Effect of ammonium on nitrous oxide emission during denitrification with different electron donors

Nitrous oxide （N2O） emission during denitrification is receiving intensive attention due to its high potential to cause greenhouse effects. In this study, denitrifiers were acclimated in sequencing batch reactors with methanol or acetate as the electron donor and nitrate as the electron acceptor. The effects of ammonium on NzO emission were examined in batch experiments with various electron donors. With the addition of ammonium, N2O emission increased under all the examined conditions compared to experiments without ammonium addition. With different electron donors, the highest ratio of N2O emission to the removed oxidized nitrogen was 0.70% for methanol, 5.34% for acetate, and 34.79% for polyhydroxybutyrate.

Nitrifiers activity and community characteristics under stress conditions in partial nitrification systems treating ammonium-rich wastewater

Long-term exposure of nitrifiers to high concentrations of free ammonia （FA） and free nitrous add （FNA） may affect nitrifiers activity and nitrous oxide （N2O） emission. Two sequencing batch reactors （SBRs） were operated at influent ammonium nitrogen （NH4-N） concentrations of 800 mg/L （SBRH） and 33S mg/L （SBRL）, respectively. The NH4-N removal rates in SBRH and SBRL were around 2.4 and 1.0 g/L/day with the nitritation efficiencies of 99.3% and 95.7%, respectively. In the simulated SBR cycle, the N20 emission factors were 1.61% in SBRH and 2.30% in SBRL. N2O emission was affected slightly by FA with the emission factor of 0.22%-0.65%, while N2O emission increased with increasing FNA concentrations with the emission factor of 0.22%～3.96%. The dominant ammonia oxidizing bacteria （AOB） were Nitrosomonas spp. in both reactors, and their relative proportions were 38.89% in SBRH and 13.36% in SBRL. Within the AOB genus, a species （i.e., operational taxonomic unit [OTU] 76） that was phylogenetically identical to Nitrosomonas europaea accounted for 99.07% and 82.04% in SBRH and SBRL, respectively. Additionally, OTU 215, which was related to Nitrosomonas stercoris, accounted for 16.77% of the AOB in SBRL.

Determination of quorum-sensing signal substances in water and solid phases of activated sludge systems using liquid chromatography–mass spectrometry

The detection of acyl homoserine lactones（AHLs） in activated sludge is essential for clarifying their function in wastewater treatment processes. An LC–MS/MS method was developed for the detection of AHLs in both the aqueous and solid phases of activated sludge. In addition, the effects of proteases and extracellular polymeric substances（EPS） on the detection of AHLs were evaluated by adding protease inhibitors and extracting EPS,respectively. Recoveries of each AHL were improved by adding 50 μL of protease inhibitor,and recoveries were also improved from 0 to 56.9% to 24.2%–105.8% by EPS extraction.Applying the developed method to determine the type and concentration of AHLs showed that C4-HSL, C6-HSL, C8-HSL and 3-oxo-C8-HSL were widely detected in a suspended activated sludge system. The dominant AHL was C8-HSL, with a highest concentration of304.3 ng/L. C4-HSL was mainly distributed in the aqueous phase, whereas C6-HSL, C8-HSL and 3-oxo-C8-HSL were preferentially distributed in the sludge phase.

Denitrification and biofilm growth in a pilot-scale biofilter packed with suspended carriers for biological nitrogen removal from secondary effluent

