Applying sheet iron to enhance the treatment efficiency of digested effluent with continuous flow and the corresponding mechanism.

Because of the unstable wastewater quantity and quality, the biological treatment efficiency of digested effluent was not as expected. A convenient and effective way was eagerly required to improve the efficiency of biological treatment. By sheet iron addition (R1), the COD and TN removal efficiencies under continuous flow condition increased by 59% and 37% respectively. The bulk pH maintained at around 7.5 which benefited most bacteria, while in the control (R0, without sheet iron addition) the pH decreased to 5.0. Both chemical and bio-removal of COD existed in R1, but the chemical removal dominated (63.71%). The enhanced COD removal efficiency came from the chemical oxidation by Fe3+ (47.43%) and Fe0 (10.86%). For the TN removal, the enhancement mainly came from the improvement of anammox activity by Fe3+ (14.87%), the bio-oxidation of ammonium with Fe3+ as electron acceptor (8.78%), and the bio-reduction of nitrate/nitrite with Fe2+ and H2 as electron donor (35.76%). By the first-order kinetic fitting analysis, the COD and TN removal rate in R1 was higher than that in R0. Thus, for a quick and high COD and TN removal from digested effluent, the addition of Fe0/Fe2+/Fe3+ was suggested, and the best form should be Fe0 (e.g., sheet iron). The addition of sheet iron reduces the cost of nitrogen removal and improves the efficiency of COD and TN removal. Comparing with the combined processes, this novel approach has potential advantages with simple operation and high efficiency. It endows the biological process much broader application in digested effluent treatment.

The long-term effect of glutaraldehyde on the bacterial community in anaerobic ammonium oxidation reactor.

A 160-day incubation was performed with two anammox reactors (GA and CK) to investigate the effect of glutaraldehyde. The results indicated that anammox bacteria were very sensitive when glutaraldehyde in GA reactor increased to 40 mg/L, the nitrogen removal efficiency sharply decreased to 11%, only one-quarter of CK. Glutaraldehyde changed spatial distribution of exopolysaccharides, caused anammox bacteria (Brocadia CK_gra75) to disassociate from granules (24.70% of the reads in CK but only 14.09% in GA granules). Metagenome analysis indicated glutaraldehyde led to the denitrifier community succession from strains without nir (nitrite reductase) and nor (nitric oxide reductases) genes to those with them, and the rapid growth of denitrifiers with NodT (an outer membrane factor)-related efflux pumps replacing those with another TolC -related ones. Meanwhile, Brocadia CK_gra75 lacks the NodT proteins. This study provides important insight into community adaptation and potential resistance mechanism in an active anammox community after exposure to disinfectant.

Aggregation enhances the activity and growth rate of anammox bacteria and its mechanisms.

The aggregation of anaerobic ammonium oxidation (anammox) bacteria is important for the start-up and biomass retention of anammox processes. However, it is unclear whether it is beneficial to the activity, growth and reproduction of anammox bacteria. In this study, four reactor systems were developed to explore the effects of aggregation on anammox activity, growth and reproduction, after excluding the contribution of aggregation to sludge settling and retention. Results demonstrated that (i) compared with free-living planktonic bacteria, the aggregated bacteria had a higher volumetric nitrogen removal rate (0.75 kg-N/(m³·d)) and specific nitrogen removal activity (1.097 kg-N/VSS/d). And after 67 days cultivation, it had the higher sludge concentration and relative abundance (92.4%); (ii) compared with acidic polysaccharides and α-d-glucopyranose polysaccharides, ß-d-glucopyranose polysaccharide play more essential roles of anammox aggregation; (iii) norspermidine triggered the secretion of α-d-glucopyranose polysaccharides to combat the toxicity, and inhibited biomass growth rate; (iv) immobilization in polyvinyl alcohol (10%) or sodium alginate (2%) gel beads was better than sodium alginate-chitosan gel beads and norspermidine (biofilm inhibitor) for the cultivation of free-living planktonic anammox bacteria. This is the first comparative study of three methods for cultivating free-living anammox bacteria. In conclusion, we found that the aggregation of anammox sludge not only facilitates biomass retention but also enhances the bioactivity, relative abundance, growth, and reproduction rate of anammox bacteria. The work is helpful to understand the formation of anammox granular sludge and contribute to the fast start-up and stable operation in anammox application.

[Effect of Different Temperatures on the Performance of Autotrophic Nitrogen Removal and Microbial Community from Swine Wastewater].

