Removal of nitrogen and phosphorus in a combined A^2/O-BAF system with a short aerobic SRT

A bench-scale anaerobic/anoxic/aerobic process-biological aerated filter （A^2/O-BAF） combined system was carded out to treat wastewater with lower C/N and C/P ratios. The A^2/O process was operated in a short aerobic sludge retention time （SRT） for organic pollutants and phosphorus removal, and denitrification. The subsequent BAF process was mainly used for nitrification. The BAF effluent was partially returned to anoxic zone of the A^2/O process to provide electron acceptors for denitrification and anoxic P uptake. This unique system formed an environment for reproducing the denitdfying phosphate-accumulating organisms （DPAOs）. The ratio of DPAOs to phosphorus accumulating organisms （PAOs） could be maintained at 28% by optimizing the organic loads in the anaerobic zone and the nitrate loads into the anoxic zone in the A^2/O process. The aerobic phosphorus over-uptake and discharge of excess activated sludge was the main mechanism of phosphorus removal in the combined system. The aerobic SRT of the A^2/O process should meet the demands for the development of aerobic PAOs and the restraint on the nitrifiers growth, and the contact time in the aerobic zone of the A^2/O process should be longer than 30 min, which ensured efficient phosphorus removal in the combined system. The adequate BAF effluent return rates should be controlled with 1--4 mg/L nitrate nitrogen in the anoxic zone effluent of A^2/O process to achieve the optimal nitrogen and phosphorus removal efficiencies.

Acclimation and Characterization of a Pseudomonas Strain for Improved Phosphorus Removal

A Pseudomonas strain(named as P.PAO-1) with phosphorous removal function was isolated and characterized.A new method of two-stage cultivation was applied to the strain to induce the synthesis of intracellular polyhydroxylbutyrate(PHB) in the cells.In the first stage,bacterial cells were enriched under a high carbon source condition;in the second stage,the bacteria cells were cultivated under the nutrient-imbalanced conditions with the carbon source-regulated medium.As a result,the PHB content of strain P.PAO-1 reached 22.8% compared with the normal 7.41% in the non-acclimated strain.This change had led to the rising of P uptake from 1 to 25 mg·L^(-1).When added the strain P.PAO-1into the activated sludge(with the addition proportion of 1:1),the ratio of biological phosphorus removal increased by 14.9%under the normal alternating anaerobic/aerobic conditions with low-carbon consumption.The results demonstrated that the isolated pure culture strain P.PAO-1 belonged to the functional group of poly-P accumulating microorganism.When cultured by the two-stage cultivation method,the initial accumulation of PHB in the strain cells could be achieved and the phosphorous removal capacity of strain P.PAO-1 could be induced subsequently.When applied to the wastewater,strain P.PAO-1 performed phosphorus removal from the wastewater with or without the addition of activated sludge.

Strain Pseudomonas putida PAO-1 Isolate with Polyphosphate Accumulating and Elongation Ability

Filamentous bacteria(FB)overgrowth is an important cause of sludge bulking in wastewater treatment plants(WWTPs).However,to date,methods for the cultivation and preservation of isolated FB in the laboratory have not been completely described.Furthermore,research on whether FB can function as phosphorus accumulating organisms(PAOs)is limited.In this study,a pure strain,a Pseudomonas putida PAO-1(P.putida PAO-1)isolate with phosphorus removal functions was isolated from the biofilm of an alternating anaerobic/aerobic biofilter(AABF),and its physiological characteristics were studied.Nitrate or nitrite could be used by the strain P.putida PAO-1 as electron acceptors for denitrification during phosphorus anoxic uptake,and 0.63 mg NO-3-N was consumed to reduce 1 mg soluble orthophosphate(SOP)by P.putida PAO-1.The strain P.putida PAO-1 consumed phosphorus within the optimal pH range of 6 to 8 and the temperature range of 25℃to 35℃.Cell deformity was a main morphological trait of the strain P.putida PAO-1,and it could elongate(with an elongation rate of 300%-500%)when it was subjected to oligotrophic or high-salt stress(15 g·L-1 NaCl).The findings in this study provide a microbiological reference for understanding the special characteristics of a denitrifying PAO.