Tertiary denitrification is an effective method for nitrogen removal from wastewater. A pilot-scale biofilter packed with suspended carriers was operated for tertiary denitrification with ethanol as the organic carbon source. Long-term performance, biokinetics of denitrification and biofilm growth were evaluated under filtration velocities of 6, 10 and 14 m/hr. The pilot-scale biofilter removed nitrate from the secondary effluent effectively, and the nitrate nitrogen（NO_3-N） removal percentage was 82%, 78% and 55% at the filtration velocities of 6, 10 and 14 m/hr, respectively. At the filtration velocities of 6 and 10 m/hr, the nitrate removal loading rate increased with increasing influent nitrate loading rates, while at the filtration velocity of 14 m/hr, the removal loading rate and the influent loading rate were uncorrelated.During denitrification, the ratio of consumed chemical oxygen demand to removed NO_3-N was 3.99-4.52 mg/mg. Under the filtration velocities of 6, 10 and 14 m/hr, the maximum denitrification rate was 3.12, 4.86 and 4.42 g N/（m^2·day）, the half-saturation constant was 2.61, 1.05 and 1.17 mg/L, and the half-order coefficient was 0.22, 0.32 and 0.24（mg/L）1/2/min,respectively. The biofilm biomass increased with increasing filtration velocity and was 2845,5124 and 7324 mg VSS/m^2 at filtration velocities of 6, 10 and 14 m/hr, respectively. The highest biofilm density was 44 mg/cm^3 at the filtration velocity of 14 m/hr. Due to the low influent loading rate, biofilm biomass and thickness were lowest at the filtration velocity of 6 m/hr.

Characterization of heavy metal desorption from road-deposited sediment under acid rain scenarios

Road-deposited sediments（RDS） on urban impervious surfaces are important carriers of heavy metals.Dissolved heavy metals that come from RDS influenced by acid rain,are more harmful to urban receiving water than particulate parts.RDS and its associated heavy metals were investigated at typical functional areas,including industrial,commercial and residential sites,in Guangdong,Southern China,which was an acid rain sensitive area.Total and dissolved heavy metals in five particle size fractions were analyzed using a shaking method under acid rain scenarios.Investigated heavy metals showed no difference in the proportion of dissolved fraction in the solution under different acid rain pHs above3.0,regardless of land use.Dissolved loading of heavy metals related to organic carbon content were different in runoff from main traffic roads of three land use types.Coarse particles（＆gt;150 μm） that could be efficiently removed by conventional street sweepers,accounted for 55.1%-47.1%of the total dissolved metal loading in runoff with pH 3.0-5.6.The obtained findings provided a significant scientific basis to understand heavy metal release and influence of RDS grain-size distribution and land use in dissolved heavy metal pollution affected by acid rain.

Removal of ammonium and nitrate through Anammox and FeS-driven autotrophic denitrification

An autotrophic denitrifying bioreactor with iron sulfide(FeS)as the electron donor was operated to remove ammonium(NH_(4)^(+))and nitrate(NO_(3)^(-))synergistically from wastewater for more than 298 d.The concentration of FeS greatly affected the removal of NH_(4)^(+)/NO_(3)^(-).Additionally,a low hydraulic retention time worsened the removal efficiency of NH_(4)^(+)/NO_(3)^(-).When the hydraulic retention time was 12 h,the optimal removal was achieved with NH_(4)^(+)and NO_(3)^(-)removal percentages both above 88%,and the corresponding nitrogen removal loading rates of NH_(4)^(+)and NO_(3)^(-)were 49.1 and 44.0 mg/(L·d),respectively.The removal of NH_(4)^(+)mainly occurred in the bottom section of the bioreactor through sulfate/ferric reducing anaerobic ammonium oxidation(Sulfammox/Feammox),nitrification,and anaerobic ammonium oxidation(Anammox)by functional microbes such as Nitrospira,Nitrosomonas,and Candidatus Kuenenia.Meanwhile,NO_(3)^(-)was mainly removed in the middle and upper sections of the bioreactor through autotrophic denitrification by Ferritrophicum,Thiobacillus,Rhodanobacter,and Pseudomonas,which possessed complete denitrification-related genes with high relative abundances.

N2O emission from a sequencing batch reactor for biological N and P removal from wastewater

Nitrous oxide （N2O） is a greenhouse gas that can be released during biological nitrogen removal from wastewater. N2O emission from a sequencing batch reactor （SBR） for biological nitrogen and phosphorus removal from wastewater was investigated, and the aims were to examine which process, nitrification or denitrification, would contribute more to N2Oemission and to study the effects of heterotrophic activities on N2O emission during nitrification. The results showed that N2O emission was mainly attributed to nitrification rather than to denitrification. N2O emission during denitrification mainly occurred with stored organic carbon as the electron donor. During nitrification, NaO emission was increased with increasing initial ammonium or nitrite concentrations. The ratio of N2O emission to the removed ammonium nitrogen （N2O- N/NH4-N） was 2.5% in the SBR system with high heterotrophic activities, while this ratio was in the range from 0.14% to 1.06% in batch nitrification experiments with limited heterotrophic activities.

