Final Report Summary - PSNOP (Engineering aspects and mechanisms of a natural pyrrhotite simultaneous nitrogen and phosphorus removal (PSNOP) biofilter technology) 1. Main Results1.1 Culturing and enrichment of autotrophic denitrifiers 50 mL of anaerobic sludge taken from a local wastewater treatment plant was added into a 1000 mL conical flask filled with 1000 mL culturing medium. The medium was made from deionized water containing 5 g/L Na2S2O3•5H2O, 2 g/L K2HPO4, 2 g/L KNO3, 1 g/L NaHCO3, 0.5 g/L NH4Cl, 0.5 g/L MgCl2•6H2O and 0.01 g/L FeSO4•7H2O. The conical flask was flushed with N2 for 10 minutes to strip air, and was sealed with a rubber stopper which had an outlet for collecting nitrogen gas (N2) produced. The conical flask was placed in an ambient temperature of 20±3 ℃ for 4 days. Successful enrichment of autotrophic denitrifiers was assessed with the volume of gas generated. After enrichment for five times with the same procedure, the volume of produced gas was around 240 mL in 4 days, indicating successful culturing of autotrophic denitrifiers. The culturing procedure was repeated continuously to produce inoculum for the following research. 1.2 Study of phosphorus (P) adsorption from wastewater using pyrrhotiteA study on adsorption capacity, adsorption kinetics and adsorption mechanisms of phosphorus (P) on pyrrhotite was conducted. It shows that natural pyrrhotite can be used as a material for P removal from wastewater. P adsorption on pyrrhotite reached the adsorption equilibrium within 24 hours, and P was removed rapidly in the first half an hour. As the initial PO43--P concentration was 17.1 mg/L, the P removal efficiency was up to 99.1% and the final PO43--P concentration was 0.15 mg/L at 29˚C. Efficient P removal was achieved in the pH range of 3.57 - 12.1. The higher wastewater temperature (in the range of 11.3 – 29 ˚C), the more efficient PO43--P removal with pyrrhotite. The overall adsorption mechanism was chemisorption. P adsorption on pyrrhotite obeyed Langmuir adsorption isotherm and the second-order kinetics. The adsorption capacity of pyrrhotite was up to 0.79 - 1.15 mg P/g pyrrhotite at 11.3 - 29˚C. 1.3 Factors influencing simultaneous N and P removal via pyrrhotite driven autotrophic denitrificationParameters influencing pyrrhotite driven autotrophic denitrification (PDAD) were investigated with batch experiment, including pyrrhotite dosage, reaction time, temperature, influent nitrate and phosphate concentrations, pH, and pyrrhotite particle size. Experiment results show that the higher pyrrhotite dosage, the faster NO3--N was removed. NO3- in the wastewater was removed completely as the pyrrhotite dosage was 15 g/50 mL or more in 12 days. PO43--P in the wastewater was removed completely.Under the conditions of pyrrhotite dosage 15 g/50 ml, temperature 19 °C, and initial NO3--N and PO43--P concentrations of 28 and 12.4 mg/L respectively, the effects of the reaction time were studied. On Day 6 PO43--P was reduced to 0.12 mg/L, on Day 12 NO3--N was reduced to 0.15 mg/L, and on Day 14 total oxidized nitrogen (TON) was reduced to below 0.05 mg/L. During NO3--N reduction, there was transitional nitrite (NO2-) accumulation, and the NO2--N concentration peaked at 9.9 mg/L on Day 4. The highest denitrification rate was observed at 29 °C and the denitrification rate at 11°C was 60% of the rate at 29 °C. As the temperature was above 34 °C, denitrification was inhibited. Denitrification was terminated as the temperature was over 40 °C. P removal was well correlated to denitrification via PDAD. The initial NO3--N concentration range of 0 to 84 mg/L was tested. Under conditions of pyrrhotite dosage 15 g/50 mL, temperature 19 °C and PO43--P 12.4 mg/L, the NO3--N reduction rate increased with the initial NO3--N concentration increasing to 42 mg/L, and decreased with initial NO3--N concentration further increasing to 84 mg/L. The optimal NO3--N reduction rate was 4.6 mg/L.d and P was removed completely in 6 days. The NO3--N reduction rate increased with initial PO43--P concentration increasing to 31 mg/L, and decreased with initial PO43--P further increasing (31 - 217 mg/L). 