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.

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.