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.

[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.

[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.

[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.