Four laboratory-scale autotrophic nitrogen removal bioreactors were implemented to investigate performance differences and microbial mechanisms under different temperatures (30, 25, 20, and 15℃). The results showed that the reactor performance under 30℃ was higher than others. When the temperature decreased from 30℃ to 25℃, total nitrogen removal efficiency reduced from 73% to 66%, and total nitrogen removal rate from 2.29 kg·(m3·d)-1 to 1.72 kg·(m3·d)-1. The morphology and particle size of the sludge did not change significantly (SMD:from 80.85 µm to 79.95 µm). When the temperature was 20℃, the total nitrogen removal efficiency reduced to 42%, the total nitrogen removal rate reduced to 1.18 kg·(m3·d)-1, and the sludge disintegration phenomenon occurred with particle size reduction (SMD:63.21 µm). When the temperature was 15℃, the total nitrogen removal efficiency reduced to 37%, and the total nitrogen removal rate got as low as 1.00 kg·(m3·d)-1. In addition to that, the reactor operation was difficult. The analysis of microbial community structure showed that the influence of temperature on anaerobic ammonia oxidizing bacteria is greater than that on ammonia oxidizing bacteria. This sensitivity to temperature of the anaerobic ammonia oxidizing bacteria was the main reason for the decreased performance under low temperature conditions.

A Phosphate-Starvation Induced RING-Type E3 Ligase Maintains Phosphate Homeostasis Partially Through OsSPX2 in Rice.

Phosphate (Pi), as the main form of phosphorus that can be absorbed by plants, is one of the most limiting macro-nutrients for plants. However, the mechanism for maintaining Pi homeostasis in rice (Oryza sativa) is still not well understood. We identified a Pi-starvation-induced E3 ligase (OsPIE1) in rice. Using an in vitro self-ubiquitination assay, we determined the E3 ligase activities of OsPIE1. Using GUS staining and GFP detection, we analyzed tissue expression patterns of OsPIE1 and the subcellular localization of its encoded protein. The function of OsPIE1 in Pi homeostasis was analyzed using OsPIE1 overexpressors and ospie1 mutants. OsPIE1 was localized to the nucleus, and expressed in epidermis, exodermis and sclerenchyma layers of primary root. Under Pi-sufficient condition, overexpression of OsPIE1 upregulated the expression of OsPT2, OsPT3, OsPT10 and OsPAP21b, resulting in Pi accumulation and acid phosphatases (APases) induction in roots. OsSPX2 was strongly suppressed in OsPIE1 overexpressors. Further comparative transcriptome analysis, tissue expression patterns and genetic interaction analysis indicated that the enhancing of Pi accumulation and APase activities upon overexpression of OsPIE1 was (at least in part) caused by repression of OsSPX2. These results indicate that OsPIE1 plays an important role in maintaining Pi homeostasis in rice.

Continuous dry fermentation of swine manure for biogas production.

A down plug-flow anaerobic reactor (DPAR) was designed for the feasibility study on continuous dry fermentation of swine manure without any additional stirring. Using fresh swine manure as the feedstock with TS concentration (w/w) of 20%, 25%, 30%, and 35%, stable volumetric biogas production rates of 2.40, 1.92, 0.911, and 0.644L · (Ld)(-1) and biogas yields of 0.665, 0.532, 0.252, and 0.178 L g(-)(1)VS were obtained respectively, and the TS degradation rates were 46.5%, 45.4%, 53.2%, and 55.6%, respectively. With the increase of feedstock TS concentration, the concentration of ammonia nitrogen grew up to the maximum value of 3500 mg L(-1). Biogas production was obviously inhibited when the concentration of ammonia nitrogen was above 3000 mg L(-1). The maximal volumetric biogas production rate of 2.34 L ·(Ld)(-1) and biogas yield of 0.649 L g(-1)VS were obtained with TS concentration of 25% at 25°C without inhibition. Liquidity experiments showed that TS concentration of digestate could be less than 15.8%, and the flow rate of digestate more than 0.98 m s(-1) when the feedstock TS concentration was less than 35%, which indicated the digestate could be easily discharged from a DPAR. Therefore, it is feasible to conduct a continuous dry fermentation in a DPAR using fresh swine manure as the feedstock with TS concentration less than 35%, whereas the feedstock TS concentration should not exceed 30% to achieve the maximal biogas production rate and biogas yield.

The effects of temperature, organic matter and time-dependency on rheological properties of dry anaerobic digested swine manure.