Aerobic N_2O emission for activated sludge acclimated under different aeration rates in the multiple anoxic and aerobic process

Nitrous oxide（N_2O） is a potent greenhouse gas that can be emitted during biological nitrogen removal. N_2O emission was examined in a multiple anoxic and aerobic process at the aeration rates of 600 m L/min sequencing batch reactor（SBRL） and 1200 m L/min（SBRH）.The nitrogen removal percentage was 89% in SBRLand 71% in SBRH, respectively. N_2O emission mainly occurred during the aerobic phase, and the N_2O emission factor was 10.1%in SBRLand 2.3% in SBRH, respectively. In all batch experiments, the N_2O emission potential was high in SBRLcompared with SBRH. In SBRL, with increasing aeration rates, the N_2O emission factor decreased during nitrification, while it increased during denitrification and simultaneous nitrification and denitrification（SND）. By contrast, in SBRHthe N_2O emission factor during nitrification, denitrification and SND was relatively low and changed little with increasing aeration rates. The microbial competition affected the N_2O emission during biological nitrogen removal.

Influence of arsanilic acid, Cu2＋, PO43- and their interaction on anaerobic digestion of pig manure

Arsanilic acid （ASA）, copper ion （Cuz ＋） and phosphate （PO43 ） are widely used as feed additives for pigs. Most of these three supplemented feed additives were excreted in feces and urine Anaerobic 2＋ digestion is often used for the management of pig manure. However the interaction ofASA with Cu 3 ＇ 2＋ 3 or P04 on anaerobic ＆gestlon is still not clear. In thin study, the influence ofASA, Cu , PO4- and their interaction on anaerobic digestion of pig manure and the possible mechanisms were investigated. The initial concentrations ofASA, Cu2＋ and PO43 were 0.46 mM, 2 mM and 2 mM in the anaerobic digester, respectively. The methanogenesis was severely inhibited in the assays with only ASA addition, only Cu2＋ addition and ASA ＋ PO43 addition with the inhibition index of 97.8%, 46.6% 2＋ and 82.6%, respectively, but the methanogenesis inhibition in the assay with ASA ＋ Cu addlt on was mitigated with the inhibition index of 39.4%. PO43 had no obvious impacts on the degradation of ASA. However, Cu2＋ addition inhibited the degradation of ASA, and mitigated the methanogcnesis inhibition. The existence of ASA would inhibit methanogenesis and generate more toxic inorganic arsenic compounds during anaerobic digestion, implying the limitation of anaerobic digestion for ASA- contaminated animal manure. However, the co-existence of ASA and Cu2＋ could mitigate the inhibition. These results could provide useful information for the management of anaerobic digestion of pig manure containing ASA and Cu2＋ .

Thermochemical pretreatment of meat and bone meal and its effect on methane production

Since the solubilization of meat and bone meal(MBM)is a prerequisite in many MBM disposal approaches,enhancement of the solubilization by means of thermochemical pretreatment was investigated in this study at two temperatures(55℃and 131℃)and six sodium hydroxide(NaOH)concentrations(0,1.25,2.5,5,10 and 20 g/L).The MBM volatile solid(VS)reduction ratio was up to 66%and 70%at 55℃and 131℃,respectively.At the same temperature,the VS reduction ratio increased with the increase in the dosage of NaOH.The study on the methane(CH4)production potential of pretreated MBM shows that the addition of NaOH at 55℃did not cause the inhibition of the succeeding CH4 production process.However,CH4 production was inhibited by the addition of NaOH at 131℃.The CH4 production potential was in the range of 389 to 503 mL CH4/g VS MBM and 464 to 555 mL CH4/g VS MBM at 55℃and 131℃,respectively.