1.4 PSNOP biofilter experimentThree biofilters labelled 1, 2 and 3 were constructed, which were filled with limestone, pyrrhotite, and pyrrhotite (50%)+Limestone (50%), respectively. The biofilters have been operated for 242 days continuously. The effects of hydraulic retention time (HRT), and influent NO3--N and PO43--P concentrations on N and P removal from wastewater were investigated. Biofilter 1 (the limestone biofilter) cannot remove NO3--N from water and slightly removed P by adsorption on limestone, but as the influent PO43--P concentration was lower than 24 mg/L, the adsorbed P was released into water. Biofilter 2 (the pyrrhotite biofilter) can simultaneously remove N and P. As the influent NO3--N and PO43--P concentrations were 27 and 6 mg/L, respectively, with HRT increasing from 12 hours to 3 days, TON and P removals increased from 76% to 99%, and from 92% to 97%, respectively. As the influent NO3--N = 27 mg/L and HRT = 1 d, with influent P concentration increasing from 6 to 24 mg/L, P removal decreased from 93.3% to 83.3%. Biofilter 3 (pyrrhotite+Limestone biofilter) also simultaneously removed N and P, but the capacity of N and P removal was lower than that of Biofilter 2. As the influent NO3--N = 27 mg/L and PO43--P = 6 mg/L, with HRT increasing from 12 hours to 3 days, TON and P removal increased from 20% to 78% and from 42% to 83%, respectively. As the influent NO3--N = 27 mg/L and HRT = 1 d, with influent PO43--P concentration increasing from 6 to 24 mg/L, PO43--P removal decreased from 50.0% to 37.5%. Secondary effluent taken from a local wastewater treatment plant was treated with those biofilters. TON was hardly removed in Biofilter 1, and effluent P concentration was even higher than in the influent wastewater because PO43- adsorbed on limestone during the start-up stage was released into water. For Biofilter 2, average removals of TON and P were 88.4% and 87.0%, respectively. TON and P was only removed by 46.5% and 55.8% averagely in Biofilter 3, respectively. The clone library analysis shows that in the pyrrhotite biofilter, biofilm consisted of Thiobacillus denitrificans (55.2% of the library), Sulfurimonas denitrificans (14.1% of the library), Thiobacillus thioparus (11.7% of the library), and sulphate-reducing bacterium STP23 (5.2% of the library). The metal ions in the water were measured by inductively coupled plasma mass spectrometry (ICP-MS). The concentrations of main heavy metal ions were very slow. The research work and results are described in detail in a separate file attached.2. ConclusionsLaboratory-scale PSNOP biofitlers were constructed and operated to examine the feasibility of simultaneous nitrogen and phosphorus removals from wastewater based on pyrrhotite driven autotrophic denitrification. The findings show that sulphur-based autotrophic denitrificants (Thiobacillus denitrificans, Sulfurimonas denitrificans and Thiobacillus thioparus) can be enriched from anaerobic sludge, which makes the PSNOP biofilter technology practical by shortening the start-up period and by reducing its complexity. Culturing sulphur-based autotrophic denitrificants from anaerobic sludge is a novelty of this research project. The performance of PSNOP biofilters in simultaneous N and P removals was affected by a number of factors. For PSNOP, we have found that as the influent NO3--N and PO43--P concentrations were 27 and 6 mg/L, respectively, at HRT of 12 hours, TON and P removals were up to 76% and 92%, with effluent N and P concentrations up to 6.5 mg/L and 0.5 mg/L, respectively. This indicates that the PSNOP technology can be used as a tertiary treatment process for wastewater treatment plants. We have observed P precipitates formed in the biofilters, indicating that we can recover P from wastewater using PSNOP biofilter technology. Another novel finding is that in the biofilms, sulphate-reducing bacteria (SRB) and sulphur-based autotrophic denitrificans co-existed. Further studies should be explored to study C, P and S cycles in PSNOP systems. 3. Socio-economic impactsPSNOP technology is considered to be the most promising technology for N and P removals from wastewater which does not contain sufficient organic matter, for example, the secondary wastewater treatment effluent. The research results have been presented in four peer-review journal papers and a number of journal papers are in preparation. This helps to demonstrate the technology and shows the strength of EU in environmental research. The research fellow has transferred his knowledge to the host institute. A final year project supervised by him won the Frank Lydon Award and the 12th International Undergraduate Awards. My research group is continuing this research with funding provided from other funding sources. This project has provided sufficient support to the research fellow. He carried out intensive studies on the PSNOP technology, obtained a huge amount of data, acquired experience in advanced analytical techniques, presented in national and international conferences, and published peer-review journal papers. He is now working full time in Nanjing University, China (Times Education World Ranking: 252-275) and is in charge of two large scale research projects in China. Therefore, this project will build a strong link between European research institutes (like NUI Galway) with research institutes in China. It produces a long-term synergy in research and fosters a spirit of collaboration between European and Chinese researchers. Related documents final1-researchwork.pdf