An efficient way to avoid the pollution of swine wastewater is the application of dry anaerobic digestion, which needs rheological parameter for stirring and pipe designing. The rheological properties of this kind of sludge have been studied for many decades, yet their effects only solid concentration has been investigated widely. In this paper, the influences of temperature, organic and time-dependency on the efficiency of anaerobic digested swine manure were studied. The viscosity decreased with temperature arranged from 10 to 60 °C which caused increase in protein from 7.18 to 8.49 g/kg. 60 °C can make the digested swine manure with TS from 16.6% to 21.5% reach to the same rheology state. The added peptone decreased the viscosity because of its function of water-reducing admixture and air entraining mixture. Time-dependent experiment showed the decrease of shear stress over time. The first and the second yield stress of dry anaerobic digested swine manure were evaluated through time-dependent model.

Comparison of constructed wetland and stabilization pond for the treatment of digested effluent of swine wastewater.

A laboratory-scale horizontal subsurface flow constructed wetland (HSFCW) and a stabilization pond (SP) were constructed to compare their performances on the treatment of digested effluent of swine wastewater. After 457 days of operation, the removal efficiencies of the HSFCW were as follows: chemical oxygen demand (COD), 17-54%; total phosphorus (TP), 32-45% and ammonia nitrogen [Formula: see text], 27-88%, while they were 25-55%, 31-56% and 56-98%, respectively, for the SP, with a hydraulic retention time of 54 days and hydraulic loading of 0.01 m³ m⁻² d⁻¹. The average removed loads for the HSFCW were as follows: COD, 0.25-4.33; TP, 0.01-0.11 and [Formula: see text], 0.34-2.54 g m⁻² d⁻¹, while they were 0.25-4.45, 0.02-0.13 and 0.72-2.87 g m⁻² d⁻¹, respectively, for the SP. The SP performed better than the HSFCW because the SP showed a 20% of higher removal efficiency for [Formula: see text] than the HSFCW. Especially, the COD removal rate of SP was 10% higher than the HSFCW when the influent concentration was at the lowest and highest stages. Meanwhile, given the lower costs, the SP is more suitable for the treatment of digested effluent of swine wastewater than the HSFCW.

[Effects of the ratio of NO3(-) -N to NO2(-) -N on the removal of sulfide and nitrogen by mixed culture and pure culture].

Effects of the ratio of NO3(-) -N to NO2(-) -N on removal of sulfide and nitrogen by Pseudomonas fluorescens, Pseudomonas aeruginosa and mixed culture were investigated at the pH value of 7.0, temperature of 30 degrees C, ratio of sulfide to nitrate of 5/3 and anaerobic condition. Along with the decrease of ratio of NO3(-) -N to NO2(-) -N, NO(x)(-) -N, the removal rate by Pseudomonas fluorescens and Pseudomonas aeruginosa increased gradually, while S(2-) removal rate reduced. The NO(x)(-) -N removal rate by mixed culture increased first and became steady along with the decrease of ratio of NO3(-) -N to NO2(-) -N. The ratio of NO3(-) -N to NO2(-) -N had hardly influence on S(2-) removal by mixed culture. Accumulation of NO2(-) -N occurred due to a faster rate of NO3(-) -N reduction over NO2(-) -N reduction in the liquid culture of Pseudomonas fluorescens. Accumulation of NO2(-) -N did not occur in the liquid culture of Pseudomonas aeruginosa because it has a stronger ability to convent NO2(-) -N than Pseudomonas fluorescens. The behavior of NO(x)(-) -N by mixed culture in located between Pseudomonas fluorescens and Pseudomonas aeruginosa. The optimum ratio of NO3(-) -N to NO2(-) -N to achieve high removals of sulfide and nitrogen for Pseudomonas fluorescens and mixed culture were 5/5, 10/0 for Pseudomonas aeruginosa. The performance of sulfide and nitrogen removal by the mixed culture was higher than that by Pseudomonas fluorescens and Pseudomonas aeruginosa.

[Continuous dry fermentation of pig manure using up plug-flow type anaerobic reactor].