Phosphorus accumulation by bacteria isolated from a continuous-flow two-sludge system

In this article, polyphosphate-accumulating organisms （PAOs） from a lab-scale continuous-flow two-sludge system was isolated and identified, the different phosphorus accumulation characteristics of the isolates under anoxic and aerobic conditions were investigated. Two kinds of PAOs were both found in the anoxic zones of the two-sludge system, one of them utilized only oxygen as electron aeceptor, and the other one utilized either nitrate or oxygen as electron aeceptor. Of the total eight isolates, five isolates were capable of utilizing both nitrate and oxygen as electron acceptors to uptake phosphorus to some extent. And three of the five isolates showed good phosphorus accumulative capacities both under anoxic or aerobic conditions, two identified as Alcaligenes and one identified as Pseudomonas. Streptococcus was observed weak anoxic phosphorus accumulation because of its weak denitrification capacity, but it showed good phosphorus accumulation capacity under aerobic conditions. One isolates identified as Enterobacteriaceae was proved to be a special species of PAOs, which could only uptake small amounts of phosphorus under anoxic conditions, although its denitrification capacity and aerobic phosphorus accumulation capacity were excellent.

Effects of Substitution of Organic Manure for Chemical Fertilizer on Phosphorus Accumulation and Grain Yield in Maize

In order to explore the response of maize phosphorus absorption to the appropriate proportion of organic fertilizer substitution for reduced chemical fertilizer,a field experiment with eight treatments was conducted in 2018.The eight treatments in the trial were:(1)CK;(2)M0+F;(3)M1+F1;(4)M1+F2;(5)M2+F1;(6)M2+F2;(7)M3+F1 and(8)M3+F2.In these treatments,M0,M1,M2 and M3 were organic fertilization of 0,15(low),30(medium)and 45(high)m3•hm-2,respectively.F1 and F2 indicated 20%and 40%reduction of conventional chemical fertilization.The soil nutrient content,phosphorus accumulation,dry weight,yield and yield components of maize were analyzed.The results showed that the phosphorus accumulation of maize stalks and leaves were 3.30%-43.17%and 10.98%-84.95%higher in M3+F1 treatment(20%reduction of chemical fertilizer with organic fertilizer of 45 m3•hm-2)than those in the conventional treatment(M0+F)during the maize reproductive period.At R2 stage,stalk and shoot P accumulation of M3+F1 treatment were 24.67%-43.18%and 20.34%-25.19%higher than other treatments,respectively.At V12 stage,leaf P accumulation of M3+F1 increased by 84.95%compared with other treatments.The maize yield of M3+F1 was significantly higher than that of other treatments,even though the partial productivity of the total phosphorus fertilizer of M3+F2 was the highest in the treatments.It could be found that the substitution of organic fertilizer for chemical fertilizer improved crop yield,phosphorus fertilizer efficiency and accumulation.M3+F1 treatment had the most positive effects on improving maize phosphorus accumulation and yield.

Contributions of Different Wetland Plants to Nitrogen and Phosphorus Removal in Constructed Wetlands

Constructed wetlands with Cyperus altrnlifolius,Pennisetum sinese Roxb and elephant grass as vegetation were built to study the nitrogen and phosphorous removal from domestic sewage in cold climate.It was found that these three plants could all grow slowly and stably under low temperature stress in winter,and the biomass,nitrogen and phosphorus absorption characteristics and absorbing capacity of the three plants were different.The growth rate and biomass were as follows:P.sinese Roxb>elephant grass>C.altrnlifolius,and these three plants could be used as winter wetland decontamination plants in Southwest China;the absorption characteristics of nitrogen and phosphorus in different tissues of the three plants were as follows:nitrogen content in leaf>nitrogen content in stem,phosphorus content in stem>phosphorus content in leaf;the removal of total nitrogen(TN)by three plants in the wetland was ranged form 4.3%to 7.8%,and the removal of total phosphorus(TP)was ranged from 3.3%to 5.3%.Different plants had different absorption effects on nitrogen and phosphorus.There was a significantly positive correlation between plant nitrogen and phosphorus accumulation and biomass,and nitrogen removal rate in wetland showed a significantly positive correlation with biomass.

