were the main end products. The removal efficiency of the MFC in the continuous mode was much higher than that in the batch mode, and its current densities in the continuous mode were more stable and higher than in the batch mode, which could be explained by the linear relationship between electrons released by the substrates and accepted on the electrodes. The electricity output in the continuous mode of the MFC was higher than that in the batch mode. MFC's operation in the continuous mode was a better strategy for the simultaneous treatment of sulfide and nitrate.     

Kinetic modelling of organic matter removal in 80 horizontal flow reed beds for domestic sewage treatment

This paper reports a comparative study of four kinetic models that can be applied in the design of subsurface horizontal flow reed beds for wastewater treatment. The models were developed from different combinations of Monod kinetics, first-order kinetics, continuous stirred-tank reactor and plug flow patterns. Using three statistical parameters (coefficient of determination, relative root mean square error, and model efficiency), critical examinations were made on the accuracy of these models. For predicting organic matter removal, the combination of Monod kinetics with plug flow pattern gave the closest match between theoretical predictions and actual performances of 80 horizontal flow reed beds. In all four models, the coefficients of BOD removal were found to increase slightly with BOD loading. The ratios of BOD/COD had no correlation with the coefficients, indicating that in the horizontal flow reed beds the degradation of organic matter is insensitive to the nature of organics in the wastewater.     

Development of model simulation based on BioWin and dynamic analyses on advanced nitrate nitrogen removal in deep bed denitrification filter

A pilot-scale deep bed denitrification filter using quartz sand as the filter media was operated under filtration velocity of 5.23 m/h. Nitrate, nitrite, ammonia, and total nitrogen removal rates were relatively high at influent C/N ratios of 4:1 and 5:1. A model was developed using software to simulate the processes operating in the filter and improve the related parameters in the actual operations. The normalized sensitivity coefficient and the mean square sensitivity measure were used for the sensitivity analysis. Results showed that the stoichiometric parameters were the most sensitive, which were related to methylotrophs and biofilm. Measured data were consistent with the simulations. Moreover, the order of significance of factors affecting nitrate nitrogen removal was as follows: influent chemical oxygen demand, influent nitrate nitrogen, and hydraulic retention time. Last, the denitrification dynamic model was obtained at influent C/N ratio of 5:1.

     

Enhancement of rural domestic sewage treatment performance, and assessment of microbial community diversity and structure using tower vermifiltration

The performance of a novel three-stage vermifiltration (VF) system using the earthworm, Eisenia fetida, for rural domestic wastewater treatment was studied during a 131-day period. The average removal efficiencies of the tower VF planted with Penstemon campanulatus were as follows: chemical oxygen demand, 81.3%; ammonium, 98%; total nitrogen, 60.2%; total phosphorus, 98.4%; total nitrogen, mainly in the form of nitrate. Soils played an important role in removing the organic matter. The three-sectional design with increasing oxygen demand concentration in the effluents, and the distribution of certain oxides in the padding were likely beneficial for ammonium and phosphorus removal, respectively. The microbial community profiles revealed that band patterns varied more or less in various matrices of each stage at different sampling times, while the presence of earthworms intensified the bacterial diversity in soils. Retrieved sequences recovered from the media in VF primarily belonged to unknown bacterium and Bacilli of Firmicutes.     

Effect of nitrate,ammonia and nitrogen starvation on the regulation of nitrate reductase in Cyanidium caldarium

Summary Cells of Cyanidium caldarium grown with ammonia or ammonium nitrate as nitrogen source do not contain appreciable nitrate reductase activity. The alga develops the capacity to synthesize the enzyme when it is transferred from the ammonium medium to a nitrogen-free medium. Nitrate is not needed as an inducer and no enhancement in the rate of enzyme synthesis is observed when it is present. By contrast, whereas the synthesis of the enzyme in nitrogen-free medium proceeds at an increasing rate, in the nitrate medium it attains a stationary level after a short time.Nitrate grown cells possess variable amount of inactive nitrate reductase (from 9 to 60%) whereas in nitrogen-free medium the enzyme occurs principally in a fully active form. Addition of ammonia inactivates reversibly the preexisting enzyme. The inactive enzyme is measurable in the crude extract after activation by heating.It is suggested that in Cyanidium the inactivating effect of ammonia, which is the end product of nitrate reduction, in association with the repression of enzyme controls the level of nitrate reductase activity.     