To solve the problems of ammonia inhibition and discharging difficulty in continuous dry fermentation of pig manure, under the experimental conditions of temperature of (25 +/- 2) degrees C and organic loading rate (TS) of 4.44 g x (L x d) (-1), a lab-scale up plug-flow type anaerobic reactor (UPAR) was setup to investigate biogas production, ammonia inhibition, effluent liquidity, and the feasibility of continuous dry fermentation of pig manure using up plug-flow type anaerobic reactor. The experiment was operated for 160 days using the pig manure with four different TS mass fractions (20%, 25%, 30%, 35%) as feeding. Results showed that the feeding TS mass fraction exerted a significant influence on the dry fermentation of pig manure; the stable volumetric biogas production rates of four different feeding TS mass fractions were 2.40, 1.73, 0.89, and 0.62 L x (L x d)(-1), respectively; the biogas producing efficiencies of the reactors with feeding TS mass fractions of 20%, 25% and 30% were obviously superior to that with feeding TS of 35%. With feeding TS mass fraction increased from 20% to 35%, obvious inhibition to biogas producing occurred when concentration of ammonia nitrogen reached more than 2 300 mg x L(-1). When the feeding TS mass fraction was 35%, the concentration of ammonia nitrogen could accumulate to 3 800 mg x L(-1) but biogas production rate decreased 74.1% of that with feeding TS of 20%. Additionally, while the feeding TS mass fraction was 35%, the effluent TS mass fraction achieved 17.1%, and the velocity of effluent was less than 0.002 m x s(-1) the effluent of UPAR could not be smoothly discharged.

Influence of sand layer depth on partial nitritation as pretreatment of anaerobically digested swine wastewater prior to anammox.

This work aimed to investigate the influence of sand layer depth on partial nitritation performance as a preparative step for anaerobic ammonium oxidation (anammox) process in treating anaerobically digested effluent of swine wastewater. A lab-scale biological sand filter system was constructed and partial nitritation was successfully maintained with nitrogen loading rate (NLR) of approximately 50 g NH(4)(+)-N m(-3) d(-1). An average NH(4)(+)-N removal efficiency of 61.34% and conversion efficiency of NH(4)(+)-N to NO(2)(-)-N of 79.77% were achieved with a sand layer depth of 32 cm. An effluent with a NH(4)(+)-N concentration of 242.52 mg L(-1) and a NO(2)(-)-N concentration of 306.39 mg L(-1) was achieved when the sand layer depth was 32 cm, giving a NO(2)(-)-N/NH(4)(+)-N ratio close to 1.32, as required by anammox. Overall, using a biological sand filter system to treat anaerobically digested effluent of swine wastewater by partial nitritation pretreatment prior to anammox is feasible.

[Effect of sulfide to nitrate ratios on the strains coupling nitrogen removal from wastewater and hydrogen sulfide removal from biogas].

Two strains Pseudomonas fluorescens and Pseudomonas aeruginosa were isolated from the reactors coupling nitrogen removal from wastewater and hydrogen sulfide removal from biogas. It was investigated that sulfide to nitrate ratios had effects on the simultaneous removal of sulfide and nitrate of the two strains under the conditions of pH 7.0, temperature 30 degrees C, anaerobic, cultured for 2 days. The results showed that the nitrate-nitrogen removal rate of Pseudomonas aeruginosa was higher than that of Pseudomonas fluorescens under the same conditions. The sulfide-sulfur removal rates of the two strains had little difference. The best molar n(S)/n(N) of sulfide and nitrate removal rates of Pseudomonas fluorescens and Pseudomonas aeruginosa were 5/2-5/3, 5/3-5/4, respectively. Pseudomonas fluorescens could transform NO3- -N into NO2-N fast, its principal NOx- -N not removed was NO2- -N, especially at the low initial concentration of NOx- -N. The NOx- -N not removed was NO3- -N by Pseudomonas aeruginosa. The best molar n(S)/n(N) of sulfur as reaction outcome of sulfide-sulfur were 5/4, 5/3 by Pseudomonas fluorescens and Pseudomonas aeruginosa, respectively.

[Effect of the ratio of height to diameter on the performance of the simultaneous reactor for nitrogen removal from swine wastewater and sulfide removal from biogas].

The effect of the ratio of height to diameter (H/D) on the process of simultaneous nitrogen removal from swine wastewater and hydrogen sulfide removal from biogas was investigated, using the bubble column reactors with packing material. The performance of the reactor with H/D of 8 : 1, 3 :1 and 2 : 1 was compared. Under temperature of 30-32 degrees C, gas retention time of 6.70 min, hydraulic retention time of 3.35 d, hydrogen sulfide concentration of 1 414-1 838 mg x m(-3) in biogas, and NO(x)(-) -N concentration of 114-243 mg x L(-1) in influent. The reactor with H/D of 2 : 1 achieved a stable and good treatment result, with the average removal rates of 96.7% for hydrogen sulfide, and 88.7% for N(x)(-) -N. While the reactors with H/D of 3 : 1 and 8 : 1 obtained unstable and inferior results, with the average removal rates of 68.0%, 80.4% for hydrogen sulfide respectively, and 89.7%, 90.2% for NO(x)(-) -N respectively. The reason could be attributed to the following facts. The reactor with H/D of 2:1 has a slower optimum gas velocity (3.12 x 10(-2) m x s(-1))- than the reactor with H/D of 3 : 1 and 8 : 1 (3.62 x 10(-2) m x s(-1) and 6.64 x 10(-2) m x s(-1) respectively), and has a higher gas-liquid mass transfer coefficient (1.79 x 10(-5) s(-1)) than the other two reactors (1.64 x 10(-5) s(-1) and 1.55 x 10(-5) s(-1) respectively). Results of the performance and the hydrodynamics parameters of the reactors all indicated that the reactor with H/D of 2 : 1 was more suitable for the process of simultaneous nitrogen and hydrogen sulfide removal.

