Sen Qiao

Innovative treatment system for digester liquor using anammox process.

This study demonstrated that partial nitritation using nitrifying activated sludge entrapped in a polyethylene glycol (PEG) gel carrier, as a pretreatment to anammox process, could be successfully applied to digester liquor of biogas plant at a nitrogen loading rate of 3.0 kg-N/m(3)/d. The nitritation process produced an effluent with a NO(2)-N/NH(4)-N ratio between 1.0 and 1.4, which was found to be suitable for the subsequent anammox process. A high SS concentration (2000-3000 mg/l) in the digester liquor did not affect partial nitritation treatment performances. Effluent from this partial nitritation reactor was successfully treated in the anammox reactor using anammox sludge entrapped in the PEG gel carrier with T-N removal rates of greater than 4.0 kg-N/m(3)/d. Influent BOD and SS contents did not inhibit anammox activity of the anammox gel carrier. The combination of partial nitritation and anammox reactors using PEG entrapped nitrifying and anammox bacteria was shown to be effective for the removal of high concentration ammonium in the digester liquor of a biogas plant.

High-rate partial nitrification performance of high ammonium containing wastewater under low temperatures

In this study, a swim-bed reactor was used for partial nitrification treatment of magnesium ammonium phosphate precipitation process treated effluent of methane fermentation digester liquor. Even without temperature, DO, and pH control, the maximum nitrite production rate of 2.66 kg NO(2)-N/m(3)/d was achieved under a nitrogen loading rate of 5.45 kg N/m(3)/d at 18 degrees C and a nitrite production rate of 0.22 kg NO(2)-N/m(3)/d was still attained at a nitrogen loading rate of 0.48 kg N/m(3)/d even the operational temperature decreased to 8 degrees C. The average effluent NO(2)-N/(NO(2)+NO(3)-N) ratio reached 95.4% during the entire experimental period. The mean particle size of suspended sludge increased from 260 to 450 microm and the microscopic observation confirmed the formation of dense-flocs. The results indicated that there were two regimes for ammonium oxidation, one at 20-30 degrees C and the other at 10-20 degrees C. Scanning electron microscopic observation and FISH analysis demonstrated that ammonium-oxidizing bacteria were the dominant microorganisms and were considered to be responsible for the satisfactory partial nitrification performance.

Application of low intensity ultrasound to enhance the activity of anammox microbial consortium for nitrogen removal.

In this study, effect of low intensity ultrasound on the activity of anammox microbial consortium for nitrogen removal was investigated through batch experiments at the same irradiation frequency of 25 kHz. Total nitrogen removal rate increased by about 25.5% when ultrasound intensity of 0.3 w cm(-2) was applied at an optimal irradiation time of 4 min, and further experiments demonstrated that this effect could last for about 6 days. Analysis of extracellular polymeric substances indicated that the maximum increase of carbohydrate, protein and total extracellular substances was obtained on the first day after ultrasound, which was 28.8%, 30.5% and 29.7%, respectively. As the time prolonged, the production rate of extracellular carbohydrate, protein decreased gradually. Transmission electron microscopy observation demonstrated that ultrasounded cell wall of anammox microbial consortium became thinner resulting in increased release of extracellular substances. The results suggested that application of low intensity ultrasound may enhance the activity of anammox microbial consortium and ultimately the potential for nitrogen removal.

Partial nitritation and anammox of a livestock manure digester liquor and analysis of its microbial community

A swim-bed reactor for partial nitritation with polymeric coagulant treatment and an UASB reactor for anammox were applied to the treatment of livestock manure digester liquor. The partial nitritation was maintained for 32 days under a 1.6 kg N/m(3)/d nitrogen loading rate (NLR) with an average conversion efficiency of 51%, and achieved 1.65 kg N/m(3)/d of the maximum nitrite production rate under 2.58 kg N/m(3)/d of NLR. Although 200 mg/L of TOC remained in the effluent of the partial nitritation reactor, the anammox nitrogen removal rate was not significantly decreased and a relatively high rate of 2.0 kg N/m(3)/d was obtained under a NLR of 2.2 kg N/m(3)/d. 16S rRNA gene analysis showed that Nitrosomonas and KSU-1 were dominant in the partial nitritation and anammox reactor, respectively. The results of this study demonstrated that the partial nitritation-anammox process has possibility of applying to the nitrogen removal of livestock manure digester liquor.

Fast start-up of Anammox process with appropriate ferrous iron concentration.

In this study, three upflow column reactors were compared for anaerobic ammonium oxidation (Anammox) process start-up time with different ferrous iron concentration in feeding. Continuous experiments indicated that the start-up time of Anammox process could be shortened from 70 to 58d in R2 (0.06mM Fe(2+)) and 50d in R3 (0.09mM Fe(2+)). The Anammox activity appeared after 16days operation in R3. Quantitative PCR (q-PCR) analysis demonstrated a significant increase in quantity of Anammox bacteria in R3 compared with the other two reactors during entire operation. At the Fe(II) concentration of 0.09mM, the heme c levels inside Anammox cell and hydrazine dehydrogenase (HDH) activity increased dramatically, which could be the trigger of fast Anammox start-up.