Improvement strategy on enhanced biological phosphorus removal for municipal wastewater treatment plants: full-scale operating parameters, sludge activities, and microbial features

The poor quality of effluent discharged by municipal wastewater treatment plants (WWTPs) is threatening the safety of water ecology. This study, which integrated a field survey, batch tests, and microbial community identification, was designed to improve the effectiveness of the enhanced biological phosphorus removal (EBPR) process for WWTPs. Over two-thirds of the investigated WWTPs could not achieve total P in effluent lower than 0.5 mg/L, mainly due to the high ratio of chemical oxygen demand to P (28.6-196.2) in the influent. The rates of anaerobic P release and aerobic P uptake for the activated sludge varied from 0.22 to 7.9 mg/g VSS/h and 0.43 to 8.11 mg/g VSS/h, respectively. The fraction of Accumulibacter (PAOs: polyphosphate accumulating organisms) was 4.8 ± 2.0% of the total biomass, while Competibacter (GAOs: glycogen-accumulating organisms) accounted for 4.8 ± 6.4%. The anaerobic P-release rate was found to be an effective indicator of EBPR. Four classifications of the principal components were identified to improve the EBPR effluent quality and sludge activity.     

Effect of domestic sewage on sand beach meiofauna at Goa,India

Meiofauna of a sewage-polluted sandy beach, where sand alone constituted > 90%, was surveyed. Nematodes dominated the fauna numerically at all stations, followed by harpacticoid copepods. Most of the animals were confined to the top 5 cm of the sediment. A seasonal pattern was observed in the distribution of the fauna. There were significant spatial and temporal variations in mean meiofauna density, attributed to organic discharge via sewage and prevailing environmental conditions in the study area.     

几种湿地植物净化生活污水COD、总氮效果比较

以无植被、基质为河砂的潜流型人工湿地为对照,研究了石菖蒲、灯心草和蝴蝶花3种类型植被、基质均为河砂的潜流型人工湿地净化生活污水COD、总氮的效果．结果表明,在污水COD浓度小于200mg·L^-1、总氮浓度小于30mg·L^-1的低浓度范围里,无植被的人工湿地和有植被的人工湿地对污水中COD、总氮均有很好的去除效果,两者差异不大,其COD去除率均达90％以上,总氮的去除率达80％以上．随着污水中COD和总氮浓度的增加,无植被人工湿地和有植被人工湿地去除COD和总氮的效果均有不同程度下降,两者差异明显,有植被的人工湿地能维持较高的COD、总氮的去除效果,无植被的人工湿地COD和总氮去除效果下降很快,植被在人工湿地系统去除污水COD和总氮过程中起着重要的作用．在整个试验阶段,石菖蒲植被人工湿地COD和总氮平均净化效率分别为80．46％和77．77％、灯心草人工湿地分别为75．53％和71．17％、蝴蝶花人工湿地分别为70．50％和66．38％,无植被人工湿地分别为61．39％和55．81％．同无植被人工湿地COD和总氮净化效果相比,石菖蒲植被人工湿地净化效果最好;其次为灯心草植被人工湿地,再次为蝴蝶花植被人工湿地．不同类型植被的人工湿地净化污水中COD和总氮的效果与其生物量关系密切,这与植被系统吸收同化有机物质和总氮数量、根际微生物分解有机物质和硝化-反硝化作用有关。     

Effect of HRT on the biological pre-denitrification process for the simultaneous removal of toxic pollutants from cokes wastewater