[Cultivation and isolation of bacteria coupling nitrogen removal from wastewater and hydrogen sulfide removal from biogas].

It was studied that during the startup of reactors the crucial bacteria coupling nitrogen removal from swine wastewater and hydrogen sulfide removal from biogas using bubbling absorption reactors without seeding sludge, with seeding anaerobic sludge and aerobic sludge, respectively. During the prophase of the experiment (before the 26th d), the removal rate of nitrogen and hydrogen sulfide were from 50% to 64% in reactors with seeding sludge, that in the reactor without seeding sludge was only 11%-14%. At the end of experiment (the 56th d after startup), the removal rates of nitrogen for three reactors were about 90%. The removal rates of hydrogen sulfide were more than 70%. The result showed that though the finishing time for startup of the reactor without seeding sludge was longer than that with seeding sludge, it could be obtained the same effect of removal of nitrogen and hydrogen sulfide as the latter after two months cultivation. In the different period of startup of the reactors, the variation of the population of bacteria was studied, which had the same trend as the removal effect of nitrogen and hydrogen sulfide. Two strains which could remove the nitrogen and hydrogen sulfide more than 60% simultaneously were isolated from the three reactors, and primarily identified as Thiobacillus denitrificans and Pseudomonas respectively, based on their morphology and physiological characters.

[Impact of proportion of adding raw wastewater on post-treatment of digested piggery wastewater].

Sequencing batch reactor (SBR) was used to treat digested piggery wastewater, in order to investigate the impact of proportion of adding raw wastewater. In consecutive experiments, the reactor with adding 30% raw wastewater could get low ammonia nitrogen (NH3-N), usually less than 10 mg/L in the effluent, while the reactors with adding 10% or 20% raw wastewater, concentration of NH3-N increased by degrees until reached 300 mg/L or 80 mg/L respectively at end of experiment. These can be explained by the facts that the reactor with adding 30% raw wastewater could maintain stable pH (about 7.7), whereas pH in the reactors with adding 10% or 20% raw wastewater decreased gradually until to below 5.5. Performance monitoring of a cycle of SBR indicate that the peak value of nitrite nitrogen (NO2(-)-N) and valley value of ammonia nitrogen (NH3-N) occur in the fourth, third and second hour after aeration beginning for the reactors with adding 10%, 20% and 30% raw wastewater respectively, which imply that the more is the proportion of adding raw wastewater, the fast does the ammonia oxidized. These results can be attributed to the facts the higher proportion of adding raw wastewater brought better denitrification resulting in stable and high pH. The batch experiment shows that the rate of denitrification has positive correlation with ratio of BOD5 to TN in influent. The consecutive and batch experiment all prove the proportion of adding raw wastewater must reach more than 30% for normal operation of post-treatment of digested piggery wastewater.

[Performance improvement of sequencing batch reactor (SBR) treating digested piggery wastewater by addition of raw wastewater].

When digested piggery wastewater was directly treated with a sequencing batch reactor (SBR) process, the efficiency was low with COD removal about 10% and NH4+ -N removal about 70%. The effluent COD concentration was higher than 1000 mg/L and effluent NH4+ -N concentration was 200 mg/L or so. The working state of the reactor was unstable and its performance deteriorated gradually during operation. After adding no-digested piggery wastewater (raw wastewater) to digested piggery wastewater in the influent, the reactor performance was significantly improved with COD removal higher than 80% and NH4+ -N removal up to 99%. The effluent COD concentration was in the range of 250 mg/L to 350 mg/L and effluent NH4+ -N concentration was lower than 10 m/L. The working stability of the reactor was greatly increased. After adding raw wastewater, the ratio of BOD5 to COD in the influent was raised from 0.19 to 0.54, and the ratio of BOD5 to TN was raised from 0.28 to 2.04, which implied an increase of carbon source for microbial growth and denitrification. The elevated denitrification resulting from the increase of carbon source not only promoted the removal of total nitrogen, but also stabilized the pH value by supplementing alkalinity to treatment system.