Effi ciency of phosphorus accumulation by plankton,periphyton developed on submerged artifi cial substrata and metaphyton:in-situ observation in two shallow ponds

Phosphorus overenrichment of shallow ponds prevailing in wetlands leads to their eutrophication causing the collapse of those vulnerable habitats.The potential of phosphorus accumulation by periphyton developed on artificial substrata has been investigated in two shallow ponds(Bara?ka and?iroki Rit)in northwest Serbia and compared to the same ability of plankton and metaphyton.The periphyton substrate carrier has been submerged from May to October.Both continuously(CS)and monthly developed(MS)periphyton were sampled.Autotrophic component of all investigated communities has been qualitatively assessed.Maximum accumulation of only 14.7 mg TP/m^(2) was recorded in three-month exposed periphyton CS.MS exposed from July to August reached maximal 12.7 mg TP/m^(2).Plankton community that was characterized by more diverse and abundantly developed algal component was more effective in phosphorus accumulation(0.7 mg/g dry weight)in comparison with dominantly inorganic and diatom-dominated periphyton in Bara?ka.Unstable conditions caused by recent revitalization(dredging organic matter and mud from pond basin—redigging)as well as rapid desiccation of?iroki Rit disabled making an unambiguous conclusion about the efficiency of phosphorus accumulation among different communities,but suggested slight potential of phosphorus harvesting by metaphyton in this pond.Due to the shorter exposure time that brings the reduced risk of unpredictable changes in the ecosystem,as well as the considerable amount of accumulated phosphorus,large-scale application of one-month exposed periphyton developed on artificial substrates would be more advisable for phosphorus harvesting in nutrient affected shallow ponds.

Biological nitrogen removal with enhanced phosphate uptake in (AO)2SBR using single sludge system

Simultaneous biological phosphorus and nitrogen removal with enhanced anoxic phosphate uptake via nitrite was investigated in an anaerobic-aerobic-anoxic-aerobic sequencing batch reactor((AO)2 SBR). The system showed stable phosphorus and nitrogen removal performance, and average removals for COD, TN and TP were 90%, 91% and 96%, respectively. The conditions of pH 7.5—8.0 and temperature 32℃ were found detrimental to nitrite oxidation bacteria but favorable to ammonia oxidizers, and the corresponding specific oxygen uptake rates(SOUR) for phase 1 and 2 of nitrification process were 0.7 and 15 mgO 2/(gVSS·h) in respect, which led to the nitrite accumulation in aerobic phase of(AO)2 SBR. Respiratory tests showed that 40 mgNO 2-N/L did not deteriorate the sludge activity drastically, and it implied that exposure of sludge to nitrite periodically enabled the biomass to have more tolerance capacity to resist the restraining effects from nitrite. In addition, batch tests were carried out and verified that denitrifying phosphorus accumulation organisms(DPAOs) could be enriched in a single sludge system coexisting with nitrifiers by introducing an anoxic phase in an anaerobic-aerobic SBR, and the ratio of the anoxic phosphate uptake capacity to aerobic phosphate uptake capacity was 45%. It was also found that nitrite(up to 20 mgNO 2-N/L) was not inhibitory to anoxic phosphate uptake and could serve as an electron acceptor like nitrate, but presented poorer efficiency compared with nitrate.

Carbon and nitrogen allocations in corn grown in Central and Northeast China: different responses to fertilization treatments

In order to reveal the impact of various fertilization strategies on carbon（C） and nitrogen（N） accumulation and allocation in corn（Zea mays L.）, corn was grown in the fields where continuous fertilization management had been lasted about 18 years at two sites located in Central and Northeast China（Zhengzhou and Gongzhuling）, and biomass C and N contents in different organs of corn at harvest were analyzed. The fertilization treatments included non-fertilizer（control）, chemical fertilizers of either nitrogen（N）, or nitrogen and phosphorus（NP）, or phosphorus and potassium（PK）, or nitrogen, phosphorus and potassium（NPK）, NPK plus manure（NPKM）, 150% of the NPKM（1.5NPKM）, and NPK plus straw（NPKS）. The results showed that accumulated C in aboveground ranged from 2 550–5 630 kg ha^–1 in the control treatment to 9 300–9 610 kg ha^–1 in the NPKM treatment, of which 57–67% and 43–50% were allocated in the non-grain organs, respectively. Accumulated N in aboveground ranged from 44.8–55.2 kg ha^-1 in the control treatment to 211–222 kg ha^–1 in the NPKM treatment, of which 35–48% and 33–44% were allocated in the non-grain parts, respectively. C allocated to stem and leaf for the PK treatment was 65 and 49% higher than that for the NPKM treatment at the both sites, respectively, while N allocated to the organs for the PK treatment was 18 and 6% higher than that for the NPKM treatment, respectively. This study demonstrated that responses of C and N allocation in corn to fertilization strategies were different, and C allocation was more sensitive to fertilization treatments than N allocation in the area.