A lab-scale serial anoxic-aerobic reactor for the pre-denitrification process was continuously operated to efficiently and economically treat actual cokes wastewater containing various pollutants, such as phenol, ammonia, thiocyanate and cyanide compounds. The biodegradation efficiencies of the pollutants were examined by changing hydraulic retention time (HRT) as a main operating variable. The long-term operation of the pre-denitrification process reactor showed that approximately 100% phenol, approximately 100% free cyanide, approximately 100% SCN(-), 97% ammonia, 85% COD, 84% TOC (total organic carbon) and 83% TN (total nitrogen) were removed at HRT above 11.9h. Removal efficiency of total cyanides significantly decreased with a decrease in the HRT. Free cyanide and some of total cyanides were removed in anoxic reactor, whereas thiocyanate was removed in aerobic reactor. Phenol was completely removed under successive anoxic and aerobic conditions. Although actual cokes wastewater contained high concentrations of various toxic pollutants, the pre-denitrification process showed stable and successful performances in both nitrification and denitrification reactions.     

The enhanced effect of supplemented lighting on nutrient removal by an aquatic vegetables (lettuce) purification system from rural domestic sewage

Abstract

Aquatic plant treatment system (APTS) is a widely used sewage purification technique; however, it requires a large area of land due to its long hydraulic retention time. In order to improve the economic value of APTS in the treatment of rural sewage, an aquatic vegetables (lettuce) purification system strengthened with a set of supplemented lighting was evaluated. The effect of supplemented lighting of blue and red light on lettuce growth and sewage purification was studied by batch experiments. The results showed that the lettuce growth and the removal rates of pollutants were enhanced by supplemented lighting, of which red light is superior to blue light, and the increase of red light intensity further promoted the growth of lettuce and the removal rate of pollutants. Supplementary light is a suitable method which could improve the purification effect of APTS in most weather conditions especially in countries where day-night light patterns change substantially between winter and summer. The results would be useful for the APTS design for treating rural domestic sewage.     

Effect of aspartate and glutamate on the fate of enhanced biological phosphorus removal process and microbial community structure

This study investigated the fate of enhanced biological phosphorus removal (EBPR) and changes in microbial speciation in a sequencing batch reactor (SBR) fed with aspartate and glutamate. It involved SBR operation for 288 days, batch tests for observation of metabolic functions together with microscopic and phylogenetic analyses. Polyphosphate accumulating organisms (PAOs) were observed in abundance with complete removal of phosphorus. Fluorescence in situ hybridization (FISH) combined with 4′,6-dia-midino-2-phenylindole (DAPI) staining confirmed the accumulation of polyphosphate by Rhodocyclus-related and Actinobacterial PAOs. Aspartate seemed to favor the competitive growth of Rhodocyclus-related PAOs since EBPR population used the common biochemical pathways followed by Rhodocyclus-related PAOs in the aspartate fed batch tests. In the glutamate fed batch reactors, however, Actinobacterial PAOs appeared to be competitively selected which explains the lower levels of PHA generation. Even though operational conditions did not change, effective EBPR could not be maintained during the latter part of the study.     

Effect of different carbon sources on the enhanced biological phosphorus removal in a sequencing batch reactor

The effect of the different carbon sources acetate, acetate/glucose or glucose on the enhanced biological phosphorus removal (EBPR) process was studied by experiments under alternating anaerobic–aerobic conditions in one sequencing batch reactor for each carbon source. The glucose was consumed completely within the first 30 min of the anaerobic phase whereas acetate degradation was slow and incomplete. Phosphate was released independently of the carbon source during the whole anaerobic phase. The highest phosphate release (27 mg P l⁻¹) and polyhydroxyalkanoate (PHA) storage (20 mg C g⁻¹ dry matter (DM)) during the anaerobic phase as well as the highest polyphosphate (poly-P) (8 mg P g⁻¹ DM) and glycogen storage (17 mg C g⁻¹ DM) during the aerobic phase were observed with acetate. In contrast to other investigations, glycogen storage did not increase with glucose as substrate but was significantly smaller than with acetate. The PHA composition was also influenced strongly by the carbon source. The polyhydroxyvalerate (PHV) portion of the PHA was maximal 17% for acetate and 82% for glucose. Due to the strong influence of the carbon source on the PHA concentration and composition, PHA storage seems to regulate mainly the phosphate release and uptake. This revised version was published online in July 2006 with corrections to the Cover Date.