Effect of C/N Ratio,Temperature,pH on Autotrophic Denitrification Rate with Hydrogen Gas,Iron(Ⅱ) and Sodium Sulfide as Electron Donors

Nitrate is considered to be one of the most widely present pollutants leading to eutrophication of environment. The purpose of this work was to isolate and identify new anaerobic denitrifying bacteria from reservoir sediments and utilize different electron donors for isolates to improve nitrate removal efficiency. Using traditional enrichment approach,one purified anaerobic bacterium( Y12) capable of NO-3-N removal from sediments was obtained. The species identity of Y12 was determined via 16 S rRNA gene sequence analysis to be Acinetobacter. In this work,the fastest denitrification rates were observed with ferrous iron as electron donor.And,slightly slower rates were observed with hydrogen and sodium sulfide as electron donors. However,when used hydrogen gas, ferrous iron and sodium sulfide as electron donors, C / N ratios had little effect on autotrophic denitrification rate at the initial C / N ratio from 1.5 to 9.0. Meanwhile,when made use of hydrogen gas,ferrous iron and sodium sulfide as electron donors,a maximum nitrate removal ratio of 100.00%,91.43%and 87.99% at the temperature of 30 ℃,respectively. Moreover,maximum denitrification activity was observed at p H 6.0-7.0.

Unraveling pharmaceuticals removal in a sulfur-driven autotrophic denitrification process:Performance,kinetics and mechanisms

The removal of eight typical pharmaceuticals(Ph ACs)(i.e.,ibuprofen(IBU),ketoprofen(KET),diclofenac(DIC),sulfadiazine(SD),sulfamethoxazole(SMX),trimethoprim(TMP),ciprofloxacin(CIP)and enoxacin(ENO))in sulfur-driven autotrophic denitrification(Sd AD)process were firstly investigated via long-term operation of bioreactor coupled with batch tests.The results indicated that IBU and KET can be effectively removed(removal efficiency>50%)compared to other six Ph ACs in Sd AD bioreactor.Biodegradation was the primary removal route for IBU and KET with the specific biodegradation rates of 5.3±0.718.1±1.8μg g ^(-1)-VSS d ^(-1)at initial concentrations of 25-200μg/L.The biotransformation intermediates of IBU and KET were examined,and the results indicated that IBU was biotransformed to three intermediates via hydroxylation and carboxylation.KET biotransformation could be initiated from the reduction of the keto group following with a series of oxidation/reduction reactions,and five intermediates of KET were observed in this study.The microbial community composition in the system was markedly shifted when long-term exposure to Ph ACs.However,the functional microbes(e.g.,genus Thiobacillus)showed high tolerance to Ph ACs,resulting in the high efficiency for Ph ACs,N and S removal during long-term Sd AD reactor operation.The findings provide better insight into Ph ACs removal in Sd AD process,especially IBU and KET,and open up an innovative opportunity for the treatment of Ph ACs-laden wastewater using sulfur-mediated biological process.

Combined biologic aerated filter and sulfur/ceramisite autotrophic denitrification for advanced wastewater nitrogen removal at low temperatures

An innovative advanced wastewater treatment process combining biologic aerated filter （BAF） and sulfur/ ceramisite-based autotrophic denitrification （SCAD） for reliable removal of nitrogen was proposed in this paper. In SCAD reactor, ceramisite was used as filter and Ca （HCO3）2 was used for supplying alkalinity and carbon source. The BAF-SCAD was used to treat the secondary treatment effluent. The performance of this process was investigated, and the impact of temperature on nitrogen removal was studied. Results showed that the combined system was effective in nitrogen removal even at low temperatures （8℃）. Removal of total nitrogen （TN）, NH4＋ -N, NO3-N reached above 90% at room temperature. Nitrification was affected by the temperature and nitrification at low temperature （8℃） was a limiting factor for TN removal. However, denitrification was not impacted by the temperature and the removal of NO3 -N maintained 98% during the experimental period. The reason of effective denitrification at low temperature might be the use of easily dissolved Ca（HCO3）2 and high-flux ceramisite, which solved the problem of low mass transfer efficiency at low temperatures. Besides, vast surface area of sulfur with diameter of 2-6 mm enhanced the rate of microbial utilization. The removal of nitrate companied with the production of SO42-, and the average concentration of SO27 was about 240mg.L^-1. These findings would be beneficial for the application of this process to nitrogen removal especially in the winter and cold regions.