Enhanced biological phosphorus removal using thermal alkaline hydrolyzed municipal wastewater biosolids

This study reports the feasibility of using municipal wastewater biosolids as an alternative carbon source for biological phosphorus removal.The biosolids were treated by a lowtemperature,thermal alkaline hydrolysis process patented by Lystek International Inc.(Cambridge,ON,Canada)to produce short-chain volatile fatty acids and other readily biodegradable organics.Two sequencing batch reactors(SBRs)were operated with synthetic volatile fatty acids(Syn VFA)and readily biodegradable organics produced from the alkaline hydrolysis of municipal wastewater biosolids(Lystek)as the carbon source,respectively.Municipal wastewaters with different strengths and COD:N:P ratios were tested in the study.The reactors’performances were compared with respect to nitrogen and phosphorus removal.It was observed that phosphorus removal efficiencies were between 98%–99%and 90%–97%and nitrogen removal efficiencies were 78%–81%,and 67%for the Syn VFA and Lystek,respectively.However,the kinetics for phosphorus release and uptake during the anaerobic and aerobic stages with Lystek were observed to be significantly lower than Syn VFA due to the presence of higher order VFAs(C4 and above)and other fermentable organics in the Lystek.

Simultaneous denitrifying phosphorus accumulation in a sequencing batch reactor

In order to achieve simultaneous nitrogen and phosphorus removal in the biological treatment process,denitrifying phosphorus accumulation(DNPA)and its affecting factors were studied in a sequencing batch reactor(SBR)with synthetic wastewater.The results showed that when acetate was used as the sole carbon resource in the influent,the sludge acclimatized under anaerobic/aerobic operation had good phos-phorus removal ability.Denitrifying phosphorus accumulation was observed soon when fed with nitrate instead of aeration following the anaerobic stage,which is a vital premise to DNPA.If DNPA sludge is fed with nitrate prior to the anaerobic stage,the DNPA would weaken or even disappear.At the high concen-tration of nitrate fed in the anoxic stage,the longer anoxic time needed,the better the DNPA was.Induced DNPA did not disap-pear even though an aerobic stage followed the anoxic stage,but the shorter the aerobic stage lasted,the higher the proportions of phosphorus removal via DNPA to total removal.

Effect of temperature on anoxic metabolism of nitrites to nitrous oxide by polyphosphate accumulating organisms

Temperature is an important physical factor, which strongly influences biomass and metabolic activity. In this study, the effects of temperature on the anoxic metabolism of nitrite （NO2） to nitrous oxide （N2O） by polyphosphate accumulating organisms, and the process of the accumulation of N2O （during nitrite reduction）, which acts as an electron acceptor, were investigated using 91% ：e 4% Candidatus Accumulibacterphosphatis sludge. The results showed that N2O is accumulated when Accumulibacter first utilize nitrite instead of oxygen as the sole electron acceptor during the denitrifying phosphorus removal process. Properties such as nitrite reduction rate, phosphorus uptake rate, N2O reduction rate, and polyhydroxyalkanoate degradation rate were all influenced by temperature variation （over the range from 10 to 30℃ reaching maximum values at 25℃）. The reduction rate of N2O by N2O reductase was more sensitive to temperature when N2O was utilized as the sole electron acceptor instead of NO2, and the N2O reduction rates, ranging from 0.48 to 3.53 N2O-N/（hr.g VSS）, increased to 1.45 to 8.60 mg N2O-N/（hr·g VSS）. The kinetics processes for temperature variation of 10 to 30℃ were （01 = 1.140-1.216 and θ2 = 1.139-1.167）. In the range of 10℃ to 30℃, almost all of the anoxic stoichiometry was sensitive to temperature changes. In addition, a rise in N2O reduction activity leading to a decrease in N2O accumulation in long term operations at the optimal temperature （27℃ calculated by the Arrhenius model）.