Nano-graphene induced positive effects on methanogenesis in anaerobic digestion

The effects of nano-graphene on methanogenesis in anaerobic digestion was investigated. Short-term results showed that graphene (30 and 120mg/L) had significantly positive effects on methane production rate, which increased by 17.0% and 51.4%. Further investigation indicated that acetate-consuming methanogenesis was enhanced. The failure of quinones to replicate graphene stimulation effects on methanogenesis suggested that graphene did not function as electron shuttles. After 55 days operation at room temperature (from 20 to 10°C, the methane production rate with 30mg/L graphene was 14.3% higher than that of the control, while 120mg/L graphene showed a slight inhibition on methane yield. Illumina sequencing data showed that the archaeal community structure remained fairly constant as the incubated sludge with graphene at low temperature, in which Methanoregula, Methanosaeta and Methanospirillum were the dominant species. Besides, Geobacter enrichment was observed with graphene, suggesting that the direct interspecies electron transfer might be promoted.

Long term effects of divalent ferrous ion on the activity of anammox biomass.

In this study, we explored the effects of Fe(II) on the activity of anammox biomass both in short and long terms. With the influent Fe(II) at 0.09 and 0.12 mM, continuous experiments demonstrated that the nitrogen removal rates increased 32.2% and 29.9% compared to that with normal Fe(II) level (0.03 mM). Influent Fe(II) variation could affect the total Fe, heme c levels and hydrazine dehydrogenase activity. At the Fe(II) concentration of 0.09 mM, the total Fe, heme c levels inside anammox cell and hydrazine dehydrogenase activity could increase about 2.0, 2.1 and 2.35 folds as much as that with normal Fe(II) level. However, when the Fe(II) elevated to 0.18 mM, it would cause a mal-effect on anammox bacteria and further deteriorate nitrogen removal performance. It was indicated that the appropriate increase of Fe(II) was beneficial for more heme c synthesis, enhancement of hydrazine dehydrogenase activity, the growth of anammox bacteria.

Treatment of high-strength corn steep liquor using cultivated polyvinyl alcohol gel beads in an anaerobic fluidized-bed reactor.

Polyvinyl alcohol (PVA) gel beads cultivated in an upflow anaerobic sludge-blanket reactor treating synthetic corn steep liquor (CSL) wastewater were used to seed a lab-scale anaerobic fluidized-bed (AFB) reactor also treating CSL. Under steady-state conditions in the AFB reactor, a COD removal efficiency in excess of 96% was achieved at an organic loading rate (OLR) of 25 g/l/d with a hydraulic retention time (HRT) of 10 h. Furthermore, a removal efficiency of 91% was achieved at an OLR of 27.5 g/l/d with an HRT of only 6 h. With a biomass attachment 1.02 g VSS/g PVA-gel beads, the biomass concentration in the AFB reactor was approximately 610 g/l, while for natural granules only 100 g/l is considered possible. Over the study period, the granular PVA gel turned from black to gray while the biomass attached on the outer surface of the beads also changed in composition. In addition, observations of the interior of the gel beads showed that colonization had progressed well into the core, indicating that effective substrate diffusion occurred within the PVA-gel matrix under the good substrate-microorganism contact conditions provided by the AFB reactor.

Start-up of the anammox process from the conventional activated sludge in a hybrid bioreactor

The anaerobic ammonium oxidation (anammox) process was successfully started up from conventional activated sludge using a hybrid bioreactor within 2 months. The average removal efficiencies of ammonia and nitrite were both over 80%, and the maximum total nitrogen removal rate of 1.85 kg N/(m3 x day) was obtained on day 362 with the initial sludge concentration of 0.7 g mixed liquor suspended solids (MLSS)/L. Scanning electron microscope (SEM) observation of the granular sludge in the hybrid reactor clearly showed a high degree of compactness and cell sphericity, and the cell size was quite uniform. Transmission electron microscope photos showed that cells were round or oval, the cellular diameter was 0.6-1.0 microm, and the percentage of the anammoxosome compartment was 51%-85% of the whole cell volume. Fluorescence in situ hybridization analysis (FISH) indicated that anammox bacteria became the dominant population in the community (accounting for more than 51% of total bacteria on day 250). Seven planctomycete 16S rRNA gene sequences were present in the 16S rRNA gene clone library generated from the biomass and affiliated to Candidatus Kuenenia stuttgartiensis and Candidatus Brocadia sp., a new anammox species. In addition, the average effluent suspended solid (MLSS) concentrations of outlets I (above the non-woven carrier) and II (below the non-woven carrier) were 0.0009 and 0.0035 g/L, respectively. This showed that the non-woven carrier could catch the biomass effectively, which increased biomass and improved the nitrogen removal rate in the reactor.

Anammox process for synthetic and practical wastewater treatment using a novel kind of biomass carriers

The anammox process, as an alternative to conventional nitrogen removal technologies, has abstracted much attention in recent years. In this study, one column-type reactor using a novel support material--net type acrylic fiber (Biofix)--was used for anammox treatment. The Biofix reactor was operated at 25 degrees C (peak summer temperature, 31.5 degrees C). Over 330 days of operation for synthetic wastewater treatment, the nitrogen loading rates of the reactor were increased to 3.6 kg-N/m3/d and T-N removal efficiencies reached to 81.3%. For the practical anaerobic sludge digester liquor treatment, the average TN removal efficiency of 72% was obtained. A protein substance was shown to be the most abundant extracellular polymeric substances (EPS) in the granular sludge with almost two times more in the attached sludge of the Biofix reactor. Considering the EPS levels and observation by scanning electron microscopy, the anammox granules in the Biofix reactor were showing dense state. Results of DNA analyses indicated that the KSU-1 strain might prefer relatively low nutrient levels, while the KU2 strain might be better suited for the high media concentration. Other kinds of bacteria were also identified with the potentials for consuming the dissolved oxygen in the influent and facilitating anammox bacteria surviving under aerobic conditions.