Autotrophic denitrification for nitrate and nitrite removal using sulfur-limestone

Sulfur-limestone was used in the autotrophic denitrification process to remove the nitrate and nitrite in a lab scale upflow biofilter.Synthetic water with four levels of nitrate and nitrite concentrations of 10,40,70 and 100 mg N/L was tested.When treating the low concentration of nitrate-or nitrite-contaminated water（10,40 mg N/L）,a high removal rate of about 90% was achieved at the hydraulic retention time（HRT） of 3 hr and temperature of 20-25°C.At the same HRT,50% of the nitrate or nitrite could be removed even at the low temperature of 5-10°C.For the higher concentration nitrate and nitrite（70,100 mg N/L）,longer HRT was required.The batch test indicated that influent concentration,HRT and temperature are important factors afiecting the denitrification eficiency.Molecular analysis implied that nitrate and nitrite were denitrified into nitrogen by the same microorganisms.The sequential two-step-reactions from nitrate to nitrite and from nitrite to the next-step product might have taken place in the same cell during the autotrophic denitrification process.

Advances and challenges of sulfur-driven autotrophic denitrification(SDAD)for nitrogen removal

Sulfur-driven autotrophic denitrification(SDAD),a process suited for the treatment of nitrogen and sulfur-polluted wastewater without extra supplement of organic carbon,is a promising biological nitrogen removal process.However,the SDAD process was affected by many factors such as various electron donors,organic carbon and exogenous substances(e.g.,antibiotics and heavy metal),which prevent further application.Thus,we conducted a detailed review of previous studies on such influence factors and its current application.Besides,a comparative analysis was adopted to recognize the current challenges and future needs for feasible application,so as to ultimately perfect the SDAD process and extend its application scope.

Sulfur-based autotrophic denitrification from the micro-polluted water

Eutrophication caused by high concentrations of nutrients is a huge problem for many natural lakes and reservoirs. Removing the nitrogen contamination from the low C/N water body has become an urgent need. Autotrophic denitrification with the sulfur compound as electron donor was investigated in the biofilter reactors. Through the lab-scale experiment,it was found that different sulfur compounds and different carriers caused very different treatment performances. Thiosulfate was selected to be the best electron donor and ceramsite was chosen as the suitable carrier due to the good denitrification efficiency, low cost and the good resistibility against the high hydraulic loads. Later the optimum running parameters of the process were determined. Then the pilot-scale experiment was carried out with the real micro-polluted water from the West Lake, China. The results indicated that the autotrophic denitrification with thiosulfate as electron donor was feasible and applicable for the micro-polluted lake water.

Control of hydrogen sulfide emissions using autotrophic denitrification landfill biocovers:engineering applications

Hydrogen sulfide(H_(2)S)emitted from construction and demolition waste landfills has received increasing attention.Besides its unpleasant odor,longterm exposure to a very low concentration of H_(2)S can cause a public health issue.In the case of construction and demolition(C&D)waste landfills,where gas collection systems are not normally required,the generated H_(2)S is typically not controlled and the number of treatment processes to control H_(2)S emissions in situ is limited.An attractive alternative may be to use chemically or biologically active landfill covers.A few studies using various types of cover materials to attenuate H_(2)S emissions demonstrated that H_(2)S emissions can be effectively reduced.In this study,therefore,the costs and benefits of H_(2)S-control cover systems including compost,soil amended with lime,fine concrete,and autotrophic denitrification were evaluated.Based on a case-study landfill area of 0.04 km^(2),the estimated H_(2)S emissions of 80900 kg over the 15-year period and costs of active cover system components(ammonium nitrate fertilizer for autotrophic denitrification cover,lime,fine concrete,and compost),ammonium nitrate fertilizer is the most cost effective,followed by hydrated lime,fine concrete,and yard waste compost.Fine concrete and yard waste compost covers are expensive measures to control H_(2)S emissions because of the large amount of materials needed to create a cover.Controlling H_(2)S emissions using fine concrete and compost is less expensive at landfills that provide on-site concrete recovery and composting facilities;however,ammonium nitrate fertilizer or hydrated lime would still be more cost effective applications.

Bio-reduction of nitrate from groundwater using a hydrogen-based membrane biofilm reactor

A hydrogen-based membrane biofilm reactor （MBfR） using H2 as electron donor was investigated to remove nitrate from groundwater. When nitrate was first introduced to the MBfR, denitrification took place on the shell side of the membranes immediately, and the effluent concentration of nitrate continuously decreased with 100% removal rate on day 45 under the influent nitrate concentration of 5 mg NO3^--N/L, which described the acclimating and enriching process of autohydrogenotrophic denitrification bacteria. A series of short-term experiments were applied to investigate the effects of hydrogen pressures and nitrate loadings on deniWification. The results showed that nitrate reduction rate improved as H2 pressure increasing, and over 97% of total nitrogen removal rate was achieved when the nitrate loading increased from 0.17 to 0.34 g NO3^--N/（m^2.day） without nitrite accumulation. The maximum deniwification rate was 384 g N/（m^3.day）. Partial sulfate reduction, which occurred in parallel to nitrate reduction, was inhibited by denitrififcation due to the competition for H2. This research showed that MBfR is effective for removing nitrate from the contaminated groundwater.